New chiral oxo-bridged calix[2]arene[2]triazine for the enantiomeric recognition of α-racemic carboxylic acids

The enantiomeric excess is a key parameter for chemical and pharmaceutical industries for its ability to determine the activity and therapeutic action of chiral compounds. The determination of the enantiomeric excess using nuclear magnetic resonance is generally based on the formation of diastereomeric complexes. Herein we report novel chiral oxo-bridged calix[2]arene[2]triazine derivatives, which were synthesized from (1S,2R)-(−)-1-amino-2-indanol or (1S,2R)-(+)-2-amino-1,2-diphenylethanol. The structures of these compounds were established by various spectroscopic methods. Their enantiomeric recognition abilities towards the enantiomers of α-racemic carboxylic acids were examined by using 1H NMR spectroscopy. The ΔΔδ values of α-H signals were appropriate to give a good baseline resolution for most of the tested analytes, which ranged from 0.005 to 0.053 ppm. The α-hydroxy acids, especially those containing aromatic group such as mandelic acid, α-methoxyphenylacetic acid, showed a bigger ΔΔδ value in comparison to the other carboxylic acids.

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(1S,1′S,2R,2′R)-Bis-(2,3-dihydro-1H-inden-2-ol)-tetraoxocalix[2]arene[2]triazineC36H28N8O6[α]D25 = −9.05 (c 0.97, CHCl3)Source of chirality: the precursorAbsolute configuration: (1S,1′S,2R,2′R)

(1S,1′S,2R,2′R)-Bis-(1,2-diphenyl-2-ethanol)-tetraoxocalix[2]arene[2]triazineC46H36N8O6[α]D25 = +29.5 (c 0.83, CHCl3)Source of chirality: the precursorAbsolute configuration: (1S,1′S,2R,2′R)