Isolation, stereochemistry, and biosynthesis of Šormosterol, a novel cyclopropane-containing sponge sterol

Šormosterol ((24R)-24,25-methylenecholesterol, XVIII, a product of the novo sterol biosynthesis in the marine sponge Lissodendoryx topsenti, was shown, trough the use of suitably labeled precursors, to be a new alternative product of the initial S-adenosylmethionine (SAM) methylation of the 24,25 double bond in the sterol side chain. Additional labeling experiments demonstrated that the cyclopropane ring is not further modifies in vivo by the sponge.