Synthesis and Evaluation of Cryptolepine Analogues for Their Potential as New Antimalarial Agents
Identifieur interne : 000708 ( Istex/Corpus ); précédent : 000707; suivant : 000709Synthesis and Evaluation of Cryptolepine Analogues for Their Potential as New Antimalarial Agents
Auteurs : Colin W. Wright ; Jonathan Addae-Kyereme ; Anthony G. Breen ; John E. Brown ; Marlene F. Cox ; Simon L. Croft ; Yaman Gökçek ; Howard Kendrick ; Roger M. Phillips ; Pamela L. PolletSource :
- Journal of Medicinal Chemistry [ 0022-2623 ] ; 2001.
Abstract
The indoloquinoline alkaloid cryptolepine 1 has potent in vitro antiplasmodial activity, but it is also a DNA intercalator with cytotoxic properties. We have shown that the antiplasmodial mechanism of 1 is likely to be due, at least in part, to a chloroquine-like action that does not depend on intercalation into DNA. A number of substituted analogues of 1 have been prepared that have potent activities against both chloroquine-sensitive and chloroquine-resistant strains of Plasmodium falciparum and also have in common with chloroquine the inhibition of β-hematin formation in a cell-free system. Several compounds also displayed activity against Plasmodium berghei in mice, the most potent being 2,7-dibromocryptolepine 8, which suppressed parasitemia by 89% as compared to untreated infected controls at a dose of 12.5 mg kg-1 day-1 ip. No correlation was observed between in vitro cytotoxicity and the effect of compounds on the melting point of DNA (ΔTm value) or toxicity in the mouse−malaria model.
Url:
DOI: 10.1021/jm010929+
Links to Exploration step
ISTEX:83F1F726A42A2C6CF0A97ED1D83863058E783D89Le document en format XML
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Antimalarial Agents</title><author><name sortKey="Wright, Colin W" sort="Wright, Colin W" uniqKey="Wright C" first="Colin W." last="Wright">Colin W. Wright</name><affiliation><mods:affiliation>The School of Pharmacy and Cancer Research Unit, University of Bradford, West Yorkshire, BD7 1DP, U.K., and theDepartment of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, Keppel Street,London WC1E 7HT, U.K.</mods:affiliation></affiliation><affiliation><mods:affiliation> The School of Pharmacy, University of Bradford.</mods:affiliation></affiliation><affiliation><mods:affiliation> Corresponding author tel: +44 (0)1274 234739; fax: +44 (0)1274235600; e-mail: c.w.wright@bradford.ac.uk.</mods:affiliation></affiliation></author><author><name sortKey="Addae Kyereme, Jonathan" sort="Addae Kyereme, Jonathan" uniqKey="Addae Kyereme J" first="Jonathan" last="Addae-Kyereme">Jonathan Addae-Kyereme</name><affiliation><mods:affiliation>The School of Pharmacy and Cancer Research Unit, University of Bradford, West Yorkshire, BD7 1DP, U.K., and theDepartment of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, Keppel Street,London WC1E 7HT, U.K.</mods:affiliation></affiliation><affiliation><mods:affiliation> The School of Pharmacy, University of Bradford.</mods:affiliation></affiliation><affiliation><mods:affiliation> Present address: Faculty of Pharmacy, University of Science andTechnology, Kumasi, Ghana.</mods:affiliation></affiliation></author><author><name sortKey="Breen, Anthony G" sort="Breen, Anthony G" uniqKey="Breen A" first="Anthony G." last="Breen">Anthony G. Breen</name><affiliation><mods:affiliation>The School of Pharmacy and Cancer Research Unit, University of Bradford, West Yorkshire, BD7 1DP, U.K., and theDepartment of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, Keppel Street,London WC1E 7HT, U.K.</mods:affiliation></affiliation><affiliation><mods:affiliation> Cancer Research Unit, University of Bradford.</mods:affiliation></affiliation></author><author><name sortKey="Brown, John E" sort="Brown, John E" uniqKey="Brown J" first="John E." last="Brown">John E. Brown</name><affiliation><mods:affiliation>The School of Pharmacy and Cancer Research Unit, University of Bradford, West Yorkshire, BD7 1DP, U.K., and theDepartment of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, Keppel Street,London WC1E 7HT, U.K.</mods:affiliation></affiliation><affiliation><mods:affiliation> The School of Pharmacy, University of Bradford.</mods:affiliation></affiliation></author><author><name sortKey="Cox, Marlene F" sort="Cox, Marlene F" uniqKey="Cox M" first="Marlene F." last="Cox">Marlene F. Cox</name><affiliation><mods:affiliation>The School of Pharmacy and Cancer Research Unit, University of Bradford, West Yorkshire, BD7 1DP, U.K., and theDepartment of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, Keppel Street,London WC1E 7HT, U.K.</mods:affiliation></affiliation><affiliation><mods:affiliation> The School of Pharmacy, University of Bradford.</mods:affiliation></affiliation><affiliation><mods:affiliation> Present address: Department of Chemistry, University of Guyana,P.O. Box 101110, Georgetown, Guyana.</mods:affiliation></affiliation></author><author><name sortKey="Croft, Simon L" sort="Croft, Simon L" uniqKey="Croft S" first="Simon L." last="Croft">Simon L. Croft</name><affiliation><mods:affiliation>The School of Pharmacy and Cancer Research Unit, University of Bradford, West Yorkshire, BD7 1DP, U.K., and theDepartment of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, Keppel Street,London WC1E 7HT, U.K.</mods:affiliation></affiliation><affiliation><mods:affiliation> London School of Hygiene and Tropical Medicine.</mods:affiliation></affiliation></author><author><name sortKey="Gokcek, Yaman" sort="Gokcek, Yaman" uniqKey="Gokcek Y" first="Yaman" last="Gökçek">Yaman Gökçek</name><affiliation><mods:affiliation>The School of Pharmacy and Cancer Research Unit, University of Bradford, West Yorkshire, BD7 1DP, U.K., and theDepartment of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, Keppel Street,London WC1E 7HT, U.K.</mods:affiliation></affiliation><affiliation><mods:affiliation> The School of Pharmacy, University of Bradford.</mods:affiliation></affiliation></author><author><name sortKey="Kendrick, Howard" sort="Kendrick, Howard" uniqKey="Kendrick H" first="Howard" last="Kendrick">Howard Kendrick</name><affiliation><mods:affiliation>The School of Pharmacy and Cancer Research Unit, University of Bradford, West Yorkshire, BD7 1DP, U.K., and theDepartment of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, Keppel Street,London WC1E 7HT, U.K.</mods:affiliation></affiliation><affiliation><mods:affiliation> London School of Hygiene and Tropical Medicine.</mods:affiliation></affiliation></author><author><name sortKey="Phillips, Roger M" sort="Phillips, Roger M" uniqKey="Phillips R" first="Roger M." last="Phillips">Roger M. Phillips</name><affiliation><mods:affiliation>The School of Pharmacy and Cancer Research Unit, University of Bradford, West Yorkshire, BD7 1DP, U.K., and theDepartment of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, Keppel Street,London WC1E 7HT, U.K.</mods:affiliation></affiliation><affiliation><mods:affiliation> Cancer Research Unit, University of Bradford.</mods:affiliation></affiliation></author><author><name sortKey="Pollet, Pamela L" sort="Pollet, Pamela L" uniqKey="Pollet P" first="Pamela L." last="Pollet">Pamela L. Pollet</name><affiliation><mods:affiliation>The School of Pharmacy and Cancer Research Unit, University of Bradford, West Yorkshire, BD7 1DP, U.K., and theDepartment of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, Keppel Street,London WC1E 7HT, U.K.</mods:affiliation></affiliation><affiliation><mods:affiliation> The School of Pharmacy, University of Bradford.</mods:affiliation></affiliation></author></analytic><monogr></monogr><series><title level="j" type="main">Journal of Medicinal Chemistry</title><title level="j" type="abbrev">J. Med. Chem.</title><idno type="ISSN">0022-2623</idno><idno type="eISSN">1520-4804</idno><imprint><publisher>American Chemical Society</publisher><date type="e-published" when="2001-08-18">2001</date><date when="2001-09-13">2001</date><biblScope unit="vol">44</biblScope><biblScope unit="issue">19</biblScope><biblScope unit="page" from="3187">3187</biblScope><biblScope unit="page" to="3194">3194</biblScope></imprint><idno type="ISSN">0022-2623</idno></series></biblStruct></sourceDesc><seriesStmt><idno type="ISSN">0022-2623</idno></seriesStmt></fileDesc><profileDesc><textClass></textClass></profileDesc></teiHeader><front><div type="abstract">The indoloquinoline alkaloid cryptolepine 1 has potent in vitro antiplasmodial activity, but it is also a DNA intercalator with cytotoxic properties. We have shown that the antiplasmodial mechanism of 1 is likely to be due, at least in part, to a chloroquine-like action that does not depend on intercalation into DNA. A number of substituted analogues of 1 have been prepared that have potent activities against both chloroquine-sensitive and chloroquine-resistant strains of Plasmodium falciparum and also have in common with chloroquine the inhibition of β-hematin formation in a cell-free system. Several compounds also displayed activity against Plasmodium berghei in mice, the most potent being 2,7-dibromocryptolepine 8, which suppressed parasitemia by 89% as compared to untreated infected controls at a dose of 12.5 mg kg-1 day-1 ip. No correlation was observed between in vitro cytotoxicity and the effect of compounds on the melting point of DNA (ΔTm value) or toxicity in the mouse−malaria model.</div></front></TEI><istex><corpusName>acs</corpusName><keywords><teeft><json:string>cryptolepine</json:string><json:string>mmol</json:string><json:string>antiplasmodial</json:string><json:string>hematin</json:string><json:string>antimalarial</json:string><json:string>cytotoxicity</json:string><json:string>antiplasmodial activity</json:string><json:string>falciparum</json:string><json:string>hematin formation</json:string><json:string>parasitemia</json:string><json:string>nch3</json:string><json:string>anal</json:string><json:string>chloroquine</json:string><json:string>derivative</json:string><json:string>relative intensity</json:string><json:string>analogue</json:string><json:string>free base</json:string><json:string>room temperature</json:string><json:string>chloroform</json:string><json:string>cytotoxic</json:string><json:string>berghei</json:string><json:string>toxicity</json:string><json:string>chem</json:string><json:string>plasmodium</json:string><json:string>medicinal chemistry</json:string><json:string>reflux</json:string><json:string>malaria parasite</json:string><json:string>alkaloid</json:string><json:string>anthranilic</json:string><json:string>dmso</json:string><json:string>parasite</json:string><json:string>drug exposure time</json:string><json:string>less toxic</json:string><json:string>reaction mixture</json:string><json:string>cryptolepine analogue</json:string><json:string>vivo antimalarial activity</json:string><json:string>hydrochloride salt</json:string><json:string>yellow solid</json:string><json:string>ftir spectrum</json:string><json:string>less active</json:string><json:string>anthranilic acid</json:string><json:string>crude yield</json:string><json:string>chloroquine diphosphate</json:string><json:string>medicinal</json:string><json:string>cryptolepine derivative</json:string><json:string>tropical medicine</json:string><json:string>plasmodium berghei</json:string><json:string>stock solution</json:string><json:string>polyphosphoric acid</json:string><json:string>plasmodium falciparum</json:string><json:string>anthranilic acid derivative</json:string><json:string>ethyl acetate</json:string><json:string>antimalarial agent journal</json:string><json:string>culture medium</json:string><json:string>nacl solution</json:string><json:string>cytotoxic property</json:string><json:string>separate determination</json:string><json:string>london school</json:string><json:string>calf thymus</json:string><json:string>toxic</json:string></teeft></keywords><author><json:item><name>WRIGHT Colin W.</name><affiliations><json:string>The School of Pharmacy and Cancer Research Unit, University of Bradford, West Yorkshire, BD7 1DP, U.K., and theDepartment of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, Keppel Street,London WC1E 7HT, U.K.</json:string><json:string>The School of Pharmacy, University of Bradford.</json:string><json:string>Corresponding author tel: +44 (0)1274 234739; fax: +44 (0)1274235600; e-mail: c.w.wright@bradford.ac.uk.</json:string></affiliations></json:item><json:item><name>ADDAE-KYEREME Jonathan</name><affiliations><json:string>The School of Pharmacy and Cancer Research Unit, University of Bradford, West Yorkshire, BD7 1DP, U.K., and theDepartment of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, Keppel Street,London WC1E 7HT, U.K.</json:string><json:string>The School of Pharmacy, University of Bradford.</json:string><json:string>Present address: Faculty of Pharmacy, University of Science andTechnology, Kumasi, Ghana.</json:string></affiliations></json:item><json:item><name>BREEN Anthony G.</name><affiliations><json:string>The School of Pharmacy and Cancer Research Unit, University of Bradford, West Yorkshire, BD7 1DP, U.K., and theDepartment of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, Keppel Street,London WC1E 7HT, U.K.</json:string><json:string>Cancer Research Unit, University of Bradford.</json:string></affiliations></json:item><json:item><name>BROWN John E.</name><affiliations><json:string>The School of Pharmacy and Cancer Research Unit, University of Bradford, West Yorkshire, BD7 1DP, U.K., and theDepartment of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, Keppel Street,London WC1E 7HT, U.K.</json:string><json:string>The School of Pharmacy, University of Bradford.</json:string></affiliations></json:item><json:item><name>COX Marlene F.</name><affiliations><json:string>The School of Pharmacy and Cancer Research Unit, University of Bradford, West Yorkshire, BD7 1DP, U.K., and theDepartment of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, Keppel Street,London WC1E 7HT, U.K.</json:string><json:string>The School of Pharmacy, University of Bradford.</json:string><json:string>Present address: Department of Chemistry, University of Guyana,P.O. Box 101110, Georgetown, Guyana.</json:string></affiliations></json:item><json:item><name>CROFT Simon L.</name><affiliations><json:string>The School of Pharmacy and Cancer Research Unit, University of Bradford, West Yorkshire, BD7 1DP, U.K., and theDepartment of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, Keppel Street,London WC1E 7HT, U.K.</json:string><json:string>London School of Hygiene and Tropical Medicine.</json:string></affiliations></json:item><json:item><name>GöKçEK Yaman</name><affiliations><json:string>The School of Pharmacy and Cancer Research Unit, University of Bradford, West Yorkshire, BD7 1DP, U.K., and theDepartment of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, Keppel Street,London WC1E 7HT, U.K.</json:string><json:string>The School of Pharmacy, University of Bradford.</json:string></affiliations></json:item><json:item><name>KENDRICK Howard</name><affiliations><json:string>The School of Pharmacy and Cancer Research Unit, University of Bradford, West Yorkshire, BD7 1DP, U.K., and theDepartment of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, Keppel Street,London WC1E 7HT, U.K.</json:string><json:string>London School of Hygiene and Tropical Medicine.</json:string></affiliations></json:item><json:item><name>PHILLIPS Roger M.</name><affiliations><json:string>The School of Pharmacy and Cancer Research Unit, University of Bradford, West Yorkshire, BD7 1DP, U.K., and theDepartment of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, Keppel Street,London WC1E 7HT, U.K.</json:string><json:string>Cancer Research Unit, University of Bradford.</json:string></affiliations></json:item><json:item><name>POLLET Pamela L.</name><affiliations><json:string>The School of Pharmacy and Cancer Research Unit, University of Bradford, West Yorkshire, BD7 1DP, U.K., and theDepartment of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, Keppel Street,London WC1E 7HT, U.K.</json:string><json:string>The School of Pharmacy, University of Bradford.</json:string></affiliations></json:item></author><arkIstex>ark:/67375/TPS-0VR0LC0H-2</arkIstex><language><json:string>unknown</json:string></language><originalGenre><json:string>research-article</json:string></originalGenre><abstract>The indoloquinoline alkaloid cryptolepine 1 has potent in vitro antiplasmodial activity, but it is also a DNA intercalator with cytotoxic properties. We have shown that the antiplasmodial mechanism of 1 is likely to be due, at least in part, to a chloroquine-like action that does not depend on intercalation into DNA. A number of substituted analogues of 1 have been prepared that have potent activities against both chloroquine-sensitive and chloroquine-resistant strains of Plasmodium falciparum and also have in common with chloroquine the inhibition of β-hematin formation in a cell-free system. Several compounds also displayed activity against Plasmodium berghei in mice, the most potent being 2,7-dibromocryptolepine 8, which suppressed parasitemia by 89% as compared to untreated infected controls at a dose of 12.5 mg kg-1 day-1 ip. No correlation was observed between in vitro cytotoxicity and the effect of compounds on the melting point of DNA (ΔTm value) or toxicity in the mouse−malaria model.</abstract><qualityIndicators><score>8.836</score><pdfWordCount>6749</pdfWordCount><pdfCharCount>38872</pdfCharCount><pdfVersion>1.2</pdfVersion><pdfPageCount>8</pdfPageCount><pdfPageSize>612 x 792 pts (letter)</pdfPageSize><pdfWordsPerPage>844</pdfWordsPerPage><pdfText>true</pdfText><refBibsNative>true</refBibsNative><abstractWordCount>153</abstractWordCount><abstractCharCount>1008</abstractCharCount><keywordCount>0</keywordCount></qualityIndicators><title>Synthesis and Evaluation of Cryptolepine Analogues for Their Potential as New Antimalarial Agents</title><genre><json:string>research-article</json:string></genre><host><title>Journal of Medicinal Chemistry</title><language><json:string>unknown</json:string></language><issn><json:string>0022-2623</json:string></issn><eissn><json:string>1520-4804</json:string></eissn><volume>44</volume><issue>19</issue><pages><first>3187</first><last>3194</last></pages><genre><json:string>journal</json:string></genre></host><ark><json:string>ark:/67375/TPS-0VR0LC0H-2</json:string></ark><categories><wos><json:string>1 - science</json:string><json:string>2 - chemistry, medicinal</json:string></wos><scienceMetrix><json:string>1 - natural sciences</json:string><json:string>2 - chemistry</json:string><json:string>3 - medicinal & biomolecular chemistry</json:string></scienceMetrix><scopus><json:string>1 - Life Sciences</json:string><json:string>2 - Pharmacology, Toxicology and Pharmaceutics</json:string><json:string>3 - Drug Discovery</json:string><json:string>1 - Life Sciences</json:string><json:string>2 - Biochemistry, Genetics and Molecular Biology</json:string><json:string>3 - Molecular Medicine</json:string></scopus><inist><json:string>1 - sciences appliquees, technologies et medecines</json:string><json:string>2 - sciences biologiques et medicales</json:string><json:string>3 - sciences biologiques fondamentales et appliquees. psychologie</json:string></inist></categories><publicationDate>2001</publicationDate><copyrightDate>2001</copyrightDate><doi><json:string>10.1021/jm010929+</json:string></doi><id>83F1F726A42A2C6CF0A97ED1D83863058E783D89</id><score>1</score><fulltext><json:item><extension>pdf</extension><original>true</original><mimetype>application/pdf</mimetype><uri>https://api.istex.fr/ark:/67375/TPS-0VR0LC0H-2/fulltext.pdf</uri></json:item><json:item><extension>zip</extension><original>false</original><mimetype>application/zip</mimetype><uri>https://api.istex.fr/ark:/67375/TPS-0VR0LC0H-2/bundle.zip</uri></json:item><json:item><extension>txt</extension><original>false</original><mimetype>text/plain</mimetype><uri>https://api.istex.fr/ark:/67375/TPS-0VR0LC0H-2/fulltext.txt</uri></json:item><istex:fulltextTEI uri="https://api.istex.fr/ark:/67375/TPS-0VR0LC0H-2/fulltext.tei"><teiHeader><fileDesc><titleStmt><title level="a" type="main">Synthesis and Evaluation of Cryptolepine Analogues for Their Potential as New
Antimalarial Agents</title></titleStmt><publicationStmt><authority>ISTEX</authority><publisher>American Chemical Society</publisher><availability><licence>Copyright © 2001 American Chemical Society</licence><p>American Chemical Society</p></availability><date type="e-published" when="2001-08-18">2001</date><date when="2001-09-13">2001</date><date type="Copyright" when="2001">2001</date></publicationStmt><notesStmt><note type="content-type" source="research-article" scheme="https://content-type.data.istex.fr/ark:/67375/XTP-1JC4F85T-7">research-article</note><note type="publication-type" scheme="https://publication-type.data.istex.fr/ark:/67375/JMC-0GLKJH51-B">journal</note></notesStmt><sourceDesc><biblStruct type="article"><analytic><title level="a" type="main" xml:lang="en">Synthesis and Evaluation of Cryptolepine Analogues for Their Potential as New
Antimalarial Agents</title><author xml:id="author-0000" role="corresp"><persName><surname>Wright</surname><forename type="first">Colin W.</forename></persName><affiliation>The School of Pharmacy and Cancer Research Unit, University of Bradford, West Yorkshire, BD7 1DP, U.K., and the
Department of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, Keppel Street,
London WC1E 7HT, U.K.
</affiliation><note place="foot"><ref>†</ref><p>
The School of Pharmacy, University of Bradford.</p></note><affiliation role="corresp"> Corresponding author tel: +44 (0)1274 234739; fax: +44 (0)1274 235600; e-mail: c.w.wright@bradford.ac.uk.</affiliation></author><author xml:id="author-0001"><persName><surname>Addae-Kyereme</surname><forename type="first">Jonathan</forename></persName><affiliation>The School of Pharmacy and Cancer Research Unit, University of Bradford, West Yorkshire, BD7 1DP, U.K., and the
Department of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, Keppel Street,
London WC1E 7HT, U.K.
</affiliation><note place="foot"><ref>†</ref><p>
The School of Pharmacy, University of Bradford.</p></note><note place="foot"><ref>‡</ref><p>
Present address: Faculty of Pharmacy, University of Science and
Technology, Kumasi, Ghana.</p></note></author><author xml:id="author-0002"><persName><surname>Breen</surname><forename type="first">Anthony G.</forename></persName><affiliation>The School of Pharmacy and Cancer Research Unit, University of Bradford, West Yorkshire, BD7 1DP, U.K., and the
Department of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, Keppel Street,
London WC1E 7HT, U.K.
</affiliation><note place="foot"><ref>§</ref><p>
Cancer Research Unit, University of Bradford.</p></note></author><author xml:id="author-0003"><persName><surname>Brown</surname><forename type="first">John E.</forename></persName><affiliation>The School of Pharmacy and Cancer Research Unit, University of Bradford, West Yorkshire, BD7 1DP, U.K., and the
Department of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, Keppel Street,
London WC1E 7HT, U.K.
</affiliation><note place="foot"><ref>†</ref><p>
The School of Pharmacy, University of Bradford.</p></note></author><author xml:id="author-0004"><persName><surname>Cox</surname><forename type="first">Marlene F.</forename></persName><affiliation>The School of Pharmacy and Cancer Research Unit, University of Bradford, West Yorkshire, BD7 1DP, U.K., and the
Department of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, Keppel Street,
London WC1E 7HT, U.K.
</affiliation><note place="foot"><ref>†</ref><p>
The School of Pharmacy, University of Bradford.</p></note><note place="foot"><ref>‖</ref><p>
Present address: Department of Chemistry, University of Guyana,
P.O. Box 101110, Georgetown, Guyana.</p></note></author><author xml:id="author-0005"><persName><surname>Croft</surname><forename type="first">Simon L.</forename></persName><affiliation>The School of Pharmacy and Cancer Research Unit, University of Bradford, West Yorkshire, BD7 1DP, U.K., and the
Department of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, Keppel Street,
London WC1E 7HT, U.K.
</affiliation><note place="foot"><ref>⊥</ref><p>
London School of Hygiene and Tropical Medicine.</p></note></author><author xml:id="author-0006"><persName><surname>Gökçek</surname><forename type="first">Yaman</forename></persName><affiliation>The School of Pharmacy and Cancer Research Unit, University of Bradford, West Yorkshire, BD7 1DP, U.K., and the
Department of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, Keppel Street,
London WC1E 7HT, U.K.
</affiliation><note place="foot"><ref>†</ref><p>
The School of Pharmacy, University of Bradford.</p></note></author><author xml:id="author-0007"><persName><surname>Kendrick</surname><forename type="first">Howard</forename></persName><affiliation>The School of Pharmacy and Cancer Research Unit, University of Bradford, West Yorkshire, BD7 1DP, U.K., and the
Department of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, Keppel Street,
London WC1E 7HT, U.K.
</affiliation><note place="foot"><ref>⊥</ref><p>
London School of Hygiene and Tropical Medicine.</p></note></author><author xml:id="author-0008"><persName><surname>Phillips</surname><forename type="first">Roger M.</forename></persName><affiliation>The School of Pharmacy and Cancer Research Unit, University of Bradford, West Yorkshire, BD7 1DP, U.K., and the
Department of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, Keppel Street,
London WC1E 7HT, U.K.
</affiliation><note place="foot"><ref>§</ref><p>
Cancer Research Unit, University of Bradford.</p></note></author><author xml:id="author-0009"><persName><surname>Pollet</surname><forename type="first">Pamela L.</forename></persName><affiliation>The School of Pharmacy and Cancer Research Unit, University of Bradford, West Yorkshire, BD7 1DP, U.K., and the
Department of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, Keppel Street,
London WC1E 7HT, U.K.
</affiliation><note place="foot"><ref>†</ref><p>
The School of Pharmacy, University of Bradford.</p></note></author><idno type="istex">83F1F726A42A2C6CF0A97ED1D83863058E783D89</idno><idno type="ark">ark:/67375/TPS-0VR0LC0H-2</idno><idno type="DOI">10.1021/jm010929+</idno></analytic><monogr><title level="j" type="main">Journal of Medicinal Chemistry</title><title level="j" type="abbrev">J. Med. Chem.</title><idno type="acspubs">jm</idno><idno type="coden">jmcmar</idno><idno type="pISSN">0022-2623</idno><idno type="eISSN">1520-4804</idno><imprint><publisher>American Chemical Society</publisher><date type="e-published" when="2001-08-18">2001</date><date when="2001-09-13">2001</date><biblScope unit="vol">44</biblScope><biblScope unit="issue">19</biblScope><biblScope unit="page" from="3187">3187</biblScope><biblScope unit="page" to="3194">3194</biblScope></imprint></monogr></biblStruct></sourceDesc></fileDesc><profileDesc><abstract><graphic url="jm0109291n00001.tif"></graphic><p>The indoloquinoline alkaloid cryptolepine <hi rend="bold">1</hi> has potent in vitro antiplasmodial activity, but it
is also a DNA intercalator with cytotoxic properties. We have shown that the antiplasmodial
mechanism of <hi rend="bold">1</hi> is likely to be due, at least in part, to a chloroquine-like action that does not
depend on intercalation into DNA. A number of substituted analogues of <hi rend="bold">1 </hi>have been prepared
that have potent activities against both chloroquine-sensitive and chloroquine-resistant strains
of <hi rend="italic">Plasmodium falciparum </hi>and also have in common with chloroquine the inhibition of
β-hematin formation in a cell-free system. Several compounds also displayed activity against
<hi rend="italic">Plasmodium berghei</hi> in mice, the most potent being 2,7-dibromocryptolepine <hi rend="bold">8</hi>, which suppressed
parasitemia by 89% as compared to untreated infected controls at a dose of 12.5 mg kg<hi rend="superscript">-1</hi> day<hi rend="superscript">-1</hi>
ip. No correlation was observed between in vitro cytotoxicity and the effect of compounds on
the melting point of DNA (Δ<hi rend="italic">T</hi><hi rend="subscript">m</hi> value) or toxicity in the mouse−malaria model.
</p></abstract><textClass ana="subject"><keywords scheme="document-type-name"><term>Article</term></keywords></textClass><langUsage><language ident="zxx"></language></langUsage></profileDesc></teiHeader></istex:fulltextTEI></fulltext><metadata><istex:metadataXml wicri:clean="corpus acs not found" wicri:toSee="no header"><istex:xmlDeclaration>version="1.0" encoding="UTF-8"</istex:xmlDeclaration><istex:document><article article-type="research-article" specific-use="acs2jats-1.1.23" dtd-version="1.1d1"><front><journal-meta><journal-id journal-id-type="acspubs">jm</journal-id><journal-id journal-id-type="coden">jmcmar</journal-id><journal-title-group><journal-title>Journal of Medicinal Chemistry</journal-title><abbrev-journal-title>J. Med. Chem.</abbrev-journal-title></journal-title-group><issn pub-type="ppub">0022-2623</issn><issn pub-type="epub">1520-4804</issn><publisher><publisher-name>American Chemical Society</publisher-name></publisher><self-uri>pubs.acs.org/jmc</self-uri></journal-meta><article-meta><article-id pub-id-type="doi">10.1021/jm010929+</article-id><article-categories><subj-group subj-group-type="document-type-name"><subject>Article</subject></subj-group></article-categories><title-group><article-title>Synthesis and Evaluation of Cryptolepine Analogues for Their Potential as New
Antimalarial Agents</article-title></title-group><contrib-group><contrib contrib-type="author" corresp="yes"><name name-style="western"><surname>Wright</surname><given-names>Colin W.</given-names></name><xref rid="jm0109291AF1">*</xref><xref rid="jm0109291AF2"><sup>†</sup></xref></contrib><contrib contrib-type="author"><name name-style="western"><surname>Addae-Kyereme</surname><given-names>Jonathan</given-names></name><xref rid="jm0109291AF2"><sup>†</sup></xref><xref rid="jm0109291AF3"><sup>‡</sup></xref></contrib><contrib contrib-type="author"><name name-style="western"><surname>Breen</surname><given-names>Anthony G.</given-names></name><xref rid="jm0109291AF4"><sup>§</sup></xref></contrib><contrib contrib-type="author"><name name-style="western"><surname>Brown</surname><given-names>John E.</given-names></name><xref rid="jm0109291AF2"><sup>†</sup></xref></contrib><contrib contrib-type="author"><name name-style="western"><surname>Cox</surname><given-names>Marlene F.</given-names></name><xref rid="jm0109291AF2"><sup>†</sup></xref><xref rid="jm0109291AF5"><sup>‖</sup></xref></contrib><contrib contrib-type="author"><name name-style="western"><surname>Croft</surname><given-names>Simon L.</given-names></name><xref rid="jm0109291AF6"><sup>⊥</sup></xref></contrib><contrib contrib-type="author"><name name-style="western"><surname>Gökçek</surname><given-names>Yaman</given-names></name><xref rid="jm0109291AF2"><sup>†</sup></xref></contrib><contrib contrib-type="author"><name name-style="western"><surname>Kendrick</surname><given-names>Howard</given-names></name><xref rid="jm0109291AF6"><sup>⊥</sup></xref></contrib><contrib contrib-type="author"><name name-style="western"><surname>Phillips</surname><given-names>Roger M.</given-names></name><xref rid="jm0109291AF4"><sup>§</sup></xref></contrib><contrib contrib-type="author"><name name-style="western"><surname>Pollet</surname><given-names>Pamela L.</given-names></name><xref rid="jm0109291AF2"><sup>†</sup></xref></contrib><aff>The School of Pharmacy and Cancer Research Unit, University of Bradford, West Yorkshire, BD7 1DP, U.K., and the
Department of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, Keppel Street,
London WC1E 7HT, U.K.
</aff></contrib-group><author-notes><corresp id="jm0109291AF1">
Corresponding author tel: +44 (0)1274 234739; fax: +44 (0)1274
235600; e-mail: c.w.wright@bradford.ac.uk.</corresp><fn id="jm0109291AF2"><label>†</label><p>
The School of Pharmacy, University of Bradford.</p></fn><fn id="jm0109291AF3"><label>‡</label><p>
Present address: Faculty of Pharmacy, University of Science and
Technology, Kumasi, Ghana.</p></fn><fn id="jm0109291AF4"><label>§</label><p>
Cancer Research Unit, University of Bradford.</p></fn><fn id="jm0109291AF5"><label>‖</label><p>
Present address: Department of Chemistry, University of Guyana,
P.O. Box 101110, Georgetown, Guyana.</p></fn><fn id="jm0109291AF6"><label>⊥</label><p>
London School of Hygiene and Tropical Medicine.</p></fn></author-notes><pub-date pub-type="epub"><day>18</day><month>08</month><year>2001</year></pub-date><pub-date pub-type="ppub"><day>13</day><month>09</month><year>2001</year></pub-date><volume>44</volume><issue>19</issue><fpage>3187</fpage><lpage>3194</lpage><history><date date-type="received"><day>16</day><month>05</month><year>2001</year></date><date date-type="asap"><day>18</day><month>08</month><year>2001</year></date><date date-type="issue-pub"><day>13</day><month>09</month><year>2001</year></date></history><permissions><copyright-statement>Copyright © 2001 American Chemical Society</copyright-statement><copyright-year>2001</copyright-year><copyright-holder>American Chemical Society</copyright-holder></permissions><abstract><graphic content-type="abstract-graphic" xlink:href="jm0109291n00001.tif" orientation="portrait" position="float"></graphic><p>The indoloquinoline alkaloid cryptolepine <bold>1</bold> has potent in vitro antiplasmodial activity, but it
is also a DNA intercalator with cytotoxic properties. We have shown that the antiplasmodial
mechanism of <bold>1</bold> is likely to be due, at least in part, to a chloroquine-like action that does not
depend on intercalation into DNA. A number of substituted analogues of <bold>1 </bold>have been prepared
that have potent activities against both chloroquine-sensitive and chloroquine-resistant strains
of <italic toggle="yes">Plasmodium falciparum </italic>and also have in common with chloroquine the inhibition of
β-hematin formation in a cell-free system. Several compounds also displayed activity against
<italic toggle="yes">Plasmodium berghei</italic> in mice, the most potent being 2,7-dibromocryptolepine <bold>8</bold>, which suppressed
parasitemia by 89% as compared to untreated infected controls at a dose of 12.5 mg kg<sup>-1</sup> day<sup>-1</sup>
ip. No correlation was observed between in vitro cytotoxicity and the effect of compounds on
the melting point of DNA (Δ<italic toggle="yes">T</italic><sub>m</sub> value) or toxicity in the mouse−malaria model.
</p></abstract><custom-meta-group><custom-meta><meta-name>document-id-old-9</meta-name><meta-value>jm010929+</meta-value></custom-meta></custom-meta-group></article-meta></front><body><sec id="d7e263"><title>Introduction</title><p>Cryptolepine (5-methyl,10<italic toggle="yes">H</italic>-indolo[3,2-<italic toggle="yes">b</italic>]quinoline; <bold>1</bold>)
is an indoloquinoline alkaloid found in the west African
climbing shrub <italic toggle="yes">Cryptolepis sanguinolenta</italic> (family Periplocaceae). A decoction of the roots of this species is used
in traditional medicine for the treatment of malaria as
well as for a number of other diseases.<xref rid="jm0109291b00001" ref-type="bibr"></xref> Previous work
has shown that cryptolepine has potent in vitro antiplasmodial activity,<xref rid="jm0109291b00002" ref-type="bibr"></xref> but this alkaloid also has cytotoxic
properties that are likely due to its abilities to intercalate into DNA and inhibit topoisomerase II as well
as DNA synthesis.<xref rid="jm0109291b00003" ref-type="bibr"></xref></p><p>In this paper, we report the synthesis of 15 cryptolepine derivatives (of which 11 are novel) to determine
whether it is possible to prepare cryptolepine analogues
that have reduced abilities to interact with DNA (and
hence may be less cytotoxic) but that retain potent
antiplasmodial activities. This hypothesis is supported
by evidence (presented below) which suggests that the
antiplasmodial activity of cryptolepine is due, at least
in part, to a chloroquine-like action that does not depend
on intercalation into DNA. Chloroquine and related
antimalarials appear to act primarily by inhibiting the
formation of hemozoin (malaria pigment), which is
formed in malaria parasites from hemin, the toxic
residue remaining following the digestion of hemoglobin
by the parasite.<xref rid="jm0109291b00004" ref-type="bibr"></xref> Drugs that have a chloroquine-like
mode of action may be detected by testing their ability
to prevent the formation of β-hematin (shown to be
identical to hemozoin<xref rid="jm0109291b00005" ref-type="bibr"></xref>) from hemin in a cell-free system.<xref rid="jm0109291b00006" ref-type="bibr"></xref> Peaks at 1660 and 1210 cm<sup>-1</sup> in the FTIR
spectrum of the product confirm the presence of β-hematin (see below). To assess cryptolepine analogues for
their potential as leads to selective antimalarial agents,
we have determined their antiplasmodial activities
against chloroquine-resistant and chloroquine-sensitive
strains of <italic toggle="yes">Plasmodium falciparum</italic>. Those compounds
displaying potent in vitro antiplasmodial activities have
been assessed for in vivo antimalarial activity against
<italic toggle="yes">Plasmodium berghei</italic> in mice. Selected compounds have
been tested for their abilities to inhibit β-hematin
formation. Thermodenaturation techniques have been
used to examine the effects of compounds on the melting
point of calf thymus DNA as an indication of their
potential to interact with DNA, and preliminary cytotoxicity tests have been carried out.
<fig id="jm0109291f1" position="float" orientation="portrait"><label></label><graphic xlink:href="jm0109291f1.tif" position="float" orientation="portrait"></graphic></fig></p></sec><sec id="d7e322"><title>Chemistry</title><p>Cryptolepine (<bold>1</bold>) was isolated from <italic toggle="yes">C. sanguinolenta
</italic>as described previously<sup>2</sup> or prepared by methylation of
quindoline, which was synthesized using methodology
based on that of Holt and Petrow (1947)<xref rid="jm0109291b00007" ref-type="bibr"></xref> (Scheme 1).
Isatin (<bold>2</bold>a) was condensed with <italic toggle="yes">O</italic>,<italic toggle="yes">N</italic>-acetylindoxyl (<bold>3a)
</bold>in the presence of KOH under oxygen-free conditions
to give quindoline-11-carboxylic acid (<bold>4a</bold>). The latter was
decarboxylated by heating in diphenyl ether to yield
quindoline (<bold>5a</bold>), which was then methylated using
iodomethane in tetramethylenesulfone<xref rid="jm0109291b00008" ref-type="bibr"></xref> (this method
was found to be much more efficient than methylation
with dimethylsulfate or methyl triflate). The 2-bromo
analogue <bold>6</bold> was prepared similarly using 5-bromoisatin
(<bold>2b</bold>) and <italic toggle="yes">O</italic>,<italic toggle="yes">N</italic>-acetylindoxyl (<bold>3a) </bold>as starting materials
while the reaction of isatin (<bold>2a</bold>) with 5-bromo-<italic toggle="yes">O</italic>,<italic toggle="yes">N</italic>-acetylindoxyl (<bold>3b</bold>) provided a route to 7-bromocryptolepine (<bold>7</bold>). Similarly, 5-bromoisatin (<bold>2b</bold>) and 5-bromo-<italic toggle="yes">O</italic>,<italic toggle="yes">N</italic>-acetylindoxyl (<bold>3b</bold>) were used as starting materials
for the synthesis of 2,7-dibromocryptolepine (<bold>8</bold>). Quindoline-11-amide (<bold>9</bold>) was synthesized by reacting <bold>4a</bold> with
thionyl chloride to give the acid chloride, followed by
ammoniolysis as previously described<sup>7</sup> (Scheme 1).
<fig id="jm0109291h00001" position="float" orientation="portrait"><label></label><graphic xlink:href="jm0109291h00001.tif" position="float" orientation="portrait"></graphic></fig></p><p>Nitration was used as a convenient method of preparing derivatives directly from <bold>1</bold> (Scheme 2). At room
temperature, nitration of <bold>1 </bold>with a mixture of nitric and
glacial acetic acids (1:1) yielded 7-nitrocryptolepine (<bold>10)
</bold>as the major product together with a smaller amount
of the 9-nitro- isomer <bold>11, </bold>which were then separated
by column chromatography over silica gel eluted with
chloroform/methanol. Refluxing the above reaction mixture afforded 7,9-dinitrocryptolepine (<bold>12) </bold>as the sole
product. Two meta-coupled doublets in the <sup>1</sup>H NMR
spectrum of <bold>12</bold> (δ 9.13 and 9.64, <italic toggle="yes">J</italic> = 2.2 Hz) together
with the downfield shift of the singlet due to H-11 (δ
9.55) initially suggested that <bold>12 </bold>was the 1,3-dinitro
analogue of <bold>1</bold>, but X-ray crystallographic analysis of <bold>12
</bold>(data not shown)<xref rid="jm0109291b00009" ref-type="bibr"></xref> proved unequivocally that <bold>12 </bold>is the
7,9-dinitro analogue of <bold>1</bold>. Reduction of 7-nitrocryptolepine (<bold>10) </bold>(Sn/HCl) gave the reactive and light-sensitive 7-amino analogue that was isolated and immediately acetylated to give 7-<italic toggle="yes">N</italic>-acetylcryptolepine <bold>13
</bold>(Scheme 2).
<fig id="jm0109291h00002" position="float" orientation="portrait"><label></label><graphic xlink:href="jm0109291h00002.tif" position="float" orientation="portrait"></graphic></fig></p><p>The 11-chloro derivative <bold>20</bold> was prepared as previously described by Bierer et al. (1998),<xref rid="jm0109291b00010" ref-type="bibr"></xref> and the same
route (Scheme 3) was used to synthesize the novel
dihalogenated derivatives <bold>21</bold><bold>−</bold><bold>24</bold>. Reaction of an anthranilic acid derivative <bold>14 </bold>with bromoacetylbromide gave
<bold>15, </bold>which was treated with an aniline derivative <bold>16</bold>. The
resulting anthranilic acid derivative <bold>17</bold> was then cyclized using polyphosphoric acid to yield quindolone <bold>18</bold>;
treatment with phosphorus oxychloride gave 11-chloroquindoline derivative <bold>19</bold>, which was then methylated
with iodomethane in tetramethylenesulfone to give the
corresponding cryptolepine analogues, <bold>20</bold><bold>−</bold><bold>24</bold>.
<fig id="jm0109291h00003" position="float" orientation="portrait"><label></label><graphic xlink:href="jm0109291h00003.tif" position="float" orientation="portrait"></graphic></fig></p></sec><sec id="d7e536"><title>Results and Discussion</title><p>The activities of compounds against <italic toggle="yes">P. falciparum</italic> in
vitro and against <italic toggle="yes">P. berghei </italic>in vivo and their effects on
β-hematin formation are shown in Table <xref rid="jm0109291t00001"></xref>; Δ<italic toggle="yes">T</italic><sub>m</sub> values
(increase in melting point of DNA) and cytotoxic activities are reported in Table <xref rid="jm0109291t00002"></xref>.
<table-wrap id="jm0109291t00001" position="float" orientation="portrait"><label>1</label><caption><p>In Vitro Antiplasmodial and In Vivo Antimalarial Activities of Cryptolepine Derivatives and Chloroquine Diphosphate against Malaria Parasites and Effects on Formation of β-Hematin</p></caption><oasis:table colsep="2" rowsep="2"><oasis:tgroup cols="7"><oasis:colspec colnum="1" colname="1"></oasis:colspec><oasis:colspec colnum="2" colname="2"></oasis:colspec><oasis:colspec colnum="3" colname="3"></oasis:colspec><oasis:colspec colnum="4" colname="4"></oasis:colspec><oasis:colspec colnum="5" colname="5"></oasis:colspec><oasis:colspec colnum="6" colname="6"></oasis:colspec><oasis:colspec colnum="7" colname="7"></oasis:colspec><oasis:tbody><oasis:row><oasis:entry colname="1"></oasis:entry><oasis:entry namest="2" nameend="3">activity vs
<italic toggle="yes">P. falciparum</italic> in vitro<italic toggle="yes"><sup>b</sup></italic><sup></sup></oasis:entry><oasis:entry colname="4"></oasis:entry><oasis:entry namest="5" nameend="7">activity against
<italic toggle="yes">P. berghei</italic> (ANKA) in mice</oasis:entry></oasis:row><oasis:row><oasis:entry namest="1" nameend="1">compd<italic toggle="yes"><sup>a</sup></italic><sup></sup></oasis:entry><oasis:entry namest="2" nameend="2">chloroquine-
resistant
strain K1</oasis:entry><oasis:entry namest="3" nameend="3">chloroquine-
sensitive
strain HB3</oasis:entry><oasis:entry namest="4" nameend="4">inhibition of
β-hematin
formation</oasis:entry><oasis:entry namest="5" nameend="5">dose schedule
(mg kg<sup>-1 </sup>for 4 d)</oasis:entry><oasis:entry namest="6" nameend="6">mean
parasitemia
(% ± SD)</oasis:entry><oasis:entry namest="7" nameend="7">suppression
of parasitemia
(%)
</oasis:entry></oasis:row><oasis:row><oasis:entry colname="1">1 (as sulfate)
</oasis:entry><oasis:entry colname="2">0.44 ± 0.22(9)
</oasis:entry><oasis:entry colname="3">0.27 ± 0.06(3)
</oasis:entry><oasis:entry colname="4">yes
</oasis:entry><oasis:entry colname="5">20<italic toggle="yes"><sup>c</sup></italic><sup></sup></oasis:entry><oasis:entry colname="6">NT<italic toggle="yes"><sup>d</sup></italic><sup></sup></oasis:entry><oasis:entry colname="7"><italic toggle="yes">e</italic></oasis:entry></oasis:row><oasis:row><oasis:entry colname="1"><bold>4a</bold></oasis:entry><oasis:entry colname="2">>100
</oasis:entry><oasis:entry colname="3">NT
</oasis:entry><oasis:entry colname="4">no
</oasis:entry><oasis:entry colname="5">NT
</oasis:entry><oasis:entry colname="6">NT
</oasis:entry><oasis:entry colname="7">NT
</oasis:entry></oasis:row><oasis:row><oasis:entry colname="1"><bold>5a</bold></oasis:entry><oasis:entry colname="2">>100
</oasis:entry><oasis:entry colname="3">NT
</oasis:entry><oasis:entry colname="4">no
</oasis:entry><oasis:entry colname="5">NT
</oasis:entry><oasis:entry colname="6">NT
</oasis:entry><oasis:entry colname="7">NT
</oasis:entry></oasis:row><oasis:row><oasis:entry colname="1"><bold>6</bold></oasis:entry><oasis:entry colname="2">0.26 ± 0.094(4)
</oasis:entry><oasis:entry colname="3">0.45 ± 0.17(3)
</oasis:entry><oasis:entry colname="4">yes
</oasis:entry><oasis:entry colname="5">25
</oasis:entry><oasis:entry colname="6">21.6 ± 1.9
</oasis:entry><oasis:entry colname="7">5.9
</oasis:entry></oasis:row><oasis:row><oasis:entry colname="1"><bold>7</bold> (as hydroiodide)
</oasis:entry><oasis:entry colname="2">0.26 ± 0.21(4)
</oasis:entry><oasis:entry colname="3">0.19 ± 0.09(3)
</oasis:entry><oasis:entry colname="4">yes
</oasis:entry><oasis:entry colname="5">20
</oasis:entry><oasis:entry colname="6">11.9 ± 2.0
</oasis:entry><oasis:entry colname="7">41.5
</oasis:entry></oasis:row><oasis:row><oasis:entry colname="1"><bold>8</bold></oasis:entry><oasis:entry colname="2">0.049 ± 0.017
</oasis:entry><oasis:entry colname="3">0.026 ± 0.005(3)
</oasis:entry><oasis:entry colname="4">yes
</oasis:entry><oasis:entry colname="5">12.5
</oasis:entry><oasis:entry colname="6">1.4 ± 0.4
</oasis:entry><oasis:entry colname="7">89.1
</oasis:entry></oasis:row><oasis:row><oasis:entry colname="1"><bold>9</bold></oasis:entry><oasis:entry colname="2">>100
</oasis:entry><oasis:entry colname="3">NT
</oasis:entry><oasis:entry colname="4">no
</oasis:entry><oasis:entry colname="5">NT
</oasis:entry><oasis:entry colname="6">NT
</oasis:entry><oasis:entry colname="7">NT
</oasis:entry></oasis:row><oasis:row><oasis:entry colname="1"><bold>10</bold></oasis:entry><oasis:entry colname="2">0.65 ± 0.28(6)
</oasis:entry><oasis:entry colname="3">0.14 ± 0.05(3)
</oasis:entry><oasis:entry colname="4">yes
</oasis:entry><oasis:entry colname="5">20
</oasis:entry><oasis:entry colname="6">6.0 ± 1.2
</oasis:entry><oasis:entry colname="7">61.4
</oasis:entry></oasis:row><oasis:row><oasis:entry colname="1"><bold>11</bold></oasis:entry><oasis:entry colname="2">6.92 ± 1.89(4)
</oasis:entry><oasis:entry colname="3">4.14 ± 2.29(3)
</oasis:entry><oasis:entry colname="4">ND<italic toggle="yes"><sup>f</sup></italic><sup></sup></oasis:entry><oasis:entry colname="5">20
</oasis:entry><oasis:entry colname="6">11.9 ± 2.0
</oasis:entry><oasis:entry colname="7">23.5
</oasis:entry></oasis:row><oasis:row><oasis:entry colname="1"><bold>12</bold></oasis:entry><oasis:entry colname="2">0.65 ± 0.21(6)
</oasis:entry><oasis:entry colname="3">0.45 ± 0.22(3)
</oasis:entry><oasis:entry colname="4">yes
</oasis:entry><oasis:entry colname="5">20
</oasis:entry><oasis:entry colname="6">20.3 ± 2.0
</oasis:entry><oasis:entry colname="7">−30.2
</oasis:entry></oasis:row><oasis:row><oasis:entry colname="1"><bold>13</bold></oasis:entry><oasis:entry colname="2">0.52 ± 0.21(5)
</oasis:entry><oasis:entry colname="3">0.47 ± 0.16(3)
</oasis:entry><oasis:entry colname="4">ND
</oasis:entry><oasis:entry colname="5">20
</oasis:entry><oasis:entry colname="6">13.3 ± 2.1
</oasis:entry><oasis:entry colname="7">14.7
</oasis:entry></oasis:row><oasis:row><oasis:entry colname="1"><bold>20</bold></oasis:entry><oasis:entry colname="2">0.24 ± 0.1(3)
</oasis:entry><oasis:entry colname="3">1.67 ± 1.27(3)
</oasis:entry><oasis:entry colname="4">ND
</oasis:entry><oasis:entry colname="5">20
</oasis:entry><oasis:entry colname="6">NT
</oasis:entry><oasis:entry colname="7"><italic toggle="yes">g</italic></oasis:entry></oasis:row><oasis:row><oasis:entry colname="1"><bold>21</bold> (as hydroiodide)
</oasis:entry><oasis:entry colname="2">4.75 ± 0.37(3)
</oasis:entry><oasis:entry colname="3">NT
</oasis:entry><oasis:entry colname="4">ND
</oasis:entry><oasis:entry colname="5">NT
</oasis:entry><oasis:entry colname="6">NT
</oasis:entry><oasis:entry colname="7">NT
</oasis:entry></oasis:row><oasis:row><oasis:entry colname="1"><bold>22</bold></oasis:entry><oasis:entry colname="2">7.18 ± 3.5(4)
</oasis:entry><oasis:entry colname="3">NT
</oasis:entry><oasis:entry colname="4">ND
</oasis:entry><oasis:entry colname="5">NT
</oasis:entry><oasis:entry colname="6">NT
</oasis:entry><oasis:entry colname="7">NT
</oasis:entry></oasis:row><oasis:row><oasis:entry colname="1"><bold>23</bold></oasis:entry><oasis:entry colname="2">7.62 ± 2.7(4)
</oasis:entry><oasis:entry colname="3">NT
</oasis:entry><oasis:entry colname="4">NT
</oasis:entry><oasis:entry colname="5">NT
</oasis:entry><oasis:entry colname="6">NT
</oasis:entry><oasis:entry colname="7">NT
</oasis:entry></oasis:row><oasis:row><oasis:entry colname="1"><bold>24</bold></oasis:entry><oasis:entry colname="2">27.0 ± 5.4(3)
</oasis:entry><oasis:entry colname="3">NT
</oasis:entry><oasis:entry colname="4">ND
</oasis:entry><oasis:entry colname="5">NT
</oasis:entry><oasis:entry colname="6">NT
</oasis:entry><oasis:entry colname="7">NT
</oasis:entry></oasis:row><oasis:row><oasis:entry colname="1">chloroquine diphosphate
</oasis:entry><oasis:entry colname="2">0.18 ± 0.025(7)
</oasis:entry><oasis:entry colname="3">0.023 ± 0.0015(3)
</oasis:entry><oasis:entry colname="4">yes
</oasis:entry><oasis:entry colname="5">10
</oasis:entry><oasis:entry colname="6">1.3 ± 0.5
</oasis:entry><oasis:entry colname="7">93.8</oasis:entry></oasis:row></oasis:tbody></oasis:tgroup></oasis:table><table-wrap-foot><p><italic toggle="yes"><sup>a</sup></italic><sup></sup> Tested as hydrochloride salt unless stated otherwise.<italic toggle="yes"><sup>b</sup></italic><sup></sup> IC<sub>50</sub> μM ± SD(<italic toggle="yes">n</italic>). <italic toggle="yes">n</italic>, number of separate determinations.<italic toggle="yes"><sup>c</sup></italic><sup></sup>Tested as hydrochloride.<italic toggle="yes"><sup>d</sup></italic><sup></sup> NT, not tested.<italic toggle="yes"><sup>e</sup></italic><sup></sup> Toxic after second dose.<italic toggle="yes"><sup>f</sup></italic><sup></sup> ND, could not be determined as compound has peaks in the IR spectrum close to 1660 cm<sup>-1</sup>.<italic toggle="yes"><sup>g</sup></italic><sup></sup> Toxic after first dose.</p></table-wrap-foot></table-wrap><table-wrap id="jm0109291t00002" position="float" orientation="portrait"><label>2</label><caption><p>Cytotoxicity and Effect on DNA Melting Point of Cryptolepine Derivatives</p></caption><oasis:table colsep="2" rowsep="2"><oasis:tgroup cols="8"><oasis:colspec colnum="1" colname="1"></oasis:colspec><oasis:colspec colnum="2" colname="2"></oasis:colspec><oasis:colspec colnum="3" colname="3"></oasis:colspec><oasis:colspec colnum="4" colname="4"></oasis:colspec><oasis:colspec colnum="5" colname="5"></oasis:colspec><oasis:colspec colnum="6" colname="6"></oasis:colspec><oasis:colspec colnum="7" colname="7"></oasis:colspec><oasis:colspec colnum="8" colname="8"></oasis:colspec><oasis:tbody><oasis:row><oasis:entry colname="1"></oasis:entry><oasis:entry colname="2"></oasis:entry><oasis:entry namest="3" nameend="8">IC<sub>50</sub><sub> </sub>(μM ± SD) (<italic toggle="yes">n</italic> = 3)<italic toggle="yes"><sup>a</sup></italic><sup></sup></oasis:entry></oasis:row><oasis:row><oasis:entry colname="1"></oasis:entry><oasis:entry colname="2"></oasis:entry><oasis:entry namest="3" nameend="4">cytotoxicity against
A549 cells</oasis:entry><oasis:entry namest="5" nameend="6">cytotoxicity against
DLD-1 cells</oasis:entry><oasis:entry namest="7" nameend="8">cytotoxicity against
MAC15a cells</oasis:entry></oasis:row><oasis:row><oasis:entry namest="1" nameend="1">compd</oasis:entry><oasis:entry namest="2" nameend="2">effect on DNA
melting point,
Δ<italic toggle="yes">T</italic><sub>m</sub> (°C)</oasis:entry><oasis:entry namest="3" nameend="3">drug
exposure
time 1 h</oasis:entry><oasis:entry namest="4" nameend="4">drug
exposure
time 96 h</oasis:entry><oasis:entry namest="5" nameend="5">drug
exposure
time 1 h</oasis:entry><oasis:entry namest="6" nameend="6">drug
exposure
time 96 h</oasis:entry><oasis:entry namest="7" nameend="7">drug
exposure
time 1 h</oasis:entry><oasis:entry namest="8" nameend="8">drug
exposure
time 96 h
</oasis:entry></oasis:row><oasis:row><oasis:entry colname="1"><bold>1</bold> (as sulfate)
</oasis:entry><oasis:entry colname="2">9
</oasis:entry><oasis:entry colname="3">61.4 ± 18.2
</oasis:entry><oasis:entry colname="4">0.55 ± 0.051
</oasis:entry><oasis:entry colname="5">93 ± 29
</oasis:entry><oasis:entry colname="6">1.44 ± 0.0015
</oasis:entry><oasis:entry colname="7">67.2 ± 26.3
</oasis:entry><oasis:entry colname="8">9.65 ± 1.37
</oasis:entry></oasis:row><oasis:row><oasis:entry colname="1"><bold>5a</bold></oasis:entry><oasis:entry colname="2">0
</oasis:entry><oasis:entry colname="3">NT<italic toggle="yes"><sup>b</sup></italic><sup></sup></oasis:entry><oasis:entry colname="4">NT
</oasis:entry><oasis:entry colname="5">NT
</oasis:entry><oasis:entry colname="6">NT
</oasis:entry><oasis:entry colname="7">NT
</oasis:entry><oasis:entry colname="8">NT
</oasis:entry></oasis:row><oasis:row><oasis:entry colname="1"><bold>6</bold></oasis:entry><oasis:entry colname="2">4
</oasis:entry><oasis:entry colname="3">>100
</oasis:entry><oasis:entry colname="4">2.07 ± 0.21
</oasis:entry><oasis:entry colname="5">>100
</oasis:entry><oasis:entry colname="6">2.29 ± 0.67
</oasis:entry><oasis:entry colname="7">>100
</oasis:entry><oasis:entry colname="8">5.79 ± 0.91
</oasis:entry></oasis:row><oasis:row><oasis:entry colname="1"><bold>7</bold> (as hydroiodide)
</oasis:entry><oasis:entry colname="2">4
</oasis:entry><oasis:entry colname="3">NT
</oasis:entry><oasis:entry colname="4">NT
</oasis:entry><oasis:entry colname="5">NT
</oasis:entry><oasis:entry colname="6">NT
</oasis:entry><oasis:entry colname="7">66.2 ± 8.02
</oasis:entry><oasis:entry colname="8">NT
</oasis:entry></oasis:row><oasis:row><oasis:entry colname="1"><bold>8</bold></oasis:entry><oasis:entry colname="2">3
</oasis:entry><oasis:entry colname="3">NT
</oasis:entry><oasis:entry colname="4">NT
</oasis:entry><oasis:entry colname="5">NT
</oasis:entry><oasis:entry colname="6">NT
</oasis:entry><oasis:entry colname="7">NT
</oasis:entry><oasis:entry colname="8">6.04 ± 0.49
</oasis:entry></oasis:row><oasis:row><oasis:entry colname="1"><bold>10</bold></oasis:entry><oasis:entry colname="2">5
</oasis:entry><oasis:entry colname="3">35.6 ± 2.2
</oasis:entry><oasis:entry colname="4">NT
</oasis:entry><oasis:entry colname="5">48.9 ± 7.6
</oasis:entry><oasis:entry colname="6">NT
</oasis:entry><oasis:entry colname="7">35.4 ± 4.8
</oasis:entry><oasis:entry colname="8">NT
</oasis:entry></oasis:row><oasis:row><oasis:entry colname="1"><bold>11</bold></oasis:entry><oasis:entry colname="2">4
</oasis:entry><oasis:entry colname="3">90.2 ± 7.8
</oasis:entry><oasis:entry colname="4">NT
</oasis:entry><oasis:entry colname="5">>100
</oasis:entry><oasis:entry colname="6">NT
</oasis:entry><oasis:entry colname="7">>100
</oasis:entry><oasis:entry colname="8">NT
</oasis:entry></oasis:row><oasis:row><oasis:entry colname="1"><bold>12</bold></oasis:entry><oasis:entry colname="2">4
</oasis:entry><oasis:entry colname="3">>100
</oasis:entry><oasis:entry colname="4">NT
</oasis:entry><oasis:entry colname="5">>100
</oasis:entry><oasis:entry colname="6">NT
</oasis:entry><oasis:entry colname="7">28.5 ± 9.3
</oasis:entry><oasis:entry colname="8">NT
</oasis:entry></oasis:row><oasis:row><oasis:entry colname="1"><bold>13</bold></oasis:entry><oasis:entry colname="2">6
</oasis:entry><oasis:entry colname="3">>100
</oasis:entry><oasis:entry colname="4">5.04 ± 1.05
</oasis:entry><oasis:entry colname="5">>100
</oasis:entry><oasis:entry colname="6">20.41 ± 1.1
</oasis:entry><oasis:entry colname="7">>100
</oasis:entry><oasis:entry colname="8">15.47 ± 4.2
</oasis:entry></oasis:row><oasis:row><oasis:entry colname="1"><bold>20</bold></oasis:entry><oasis:entry colname="2">0
</oasis:entry><oasis:entry colname="3">NT
</oasis:entry><oasis:entry colname="4">NT
</oasis:entry><oasis:entry colname="5">NT
</oasis:entry><oasis:entry colname="6">NT
</oasis:entry><oasis:entry colname="7">30.5 ± 6.2
</oasis:entry><oasis:entry colname="8">NT
</oasis:entry></oasis:row><oasis:row><oasis:entry colname="1"><bold>22</bold></oasis:entry><oasis:entry colname="2">9
</oasis:entry><oasis:entry colname="3">NT
</oasis:entry><oasis:entry colname="4">NT
</oasis:entry><oasis:entry colname="5">NT
</oasis:entry><oasis:entry colname="6">NT
</oasis:entry><oasis:entry colname="7">23.1 ± 2.7
</oasis:entry><oasis:entry colname="8">NT
</oasis:entry></oasis:row><oasis:row><oasis:entry colname="1"><bold>24</bold></oasis:entry><oasis:entry colname="2">9
</oasis:entry><oasis:entry colname="3">NT
</oasis:entry><oasis:entry colname="4">NT
</oasis:entry><oasis:entry colname="5">NT
</oasis:entry><oasis:entry colname="6">NT
</oasis:entry><oasis:entry colname="7">14.4 ± 2.8
</oasis:entry><oasis:entry colname="8">NT</oasis:entry></oasis:row></oasis:tbody></oasis:tgroup></oasis:table><table-wrap-foot><p><italic toggle="yes"><sup>a</sup></italic><sup></sup> <italic toggle="yes">n</italic>, number of separate determinations.<italic toggle="yes"><sup>b</sup></italic><sup></sup> NT, not tested.</p></table-wrap-foot></table-wrap></p><p><bold>In Vitro Antiplasmodial Activity.</bold> Cryptolepine (<bold>1</bold>)
was found to have potent in vitro activity (IC<sub>50</sub> = 0.44
μM) against <italic toggle="yes">P. falciparum</italic> (multidrug resistant strain
K1) similar to that published in previous reports.<named-content content-type="bibref-group"><xref rid="jm0109291b00002" ref-type="bibr"></xref>,<xref rid="jm0109291b00011" ref-type="bibr"></xref></named-content>
However, quindoline (<bold>5a</bold>), quindoline-11-carboxylic acid
(<bold>4a), </bold>and its amide <bold>9</bold> were inactive against malaria
parasites (strain K1), indicating that the 5-methyl group
in <bold>1</bold> is a prerequisite for antiplasmodial activity. The
7-nitro <bold>(10</bold>), 7,9-dinitro (<bold>12), </bold>and 7-<italic toggle="yes">N</italic>-acetyl (<bold>13</bold>) derivatives were of similar potency to <bold>1 </bold>against <italic toggle="yes">P. falciparum
</italic>while 9-nitrocryptolepine (<bold>11</bold>) was 10-fold less active.
Monohalogenated derivatives <bold>6</bold>, <bold>7</bold>, and <bold>20</bold> were slightly
more potent than <bold>1</bold> against <italic toggle="yes">P. falciparum </italic>(strain K1).
Compound <bold>8</bold> (2,7-dibromocryptolepine) was prepared
because both the 2-bromo (<bold>6</bold>) and the 7-bromo (<bold>7</bold>)
analogues showed improved antiplasmodial activities as
compared with <bold>1</bold>. This strategy was successful as the
antiplasmodial activity of <bold>8 </bold>was found to be 9-fold
greater than that of <bold>1</bold>. However, in contrast, the
2-bromo,11-chloro derivative (<bold>21</bold>) was found to be about
20-fold less active than the 2-bromo (<bold>6</bold>) and 11-chloro
(<bold>20</bold>) derivatives. Similarly, the other dihalogenated
analogues that were 11-chloro-substituted (<bold>22</bold><bold>−</bold><bold>24</bold>) have
little antiplasmodial activity.
</p><p>Compounds active against <italic toggle="yes">P. falciparum </italic>(strain K1)
were also tested against chloroquine-sensitive strain
HB3 to determine whether they exhibit cross-resistance
with chloroquine. As shown in Table <xref rid="jm0109291t00001"></xref>, chloroquine was
8-fold less active against chloroquine-resistant strain K1
than against strain HB3. The antiplasmodial activities
of seven of the nine compounds tested were similar
against both parasite strains (less than a 2-fold variation). One compound, 7-nitrocryptolepine (<bold>10</bold>), was
4-fold less active against strain HB3 while the 11-choro
analogue <bold>20</bold> was 7-fold more active against chloroquine-resistant strain K1. These results suggest that cryptolepine and its derivatives with the possible exception
of <bold>10</bold> do not show cross-resistance with chloroquine,
although, as discussed below, they share the ability to
inhibit β-hematin formation.
</p><p><bold>In Vivo Antimalarial Activity.</bold> Cryptolepine (<bold>1)
</bold>was toxic to <italic toggle="yes">P. </italic><italic toggle="yes">berghei</italic>-infected mice by ip injection at
a dose of 12.5 mg kg<sup>-1</sup> day<sup>-1</sup> (Table <xref rid="jm0109291t00001"></xref>). Toxicity appears
to be related to the route of administration as no deaths
were reported in previous studies in which subcutaneous (at 113 mg<sup>-1</sup> kg<sup>-1</sup> day)<sup>11</sup> or oral (50 mg kg<sup>-1</sup> day<sup>-1</sup>)<sup>2</sup>
routes were used. In the former study, no effect on
parasitemia was observed, but oral administration of <bold>1</bold>
at 50 mg kg<sup>-1</sup> day<sup>-1</sup> for 4 days suppressed parasitemia
by 80.5%<sup>2</sup>.
</p><p>In this study, <bold>7</bold>, <bold>8</bold>, <bold>10</bold>, and <bold>11</bold> suppressed parasitemia
by more than 20%. Although<bold> 11 </bold>displayed only weak in
vitro antiplasmodial activity it was found to have
greater in vivo activity (23% suppression of parasitemia)
than compounds <bold>6, </bold><bold>12</bold>, and <bold>13, </bold>which all have potent
in vitro antiplasmodial activities. Interestingly, mice
treated with <bold>12</bold> were found to have a mean parasitemia
30% above that of untreated control animals, while in
common with (<bold>1</bold>), the 11-chloro analogue <bold>20 </bold>was toxic
to mice. Compounds <bold>7 </bold>and <bold>10</bold> possess moderate in vivo
antimalarial activities (42 and 61%, respectively, at 20
mg kg<sup>-1</sup> day<sup>-1</sup>), but the most potent compound, 2,7-dibromocryptolepine (<bold>8</bold>), was found to suppress parasitemia by 89% at a daily dose of 12.5 mg kg<sup>-1</sup>. The in
vivo activity of <bold>8 </bold>is comparable to that of chloroquine,
and further studies to determine the oral effectiveness
this compound and its ability to cure malaria in mice
are currently being carried out.
</p><p><bold>Effect on </bold><bold>β</bold><bold>-Hematin Formation.</bold> Cryptolepine (<bold>1)
</bold>prevented the formation of β-hematin (Figure <xref rid="jm0109291f00001"></xref>), which
suggests that its antiplasmodial effect depends (at least
in part) on a quinine-like mode of action, although it is
possible that its effects on DNA synthesis and inhibition
of topoisomerase II may also contribute. This is supported by a recent study using fluorescence microscopy,
which suggests that <bold>1</bold> accumulates into parasite structures that may correspond to the parasite nucleus.<xref rid="jm0109291b00012" ref-type="bibr"></xref> In
contrast, <bold>4</bold>, <bold>5</bold>, and <bold>9</bold>, which are inactive against malaria
parasites, failed to inhibit β-hematin formation (Table
<xref rid="jm0109291t00001"></xref>). Several of the derivatives possessing potent antiplasmodial activities (<bold>6</bold><bold>−</bold><bold>8</bold>, <bold>10</bold>, and <bold>12</bold>) like <bold>1</bold> inhibited
β-hematin formation, indicating that this property may
be important for their action against malaria parasites.
It was not possible to determine the effects of <bold>11, 13,
</bold>and <bold>20</bold> on β-hematin formation because their IR spectra
have peaks close to 1660 cm<sup>-1</sup>, which may mask the
peak of β-hematin that occurs at this wavelength.
<fig id="jm0109291f00001" position="float" orientation="portrait"><label>1</label><caption><p>Inhibition of β-hematin formation by<bold>1</bold>. (A) FTIR
spectrum of control reaction product showing peaks at 1663
and 1210 cm<sup>-1</sup> characteristic of β-hematin. (B) As above in the
presence of <bold>1</bold>, demonstrating inhibition of β-hematin formation.</p></caption><graphic xlink:href="jm0109291f00001.tif" position="float" orientation="portrait"></graphic></fig></p><p><bold>Cytotoxicity and Effect on Δ</bold><bold><italic toggle="yes">T</italic></bold><bold><sub>m</sub> Value.</bold> As <bold>1 </bold>is
known to be toxic to cancer cells,<xref rid="jm0109291b00003" ref-type="bibr"></xref> initial tests for
cytotoxicity were carried out by exposing cancer cells
(A549, DLD-1, and MAC15A) to compounds for 1 h
followed by a 96-h incubation period. The results suggested that three compounds <bold>6</bold>, <bold>11</bold>, and <bold>13</bold> may be less
toxic than <bold>1 </bold>against all three cell lines (Table <xref rid="jm0109291t00002"></xref>).
However, as the IC<sub>50</sub> values for <bold>1 </bold>are close to 100 μM,
the highest concentration tested, further experiments
using a drug−cell contact time of 96 h were carried out
to determine the extent by which <bold>6 </bold>and <bold>13</bold> are less toxic
than <bold>1</bold>; the latter were selected as they possess good
antiplasmodial activities. Against A549 and DLD-1 cells,
<bold>6</bold> was found to be about 4- and 2-fold less toxic,
respectively, than <bold>1</bold>, but it was about 2-fold more toxic
than<bold> 1 </bold>against MAC15A cells. The best selectivity was
seen with <bold>13 </bold>against DLD-1 cells (about 14-fold less
toxic) and against A549 cells (about 9-fold less toxic),
but little difference was observed with MAC15A cells
(about 1.6-fold less toxic). However, there appears to be
little correlation between the in vitro cytoxicity of these
compounds and toxicity in the mouse−malaria model.
While <bold>10</bold> and <bold>20</bold> were about twice as toxic to MAC15A
cells than <bold>1</bold>, in the antimalarial test only <bold>20 </bold>was toxic
to mice. Compound <bold>8 </bold>was slightly more cytotoxic to
cancer cells than <bold>1</bold>, but no apparent toxicity was seen
in mice in striking contrast to <bold>1</bold>, which was substantially toxic to mice after two doses, although it must be
noted that the daily dose of <bold>1 </bold>given to mice (20 mg kg<sup>-1</sup>)
was greater than that of <bold>8</bold> (12.5 mg kg<sup>-1</sup>).
</p><p>The effects of compounds on the melting point of calf
thymus DNA (Δ<italic toggle="yes">T</italic><sub>m</sub> values) were measured in an attempt to obtain an indication of their propensities to
interact with DNA. The value of 9 °C found for <bold>1 </bold>is
consistent with its known DNA-intercalating ability<sup>3</sup>.
With the exceptions of <bold>22</bold> and <bold>24</bold>, the Δ<italic toggle="yes">T</italic><sub>m</sub> values of the
other compounds tested were all 6 °C or less (Table <xref rid="jm0109291t00002"></xref>),
which may indicate a reduced tendency of the latter to
interact with DNA as compared to <bold>1</bold>. However, no
correlation was observed between Δ<italic toggle="yes">T</italic><sub>m</sub> value and cytotoxicity or toxicity in the mouse−malaria model; this is
well illustrated with reference to <bold>1</bold> and <bold>20</bold>, which were
both toxic to mice but were found to have Δ<italic toggle="yes">T</italic><sub>m</sub> values
of 9 and 0 °C, respectively.
</p></sec><sec id="d7e1715"><title>Conclusion</title><p>A number of analogues of <bold>1</bold> have been synthesized
that have improved antiplasmodial activities as compared to the parent against both chloroquine-sensitive
and chloroquine-resistant strains of <italic toggle="yes">P. falciparum.</italic> With
the possible exception of <bold>10</bold>, there was no evidence of
cross-resistance with chloroquine even though these
compounds (like the parent) appear to have a chloroquine-like mode of action against malaria parasites.
Several compounds were found to have some activity
against <italic toggle="yes">P. berghei</italic> in mice, the most potent being 2,7-dibromocryptolepine (<bold>8</bold>), which suppressed parasitemia
by 89% at a dose of 12.5 mg kg<sup>-1</sup> day<sup>-1</sup> with no apparent
toxicity to the mice. There appears to be no correlation
between the in vitro cytotoxicity and the effect of
compounds on the melting point of DNA or toxicity in
the mouse−malaria model.
</p><p>This study has shown that some derivatives of <bold>1</bold>,
particularly <bold>8</bold>, are promising leads in the search for new
antimalarial agents. In addition, analogues of <bold>1, </bold>which
have enhanced cytotoxicity (such as <bold>24</bold>, which was 4−5-fold more active than <bold>1 </bold>against MAC15A cells), may be
worthy of investigation as antitumor agents. This is
supported by recent studies on the cytotoxic properties
of compounds related to <bold>1</bold>.<named-content content-type="bibref-group"><xref rid="jm0109291b00013" ref-type="bibr"></xref>−<xref rid="jm0109291b00014" specific-use="suppress-in-print" ref-type="bibr"></xref><xref rid="jm0109291b00015" ref-type="bibr"></xref></named-content></p></sec><sec id="d7e1767"><title>Experimental Section</title><p><bold>Chemistry. </bold>Chemicals were purchased from Sigma-Aldrich
Chemical Co. Ltd., Poole, U.K. <sup>1</sup>H NMR spectra were acquired
on a JEOL GX270 FT NMR spectrometer at 270 MHz. Mass
spectra were run on an AEI MS902 spectrometer equipped
with an MSS data acquisition system, version 10 (Mass
Spectrometer Services, Manchester, U.K.). C, H, and N
analyses were carried out by the Chemical and Materials
Analysis Unit, University of Newcastle, U.K., on a Carlo Erba
1106 elemental analyzer. FTIR spectra were recorded on a
Mattson Galaxy 6020 FTIR spectrometer.
</p><p><bold>General Method for Preparation of 2-Bromoquindoline (5b) and 7-Bromoquindoline (5c).</bold> <italic toggle="yes">O,N</italic>-Acetylindoxyl
(<bold>3a</bold>) (5 g, 23.0 mmol) for <bold>5b </bold>or 5-bromo-<italic toggle="yes">O,N</italic>-acetylindoxyl (<bold>3b</bold>)(6.84 g, 23.0 mmol) for <bold>5c</bold> and water (50 mL) were stirred
under nitrogen at room temperature. A solution of 5-bromoisatin (<bold>2b</bold>) (5.73 g, 25.3 mmol) for <bold>5b </bold>or isatin (<bold>2a</bold>) (4.41 g,
25.3 mmol) for <bold>5c</bold> and KOH (26 g 0.46 M) in water (50 mL)
was slowly added. Stirring was continued for 10 days at room
temperature and then additional water (20 mL) was added,
and the mixture was heated to 70 °C while air was bubbled
through it for 20 min. The mixture was filtered through Celite,
which was then washed with hot water (60 °C), and an equal
volume of ethanol was added to the filtrate followed by
acidification to pH 1 with concentrated HCl. The product
(bromoquindoline-11-carboxylic acid) <bold>4b</bold> or <bold>4c</bold> was collected,
washed with 1:1 ethanol:water, and dried. Decarboxylation
was carried out by refluxing the derivative (7.3 g, 21.3 mmol)
and diphenyl ether (50 mL) for 6 h with stirring. After the
mixture was cooled, petroleum ether (55 mL) was added, and
the precipitate was collected and dried, dissolved in methanol
(300 mL), and filtered. Concentration of the filtrate gave the
brominated quindoline derivatives <bold>5b </bold>and <bold>5c</bold> that were used
without further purification.
</p><p><bold>2-Bromocryptolepine Hydrochloride (6). </bold>2-Bromoquindoline (<bold>5b</bold>) (0.116 g, 0.34 mmol), dimethylsulfate (0.265 g, 3.4
mmol), and chloroform (20 mL) were stirred under reflux for
10 days; the course of the reaction was monitored using TLC
over silica gel G with chloroform:methanol:concentrated ammonia (9:1:0.1). Following evaporation of the solvent, NaOH
solution (10%, 20 mL) was added to the residue, and the
mixture was extracted with chloroform, washed with saturated
NaCl solution, and dried over anhydrous Na<sub>2</sub>SO<sub>4</sub>. The dried
product was column-chromatographed over silica gel eluted
with chloroform:methanol:ammonia (9:1:0.1), converted to the
hydrochloride salt with concentrated HCl, and crystallized
from chloroform:methanol (3:1) to give <bold>6 </bold>as a yellow-brown
solid; overall yield 13%. (Note: This yield may be increased
significantly if methylation is carried out using iodomethane
and tetramethylenesulfone as described below for the preparation of <bold>7</bold>.) <sup>1</sup>H NMR of free base (CD<sub>3</sub>OD, δ): 5.11 (3H, s, NC<italic toggle="yes">H</italic><sub>3</sub>),
7.62 (1H, t, <italic toggle="yes">J</italic> = 8.0 Hz, 7 or 8-<italic toggle="yes">H</italic>), 7.94 (1H, d, <italic toggle="yes">J</italic> = 8.8 Hz,
6-<italic toggle="yes">H</italic>), 8.05 (1H, t, <italic toggle="yes">J</italic> = 8 Hz, 7 or 8-<italic toggle="yes">H</italic>), 8.24 (1H, dd, <italic toggle="yes">J</italic> = 9.5,
2.2 Hz, 3-<italic toggle="yes">H</italic>), 8.62 (1H, d, <italic toggle="yes">J</italic> = 9.5 Hz, 4-<italic toggle="yes">H</italic>), 8.72 (1H, d, <italic toggle="yes">J</italic> =
2.2 Hz, 1-<italic toggle="yes">H</italic>), 8.79 (1H, d, <italic toggle="yes">J</italic> = 8.4 Hz, 9-<italic toggle="yes">H</italic>), 9.26 (1H, s, 11-<italic toggle="yes">H</italic>).
MS (EI, <italic toggle="yes">m</italic>/<italic toggle="yes">z</italic>, relative intensity, %) 312 (97), 310 (100) [M<sup>+</sup> +
H], 297 (7), 295 (7), 230 (18), 154 (18), 156 (18), 115 (24). Anal.
(C<sub>16</sub>H<sub>11</sub>N<sub>2</sub>Br·HCl·H<sub>2</sub>O) H, N; C: calcd, 52.5; found 52.0.
</p><p><bold>7-Bromocryptolepine Hydroiodide (7). </bold>7-Bromoquindoline (<bold>5b</bold>) (0.06 g, 0.18 mmol), tetramethylenesulfone (2 mL),
and iodomethane (0.06 g, 23.4 mmol) were stirred overnight
at 50 °C in a sealed container. After the solution was cooled,
ether (8 mL) and a few drops of methanol were added, and
the resulting precipitate was washed twice with ethyl acetate
(2 × 5 mL) and crystallized from chloroform:methanol (3:1) to
give <bold>7 </bold>as orange-brown needles; overall yield 38%. <sup>1</sup>H NMR of
free base (CD<sub>3</sub>OD, δ): 4.70 (3H, s, NC<italic toggle="yes">H</italic><sub>3</sub>), 7.54 (1H, dd, <italic toggle="yes">J</italic> =
9.2, 1.8 Hz, 8-<italic toggle="yes">H</italic>), 7.64 (1H, t, <italic toggle="yes">J</italic> = 7.3 Hz, 2 or 3-<italic toggle="yes">H</italic>), 7.71 (1H,
d, <italic toggle="yes">J</italic> = 9.2 Hz, 9-<italic toggle="yes">H</italic>), 7.86 (1H, t, <italic toggle="yes">J</italic> = 7.9 Hz, 2 or 3-<italic toggle="yes">H</italic>), 8.11
(1H, d, <italic toggle="yes">J</italic> = 8.8 Hz, 1 or 4-<italic toggle="yes">H</italic>), 8.20 (1H, d, <italic toggle="yes">J</italic> = 8.1 Hz, 1 or
4-<italic toggle="yes">H</italic>), 8.30 (1H, d. <italic toggle="yes">J</italic> = 1.8 Hz, 6-<italic toggle="yes">H</italic>), 8.80 (1H, s, 11-<italic toggle="yes">H</italic>). MS (EI,
<italic toggle="yes">m</italic>/<italic toggle="yes">z</italic>, relative intensity, %) 312 (100), 310 (100) [M<sup>+</sup> + H], 296
(26), 294 (24), 216 (18), 154 (15), 115 (13), 89 (28). Anal.
(C<sub>16</sub>H<sub>11</sub>N<sub>2</sub>Br·HI) C, H, N.
</p><p><bold>2,7-Dibromocryptolepine Hydrochloride (8).</bold> The title
compound was prepared from 5-bromo-<italic toggle="yes">O</italic>,<italic toggle="yes">N</italic>-acetylindoxyl (<bold>3b</bold>)(6.84 g, 23 mmol) and 5-bromoisatin (<bold>2b</bold>) (5.73 g, 25.3 mmol)
as starting materials using the same methodology as for <bold>6</bold>
except that the reaction mixture for the first step was refluxed
for 4 h instead of stirring at room temperature. Recrystallization from chloroform:acetone (3:1) gave <bold>8 </bold>as an orange-yellow solid; overall yield 23%. <sup>1</sup>H NMR of free base (CDCl<sub>3</sub>,
δ): 4.72 (3H, s, NC<italic toggle="yes">H</italic><sub>3</sub>), 7.53 (1H, dd, <italic toggle="yes">J</italic> = 9.2, 1.8 Hz, 3-<italic toggle="yes">H</italic> or
8-<italic toggle="yes">H</italic>), 7.66 (1H, d, <italic toggle="yes">J</italic> = 9.2 Hz, 4-<italic toggle="yes">H</italic> or 9-<italic toggle="yes">H</italic>), 7.91 (1H, dd, <italic toggle="yes">J</italic> =
9.2, 2.2 Hz, 3-<italic toggle="yes">H</italic> or 8-<italic toggle="yes">H</italic>), 8.0 (1H, d, <italic toggle="yes">J</italic> = 9.2 Hz, 4-<italic toggle="yes">H</italic> or 9-<italic toggle="yes">H</italic>),
8.19 (1H, d, <italic toggle="yes">J</italic> = 1.8 Hz, 1-<italic toggle="yes">H</italic> or 6-<italic toggle="yes">H</italic>), 8.27 (1H, d, <italic toggle="yes">J</italic> = 2.2 Hz,
1-<italic toggle="yes">H</italic> or 6-<italic toggle="yes">H</italic>), 8.74 (1H, s, 11-<italic toggle="yes">H</italic>). MS (EI, <italic toggle="yes">m</italic>/<italic toggle="yes">z</italic>, relative intensity,
%) 392 (46), 390 (92), 388 (38) [M<sup>+</sup>], 378 (42), 376 (100), 374
(42), 297 (14), 295 (14), 216 (16), 215 (18). Anal. (C<sub>16</sub>H<sub>10</sub>N<sub>2</sub>Br<sub>2</sub>·1.5HCl) C, H, N.
</p><p><bold>7-Nitro- (10) and 9-Nitrocryptolepine Hydrochloride
(11).</bold> Cryptolepine (<bold>1</bold>) as sulfate (1 g, 3 mmol) was dissolved
in 40 mL of nitric acid (69%):glacial acetic acid (1:1) and stirred
at room temperature for 24−48 h. The reaction mixture was
cooled on ice, basified with strong NaOH solution, and filtered,
and the precipitate was washed with ice cold water. The dried
product was column-chromatographed over silica gel under
positive pressure eluted with chloroform containing increasing
amounts of methanol (1−20%) to yield fractions containing <bold>10</bold>
(less polar) and <bold>11</bold> (more polar). The total yield of nitrated
products was 56%. These were converted to their hydrochloride
salts with concentrated HCl and crystallized from choroform:methanol (3:1).
</p><p><bold>10. </bold>Yellow solid, yield 45%. <sup>1</sup>H NMR of free base (CDCl<sub>3</sub>,
δ): 4.99 (3H, s, NC<italic toggle="yes">H</italic><sub>3</sub>), 7.78 (1H, t, <italic toggle="yes">J</italic> = 7.2 Hz, 7-<italic toggle="yes">H</italic>), 7.86 (1H,
d, <italic toggle="yes">J</italic> = 9.5 Hz, 9-<italic toggle="yes">H</italic>), 8.01 (1H, t, <italic toggle="yes">J</italic> = 7.3 Hz, 8-<italic toggle="yes">H</italic>), 8.28 (1H, d,
<italic toggle="yes">J</italic> = 9.5 Hz, 1-<italic toggle="yes">H</italic>), 8.33 (1H, d, <italic toggle="yes">J</italic> = 8.4 Hz, 6-<italic toggle="yes">H</italic>), 8.44 (1H, d, <italic toggle="yes">J</italic>
= 9.5 Hz, 2-<italic toggle="yes">H</italic>), 9.04 (1H, s, 11-<italic toggle="yes">H</italic>), 9.38 (1H, s, 4-<italic toggle="yes">H</italic>). MS (EI,
<italic toggle="yes">m</italic>/<italic toggle="yes">z</italic>, relative intensity. %) 277 (16) [M<sup>+</sup>], 263 (100), 247 (32),
232 (36), 217 (59), 190 (19), 111 (20). Anal. (C<sub>16</sub>H<sub>11</sub>N<sub>3</sub>·HCl) C,
H, N.
</p><p><bold>11.</bold> Yellow solid, yield 11%. <sup>1</sup>HMR of base (270 MHz, CD<sub>3</sub>OD, δ): 5.1 (3H, s, NC<italic toggle="yes">H</italic><sub>3</sub>), 7.54 (1H, t, <italic toggle="yes">J</italic> = 8.8 Hz, 7-<italic toggle="yes">H</italic>), 7.93
(1H, t, <italic toggle="yes">J</italic> = 7.7 Hz, 8-<italic toggle="yes">H</italic>), 8.19 (1H, t, <italic toggle="yes">J</italic> = 7.5 Hz, 3-<italic toggle="yes">H</italic>), 8.48
(1H, d, <italic toggle="yes">J</italic> = 8.4 Hz, 6-<italic toggle="yes">H</italic>), 8.67 (1H, d, <italic toggle="yes">J</italic> = 9.2 Hz, 9-<italic toggle="yes">H</italic>), 8.75
(1H, d, <italic toggle="yes">J</italic> = 8.1 Hz, 4-<italic toggle="yes">H</italic>), 9.11 (1H, d, <italic toggle="yes">J</italic> = 8.1 Hz, 2-<italic toggle="yes">H</italic>), 9.21
(1H, s, 11-<italic toggle="yes">H</italic>). MS (EI, <italic toggle="yes">m</italic>/<italic toggle="yes">z</italic>, relative intensity, %) 277 (9) [M<sup>+</sup>],
263 (26), 232 (100), 217 (44), 190 (18), 111 (8). Anal. (C<sub>16</sub>H<sub>11</sub>N<sub>3</sub>·HCl) C, H, N.
</p><p><bold>7,9-Dinitrocryptolepine Hydrochloride (12). </bold>Cryptolepine (<bold>1</bold>) as sulfate (0.5 g, 1.5 mmol) was refluxed for 30 min
in 30 mL of nitric acid (69%):glacial acetic acid (1:1). The
product was isolated and purified as described above for <bold>10
</bold>
and <bold>11</bold>. Recrystallization from chloroform:methanol (3:1) gave
<bold>12 </bold>as orange-red crystals; yield 69%. <sup>1</sup>H NMR of free base
(DMSO-<italic toggle="yes">d</italic><sub>6</sub>, δ): 4.71 (3H, s, NC<italic toggle="yes">H</italic><sub>3</sub>), 7.99 (1H, t, <italic toggle="yes">J</italic> = 8.1 Hz,
7-<italic toggle="yes">H</italic>), 8.69 (1H, t, <italic toggle="yes">J</italic> = 7.4 Hz, 8-<italic toggle="yes">H</italic>), 8.72 (1H, d, <italic toggle="yes">J</italic> = 7.3 Hz,
9-<italic toggle="yes">H</italic>), 8.43 (1H, d, <italic toggle="yes">J</italic> = 7.3 Hz, 6-<italic toggle="yes">H</italic>), 9.13 (1H, d, <italic toggle="yes">J</italic> = 2.2 Hz,
4-<italic toggle="yes">H</italic>), 9.55 (1H, s, 11-<italic toggle="yes">H</italic>), 9.64 (1H, d, <italic toggle="yes">J</italic> = 2.2 Hz, 2-<italic toggle="yes">H</italic>). MS (EI,
<italic toggle="yes">m</italic>/<italic toggle="yes">z</italic>, relative intensity, %) 322 (38) [M<sup>+</sup>], 308 (100), 292 (14),
262 (35), 230 (22), 216 (56), 188 (10). Anal. (C<sub>16</sub>H<sub>10</sub>N<sub>4</sub>O<sub>4</sub>·HCl)
C, H, N.
</p><p><bold>7-</bold><bold><italic toggle="yes">N</italic></bold><bold>-Acetylcryptolepine Hydrochloride (13). </bold>Compound
<bold>10 </bold>(0.443 g, 1.6 mmol) was dissolved in 30 mL of methanol:concentrated HCl (95:5) in the presence of granulated tin (0.2
g, 1.7 mmol) in a nitrogen atmosphere protected from light
and was stirred for 3 h. The reaction mixture was basified with
saturated NaOH solution, filtered, and extracted with chloroform. The concentrated chloroform extract was column-chromatographed over alumina gradient eluted with chloroform
followed by chloroform containing increasing amounts of
methanol (1−10%) to yield a blue fraction containing 7-aminocryptolepine, which is photosensitive. Acetic anhydride (3 mL)
was added to the fraction, which was then refluxed for 15 min,
cooled, basified with saturated NaOH, and extracted with
chloroform:methanol (3:1). Concentrated HCl was added to the
extract, which was then dried to give <bold>13</bold>. Crystallization from
chloroform:methanol (3:1) gave <bold>13</bold> as red-brown needles; yield
51%. <sup>1</sup>H NMR of hydrochloride (DMSO-<italic toggle="yes">d</italic><sub>6</sub>, δ): 2.15 (3H, s,
CONC<italic toggle="yes">H</italic><sub>3</sub>), 5.01 (3H, s, NC<italic toggle="yes">H</italic><sub>3</sub>), 7.84 (1H, d, <italic toggle="yes">J</italic> = 9.2 Hz, 1-<italic toggle="yes">H</italic>),
7.95 (1H, t, <italic toggle="yes">J</italic> = 8.0 Hz, 7-<italic toggle="yes">H</italic>), 8.04 (1H, d, <italic toggle="yes">J</italic> = 8.8 Hz, 6-<italic toggle="yes">H</italic>),
8.18 (1H, t, <italic toggle="yes">J</italic> = 7.9 Hz, 8-<italic toggle="yes">H</italic>), 8.58 (1H, d, <italic toggle="yes">J</italic> = 8.4 Hz, 9-<italic toggle="yes">H</italic>),
8.73 (1H, d, <italic toggle="yes">J</italic> = 9.2 Hz, 2-<italic toggle="yes">H</italic>), 9.15 (1H, s, 4 or 11-<italic toggle="yes">H</italic>), 9.30
(1H, s, 4 or 11-<italic toggle="yes">H</italic>), 10.5 (1H, s, 3-N<italic toggle="yes">H</italic>), 13.0 (1H, s, 10-N<italic toggle="yes">H</italic>). MS
(EI, <italic toggle="yes">m</italic>/<italic toggle="yes">z</italic>, relative intensity, %) 289 (6) [M<sup>+</sup>], 246 (8), 232 (3),
159 (2), 149 (4), 60 (32), 44 (100). Anal. (C<sub>18</sub>H<sub>15</sub>N<sub>3</sub>O.HCl·CHCl<sub>3</sub>)
C, H, N.
</p><p><bold>General Method for Preparation of 11-Chloro-Substituted Derivatives 20</bold><bold>−</bold><bold>24. </bold><italic toggle="yes">Step 1</italic>. Anthranilic acid or a
substituted anthranilic acid derivative, <bold>14</bold> (96.6 mmol), dimethylformamide (35 mL), and dioxane (35 mL) were placed
in a sealed flask, which was cooled to 0 °C, and then
bromoacetylbromide (19.5 g, 96.6 mmol) was slowly added so
that the temperature did not rise above 1 °C. At the end of
the addition, the temperature was maintained at 0 °C for a
further 10 min, and then the mixture was stirred overnight
at room temperature. The contents of the flask were poured
into water (300 mL), and the resulting precipitate <bold>15</bold> was
filtered, washed with neutral water (3 × 15 mL), and then
dried.
</p><p><italic toggle="yes">Step 2</italic>. Aniline or a substituted aniline derivative, <bold>16</bold> (0.28
M), and the crude acid <bold>15</bold> (90 mmol) were stirred and heated
under reflux at 120 °C for 30 h. After the cooling process, the
reaction mixture was poured onto ice and water (800 mL), and
sufficient KOH solution (5%) was added to dissolve the
precipitate. The pH was checked, and if necessary, more KOH
solution was added to raise the pH to 11. The mixture was
extracted with dichloromethane, and the aqueous phase was
then acidified to pH 3 with hydrobromic acid solution (5%).
The product <bold>17 </bold>was collected in the form of a precipitate or as
an oil that solidified on standing overnight at room temperature.
</p><p><italic toggle="yes">Step 3</italic>. The crude product from above <bold>17 </bold>(15.8 mmol) and
polyphosphoric acid (150 g) were stirred at 130 °C for 2 h, and
then the mixture was poured into ice/water (1000 mL) and
neutralized with saturated KOH solution. The mixture was
then extracted with ethyl acetate (3 × 250 mL), washed with
saturated NaCl solution and water, and dried (Na<sub>2</sub>SO<sub>4</sub>).
Following evaporation of the solvent, the dried product <bold>18 </bold>was
column-chromatographed over silica gel eluted with ethyl
acetate:methanol (5:1).
</p><p><italic toggle="yes">Step 4</italic>. The latter product <bold>18</bold> (23.8 mmol) and phosphorus
oxychloride (60 mL) were stirred under reflux at 120 °C for 2
h. After the reaction mixture was cooled, it was poured onto
ice/water (150 mL) and then neutralized with saturated KOH
solution, taking care to prevent the temperature rising above
40 °C. The product was extracted into ethyl acetate (3 × 200
mL), washed with saturated NaCl solution and water, and
then dried (Na<sub>2</sub>SO<sub>4</sub>). Evaporation of the solvent gave the crude
product <bold>19</bold>, which was chromatographed over silica gel twice;
the eluent was ethyl acetate:hexane (1:6) followed by chloroform:methanol (9.5:0.5).
</p><p><italic toggle="yes">Step 5</italic>. Finally, methylation of <bold>19 </bold>was carried out as
described above as in the preparation of <bold>7</bold>. Compounds <bold>22</bold><bold>−</bold><bold>24</bold> were converted to their hydrochloride salts by the addition
of dilute NH<sub>4</sub>OH (10%) and extraction with chloroform followed
by the addition of concentrated HCl. The hydrochloride salts
were recrystallized from chloroform:methanol (3:1).
</p><p><bold>2-Bromo-11-chlorocryptolepine Hydroiodide (21). </bold>Prepared as above using 5-bromoanthranilic acid (20.1 g, 96.6
mmol) and aniline (26.1 g, 0.28 M) as starting materials. Crude
yields were 70%, 38%, 51%, 70%, and 74% for steps 1−5,
respectively; overall yield of <bold>21 </bold>obtained as a yellow-brown
solid, 7%. <sup>1</sup>H NMR of free base (DMSO-<italic toggle="yes">d</italic><sub>6</sub>, δ): 4.96 (3H, s,
NC<italic toggle="yes">H</italic><sub>3</sub>), 7.55 (1H, t, <italic toggle="yes">J</italic> = 8.0 Hz, 7-<italic toggle="yes">H</italic>), 7.90 (1H, d, <italic toggle="yes">J</italic> = 8.4 Hz,
6-<italic toggle="yes">H</italic>), 7.99 (1H, t, <italic toggle="yes">J</italic> = 7.0 Hz, 8-<italic toggle="yes">H</italic>), 8.31 (1H, dd, <italic toggle="yes">J</italic> = 9.5, 2.2
Hz, 3-<italic toggle="yes">H</italic>), 8.62 (1H, d, <italic toggle="yes">J</italic> = 2.2 Hz, 1-<italic toggle="yes">H</italic>), 8.76 (1H, d, <italic toggle="yes">J</italic> = 9.52,
4-<italic toggle="yes">H</italic>), 8.79 (1H, d, <italic toggle="yes">J</italic> = 8.43, 8-<italic toggle="yes">H</italic>). MS (EI, <italic toggle="yes">m</italic>/<italic toggle="yes">z</italic>, relative
intensity, %) 346 (100), 344 (76) [M<sup>+</sup>], 332 (78), 330 (60), 250
(10), 215 (36), 173 (12). Anal. (C<sub>16</sub>H<sub>10</sub>N<sub>2</sub>BrCl·HI) C, H, N.
</p><p><bold>8-Bromo-11-chlorocryptolepine Hydrochloride (22).</bold>
Prepared from anthranilic acid (13.2 g, 96.6 mmol) and
3-bromoaniline (48.4 g 0.28 M). Crude yields, 74%, 75%, 30%,
66%, and 50% for steps 1−5, respectively; overall yield of <bold>22</bold>
obtained as a yellow solid, 6%. <sup>1</sup>H NMR of free base (DMSO-<italic toggle="yes">d</italic><sub>6</sub>, δ): 4.60 (3H, s, NC<italic toggle="yes">H</italic><sub>3</sub>), 6.94 (1H, dd, <italic toggle="yes">J</italic> = 8.8, 1.8 Hz, 1 or
4-<italic toggle="yes">H</italic>), 7.70 (1H, t, <italic toggle="yes">J</italic> = 7.3 Hz, 2 or 3-<italic toggle="yes">H</italic>), 7.73 (1H, d, <italic toggle="yes">J</italic> = 1.1
Hz, 9-<italic toggle="yes">H</italic>), 7.78 (1H, d, <italic toggle="yes">J</italic> = 9.2 Hz, 1, 4 or 6-<italic toggle="yes">H</italic>), 7.91 (1H, t, <italic toggle="yes">J</italic>
= 7.3 Hz, 2 or 3-<italic toggle="yes">H</italic>), 8.10 (1H, d, <italic toggle="yes">J</italic> = 9.2 Hz, 1, 4 or 6-<italic toggle="yes">H</italic>), 8.45,
(1H, dd, <italic toggle="yes">J</italic> = 9.0, 1.1 Hz, 7-<italic toggle="yes">H</italic>). MS (EI, <italic toggle="yes">m</italic>/<italic toggle="yes">z</italic>, relative intensity,
%) 346 (2), 344 (2) [M<sup>+</sup>], 328 (98), 326 (100) [M − CH<sub>3</sub>], 313
(35), 311 (37), 285 (8), 283 (8), 204 (7), 164 (11), 163 (11), 150
(12), 149 (12). Anal. (C<sub>16</sub>H<sub>10</sub>N<sub>2</sub>BrCl·HCl) C, H, N.
</p><p><bold>7,11-Dichlorocryptolepine Hydrochloride (23).</bold> Prepared from anthranilic acid (13.2 g, 96.6 mmol) and 4-chloroaniline (36 g, 0.28 M). Crude yields, 74%, 43%, 48%, 88%, and
47% for steps 1−5, respectively; overall yield of <bold>23 </bold>obtained
as a yellow solid, 6%. <sup>1</sup>H NMR of free base (DMSO-<italic toggle="yes">d</italic><sub>6</sub>, δ): 5.08
(3H, s, NC<italic toggle="yes">H</italic><sub>3</sub>), 7.87 (1H, d, <italic toggle="yes">J</italic> = 8.9 Hz, 9-<italic toggle="yes">H</italic>), 7.99 (1H, dd, <italic toggle="yes">J</italic> =
8.9, 1.8 Hz, 8-<italic toggle="yes">H</italic>), 8.09 (1H, t, <italic toggle="yes">J</italic> = 7.7 Hz, 2 or 3<italic toggle="yes">H</italic>), 8.29 (1H,
t, <italic toggle="yes">J</italic> = 8.1 Hz, 2 or 3-<italic toggle="yes">H</italic>), 8.75 (1H, d, <italic toggle="yes">J</italic> = 9.5 Hz, 1 or 4-<italic toggle="yes">H</italic>),
8.82 (1H d, <italic toggle="yes">J</italic> = 10.1 Hz, 1 or 4-<italic toggle="yes">H</italic>), 8.82 (1H, d, <italic toggle="yes">J</italic> = 1.7 Hz,
6-<italic toggle="yes">H</italic>). MS (EI, <italic toggle="yes">m</italic>/<italic toggle="yes">z</italic>) 302, 300, [M<sup>+</sup>], 285, 287, 250, 215, 149, 125.
Anal. (C<sub>16</sub>H<sub>10</sub>N<sub>2</sub>Cl<sub>2</sub>·HCl·H<sub>2</sub>O) N; C: calcd, 54.2; found, 52.9;
H: calcd, 3.66; found, 3.21.
</p><p><bold>8,11-Dichlorocryptolepine Hydrochloride (24).</bold> Prepared from anthranilic acid (13.2 g, 96.6 mmol) and 3-chloroaniline (36 g, 0.28 M). Crude yields, 74%, 69%, 32%, 41%,
and 48% for steps 1−5, respectively; overall yield of <bold>24</bold>, 3%
obtained as a yellow solid. <sup>1</sup>H NMR of free base (CD<sub>3</sub>OD, δ):
5.08 (3H, s, NC<italic toggle="yes">H</italic><sub>3</sub> ), 7.87 (1H, d, <italic toggle="yes">J</italic> = 9.0 Hz, 6-<italic toggle="yes">H</italic>), 7.99 (1H,
dd, <italic toggle="yes">J</italic> = 8.9, 1.8 Hz, 7-<italic toggle="yes">H</italic>), 8.09 (1H, t, <italic toggle="yes">J</italic> = 7.7 Hz, 2 or 3-<italic toggle="yes">H</italic>),
8.29 (1H, t, <italic toggle="yes">J</italic> = 7.4 Hz, 2 or 3-<italic toggle="yes">H</italic>), 8.75 (1H, d, <italic toggle="yes">J</italic> = 9.5 Hz, 1 or
4-<italic toggle="yes">H</italic>), 8.79 (1H, d, <italic toggle="yes">J</italic> = 10.1 Hz, 1 or 4-<italic toggle="yes">H</italic>), 8.82 (1H, d, <italic toggle="yes">J</italic> = 1.7,
9-<italic toggle="yes">H</italic>). MS (EI, <italic toggle="yes">m</italic>/<italic toggle="yes">z</italic>, relative intensity, %) 302 (64), 300 (100)
[M<sup>+</sup>], 286 (15), 149 (46). Anal. (C<sub>16</sub>H<sub>10</sub>N<sub>2</sub>Cl<sub>2</sub>·HCl·H<sub>2</sub>O) C, H,
N.
</p><p><bold>Antiplasmodial Assay. </bold><italic toggle="yes">P. falciparum</italic> strain K1 was kindly
supplied by Professor D. C. Warhurst (London School of
Hygiene and Tropical Medicine) and <italic toggle="yes">P. falciparum </italic>strain HB3
was generously provided by Dr L. C. Ranford-Cartwright
(Division of Infection and Immunity, University of Glasgow).
Malaria parasites were maintained in human A<sup>+</sup> erythrocytes
suspended in RPMI 1640 medium supplemented with A<sup>+</sup>
serum and <sc>d</sc>-glucose according to the methods of Trager and
Jensen (1976)<xref rid="jm0109291b00016" ref-type="bibr"></xref> and Fairlamb et al. (1985).<xref rid="jm0109291b00017" ref-type="bibr"></xref> Cultures containing predominantly early ring stages were used for testing.
Compounds were dissolved or micronized in DMSO and further
diluted with RPMI 1640 medium (the final DMSO concentration did not exceed 0.5% which did not affect parasite growth).
Twofold serial dilutions were made in 96-well microtiter plates
in duplicate, and infected erythrocytes were added to give a
final volume of 100 μL with 2.5% hematocrit and 1% parasitemia. Chloroquine diphosphate was used as a positive
control, and uninfected and infected erythrocytes without
compounds were included in each test. Plates were placed into
a modular incubator gassed with 93% nitrogen, 3% oxygen,
and 4% carbon dioxide and incubated at 37 °C for 48 h.
Parasite growth was assessed by measuring lactate dehydrogenase activity as described by Makler et al. (1993).<xref rid="jm0109291b00018" ref-type="bibr"></xref> The
reagent used contained the following in each milliliter: acetylpyridine adenine dinucleotide (APAD), 0.74 mg; lithium
lactate, 19.2 mg; diaphorase, 0.1 mg; Triton X-100, 2 μL;
nitroblue tetrazolium, 1 mg; and phenazine ethosulfate, 0.5
mg. Fifty microliters of this reagent was added to each well
and mixed, and plates were incubated for 15 min at 37 °C.
Optical densities were read at 550 nm using a Dynatech
Laboratories MRX microplate reader, and percent inhibition
of growth was calculated by comparison with control values.
IC<sub>50</sub> values were determined using linear regression analysis
(Microsoft Excel). A minimum of three separate determinations
was carried out for each compound.
</p><p><bold>In Vivo Antimalarial Test. </bold>This was carried out using
Peters' 4-day suppressive test<xref rid="jm0109291b00019" ref-type="bibr"></xref> against <italic toggle="yes">P. </italic><italic toggle="yes">berghei</italic> infection
in mice. Female BALB/C mice, weight 18−20 g, were inoculated with <italic toggle="yes">P. </italic><italic toggle="yes">berghei</italic> (ANKA); each mouse received 1 × 10<sup>7</sup>
infected erythrocytes by iv injection. Drugs were administered
to mice by ip injection in 0.2 mL of inoculum daily for four
consecutive days. Control and test groups all contained 5 mice.
On day 5 of the test a blood smear was taken, and the animals
were killed. The percent suppression of parasitemia was
calculated for each dose level by comparing the parasitemias
present in infected controls with those of test animals. Chloroquine diphosphate was used as a positive control.
</p><p><bold>Inhibition of </bold><bold>β</bold><bold>-Hematin Formation. </bold>The methodology
used was adapted from that of Egan et al. (1994).<xref rid="jm0109291b00006" ref-type="bibr"></xref> Hemin (7.5
mg) was dissolved in 1.25 mL of 0.1 M NaOH, and then 0.125
mL of 1 M HCl was added. The 3 mol equiv of the compound
under test (with respect to hemin) was then added followed
by 1.15 mL of 9.78 M acetate buffer at pH 5.0, preincubated
at 60 °C. The pH was adjusted to 5.0 by the addition of glacial
acetic acid, and the mixture was then stirred for 30 min at 60
°C. After being cooled on ice, the precipitate was filtered using
a 5-μm membrane filter and washed with water. After being
dried under vaccuum for 24 h, the FTIR spectrum of the
product was recorded. A control in which no compound was
added was also carried out. The formation of β-hematin was
detected by the presence of peaks at 1660 and 1210 cm<sup>-1</sup>.
</p><p><bold>Thermal Denaturation Studies.</bold> These were performed
as previously described<xref rid="jm0109291b00020" ref-type="bibr"></xref> using a Perkin-Elmer Lambda 5 UV−Vis spectrophotometer linked to a Perkin-Elmer Peltier-Temperature Controller 6 unit that was programmed to
produce the following conditions: preheat cell to 50 °C from
room temperature over 20 min; heat to 110 °C at 1 °C/min
taking absorbance readings at 260 nm every min; hold at 110
°C for 1 min; cool to 25 °C over 30 min. Approximately 20 mg
of double-stranded calf thymus DNA (type 1, highly polymerized) was dissolved in 50 mL of buffer containing Tris-HCl
(0.008 M) and NaCl (0.05 M) adjusted to pH 7.4 and diluted
to give a DNA stock solution containing 2.88 mM Tris-HCl
and 18 mM NaCl. A working buffer containing 2.88 × 10<sup>-3</sup> M
Tris-HCl and 0.018 M NaCl was prepared and then used for
all subsequent dilutions. The DNA stock solution (3.3 mL) was
further diluted to 10 mL with the working buffer. The
absorbance was then determined at 260 nm, and the concentration of DNA was expressed according to the phosphate
group concentration, using a molar absorptivity ε value of 6600
cm<sup>-1</sup> M<sup>-1</sup> at 260 nm.<xref rid="jm0109291b00020" ref-type="bibr"></xref> Drug−DNA solutions were prepared
from the DNA stock solution and from drug solutions at 10
mM in DMSO. Drug−DNA ratios of 1:10 were used, and
absorbances were determined against blanks containing drugs
diluted in the working buffer.
</p><p><bold>Cytotoxicity Test.</bold> The cell lines used in this study were
A549 (human nonsmall cell lung carcinoma) and DLD-1
(human colon carcinoma) obtained from the European Collection of Animal Cell Cultures (ECACC) and MAC15A (murine
adenocarcinoma of the colon) available in our laboratory. All
cells were routinely maintained as monolayer cultures in RPMI
1640 culture medium supplemented with foetal calf serum
(10%), sodium pyruvate (1 mM), <sc>l</sc>-glutamine (2 mM), and
penicillin/streptomycin (50 IU mL<sup>-1</sup>/50 μg mL<sup>-1</sup> and buffered
with HEPES (25 mM). Chemosensitivity was assessed using
the MTT assay.<xref rid="jm0109291b00021" ref-type="bibr"></xref> Briefly, 2 × 10<sup>3</sup> cells were inoculated into
each well of a 96-well plate and incubated overnight at 37 °C
in an humidified atmosphere containing 5% CO<sub>2</sub>. All drugs
were dissolved in DMSO and diluted in culture medium to give
a broad range of drug concentrations; the maximum DMSO
concentration in any well was 0.1%. Medium was removed
from each well and replaced with drug solutions (8 wells per
drug concentration). For experiments with a 1-h drug exposure, medium was removed after 1 h, and the cells were
washed twice with Hanks balanced salt solution. RPMI 1640
medium was added (200 μL/well) and cells were incubated at
37 °C for a further 4 days before cell survival was determined
using the MTT assay. Culture medium was replaced with fresh
medium (180 μL) prior to the addition of 20 μL of MTT solution
(0.5 mg mL<sup>-1</sup>). Following 24-h incubation at 37 °C, medium
plus MTT was removed from each well, and the formazan
crystals were dissolved in DMSO (150 μL/well). Absorbances
of the resulting solutions were read at 550 nm, and cell
survival was calculated as the absorbance of treated cells
divided by the absorbance of the control (RPMI medium plus
0.1% DMSO) wells. Results were expressed in terms of IC<sub>50</sub>
values (i.e., concentration of drug required to kill 50% of cells),
and all experiments were performed in triplicate.
</p></sec></body><back><ack><title>Acknowledgments</title><p>This work was supported by
WHO TDR Grant 980375. J.A.-K. was supported by the
Ghanaian government. A.G.B. and R.M.P. were funded
by the Cancer Research Campaign Grant SP252301.
M.F.C. is grateful to the Association of Commonwealth
Universities for a scholarship. H.K. and S.L.C. received
financial support from the UNDP/World Bank/WHO
Programme for Research on Tropical Diseases (TDR).
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Box 101110, Georgetown, Guyana.</affiliation><role><roleTerm type="text">author</roleTerm></role></name><name type="personal"><namePart type="family">CROFT</namePart><namePart type="given">Simon L.</namePart><affiliation>The School of Pharmacy and Cancer Research Unit, University of Bradford, West Yorkshire, BD7 1DP, U.K., and theDepartment of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, Keppel Street,London WC1E 7HT, U.K.</affiliation><affiliation> London School of Hygiene and Tropical Medicine.</affiliation><role><roleTerm type="text">author</roleTerm></role></name><name type="personal"><namePart type="family">GöKçEK</namePart><namePart type="given">Yaman</namePart><affiliation>The School of Pharmacy and Cancer Research Unit, University of Bradford, West Yorkshire, BD7 1DP, U.K., and theDepartment of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, Keppel Street,London WC1E 7HT, U.K.</affiliation><affiliation> The School of Pharmacy, University of Bradford.</affiliation><role><roleTerm type="text">author</roleTerm></role></name><name type="personal"><namePart type="family">KENDRICK</namePart><namePart type="given">Howard</namePart><affiliation>The School of Pharmacy and Cancer Research Unit, University of Bradford, West Yorkshire, BD7 1DP, U.K., and theDepartment of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, Keppel Street,London WC1E 7HT, U.K.</affiliation><affiliation> London School of Hygiene and Tropical Medicine.</affiliation><role><roleTerm type="text">author</roleTerm></role></name><name type="personal"><namePart type="family">PHILLIPS</namePart><namePart type="given">Roger M.</namePart><affiliation>The School of Pharmacy and Cancer Research Unit, University of Bradford, West Yorkshire, BD7 1DP, U.K., and theDepartment of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, Keppel Street,London WC1E 7HT, U.K.</affiliation><affiliation> Cancer Research Unit, University of Bradford.</affiliation><role><roleTerm type="text">author</roleTerm></role></name><name type="personal"><namePart type="family">POLLET</namePart><namePart type="given">Pamela L.</namePart><affiliation>The School of Pharmacy and Cancer Research Unit, University of Bradford, West Yorkshire, BD7 1DP, U.K., and theDepartment of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, Keppel Street,London WC1E 7HT, U.K.</affiliation><affiliation> The School of Pharmacy, University of Bradford.</affiliation><role><roleTerm type="text">author</roleTerm></role></name><typeOfResource>text</typeOfResource><genre type="research-article" displayLabel="research-article" authority="ISTEX" authorityURI="https://content-type.data.istex.fr" valueURI="https://content-type.data.istex.fr/ark:/67375/XTP-1JC4F85T-7">research-article</genre><originInfo><publisher>American Chemical Society</publisher><dateCreated encoding="w3cdtf">2001-08-18</dateCreated><dateIssued encoding="w3cdtf">2001-09-13</dateIssued><copyrightDate encoding="w3cdtf">2001</copyrightDate></originInfo><abstract>The indoloquinoline alkaloid cryptolepine 1 has potent in vitro antiplasmodial activity, but it is also a DNA intercalator with cytotoxic properties. We have shown that the antiplasmodial mechanism of 1 is likely to be due, at least in part, to a chloroquine-like action that does not depend on intercalation into DNA. A number of substituted analogues of 1 have been prepared that have potent activities against both chloroquine-sensitive and chloroquine-resistant strains of Plasmodium falciparum and also have in common with chloroquine the inhibition of β-hematin formation in a cell-free system. Several compounds also displayed activity against Plasmodium berghei in mice, the most potent being 2,7-dibromocryptolepine 8, which suppressed parasitemia by 89% as compared to untreated infected controls at a dose of 12.5 mg kg-1 day-1 ip. No correlation was observed between in vitro cytotoxicity and the effect of compounds on the melting point of DNA (ΔTm value) or toxicity in the mouse−malaria model.</abstract><relatedItem type="host"><titleInfo><title>Journal of Medicinal Chemistry</title></titleInfo><titleInfo type="abbreviated"><title>J. Med. Chem.</title></titleInfo><genre type="journal" authority="ISTEX" authorityURI="https://publication-type.data.istex.fr" valueURI="https://publication-type.data.istex.fr/ark:/67375/JMC-0GLKJH51-B">journal</genre><identifier type="ISSN">0022-2623</identifier><identifier type="eISSN">1520-4804</identifier><identifier type="acspubs">jm</identifier><identifier type="coden">JMCMAR</identifier><identifier type="uri">pubs.acs.org/jmc</identifier><part><date>2001</date><detail type="volume"><caption>vol.</caption><number>44</number></detail><detail type="issue"><caption>no.</caption><number>19</number></detail><extent unit="pages"><start>3187</start><end>3194</end></extent></part></relatedItem><identifier type="istex">83F1F726A42A2C6CF0A97ED1D83863058E783D89</identifier><identifier type="ark">ark:/67375/TPS-0VR0LC0H-2</identifier><identifier type="DOI">10.1021/jm010929+</identifier><accessCondition type="use and reproduction" contentType="restricted">Copyright © 2001 American Chemical Society</accessCondition><recordInfo><recordContentSource authority="ISTEX" authorityURI="https://loaded-corpus.data.istex.fr" valueURI="https://loaded-corpus.data.istex.fr/ark:/67375/XBH-X5HBJWF8-J">ACS</recordContentSource><recordOrigin>Copyright © 2001 American Chemical Society</recordOrigin></recordInfo></mods><json:item><extension>json</extension><original>false</original><mimetype>application/json</mimetype><uri>https://api.istex.fr/ark:/67375/TPS-0VR0LC0H-2/record.json</uri></json:item></metadata><annexes><json:item><extension>tiff</extension><original>true</original><mimetype>image/tiff</mimetype><uri>https://api.istex.fr/document/83F1F726A42A2C6CF0A97ED1D83863058E783D89/annexes/tiff</uri></json:item></annexes><serie></serie></istex></record>Pour manipuler ce document sous Unix (Dilib)
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