Chromenes from the brown alga Sargassum siliquastrum.

Sargachromanols A-P (1-16), sixteen new meroterpenoids of the chromene class, were isolated from the brown alga Sargassum siliquastrum collected from Jaeju Island, Korea. On the basis of the combined results of spectral and chemical analyses, the structures of the polyprenyl portions of these chromanol-containing compounds were determined to be linear triprenyls (1 and 2) and tetraprenyls (3-11), while others were the corresponding rearranged (12-15) and cyclized (16) tetraprenyls, respectively. The new compounds exhibited significant antioxidant activity in the DPPH assay. Compounds 7 and 15 also showed inhibitory activity toward butylcholine esterase.