Discovery of a Conformationally Constrained Oxazolidinone with Improved Safety and Efficacy Profiles for the Treatment of Multidrug-Resistant Tuberculosis

Design, Synthesis, and Evaluation of the Antitubercular Activity of 5-Phenyl Substituted-5, 6-dihydropyrido[2, 3-d]pyrimidine-4, 7(3H, 8H)-dione Compounds

Tuberculosis (TB) remains a major public health challenge, with research on new anti-TB drugs crucial for global TB elimination efforts. Here, we report a novel class of anti-TB agents. Especially, compounds 5b and 5j exhibited the highest activity [minimum inhibitory concentration (MIC) H37Rv: 0.16 and 0.12 μg/mL]. Chiral resolution was performed on compounds 5b and 5j; the isomers were evaluated for their activity and safety, confirming that the R-isomer 5bb and 5jb displayed significant anti-TB activity (MIC H37Rv: 0.03-0.06 μg/mL; MDR-Mtb: 0.125-0.06 μg/mL) and low hERG toxicity. Further evaluations on 5bb and 5jb demonstrated good metabolic stability, favorable kinetic parameters and oral bioavailability (F: 56.7 and 63.8%, respectively). The results of in vivo activity assessment indicate that 5bb and 5jb exhibit protective and therapeutic effects on zebrafish larvae and adult zebrafish infected with Mycobacterium marinum. Based on these results, compounds 5bb and 5jb are considered promising candidates for further in-depth studies.

New Oxazolidinones for Tuberculosis: Are Novel Treatments on the Horizon?

Multidrug-resistant tuberculosis (MDR-TB) is a global health concern. Standard treatment involves the use of linezolid, a repurposed oxazolidinone. It is associated with severe adverse effects, including myelosuppression and mitochondrial toxicity. As such, it is imperative to identify novel alternatives that are better tolerated but equally or more effective. Therefore, this review aims to identify and explore the novel alternative oxazolidinones to potentially replace linezolid in the management of TB. The keywords tuberculosis and oxazolidinones were searched in PubMed to identify eligible compounds. The individual drug compounds were then searched with the term tuberculosis to identify the relevant in vitro, in vivo and clinical studies. The search identified sutezolid, tedizolid, delpazolid, eperezolid, radezolid, contezolid, posizolid and TBI-223, in addition to linezolid. An additional search resulted in 32 preclinical and 21 clinical studies. All novel oxazolidinones except posizolid and eperezolid resulted in positive preclinical outcomes. Sutezolid and delpazolid completed early phase 2 clinical studies with better safety and equal or superior efficacy. Linezolid is expected to continue as the mainstay therapy, with renewed interest in drug monitoring. Sutezolid, tedizolid, delpazolid and TBI-223 displayed promising preliminary results. Further clinical studies would be required to assess the safety profiles and optimize the dosing regimens.

Drug repurposing for bacterial infections

Repurposing pharmaceuticals is a technique used to find new, alternate clinical applications for approved drug molecules. It may include altering the drug formulation, route of administration, dose or the dosage regimen. The process of repurposing medicines starts with screening libraries of previously approved drugs for the targeted disease condition. If after an the initial in silico, in vitro or in vivo experimentation, the molecule has been found to be active against a particular target, the molecule is considered as a good candidate for clinical trials. As the safety profile of such molecules is available from the previous data, significant time and resources are saved. These advantages of drug repurposing approach make it especially helpful for finding treatments for rapidly evolving conditions including bacterial infections. An ever-increasing incidence of antimicrobial resistance, owing to the mutations in bacterial genome, leads to therapeutic failure of many approved antibiotics. Repurposing the approved drug molecules for use as antibiotics can provide an effective means for the combating life-threatening bacterial diseases. A number of drugs have been considered for drug repurposing against bacterial infections. These include, but are not limited to, Auranofin, Closantel, and Toremifene that have been repurposed for various infections. In addition, the reallocation of route of administration, redefining dosage regimen and reformulation of dosage forms have also been carried out for repurposing purpose. The current chapter addresses the drug discovery and development process with relevance to repurposing against bacterial infections.

Recent advances in the exploration of oxazolidinone scaffolds from compound development to antibacterial agents and other bioactivities

Bacterial infections cause a variety of life-threatening diseases, and the continuous evolution of drug-resistant bacteria poses an increasing threat to current antimicrobial regimens. Gram-positive bacteria (GPB) have a wide range of genetic capabilities that allow them to adapt to and develop resistance to practically all existing antibiotics. Oxazolidinones, a class of potent bacterial protein synthesis inhibitors with a unique mechanism of action involving inhibition of bacterial ribosomal translation, has emerged as the antibiotics of choice for the treatment of drug-resistant GPB infections. In this review, we discussed the oxazolidinone antibiotics that are currently on the market and in clinical development, as well as an updated synopsis of current advances on their analogues, with an emphasis on innovative strategies for structural optimization of linezolid, structure-activity relationship (SAR), and safety properties. We also discussed recent efforts aimed at extending the activity of oxazolidinones to gram-negative bacteria (GNB), antitumor, and coagulation factor Xa. Oxazolidinone antibiotics can accumulate in GNB by a conjugation to siderophore-mediated β-lactamase-triggered release, making them effective against GNB.

Design, synthesis, and antiproliferative evaluation of novel dehydroabietic acid-1,2,3-triazole-oxazolidinone hybrids

A series of novel dehydroabietic acid derivatives containing both 1,2,3-triazole and oxazolidinone 4a-4t have been synthesized and their antiproliferative activity in vitro against HeLa, HepG2, MGC-803 and T-24 cell lines evaluated. Most of them displayed cell proliferation inhibition on four tested human malignant tumour cell lines to some degree. Among them, compound 4p exhibited promising cytotoxicity with IC50 values ranging from 3.18 to 25.31 μM and weak cytotoxicity toward normal cells. The mechanism of action of 4p was then studied using flow cytometry, Hoechst 33258 staining, ROS generation assay, and JC-1 mitochondrial membrane potential staining, which illustrated that compound 4p induced apoptosis, arrested mitotic process at the G1 phase of the cell cycle, reduced the mitochondrial membrane potential, and increased intracellular ROS levels. In summary, the introduction of an oxazolidinone group via a "1,2,3-triazole" linker significantly improved the antitumor activity of dehydroabietic acid, and deserves to be further investigated.

Bioisosteric modification of Linezolid identified the potential M. tuberculosis protein synthesis inhibitors to overcome the myelosuppression and serotonergic toxicity associated with Linezolid in the treatment of the multi-drug resistance tuberculosis (MDR-TB)

Linezolid is the first and only oxazolidinone antibacterial drug was approved in the last 35 years. It exhibits bacteriostatic efficacy against M. tuberculosis and is a crucial constituent of the BPaL regimen (Bedaquiline, Pretomanid, and Linezolid), which was authorized by the FDA in 2019 for the treatment of XDR-TB or MDR-TB. Despite its unique mechanism of action, Linezolid carries a considerable risk of toxicity, including myelosuppression and serotonin syndrome (SS), which is caused by inhibition of mitochondrial protein synthesis (MPS) and monoamine oxidase (MAO), respectively. Based on the structure toxicity relationship (STR) of Linezolid, in this work, we used a bioisosteric replacement approach to optimize the structure of Linezolid at the C-ring and/or C-5 position for myelosuppression and serotogenic toxicity. Extensive hierarchical multistep docking, drug likeness prediction, molecular binding interactions analyses, and toxicity assessment identified three promising compounds (3071, 7549 and 9660) as less toxic potential modulators of Mtb EthR protein. Compounds 3071, 7549 and 9660 were having the significant docking score of -12.696 Kcal/mol, -12.681 Kcal/mol and -15.293 Kcal/mol towards the Mtb EthR protein with less MAO-A and B affinity [compound 3071: MAO A (-4.799 Kcal/mol) and MAO B (-6.552 Kcal/mol); compound 7549: MAO A (> -2.00 Kcal/mol) and MAO B (> -2.00 Kcal/mol) and compound 9660: MAO A (> -5.678 Kcal/mol) and MAO B (> -6.537Kcal/mol) and none of them shown the Leukopenia as a side effect due to the Myelosuppression. The MD simulation results and binding free energy estimations correspond well with docking analyses, indicating that the proposed compounds bind and inhibit the EthR protein more effectively than Linezolid. The quantum mechanical and electrical characteristics were evaluated using density functional theory (DFT), which also demonstrated that the proposed compounds are more reactive than Linezolid.Communicated by Ramaswamy H. Sarma.

Repurposing Azoles to Resolve Serotogenic Toxicity Associated with Linezolid to Combat Multidrug-Resistant Tuberculosis

Serotogenic toxicity is a major hurdle associated with Linezolid in the treatment of drug-resistant tuberculosis (TB) due to the inhibition of monoamine oxidase (MAO) enzymes. Azole compounds demonstrate structural similarities to the recognized anti-TB drug Linezolid, making them intriguing candidates for repurposing. Therefore, we have repurposed azoles (Posaconazole, Itraconazole, Miconazole, and Clotrimazole) for the treatment of drug-resistant TB with the anticipation of their selectivity in sparing the MAO enzyme. The results of repurposing revealed that Clotrimazole showed equipotent activity against the Mycobacterium tuberculosis (Mtb) H37Rv strain compared to Linezolid, with a minimal inhibitory concentration (MIC) of 2.26 μM. Additionally, Clotrimazole exhibited reasonable MIC50 values of 0.17 μM, 1.72 μM, 1.53 μM, and 5.07 μM against the inhA promoter+, katG+, rpoB+, and MDR clinical Mtb isolates, respectively, compared to Linezolid. Clotrimazole also exhibited 3.90-fold less inhibition of MAO-A and 50.35-fold less inhibition of MAO-B compared to Linezolid, suggesting a reduced serotonergic toxicity burden.

Strategies for the Discovery of Oxazolidinone Antibacterial Agents: Development and Future Perspectives

Oxazolidinones represent a significant class of synthetic bacterial protein synthesis inhibitors that are primarily effective against Gram-positive bacteria. The commercial success of linezolid, the first FDA-approved oxazolidinone antibiotic, has motivated researchers to develop more potent oxazolidinones by employing various drug development strategies to fight against antimicrobial resistance, some of which have shown promising results. Thus, this Perspective aims to discuss the strategies employed in constructing oxazolidinone-based antibacterial agents and summarize recent advances in discovering oxazolidinone antibiotics to provide valuable insights for potentially developing next-generation oxazolidinone antibacterial agents or other pharmaceuticals.

In vitro activities of contezolid (MRX-I) against drug-sensitive and drug-resistant Mycobacterium tuberculosis

A novel oxazolidinone for the treatment of Mycobacterium tuberculosis has been developed, but the activity of contezolid (MRX-I) still needs to be clarified. In this study, we isolated Mycobacterium tuberculosis from 48 clinical patients with pulmonary tuberculosis. Roche drug susceptibility tests identified drug-sensitive and 39 drug-resistant M. tuberculosis isolates. Drug susceptibility assays indicated that MRX-I exhibited anti-Mycobacterium tuberculosis activity against both drug-sensitive and drug-resistant isolates, with an advantage against drug-resistant isolates. The results also showed that the anti-Mycobacterium tuberculosis activity was comparable to that of linezolid. IMPORTANCE Currently, Mycobacterium tuberculosis has exhibited increased drug resistance, leading to ineffective drug treatment in many patients with tuberculosis. Among the anti-Mycobacterium tuberculosis drugs, oxazolidinones have been gradually developed. Contezolid (MRX-I) has been newly developed in China with advantages versus the first oxazolidinone antibiotic approved by the Food and Drug Administration for clinical use, but the anti-M. tuberculosis activity needs to be further clarified. In this study, in vitro activities of MRX-I against M. tuberculosis were tested. The drug susceptibility assays indicated that MRX-I exhibited anti-M. tuberculosis activity comparable to that of linezolid, with an advantage against drug-resistant isolates.

Oxazolidinones as versatile scaffolds in medicinal chemistry

Oxazolidinone is a five-member heterocyclic ring with several biological applications in medicinal chemistry. Among the three possible isomers, 2-oxazolidinone is the most investigated in drug discovery. Linezolid was pioneered as the first approved drug containing an oxazolidinone ring as the pharmacophore group. Numerous analogues have been developed since its arrival on the market in 2000. Some have succeeded in reaching the advanced stages of clinical studies. However, most oxazolidinone derivatives reported in recent decades have not reached the initial stages of drug development, despite their promising pharmacological applications in a variety of therapeutic areas, including antibacterial, antituberculosis, anticancer, anti-inflammatory, neurologic, and metabolic diseases, among other areas. Therefore, this review article aims to compile the efforts of medicinal chemists who have explored this scaffold over the past decades and highlight the potential of the class for medicinal chemistry.

Oxazolidinone: A promising scaffold for the development of antibacterial drugs

Due to the long-term and widespread use of antibiotics in clinic, the problem of bacterial resistance is increasingly serious, and the development of new drugs to treat drug-resistant bacteria has gradually become the mainstream direction of antibiotic research. The oxazolidinone-containing drugs linezolid, tedizolid phosphate and contezolid have been approved to the market, which are effective against a variety of Gram-positive bacterium infections. Moreover, there are also many antibiotics containing oxazolidinone fragment under clinical investigation that show good pharmacokinetic and pharmacodynamic properties with unique mechanism of action against resistant bacteria. In this review, we summarized the oxazolidinone-based antibiotics already on the market or in clinical trials and the representative bioactive molecules, and mainly focused on their structural optimizations, development strategies and structure-activity relationships in hope of insight into the reasonable design for medical chemists to develop new oxazolidinone antibiotics with highly potency and fewer side effects.

Efficacy of Replacing Linezolid with OTB-658 in Anti-Tuberculosis Regimens in Murine Models

Linezolid (LZD) was the first oxazolidinone approved for treating drug-resistant tuberculosis. A newly approved regimen combining LZD with bedaquiline (BDQ) and pretomanid (PMD) (BPaL regimen) is the first 6-month oral regimen that is effective against multidrug- and extensively drug-resistant tuberculosis. However, LZD toxicity, primarily due to mitochondrial protein synthesis inhibition, may undermine the efficacy of LZD regimens, and oxazolidinones with higher efficacy and lower toxicity during prolonged administration are needed. OTB-658 is an oxazolidinone anti-TB candidate derived from LZD that could replace LZD in TB treatment. We previously found that OTB-658 had better anti-TB activity and safety than LZD in vitro and in vivo. In the present work, two murine TB models were used to evaluate replacing LZD with OTB-658 in LZD-containing regimens. In the C3HeB/FeJ murine model, replacing 100 mg/kg LZD with 50 mg/kg OTB-658 in the BDQ + PMD backbone significantly reduced lung and spleen CFU counts (P < 0.05), and there were few relapses at 8 weeks of treatment. Replacing 100 mg/kg LZD with 50 or 100 mg/kg OTB-658 in the pyrifazimine (previously called TBI-166) + BDQ backbone did not change the anti-TB efficacy and relapse rate. In BALB/c mice, replacing 100 mg/kg LZD with 100 mg/kg OTB-658 in the TBI-166 + BDQ backbone resulted in no culture-positive lungs at 4 and 8 weeks of treatment, and there were no significant differences in relapses rate between the groups. In conclusion, OTB-658 is a promising clinical candidate that could replace LZD in the BPaL or TBI-166 + BDQ + LZD regimens and should be studied further in clinical trials.

Synthetic approaches to potent heterocyclic inhibitors of tuberculosis: A decade review

Tuberculosis (TB) continues to be a significant global health concern with about 1.5 million deaths annually. Despite efforts to develop more efficient vaccines, reliable diagnostics, and chemotherapeutics, tuberculosis has become a concern to world health due to HIV, the rapid growth of bacteria that are resistant to treatment, and the recently introduced COVID-19 pandemic. As is well known, advances in synthetic organic chemistry have historically enabled the production of important life-saving medications that have had a tremendous impact on patients' lives and health all over the world. Small-molecule research as a novel chemical entity for a specific disease target offers in-depth knowledge and potential therapeutic targets. In this viewpoint, we concentrated on the synthesis of a number of heterocycles reported in the previous decade and the screening of their inhibitory action against diverse strains of Mycobacterium tuberculosis. These findings offer specific details on the structure-based activity of several heterocyclic scaffolds backed by their in vitro tests as a promising class of antitubercular medicines, which will be further useful to build effective treatments to prevent this terrible illness.

Synthesis and hydrolysis of monocarbamate from allylic 1,4-dicarbamate: Bis-homodichloroinositol

The synthesis of novel bis-homodichloroinositol with a configuration similar to that of conduritol-D is reported for the first time. The photooxygenation of cis-dichloro-diene obtained using cyclooctatetraene as the starting molecule afforted the tricyclic endoperoxide. The reduction of the endoperoxide with thiourea gave the corresponding allylic cis-diol. Formation of the bis-carbamate groups with p-TsNCO of allylic cis-diol followed by the [(dba)₃Pd₂CHCl₃] in the presence of trimethylsilyl azide, gave a new monocarbamate as well as oxazolidinone derivative. Oxidation of the double bond in the monocarbamate with osmium tetraoxide followed by acetylation furnished the desired monocarbamate triacetate. Eventually, the desired halogenated bicyclo[4.2.0] inositol (bis-homodichloroinositol) were obtained in high yield by hydrolysis of the acetate groups and monocarbanate group by potassium carbonate in methanol. Characterization of all the synthesized compounds were performed by FT-IR, ¹H NMR, ¹³C NMR, COSY (2D-NMR), HRMS, and Elemental Analysis techniques.

Recent advances in oxazolidinones as antituberculosis agents

Tuberculosis (TB) is an infectious and fatal disease caused by Mycobacterium tuberculosis (Mtb) and remains a serious public health threat; therefore, the development of new antitubercular agents is a priority for the World Health Organization's End TB strategy and the United Nations' Sustainable Development Goals to eradicate TB. Oxazolidinones are a class of synthetic antibacterial agents with a distinct mode of action developed for the treatment of Gram-positive bacterial infections. Many oxazolidinones exhibit good activity against Mtb, and some are currently in clinical trials for multidrug-resistant TB and extensively drug-resistant TB therapy. In this review, the mechanism of action, activity and toxicity of oxazolidinones and recent progress in the research and development of oxazolidinones as anti-TB agents are summarized.

Drug re-engineering and repurposing: A significant and rapid approach to tuberculosis drug discovery

The prevalence of tuberculosis (TB) remains the leading cause of death from a single infectious agent, ranking it above all other contagious diseases. The problem to tackle this disease seems to become even worse due to the outbreak of SARS-CoV-2. Further, the complications related to drug-resistant TB, prolonged treatment regimens, and synergy between TB and HIV are significant drawbacks. There are several drugs to treat TB, but there is still no rapid and accurate treatment available. Intensive research is, therefore, necessary to discover newer molecular analogs that can probably eliminate this disease within a short span. An increase in efficacy can be achieved through re-engineering old TB-drug families and repurposing known drugs. These two approaches have led to the production of newer classes of compounds with novel mechanisms to treat multidrug-resistant strains. With respect to this context, we discuss structural aspects of developing new anti-TB drugs as well as examine advances in TB drug discovery. It was found that the fluoroquinolone, oxazolidinone, and nitroimidazole classes of compounds have greater potential to be further explored for TB drug development. Most of the TB drug candidates in the clinical phase are modified versions of these classes of compounds. Therefore, here we anticipate that modification or repurposing of these classes of compounds has a higher probability to reach the clinical phase of drug development. The information provided will pave the way for researchers to design and identify newer molecular analogs for TB drug development and also broaden the scope of exploring future-generation potent, yet safer anti-TB drugs.

Tuberculosis Drug Discovery: Challenges and New Horizons

Over the past 2000 years, tuberculosis (TB) has claimed more lives than any other infectious disease. In 2020 alone, TB was responsible for 1.5 million deaths worldwide, comparable to the 1.8 million deaths caused by COVID-19. The World Health Organization has stated that new TB drugs must be developed to end this pandemic. After decades of neglect in this field, a renaissance era of TB drug discovery has arrived, in which many novel candidates have entered clinical trials. However, while hundreds of molecules are reported annually as promising anti-TB agents, very few successfully progress to clinical development. In this Perspective, we critically review those anti-TB compounds published in the last 6 years that demonstrate good in vivo efficacy against Mycobacterium tuberculosis. Additionally, we highlight the main challenges and strategies for developing new TB drugs and the current global pipeline of drug candidates in clinical studies to foment fresh research perspectives.

Identification of thiophene-benzenesulfonamide derivatives for the treatment of multidrug-resistant tuberculosis

A series of thiophene-benzenesulfonamide derivatives was designed and synthesized by exploring the structure-activity relationship of lead compounds 2,3-disubstituted thiophenes 25a and 297F as antituberculosis agents, which displayed potent antimycobacterial activity against drug-susceptible and clinically isolated drug-resistant tuberculosis. In particular, compound 17b, which had improved activity (minimum inhibitory concentration of 0.023 μg/mL) compared with the lead compounds, displayed good intracellular antimycobacterial activity in macrophages with a reduction of 1.29 log10 CFU. A druggability evaluation indicated that compound 17b had favorable hepatocyte stability, low cytotoxicity, and low hERG channel inhibition. Moreover, compound 17b exhibited modest in vivo efficacy in an acute mouse model of tuberculosis. In addition, the molecular docking study elucidated the binding mode of compound 17b in the active site of DprE1. Therefore, compound 17b may be a promising antituberculosis lead for further research.

In vitro and in vivo activity of oxazolidinone candidate OTB-658 against Mycobacterium tuberculosis

In this work, we assess anti-tuberculosis activity of OTB-658 in vitro and in vivo. In vitro, OTB-658 showed bacteriostatic effectiveness with a lower minimum inhibitory concentration than linezolid against Mycobacterium tuberculosis. The minimal bactericidal concentrations and time-kill curves for OTB-658 indicated similar inhibition activity to that of linezolid. OTB-658 entered macrophages to inhibit of M. tuberculosis growth. OTB-658 had a low mutant frequency (10^-8), which would prevent drug-resistant mutations from emerging in combination regimens. In vivo, OTB-658 reduced colony-forming unit counts in the lungs and slightly inhibited bacterial growth in the spleen in the early stage and steady state in acute and chronic murine TB models. These results support the preclinical evaluation of OTB-658 and further clinical trials in China.

Current Landscape and Future Perspective of Oxazolidinone Scaffolds Containing Antibacterial Drugs

The widespread use of antibiotics has made the problem of bacterial resistance increasingly serious, and the study of new drug-resistant bacteria has become the main direction of antibacterial drug research. Among antibiotics, the fully synthetic oxazolidinone antibacterial drugs linezolid and tedizolid have been successfully marketed and have achieved good clinical treatment effects. Oxazolidinone antibacterial drugs have good pharmacokinetic and pharmacodynamic characteristics and unique antibacterial mechanisms, and resistant bacteria are sensitive to them. This Perspective focuses on reviewing oxazolidinones based on the structural modification of linezolid and new potential oxazolidinone drugs in the past 10 years, mainly describing their structure, antibacterial activity, safety, druggability, and so on, and discusses their structure-activity relationships, providing insight into the reasonable design of safer and more potent oxazolidinone antibacterial drugs.

Oxazolidinone Antibiotics: Chemical, Biological and Analytical Aspects

This review covers the main aspects concerning the chemistry, the biological activity and the analytical determination of oxazolidinones, the only new class of synthetic antibiotics advanced in clinical use over the past 50 years. They are characterized by a chemical structure including the oxazolidone ring with the S configuration of substituent at C5, the acylaminomethyl group linked to C5 and the N-aryl substituent. The synthesis of oxazolidinones has gained increasing interest due to their unique mechanism of action that assures high antibiotic efficiency and low susceptibility to resistance mechanisms. Here, the main features of oxazolidinone antibiotics licensed or under development, such as Linezolid, Sutezolid, Eperezolid, Radezolid, Contezolid, Posizolid, Tedizolid, Delpazolid and TBI-223, are discussed. As they are protein synthesis inhibitors active against a wide spectrum of multidrug-resistant Gram-positive bacteria, their biological activity is carefully analyzed, together with the drug delivery systems recently developed to overcome the poor oxazolidinone water solubility. Finally, the most employed analytical techniques for oxazolidinone determination in different matrices, such as biological fluids, tissues, drugs and natural waters, are reviewed. Most are based on HPLC (High Performance Liquid Chromatography) coupled with UV-Vis or mass spectrometer detectors, but, to a lesser extent are also based on spectrofluorimetry or voltammetry.

Discovery of Novel Thiophene-arylamide Derivatives as DprE1 Inhibitors with Potent Antimycobacterial Activities

In this study, we report the design and synthesis of a series of novel thiophene-arylamide compounds derived from the noncovalent decaprenylphosphoryl-β-d-ribose 2'-epimerase (DprE1) inhibitor TCA1 through a structure-based scaffold hopping strategy. Systematic optimization of the two side chains flanking the thiophene core led to new lead compounds bearing a thiophene-arylamide scaffold with potent antimycobacterial activity and low cytotoxicity. Compounds 23j, 24f, 25a, and 25b exhibited potent in vitro activity against both drug-susceptible (minimum inhibitory concentration (MIC) = 0.02-0.12 μg/mL) and drug-resistant (MIC = 0.031-0.24 μg/mL) tuberculosis strains while retaining potent DprE1 inhibition (half maximal inhibitory concentration (IC₅₀) = 0.2-0.9 μg/mL) and good intracellular antimycobacterial activity. In addition, these compounds showed good hepatocyte stability and low inhibition of the human ether-à-go-go related gene (hERG) channel. The representative compound 25a with acceptable pharmacokinetic property demonstrated significant bactericidal activity in an acute mouse model of tuberculosis. Moreover, the molecular docking study of template compound 23j provides new insight into the discovery of novel antitubercular agents targeting DprE1.

Tuberculosis: An Overview of the Immunogenic Response, Disease Progression, and Medicinal Chemistry Efforts in the Last Decade toward the Development of Potential Drugs for Extensively Drug-Resistant Tuberculosis Strains

Tuberculosis (TB) is a slow growing, potentially debilitating disease that has plagued humanity for centuries and has claimed numerous lives across the globe. Concerted efforts by researchers have culminated in the development of various strategies to combat this malady. This review aims to raise awareness of the rapidly increasing incidences of multidrug-resistant (MDR) and extensively drug-resistant (XDR) tuberculosis, highlighting the significant modifications that were introduced in the TB treatment regimen over the past decade. A description of the role of pathogen-host immune mechanisms together with strategies for prevention of the disease is discussed. The struggle to develop novel drug therapies has continued in an effort to reduce the treatment duration, improve patient compliance and outcomes, and circumvent TB resistance mechanisms. Herein, we give an overview of the extensive medicinal chemistry efforts made during the past decade toward the discovery of new chemotypes, which are potentially active against TB-resistant strains.

Identification of Novel Tricyclic Benzo[1,3]oxazinyloxazolidinones as Potent Antibacterial Agents with Excellent Pharmacokinetic Profiles against Drug-Resistant Pathogens

A series of conformationally constrained novel benzo[1,3]oxazinyloxazolidinones were designed, synthesized, and evaluated on their activities against Mycobacterium tuberculosis, Gram-positive bacteria, and Gram-negative bacteria. The studies identified a new compound 20aa that displayed good to excellent antibacterial and antitubercular profiles against drug-resistant TB strains (MIC = 0.48-0.82 μg/mL), MRSA (MIC = 0.25-0.5 μg/mL), MRSE (MIC = 1 μg/mL), VISA (MIC = 0.25 μg/mL), and VRE (MIC = 0.25 μg/mL) and some linezolid-resistant strains (MIC 1-2 μg/mL). Compound 20aa was demonstrated as a promising candidate through ADME/T evaluation including microsomal stability, cytotoxicity, and inhibition of hERG and monoamine oxidase. Notably, 20aa showed excellent mouse PK profile with high plasma exposure (AUC_0-∞ = 78 669 h·ng/mL), high peak plasma concentration (C_max = 10 253 ng/mL), appropriate half-life of 3.76 h, and superior oral bioavailability (128%). The present study not only successfully provides a novel benzo[1,3]oxazinyloxazolidinone scaffold with superior druggability but also lays a good foundation for new antibacterial drug development.

Simultaneous determination of a novel oxazolidinone anti-tuberculosis OTB-658 and its metabolites in monkey blood by LC-MS/MS

OTB-658, a novel oxazolidinone anti-tuberculosis agent, has potent antibacterial activity against Mycobacterium tuberculosis, especially multi-drug resistant tuberculosis (MDR-TB) in vitro and in vivo. In this study, after metabolite identification of parent drug OTB-658, a specific and sensitive liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was established and validated to quantify OTB-658 and its metabolites OTB-665 and OTB-698 in monkey blood. HHY-1442, an analogue compound of OTB-658, was used as the internal standard. Blood samples were prepared by direct protein precipitation. Separation was performed on a Zorbax SB C18 column (50 mm × 2.1 mm, 3.5 μm) with a gradient mobile phase of methanol/water at a flow rate of 0.3 mL/min. The detection was conducted by a positive electrospray ionization in multiple-reaction monitoring mode on a triple quadrupole MS. The monitored transitions were m/z 382.2 → 221.1 for OTB-658, m/z 398.2 → 308.1 for OTB-665, m/z 414.1 → 372.3 for OTB-698 and m/z 418.2 → 311.3 for HHY-1442, respectively. Good linearity was observed over the range of 10-2000 ng/mL for OTB-658 and OTB-665, and 5-1000 ng/mL for OTB-698. All the intra-day and inter-day precision for the three analytes was below 8.4%, and the accuracy ranged from 96.0% to 106.0%. All analytes were stable during storage, preparation, and analytical procedures. The validated method was successfully applied to pharmacokinetic and bioavailability studies of OTB-658 in cynomolgus monkeys and the absolute bioavailability of OTB-658 was 25.0% at an oral dose of 10 mg/kg.