| This dissertation describes the first systematic study of the solution conformation of model cyclic hexapeptides of general structure cyclo(Xxx-Pro-Gly-Yyy-Pro-Gly), where Xxx and Yyy are trifunctional amino acids. In all, nine cyclic peptides with varying Xxx and Yyy residues were synthesized, where Xxx = Glu, Arg, Trp, Lys and Yyy = Glu, Arg, Tyr.;This dissertation also describes the first application of a novel cleavage procedure, phase transfer catalysis (PTC), for the synthesis of the above cyclic peptides. The PTC cleavage procedure involves the use of Bu;Conformational studies were carried out using various 1D and 2D NMR techniques. Simpler systems such as cyclo(Glu-Pro-Gly);When Xxx/Yyy = Trp/Tyr, the bis-cis conformation was greatly favored (;In the case of cyclic peptides with one D and one L trifunctional amino acid, two of the compounds (D-Arg/Tyr and D-Trp/Tyr), showed a single major conformer with one cis Yyy-Pro and one trans Xxx-Pro bond. When Xxx = D-Lys and Yyy = Glu, two conformers could be clearly detected in the carbon NMR spectrum.;Fluorescence spectroscopy was used to estimate intramolecular distances by resonance energy transfer in cyclo(Trp-Pro-Gly-Tyr-Pro-Gly) and in cyclo(D-Trp-Pro-Gly-Tyr-Pro-Gly). The distance between tryptophan and tyrosine in cyclo(Trp-Pro-Gly-Tyr-Pro-Gly) was estimated from such experiments to be 4.5 A... |
