N-Boc-N'- (PEG1-t-butyl ester) -L-Lysine-amido-Mal

N-Boc-N'- (PEG1-t-butyl ester) -L-Lysine-amido-Mal is the amino acid, lysine, with a maleimide at its C-terminus, a Boc-protecting group on its α-amine, and an amido-PEG1-t-butyl ester on its ε-amine. Maleimide is a thiol-reactive covalent group used to conjugate cysteine residues, while the Boc and the t-butyl ester can be later deprotected to perform further reactions.