Abstract:The total antioxidative activity, and the scavenging abilities of DPPH, superoxide and hydroxyl free radicals of the different organic extracts from the dominant squirt Styela plicata of Beibu Gulf were evaluated for the first time by ultraviolet spectrophotometry. In the total reducing power experiments, the absorbance values of the ethyl acetate phase and water phase at the concentration of 100 μg/mL were 0.149 and 0.122, respectively. The DPPH· scavenging ability is greater in the water phase, with the IC50 value being 6.10 μg/mL. The IC50 values of the water phase and ethyl acetate phase for superoxide anion were 10.26 μg/mL and 2.18 μg/mL, respectively, with their corresponding IC50 values for hydroxyl free radical were 2.30 μg/mL and 9.65 μg/mL, respectively. The results showed that the active components of the squirt’s secondary metabolites possessing significant in vitro antioxidant activity were mainly concentrated in the aqueous phase and ethyl acetate phase. The ethyl acetate phase was subjected to further separation and purification by normal- and reversed-phase silica gel column chromatography, Sephadex LH-20 column chromatography and semi-preparative HPLC. The structures of active compounds were characterized by spectroscopic methods including NMR and MS, and three of which were identified as polyhydroxy sterols cholestane-1,3,5,6-tetraol(1), (5)-cholestane-3,5,6-triol(2) and suberoretisteroids D(3). These three compounds were obtained from S. plicata for the first time. The experimental results provide fundamental information and guidance for increasing the application value of S. plicata and also offers resources for the development of food-derived natural antioxidants.
