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Role of Hollow Fiber Contactor-Based Technology in Fermentation and Enzymatic Transformation and in Chiral Separations
Published in Anil K. Pabby, S. Ranil Wickramasinghe, Kamalesh K. Sirkar, Ana-Maria Sastre, Hollow Fiber Membrane Contactors, 2020
G. P. Syed Ibrahim, A. M. Isloor, R. Farnood
In another study, enantioselective hydrolysis of cis-cyclohex-4-ene-1, 2-dicarboxylate (cis-DE) to (1S, 2R)-cyclohex-4-ene-1, 2-dicarboxylic acid monomethyl ester ((1S,2R)-ME) was performed using pig liver esterase (PLE) immobilized HF membrane biphasic contactor [53]. The stability, lower cost, and capacity to hydrolyze large verities of esters made PLE a potential candidate. The reaction scheme for the enantioselective hydrolysis is given in Figure 18.6. The enzyme was immobilized on the HF membrane both by covalent bonding and physical entrapment. In the covalent bonding, the terminal amino group of the nylon microporous membrane was reacted with a carboxylic acid group of the PLE enzyme. In the case of physical immobilization, the enzymes were filtered from outside to the inside of the polysulfone HF UF membrane (MWCO 30 kDa) in dead-end mode. The typical schematic representation of the experimental set-up is represented in Figure 18.7. In summary, the enantiomeric excess (ee) of the final product was in the range of 94 to 97%. In addition, the enzymatic activity was decreased with time in the case of covalent immobilization, which was attributed to the longer immobilization process. However, the physical immobilization of the enzyme on the membrane surface exhibited a moderate decrease in the enzyme activity. Reaction scheme for the enantioselective hydrolysis of cis-cyclohex-4-ene-1, 2-dicarboxylate [53].
Twelve Principles of Green Chemistry
Published in Vera M. Kolb, Green Organic Chemistry and Its Interdisciplinary Applications, 2017
Many catalysts have been developed to either enable or enhance selectivity of the reaction. Stereoselectivity and achievement of enantiomeric excess are necessary in the syntheses of fine chemicals, especially drugs. Enantiomers exhibit the opposite handedness, like the left and the right hand. Often only one of the enantiomers has the desired biological properties, and the other one may either be toxic or place burden on the organism’s detoxification system. The production of the undesired enantiomers creates waste, but the more serious problem is the required separation of enantiomers for the purpose of isolating the biologically active one. This process is often difficult, lengthy, and expensive. It is often a major factor that drives up the cost of drugs. It is therefore very important that the chemical synthesis yields the desired enantiomer either exclusively or in excess. This is often achieved with special catalysts. We shall address such catalysts in Chapters 9 and 10, especially on the examples of green pharmaceutical syntheses.
Helical twisting power and compatibility in twisted nematic phase of new chiral liquid crystalline dopants with various liquid crystalline matrices
Published in Liquid Crystals, 2019
Łukasz Duda, Maciej Czajkowski, Bartłomiej Potaniec, Petra Vaňkátová
The enantiomeric excess was calculated from obtained chromatograms from areas of the R and S enantiomer peaks. Only one enantiomer of each compound was available for the analysis. Thus, the identification of individual enantiomers peaks could not be done by comparing the retention times. The peaks of enantiomers were identified based on the identical UV spectra instead and second column with different chiral stationary phase was used to confirm the results. For three out of five compounds good correlation between the results of Chiralpak AD-3 and Lux Amylose 2 column was found. The acidic compounds CB15 acid and ZW 8520 could not be resolved on Lux Amylose 2 column. Nevertheless, the results obtained with Chiralpak AD-3 are in agreement with the enantiomer excess estimated based on the optical purity of the precursors.