Inhibitory effects of cardols and related compounds on superoxide anion generation by xanthine oxidase

5-Pentadecatrienylresorcinol, isolated from cashew nuts and commonly known as cardol (C15:3), prevented the generation of superoxide radicals catalysed by xanthine oxidase without the inhibition of uric acid formation. The inhibition kinetics did not follow the Michelis–Menten equation, but instead followed the Hill equation. Cardol (C10:0) also inhibited superoxide anion generation, but resorcinol and cardol (C5:0) did not inhibit superoxide anion generation. The related compounds 3,5-dihydroxyphenyl alkanoates and alkyl 2,4-dihydroxybenzoates, had more than a C9 chain, cooperatively inhibited but alkyl 3,5-dihydroxybenzoates, regardless of their alkyl chain length, did not inhibit the superoxide anion generation. These results suggested that specific inhibitors for superoxide anion generation catalysed by xanthine oxidase consisted of an electron-rich resorcinol group and an alkyl chain having longer than C9 chain.