Isolation of flavonol rhamnosides from Pometia pinnata leaves and investigation of α-glucosidase inhibitory activity of flavonol derivatives

Abstract

Pometia pinnata belonging to the Sapindaceae family has been traditionally used as the therapeutic agent for burns and wounds in Indonesia. Based on the result of the experiment conducted, the ethyl acetate fraction of P. pinnata leaves showed strong α-glucosidase inhibitory activity. After two flavonol rhamnoside compounds were isolated from ethyl acetate fraction of P. pinnata leaves methanol extract using chromatography method, their structures were identified as kaempferol-3-O-rhamnoside (1) and quercetin-3-O-rhamnoside (2). The ultra-performance liquid chromatographyelectrospray ionization time-of-flight mass spectrometry (UPLC-ESI-TOFMS) chromatogram showed compounds 1 and 2 were the major compounds of the ethyl acetate fraction. In this study, the structure-activity relationship among the kaempferol, quercetin, and their derivatives bearing sugar moiety were also evaluated. Among tested eight compounds, kaempferol 7 (percent inhibition = 80.10% ± 0.8) and quercetin 8 (percent inhibition = 82.93% ± 0.4) had stronger α-glucosidase inhibitory activity than that of other derivatives. Among kaempferol derivatives bearing sugar moiety, compound 1 showed the strongest activity. Moreover, compound 2 showed strong α-glucosidase inhibitory activity among quercetin derivatives. Therefore, it can be confirmed that the hydroxyl group at C-3 position is very important for α-glucosidase inhibitory activity of flavonol compounds.