Minor Strecker degradation products of phenylalanine and phenylglycine

Abstract

Phenylalanine (Phe) was oxidized with either potassium peroxodisulfate or glyoxal. Volatile reaction products were isolated and analyzed by GC/FID and GC/MS. Nonvolatile products were derivatized with diazomethane and analyzed by the same methods. Under the experimental reaction conditions (equimolar ratio of reactants, 100 °C, 1 h), the decomposed amount of amino acid was 28% (glyoxal) and to 74% (peroxodisulfate), respectively. Sixteen volatile compounds having their origin in the amino acid molecule were detected and identified. The major compound was phenylacetaldehyde (208 mg/peroxodisulfate, 11 mg/glyoxal), followed by bibenzyl, benzaldehyde, and benzyl alcohol. Other products were present in concentrations lower then 0.1 mg. For comparison, the lower homologue of Phe, phenylglycine, was oxidized under the same conditions. Analogously, 21% (glyoxal) and 65% (peroxodisulfate) of this amino acid decomposed, predominantly to benzaldehyde (242 mg/peroxodisulfate, 95 mg/glyoxal). A minor decomposition product was benzoic acid (2.9 mg), other ten products arose at levels lower then 0.1 mg. The formation of minor oxidation products during Strecker degradation of amino acids suggests the importance of radical reactions. In systems comprising glyoxal, ten heterocyclic compounds arose as minor products (3-furancarbaldehyde, 5-methyl-2-furancarbaldehyde, 2-pyrrolcarbaldehyde, 3-phenylpyridine, pyrazine, methyl-, ethyl-, vinyl-, and 2-phenylethylpyrazine).