Aplysiols C-E, Brominated Triterpene Polyethers from the Marine Alga Chondria armata and a Revision of the Structure of Aplysiol B

Three new brominated triterpene polyethers, aplysiols C-E (1-3), were isolated from extracts of the red alga Chondria armata. Structures were determined by comparison with the closely related metabolite, aplysiol B, which was previously reported from the anaspidean mollusc Aplysia dactylomela. The relative stereochemistry of the tetracyclic ring system was determined from 1D gradient selective NOESY experiments and from biogenetic considerations that support a revision of the stereochemistry proposed for aplysiol B. In addition, three known brominated C(15) acetogenin acetylenic ethers: (-)-pinnatifidenyne, (+)-laurenyne, and (+)-obtusenyne, two brominated diterpenes: (-)-ent-angasiol and (-)-ent-angasiol acetate, and the symmetrical halogenated triterpene polyether intricatetraol were isolated.