Sterols in Marine Invertebrates. 22. Isolation and Structure Elucidation of Conicasterol and Theonellasterol, Two New 4-Methylene Sterols from the Red Sea Sponges Theonella conica and Theonella swinhoei

Two new and unusual sterols with unsaturation in the ∆⁸⁽¹⁴⁾ position and a heretofore unprecedented 4-methylene nucleus, conicasterol (12c, 4-methylene-24(R)-methylcholest-8(14)-en-3β-ol) and theonellasterol (12d, 4- methylene-24(S)-ethylcholest-8(14)-en-3β-ol), were isolated as the principal sterol constituents from the Red Sea sponges Theonella conica (Kieschnick) and Theonella swinhoei (Gray), respectively. The structures were determined by chemical and spectral analysis and comparison to the spectral data of the newly synthesized 4-methylenecholestan-3β-ol (11a).