Abstract
Two pairs of diastereomeric diterpenes, xeniolone (1) and isoxeniolone (3), and hydratoxeniolone (16) and hydratoisoxeniolone (18), were isolated, together with their putative biogenetic precursor, germacrexeniolone (20), from an Okinawan soft coral of Xenia sp. (Xeniidae). On the basis of chemical and physiochemical evidence, the absolute stereostructures of these five diterpenes have been elucidated. It has also been shown that germacrexeniolone (20) is gradually air-oxidized to yield xeniolone (1) and isoxeniolone (3) upon standing, while in an aqueous acetone solution, it yields hydratoxeniolone (16) and hydratoisoxeniolone (18).
