Enzymatic reduction of xenobiotic alpha,beta-unsaturated ketones: formation of allyl alcohol metabolites from shogaol and dehydroparadol.

A novel reductive metabolism of shogaol [1-(4'-hydroxy-3'-methoxyphenyl)-deca-4-ene-3-one], a major pungent and pharmacologically active principle of ginger, was investigated in rat liver in vitro. The ethyl acetate extractable metabolites formed by incubation of this alpha,beta-unsaturated ketone with rat liver 12,000 x g supernatant fortified with NADPH-generating system were analyzed by high performance chromatography and gas chromatography/mass spectrometry. In addition to the saturated ketone and reduced alcohol metabolites, an allyl alcohol, 1-(4'-hydroxy-3'-methoxyphenyl)-deca-4-ene-3-ol, was identified as a new metabolite of shogaol. Likewise, dehydroparadol [1-(4'-hydroxy-3'-methoxyphenyl)-deca-1-ene-3-one], a non-pungent analog of shogaol, was also reduced to the corresponding allyl alcohol by the postmitochondrial fraction of rat kidney in the presence of NADPH-generating system.