Analytical and semipreparative high performance liquid chromatography enantioseparation of new substituted 1-thiocarbamoyl-3,5-diaryl-4,5-dihydro-(1H)-pyrazoles on polysaccharide-based chiral stationary phases in normal-phase, polar organic and reversed-phase conditions.

The most effective polysaccharide-based chromatographic selectors are semi-synthetic polymers prepared by conversion of hydroxyl groups of monosaccharide unit of cellulose or amylase to arylcarboxylate or arylcarbamate moieties. Because the linkage between silica matrix and polysaccharide derivatives is achieved by physical adsorption, the use of solvents of intermediate polarity such as chlorinated solvents, tetrahydrofuran or ethyl acetate, which may dissolve or swell the polymeric selector, must be carefully avoided. This restriction not only reduces the development of enantioselective CSP/mobile phase combinations but it may become a serious drawback in the enantioseparation at preparative scale, because the loading capacity strictly depends on solubility of sample in eluent. To overcome these problems and to obtain more versatile and solvent compatible CSPs, different methods to linkage, through covalent bond, cellulose or amylose derivatives onto silica matrix were described. The direct HPLC enantioseparation of five pairs of new chiral pyrazole derivatives on coated cellulose- and amylose-based chiral stationary phases (Chiralpak AD, Chiralcel OJ and Chiralcel OJ-RH) and new immobilised amylose-based Chiralpak IA CSP was performed. Very high enantioselectivity factor (?) values were achieved in polar organic and reversed-phase conditions by using OJ-RH as CSP. Chiralpak IA exhibited an excellent chiral resolving ability in normal-phase mode and it allowed the enantioseparation of analytes investigated with resolution factors (Rs) >20. Due to its bonded nature, it was successfully employed at analytical and semipreparative scale in combination with normal-phase eluents containing “non-standards” solvents such as acetone.