Marine sterols. Part 20. Polyhydroxy sterols of the soft corals of the Andaman and Nicobar coasts. Part 4. Andamansterol and nicobarsterol, novel sterols with 3,9,11,21-tetrahydroxylated, and 11,21-epoxy-9,11-secosteroid skeletons, from a Sclerophytum sp. of soft coral. X-Ray molecular structure of andamansterol

Abstract

The lipid extract of a Sclerophytum sp. of soft coral, collected off the coast of the Andaman and Nicobar Islands, afforded two new polyhydroxy sterols, designated andamansterol 3 and nicobarsterol 4. The structure of compounds 3 and 4 was shown to be gorgost-5-ene-3β,9α,11α,21 -tetraol and (11R,24S)-3β,6α,11 -trihydroxy-1 1,21 -epoxy-9,11 -secoergostan-9-one, respectively, by spectral analysis (¹H–¹H COSY, HMQC*, HMBC*). X-Ray crystallography of andamansterol 3 confirmed the proposed structure, including the configuration at C-20. Lead tetraacetate treatment of andamanstero 3 gave the 9,11-seco derivative 6 having the same seven-membered hemiacetal ring as nicobarsterol 4