In vitro bioactive analysis and antioxidant activity of two species of seaweeds from the Gulf of Mannar

Evaluation of in vitro standard antioxidant assays, such as 1,1-diphenyl-2- picrylhydrazyl (DPPH), 2,2'-azino-bis-3 ethylbenzothiozoline-6-sulphonic acid diammonium salt (ABTS(+)) radical scavenging, lipid peroxidation inhibitory (or thiobarbituric acid formation inhibitory activity) and ferrous ion (Fe+2) chelating activities of different solvent extracts of seaweeds, Jania rubens and Kappaphycus alvarezii collected from the Gulf of Mannar of the Peninsular India, were carried out. The methodology utilised bioactivity-guided extraction of seaweed with effective solvent comprised classical chromatographic and spectroscopic techniques. The ethyl acetate extraction of seaweeds displayed significantly greater antioxidant activity than dichloromethane and n-hexane extraction. Bioactivity-guided chromatographic separation of the ethyl acetate extract of seaweeds with potentially greater antioxidant activities, yielded 6 alpha-methoxy-4b beta-methyl-7 beta-vinyl-1,2,3,4,4a, 4b, 5,6,7,8,8a, 9-dodecahydro- 2 beta-phenanthrenol (1) from J. rubens, whereas K. alvarezii yielded 2 beta-ethyl-9-oxo-5 alpha-vinyl-1,2,5,5a, 6,7,8,9-octahydroheptalene- 10,1-carbolactone (2) and methyl-2-ethyl-9-oxo- 5 alpha-vinyl-1,2,5,5a, 6,7,10,10a-octahydroheptalene-1 alpha-carboxylate (3). Compound 1 displayed significantly greater DPPH scavenging activities (IC50 0.22 mg/mL) than alpha-tocopherol (IC50 0.63 mg/mL). The order of DPPH radical-scavenging activities were compounds 1 > 2 > 3. [GRAPHICS]