Glycosides and xanthine oxidase inhibitors from Conyza bonariensis

Fractionation of the xanthine oxidase inhibitory methanol extract of Conyza bonariensis afforded three glycosides, in addition to nine known compounds including amyrin, beta-sitostero1 daucosterol, syringic acid 3-hydroxy-5-methoxybenzoic acid, eugenol 4-O-glucopyranoside, and luteolin, apigenin and takakin 8-O-glucuronide. The structures of the glycosides were established by a combination of spectroscopic methods (IR, MS, 1H and 13C NMR, DEPT, COSY, HMQC and HMBC) as 4-hydroxypyridin-3-carboxylic acid 4-O-glucopyranoside, 8-hydroxy-6,7-dihydrolinalool 8-O-glucopyranoside and bonaroside [viz. 1,3,4,12-tetrahydroxy-2-(9-hexadecenoylamino)octadecane 1-O-glucopyranoside]. The in vitro enzyme assay showed that syringic acid and takakin 8-O-glucuronide displayed weak inhibitory activity against xanthine oxidase with IC50 values of 500+/-41 microM and 170+/-12 microM, respectively.