Chiral separation of atropine by high-performance liquid chromatography

Human Plasma Butyrylcholinesterase Hydrolyzes Atropine: Kinetic and Molecular Modeling Studies

The participation of butyrylcholinesterase (BChE) in the degradation of atropine has been recurrently addressed for more than 70 years. However, no conclusive answer has been provided for the human enzyme so far. In the present work, a steady-state kinetic analysis performed by spectrophotometry showed that highly purified human plasma BChE tetramer slowly hydrolyzes atropine at pH 7.0 and 25 °C. The affinity of atropine for the enzyme is weak, and the observed kinetic rates versus the atropine concentration was of the first order: the maximum atropine concentration in essays was much less than Km. Thus, the bimolecular rate constant was found to be kcat/Km = 7.7 × 104 M-1 min-1. Rough estimates of catalytic parameters provided slow kcat < 40 min-1 and high Km = 0.3-3.3 mM. Then, using a specific organophosphoryl agent, echothiophate, the time-dependent irreversible inhibition profiles of BChE for hydrolysis of atropine and the standard substrate butyrylthiocholine (BTC) were investigated. This established that both substrates are hydrolyzed at the same site, i.e., S198, as for all substrates of this enzyme. Lastly, molecular docking provided evidence that both atropine isomers bind to the active center of BChE. However, free energy perturbations yielded by the Bennett Acceptance Ratio method suggest that the L-atropine isomer is the most reactive enantiomer. In conclusion, the results provided evidence that plasma BChE slowly hydrolyzes atropine but should have no significant role in its metabolism under current conditions of medical use and even under administration of the highest possible doses of this antimuscarinic drug.

Alkaloids in food: a review of toxicity, analytical methods, occurrence and risk assessments

Alkaloids have been utilized by humans for years. They have diverse applications in pharmaceuticals. They have been proven to be effective in treating a number of diseases. They also form an important part of regular human diets, as they are present in food items, food supplements, diet ingredients and food contaminants. Despite their obvious importance, these alkaloids are toxic to humans. Their toxicity is dependent on a range of factors, such as specific dosage, exposure time and individual properties. Mild toxic effects include nausea, itching and vomiting while chronic effects include paralysis, teratogenicity and death. This review summarizes the published studies on the toxicity, analytical methods, occurrence and risk assessments of six major alkaloid groups that are present in food, namely, ergot, glycoalkaloids, purine, pyrrolizidine, quinolizidine and tropane alkaloids.

A validated LC-MS/MS method for the determination of L-hyoscyamine in human plasma: Application in clinical study

Atropine is a racemic mixture of D- and L-hyoscyamine, while L-hyoscyamine is the only effective ingredient. In this study, a new sensitive, stable, and selective LC/MS assay was developed for determination of L-hyoscyamine and applied to the clinical study. The parent-product (m/z) transition pair of L-hyoscyamine was 290.1→124.1. Chromatographic separations were performed using a Chiral MZ column (250 mm×4.6 mm, 5.0 μm) by a stepwise gradient elution mode with n-hexane, isopropanol and diethylamine as mobile phases. L-hyoscyamine in human plasma were extracted using liquid-liquid extraction process. This assay displayed a good linearity over a concentration range of 20.0-400 pg/mL for L-hyoscyamine. The accuracy of the validation assay for L-hyoscyamine ranged from -2.7% to 4.5%, and the precision were within 6.3% coefficient of variation. L-hyoscyamine in human plasma were stable at different storage conditions. The method has been successfully applied to plasma samples obtained from a safety study in human.

Complexation of tropane alkaloids by cyclodextrins

Complexes of atropine, homatropine, scopolamine, and ipratropium with cyclodextrins were investigated by NMR and capillary electrophoresis. It has been demonstrated that tropane alkaloids form complexes with β- and γ-cyclodextrins of 1:1 stoichiometry. NMR measurements indicate the formation of complexes where both aliphatic and aromatic parts of tropane alkaloids interact with β-cyclodextrin. The stability constants of the investigated alkaloids with β- and γ-cyclodextrins were determined by capillary electrophoresis. It has been found that β-cyclodextrin forms ten times more stable complexes than γ-cyclodextrin. Moreover, the analysis of the obtained crystal structure of β-cyclodextrin/(-)-hyoscyamine complex reveals that two molecules of (-)-hyoscyamine oriented in head-to-tail mode are tightly fitted inside head-to-head β-cyclodextrin dimer. Conformation of (-)-hyoscyamine as well as scopolamine changes substantially upon complexation adapting to the cavity of β-cyclodextrin as shown by X-ray analysis, NMR and DFT calculations data.

High performance affinity chromatography and related separation methods for the analysis of biological and pharmaceutical agents

The last few decades have witnessed the development of many high-performance separation methods that use biologically related binding agents. The combination of HPLC with these binding agents results in a technique known as high performance affinity chromatography (HPAC). This review will discuss the general principles of HPAC and related techniques, with an emphasis on their use for the analysis of biological compounds and pharmaceutical agents. Various types of binding agents for these methods will be considered, including antibodies, immunoglobulin-binding proteins, aptamers, enzymes, lectins, transport proteins, lipids, and carbohydrates. Formats that will be discussed for these methods range from the direct detection of an analyte to indirect detection based on chromatographic immunoassays, as well as schemes based on analyte extraction or depletion, post-column detection, and multi-column systems. The use of biological agents in HPLC for chiral separations will also be considered, along with the use of HPAC as a tool to screen or study biological interactions. Various examples will be presented to illustrate these approaches and their applications in fields such as biochemistry, clinical chemistry, and pharmaceutical research.

Chromatographic Studies of Protein-Based Chiral Separations

The development of separation methods for the analysis and resolution of chiral drugs and solutes has been an area of ongoing interest in pharmaceutical research. The use of proteins as chiral binding agents in high-performance liquid chromatography (HPLC) has been an approach that has received particular attention in such work. This report provides an overview of proteins that have been used as binding agents to create chiral stationary phases (CSPs) and in the use of chromatographic methods to study these materials and protein-based chiral separations. The supports and methods that have been employed to prepare protein-based CSPs will also be discussed and compared. Specific types of CSPs that are considered include those that employ serum transport proteins (e.g., human serum albumin, bovine serum albumin, and alpha1-acid glycoprotein), enzymes (e.g., penicillin G acylase, cellobiohydrolases, and α-chymotrypsin) or other types of proteins (e.g., ovomucoid, antibodies, and avidin or streptavidin). The properties and applications for each type of protein and CSP will also be discussed in terms of their use in chromatography and chiral separations.

Enantiomeric differentiation of atropine/hyoscyamine by (13) C NMR spectroscopy and its application to Datura stramonium extract

INTRODUCTION

The two enantiomers of hyoscyamine, an alkaloid found in many plant species, have distinct pharmacological and biological properties. Methods for the discrimination of both enantiomers are almost exclusively based on chiral HPLC/UV. Determination of the enantiomeric ratio (e.r.) of hyoscyamine is a challenging problem since this compound tends to racaemise, forming atropine during acid-base extraction.

OBJECTIVE

To develop a protocol for the calculation of enantiomeric ratio of hyoscyamine in a plant extract using a (13) C NMR method.

METHODOLOGY

Samples were prepared by extraction of dried Datura stramonium seeds. Observation of C12 and C15 NMR signals of hyoscyamine in the presence of one equivalent of TFA and sub-stoichiometric amount of Yb(hfc)(3) allowed the calculation of the e.r. of S-(-) and R-(+)-hyoscyamine.The method was optimised with various mixtures of (+) and (-)-hyoscyamine ranging from 50:50 (racaemic mixture, i.e. atropine) to 98.5:1.5. The e.r. measured by NMR on the signals of aromatic C12 and C15 were in agreement with the gravimetrically prepared samples. The method was then applied to an extract of Datura stramonium and S-(-)-hyoscyamine was the unique enantiomer.

CONCLUSION

The study showed that the e.r. determination of atropine/hyoscyamine was achieved with a routine NMR spectrometer, using CLSR/TFA on pure compounds as well as on the crude extract of Datura stramonium.

High performance liquid chromatography–tandem mass spectrometry (HPLC/MS/MS) assay for chiral separation of lactic acid enantiomers in urine using a teicoplanin based stationary phase

A novel method for the separation and simultaneous determination of urinary D- and L-lactic acid enantiomers by high performance liquid chromatography-tandem mass spectrometry (HPLC/MS/MS) is presented. The chiral separation was optimized on a Chirobiotic teicoplanin aglyocone (TAG) column. Most interestingly, the addition of water in small volume fraction to the polar organic mobile phase was found to significantly improve the chromatography. Calibration curves were linear (r2>0.9950) over the range 3-1000 mg/L for L-lactic acid and 0.5-160.8 mg/L for D-lactic acid. The limit of detection (LOD) (S/N=3) and limit of quantification (LOQ) (S/N=10) were determined experimentally (n=3) to be 0.2 and 0.5mg/L for L-lactic acid and 0.4 and 1.3 mg/L for D-lactic acid, respectively. The normal patient range of L-lactic acid was 1-20 microg/mg creatinine with an elevated value of 85 microg/mg creatinine. For D-lactic acid, the range of normal values were between 0 and 5 microg/mg creatinine with an elevated value of 40 microg/mg creatinine. Finally, the validated method allows for rapid analysis with a total run time of 7.5 min.