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beta-Turn Analogues in Model a ss-Hybrid Peptides: Structural Characterization of Peptides Containing ss 2,2Ac6c and ss 3,3Ac6c Residues

Basuroy, Krishnayan and Rajagopal, Appavu and Raghothama, Srinivasarao and Shamala, Narayanaswamy and Balaram, Padmanabhan (2012) beta-Turn Analogues in Model a ss-Hybrid Peptides: Structural Characterization of Peptides Containing ss 2,2Ac6c and ss 3,3Ac6c Residues. In: CHEMISTRY-AN ASIAN JOURNAL, 7 (7). pp. 1671-1678.

Full text not available from this repository.
Official URL: http://dx.doi.org/10.1002/asia.201200052

Abstract

The effect of gem-dialkyl substituents on the backbone conformations of beta-amino acid residues in peptides has been investigated by using four model peptides: Boc-Xxx-beta 2,2Ac6c(1-aminomethylcyclohexanecarboxylic acid)-NHMe (Xxx=Leu (1), Phe (2); Boc=tert-butyloxycarbonyl) and Boc-Xxx-beta 3,3Ac6c(1-aminocyclohexaneacetic acid)-NHMe (Xxx=Leu (3), Phe (4)). Tetrasubstituted carbon atoms restrict the ranges of stereochemically allowed conformations about flanking single bonds. The crystal structure of Boc-Leu-beta 2,2Ac6c-NHMe (1) established a C11 hydrogen-bonded turn in the a beta-hybrid sequence. The observed torsion angles (a(similar to-60 degrees, similar to-30 degrees), beta(similar to-90 degrees, similar to 60 degrees, similar to-90 degrees)) corresponded to a C11 helical turn, which was a backbone-expanded analogue of the type III beta turn in aa sequences. The crystal structure of the peptide Boc-Phe-beta 3,3Ac6c-NHMe (4) established a C11 hydrogen-bonded turn with distinctly different backbone torsion angles (a(similar to-60 degrees, similar to 120 degrees), beta(similar to 60 degrees, ?60 degrees, similar to-60 degrees)), which corresponded to a backbone-expanded analogue of the type II beta turn observed in aa sequences. In peptide 4, the two molecules in the asymmetric unit adopted backbone torsion angles of opposite signs. In one of the molecules, the Phe residue adopted an unfavorable backbone conformation, with the energetic penalty being offset by a favorable aromatic interaction between proximal molecules in the crystal. NMR spectroscopy studies provided evidence for the maintenance of folded structures in solution in these a beta-hybrid sequences.

Item Type: Journal Article
Keywords: amino acids;aromatic interactions;beta-turn analogues; peptides;conformation analysis
Department/Centre: Division of Biological Sciences > Molecular Biophysics Unit
Division of Chemical Sciences > Sophisticated Instruments Facility
Division of Physical & Mathematical Sciences > Physics
Date Deposited: 21 Jul 2012 10:38
Last Modified: 21 Jul 2012 10:38
URI: http://eprints.iisc.ernet.in/id/eprint/44803

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