Although there is no direct evidence linking the presence of the referred +27 amu impurity to the potential presence of hydrogen cyanide in Acetonitrile, it is assumed that the product may be subject to a nucleophilic attack from any residual hydrogen cyanide accumulated in Acetonitrile, especially in light of the target peptide molecule's vulnerable ketone carbonyl moiety, which acts as the receptor for cyanide addition.

The aforementioned potential side reaction caused by Acetonitrile may not be significant for the majority of peptides, but under specific circumstances where the quality of the Acetonitrile, the presence of a functional group that is susceptible, the pH, temperature, and reaction time interact synergistically, the severity of this undesirable phenomenon may be increased.

 A second Acetonitrile-induced side reaction results from the hydrolysis of Acetonitrile, which is catalysed by both acid and base. Acetonitrile is first hydrolyzed to acetamide, which is then further transformed to acetic acid, in two successive phases of this process.

If acetamide is not properly eliminated by lyophilisation or other workup handlings, its presence may compromise the product quality. Acetamide formation under basic conditions is directly impacted by the water concentration in the system.

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