Synthesis of symmetrically and asymmetrically branched pegylating reagents.

A solution-phase procedure using an orthogonal protection scheme was developed for the synthesis of a novel family of multi-pegylating reagents. The procedure was exemplified by the synthesis of bis- and tris-pegylating reagents prepared by stepwise insertion of the poly(ethylene glycol) units thereby enabling the preparation of both symmetrical and asymmetrical pegylating reagents. Asymmetrical pegylation and tris-pegylation of peptides and proteins introduces new variables for use in the optimization of pegylated peptides and proteins. These reagents are ideally suited for conjugation to peptides and proteins as they possess a required functional group and will be useful intermediates for the synthesis of a new generation of pegylated products. Tris-pegylation can also provide more effective protection from proteolysis by shielding the protein surface from approaching macromolecules. To illustrate this potential, conditions were developed for the successful coupling of the tris-pegylating reagent to a model pentapeptide.