Abstract
A series of small-membered heterocycle probes, so-called azaheterocycle-containing diphenylmethanol chiral solvating agents (CSAs), have been developed for NMR enantiodiscrimination. These chiral sensors were readily synthesized were inexpensive and efficiently used for the chiral analysis of alpha-substituted carboxylic acids. The sensing method was operationally simple and the processing was straightforward. Notably, we propose (S)-aziridinyl diphenylmethanol as a promising CSA, which has excellent chiral discriminating properties and offers multiple detectable possibilities pertaining to the 1H NMR signals of diagnostic split protons (including 25 examples, up to 0.194 ppm, 77.6 Hz). Its ability to detect the molecular recognition of fluorinated carboxylic acids were further investigated, with a good level of discrimination via the 19F NMR spectroscopic analysis. In addition, an accurate enantiomeric excess (ee) analysis of the p-methoxyl-mandelic acid with different optical compositions have been calculated based on the integration of well-separated proton signals.
Highlights
Gao-Wei Li, ab Xiao-Juan Wang, *a Dan-Dan Cui,a Yu-Fei Zhang,a Rong-Yao Xu,a Shuai-Hua Shi,a Lan-Tao Liu,*a Min-Can Wang, b Hong-Min Liu b and Xin-Xiang Lei *c
Spectroscopic and chromatographic approaches are generally utilized for the enantioselective molecular recognition or quantitative analysis including enantio-discrimination, measurement of enantiomeric excess and assignment of absolute con guration.[2]
The literature concerning the guests of chiral analysis using a smallmembered N-heterocyclic moiety and the study on enantiodiscrimination in isotropic solutions by nuclear magnetic resonance (NMR) techniques are still not abundant
Summary
Uorine-substituted aromatic carboxylic acids (Table 2, entries 4–7, 9 and 11) almost showed more baseline resolution and had larger DDd values than other diverse substituents such as chlorine and bromine, irrespective of their electronic nature or positions, the role of uorine in the aromatic MA systems for the strongly enhance the binding ability of the aziridinyl diphenylmethanol (S)-CSA 1, which results in a better splitting of the NMR signal of the corresponding guests.
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