Heterobifunctional polyethylene glycol (PEG) derivatives BocNH(CH2CH2O)nCONHCH2CO2H were attached cleanly onto aminomethyl copoly(styrene-1% divinylbenzene) (PS) resins by oxidation-reduction couplings mediated by tri-n-butylphosphine plus 2,2′-dipyridyl disulfide. The amount of PEG incorporated into the resultant PEG-PS graft resins can be controlled through the degree of aminomethylation of the starting cross-linked PS and/or by use of PEG derivatives of different molecular weight (i.e., ∼ 2000 for n = 45; ∼ 4000 for n = 90). The new PEG-PS supports, which have good swelling properties in an extended range of solvents, were evaluated as supports for stepwise solid-phase peptide synthesis (SPPS) using tert.-butyloxycarbonyl (Boc), 9-fluorenylmethyloxycarbonyl (Fmoc) or dithiasuccinoyl (Dts) for Nα-amino protection, along with compatible anchoring handles for the C-terminal residue. Several peptide syntheses were carried out in parallel in order to compare PEG-PS supports with the corresponding parent PS resins; reproducible advantages were observed with PEG-PS. In addition, PEG-PS supports were shown to be uniquely suited for SPPS using acetonitrile as the solvent for all coupling steps and washes.
Bibliographical noteFunding Information:
We thank Professors Gary Gray and Wilmer Miller (University of Minnesota, Chemistry) for their advice on the use of ion-exchange chromatography of polymers, Mr. David Miller and Professor D.F. Evans (University of Minnesota, Chemical Engineering) for their help with the microscopy (Fig. 1 and Table 1), and Drs. Derek Hudson (Biosearch) and Gregg Fields (University of Minnesota, Laboratory Medicine) for encouragement and critiques of the manuscript. Some of the experimental work reported herein was extended through the much appreciated efforts of Ms. Susan Bontems, Ms. Xiao-dong Wu, Ms. Janell Zadlo, and Dr. Zhenping Tian. We are grateful to the National Institutes of Health (GM 28934 and 42722) and NATO (Collaborative Research Grant 0841/88) for financial support.
- Ion-exchange chromatography of polymers
- Polyethylene glycol-polystyrene graft supports
- Polymer swelling
- Solid-phase peptide synthesis