Isolation and characterization of 2-hydroxy-3-[4-hydroxyphenyl]-2-propenoic acid and 4-bromophenol from anti-diabetic extract of the root bark of Uvaria afzelii

The anti-diabetic activity of the methanolic extract of Uvaria afzelii (Annonaceae) root bark was investigated in normoglycaemic, glucose and alloxan-induced diabetic rats using glibenclamide (5 mg/kg) and normal saline as positive and negative controls respectively. The acute oral toxicity test of the extract in rats using Lorke's method showed LD50 of 693 mg/kg. The results showed that the extract at the tested doses (100, 200 and 400 mg/kg), gave a statistically lower hypoglycaemic activity (p < 0.05) than glibenclamide (5 mg/kg) in normoglycaemic rats. In glucose-loaded hyperglycaemic rats, the extract elicited a dose dependent activity with 400 mg/kg showing comparable activity (p > 0.05) with glibenclamide (5 mg/kg) at 1 h. The extract (400 m/kg) caused 75% blood glucose level reduction in a 14 day treatment in alloxan-induced diabetic rats that was significantly higher than the 58% of glibenclamide (5 mg/kg). The ethyl acetate fraction (200 and 400 mg/kg) gave a comparable activity with glibenclamide (5 mg/kg) at all-time points in glucose loaded rats while other fractions lacked appreciable activity. The ethyl acetate fraction afforded two compounds namely; 2-hydroxy-3-(4-hydroxyphenyl) acrylic acid (1) and 4-bromophenol (2). The structures of these compounds were elucidated and characterized by Infrared spectroscopy (IR), 1D- and 2D-Nuclear Magnetic Resonance spectroscopy (NMR) and Mass spectrometry (MS).