Pyranocoumarins from Tropical Species of the Genus Calophyllum:  A Chemotaxonomic Study of Extracts in the National Cancer Institute Collection

(+)-Calanolide A, a novel dipyranocoumarin from the Malesian tree Calophyllum lanigerum var. austrocoriaceum, and a closely related compound, (−)-calanolide B, isolated from Calophyllum teysmannii var. inophylloide, are representatives of a distinct class of nonnucleoside HIV-1 specific reverse-transcriptase inhibitor under development as an AIDS chemotherapeutic. NCI repository specimens totalling 315 organic extracts from 31 taxa of Calophyllum were analyzed for related pyranocoumarins using a simple TLC system. A total of 127 extracts was initially classified as “positive”; eight out of the 31 taxa examined, representing perhaps 28 species already described (1/7−1/8 of all the species in this genus), contained prenylated coumarins, suggesting that these compounds, while sometimes abundantly present, are not widespread in the genus. Representative members of the TLC-positive extracts were partitioned between CH2Cl2 and 25% aqueous MeOH; the CH2Cl2-soluble materials were then analyzed by TLC and 1H NMR to confirm the presence of pyranocoumarins. The anti-HIV activity of the partitioned extracts are also presented. This study suggested that there are several distinctive coumarin chemotaxonomic markers distinguishing species of this genus.