A new 3,4-dinorsteroid from the marine sponge sp.

A new steroid, 2a-oxa-2-oxo-5-hydroxy-3,4-dinor-24-methylcholesta-22-ene (), together with 10 known ones (), was isolated from the marine sponge sp. The structures of these compounds were determined by the spectroscopic methods (UV, IR, MS, and NMR) and X-ray diffraction analysis. Compound was the third example of 3,4-dinorsteroid with a hemiketal at C-5 that was isolated from the natural source. In addition, the antibacterial activities of these compounds were also evaluated. However, none of them exhibited significant inhibition effects.