m-PEG4-t-butyl ester linker contains a t-butyl ester. The t-butyl protected carboxyl group can be deprotected under acidic conditions to form free acid that can conjugate with amine-containing molecules. The PEG spacer increases the aqueous solubility of the resulting compound.
AxisPharm offers 5000+ PEG Linkers with high purity. Different kinds of PEG Reagents may be available by custom synthesis.