Four series of inverse substrates, position isomers of guanidinonaphthyl esters derived from N-(tert-butyloxycarbonyl)amino acid, were prepared as acyl donor components for trypsin-catalyzed peptide synthesis. The kinetic behavior of these synthetic inverse substrates toward spontaneous and tryptic hydrolysis was analyzed. These substrates were found to readily couple with α-amino acid p-nitroanilide to produce peptide. 4-Guanidino-1-naphthyl esters, in which the guanidino group and the carbonyl group are aligned linearly on the shorter axis of the naphthalene ring, were the most efficient substrates for enzymatic peptide synthesis. The method was especially useful for the preparation of peptides containing α, α-dialkyl amino acids. The enzymatic hydrolysis of the resulting products was negligible.