Proline n-oxide : manipulation of the 3D conformation of linear peptides.

Abstract

During the last the few years, the number of peptide pharmaceutical drugs reaching the market has notably increased. Drug based peptides have many advantages, such as high potency of action and limited off-target side effects that are not present in most small molecules. However, oral bioavailability of peptides is a major obstacle that hinders the development of more therapeutic formulations. Physiochemical properties of peptides, such as short plasma half-life, sensitivity to enzyme degradation and the tendency to undergo aggregation, are some of the main reasons for the lack of bioavailability. Enhancement of bioavailability can be achieved when the flexibility of peptides is reduced to a more defined stereochemical structure. There are some approaches that can reduce the flexibility of peptide backbones to a more defined structure e.g. application of peptidomimetics and cyclic peptides. Here, we have investigated another new tool that can lead us to the same goal. The purpose of this study was to investigate the possibility of modulating the secondary structure of short peptides. This was envisaged via the application of a proline N-oxide moiety and by N-methylation of the peptide backbone. The major objectives for this study were: 1. To synthesise a series of tetrapeptides to investigate the effect of proline N-oxide on their secondary structure. 2. The effect of N-methylation of the amide bond on isomerization of the N-oxide peptide backbone in terms of cis- and trans-isomers and how it directs the potential hydrogen bonding interactions 3. To study the effect of side chain bulkiness on the potential of hydrogen bonding interactions of the selected peptides. 4. Analyses of the formed secondary structures with advanced NMR techniques. 5. To perform a thermal coefficient NMR study on these molecules in order to obtain an improved understanding of the nature of hydrogen bond interactions of these peptides.