Abstract
Melithasterols A-D (1-4), isolated from a gorgoinan coral Melithaea ocracea of Okinawa, were shown to be cholestane-, 24-methyl-22-dehydrocholestane-, 22-dehydrocholestane-, and 24-methylenecholestane-derivatives. respectively, having a common 3β, 7α -dihydroxy-5α, 6α-epoxy-Δ^8 steroid nucleus. This was confirmed by direct comparison with the authentic sample prepared by lead tetra-acetate oxydation of cholest-6-ene- 3β, 5α, 8α-triol 3-monoacetate. Twelve new polyhydroxysterols were isolated from an Alcyonium sp. (7,8,9), and Sclerophytum sp. (14,16,19b,20,21,22a,23,26,28) soft corals collected off the coasts of the Andaman and Nicobar Islands in the Indian Ocean. All the Sclerophytum sp. soft corals contained 17a or its 25-deacetyl derivative. Compounds 7 to 9 were identified as 24-methylenecholest-5-ene- 3β, 16β-diol-3-0-α-L fucoside (7) and its 7β-(8) and 7α-hydroxy (9) derivatives. Compound 14 was shown to be 24S-24-methylcholest-5-ene-3β,25ξ,26-triol and was correlated to the known compound 15 by 5α, 6β-glycolation. Compound 16 was shown to be 5β, 6α-isomer of 17b, correlating to 17b by PCC oxidation followed by dehydration. Compound 19b was identified with 25-deacetyl derivative of the known compound lobosterol (19a) by hydrolysis of authentic lobosterol. Compounds 20 and 21 were shown to be 7-dehydro-(20) and 22E-dehydro-(21) derivative of 17a and 17b, respectively, by comparisons of their spectral data with reference compounds. Compounds 22a and 23 were 24S-methylcholestane-3β, 5α 25-triol-6-one 25-monoacetate (22a) and its 25-deacetoxyl derivative (23). Partial PCC oxidation of 17a afforded 22a. Compounds 26 (andamansterol) and 28 (nicobarsterol) were shown to be gorgost-5-ene-3β, 9α. 11α, 21-tetrol and novel secosteroid, 11,21-cyclo-B-homo-11-oxa-9, 11-secoergostane-3β, 6α, 12ξ-triol-9-one, respectively, by spectral analyses (H-HCOSY, HMQC, HMBC).
