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

Two new steroids, crellasterones A () and B (), together with the previously reported compound chalinasterol () and several nucleosides (-), were isolated from the sponge , 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.