C-hexaphenyl-substituted trianglamine as a chiral solvating agent for carboxylic acids

Abstract

Chiral hexaazamacrocycles with a trianglamine structure and C₃-symmetry, containing six ring substituents and twelve stereocenters have been tested as chiral solvating agents (CSAs) for α-substituted carboxylic acids. Excellent results have been obtained with a hexaphenyl-substituted macrocycle. The optimal ratio between the macrocycle and racemic acid, allowing for baseline separation of the enantiomers’ signals in the ¹H NMR spectrum, was dependent on the type of acid, in particular on its degree of acidity. The analyte and the CSA could be separated and recovered by a simple acid–base extraction and reused without purification. The conformations of the free and protonated hexaamino macrocycles were inferred by CD spectroscopic studies and DFT calculations.