Pleuromutilin derivatives having a purine ring. Part 1: new compounds with promising antibacterial activity against resistant Gram-positive pathogens

Navigating Antibacterial Frontiers: A Panoramic Exploration of Antibacterial Landscapes, Resistance Mechanisms, and Emerging Therapeutic Strategies

The development of effective antibacterial solutions has become paramount in maintaining global health in this era of increasing bacterial threats and rampant antibiotic resistance. Traditional antibiotics have played a significant role in combating bacterial infections throughout history. However, the emergence of novel resistant strains necessitates constant innovation in antibacterial research. We have analyzed the data on antibacterials from the CAS Content Collection, the largest human-curated collection of published scientific knowledge, which has proven valuable for quantitative analysis of global scientific knowledge. Our analysis focuses on mining the CAS Content Collection data for recent publications (since 2012). This article aims to explore the intricate landscape of antibacterial research while reviewing the advancement from traditional antibiotics to novel and emerging antibacterial strategies. By delving into the resistance mechanisms, this paper highlights the need to find alternate strategies to address the growing concern.

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.

Pharmacokinetic/pharmacodynamic integration of amphenmulin: a novel pleuromutilin derivative against Mycoplasma gallisepticum

Amphenmulin is a novel pleuromutilin derivative with great anti-mycoplasma potential. The present study evaluated the action characteristics of amphenmulin against Mycoplasma gallisepticum using pharmacokinetic/pharmacodynamic (PK/PD) modeling approaches. Following intravenous administration, amphenmulin exhibited an elimination half-life of 2.13 h and an apparent volume of distribution of 3.64 L/kg in healthy broiler chickens, demonstrating PK profiles of extensive distribution and rapid elimination. The minimum inhibitory concentration (MIC) of amphenmulin against M. gallisepticum was determined to be 0.0039 µg/mL using the broth microdilution method, and the analysis of the static time-kill curves through the sigmoid Emax model showed a highly correlated relationship (R ≥ 0.9649) between the kill rate and drug concentrations (1-64 MIC). A one-compartment open model with first-order elimination was implemented to simulate the in vivo anti-mycoplasma effect of amphenmulin, and it was found that bactericidal levels were reached with continuous administration for 3 days at doses exceeding 0.8 µg/mL. Furthermore, the area under the concentration-time curve divided by MIC (AUC/MIC) correlated well with the anti-mycoplasma effect of amphenmulin within 24 h after each administration, with a target value of 904.05 h for predicting a reduction of M. gallisepticum by 1 Log10CFU/mL. These investigations broadened the antibacterial spectrum of amphenmulin and revealed its characteristics of action against M. gallisepticum, providing a theoretical basis for further clinical development.IMPORTANCEMycoplasma has long been recognized as a significant pathogen causing global livestock production losses and public health concerns, and the use of antimicrobial agents is currently one of the mainstream strategies for its prevention and control. Amphenmulin is a promising candidate pleuromutilin derivative that was designed, synthesized, and screened by our laboratory in previous studies. Moreover, this study further confirms the excellent antibacterial activity of amphenmulin against Mycoplasma gallisepticum and reveals its action characteristics and model targets on M. gallisepticum by establishing an in vitro pharmacokinetic/pharmacodynamic synchronization model. These findings can further broaden the pharmacological theoretical basis of amphenmulin and serve as data support for its clinical development, which is of great significance for the discovery of new antimicrobial drugs and the control of bacterial diseases in humans and animals.

Borinic Acid Catalyzed Regioselective N-Alkylation of Azoles

A method for regioselective N-alkylation of ambident, azole-type heterocycles with alkene or epoxide electrophiles is described. In the presence of diphenylborinic acid (Ph₂BOH) and an amine cocatalyst, heterocyclic nucleophiles such as 1,2,3- and 1,2,4-triazoles, substituted tetrazoles, and purine are activated toward selective N-functionalization. The scope of electrophilic partners includes enones, 2-vinylpyridine, phenyl vinyl sulfone, a dehydroalanine derivative, and epoxides. Mechanistic studies, including in situ ¹¹B NMR spectroscopy and kinetic analysis, are discussed.

Antibacterial Activity and Pharmacokinetic Profile of a Promising Antibacterial Agent: 22-(2-Amino-phenylsulfanyl)-22-Deoxypleuromutilin

A new pleuromutilin derivative, 22-(2-amino-phenylsulfanyl)-22-deoxypleuromutilin (amphenmulin), has been synthesized and proved excellent in vitro and in vivo efficacy than that of tiamulin against methicillin-resistant Staphylococcus aureus (MRSA), suggesting this compound may lead to a promising antibacterial agent to treat MRSA infections. In this study, the effectiveness and safety of amphenmulin were further investigated. Amphenmulin showed excellent antibacterial activity against MRSA (minimal inhibitory concentration = 0.0156~8 µg/mL) and performed time-dependent growth inhibition and a concentration-dependent postantibiotic effect (PAE). Acute oral toxicity test in mice showed that amphenmulin was a practical non-toxic drug and possessed high security as a new drug with the 50% lethal dose (LD50) above 5000 mg/kg. The pharmacokinetic properties of amphenmulin were then measured. After intravenous administration, the elimination half-life (T1/2), total body clearance (Clβ), and area under curve to infinite time (AUC0→∞) were 1.92 ± 0.28 h, 0.82 ± 0.09 L/h/kg, and 12.23 ± 1.35 μg·h/mL, respectively. After intraperitoneal administration, the T1/2, Clβ/F and AUC0→∞ were 2.64 ± 0.72 h, 4.08 ± 1.14 L/h/kg, and 2.52 ± 0.81 μg·h/mL, respectively, while for the oral route were 2.91 ± 0.81 h, 6.31 ± 2.26 L/h/kg, 1.67 ± 0.66 μg·h/mL, respectively. Furthermore, we evaluated the antimicrobial activity of amphenmulin in an experimental model of MRSA wound infection. Amphenmulin enhanced wound closure and promoted the healing of wound, which inhibited MRSA bacterial counts in the wound and decreased serum levels of the pro-inflammatory cytokines TNF-α, IL-6, and MCP-1.

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.

Unraveling the Metabolic Routes of Retapamulin: Insights into Drug Development of Pleuromutilins

Retapamulin, a semisynthetic pleuromutilin derivative, is exclusively used for the topical short-term medication of impetigo and staphylococcal infections. In the present study, we report that retapamulin is adequately and rapidly metabolized in vitro via various metabolic pathways, such as hydroxylation, including mono-, di-, and trihydroxylation, and demethylation. Like tiamulin and valnemulin, the major metabolic routes of retapamulin were hydroxylation at the 2β and 8α positions of the mutilin moiety. Moreover, in vivo metabolism concurred with the results of the in vitro assays. Additionally, we observed significant interspecies differences in the metabolism of retapamulin. Until now, modifying the side chain was the mainstream method for new drug discovery of the pleuromutilins. This approach, however, could not resolve the low bioavailability and short efficacy of the drugs. Considering the rapid metabolism of the pleuromutilins mediated by cytochrome P450 enzymes, we propose that blocking the active metabolic site (C-2 and C-8 motif) or administering the drug in combination with cytochrome P450 enzyme inhibitors is a promising pathway in the development of novel pleuromutilin drugs with slow metabolism and long efficacy.

Synthesis and Antimicrobial Activity of the Hybrid Molecules between Sulfonamides and Active Antimicrobial Pleuromutilin Derivative

A series of novel hybrid molecules between sulfonamides and active antimicrobial 14-o-(3-carboxy-phenylsulfide)-mutilin were synthesized, and their in vitro antibacterial activities were evaluated by the broth microdilution. Results indicated that these compounds displayed potent antimicrobial activities in vitro against various drug-susceptible and drug-resistant Gram-positive bacteria such as Staphylococci and streptococci, including methicillin-resistant Staphylococcus aureus, and mycoplasma. In particular, sulfapyridine analog (6c) exhibited more potent inhibitory activity against Gram-positive bacteria and mycoplasma, including Staphylococcus aureus (MIC = 0.016-0.063 μg/mL), methicillin-resistant Staphylococcus aureus (MIC = 0.016 μg/mL), Streptococcus pneumoniae (MIC = 0.032-0.063 μg/mL), Mycoplasma gallisepticum (MIC = 0.004 μg/mL), with respect to other synthesized compounds and reference drugs sulfonamide (MIC = 8-128 μg/mL) and valnemulin (MIC = 0.004-0.5 μg/mL). Furthermore, comparison between MIC values of pleuromutilin-sulfonamide hybrids 6a-f with pleuromutilin parent compound 3 revealed that these modifications at 14 position side chain of the pleuromutilin with benzene sulfonamide could greatly improve the antibacterial activity especially against Gram-positives.

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.

Novel pleuromutilin derivatives as antibacterial agents: synthesis, biological evaluation and molecular docking studies

Owing to the increasingly serious problems caused by multidrug resistance in community-acquired infection pathogens, it has become an urgent need to develop new classes of antibiotics for overcoming the resistance. In this paper, we describe the design and synthesis of novel pleuromutilin derivatives containing the (2-aminothiazol-4-yl)-4-methyl group, as well as their in vitro antibacterial activities against Gram-positive clinical bacteria. Most of the tested compounds displayed strong antibacterial activities against these methicillin-susceptible and methicillin-resistant bacteria. Particularly noteworthy compound 15 and its derivative 16e, both showed potent antibacterial properties (0.0625-0.5μg/mL) that are superior to amoxicillin and tiamulin. Molecular docking studies suggested that the amino thiazole ring on the side chains of the pleuromutilin derivatives can in general be accommodated near the mutilin core in the binding pocket, and thus play an important role in the activity of the whole molecule. The findings reported herein may provide a new insight into the design of novel pleuromutilin derivatives for human clinical use.

Synthesis and structure-activity relationship studies of 4-arylthiosemicarbazides as topoisomerase IV inhibitors with Gram-positive antibacterial activity. Search for molecular basis of antibacterial activity of thiosemicarbazides

1-(indol-2-carbonyl)-4-(4-nitrophenyl)-thiosemicarbazide was synthesized and antibacterial and type IIA topoisomerases (DNA gyrase and topoisomerase IV) activity was evaluated. It was found that it shows activity against Gram-positive bacteria with MICs of 50 μg/mL and inhibitory action against topoisomerase IV with an IC(50) of 14 μM. Although modification of its structure resulted in molecules with a lower biological profile, our observations strongly implicate that thiosemicarbazide derivatives participate in at least two different mechanisms of antibacterial activity; one is connected with the inhibition of topoisomerase IV, while the nature of the other cannot be elucidated from the limited data collected thus far. The differences in bioactivity further investigated by the molecular modeling approach and docking studies suggest that inhibitory activity of 4-arylthiosemicarbazides is connected with electronic structure rather than the geometry of the molecule.

Synthesis and Antibacterial Activities of Pleuromutilin Derivatives with Thiazole-5-Carboxamide and Thioether Moiety

Seven novel pleuromutilin derivatives with thiazole-5-carboxamide and thioether moiety in the C14 side chain were designed and synthesised. The antibacterial activities of the target compounds were tested via agar-well diffusion method in vitro. The results showed that three target compounds still had antibacterial activity against Staphylococcus aureus ATCC26112 and Staphylococcus aureus SC at a low concentration of 0.05 μg mL−1.

Synthesis and Antibacterial Activities of Pleuromutilin Derivatives with Quinazolinone and Thioether Groups

Ten novel pleuromutilin derivatives with quinazolinone and thioether groups in the C14 side chain have been designed and synthesised. The antibacterial activities of the target compounds were tested via the agar-well diffusion method in vitro in the concentration of 5.0 μg mL−1 The results showed that all target compounds had displayed obvious antibacterial activity against Staphylococcus aureus ATCC26112 and Staphylococcus aureus SC.

Study on the Structure-Activity Relations of Pleuromutilin Derivatives with an Aromatic Amide and a Thioether Group in the C14 side Chain

Nine novel pleuromutilin derivatives having benzamide substituents have been synthesised permitting structure-activity relations of pleuromutilin derivatives with aromatic amide and thioether groups in the C14 side chain to be studied. The results showed that the heterocyclic carboxamide group was necessary to enhance bio-activities.

Novel pleuromutilin derivatives with excellent antibacterial activity against Staphylococcus aureus

Ten novel pleuromutilin derivatives with thioether moiety and heterocyclic carboxamide or chloroformate group in the side chain were synthesized and confirmed by (1)H NMR, IR and HRMS. The results of the antibacterial activity showed that the title compounds had excellent antibacterial activity against Staphylococcus aureus, among which the MIC of 5f reached 0.03125 microg/mL.

Pleuromutilin derivatives having a purine ring. Part 2: influence of the central spacer on the antibacterial activity against Gram-positive pathogens

Structural modification of the 4-piperidinethio moiety, as a spacer of the first pleuromutilin analogues 2A and 2B having a purine ring, led to discovery of the novel pleuromutilin derivatives 14B and 17B. These compounds with good solubility in water showed promising in vitro antibacterial activity against various Gram-positive bacteria including MRSA, PRSP, and VRE and have potent in vivo efficacy.

Pleuromutilin derivatives having a purine ring. Part 3: synthesis and antibacterial activity of novel compounds possessing a piperazine ring spacer

SAR studies on the water-soluble thioether pleuromutilin analogue 6, which has excellent in vitro and in vivo antibacterial activities, led to discovery of the novel pleuromutilin derivatives having a piperazine ring spacer. These derivatives displayed potent and well-balanced in vitro antibacterial activity against various drug-susceptible and -resistant Gram-positive bacteria. In particular, the promising pleuromutilin analogues 37 and 40 were found to exhibit strong in vivo efficacy against Staphylococcus aureus Smith.

The reaction of beta-amino-alpha,gamma-dicyanocrotononitrile with acetophenone: synthesis of pyridine, pyridazine and thiophene derivatives with antimicrobial activities

Condensation of beta-amino-alpha,gamma-dicyanocrotononitrile (1) with acetophenone gave 2-amino-4-phenylpenta-1,3-diene-1,1,3-tricarbonitrile (2). The latter product was used in a series of heterocyclization reactions with different reagents such as diazonium salts, hydrazines, hydroxylamines and elemental sulfur to give pyridazine, pyrazole, isoxazole and thiophene derivatives, respectively. On the other hand, it gave pyridine derivatives with aromatic aldehydes folowed by reaction with cyanomethylene reagents. The MIC values for the newly synthesized product were measured against E. coli, B. cereus, B. subtilis and C. albicans.