Studies On Oxidative Decarboxylation Of N-acyl Amino Acids Induced By S₂O₈^2-/Ag⁺/Cu²⁺

A further study on the oxidative decarboxylation of N-acyl amino acids wasinvestigated in this paper. First using N-benzoylalanine as a model compound, wehave studied the effect of the catalyst, oxidant, solvent, reaction time and temperatureon the reaction. And we found that the optimal conditions for conversion ofN-benzoylalanine to N-acetylbenzamide were as follows: 20 mol% AgNO₃, 20 mol%CuSO₄ , 3 equiv of (NH₄)₂S₂O₈, and water as solvent with the best yield (84%). Whenreplacing alanine with glycine,α-phenylglycine, proline and other amino acids, wealso obtained the corresponding diacyl imides in 24-89% yield.For replacing alaine with valine and leucine, we found that N-formylbenzamiedwas obtained in 85% and 60% yield respectively instead of N-isobutyrylbenzamdeand N-(3-methylbutanoyl)benzamide respectively. We suggested the iminium intermediateformed from the oxidative decarboxylation of N-acyl amino acids cendeigoertautomerization to form the corresponding N-benzoyl enamide, which was furtheroxidised via the cleavage of carbon-carbon bond to afford N-formylbenzamide.Such a coversion of N-acyl amino acids to corresponding imides was performedat room temperature using catalytic amounts of metals, cheap oxidant and water as thesolvent. It not only provides a concise way to access diacyl imides, but also has thepotential to be applied in the end-modification of peptides.