New cembranoid lactones from the Indian Ocean soft coral Sinularia flexibilis

A detailed chemical examination of the Indian Ocean soft coral Sinularia flexibilis yielded two new cembranolide epsilon-lactones, sandensolide monoacetate (1) and flexibolide (4), in addition to the previously reported cembranolide delta-lactones, flexibilolide and dihydronexibilolide, and the known cembranoid derivatives, sandensolide, cembrene A, and flexibilene. Their structures have been established by a study df their spectral data (UV, IR, H-1 and C-13 NMR, 2D NMR (H-1-H-1, COSY and NOESY), and mass spectrometry.