Sesquiterpenes from Chinese Red Alga Laurencia okamurai

AimTo study chemical constituents of red alga Laurencia okamurai Yamada to search new bioactive substances.MethodsThe Et2O extract of Laurencia okamurai was subjected to repeated column chromatography on Sephadex LH-20 and silica gel to afford nine pure compounds (1-9), whose structures were elucidated on the basis of spectroscopic analysis and by comparison with the data reported in the literature.ResultsNine sesquiterpenes were isolated and identified as laurokamurene C (1), debromoaplysinol (2), aplysinol acetate (3), debromoisolaurinterol (4), isolaurinterol (5), filiformin (6), α-isobromocuparene (7), cuparene-type ether (8) and deoxyprepacifenol (9), respectively.ConclusionsCompound 1, a new sesquiterpene, represents the third example with a novel rearranged laurane-type skeleton, exceptionally prone to decompose at room temperature. Compound 3 was shown for the first time to be true natural product. In antifungal bioassay, compounds 2-9 were found to be inactive against the fungus Cladosporium cucumerinum.