END-GROUP MODIFICATION OF ALPHA-HYDRO-OMEGA-METHOXY-POLY(OXYETHYLENE) .3. FACILE METHODS FOR THE INTRODUCTION OF A THIOL-SELECTIVE REACTIVE END-GROUP

Three methods for the introduction of a thiol-selective reactive end-group into alpha-hydro-omega-methoxypoly(oxyethylene) are described and evaluated. In a first method, alpha-amino-omega-methoxy-poly(oxyethylene) was reacted with succinimido 3-(2-pyridyldithio)propionate (SPDP). In a second approach, the hydroxyl end-group of alpha-hydro-omega-methoxypoly(oxyethylene) was activated with 4-nitrophenyl chloroformate, and subsequently reacted with 2-tritylthioethylamine. Conversion of the trityl thioether into an aromatic disulfide with 2-nitrophenylsulfenyl chloride yielded a polymer with a thiol-specific reactive disulfide end-group. However, it was shown that dismutation in buffer medium does occur, what makes this approach less attractive. A third method involved the conversion of the trityl thioether into a sulfenyl thiocarbonate by reaction with an alkoxycarbonylsulfenyl chloride. Both the SPDP-modified and the alkoxycarbonyl disulfide-modified poly(oxyethylene) were found to be suitable thiol-specific reactive polymers for protein modification. This was demonstrated in a model reaction using reduced glutathione as a thiol-carrying peptide.