Other Methods for the Elucidation of Molecular Structures and Mechanistic Details of Enantiomers

As outlined earlier, the notorious lack of well-validated standards of highest optical purity is still a considerable drawback for reliable peak assignments and quantitation (Landagaray et al. 2016; Naile et al. 2016; Hasan et al. 2017; Ulrich et al. 2018). Furthermore, enantioselective analyses today are an integrated part of toxicological and mechanistic studies aiming at enzyme/pollutant interactions and at deepened insight into the effects of chiral drugs and other bioactive chemicals (Joseph et al. 1986; Nikolic et al. 2009; Newmeyer et al. 2014; Christoffersen et al. 2015; Chai et al. 2016; McTier et al. 2016; Hambuchen et al. 2017; Bedewy et al. 2018). The absolute structure information of enantiomeric pure target substances is an important information for the identification of retention properties, elution sequence for the chromatographic separation and consequently for the evaluation of potential biological effects and toxicity. Therefore, the preparation or separation, as well as the determination of the absolute configuration of enantiomeric pure compounds, is a crucial prerequisite of such complex scientific endeavours. Very powerful methods, although with limited sensitivity, can be employed absolute structure elucidations and/or mechanistic studies. These elucidation methods include X-ray crystallography, nuclear magnetic resonance (NMR), mass spectrometry, refractive index and vibrational circular dichroism.