| Popis: |
Publisher Summary The chapter presents the general aspects of peptide synthesis and deals with the manipulation of the various amino-protecting groups, the handling of the esters, and the numerous methods of condensation. Most peptide syntheses proceed according to the classical scheme in which the amino group of a peptide ester or an amino acid ester is condensed with the carboxyl group of another peptide or amino acid, the terminal amino group of which has been protected. The product is the ester of an amino-protected peptide. The free peptide can be liberated from this derivative, or if the synthesis is to be carried further, only one of the terminal groups is removed. In a variant of this general type, a peptide or amino acid itself, instead of its ester, is brought into the condensation reaction, which must then be carried out in an aqueous medium. Many peptides contain more than one asymmetric carbon atom and therefore exist in diastereoisomeric forms. This diastereoisomer may be removed by, say, crystallization or countercurrent distribution of the product, but avoidance of substantial racemization is a necessary attribute of a general method for peptide synthesis. A method that is prone to racemization has a limited value for condensation at the carboxyl group of glycine residues and for the condensation of benzyloxycarbonyl-, toluene-p-sulfonyl-, and phthaloylamino acids, because these derivatives are much more resistant than the corresponding peptides to racemization during a condensation. |
