Studies On Two Chinese Red Algae Of The Genus Laurencia (L. Okamurai And L. Composita):Chemistry And Bioactivities

Red algae of the genus Laurencia (family Rhodomalaceae, order Ceramiales, class Rhodophyceae, and phylum Rhodophyta), found in all oceans and seas as well as almost all latitudes, mostly in tropical and subtropical regions, comprise approximately 135 species in the world, of which 31 species are distributed in China, and are well-known for their ability to biosynthesize an astonishing variety of structurally unusual secondary metabolites with diverse bioactivities. Secondary metabolites from these algae are C15-acetogenins, sesquiterpenes, diterpenes, triterpenes, alkaloids, and sterols, the former two types of compounds, which are predominant, are usually characterized by the presence of halogen atoms in their molecules and have been reported to possess antibacterial, insecticidal and cyotoxic activities. During the course of our search for bioactive secondary metabolites, two species of the genus Luarencia, including L. okamurai and L. composite collected from the Nanji Island, Zhejiang Province, China, have chemically been investigated.The two fresh algae materials were extracted with EtOH, Each extract was partitioned between water and EtO2. The EtO2 fraction was purified by repeated silica gel, Sephadex LH-20 column chromatography and high performance liquid chromatography (HPLC) to yield pure compounds, and their structures were elucidated mainly by NMR, mass, infrared spectroscopic techniques and comparison with those reported data in the liaterature. As results, a total of 80 compounds (6 compounds were isolated from the two Laurencia species) including 68 sesquiterpenes,5 diterpenes,1 triterpenes,5 aliphatic esters and 1 steroids were isolated and identified from these two Laurencia species, with 31 new compounds and 1 new natural products.44 compounds including 10 new compounds were isolated and elucidated from L. okamurai Yamada,7 new sesquiterpenes with 4 laurane-3α-hydroperoxy-3-epiaplysin (1-11),3β-hydroperoxyaplysin (1-13) laurepoxyene (1-22), 8,14-dibromoaplysin (1-23),1 bisabolane-(5S)-5-acetoxy-β-bisabolene (1-26),1 laurokamurane-laurokamurene D (1-24) and 1 seco-laurokamurane skeleton seco-laurokamurone (1-25),1 dimeric sesquiterpenoids isolaurebiphenyl (1-32) and 2 aliphatic esters. Interestedly, seco-laurokamurone (1-25), a new sesquiterpenes with seco-laurokamurone skeleton, It may come from the oxidations of laurokamurane-skeleton, more interestedly, (1-24) was some parts converted into (1-25) in the proess of Nuclear Magnetic Resonance Spectrum testing, which further confirmed the relationship of the above biotransformation. In addition, (1-24) was the fourth laurokamurane sesquiterpene from nature world.42 Compounds including 21 new sesquiterpenes and 1 new natural products were identified from L. composita Yamada. The new sesquiterpenes were 19 chamigrane-(2-3,2-5-2-7,2-9,2-11,2-14,2-18,2-21,2-24,2-26-2-33),1 bisabolane-(2-34 and 2-35), 1 acyclic sesquiterpenes (2-38), at the same time, this is the first report of the discovery of chamigrane-sesquiterpenes(2-26-2-28)with C-10 carbonyl substituted, and (2-3,2-4) C-9 is replaced by chlorine atoms, In the previous reported literature, chamigrane-sesquiterpenes were substituted with C-10 bromine ether, but (2-3,2-7 and 2-9) were substituted with C-10 hemiketal fragment, The isolation of new compounds and new natural products was a new addition to the molecular diversity of the genus Laurencia.Bioactivity assay including antibacterial against Staphylococcus aureus and pseudomonas aeruginosa, antifungal against Cryptococcus neoformans, Candida glabrata, Aspergillus fumigatus and Trichophyton rubrum, antitumor against A549 and HL60 tumor cell lines showed that some secondary metabolites from these two Laurencia species, possessed antibacterial, antibacterial, antifungal and antitumor activities, In the bioscreening experiment, (1-17) showed a strong bactericidal activity (Staphylococcus aureus), (1-18) partially inhibited the growth of Staphylococcus aureus, (1-2,1-9,1-17,1-22,1-27,1-32) showed partially inhibition (Candida glabrata) of inhibition; (1-10,1-17,1-18,1-19,1-29) have weak inhibition of human leukemia cell line HL60, while (1-17,1-18,1-19,1-28) showed weak inhibition on human lung cancer cell line A549.