Racemic mixtures, usefulness

Four general methods have been used for obtaining chiral ligands resolution of a racemic mixture, use of a chiral naturally occurring product 33), and asymmetric homogeneous or heterogeneous hydrogenation. 

Enantiomeric assay determinations are typically applied to characterize racemic mixtures using the normalized peak area (area%) calculation procedure. The selectivity solution is utilized to demonstrate the separation capability in the method and to allow peak identification. A suggested sample injection sequence can be... 

R,2R-Hydroxymethylcyclohexanol (6). ls,2R-Hydroxycyclohexane-carboxylic acid was obtained by resolution of the racemic mixture using the procedure reported by Torne (25). The rotation agreed with that previously reported (25, 26). The acid was converted to the methyl ester using diazomethane, and the ester was reduced by the usual method... 

Fig. 41 Scheme of the synthesis of L-glyceraldehyde by reduction of D-glyceraldehyde out of the racemic mixture using NADP-dependent glycerol dehydrogenase from Gluconobacter... 

As mentioned, asymmetrically pure compounds are important for many applications, and many different strategies are pursued. However, in spite of many methods being developed, the classic resolution technique of diastereomeric crystallization is still preferentially used to prepare optically active pure compounds in bulk quantity. Crystallization is commonly used in the last purification steps for solid compounds because it is the most economic technique for purification and resolution. Attempts to achieve crystallization after completed reaction without workup and extraction is called a direct isolation process. This technique can be cost-effective even though the product yield obtained is lower. Special conditions may be needed in this case, and the diastereomers can be classified into two types diastereomeric salts and covalent diastereomeric compounds, respectively. Diastereomeric salts can, for example, be used in the crystallization of a desired amine from its racemic mixture using a chiral acid. Covalent diastereomers can, on the other hand, be separated by chromatography, but are more difficult to prepare. Another advantage of crystallization is the possibility of combining in situ racemi-zation reactions and diastereomeric formation reactions to get the desired pure compounds. This crystallization-induced resolution technique is still under development because of its requirements for optimized conditions [55, 56],... 

Fig. 6.28 Comparison of experimental and simulated profiles for the separation of EMD53986 racemic mixture using single- and multi-component isotherms (exp = experimental sim. = simulated ...

Resolution of racemic mixtures using a chiral resolving agent is based on the formation of two diastereoisomeric entities, usually salts differing in their solubility, leading to preferential crystallization of one of them (Figure 13.3). The chemical nature of the racemate usually defines the compatible chemical character of the... 

In addition to the more common (S)-amidase activities, (RJ-specific enzymes have also been identified. Thus (S)-ketoprofenamide has been derived from the racemic mixture using a biocatalyst from Comamonas acidovorans KPO 2771-4 to hydrolyze the (R)-enantiomer with high selectivity1141 (see Scheme 12.2-6). 

EMD53986 racemic mixture using single- and multicomponent isotherms (exp., experimental ... 

Resolving Racemic Mixtures Using Parallel Combinatorial Libraries... 

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