Vanillic acid, a metabolite of 4-hydroxy-3-methoxyphenylglycol and 4-hydroxy-3-methoxymandelic acid in man.

4-Hydroxy-3-methoxyphenylglycol (HMPG) labelled with 14C was used to study the metabolic fate of HMPG in six healthy volunteers. Besides conjugation and oxidation to 4-hydroxy-3-methoxymandelic acid (HMMA, VMA) a minor portion, 8.4 +/- 1.1% (mean +/- SEM) was excreted as 14C-labelled vanillic acid (VA). To study if VA was formed from HMPG or HMMA (VMA), deuterium-labelled HMPG [( 2H3]HMPG) and HMMA [( 2H6]HMMA) were simultaneously injected intravenously to seven healthy volunteers. The recovery of [2H3]VA from [2H3]HMPG was 8.3 +/- 2.1% and the recovery of [2H6]VA from [2H6]HMMA was 9.0 +/- 2.1%. The 2H-labelled VAs were probably formed by a decarboxylation reaction, in the case of HMPG after previous oxidation to HMMA.