Investigation of conventional and non-conventional hydrogen bonds: a comparison of fluorine-substituted and non-fluorine substituted compounds

Abstract

Two fluorine and bromine Boc protected phenoxypropanamine compounds were investigated to determine how hydrogen bonds affect the dynamic behaviour of an organic molecule. Using single crystal X-ray diffraction, the presence of a folded backbone for the fluorine-containing compound was established. In addition, the presence of an inter-molecular (conventional and non-conventional) hydrogen bond was detected by XRD. To investigate the conformational preference and available interactions in solution, variable temperature NMR at two different concentrations, 2D NMR at low temperature and quantum mechanics studies were performed. These investigations confirmed that the observed interactions in the solid phase were maintained in solution. However, competition between inter- and intra non-conventional hydrogen bond (originating from fluorine atoms) was detected at high temperature in dilute solution. Our studies suggest that fluorine assisted inter-molecular cross-coupling at room temperature. This study possibly introduces a new tool for manipulation of peptide and protein structures towards desired biological applications.