Metabolism of the cinnamon constituent o-methoxycinnamaldehyde in the rat

The metabolism of o-methoxycinnamaldehyde (1.3 mmol/kg, intragastrically) was studied in rats. Identification of the urinary metabolites by g.l.c.-mass spectrometry and quantification by h.p.l.c. showed that the major metabolic pathway (approx. two-thirds of the dose) was oxidation to the corresponding cinnamic and phenylpropionic acids (C6-C3 acids) which were largely excreted as glycine conjugates. Intermediate amounts (approx. 10% of the dose) of the O-demethylated C6-C3 acids were excreted. Relatively large amounts of the beta-hydroxylated phenylpropionic acid derivative were found, however only traces of the further products of beta-oxidation (2-methoxylated derivatives of benzoic and hippuric acid) were excreted. No evidence was obtained for conjugation of o-methoxycinnamaldehyde with glutathione. Urinary excretion of metabolites was rapid (91% in 24 h and 98% in 48 h).