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HPLC enantio-separation and chiral recognition mechanism of quinolones on Vancomycin CSP
Abstract
A new HPLC method was developed for the enantio-separation and chiral recognition mechanism of quinolones (lomefloxacine, ofloxacine, primaquine and quinacrine) on Vancomycin CSP. The column used was Chirabiotic V column (150 x 4.6 mm, 5.0 μm) with two mobile phases i.e. (I) MeOH:ACN:H2O:TEA (50:30:20:0.1%) and (II) MeOH:ACN: H2O:TEA (70:10:20:0.1%) at 1.0 mL/minute flow rate with various UV detection. The values of retention, separation and resolution factors in a solvent system I were ranged from 2.20 to 5.05, 1.70 to 1.96 and 1.75 to 2.20 while these values were 1.93 to 6.85, 1.62 & 2.01 and 2.30 & 2.40 in solvent system II. The limits of detection and quantification were ranged from 8.0 to 10.5 µg and 24.4 to 33.5 µg. The resolution was controlled mainly by π-π interactions along with other forces like hydrogen bonding, van der Waal’s forces, steric effects, etc. The determination of the chiral recognition mechanism may be beneficial to separate other racemates successfully. The method is fast precise and efficient and may be utilized to analyze enantiomers of the reported quinolones.
... Of course, the simulation study has played an important role in the reaction mechanism [24], chiral separation [25][26][27][28], isolation of the most active gradient from the plant [29], and biological chemistry [30][31][32][33][34], but this is the first time the computational method has been applied to know the quantum background of the molecular disease. For the study at the quantum level, the pdb file of deoxygenated hemoglobin S (βGlu6 → Val) with PDB Code 2hbs [35] was obtained from the protein data bank. ...
Sickle cell anemia disease has been a great challenge for the world in the present situation. It occurs only due to the polymerization of sickle hemoglobin (HbS) having Pro-Val-Glu (PVG) typed mutation, while the polymerization does not occur in normal hemoglobin (HbA) having Pro-Glu-Glu (PGG) residues. According to data from the literature, Val-beta6 of Pro-Val-Glu is hydrophobic in nature, which appears to fit into a hydrophobic pocket in the adjacent HbS. After the insertion of Pro-Val-Glu into a hydrophobic pocket on the adjacent HbS, the polymerization is started. This is a questionable point on how the replacement of glutamic acid with valine in HbS makes it more reactive to fit into a hydrophobic pocket on adjacent HbS for polymerization. No data from the literature on the reactivity of HbS for polymerization was found yet. This is the first time that the theoretical calculation was done in both HbA and HbS where they were structurally different. After that, a comparative study between PVG and PGG was done at quantum level for the evaluation of the reactivity to fit into a hydrophobic pocket on adjacent HbS. At a quantum level, it was found that the HOMO-LUMO gap of Pro-Val-Glu was lower than that of Pro-Glu-Glu. According to the data from the literature, the lesser HOMO-LUMO gap promotes the initiation of the polymerization reaction. On the basis of the results, it was also shown how the mutation point (Pro-Val-Glu) in HbS becomes more reactive to polymerization, whereas Pro-Glu-Glu in HbA does not. The computational method developed for the first time will be very helpful not only for molecular biologists but also for computational and medicinal chemists. Additionally, the required modifications based on gaps in anti-sickling drug development are also suggested in the presented article.
... Similar types of interactions were also found to control the chiral recognition of quinolones on a vancomycin-based CSP. In 2020, AlOthman et al. [178] demonstrated how chiral resolution occurs due to different stereospecific fittings of enantiomers on the stereospecific sites of vancomycin CSP, which is stabilized by various interactions. This effect was obvious when they studied quinolones that varied in the number of aromatic rings and H-bonding sites. ...
For decades now, the separation of chiral enantiomers of drugs has been gaining the interest and attention of researchers. In 1991, the first guidelines for development of chiral drugs were firstly released by the US-FDA. Since then, the development in chromatographic enantioseparation tools has been fast and variable, aiming at creating a suitable environment where the physically and chemically identical enantiomers can be separated. Among those tools, the immobilization of chiral selectors (CS) on different stationary phases and the chiral mobile phase additives (CMPA) which have been progressed and studied extensively. This review article highlights the major advances in immobilization of CS together with their different recognition mechanisms as well as CMPA as a cheaper and successful alternative for chiral stationary phases. Moreover, the role of molecular modelling tool as a pre-step in the choice of CS for evaluating possible interactions with different ligands has been pointed up. Illustrations of reported methods and updates for immobilized CS and CMPA have been included.
... These findings suggest that vancomycin-based CSPs can serve as a highly effective approach for the enantioseparation of quinolones using HPLC. [58] A recent study has developed a greener method for preparing chiral stationary phases (CSPs) based on macrocyclic antibiotics using a photosynthesis reaction instead of a chemical one. The method involves using vancomycin as a chiral selector (CS) with monodisperse silica support and diazoresin as a photosensitive agent. ...
Chiral separation techniques play a crucial role in the pharmaceutical industry, where the enantiomeric purity of drugs can have a significant impact on their efficacy and safety. Macrocyclic antibiotics are highly effective chiral selectors used in various chiral separation techniques, including LC, HPLC, SMB, and TLC, offering reproducible results and a wide range of applications. However, developing robust and efficient immobilization mechanisms for these chiral selectors remains a challenge. This review article focuses on various immobilization approaches, such as immobilization, coating, encapsulation, and photosynthesis, that have been applied to immobilize macrocyclic antibiotics on their support. Commercially available macrocyclic antibiotics for conventional liquid chromatography include Vancomycin, Norvancomycin, Eremomycin, Teicoplanin, Ristocetin A, Rifamycin, Avoparcin, Bacitracin, and others. In addition, capillary (nano) liquid chromatography has also been used in chiral separation utilizing Vancomycin, Polymyxin B, Daptomycin, and Colistin Sulfate. Macrocyclic antibiotic-based CSPs have been extensively applied due to their reproducible results, ease of use, and broad range of applications, capable of separating a large number of racemates.
... A class of drugs that has attracted many scientists involves chirality, due to which they exist in more than one enantiomeric form [6]. Chirality is found in those drugs which have at least one chiral center because of which they exist in more than one form. The most interesting point regarding chiral drugs is the different biological activities of different enantiomers of such drugs [7,8]. Hence, it becomes a great challenge for researchers to find the most biologically active enantiomer of a chiral drug. ...
Chiral metallic drugs are becoming the hottest point of discussion in the field of medicinal chemistry. As we know that more than 80% drugs are chiral in nature, and prescribed in the racemic form. The main problem with chiral drugs is the different biological activities of different enantiomers. This is because the human body has a chiral environment, as there is the presence of protein, carbohydrates, enzymes, and other chiral macromolecules. Hence, if a chiral anticancer drug is being prescribed to the patient in the racemic form, it means two or more drugs are being prescribed. Therefore, the chiral separation and analysis of chiral anticancer drugs are important for improving the quality of chiral drug medication. Many metal complexes are used as anticancer drugs, but the conditions become more critical if they have chirality or a chiral moiety, because of which they exist in two or more forms. Because of the presence of chirality or chiral moiety, the complex of metals is termed a chiral metallic complex. Of course, the enantioseparation of the chiral metallic complexes must be done before their prescription. Enantioseparation of the chiral metallic complex will not only provide a pharmaceutically active form to the patient but also reduce the side effects caused by the racemic mixture. Hence, the accessible article reviews the chiral metallic complexes having ruthenium, osmium, palladium, gold, silver, and platinum, etc. as central metal atoms. Besides, the future perspectives regarding the chiral metallic anticancer drugs and the role of their enantioseparation are also discussed.
... Ultimately, Agilent Poroshell Chiral-V allowed for optima separation of all three analytes as well as full enantiomeric separation of d,l-MPH, d,l-EPH and d,l-MPH-d10. The vancomycin glycopeptide within the Chiral-V column contains 18 chiral centers, 5 aromatic rings and 3 cavities in which the enantiomers can get trapped (by stereoselectivity) leading to separation [36]. This glycopeptide is suggested for use when performing reverse-phase LC separation of amines. ...
Drugs such as methylphenidate (MPH) are commonly prescribed for Attention-Deficit/Hyperactivity Disorder but may be abused recreationally. Erythro-MPH is associated with pharmacological effects and is present as dextro (d) or levo (l) configuration, with the d configuration being more potent. However, many medications are sold as a racemic mixture and thus analytic separation of isomers is essential. Additionally, enantiomeric separation can be used to potentially determine illegal production. MPH metabolizes into ritalinic acid (RA) as well as ethylphenidate (EPH) in the presence of ethanol. Chiral analysis poses challenges to researchers. Due to limited assays, this project aimed to develop a method that separates and quantifies the enantiomers of MPH and EPH as well as RA in blood. Methods such as this are critical to understanding the pharmacokinetics of chiral cognitive stimulants. This method uses solid phase extraction and analysis by liquid chromatography-tandem mass spectrometry (LC-MS/MS) and was fully validated. The linear range for MPH and EPH was 0.5-200 ng/mL and 0.5-500 ng/mL for RA. Limit of detection was 0.1 ng/mL (with the exception of RA with an LOD of 0.5 ng/mL) and the limit of quantification was 0.5 ng/mL, despite significant matrix effects. Extraction recovery was >79%. Bias was -4.8 to -12.7% and maximum within-run precision was ±12.5% for all analytes. The optimized and validated technique offers chiral separation of the threo-enantiomers of d,l-MPH, d,l-EPH and RA and quantification in blood utilizing LC-MS/MS.
... Therefore, various types of b-CD CSPs are widely prepared and used in chiral separations. Moreover, compared with vancomycin, 15 teicoplanin, 16 cellulose, 17 amylos 18 and polymer CSPs, 19 such multi-functional enantiomeric separation mode is also an important reason why b-CD CSPs have received widespread attention and application. ...
A bridged bis(β-cyclodextrin) ligand was firstly synthesized via a thiol-ene click chemistry reaction between allyl-ureido-β-cyclodextrin and 4-4'-thiobisthiophenol, which was then bonded onto a 5 μm spherical silica gel to obtain a novel bridged bis(β-cyclodextrin) chiral stationary phase (HTCDP). The structures of HTCDP and the bridged bis(β-cyclodextrin) ligand were characterized by the 1H nuclear magnetic resonance (1H NMR), solid state 13C nuclear magnetic resonance (13C NMR) spectra spectrum, scanning electron microscope, elemental analysis, mass spectrometry, infrared spectrometry and thermogravimetric analysis. The performance of HTCDP in enantioseparation was systematically examined by separating 21 chiral compounds, including 8 flavanones, 8 triazole pesticides and 5 other common chiral drugs (benzoin, praziquantel, 1-1'-bi-2-naphthol, Tröger's base and bicalutamide) in the reversed-phase chromatographic mode. By optimizing the chromatographic conditions such as formic acid content, mobile phase composition, pH values and column temperature, 19 analytes were completely separated with high resolution (1.50-4.48), in which the enantiomeric resolution of silymarin, 4-hydroxyflavanone, 2-hydroxyflavanone and flavanone were up to 4.34, 4.48, 3.89 and 3.06 within 35 min, respectively. Compared to the native β-CD chiral stationary phase (CDCSP), HTCDP had superior enantiomer separation and chiral recognition abilities. For example, HTCDP completely separated 5 other common chiral drugs, 2 flavanones and 3 triazole pesticides that CDCSP failed to separate. Unlike CDCSP, which has a small cavity (0.65 nm), the two cavities in HTCDP joined by the aryl connector could synergistically accommodate relatively bulky chiral analytes. Thus, HTCDP may have a broader prospect in enantiomeric separation, analysis and detection.
... [1][2][3] This is because these aspects have a noteworthy impact on drug discovery from efficacy and safety points of view. 4 The need for optically active pure drugs is growing rapidly in the developing world because of their high medicinal values and non-toxic nature, especially with regard to quinolones. 5,6 Therefore, attempts have been made to determine the enantio-separation, absolute configuration and chiral recognition mechanism of two important quinolones as model compounds. ...
BACKGROUND
The determination of enantio‐separation, absolute configuration and chiral recognition mechanism of ofloxacin and flumequine was carried out by high‐performance liquid chromatography (HPLC) and modeling studies. The column used was a Chiralcel OD‐H with normal and polar organic mobile phase modes. The exhaustive chiral separation was optimized through various HPLC parameters.
RESULTS
The selectivity, separation factors and resolution factors for ofloxacin were 8.2 and 9.4, 1.15 and 2.43 in the normal mobile phase, while these values were 10.5 and 12.0, 1.14 and 2.40 for flumequine in polar organic mobile phase mode, respectively. The thermodynamic parameters were ΔH (−0.137 J mol⁻¹), ΔS (7.35 × 10⁻⁴ J mol⁻¹) and ΔG (−0.360 J mol⁻¹ K⁻¹) for ofloxacin, and ΔH (−0.035 J.mol⁻¹), ΔS (21.3 × 10⁻⁴ J mol⁻¹) and ΔG (−0.105 J mol⁻¹ K⁻¹) for flumequine, confirming spontaneous chiral separation at all temperatures. The chiral recognition mechanism was established by HPLC and modeling results. The modeling binding affinity were −2.5 kcal mol–1 (R‐enantiomer) and −2.6 kcal mol–1 (S‐enantiomer) for ofloxacin, and −2.30 kcal mol–1 (R‐enantiomer) and −2.40 kcal mol–1 (S‐enantiomer) for flumequine enantiomers. The chiral resolution is controlled by hydrogen bonding, π–π interactions and other forces.
CONCLUSION
These methods were applied to monitor ofloxacin and flumequine quinolones in urine samples. Briefly, the developed chiral HPLC methods are effective and may be used to analyze the reported enantiomers in any biological sample. © 2021 Society of Chemical Industry (SCI).
The selective, specific, precise, linear, accurate, and robust analytical method was developed and validated for the assay of Vancomycin HCl in Vancomycin Hydrochloride Injection. Comparative UV spectrophotometric and reverse phase HPLC developed the quantitative determination. Acetonitrile and pH 2.2 phosphate buffer in the ratio (20:80 v/v) used as mobile phase, and flow rate 1.0 mL/min with 20 mins run time. The detection was carried out at 235 nm with Nucleosil C18 (250 mm × 4.6 mm) 10 μm column, and the ambient column temperature was maintained. The method uses the 20 μL injection volume and diluent as a blank solution in this connection. The method was validated as per the current regulatory guidelines. The linearity of this method was found to be linear in the range of 50% to 150% of the working concentration, and the correlation coefficient was more than 0.999. The method's accuracy was within the acceptable range, which was found to be 98.1 % to 101.5 %. The method's precision was within an acceptable range of about % RSD of 0.32 %. The analytical solution was found stable for up to 48 hrs at room temperature. The method's robustness was proved by utilizing quality design tools. Stress studies demonstrated method stability indicating nature.
Enantioselective analytical approaches are essential for monitoring pharmacokinetics and acquiring accurate data to better understand the role of stereochemistry in pharmacokinetics. Enantioselectivity significantly impacts the pharmacokinetics of chiral drugs, especially in metabolic profile, leading to toxicity of enantiomer. Consequently, there is a need to study the pharmacokinetics of enantiomerically pure drugs and racemates as they differ in affinity with enzymes and proteins. Combining the best enantioseparation conditions with the specified biological matrix and the intended purpose of the analysis is a challenging task. This review discusses the importance of chirality in stereoselective pharmacokinetics with more relevant examples, various enantioselective analytical techniques, and stationary phases employed. Challenges such as lack of universal chiral columns, biological inversion of the isomers, and others have been discussed. Further presented the recent advances in the screening of chiral drugs and innovative improvements in the analytical approaches for chiral molecule analysis such as supercritical fluid chromatography, simulated moving bed chromatography, and other techniques are discussed.
Vancomycin is a highly efficient glycopeptide antibiotic and a chiral separation material with excellent performance, whose structure contains multiple chiral sites. The change of structure can alter the binding performance between chiral stationary phase (CSP) and chiral drugs, ransforming the enantioseparation ability. Herein, vancomycin-immobilized CSP (V-CSP) and 3,5-dimethylphenyl isocyanate (DMP) derivatized vancomycin-immobilized CSP (D-V-CSP) were prepared. Both V-CSP and D-V-CSP were characterized through elemental analysis, Fourier transform infrared (FT-IR), thermogravimetric analysis (TGA) and scanning electron microscopy (SEM), and then explored to separate chiral drugs in high-performance liquid chromatography (HPLC). After further optimizing the chromatographic separation conditions such as pH value, organic phase and flow rate, the enantioseparation of fluoxetine, labetalol, verapami, rosiglitazone, mirtazapine and chlorphenamine maleate were obtained. Due to the change of structure of vancomycin, two as-synthesized CSPs exhibited different chiral recognition ability. Partial separation of labetalol (Rs=0.682) and mirtazapine (Rs=0.913) was achieved on V-CSP, which was better than that on D-V-CSP. The interaction force between the derivatized stationary phase and the chiral drugs was significantly enhanced, therefore, on D-V-CSP chiral columns, baseline separation of fluoxetine (Rs=2.149), rosiglitazone (Rs=2.050) and chlorpheniramine maleate (Rs=1.815) and partial separation of verapamil (Rs=0.946) were achieved. Based on the above results, both V-CSP and D-V-CSP would successfully be applied in the separation of chiral drugs, and changing the structure of the stationary phase is beneficial to the improvement of chiral recognition ability for specific chiral drugs.
A novel and easy environmental deep eutectic solvent based liquid phase microextraction method has been developed for the separation-preconcentration and spectrophotometric determination of amaranth. The deep eutectic solvent system is composed of tetrabutyl ammonium bromide (TBABr) and decanoic acid (DA). 300 µL of emulsifying agent tetrahydrofuran (THF) and 600 µL of deep eutectic solvent (DES) were employed. Quantitative recoveries were obtained at pH 5.0, sonication and centrifugation times of two minutes, and a model solution volume of 20 mL. The amaranth concentration was measured in a micro-cuvette spectrophotometer at 520 nm. The limit of detection (LOD), limit of quantification (LOQ), and preconcentration factor (PF) were 23 µg/L, 76 µg/L, and 33.3, respectively. The presented microextraction method has been validated by analyzing food and water samples by the method of standard addition.
It has been a great challenge for scientists to develop an anti-Covid drug/vaccine with fewer side effects, since the coronavirus pandemic began. Of course, the prescription of chiral drugs (chloroquine or hydroxychloroquine) has been proved wrong because these chiral drugs neither kill the virus nor eliminate it from the body, but block SARS-CoV-2 from binding to human cells. Another hurdle facing the world is not only the positive test of the patient recovered from coronavirus, but also the second wave of Covid-19. Hence, the world demands such a drug or drug combination which not only prevents the entry of SARS-CoV-2 in the human cell but also ejects it or its material from the body completely. The current computational study not only utilizes a structure-based drug design approach to find possible drug candidates but also explains (i) why the prescription of chiral drugs was not satisfactory, (ii) what types of modification can make their prescription satisfactory, (iii) the mechanism of action of chiral drugs (chloroquine and hydroxychloroquine) to block SARS-CoV-2 from binding to human cells, and (iv) the strength of mefloquine to eliminate SARS-CoV-2. As the main protease (M[Formula: see text]) of microbes is considered as an effective target for drug design and development, the binding affinities of mefloquine with the M[Formula: see text] of JC virus and SARS-CoV-2 were calculated, and then compared to know the eliminating strength of mefloquine against SARS-CoV-2. The M[Formula: see text] of JC virus was taken because mefloquine has already shown a tremendous result of eliminating it from the body. The prescription of a combination of S-[Formula: see text]-hydroxychloroquine and [Formula: see text]-mefloquine is considered as a boon by the predicted study.
Enantiomeric separation of six antihistamine agents was first systematically investigated on a cellulose‐based chiral stationary phase (CSP), i.e., cellulose tris‐(3,5‐dimethyl phenyl carbamate) (Chiralcel OD‐RH), under the reversed‐phase mode. Orphenadrine, meclizine, terfenadine, dioxopromethazine, and carbinoxamine enantiomers were completely separated under the optimized mobile phase conditions with resolutions of 5.02, 1.93, 1.68, 1.67, and 1.54, respectively. Mequitazine was partially separated with a resolution of 0.77. The influences of type and concentration of buffer salt, the pH of buffer solution, and the type and ratio of organic modifier on the chiral separation were evaluated and optimized. For a better insight into the enantiorecognition mechanisms, molecular docking was carried out via the Autodock software. The lowest binding energy and the optimal conformations of the analytes/CSP complexes were supplied, and the mechanisms of chiral recognition were determined. According to the results, the key interactions for the chiral recognition of these six analytes on CDMPC were π–π interactions, hydrophobic interactions, hydrogen bond interactions, and some special interactions. This article is protected by copyright. All rights reserved
Chiral HPLC methods using macrocyclic glycopeptide-based chiral stationary phases have been widely used and reported; however, the development of efficient methods to separate and quantify the analytes with high resolution is a challenging task. Therefore, the knowledge regarding the optimization of chromatographic parameters regarding this type of chiral chromatography is essential. This review presents and discusses the optimization of HPLC conditions and parameters for the chiral resolution of racemic drugs on macrocyclic glycopeptide-based chiral stationary phases. Strategies for chiral method development are presented, using polar ionic, reversed phase, normal phase and polar organic modes. The effect of the most important chromatographic parameters, such as mobile phase composition, flow rate and temperature on the enantioseparation are discussed aiming the adequate screening and optimization protocol for each mode.
Since their introduction by Armstrong in 1994, macrocyclic antibiotic-based chiral stationary phases have proven their applicability for the chiral resolution of various types of racemates. The unique structure of macrocyclic glycopeptides and their large variety of interactive sites (e.g., hydrophobic pockets, hydroxyl, amino and carboxyl groups, halogen atoms, aromatic moieties, etc.) are the reason for their wide-ranging selectivity. The commercially available Chirobiotic™ phases, which display complementary characteristics, are capable of separating a broad variety of enantiomeric compounds with good efficiency, good column loadability, high reproducibility, and long-term stability. These are the major reasons for the use of macrocyclic antibiotic-based stationary phases in HPLC enantioseparations.
This overview chapter provides a brief summary of general aspects of macrocyclic antibiotic-based chiral stationary phases including their preparation and their application to direct enantioseparations of various racemates focusing on the literature published since 2004.
In a non-chiral environment, the enantiomers of a racemate possess the same physico-chemical properties but in the biological systems they possess different activities. One of the enantiomers may be more toxic or carcinogenic, and, therefore, the present data available on the toxicity and carcinogenesis of the racemic mixtures of these chiral pollutants are not reliable and need modification in terms of the enantioselective toxicity and carcinogenesis. It is essential to explore the enantioselective toxicity and carcinogenesis due to the different enantiomers of the chiral pollutants. The knowledge of the stereoselective metabolisms of the chiral pollutants may be useful for the treatment of cancer and other diseases. The enantioselective toxicity and carcinogenesis due to the chiral pesticides, pollutants and some drugs have been discussed in this review article.
Most of the pollutants are present in the environment as a mixture of their chiral isomers. Studies have revealed that these isomers have an enantioselective distribution, metabolism, and toxicity of these pollutants, in the light of the toxicity of their individual chiral isomers. We describe here, the different chiral isomers of common pollutants, their metabolism and toxicity, and methods for their separation and quantification. POLLUTION of the environment, one of the most pressing problems of our age, has now reached a level that it poses a potential threat not only to the health of people but also to entire populations. Among various environmental pollutants, organic contaminants, i.e. pesticides, phenols, plasticizers and polyaromatic hydrocarbons are the most toxic due to their carcinogenic nature 1–3 . The monitoring of these pollut-ants in the environment is essential and important. Many reports are available on the analysis of organic pollutants but these do not distinguish which mirror images of pollutants are present and which is harmful in the case of chiral pollut-ants. Scientists and other regulatory authorities are in demand for tackling associated problems in these areas.
Direct reversed-phase high-performance liquid chromatographic methods were developed for the separation of enantiomers of
eighteen unnatural β-amino acids, including several β-3-homo-amino acids. The direct separations of the underivatized analytes were performed on chiral stationary phases containing
macrocyclic glycopeptide antibiotics such as teicoplanin (Chirobiotic T and T2), teicoplanin aglycone (Chirobiotic TAG), vancomycin
(Chirobiotic V and V2), and ristocetin A (Chirobiotic R) as chiral selectors. The effects of the organic modifier, mobile
phase composition and pH on the separations were investigated. A comparison of the separation performances of the macrocyclic
glycopeptide stationary phases revealed that the Chirobiotic T2 column exhibited better selectivity than the Chirobiotic T
column for the separation of β-3-homo-amino acid enantiomers; vancomycin or ristocetin A exhibited lower selectivity. The elution sequence was determined
in some cases: the S enantiomers eluted before the R enantiomers, with the exception of the Chirobiotic R column, where the elution sequence R < S was observed.
Fluoroquinolones are one of the most promising and intensively studied drugs of contemporary anti-infective chemotherapy. New fluoroquinolone antibacterials with improved pharmacokinetic properties and a broad spectrum of activity have been developed, opening new windows of opportunity for clinical use. To our knowledge, no comprehensive and critical review of the analytical methods for the determination of these agents, which correspond to the third- and fourth-generation quinolones, has yet been published. This work summarizes for the first time most of the liquid chromatographic methods reported in the literature for the separation and quantification of the new fluoroquinolones in biological matrices and pharmaceutical formulations. A systematic and detailed survey of physicochemical properties, sample preparation procedures, and chromatographic and detection conditions is presented herein. In the course of this review several liquid chromatographic methods are discussed: reversed-phase high-performance liquid chromatography (RP-HPLC), ion-exchange high-performance liquid chromatography (IEX-HPLC), hydrophilic interaction liquid chromatography (HILIC), high-performance thin-layer chromatography (HPTLC) and other chiral chromatographic methods. Their advantages, applicability and limitations are also examined.
Figure
Liquid chromatographic methods for determination of new fluoroquinolones in biological matrices and pharmaceutical formulations.
The in vitro activity of nemonoxacin (TG-873870), a novel nonfluorinated quinolone, was tested against 2,440 clinical isolates.
Nemonoxacin was at least fourfold more active than levofloxacin and moxifloxacin against most gram-positive cocci tested (shown
by the following MIC90/range [μg/ml] values; community-associated methicillin [meticillin]-resistant Staphylococcus aureus, 0.5/0.015 to 2; Staphylococcus epidermidis, 0.5/0.015 to 4 for methicillin-susceptible staphylococci and 2/0.12 to 2 for methicillin-resistant staphylococci; Streptococcus pneumoniae, 0.015/≤0.008 to 0.25; Enterococcus faecalis, 1/0.03 to 128). Nemonoxacin activity against gram-negative bacilli was similar to levofloxacin and moxifloxacin (MIC90/range [μg/ml]; Escherichia coli, 32/≤0.015 to ≥512; Klebsiella pneumoniae, 2/≤0.015 to 128; K. oxytoca, 0.5/0.06 to 1; Proteus mirabilis, 16/0.25 to ≥512; Pseudomonas aeruginosa, 32/≤0.015 to ≥512; Acinetobacter baumannii, 1/0.12 to 16).
Quinolones are a very important family of antibacterial agents that are widely prescribed for the treatment of infections in humans. Since their discovery in the early 1960s, the quinolone group of antibacterials has generated considerable clinical and scientific interest. Two major groups of compounds have been developed from the basic molecule: quinolones and naphthyridones. The 4-pyridone-3-carboxylic acid associated with a 5, 6-fused aromatic ring is the common chemical feature of bactericidal quinolones. In the resulting bicyclic ring, the 1-, 5-, 6-, 7-, and 8-positions are the major targets of chemical variation. Manipulations of the basic molecule, including replacing hydrogen with fluorine at position 6, substituting a cyclic amine residue at position 7 and adding new residues at position 1 of the quinolone ring, have led to improved breadth and potency of antibacterial activity and pharmacokinetics. One of the most significant developments has been the improved anti-Gram-positive activity of the newer compounds, such as moxifloxacin and garenoxacin. However, some of these structural changes have been found to correlate with specific adverse effects: the addition of fluorine or chlorine at position 8 being associated with photoreactivity, e.g. sparfloxacin; and the substitution of an amine or a methyl group at position 5 having a potential role in QTc prolongation, e.g. sparfloxacin and grepafloxacin. The clinical utility of this expanding class of antimicrobial agents, and the lower propensity for the development of resistance with the newer quinolones will need to be continually monitored in the changing therapeutic environment. Antibiotic drug choice will remain difficult in the presence of increasing resistance, but introduction of the new quinolones has created a new and exciting era in antimicrobial chemotherapy.
The fluoroquinolones represent a major class of antibacterials with great therapeutic potential. Over the years, several structure-activity and side-effect relationships have been developed, covering thousands of analogues, in an effort to improve overall antimicrobial efficacy while reducing undesirable side-effects. In this review, the various structural features of the quinolones which govern antibacterial efficacy and influence the side-effect profile are delineated and summarized at the molecular level. Those features which most remarkably enhance antimicrobial effectiveness are: a halogen (F or Cl) at the 8-position which improves oral absorption and activity against anaerobes; an alkylated pyrrolidine or piperazine at C7 which increases serum half-life and potency vs Gram-positive bacteria; and a cyclopropyl group at N1 and an amino substituent at C5, both of which improve overall potency. Some side-effects of the quinolones are class effects, and cannot be modulated by molecular variation. These include gastrointestinal irritation and arthropathy. Several other potential side-effects are directly influenced by structural modification. For example, CNS effects and drug interactions with theophylline and NSAIDs are strongly influenced by the C7 substituent with simple pyrrolidines and piperazines the worst actors. Increasing steric bulk through alkylation ameliorates these effects. Phototoxicity is determined by the nature of the 8-position substituent with halogen causing the greatest photo reaction while hydrogen and methoxy show little light induced toxicity. Genetic toxicity is controlled in additive fashion by the choice of groups at the 1, 7 and 8 positions. From the analysis, those groups which mutually improve efficacy while reducing side-effects are identified. In addition, preclinical models for determining potential side-effects are discussed.
Some bacteria are resistant to the few antibiotics, which are being used to treat bacterial diseases. Therefore, there is a great need of new antibacterial compounds. Two antibacterial compounds were synthesized with two chiral centres in each molecule. The stereomers have different pharmacutical activities and, therefore, the efforts were made to resolve four stereomers on Chiral (+)-Crownpack column (250 mm × 4.6 mm, 5 µm) using 50 mM H2SO4 as mobile phase. The values of the retention, separation and resolution factors of four resolved stereomers of 13-methyl-11-phenyl-12-oxa-2,15-diazatetracyclo[8.6.0.0³,⁸.0¹¹,¹⁵]hexadeca-1(10),3(8),4,6-tetraene-9,16-dione (I) were 0.36, 1.26, 2.15 & 3.42; 3.50, 1.70, & 1.59 and 3.54, 3.55 & 3.80 while these values for 6,13‐dimethyl‐11‐phenyl‐12‐oxa‐2,15-diazatetracyclo[8.6.0.03,8.011,15] hexadeca‐1(10),3(8),4,6‐tetraene‐9,16‐dione (II) were 0.44, 1.38, 2.50 and 6.66; 3.13, 1.81 and 2.66 and 4.72, 6.06 and 1.53, respectively. The values of the detection limits of four stereomers of I and II were 5.8, 2.5, 2.1 & 8.0 and 3.6, 2.0, 5.4 & 7.8 ng. The mechanism of the chiral separation of four stereomers was developed using modeling studies. The hydrogen bondings were responsible for the chiral resolution. The binding energies of the stereomers; with the chiral column; were in the range of −3.0 to −3.5 Kcal/mol. The developed method may be used to separate four stereomers of these two compounds to get optically active drugs.
Macrocyclic antibiotics represent a class of antibiotics used in therapy against infections caused by gram-positive and gram-negative bacteria and having ring structures with at least 10 members. Despite their common features, macrocyclic antibiotics differ in several of their physicochemical properties and in biological activity. There are hundreds of natural and semisynthetic macrocyclic antibiotics, which comprise a large variety of structural types, including polyene-polyols, ansa compounds (e.g., aliphatic-bridged aromatic ring systems), glycopeptides, peptides, and peptideheterocycle conjugates. In general, these compounds have molecular masses ranging between 600 and 2200 and a variety of functional groups. There are acidic, basic, and neutral types. Some macrocyclic antibiotics absorb quite weakly in the ultraviolet (UV) and visible spectrum while others possess large conjugated groups and absorb intensely [1–3].
New chiral high‐performance liquid chromatography (HPLC) method for the enantiomeric resolution of quinolones is developed and described. The column used was Chirobiotic T (150 × 4.6 mm, 5.0 μm). Three mobile phases used were MeOH:ACN:Water:TEA (70:10:20:0.1%), (60:30:10:0.1%), and (50:30:20:0.1%). The flow rate of the mobile phases was 1.0 mL/min with UV detection at different wavelengths. The values of retention, resolution, and separation factors ranged from 1.5 to 6.0, 1.80 to 2.25, and 2.86 to 6.0, respectively. The limit of detection and quantification ranged from 4.0 to 12 ng and 40 to 52 ng, respectively. The modeling studies indicated strong interactions of R‐enantiomers with teicoplanin chiral selector than S‐enantiomers. The supra molecular mechanism of the chiral recognition was established by modeling and chromatographic studies. It was observed that hydrogen bondings and π‐π interactions are the major forces for chiral separation. The present chiral HPLC method may be used for enantiomeric resolution of quinolones in any matrices.
This review article is aimed at providing an overview of the current market of chiral drugs by exploring which is the nowadays tendency, for the pharmaceutical industry, either to exploit the chiral switching practice from already marketed racemates or to develop de novo enantiomerically pure compounds. A concise illustration of the main techniques developed to assess the absolute configuration (AC) and enantiomeric purity of chiral drugs has been given, where greater emphasis was placed on the contribution of enantioselective chromatography (both HPLC and SFC).
The quinolones are derivatives of oxoquinolines and mostly known for their antibacterial and antiviral activities. Many quinolones are chiral compounds having asymmetric centers and important due to their enantioselective biological activities. In order to study the biological activities of quinolone enantiomers, to control the manufacturing of homochiral drugs and to prepare necessary quantities of pure enantiomers for pre-clinical or clinical trials, respective chiral separation methods are urgently needed. In this context, the present review discusses chromatographic and electrophoretic methods for the enantioseparation of chiral quinolones and provides some useful information on their physical and pharmaceutical properties. The drawbacks of currently used techniques are revealed and ways to overcome them are outlined. Moreover, recommendations for an optimal choice of a separation protocol are given. This article is protected by copyright. All rights reserved.
Quinolone agents exhibit a bicyclic aromatic core, containing a carbon at the 8th position, yielding a true quinolone, or a nitrogen, and provide a ring system technically termed as naphthyridone. In common usage, both quinolone and naphthyridone structures are encompassed in the class descriptor “quinolone antibacterial agents.” The first generation quinolone compounds generally displayed increased Gram-negative activity over nalidixic acid, but lacked useful activity against Gram-positive cocci, Pseudomonas aeruginosa, and anaerobes. They were, however, generally well absorbed after oral administration and attained high concentrations in the urinary tract, making them useful therapeutically for treatment of urinary tract infections. In the second-generation quinolones, the piperazine ring remains relatively undisturbed, except for alkylation on the distal nitrogen or, less frequently, on the ring carbons. The second-generation compounds are characterized by good to excellent Gram-negative activity, with ciprofloxacin exhibiting the strongest Gram-negative spectrum. The third- and fourth-generation quinolones are characterized by increased structural novelty and complexity, which has resulted in new and useful characteristics. Clinafloxacin, sitafloxacin, and BAY y 3118, all of which bear a chlorine atom at C-8, are among the most potent broad-spectrum agents that have been in the development, and are the only compounds that exhibit Gram-negative activity superior to that of ciprofloxacin. These compounds, with the exception of pazufloxacin, show improved activity against S. pneumoniae compared to ciprofloxacin. The most potent of these agents are gemifloxacin and BAY y 3118, followed by clinafloxacin, sitafloxacin, moxifloxacin, and trovafloxacin.
Many chemical and biological processes are controlled by the stereochemistry of small polypeptides (di-, tri-, tetra-, penta-, hexapeptides, etc). The biological importance of peptide stereoisomers is of great value. Therefore, the chiral resolution of peptides is an important issue in biological and medicinal sciences and drug industries. The chiral resolutions of peptide racemates have been discussed with the use of capillary electrophoresis and chromatographic techniques. The various chiral selectors used were polysaccharides, cyclodextrins, Pirkle types, macrocyclic antibiotics, crown ethers, imprinted polymers, etc. The stereochemistry of dipeptides is also discussed. Besides, efforts are made to explain the chiral recognition mechanisms, which will be helpful in understanding existing and developing new stereoselective analyses. Future perspectives of enantiomeric resolution are also predicted. Finally, the review concludes with the demand of enantiomeric resolution of all naturally occurring and synthetic peptides.This article is protected by copyright. All rights reserved
During the last decade, chiral monolithic stationary phases (CSPs) have been prepared and used for rapid enantioseparations in capillary electrochromatography and HPLC. Various chiral selectors are used to prepare these CSPs. The preparation, properties and applications of these CSPs are discussed in this paper. The attempts have been made to describe optimization strategies and the chiral recognition mechanisms. A comparison of chiral separations in capillary electrochromatography and HPLC is described. Efforts have also been made to predict the future perspectives and challenges of chiral monolithic stationary phases. The most effective chiral selectors include polysaccharides, cyclodextrins and macrocyclic glycopeptide antibiotics. These chiral phases produced acceptable analytical enantiomeric separation of a variety of racemates. However, the development of these CSPs for preparative-scale separations is needed.This article is protected by copyright. All rights reserved
Non aqueous capillary electrophoresis (NACE) is an alternative technique to aqueous CE in the chiral separations of partially soluble racemates. Besides, partially water soluble or insoluble chiral selectors may be exploited in the enantiomeric resolution in NACE. The high reproducibility due to low Joule heat generation and no change in BGE concentration may make NACE a routine analytical technique. These facts attracted scientists to use NACE for the chiral resolution. The present review describes the advances in the chiral separations by NACE and its application in pharmaceutical and biomedical analysis. The emphasis has been given to discuss the selection of the chiral selectors and organic solvents, applications of NACE, comparison between NACE and aqueous CE and chiral recognition mechanism. Besides, efforts have also been made to predict the future perspectives of NACE. This article is protected by copyright. All rights reserved.
Chiral analysis of β-adrenergic blockers in human plasma is an important research area due to their different pharmaceutical
activities. The solid phase extraction of alprenolol, carazolol, metoprolol, oxprenolol from human plasma was achieved on
C18 cartridges using phosphate buffer (50 mM, pH 9.0) followed by elution with methanol containing 0.1% acetic acid. Chiral-HPLC
was carried out on CelluCoat (250 × 4.6 mm, 5.0 μm silica particle size) column using different combinations of n-heptane–ethanol–diethylamine at 1.0 and 2.0 mL min−1 flow rates, respectively. The detection was achieved at 225 nm with 27 ± 1 °C as working temperature. The chromatographic
parameters, i.e., retention (k), separation (α) and resolution (Rs) factors ranged from 0.26 to 10.64, 1.12 to 2.10 and 1.05 to 2.26, respectively. The
binding differences of enantiomeric concentrations of oxprenolol, carazolol, alprenolol, and metoprolol were 0.12, 0.08, 0.05,
and 0.01, respectively. These values suggest that their activities may be in the order of oxprenolol > carazolol > alprenolol > metoprolol.
The reported SPE-Chiral HPLC methods may be used to study the enantiomeric concentrations of these β-adrenergic blockers in
human and other animal plasmas for further studies.
Chiral resolution has achieved an independent identity in the separation sciences and polysaccharide CSPs are viewed as effective and efficient CSPs due to their many unique advantages. The present review article highlights the separations of chiral pharmaceuticals and drugs by liquid chromatographic modalities (high performance liquid chromatography, capillary electro‐chromatography, sub‐ and super critical fluid chromatography and thin layer chromatography) utilizing polysaccharide CSPs. Enantiomeric resolution at analytical and preparative scales and a comparison of coated and immobilized CSPs is discussed. The optimization strategies for enantiomeric separation have also been presented. The possible mechanisms of chiral resolution of racemates were also included. The commercial CSPs of all the Companies i.e., Daicel, Kromasil, Macherey Nagel, Knauer and Sepaserve have been compared and discussed. Finally, the role of these CSPs in chiral drugs development programs has also been identified.
High speed countercurrent chromatography was applied to the separation of racemic ofloxacin using L-(+)-tartaric acid as chiral selectors. The two-phase system composed of ethyl acetate/methanol/water = 10:1:9 was chosen. The upper phase contained 200 mmol/L of chiral selector. The maximum amount of sample in a one-time injection can be up to 20 mg. The enantiomers separated were identified by HPCE, which confirmed that this method was very useful for the chiral preparative separation.
Four macrocyclic glycopeptide chiral stationary phases (CSPs) based on native teicoplanin (Chirobiotic T), methylated teicoplanin aglycone (Chirobiotic m‐TAG), teicoplanin aglycone (Chirobiotic TAG), and vancomycin (Chirobiotic V) were compared for the high performance liquid chromatographic (HPLC) separation of enantiomers of 1‐methyl‐2‐piperidinoethylesters of 2‐, 3‐and 4‐ alkoxyphenylcarbamic acid (potential local anaesthetic drugs). The enthalpies (ΔHi), entropies (ΔSi), and Gibbs energies (ΔGi) of transfer were evaluated for the separation of these compounds. The enantiomers were separated isothermally in the range of 0–50°C with 10°C increments, in the polar organic mode. The thermodynamic parameters were calculated in order to gain an understanding of the driving forces for retention in this chromatographic system. From these results, it is evident that the elongation of the alkoxy‐chain has major influence on the values of (ΔSi) when using the vancomycin CSP and on the values of (ΔHi) using the teicoplanin‐type CSPs.
Thousands of organic compounds are present in our water resources and exist in dynamic equilibrium with sediment. Among them are drug and pharmaceutical residues. Many of these residues are chiral, and their metabolites or degradation products may also be chiral in nature. Therefore, the determination of chiral ratio of these chiral compounds is required to predict the exact toxicities. The present article describes the presence of ibuprofen, the third most popular clinically used drug in the world, in water resources, its enantiomeric degradation, and the monitoring of chiral ratio of ibuprofen enantiomers and its degradation products. Attempts have also been made to describe the future scope of chiral analyses of drug and pharmaceutical residues in the environment.
Pyrazolealdehydes (4a-d), Knoevenagel’s condensates (5a-d) and Schiff’s bases (6a-d) of curcumin-I
were synthesized, purified and characterized. Hemolysis assays, cell line activities, DNA bindings and
docking studies were carried out. These compounds were lesser hemolytic than standard drug
doxorubicin. Minimum cell viability (MCF-7; wild) observed was 59% (1.0 μg/mL) whereas the DNA
binding constants ranged from 1.4 × 103 to 8.1 × 105 M−1. The docking energies varied from −7.30
to−13.4 kcal/mol. It has been observed that DNA-compound adducts were stabilized by three
governing forces (Van der Wall’s, H-bonding and electrostatic attractions). It has also been observed
that compounds 4a-d preferred to enter minor groove while 5a-d and 6a-d interacted with major
grooves of DNA. The anticancer activities of the reported compounds might be due to their
interactions with DNA. These results indicated the bright future of the reported compounds as
anticancer agents.
The S-(-)-enantiomer of ofloxacin, a chiral fluoroquinolone antibiotic, exhibits an antibacterial activity 8-128 times higher than that of the R-(+)-isomer. A new stereospecific nano-LC method for the enantioseparation of the ofloxacin racemic mixture was developed using an achiral reversed phase column (Pinnacle II Phenyl 3 μm, 15 cm x 100 μm ID) and heptakis-(2,3-diacetyl-6-sulfo)-β-cyclodextrin (HDAS-β-CD) as a mobile phase chiral additive. Best enantioresolution was achieved using a mobile phase containing acetonitrile, 50 mM sodium acetate buffer pH 3 (30:70, v/v) and 5 mM of HDAS-β-CD. The flow rate thorough the capillary column was estimated in 620 nL/min and the wavelength for the UV detection was set at 290 nm. Good separation of the enantiomers was obtained is less than 10 min with a resolution and selectivity factor of 1.66 and 1.88, respectively. The effect of several experimental parameters on the chiral separation was also evaluated and the method was successfully validated in terms of linearity, accuracy and precision, showing the enantiorecognition capability of the employed sulfated β-CD toward the ofloxacin chiral drug.
Fluoroquinolones, such as ciprofloxacin and ofloxacin have recently gained wide acceptance for use in the treatment of respiratory tract, skin/soft tissue, sexually transmitted diseases and urinary tract infections. The broad spectrum activity and good oral absorption characteristics of these antimicrobials promotes their use in both community and hospital settings. Despite these favourable properties, ciprofloxacin and ofloxacin have limited potency against some clinically important organsims, such as Streptococcus pneumoniae, enterococci and anaerobes including Bacteroides fragilis and many methicillin-resistant staphylococci. In addition, occasional clinical isolates of Enterobacteriaceae and Pseudomonas aeruginosa have emerged resistant to these compounds following their introduction. In an effort to expand upon the clinical utility of the existing fluoroquinolones, several new agents of this class have been identified and are in various stages of development. Some of these newer fluoroquinolones have significantly improved antimicrobial potency against the organisms mentioned above and/or possess pharmacokinetic characterisitics in humans that suggest they could be dosed less frequently than ciprofloxacin. This review will summarise the antimicrobial and human pharmacokinetic properties of sparfloxacin, clinafloxacin, PD-131628, PD-138312, PD-140248, Q-35, AM-1155, NM394, T-3761, rufloxacin, levofloxacin, CP-99,219, OPC-17116 and DU-6859a, which appear to be among the most interesting new fluoroquinolones currently in development. An attempt will be made to distinguish the most important characterisitics of these new agents, based upon the available preclinical data and results from single dose pharmacokinetic studies in humans. The data suggest that several of these fluoroquinolones possess properties that could translate into significant clinical advantages over the currently available compounds in this class.
The chromic acid oxidation, Cannizzaro reaction and benzoin condensation have been studied using benzaldehyde-d1. The chromic acid oxidation was found to have a deuterium isotope effect, kH/kD, of 4.3, indicating that the cleavage of the carbon-hydrogen bond of the aldehyde is the rate-determining step. Since the reaction is acid catalyzed, the formation of an ester intermediate similar to that in the permanganate oxidation of benzaldehyde is suggested. The Cannizzaro reaction was found to have an isotope effect of 1.8. The observation of an isotope effect is in accord with the currently accepted mechanism, but the value is unusually low for an ionic reaction. The benzoin condensation appeared to give an isotope effect which evidenced itself as an induction period with the labeled aldehyde. It was also shown that exchange of the aldehyde hydrogen with the solvent occurred during the reaction at about the same rate as the condensation. These observations are not in agreement with the Lapworth mechanism.
There are a large number of antibiotic macrocycles which include several different structural types. Three representative macrocyclic compounds were covalently linked to silica gel and evaluated by HPLC for their ability to resolve racemic mixtures as well as for their stability and loadability. Over 70 compounds were resolved. In some cases separations were achieved that have not been reported on any other chiral stationary phase (CSP). These stationary phases appear to be multimodal in that they can be used in both the normal-phase and reversed-phase modes. Different compounds are resolved in each mode. There does not appear to be any deleterious effects to the stationary phases or any irreversible changes in the enantioselectivity when changing from one mode to another. The diversity of functionality of some of these chiral selectors is only approached by that of glycoproteins. Consequently, enantioseparation may be possible via several different mechanisms including pi-pi complexation, hydrogen bonding, inclusion in a hydrophobic pocket, dipole stacking, steric interactions, or combinations thereof. While all other CSPs avail themselves of the same type of interactions, they are not all necessarily available in a single chiral selector and in relatively close proximity to one another. Macrocyclic antibiotics seem to have many of the useful enantioselectivity properties of proteins and other polymeric chiral selectors without their inherent problems of instability and low capacities.
A chiral stationary phase derived from (+)-(18-crown-6)-2,3,11,12-tetracarboxylic acid has been successfully used for the
direct separation of the enantiomers of recemic fluoroquinolines containing a primary amino group being investigated as antibacterial
agents. The chromatographic resolution behavior was found to depend on the content and the type of acidic and organic modifiers
in the mobile phase and on the column temperature.
The enantiomeric resolution of (±)-econazole, (±)-miconazole and (±)-sulconazole was achieved on a Chiralpak WH column. The
mobile phase used was hexane-2-propanol-diethylamine (400:99:1,v/v/v). The flow rates of the mobile phase used were 0.50 and 1.00 mL min−1. The values of α of the resolved enantiomers of econazole, miconazole and sulconazole were in the range of 1.68 to 1.23 while
the values of Rs varied from 2.42 to 1.10. The resolution of these antifungal agents on Chiralpak WH column is governed by
ligand exchange mechanism. Hydrophobic interactions also play an important role for the enantiomeric resoltuion of antifungal
agents on the reported CSP.
Due to the importance of chiral separations of drugs, pharmaceuticals, agrochemicals and xenobiotics by high performance liquid
chromatography (HPLC) and capillary electrophoresis (CE), it is important to have the knowledge of the enantiomeric recognition
mechanisms so that scientists may design and module the new chiral selectors for rapid, inexpensive and reproducible chiral
separations; specially at preparative scale. The mechanisms of the chiral separation by HPLC and CE using polysaccharides,
cyclodextrins, macrocyclic glycopeptide antibiotics, Pirkle type, ligand exchangers, crown ethers and other several types
of chiral selectors have been discussed. Various complex formation and different types of interactions responsible for chiral
resolution have been presented in detail.
The separation of enantiomers by liquid chromatography and capillary electrophoresis is important in pharmaceutical, environmental,
and agricultural analysis. Of the different types of chiral selector used for enantiomer resolution the macrocyclic antibiotics
are considered particularly effective. Only eight antibiotics, vancomycin, teicoplanin, thiostrepton, rifamycin B, kanamycin,
streptomycin, fradiomycin, and ristocetin A have yet been used as chiral selectors for separation of the enantiomers of a
variely of compounds by liquid chromatography and capillary electrophoresis. This review describes the chemistry of these
antibiotics, the effect of chromatographic conditions on enantioselectivity, the mechanism of resolution, the applications
and limitations of the compounds, and detection in liquid chromatography and capillary electrophoresis with these antibiotics
as the chiral selectors.
Over the last decade we have witnessed the emergence of technologies such as libraries, Object Orientation, software architecture and visual programming. The common goal of these technologies is to achieve software reuse. Even though, many significant advances have been made in areas such as library design, domain analysis, metric of reuse and organization for reuse, there are still unresolved problems such as component inter-operability and framework design[1]. We have investigated the use of interpreted languages to create a programmable, dynamic environment in which components can be tied together at a high level. This work has demonstrated the benefits of such an approach and has taught us about the features of the interpreted language that are key to a successful component integration.
The chiral recognition mechanism of amylose CSPs has been described by achieving the enantiomeric resolution of (±)-nebivolol on Chiralpak AD and Chiralpak AD-RH columns with methanol, ethanol, 1-propanol, 2-propanol, 1-butanol as mobile phases at different flow rates. The energies of interactions of methanol, ethanol, 1-propanol, 2-propanol and 1-butanol with both phases were calculated. The (+)-RRRS enantiomer eluted first when using methanol, ethanol and 1-propanol, while the elution order was reversed when using 2-propanol and 1-butanol as the mobile phases. It has been concluded that the reversal elution order observed was due in part to the chiral cavities on the amylose CSP which were responsible for the bondings of different magnitude between chiral stationary phase and enantiomers, which are influenced with the type of alcohol used as mobile phase on the conformation of the 3,5-dimethyl phenyl carbamate moiety on the pyranose ring system of the amylose.
The octanol/water partition coefficients of nine antibacterial fluoroquinolones and nalidixic and oxolinic acids were investigated. The pH-partition profile of amphoteric fluoroquinolones obtained between pH 4 and 10 showed maximum partitioning at the isoelectric point. From the two microspecies (zwitterionic and nonionic forms) which exist predominantly at this pH, the nonionic form is assumed to be transferred into the octanol phase. A relationship is derived between the apparent and true partition coefficients, valid for ampholyte compounds capable of forming zwitterions and having nonionic microspecies present in significant amounts. On the bases of true partition coefficients, three groups of examined fluoroquinolones are distinguished: lipophilic compounds (e.g., pefloxacin and amifloxacin), molecules of intermediate lipophilicity (such as ciprofloxacin and ofloxacin, etc.) and hydrophilic derivatives (e.g., norfloxacin and lomefloxacin, etc.). The influence of structural modification on the lipophilicity of these drugs is discussed.
The chiral separation of 10 beta-adrenergic blockers (acebutalol, alprenolol, bufuralol, bisoprolol, celiprolol, carazolol, indenolol, metoprolol, oxprenolol and propranolol) was achieved on CelluCoat column (250 mm x 4.6mm, 5 microm particle size). The mobile phases used were (90:10:0.2, v/v/v) and (95:5:0.2, v/v/v) combinations of n-heptane-ethanol-diethylamine, respectively. The flow rates were 0.5, 1.0 and 2.0 mL min(-1) with detection at 225 nm. The capacity (k), selectivity (alpha) and resolution (R(s)) factors were 0.44-12.91, 1.12-2.19 and 1.00-9.50, respectively. The proposed supra-molecular models indicated that the chiral resolution were governed by pi-pi interactions, hydrogen bondings and steric effect.
Recently, two new immobilized polysaccharides based CSPs, namely tris-(3,5-dimethylphenylcarbamate) derivatives of amylose and cellulose known as Chiralpak IA and Chiralpak IB were introduced, which may be used with a wide range of solvents including standard and prohibited ones. Several racemic piperidine-2,6-dione analogues [aminoglutethimide, p-nitro-glutethimide, p-nitro-5-aminoglutethimide, cyclohexylaminoglutethimide, phenglutarimide and thalidomide] have been resolved on Chiralpak IA and Chiralpak IB columns (25cmx0.46cm). The non-conventional mobile phases used were methyl-tert-butyl ether-THF (90:10, v/v) [I], 100% dichloromethane [II] and 100% acetonitrile [III] separately at a flow rate of 1.0mL/min using a UV detector at 254nm. The resolution factors for Chiralpak IA and Chiralpak IB columns were 1.00-5.33 and 0.33-0.67, respectively. Chiralpak IA column gave better results than Chiralpak IB column for the reported molecules using the developed HPLC conditions. Experimental conditions and the possible chiral recognition mechanisms have been discussed.
Primaquine was firstly synthesized in 1946 in the USA, and is the most representative member of the anti-malarial 8-aminoquinolines. Six decades have passed and primaquine is still the only transmission-blocking anti-malarial clinically available, displaying a marked activity against gametocytes of all species of human malaria, including multi-resistant Plasmodium falciparum strains. Primaquine is also effective against all exoerythrocytic forms of the parasite and is used in conjunction with other anti-malarials for the treatment of vivax and ovale malaria. However, primaquine is often associated with serious adverse effects, in consequence of its toxic metabolites. 5-Hydroxyprimaquine or 6-methoxy-8-aminoquinoline has been considered to be directly responsible for complications such as hemolytic anemia. Primaquine toxicity is aggravated in people deficient of 6-glucose phosphate dehydrogenase or glutathione synthetase. Adverse effects are further amplified by the fact that primaquine must be repeatedly administered at high doses, due to its limited oral bioavailability. Over the last two decades, Medicinal Chemists have battled against primaquine's disadvantages, while keeping or even improving its unequalled performance as an anti-malarial. The present text revisits primaquine and its properties on the occasion of its 60th anniversary and aims to give a general overview of what has been the path towards the development of effective and safe primaquine-based anti-malarials. Presently, aablaquine and tafenoquine the two most promising primaquine analogues are already in the final stages of clinical trials against Plasmodium vivax and P. falciparum. Both compounds are a new hope against malaria and other primaquine-sensitive illnesses, such as Pneumocystis Pneumonia or the Chagas disease.
The development of methods for the separation of enantiomers has attracted great interest in the past 20 years, since it became evident that the potential biological or pharmacological applications are mostly restricted to one of the enantiomers. In the past decade, macrocyclic antibiotics have proved to be an exceptionally useful class of chiral selectors for the separation of enantiomers of biological and pharmacological importance by means of high-performance liquid chromatography (HPLC), thin-layer chromatography and electrophoresis. The glycopeptides avoparcin, teicoplanin, ristocetin A and vancomycin have been extensively used as chiral selectors in the form of chiral bonded phases in HPLC, and HPLC stationary phases based on these glycopeptides have been commercialized. In fact, the macrocyclic glycopeptides are to some extent complementary to one another: where partial enantioresolution is obtained with one glycopeptide, there is a high probability that baseline or better separation can be obtained with another. This review sets out to characterize the physicochemical properties of these macrocyclic glycopeptide antibiotics and, through their application, endeavors to demonstrate the mechanism of separation on macrocyclic glycopeptides. The sequence of elution of the stereoisomers and the relation to the absolute configuration are also discussed.
Macrocyclic glycopeptide selectors are naturally occurring antibiotics produced by microorganisms. They were found to be excellent chiral selectors for a wide range of enantiomers, including amino acids. Four selectors are commercialized as chiral stationary phases (CSP) for chromatography. They are ristocetin, teicoplanin, vancomycin, and the teicoplanin aglycone (TAG). The key docking interaction for amino acid recognition was established to be a charge-charge interaction between the anionic carboxylate group of the amino acid and a cationic amine group of the macrocyclic peptidic selector basket. The carbohydrate units are responsible for secondary interactions. However, they hinder somewhat the charge-charge docking interaction. The TAG selector is more effective for amino acid enantioseparations than the other CSPs. The "sugar" units are however useful allowing for chiral recognitions of other analytes, e.g., beta-blockers, not possible with the aglycone. Thermodynamic studies established that normal phase and reversed phase enantioseparations were enthalpy-driven. With polar waterless mobile phases used in the polar ionic mode, some separations were enthalpy-driven and others were entropy-driven. The linear solvation energy method was tentatively used to gain knowledge about the chiral recognition mechanism. It appeared to be a viable approach with neutral molecules but it failed with ionizable solutes. With molecular solutes and the teicoplanin CSP, the study showed a significant role of the surface charge-induced dipole interaction and steric effects. The remarkable complementary enantioselectivity effect observed with the four CSPs is discussed.
The newer quinolones, ciprofloxacin, enoxacin, fleroxacin, lomefloxacin, norfloxacin, ofloxacin and pefloxacin are highly effective antimicrobial agents against the majority of bacteria responsible for urinary tract infections and bacterial prostatitis. The pharmacokinetic properties of these agents after oral administration result in high concentrations in human urine, as well as in prostatic fluid and prostatic tissue. Ciprofloxacin, enoxacin and lomefloxacin produce the highest concentrations in prostatic tissue, followed by norfloxacin, ofloxacin and fleroxacin. More than 400 patients with chronic bacterial prostatitis have been treated with one of the newer quinolones in varying doses for 10 to 84 days. The results indicate a cure rate of approximately 70%, although the follow-up period is quite variable in these studies. Clinical trials of short-term (single dose vs three days) therapy with the newer quinolones conducted in women with uncomplicated lower urinary tract infections were reviewed. Although bacteriologic cure rates were high with single doses of ciprofloxacin, fleroxacin, norfloxacin, ofloxacin and pefloxacin, approximately one in five women with suspected uncomplicated lower urinary tract infection experience failure of single-dose therapy. In contrast, a three-day regimen with these agents is more effective than a single-dose in the treatment of uncomplicated lower urinary tract infections in women.
Vancomycin is one of a family of related macrocyclic glycopeptide antibiotics that were discovered by scientists at the Eli Lilly Company in the 1950s. It has been used to treat severe staphylococcal infections, particularly when bacterial resistance to other antibiotics has developed. Vancomycin is a naturally occurring chiral compound and has a number of stereogenic centers. Furthermore, it contains a variety of functionalities that are known to be useful for enantioselective interactions (e.g., hydrogen bonding groups, hydrophobic pockets, aromatic groups, amide linkages, etc.). The physiochemical properties of vancomycin, including its stability in solution, are discussed as they pertain to capillary electrophoresis. Over 100 racemates were resolved including many nonsteroidal antiinflammatory drugs, antineoplastic compounds and N-derivatized amino acids. Many of these compounds had very high resolution factors. Optimization and the effect of different experimental parameters on the enantioselective separations are discussed.
On 27 May 1992, the FDA announced the availability of a policy statement on the development of stereoisomeric drugs. This statement has significant implications for the chemist who is working on the development and validation of analytical controls for chiral drug substances and products. The testing of the bulk drug, the manufacturing of the finished product, the design of stability testing protocols, and the labelling of the drug must all take the chirality of the active ingredient into consideration.
This review attempts to predict the future of the newer fluoroquinolones by examining what we have learned about this class of compounds during the past decade, as well as what we are currently learning from research and developmental efforts. The molecular mechanism of action of these compounds provides the potential for use in clinical medicine in areas other than their role as antibacterial agents.
The newer fluoroquinolones that are currently available and those that have been introduced into the pipeline are categorised by their current stage of development. Also listed are those compounds that have been withdrawn from further investigation.
Office practice physicians consider the oral fluoroquinolones to be very effective therapeutic agents for many of their patients. Thus, the future of the fluoroquinolones looks promising because of their unique mechanism of action, the possibility of developing novel and improved compounds in this class, and the acceptance of these compounds as effective therapeutic agents by clinicians.