Ethyl 2-(tert-Butoxycarbonyloxyimino)-2-cyanoacetate (Boc-Oxyma) as Coupling Reagent for Racemization-Free Esterification, Thioesterification, Amidation and Peptide Synthesis

Here we report the synthesis and utility of ethyl 2‐(tert‐butoxycarbonyloxyimino)‐2‐cyanoacetate (Boc‐Oxyma) as an efficient coupling reagent for racemization‐free esterification, thioesterification, amidation reactions and peptide synthesis that uses equimolar amounts of acids and alcohols, thiols, amines or amino acids, respectively. Its application to solid phase as well as solution phase peptide synthesis is also demonstrated and a mechanistic investigation is discussed. Boc‐Oxyma is similar to the well known coupling agent COMU {1‐[1‐cyano‐2‐ethoxy‐2‐oxoethylideneaminooxy)‐dimethylaminomorpholino]uronium hexafluorophosphate} in terms of its high reactivity and mechanism of action. However, it is not only much easier to prepare, but also to recover and reuse, thereby generating far less chemical waste.