In two Nto C-peptide synthesis strategies, transamidation has relied on the respective usefulness of the reactivity of N-alkyl N-acylsulfonamides, and of zinc-complexes of 2amido pyridine intermediates. The switch in reactivity from relatively stable Nacylsulfonamide (e.g., 88) to reactive N-alkyl N-acylsulfonamide (e.g., 89) has been effectively employed in the "safety catch principle" in solid phase peptide synthesis, and hypothesized to result from amide bond twisting from planarity. Without resonance stabilization, twisted amides exhibit increased carbonyl electrophilicity as indicated by downfield shifted C, N and O chemical shifts. Moreover, NMR spectroscopic studies of deuterium exchange have indicated that epimerization during aminolysis is suppressed by an intramolecular hydrogen bond between the N-alkyl sulfonamide oxygen and the amide NH of the activated amino acyl residue (e.g., 90, Scheme 11) which prevents oxazalone formation.