ABSTRACT: A new C11-norisoprenoid derivative, sargassumone (1), has been isolated from Sargassum naozhouense together with six known norisoprenoids and a highly oxygenated cyclopentene: (2R,6S,8S,9S)-hexahydro-2,9-dihydroxy-4,4,8-trimethyl-6-acetyloxy-3(2H)-benzofuranone (2), (6S,8S,9R)-hexahydro-6,9-dihydroxy-4,4,8-trimethyl-2(2H)-benzofuranone (3), (6S,8S,9R)-hexahydro-6,9-dihydroxy-4,4,8-trimethyl-2(2H)-benzofuranone (4), loliolide (5), (+)-epiloliolide (6), spheciospongones A (7), and (+)-kjellmanianone (8). Compound 1 was identified on the basis of nuclear magnetic resonance (NMR) and mass spectrometry (MS) analysis, and the absolute stereochemistry was defined by NOESY spectroscopy, minimizing energy calculation, and circular dichroism (CD) spectra. The known compounds 2-8, isolated from S. na
