Isolation of the antidiarrhoeal tiliroside and its derivative from Waltheria indica leaf extract
The antidiarrhoeal effect of Waltheria indica methanol extract and fractions have been reported earlier but, the present work examined the intestinal relaxant effects of two flavonoid-phenyl propanoids isolated from the methanol extract. The active aqueous fraction was subjected to vacuum liquid chromatography using dichloromethane with increasing concentration of ethyl acetate, and that of methanol and water successively. The ten (10) fractions obtained were combined to give seven (7). The fraction 2 (C, D) was subjected to preparative thin layer chromatography on silica gel GF254 (10-40μm) using CHCl3-CH3OH (8:2) to obtain compound coded F2. Fraction 4 (F) was subjected to column chromatography using silica gel (60-120μm mesh) and eluted with dichloromethane with increasing concentrations of methanol. Fractions 9-28 were combined and subjected to column chromatography using chloroform with increasing concentration of methanol. The fractions 1-16 of these were purified on Sephadex LH-20 to obtain compound BAA. The identities of the two compounds were established using spectroscopic methods. The antidiarrheal effect of compound F2 was evaluated on mice using charcoal transit (100,200, 400mg/kg), castor oil (40, 60 mg/kg) while the two compounds were examined for their inhibitory effects on Ach-induced ileum contraction. The effects of the compounds were compared with loperamide (3mg/kg) and atropine (80μg). Compounds F2 and BAA were identified as tiliroside and 3’’’, 5’’’-dimethoxy tiliroside respectively. Tiliroside inhibited the charcoal transition in the animals in a dose dependent pattern with 400mg/ mL eliciting 63.41% inhibition compared to 59.23% produced by loperamide. The compound also elicited significantly (P<0.05) prolonged onset of stooling and reduced the number and weight of stools produced lower than the control. The two compounds drastically inhibited the Ach-induced contractions of the ileum. The compound, tiliroside at 10mg, completely abolished the contraction by Ach unlike 3’’’, 5’’’-dimethoxy tiliroside which reduced the contraction to 1.92% at 20mg. The identified compounds seem to be responsible for the ethnomedicinal use of the plant in treating diarrhea.