Column enantioseparation

Other examples of enantioseparations include the separation of the antihelmintic drug, prazinquatel [35], which used a 4-column SMB system composed of columns of 12.5 mm i.d. packed with CTA and with methanol as the eluent. Ikeda and Murata separated the enantiomers of (3-blockers [36]. 

Chankvetadze, B., Yamamoto, C., Tanaka, N., Nakanishi, K., Okamoto, Y. (2004). High-performance liquid chromatographic enantioseparations on capillary columns containing monolithic silica modified with cellulose tris(3,5-dimethylphenylcarbamate). J. Sep. Sci. 27, 905-911. 

Figure 3.12 Enantioseparation of TrOger s base on (a) microcrystalline cellulose triacetate (CTA I) and (b) 21 coated on silica gel. Column, 25 x 0.46 (i.d.) cm eluent ethanol-HoO (7/3) flow rate, 0.5 ml/min).

Figure 3.21 Enantioseparation of 2-(benzylsulfinyl)benzamide on 23aa using 2-propanol as an eluent. Column 25 x 0.46 (i.d.) cm flow rate 0.5 ml/min. (Reprinted with permission from Ref. 165. Copyright 2000 by the Chemical Society of Japan.)...

Direct and indirect chromatographic methods were developed and compared in systematic examinations for the enantioseparation of P-amino acids direct separation of underivatized analytes involved the use of commercially available Crownpak CR(-I-), teicoplanin, and ristocetin A CSPs [148], while indirect separation was based on precolumn derivatization with 2,3,4,6-tetra-G-acetyl-f)-D-glucopyranosyl isothiocyanate (GITC) or A - a-(2,4-dinitro-5-fluorophenyl)-L-alaninamide (EDAA, Marfey s reagent), with subsequent separation on a nonenantioselective column. 

Berkecz, R. et al., LC enantioseparation of -lactam and P-amino acid stereoisomers and a comparison of macrocyclic glycopeptide and P-cyclodextrin-based columns, Chromatographia, 63, S37, 2006. 

Peter, A. et al.. Comparison of column performances in direct high performance hquid chromatographic enantioseparation of 1- or 3-methyl-substituted tetrahy-droisoquinohne analogs. Application of direct and indirect methods, Biomed. Chromatogr, 19, 459, 2005. 

Enantioselective separation by supercritical fluid chromatography (SFC) has been a field of great progress since the first demonstration of a chiral separation by SFC in the 1980s. The unique properties of supercritical fluids make packed column SFC the most favorable choice for fast enantiomeric separation among all of the separation techniques. In this chapter, the effect of chiral stationary phases, modifiers, and additives on enantioseparation are discussed in terms of speed and resolution in SFC. Fundamental considerations and thermodynamic aspects are also presented. 

Chiral SFC can be performed in open tubular [41,42], and packed column [43,44] modes. Packed column SFC can be further categorized into analytical, semipreparative, and preparative SFC [7, 8], Packed column SFC is more suitable for fast separations than open tubular column SFC, since a packed column generally provides low mass transfer resistance and high selectivity [45, 46], Packed column SFC also provides high sample loading capacity [27,47], which can increase sensitivity. Only packed column SFC is suitable for preparative-scale enantioseparation. This chapter will focus on chiral separation using packed column SFC in the analytical scale. 

Note that not all enantioseparations in SFC are better than in HPLC [34], Bernal et al. [62] described the enantiomeric separation of several pharmaceutical-related compounds on a polysaccharide-based column using HPLC and SFC. They showed that most of the separations obtained by SFC are better, in terms of resolution and analysis time, than the separations obtained by HPLC. However, one compound could not be resolved using SFC, but LC provided baseline resolution. 

The use of polysaccharide-based CSPs instead of protein-based CSPs often increases the peak efficiency and facilifafes faster separafions. Papini ef al. [159] recently developed a method for the enantioseparation of lorazepam and on a Chiralpak OD-R column and an enzymatic hydrolysis was used to determine the amount of the glucoronide metabolite of lorazepam present. The separation was performed in 7 min with an LOQ of 1 and 10 ng/mL for lorazepam in plasma and urine, respectively. Another relatively fast separation for chiral analysis was published by Lausecker and Eischer [188]. They developed a method for determination of the drug candidate R483 within... 

The progress toward enantiomerically pnre drngs makes the selective and rapid analysis of enantiomers an important issue, both for chiral parity determinations and for enantioselective bioanalysis. Chankvetadze et al. [198] performed enantioseparations within an analysis time of 1 min for each of two chiral compounds (1,2,2,2-tetraphenylethanol and 2,2 -dihydroxy-6,6 -dimethylbiphenyl) by nsing a homemade capillary column containing monolithic silica modified with amylose tris(3,5-dimethylphenylcarbamate) (Figure 17.10). 

The analysis time for chiral HPLC separations will probably remain relatively long until CSPs with higher efficiency than the present ones become available. But monolithic columns, columns with a smaller particle size (i.e., UPLC ), and miniaturized systems would increase the efficiency and speed up the enantioseparation of existing types of CSPs. 

Figure 10c. Enantioseparation of chlortalidon on a ChiraSpher column. Reprinted with permission from ref 93.

Figure 16. Enantioseparation of representative examples on a 150 x 4 mm i.d. column packed with CSPI. Reprinted with permission from ref 110b.

In the topologically chiral catenane 79 the succession of amide and sulfonamide units defines sequence information for each macrocycle (Figure 47). Consequently one wheel gives an orientation to space and the other defines the configuration [60 b], Remarkably, the enantioseparation performed by Okamoto and Vogtle et al. by HPLC on chiral column materials resulted in baseline separation with a very large separation factor a = 6.95 [61, 62],... 

Karlsson and Hermansson [30] used chemometrics for optimization of chiral separation of omeprazole and one of its metabolites on immobilized al-acid glycoprotein. Plasma was centrifuged at 2500 rpm and a portion (20-50 ji ) was injected into a 5-/rm Chiral-AGP column (10 cm x 4 mm) with al-acid glycoprotein immobilized to silica as a chiral stationary phase and acetonitrile-phosphate buffer of pH 5.7-7.2 as mobile phase (1 ml/min). Detection of omeprazole and its main metabolite, hydroxy-lated omeprazole, was performed at 302 nm. A statistical model was developed for the optimization of the operational parameters. The experimental data were evaluated with multivariate analyses column temperature and acetonitrile concentration were the most important variables for the enantioseparations. Complete enantiomeric separation for omeprazole and hydoxylated omeprazole was obtained within 15 min. 

Cass et al. [66] used a polysaccharide-based column on multimodal elution for the separation of the enantiomers of omeprazole in human plasma. Amylose tris (3,5-dimethylphenylcarbamate) coated onto APS-Hypersil (5 /im particle size and 120 A pore size) was used under normal, reversed-phase, and polar-organic conditions for the enantioseparation of six racemates of different classes. The chiral stationary phase was not altered when going from one mobile phase to another. All compounds were enantioresolved within the elution modes with excellent selectivity factor. The separation of the enantiomers of omeprazole in human plasma in the polar-organic mode of elution is described. 

Cass et al. [71] described a direct injection HPLC method, with column-switching, for the determination of omeprazole enantiomers in human plasma. A restricted access media of bovine serum albumin octyl column has been used in the first dimension for separation of the analyte from the biological matrix. The omeprazole enantiomers were eluted from the restricted access media column onto an amylose tris (3,5-dimethylphenylcarbamate) chiral column by the use of a columnswitching valve and the enantioseparation was performed using acetonitrile-water (60 40) as eluent. The analytes were detected by their UV absorbance at 302 nm. The validated method was applied to the analysis of the plasma samples obtained from 10 Brazilian volunteers who received a 40-mg oral dose of racemic omeprazole and was able to quantify the enantiomers of omeprazole in the clinical samples analyzed. 

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