Very recently, our group developed a novel bifunctional EBX reagent 1a for Lys-Cys peptide stapling. In this case, thiol attack onto EBXs occurs first followed by proximity driven amide bond formation on the pentafluorophenyl (PFP) ester. Considering the low abundance of cysteine in biomolecules, we wondered if a direct reaction between Lys or the N-terminus could be developed in absence of free thiols to introduce the highly reactive EBXs core into biomolecules. As a model reaction, we first examined selective amide formation of bifunctional EBX 1a with benzyl amine (2a) (Fig ). We were pleased to see that the desired product 3a was formed, albeit with small amount of undesired O-VBX product 4a generated through the addition of PFP to the triple bond. To diminish the electrophilicity of 1a, we synthesized modified bifunctional reagent 1b containing one CH2 between the EBX core and the activated ester. Indeed, no O-VBX product 4b was formed, but amide bond formation was still efficient.