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

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.

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 in vitro evaluation of antibacterial and antibiofilm activities of novel triphenylphosphonium-functionalized substituted pyrimidines

The increase in the prevalence of antibiotic-resistant pathogens leads to a decrease in the number of antimicrobial agents for the treatment of infections and prompts researchers to search for new effective antimicrobial drugs. This study reports the synthesis of novel triphenylphosphonium-functionalized substituted pyrimidines and in vitro evaluation of their antibacterial and antibiofilm activity. Most of the synthesized derivatives showed high antibacterial activity (MIC = 0.39-1.56 μg/mL) against the methicillin-resistant strain of S. aureus 222. Compounds 2a and 11 exhibited a high level of antibiofilm activity against S. aureus 222 and E. coli 311. The triphenylphosphonium-containing pyrimidines 11 and 2a reduced S. aureus 222 biofilm formation by 99.1% and 95.8%, respectively. In addition, compound 2a was the most active against E. coli 311 biofilm formation (the biomass decreased by 98.4%).

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.

Heterocyclic pyrimidine derivatives as promising antibacterial agents

Antibiotic resistance is a growing public health concern. The quest to understand the underlying mechanisms of drug resistance needs to be accompanied by an expanded arsenal of drugs. This calls for the development of new compounds with anti-bacterial properties. The ease of functionalization of the pyrimidine core, to produce structurally distinct compound libraries, has made pyrimidine a privileged structure for identifying anti-bacterial hits. The activity of pyrimidine derivatives can be attributed to the various subunits linked with the main core, especially at C-2 or C-4 or C-6. Particularly, presence of NH2 attached to C-2 of the pyrimidine nucleus has been shown to enhance the anti-bacterial activity against pathogenic Gram-positive and Gram-negative bacteria. The diversity of synthetic routes used for the synthesis of such compounds, the reported biological activities, and a growing need to develop novel anti-bacterial agents warrant a review that presents recent reports on the synthesis and anti-bacterial activities of pyrimidine-containing compounds.

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 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.

Tandem construction of biological relevant aliphatic 5-membered N-heterocycles

Nature often uses cascade reactions in a highly stereocontrolled manner for assembly structurally diverse nitrogen-containing heterocyclic scaffolds, i.e. secondary metabolites, important for medicinal chemistry and pharmacy. Five-membered nitrogen-containing heterocycles as standalone rings, as well as spiro and polycyclic systems are pharmacophores of drugs approved in various therapies, i.a. antibacterial or antiviral, antifungal, anticancer, antidiabetic, as they target many key enzymes. Furthermore, a large number of pyrrolidine derivatives are currently considered as drug candidates. Cascade transformations, also known as domino or tandem reactions, offer straightforward methods to build N-heterocyclic libraries of the great structural variety desired for drawing SAR conclusions. The tandem transformations are often atom economic and time-saving because they are performed as the one-pot, so no need for purification after each 'virtual' step and the limited necessity of protective groups are characteristic for these processes. Thus, the same results as in classical multistep synthesis can be achieved at markedly lower costs and shorter time, which is in line with modern green chemistry rules. Great advantage of cascade reactions is often reflected in their high regio- and stereoselectivities, enabling the preparing of the heterocyclic compound better fitted to the expected target in cells. This review reveals the biological relevance of N-heterocyclic scaffolds based on saturated 5-membered rings since we showed a number of examples of approved drugs together with the recent biologically attractive leading structures of drug candidates. Next, novel cascade synthetic procedures, taking into account the structure of the reactants and reaction mechanisms, enabling to obtain biological-relevant heterocyclic frameworks with good yields and relatively high stereoselectivity, were reviewed and compared. The review covers the advances of designing biological active N-heterocycles mainly from 2018 to 2021, whereas the synthetic part is focused on the last 7 years.

Crystal structure of 14-O-[(4-(4-hydroxypiperidine-1-yl)-6-methylpyrimidine-2-yl)thioacetyl]-mutilin monohydrate, C32H49N3O6S

C32H49N3O6S, orthorhombic, P212121 (no. 19), a = 9.2618(2) Å, b = 12.4066(2) Å, c = 27.2256(5) Å, V = 3128.42(12) Å3, Z = 4, R gt (F) = 0.0517, wR ref (F 2) = 0.1355, T = 173.20(2) K.

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.

Cprp-An Unusual, Repetitive Protein Which Impacts Pleuromutilin Biosynthesis in the Basidiomycete Clitopilus passeckerianus

Interrogation of an EST database for Clitopilus passeckerianus identified a putative homolog to the unusual stress response gene from yeast; ddr48, as being upregulated under pleuromutilin production conditions. Silencing of this gene, named cprp, produced a population of transformants which demonstrated significantly reduced pleuromutilin production. Attempts to complement a Saccharomyces cerevisiae ddr48 mutant strain (strain Y16748) with cprp were hampered by the lack of a clearly identifiable mutant phenotype, but interestingly, overexpression of either ddr48 or cprp in S. cerevisiae Y16748 led to a conspicuous and comparable reduction in growth rate. This observation, combined with the known role of DDR48 proteins from a range of fungal species in nutrient starvation and stress responses, raises the possibility that this family of proteins plays a role in triggering oligotrophic growth. Localization studies via the production of a Cprp:GFP fusion protein in C. passeckerianus showed clear localization adjacent to the hyphal septa and, to a lesser extent, cell walls, which is consistent with the identification of DDR48 as a cell wall-associated protein in various yeast species. To our knowledge this is the first study demonstrating that a DDR48-like protein plays a role in the regulation of a secondary metabolite, and represents the first DDR48-like protein from a basidiomycete. Potential homologs can be identified across much of the Dikarya, suggesting that this unusual protein may play a central role in regulating both primary and secondary metabolism in fungi.