Investigation on Supramolecular Arrangement and On-Resin Modification of Small Peptides

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The thesis contributes a large scale of structural information, supramolecular self-assembly, conformation, and the morphology of various natural/unnatural amino acids containing peptides, both solid-state and solution. We demonstrated twisted β-sheet and cross β-sheet structure of the Alzheimer's Aβ39–40 and Aβ41–42; nano-rod and nano-tube like structure from alternating D/L amino acid-containing dipeptides. The nano-rods are found to more stable than nano-tubes due to their different packing mode obtained from the crystal structure. We described a novel ‘open turn’ structure and the role of side-chains on peptide backbone from small tripeptides. They self-assembled to build supramolecular herringbone helical structure in the crystalline state. We also demonstrated the self-assembly and conformational polymorphism of alternating D/L amino acid-containing tripeptides. They self-assembled to form a single and double helix-like structure in the crystalline state. A mild, cost-effective, eco-friendly Lewis acid FeCl3 based method for the removal of tert-butyl group from the side-chain of Asp/Glu during the elongation of peptide on the acid-sensitive Rink amide resin has been demonstrated. Boc-chemistry is performed on acid-sensitive Fmoc resin by using FeCl3 instead of corrosive TFA. Interestingly, both Fmoc and Boc chemistry is performed on the same resin.
Supervisor: Bhubaneswar Mandal