Chemical constituents of Citrus grandis (L.) Osbeck (Rutaceae) and their α-glucosidase inhibitory activity

The chemical investigation of the methanolic bark extract of Citrus grandis (L.) Osbeck (Rutaceae) led to the isolation of one saponin named aridanin (1) isolated for the first time in the genus Citrus, together with seventeen known compounds including eight acridone-type alkaloids, two limonoids, two coumarins, one sugar, one lactam derivative, and three common steroids. Their structures were conclusively established using 1D- and 2D-NMR spectral data. The isolated compounds 1-9 were tested for their α-glucosidase inhibitory activity and the results showed that they all have potency higher than the reference acarbose (IC50 = 218.2 ± 2.8 μM) and aridanin was the strongest one which could be due to its sugar unit as usually observed for triterpene saponins. Furthermore, the structure-activity relationship of the tested compounds has been discussed as well as the chemotaxonomic significance of the study. The present study enriches the chemistry of Citrus with three additional compounds (1, 14, 15) and classifies the plant C. grandis as a good source of leads for the development of anti-diabetic drugs.