The metabolism of eugenol in man

Abstract

1. The metabolism of eugenol (4-hydroxy-3-methoxy-allylbenzene) was investigated in male and female healthy volunteers. It was rapidly absorbed and metabolized after oral administration and was almost completely excreted in the urine within 24 h. Unmetabolized eugenol excreted in urine amounted to less than 0.1% of the dose. 2. The urine contained conjugates of eugenol and of nine metabolites. The structures of these metabolites, elucidated using g.l.c.-mass spectrometry, and by comparison with synthetic reference compounds, were identified as: eugenol, 4-hydroxy-3-methoxyphenyl-propane, cis- and trans-isoeugenol, 3-(4-hydroxy-3-methoxyphenyl)-propylene-1,2-oxide, 3-(4-hydroxy-3-methoxyphenyl)-propane-1,2-diol, and 3-(4-hydroxy-3-methoxyphenyl)-propionic acid. 3. The structures of the following metabolites were tentatively deduced from mass spectra only, as reference compounds were not available: 3-hydroxy-3-(4-hydroxy-3-methoxyphenyl)-allylbenzene, 3-(6?-mercapto-4-hydroxy-3-methoxyphenyl)-propane, and 2-hydroxy-3-(4-hydroxy-3-methoxyphenyl)-propionic acid. 4. The amounts of the individual metabolites excreted were determined by g.l.c. Some 95% of the dose was recovered in the urine, most of which (greater than 99%) consisted of phenolic conjugates; 50% of the conjugated metabolites were eugenol-glucuronide and sulphate. Other metabolic routes observed were the epoxide-diol pathway, synthesis of a thiophenol and of a substituted propionic acid, allylic oxidation, and migration of the double bond.