Methanolic extracts of edible plants and seaweeds were tested for their inhibitory activity against Jack bean urease. Quercetin-4′-O-β-D-glucopyranoside was isolated from Allium cepa as a urease inhibitor with an IC50 value of 190 μM. Quercetin and two quercetin glycosides, avicularin and guaijaverin, were isolated from Psidium guajava as urease inhibitors with respective IC50 values of 80 μM, 140 μM, and 120 μM.
