An apigenin-derived xanthine oxidase inhibitor from Palhinhaea cernua.

Fractionation of the ethanol extract of Palhinhaea cernua afforded a new (1) and two known p-coumaroylated apigenin glycosides (2, 3) in addition to dillenetin, rhamnazin, alpha-onocerin, beta-sitosterol, and (E)-2-hydroxy-5-methoxycinnamic acid. The structure of compound 1 was elucidated as apigenin-4'-O-(2' '-O-p-coumaroyl)-beta-D-glucopyranoside by a combination of its spectroscopic data. The new glycoside 1 inhibits xanthine oxidase (IC(50): 23.95 +/- 0.43 microM) in a competitive-noncompetitive manner with K(i) and K(I) values of 14.35 and 93.68 microM, whereas compounds 2 and 3 were inactive. The distribution and significance of acylated flavonoid glycosides are discussed.