Enantiomer Separation of Nitriles and Epoxides by Crystallization with Chiral Organic Salts: Chirality Switching Modulated by Achiral Acids

Abstract

Enantiomer separation of nitriles and epoxides by inclusion crystal formation with organic-salt type chiral hosts was achieved. The stereochemistry of the preferentially included nitrile could be switched only by changing the achiral carboxylic acid component. Crystallographic analysis of the inclusion crystals reveals that the hydrogen-bonding networks are controlled by the acidity of the phenol group of the acids, which results in chirality switching.

Switching of Guest Selectivity for the Inclusion of Regioisomers of Monosubstituted Phenols with Crystals of p-tert-Butylcalix[4]arene

“…In diastereomeric salt resolution of racemic compounds, Sakai et al reported selectivity switching of diastereomers that preferentially crystallize, via the polarity of the solvent. , In optical resolution via the diastereomer-salt method, Hirose et al. reported selectivity switching of preferentially crystallizable diastereomers, via the solvent type and addition of organic molecules. , Iwasawa et al reported switching of guest selectivity by changing the crystallization solvent in the inclusion of organic molecules with macrocyclic boronic acid esters . Although it was reported that MOFs made of the same components can exhibit different guest selectivities, depending on their topologies, the switching of guest selectivity in the direct absorption of guest molecules using solid materials, without changing their structures, is considered to be difficult.…”