Azadipeptide Nitriles: Highly Potent and Proteolytically Stable Inhibitors of Papain‐Like Cysteine Proteases

Nitrogen instead of carbon: Azadipeptide nitriles resulting from CH/N exchange in the P1 position (see picture) are hitherto unknown. To access these compounds by conversion of amino acid-derived hydrazides with cyanogen bromide both nitrogen atoms of the hydrazide must be substituted. Despite a methylated P2-P1 peptide bond, the azadipeptide nitriles show a strong inhibitory activity against cysteine proteases, and a high stability towards chymotryptic hydrolysis.