Preparation Of Bonded Chiral Stationary Phases For High-Pertormance Liquid Chromatography And Their Chiral Resolution Abilities

With the development of science and technology, people have had a deep insight into the phenomenon that drugs with different abilities to rotate the plane of polarization of polarized light have distinct physiological activities. Therefore, it is becoming more and more important to analyze and separate optical enantiomers in biochemistry, medicinal chemistry, and organic chemistry as well as asymmetric synthesis and catalysis. Among these methods that can separate and analyze optically active compounds, the direct resolution by means of high- performance liquid chromatography chiral stationary phases (HPLC-CSPs) is one of the rapid, convenient, and prospective ones. Because CSPs prepared by chemical bonding are usually more stable than those prepared by physical coating, all of the CSPs studied in this paper are chemically bonded ones. In order to comprehend the development of HPLC-CSPs, we collected enough literature at home and abroad. Based on these documents, seven novel CSPs were prepared. According to the kinds of chiral selectors, these seven CSPs could be classified into the following three types: cyclodextrin-bonded CSPs, macrocyclic antibiotic-bonded CSPs, and alkaloid-bonded CSP (brush-type CSP). The work done was as follows:(1) Three (L)-DNP-amino acid modifiedβ-CD CSPs, i.e., (L)-DNP-alanylatedβ-CD CSP, (L)-DNP-phenylalanylated CSP, and (L)-DNP-valylatedβ-CD CSP were synthesized. Nine chiral drugs such as nimodipine, ketamine, and chlorpheniramine were used to investigate the chiral separation abilities of these three CSPs. The results obtained indicated that (L)-DNP- valylatedβ-CD CSP had the best resolution ability, while (L)-DNP-alanylatedβ-CD CSP was the worst one among the three. On (L)-DNP-alanylatedβ-CD CSP, two chiral drugs, i.e., nimodipine and verapamil were separated into their enantiomers. Their separation factors (α) were 5.77 and 2.11, and the resolution factors (Rs) were 0.79 and 0.37, respectively. On (L)-DNP-phenylalanylatedβ-CD CSP, phenylpropanolamine, 1, 1'-bi-2-naphthol, atenolol, chlorpheniramine, and verapamil were separated into their enantiomers. Their separation factors (α) were 16.98, 1.34, 3.47, 2.53, and 2.38, and the resolution factors (Rs) were 0.50, 0.43, 0.20, 0.26, and 0.17, respectively. On (L)-DNP-valylatedβ-CD CSP, promethazine, chlorpheniramine, phenylpropanolamine, propranolol, ketamine and 1, 1'-bi-2-naphthol were resolved. Their separation factors (α) were 1.36, 1.75, 2.96, 1.75, 3.81, and 1.84, and the resolution factors (Rs) were 0.66, 0.59, 0.90, 0.52, 0.82, and 0.14, respectively. Meanwhile, the possible resolution mechanism was proposed. The experiment demonstrated that inclusive effects dominated the resolution processes on these three CSPs, however, it was shown that (L)-DNP-amino acid moieties linked to the periphery ofβ-CD were conducive to the resolution processes.(2) Rifampin-erythromycin mixture bonded CSP, as well as rifampin-bonded CSP and erythromycin-bonded CSP, was prepared. Propranolol et al were used to investigate the chiral resolution abilities of these CSPs. Under the optimized chromatographic conditions, nimodipine, promethazine, chlorpheniramine, propranolol, atenolol, and 1, 1'-bi-2-naphthol were separated into their enantiomers on rifampin-erythromycin mixture bonded CSP. Their separation factors (α) were 2.14, 1.90, 1.87, 1.69, 1.38, and 1.59, and the resolution factors (Rs) were 0.10, 0.33, 0.12, 0.70, 0.66, and 0.14, respectively. Furthermore, it was indicated that synergistic effects played an important role in the resolution processes.(3) Bis-quinine bonded CSP was synthesized. Five chiral drugs such as chlorpheniramine were used as tested samples to investigate the chiral resolution ability of this CSP. Under the optimized chromatographic conditions, the separation factors (α) of chlorpheniramine, 1,1'-bi-2-naphthol, promethazine, and propranolol were 3.08, 3.09, 1.43, and 1.16, and the resolution factors (Rs) were 1.87, 0.73, 0.54, and 0.29, respectively. Furthermore, based on the analysis of the structure of bis-quinine as well as the chromatographic data, a conclusion was drawn that structural rigidity of the chrial selector could improve the enantioselectivity to certain racemates.