Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
5418496 | Journal of Molecular Structure: THEOCHEM | 2008 | 9 Pages |
Abstract
Dehydroamino acids with a methylated N-terminal tertiary amide bond occur in natural small cyclic peptide toxins. To investigate their conformational preferences a systematic theoretical analysis was performed on Nâ²-methylamides of N-acetyl-N-methyldehydroamino acids (Ac-Î(Me)Xaa-NHMe, where Xaa = (Z)-Abu, (E)-Abu, Val, (Z)-Phe, and (E)-Phe) considering the configuration trans and cis of the tertiary amide bond. The Ï, Ï potential energy surfaces were calculated at the B3LYP/6-31+Gââ//HF/3-21G level with inclusion of the solvent (water) effect (SCRF method). The conformers localised were fully optimised at the B3LYP/6-31+Gââ in vacuo. The accessible areas of the potential energy surfaces; the number of conformers and the stabilising internal forces were compared for all the studied molecules. The main feature of the studied N-methyldehydroamino acids is their considerable tendency to adopt the configuration cis for the N-terminal tertiary amide bond. It results from the specific ability of these dehydroamino acids to be able to gain stability from the Ï-electron conjugation between the CαCβ double bond and the neighbouring C-terminal amide group. This stabilising force concomitant with the short NHâ¯N hydrogen bond makes the conformer cis C7eq (Ï, Ï â¼Â â105°, 8°) the lowest in energy. The data presented hereinto indicates that N-methyldehydroamino acids can potentially be new promoters of trans-cis isomerisation of the amide bond.
Related Topics
Physical Sciences and Engineering
Chemistry
Physical and Theoretical Chemistry
Authors
Dawid SiodÅak, Agnieszka Macedowska-Capiga, Justyna Grondys, Katarzyna Paczkowska, Barbara Rzeszotarska,