Chiral metal-ion complexes for enantioseparation by capillary electrophoresis and capillary electrochromatography: a selective review.

This review gives an overview about chiral separation by capillary electrophoresis and capillary electrochromatography using different chiral metal-ion complexes. The topic enantioseparation is still of big interest for chiral drugs and natural compounds. Regarding chiral drugs it is often the case that the enantiomers differ in activity. The chiral separation principle of ligand-exchange (LE) can be enabled for liquid chromatography, capillary electrophoresis as well as for capillary electrochromatography. Ligand-exchange can be applied particularly for chiral amino acids, amino alcohols or α-hydroxy acids. Examples and applications are given along with the latest developments.

Chiral separation of beta-methyl-amino acids by ligand exchange using capillary electrophoresis and HPLC.

This paper deals with the chiral separation of optical isomers of beta-methyl-amino acids by CE and HPLC using the principle of ligand-exchange. Capillary zone electrophoresis was carried out using Cu(II) complexes of L-4-hydroxyproline (L-4-Hypro), N-(2-hydroxypropyl)-L-4-hydroxyproline (HP-L-4-Hypro) and N-(2-hydroxyoctyl)-L-4-hydroxyproline (HO-L-4-Hypro) as chiral selectors, added to the electrolyte. The HPLC separations were performed on a chiral stationary ligand-exchange chromatography phase containing L-4-Hypro chemically bonded to silica gel. With both techniques nearly all compounds investigated are baseline resolved using different background electrolytes and mobile phases, respectively.

Chiral separation of pharmacologically active dihydropyrimidinones with carboxymethyl-beta-cyclodextrin.

We report on the chiral separation of pharmacologically active dihydropyrimidinones by capillary electrophoresis (CE) using carboxymethyl-beta-cyclodextrin as chiral selector. The influence of selector concentration, pH, and the addition of varying amounts of methanol is investigated. Out of 21 compounds investigated, 19 were resolved, 13 with baseline separation.

Enantioseparation of hydroxy acids on easy-to-prepare continuous beds for capillary electrochromatography.

This paper deals with the enantioseparation of hydroxy acids by ligand-exchange capillary electrochromatography. A chiral continuous bed was easily prepared by in situ polymerization of monomers, including an L-4-hydroxyproline derivative. This phase showed chiral recognition for several hydroxy acids, in addition to amino acids.

Chiral ligand-exchange capillary electrophoresis.

This review summarizes the application of capillary electrophoresis and capillary electrochromatography for the chiral separation of various substance classes using the principle of ligand exchange. The application of this principle to various substance classes is reported.

Chiral separation by chromatographic and electromigration techniques. A review.

This review gives a survey of different chiral separation principles and their use in high-performance liquid chromatography (HPLC), gas chromatography (GC), supercritical fluid chromatography (SFC), thin-layer chromatography (TLC), capillary electrophoresis (CE) and capillary electrochromatography (CEC) highlighting new developments and innovative techniques. The mechanisms of the different separation principles are briefly discussed and some selected applications are shown.

A new easy-to-prepare homogeneous continuous electrochromatographic bed for enantiomer recognition.

Completely homogeneous polyacrylamide-based gels were used for capillary electrochromatography (CEC) of drug enantiomers. Like continuous beds (also called continuous polymer rods, silica rods, monoliths) they do not require frits to support the bed because it is covalently linked to the capillary wall. A long lifetime is an important feature of the beds. The gel matrices can be prepared in any laboratory and for specific interactions they can be derivatized with appropriate ligands. The application range is, therefore, broad. For chiral electrochromatography, negatively and positively charged polyacrylamide gels copolymerized with 2-hydroxy-3-allyloxy-propyl-beta-cyclodextrin (allyl-beta-CD) were prepared. The latter monomer was synthesized from beta-CD and allylglycidyl ether by a very simple one-step procedure. Eight acidic, neutral and basic drug compounds were resolved into their enantiomers, most of them with baseline separation. Interestingly, the resolution is independent of the electroendosmotic velocity, i.e., rapid analyses will not give low resolution. Upon increasing this velocity, the plate height for the fast enantiomer did not change (or decreased slightly), whereas that for the slow enantiomer increased. Only the last term in the van Deemter equation contributed significantly to the total plate height. The composition of the gel was chosen such that the "pores" became large enough to guarantee a satisfactory electroendosmotic flow (EOF). This open gel structure explains why acetone diffused as in free solution, i.e., independently of the presence of the gel matrix. This finding also indicates that the separation of small molecules in polyacrylamide gels cannot be explained by "molecular-sieving", but rather by some type of adsorption ("aromatic adsorption"?).

Chiral separation of amino acids by ligand-exchange capillary electrochromatography using continuous beds.

A chiral ligand-exchange phase for capillary electrochromatography based on continuous bed technology was developed. The chiral stationary phase is prepared by a one-step in situ copolymerization procedure using methacrylamide, piperazine diacrylamide, vinylsulfonic acid and N-(2-hydroxy-3-allyloxypropyl)-L-4-hydroxyproline. These chiral continuous beds are inexpensive and easy to prepare. They also have several advantages over silica-based packed capillaries. Since the bed is covalently attached to the capillary wall, no frit is required. The applicability of this new approach to the chiral separation of underivatized amino acids is demonstrated.

Application of ligand-exchange capillary electrophoresis to the chiral separation of alpha-hydroxy acids and beta-blockers.

The application of the principle of ligand-exchange capillary electrophoresis to two substance classes is described. As chiral selector N-(2-hydroxyoctyl)-L-4-hydroxyproline-copper(II) complex was used. This principle was applied to the chiral separation of alpha-hydroxy acids and drugs containing amino alcohol structure such as beta-blockers. The enantioselectivity was found to be strongly dependent on pH corresponding to the optimal conditions for complex formation for each structure class.

Triterpenoid saponins and sapogenin lactones from Albizia gummifera.

The structures of two new monodesmosidic and bisdesmosidic triterpenoid saponins (1 and 2) and the known compound delta 5-stigmasterol-3-O-beta-D-glucopyranoside (3) as well as two new oleanane type triterpene lactone glycosides 4, 5 and a new sapogenin lactone 6 isolated from the stem bark of Albizia gummifera C.A. Smith (Mimosaceae) have been elucidated as 3-O-¿beta-D-glucopyranosyl(1-->2)-[alpha-L-arabinopyranosyl(1-->6) ]-beta-D- glucopyranosyl¿-oleanolic acid (1), beta-D-glucopyranosyl(1-->2)-beta-D-glucopyranosyl 3-O-¿beta-D-glucopyra-nosyl(1-->2)-[alpha-L-arabinopyrano syl(1-->6)]-beta-D- glucopyranosyl¿-oleanolate (2), 3 beta-¿O-D-glucopyranosyl-(1-->2)-[O-alpha-L-arabinopyranosyl(1-->6 )] beta-D-glucopyranosyloxy¿-machaerinic acid gamma-lactone (4), 3 beta-O-beta-D-glucopyranosiduronic acid (1-->2)-beta-D-glucopyranosyloxy]-machaerinic acid gamma-lactone (5), and A-homo-3a-oxa-5 beta-olean-12-en-3-one-28-oic acid (6), respectively. The complete assignment of the 1H and 13C resonances of 1, 2, 4 and 6 and of the peracetate of 5 were achieved by means of 2D-NMR studies.

Chiral separation by capillary electrochromatography.

The state of art in chiral capillary electrochromatography is reviewed. Chiral separations by capillary electrochromatography were carried out using capillaries packed with chiral stationary phases or achiral stationary phases in combination with a chiral selector added to the mobile phase. Furthermore, the use of open tubular capillaries containing the chiral selector coated to the capillary wall was also reported. Among other separation principles moleculary imprinted polymers represent a challenging approach for chiral capillary electrochromatography. A recent trend is the use of polymeric continuous beds with a chiral selector incorporated.

Recent progress in chiral separation principles in capillary electrophoresis.

This review summarizes recent developments in the field of chiral separations by electromigration techniques including capillary zone electrophoresis (CZE), capillary gel electrophoresis (CGE), isotachophoresis (ITP), electrokinetic chromatography (EKC), and capillary electrochromatography (CEC). This overview focuses on the development of new chiral selectors and the introduction of new techniques rather than applications of already established selectors and methods. The mechanisms of the different chiral separation principles are discussed.

Chiral separation of sympathomimetics by ligand exchange capillary electrophoresis.

A rapid and simple approach to the chiral separation of sympathomimetic drugs with amino alcohol structure by ligand exchange capillary electrophoresis is described. An N-(2-hydroxyoctyl)-L-4-hydroxyproline/copper(II) complex is used as chiral selector. Thirteen sympathomimetics were resolved, nine with baseline resolution. The influence of pH and composition of the electrolyte on resolution was investigated. The optimal pH for complexation of these amino alcohols was found to be 12.

Chiral separation of alpha-amino acids by ligand-exchange capillary electrophoresis using N-(2-hydroxy-octyl)-L-4-hydroxyproline as a selector.

The direct chiral resolution of underivatized alpha-amino acids by capillary zone electrophoresis (CZE) based on the principle of ligand exchange is described. An N-(2-hydroxyoctyl)-L-4-hydroxyproline/Cu(II) complex was used as a chiral selector. Besides amino acids containing aromatic residues, the basic amino acid histidine was resolved. Baseline separations were obtained for all amino acids investigated. The influence of selector concentration, electrolyte composition and pH on the resolution was investigated. It was found that there is a correlation between pI of the amino acids and the optimal pH.

Biocompatibility of heparin and low-molecular mass heparin in a new implantable medication pump.

The present paper deals with the evaluation of normal heparin and low-molecular mass heparin as to their use in a new implantable medication pump. Latest versions of different Pharmacopoeias recommend techniques, which require large sample volumes for aqueous injectable drug solutions. Therefore, a commercially available enzymatic kit was used to determine heparin activity. As this test is designed for heparin plasma levels, transformation of the chromophore occurred only after adding heparin AT III complex, which is usually present in plasma. The applied test was found to be suitable regarding reproducibility, selectivity and sensitivity. There was no loss of enzyme activity of both normal heparin and low-molecular mass heparin within an investigation period of 8 weeks; thus, no decomposition products are to be expected and the biocompatibility of pump materials with both tested heparin preparations is evident.

Stereoselective interaction of drug enantiomers with human serum transferrin in capillary zone electrophoresis (II).

Further studies on chiral resolution of drugs with different chemical structures by capillary zone electrophoresis using iron-free human serum transferrin are described. The substances passed a highly concentrated pseudo-stationary protein zone applied in a coated capillary and the possible chiral separation of the optical isomers was followed. Eighteen drugs with different structures were screened, and the enantiomers of clofedanol, buphenine, acebutolol and chlorphenamine were resolved. Several, but not all drugs, showed longer migration times while passing the protein zone, indicating an interaction with transferrin, although chiral resolution was not observed in all cases. The observations provided further information about the properties of the surface interaction sites of transferrin.

Chiral resolution of the dansyl derivative of 2-methyltaurine by capillary electrophoresis.

A cyclodextrin-modified micellar capillary electrophoretic method was developed for the chiral separation of 2-methyltaurine. The racemic mixture was separated after derivatization with dansyl chloride. The enantiomeric separation of the dansyl derivative was done using electrolyte solutions containing beta-cyclodextrin (beta-CD) or different ratios of beta- and gamma-CD. The mixture of beta- and gamma-CD optimally resolved the compound studied.

A water phantom controller for automated acquisition of linac beam parameters.

Three-dimensional water phantoms are routinely used when acquiring the data necessary to commission medical linear accelerators. A new water phantom controller has been developed at our institution that is unique in several aspects. The water phantom controller is based on an IBM XT compatible computer. This has been interfaced to an Artronix three-dimensional water phantom and a commercially available linac setup controller. Some of the unique features of the new controller are (i) its ability to perform three-dimensional coordinate transformations on the fly (this removes the need to level and align the water tank with the beam axes and greatly reduces setup time). (ii) Its ability to communicate with a device which can control the linac operating parameters (this allows the water phantom controller to adjust, for example, the jaw size of the accelerator as it acquires data). (iii) Its ability to output the acquired data in a number of modes, including screen display, hardcopy plot, or disk file that may be transferred to a central treatment planning computer). (iv) Its ability to digitally process the acquired data. This water phantom controller may be used to gather machine data in a highly automated manner, greatly reducing the time required to gather the desired data.

An accurate temperature controller for linear accelerators.

Linear accelerators use water cooling systems to ensure that certain components operate at specific temperatures. The water cooling system used on a Siemens Mevatron 77 has been found by us to be inadequate for our purposes for three major reasons. First, the controller is not able to regulate the machine temperature accurately when the beam is on for more than 10 min. Second, there is a high risk of failure at our site due to a high level of impurities in the utility water, and finally, changes in the temperature of the utility water necessitate adjustments to the temperature controller. A microprocessor-based temperature controller has been designed and built for use with a Mevatron 77. The three areas of concern mentioned have been eliminated by the use of the new controller.