Covalent capture purification of polypeptides after SPPS via a linker removable under very mild conditions

The covalent purification of polypeptides possessing an N-terminal cysteine or threonine residue via formation of a thiazolidine or oxazolidine with an aldehyde-functionalized-resin has been successfully demonstrated. To extend the applicability of this approach to any possible N-terminal residue, a special linker derived from (S)-4-amino-2-hydroxy-butyric acid was incorporated into peptidyl-resin. This linker represents the connecting point between the capture unit (cysteine) useful for the isolation of the desired polypeptide and the desired N-terminus. The target polypeptide was recovered by periodate oxidation, which cleaved the covalent bond between the linker and the last residue of polypeptide under very mild conditions.