| Species of the red alga genus Laurencia belongs to Rhodomela confervoides, and produce an astonishing variety of halogenated terpenes. The vast majority of these are halogenated sesquiterpenes, diterpenes and triterpenes. Some metabolites have been shown to possess insecticidal, antibacterial and antifungal activities. So the study on chemical constituents towards Laurencia can enrich the knowledge of this genus and provide a new way for seeking the lead compounds of new medicine.In this dissertation, the chemical constituents of the red algae Laurencia cartilaginea and Laurencia majuscula collected from the South China Sea of the Xisha Islands were studied, and 12 compounds were isolated by combination of extraction and separation and identified by various kinds of spectrum. These chemical compounds were found for the first time from this alga and compound 9 had never been reported in previous literatures.In Laurencia cartilaginea, nine compounds (compoundsl-9) have been isolated and identified from the extraction of EtOAc fraction. They are established as: hexadecanoic 1; 5 α ,8 α -epidioxyergosta-6,22-dien-3 β -ol 2; a mixture of sterols 3; cholest-4-ene-3 β ,6 β -diol 4; octadecanal 5; N-(1-hydroxyrnethyl-2,3-dihydroxyl)hep tadecyl-2-hydroxyltetracosanamide 6; stigmast-5,22-dien-3-O- β -D-glucopyranoside 7; N-(l-hydroxymethyl-2-hydroxyl)heptadecyl-2,3-dihydroxyltetracosanamide 8; N-(1-hydroxymethyl-2,6,8-trihydroxyl)heneicosyl-2-hydroxyl-10-(2-octylcyclopropyl)-d ecanamide 9 by IR, 1H-NMR, 13C-NMR, EI-MS, GC-MS, FAB-MS and ESI.In the red alga Laurencia majuscula, three compounds (compounds 10-12) have been isolated and identified from the extraction of EtOAc fraction. They are established as: 1,2-di-O-hexadecadienoyl-3-O-β-D-galactopyranosyl-sn-glycerol 10;1-O-hexadecadienoyl-2-O-tetradecadienoyl-3-O- β -D-galactopyranosyl-sn-glycerol11 and uracil 12 by spectrum analysis such as IR, 1H-NMR, 13C-NMR, 1H-1HCOSY, HMQC, HMBC , EI-MS and FAB-MS.
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