A glucomannan with alpha-glucosidase inhibitory activity isolated from the leaves of Antidesma microcarpum Elmer (Euphorbiaceae)
The alpha-glucosidase inhibition is seen as a possible approach to controlling post-prandial hyperglycemia in diabetes mellitus. Some species of the genus Antidesma L. are reported to be of use in the treatment of diabetes. In search of indigenous and/or endemic Antidesma species with potential use as adjuvants of antidiabetic agents the extracts of A. curranii, A. fusicarpum, A. microcarpum, and A. montanum were screened for alpha-glucosidase inhibitory activity and to isolate the active constituent from the most active extract. The Antidesma extracts were assayed by an in vitro method using yeast alpha-glucosidase. The in vitro alpha-glucosidase inhibitory assay was also used for the bioassay-guided isolation of the active constituent. A. microcarpum extract exhibited the highest glucosidase inhibitory activity with an IC50 of 1.42±0.03 upsilon g/mL. The bioassay-guided isolation of the active constituent in the extract of A. microcarpum afforded a glucomannan having the structure beta-Dmannopyranosyl-(1->3)-alpha-D-mannopyranosyl-(1->4)-[beta-D-glucopyranosyl-(1->3)]-alpha-Dglucopyranose and with an IC50 alpha-glucosidase inhibitory activity of 0.22 ±0.04 upsilon g/mL which is higher than the inhibitory activity of standard acarbose.
Keywords: Antidesma microcarpum, Euphorbiaceae, alpha-glucosidase inhibitory activity, glucomannan