Cyclopeptide alkaloids of Ziziphus oxyphylla Edgw as novel inhibitors of α-glucosidase enzyme and protein glycation

Three cyclopeptide alkaloids, nummularine-R (1), nummularin-C (2), and hemsine-A (3), isolated from locally used antidiabetic plant Ziziphus oxyphylla Edgw (Rhamnaceae), showed a potent alpha-glucosidase inhibition, and moderate anti-glycation activities but no inhibition for alpha-chymotrypsin. This is the first report of the antidiabetic activities of cyclopeptide alkaloids. All compounds 1-3 exhibited inhibition for alpha-glucosidase enzyme having IC50 = 212.1 +/- 1.6 mu M, 215.1 +/- 1.2 mu M, and 394.0 +/- 2.4 mu M respectively, which are more potent than the standard, 1-deoxynojirimycin (IC50 = 441.0 +/- 0.1 mu M). Compounds 1 (IC50 = 720.2 +/- 10.9 mu M), and 3 (IC50 = 277.7 +/- 7.6 mu M) were also found to have a moderate anti-glycation activity. All compounds were non-toxic to PC-3 cell line. These compounds seem to have potential to control the postprandial hyperglycemia, and associated diabetes complications due to glycation of proteins. (C) 2011 Phytochemical Society of Europe. Published by Elsevier B. V. All rights reserved.