H-1 NMR and theoretical studies on the conformational equilibrium of tryptophan methyl ester

Author(s)

Duarte, Claudimar J. ^[1] ; Cormanich, Rodrigo A. ^[1] ; Ducati, Lucas C. ^[2] ; Rittner, Roberto ^[1]

Affiliation

^[1] Univ Estadual Campinas, Inst Chem, BR-13083970 Campinas, SP - Brazil

^[2] Univ Sao Paulo, Inst Chem, BR-05513970 Sao Paulo - Brazil

• Document type: Journal article
• Source: Journal of Molecular Structure; v. 1050, p. 174-179, OCT 24 2013.
• Web of Science Citations: 8

Abstract

Selected (3)J(HH) coupling constants and theoretical calculations were used to explain the conformational equilibrium of L-tryptophan methyl ester (Trp-OMe) in several solvents. The obtained (3)J(H alpha H beta) values did not exhibit any significant variability and thus indicate that there are no conformational population variations for the side chain of the Trp-O-Me depending on the solvent. Moreover, the potential energy surfaces obtained at the B3LYP/cc-pVDZ theoretical level produced eight energy minima that were analysed by QTAIM and NBO methods. It was possible to conclude that the Trp-OMe conformational preferences were due to hyperconjugative effects involving the nonbonding electron pairs of the main chain nitrogen atom and certain antibonding orbitals (sigma(C4-C13){*}, sigma(C1-C4){*} and sigma(C4-H12){*}) and also to the steric effects from the nonbonding electron pairs of oxygen atoms and the main and side chain of this system. (C) 2013 Elsevier B.V. All rights reserved. (AU)

• FAPESP's process: 11/01170-1 - Physicochemical studies of organic compounds: long range inractions and conformational analysis of organofluorine compounds.
• Grantee: Rodrigo Antonio Cormanich
• Support Opportunities: Scholarships in Brazil - Doctorate
• FAPESP's process: 12/03933-5 - Conformational equilibria and intramolecular interactions for a series of amino-acids: theoretical and experimental approaches
• Grantee: Roberto Rittner Neto
• Support Opportunities: Regular Research Grants
• FAPESP's process: 11/11098-6 - Conformational analysis of some methyl esters of amino acids and their N-acetyl-derivatives.
• Grantee: Claudimar Junker Duarte
• Support Opportunities: Scholarships in Brazil - Doctorate