Peptide Mechanosynthesis by Direct Coupling of N-Protected α-Amino Acids with Amino Esters

In view of developing alternatives to classical peptide synthesis strategies that suffer from low efficacy and negative environmental impact, the reactivity of N‐protected α‐amino acids, amino esters, and N‐ethyl‐N′‐(3‐dimethylaminopropyl)carbodiimide was studied under liquid‐assisted grinding (LAG) conditions. The optimal reaction conditions enabled the intensive and environmentally benign mechanosynthesis of a wide range of dipeptides that could be produced up to the multigram scale. The critical influence of the nature of the liquid additive on the course of the reaction was revealed. Combined with solvent‐free tert‐butoxycarbonyl deprotection steps, this approach was applied to the synthesis of tri‐ and tetrapeptides, thus opening the way to the synthesis of much longer peptides. Liquid‐assisted grinding (LAG) enables intensive, scalable, and environmentally benign production of peptides by direct coupling of N‐protected α‐amino acids with amino esters mediated by N‐ethyl‐N′‐(3‐dimethylaminopropyl)carbodiimide. Association of ball‐milling, judiciously selected liquid additive, and reagents with reduced safety profiles furnish the peptides in good to excellent yields.