Exploring Delta Amino Acids in the Design of New Peptide Foldamers and Biomaterials

Abstract

Over the last two decades, backbone homologated α-amino acids such as β- and -amino acids have been extensively explored as building blocks to design various types of functional foldamers. In contrast to the β- and -peptides, foldamers constituted with δ-amino acids have been less explored. This is probably due to the difficulties in the synthesis of enantiopure δ-amino acids as well as issues related to the solubility of δ-peptide foldamers. Instructively, δ-amino acids can be used as mimics of α-dipeptides. In this context, we have designed new δ-amino acids encompassing “O” atom in the backbone, (O)-δ5-amino acids, and explored their utility in the design of novel foldamers and biomaterials. In contrast to the δ-peptides with complete carbon backbone, δ-peptides with (O)-δ5-amino acids have showed better solubility in organic solvents. We have utilized these δ-amino acids to induce single residue β-turns. We have examined solution and single crystal conformations of β-hairpin consisting of single residue δ-amino acid β-turns. Further, we have demonstrated the disruption of β-amyloid aggregation through designed amphiphilic β-hairpin models. The Aβ-amyloid disruption was studied in solution using various spectroscopic and microscopic techniques. Along with reverse turns, we have also utilized the δ-amino acids to construct hybrid peptide helical foldamers. As the amino acid is mimic of α-dipeptide, we further examined the proteolytic stability of peptides composed these amino acids against various proteases. Furthermore, we have utilized these δ-amino acids to construct a new class of cyclic peptide macrocycles. Instructively, some of these macrocycles self-assembled into polar tubular assembly in single crystals. We have examined the transmembrane ion channel activity of these cyclic peptides using vesicle leakage assay and their electrophysiological characterization in the transmembrane ion channels are under investigation. Along with the utilization of these amino acids in the peptide design, we have also examined the supramolecular gelation properties of short hybrid peptides composed of backbone modified δ-amino acids. Overall, the basic conformational properties of δ-amino acids presented in this thesis can be further utilized to construct new functional foldamers as well as functional biomaterials.