Development of chiral stationary phases consisting of low-molecular-weight cellulose covalently bonded to silica gel

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We prepared chiral supports whose chiral stationary phase (CSP), consisting of a low-molecular-weight cellulose derivative (degree of polymerization : 15), is covalently bonded to silica gel. The cellulose used as the base material of the CSP was pre-hydrolysed with phosphoric acid before the coupling reaction to unite a reducing terminal in the cellulose and anaminopropyl group on the surface of silanized silica. After substituting hydroxyl groups in cellulose by using 3,5-dichlorophenyl isocyanate or phenylisocyanate, we tested the CSP thus obtained for its performance in chiral recognition and found a wide range of chiral discrimination ability. We also confirmed that an elution using ‘strong' solvents as a mobile phase could be achieved, which is difficult for the coated-type CSPs because the mobile phase may dissolve the CSP. However, more enantiomeric mixtures showed larger selectivity factors (α) when eluted on the coated-type CSPs than on the covalently bonded CSPs. A coated-type CSP consisting of the low-molecular-weight cellulose phenylcarbamate, prepared as a control CSP sample, showed comparable performance with the commercial coated-type column (CHIRALCEL【○!R】 OC), so the slightly poorer performance of the chemically bonded CSPs may be explained by the difficulty of the polymer consisting of the CSPs in taking an optimal supermolecular structure required for chiral recognition due to the fixation to the silica gel. The low degree of polymerization may have an additional effect.