Bioactivation potential of thiophene-containing drugs

A computer-aided method for controlling chemical resistance of drugs using RRKM theory in the liquid phase

The chemical resistance of drugs against any change in their composition and studying the rate of multiwell-multichannel reactions in the liquid phase, respectively, are the important challenges of pharmacology and chemistry. In this article, we investigate two challenges together through studying drug stability against its unimolecular reactions in the liquid phase. Accordingly, multiwell-multichannel reactions based on 1,4-H shifts are designed for simplified drugs such as 3-hydroxyl-1H-pyrrol-2(5H)-one, 3-hydroxyfuran-2(5H)-one, and 3-hydroxythiophen-2(5H)-one. After that, the reverse and forward rate constants are calculated by using the Rice Ramsperger Kassel Marcus theory (RRKM) and Eckart tunneling correction over the 298-360 K temperature range. Eventually, using the obtained rate constants, we can judge drug resistance versus structural changes. To attain the goals, the potential energy surfaces of all reactions are computed by the complete basis set-quadratic Becke3 composite method, CBS-QB3, and the high-performance meta hybrid density functional method, M06-2X, along with the universal Solvation Model based on solute electron Density, SMD, due to providing more precise and efficient results for the barrier heights and thermodynamic studies. To find the main reaction pathway of the intramolecular 1,4-H shifts in the target molecules, all possible reaction pathways are considered mechanistically in the liquid phase. Also, the direct dynamics calculations that carry out by RRKM theory on the modeled pathways are used to distinguish the main reaction pathway. As the main finding of this research, the results of quantum chemical calculations accompanied by the RRKM/Eckart rate constants are used to predict the stability of drugs. This study proposes a new way to examine drug stability by the computer-aided reaction design of target drugs. Our results show that 3-hydroxyfuran-2(5H)-one based drugs are the most stable and 3-hydroxythiophen-2(5H)-one based drugs are more stable than 3-hydroxy-1H-pyrrol-2 (5H)-one based drugs in water solution.

Selective Oxidation of Clopidogrel by Peroxymonosulfate (PMS) and Sodium Halide (NaX) System: An NMR Study

A selective transformation of clopidogrel hydrogen sulfate (CLP) by reactive halogen species (HOX) generated from peroxymonosulfate (PMS) and sodium halide (NaX) is described. Other sustainable oxidants as well as different solvents have also been investigated. As result of this study, for each sodium salt the reaction conditions were optimized, and four different degradation products were formed. Three products were halogenated at C-2 on the thiophene ring and have concomitant functional transformation, such as N-oxide in the piperidine group. A halogenated endo-iminium product was also observed. With this condition, a fast preparation of known endo-iminium clopidogrel impurity (new counterion) was reported as well. The progress of the reaction was monitored using nuclear magnetic resonance spectroscopy as an analytical tool and all the products were characterized by 1D-, 2D-NMR and HRMS.

Oxidative metabolism of razuprotafib (AKB-9778), a sulfamic acid phosphatase inhibitor, in human microsomes and recombinant human CYP2C8 enzyme

Razuprotafib, a sulphamic acid-containing phosphatase inhibitor, is shown in vivo to undergo enzymatic oxidation and methylation to form a major metabolite in monkey and human excreta with an m/z^- value of 633.LC-MS/MS analysis of samples derived from incubations of razuprotafib with human liver microsomes and recombinant CYP2C8 enzyme has elucidated the metabolic pathway for formation of the thiol precursor to the S-methyl metabolite MS633 (m/z^- 633).Under in vitro conditions, the major pathway of razuprotafib metabolism involves extensive oxidation of the thiophene and phenyl rings.A single oxidation takes place at one of the phenyl groups. Multiple oxidations occur at the thiophene moiety: initial oxidation results in the formation of a thiolactone followed by a second oxidation giving rise to an S-oxide of the thiolactone, which is further metabolised to the ring-opened form and ultimate formation of a thiol (m/z^- 619).An additional mono-oxidation pathway involves epoxidation of the thiophene followed by hydrolysis to a diol.The thiol and diol metabolites are trapped by the addition of a nucleophilic trapping agent, 3-methoxyphenacyl bromide (MPB), giving adducts with m/z^- 767.The thiol is a likely precursor to the major in vivo razuprotafib metabolite, MS633.

Positive allosteric mechanisms of adenosine A1 receptor-mediated analgesia

The adenosine A1 receptor (A1R) is a promising therapeutic target for non-opioid analgesic agents to treat neuropathic pain1,2. However, development of analgesic orthosteric A1R agonists has failed because of a lack of sufficient on-target selectivity as well as off-tissue adverse effects3. Here we show that [2-amino-4-(3,5-bis(trifluoromethyl)phenyl)thiophen-3-yl)(4-chlorophenyl)methanone] (MIPS521), a positive allosteric modulator of the A1R, exhibits analgesic efficacy in rats in vivo through modulation of the increased levels of endogenous adenosine that occur in the spinal cord of rats with neuropathic pain. We also report the structure of the A1R co-bound to adenosine, MIPS521 and a Gi2 heterotrimer, revealing an extrahelical lipid-detergent-facing allosteric binding pocket that involves transmembrane helixes 1, 6 and 7. Molecular dynamics simulations and ligand kinetic binding experiments support a mechanism whereby MIPS521 stabilizes the adenosine-receptor-G protein complex. This study provides proof of concept for structure-based allosteric drug design of non-opioid analgesic agents that are specific to disease contexts.

In-silico evaluation of Malawi essential medicines and reactive metabolites for potential drug-induced toxicities

BACKGROUND

Drug-induced toxicity is one of the problems that have negatively impacted on the well-being of populations throughout the world, including Malawi. It results in unnecessary hospitalizations, retarding the development of the country. This study assessed the Malawi Essential Medicines List (MEML) for structural alerts and reactive metabolites with the potential for drug-induced toxicities.

METHODS

This in-silico screening study used StopTox, ToxAlerts and LD-50 values toxicity models to assess the MEML drugs. A total of 296 drugs qualified for the analysis (those that had defined chemical structures) and were screened in each software programme. Each model had its own toxicity endpoints and the models were compared for consensus of their results.

RESULTS

In the StopTox model, 86% of the drugs had potential to cause at least one toxicity including 55% that had the potential of causing eye irritation and corrosion. In ToxAlerts, 90% of the drugs had the potential of causing at least one toxicity and 72% were found to be potentially reactive, unstable and toxic. In LD-50, 70% of the drugs were potentially toxic. Model consensus evaluation results showed that the highest consensus was observed between ToxAlerts and StopTox (80%). The overall consensus amongst the three models was 57% and statistically significant (p < 0.05).

CONCLUSIONS

A large number of drugs had the potential to cause various systemic toxicities. But the results need to be interpreted cautiously since the clinical translation of QSAR-based predictions depends on many factors. In addition, inconsistencies have been reported between screening results amongst different models.

One-Pot Synthesis of 2-Acetyl-1H-pyrroles from N-Propargylic β-Enaminones via Intermediacy of 1,4-Oxazepines

A one-pot two-step protocol for the synthesis of 2-acetyl-1H-pyrroles from N-propargylic β-enaminones was described. When treated with zinc chloride in refluxing chloroform, N-propargylic β-enaminones produced in situ 2-methylene-2,3-dihydro-1,4-oxazepines, which, upon further refluxing in methanol with zinc chloride, afforded 2-acetyl-1H-pyrroles. The process was found to be general for a wide variety of N-propargylic β-enaminones and yielded a diverse range of 2-acetyl-1H-pyrroles in good to high yields with large substrate scope and good functional group tolerance. This operationally easy method may provide a rapid access to functionalized 2-acetyl-1H-pyrroles of pharmacological interest.

Reactive Metabolites from Thiazole-Containing Drugs: Quantum Chemical Insights into Biotransformation and Toxicity

Drugs containing thiazole and aminothiazole groups are known to generate reactive metabolites (RMs) catalyzed by cytochrome P450s (CYPs). These RMs can covalently modify essential cellular macromolecules and lead to toxicity and induce idiosyncratic adverse drug reactions. Molecular docking and quantum chemical hybrid DFT study were carried out to explore the molecular mechanisms involved in the biotransformation of thiazole (TZ) and aminothiazole (ATZ) groups leading to RM epoxide, S-oxide, N-oxide, and oxaziridine. The energy barrier required for the epoxidation is 13.63 kcal/mol, that is lower than that of S-oxidation, N-oxidation, and oxaziridine formation (14.56, 17.90, and 20.20, kcal/mol respectively). The presence of the amino group in ATZ further facilitates all the metabolic pathways, for example, the barrier for the epoxidation reaction is reduced by ∼2.5 kcal/mol. Some of the RMs/their isomers are highly electrophilic and tend to form covalent bonds with nucleophilic amino acids, finally leading to the formation of metabolic intermediate complexes (MICs). The energy profiles of these competitive pathways have also been explored.

Mechanism-Based Inactivation of Cytochrome P450 Enzymes: Computational Insights

Mechanism-based inactivation (MBI) refers to the metabolic bioactivation of a xenobiotic by cytochrome P450s to a highly reactive intermediate which subsequently binds to the enzyme and leads to the quasi-irreversible or irreversible inhibition. Xenobiotics, mainly drugs with specific functional units, are the major sources of MBI. Two possible consequences of MBI by medicinal compounds are drug-drug interaction and severe toxicity that are observed and highlighted by clinical experiments. Today almost all of these latent functional groups (e.g., thiophene, furan, alkylamines, etc.) are known, and their features and mechanisms of action, owing to the vast experimental and theoretical studies, are determined. In the past decade, molecular modeling techniques, mostly density functional theory, have revealed the most feasible mechanism that a drug undergoes by P450 enzymes to generate a highly reactive intermediate. In this review, we provide a comprehensive and detailed picture of computational advances toward the elucidation of the activation mechanisms of various known groups with MBI activity. To this aim, we briefly describe the computational concepts to carry out and analyze the mechanistic investigations, and then, we summarize the studies on compounds with known inhibition activity including thiophene, furan, alkylamines, terminal acetylene, etc. This study can be reference literature for both theoretical and experimental (bio)chemists in several different fields including rational drug design, the process of toxicity prevention, and the discovery of novel inhibitors and catalysts.

N-(1,3,4-Oxadiazol-2-yl)Benzamides as Antibacterial Agents against Neisseria gonorrhoeae

The Centers for Disease Control and Prevention (CDC) recognizes Neisseria gonorrhoeae as an urgent-threat Gram-negative bacterial pathogen. Additionally, resistance to frontline treatment (dual therapy with azithromycin and ceftriaxone) has led to the emergence of multidrug-resistant N. gonorrhoeae, which has caused a global health crisis. The drug pipeline for N. gonorrhoeae has been severely lacking as new antibacterial agents have not been approved by the FDA in the last twenty years. Thus, there is a need for new chemical entities active against drug-resistant N. gonorrhoeae. Trifluoromethylsulfonyl (SO2CF3), trifluoromethylthio (SCF3), and pentafluorosulfanyl (SF5) containing N-(1,3,4-oxadiazol-2-yl)benzamides are novel compounds with potent activities against Gram-positive bacterial pathogens. Here, we report the discovery of new N-(1,3,4-oxadiazol-2-yl)benzamides (HSGN-237 and -238) with highly potent activity against N. gonorrhoeae. Additionally, these new compounds were shown to have activity against clinically important Gram-positive bacteria, such as methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant enterococci (VRE), and Listeria monocytogenes (minimum inhibitory concentrations (MICs) as low as 0.25 µg/mL). Both compounds were highly tolerable to human cell lines. Moreover, HSGN-238 showed an outstanding ability to permeate across the gastrointestinal tract, indicating it would have a high systemic absorption if used as an anti-gonococcal therapeutic.

Chimeric Drug Design with a Noncharged Carrier for Mitochondrial Delivery

Recently, it was proposed that the thiophene ring is capable of promoting mitochondrial accumulation when linked to fluorescent markers. As a noncharged group, thiophene presents several advantages from a synthetic point of view, making it easier to incorporate such a side moiety into different molecules. Herein, we confirm the general applicability of the thiophene group as a mitochondrial carrier for drugs and fluorescent markers based on a new concept of nonprotonable, noncharged transporter. We implemented this concept in a medicinal chemistry application by developing an antitumor, metabolic chimeric drug based on the pyruvate dehydrogenase kinase (PDHK) inhibitor dichloroacetate (DCA). The promising features of the thiophene moiety as a noncharged carrier for targeting mitochondria may represent a starting point for the design of new metabolism-targeting drugs.

Identification of potential descriptors of water-soluble fullerene derivatives responsible for antitumor effects on lung cancer cells via QSAR analysis

Water-soluble fullerene derivatives are actively investigated as potential drugs for cancer treatment due to their favorable membranotropic properties. Herein, cytotoxic effects of twenty fullerene derivatives with different solubilizing addends were evaluated in three different types of non-small-cell lung carcinoma (NSCLC). The potential structural descriptors of the solubilizing addends related to the inhibitory activities on each type of lung cancer cell were investigated by the quantitative structure-activity relationship (QSAR) approach. The determination coefficient r2 for the recommended QSAR model were 0.9325, 0.8404, and 0.9011 for A549, H460, and H1299 cell lines, respectively. The results revealed that the chemical features of the fullerene-based compounds including aromatic bonds, sulfur-containing aromatic rings, and oxygen atoms are favored properties and promote the inhibitory effects on H460 and H1299 cells. Particularly, thiophene moiety is the key functional group, which was positively correlated with strong inhibitory effects on the three types of lung cancer cells. The useful information obtained from our regression models may lead to the design of more efficient inhibitors of the three types of NSCLC.

Design, Synthesis, Molecular Docking, and Tumor Resistance Reversal Activity Evaluation of Matrine Derivative with Thiophene Structure

Nasopharyngeal carcinoma (NPC) frequently occurs in Southern China. The main treatments of NPC are chemotherapy and radiotherapy. However, chemo-resistance arises as a big obstacle in treating NPC. Therefore, there is a great need to develop new compounds that could reverse tumor drug resistance. In this study, eight matrine derivatives containing thiophene group were designed and synthesized. Structures of these 8 compounds were characterized by 1H-NMR, 13C-NMR, and high-resolution mass spectrometer (HRMS). The cytotoxicity and preliminary synergistic effects of these 8 compounds were detected against nasopharyngeal carcinoma (NPC) cells and cisplatin-resistant NPC cells (CNE2/CDDP), respectively. Furthermore, the in vivo and in vitro tumor resistance reversal effects of compound 3f were evaluated. Moreover, docking studies were performed in Bclw (2Y6W). The results displayed that compound 3f showed synergistic inhibitory effects with cisplatin against CNE2/CDDP cells proliferation via apoptosis induction. Docking results revealed that compound 3f may exert its effects via inhibiting anti-apoptosis protein Bcl-w.

Formation of β-Oxo-N-vinylimidates via Intermolecular Ester Incorporation in Huisgen Cyclization/Carbene Cascade Reactions

Unusual intermolecular trapping of esters by carbenes generated via a Huisgen cyclization/retroelectrocyclization/dediazotization cascade reaction is presented. β-Oxo-N-vinylimidates could be obtained in one step from propargyl carbonazidates. Mechanistic control experiments suggested reversible dipole formation by ester addition to the carbene, and nitrogen attack to the ester carbonyl was irreversibly followed by stereoselective decarboxylative elimination to give the Z-vinyl imidate. The cross-conjugated enone, imidate, and enamine functional groups in the β-oxo-N-vinylimidates offer novel syntheses of functionalized oxazoles.

Ultrapotent Inhibitor of Clostridioides difficile Growth, Which Suppresses Recurrence In Vivo

Clostridioides difficile is the leading cause of healthcare-associated infection in the U.S. and considered an urgent threat by the Centers for Disease Control and Prevention (CDC). Only two antibiotics, vancomycin and fidaxomicin, are FDA-approved for the treatment of C. difficile infection (CDI), but these therapies still suffer from high treatment failure and recurrence. Therefore, new chemical entities to treat CDI are needed. Trifluoromethylthio-containing N-(1,3,4-oxadiazol-2-yl)benzamides displayed very potent activities [sub-μg/mL minimum inhibitory concentration (MIC) values] against Gram-positive bacteria. Here, we report remarkable antibacterial activity enhancement via halogen substitutions, which afforded new anti-C. difficile agents with ultrapotent activities [MICs as low as 0.003 μg/mL (0.007 μM)] that surpassed the activity of vancomycin against C. difficile clinical isolates. The most promising compound in the series, HSGN-218, is nontoxic to mammalian colon cells and is gut-restrictive. In addition, HSGN-218 protected mice from CDI recurrence. Not only does this work provide a potential clinical lead for the development of C. difficile therapeutics but also highlights dramatic drug potency enhancement via halogen substitution.

Synthesis, ADMET Properties, and In Vitro Antimicrobial and Antibiofilm Activity of 5-Nitro-2-thiophenecarbaldehyde N-((E)-(5-Nitrothienyl)methylidene)hydrazone (KTU-286) against Staphylococcus aureus with Defined Resistance Mechanisms

The emergence of drug-resistant Staphylococcus aureus is responsible for high morbidity and mortality worldwide. New therapeutic options are needed to fight the increasing antimicrobial resistance among S. aureus in the clinical setting. We, therefore, characterized the in silico absorption, distribution, metabolism, elimination, and toxicity (ADMET) and in vitro antimicrobial activity of 5-nitro-2-thiophenecarbaldehyde N-((E)-(5-nitrothienyl)methylidene)hydrazone (KTU-286) against drug-resistant S. aureus strains with genetically defined resistance mechanisms. The antimicrobial activity of KTU-286 was determined by CLSI recommendations. The ADMET properties were estimated by using in silico modeling. The activity on biofilm integrity was examined by crystal violet assay. KTU-286 demonstrated low estimated toxicity and low skin permeability. The highest antimicrobial activity was observed among pan-susceptible (Pan-S) S. aureus (minimal inhibitory concentration (MIC) 0.5–2.0 µg/mL, IC₅₀ = 0.460 µg/mL), followed by vancomycin resistant S. aureus (VRSA) (MIC 4.0 µg/mL, IC₅₀ = 1.697 µg/mL) and methicillin-resistant S. aureus (MRSA) (MIC 1.0–16.0 µg/mL, IC₅₀ = 2.282 µg/mL). KTU-286 resulted in significant (p < 0.05) loss of S. aureus biofilm integrity in vitro. Further studies are needed for a better understanding of safety, synergistic relationship, and therapeutic potency of KTU-286.

Novel pyrazole-clubbed thiophene derivatives via Gewald synthesis as antibacterial and anti-inflammatory agents

The aim of this study was to synthesize newer potent Schiff bases by condensing 2-amino-5-(2,4-dichlorophenyl)thiophene-3-carbonitrile and 1,3-disubstituted-1H-pyrazole-4-carbaldehydes, and to investigate their biological activity. The compounds were synthesized via Gewald synthesis and characterized by spectral data and elemental analyses. They were screened for their in vitro antibacterial and anti-inflammatory activities. The synthesized compounds were also evaluated for in vitro antitubercular activity against Mycobacterium tuberculosis H37Rv using the microplate Alamar Blue assay. Compounds 8b, 8c, 8f, 8g, 8k, 8n, and 8o showed promising antibacterial activity. The interactions between the substituted pyrazoles and bovine protein showed promising anti-inflammatory activity. The experimental results revealed compound 8a as a promising antitubercular agent. Hemolytic assays confirmed that the compounds are nontoxic, with percentage hemolysis ranging from 3.6 to 20.1, at a concentration of 1 mg/ml. The results suggest that the pyrazole ring and the substitution pattern on the heterocyclic moiety have an effect on the bioactivity.

Focused structure-activity relationship profiling around the 2-phenylindole scaffold of a cannabinoid type-1 receptor agonist-positive allosteric modulator: site-III aromatic-ring congeners with enhanced activity and solubility

Specific tuning of cannabinoid 1 receptor (CB1R) activity by small-molecule allosteric modulators is a therapeutic modality with multiple properties inherently advantageous to therapeutic applications. We previously generated a library of unique CB1R positive allosteric modulators (PAMs) derived from GAT211, which has three pharmacophoric sites critical to its ago-PAM activity. To elaborate our CB1R PAM library, we report the rational design and molecular-pharmacology profiling of several 2-phenylindole analogs modified at the "site-III" aromatic ring. The comprehensive structure-activity relationship (SAR) investigation demonstrates that attaching small lipophilic functional groups on the ortho-position of the GAT211 site-III phenyl ring could markedly enhance CB1R ago-PAM activity. Select site-III modifications also improved GAT211's water solubility. The SAR reported both extends the structural diversity of this compound class and demonstrates the utility of GAT211's site-III for improving the parent compound's drug-like properties of potency and/or aqueous solubility.

Synthesis of 2-Organylchalcogenopheno[2,3-b]pyridines from Elemental Chalcogen and NaBH4 /PEG-400 as a Reducing System: Antioxidant and Antinociceptive Properties

An alternative method to prepare 2-organylchalcogenopheno[2,3-b]pyridines was developed by the insertion of chalcogen species (selenium, sulfur or tellurium), generated in situ, into 2-chloro-3-(organylethynyl)pyridines by using the NaBH₄ /PEG-400 reducing system, followed by an intramolecular cyclization. It was possible to obtain a series of compounds with up to 93 % yield in short reaction times. Among the synthesized products, 2-organyltelluropheno[2,3-b]pyridines have not been described in the literature so far. Moreover, the compounds 2-phenylthieno[2,3-b]pyridine (3 b) and 2-phenyltelluropheno[2,3-b]pyridine (3 c) exhibited significant antioxidant potential in different in vitro assays. Further studies demonstrated that compound 3 b exerted an antinociceptive effect in acute inflammatory and non-inflammatory pain models, thus indicating the involvement of the central and peripheral nervous systems on its pharmacological action. More specifically, our results suggest that the intrinsic antioxidant property of compound 3 b might contribute to attenuating the nociception and inflammatory process on local injury induced by complete Freund's adjuvant (CFA).

Medicinal Chemistry Optimization of a Diaminopurine Chemotype: Toward a Lead for Trypanosoma brucei Inhibitors

Human African trypanosomiasis (HAT), or sleeping sickness, is caused by the protozoan parasite Trypanosoma brucei and transmitted through the bite of infected tsetse flies. The disease is considered fatal if left untreated. To identify new chemotypes against Trypanosoma brucei, previously we identified 797 potent kinase-targeting inhibitors grouped into 59 clusters plus 53 singleton compounds with at least 100-fold selectivity over HepG2 cells. From this set of hits, a cluster of diaminopurine-derived compounds was identified. Herein, we report our medicinal chemistry investigation involving the exploration of structure-activity and structure-property relationships around one of the high-throughput screening (HTS) hits, N²-(thiophen-3-yl)-N⁶-(2,2,2-trifluoroethyl)-9H-purine-2,6-diamine (1, NEU-1106). This work led to the identification of a potent lead compound (4aa, NEU-4854) with improved in vitro absorption, distribution, metabolism, and excretion (ADME) properties, which was progressed into proof-of-concept translation of in vitro antiparasitic activity to in vivo efficacy.

Influence of solvent mixture on nucleophilicity parameters: the case of pyrrolidine in methanol-acetonitrile

The course of organic chemical reactions is efficiently modelled through the concepts of “electrophiles” and “nucleophiles” (meaning electron-seeking and nucleus-seeking reactive species). On the one hand, an advanced approach of the correlation of the nucleophilicity parameters N and electrophilicity E has been delivered from the linear free energy relationship log k (20 °C) = s(N + E). On the other hand, the general influence of the solvent mixtures, which are very often employed in preparative synthetic chemistry, has been poorly explored theoretically and experimentally, to date. Herein, we combined experimental and theoretical studies of the solvent influence on pyrrolidine nucleophilicity. We determined the nucleophilicity parameters N and s of pyrrolidine at 20 °C in CH₃OH/CH₃CN mixtures containing 0, 20, 40, 60, 80 and 100% CH₃CN by kinetic investigations of their nucleophilic substitution reactions to a series of 2-methoxy-3-X-5-nitrothiophenes 1a–e (X = NO₂, CN, COCH₃, CO₂CH₃, CONH₂). Depending on the resulting solvation medium, the N parameters range from 15.72 to 18.32 on the empirical nucleophilicity scale of Mayr. The nucleophilicity parameters N first evolve linearly with the content of acetonitrile up to 60% CH₃CN by volume, but is non linear for higher amounts. We designed a general computation protocol to investigate the solvent effect at the atomistic scale. The nucleophilicity in solvent mixtures was evaluated by combining classical molecular dynamic (MD) simulations of solvated pyrrolidine and a few density functional theory (DFT) calculations of Parr nucleophilicity. The pyrrolidine theoretical nucleophilicity 1/ω obtained in various CH₃OH/CH₃CN mixtures are in excellent agreement with Mayr's nucleophilicity (N) parameters measured. Analyses of the molecular dynamic trajectories reveal that the decrease of the nucleophilicity in methanol rich mixtures arises predominantly from the solvation of the pyrrolidine by methanol molecules through strong hydrogen bonds. Last, we proposed a simple model to predict and accurately reproduce the experimentally obtained nucleophilicity values.

Combined experiments and modelling rationalize the large influence of solvent composition on pyrrolidine nucleophilicity.

Chalcone hybrids as potential anticancer agents: Current development, mechanism of action, and structure-activity relationship

The continuous emergency of drug-resistant cancers and the low specificity of anticancer agents have been the major challenges in the control and treatment of cancer, making an urgent need to develop novel anticancer agents with high efficacy. Chalcones, precursors of flavonoids and isoflavonoids, exhibit structural heterogeneity and can act on various drug targets. Chalcones which demonstrated potential in vitro and in vivo activity against both drug-susceptible and drug-resistant cancers, are useful templates for the development of novel anticancer agents. Hybridization of chalcone moiety with other anticancer pharmacophores could provide the hybrids which have the potential to overcome drug resistance and improve the specificity, so it represents a promising strategy to develop novel anticancer agents. This review emphasizes the development, the mechanisms of action as well as structure-activity relationships of chalcone hybrids with potential therapeutic application for many cancers in recent 10 years.

Generation and NMR Study of Short-Lived and Reactive Trifluoroalkyl Carbocations of the α-Halogenothiophene Series in Brønsted Superacids: Reactions of the Cations with Arenes

Protonation of oxygen in the side chain of the Me₃SiO group (followed by the elimination of Me₃SiOH) and protonation of the thiophene ring in 2-chloro(or bromo)-5-(1'-Me₃SiO-1'-trifluoromethyl-alkyl)thiophenes in Brønsted superacids (CF₃SO₃H, FSO₃H) gave rise to short-lived and reactive trifluoroalkyl carbocations of the thiophene series. These cations were studied by low-temperature NMR spectroscopy in the superacids, which shed light on their reactivity and reaction mechanisms. The cations may react with (hetero)aromatic π-nucleophiles in various directions, depending on their structures as well as the reaction temperature and time. These transformations resulted in the formation of novel fluoro-organics of the thiophene family, namely, products of arylation of both the thiophene system and its side chain, hydrodehalogenation of halothiophenes, or electrophilic "dimerization".

Synthesis of 3-[(4-Nitrophenyl)thio]-Substituted 4-Methylene-1-pyrrolines from N-Propargylic β-Enaminones

A facile and efficient method for the synthesis of 3-[(4-nitrophenyl)thio]-substituted 4-methylene-1-pyrrolines is described. When treated with 4-nitrobenzenesulfenyl chloride in refluxing acetonitrile, N-propargylic β-enaminones produced α-sulfenylated N-propargylic β-enaminones, which, in the presence of sodium hydride or cesium carbonate, underwent nucleophilic cyclization to afford 4-methylene-3-[(4-nitrophenyl)thio]-1-pyrrolines in good to high yields. It was shown for the first time that on N-propargylic β-enaminone systems, α-sulfenylation dominates over the formation of thiirenium ion. This one-pot two-step process was found to be general for a variety of N-propargylic β-enaminones and demonstrated good tolerance to a diversity of aromatic and heteroaromatic groups with electron-withdrawing and electron-donating substituents. This process is also applicable to the cyclization of internal alkyne-tethered N-propargylic β-enaminones. The enrichment of 1-pyrroline core with an aryl sulfide moiety might exhibit potential for the synthesis of molecules of pharmacological interest.

1-(Benzo[b]thiophen-4-yl)piperazine Ring Induced Bioactivation of Brexpiprazole in Liver Microsomes: Identification and Characterization of Reactive Conjugates Using Ultra-High-Performance Liquid Chromatography/Quadrupole Time-of-Flight Mass Spectrometry

BACKGROUND AND OBJECTIVES

Brexpiprazole is an atypical antipsychotic approved for the treatment of schizophrenia and major depressive disorders in adults. The structure of brexpiprazole contains well-known structural alerts like a thiophene ring, piperazine ring and quinolinone motifs. Additionally, the literature reveals that its structural analog, aripiprazole, could generate reactive intermediates. However, the bioactivation potential of brexpiprazole is yet unknown. Therefore, this study was planned to identify and characterize reactive adducts of brexpiprazole and its metabolites.

METHODS

Based on the reactivity, the potential atomic sites for a reactive intermediate generation were predicted by a xenosite web predictor tool for glutathione, cyanide, protein and DNA. To study the metabolic activation of brexpiprazole, the drug was individually incubated for 2 h at 37 °C with pooled male rat liver microsomes and human liver microsomes in microcentrifuge tubes fortified with glutathione/N-acetyl cysteine. Nicotinamide adenine dinucleotide phosphate reduced tetrasodium salt was used as a co-factor.

RESULTS

A total of six glutathione and N-acetyl cysteine conjugates of brexpiprazole metabolites were identified and characterized using ultra-high-performance liquid chromatography/quadrupole time-of-flight tandem mass spectrometry. Reactive metabolite 1 (RM1), RM3, RM4 and RM6 reactive conjugates were formed due to reactive quinone-imine or quinone intermediates, while RM2 and RM5 reactive adducts were generated because of a thiophene-S-oxide intermediate.

CONCLUSION

Brexpirazole is bioactivated due to the presence of a 1-(benzo[b]thiophen-4-yl)piperazine ring in its structure. In contrast to aripiprazole, the quinolinone motif was found latent towards bioactivation in brexpiprazole.

Cascade cyclization versus chemoselective reduction: a solvent-controlled product divergence

A convenient controllable cascade cyclization and partial reduction of enones for the divergent construction of two types of valuable compounds including polysubstituted thiophenes and saturated ketones are developed.

Synthesis of tetrasubstituted thiophenes via a [3+2] cascade cyclization reaction of pyridinium 1,4-zwitterionic thiolates and activated allenes

A [3+2] cascade cyclization reaction of pyridinium 1,4-zwitterionic thiolates and activated allenes was developed to access tetrasubstituted thiophenes.

Toxicity and Antitumor Activity of a Thiophene-Acridine Hybrid

The antitumor effects of thiophene and acridine compounds have been described; however, the clinical usefulness of these compounds is limited due to the risk of high toxicity and drug resistance. The strategy of molecular hybridization presents the opportunity to develop new drugs which may display better target affinity and less serious side effects. Herein, 2-((6-Chloro-2-methoxy-acridin-9-yl)amino)-5,6,7,8-tetrahydro-4H-cyclohepta[b]-thiophene-3-carbonitrile (ACS03), a hybrid thiophene–acridine compound with antileishmanial activity, was tested for toxicity and antitumor activity. The toxicity was evaluated in vitro (on HaCat and peripheral blood mononuclear cells) and in vivo (zebrafish embryos and acute toxicity in mice). Antitumor activity was also assessed in vitro in HCT-116 (human colon carcinoma cell line), K562 (chronic myeloid leukemic cell line), HL-60 (human promyelocytic leukemia cell line), HeLa (human cervical cancer cell line), and MCF-7 (breast cancer cell line) and in vivo (Ehrlich ascites carcinoma model). ACS03 exhibited selectivity toward HCT-116 cells (Half maximal inhibitory concentration, IC50 = 23.11 ± 1.03 µM). In zebrafish embryos, ACS03 induced an increase in lactate dehydrogenase, glutathione S-transferase, and acetylcholinesterase activities. The LD50 (lethal dose 50%) value in mice was estimated to be higher than 5000 mg/kg (intraperitoneally). In vivo, ACS03 (12.5 mg/kg) induced a significant reduction in tumor volume and cell viability. In vivo antitumor activity was associated with the nitric oxide cytotoxic effect. In conclusion, significant antitumor activity and weak toxicity were recorded for this hybrid compound, characterizing it as a potential anticancer compound.

Direct Vicinal Difunctionalization of Thiophenes Enabled by the Palladium/Norbornene Cooperative Catalysis

Herein we report a direct vicinal difunctionalization of thiophenes via the palladium/norbornene (Pd/NBE) cooperative catalysis. A series of mono- and disubstituted thiophenes can be difunctionalized site-selectively and regioselectively at the C4 and C5 positions in good yields, enabled by an arsine ligand and a unique amide-based NBE. The synthetic utility has been shown in derivatizations of complex bioactive compounds and an open-flask gram-scale preparation. Preliminary results have been obtained in the difunctionalization of furans and a direct C4-selective arylation of 2-substituted thiophenes.

Discovery of BAY-298 and BAY-899: Tetrahydro-1,6-naphthyridine-Based, Potent, and Selective Antagonists of the Luteinizing Hormone Receptor Which Reduce Sex Hormone Levels in Vivo

The human luteinizing hormone receptor (hLH-R) is a member of the glycoprotein hormone family of G-protein-coupled receptors (GPCRs), activated by luteinizing hormone (hLH) and essentially involved in the regulation of sex hormone production. Thus, hLH-R represents a valid target for the treatment of sex hormone-dependent cancers and diseases (polycystic ovary syndrome, uterine fibroids, endometriosis) as well as contraception. Screening of the Bayer compound library led to the discovery of tetrahydrothienopyridine derivatives as novel, small-molecule (SMOL) hLH-R inhibitors and to the development of BAY-298, the first nanomolar hLH-R antagonist reducing sex hormone levels in vivo. Further optimization of physicochemical, pharmacokinetic, and safety parameters led to the identification of BAY-899 with an improved in vitro profile and proven efficacy in vivo. BAY-298 and BAY-899 serve as valuable tool compounds to study hLH-R signaling in vitro and to interfere with the production of sex hormones in vivo.

Combretastatin analogues in cancer biology: A prospective view

The stilbenoid combretastatin and its derivatives are potent inhibitors of angiogenesis and cell proliferation and induce apoptosis. They disrupt cytoskeletal dynamics and modulate cell morphology, motility, and invasion. Hence they have been viewed as potential as anticancer agents. The impediments of poor solubility and bioavailability and the spontaneous geometric isomerisation of combretastatin into an inactive form have led to intensive efforts towards evolving novel analogues to provide more efficacious biological outcome. Importantly, isomerically stable and biologically active cis-restricted analogues have been synthesised and tested. However, very few analogues have been tested in preclinical models to assess their effects on processes relevant to cancer development and progression. Hence the accent here is on the signalling systems operated by the new derivatives and their biological effects with reference to cancer progression. Combretastatins modulate an extensive network of signalling emphasising their varied versatility. Harnessing these systems and accentuating or counteracting aberrant signalling could open potential avenues of approach to the designing of novel derivatives with enhanced performance. The import of mammalian target of rapamycin pathway, which co-ordinates growth factor receptor signalling, epithelial-mesenchymal transition activation and angiogenic signalling, is emphasised. It may be viewed as a prime target for allosteric inhibition in combination with combretastatin analogues to ascertain their potential in cancer control.

Structure-Activity Relationship Studies of a Novel Class of Transmission Blocking Antimalarials Targeting Male Gametes

Malaria is still a leading cause of mortality among children in the developing world, and despite the immense progress made in reducing the global burden, further efforts are needed if eradication is to be achieved. In this context, targeting transmission is widely recognized as a necessary intervention toward that goal. After carrying out a screen to discover new transmission-blocking agents, herein we report our medicinal chemistry efforts to study the potential of the most robust hit, DDD01035881, as a male-gamete targeted compound. We reveal key structural features for the activity of this series and identify analogues with greater potency and improved metabolic stability. We believe this study lays the groundwork for further development of this series as a transmission blocking agent.