The calanolides, a novel HIV-inhibitory class of coumarin derivatives from the tropical rainforest tree, Calophyllum lanigerum

Kashman, Y., Gustafson, K.R., Fuller, R.W., Cardellina, J.H., II, McMahon, J.B., Currens, M.J., Buckheit, R.W., Hughes, S.H., Cragg, G.M., Boyd, M.R.J. Med. Chem. 35: 2735-2743, 1992.


Eight new coumarin compounds (1-8) were isolated by anti-HIV bioassay-guided fractionation of an extract of Calophyllum lanigerum. The structures of calanolide A (1), 12-acetoxycalanolide A (2), 12-methoxycalanolide A (3), calanolide B (4), 12-methoxycalanolide B (5), calanolide C (6) and related derivatives 7 and 8 were solved by extensive spectroscopic analyses, particularly HMQC, HMBC, and difference NOE NMR experiments. The absolute stereochemistry of calanolide A (1) and calanolide B (4) was established by a modified Mosher's method. Calanolides A (1) and B (4) were completely protective against HIV-1 replication and cytopathicity (EC50 values of 0.1 µM and 0.4 µM, respectively), but were inactive against HIV-2. Some of the related compounds also showed evidence of anti-HIV activity. Studies with purified bacterial recombinant reverse transcriptases (RT) revealed that the calanolides are HIV-1 specific RT inhibitors. Moreover, calanolide A was active not only against the AZT-resistant G-9106 strain of HIV-1 but also against the pyridinone-resistant A17 strain. This was of particular interest since the A17 virus is highly resistant to previously known HIV-1 specific, non-nucleoside RT inhibitors (e.g., TIBO; BI-RG-587; L693,593) which comprise a structurally diverse but apparently common pharmacologic class. The calanolides represent a substantial departure from the known class and therefore provide a novel new anti-HIV chemotype for drug development.

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