Stabilization of N‐, N,N‐, N,N′‐methylated and unsubstituted simple amidine salts by multifurcated hydrogen bonds

Abstract

In the light of the usefulness of amidines in medicinal chemistry, this paper considers the effects on biological properties and chemical reactivities of organic molecules affected by intramolecular interactions. The study of chemical shifts has been an important source of information on the electronic structure of amidine salts and their ability to form non-covalent bonds with nucleic acids. The NMR and IR results demonstrate that hydrogen bonds are a force for promoting chemical reactions. The thymine O2 carbonyl oxygen in a close proximity to the amidinium cation does interact with the appropriately spaced amidinium NH donor moieties. The1H-15N 2D NMR (GHSQC and GHMBC) spectra with natural isotopic abundance of15N fully confirm the intramolecular character of the bonds. A rule able to estimate the relative strength of the new multifurcated hydrogen bonds is given. The appearance of the ΔδNHchemical shift differences near zero is due to the strong intramolecular interactions. The strength of the H-bond donation by acetamidines is reflected in the N–H dissociation/recombination process (positive charge shift has been invoked to explain other effects on benzamidines). The temperature dependence of chemical shift for the amidine NH protons in dimethyl sulfoxide solutions is herein discussed.

The CON−H…+NH2 Blue-Shifting H-Bond Stabilizing Effect on Z Secondary Amides and Cyclic System Conformational Rearrangement through an Alkylamine-Chain Migration Pathway

“…e hitherto reported data leave no doubt that the strength of these bonds is of fundamental importance for the explanation of the reactivity di erences (intramolecular "noncovalent" catalysis). Multifurcated hydrogen bonds can alter both the stability and the reactivity of thioamides towards zinc ammoniates [4]. ese results are in touch with the previous hydrolysis and cyclization studies [2].…”

“…e most important features were opposite to those characteristics of classical H-bonds (red shift [4]). e range of study of blue-shifting H-bonds is here extended to other bonding types.…”

“…NMR spectra were recorded on a Varian 300 Gemini spectrometer in DMSO-d 6 with TMS as a standard and IR spectra on a Bruker 113v FT-IR spectrometer (] max , KBr discs). e GHSQC (gradient heteronuclear single quantum coherence) and GHMBC (gradient heteronuclear multiple bond correlation) spectra were measured under standard conditions [2][3][4] on a Bruker Avance DRX 600 spectrometer operating at 600.3 MHz for 1 H and 60.8 MHz for 15 15 N resonances were referenced externally to the signal of liquid CH 3 NO 2 (381.7 ppm). All spectra were obtained with the natural abundance of the nitrogen-15 isotope.…”

“…15 N Spin-Spin Interactions of 2, 4, 7, and 8. e importance of 15 N-NMR spectroscopy is recently increasing, since it is attractive in the context of the spin-spin interactions and this strategy makes it a potentially powerful tool (as a basic research tool). [2][3][4]24] Since then not much attention has been paid to other possible developments of that concept. e two-dimensional correlation experiments presented here have a qualitative value for con rming the existence of geometrical stereoisomers of secondary amides.…”

“…Reversibility in biology is associated with well-ordered structures formed from exible molecules. Ionic hydrogen bonds are an important subclass of hydrogen bonds and have recently come into focus [1][2][3][4][5][6]. ey appear in many biologically important aggregates [7][8][9].…”