Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
5270138 | Tetrahedron Letters | 2014 | 4 Pages |
Abstract
Bending at the valence angle N-Cα-Câ² (Ï) is a known control feature for attenuating the stability of the rare intramolecular iâi hydrogen bonded pseudo five-membered ring C5 structures, the so called 2.05 helices, at Aib. The competitive 310-helical structures still predominate over the C5 structures at Aib for most values of Ï. However at Aibâ, a mimic of Aib where the carbonyl O of Aib is replaced with an imidate N (in 5,6-dihydro-4H-1,3-oxazine = Oxa), in the peptidomimic Piv-Pro-Aibâ-Oxa (1), the C5i structure is persistent in both crystals and in solution. Here we show that the iâi hydrogen bond energy is a more determinant control for the relative stability of the C5 structure and estimate its value to be 18.5 ± 0.7 kJ/mol at Aibâ in 1, through the computational isodesmic reaction approach, using two independent sets of theoretical isodesmic reactions.
Related Topics
Physical Sciences and Engineering
Chemistry
Organic Chemistry
Authors
Ravula Thirupathi, Erode N. Prabhakaran,