Differentiation of natural and synthetic phenylacetic acids by 2H NMR of the derived benzoic acids

The origin of 11 samples of phenylacetic acid 4, including those microbially produced from L-phenylalanine 1 and obtained by hydrolysis of penicillin G, has been studied by natural abundance deuterium NMR spectroscopy. The analysis performed on 4 failed since the (D/H) values relative to the aromatic ring nuclei and to the methylene moieties of the analysed phenylacetic acid samples resulted as similar. The permanganate oxidation of 4 into benzoic acid 5 allowed a differentiation in the H-2 NMR spectrum of the signals of the ortho, meta and para nuclei of the aromatic ring, which instead for phenylacetic acid collapse in a single signal. Considering the deuterium content of the different positions in the aromatic ring, the differentiation between the natural rather than synthetic origin of the skeleton of the examined products was possible. The deuterium content of the aromatic ring for the synthetic materials is near to the statistical distribution, whereas for the products of natural derivation it follows a para>ortho>meta enrichment.