Antihyperglycaemic flavonoids from Syzygium samarangense (Blume) Merr. and Perry.

2',4'-Dihydroxy-3',5'-dimethyl-6'-methoxychalcone 1, its isomeric flavanone 5-O-methyl-4'-desmethoxymatteucinol 2 and 2'4'-dihydroxy-6'-methoxy-3'-methylchalcone 3 were isolated from the leaves of S. samarangense using a bioassay-directed scheme. In an oral glucose tolerance test, at a dosage of 1.0 mg/20 g mouse, 1 and 2 significantly (alpha = 0.05) lowered the blood glucose levels (BGLs) in glucose-hyperglycaemic mice when administered 15 min after a glucose load. When co-administered with glucose, only 1 showed a significant lowering of BGLs 45 min after its oral administration. When administered 15 min before glucose, none of the flavonoids showed a positive effect. Only 1 decreased significantly, at alpha = 0.05, the BGLs of alloxan-diabetic mice at t = 90-150 min. Copyright 2005 John Wiley & Sons, Ltd.