Impurity Dimethylcarbamoyl-OBt Detected in an API Induced by the Degradation of HBTU in DMF

A non-peptide-related impurity with an abundance of 0.09% was detected in a batch of Ferring Pharmaceuticals’ peptide active pharmaceutical ingredient (API) Peptide Q. A dedicated simulative reaction and comparison with the references revealed that the impurity was induced by the degradation of the uronium coupling reagent HBTU in the dimethylformamide (DMF) solution at the HBTU-directed peptide amidation cyclization step. The structure of the subject non-peptide-related impurity has been confirmed as 1-[((dimethylamino)­carbonyl]­oxy)-1H-benzotriazole or its isomer 1-(dimethylcarbamoyl)-1H-1,2,3-benzotriazol-3-ium-3-olate (both are abbreviated as dimethylcarbamoyl-OBt in this paper). The formation of dimethylcarbamoyl-OBt could also be realized in N-methyl-2-pyrrolidone (NMP) or acetonitrile (ACN) as the organic solvent. This finding is relevant to a myriad of syntheses of peptides and small molecules involved in uronium coupling reagent-mediated amidation/esterification reactions, such as cyclization, side-chain modification, and segment condensation. In such cases, particularly those that proceed with the subject HBTU-mediated reaction in DMF, NMP, or ACN as the very last step of the whole synthetic process, scrutiny of the API for dimethylcarbamoyl-OBt as an impurity should be considered.