Sterols of Marine Invertebrates. 63.¹ Isolation and Structure Elucidation of Sutinasterol, the Major Sterol of the Marine Sponge Xestospongia sp.

A new sterol, sutinasterol ((24R)-24-ethyl-26,26-dimethyl-3β-hydroxycholesta-7,25(27)-diene) with a side chain arising from quadruple biomethylation has been isolated from the marine sponge Xestospongia sp. Since it represents the bulk (94%) of the sterol fraction, it presumably plays a biological role in membrane function. Four minor sterols were also characterized, one of which appears to be a biosynthetic intermediate of sutinasterol. A second trace sterol contains a side chain that is the result of five biomethylations and is the largest sterol isolated from natural sources to date. The structures of these sterols were deduced from spectral data (¹H and ¹³C NMR and MS). A crystal structure study of sutinasterol was performed to determine the stereochemistry of the C₂₄ ethyl group.