Quercetin glycosides in Psidium guajava L: leaves and determination of a spasmolytic principle

RESUMO

The traditional herbal remedy from Psidium guajava leaves had been medically proposed in mexico as effective treatment of acute diarrhea. A methanolic leaf extract was subjected to a bioassay-guided isolation of spasmolytic constituents. Six fractions were separated on a polyvinylpolypyrrolidine (PVPP) columm using a water methanol-gradient. The fraction containing flavonols inhibited peristalsis of guinea pig ileum in vitro. A trace of quercetin aglycone together with five glycosides was isolated from this active fraction and identified as quercentin 3-O-alpha-L-arabinoside (guajaravin); quercetin 3-O-ß-D-glucoside (isoquercetin); quercetin 3-O-ß-D-galactoside (hyperin); quercetin 3-O-ß-L-rhamnoside (quercitrin) and quercetin 3-O-gentobioside. Biological activity of each pure compound was studied in the same bioassay. Obtained results suggets that the spasmolytic activity of the Psidium guajava leaf remedy is mainly due to the aglycone quercetin, present in the leaf and in the extract mainly in the form of live flavonols, and whose effect is produced when these products are hydrolyzed by gastrointestinal fluid