Steroids in Porifera. II. Steroid derivatives from two sponges of the family Halichondriidae. Sokotrasterol sulfate, a marine steroid with a new pattern of side chain alkylation.

A trisulfated derivative of 24,25,26,26-tetramethyl-5 alpha-cholest-23E-ene-2 alpha, 3 beta, 6 alpha-triol (sokotrasterol sulfate) has been isolated from the sponge Halichondriidae gen. sp., collected near Sokotra Island (Arabian Sea), and its structure has been elucidated. The side chain of the new steroid involves a "normal" alkylation at C-24 and the unprecedented addition of two extra methyl groups at C-26 and one extra methyl group at C-25. A free sterol fraction contained only 24-isopropyl-5-cholesten-3 beta-ol and 24-isopropyl-5, 22E-cholestadien-3 beta-ol. 24-Isopropyl-5, 22E-cholestadien-3 beta-ol as sole monohydroxy sterol and halistanol sulfate as major polyhydroxylated steroid derivative have been detected in Halichondria sp., a Madagascar sponge.