Influence of Side Chain Restriction and NH --- p Interaction on the b-Turn Folding Modes of Dipeptides Incorporating Phenylalanine Cyclohexane Derivatives
- Jiménez, A.I. 2
- Cativiela, C. 2
- Gómez-Catalán, J. 1
- Pérez, J.J. 1
- Aubry, A. 3
- París, M. 45
- Marraud, M. 4
-
1
Universitat Politècnica de Catalunya
info
-
2
Universidad de Zaragoza
info
-
3
University of Lorraine
info
- 4 Lab. of Macromolec. Phys. Chemistry, UMR-7568 CNRS-INPL, ENSIC, BP 451, 54001 Nancy, France
-
5
Universidad de La Rioja
info
ISSN: 0002-7863
Any de publicació: 2000
Volum: 122
Número: 24
Pàgines: 5811-5821
Tipus: Article
Altres publicacions en: Journal of the American Chemical Society
Resum
We have synthesized the model dipeptides Piv-L-Pro-c6Phe-NH(i)pr, incorporating each of the two cis cyclohexane analogues of phenylalanine: (S,S)- and (R,R)-1-amino-2-phenylcyclohexanecarboxylic acid. Their structural analysis has been carried out in solution by 1H NMR and FTIR absorption spectroscopy and in the solid state by X-ray diffraction. In weakly polar chlorinated solvents, the (S,S)c6Phe-containing dipeptide mainly accommodates a type I β-turn, whereas the (R,R) residue shows a greater propensity to βII-folding. This behavior does not differ significantly from that exhibited by the analogous dipeptides containing L- and D-Phe. However, the L-Pro-L-Phe sequence has been shown to undergo a βI-to-βII transition in the presence of a strong solvating medium, such as DMSO, or in the crystalline state. Interestingly, Piv-L-Pro-(S,S)c6PheNH(i)pr, incorporating its cyclohexane analogue with χ1 fixed at +60°, retains the βI-folded structure under these conditions. Theoretical calculations, supported by the experimental data, indicate that a c6Phe-NH to aromatic π-orbitals interaction has an important influence on the observed β-folding preferences.