Investigation of α-glucosidase and tyrosinase inhibitory effects of potentilla speciosa willd. var. speciosa willd. and its secondary metabolites

Potentilla species are plants that belongs to Roseceae family and distributed the temperate areas of northern hemisphere. These species are used for the treatment of diabetes, diarrhea, inflammation, cancer and as blood stopper. In the present study, α-glucosidase and tyrosinase inhibitory effects of the aerial parts of Potentilla speciosa Willd. var. speciosa Willd, which is used as folk medicine, were investigated. The enzyme inhibition of crude methanol extract of the plant and butanol and water extracts prepared from it were tested, phytochemical studies were carried out on the butanol extract. A condensed tannin precursor, catechin (PS-1), two flavonol [quercetin-3-O-glucuronide (PS-2) and kaempferol 3-O-(6''-coumaroyl)-β- glucopyranoside (PS-3)] and a condensed tannin, cinnamtannin D1 were isolated by using different chromatographic studies. The structures of isolated compounds elucidated by means of 1D (1H and 13C) and 2D (DQF-COSY, HSQC and HMBC)-NMR techniques. When α-glucosidase and tyrosinase inhibitory effects of isolated compounds, cinnamtannin D1 was found to be a stronger inhibitor than that of positive control, acarbose with an IC50 value of 0,85 μM. When enzyme kinetic analysis of the compound investigated, it was found that the compound was a noncompetetive inhibitor with Ki value of 0,24 μM.