ChemMatrix resin

Another class of resins consists mainly of PEG and contains no polystyrene. They rely on cross-linking of PEG chains. This class includes the poly(ethylene glycol)-poly-(2i/i2i/ dimethylacrylamide) copolymer (PEGA) supports, developed by Meldal [38], and the newer ChemMatrix [39] resins. While PEGA is unique in being permeable to proteins up to 35-70 kDa, which makes it well suited for biochemical studies of peptides immobilized to the support, the ChemMatrix resins have gained in importance for standard Fmoc-SPPS. See Chapter 2. 

Since the invention of SPPS, divinylbenzene-cross-linked polystyrene has been the predominant solid support used. There have been several alternatives developed along the way, with the most important advancement being the introduction of PEG, including PEG-grafted polystyrene resin [39, 40] and all-PEG-based resin (ChemMatrix) [41, 42]. PEG-based resins can produce crude products with better quality than the polystyrene resins, particularly in the case of difficult sequences [43]. This superiority is explained by the H-bond acceptor function of PEG which interrupts peptide inter-chain H-lxMiding, effectively inhibiting peptide chain aggregation [44],... 

On the other hand, if the phosphopeptides are intended to be used in solution-phase assays, the synthesis can be carried out on a standard resin with common linkers. This includes the Rink amide or Wang-type linkers on polystyrene, TentaGel, or ChemMatrix supports. Upon completion of the peptide chain assembly, the peptides are released from the solid support by treatment with TFA-containing cocktails with concomitant removal of acid-labile side-chain protecting groups. Using these conditions robust protocols for rapid and efficient synthesis of phosphopeptides have been established. 

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