Detailed oxidation/reduction pathways that lead to the formation of 2,4,5-trihydroxyphenolic compounds during the oxidation of dopa, hydrocaffeic acid and N-acetyldopa are described. Data suggest that (i) oxidation of dopa, hydrocaffeic acid and N-acetyldopa results in the formation of their corresponding o-quinones, (ii) the o-quinones undergo intramolecular nucleophilic addition through the side chain carboxy group to form lactones under weak acid conditions, (iii) oxidation of the lactones produces their corresponding lactone-o-quinones, (iv) the lactone-o-quinones, once formed, undergo rapid hydrolysis that leads to the formation of 2-hydroxy-1,4-benzoquinones (p-quinones) as relatively stable products and (v) reduction of the p-quinones results in the formation of their corresponding 6-hydroxydopa, 6-hydroxyhydrocaffeic acid and N-acetyl-6-hydroxydopa. Data suggest that 6-hydroxydopa also can be produced by direct hydrolysis of dopa-lactone.