Chromatographic evaluation of structure selective and enantioselective retention of amines and acids on cellobiohydrolase I wild type and its mutant D214N

The mechanisms of structure selective and enantioselective retentions of amines and acids on two chiral stationary phases based on wild type cellobiohydrolase I (CBH I) and its mutant D214N have been investigated. All the amino alcohols tested had an enantioselective site that overlaps with the catalytically active site of CBH I, whereas the enantioselectivity of prilocaine was not affected by the mutation. The hydroxyl group of the amino alcohols did not seem to be an important contributor to the total binding strength whereas a bromo substituent in the aromatic ring promotes a high enantioselectivity (alpha=7.05). Interestingly, the chiral recognition site of the acid warfarin overlaps with the binding site of the amino alcohols. Di-p-toluoyltartaric acid and dibenzoyltartaric acid were strongly retained probably due to electrostatic attraction, but no enantioselectivity was observed. The difference in retention characteristics for the amino alcohols on the two stationary phases was strongly pH-dependent. A change in elution order of different amino alcohols occurred when changing the pH from 5.0 to 7.0. The difference between the two phases was lower at low pH. The retention times could also be affected by ionic strength and by use of cellobiose as a mobile phase additive but no indication of ion-pair retention of the amines was observed, when adding hexanesulphonate as counter ion to the mobile phase. The temperature dependence of the retention of the enantiomers of propranolol at pH 7.0 on the mutant D214N was similar to what was earlier observed on the wild type CBH I at lower pH.

Protection of metabolic and exercise capacity in unselected weight-losing cancer patients following treatment with recombinant erythropoietin: a randomized prospective study

This study was aimed at evaluating whether anemia could be prevented in unselected weight-losing cancer patients on anti-inflammatory treatment by early and prophylactic treatment with recombinant human erythropoietin (rhEPO) and whether such a benefit could be translated into improved physical function and metabolic efficiency. One hundred eight cancer patients who experienced progressive cachexia due to solid, mainly gastrointestinal tumors were randomized to receive twice daily a cyclo-oxygenase inhibitor (controls; indomethacin, 50 mg twice a day) or indomethacin and erythropoietin, provided on individual basis to prevent development of progressive anemia (study patients; indomethacin, 50 mg twice a day plus rhEPO; range, 12,000-30,000 units per week). All patients were treated and followed up until death or to preterminal stage. Biochemical tests (blood, liver, kidney, and thyroid), nutritional state assessment (food intake and body composition), and exercise testing with simultaneous measurements of respiratory gas exchanges before and during exercise were performed before institution of treatments and then at regular intervals during the treatment period (2-30 months after start). Study and control patients did not differ in survival. rhEPO prevented development of anemia during the entire observation period. This was associated with a significantly more preserved maximum exercise capacity in study patients compared to control patients during the follow-up period (101 +/- 10 versus 66 +/- 6 W; P < 0.0001), based on more effective ventilation and whole-body respiratory gas exchanges. These improvements were also evident when exercise performance was normalized to lean body mass, an indirect measure of the skeletal muscle mass. The metabolic efficiency, expressed as oxygen uptake per watt produced, was also significantly preserved in rhEPO-treated patients compared to controls (14.1 +/- 1.1 versus 16.3 +/- 0.9 ml O2/W, P < 0.05). Our results demonstrate that institution of early and prophylactic rhEPO treatment to patients with progressive cancer prevents development of tumor-induced anemia. This achievement was associated with a better preserved exercise capacity, which is explained in part by improved whole-body metabolic and energy efficiency during work load.

Enantioresolution of disopyramide by capillary affinity electrokinetic chromatography with human alpha1-acid glycoprotein (AGP) as chiral selector applying a partial filling technique

A method using alpha1-acid glycoprotein (AGP) as chiral selector for disopyramide by means of affinity electrokinetic chromatography has been developed. In order to avoid UV absorbance interferences, less than the effective length of the capillary was filled with the chiral selector. The electrophoretic conditions were chosen to give opposite migration directions for the chiral selector and the analyte; AGP migrated away from the detector. Enantiomers of disopyramide were separated on a methylcellulose-coated capillary with 20 cm length to the detector. The enantioresolution of the solute was affected by the concentration of the chiral selector, the plug length of the selector in the capillary, and the applied voltage. Resolution factors and migration times decreased with reduction of the plug length, while the efficiency of the separation system and peak performance were improved by decreasing the separation zone. A special feature of the technique is an enhanced selectivity due to increasing separation of the enantiomers when the fastest has migrated from the selector zone, while the second one still is retained. Equations relating selectivity and resolution with the difference in effective plug lengths between the two enantiomers are developed. Optimized conditions yielding complete resolution, requiring an 0.75 mM AGP plug of only 4.5 cm effective length, also gave high efficiencies (about 400,000 plates/m) for both enantiomer peaks.

Diversity and distribution of subterranean bacteria in groundwater at Oklo in Gabon, Africa, as determined by 16S rRNA gene sequencing

This paper describes how ground water was sampled, DNA extracted, amplified and cloned and how information available in the ribosomal 16S rRNA gene was used for mapping diversity and distribution of subterranean bacteria in groundwater at the Bangombé site in the Oklo region. The results showed that this site was inhabited by a diversified population of bacteria. Each borehole was dominated by species that did not dominate in any of the other boreholes; a result that probably reflects documented differences in the geochemical environment. Two of the sequences obtained were identified at genus level to represent Acinetobacter and Zoogloea, but most of the 44 sequences found were only distantly related to species in the DNA database. The deepest borehole, BAX01 (105 m), had the highest number of bacteria and also total organic carbon (TOC). This borehole harboured only Proteobacteria beta group sequences while sequences related to Proteobacteria beta, gamma and delta groups and Gram-positive bacteria were found in the other four boreholes. Two of the boreholes, BAX02 (34 m) and BAX04 (10 m) had many 16S rRNA gene sequences in common and also had similar counts of bacteria, content of TOC, pH and equal conductivity, suggesting a hydraulic connection between them.

Enantiomeric separation of basic drugs using N-benzyloxycarbonylglyclyl-L-proline as counter ion in methanol

Direct separation of enantiomeric amines using mainly N-benzyloxycarbonylglycyl-L-proline (L-ZGP) but also N-benzyloxycarbonylglyclglcyl-L-proline (L-ZGGP) as the chiral counter ion in methanol is described. The solid phase was Hypercarb porous graphitic carbon. Several amines of pharmacological interest (e.g., alprenolol, sotalol, terbutaline, promethazine and trimipramine) were separated with high enantioselectivity (alpha = 1.16-1.98) using L-ZGP and L-ZGGP as chiral selectors. In accordance with ion-pair chromatography, the retention of the enantiomeric amines was found to increase with increasing concentration of the anionic form of L-ZGP. Addition of a base (sodium hydroxide or an alkylamine) in excess of L-ZGP gave rise to a decrease in retention and enantioselectivity. The enantioselective retention was also affected by adding 2-propanol or acetonitrile to the mobile phase.

Enantioselective high-performance liquid chromatographic determination of (SR)- and (RS)-mefloquine in plasma using N-benzyloxycarbonyl-glycyl-L-proline as chiral counter ion

A stereoselective HPLC method is described for the determination of (SR)- and (RS)-mefloquine in plasma. The direct chiral separation is carried out on a Hypercarb-S column (porous graphitised carbon) with N-benzyloxycarbonyl-glycyl-L-proline (L-ZGP) as a chiral counter-ion in a reversed-phase system. The sample work-up included protein precipitation by addition of zinc sulphate and acetonitrile followed by liquid-liquid extraction with methyl-tert.-butyl ether. After evaporation of the organic phase, the residue is dissolved in the mobile phase and injected onto the column. Analyses of the enantiomers in plasma after a single oral dose of mefloquine indicates that the pharmacokinetics of the two enantiomers are different. The method is validated by determining the absolute recovery, linearity, accuracy, precision and inter- and intra-assay variation.

Separation of (R)- and (S)-naproxen using micellar chromatography and an alpha 1-acid-glycoprotein column: application for chiral monitoring in human liver microsomes by coupled-column chromatography

A column-switching system for fast determination of (R)- and (S)-naproxen in liver microsomes has been developed. The centrifuged sample was injected directly onto a pre-column with octadecylcoated silica. The retained analytes were then directed to an alpha 1-AGP column using a mobile phase composed of phosphate buffer (pH 6.5), dimethylocytylamine (30 mM) and the nonionic surfactant, Tween 20 (40 g/l). The method gave high absolute recoveries and good repeatabilities: 99.6% (1.7% relative standard deviation) and 94.9% (2.4% R.S.D.) for the (R)- and (S)-naproxen, respectively. The use of a surfactant in combination with an aliphatic amine in the mobile phase involves reduced retention times with retained enantioselectivity. Furthermore, the presence of the surfactant makes it possible to inject biological samples directly into the chromatographic system.

(R)- and (S)-5-hydroxy-2-(dipropylamino)tetralin (5-OH DPAT): assessment of optical purities and dopaminergic activities

Racemic 5-hydroxy-2-(dipropylamino)tetralin (5-OH DPAT), a potent and selective dopamine (DA) D2-receptor agonist, was resolved into the enantiomers by a new method. The enantiomers of 5-OH DPAT were determined by chiral ion-pair chromatography using N-benzyloxycarbonylglycyl-L-proline as the counter ion. The enantiomeric purity of (R)-5-OH DPAT was found to be greater than 99.7%. The ability of the enantiomers to change the rat brain DOPA levels was evaluated in vivo. The results indicate that (R)-5-OH DPAT is a weakly potent DA D2-receptor antagonist.

Determination of (R)- and (S)-propranolol in plasma by high-performance liquid chromatography using N-benzoxycarbonylglycyl-L-proline as chiral selector in the mobile phase

A normal-phase chromatographic method for the determination of (R)- and (S)-propranolol in plasma is described. The chiral separation is performed by adding an optically active complexing agent, N-benzoxycarbonylglycyl-L-proline, to the mobile phase (dichloromethane). The solid phase is LiChrosorb DIOL. After adjustment of the pH of the plasma, the propranolol enantiomers are extracted into hexane-dichloromethane-n-butanol (72:18:10). The organic phase is evaporated and the residue dissolved in the mobile phase before injection on to the column. Quantifications are performed by using internal standardization, giving a precision of better than 2% (coefficient of variation). The method employs 1-ml plasma samples and has linear calibration graphs (r = 0.999) over the concentration range studied, 9.2-288 nmol/l. injections of sample solutions with a composition different from that of the mobile phase gave system peaks that might affect the shape of the solute peaks. Several possibilities for avoiding these disturbing system peaks in the chromatogram by changing the mobile phase composition are discussed.

Determination of binding affinity of enantiomers to albumin by liquid chromatography

The principles of the determination of the binding affinity constants of small molecules to albumin by liquid chromatography, using albumin as a mobile phase additive, are outlined. Chromatographic conditions for determinations of constants are presented and applied to enantiomers of tryptophan and omeprazole. The influence of albumin on the retaining properties of LiChrosorb RP-8, Phenyl Hypersil and LiChrosorb Diol was studied.

Separation of enantiomeric acids using immobilized acetylquinine as a chiral stationary phase

Acetylquinine chemically bonded to silica was used as a chiral selector in reversed-phase chromatography for the separation of enantiomers of carboxylic acids and amino acid derivatives, e.g., 2-(4-bromophenoxy)propionic acid, warfarin and N-benzoxycarbonylphenylalanine. An organic modifier (methanol) could be used to regulate the retention without significant influence on the stereoselectivity.

Chromatographic resolution of enantiomers using albumin as complexing agent in the mobile phase

Enantiomers of carboxylic acids have been separated with albumin as a chiral complexing agent in the mobile phase. Stereoselective separation has been obtained for different types of acids, in some cases with very high separation factor, as shown for di-p-toluoyltartaric acid (alpha(s) = 5.8). The stereoselectivity and retention properties depend on pH and on the concentration of albumin in the mobile phase. Retention can also be regulated by modifying the nature of the solid phase as well as by the use of additives in the mobile phase. Acids with low molar absorptivity, or with absorbance in the same wavelength range as albumin, can be detected by an indirect technique based on the use of a cationic mobile phase additive, such as 1-ethylquinolinium, which has high UV-absorptivity at a wavelength remote from that of albumin.