MODES OF LINKAGE BY COVALENT BONDS 77 



III. PEPTIDE BOND 



The peptide bond is an amide linkage resulting from the reaction of a 

 carboxyl group with an amino group, with the elimination of water. 

 Peptides are the result of joining two or more amino acids by the peptide 

 linkage. Example : 



2 CH3— CH— COOH > CH3— CH— COOH + H2O 



NH, NH— CO— CH— CH3 



NH2 



Alanylalanine 

 (a dipeptide) 



A. Synthetic Peptides 



The synthesis of peptides is of great interest, for, as we shall see, the 

 synthesis of an important natural polypeptide has confirmed the structure 

 assigned to it. 



The most important synthetic method at the present time is that of 

 Bergmann and Zervas. It is based upon the fact that carbobenzoxy- 

 (CeHgCHaOCO-) derivatives of amino acids may be split by catalytic 

 hydrogenation. 



Among other recent methods, we may quote the conversion of amino 

 acids into mixed anhydrides with carbonic acid; these latter compounds 

 react with an amino group to form a peptide bond. Similarly, carboben- 

 zoxy-amino acid anhydrides react readily with other amino acids. 



B. Natural Peptides 



(a) Glutathione, Anserine, Carnosine 



Glutathione, a tripeptide found in animal and vegetable cells, has been 

 known for a long time. 



REFERENCES 



Celmer, W. D. & Carter, H. E. (1952). Chemistry of phosphatides and cere- 



brosides. PhysioL Rev., 32, 167-196. 

 Kenner, G. W. (1951). The chemistry of nucleotides. Fortschr. Chem. org. 



Naturstoffe, 8, 96-145. 

 Leloir, L. F. (1951). Sugar phosphates. Fortschr. Chem. org. Naturstoffe, 8, 47-95. 

 Singer, T. P. & Kearney, E. K. (1954). Chemistry, metaboUsm and scope of 



action of the pyridine nucleotide coenzymes. Advances in Enzymology 15, 



79-139. 

 ToDD, A. R. (1953). The nucleotides : Some recent chemical research and its 



biological implications. Harvey Lectures, 47, 1-20. 



