Biosynthesis and Metabolism of Hydroxyphenylacetic Acids in Higher Plants

Abstract

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‐hydroxyphenylacetic acid have been detected in extracts from various species of Astilbe and identified by paper chromatography. These two acids are metabolic products of 4‐hydroxyphenylacetic acid. Experiments with [U‐14C]shikimic acid and dl‐[α‐14C]phenylalanine seem to indicate that the regulation of the biosynthesis of 2‐hydroxyphenylacetic acid and 4‐hydroxyphenylacetic acid takes place on the level of prephenic acid. Preliminary results were obtained consistent with the hypothesis that in Astilbe chinensis the 2,3‐dihydroxyphenylacetic acid, 3,4‐dihydroxyphenylacetic acid and 2,5‐dihydroxyphenylacetic acid are further metabolized and can be degraded by ring cleavage. Copyright © 1969, Wiley Blackwell. All rights reserved