Selective synthesis of heterobifunctional poly(ethylene glycol) derivatives containing both mercapto and acetal terminals

A novel synthetic route to heterobifunctional poly(ethylene glycol) (PEG) derivatives containing both mercapto and acetal terminal groups was established in this study using anionic ring opening polymerization of ethylene oxide (EO) using potassium 3,3-diethoxypropanolate (PDP) as the initiator, followed by the successive conversion of the end-alkoxide group to a methanesulfonic group, and then to an ethyldithiocarbonate moiety. Molecular functionalities of the acetal and the mercapto terminal groups of the heterotelechelic PEG (acetal-PEG-SH) thus prepared were confirmed to 1.00 and 0.85, respectively, indicating that the reaction proceeds almost quantitatively. The obtained acetal-PEG-SH products, including 2-pyridyldithio derivatives, have a promising utility for bioconjugation in the fields of medicine and biology.