Separation enantiomeric

Enantioseparation is an important goal for separation scientists. The most common strategy to achieve enantioselectivity is to perform the separation on a chiral column using a chiral selector immobilized onto the chromatographic stationary phase. The two enantiomers are selectively retained based on their different adsorption 

The simultaneous presence of a chiral selector and a charged non-chiral IPR was studied successfully [129]. The presence of a non-chiral IPR dramatically improved the separation of oppositely charged compounds on a chiral column, probably because the IPR increased retention and hence interactions with the chiral packing, as in the speciation of selenium-containing amino acids, on a crown ether column 

Srijaranai, S. et al. Flow-injection in-line complexation for ion-pair reversed phase high performance liquid chromatography of some metal -(2-pyridylazo) resorcinol chelates. Talanta 2006, 68, 1720-1725. 

Morrison, J.M., and Goldhaber, M.B. Simultaneous determination of Cr(iii) and Cr(vi) using reversed-phased ion-pairing liquid chromatography with dynamic reaction cell inductively coupled plasma mass spectrometry. J. Anal. Atom. Spectrom. 2007, 22, 1051-1060. 

Helfrich, A. and Bettmer, J. Determination of phytic acid and its degradation products hy ion-pair chromatography (IPC) coupled to inductively coupled plasma-sector field-mass spectrometry (ICP-SF-MS). /. Anal. Atom. Spectrom. 2004, 19, 1330-1334. 

Since the host compound remaining after the distillation can be used again and again, the process is economically and ecologically favorable. 

Some enantiomeric separations based on the host-guest inclusion technique have already been described so far in reviews and books [1] and this chapter describes enantiomeric separations summarized from the viewpoint of achieving more green processes. 

Enantiomeric Separation of Hydrocarbons and Their Halogeno Derivatives 

Preparation of enantiomerically active hydrocarbons is difficult and only a few examples of the preparation of chiral hydrocarbons have been reported. For example, chiral 3-phenylcyclohexene has been derived from tartaric acid through eight synthetic steps. Enantiomeric separation by host-guest complexation with a chiral host is more fruitful for the preparation of chiral hydrocarbons. For example, when a solution of fR,Rh( )-t ws-4,5-bis(hydroxydiphenylmethyl)-l,4-dioxaspiro[4.4]-nonane (lb) [2] (3 g, 6.1 mmol) and rac-3-methylcyclohexene (2a) (0.58 g, 6.1 mmol) in ether (15 ml) was kept at room temperature for 12 h, a 2 1 inclusion complex of lb and 2a (2.5 g, 75%) was obtained as colorless prisms in the yield indicated. The crystals were purified by recrystallization from ether to give the inclusion complex (2.4 g, 71%), which upon heating in vacuo gave (-)-2a of 75% ee by distillation (0.19 g, 71%) [3]. By the same inclusion complexation, (-i-)-4-methyl- (2b) (33% ee, 55%), (-)-4-vinylcyclohexene (2c) (28% ee, 73%), (-)-bicyclo[4.3]-nonane-2,5-diene 

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Tran, C. D. Dotlich, M. Enantiomeric Separation of Beta-Blockers by High Performance Liquid Chromatography, ... 

As mentioned previously, cellulosic phases as well as amylosic phases have also been used extensively for enantiomeric separations more recently (89,90). Most of the work ia this area has been with various derivatives of the native carbohydrate. The enantioresolving abiUties of the derivatized cellulosic and amylosic phases are reported to be very dependent on the types of substituents on the aromatic moieties that are appended onto the native carbohydrate (91). Table 3 fists some of the cellulosic and amylosic derivatives that have been used. These columns are available through Chiral Technologies, Inc. and J. T. Baker, Inc. 

Fig. 13. Enantiomeric separations of monohalohydrocarbons on a 2,6-0-dipentyl-3-0-trifluoroacetyl-y-cyclodexttin coated capillary column (10 m, 0.25...

D. A. Armstrong, C. Chau-Dung and W. Yong Li, Relevance of enantiomeric separations in food and beverage analyses , 7. Agric. Food Chem. 38 1674-1677 (1990). 

K.-M. Chu, S.-M. Sliieh, S.-H. Wu and O. Y.-P. Hu, Enantiomeric separation of a cardiotonic agent pimobendan and its major active metabolite, UD-CG 212 BS, by coupled achiral-cliiral normal-phase high-performance liquid chromatography , 7. Chromatogr. Sci 30 171-176(1992). 

Recently, two examples of the separation of enantiomers using CCC have been published (Fig. 1-2). The complete enantiomeric separation of commercial d,l-kynurenine (2) with bovine serum albumin (BSA) as a chiral selector in an aqueous-aqueous polymer phase system was achieved within 3.5 h [128]. Moreover, the chiral resolution of 100 mg of an estrogen receptor partial agonist (7-DMO, 3) was performed using a sulfated (3-cyclodextrin [129, 130], while previous attempts with unsubstituted cyclodextrin were not successful [124]. The same authors described the partial resolution of a glucose-6-phosphatase inhibitor (4) with a Whelk-0 derivative as chiral selector (5) [129]. 

Method Development and Optimization of Enantiomeric Separations Using Macrocyclic Glycopeptide Chiral Stationary Phases... 

Enantiomeric separations have become increasingly important, especially in the pharmaceutical and agricultural industries as optical isomers often possess different biological properties. The analysis and preparation of a pure enantiomer usually involves its resolution from the antipode. Among all the chiral separation techniques, HPLC has proven to be the most convenient, reproducible and widely applicable method. Most of the HPLC methods employ a chiral selector as the chiral stationary phase (CSP). 

Fig. 2-4. The enantiomeric separation of a-hydroxy/halogen acids on ristocetin A CSP (250 x 4.6 mm) with the same mobile phase composition methanol with 0.02 % acetic acid and 0.01 % triethylamine (v/v). The flow rate was 1.0 mL min at ambient temperature (23 °C).

Effect of Flow Rate and Temperature on Enantiomeric Separations... 

Optimization of Enantiomeric Separations in the New Polar Organic Mode... 

If the end-users of these tools have different objectives and requirements depending on the field of their activity, they do have in common the same issue which CSP and working conditions should be selected for the enantiomeric separation of a given pair of enantiomers ... 

In supported liquid membranes, a chiral liquid is immobilized in the pores of a membrane by capillary and interfacial tension forces. The immobilized film can keep apart two miscible liquids that do not wet the porous membrane. Vaidya et al. [10] reported the effects of membrane type (structure and wettability) on the stability of solvents in the pores of the membrane. Examples of chiral separation by a supported liquid membrane are extraction of chiral ammonium cations by a supported (micro-porous polypropylene film) membrane [11] and the enantiomeric separation of propranolol (2) and bupranolol (3) by a nitrate membrane with a A/ -hexadecyl-L-hydroxy proline carrier [12]. 

Fig. 11-1. Effect of the addition of methanol on the enantiomeric separation of terbutaline using 2 % sulfated cyclodextrin in 25 mM phosphate buffer (pH 3).

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