Combination of silyl carbamate and amino acid fluoride for solid-phase peptide synthesis

Diketopiperadine (DKP) formation is an often encountered side reaction in the synthesis of peptide having C-terminal proline ester. A novel strategy for the avoidance of this side reaction was developed, which utilizes Pfp ester of Tsoc-amino acid and Fmoc-amino acid fluoride as the second and the third amino acid, respectively. This strategy was applied to the synthesis of 37–53 fragment of the β-chain of human chorionic gonadotropin (hCG).