Immobilization of a cellulose carbamate-type chiral selector onto silica gel by alkyne-azide click chemistry for the preparation of chiral stationary chromatography phases

Abstract

A new synthesis strategy for the preparation of cellulose derivative-based chiral selectors and the subsequent mild immobilization onto pre-functionalized silica gel are introduced, utilizing Cu(I)-catalyzed alkyne-azide Huisgen cycloaddition (“click”) chemistry. A cellulose 3,5-dimethylphenyl carbamate derivative carrying propynyl carbamate groups was prepared by a combination of carbonate aminolysis and isocyanate chemistry. For immobilization, 3-azidopropyl-functionalized silica gel as an inert carrier was used, synthesized via a 3-chloropropyl intermediate. The chiral selector, as well as the inorganic/organic hybrid materials (silica gel/chiral selector), were comprehensively characterized by ATR-FTIR, solid-state 13C and 29Si NMR, liquid-state NMR, GPC, TGA, and elemental analysis. The enantioseparation performance of the immobilized-type chiral stationary phase was evaluated by HPLC with a set of representative chiral test analytes and different eluents and compared to a respective coated-type (=non-covalently bound) chiral stationary phase carrying the same selector quality and quantity on the same silica gel matrix. The immobilization did not adversely affect the chiral separation performance; on the contrary, in some chromatographic separations the immobilized-type chiral stationary phase surprisingly even surpassed the coated reference material. Graphical abstract: [Figure not available: see fulltext.].