DIFFERENT APPROACHES FOR THE PREPARATION OF PEPTIDES WITH STABILIZED PREDICTABLE SECONDARY STRUCTURE

Considering the importance of structural patterns in regulating protein-protein interactions (PPIs), the study of possible synthetic strategies to obtain the control on the preferred conformation of active biomolecules is undoubtedly a field of proven interest in contemporary science. Nonetheless, beside the modulation of molecules biological activity via structure control, a wide interest in drug discovery deals with possible ways to improve the pharmaceutical properties, e.g. metabolic stability, of defined compounds or classes of compounds. A further possibility is to combine these two synthetic goals by influencing at the same time both biological activity and druggability of a molecule. In this context, a comprehensive knowledge of either the synthetic and the analytic tools available to investigate and to reproduce biomolecules structure is necessary. A very efficient synthesis of orthogonally protected 1H-azepine-4-amino-4-carboxylic acid, named Azn, a conformational constricted analogue of ornitine, was realized. It was obtained in gram scale and good overall yield in five steps, three of which without isolation of the intermediates, starting from the readily available 1-amino-4-oxo-cyclohexane-4-carboxylic acid. Both enantiomers were used for the preparation of pentapeptide models containing Ala, Aib and Azn. Conformational studies using both spectroscopic techniques (NMR, CD) and molecular dynamics on model 5-mer peptides showed that (R)-Azn isomer possesses a marked helicogenic effect. Moreover, the study of structure-activity relationships of bioactive peptide χ-conotoxin MrIA was performed by the synthesis of new constrained analogues via different approaches. A series of new MrIA analogues has been realized through solid phase synthetic procedures, in particular referring to the elements that induce structural constraints within the molecule. The study has mainly focused on the realization of cyclic compounds and on strategies to replace disulfide bonds with disulfide mimics characterized by a higher chemical and metabolic stability. All of the synthetic new MrIA derivatives produced are at the present undergoing to biological activity essays, structural analysis and stability evaluation.