Studies On The Influence Elements Of Enantioseparation Ability Of Biselector Stationary Phases Derived From Polysaccharides Derivatives

Chirality is one of the basic properties of the nature, closely related to human lifeand health. High-performance liquid chromatography (HPLC) based on the applicationof chiral stationary phase (CSPs) has become a significant technique to separateenantiomers of chiral compounds, to determine optical purity and to monitor asymmetricsynthesis because of its convenience, high efficiency, satisfactory accuracy andreproducibility. Therefore, it is very important to study the preparation and the structuraldependence on the properties of novel CSPs. In this work, a series of biselector chiralstationary phases (CSPs) derived from cellulose, amylose and chitin were designed andprepared. The enantioseparation ability and stability of these CSPs was evaluated. Inaddition, the structural dependence on the properties of the biselector CSPs and thetrends in consistency or anti-consistency of the two chiral selectors in the biselector CSPsduring separation were studied. These works are summarized as follows:(1) Cellulose tris(3,5-dimethylphenylcarbamate)(I), cellulose tris(4-methylbenzoate)(II), amylose tris(3,5-dimethylphenylcarbamate)(III) and amylose tris(4-methylbenzoate)(IV) were prepared. CSP2-5, CSP2-8, CSP2-7and CSP2-6were prepared by coating thecorresponding blends of I and II, I and IV, II and III as well as III and IV on aminatedsilica gel. These blends were prepared with two polysaccharides derivatives at an equalmolar ratio of glucose unit. For the sake of enantioseparation comparison, thecorresponding single selector chiral stationary phases were also prepared with the twoindividual derivatives of cellulose and amylose. The enantioseparation ability of theseCSPs was evaluated with structurally various chiral analytes. CSP2-7showed overallimproved enantioseparation ability in comparison with the two single selector CSPs.CSP2-5displayed equivalent enantioseparation ability compared with the ones of twosingle selector CSPs as a whole. Nevertheless, CSP2-6and CSP2-8exhibited chiralrecognition abilities that intermediate between the ones of the two individual phases. These results indicate that the biselector CSPs on the basis of the appropriate matches instructures of polysaccharides derivatives demonstrated enhanced chiral recognitionability.(2) Cellulose tris(benzoate)(V) and cellulose tris(4-chlorobenzoate)(VI) wereprepared. CSP3-2and CSP3-4were prepared by coating the blends of V and III as wellas VI and III on aminated silica gel in the same manner described in section (1). Similarto CSP2-7, CSP3-2exhibited enhanced chiral recognition ability. Whereas CSP3-4demonstrated chiral recognition ability intermediates between those of the two individualphases. The CSP derived from cellulose tris(4-chlorobenzoate) is not commerciallyavailable because of its weak enantioseparation ability. Therefore, only the biselectorCSPs consisted of two selectors bearing strong enantioseparation ability may showenhanced chiral recognition ability.(3) CSP4-1and CSP4-2were prepared by increasing the loadings of the twoselectors in CSP2-5and CSP2-6, meanwhile the fed ratios of glucose units in eachpolysaccharide derivative remained the same. The enantioseparation ability of theseCSPs was evaluated. Comparing the separation result, it was found that CSP4-1with ahigher loading of biselector derived from the two cellulose derivatives exhibitedenhanced chiral recognition ability in comparison with CSP2-5with a lower biselectorloading only in few mobile phases, such as isopropanol-containing mobile phases.However, the biselector CSP4-2with higher loading of biselector prepared from twoamylose derivatives showed improved chiral recognition ability in comparison withCSP2-6with a lower biselector loading.(4) Chitin bi(3,5-dimethylphenylcarbamate)(VII) were prepared. CSP5-2andCSP5-3were prepared by coating the blends of II and VII as well as I and VII onaminated silica gel using the method described in section (1). The enantioseparationability of these CSPs was evaluated with structurally various chiral analytes. CSP5-2andCSP5-3demonstrated chiral recognition abilities intermediate between those of the twoindividual phases. The biselector CSPs derived from chitin derivatives could be used in the mobile phase containing organic additives, such as chloroform and ethyl acetate,owing to its low solubility in organic solvents, thereby expanding the range of mobilephase and chiral recognition ability of the CSPs. Furthermore, after being used for a longtime, the chiral recognition ability of CSP5-2and CSP5-3did not decrease, but increasedprominently, CSP5-2in particular. The reason may be that the supramolecular structureof the biselector seems to be altered by the mobile phase due to the interaction betweenselectors and mobile phase, and the alternation is advantageous to chiral recognition. Thesame phenomenon on the single selector CSPs derived from cellulose and amylosederivatives was not observed. Therefore, the biselector CSPs prepared with the blend ofchitin and cellulose derivatives demonstrated markedly improved durability.