Unexpected enantioseparation of mandelic acids and their derivatives on 1,2,3-triazolo-linked quinine tert-butyl carbamate anion exchange-type chiral stationary phase
✍ Scribed by Karol Kacprzak; Norbert Maier; Wolfgang Lindner
- Publisher
- John Wiley and Sons
- Year
- 2010
- Tongue
- English
- Weight
- 266 KB
- Volume
- 33
- Category
- Article
- ISSN
- 1615-9306
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✦ Synopsis
Abstract
Replacement of the flexible thioether linker for the novel, rigid 1,2,3‐triazole spacer group in the course of immobilization of quinine tert‐butyl carbamate onto a silica surface led to a chiral stationary phase (CSP) with enhanced enantioselectivity for the resolution of mandelic acid and derivatives thereof. These new CSPs allowed efficient resolution of a wide set of mandelic acids with α‐values between 1.08 and 1.68. The high loadability of these chiral ion exchange type CSPs allows preparative separation in the milligram range on an analytical column of 100×4 mm id in a single run as it was demonstrated for 4‐trifluoromethylmandelic, 2‐naphthylglycolic and 3,4‐methylenedioxymandelic acids. The chiral recognition process has been studied using a library of 25 diverse racemic probes. A tentative model suggests that the rigid 1,2,3‐triazole group takes part in the formation of an enantioselective‐binding pocket of the entire and immobilized selector moiety of the CSP. The primary interaction site is given by the ionizable quinuclidine group of the Cinchona alkaloid supported by possible π–π stabilization effects within the selector–selectand complex.