t-Boc-N-Amido-PEG5-Ms is a PEG derivative that contains a Boc protecting group and a mesyl group. The t-Boc group can be removed under acidic conditions to produce a reactive free amine. 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.