A remarkable aspect of enzyme evolution is the portability of catalytic mechanisms for fundamentally different chemical reactions. For example, aspartyl proteases, which contain two active site carboxylic acid groups, catalyze the hydrolysis of amide bonds, while glycosyltransferases (and glycosyl hydrolases), which often also contain two active site carboxylates, have evolved to form (or break) glycosidic bonds. However, neither catalyst exhibits cross-reactivity in the intracellular environment. The large, macromolecular architectures of these biocatalysts tailor their active sites to their precise, divergent functions. The analogous portability of a small-molecule catalyst for truly orthogonal chemical reactivity is rare. Herein, we report aspartic acid containing peptides that can be directed to different sectors of a substrate for which the danger of cross-reactivity looms large. A transiently formed aspartyl peracid catalyst can participate either as an electrophilic oxidant to catalyze alkene epoxidation or as a nucleophilic oxidant to mediate the Baeyer-Villiger oxidation (BVO) of ketones. We show in this study that an appended peptide sequence can dictate the mode of reactivity for this conserved catalytic functional group within a substrate that has the potential to undergo both alkene epoxidation and BVO; in both cases the additional aspects of chemical selectivity (regio- and stereoselectivity) are high. This sequence-dependent tuning of a common catalytic moiety for functional group selective reactions constitutes a biomimetic strategy that may impact late-stage diversification of complex polyfunctional molecules.