Spontaneous Deracemization of the DMY Racemic Compound with Two Stereocenters through a Stepwise Process of Cocrystallization-Induced Resolution and Solution Racemization

Abstract

Processes that allow access to enantiomerically pure drugs are of the utmost importance to maximize pharmacological activity while minimizing the side effects. This work develops a novel diastereomeric cocrystallization-induced spontaneous deracemization process for a racemic compound, dihydromyricetin (DMY), which contains two stereocenters. A pair of diastereomeric cocrystals, (2R,3R-DMY)₂:R-N-benzyl-1-phenylethylamine and (2R,3R-DMY)₂:S-N-benzyl-1-phenylethylamine, the latter of which is equivalent to (2S,3S-DMY)₂:R-N-benzyl-1-phenylethylamine, was discovered via a complete screening of 12 chiral coformers using both slurry and liquid-assisted grinding methods. Crystal structure of these cocrystals was determined using single-crystal X-ray diffraction and reported for the first time. Enantioseparation of rac-DMY by virtue of diastereomeric cocrystals was designed and optimized through slurry and cooling crystallization methods, resulting in a product of 81% enantiomeric purity with a yield of only 31%. Further, the racemization process of DMY enantiomers with various influence factors was examined, and the optimal racemization condition that achieves simultaneous racemization of the two stereocenters was determined. Finally, a stepwise cocrystallization-induced deracemization process of rac-DMY that combines chiral resolution by cocrystallization and racemization of recycling mother liquor was developed, producing an enantiomeric purity of 97.5% and a maximal yield of 68%.