Studies on Pidotimod Enantiomers With Chiralpak-IA: Crystal Structure, Thermodynamic Parameters and Molecular Docking

Comparative studies of immobilized polysaccharide derivatives chiral stationary phases for enantioseparation of furanocoumarins and dihydroflavones and discussion on chiral recognition mechanism

Enantiomeric separation of furanocoumarins and dihydroflavones compounds were systematically studied in the normal-phase mode using four different polysaccharide-type chiral stationary phases, namely, Chiralpak IA, Chiralpak IC, Chiralpak IG, and Chiralpak IK-3 by high-performance liquid chromatography. The effect of alcohol modifiers and alcohol content on enantiomeric separation was evaluated for the separation of furanocoumarins and dihydroflavones. All the eight compounds have achieved baseline separation with the resolutions ranging between 1.52 and 23.11. For a better insight into the enantiorecognition mechanisms, thermodynamic analysis was carried out. The mechanisms of chiral recognition have been discussed. Among four chiral columns, Chiralpak IG exhibited the most universal and the best enantioseparation ability toward furanocoumarins and dihydroflavones when used n-hexane-isopropanol and n-hexane-ethanol as mobile phase, respectively. The steric hindrance, hydrogen bonding, and π-π interaction played major roles in chiral recognition on Chiralpak IG. By comparing four chiral columns, this work systematically analyzed the separation methods of furanocoumarins and dihydroflavones for the first time and reported some active chiral ingredients of traditional Chinese medicine that have never been separated, which provided a further insight into the enantioseparation of furanocoumarins and dihydroflavones on chiral stationary phases.

Recent advances in chiral selectors immobilization and chiral mobile phase additives in liquid chromatographic enantio-separations: A review

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 modeling 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.

Polysaccharides as separation media for the separation of proteins, peptides and stereoisomers of amino acids

Reliable separation of peptides, amino acids and proteins as accurate as possible with the maximum conformation and biological activity is crucial and essential for drug discovery. Polysaccharide, as one of the most abundant natural biopolymers with optical activity on earth, is easy to be functionalized due to lots of hydroxyl groups on glucose units. Over the last few decades, polysaccharide derivatives are gradually employed as effective separation media. The highly-ordered helical structure contributes to complex, diverse molecular recognition ability, allowing polysaccharide derivatives to selectively interact with different analytes. This article reviews the development, application and prospects of polysaccharides as separation media in the separation of proteins, peptides and amino acids in recent years. The chiral molecules mechanism, advantages, limitations, development status and challenges faced by polysaccharides as separation media in molecular recognition are summarized. Meanwhile, the direction of its continued development and future prospects are also discussed.

Pidotimod in the treatment of pediatric recurrent respiratory tract infection

Objective:

To observe the clinical efficacy of pidotimod in the treatment of recurrent respiratory tract infection in children.

Methods:

One hundred thirty-two patients with recurrent respiratory tract infection who received treatment in Tianan City Central Hospital were selected and divided into an observation group and a control group using random number table, 66 in each group. Patients in the control group were given conventional treatment, while patients in the observation group were given conventional treatment and pidotimod treatment; the clinical efficacy of the two therapies was compared. The levels of IgG and IgM were measured after treatment.

Results:

The vital signs and the content of inflammatory mediator and Th1/Th2 in serum before and after treatment were compared, and the clinical efficacy of the two groups was evaluated. The fever, pulmonary rale, cough and antiadoncus of patients in the observation group disappeared earlier than those in the control group (P<0.05). The onset duration of respiratory tract infection and days of antibiotic application of the observation group were shorter than those of the control group after treatment (P<0.05). The times of infection of the observation group were less than that of the control group (P<0.05). Before treatment, the two groups had no significant difference in the content of inflammatory mediators and Th1/Th2 in the serum (P>0.05). The serum content of tumor necrosis factor (TNF)-α and interleukin (IL)-4 of the two groups one week after treatment was lower than that before treatment, and the content of interferon (IFN)-γ and IFN-γ/IL-4 were higher than that before treatment; moreover the observation group had lower serum content of TFN-α and IL-4 and lower content of IFN-γ and IFN-γ/IL-4 compared to the control group (P<0.05). The overall response rate of the observation group was 92.4%, much higher than 81.8% in the control group (P<0.05).

Conclusion:

Pidotimod has a remarkable efficacy in the treatment of pediatric recurrent respiratory tract infection because it can effectively inhibit the infection and optimize Th1/Th2 immune function.

Recent studies of docking and molecular dynamics simulation for liquid-phase enantioseparations

Liquid-phase enantioseparations have been fruitfully applied in several fields of science. Various applications along with technical and theoretical advancements contributed to increase significantly the knowledge in this area. Nowadays, chromatographic techniques, in particular HPLC on chiral stationary phase, are considered as mature technologies. In the last thirty years, CE has been also recognized as one of the most versatile technique for analytical scale separation of enantiomers. Despite the huge number of papers published in these fields, understanding mechanistic details of the stereoselective interaction between selector and selectand is still an open issue, in particular for high-molecular weight chiral selectors like polysaccharide derivatives. With the ever growing improvement of computer facilities, hardware and software, computational techniques have become a basic tool in enantioseparation science. In this field, molecular docking and dynamics simulations proved to be extremely adaptable to model and visualize at molecular level the spatial proximity of interacting molecules in order to predict retention, selectivity, enantiomer elution order, and profile noncovalent interaction patterns underlying the recognition process. On this basis, topics and trends in using docking and molecular dynamics as theoretical complement of experimental LC and CE chiral separations are described herein. The basic concepts of these computational strategies and seminal studies performed over time are presented, with a specific focus on literature published between 2015 and November 2018. A systematic compilation of all published literature has not been attempted.

A robust LC-MS/MS method for the determination of pidotimod in different biological matrixes and its application to in vivo and in vitro pharmacokinetic studies

Pidotimod, (R)-3-[(S)-(5-oxo-2-pyrrolidinyl) carbonyl]-thiazolidine-4-carboxylic acid, was frequently used to treat children with recurrent respiratory infections. Preclinical pharmacokinetics of pidotimod was still rarely reported to date. Herein, a liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed and validated to determine pidotimod in rat plasma, tissue homogenate and Caco-2 cells. In this process, phenacetin was chosen as the internal standard due to its similarity in chromatographic and mass spectrographic characteristics with pidotimod. The plasma calibration curves were established within the concentration range of 0.01-10.00μg/mL, and similar linear curves were built using tissue homogenate and Caco-2 cells. The calibration curves for all biological samples showed good linearity (r>0.99) over the concentration ranges tested. The intra- and inter-day precision (RSD, %) values were below 15% and accuracy (RE, %) was ranged from -15% to 15% at all quality control levels. For plasma, tissue homogenate and Caco-2 cells, no obvious matrix effect was found, and the average recoveries were all above 75%. Thus, the method demonstrated excellent accuracy, precision and robustness for high throughput applications, and was then successfully applied to the studies of absorption in rat plasma, distribution in rat tissues and intracellular uptake characteristics in Caco-2 cells for pidotimod.

Chiral recognition in separation science - an update

Stereospecific recognition of chiral molecules is an important issue in various aspects of life sciences and chemistry including analytical separation sciences. The basis of analytical enantioseparations is the formation of transient diastereomeric complexes driven by hydrogen bonds or ionic, ion-dipole, dipole-dipole, van der Waals as well as π-π interactions. Recently, halogen bonding was also described to contribute to selector-selectand complexation. Besides structure-separation relationships, spectroscopic techniques, especially NMR spectroscopy, as well as X-ray crystallography have contributed to the understanding of the structure of the diastereomeric complexes. Molecular modeling has provided the tool for the visualization of the structures. The present review highlights recent contributions to the understanding of the binding mechanism between chiral selectors and selectands in analytical enantioseparations dating between 2012 and early 2016 including polysaccharide derivatives, cyclodextrins, cyclofructans, macrocyclic glycopeptides, proteins, brush-type selectors, ion-exchangers, polymers, crown ethers, ligand-exchangers, molecular micelles, ionic liquids, metal-organic frameworks and nucleotide-derived selectors. A systematic compilation of all published literature on the various chiral selectors has not been attempted.