5 Solid phase syntheses 150

2. Solid phase syntheses of a peptide.(inset)Tertiary butyloxycarbonyl chloride(tBocCl)is an excellent reagent for blocking amino groups of amino acids during organic synthesis.Dicyclohexylcarbodiimide(DCCD)is a powerful agent for activating carboxyl groups to condense with amino groups to form peptide bonds.The carboxyl group of the first amino acid(the carboxyl-terminal amino acid of the peptide to be synthesized)is attached to an insoluble resin particle(the aminoacyl-resin particle).The next amino acid,with its amino group blocked by a tBoc group and tis carboxyl group activated with DCCD,is reacted with the aminoacyl-resin particle to form a peptide linkage,with elimination of DCCD as dicyclohexylurea.Acid treatment removes the N-terminal tBoc blocking group as the gaseous products CO2 and isobutylene,exposing the N-terminus of the dipeptide for another cycle of amino acid addition.The growing peptide chain is easily recovered after cyclic additions of amino acids simply by filtering or centrifuging the reaction mixture.