Studies On Sesquiterpenes And C₁₅^-acetogenins From Laurencia Okamurai

The marine red algal species of the genus Laurencia (family Rhodomalaceae, order Ceramiales, class Rhodophyceae, and phylum Rhodophyta) are consisted of 135 species in the world and over 20 of them distributed in China. They mainly spread along tropical, subtropical, and temperate coasts. The secondary metabolites of the genus Laurencia are mainly sesquiterpenes, diterpenes, triterpenes/polyethers, and C15-acetogenins. Sesquiterpenes and C15-acetogenins with the majority bonding to halogen are quite common in the species of Laurencia okamurai. In this thesis, the halogenation mechanism of Laurencia sp. was summarized and sesquiterpenes and C15-acetogenins isolated from the species as well as their synthetic approachs in the last 10 years were reviewed. Chemical investigation of Laurencia okamurai collected respectively from Shandong (northern China) and Guangdong (southern China) was conducted. The results showed that geographic settings exerted remarkable influence on the chemical components of the red alga Laurencia okamurai.Dried and powdered algal material was extracted with organic solvents. The extract was purified by repeated silica gel and Sephadex LH-20 and RP-18 column chromatography and by preparative thin layer chromatography (PTLC) to yield pure compounds, their structures were elucidated mainly by 1D and 2D NMR, mass, and infrared spectroscopic techniques. As results, a total of 30 compounds were isolated and identified. Among them, there were 8 new compounds, which were determined and named as laurenokamurenes A-E (LA1-LA5),laurenokamurin (LA6),laurenokaldehyde (LA7) and isochlorolaurenol (LB1), and 1 new natural product (LA12) together with 21 known compounds. Secondary metabolites of the species from Shandong province comprising 4 bisabolane-type, 5 chamigrane-type, and 6 laurane-type sesquiterpenes, 5 C15-acetogenins, and 1 other compound, were more diversified in comparison with those from Guangdong province, which included 7 laurane-type sesquiterpenes and 2 other compounds.Antibacterial bioassay against Staphylococcus showed that the tested compounds didn't possess antibacterial activities.