Azapeptides as an Efficient Tool to Improve the Activity of Biologically Effective Peptides

Peptides are highly potent biological active compounds with excellent selectivity and binding, but they have some drawbacks (e.g., low stability in vivo because of the enzymatic degradation, and fast elimination). To overcome their drawbacks, various peptidomimetics have been gaining ground. Different modifications have been examined, such as the modification of peptide backbone. One such seemingly simple modification is the replacement of the CHα group by an N atom. These amino acid derivatives are called azaamino acids, and peptides containing azaamino acid are called azapeptides. This exchange results in both steric and electronic differences from the original amino acids, thus affecting the structure and biological activity of the modified peptide. In this review, the synthesis possibilities of azapeptides and the impact of azaamino acid incorporation on the structure and biological activity are presented through examples. Different synthetic solutions for azaamino acid introduction and the various routes to build in the side chain are summarized to illustrate the improvement of the field of azaamino acid chemistry. The influence of the altered electronic and steric properties of N-atom on the structure is described, too. Finally, some examples are given with potent biological activity.