NMR studies of hydrogen bonding interactions with secondary amide and urea groups

Abstract

The cis/trans ratios for six model secondary amides were determined by 1H NMR in a range of solvent systems. The trans to cis equilibrium in chloroform is only slightly affected by addition of the hydrogen bond donor, trifluorethanol, but the cis rotamer is stabilized by an average of 0.7 kcal mol−1 when acetic acid is used as an intermolecular donor–acceptor template. Conversely, amide interaction with anionic hydrogen bond acceptors decreases the percentage of cis rotamer. 15N NMR spectroscopy was used to determine the effect of hydrogen bonding on the trans amide structure. The direction and the magnitude of 15N complex‐induced‐shifts indicate that both hydrogen bond donors and acceptors raise the secondary amide rotational barrier by increasing the CN bond order. The relationship of these results to protein structure is discussed. Copyright © 2001 John Wiley & Sons, Ltd.

Difference between 1H NMR signals of primary amide protons as a simple spectral index of the amide intramolecular hydrogen bond strength

“…Moreover, the presence of H‐bond makes it possible to change the reactivity of aminoacids towards the formation of peptide bond or assists hydrolysis of peptides . The abundance of amides in biomolecules and the overall complexity of the systems encourage scientists to focus their attention on small model systems with intramolecular or intermolecular H‐bonded amide groups . In these models the chemical shifts of the amide protons were used as spectral indexes to inspect the effects of temperature, solvent and concentration on the strength of the H‐bonds.…”

“…[10] The abundance of amides in biomolecules and the overall complexity of the systems encourage scientists to focus their attention on small model systems with intramolecular or intermolecular H-bonded amide groups. [11][12][13][14][15][16][17] In these models the chemical shifts of the amide protons were used as spectral indexes to inspect the effects of temperature, [14][15][16][17] solvent and concentration [17] on the strength of the H-bonds. Such factors can be classified as external.…”

1H NMR spectra part 31: 1H chemical shifts of amides in DMSO solvent

“…The assignment is the same as that of the pure liquid [33] and in d 6 -acetone and in d 3 -acetonitrile. [34] The more deshielded NH is the proton trans to the carbonyl. The assignments of the cis and trans conformers of N-methylformamide (2) follow from the H.C.N.H couplings.…”

Design, Synthesis and Testing of Novel Classes of Inhibitors Against Metallo-β-lactamases: Towards Drug Leads to Combat Antibiotic Resistance

“…This can be explained by the minimised steric hindrance between the two carboxylic groups and the CH 2 chain. 45 The moderate yields of the dicarboxylic acids 2.3.1 -2.3.3 synthesised might be because of the high polarity of the compounds, thus making them difficult to be extracted from the aqueous layers during the work up after the reactions.…”

“…This can be explained by the minimised steric hindrance between the carboxylic group, CH 2 chain and thiol group. 45 All the final compounds (thiols) 2.1.1 -2.1.3 were kept in sealed vials under argon as they are easily oxidised and forms disulfides. This phenomenon is common in thiols including captopril 1.40.…”