Biol. Pharm. Bull. 28(2) 374—377 (2005)

cales) are known to contain structurally unique secondary metabolites, such as plastoquinones, chromanols, a cyclopentenone, and polysaccharides. These compounds show various biological activities due to their unique structure. We previously reported that the methanolic extract of the brown alga, Sargassum micracanthum (KUETZING) ENDLICHER, “Togemoku” in Japanese, showed strong antioxidant activity. In the course of investigations on the biologically active metabolites from this alga, two known plastoquinones, 1 and 2, were isolated as major constituents. This paper describes their isolation, determination of the absolute configuration via a new chromene derivative 3, and evaluation of the antioxidant and antiviral activities of these compounds.