t-Boc-N-Amido-PEG4-Ms is contains a t-Boc protected amine and a mesyl group. The t-Boc can be removed under acidic conditions. The mesyl group is a good leaving group for nucleophilic substitution reactions. The hydrophilic PEG spacer increases the water solubility of the compound. Longer PEG chains increase the water solubility properties of the compound.