Caribenolide revisited. Reisolation of caribenolide-I together with new congeners

Caribenolide-I [1] was originally discovered from the cell extract of a free-swimming Caribbean dinoflagellate Amphidinium gibbosum by Shimizu and coworkers. The structure was interpreted to be a 26-membered macrolide containing a 6-membered hemiacetal ring, a tetrahydrofuran ring, an epoxide, a ketone carbonyl, four C1 branches, and five hydroxyl groups. On the other hand, Kobayashi et al. reported the isolation of amphidinolide N [2] isolated from a symbiotic dinoflagellate Amphidinium species earlier than the report of caribenolide-I. The structure of amphidinolide N was elucidated to be the ring-opening form at the C-21-C-24 tetrahydrofuran ring for caribenolide-I.