Identification of α-glucosidase inhibitors from the leaves of Pluchea indica (L.) Less., a traditional Indonesian herb: promotion of natural product use
A promising approach for treating diabetes mellitus (DM) is to decrease postprandial hyperglycaemia by suppressing carbohydrate digestion using α-glucosidase inhibitors. Pluchea indica leaf extracts possess inhibitory activity against intestinal maltase. Enzyme assay-guided fractionation by chromatography yielded five active caffeoylquinic acid derivatives (1–5). Their structures were elucidated by mass spectrometry and NMR analysis and completed by comparison with reference data. 3,5-Di-O-caffeoylquinic acid (1), 4,5-di-O-caffeoylquinic acid methyl ester (2), 3,4,5-tri-O-caffeoylquinic acid methyl ester (3), 3,4,5-tri-O-caffeoylquinic acid (4) and 1,3,4,5-tetra-O-caffeoylquinic acid (5) were isolated. Comparison of the activities of each isolate suggested that both methyl esterification of quinic acid and the number of caffeate groups in the molecule were important for the inhibitory activity. This study provides basic information for further examination of the suitability of P. indica as a functional food and medicinal supplement for the treatment and prevention of diabetes.