| Summary: | This study reports on the antioxidant activity and α-glucosidase inhibitory activity of five cycloartane-type triterpenes isolated from Indonesian stingless bee (<i>Tetragonula sapiens</i> Cockerell) propolis and their structure−activity relationships. The structure of the triterpenes was determined to include mangiferolic acid (<b>1</b>), Cycloartenol (<b>2</b>), ambonic acid (<b>3</b>), mangiferonic acid (<b>4</b>), and ambolic acid (<b>5</b>). The inhibitory test results of all isolated triterpenes against α-glucosidase showed a high potential for inhibitory activity with an IC<sub>50</sub> range between 2.46 and 10.72 µM. Among the compounds tested, mangiferonic acid (4) was the strongest α-glucosidase inhibitor with IC<sub>50</sub> 2.46 µM compared to the standard (−)-epicatechin (1991.1 µM), and also had antioxidant activities with IC<sub>50</sub> values of 37.74 ± 6.55 µM. The study on the structure−activity relationships among the compounds showed that the ketone group at C-3 and the double bonds at C-24 and C-25 are needed to increase the α-glucosidase inhibitory activity. The carboxylic group at C-26 is also more important for increasing the inhibitory activity compared with the methyl group. This study provides an approach to help consider the structural requirements of cycloartane-type triterpenes from propolis as α-glucosidase inhibitors. An understanding of these requirements is deemed necessary to find a new type of α-glucosidase inhibitor from the cycloartane-type triterpenes or to improve those inhibitors that are known to help in the treatment of diabetes.
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