Benzyloxy carbonyl-PEG3-t-butyl ester is a PEG linker containing a benzyloxy carbonyl group and a t-butyl ester protecting group. The benzyloxy carbonyl helps to enhance chemoselectivity of a reaction. The t-butyl ester can be removed under acidic conditions. The hydrophilic PEG linker increases the water solubility of the compound in aqueous media.