Tos-PEG2-t-butyl ester linker bears a t-butyl ester and a tosyl group. The PEG spacer increases the aqueous solubility of the resulting compound. The t-butyl protected carboxyl group can be deprotected under acidic condition to form free acid, which can undergo conjugation with terminal amino group of biomolecules through amide coupling reactions. The tosyl group is a very good leaving group for nucleophilic substitution reactions. It is readily replaced by thiol groups.
Axispharm offers 3000+ PEG Linkers with high purity. Different kinds of PEG Reagents may be available by custom synthesis.