Chemical Constituents And Tyrosinase Inhibition Activities Of Saxifraga Umbellulata Var. Pectinata

Nowadays, researches of tyrosinase inhibitors are hotspot in cosmetics industry. It has great significance to find natural tyrosinase inhibitors from natural resources, such as plants, and microorganisms. The plant Saxifraga umbellulata var. Pectinata, growing in eastern Tibet, China, has antibacterial effect, and antioxidant activity comparable with Vc, shown by preliminary pharmacological experiments. To further understand its chemical composition as well as its potential in whitening, this paper investigated the chemical composition of the extracts of S. umbellulata with strong inhibition, and the inhibition activities of major flavonoids isolated.The inhibitiory effects of ethanol, chloroform, acetone extracts of S. umbellulata on tyrosinase were assayed, all exhibited potent activities (IC50 value 1:1052,1:499.8, and 1:564.3(v/v), respectively). The effectiveness order of the extract was:ethanol> acetone> chloroform. Maximum inhibition rate of ethanol crude extract was 84.94%.Ethanol was used herein as extraction solvent. The effects of different solvent for separation of ethanol crude extracts were discussed, ethyl acetate and n-butanol fractions were found to be most active (IC50 value 1:882.6 and 1:624.6, respectively), and had maximum inhibition rate of 96.63% and 87.17%, respectively.Using different separation and purification method including silica gel column chromatography,26 compounds were obtained from ethyl acetate and n-butanol portions of S. umbellulata ethanol crude extract. The structures of 25 compounds were identified according to their physical and chemical properties and spectroscopic techniques such as NMR, which were characterized as stigmasterol (B1),β-sitosterol (B2), daucosterol (B3), moscatin (B4), gallic acid (B5),4-O-ethylgallic acid (B6), dueicosanyl caffeate (B7), pedicularioside G (B8), norswertianin (B10), decussatin (B11),1,8-dihydroxy-3,5-dimethoxyxanthone (B12),5,7,3’, 4’-tetrahydroxy-6,5’-dimethoxyflavone (B13),5,7,2’,4’-tetra-hydroxy-5’-methoxy-flavone (B14), acrapillin (B15), quercetin (B16), quercetin-4’-O-β-D-galactoside (B17), Quercetin-4’-O-β-D-glucoside (B18), rutin (B19), kaempferol (B20), Chrysoeriol (B21),β-amyrin (B23), oleanolic acid (B24),β-amyrin acetate (B25), and uvaol (B26). Among them, Bl、B4、B5、 B6、B7、B8、B10、Bll、B12、B13、B14、B17、B18、B20、B21、B23、B24、B25、 B26 were found in this plant for the first time.Six flavonoids isolated from S. umbellulata, B10, B11, B13, B14, B15 and B16 were tested and all showed tyrosinase inhibition in a concentration-dependent manner (IC50 461.22,621.94, 170.52,145.23,338.87 and 41.37μg/mL, respectively). It is noteworthing that quercetin (B16) had stronger inhibitory activity than the positive control arbutin(IC50 59.48/μg/mL).The results of this paper greatly enriched the chemical study of S. umbellulata, and provided a theoretical basis for the further development of this medicinal plant.