Discovery of torezolid as a novel 5-hydroxymethyl-oxazolidinone antibacterial agent

Tricyclic Benzo[1,3]oxazinyloxazolidinones as Potent Antibacterial Agents against Drug-Resistant Pathogens

Herein, we developed a series of benzo[1,3]oxazinyloxazolidinones as potent antibacterial agents. Some of the compounds exhibited potent antibacterial activity against a range of clinical drug-resistant pathogens, including Mtb, MRSA, MRSE, VISA, and VRE. Notably, compound 16d inhibited protein synthesis and displayed potent activity against linezolid-resistant Enterococcus faecalis. Although 16d showed cross-resistance to linezolid-resistant MRSA, the frequency of resistance development of MRSA against 16d was lower compared to that of linezolid. Additionally, 16d exhibited excellent pharmacokinetic properties and superior in vivo efficacy compared to linezolid. Furthermore, compound 16d modulated cytokine levels and ameliorated histopathological changes in major organs of bacterially infected mice. Hoechst-PI double staining and scanning electron microscopy analyses revealed that 16d exhibited some similarities with linezolid in its effects while also demonstrating a distinct mechanism characterized by cell membrane damage. Moreover, 16d significantly disrupted the MRSA biofilms. The antibacterial agent 16d represents a promising candidate for the treatment of serious infections caused by drug-resistant bacteria.

Novel biaryloxazolidinone derivatives with broad-spectrum antibacterial activity, favorable drug-like profiles and in vivo efficacy against linezolid-resistant Staphylococcusaureus

The emergence of multidrug-resistant bacteria along with a declining pipeline of clinically useful antibiotics has led to the urgent need for the development of more effective antibacterial agents to treat drug-resistant bacteria. We previously discovered compound OB-158 with potent antibacterial activity but exhibited poor oral bioavailability. Herein, a systematic structural optimization of OB-158 to improve pharmacokinetic profiles yielded 26 novel biaryloxazolidinone analogues, and their activities against Gram-positive S. aureus, multidrug resistant S. aureus and Enterococcus faecalis were evaluated. Remarkably, compound 8b was identified with potent antibacterial activity against S. aureus (MIC = 0.06 μg/mL), MSSA (MIC = 0.125 μg/mL), MRSA (MIC = 0.06 μg/mL), LRSA (MIC = 0.125 μg/mL) and LREFa (MIC = 0.5 μg/mL). Compound 8b was demonstrated as a promising candidate through druglikeness evaluation including metabolism in microsomes and plasma, Caco-2 cell permeability, plasma protein binding, cytotoxicity, and inhibition of CYP450 and human monoamine oxidase. Notably, compound 8b displayed excellent PK profile with appropriate T1/2 of 1.49 h, high peak plasma concentration (Cmax = 2320 ng/mL), high plasma exposure (AUC0-t = 8310 h ng/mL), and superior oral bioavailability (F = 68.1 %) in Sprague-Dawley rats. Ultimately, in vivo efficacy of compound 8b in a mouse model of LRSA systemic infection was also demonstrated. Taken together, compound 8b represents a promising drug candidate for the treatment of linezolid-resistant Gram-positive bacterial strains infection.

Tedizolid phosphate alleviates DSS-induced ulcerative colitis by inhibiting senescence of cell and colon tissue through activating AMPK signaling pathway

Ulcerative colitis (UC) is a subtype of inflammatory bowel disease. Previous studies have suggested a link between senescence process and the body's inflammatory reaction, indicating that senescence may exacerbate UC, yet the relation between UC and senescence remains unclear. Tedizolid Phosphate (TED), a novel oxazolidinone antimicrobial, is indicated in acute bacterial skin infections, its impact on senescence is not known. Our research revealed that the UC inducer dextran sulfate sodium (DSS) triggers senescence in both colon epithelial NCM460 cells and colon tissues, and TED that screened from a compound library demonstrated a strong anti-senescence effect on DSS treated NCM460 cells. As an anti-senescence medication identified in this research, TED efficiently alleviated UC and colonic senescence in mice caused by DSS. By proteomic analysis and experimental validation, we found that DSS significantly inhibits the AMPK signaling pathway, while TED counteracts senescence by restoring AMPK activity. This research verified that the development of UC is accompanied with colon tissue senescence, and TED, an anti-senescence medication, can effectively treat UC caused by DSS and alleviate colon senescence. Our work suggests anti-senescence strategy is an effective approach for UC treatment.

Prodrugs as empowering tools in drug discovery and development: recent strategic applications of drug delivery solutions to mitigate challenges associated with lead compounds and drug candidates

The delivery of a drug to a specific organ or tissue at an efficacious concentration is the pharmacokinetic (PK) hallmark of promoting effective pharmacological action at a target site with an acceptable safety profile. Sub-optimal pharmaceutical or ADME profiles of drug candidates, which can often be a function of inherently poor physicochemical properties, pose significant challenges to drug discovery and development teams and may contribute to high compound attrition rates. Medicinal chemists have exploited prodrugs as an informed strategy to productively enhance the profiles of new chemical entities by optimizing the physicochemical, biopharmaceutical, and pharmacokinetic properties as well as selectively delivering a molecule to the site of action as a means of addressing a range of limitations. While discovery scientists have traditionally employed prodrugs to improve solubility and membrane permeability, the growing sophistication of prodrug technologies has enabled a significant expansion of their scope and applications as an empowering tool to mitigate a broad range of drug delivery challenges. Prodrugs have emerged as successful solutions to resolve non-linear exposure, inadequate exposure to support toxicological studies, pH-dependent absorption, high pill burden, formulation challenges, lack of feasibility of developing solid and liquid dosage forms, first-pass metabolism, high dosing frequency translating to reduced patient compliance and poor site-specific drug delivery. During the period 2012-2022, the US Food and Drug Administration (FDA) approved 50 prodrugs, which amounts to 13% of approved small molecule drugs, reflecting both the importance and success of implementing prodrug approaches in the pursuit of developing safe and effective drugs to address unmet medical needs.

Investigating the Antibacterial Effects of Synthetic Gamma-Lactam Heterocycles on Methicillin-Resistant Staphylococcus aureus Strains and Assessing the Safety and Effectiveness of Lead Compound MFM514

Methicillin-resistant Staphylococcus aureus (MRSA) continues to be one of the main causes of hospital-acquired infections in all regions of the world, while linezolid is one of the only commercially available oral antibiotics available against this dangerous gram-positive pathogen. In this study, the antibacterial activity from 32 analogues of synthetic gamma-lactam heterocycles against MRSA was determined. Amongst screened analogues for the minimum inhibitory concentration (MIC) assay, compound MFM514 displayed good inhibitory activity with MIC values of 7.8–15.6 µg/mL against 30 MRSA and 12 methicillin-sensitive S. aureus (MSSA) clinical isolates, while cytotoxicity evaluations displayed a mean inhibitory concentration (IC50) value of > 625 µg/mL, displaying a potential to becoming as a lead compound. In subsequent animal studies for MFM514, a single-dose oral acute toxicity test revealed an estimated mean lethal dose (LD50) value of <5000 mg/kg, while in the mice infection test, a mean effective dose (ED50) value of 29.39 mg/kg was obtained via oral administration. These results suggest that gamma-lactam carbon skeleton, particularly MFM514, is highly recommended to be evaluated further as a new safe and efficacious orally delivered antibacterial agent against MRSA.

Fabrication and Characterization of Tedizolid Phosphate Nanocrystals for Topical Ocular Application: Improved Solubilization and In Vitro Drug Release

Positively charged NCs of TZP (0.1%, w/v) for ocular use were prepared by the antisolvent precipitation method. TZP is a novel 5-Hydroxymethyl-Oxazolidinone class of antibiotic and is effective against many drug-resistant bacterial infections. Even the phosphate salt of this drug is poorly soluble, therefore the NCs were prepared for its better solubility and ocular availability. P188 was found better stabilizer than PVA for TZP-NCs. Characterization of the NCs including the particle-size, PDI, and ZP by Zeta-sizer, while morphology by SEM indicated that the preparation technique was successful to get the optimal sized (151.6 nm) TZP-NCs with good crystalline morphology. Mannitol (1%, w/v) prevented the crystal growth and provided good stabilization to NC₁ during freeze-drying. FTIR spectroscopy confirmed the nano-crystallization did not alter the basic molecular structure of TZP. DSC and XRD studies indicated the reduced crystallinity of TZP-NC₁, which potentiated its solubility. An increased solubility of TZP-NC₁ (25.9 µgmL⁻¹) as compared to pure TZP (18.4 µgmL⁻¹) in STF with SLS. Addition of stearylamine (0.2%, w/v) and BKC (0.01%, w/v) have provided cationic (+29.4 mV) TZP-NCs. Redispersion of freeze-dried NCs in dextrose (5%, w/v) resulted in a clear transparent aqueous suspension of NC₁ with osmolarity (298 mOsm·L⁻¹) and viscosity (21.1 cps at 35 °C). Mannitol (cryoprotectant) during freeze-drying could also provide isotonicity to the nano-suspension at redispersion in dextrose solution. In vitro release in STF with SLS has shown relatively higher (78.8%) release of TZP from NC₁ as compared to the conventional TZP-AqS (43.4%) at 12 h. TZP-NC₁ was physically and chemically stable at three temperatures for 180 days. The above findings suggested that TZP-NC₁ would be a promising alternative for ocular delivery of TZP with relatively improved performance.

3,4-Diaminopyridine-2,5-dicarbonitrile

Pyridines fused with heterocyclic rings are of great interest as both photovoltaic materials and biologically active compounds. The most convenient precursors for these compounds are pyridine-2,3-diamines. In this communication, 3,4-diaminopyridine-2,5-dicarbonitrile was synthesized by the reaction of 2,5-dibromo-3,4-diaminopyridine with copper cyanide; the best yield of the target compound was achieved by heating the reaction mixture in N,N-dimethylformamide at 120 °C for 6 h. The structure of the newly synthesized compound was established by means of elemental analysis, high resolution mass-spectrometry, 1H, 13C NMR, IR, UV spectroscopy and mass-spectrometry.

Strategies to Improve the Potency of Oxazolidinones towards Bacterial Biofilms

Biofilms are part of the natural lifecycle of bacteria and are known to cause chronic infections that are difficult to treat. Most antibiotics are developed and tested against bacteria in the planktonic state and are ineffective against bacterial biofilms. The oxazolidinones, including the last resort drug linezolid, are one of the main classes of synthetic antibiotics progressed to clinical use in the last 50 years. They have a unique mechanism of action and only develop low levels of resistance in the clinical setting. With the aim of providing insight into strategies to design more potent antibiotic compounds with activity against bacterial biofilms, we review the biofilm activity of clinically approved oxazolidinones and report on structural modifications to oxazolidinones and their delivery systems which lead to enhanced anti-biofilm activity.

Identification of NVP-CLR457 as an Orally Bioavailable Non-CNS-Penetrant pan-Class IA Phosphoinositol-3-Kinase Inhibitor

Balanced pan-class I phosphoinositide 3-kinase inhibition as an approach to cancer treatment offers the prospect of treating a broad range of tumor types and/or a way to achieve greater efficacy with a single inhibitor. Taking buparlisib as the starting point, the balanced pan-class I PI3K inhibitor 40 (NVP-CLR457) was identified with what was considered to be a best-in-class profile. Key to the optimization to achieve this profile was eliminating a microtubule stabilizing off-target activity, balancing the pan-class I PI3K inhibition profile, minimizing CNS penetration, and developing an amorphous solid dispersion formulation. A rationale for the poor tolerability profile of 40 in a clinical study is discussed.

Pharmacokinetics and Pharmacodynamics of Tedizolid

Tedizolid is an oxazolidinone antibiotic with high potency against Gram-positive bacteria and currently prescribed in bacterial skin and skin-structure infections. The aim of the review was to summarize and critically review the key pharmacokinetic and pharmacodynamic aspects of tedizolid. Tedizolid displays linear pharmacokinetics with good tissue penetration. In in vitro susceptibility studies, tedizolid exhibits activity against the majority of Gram-positive bacteria (minimal inhibitory concentration [MIC] of ≤ 0.5 mg/L), is four-fold more potent than linezolid, and has the potential to treat pathogens being less susceptible to linezolid. Area under the unbound concentration-time curve (fAUC) related to MIC (fAUC/MIC) was best correlated with efficacy. In neutropenic mice, fAUC/MIC of ~ 50 and ~ 20 induced bacteriostasis in thigh and pulmonary infection models, respectively, at 24 h. The presence of granulocytes augmented its antibacterial effect. Hence, tedizolid is currently not recommended for immunocompromised patients. Clinical investigations with daily doses of 200 mg for 6 days showed non-inferiority to twice-daily dosing of linezolid 600 mg for 10 days in patients with acute bacterial skin and skin-structure infections. In addition to its use in skin and skin-structure infections, the high pulmonary penetration makes it an attractive option for respiratory infections including Mycobacterium tuberculosis. Resistance against tedizolid is rare yet effective antimicrobial surveillance and defining pharmacokinetic/pharmacodynamic targets for resistance suppression are needed to guide dosing strategies to suppress resistance development.

Importance and Reality of TDM for Antibiotics Not Covered by Insurance in Japan

Under the Japanese health insurance system, medicines undergoing therapeutic drug monitoring (TDM) can be billed for medical fees if they meet the specified requirements. In Japan, TDM of vancomycin, teicoplanin, aminoglycosides, and voriconazole, which are used for the treatment of infectious diseases, is common practice. This means the levels of antibiotics are measured in-house using chromatography or other methods. In some facilities, the blood and/or tissue concentrations of other non-TDM drugs are measured by HPLC and are applied to treatment, which is necessary for personalized medicine. This review describes personalized medicine based on the use of chromatography as a result of the current situation in Japan.

Regio- and enantioselective formation of tetrazole-bearing quaternary stereocenters via palladium-catalyzed allylic amination

A general and efficient method via catalysis by readily available Pd(0)/DACH-naphthyl catalyst under mild conditions, unlocks a new platform that permits the synthesis of elusive quaternary N2-allylic tetrazoles, even in the context of late-stage functionalization.

Design, synthesis, and antibacterial evaluation of a novel series of biaryloxazolidinone derivatives against Gram-positive bacteria

A series of new biaryloxazolidinone derivatives has been designed and synthesized using the combination principle and blocking metabolic site to improve their antibacterial activity and stability.

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.

Tedizolid-Cyclodextrin System as Delayed-Release Drug Delivery with Antibacterial Activity

Progressive increase in bacterial resistance has caused an urgent need to introduce new antibiotics, one of them being oxazolidinones with their representative tedizolid. Despite the broad spectrum of activity of the parent tedizolid, it is characterized by low water solubility, which limits its use. The combination of the active molecule with a multifunctional excipient, which is cyclodextrins, allows preservation of its pharmacological activity and modification of its physicochemical properties. Therefore, the aim of the study was to change the dissolution rate and permeability through the model membrane of tedizolid by formation of solid dispersions with a cyclodextrin. The research included identification of tedizolid-hydroxypropyl-β-cyclodextrin (tedizolid/HP-β-CD) inclusion complex by thermal method (Differential Scanning Colorimetry), spectroscopic methods (powder X-ray diffraction, Fourier-Transform Infrared spectroscopy), and molecular docking. The second part of the research concerned the physicochemical properties (dissolution and permeability) and the biological properties of the system in terms of its microbiological activity. An increase in the dissolution rate was observed in the presence of cyclodextrin, while maintaining a high permeation coefficient and high microbiological activity. The proposed approach is an opportunity to develop drug delivery systems used in the treatment of resistant bacterial infections, in which, in addition to modifying the physicochemical properties caused by cyclodextrin, we observe a favorable change in the pharmacological potential of the bioactives.

The solution and solid-state degradation study followed by identification of tedizolid related compounds in medicinal product by high performance liquid chromatography with diode array and tandem mass spectrometry detection

The aim of the study was to investigate the intrinsic stability and to identify potential degradation products of tedizolid disodium phosphate (TED-OPO₃Na₂), which belongs to the antimicrobial agents of the oxazolidinone class. Tedizolid, as disodium phosphate (prodrug), is registered under the trade name SIVEXTRO®, at a dose of 200 mg, in the form of powder for injection or infusion. The stability-indicating assay method was optimised using HPLC with diode array detection and with electrospray ionisation time-of-flight mass spectrometry. In solution-state studies, the forced decomposition of TED-OPO₃Na₂ carried out under acidic, basic, oxidative, photocatalytic, and thermal conditions revealed the lability of TED-OPO₃Na₂ to acidic, basic, and photocatalytic (UV) conditions, while it was relatively stable in oxidative conditions and during thermolysis processes. The kinetics of degradation and shelf-life values in solution-state studies were determined, and activation energies were calculated for alkaline and thermolytic degradation. In contrast, in the solid state degradation study, TED-OPO₃Na₂ was stable under thermal conditions at high humidity and in visible light, while moderate degradation was observed under thermal conditions of low humidity and ultraviolet light. The developed method enabled the identification of 12 new degradation products and 3 new by-products.

Installation of an aryl boronic acid function into the external section of N-aryl-oxazolidinones: Synthesis and antimicrobial evaluation

N-aryl-oxazolidinones is a prominent family of antimicrobials used for treating infections caused by clinically prevalent Gram-positive bacteria. Recently, boron-containing compounds have displayed intriguing potential in the antibiotic discovery setting. Herein, we report the unprecedented introduction of a boron-containing moiety such as an aryl boronic acid in the external region of the oxazolidinone structure via a chemoselective acyl coupling reaction. As a result, we accessed a series of analogues with a distal aryl boronic pharmacophore on the oxazolidinone scaffold. We identified that a peripheric linear conformation coupled with freedom of rotation and no further substitution on the external aryl boronic ring, an amido linkage with hydrogen bonding character, in addition to a para-relative disposition between boronic group and linker, are the optimal combination of structural features in this series for antimicrobial activity. In comparison to linezolid, the analogue comprising all those features, compound 20b, displayed levels of antimicrobial activity augmented by an eight-fold to a thirty-two-fold against a panel of Gram-positive strains, and a near one hundred-fold against Escherichia coli JW5503, a Gram-negative mutant strain with a defective efflux capability.

Design, synthesis and antibacterial evaluation of novel oxazolidinone derivatives nitrogen-containing fused heterocyclic moiety

A series of novel oxazolidinone derivatives with nitrogen-containing fused heterocyclic moiety were designed and synthesized in this article. Their antibacterial activities were measured against S. aureus, MRSA and MSSA by MIC assay. Most of them exhibited potent activity against Gram-positive pathogens comparable to Linezolid and Radezolid. Compound 3b, which exhibited significant antibacterial activity with MIC values ranging 0.5-1.0 μg/mL, might be a promising drug candidate for further investigation.

Regioselectivity of the trifluoroethanol-promoted intramolecular N-Boc-epoxide cyclization towards 1,3-oxazolidin-2-ones and 1,3-oxazinan-2-ones

The intramolecular N-Boc-epoxide cyclization leading to the formation of 1,3-oxazolidin-2-one and 1,3-oxazinan-2-one derivatives has scarcely been reported in the literature. More specifically, the intramolecular cyclization of N-Boc aniline-tethered 2,3-disubstitued epoxides has never been disclosed. Herein, we demonstrate that this reaction could proceed in a diastereoselective fashion in refluxing trifluoroethanol, in the absence of any external promoter or catalyst. Substrates bearing an alkyl group at the C-3 position furnished 1,3-oxazolidin-2-ones in a completely regioselective fashion via 5-exo epoxide ring-opening cyclization, thereby paving the way to synthesize alkyl side chain-bearing analogs of the antidepressant drug toloxatone. On the other hand, replacing the alkyl group with an aryl group resulted in easily separable mixtures of 1,3-oxazolidin-2-ones and 1,3-oxazinan-2-ones, the former being obtained as the major products. Remarkably, a tetralin-bearing substrate underwent fully regioselective 6-endo ring closure to form the corresponding 1,3-oxazinan-2-one. Our present study on the intramolecular ring opening-cyclization of epoxides with a tethered N-Boc group is the most comprehensive to date and features broad substrate scope, mild transition metal-free conditions, excellent functional group tolerance, and scalability.

1,2,4-Triazole hybrids with potential antibacterial activity against methicillin-resistant Staphylococcus aureus

Methicillin-resistant Staphylococcus aureus (MRSA) has developed numerous mechanisms of virulence and strategies to evade the human immune system, and it can be transmitted between humans, animals, and the environment. Thus, MRSA is an important cause of morbidity and mortality in both hospitals and in the community, creating an urgent demand for the development of novel anti-MRSA candidates. The 1,2,4-triazole nucleus is a bioisostere of amide, ester, and carboxylic acid, and the 1,2,4-triazole ring is found in many compounds with diverse biological effects. 1,2,4-Triazole derivatives could exert their antibacterial activity through inhibition of efflux pumps, filamentous temperature-sensitive protein Z, penicillin-binding protein, DNA gyrase, and topoisomerase IV, and they play an important role in the discovery of novel antibacterial agents. Among them, 1,2,4-triazole hybrids, which have the potential to exert dual/multiple mechanisms of action, possess a promising broad-spectrum antibacterial activity against a panel of clinically important drug-resistant pathogens including MRSA. This review outlines the recent developments of 1,2,4-triazole hybrids with a potential anti-MRSA activity, covering articles published between 2010 and 2020. The mechanisms of action, critical aspects of their design, and structure-activity relationships are also discussed.

1,2,3-Triazole-containing hybrids with potential antibacterial activity against methicillin-resistant Staphylococcus aureus (MRSA)

Methicillin-resistant Staphylococcus aureus (MRSA), as a classic reason for genuine skin and flimsy tissues diseases, is a worldwide general wellbeing risk and has already tormented humanity for a long history, creating a critical need for the development of new classes of antibacterials. 1,2,3-Triazole moiety, readily interact with diverse enzymes and receptors in organisms through weak bond interaction, is among the most common frameworks present in the bioactive molecules. 1,2,3-Triazole derivatives, especially 1,2,3-triazole-containing hybrids, possess broad-spectrum activity against a panel of clinically important bacteria including drug-resistant pathogens, so rational design of 1,2,3-triazole derivatives may open a door for the opportunities on the development of novel anti-MRSA agents. This review is an endeavour to highlight the current scenario of 1,2,3-triazole-containing hybrids with potential anti-MRSA activity, covering articles published between 2010 and 2020.

Characterization of the Core Ribosomal Binding Region for the Oxazolidone Family of Antibiotics Using Cryo-EM

Linezolid and tedizolid are oxazolidinones with established clinical utility for the treatment of Gram-positive pathogens. Over time it has become apparent that even modest structural changes to the core phenyl oxazolidinone leads to drastic changes in biological activity. Consequently, the structure-activity relationship around the core oxazolidinone is constantly evolving, often reflected with new structural motifs present in nascent oxazolidinones. Herein we describe the use of cryo-electron microscopy to examine the differences in binding of several functionally different oxazolidinones in the hopes of enhanced understanding of their SAR. Tedizolid, radezolid, T145, and contezolid have been examined within the peptidyl transferase center (PTC) of the 50S ribosomal subunit from methicillin resistant Staphylococcus aureus. The ribosome-antibiotic complexes were resolved to a resolution of around 3 Å enabling unambiguous assignment of how each antibiotic interacts with the PTC.

Single Heterocyclic Compounds as Monoamine Oxidase Inhibitors: From Past to Present

Inhibitors of monoamine oxidase (MAO) have shown therapeutic values in a variety of neurodegenerative diseases such as depression, Parkinson's disease and Alzheimer's disease. Heterocyclic compounds exhibit a broad spectrum of biological activities and vital leading compounds for the development of chemical drugs. Herein, we focus on the synthesis and screening of novel single heterocyclic derivatives with MAO inhibitory activities during the past decade. This review covers recent pharmacological advancements of single heterocyclic moiety along with structure- activity relationship to provide better correlation among different structures and their receptor interactions.

Efficient and stereoselective one-pot synthesis of benzo[b]oxazolo[3,4-d][1,4]oxazin-1-ones

An efficient and mild one-pot convergent synthesis protocol has been developed for benzo[b]oxazolo[3,4-d][1,4]oxazin-1-one derivatives through the Mitsunobu reaction and sequential cyclization. Various tricyclic fused benzoxazinyl-oxazolidinones (20 examples) were obtained in good to excellent yields and high enantioselectivities with facile operation. Furthermore, four stereoisomers were afforded respectively in high ee values (>97.8%) via using different chiral 2,3-epoxy-4-trityloxybutanol. This methodology has been applied to the synthesis of key intermediates of drug candidates.

An efficient and mild one-pot convergent synthesis protocol has been developed for benzo[b]oxazolo[3,4-d][1,4]oxazin-1-one derivatives through the Mitsunobu reaction and sequential cyclization.

New Poly(Propylene Imine) Dendrimer Modified with Acridine and Its Cu(II) Complex: Synthesis, Characterization and Antimicrobial Activity

A second-generation poly(propylene imine) dendrimer modified with acridine and its Cu(II) complex have been synthesized for the first time. It has been found that two copper ions form complexes with the nitrogen atoms of the dendrimeric core by coordinate bonds. The new compounds have been characterized by nuclear magnetic resonance (NMR), electron paramagnetic resonance (EPR), fourier-transform infrared spectroscopy (FTIR) and fluorescence spectroscopy. The spectral characteristics of the modified dendrimer have been measured in different organic solvents, and a negative fluorescence solvatochromism has been observed. The antimicrobial activity of the dendrimers has been tested against model pathogenic microorganisms in agar and by broth dilution method. The cotton fabric treated with both dendrimers has been evaluated towards pathogenic microorganisms. The obtained modified cotton fabrics have been shown to hamper bacterial growth and to prevent biofilm formation. Dendrimer cytotoxicity has been investigated in vitro in the model HEp-2 cell line.

Facile synthesis of 1,5-disubstituted tetrazoles by reacting a ruthenium acetylide complex with trimethylsilyl azide

Treatment of [Ru]-C[triple bond, length as m-dash]CPh (1, [Ru] = (η⁵-C₅H₅)(dppe)Ru, dppe = Ph₂PCH₂CH₂PPh₂) with trimethylsilyl azide afforded the cationic nitrile complex {[Ru]NCCH₂Ph}[N₃] (2) and the further cycloaddition of 2 with trimethylsilyl azide at 60 °C afforded the N(2)-bound tetrazolato complex [Ru]N₄CCH₂Ph (3). The regiospecific alkylation of 3 gave a series of cationic N(2)-bound N(4)-alkylated-5-benzyl tetrazolato complexes {[Ru]N₄(CH₂R)CCH₂Ph}[Br] (4a, R = C₆F₅; 4b, R = Ph; 4c, R = 4-CN-C₆H₄; 4d, R = 2,6-F₂-C₆H₃; 4e, R = 6-CH₂Br-C₅NH₃) and the subsequent cleavage of the Ru-N bond of 4a-4e gave N(1)-alkylated-5-benzyl tetrazoles N₄(CH₂R)CCH₂Ph (5a-5e) in good to excellent yields and [Ru]-Br, which, on reacting with phenylacetylene, resulted in the formation of 1 thus forming a reaction cycle. The structures of 2, 3, 4a, 4c and 5a were confirmed by single-crystal X-ray diffraction analysis.

Prolonged inhibition and incomplete recovery of mitochondrial function in oxazolidinone-treated megakaryoblastic cell lines

Thrombocytopenia is commonly seen in patients receiving linezolid for >14 days. Linezolid is a reversible inhibitor of mitochondrial function in various cell types. This study investigated the inhibitory effects of linezolid and tedizolid, and their potential recovery on (i) CYTox I expression (subunit I of cytochrome c-oxidase; encoded by the mitochondrial genome), (ii) cytochrome c-oxidase activity and (iii) mitochondrial respiration (Seahorse bioanalysis) in two megakaryocytic cell lines [UT-7 WT (human acute megakaryoblastic leukaemia cells) and UT-7 MPL (transduced to express the thrombopoietin receptor)]. Cells were exposed to linezolid (0.5-25 mg/L) or tedizolid (0.1-5 mg/L) for up to 5 days and recovery followed after drug removal. Both oxazolidinones caused concentration- and time-dependent inhibition of CYTox I expression, cytochrome c-oxidase activity and mitochondrial spare capacity. On electron microscopy, mitochondria appeared dilated with a loss of cristae. Globally, tedizolid exerted stronger effects than linezolid. While CYTox I expression recovered completely after 6 days of drug washout, only partial (linezolid) or no (tedizolid) recovery of cytochrome c-oxidase activity, and no rescue of mitochondrial spare capacity (after 3 days) was observed. Thus, and in contrast to previous studies using a variety of cell lines unrelated to megakaryocytic lineages, the inhibitory effects exerted by oxazolidinones on the mitochondrial function of megakaryoblastic cells appear to be particularly protracted. Given the dynamics of platelet production and destruction, these results may explain why oxazolidinone-induced thrombocytopenia is one of the most common side effects in patients exposed to these antibiotics.

Nuclear magnetic resonance spectroscopic study of the inclusion complex of (R)-tedizolid with HDAS-β-CD, β-CD, and γ-cyclodextrin in aqueous solution

NMR spectroscopy is used to investigate the host-guest complexation of (R)-tedizolid, such as tedizolid with the hydroxymethyl substituent at the C5 position of the oxazolidinone ring ((R)-TED) or tedizolid with 5-methyl dihydrogen phosphate ((R)-TED-PO₄) with heptakis-(2,3-diacetyl-6-sulfo)-β-cyclodextrin (HDAS-β-CD), β-CD and γ-CD, in particular to obtain information about the mode and strength of the guest complexation into the hydrophobic cavity of the host. The complex stoichiometries of 1:1 (host:guest) and 1:2 were detected in millimolar concentrations for HDAS-β-CD and γ-CD with TED-PO₄ complexes, respectively. In the meantime, the mixed of complexes with stoichiometries of 1:1 and 2:1 were found for β-CD with both TED and TED-PO₄, however the 1:1 complex had a significant advantage.The binding mode was proposed. The estimated binding constants K_a of the complexes of TED or TED-PO₄ with CDs differ significantly in the order HDAS-β-CD<<β-CD<<γ-CD.

Enantioselective recognition of sutezolid by cyclodextrin modified non-aqueous capillary electrophoresis and explanation of complex formation by means of infrared spectroscopy, NMR and molecular modelling

A method for the enantioseparation of sutezolid, the next analogue after linezolid and tedizolid, belonging to the truly new class of antibacterial agents, the oxazolidinones, was developed based on non-aqueous capillary electrophoresis (NACE), using a single isomer of cyclodextrins as a chiral pseudophase. During the experiment, the enantioseparation of sutezolid together with its predecessor, linezolid, both weak base antibacterial agents, was evaluated using anionic single-isomers of cyclodextrins from hydrophilic, up to hydrophobic: heptakis-(2,3-dihydroxy-6-sulfo)-β-cyclodextrin, heptakis-(2,3-diacetyl-6-sulfo)-β-cyclodextrin (HDAS-β-CD), as well as heptakis-(2,3-dimethyl-6-sulfo)-β-cyclodextrin (HDMS-β-CD), respectively. Based on the observed results, the cyclodextrins, HDAS-β-CD and HDMS-β-CD which carry the acetyl and methyl groups at the C2 and C3 positions, respectively, provided the baseline separation of sutezolid enantiomers. However, HDMS-β-CD led to a reversal of enantiomer migration order (EMO) in comparison to HDAS-β-CD. Instead, enantiomers of linezolid were separated only by HDMS-β-CD. During the experiments, different organic solvents and their mixtures in various ratios were tested. The selectivity and separation efficiency were critically affected by the nature of the buffer system, the type of organic solvent, and the concentrations of trifluoroacetic acid (TFA) in the NACE buffer system. Focusing on the desired EMO in which the eutomers (S)-sutezolid and (S)-linezolid migrated last, the highest enantioresolution using the NACE method was achieved at normal polarity mode with 45  mM HDMS-β-CD dissolved in MeOH/ACN (85:15, v/v) containing 200  mM TFA/20  mM ammonium formate. Moreover, infrared spectroscopy, NMR and molecular modelling were investigated to provide information about complex formation.

In Vitro Activity of Tedizolid, Dalbavancin, and Ceftobiprole Against Clostridium difficile

Background:Clostridium difficile (C. difficile) is a major nosocomial pathogen that colonizes in the human gut. Recently, the U.S. FDA approved three new antimicrobial agents against gram-positive bacteria: Tedizolid, Dalbavancin, and Ceftobiprole. The efficacy of these antibiotics for treatment of C. difficile infection has not been thoroughly examined. The current study aimed to examine the in vitro activity of these antibiotics against C. difficile. In addition, to compare between Dalbavancin and Ceftobiprole to antibiotics from the same class: Vancomycin and Ceftriaxone, respectively. Methods: Eighty-four C. difficile isolates were tested for susceptibility to Tedizolid, Dalbavancin, Ceftobiprole, Vancomycin, and Ceftriaxone by Etest technique in order to determine the minimum inhibitory concentration (MIC). Results: Upon comparison of the novel antibiotic agents, Dalbavancin demonstrated the lowest MIC values and ceftobiprole the highest at MIC₅₀ (0.016, 0.38, and 1.5 μg/mL, for Dalbavancin, Tedizolid, and Ceftobiprole, respectively) and MIC₉₀ (0.03, 0.78, and 3.17 μg/mL, respectively). Dalbavancin demonstrated significantly lower MIC₅₀ and MIC₉₀ values compared to Vancomycin (0.016 vs. 0.38 and 0.03 vs. 3.5, respectively) (p < 0.001) and ceftobiprole had significantly lower MIC values compare to ceftriaxone (1.5 vs. 32 and 3.17 vs. 28.8, respectively) (p < 0.001). Conclusion: Dalbavancin and Tedizolid may play a role as potential therapeutic agents for treatment of C. difficile infection. Examination of antibiotic effect on the intestinal microbiome and clinical trials are needed for more accurate results.

Design, synthesis and biological evaluation of spiropyrimidinetriones oxazolidinone derivatives as antibacterial agents

Gram-positive bacteria are among the most common human pathogens associated with clinical infections which range from mild skin infections to sepsis. Resistance towards existing class of drugs by Gram-positive bacteria including methicillin resistant Staphylococcus aureus (MRSA), Staphylococcus epidermidis (MRSE) and vancomycin resistant enterococci (VRE) is a growing concern. There is an urgent need to discover new antibiotics which are active against resistant strains of Gram positive bacteria. We report herein a novel class of spiropyrimidinetrione oxazolidinone derivatives as novel antibacterial agents. Key step towards the synthesis of title compounds involved the use of tert-amino reaction with [1,5]-hydride shift leading to the new CC bond formation. Compound 30n has demonstrated potent antibacterial activity against a panel of Gram-positive microbial strains including MRSA, MRSE, and LNZ and vancomycin resistant strains of E. faecalis. Further, molecular docking studies suggest that 30n has binding mode similar to that of LNZ in 50S RNA ribosome.

Mitochondrial Alterations (Inhibition of Mitochondrial Protein Expression, Oxidative Metabolism, and Ultrastructure) Induced by Linezolid and Tedizolid at Clinically Relevant Concentrations in Cultured Human HL-60 Promyelocytes and THP-1 Monocytes

Linezolid, the first clinically available oxazolidinone antibiotic, causes potentially severe toxicities (myelosuppression, lactic acidosis, and neuropathies) ascribed to impairment of mitochondrial protein synthesis and consecutive mitochondrial dysfunction. Tedizolid, a newly approved oxazolidinone, shows an enhanced activity compared to linezolid but is also a more potent inhibitor of mitochondrial protein synthesis. We compared linezolid and tedizolid for (i) inhibition of the expression of subunit I of cytochrome c-oxidase (CYTox I; Western blot analysis), (ii) cytochrome c-oxidase activity (biochemical assay), (iii) mitochondrial oxidative metabolism (Seahorse technology), and (iv) alteration of mitochondrial ultrastructure (electron microscopy) using HL-60 promyelocytes and THP-1 monocytes exposed to microbiologically (multiples of modal MIC against Staphylococcus aureus) and therapeutically (C_min - C_max) pertinent concentrations. Both drugs caused a rapid and complete (48 to 72 h) inhibition of CYTox I expression, cytochrome c-oxidase activity, and spare respiratory capacity, with conspicuous swelling of the mitochondrial matrix and loss of their cristae. Globally, tedizolid was a more potent inhibitor than linezolid. For both drugs, all effects were quickly (48 to 72 h) and fully reversible upon drug withdrawal. Using an alternation of exposure to and withdrawal from drug mimicking their approved schedule of administration (twice daily and once daily [qD] for linezolid and tedizolid, respectively), only partial inhibition of CYTox I expression was noted for up to 96 h. Thus, rapid reversal of toxic effects upon discontinuous administration may mitigate oxazolidinone toxicity. Since tedizolid is given qD, this may help to explain its reported lower preclinical and clinical toxicity.

A new strategy for battling bacterial resistance: Turning potent, non-selective and potentially non-resistance-inducing biocides into selective ones

Antibiotic alternatives are in great need for combating antibiotic resistance. Selective delivery of a potent non-selective non-resistance-inducing biocide (C17) to MRSA was achieved by encapsulating it in solid lipid nanoparticles (SLNs) conjugated with a MRSA-specific antibody (termed as "Ab"). The C17-loaded Ab-conjugated SLNs (C17-SLN-Ab) demonstrated significantly better antimicrobial activity than its antibody free counterpart (C17-loaded SLN) and C17-loaded SLN with a non-specific IgG antibody. In a new MRSA/fibroblast co-culture assay, C17-SLN-Ab showed selective toxicity toward MRSA than fibroblast cells. C17-SLN-Ab possesses double selectivity, exhibiting higher toxicity to MRSA than to Pseudomonas aeruginosa. This same strategy was used to successfully increase C17's selectivity against E. coli K12 by switching the conjugated anti-MRSA antibody to an anti-E. coli antibody, demonstrating versatility of this new strategy. This proof-of-concept research can be extended to other non-selective antimicrobials, against which bacterial resistance is unlikely to develop, to generate a new group of promising antibiotic alternatives.

Design, Synthesis, and Antibacterial Evaluation of Oxazolidinones with Fused Heterocyclic C-Ring Substructure

A series of novel oxazolidinone antibacterials with diverse fused heteroaryl C-rings bearing hydrogen bond donor and hydrogen bond acceptor functionalities were designed and synthesized. The compound with benzoxazinone C-ring substructure (8c) exhibited superior activity compared to linezolid against a panel of Gram-positive and Gram-negative bacteria. Structural modifications at C5-side chain of 8c resulted in identification of several potent compounds (12a, 12b, 12g, and 12h). Selected compounds 8c and 12a showed very good microsomal stability and no CYP₄₅₀ liability, thus clearing preliminary safety hurdles. A docking model of 12a binding to 23S rRNA suggested that the increased potency of 12a is due to additional ligand-receptor interaction.

Comprehensive spectral identification of key intermediates to the final product of the chiral pool synthesis of radezolid

Radezolid (RAD, 12), biaryl oxazolidinone, was synthesised with small modifications according to the methods described in the literature. The pharmacological activity is observed only for (S)-enantiomer, therefore its synthesis is oriented towards obtaining a single isomer of required purity and desired optical configuration. The intermediate products of RAD synthesis were characterised using ¹H- and ¹³C-NMR, as well as the 2D correlation HSQC and HMBC (2, 5, 9, 10), furthermore studied using infrared radiation (FT-IR), Raman scattering (3, 5, 9), and electronic circular dichroism (ECD) (5, 12) spectroscopy. Each technique provides a unique and specific set of information. Hence, the full spectral characteristics of key intermediates obtained from the chiral pool synthesis to the finished product of RAD were summarised and compared. For a more accurate analysis, and due to the lack of reliable and reproducible reference standards for intermediate products, their vibrational analysis was supported by quantum chemical calculations based on the density functional theory (DFT) utilising the B3LYP hybrid functional and the 6-311G(d,p) basis set. Good agreement was observed between the empirical and theoretical spectra.Graphical abstract

Application of spectroscopic methods (FT-IR, Raman, ECD and NMR) in studies of identification and optical purity of radezolid

In the presented study, N-{[(5S)-3-(2-fluoro-4'-{[(1H-1,2,3-triazol-5-ylmethyl)amino]methyl}biphenyl-4-yl)-2-oxo-1,3-oxazolidin-5-yl]methyl}acetamide (radezolid) was synthesized and characterized using FT-IR, Raman, ECD and NMR. The aim of this work was to assess the possibility of applying classical spectral methods such as FT-IR, Raman, ECD and NMR spectroscopy for studies on the identification and optical purity of radezolid. The experimental interpretation of FT-IR and Raman spectra of radezolid was conducted in combination with theoretical studies. Density functional theory (DFT) with the B3LYP hybrid functional was used for obtaining radezolid spectra. Full identification was carried out by COSY, ¹H {¹³C} HSQC and ¹H {¹³C} HMBC experiments. The experimental NMR chemical shifts and spin-spin coupling constants were compared with theoretical calculations using the DFT method and B3LYP functional employing the 6-311++G(d,p) basis set and the solvent polarizable continuum model (PCM). The experimental ECD spectra of synthesized radezolid were compared with experimental spectra of the reference standard of radezolid. Theoretical calculations enabled us to conduct HOMO and LUMO analysis and molecular electrostatic potential maps were used to determine the active sites of microbiologically active form of radezolid enantiomer. The relationship between results of ab initio calculations and knowledge about chemical-biological properties of S-radezolid and other oxazolidinone derivatives are also discussed.

In Vitro Evaluations and In Vivo Toxicity and Efficacy Studies of MFM501 against MRSA

Previously we have discovered a synthetically derived pyrrolidone alkaloid, MFM501, exhibiting good inhibitory activity against 53 MRSA and MSSA isolates with low cytotoxicity against three normal cell-lines with IC₅₀ values at >625 µg/ml. Time-kill assay, scanning electron microscopy (SEM) analysis, in vivo oral acute toxicity test, and mice peritonitis model were carried out in this study. In the time-kill study, MFM501 showed a less than 3 log₁₀ decrease in bacterial colony concentration value (CFU/ml) which represented a bacteriostatic action while displaying a time-dependent inhibitory mechanism. Following that, SEM analysis suggested that MFM501 may exert its inhibitory activity via cytoplasmic membrane disruption. Moreover, MFM501 showed no toxicity effect on treated mice at an estimated median acute lethal dose (LD₅₀) value of more than 300 mg/kg and less than 2000 mg/kg. For the efficacy test, a mean effective dose (ED₅₀) of 87.16 mg/kg was obtained via a single dose oral administration. Our data demonstrated that MFM501 has the potential to be developed further as a new, safe, and effective oral-delivered antibacterial agent against MRSA isolates.