Alpha-glucosidase and tyrosinase inhibiton of polyphenols isolated from Potentilla speciosa var. speciosa: In vitro and in silico perspectives

In order to explore the antidiabetic and anti-pigmentation potential of Potentilla species, which have been used for the treatment of diabetes and some skin problems, α-glucosidase and tyrosinase inhibitory effects of Potentilla speciosa Willd. var. speciosa Willd. were tested. The n-butanol extract showed significant α-glucosidase inhibition (IC₅₀ = 3.08 ± 0.48 ppm). Phytochemical studies on this extract led to isolation of catechin, miquelianin, tiliroside, and cinnamtannin D1, the occurrence of the latter in the genus Potentilla is reported for the first time in this study. Miquelianin showed the highest inhibitory effect on tyrosinase with an IC₅₀ value of 86.60 ± 1.90 μM. Cinnamtannin D1 emerged as an excellent α-glucosidase inhibitor with an IC₅₀ value (0.849 ± 0.014 μM), approximately 53 times higher than the value of the positive control, acarbose. It was found to inhibit α-glucosidase in a noncompetitive manner with a K_i value of 0.240 ± 0.010 μM. Molecular modeling studies showed that cinnamtannin D1 most likely bound to an allosteric site of the enzyme.