Patent ID: 7994280

Claim:
Method of peptide synthesis, comprising the steps of a) synthesizing a peptide linked to a solid phase which peptide comprises at least one cysteine, homo- or nor-cysteine residue, which cysteine is protected in its side chain by a S-tert.butyl-sulphenyl group and wherein said cysteine is the last C-terminal residue, wherein said S-tert.butyl-sulphenyl protected C-terminal cysteine is bonded via the carboxy-terminus by means of an ester or amide bond to the solid phase, with the proviso, that said linking bond is not a benzylester bond, but is an acid-labile bond that is cleaved under weakly acidic reaction conditions, b) either coupling N-terminally a further amino acid having a 3-[(2-carboxyethyl)dithio]propionyl-radical- on its Nα or deprotecting the Nα of the N-terminal amino acid and reacting the free Nα with dithio-3,3′-dipropionic acid to yield the corresponding Nα-3-[(2-carboxyethyl)dithio]propionamide or deprotecting the Nα of the N-terminal amino acid and reacting the free Na with a compound of formula IV R7-S—S—[CH 2 ] 2 —COOH IV wherein R7 is aryl-, including heteronuclear aryl, or is aralkyl-, alkylaryl- or alkyl-, which may be further substituted with halogeno, amido, ester, carboxy or ether, and c) reacting the peptide with a S-tert.Butyl-sulphenyl-protection group removing reagent, and d) cyclizing the peptide on-resin by means of disulfide bond formation.