Inherently chiral dialkyloxy-calix[4]arene acetic acids with asymmetric placement of substituents on the lower rim of the macrocycle were first studied as enantiodiscriminating additives to the mobile phase MeCN/H 2 O/HCOOH (75/25/0.02 by volume) in the high-performance liquid chromatography (HPLC) separation of D,L-alanine and D,L-valine on the achiral stationary phase ZORBAX Original CN. The dependence of enantio-binding properties on the position of alkyl groups is demonstrated. The highest resolution (1.65) and enantioselectivity (1.80) were obtained for the 1,2-dipropyloxy-calix[4]arene acetic acid.
The enantiodiscrimination properties of stereomerically pure inherently chiral calix[4]arene acetic acids, as well as their esters and amides in relation to 1-phenylethylamine stereoisomers in liquid and gaseous phases were studied by means of proton magnetic resonance spectroscopy ( 1 H NMR) and quartz crystal microbalance (QCM) techniques. Series of QCM sensors with thin films of inherently chiral calix[4]arenes, immobilized on the quartz resonator surfaces by spin-coating and spreading drop methods have been fabricated. It was shown that sensors based on calix[4]arene acetic acids are able to recognize Rand S-forms of 1-phenylethylamine in gaseous phase under concentration level of 10-400 ppm.
This paper shows that 25‐propyloxy‐26,27‐dibenzoyloxy‐calix[4]arene can be a convenient precursor for the formation of inherently chiral configuration on the calixarene platform. The methods for sequential regioselective debenzoylation and electrophilic substitution on the upper rim were developed. The inherently chiral calix[4]renes with two and three different functional groups on the upper rim were synthesized.
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