Preparative chiral

Thus, racemic acid 12 (R = H) was obtained by [3+2] cycloaddition in 90-95% yield (Scheme 5.9) [28]. Its resolution into enantiomers could be achieved either by chiral preparative HPLC, or by fractional crystallization of its cinchonidine salts. Better results were obtained upon enzymatic kinetic resolution of its iso-butyl ester 12 (R = i-Bu) [29]. However, further work showed that racemic thiolester 13, which... 

Notes Chiral preparations include the proline-catalyzed reactions2 and recently an aldolase antibody 38C2 method has been reported.3 See also 4... 

Enantiomers of racemic cis-3H,7H- and frans-3H,7H-3-substituted 7-amino-l,2,3,5,6,7-hexahydropyrido[3,2,l-zy]quinazolin-l-ones were separated by using chiral preparative HPLC method (06USA2006/0004028, 07JP2007131577). 

DIFLUORPHOS (117b) has been prepared by the same chemistry shown in Scheme 12.43 with similar yields, with the exception that the resolution of rac-7b had failed with DBTA. Resolution could only be performed by chiral preparative HPLC.145146... 

Chiral capillary gas chromatography (GC), performed with a 7-cyclodextrin trifluoroacetyl column, was also used for the determination of ee of isoxazolines <2000JOC8527>. Chiral preparative HPLC has been used to obtain optically pure isoxazolines <1997JME50>. 

Svec, F., Wulff, D., Frechet, J. M. Combinatorial Approaches to recognition of chirality preparation and use of materials for the separation of enantiomers, in Chiral Separation Techniques, Subramanian, G. (Ed.), Wiley-VCH, Weinheim, 2001. 

Electrophoretic methods are widely used alternatives for the analytical determination of the enantiomeric purity of chiral compounds [194]. Due to the high elTi-ciency of capillary electrophoresis, separations can be achieved even when very low selectivities are observed. At a preparative scale, these methods are well established for the purification of proteins and cells [195] but there is very little published on enantioselective separations. Only recently, some interest in chiral preparative applications has been manifested. Separation of the enantiomers ofterbu-taline [196] and piperoxan [197] have been reported by classical gel electrophoresis using sulfated cyclodextrin as a chiral additive, while the separation of the enantiomers of methadone could be successfully achieved by using free-fluid isotachophoresis [198] and by applying a process called interval-flow electrophoresis [199]. 

Nevertheless, the operating procedure and the problems associated with preparative chiral chromatography are very similar to those met in general preparative work. Consequently, the general operating conditions and procedures in general preparative LC will be discussed, but particular emphasis will be given to those aspects that are important in chiral preparative work. 

With the access to diverse and stable biocatalysts, more and more conventional chemical processes (first generation) in pharmaceutical manufacturing have been replaced by second-generation biocatalysis processes with substantial impact on the pharmaceutical industry. In this chapter, some commonly used biocatalytic reactions for chiral preparation, including hydrolytic reactions, acyl and glycosyl transfer reactions, asymmetric reduction/ oxidation reactions, and asymmetric formation of C-C bonds, are introduced and exemplified by the research achievements developed by the authors laboratory as well as other research groups. Some of the bioprocesses described herein have been successfully applied on pilot or even industrial scale. ... 

Due to the possible rotation of the P—C bonds, e ht stereoisomers were postulated. In accordance with DFT calculations, one type of the possible structures dominated the others by a 98 2 ratio. The enantiomerization barrier strongly depends on the nature of the R-group. Indeed, phosphine oxide 96 (R=Me) having a 2-methyl substituent showed a half-life of 7 h whereas for the 96 (R= -Pr), which bears a larger isopropyl group, it was estimated to be 10° years. Resolution by chiral preparative-HPLC confirmed the stability of the isopropyl indolylphosphine at temperature up to 60 °C. 

Chiral chromatographic separation techniques such as GC, HPLC, and CE provide the real separation of enantiomers. By real, one means that the two enantiomers of the racemates can actually be separated and obtained in individual containers. Particularly for chiral preparative HPLC, both the optically pure enantiomers can be obtained after the chiral chromatographic separation. However, in spectroscopic techniques, there is no real separation of enantiomers. Nonetheless, chiral spectroscopic techniques are still very important and useful resources for chiral technology in that they can rapidly and accurately determine the enantiopurity of chiral compounds. In addition, they can offer important information regarding the structure-property relationship and differentiation mechanism during chiral interaction and recognition. Recently, CILs have been used as the chiral selectors in spectroscopic techniques such as nuclear magnetic resonance (NMR), fluorescence, and near infrared (NIR). 

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