4-amino-N-(4-(2-cyanoethynyl)phenyl)butanamide

APN-amine is a heterobifunctional linker containing an APN moiety with exquisite chemoselectivity for cysteine and an amine group. The superior stability of APN-cysteine conjugates in aqueous media, human plasma, and living cells makes this new thiol-click reaction a promising methodology for applications in bioconjugation.