Assignment of the absolute configuration of molecules that are chiral by virtue of deuterium substitution using chiral tag molecular rotational resonance spectroscopy

Abstract

Chiral tag molecular rotational resonance (MRR) spectroscopy is used to assign the absolute configuration of molecules that are chiral by virtue of deuterium substitution. Interest in the improved performance of deuterated active pharmaceutical ingredients has led to the development of precision deuteration reactions. These reactions often generate enantioisotopomer reaction products that pose challenges for chiral analysis. Chiral tag rotational spectroscopy uses noncovalent derivatization of the enantioisotopomer to create the diastereomers of the 1:1 molecular complexes of the analyte and a small, chiral molecule. Assignment of the absolute configuration requires high‐confidence determinations of the structures of these weakly bound complexes. A general search method, CREST, is used to identify candidate geometries. Subsequent geometry optimization using dispersion corrected density functional theory gives equilibrium geometries with sufficient accuracy to identify the isomers of the chiral tag complexes produced in the pulsed jet expansion used to introduce the sample into the MRR spectrometer. Rotational constant scaling based on the fact that the diastereomers have the same equilibrium geometry gives accurate predictions allowing identification of the homochiral and heterochiral tag complexes and, therefore, assignment of absolute configuration. The method is successfully applied to three oxygenated substrates from enantioselective Cu‐catalyzed alkene transfer hydrodeuteration reaction chemistry.

Revisiting the Absolute Configuration of Peyssonnoside A Using Vibrational Circular Dichroism Spectroscopy

“…For scientific inquiry, it is helpful to be aware of other useful techniques that do not depend on the differential response to circularly polarized light for probing chiral molecules. Such techniques include Nuclear Magnetic Resonance (NMR) and Microwave Symmetry 2024, 16, 133 2 of 13 Rotational Resonance (MRR) [11], which is also referred to as microwave three-wave mixing (M3WM) [12] spectroscopy. For the former method, the chiral sample of interest is converted to a diastereomer by complexing it with another chiral sample of known AC and then studied in the solution phase.…”