Chiral separation with principles

An overview of the principles of chiral separations in CE and HPLC is given in the first part of this chapter. The second part is dedicated to an overview of chiral separation with CE. The popularity of electrophoretic techniques has grown spectacularly in recent years, mainly due to their exceptional performances in the chiral field. Various selectors can easily... 

Investigation with the two optical transduction principles mentioned before confirmed the preferential enrichment of the S-enantiomer resulting in more than ninefold higher signals, which is the highest separation factor found for chiral separation on cyclodextrins up to now. The good agree-... 

Membrane bioreactors have been reported for the production of diltiazem chiral intermediate with a multiphase/extractive enzyme membrane reactor [15, 16]. The reaction was carried out in a two-separate phase reactor. Here, the membrane had the double role of confining the enzyme and keeping the two phases in contact while maintaining them in two different compartments. This is the case of the multiphase/ extractive membrane reactor developed on a productive scale for the production of a chiral intermediate of diltiazem ((2R,3S)-methylmethoxyphenylglycidate), a drug used in the treatment of hypertension and angina [15]. The principle is illustrated in... 

Chiral separation or sorption is another important technique in chirotechnology. In fact, due to the high cost of chiral catalysts, industries generally prefer chiral separation over asymmetric catalysis to obtain optically pure compounds. As in asymmetric heterogeneous catalysis, a chiral selector (a chiral molecule in optically pure form) can be immobilized on a solid support to make a chiral stationary phase (CSP) of use in direct chiral separation. The basic principle of chiral separation is that the chiral selector interacts differently with the enantiomers of a racemic or enantioenriched mixture to form transient diastereoisomeric species of different stability, and this fine distinction leads to the separation of enantiomers during elution. This topic has also produced a huge number of papers and the readers are referred to the previous reviews for more knowledge on this field [70-73]. 

Additionally, the submonomer process enables installation of nearly any commercially or synthetically accessible primary amine as a side chain in peptoids. To date, 230 different amine monomers have been incorporated into peptoids as side chains, a number that likely equals or exceeds all possible commercially available a-amino acids, and yet represents a mere fraction of the possible chemical diversity of peptoids. The synthesis of any new a-amino acid requires either asymmetric synthesis or chiral separations, both of which contribute to high costs associated with synthesizing new amino acids. With peptoids, however, new residues can in principle use any of the thousands of commercially available primary amines, which also include a plethora of a-chiral amines (inexpensive due to their use in industrial chiral separations) that have... 

While the migration principle, i.e., the driving forces moving the analytes through the separation capillary, is based on electrophoretic mechanisms the chiral separation is based on enantioselective interactions between the analyte enantiomers and a chiral selector and is, therefore, a chromatographic separation principle. The fact that the selector is in the same phase as the analytes in CE and not part of a stationary phase that is immiscible with the mobile phase as found in chromatography does not represent a conceptional difference between both techniques. The chiral selector in CE is also called pseudophase as it is not a physically different phase and may also possess an electrophoretic mobility. Enantioseparations in CE have also been termed capillary electrokinetic chromatography . 

About 40% of the drugs contain at least one chiral center. Isomers have very close chemical structures however, in many cases they exhibit different biological effects, bind to proteins, or are metabolized differently. Thus, chiral separation is very important. The principles of this technique in CE depend on the addition to the buffer an additive compound with a special cavity such as cyclo-dextrins, heparin, or certain antibiotics, which... 

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