Resolution and comparative anti-HIV evaluation of the enantiomers of calanolides A and B

Methods for the chiral resolution of (+)-calanolide A and (−)-calanolide A from synthetic (±)-calanolide A, and of (+)-calanolide B and (−)-calanolide B (costatolide) from a scalemic mixture isolated from C. lanigerium, have been developed. Calanolide A was originally isolated as the pure (+) enantiomer from C. lanigerum, but now is also shown to occur as a scalemic mixture in latex of C. teysmannii. Interestingly, (+)-calanolide A and (−)-calanolide B are potent HIV-1 inhibitors, while (−)-calanolide A and (+)-calanolide B are inactive against the virus.