4-Chloromethylphenoxyacetyl polystyrene and polyamide supports for solid-phase peptide synthesis.

Two functionalised supports for the solid-phase synthesis of peptides under mild reaction conditions were prepared: 4-chloromethylphenoxyacetamidomethyl-copoly (styrene-1%-divinylbenzene) and 4-chloromethylphenoxyacetyl-norleucyl-poly (dimethylacrylamide). They were devised in order to avoid the danger of racemization which exists during base-catalyzed esterification of the first protected amino acid to the 4-alkoxybenzyl alcohol resins formerly employed in combination with N alpha-9-fluorenylmethoxycarbonyl and tert.-butyl side-chain protecting groups. Esterification of N alpha-protected amino acids to the new resins can be achieved easily and without significant levels of racemization by means of their caesium salts, while cleavage from the supports is possible by treatment with trifluoroacetic acid. The 4-chloromethylphenoxyacetyl polystyrene resin was tested by the synthesis of Leu-enkephalin which was cleaved, at the end of the synthesis, from the solid support in 91% yield by 60% trifluoroacetic acid in methylene chloride, and was shown to be more than 99% pure by ion-exchange chromatography and reverse phase high pressure liquid chromatography.