Hydroxyphenylacetic acid, structure

Figure 11.2.3 Structures of the hydroxybenzoic acids (A), hydroxyphenylacetic acid (B), and hydroxycinnamic acids (C). Also see UNIT 11.3.

Rule-based or systematic nomenclature (e.g., International Union of Pure and Applied Chemistry [IUPAC] or CAS nomenclature) is based on a set of linguistic rules that apply to its structure. For example, the IUPAC and CAS names for mandelic acid are 2-phenyl-2-hydroxyacetic acid and benzeneacetic acid, a-hydroxy-, respectively. The number of possible systematic names is practically endless. A small, but not nearly exhaustive, set of other systematic names includes phenylglycolic acid, phe-nylhydroxyacetic acid, ( )-a-hydroxybenzeneacetic acid, ( )-a-hydroxyphenylacetic acid, ( )-2-hydroxy-2-phenylethanoic acid, ( )-Mandelic acid, (RS)-Mandelic acid, DL-Amygdalicacid,DL-Hydroxy(phenyl)aceticacid,DL-mandelicacid,paramandelic acid, a-hydroxy- a-toluic acid, a-hydroxyphenylacetic acid, a-hydroxybenzeneacetic... 

The structures of pterocarpin and of homopterocarpin were elucidated (ref.105) and the synthesis described of pterostilbene (ref.106) by the reaction of 3,5-dimethoKybenzaldehyde with 4-hydroxyphenylacetic acid in hot acetic anhydride, followed by hydrolysis of the acetyl derivative formed and decarboxylation in quinoline containing copper as depicted in Scheme 29. 

The 4-hydroxy-2-ketopentanoic acid product is converted by an aldolase enzyme into pyruvate and acetaldehyde. Aldolase MhpE on the phenylpropionate pathway in E. coli has been shown to be a class I aldolase, and is coupled to a dehydrogenase MhpF, which converts acetaldehyde into acetyl-CoA. The terminal aldolase on the homoprotocatechuate pathway of E. coli, HpcH, has in contrast been shown to be a class II aldolase, requiring a divalent metal ion cofactor, and its structure has been determined." Aldolase Hpal on the E. coli hydroxyphenylacetate degradation pathway has also been characterized, and shown to be a class II aldolase. "... 

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