t-Boc-Aminooxy-PEG8-Ms is a crosslinker containing a t-Boc-aminooxy group and a mesyl group. The protected amine can be deprotected under mild acidic conditions. The hydrophilic PEG spacer increases solubility in aqueous media. The mesyl group is good leaving group and can also be used as protecting groups for primary alcohols. It can be deprotected in the presence of sodium amalgam.