Stereoselective binding of chiral drugs to plasma proteins

Application of Hosomi-Sakurai allylation reaction in total synthesis of biologically active natural products

The Hosomi-Sakurai allylation reaction has been widely applied in the total synthesis of biologically active natural products, especially in synthesising complex polycyclic compounds containing multi-stereogenic centres since its discovery in 1976. The Hosomi-Sakurai allylation is the allylation of ketones and aldehyde with nucleophilic allylsilanes catalyzed with Lewis acid mainly used to extend the C-C bond in a molecule and also create a new site for manipulation due to the facile transformation of the pi (π) bond at the end of its chain. This review highlights only portions of natural product synthetic works that feature the Hosomi-Sakurai allylation reaction or its modification as a key transformation in the synthetic route.

LC-MS/MS Analyzing Praziquantel and 4-Hydroxypraziquantel Enantiomers in Black Goat Plasma and Mechanism of Stereoselective Pharmacokinetics

Praziquantel (PZQ) is the most effective treatment for schistosomiasis, commonly administered as a racemic mixture of the two enantiomers. Despite many reports on the pharmacokinetics of PZQ, the stereoselective pharmacokinetics of PZQ and its major metabolite 4-hydroxypraziquantel (4-OH-PZQ) remain poorly understood in goats. In this study, the chiral LC-MS/MS method was further optimized for separating and quantifying PZQ, trans-4-OH-PZQ, and cis-4-OH-PZQ and their enantiomers and then applied for the molecular pharmacokinetics of three analytes in black goat plasma. The findings showed that PZQ was rapidly absorbed and metabolized to 4-OH-PZQ. The Cmax of trans-4-OH-PZQ was about 3 times and 6 times higher than those of cis-4-OH-PZQ and PZQ, respectively. The stereoselectivity of the PZQ and cis-4-OH-PZQ enantiomers was insignificant in black goat plasma (p > 0.05), whereas the trans-4-OH-PZQ enantiomers exhibited obvious stereoselectivity (p < 0.05). The Cmax of S-trans-4-OH-PZQ were ~3.1 times higher than that of R-trans-4-OH-PZQ. Further computer simulations indicated that these differences in the stereoselectivity might mainly stem from the different binding energies of the corresponding R- and S-enantiomers of the target analytes to black goat plasma albumin. It has guiding significance for the research on the stereoselectivity of chiral veterinary drugs and their precision medication.

In-Bridge Stereochemistry: A Determinant of Stapled Peptide Conformation and Activity

Peptide side chain stapling has been proven to be an effective strategy for fine-tuning peptide properties. This innovative approach leads to the creation of stapled peptides characterized by stabilized α-helical conformations, enhanced protein-binding affinity, improved cell permeability, superior enzymatic stability, and numerous other advantages. Extensive research has explored the impact of various stapling bridges on the properties of these peptides, with limited investigation into the influence of bridge chirality, until very recently. In this concise review, we provide a brief overview of the current state of knowledge regarding the stereochemistry within the bridges of stapled peptides, offering insights into the potential applications of chiral bridges in the design and development of stapled peptides.

Antidepressants enter cells, organelles, and membranes

We begin by summarizing several examples of antidepressants whose therapeutic actions begin when they encounter their targets in the cytoplasm or in the lumen of an organelle. These actions contrast with the prevailing view that most neuropharmacological actions begin when drugs engage their therapeutic targets at extracellular binding sites of plasma membrane targets-ion channels, receptors, and transporters. We review the chemical, pharmacokinetic, and pharmacodynamic principles underlying the movements of drugs into subcellular compartments. We note the relationship between protonation-deprotonation events and membrane permeation of antidepressant drugs. The key properties relate to charge and hydrophobicity/lipid solubility, summarized by the parameters LogP, pKa, and LogDpH7.4. The classical metric, volume of distribution (Vd), is unusually large for some antidepressants and has both supracellular and subcellular components. A table gathers structures, LogP, PKa, LogDpH7.4, and Vd data and/or calculations for most antidepressants and antidepressant candidates. The subcellular components, which can now be measured in some cases, are dominated by membrane binding and by trapping in the lumen of acidic organelles. For common antidepressants, such as selective serotonin reuptake inhibitors (SSRIs) and serotonin/norepinephrine reuptake inhibitors (SNRIs), the target is assumed to be the eponymous reuptake transporter(s), although in fact the compartment of target engagement is unknown. We review special aspects of the pharmacokinetics of ketamine, ketamine metabolites, and other rapidly acting antidepressants (RAADs) including methoxetamine and scopolamine, psychedelics, and neurosteroids. Therefore, the reader can assess properties that markedly affect a drug's ability to enter or cross membranes-and therefore, to interact with target sites that face the cytoplasm, the lumen of organelles, or a membrane. In the current literature, mechanisms involving intracellular targets are termed "location-biased actions" or "inside-out pharmacology". Hopefully, these general terms will eventually acquire additional mechanistic details.

Stereoselective Voltammetric Biosensor for Myo-Inositol and D-Chiro-Inositol Recognition

This paper describes the development of a simple voltammetric biosensor for the stereoselective discrimination of myo-inositol (myo-Ins) and D-chiro-inositol (D-chiro-Ins) by means of bovine serum albumin (BSA) adsorption onto a multi-walled carbon nanotube (MWCNT) graphite screen-printed electrode (MWCNT-GSPE), previously functionalized by the electropolymerization of methylene blue (MB). After a morphological characterization, the enantioselective biosensor platform was electrochemically characterized after each modification step by differential pulse voltammetry (DPV) and electrochemical impedance spectroscopy (EIS). The results show that the binding affinity between myo-Ins and BSA was higher than that between D-chiro-Ins and BSA, confirming the different interactions exhibited by the novel BSA/MB/MWCNT/GSPE platform towards the two diastereoisomers. The biosensor showed a linear response towards both stereoisomers in the range of 2-100 μM, with LODs of 0.5 and 1 μM for myo-Ins and D-chiro-Ins, respectively. Moreover, a stereoselectivity coefficient α of 1.6 was found, with association constants of 0.90 and 0.79, for the two stereoisomers, respectively. Lastly, the proposed biosensor allowed for the determination of the stereoisomeric composition of myo-/D-chiro-Ins mixtures in commercial pharmaceutical preparations, and thus, it is expected to be successfully applied in the chiral analysis of pharmaceuticals and illicit drugs of forensic interest.

Enantioseparation Membranes: Research Status, Challenges, and Trends

The purity of enantiomers plays a critical role in human health and safety. Enantioseparation is an effective way and necessary process to obtain pure chiral compounds. Enantiomer membrane separation is a new chiral resolution technique, which has the potential for industrialization. This paper mainly summarizes the research status of enantioseparation membranes including membrane materials, preparation methods, factors affecting membrane properties, and separation mechanisms. In addition, the key problems and challenges to be solved in the research of enantioseparation membranes are analyzed. Last but not least, the future development trend of the chiral membrane is expected.

Detection and analysis of chiral molecules as disease biomarkers

The chirality of small metabolic molecules is important in controlling physiological processes and indicating the health status of humans. Abnormal enantiomeric ratios of chiral molecules in biofluids and tissues occur in many diseases, including cancers and kidney and brain diseases. Thus, chiral small molecules are promising biomarkers for disease diagnosis, prognosis, adverse drug-effect monitoring, pharmacodynamic studies and personalized medicine. However, it remains difficult to achieve cost-effective and reliable analysis of small chiral molecules in clinical procedures, in part owing to their large variety and low concentration. In this Review, we describe current and emerging techniques that detect and quantify small-molecule enantiomers and their biological importance.

Stereoisomers of octahydrocurcumin, the hydrogenated metabolites of curcumin, display stereoselective activity on the CYP2E1 enzyme in L-02 cells

As the final hydrogenated metabolite of curcumin, octahydrocurcumin (OHC) exhibits increased powerful bioactivities. The chiral and symmetric chemical structure indicated that there were two OHC stereoisomers, (3R,5S)-octahydrocurcumin (Meso-OHC) and (3S,5S)-octahydrocurcumin ((3S,5S)-OHC), which may induce different effects on metabolic enzymes and bioactivities. Thus, we detected OHC stereoisomers from rat metabolites (blood, liver, urine and feces) after oral administration of curcumin. In addition, OHC stereoisomers were prepared and then their different influences on cytochrome P450 enzymes (CYPs) and UDP-glucuronyltransferases (UGTs) in L-02 cells were tested to explore the potential interaction and different bioactivities. Our results proved that curcumin could be metabolised into OHC stereoisomers first. In addition, Meso-OHC and (3S,5S)-OHC exhibited slight induction or inhibition effects on CYP1A2, CYP2A6, CYP2C8, CYP2C9, CYP3A4 and UGTs. Furthermore, Meso-OHC exhibited more intensive inhibition toward CYP2E1 expression than (3S,5S)-OHC, ascribed to the different mode of binding to the enzyme protein (P < 0.05), which finally induced more effective liver protection effects in acetaminophen-induced L-02 cell injury.

Chiral 8-aminoBODIPY-based fluorescent probes with site selectivity for the quantitative detection of HSA in biological samples

Human serum albumin (HSA) is one of the vital proteins in blood serum, and its optimum level is a reflection of the physiological well-being of an individual. Any abnormalities in serum HSA levels could often be a sign of disguised physiological disorders. The importance of fast and accurate determination of serum HSA levels has led to the development of various quantification methods. Among these, fluorescence-based methods employ molecular probes capable of producing selective responses on interaction with HSA. Herein, we report chiral 8-aminoBODIPY-based probes having blue emission for the quantitative detection of HSA in buffer and human blood serum. A pair of 8-aminoBODIPY enantiomers, namely R-PEB and S-PEB, were synthesized. They exhibited a fast 'turn-on' fluorescence response towards HSA, allowing its detection and quantification. In PBS buffer, R-PEB and S-PEB showed very good sensitivity with a limit of detection (LoD) of 25 nM (K_D = 9.84 ± 0.14 μM) and 39 nM (K_D = 18.67 ± 0.21 μM), respectively. The linear relationship observed between the fluorescence intensity of R-PEB/S-PEB and the HSA concentration in serum samples allowed us to generate a reference curve for HSA estimation for practical applications. Examination of unknown serum samples showed a good correlation with the results obtained by the benchmark BCG method. Interestingly, the difference in these probes' dissociation constants and LoD indicated their differential binding to HSA. Considering the availability of multiple ligand binding sites in HSA, their binding preferences were investigated in detail by displacement assays using site-specific drugs. These studies showed the preferential affinity of R-PEB towards site II, which was further substantiated using molecular docking studies. However, these displacement assays could not identify the preferred binding site of S-PEB. Blind docking studies indicated that S-PEB occupied a site closer to FA5. Selective binding of R-PEB to site II and its characteristic photophysical response can be utilized to quickly screen potential site II binding drugs.

Analysis of drug interactions with serum proteins and related binding agents by affinity capillary electrophoresis: A review

Biomolecules such as serum proteins can interact with drugs in the body and influence their pharmaceutical effects. Specific and precise methods that analyze these interactions are critical for drug development or monitoring and for diagnostic purposes. Affinity capillary electrophoresis (ACE) is one technique that can be used to examine the binding between drugs and serum proteins, or other agents found in serum or blood. This article will review the basic principles of ACE, along with related affinity-based capillary electrophoresis (CE) methods, and examine recent developments that have occurred in this field as related to the characterization of drug-protein interactions. An overview will be given of the various formats that can be used in ACE and CE for such work, including the relative advantages or weaknesses of each approach. Various applications of ACE and affinity-based CE methods for the analysis of drug interactions with serum proteins and other binding agents will also be presented. Applications of ACE and related techniques that will be discussed include drug interaction studies with serum agents, chiral drug separations employing serum proteins, and the use of CE in hybrid methods to characterize drug binding with serum proteins.

Insight into the Interaction Mechanism of HSA with Aztreonam: A Multispectroscopic and Computational Approach

Aztreonam is a Gram-negative bacteria-targeting synthetic monobactam antibiotic. Human serum albumin (HSA) plays an important role in the transference of pharmaceuticals, hormones, and fatty acids, along with other compounds, determining their biodistribution and physiological fate. Using several biophysical and in silico approaches, we studied the interaction of aztreonam with HSA under physiological environments in this study. Results confirm the formation of HSA-aztreonam complex where aztreonam showed moderate affinity towards HSA. A static mode of quenching was confirmed from the steady state fluorescence data. FRET findings also showed that there was a significant feasibility of energy transfer between HSA and aztreonam. Site marker displacement experimental conclusion suggested the binding site of aztreonam was the sub-domain IB of HSA. Circular dichroic spectroscopic analysis suggested that aztreonam interaction decreases the α-helical content of HSA. Changes in microenvironment were studied through synchronous fluorescence data. According to molecular docking results, the HSA-aztreonam complex is mostly maintained by non-covalent forces, with a binding energy of 7.7 kcal mol^-1. The presence of a hydrogen bond, van der Waal interaction, and pi-anion interaction in the binding process, as well as conformational changes in HSA after binding with aztreonam, are all confirmed by molecular dynamic simulation.

Organism-specific differences in the binding of ketoprofen to serum albumin

Serum albumin is a circulatory transport protein that has a highly conserved sequence and structure across mammalian organisms. Its ligand-binding properties are of importance as albumin regulates the pharmacokinetics of many drugs. Due to the high degree of structural conservation between mammalian albumins, nonhuman albumins such as bovine serum albumin or animal models are often used to understand human albumin-drug interactions. Ketoprofen is a popular nonsteroidal anti-inflammatory drug that is transported by albumin. Here, it is revealed that ketoprofen exhibits different binding-site preferences when interacting with human serum albumin compared with other mammalian albumins, despite the conservation of binding sites across species. The reasons for the observed differences were explored, including identifying ketoprofen binding determinants at specific sites and the influence of fatty acids and other ligands on drug binding. The presented results reveal that the drug-binding properties of albumins cannot easily be predicted based only on a complex of albumin from another organism and the conservation of drug sites between species. This work shows that understanding organism-dependent differences is essential for assessing the suitability of particular albumins for structural or biochemical studies.

Recognition in the Domain of Molecular Chirality: From Noncovalent Interactions to Separation of Enantiomers

It is not a coincidence that both chirality and noncovalent interactions are ubiquitous in nature and synthetic molecular systems. Noncovalent interactivity between chiral molecules underlies enantioselective recognition as a fundamental phenomenon regulating life and human activities. Thus, noncovalent interactions represent the narrative thread of a fascinating story which goes across several disciplines of medical, chemical, physical, biological, and other natural sciences. This review has been conceived with the awareness that a modern attitude toward molecular chirality and its consequences needs to be founded on multidisciplinary approaches to disclose the molecular basis of essential enantioselective phenomena in the domain of chemical, physical, and life sciences. With the primary aim of discussing this topic in an integrated way, a comprehensive pool of rational and systematic multidisciplinary information is provided, which concerns the fundamentals of chirality, a description of noncovalent interactions, and their implications in enantioselective processes occurring in different contexts. A specific focus is devoted to enantioselection in chromatography and electromigration techniques because of their unique feature as "multistep" processes. A second motivation for writing this review is to make a clear statement about the state of the art, the tools we have at our disposal, and what is still missing to fully understand the mechanisms underlying enantioselective recognition.

Probing the serum albumin binding site of fenamates and photochemical protein labeling with a fluorescent dye

Human serum albumin (HSA) can bind with numerous drugs, leading to a significant influence on drug pharmacokinetics as well as undesirable drug-drug interactions due to competitive binding. Probing the HSA drug binding site thus offers great opportunities to reveal drug-HSA binding profiles. In the present study, a fluorescent probe (E)-4-(2-(5-(4-(diphenylamino)phenyl)thiophen-2-yl)vinyl)-1-propylpyridin-1-ium (TTPy) has been prepared, which exhibits enhancement of deep-red to near-infrared (NIR) fluorescence upon HSA binding. The competitive binding assay indicated that TTPy can target the HSA binding site of fenamates, a group of non-steroidal anti-inflammatory drugs (NSAIDs), with moderate binding affinity (1.95 × 10⁶ M^-1 at 303 K). More interestingly, TTPy enables fluorescent labeling of HSA upon visible light irradiation. This study provides promising ways for HSA drug binding site identification and photochemical protein labeling.

Application of Mathematical Modeling and Computational Tools in the Modern Drug Design and Development Process

The conventional drug discovery approach is an expensive and time-consuming process, but its limitations have been overcome with the help of mathematical modeling and computational drug design approaches. Previously, finding a small molecular candidate as a drug against a disease was very costly and required a long time to screen a compound against a specific target. The development of novel targets and small molecular candidates against different diseases including emerging and reemerging diseases remains a major concern and necessitates the development of novel therapeutic targets as well as drug candidates as early as possible. In this regard, computational and mathematical modeling approaches for drug development are advantageous due to their fastest predictive ability and cost-effectiveness features. Computer-aided drug design (CADD) techniques utilize different computer programs as well as mathematics formulas to comprehend the interaction of a target and drugs. Traditional methods to determine small-molecule candidates as a drug have several limitations, but CADD utilizes novel methods that require little time and accurately predict a compound against a specific disease with minimal cost. Therefore, this review aims to provide a brief insight into the mathematical modeling and computational approaches for identifying a novel target and small molecular candidates for curing a specific disease. The comprehensive review mainly focuses on biological target prediction, structure-based and ligand-based drug design methods, molecular docking, virtual screening, pharmacophore modeling, quantitative structure-activity relationship (QSAR) models, molecular dynamics simulation, and MM-GBSA/MM-PBSA approaches along with valuable database resources and tools for identifying novel targets and therapeutics against a disease. This review will help researchers in a way that may open the road for the development of effective drugs and preventative measures against a disease in the future as early as possible.

The 2-hydroxy-3-(4-aryl-1-piperazinyl)propyl Phthalimide Derivatives as Prodrugs—Spectroscopic and Theoretical Binding Studies with Plasma Proteins

Many publications in databases deal with the interactions of new drugs with albumin. However, it is not only albumin that is responsible for binding pharmaceutical molecules to proteins in the human body. There are many more proteins in plasma that are important for the study of the ADME pathway. Therefore, in this study, we have shown the results of the interactions between the plasma proteins albumin, orosomucoid, and gamma globulins and non-toxic anti-inflammatory phthalimide analogs, which due to the promising obtained results, may be potential candidates in the group of analgesic and anti-inflammatory drugs. Using spectroscopic methods and molecular modeling, we showed that all four tested compounds form complexes with the analyzed proteins. The formation of a complex with proteins raises the pharmacological efficacy of the drug. Therefore, the obtained results could be a step in the study of the pharmacokinetics and pharmacodynamics of new potential pharmaceuticals.

Stereoselective Covalent Adduct Formation of Acyl Glucuronide Metabolite of Nonsteroidal Anti-Inflammatory Drugs with UDP-Glucuronosyltransferase

A reactive metabolite of nonsteroidal anti-inflammatory drugs (NSAIDs), acyl-β-D-glucuronide (AG), covalently binds to endogenous proteins. The covalent adduct formation of NSAIDs-AG may lead to the dysfunction of target proteins. Therefore, it is important to clarify the detailed characterization of the formation of covalent protein adducts of NSAID-AG. UDP-glucuronosyltransferase (UGT) catalyzes the conversion of NSAIDs to NSAIDs-AG. The aim of this study was to perform a quantitative analysis of the covalent adduct formation of NSAIDs-AG with UGT. Diclofenac-AG and ketoprofen-AG formed covalent adducts with organelle proteins. Next, the number of covalent adducts formed between NSAIDs-AG and UGT isoforms (UGT1A1, UGT1A9, UGT2B4, and UGT2B9) was determined. The capacity of diclofenac-AG to form covalent adducts with UGT1A9 or UGT2B7 was approximately 10 times higher than that of mefenamic acid-AG. The amounts of covalent adducts of AG of propionic acid derivative NSAIDs with UGT2B were higher than those with UGT1A. Stereoselectivity was observed upon covalent binding to UGT. A significant negative correlation between the half-lives of NSAIDs-AG in phosphate buffers and the amount of covalent adduct with UGT2B7 was observed, suggesting the more labile NSAID-AG forms higher irreversible bindings to UGT. This report provides comprehensive information on the covalent adduct formation of NSAIDs-AGs with UGT.

Herbicidal activity and differential metabolism of lactofen in rat and loach on an enantiomeric level

Enantioselectivity of chiral compounds is receiving growing concern. Lactofen, a chiral herbicide widely used in field crops and vegetables to control broadleaf weeds, is still sold as racemate. In this work, the herbicidal activity and metabolism behavior of lactofen were investigated on an enantiomeric level. Two common broadleaf weeds (Eclipta prostrata L. and Portulaca oleracea L.) were used to evaluate the herbicidal activity of rac-/R- and S-lactofen, and their metabolism behavior in loach and rat liver microsomes was explored. Higher herbicidal activity of S-lactofen was observed, with the 20d-EC₅₀ values being 1.9-3.4 times lower than R-lactofen. Both loach and rat liver microsomes had ability to metabolize rac-lactofen, with half-lives of 1.93 and 1.28 h, respectively. Enantioselective metabolism behaviors were observed in loach and rat liver microsomes and the direction of enantioselectivity were different. R-lactofen was preferentially metabolized in loach liver microsome, while S-lactofen was preferentially metabolized in rat liver microsome. No interconversion of R- and S-lactofen was found. Besides, the main metabolic pathways of R- and S-lactofen were found to be significantly different. R-lactofen was metabolized to R-desethyl lactofen in both loach and rat liver microsomes without further metabolism. However, S-lactofen was metabolized to both S-desethyl lactofen and acifluorfene in rat liver microsome, which was mainly metabolized to acifluorfene in loach liver microsome. This study indicated enantioselectivity and metabolites should be taken into consideration when overall evaluating the environmental behavior of lactofen.

Toxicokinetic evaluation during intoxication of psychotropic drugs using brain microdialysis in mice

In the event of an overdose, the pharmacokinetics of the drug may be altered, resulting in an unexpectedly rapid increase in blood and tissue drug concentrations. Because central nervous system (CNS)-acting drugs are the major cause of hospitalization for overdose, brain concentrations, which are closely related to the development of acute psychotropic symptoms, would be important. However, due to the lack of an appropriate model for overdose, it is difficult to predict the CNS symptoms of patients with acute poisoning. To clarify the toxicokinetics during intoxication with CNS-acting drugs, we investigated the relationship between the dose and concentrations in the blood and brain in mice. Therapeutic or toxic doses of phenobarbital, flunitrazepam, imipramine, and amoxapine were administered intraperitoneally to mice. Serum and extracellular fluid of the brain were collected up to 24 hr after administration and analyzed using LC-MS/MS to determine the pharmacokinetic parameters in the serum and brain. A comparison of the four psychotropic drugs showed that the toxicokinetics of amoxapine in the blood and brain are clearly different from others, with the brain concentrations being specifically highly susceptible to increase during dose escalation. These results are consistent with the CNS-related symptoms observed in amoxapine overdose. Therefore, the methodology of the current study could be useful for predicting CNS toxicity during psychotropic drug poisoning.

Discovery of new chiral sulfonamides bearing benzoxadiazole as HIF inhibitors for non-small cell lung cancer therapy: design, microwave-assisted synthesis, binding affinity, in vitro antitumoral activities and in silico studies

Thirty-four chiral compounds having benzoxadiazole and sulfonamide moieties on the skeleton have been synthesized. The in vitro cytotoxic activity and apoptotic effects of these compounds have been evaluated using the A549 lung cancer cell line.

Enantioresolution and Binding Affinity Studies on Human Serum Albumin: Recent Applications and Trends

The interaction between proteins and drugs or other bioactive compounds has been widely explored over the past years. Several methods for analysis of this phenomenon have been developed and improved. Nowadays, increasing attention is paid to innovative methods, such as high performance affinity liquid chromatography (HPALC) and affinity capillary electrophoresis (ACE), taking into account various advantages. Moreover, the development of separation methods for the analysis and resolution of chiral drugs has been an area of ongoing interest in analytical and medicinal chemistry research. In addition to bioaffinity binding studies, both HPALC and ACE al-low one to perform other type of analyses, namely, displacement studies and enantioseparation of racemic or enantiomeric mixtures. Actually, proteins used as chiral selectors in chromatographic and electrophoretic methods have unique enantioselective properties demonstrating suitability for the enantioseparation of a large variety of chiral drugs or other bioactive compounds. This review is mainly focused in chromatographic and electrophoretic methods using human serum albumin (HSA), the most abundant plasma protein, as chiral selector for binding affinity analysis and enantioresolution of drugs. For both analytical purposes, updated examples are presented to highlight recent applications and current trends.

Asymmetric synthesis of chiral organosilicon compounds via transition metal-catalyzed stereoselective C-H activation and silylation

This feature article details the progress of transition metal-catalyzed stereoselective sp² and sp³ C-H activation and silylation in the synthesis of chiral organosilicon compounds, and the asymmetric C-H silylation includes intramolecular cyclizing silylation and intermolecular silylation. The silylating reagents include monohydrosilanes, dihydrosilanes, silacylcobutanes and disilanes. In general, catalytic systems include a transition metal salt as the catalyst and a chiral ligand. No external chiral ligand is required in some cases where the chiral substrates act as the source of chirality. Many kinds of silylated compounds with central, axial, planar, or helical chirality have been constructed via C-H activation by asymmetric rhodium, iridium or palladium catalysis. Some pharmacophores and material building blocks were successfully introduced into the target molecules. Some silylated products proved to be useful in medicinal chemistry, synthetic organic chemistry, and materials science. Besides reaction development, mechanisms for stereoselective C-H activation and silylation are also discussed.

Molecular determinants of pro-arrhythmia proclivity of d- and l-sotalol via a multi-scale modeling pipeline

Drug isomers may differ in their proarrhythmia risk. An interesting example is the drug sotalol, an antiarrhythmic drug comprising d- and l- enantiomers that both block the hERG cardiac potassium channel and confer differing degrees of proarrhythmic risk. We developed a multi-scale in silico pipeline focusing on hERG channel – drug interactions and used it to probe and predict the mechanisms of pro-arrhythmia risks of the two enantiomers of sotalol. Molecular dynamics (MD) simulations predicted comparable hERG channel binding affinities for d- and l-sotalol, which were validated with electrophysiology experiments. MD derived thermodynamic and kinetic parameters were used to build multi-scale functional computational models of cardiac electrophysiology at the cell and tissue scales. Functional models were used to predict inactivated state binding affinities to recapitulate electrocardiogram (ECG) QT interval prolongation observed in clinical data. Our study demonstrates how modeling and simulation can be applied to predict drug effects from the atom to the rhythm for dl-sotalol and also increased proarrhythmia proclivity of d- vs. l-sotalol when accounting for stereospecific beta-adrenergic receptor blocking.

Enantioselectivity in Drug Pharmacokinetics and Toxicity: Pharmacological Relevance and Analytical Methods

Enzymes, receptors, and other binding molecules in biological processes can recognize enantiomers as different molecular entities, due to their different dissociation constants, leading to diverse responses in biological processes. Enantioselectivity can be observed in drugs pharmacodynamics and in pharmacokinetic (absorption, distribution, metabolism, and excretion), especially in metabolic profile and in toxicity mechanisms. The stereoisomers of a drug can undergo to different metabolic pathways due to different enzyme systems, resulting in different types and/or number of metabolites. The configuration of enantiomers can cause unexpected effects, related to changes as unidirectional or bidirectional inversion that can occur during pharmacokinetic processes. The choice of models for pharmacokinetic studies as well as the subsequent data interpretation must also be aware of genetic factors (such as polymorphic metabolic enzymes), sex, patient age, hepatic diseases, and drug interactions. Therefore, the pharmacokinetics and toxicity of a racemate or an enantiomerically pure drug are not equal and need to be studied. Enantioselective analytical methods are crucial to monitor pharmacokinetic events and for acquisition of accurate data to better understand the role of the stereochemistry in pharmacokinetics and toxicity. The complexity of merging the best enantioseparation conditions with the selected sample matrix and the intended goal of the analysis is a challenge task. The data gathered in this review intend to reinforce the importance of the enantioselectivity in pharmacokinetic processes and reunite innovative enantioselective analytical methods applied in pharmacokinetic studies. An assorted variety of methods are herein briefly discussed.

Peptoids as a Chiral Stationary Phase for Liquid Chromatography: Insights from Molecular Dynamics Simulations

Peptoids are peptide regioisomers with attractive structural tunability in terms of sequence and three-dimensional arrangement. Peptoids are foreseen to have a great potential for many diverse applications, including their utilization as a chiral stationary phase in chromatography. To achieve chiral recognition, a chiral side chain is required to allow specific interactions with a given enantiomer from a racemic mixture. One of the most studied chiral stationary phases, built with (S)-N-1-phenylethyl (Nspe) units, was shown to be successful in resolving racemic mixtures of binaphthyl derivatives. However, there is currently no description at the atomic scale of the factors favoring its enantioselectivity. Here, we take advantage of steered molecular dynamics simulations to mimic the elution process at the atomic scale and present evidence that the predominantly right-handed helical conformation of Nspe peptoids and their ability to form stronger hydrogen bonds with the (S) enantiomer are responsible for the chiral recognition of the popular chiral probe 2,2'-bihydroxy-1,1'-binaphthyl.

Carvone Enantiomers Differentially Modulate IgE-Mediated Airway Inflammation in Mice

Carvone is a monoterpene found in nature in the form of enantiomers (S- and R-). While previous research has demonstrated the anti-inflammatory and anti-allergic effects of carvone, the influence of carvone enantiomeric composition on its anti-allergic activity remains to be investigated. This study aimed to evaluate the anti-allergic activity of carvone enantiomers in a murine model of airway allergic inflammation induced by sensitization and challenge with ovalbumin (OVA). The oral treatment with R-carvone or S-carvone 1 h before each challenge inhibited the number of leukocytes and eosinophils in the bronchoalveolar lavage (BAL). R-carvone inhibited leukocyte infiltration and mucus production in the lung, which was correlated with decreased production of OVA-specific IgE in the serum and increased concentrations of IL-10 in the BAL. On the other hand, the administration of S-carvone had little inhibitory effect on inflammatory infiltration and mucus production in the lung, which might be associated with increased production of IFN-γ in the BAL. When administered 1 h before each sensitization, both enantiomers inhibited eosinophil recruitment to the BAL but failed in decreasing the titers of IgE in the serum of allergic mice. Our data indicate that carvone enantiomers differentially modulated IgE-mediated airway inflammation in mice. In conclusion, unlike S-carvone, R-carvone has the potential to be used in anti-allergic drug development.

Development of a UHPLC-MS/MS method for the quantification of ilaprazole enantiomers in rat plasma and its pharmacokinetic application

In Korea and China, ilaprazole is a widely used proton pump inhibitor in the treatment of gastric ulcers. In this study, a specific and sensitive LC-MS/MS method has been developed and validated for the quantification of ilaprazole enantiomers in the rat plasma, using R-lansoprazole as the internal standard. The enantioseparation was achieved on a CHIRALPAK AS-RH column (4.6 mm × 150 mm, i.d. 5 μm), with a mobile phase composed of 10 mM ammonium acetate aqueous solution and acetonitrile (60:40, V/V), at a flow-rate of 0.5 mL/min. The method was validated over the concentration range of 0.5-300 ng/mL for both, R- and S -ilaprazole. The lower limit of quantification was 0.5 ng/mL for both enantiomers. The relative standard deviation (RSD) of intra- and inter-day precision of R-ilaprazole and S-ilaprazole was less than 10.9%, and the relative error accuracy (RE) ranged from -0.5%-2.0%. Finally, the method was successfully evaluated in rats in a stereoselective pharmacokinetic study of the ilaprazole racemate.

Atropselective Partitioning of Polychlorinated Biphenyls in a HepG2 Cell Culture System: Experimental and Modeling Results

Cell culture models are used to study the toxicity of polychlorinated biphenyls (PCBs); however, it is typically unknown how much PCB enters the cells and, for chiral PCBs, if the partitioning is atropselective. We investigated the partitioning of racemic PCB 91, PCB 95, PCB 132, and PCB 136 in HepG2 cells following a 72 h incubation. PCBs were present in the cell culture medium (60.7-88.8%), cells (8.0-14.6%), and dishes (2.3-7.8%) and displayed atropisomeric enrichment in the cells (enantiomeric fraction [EF] = 0.55-0.77) and dishes (EF = 0.53-0.68). Polyparameter linear free energy relationships coupled with a composition-based model provided a good estimate of the PCB levels in the cells and cell culture medium. The free concentration was subsequently used to extrapolate from the nominal cell culture concentration to PCB tissue levels and vice versa. This approach can be used for in vitro-in vivo extrapolations for all 209 PCB congeners. However, this model (and modified models based on descriptors incorporating atropselective interactions, i.e., relative retention times on chiral columns) did not predict the atropselective partitioning in the cell culture system. Improved chemical descriptors that account for the atropselective binding of PCBs to biological macromolecules are, therefore, needed to predict the atropselective partitioning of PCBs in biological systems.

Enantioselective disposition and metabolic products of isofenphos-methyl in rats and the hepatotoxic effects

Isofenphos-methyl (IFP), a chiral organophosphorus pesticide, is one of the main chemicals used to control underground insects and nematodes. Recently, the use of IFP on vegetables and fruits has been prohibited due to its high toxicity. In this study, we investigated the enantioselective distribution and metabolism of IFP and its metabolites, namely, isofenphos-methyl oxon (IFPO) and isocarbophos oxon (ICPO), in male Sprague Dawley (SD) rats. Forty eight hours (48 h) after exposure, ICPO was the main detectable compound in blood (up to 75%) and urine (up to 77%), and we found that (S)-ICPO was significantly more stable than (R)-ICPO (p < 0.05). Therefore, (S)-ICPO was proposed as a suitable candidate biomarker for the biomonitoring of IFP in human urine and blood. After 48 h exposure, 21.2-41.0%, 4.1-15.1%, and 8.6-18.7% of dosed IFP was detected in the liver of racemic, R and S enantiomer-exposed rats, respectively, and R-IFP and R-IFPO showed a faster degradation (p < 0.05). Our results showed that after one week of consecutive exposure to IFP, ICPO was accumulated in the liver of rats in both racemic and enantiopure groups (no difference between the groups, p > 0.05). We found that cytochrome P450 (CYP) (i.e. CYP2C11, CYP2D2 and CYP3A2 enzymes and carboxylesterases) is responsible for the enantioselective metabolism of IFP in liver. In addition, rats exposed to (S)-IFP exhibited hepatic lipid peroxidation, liver inflammation and hepatic fibrosis. This study provides useful information and a reference for the biomonitoring and risk assessment of IFP and organophosphorus pesticide exposure.

Investigation of the enantioselective interaction between selected drug enantiomers and human serum albumin by mobility shift-affinity capillary electrophoresis

Mobility shift-affinity capillary electrophoresis was employed for enantioseparation and simultaneous binding constant determination. Human serum albumin was used as a chiral selector in the background electrolyte composed of 20 mM phosphate buffer, pH 7.4. The applied setup supports a high mobility shift since albumin and the drug-albumin complex hold negative net charges, while model compounds of amlodipine and verapamil are positively charged. In order to have an accurate effective mobility determination, the Haarhoff-van der Linde function was utilized. Subsequently, the association constant was determined by nonlinear regression analysis of the dependence of effective mobilities on the total protein concentration. Differences in the apparent binding status between the enantiomers lead to mobility shifts of different extends (α). This resulted in enantioresolutions of Rs = 1.05-3.63 for both drug models. R-(+)-Verapamil (K_A 1844 M^-1 ) proved to bind stronger to human serum albumin compared to S-(-)-verapamil (K_A 6.6 M^-1 ). The association constant of S-(-)-amlodipine (K_A 25 073 M^-1 ) was found to be slightly higher compared to its antipode (K_A 22 620 M^-1 ) when applying the racemic mixture. The low measurement uncertainty of this approach was demonstrated by the close agreement of the association constant of the enantiopure S-(-)-form (K_A 25 101 M^-1 ).

Stereoselective Pharmacokinetics and Chiral Inversions of Some Chiral Hydroxy Group Drugs

BACKGROUND

Chiral safety, especially chiral drug inversion in vivo, is the top priority of current scientific research. Medicine researchers and pharmacists often ignore that one enantiomer will be converted or partially converted to another enantiomer when it is ingested in vivo. So that, in the context that more than 50% of the listed drugs are chiral drugs, it is necessary and important to pay attention to the inversion of chiral drugs.

METHODS

The metabolic and stereoselective pharmacokinetic characteristics of seven chiral drugs with one chiral center in the hydroxy group were reviewed in vivo and in vitro including the possible chiral inversion of each drug enantiomer. These seven drugs include (S)-Mandelic acid, RS-8359, Tramadol, Venlafaxine, Carvedilol, Fluoxetine and Metoprolol.

RESULTS

The differences in stereoselective pharmacokinetics could be found for all the seven chiral drugs, since R and S isomers often exhibit different PK and PD properties. However, not every drug has shown the properties of one direction or two direction chiral inversion. For chiral hydroxyl group drugs, the redox enzyme system may be one of the key factors for chiral inversion in vivo.

CONCLUSION

In vitro and in vivo chiral inversion is a very complex problem and may occur during every process of ADME. Nowadays, research on chiral metabolism in the liver has the most attention, while neglecting the chiral transformation of other processes. Our review may provide the basis for the drug R&D and the safety of drugs in clinical therapy.

Association of Lipid Levels with Mefloquine and Carboxy-Mefloquine Concentrations in Patients with Uncomplicated Falciparum Malaria

Mefloquine shows a high capacity to bind plasma proteins, which influences the amount of drug in erythrocytes. The study investigated the association of lipids levels with plasma concentrations of mefloquine and carboxy-mefloquine in 85 Brazilian patients with uncomplicated falciparum malaria. There were no significant associations between the total cholesterol or triglycerides with plasma concentrations of mefloquine and of carboxy-mefloquine. Lipoprotein levels explained 25.68% and 18.31% of mefloquine and carboxy-mefloquine plasma concentrations, respectively.

Spin effects as a tool to study photoinduced processes in (S/R)-ketoprofen-(S)-N-methylpyrrolidine dyads

(S/R)-Ketoprofen (KP) is considered to be the strongest photosensitizer among nonsteroidal anti-inflammatory drugs. The photosensitizing reactions are caused by a substituted benzophenone chromophore. It produces various toxic effects through the formation of active paramagnetic intermediates and photoproducts able to attack biological substrates. Photoinduced transformations of KP have been extensively studied in order to identify paramagnetic intermediates. Considerable attention is also paid to photoinduced processes in dyads, where KP is linked with chiral partners, since such processes believed to model the binding of chiral drugs with enzymes and receptors. In the present study, the dyads containing (S)/(R)-KP covalently linked with (S)-N-methylpyrrolidine have been synthesized to examine the peculiarities of photoinduced electron transfer (ET) and hydrogen transfer (HT) in chiral systems. To detect short-lived paramagnetic intermediates, in dyad's excited triplet state, such as biradical zwitter ion (BZI) and neutral biradical (BR), spin chemistry methods [chemically induced dynamic nuclear polarization (CIDNP) and chemically induced dynamic electron polarization (CIDEP) in arbitrary magnetic fields], allowing indirect detection of transient paramagnetic particles by NMR, have been utilized. Both mentioned processes have been found to begin with the excitation of KP into the triplet state followed by the formation of BZI for ET and BR for HT, respectively. Products of stereoselective attachment of the N-methylpyrrolidine residue to the carbonyl carbon atom of KP occurring in both BZI and BR have been detected by NMR spectral analysis. The value of electronic exchange interaction in biradicals has been determined from the position of the characteristic maximum of hyperpolarization in the CIDNP magnetic field dependences.

Simultaneous enantioseparation of nonsteroidal anti-inflammatory drugs by a one-dimensional liquid chromatography technique using a dynamically coated chiral porous silicon pillar array column

The preparation of a highly efficient chiral liquid chromatography (LC) column is explored by dynamically coating a reversed-phase porous silicon pillar array column with hydroxypropyl-β-cyclodextrin (Hp-β-CD) as the chiral selector. Analyte mixtures composed of non-steroidal anti-inflammatory drugs were tested to reveal the enantioseparation potential of the column. The mechanism of chiral discrimination was investigated. The adsorbed Hp-β-CDs on the column surface experience different interaction with enantiomers. The chiral stationary phase showed satisfying stability and could be easily restored by recovering the selector with sufficient flushing and repeating the loading procedure. The peak capacity of the column was evaluated, and it was found high enough to separate three enantiomer couples using a one-dimensional LC technique.

Human serum albumin-resveratrol complex formation: Effect of the phenolic chemical structure on the kinetic and thermodynamic parameters of the interactions

The thermodynamics and kinetics of binding between human serum albumin (HSA) and resveratrol (RES) or its analog (RESAn1) were investigated by surface plasmon resonance (SPR). The binding constant and the kinetic constants of association and dissociation indicated that RESAn1 has higher affinity toward HSA than does RES. The formation of these complexes was entropically driven ( [Formula: see text] , [Formula: see text]  KJ mol^-1). However, for both polyphenols, the activation energy (E_act) of association (a) of free molecules was higher than that for dissociation (d) of the stable complex ( [Formula: see text]  KJ mol^-1), and the rate of association was faster than that of dissociation since the activation Gibbs free energy (ΔG^‡) was lower for the former (ΔG_aHSA-RES^‡≅54.73,ΔG_dHSA-RES^‡≅73.83,ΔG_aHSA-RESAn1^‡≅54.14,ΔG_dHSA-RESAn1^‡≅73.97 KJ mol^-1). This study showed that small differences in the structure of polyphenols such as RES and RESAn1 influenced the thermodynamics and kinetics of the complex formation with HSA.

Stereoselectivity evaluation of chiral chitosan microspheres delivery system containing rac-KET in vitro and in vivo

The influence of chiral excipient D-chitosan (CS) on the stereoselective release of racemic ketoprofen (rac-KET) microspheres has been investigated in comparison to those microspheres containing individual enantiomers in vitro and in vivo. Stereoselectivity was observed in vitro release test, with R-KET release slightly higher than that of S-KET, especially in 3% rac-KET loading microspheres. Stereoselectivity is dependent on the content of chiral excipient and pH of release medium. A molecular docking study between CS and KET enantiomers further revealed that S-KET has a stronger interaction with CS compared to R-KET. Moreover, the plasma concentration of KET enantiomers in rats shows substantial differences, as the plasma levels of S-KET were higher than those of R-KET. Plasma levels of enantiomers from the R-KET microspheres had similar stereoselectivity as rac-KET microspheres. The S/R ratio of rac-KET microspheres was significantly lower than that of rac-KET suspension (regular-release formulation) (p<.05), and the differences is 3–5 fold. Besides, rates of R-KET converted to S-KET exhibited differences between rac-KET microspheres and suspension. Similar results were also found between R-KET microspheres and suspension. All investigations suggest that the chitosan interacting preferentially with S-KET to R-KET significantly affect the stereoselective pharmacokinetics of rac-KET from chitosan microspheres in rats.

Pursuing Specific Chemotherapy of Orthotopic Breast Cancer with Lung Metastasis from Docking Nanoparticles Driven by Bioinspired Exosomes

Breast cancer develops from local tissue but is characterized by a distinct metastatic pattern involving regional lymph nodes and distant organs, which is the primary cause of high mortality in breast cancer patients. Herein, optimal docking nanoparticles (NPs) composed of a laurate-functionalized Pt(IV) prodrug (Pt(lau)), human serum albumin (HSA), and lecithin were predicted by computational modeling, prepared by nanoprecipitation, and validated by fluorescence spectroscopy. As macrophages have been reported to be preferentially recruited by breast cancer, Rex, the exosome spontaneously secreted by murine RAW 264.7 cells, was isolated to encapsulate the NPs. This high-performance delivery system, called NPs/Rex, possessed the desired physicochemical properties, enhanced colloidal stability, and redox-triggered release profile. Investigations of cytodynamics proved that NPs/Rex was internalized through multiple pathways, avoided entrapment by bilayers, and successfully platinized nucleic acids after bioreduction in the cytosol. Intracellular activation of Pt(lau) was confirmed by observing the characteristic effects of cisplatin on cell proliferation and the cell cycle following treatment with NPs/Rex. During in vivo application, the bioinspired Rex coating endowed docking NPs with prolonged blood circulation, smart organ tropism, and enhanced biocompatibility, as well as robust platinum (Pt) chemotherapy for breast cancer cells in orthotopic tumors of fat pads and metastatic nodules of lungs. Therefore, this favorable nanoplatform might provide valuable insight into the derivatization and development of Pt anticancer drugs used currently in the clinic.

Stereoselective glucuronidation metabolism, pharmacokinetics, anti-amnesic pharmacodynamics, and toxic properties of vasicine enantiomers in vitro and in vivo

Vasicine (VAS) is a potential natural cholinesterase inhibitor for treatment of Alzheimer's disease. Due to one chiral centre (C-3) presenting in molecule, VAS has two enantiomers, d-vasicine (d-VAS) and l-vasicine (l-VAS). The study was undertaken to investigate the stereoselective glucuronidation metabolism, pharmacokinetics, anti-amnesic effect and acute toxicity of VAS enantiomers. In results, the glucuronidation metabolic rate of l-VAS was faster than d-VAS in human liver microsomes and isoenzymes tests, and it was proved that the UDP-glucuronosyltransferase (UGT) 1A9 and UGT2B15 were the major metabolic enzymes for glucuronidation of l-VAS, while only UGT1A9 for d-VAS, which take responsibility of the significantly less metabolic affinity of d-VAS than l-VAS in HLM and rhUGT1A9. The plasma exposure of d-VAS in rats was 1.3-fold and 1.6-fold higher than that of l-VAS after intravenous and oral administration of d-VAS and l-VAS, respectively. And the plasma exposure of the major glucuronidation metabolite d-VASG was one of tenth of l-VASG or more less, no matter by intravenous or oral administration. Both d-VAS and l-VAS were exhibited promising acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) inhibitory activities, and the BChE inhibitory activity of d-VAS with IC₅₀ of 0.03 ± 0.001 μM was significantly stronger than that of l-VAS with IC₅₀ of 0.98 ± 0.19 μM. The molecular docking results indicated that d-VAS and l-VAS could bind to the catalytic active site (CAS position) either of human AChE and BChE, and the BChE combing ability of d-VAS (the score of GBI/WAS dG -7.398) was stronger than that of l-VAS (the score of GBI/WAS dG -7.135). Both d-VAS and l-VAS could improving the learning and memory on scopolamine-induced memory deficits in mice. The content of acetylcholine (ACh) after oral administration d-VAS increased more than that of l-VAS in mice cortex, through inhibiting cholinesterase (ChE) and increasing choline acetyltransferase (ChAT). In addition, the LD₅₀ value of d-VAS (282.51 mg·kg^-1) was slight lower than l-VAS (319.75 mg·kg^-1). These results indicated that VAS enantiomers displayed significantly stereoselective metabolic, pharmacokinetics, anti-amnesic effect and toxic properties in vitro and in vivo. The d-VAS might be the dominant configuration for treating Alzheimer's disease.

Spectroscopic methods to analyze drug metabolites

Drug metabolites have been monitored with various types of newly developed techniques and/or combination of common analytical methods, which could provide a great deal of information on metabolite profiling. Because it is not easy to analyze whole drug metabolites qualitatively and quantitatively, a single solution of analytical techniques is combined in a multilateral manner to cover the widest range of drug metabolites. Mass-based spectroscopic analysis of drug metabolites has been expanded with the help of other parameter-based methods. The current development of metabolism studies through contemporary pharmaceutical research are reviewed with an overview on conventionally used spectroscopic methods. Several technical approaches for conducting drug metabolic profiling through spectroscopic methods are discussed in depth.

Spin Selectivity in Chiral Linked Systems

This work has shown spin selectivity in electron transfer (ET) of diastereomers of (R,S)-naproxen-(S)-N-methylpyrrolidine and (R,S)-naproxen-(S)-tryptophan dyads. Photoinduced ET in these dyads is interesting because of the still unexplained phenomenon of stereoselectivity in the drug activity of enantiomers. The chemically induced dynamic nuclear polarization (CIDNP) enhancement coefficients of (R,S)-diastereomers are double those of the (S,S)-analogue. These facts are also interesting because spin effects are among the most sensitive, even to small changes in spin and molecular dynamics of paramagnetic particles. Therefore, CIDNP reflects the difference in magnetoresonance parameters (hyperfine interaction constants (HFIs), g-factor difference) and lifetimes of the paramagnetic forms of (R,S)- and (S,S)-diastereomers. The difference in HFI values for diastereomers has been confirmed by a comparison of CIDNP experimental enhancement coefficients with those calculated. Additionally, the dependence of the CIDNP enhancement coefficients on diastereomer concentration has been observed for the naproxen-N-methylpyrrolidine dyad. This has been explained by the participation of ET in homo-(R,S-R,S or S,S-S,S) and hetero-(R,S-S,S) dimers of dyads. In this case, the effectivity of ET, and consequently, CIDNP, is supposed to be different for (R,S)- and (S,S)-homodimers, heterodimers, and monomers. The possibility of dyad dimer formation has been demonstrated by using high-resolution X-ray and NMR spectroscopy techniques.