Enantiopurity analysis of new types of acyclic nucleoside phosphonates by capillary electrophoresis with cyclodextrins as chiral selectors

Determination of Kynurenine Enantiomers by Alpha-Cyclodextrin, Cationic-βeta-Cyclodextrin and Their Synergy Complemented with Stacking Enrichment in Capillary Electrophoresis

We present high resolution fast, cost-effective and sensitive Capillary zone electrophoresis (CZE) methods for determination of enantiomeric compounds of Kynurenine pathway, i.e. D, L-Kynurenine (KYN), in human serum and urine samples by cationic-β-CD and its synergistic dual chiral selector system (SD-CSs) with α-CD in 50 mM borax borate buffer (pH 9.0) as BGE. Acid-mediated stacking enrichment by HCl delivered 15 nM limit of detection (LOD) and 50 nM limit of quantification (LOQ). The methods gave advantages of linearity in the concentration range of 50 nM-1000 nM, reproducibility (RSD ≤ 3.35), selectivity against interfering amino acids, and remarkable recoveries. SD-CSs delivered resolution of D, L-KYN twice that of individual chiral selectors (CSs) under similar conditions. The binding constants (Kb) and electrophoretic mobilities (µeff) of D, L-KYN with different concentrations of CSs were calculated to find the migration order of enantiomers. The chiral recognition mechanism was investigated by molecular docking and molecular mechanics, which revealed strong hydrogen bonding between Kynurenine enantiomers and the SD-CSs as compared to individual CS as the key player in binding, formation of stable complexes which led to the ultimate separation.

Effectively enhancing the enantioseparation ability of β-cyclodextrin derivatives by de novo design and molecular modeling

Rational engineering of native β-CD as an ideal chiral selector for a definite analyte in capillary electrophoresis represents a challenge in separation science. Herein, a rational and systematic strategy that combines the de novo design and molecular modeling is firstly described to expedite the manipulation and selection of effective selector for enantioseparation in capillary electrophoresis. Using β-adrenoreceptor agonists as model analytes, we demonstrate how this strategy efficiently improves the enantiorecognition in chiral discrimination sites of inclusion complexes. The evolved β-CD derivative could be utilized as a chiral receptor to achieve the effective enantioseparation (R_s > 1.5) of racemic β-adrenoreceptor agonists. We highlight a novel strategy for efficiently and rapidly manipulating native CD based on the characteristics of analyte so as to gain an excellent chiral selector.

Use of various β-cyclodextrin derivatives as chiral selectors for the enantiomeric separation of ofloxacin and its five related substances by capillary electrophoresis

A capillary electrophoretic method for the enantioseparation of ofloxacin and its five related substances (potential impurities, indicated as impurities B-F) was developed using β-cyclodextrin derivatives as chiral selectors. To our knowledge, there are no previous studies about using capillary electrophoresis for the separation of impurities B-D. Six β-cyclodextrin derivatives including cationic (piperidine- and cyclohexylamine-), neutral (dimethyl- and hydroxypropyl-), and anionic (carboxymethyl- and sulfated-) β-cyclodextrin derivatives were tested and operational parameters such as buffer pH and concentration of β-cyclodextrin derivatives were investigated. The best resolutions were all obtained with anionic β-cyclodextrin derivatives: ofloxacin, impurities C-F could be best resolved with carboxymethyl-β-cyclodextrin at satisfactory resolutions of 8.27, 9.98, 5.92, 8.49 and 6.78, respectively, while for impurity B, a particularly impressive resolution value, up to 21.38, was observed using sulfated-β-cyclodextrin. The enhancement of enantioseparation observed for the tested analytes using anionic β-cyclodextrin derivatives might be due to some favorable interaction between selectors and analytes. Given the fact that the selection of chiral selector depends on the structures of analytes, with the help of structural similarities and differences of the analytes, the structure-separation relationship was further discussed.

Design and Synthesis of Fluorescent Acyclic Nucleoside Phosphonates as Potent Inhibitors of Bacterial Adenylate Cyclases

Bordetella pertussis adenylate cyclase toxin (ACT) and Bacillus anthracis edema factor (EF) are key virulence factors with adenylate cyclase (AC) activity that substantially contribute to the pathogenesis of whooping cough and anthrax, respectively. There is an urgent need to develop potent and selective inhibitors of bacterial ACs with prospects for the development of potential antibacterial therapeutics and to study their molecular interactions with the target enzymes. Novel fluorescent 5-chloroanthraniloyl-substituted acyclic nucleoside phosphonates (Cl-ANT-ANPs) were designed and synthesized in the form of their diphosphates (Cl-ANT-ANPpp) as competitive ACT and EF inhibitors with sub-micromolar potency (IC50 values: 11-622 nm). Fluorescence experiments indicated that Cl-ANT-ANPpp analogues bind to the ACT active site, and docking studies suggested that the Cl-ANT group interacts with Phe306 and Leu60. Interestingly, the increase in direct fluorescence with Cl-ANT-ANPpp having an ester linker was strictly calmodulin (CaM)-dependent, whereas Cl-ANT-ANPpp analogues with an amide linker, upon binding to ACT, increased the fluorescence even in the absence of CaM. Such a dependence of binding on structural modification could be exploited in the future design of potent inhibitors of bacterial ACs. Furthermore, one Cl-ANT-ANP in the form of a bisamidate prodrug was able to inhibit B. pertussis ACT activity in macrophage cells with IC50 =12 μm.

Capillary electrophoretic enantioseparation of basic drugs using a new single-isomer cyclodextrin derivative and theoretical study of the chiral recognition mechanism

A novel single-isomer cyclodextrin derivative, heptakis {2,6-di-O-[3-(1,3-dicarboxyl propylamino)-2-hydroxypropyl]}-β-cyclodextrin (glutamic acid-β-cyclodextrin) was synthesized and used as a chiral selector in capillary electrophoresis for the enantioseparation of 12 basic drugs, including terbutaline, clorprenaline, tulobuterol, clenbuterol, procaterol, carvedilol, econazole, miconazole, homatropine methyl bromide, brompheniramine, chlorpheniramine and pheniramine. The primary factors affecting separation efficiency, which include the background electrolyte pH, the concentration of glutamic acid-β-cyclodextrin and phosphate buffer concentration, were investigated. Satisfactory enantioseparations were obtained using an uncoated fused-silica capillary of 50 cm (effective length 40 cm) × 50 μm id with 120 mM phosphate buffer (pH 2.5-4.0) containing 0.5-4.5 mM glutamic acid-β-cyclodextrin as background electrolyte. A voltage of 20 kV was applied and the capillary temperature was kept at 20°C. The results proved that glutamic acid-β-cyclodextrin was an effective chiral selector for studied 12 basic drugs. Moreover, the possible chiral recognition mechanism of brompheniramine, chlorpheniramine and pheniramine on glutamic acid-β-cyclodextrin was investigated using the semi-empirical Parametric Method 3.

Synthesis and biological properties of prodrugs of (S)-3-(adenin-9-yl)-2-(phosphonomethoxy)propanoic acid

The lack of antiviral activity of recently described (S)-3-(adenin-9-yl)-2-(phosphonomethoxy)propanoic acid, or (S)-CPMEA in brief, has been speculated to possibly be due to the increased hydrophilicity of the molecule and, thus, by its limited cellular permeability. Efficient syntheses of novel lipophilic prodrugs of (S)-CPMEA masking either the carboxylic group or preferably both the phosphonate and carboxylic moieties, have been developed in order to increase bioavailability of the parent compound. Two prodrugs of (S)-CPMEA, namely phosphonate bis-amidate 15 and phenyloxy amidate 16, exhibited pan-genotypic anti-HCV activity at submicromolar concentrations.