Application of NMR Spectroscopy in Chiral Recognition of Drugs

Objective: The objective of this chapter is to highlight the current developments in NMR spectroscopy for chiral recognition of pharmaceuticals reported during the past five years.

Introduction: NMR spectroscopy is an effective technique to contextualize structural characteristics and chirality discrimination of various compounds. During the past few decades, extensive studies have been carried out on chirality recognition (CR) of organic compounds, including pharmaceuticals. The assessment of enantiomeric drugs and related methods have become a customary assignment in most NMR labs, enabling the identification of molecular connectivity as well as the development of conceptual frameworks.

Background: Various NMR active nuclei (1H, 13C, 19F, & 31P, etc.) can be used to strengthen the CR abilities of NMR spectroscopy. NMR active nuclei are isochronic in the optically inactive environment and thus unable to exhibit CR. However, certain nuclei are anisochronic in a chiral atmosphere making CR feasible. CR capabilities of NMR are dependent on the application of chiral discriminating agents such as chiral derivatizing agents (CDAs), chiral lanthanide shift reagents (CLSRs), and chiral solvating agents (CSAs) that essentially contain a chiral auxiliary. CDAs tend to bind covalently with a functional group of the analytes, whereas CSAs bind vis non-covalent associations, like dipoledipole

and ion-pair, etc. However, CLSRs, like CSAs, do not bind covalently with the enantiomers of analytes. However, CLSRs, like CSAs, do not bind covalently with the enantiomers of analytes rather they comprise a paramagnetic center that can bring chemical shift difference of diastereotopic nuclei.

Method: Herein, the recent developments in methods based on NMR spectroscopy for CR of certain chiral drugs using various chiral discriminating agents are discussed.

Application: The methods described herein can be an assessment tool to provide details of molecular geometry and the construction of spatial relationships of chiral molecules.