Synthesis and antibacterial activities of novel pleuromutilin derivatives with a substituted pyrimidine moiety

Pyrimidine-based sulfonamides and acetamides as potent antimicrobial Agents: Synthesis, Computational Studies, and biological assessment

A series of novel sulfonamide and acetamide derivatives of pyrimidine were synthesized and their antimicrobial activities were assessed. Based on the Microbroth dilution method, the minimum inhibitory concentration (MIC) of the synthesized compounds demonstrated moderate to good levels of antifungal and antibacterial activity. Structure-activity relationship analysis suggested that the presence of electron-withdrawing groups, such as halogens, nitrile, and nitro groups, on the pyrimidine ring contributed to the enhanced antimicrobial potency, while electron-donating substituents led to a decrease in activity. Computational studies, including density functional theory (DFT), frontier molecular orbitals (FMO), and molecular electrostatic potential (MEP) analysis, provided insights into the electronic properties and charge distribution of the compounds. Drug-likeness evaluation using ADME/Tox analysis indicated that the synthesized compounds possess favorable physicochemical properties and could be potential drug candidates. Molecular docking against the Mycobacterium TB protein tyrosine phosphatase B (MtbPtpB) revealed that the synthesized compounds exhibited strong binding affinities (-46 kcal/mol to - 61 kcal/mol) and formed stable protein-ligand complexes through hydrogen bonding and π-π stacking interactions with key residues in the active site. The observed interactions from the docking simulations were consistent with the predicted interaction sites identified in the FMO and MEP analyses. These findings suggest that the synthesized pyrimidine derivatives could serve as promising antimicrobial agents and warrant further investigation for drug development.

Antimicrobial activity, safety and pharmacokinetics evaluation of PMTM: A novel pleuromutilin candidate

The prevalence of infections by methicillin-resistant Staphylococcus aureus (MRSA) has led to dramatically increased mortality and threated the public health worldwide. Pleuromutilin compound 14-O-[(4-(pyrrolidine-1-yl)-6-methylpyrimidine-2-yl) thioacetyl] mutilin (PMTM) is a new antibacterial agent with excellent antibacterial efficacy against Gram positive bacteria. For further developing PMTM as a potential drug against MRSA infections, the in vitro antibacterial efficacy and preclinical safety were explored in this study. The results revealed that PMTM presented the higher anti-MRSA activity, increasing post-antibiotic effect (PAE) and limited potential to develop resistance. In safety evaluation, PMTM demonstrated low cytotoxicity, poor hemolytic activity, tolerable oral acute toxic effects in rats, devoid of mutagenic response and weak inhibitory potential on CYP3A4, but displayed moderate potential hERG K+ channel inhibition. Furthermore, two salts of PMTM with sulfuric acid and hydrochloric acid were prepared and confirmed. The sulfate salt of PMTM exhibited the highest solubility based on powder dissolution experiments and was chosen to evaluate pharmacokinetics properties, in which it displayed improved mouse pharmacokinetics parameters and oral bioavailability. The present study successfully provides a good foundation of PMTM for new antibacterial drug development.

Recent advances in developing modified C14 side chain pleuromutilins as novel antibacterial agents

Owing to the increasing resistance to most existing antimicrobial drugs, research has shifted towards developing novel antimicrobial agents with mechanisms of action distinct from those of current clinical options. Pleuromutilins are antibiotics known for their distinct mechanism of action, inhibiting bacterial protein synthesis by binding to the peptidyl transferase center of the ribosome. Recent studies have revealed that pleuromutilin derivatives can disrupt bacterial cell membranes, thereby enhancing antibacterial efficacy. Both marketed pleuromutilin derivatives and those in clinical trials have been developed by structurally modifying the pleuromutilin C14 side chain to improve their antimicrobial activity. Therefore, this review aims to review advancement in the chemical structural characteristics, antibacterial activities, and structure-activity relationship studies of pleuromutilins, specifically focusing on modifications made to the C14 side chain in recent years. These findings provide a valuable reference for future research and development of pleuromutilins.

Synthesis and evaluation of novel pleuromutilin derivatives targeting the 50S ribosomal subunit for antibacterial ability

Multidrug-resistant bacteria, particularly methicillin-resistant Staphylococcus aureus, have become a major global public health concern. Therefore, developing new antibiotics that do not possess cross-resistance for the currently available antibiotics is critical. Herein, we synthesized a novel class of pleuromutilin derivatives containing substituted triazine with improved antibacterial activity. Among these derivatives, 6d, which contains 4-dimethylamino-1,3,5-triazine in the side chain of pleuromutilin, exhibited highly promising antimicrobial activity and mitigated antibiotic resistance. The high antibacterial potency of 6d was further supported by docking model analysis and green fluorescent protein inhibition assay. Additionally, cytotoxicity and acute oral toxicity evaluation and in vivo mouse systemic infection experiments revealed that 6d possessed tolerable toxicity and promising therapeutic efficacy.

Design, synthesis, and evaluation of novel pleuromutilin aryl acrylate derivatives as promising broad-spectrum antibiotics especially for combatting multi-drug resistant gram-negative bacteria

The emergence of drug-resistant strains presents a grave challenge for traditional antibiotics, underscoring the exigency of exploring novel antibacterial drugs. To address this, the present study endeavors to design and synthesize a collection of pleuromutilin aromatic acrylate derivatives, guided by combination principles. The antibacterial activity and structure-activity relationship of these derivatives were evaluated, and most of the derivatives displayed moderate to excellent antibacterial activity against both Gram-positive bacteria and Gram-negative bacteria. Among these derivatives, 5g exhibited the strongest antibacterial activity, with MIC (minimum inhibitory concentration) values ranging from 1-32 μg/mL, and a MIC value against clinically isolated drug-resistant strains of 4-64 μg/mL. Additionally, 5g exhibited negligible cytotoxicity, superior anti-mycoplasma activity, and a greater propensity to perturb bacterial cell membranes. Notably, the administration of 5g resulted in an increased survival rate of MRSA (Methicillin-resistant Staphylococcus aureus)-infected mice, with an ED50 (median effective dose) value of 9.04 mg/kg. These results indicated the potential of 5g to be further developed as an antibacterial drug for the clinical treatment of drug-resistant bacterial infections.

Anti-methicillin-resistant Staphylococcus aureus activity and safety evaluation of 14-O-[(5-ethoxycarbonyl-4,6-dimethylpyrimidine-2-yl) thioacetyl] mutilin (EDT)

Infections caused by methicillin-resistant Staphylococcus aureus (MRSA) have threated the public health worldwide, which emphasizes the urgent need for new drugs with novel mechanism of actions. 14-O-[(5-ethoxycarbonyl-4,6-dimethylpyrimidine-2-yl) thioacetyl] mutilin (EDT) is a pleuromutilin compound with high activity against several Gram-positive bacteria in vitro and in vivo. This study aimed to verifying the potential anti-MRSA activity and evaluating the safety of EDT. In in vitro antibacterial activity assays, EDT exhibited potent antibacterial activity against MRSA isolated from clinic (minimum inhibitory concentration = 0.0313-0.125 μg/mL), increased post-antibiotic effect (PAE) values and limited potential for the development of resistance. Docking model and green fluorescent protein (GFP) inhibition assay further elucidated the higher antibacterial activities of EDT via mechanism of action. In safety evaluation, EDT exhibited low cytotoxic effect and acute oral toxicity in mice and avoided to significantly increase the number of revertant colonies of six tested strains in the Ames study. Furthermore, EDT displayed a moderate inhibitory effect on CYP3A4 and moderate stability in mouse and human liver microsomes, providing a promising agent for the development of new antimicrobial candidate.

Design, Synthesis, and Biological Activity of Thioguanine-Modified Pleuromutilin Derivatives

Antibiotic overuse has caused the increasingly serious problem of bacterial drug resistance, with numerous marketed antibiotics exhibiting significantly reduced activity against drug-resistant bacteria. Therefore, there is urgent demand for the development of novel antibiotics. Pleuromutilin is a tricyclic diterpene exhibiting antibacterial activity against Gram-positive bacteria and is currently considered the most promising natural antibiotic. In this study, novel pleuromutilin derivatives were designed and synthesized by introducing thioguanine units, and their antibacterial activities against drug-resistant strains were evaluated in vitro and in vivo. Compound 6j was observed to have a rapid bactericidal effect, low cytotoxicity, and potent antibacterial activity. The in vitro results suggest that 6j has a significant therapeutic effect on local infections, and its activity is equal to that of retapamulin, an anti-Staphylococcus aureus pleuromutilin derivative.

Novel pyridinium cationic pleuromutilin analogues overcoming bacterial multidrug resistance

A series of pyridinium cation-substituted pleuromutilin analogues were designed, synthesized and evaluated for their antibacterial activities in vitro and in vivo. Most derivatives showed potent antibacterial activities, especially e4 that displayed the highest antibacterial activity against multi-drug resistant bacteria and was subjected to time-kill kinetics, resistance studies, cytotoxicity and molecular docking assays. Molecular docking results, scanning electron microscopy and o-nitrophenyl-β-galactopyranoside tests showed that e4 not only inhibited bacterial protein synthesis but also disrupted bacterial cell walls. Compound e4 showed an ED₅₀ of 5.68 mg/kg against multi-drug resistant Staphylococcus aureus in infected mice model. In in vivo and in vitro toxicity tests, e4 showed low toxic effects with an LD₅₀ of 879 mg/kg to mice. These results suggest that compound e4 may be considered as a new therapeutic candidate for bacterial infections.

A Comprehensive Overview of the Antibiotics Approved in the Last Two Decades: Retrospects and Prospects

Due to the overuse of antibiotics, bacterial resistance has markedly increased to become a global problem and a major threat to human health. Fortunately, in recent years, various new antibiotics have been developed through both improvements to traditional antibiotics and the discovery of antibiotics with novel mechanisms with the aim of addressing the decrease in the efficacy of traditional antibiotics. This manuscript reviews the antibiotics that have been approved for marketing in the last 20 years with an emphasis on the antibacterial properties, mechanisms, structure-activity relationships (SARs), and clinical safety of these antibiotics. Furthermore, the current deficiencies, opportunities for improvement, and prospects of antibiotics are thoroughly discussed to provide new insights for the design and development of safer and more potent antibiotics.

Design, synthesis and antibacterial activity of novel pleuromutilin derivatives with thieno[2,3-d]pyrimidine substitution

A series of novel pleuromutilin derivatives with substituted thienopyrimidines were designed, synthesized, and evaluated for antibacterial act ivity. In this study, the activities of these compounds were investigated using the inhibition circle test, the minimum inhibitory concentration (MIC) test, real-time growth curves, time-kill kinetic assays, cytotoxicity assays, and molecular docking. Most of the tested compounds exhibited moderate antibacterial activity against Staphylococcus aureus, Streptococcus agalactiae, and Escherichia coli. Compound A11 was the most active and displayed bacteriostatic activities against methicillin-resistant S. aureus, with MIC values as low as 0.00191 μg/mL, which is 162 and 32 times lower than that of the marketed antibiotics tiamulin and retapamulin, respectively. Furthermore, the mechanism of action of A11 was confirmed by molecular docking studies.

Discovery of novel pleuromutilin derivatives as potent antibacterial agents

Novel pleuromutilin derivatives with 3,4-dihydropyrimidin and pyrimidine moieties were designed, synthesized, and evaluated for their antibacterial activities. Most of the synthesized derivatives, especially the compounds bearing the pyrimidine moieties, exhibited potent antibacterial activities against methicillin-resistant Staphylococcus aureus BNCC 337371 (MRSA-337371), Staphylococcus aureus ATCC 25923 (S. aureus-25923) and methicillin-resistant Staphylococcus epidermidis ATCC 51625 (MRSE-51625). Compounds 5a, 5g and 5h exerted the excellent antibacterial activities and selected to evaluate their bacterial killing kinetics. Compound 5h displayed the highest antibacterial activities with bacteriostatic activities against MRSA and further evaluated its efficacy in mouse systemic infection. The results showed that compound 5h exhibited potent in vivo antibacterial effects to significantly improve the survival rate of mice (ED50 = 16.14 mg/kg), reduce the bacterial load and alleviate the pathological changes in the lungs of the affected mice. Furthermore, molecular docking studies revealed that the selected compounds successfully localized in the pocket of 50S ribosomal subunit and the formed hydrogen bonds were the main interaction.

Synthesis, biological activities and docking studies of pleuromutilin derivatives with piperazinyl urea linkage

Antibiotics resistance is becoming increasingly common, involving almost all antibiotics on the market. Diseases caused by drug resistant bacteria, such as MRSA, have high mortality and negatively affect public health. The development of new drugs would be an effective means of solving this problem. Modifications based on bioactive natural products could greatly shorten drug development time and improve success rate. Pleuromutilin, a natural product from the basidiomycete bacterial species, is a promising antibiotic candidate. In this study, a series of novel pleuromutilin derivatives possessing piperazinyl urea linkage were efficiently synthesised, and their antibacterial activities and bactericidal properties were evaluated via MIC, MBC and Time-kill kinetics assays. The results showed that all compounds exhibited potent activities against tested strains, especially MRSA strains with MIC values as low as 0.125 μg/mL; 8 times lower than that of marketed antibiotic Tiamulin. Docking studies indicate substituted piperazinyl urea derivatives could provide hydrogen bonds and initiate π-π stacking between molecules and surrounding residues.

14-O-[(4,6-Diamino-pyrimidine-2-yl) thioacetyl] mutilin inhibits α-hemolysin and protects Raw264.7 cells from injury induced by methicillin-resistant S. aureus

A new pleuromutilin derivative, 14-O-[(4,6-Diaminopyrimidine-2-yl) thioacetyl] mutilin (DPTM), has been synthesized and proven to be a potent agent against Gram-positive pathogens, especially for Staphylococcus aureus (S. aureus). However, its pharmacological activities against α-hemolysin (Hla), a major virulence factor produced by S. aureus, and inflammations related to S. aureus are still unknown. In the present study, we investigated the DPTM inhibition activities against methicillin-resistant S. aureus (MRSA) Hla and protective efficacy of Raw264.7 cells from injury induced by MRSA. The results showed that DPTM with sub-inhibitory concentrations significantly inhibited Hla on the hemolysis of rabbit erythrocytes and down-regulated the gene expressions of Hla and agrA with a dose-dependent fashion. In Raw264.7 cells infected with MRSA, DPTM efficiently attenuated the productions of lactate dehydrogenase (LDH), nitric oxide (NO) and pro-inflammatory cytokines, as well as the express levels of nuclear factor-kappaB (NF-κB), nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2). Furthermore, DPTM inhibited the translocation of p-65 to nucleus in RAW264.7 cells infected by MRSA.

In Vitro and In Vivo Activity of 14-O-[(4,6-Diamino-pyrimidine-2-yl) thioacetyl] Mutilin against Methicillin-Resistant Staphylococcus aureus

Staphylococcus aureus (S. aureus) is a major human pathogen that requires new antibiotics with unique mechanism. A new pleuromutilin derivative, 14-O-[(4,6-Diamino-pyrimidine-2-yl) thioacetyl] mutilin (DPTM), has been synthesized and proved as a potent antibacterial agent using in vitro and in vivo assays. In the present study, DPTM was further in vitro evaluated against methicillin-resistant Staphylococcus aureus (MRSA) isolated from dairy farms and outperformed tiamulin fumarate, a pleuromutilin drug used for veterinary. Moreover, a murine skin wound model caused by MRSA infection was established, and the healing effect of DPTM was investigated. The results showed that DPTM could promote the healing of MRSA skin infection, reduce the bacterial burden of infected skin MRSA and decrease the secretion of IL-6 and TNF-α inflammatory cytokines in plasma. These results provided the basis for further in-depth drug targeted studies of DPTM as a novel antibacterial agent.

Novel pleuromutilin derivatives with substituted 6-methylpyrimidine: Design, synthesis and antibacterial evaluation

A series of novel pleuromutilin derivatives with substituted 6-methylpyrimidine moieties was designed, synthesized, and evaluated for their antibacterial activities. Most of the tested compounds exhibited potent antibacterial activities against Staphylococcus aureus ATCC 25923 (S. aureus-25923), methicillin-resistant Staphylococcus epidermidis ATCC 51625 (MRSE-51625), methicillin-resistant Staphylococcus aureus BNCC 337371 (MRSA-337371), Streptococcus dysgalactiae (S. dysgalactiae) and Streptococcus agalactiae (S. agalactiae). Compounds 5c and 5g were the most active and displayed bacteriostatic activities against MRSA. In vivo mouse systemic infection experiment showed that 5c significantly improved the survival rate of mice (ED50 = 18.02 mg/kg), reduced the bacterial load and alleviated the pathological changes in the lungs of the affected mice.

Cytochrome P450 inhibition potential and initial genotoxic evaluation of 14-O-[(4,6-diaminopyrimidine-2-yl)thioacetyl] mutilin

14-O-[(4,6-Diaminopyrimidine-2-yl)thioacetyl] mutilin (DPTM) is a promising drug candidate with excellent antibacterial activity against Gram-positive bacteria. The present study was designed to characterize its Cytochrome P450 (CYP) enzymes inhibition activities and the genotoxicity with the standard Ames test. We determined the inhibitory effects of DPTM on CYP1A2, CYP2D1/6, CYP2E1, CYP2C11/9 and CYP3A/4 in rat liver microsomes (RLMs) and in human liver microsomes (HLMs). The mRNA expressions of the above CYP isoforms and their transcriptional regulators were also evaluated using the Hep G2 cell model. The results showed DPTM exhibited a moderate inhibitory potential against CYP3A/4 (IC₅₀ values of 10 ± 2 and 8 ± 2 μM, respectively) and weak against the other CYP enzymes based on their IC₅₀ values. Compared to the control, CYP isoforms and their transcriptional regulators mRNA expressions significantly increased when the Hep G2 cells were treated with DPTM for a certain period of time. In the Ames test, Salmonella strains TA97, TA98, TA100, TA102 and TA1535 were treated with or without the metabolic activation (S9). Analysis showed the average number of revertant colonies per plate was less in double in the groups treated with DPTM than that in the negative control plate and showed no dose-related increase.

A Validated HPLC-MS/MS Assay for 14-O-[(4,6-Diaminopyrimidine-2-yl)thioacetyl] Mutilin in Biological Samples and Its Pharmacokinetic, Distribution and Excretion via Urine and Feces in Rats

14-O-[(4,6-Diaminopyrimidine-2-yl)thioacetyl] mutilin (DPTM), a novel pleuromutilin candidate with a substituted pyrimidine moiety, has been confirmed to possess excellent antibacterial activity against Gram-positive bacteria. To illustrate the pharmacokinetic profile after intravenous (i.v.), intramuscular (i.m.) and oral (p.o.) administrations with DPTM, as well as tissue distribution and excretion via urine and feces in vivo, a specific, sensitive and robust HPLC-MS/MS method was first developed to determine DPTM in rat plasma, various tissues, urine and feces. The plasma, tissues, urine and feces samples were treated by protein precipitation with acetonitrile using tiamulin fumarate as an internal standard (IS). This method which was achieved on an HPLC system detector equipped with an ESI interface, was sensitive with 5 ng/mL as the lower limit of detection and exhibited good linearity (R² > 0.9900) in the range of 5⁻4000 ng/mL for plasma, various tissues, urine and feces, as well as intra-day precision, inter-day precision and accuracy. The matrix effects ranged from 94.2 to 109.7% with RSD ≤ 9.4% and the mean extraction recoveries ranged from 95.4 to 109.5% in plasma, tissue homogenates, urine and feces (RSD ≤ 9.9). After i.v., i.m. and p.o. administrations, DPTM was rapidly absorbed and metabolized in rats with the half-life (t1/2) of 1.70⁻1.86, 3.23⁻3.49 and 4.38⁻4.70 for 10, 25 and 75 mg/kg doses, respectively. The tissue distribution showed that DPTM was diffused into all the tested tissues, especially into the intestine and lung. Excretion via urine and feces studies demonstrated that DPTM was mainly excreted by feces after administration.

A new pleuromutilin candidate with potent antibacterial activity against Pasteurella multocida

This study assessed the antimicrobial activity of 14-O-[(4,6-Diaminopyrimidine-2-yl) thioacetyl] mutilin (DPTM), a novel pleuromutilin candidate with a substituted pyrimidine moiety, against Pasteurella multocida. Minimum Inhibitory Concentration (MIC), Oxford Cup assay, and time-kill experiments were used to measure the activity of DPTM against P. multocida serotype A in vitro. We observed that DPTM was potent against Pasteurella multocida serotype A with the MIC value of 0.781 μg/mL. The mean inhibition-zone diameters of DPTM (50, 25, and 12.5 μg/mL) were 29.4, 24.2 and 20.1 mm, respectively. Time-kill experiments showed that the drug caused a rapid decline in the number of bacteria compared with the initial inoculum at 4 h and killed 94.6% of the bacteria during 24 h. Furthermore, DPTM activity was also assessed in a lung infection model challenged with 4.0 × 109 CFU/mL P. multocida serotype A. The results showed that DPTM significantly reduced mortality rate and bacterial load, and alleviated the pathological changes of lung. The antibacterial effect of DPTM found in this study suggested that it was useful in the prevention or control of pneumonia caused by P. multocida.

Antibacterial properties and clinical potential of pleuromutilins

Covering: up to 2018Pleuromutilins are a clinically validated class of antibiotics derived from the fungal diterpene (+)-pleuromutilin (1). Pleuromutilins inhibit bacterial protein synthesis by binding to the peptidyl transferase center (PTC) of the ribosome. In this review we summarize the biosynthesis and recent total syntheses of (+)-pleuromutilin (1). We review the mode of interaction of pleuromutilins with the bacterial ribosome, which involves binding of the C14 extension and the tricyclic core to the P and A sites of the PTC, respectively. We provide an overview of existing clinical agents, and discuss the three primary modes of bacterial resistance (mutations in ribosomal protein L3, Cfr methylation, and efflux). Finally we collect structure-activity relationships from publicly available reports, and close with some forward looking statements regarding future development.

Synthesis of dibenzothiazepine analogues by one-pot S-arylation and intramolecular cyclization of diaryl sulfides and evaluation of antibacterial properties

Dibenzothiazepine analogues containing lactam, amidine and imine moieties were prepared from 2-aminophenyl disulfides via one-pot S-arylation. The S-arylation involved cleavage of an S-S bond of disulfides and SNAr reaction in aqueous ammonia solution of L-cysteine to afford diaryl sulfides. Dibenzothiazepine analogues having lactam and amidine moieties were obtained by cyclization of the corresponding diaryl sulfides under acidic conditions. One-pot S-arylation of 2-bromo-5-nitrobenzaldehyde gave dibenzothiazepine analogues with an imine moiety in one step through intramolecular cyclization. Compounds with antibacterial activities against Staphylococcus aureus and Escherichia coli were obtained.

Antibacterial activity and pharmacokinetic profile of a promising antibacterial agent: 14-O-[(4-Amino-6-hydroxy-pyrimidine-2-yl)thioacetyl] mutilin

A new pleuromutilin derivative, 14-O-[(4-Amino-6-hydroxy-pyrimidine-2-yl)thioacetyl] mutilin (APTM), has been synthesized and proved most potent antibacterial agent in in vitro assays, suggesting that further development of this compound may lead to a promising antibacterial drug. In this study, we further evaluated the cytotoxicity, antibacterial efficacy and the pharmacokinetic profile of APTM. In BRL 3A cells, 50% of viability was obtained when 363μg/mL of APTM was used, while retapamulin and tiamulin fumarate needed 49 and 28μg/mL, respectively, to reach this viability. Compared to tiamulin fumarate, APTM showed higher inhibition efficacy and faster bactericidal activity against S. aureus and lower 50% effective dose (ED₅₀) in mice after a lethal challenge with methicillin-resistant Staphylococcus aureus (MRSA). Docking experiment for APTM showed a similar binding pattern with tiamulin. Furthermore, a simple, accurate and sensitive HPLC method for the determination of APTM in rabbit plasma was developed and successfully applied to pharmacokinetic study, in which the half life (t_1/2), clearance rate (Cl) and the area under the plasma concentration-time curve (AUC_0→∞) were 3.37h, 0.35L/h/kg and 70.68μg·h/m, respectively.