Three new steroidal sulfate pentaglycosides (asterosaponins), goniopectenosides A-C (1-3), were isolated from the polar extract of the starfish Goniopecten demonstrans. The pentasaccharide moiety linked to C-6 of 3β-sulfated steroidal aglycones, consists of D-xylose, D-fucose, D-quinovose, and the unprecedented 3-O-methyl-D-quinovose. The three asterosaponins differ from each other in the side chains. Their structures were elucidated by extensive NMR experiments including 1H-1H (COSY, TOCSY, ROESY) and 1H-13C (HMQC and HMBC) spectroscopy as well as chemical evidence. The isolated asterosaponins have been found to significantly inhibit the settlement of the biofouling marine brown macroalga Hincksia inegularis. © Wiley-VCH Verlag GmbH, 2000.