Finally we note the N-terminal β-keto amide and γ-keto amide peptides generated are suitable substrates for many other macrocyclization or late-stage diversification reactions . Potential reactions of N-terminal β-and γ-keto amides include those that generate pyridines (Hantzsch reaction ), pyrazoles ), pyrroles (Hantzsch, Knorr, Paal-Knorr ), dihydropyrimidinones (Biginelli ), and carbocycles (Conia-Ene ), in addition to Michael additions, alkylations, acylations, and arylations. Some of these reactions also have the potential to install atropisomeric axes into the macrocyclic product. These modifications could be used alone or combined with more traditional backbone diversification strategies to generate biased libraries containing pharmacophores and drug-like motifs. We envision the ribosomal incorporation of βand γ-keto amides as an important development in the late-stage functionalization and macrocyclization of peptides with validated drug-like features.