Marine Natural Products. XV

Four new polyhydroxysterols, named xeniasterol-a (4), xeniasterol-b (5), xeniasterol-c (6), and xeniasterol-d (7), were isolated from an Okinawan soft coral of Xenia sp. (Xeniidae). On the basis of chemical and physicochemical evidence, the structures of xeniasterol-a, -b, -c, and -d have been elucidated respectively as 7-O-acetylergost-22E-ene-3β, 5α, 6β, 7β-tetraol (4), 7-O-acetylergosta-3β, 5α, 6β, 7β-tetraol (5), gorgosta-3β, 5α, 6β-triol (6), and 7-O-acetylgorgosta-3β, 5α, 6β, 7β-tetraol (7). Germacrene-c (1) was also isolated from the same soft coral together with two guaiane-type compounds (2, 3), and it has been shown that germacrene-c (1) is readily air-oxidized to yield these cyclization products (2, 3).