Poteqnmadeoseby pcaioofchemalseeencngmehedol1egbl000reside) peptide ynthesrprotectin f tofore thepepidebond heee9martawereael9Seaetoheemeaoa 二 mprkadfGb-M 26-7 Merrifield Solid-Phase Peptide Synthesis ,C0 C-00 7 7 Protein sequencing is made possible by recombinant DNA technology. Application of chemical sequencing methods to long (>1,000 residues) polypeptides is expensive, laborious and time consuming. When a sample of DNA or messenger RNA that codes for a protein is available, recombinant DNA technology can be used to easily and quickly determine the protein sequence through the DNA sequence and knowledge of the genetic code. Synthesis of Polypeptides: a Challenge in the Application of Protecting Groups 26-6 Selective peptide synthesis requires protecting groups. Chemical synthesis of a polypeptide chain from individual amino acids requires: Activation of the amino acids to force the peptide bond to form; Protection of reactive functional groups within the amino acids that may interfere with the desired peptide bond formation. The amino end of an amino acid can be blocked in one of several ways: Peptide bonds are formed by using carboxy activation. The most commonly used carboxy-activating reagent is dicyclohexylcarbodiimide (DCC). To produce a tripeptide, deprotection of only one end is required, followed by renewed coupling. 26-7 Merrifield Solid-Phase Peptide Synthesis The Merrifield solid-phase peptide synthesis, uses a solid support of polystyrene to anchor a peptide chain. A dipeptide synthesis using the Merifield method would proceed as follows: