The synthesis of suitably protected β-selenophenylalanine and β-selenoleucine amino acids was accomplished from Garner's aldehyde as a common starting point. These selenoamino acids were incorporated into model peptides and shown to facilitate rapid diselenide-selenoester ligation (DSL) with peptide selenoesters which, when coupled with in situ deselenization, afforded native peptide products. The utility of one-pot DSL-deselenization chemistry at phenylalanine and leucine was demonstrated through the rapid synthesis of a glycosylated interferon-γ fragment and the chemokine-binding protein UL22A, respectively.