Chirality polysaccharides

Miller, L., Orihuela, C., Fronek, R., and Murphy, J., Preparative chromatographic resolution of enantiomers using polar organic solvents with polysaccharide chiral stationary phases,. Chromatogr. A, 865, 211, 1999. 

Most screening and optimization approaches in HPLC were defined using polysaccharide chiral stationary phases (CSP), thanks to their broad chiral recognition ability toward a large number of compounds. 

RMC Sutton, KL Sutton, AM Stalcup. Chiral capillary electrophoresis with noncyclic oligo- and polysaccharide chiral selectors. Electrophoresis 18 2297-2304, 1997. 

The cellulose derivatives used for chiral TLC are trisphenylcarbamate, 2,3-dichlorophenylcarbamate, 2,4 -dichlorophenylcarbamate, 2,6 -dichlorophenylcar-bamate, 3,4-dichlorophenylcarbamate, 3,5-dichlorophenylcarbamate, 2,3-dimethyl-phenylcarbamate, and 3,5-dimethylphenylcarbamate. Aboul-Enein et al. [178] have reviewed the chiral resolution of racemates on polysaccharide chiral TLC plates. They discussed the role of the substituents of polysaccharide derivatives on chiral resolution. The effects of the substituents of cellulose derivatives and the mechanisms of chiral resolution on these plates are similar to what is found for HPLC CSPs. 

Yashima E, Okamoto Y, Chiral recognition mechanism of polysaccharides chiral stationary phase in The Impact of Stereochemistry on Drugs Development and Use (Aboul-Enein, HY, Wainer IW, Eds.), John Wiley Sons, New York, p. 345 (1997). 

Cox, G. B., Amoss, C. W. Extending the range of solvents for chiral analysis using a new immobilized polysaccharide chiral stationary phase... 

The chiral selectors applied to CE include native cyclodextrins as well as neutral and charged derivatives, oligo- and polysaccharides, chiral crown ethers. 

Preparation and Chiral Recognition of Polysaccharide Chiral Selectors. . . ... 

Analytical techniques that utilise biopolymers, ie, natural macromolecules such as proteias, nucleic acids, and polysaccharides that compose living substances, represent a rapidly expanding field. The number of appHcations is large and thus uses hereia are limited to chiral chromatography, immunology, and biosensors. 

Separation of enantiomers by physical or chemical methods requires the use of a chiral material, reagent, or catalyst. Both natural materials, such as polysaccharides and proteins, and solids that have been synthetically modified to incorporate chiral structures have been developed for use in separation of enantiomers by HPLC. The use of a chiral stationary phase makes the interactions between the two enantiomers with the adsorbent nonidentical and thus establishes a different rate of elution through the column. The interactions typically include hydrogen bonding, dipolar interactions, and n-n interactions. These attractive interactions may be disturbed by steric repulsions, and frequently the basis of enantioselectivity is a better steric fit for one of the two enantiomers. ... 

The type of CSPs used have to fulfil the same requirements (resistance, loadabil-ity) as do classical chiral HPLC separations at preparative level [99], although different particle size silica supports are sometimes needed [10]. Again, to date the polysaccharide-derived CSPs have been the most studied in SMB systems, and a large number of racemic compounds have been successfully resolved in this way [95-98, 100-108]. Nevertheless, some applications can also be found with CSPs derived from polyacrylamides [11], Pirkle-type chiral selectors [10] and cyclodextrin derivatives [109]. A system to evaporate the collected fractions and to recover and recycle solvent is sometimes coupled to the SMB. In this context the application of the technique to gas can be advantageous in some cases because this part of the process can be omitted [109]. 

Examples with other Pirkle-type CSPs have also been described [139, 140]. In relation to polysaccharides coated onto silica gel, they have shown long-term stability in this operation mode [141, 142], and thus are also potentially good chiral selectors for preparative SFC [21]. In that context, the separation of racemic gliben-clamide analogues (7, Fig. 1-3) on cellulose- and amylose-derived CSPs was described [143]. 

J. Dingenen, Polysaccharide phases in enantioseparations in A practical approach to chiral separations by liquid chromatography, G. Subramanian, VCH, Weinheim (1994) Chapter 6. 

By clicking the appropriate buttons on the form, the user can combine molecular structure queries of sample, CSP and solvent, using operators AND, OR, NOT with data queries in one search. A query for the search of chiral separations of alpha-aromatic acids on any polysaccharide phases coated on silica gel providing an alpha value superior to 1.2 is shown in Eig. 4-4. 

Mourier s report was quickly followed by successful enantiomeric resolutions on stationary phases bearing other types of chiral selectors, including native and deriva-tized cyclodextrins and derivatized polysaccharides. Many chiral compounds of pharmaceutical interest have now been resolved by packed column SFC, including antimalarials, (3-blockers, and antivirals. A summary is provided in Table 12-2. Most of the applications have utilized modified CO, as the eluent. 

Polysaccharide-based CSPs incorporate derivatives of cellulose and amylose adsorbed on silica gel. The selectivity of these CSPs depends upon the nature of the substituents introduced during the derivatization process. The secondary structure of the modified polysaccharide is believed to play a role in selectivity, but the chiral recognition mechanisms have not been fully elucidated [55]. 

Kunz H., Hofmeister A., Glaser B. Stereoselective Syntheses Using Carbohydrates as Carriers of Chiral Information in Polysaccharides 1998 539, Ed. Severian D., Pb. Dekker N.Y. 

Fig. 4-4. The query menu form search of chiral separations of alpha-aromatic acids on any polysaccharide CSPs with a > 1.2.

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