A unique route to perfectly alternating oligopeptides is described. First, AG-OEt was prepared by standard chemical coupling. Then, AG-OEt was converted by papain-catalysis in 30 s to (AG)_x (80%-yield, x = 9.4 ± 0.3). Extension of this strategy to other alternating peptide compositions as well as the importance of selecting a protease and reaction conditions that avoid competing transamidation and hydrolysis reactions is discussed.