Solvent-induced reversed stereoselectivity in reciprocal resolutions of mandelic acid and erythro-2-amino-1,2-diphenylethanol.
Solvent-induced chirality switching in reciprocal optical resolution between mandelic acid (1) and erythro-2-amino-1,2-diphenylethanol (2) has been demonstrated. The stereochemistry of the deposited salts was controlled by changing the crystallization solvent from 1-PrOH or 1-BuOH to 1,4-dioxane. It was revealed from (1)H NMR spectra, thermogravimetric analysis, and X-ray crystallography of the salts that an equimolar amount of the crystallization solvent was incorporated in each diastereomeric salt. On the basis of the crystal structures, it was found that both the hydrogen-bonding ability and the size of the solvent molecule played an important role. Differences in the formed hydrogen-bonding networks (columnar or sheetlike structure) and their packing manner were found to be crucial for the reversed stereoselectivity. Furthermore, pseudopolymorphic salt crystals that incorporated 1,4-dioxane were obtained during the enantioseparation of racemic 2, and their solid-state properties were examined by measurement of their IR spectra. This solvent-induced dual stereocontrol technique was successfully applied to the successive resolution process, eliminating the need to change the resolving agent for access to both enantiomers of 1 and 2.
Technical Support Center and §Graduate School of Science and Engineering, Saitama University , Shimo-Ohkubo, Sakura-ku, Saitama City, Saitama 338-8570, Japan.
Hiroaki
H
Shitara
Toshiki
T
Shintani
Koichi
K
Kodama
Takuji
T
Hirose
D018360:Crystallography, X-Ray; D004983:Ethanolamines / Q000737:chemistry*; D008333:Mandelic Acids / Q000737:chemistry*; D008958:Models, Molecular; D015394:Molecular Structure; D012997:Solvents / Q000737:chemistry; D013237:Stereoisomerism
C530675:2-amino-1,2-diphenylethanol; D004983:Ethanolamines; D008333:Mandelic Acids; D012997:Solvents; C037938:mandelic acid