A new sterol, named thunberol (1), along with four known analogs, 24-ethylcholesta-4,24(28)-dien-3-one (2), stigmasta-5,28-dien-3β-ol (3), cholesta-5,14-dien-3β-ol (4), and cholesta-5,23-dien-3β,25-diol (5), were isolated from the brown alga Sargassum thunbergii collected from East China Sea. The structures of these metabolites were elucidated on the basis of detailed spectroscopic analysis and by comparison with the literature data. Thunberol (1) exhibited significant inhibitory activity against protein tyrosine phosphatase 1B, a potential drug target for the treatment of Type-II diabetes and obesity, with an IC50 value of 2.24 μg/ml.
Keywords: Sargassum thunbergii; brown alga; oxygenated steroid; sterol.