Covalent anchoring of a cellulose per(phenyl carbamate) chiral selector onto silica gel through alkyne-azide click chemistry and its utilization in HPLC

Abstract High-performance liquid chromatography is a powerful tool for enantioseparation, based on chiral stationary phases as separation media. Cellulose-based chiral selectors are among the most successful ones used for the preparation of chiral separation materials, exploiting the inherent chirality of the homopolymer. Compared to initial coating-type chiral stationary phases solely deposited onto silica as the chromatographic support, covalently immobilized selectors exhibit a significantly broader scope of applicable eluents, but appropriate synthetic strategies are still scarce. In this work, we present the application of the Cu(I)-catalyzed Huisgen alkyne-azide click reaction as a means to covalently immobilize a cellulose 3,5-dichlorophenyl carbamate-type chiral selector to a silica-based chromatographic support. Cellulose was first functionalized with 3,5-dichlorophenyl carbamate groups (DS = 2.35) and 4-propargyloxy-3,5-dichlorophenyl carbamate groups (propargyl carbamate DS = 0.45, overall DS = 2.80), then clicked to 3-azidopropyl-functionalized silica gel as the chromatographic support affording a 9 wt.% covalently functionalized chiral stationary phase. The chiral selector was comprehensively characterized by means of ATR-FTIR and NMR spectroscopy, and elemental analysis. The degrees of substitution of both, overall functionalization and propargyl-anchor substitution, were estimated by NMR spectroscopy. Additionally, coating-type chiral stationary phases with 9 and 20 wt.% loadings were prepared. All chiral phases were tested with regard to their separation performance using a representative set of racemic analytes under usual normal-phase conditions. Solvent compatibility and thus the chemical robustness of the immobilized stationary phase was studied using higher shares of stronger, more polar solvents in the eluent, i.e. , ethyl acetate, tetrahydrofuran and chloroform. The covalently linked selectors performed very favorably with regard to separation performance and stability. Graphical abstract