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- Title
C<sub>12</sub>-Helix Development in (αγ) <sub>n</sub> Sequences - Spectroscopic Characterization of Boc-[Aib-γ<sup>4</sup>( R)Val]-OMe Oligomers.
- Authors
Dinesh, Bhimareddy; Vinaya, Vishwanathan; Raghothama, Srinivasarao; Balaram, Padmanabhan
- Abstract
The solution conformations of the αγ-hybrid oligopeptides Boc-[Aib-γ4( R)Val] n-OMe ( n = 1-8) in organic solvents have been probed by NMR, IR, and CD spectroscopic methods. In the solid state, this peptide series favors C12-helical conformations, which are backbone-expanded analogues of 310 helices in α-peptide sequences. NMR studies of the six- ( n = 3) and 16-residue ( n = 8) peptides reveal that only two NH protons attached the N-terminus residues Aib(1) and γ4( R)Val(2) are solvent-exposed. Sequential N iH-N i+1H NOEs characteristic of local helical conformations are also observed at the α residues. IR studies establish that chain extension leads to a large enhancement in the intensities of the hydrogen-bonded NH stretching bands (3343-3280 cm-1), which suggest elongation of intramolecularly hydrogen-bonded structures. The development of C12-helical structures upon lengthening of the αγ sequence is supported by the NMR and IR observations. The CD spectra of the (αγ) n peptides reveal a negative maximum at ca. 206 nm and a positive maximum at ca. 192 nm, spectral feature that are distinct from those of 310 helices in α-peptides.
- Subjects
OLIGOMERS; OLIGOPEPTIDES; ORGANIC solvents; NUCLEAR magnetic resonance; PROTONS; PEPTIDES
- Publication
European Journal of Organic Chemistry, 2013, Vol 2013, Issue 17, p3590
- ISSN
1434-193X
- Publication type
Article
- DOI
10.1002/ejoc.201300264