Chondropsin D, a new 37-membered-ring macrolide lactam from the marine sponge Chondropsis species

Chondropsin D (2), a new 37-membered-ring macrolide lactam, was isolated as a minor constituent of an aqueous extract of the marine sponge Chondropsis sp. This sponge sample had previously been the source of chondropsins A (1 ) and B, two novel polyketide-derived macrolides with potent cytotoxic acti vity. The structure of 2 was initially deduced from analysis of spectral da ta. This assignment was supported by the observation that chondropsin A (1) , which contains a 35-membered macrocyclic ring, could be converted to chon dropsin D (2) by a base-catalyzed intramolecular transesterification reacti on. Rearrangement of the methylated derivative of chondropsin A (3) to the corresponding methylated analogue of chondropsin D (4) confirmed the struct ure of 2.