Phlorotannins and Sulfoquinovosyl Diacylglycerols: Promoters of Larval Metamorphosis in Ascidians, Isolated from the Brown Alga Sargassum thunbergii

Three active compounds have been isolated from the brown alga Sargassum thunbergii whose lipophilic extract promoted larval metamorphosis in two kinds of ascidians Halocynthia roretzi and Ciona savignyi. The most active compound was identified as diphlorethol by means of spectral data, while a mixture of phlorotannins was also afforded as a promoter. The last active compound was determined to be a mixture of sulfoquinovosyl diacylglycerols by spectral analysis. All compounds induced larval metamorphosis of H. roretzi and C. savignyi at a concentration of 25 μg/ml.