A click chemistry approach to pleuromutilin derivatives. Part 3: extended footprinting analysis and excellent MRSA inhibition for a derivative with an adenine phenyl side chain

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.

Hit-to-Lead Identification and Validation of a Triaromatic Pleuromutilin Antibiotic Candidate

Herein, we report the hit-to-lead identification of a drug-like pleuromutilin conjugate 16, based on a triaromatic hit reported in 2020. The lead arose as the clear candidate from a hit-optimization campaign in which Gram-positive antibacterial activity, solubility, and P-gp affinity were optimized. Conjugate 16 was extensively evaluated for its in vitro ADMET performance which, apart from solubility, was overall on par with lefamulin. This evaluation included Caco-2 cell permeability, plasma protein binding, hERG inhibition, cytotoxicity, metabolism in microsomes and CYP3A4, resistance induction, and time-kill kinetics. Intravenous pharmacokinetics of 16 proved satisfactory in both mice and pigs; however, oral bioavailability was limited likely due to insufficient solubility. The in vivo efficacy was evaluated in mice, systemically infected with Staphylococcus aureus, where 16 showed rapid reduction in blood bacteriaemia. Through our comprehensive studies, lead 16 has emerged as a highly promising and safe antibiotic candidate for the treatment of Gram-positive bacterial infections.

Design and Synthesis of Pleuromutilin Derivatives as Antibacterial Agents Using Quantitative Structure-Activity Relationship Model

The quantitative structure-activity relationship (QSAR) is one of the most popular methods for the virtual screening of new drug leads and optimization. Herein, we collected a dataset of 955 MIC values of pleuromutilin derivatives to construct a 2D-QSAR model with an accuracy of 80% and a 3D-QSAR model with a non-cross-validated correlation coefficient (r2) of 0.9836 and a cross-validated correlation coefficient (q2) of 0.7986. Based on the obtained QSAR models, we designed and synthesized pleuromutilin compounds 1 and 2 with thiol-functionalized side chains. Compound 1 displayed the highest antimicrobial activity against both Staphylococcus aureus ATCC 29213 (S. aureus) and Methicillin-resistant Staphylococcus aureus (MRSA), with minimum inhibitory concentrations (MICs) < 0.0625 μg/mL. These experimental results confirmed that the 2D and 3D-QSAR models displayed a high accuracy of the prediction function for the discovery of lead compounds from pleuromutilin derivatives.

Synthesis and Biological Activities of Oxazolidinone Pleuromutilin Derivatives as a Potent Anti-MRSA Agent

A series of pleuromutilin derivatives containing an oxazolidinone skeleton were synthesized and evaluated in vitro and in vivo as antibacterial agents. Most of the synthesized derivatives exhibited potent antibacterial activities against three strains of Staphylococcus aureus (including MRSA ATCC 33591, MRSA ATCC 43300, and MSSA ATCC 29213) and two strains of Staphylococcus epidermidis (including MRSE ATCC 51625 and MSSE ATCC 12228). Compound 28 was the most active antibacterial agent in vitro (MIC = 0.008-0.125 μg·mL-1) and exhibited a significant bactericidal effect, low cytotoxicity, and weak inhibition (IC50 = 20.66 μmol·L-1) for CYP3A4, as well as exhibited less possibility to cause bacterial resistance. Furthermore, in vivo activities indicated that the compound was effective in reducing MRSA load in a murine thigh infection model. Moreover, it clearly facilitated the healing of MRSA skin infection and inhibited the secretion of the TNF-α, IL-6, and MCP-1 inflammatory factors in serum. These results suggest that oxazolidinone pleuromutilin is a promising therapeutic candidate for drug-resistant bacterial infections.

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.

Design, synthesis and antibacterial activity evaluation of pleuromutilin derivatives according to twin drug theory

A series of novel pleuromutilin derivatives were designed and synthesized based on the twin drugs theory. Piperazinyl and thioether were used as the linkage to connect the pleuromutilin nuclear and sulfonamide to improve the biological activity and water solubility of derivatives. The in vitro antibacterial activities against drug-sensitive and drug-resistance bacteria were evaluated by agar dilution method. Most of the 25 compounds displayed excellent antibacterial activities against drug-sensitive bacteria, particularly, five compounds (9, 10, 11, 14a and 14b) exerted the excellent antibacterial activities against drug-resistance bacteria.

A click chemistry approach to pleuromutilin derivatives, evaluation of anti-MRSA activity and elucidation of binding mode by surface plasmon resonance and molecular docking

Novel series of pleuromutilin analogs containing substituted 1,2,3-triazole moieties were designed, synthesised and assessed for their in vitro antibacterial activity against Methicillin-resistant Staphylococcus aureus (MRSA). Initially, the in vitro antibacterial activities of these derivatives against 4 strains of S. aureus (MRSA ATCC 43300, ATCC 29213, AD3, and 144) were tested by the broth dilution method. Most of the synthesised pleuromutilin analogs displayed potent activities. Among them, compounds 50, 62, and 64 (MIC = 0.5∼1 µg/mL) showed the most effective antibacterial activity and their anti-MRSA activity were further studied by the time-killing kinetics approach. Binding mode investigations by surface plasmon resonance (SPR) with 50S ribosome revealed that the selected compounds all showed obvious affinity for 50S ribosome (KD = 2.32 × 10-8∼5.10 × 10-5 M). Subsequently, the binding of compounds 50 and 64 to the 50S ribosome was further investigated by molecular modelling. Compound 50 had a superior docking mode with 50S ribosome, and the binding free energy of compound 50 was calculated to be -12.0 kcal/mol.

Antibacterial Activity of a Promising Antibacterial Agent: 22-(4-(2-(4-Nitrophenyl-piperazin-1-yl)-acetyl)-piperazin-1-yl)-22-deoxypleuromutilin

A novel pleuromutilin derivative, 22-(4-(2-(4-nitrophenyl-piperazin-1-yl)-acetyl)-piperazin-1-yl)-22-deoxypleuromutilin (NPDM), was synthesized in our laboratory and proved excellent antibacterial activity against methicillin-resistant Staphylococcus aureus (MRSA). In this study, more methods were used to further study its preliminary pharmacological effect. The antibacterial efficacy and toxicity of NPDM were evaluated using tiamulin as the reference drug. The in vitro antibacterial activity study showed that NPDM is a potent bactericidal agent against MRSA that induced time-dependent growth inhibition and a concentration-dependent post-antibiotic effect (PAE). Toxicity determination showed that the cytotoxicity of NPDM was slightly higher than that of tiamulin, but the acute oral toxicity study proved that NPDM was a low-toxic compound. In an in vivo antibacterial effect study, NPDM exhibited a better therapeutic effect than tiamulin against MRSA in a mouse thigh infection model as well as a mouse systemic infection model with neutropenia. The 50% effective dose (ED50) of NPDM in a Galleria mellonella infection model was 50.53 mg/kg. The pharmacokinetic properties of NPDM were also measured, which showed that NPDM was a rapid elimination drug in mice.

Discovery of a Potent Adenine-Benzyltriazolo-Pleuromutilin Conjugate with Pronounced Antibacterial Activity against MRSA

Conjugation of pleuromutilin is an attractive strategy for the development of novel antibiotics and the fight against multiresistant bacteria as the class is associated with low rates of resistance and cross-resistance development. Herein, the preparation of 35 novel (+)-pleuromutilin conjugates is reported. Their design was based on a synthetically more efficient benzyl adaption of a potent lead but still relied on the Cu(I)-catalyzed alkyne-azide [3 + 2] cycloaddition for conjugation onto pleuromutilin. Their antibacterial activity was evaluated against the multiresistant Staphylococcus aureus strain USA300 for which they displayed moderate to excellent activity. Compound 35, bearing a para-benzyladenine substituent, proved particularly potent against USA300 and additional strains of MRSA and displayed as importantly no cytotoxicity in four mammalian cell lines. Structure-activity relationship analysis revealed that the purine 6-amino is essential for high potency, likely because of strong hydrogen bonding with the RNA backbone of C2469, as suggested by a molecular model based on the MM-GBSA approach.

Design, synthesis and biological activities of novel pleuromutilin derivatives with a substituted triazole moiety as potent antibacterial agents

A series of novel pleuromutilin derivatives possessing 1,2,3-triazole moieties were synthesized via click reactions under mild conditions. The in vitro antibacterial activities of these derivatives against 4 strains of S. aureus (MRSA ATCC 43300, ATCC 29213, AD 3, and 144) and 1 strain of E. coli (ATCC 25922) were tested by the broth dilution method. The majority of the synthesized derivatives displayed potent antibacterial activities against MRSA (MIC = 0.125-2 μg/mL). It was also found that most compounds had no significant inhibitory effect on the proliferation of RAW264.7 cells at the concentration of 8 μg/mL. Among these derivatives, compound 32 (∼1.71 log10 CFU/g) containing dimethylamine group side chain displayed more effective than tiamulin (∼0.77 log10 CFU/g) at the dose of 20 mg/kg in reducing MRSA load in thigh infected mice. Additionally, compound 32 (the survival rate was 50%) also displayed superior in vivo efficacy to that of tiamulin (the survival rate was 20%) in the mouse systemic model. Structure-activity relationship (SAR) studies resulted in compound 32 with the most potent in vitro and in vivo antibacterial activity among the series. Moreover, compound 32 was evaluated in CYP450 inhibition assay and showed moderate in vitro inhibition of CYP3A4 (IC50 = 6.148 μM).

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.

Design, synthesis and biological evaluation of novel pleuromutilin derivatives possessing acetamine phenyl linker

A series of novel acetamine phenyl pleuromutilin derivatives incorporating 2-aminothiophenol moieties into the C14 side chain were synthesized via acylation reactions under mild conditions. The in vitro antibacterial activities of the synthesized derivatives against three Staphylococcus aureus (MRSA ATCC 43300, ATCC 29213 and AD 3) and two Escherichia coli (ATCC 25922 and 9-1) were evaluated by the broth dilution method. Most of the synthesized derivatives displayed potent activities. Compound 27 was found to be the most active antibacterial derivative against MRSA (minimal inhibitory concentration = 0.015 μg/mL) which may lead to a promising antibacterial drug. Furthermore, compound 27 displayed more rapid bactericidal kinetic than tiamulin in in vitro time-kill studies and possessed a longer PAE than tiamulin against MRSA. The PK properties of compound 27 were then measured. The half life (t1/2), clearance rate (Cl) and the area under the plasma concentration-time curve (AUC0→∞) of compound 27 were 6.88 h, 21.64 L/h/kg and 0.48 μg h/mL, respectively. The in vivo antibacterial activities of compound 27 against MRSA were further evaluated using thigh infection model and systemic infection model. Compound 27 possessed superior antibacterial efficacy to tiamulin against MRSA infection in both model.

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 and antibacterial activities of novel pleuromutilin derivatives bearing an aminothiophenol moiety

We synthesized a series of novel thioether pleuromutilin derivatives incorporating 2-aminothiophenol moieties into the C14 side chain via acylation reactions under mild conditions. We evaluated the in-vitro antibacterial activities of the derivatives against methicillin-resistant Staphylococcus aureus (MRSA, ATCC 43300), Staphylococcus aureus (ATCC 29213) and Escherichia coli (ATCC 25922). The majority of the synthesized derivatives possessed moderate antibacterial activities. Compound 8 was found to be the most active antibacterial derivative against MRSA. We conducted docking experiments to understand the possible mode of interactions between compounds 8, 9b, 11a and 50S ribosomal subunit. The docking results proved that there is a reasonable correlation between the binding free energy and the antibacterial activity. Compound 8 was evaluated for its in-vivo antibacterial activity and showed higher efficacy than tiamulin against MRSA in mouse infection model.

Design, synthesis and antibacterial evaluation of novel pleuromutilin derivatives possessing piperazine linker

A series of pleuromutilin derivatives bearing piperazine ring have been reported. The in vitro antibacterial activities of the synthetic derivatives against MRSA (ATCC 43300), Staphylococcus aureus (ATCC 29213), Enterococcus faecalis (ATCC 29212), Enterococcus faecium (ATCC35667) and Escherichia coli (ATCC25922) were evaluated by the broth dilution method. Most of the synthesized derivatives displayed potent activities. Compounds 11c, 12a and 12c were found to be the most active antibacterial derivatives against MRSA (minimum inhibitory concentration = 0.015 μg/mL). The binding of compounds 11c, 12a and 12c to the 50s ribosome were investigated by molecular modeling. Compound 11c possessed lower binding free energy compared with compounds 12a and 12c. Compound 11c was further evaluated in MRSA systemic infection model and displayed superior in vivo efficacy to that of tiamulin.

Design, synthesis, and structure-activity relationship studies of novel pleuromutilin derivatives having a piperazine ring

A series of novel pleuromutilin derivatives possessing piperazine moieties were synthesized under mild conditions. The in vitro antibacterial activities of these derivatives against Staphylococcus aureus and Escherichia coli were tested by the agar dilution method. Structure-activity relationship studies resulted in compounds 11b, 13b, and 14a with the most potent in vitro antibacterial activity among the series (minimal inhibitory concentration = 0.0625-0.125 μg/mL). The binding of compounds 11b, 13b, and 14a to the E. coli ribosome was investigated by molecular modeling, and it was found that there is a reasonable correlation between the binding free energy and the antibacterial activity.

Antitubercular activity of 1,2,3-triazolyl fatty acid derivatives

A collection of 1,2,3-triazoles unsaturated fatty acid mimics were efficiently synthesized by click chemistry. The 1,4-disubstituted analogs prepared covered different alkyl chain lengths and triazole positions. The compounds were subsequently tested against Mycobacterium tuberculosis, being most of them active with some of the analogs displaying activity at micromolar concentration. The most potent member of the series has the triazole moiety on the C-2 position with a carbon chain of eight or ten carbon atoms. The 1,5-isomers of the most active analog were significantly less active than the original isomer. The activity of the selected hit was assayed on several clinical MTB multi-drug resistant strains providing the same MIC.

Synthesis and evaluation of novel pleuromutilin derivatives with a substituted pyrimidine moiety

A series of novel pleuromutilin derivatives possessing 6-hydroxy pyrimidine moieties were synthesized via acylation reactions under mild conditions. The in vitro antibacterial activities of the synthesized derivatives against methicillin-resistant Staphylococcus aureus (MRSA), methicillin-resistant Staphylococcus epidermidis (MRSE), Bacillus subtilis (B. subtilis), and Escherichia coli (E. coli) were tested by the agar dilution method. The majority of the screened compounds displayed potent activities. Compounds 3 and 6a were found to be the most active antibacterial agents against MRSA and MRSE. Moreover, in the vivo experiment, compound 6a showed comparable antibacterial activity to that of tiamulin, with ED50 of 5.47 mg/kg body weight against MRSA.

In vivo efficacy and toxicity studies of a novel antibacterial agent: 14-o-[(2-amino-1,3,4-thiadiazol-5-yl)thioacetyl] mutilin

A new pleuromutilin derivative with excellent antibacterial activity, 14-O-[(2-amino-1,3,4-thiadiazol-5-yl) thioacetyl] mutilin (ATTM), may serve as a possible lead compound for the development of antibacterial drugs. However, in vivo efficacy and toxicity evaluations of this compound have not been performed. In this study, we evaluated the efficacy of ATTM by measuring the survival of mice after a lethal challenge with methicillin-resistant Staphylococcus aureus (MRSA), and the 50% effective dose (ED50) was 5.74 mg/kg by the intravenous route. In an oral single-dose toxicity study, ATTM was orally administered to mice at different doses and the 50% lethal dose (LD50) was calculated to be 2304.4 mg/kg by the Bliss method. The results of the subchronic oral toxicity study in rats showed no mortality, exterior signs of toxicity, or differences in the total weight gain or relative organ weights between the treated groups and control group after administration. The hematological and serum biochemical data showed no differences between the treated and control groups, except for the levels of alkaline phosphatase (ALP), creatinine (CR) and blood glucose (GLU), which were significantly different in the high-dose group. The differences in the histopathological findings between the treated groups and the control group were not considered to be treatment-related. Our results indicated that the no observed adverse effect level (NOAEL) for ATTM was 5 mg/kg in this study.

Synthesis and Antibacterial Activity of Novel Pleuromutilin Derivatives

In this study we describe the design, synthesis, and antibacterial activity of novel pleuromutilin analogs. A series of new compounds containing piperazine and alkylamino or arylamino groups was synthesized. The new compounds were characterized via (1)H-NMR, (13)C-NMR, Fourier transform (FT)-IR and MS, and were further evaluated for their in vitro activity against seven Gram-positive, and one Gram-negative, pathogens. Antibacterial data revealed that all compounds exhibited moderate to good antibacterial activities against sensitive Gram-positive pathogens. Specifically, 9d displayed the best activity: its activity to Staphylococcus aureus (ATCC25923) is 0.125 µg/mL, which is equal to the control compound tiamulin. The antibacterial activities of 9d to Streptococcus suis (minimum inhibitory concentration (MIC) of 2 µg/mL), Streptococcus agalactiae (MIC of 0.5 µg/mL), and Streptococcus dysgalactiae (MIC of 0.5 µg/mL) were also excellent compared with the control drug erythromycin (MIC of >128 µg/mL). The binding modes of these compounds with active sites were calculated using the programs of Molecular Operating Environment (MOE) and Pymol.