Joziknipholones A and B: the first dimeric phenylanthraquinones, from the roots of Bulbine frutescens |
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Authors: | Bringmann Gerhard Mutanyatta-Comar Joan Maksimenka Katja Wanjohi John M Heydenreich Matthias Brun Reto Müller Werner E G Peter Martin G Midiwo Jacob O Yenesew Abiy |
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Affiliation: | 1. Institut für Organische Chemie, Universit?t Würzburg, Am Hubland, 97074 Würzburg, Germany, Fax: (+49)?931‐888‐4755;2. Department of Chemistry, University of Nairobi, PO Box 30197, Nairobi, Kenya, Fax: (+254)?2‐444‐6138;3. Institut für Chemie, Universit?t Potsdam, PO Box 60 15 53, 14415 Potsdam, Germany;4. Schweizerisches Tropeninstitut, Socinstrasse 57, 4002 Basel, Switzerland;5. Institut für Physiologische Chemie, Abteilung Angewandte Molekularbiologie, Universit?t Mainz, Duesbergweg 6, 55099 Mainz, Germany |
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Abstract: | From the roots of the African plant Bulbine frutescens (Asphodelaceae), two unprecedented novel dimeric phenylanthraquinones, named joziknipholones A and B, possessing axial and centrochirality, were isolated, together with six known compounds. Structural elucidation of the new metabolites was achieved by spectroscopic and chiroptical methods, by reductive cleavage of the central bond between the monomeric phenylanthraquinone and -anthrone portions with sodium dithionite, and by quantum chemical CD calculations. Based on the recently revised absolute axial configuration of the parent phenylanthraquinones, knipholone and knipholone anthrone, the new dimers were attributed to possess the P-configuration (i.e., with the acetyl portions below the anthraquinone plane) at both axes in the case of joziknipholone A, whereas in joziknipholone B, the knipholone part was found to be M-configured. Joziknipholones A and B are active against the chloroquine resistant strain K1 of the malaria pathogen, Plasmodium falciparum, and show moderate activity against murine leukemic lymphoma L5178y cells. |
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Keywords: | antimalarial activity chirality joziknipholones natural products structure elucidation |
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