Unexpected enantioseparation of mandelic acids and their derivatives on 1,2,3-triazolo-linked quinine tert-butyl carbamate anion exchange-type chiral stationary phase.
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.
Kacprzak
Karol
K
Department of Chemistry, Adam Mickiewicz University, Poznan, Poland. karol.kacprzak@gmail.com
Maier
Norbert
N
Lindner
Wolfgang
W