Crellasterones A and B: A-Norsterol Derivatives from the New Caledonian Sponge Crella incrustans.

Two new steroids, crellasterones A ( 1 ) and B ( 2 ), together with the previously reported compound chalinasterol ( 3 ) and several nucleosides ( 4 - 7 ), were isolated from the sponge Crella incrustans , collected in New Caledonia. The structures of the new compounds were established by extensive NMR and mass spectroscopic analysis and revealed unprecedented marine natural products with a ring-contracted A-norsterone nucleus and 2-hydroxycyclopentenone chromophore. The absolute configurations were derived from electronic circular dichroism (ECD) measurements in conjunction with high-level density functional theory (DFT) calculations.