Biosynthesis and Metabolism of Hydroxyphenylacetic Acids in Higher Plants

2‐Hydroxyphenylacetic acid, a natural phenolic product found in the genus Astilbe, derives from the shikimic acid pathway via phenylpyruvic acid. The existence of two routes for the biosynthesis of 2‐hydroxyphenylacetic acid could be demonstrated:a) A direct transformation of phenylpyruvic acid into 2‐hydroxyphenylacetic acid involving a migration of the side chain. More than 95% of the tritium activity of 2‐hydroxyphenylacetic acid was localized in position 5 when l‐[4‐3H]phenylalanine was fed. This complex oxidation is analogous to the known conversion of 4‐hydroxyphenylpyruvic acid to homogentisic acid.b) A hydroxylation of [4‐3H]phenylacetic acid to [4‐3H]2‐hydroxyphenylacetic acid was observed in vivo, and was also found to take place in vitro utilizing the system peroxidaseendiol‐O2. 2,3‐Dihydroxyphenylacetic acid and 2‐hydroxy‐3‐methoxyphenylacetic acid could be established as natural products occurring in higher plants. Their chemical synthesis is described. By feeding experiments the following metabolic pathway is suggested: 2‐hydroxyphenylacetic acid → 2,3‐dihydroxyphenylacetic acid → 2‐hydroxy‐3‐methoxyphenylacetic acid. 3,4‐Dihydroxyphenylacetic acid and 3‐methoxy‐4‐h