Pyrazine Formation from Amino Acids and Reducing Sugars, a Pathway Other than Strecker Degradation

Because the reaction of acyloins with ammonia generates pyrazines and acyloins are not involved with Strecker degradation, this study uses acetoin (a simple acyloin, from sugar degradation) to react with amino acids to determine whether ammonia is released, leading to the formation of tetramethylpyrazine. The results show that all reactions between α-amino acids and acetoin generate not only tetramethylpyrazine but also the corresponding Strecker aldehydes. However, the reactions between β-, γ-, or ε-amino acid and acetoin generate only tetramethylpyrazine. Quantitative analysis shows that among such reactions, both α- and β-amino acids generate significantly higher amounts of tetramethylpyrazine than γ- and ε-amino acids. On the basis of these data, it is proposed mechanistically that α-amino acids decarbonylate to generate the reactive intermediates, 1-hydroxyamines, deamination of which leads to the formation of the Strecker aldehydes. This study demonstrates that pyrazines and Strecker aldehydes are also formed from α-amino acids and reducing sugar via deamination in addition to their formation via the well-known Strecker degradation.