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Stabilization of Azapeptides by Namide···H-Namide Hydrogen Bonds.

Kalpita BaruahBiswajit SahariahSushil S SakpalJugal Kishore Rai DekaArun Kumar BarSayan BagchiBani Kanta Sarma
Published in: Organic letters (2021)
An unusual Namide···H-Namide hydrogen bond (HB) was previously proposed to stabilize the azapeptide β-turns. Herein we provide experimental evidence for the Namide···H-Namide HB and show that this HB endows a stabilization of 1-3 kcal·mol-1 and enforces the trans-cis-trans (t-c-t) and cis-cis-trans (c-c-t) amide bond conformations in azapeptides and N-methyl-azapeptides, respectively. Our results indicate that these Namide···H-Namide HBs can have stabilizing contributions even in short azapeptides that cannot fold to form β-turns.
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