Cyclic Peptides through Hydrogen Bonding

Interaction of Cyclic Peptides through Hydrogen Bonding 

Stabilization of the bent form in cy(dic peptides by intramolecular hydrogen bonds has been described above. Hydrogen bonding of peptides with solvent is (piite a familiar event and will not be discussed here. Examples of bydn n bonding of cyclic peptides with additives are described here in relaticm to conformatioi anal-yas. 

Broadening of the NMR signal of peptide due to the contact drift caused by a coordination of stable free radical has been used to assign the resonance dgnak and the conformational analysis of peptide (85). This method has been recen% extended to cycdic peptides. 

With synthetic cyclic hexapeptides Cycio-(X-D-Phe-fto)2 (87) and Cyclo-(X-Pro-D-Phe)2 (88), where X = Ala, Om, and His, the extent of solvent exposure of NH proton was also assessed on the basis of the line broadenittg due to the added stable free radical. 

The C H2 region of the NMR spectrum of Cyclo-(Gly-Sar) (71) is shown in Fig. 11. The di-tert-butyl rritroxide nrethod was used to assign the broad singlet and 

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Urea is a well-known denaturant for proteins, and mechanistic investi tions have been carried out on the denaturing action of urea (97). Urea may interact with proteins through hydrogen bonding. To investigate this possibility in detail, interactions of urea and related compounds with cyclic peptide were investigated by means of NMR spectroscopy (92). 

One of the most well-developed system that exemplifies the stacked-disk motif is the work of Ghadiri and coworkers on cyclic D,L-peptides [89,91-93]. The disks are held together through hydrogen bonds and intermolecular contacts between the peptide side chains. The potential for derivatization and functionalization is great because the disks are made from amino acids. These materials have shown the ability to assemble into lipid bilayers and transport ions across them. In addition these materials have recently been shown to act as self-assembled antibacterial agents with utility as therapeutics [93]. There are other systems that have been synthesized from shape persistent macrocycles to assemble into tubes [91,94]. 

Analytical Properties Substrate has 20 chiral centers and 7 aromatic rings surrounding 4 cavities (A, B, C, D) substrate has a relative molecular mass of 1885 separation occurs through chiral hydrogen bonding sites, 7i-7i interactions, and inclusion complexation in polar organic, normal, and reverse mobile phases useful for the resolution of a, (3, and y or cyclic amino acids, small peptides, and N-derivatized amino acids Reference 49, 50... 

The bond highlighted m yellow is the peptide bond ) Pencyclic reaction (Section 10 12) A reaction that proceeds through a cyclic transition state Period (Section 1 1) A honzontal row of the penodic table Peroxide (Section 6 8) A compound of the type ROOR Peroxide effect (Section 6 8) Reversal of regioselectivity oh served m the addition of hydrogen bromide to alkenes brought about by the presence of peroxides m the reaction mixture... 

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