Antioxidant and Antiviral Activities of Plastoquinones from the Brown Alga <i>Sargassum micracanthum</i>, and a New Chromene Derivative Converted from the Plastoquinones

Two plastoquinones were isolated from the methanolic extract of the brown alga Sargassum micracanthum, and these were identified as a known 2-geranylgeranyl-6-methylbenzoquinone and its hydroquinone, respectively, based on spectroscopic analysis. The absolute configuration of the secondary hydroxyl group was determined by the modified Mosher's method using the new chromene derivative converted from plastoquinones. One of the plastoquinones and the chromene exhibited significant antioxidant activities, such as an inhibitory effect on lipid peroxidation and a radical scavenging effect on 1,1-diphenyl-2-picrylhydrazyl (DPPH). The benzoquinone-type compound and the chromene derivative were found to have potent antiviral activity against human cytomegalovirus (HCMV).