Format

Send to

Choose Destination
Amino Acids. 2011 Jun;41(1):181-6. doi: 10.1007/s00726-010-0504-8. Epub 2010 Mar 12.

Quantum mechanical origin of the conformational preferences of 4-thiaproline and its S-oxides.

Author information

1
Graduate Program in Biophysics, University of Wisconsin-Madison, 53706, USA.

Abstract

The saturated ring and secondary amine of proline spawn equilibria between pyrrolidine ring puckers as well as peptide bond isomers. These conformational equilibria can be modulated by alterations to the chemical architecture of proline. For example, C(γ) in the pyrrolidine ring can be replaced with sulfur, which can be oxidized either stereoselectively to yield diastereomeric S-oxides or completely to yield a sulfone. Here, the thiazolidine ring and peptide bond conformations of 4-thiaproline and its S-oxides were analyzed in an Ac-Xaa-OMe system using NMR spectroscopy, X-ray crystallography, and hybrid density functional theory. The results indicate that the ring pucker of the S-oxides is governed by the gauche effect, and the prolyl peptide bond conformation is determined by the strength of the n → π* interaction between the amide oxygen and the ester carbonyl group. These findings, which are consistent with those of isologous 4-hydroxyprolines and 4-fluoroprolines, substantiate the importance of electron delocalization in amino acid conformation.

PMID:
20221839
PMCID:
PMC2910815
DOI:
10.1007/s00726-010-0504-8
[Indexed for MEDLINE]
Free PMC Article

Supplemental Content

Full text links

Icon for Springer Icon for PubMed Central
Loading ...
Support Center