Flavonoids isolated from Syzygium aqueum leaf extract as potential antihyperglycaemic agents

Syzygium aqueum is a medicinal plant which is grown in tropical regions. In this study, the ethanolic extracts of S. aqueum leaf were investigated for its antihyperglycaemic activity. Our investigation revealed its effectiveness in inhibiting the carbohydrate hydrolysing enzymes, alpha-glucosidase (EC50 = 11 mu g/ml) and alpha-amylase (EC50 = 8 mu g/ml), at significant level than the commercial drug acarbose (EC50 = 28 mu g/ml, alpha-glucosidase; EC50 = 12 mu g/ml, alpha-amylase). In addition, the ethanolic leaf extracts were able to inhibit the key enzyme in the polyol pathway, aldose reductase (EC50 = 0.03 mu g/ml) and prevent the AGEs formation by 89%. Six flavonoid compounds, 4-hydroxybenzaldehyde (1), myricetin-3-O-rhamnoside (2), europetin-3-O-rhamnoside (3), phloretin (4), myrigalone-G (5) and myrigalone-B (6), were isolated from the ethanolic leaf extracts. Compounds (2) and (3) showed high inhibitory activities, with EC50 values of 1.1 mu M and 1.9 mu M against alpha-glucosidase and EC50 values of 1.9 mu M and 2.3 mu M against alpha-amylase, respectively. These findings provide a strong rationale to establish S. aqueum's capability as an antihyperglycaemic agent. (C) 2011 Elsevier Ltd. All rights reserved.