CLEAR:  A Novel Family of Highly Cross-Linked Polymeric Supports for Solid-Phase Peptide Synthesis

Cross-Linked Ethoxylate Acrylate Resin (CLEAR) supports were prepared by radical copolymerization, either in the bulk or suspension mode, of the branched cross-linker trimethylolpropane ethoxylate (14/3 EO/OH) triacrylate (1) with one or more of allylamine (2), 2-aminoethyl methacrylate·HCl (3), poly(ethylene glycol-400) dimethacrylate (4), poly(ethylene glycol) ethyl ether methacrylate (5), and trimethylolpropane trimethacrylate (6). The resultant highly cross-linked copolymers by the bulk procedures were ground and sieved to particles, whereas the suspension polymerization procedure gave highly cross-linked spherical beaded supports. CLEAR polymeric supports showed excellent swelling properties in an unusually broad range of solvents, including water, alcohols, tetrahydrofuran, dichloromethane, and N,N-dimethylformamide. To demonstrate their usefulness for peptide synthesis, CLEAR supports were derivatized with an “internal reference” amino acid [norleucine] and a handle [5-(4-Fmoc-aminomethyl-3,5-dimethoxyphenoxy)valeric acid] and were tested for both batchwise and continuous-flow solid-phase syntheses of challenging peptides such as acyl carrier protein (65-74), retro-acyl carrier protein (74-65), and the 17-peptide human gastrin-I. Comparisons to commercially available supports, e.g., polystyrene, Pepsyn K, Polyhipe, PEG-PS, TentaGel, and PEGA were also carried out. CLEAR supports are entirely stable under standard conditions of peptide synthesis but are in some cases labile to certain strong bases. (J. Am. Chem. Soc. 1996, 118, 30, 7083–7093.)