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

N-Boc-N'- (PEG1-t-butyl ester) -L-Lysine-amido-Mal is a lysine amino acid derivative with a maleimide group at the C-terminus. The α-amino group is protected by a Boc group, and the ε-amino group is capped with an amide-PEG1-t-butyl ester. The maleimide group is a thiol-reactive covalent moiety for attaching to cysteine residues, while the Boc and t-butyl ester groups can be deprotected for subsequent reactions.