Structure–activity relationship of 2-hydroxy-2-aryl-2,3-dihydro-imidazo[1,2-a]pyrimidinium salts and 2N-substituted 4(5)-aryl-2-amino-1H-imidazoles as inhibitors of biofilm formation by Salmonella Typhimurium and Pseudomonas aeruginosa

Optimizing biofilm inhibitors: Balancing activity and toxicity in 2N-aminated 5-aryl-2-aminoimidazoles

To evaluate the effect of amination on biofilm inhibition against Escherichia coli, Pseudomonas aeruginosa and Staphylococcus aureus, representative compounds of two previously described 5-aryl-2-aminoimidazole (5-Ar-2-AI) classes were aminated by installing an amino group at the end of the substituted n-alkyl chain. Amination led to an improvement in activity for one of the two classes, the 2N-substituted 5-Ar-2-AI class. Based on these findings, a more extensive library of 2N-substituted-aminated 5-Ar-2-AIs was synthesized having different n-alkyl and halogen substitutions on the 2N-position and the 4(5)-phenyl ring, respectively. Compounds were evaluated for their biofilm inhibitory activity against E. coli, P. aeruginosa, S. aureus, Staphylococcus epidermidis and MRSA. Additionally, their toxicity was tested on eight continuous cell lines, peripheral blood mononuclear cells and Caenorhabditis elegans, along with their genotoxicity on Capan-1. Halogenation and elongation of the n-alkyl substituent showed a positive effect on biofilm inhibitory activity, but also increased toxicity. Compromising between activity and toxicity, a non-halogenated 2N-substituted-aminated 5-Ar-2-AI compound with an intermediate n-heptyl substitution demonstrated promising broad-spectrum biofilm inhibition, making it a suitable candidate for further research in anti-infectious medical applications.

Effect of chemical modifications of tannins on their antimicrobial and antibiofilm effect against Gram-negative and Gram-positive bacteria

Background

Tannins have demonstrated antibacterial and antibiofilm activity, but there are still unknown aspects on how the chemical properties of tannins affect their biological properties. We are interested in understanding how to modulate the antibiofilm activity of tannins and in delineating the relationship between chemical determinants and antibiofilm activity.

Materials and methods

The effect of five different naturally acquired tannins and their chemical derivatives on biofilm formation and planktonic growth of Salmonella Typhimurium, Pseudomonas aeruginosa, Escherichia coli and Staphylococcus aureus was determined in the Calgary biofilm device.

Results

Most of the unmodified tannins exhibited specific antibiofilm activity against the assayed bacteria. The chemical modifications were found to alter the antibiofilm activity level and spectrum of the tannins. A positive charge introduced by derivatization with higher amounts of ammonium groups shifted the anti-biofilm spectrum toward Gram-negative bacteria, and derivatization with lower amounts of ammonium groups and acidifying derivatization shifted the spectrum toward Gram-positive bacteria. Furthermore, the quantity of phenolic OH-groups per molecule was found to have a weak impact on the anti-biofilm activity of the tannins.

Conclusion

We were able to modulate the antibiofilm activity of several tannins by specific chemical modifications, providing a first approach for fine tuning of their activity and antibacterial spectrum.

Drug repurposing: phosphate prodrugs of anticancer and antiviral FDA-approved nucleosides as novel antimicrobials

OBJECTIVES

Following a drug repurposing approach, we aimed to investigate and compare the antibacterial and antibiofilm activities of different classes of phosphate prodrugs (HepDirect, cycloSal, SATE and mix SATE) of antiviral and anticancer FDA-approved nucleoside drugs [zidovudine (AZT), floxouridine (FUDR) and gemcitabine (GEM)] against a variety of pathogenic Gram-positive and -negative bacteria.

METHODS

Ten prodrugs were synthesized and screened for antibacterial activity against seven Gram-negative and two Gram-positive isolates fully susceptible to traditional antibiotics, alongside six Gram-negative and five Gram-positive isolates with resistance mechanisms. Their ability to prevent and eradicate biofilms of different bacterial pathogens in relation to planktonic growth inhibition was also evaluated, together with their effect on proliferation, viability and apoptosis of different eukaryotic cells.

RESULTS

The prodrugs showed decreased antibacterial activity compared with the parent nucleosides. cycloSal-GEM-monophosphate (MP) prodrugs 20a and 20b were the most active agents against Gram-positive bacteria (Enterococcus faecalis and Staphylococcus aureus) and retained their activity against antibiotic-resistant isolates. cycloSal-FUDR-MP 21a partially retained good activity against the Gram-positive bacteria E. faecalis, Enterococcus faecium and S. aureus. Most of the prodrugs tested displayed very potent preventive antibiofilm specific activity, but not curative. In terms of cytotoxicity, AZT prodrugs did not affect apoptosis or cell viability at the highest concentration tested, and only weak effects on apoptosis and/or cell viability were observed for GEM and FUDR prodrugs.

CONCLUSIONS

Among the different prodrug approaches, the cycloSal prodrugs appeared the most effective. In particular, cycloSal (17a) and mix SATE (26) AZT prodrugs combine the lowest cytotoxicity with high and broad antibacterial and antibiofilm activity against Gram-negative bacteria.

2-Aminoimidazoles as potent inhibitors of contaminating brewery biofilms

Cleaning and disinfection protocols are not always able to remove biofilm microbes present in breweries, indicating that novel anti-biofilm strategies are needed. The preventive activities of three in-house synthesized members of the 2-aminoimidazole class of anti-biofilm molecules were studied against 17 natural brewery biofilms and benchmarked against 18 known inhibitors. Two 2-aminoimidazoles belonged to the top six inhibitors, which were retested against 12 defined brewery biofilm models. For the three best inhibitors, tannic acid (n° 1), 2-aminoimidazole imi-AAC-5 (n° 2), and baicalein (n° 3), the effect on the microbial metabolic activity was evaluated. Here, the top three inhibitors showed similar effectiveness, with baicalein possessing a slightly higher efficacy. Even though the 2-aminoimidazole was the second-best inhibitor, it showed a lower biocidal activity than tannic acid, making it less prone to resistance evolution. Overall, this study supports the potential of 2-aminoimidazoles as a preventive anti-biofilm strategy.

Inhibiting bacterial cooperation is an evolutionarily robust anti-biofilm strategy

Bacteria commonly form dense biofilms encased in extracellular polymeric substances (EPS). Biofilms are often extremely tolerant to antimicrobials but their reliance on shared EPS may also be a weakness as social evolution theory predicts that inhibiting shared traits can select against resistance. Here we show that EPS of Salmonella biofilms is a cooperative trait whose benefit is shared among cells, and that EPS inhibition reduces both cell attachment and antimicrobial tolerance. We then compare an EPS inhibitor to conventional antimicrobials in an evolutionary experiment. While resistance against conventional antimicrobials rapidly evolves, we see no evolution of resistance to EPS inhibition. We further show that a resistant strain is outcompeted by a susceptible strain under EPS inhibitor treatment, explaining why resistance does not evolve. Our work suggests that targeting cooperative traits is a viable solution to the problem of antimicrobial resistance.

Bacterial biofilms rely on shared extracellular polymeric substances (EPS) and are often highly tolerant to antibiotics. Here, the authors show in in vitro experiments that Salmonella does not evolve resistance to EPS inhibition because such strains are outcompeted by a susceptible strain under inhibitor treatment.

Novel (2-amino-4-arylimidazolyl)propanoic acids and pyrrolo[1,2-c]imidazoles via the domino reactions of 2-amino-4-arylimidazoles with carbonyl and methylene active compounds

The unexpectedly uncatalyzed reaction between 2-amino-4-arylimidazoles, aromatic aldehydes and Meldrum’s acid has selectively led to the corresponding Knoevenagel–Michael adducts containing a free amino group in the imidazole fragment. The adducts derived from Meldrum’s acid have been smoothly converted into 1,7-diaryl-3-amino-6,7-dihydro-5H-pyrrolo[1,2-c]imidazol-5-ones and 3-(2-amino-4-aryl-1H-imidazol-5-yl)-3-arylpropanoic acids. The interaction of 2-amino-4-arylimidazoles with aromatic aldehydes or isatins and acyclic methylene active compounds has led to the formation of pyrrolo[1,2-c]imidazole-6-carbonitriles, pyrrolo[1,2-с]imidazole-6-carboxylates and spiro[indoline-3,7'-pyrrolo[1,2-c]imidazoles], which can be considered as the analogues of both 3,3’-spirooxindole and 2-aminoimidazole marine sponge alkaloids.

An antibiofilm coating of 5-aryl-2-aminoimidazole covalently attached to a titanium surface

Biofilms, especially those formed by Staphylococcus aureus, play a key role in the development of orthopedic implant infections. Eradication of these infections is challenging due to the elevated tolerance of biofilm cells against antimicrobial agents. In this study, we developed an antibiofilm coating consisting of 5-(4-bromophenyl)-N-cyclopentyl-1-octyl-1H-imidazol-2-amine, designated as LC0024, covalently bound to a titanium implant surface (LC0024-Ti). We showed in vitro that the LC0024-Ti surface reduces biofilm formation of S. aureus in a specific manner without reducing the planktonic cells above the biofilm, as evaluated by plate counting and fluorescence microscopy. The advantage of compounds that only inhibit biofilm formation without affecting the viability of the planktonic cells, is that reduced development of bacterial resistance is expected. To determine the antibiofilm activity of LC0024-Ti surfaces in vivo, a biomaterial-associated murine infection model was used. The results indicated a significant reduction in S. aureus biofilm formation (up to 96%) on the LC0024-Ti substrates compared to pristine titanium controls. Additionally, we found that the LC0024-Ti substrates did not affect the attachment and proliferation of human cells involved in osseointegration and bone repair. In summary, our results emphasize the clinical potential of covalent coatings of LC0024 on titanium implant surfaces to reduce the risk of orthopedic implant infections. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 1908-1919, 2019.

2-Aminobenzimidazoles as antibiofilm agents against Salmonella enterica serovar Typhimurium

Serovars within the species Salmonella enterica are some of the most common food and water-borne pathogens worldwide. Some S. enterica serovars have shown a remarkable ability to persist both inside and outside the human body. Salmonella enterica serovar Typhi can cause chronic, asymptomatic infection of the human gallbladder. This organism's ability to survive inside the gallbladder centers around its ability to form biofilms on gallstone surfaces. Currently, chronic carriage of S. Typhi is treated by invasive methods, which are not well suited to areas where Salmonella carriage is prevalent. Herein, we report 2-aminobenzimidazoles that inhibit S. enterica serovar Typhimurium (a surrogate for S. Typhi) biofilm formation in low micromolar concentrations. Modifications to the head, tail, and linker regions of the original hit compound elucidated new, more effective analogues that inhibit S. Typhimurium biofilm formation while being non-toxic to planktonic bacterial growth.

Enhancing the anti-biofilm activity of 5-aryl-2-aminoimidazoles through nature inspired dimerisation

The increased tolerance of biofilms against disinfectants and antibiotics has stimulated research into new methods of biofilm prevention and eradication. In our previous work, we have identified the 5-aryl-2-aminoimidazole core as a scaffold that demonstrates preventive activity against biofilm formation of a broad range of bacterial and fungal species. Inspired by the dimeric nature of natural 2-aminoimidazoles of the oroidin family, we investigated the potential of dimers of our decorated 5-aryl-2-aminoimidazoles as biofilm inhibitors. A synthetic approach towards 2-aminoimidazole dimers linked by an alkyl chain was developed and a total of 48 dimers were synthesized. The linkers were introduced at two different positions, the N1-position or the N2-position, and the linker length and the substitution of the 5-phenyl ring (H, F, Cl, Br) were varied. Although, no clear correlation between linker length and biofilm inhibition was observed, a strong increase in anti-biofilm activity for almost all N1,N1'-linked dimers was obtained, compared to the respective monomers against Salmonella Typhimurium, Escherichia coli and Staphylococcus aureus. The N2,N2'-linked dimers, having a H- or F-substitution, were also found to show a strong increase in anti-biofilm activity compared to the respective monomers against these three bacterial species and against Pseudomonas aeruginosa. In addition, the obtained growth measurements suggest a broad concentration range with specific biofilm inhibition and no effect on the planktonic growth against Salmonella Typhimurium and Pseudomonas aeruginosa.

Smart Metal-Organic Framework Coatings: Triggered Antibiofilm Compound Release

Metal-organic frameworks (MOFs) have a large potential for delivery of active molecules. Here, a MOF coating is investigated as a smart host matrix for triggered release of antibiofilm compounds. In addition to a coating consisting of the regular Fe-terephthalate MIL-88B(Fe), a new hydrophobic MIL-88B(Fe) coating is synthesized in hydrothermal conditions using palmitic acid as a lattice terminating group. These porous materials are used as a host matrix for the antibiofilm compound 5-(4-chlorophenyl)-N-(2-isobutyl)-2-aminoimidazole, which has a specific biofilm-inhibiting effect at concentrations at which no activity against planktonic cells is detected. The stability of MIL-88B(Fe) in distilled water and tryptic soy broth medium is investigated, together with the ability of iron(III) chelators to serve as a trigger for controlled decomposition of MIL-88B(Fe) by metal complexation. Organic iron chelators are used to mimic the iron chelating function of siderophores, which are specific molecules excreted by biofilm-forming bacteria. Trisodium citrate is able to chelate metal ions from the junctions of the framework. By sequestration of these metal ions, the host matrix is partially degraded, resulting in an antibiofilm compound release. Finally, the antibiofilm properties against Salmonella Typhimurium are validated by monitoring biofilm growth on MOF layers either loaded or not with aminoimidazole. A strong proof-of-concept is shown for efficient inhibition of biofilm growth through triggered antibiofilm compound release.

Antibacterial and anti-biofilm efficacy of fluoropolymer coating by a 2,3,5,6-tetrafluoro-p-phenylenedimethanol structure

Fluorinated polymers generally function as antibacterial agents, but their anti-biofilm effect remains unresolved. This study investigates the efficacy of fluoropolymers containing 2,3,5,6-tetrafluoro-p-phenylenedimethanol (TFPDM) in preventing biofilm formation by Bacillus subtilis and Escherichia coli (Gram-positive and Gram-negative bacterial species). To this end, TFPDM-based acrylate and epoxy polymers (AF and EF, respectively) and their structural analogues without TFPDM (A and E, respectively) were synthesized. All polymers were coated onto polyethylene terephthalate (PET) sheets. Relative to pristine PET, sheets coated with AF reduced the initial bacterial adhesion (72h) and biofilm formation (30days) of B. subtilis by 27.6% and 68.7% and of E. coli by 89.2% and 93.8%, respectively. The comparable antibacterial and anti-biofilm efficacies were obtained by sheets with EF. The biofilm detachment was substantially facilitated from the AF, compared with the structural analogue without TFPDM (A). In this comprehensive study, the bacterial adhesion and subsequent biofilm formation were prevented by TFPDM-containing polymers effectively.

Modulation of the Substitution Pattern of 5-Aryl-2-Aminoimidazoles Allows Fine-Tuning of Their Antibiofilm Activity Spectrum and Toxicity

We previously synthesized several series of compounds, based on the 5-aryl-2-aminoimidazole scaffold, that showed activity preventing the formation of Salmonella enterica serovar Typhimurium and Pseudomonas aeruginosa biofilms. Here, we further studied the activity spectrum of a number of the most active N1- and 2N-substituted 5-aryl-2-aminoimidazoles against a broad panel of biofilms formed by monospecies and mixed species of bacteria and fungi. An N1-substituted compound showed very strong activity against the biofilms formed by Gram-negative and Gram-positive bacteria and the fungus Candida albicans but was previously shown to be toxic against various eukaryotic cell lines. In contrast, 2N-substituted compounds were nontoxic and active against biofilms formed by Gram-negative bacteria and C. albicans but had reduced activity against biofilms formed by Gram-positive bacteria. In an attempt to develop nontoxic compounds with potent activity against biofilms formed by Gram-positive bacteria for application in antibiofilm coatings for medical implants, we synthesized novel compounds with substituents at both the N1 and 2N positions and tested these compounds for antibiofilm activity and toxicity. Interestingly, most of these N1-,2N-disubstituted 5-aryl-2-aminoimidazoles showed very strong activity against biofilms formed by Gram-positive bacteria and C. albicans in various setups with biofilms formed by monospecies and mixed species but lost activity against biofilms formed by Gram-negative bacteria. In light of application of these compounds as anti-infective coatings on orthopedic implants, toxicity against two bone cell lines and the functionality of these cells were tested. The N1-,2N-disubstituted 5-aryl-2-aminoimidazoles in general did not affect the viability of bone cells and even induced calcium deposition. This indicates that modulating the substitution pattern on positions N1 and 2N of the 5-aryl-2-aminoimidazole scaffold allows fine-tuning of both the antibiofilm activity spectrum and toxicity.

An efficient one-pot synthesis of thiochromeno[3,4-d]pyrimidines derivatives: Inducing ROS dependent antibacterial and anti-biofilm activities

An efficient synthesis of thiochromeno[3,4-d]pyrimidine derivatives has been achieved successfully via a one-pot three-component reaction of thiochrome-4-one, aromatic aldehyde and thiourea in the presence of 1-butyl-3-methyl imidazolium hydrogen sulphate [Bmim]HSO4. This new protocol has the advantages of environmental friendliness, high yields, short reaction times, and convenient operation. Furthermore, among all the tested derivatives, compounds 4b and 4c exhibited promising antibacterial, minimum bactericidal concentration and anti-biofilm activities against Staphylococcus aureus MTCC 96, Staphylococcus aureus MLS16 MTCC 2940 and Bacillus subtilis MTCC 121. The compound 4c also showed promising intracellular ROS accumulation in Staphylococcus aureus MLS16 MTCC 2940 comparable to that of ciprofloxacin resulting in apoptotic cell death of the bacterium.

What's on the Outside Matters: The Role of the Extracellular Polymeric Substance of Gram-negative Biofilms in Evading Host Immunity and as a Target for Therapeutic Intervention

Biofilms are organized multicellular communities encased in an extracellular polymeric substance (EPS). Biofilm-resident bacteria resist immunity and antimicrobials. The EPS provides structural stability and presents a barrier; however, a complete understanding of how EPS structure relates to biological function is lacking. This review focuses on the EPS of three Gram-negative pathogens: Pseudomonas aeruginosa, nontypeable Haemophilus influenzae, and Salmonella enterica serovar Typhi/Typhimurium. Although EPS proteins and polysaccharides are diverse, common constituents include extracellular DNA, DNABII (DNA binding and bending) proteins, pili, flagella, and outer membrane vesicles. The EPS biochemistry promotes recalcitrance and informs the design of therapies to reduce or eliminate biofilm burden.

Evaluation of the toxicity of 5-aryl-2-aminoimidazole-based biofilm inhibitors against eukaryotic cell lines, bone cells and the nematode Caenorhabditis elegans

Previously, we have synthesized several series of compounds based on the 5-aryl-2-aminoimidazole scaffold, which showed a preventive activity against microbial biofilms. We here studied the cytotoxicity of the most active compounds of each series. First, the cytostatic activity was investigated against a number of tumor cell lines (L1210, CEM and HeLa). A subset of monosubstituted 5-aryl-2-aminoimidazoles showed a moderate safety window, with therapeutic indices (TIs) ranging between 3 and 20. Whereas introduction of a (cyclo-)alkyl chain at the N1-position strongly reduced the TI, introduction of a (cyclo-)alkyl chain or a triazole moiety at the 2N-position increased the TI up to 370. Since a promising application of preventive anti-biofilm agents is their use in anti-biofilm coatings for orthopedic implants, their effects on cell viability and functional behavior of human osteoblasts and bone marrow derived mesenchymal stem cells were tested. The 2N-substituted 5-aryl-2-aminoimidazoles consistently showed the lowest toxicity and allowed survival of the bone cells for up to 4 weeks. Moreover they did not negatively affect the osteogenic differentiation potential of the bone cells. Finally, we examined the effect of the compounds on the survival of Caenorhabditis elegans, which confirmed the higher safety window of 2N-substituted 5-aryl-2-aminoimidazoles.

Derivatives of the mouse cathelicidin-related antimicrobial peptide (CRAMP) inhibit fungal and bacterial biofilm formation

We identified a 26-amino-acid truncated form of the 34-amino-acid cathelicidin-related antimicrobial peptide (CRAMP) in the islets of Langerhans of the murine pancreas. This peptide, P318, shares 67% identity with the LL-37 human antimicrobial peptide. As LL-37 displays antimicrobial and antibiofilm activity, we tested antifungal and antibiofilm activity of P318 against the fungal pathogen Candida albicans. P318 shows biofilm-specific activity as it inhibits C. albicans biofilm formation at 0.15 μM without affecting planktonic survival at that concentration. Next, we tested the C. albicans biofilm-inhibitory activity of a series of truncated and alanine-substituted derivatives of P318. Based on the biofilm-inhibitory activity of these derivatives and the length of the peptides, we decided to synthesize the shortened alanine-substituted peptide at position 10 (AS10; KLKKIAQKIKNFFQKLVP). AS10 inhibited C. albicans biofilm formation at 0.22 μM and acted synergistically with amphotericin B and caspofungin against mature biofilms. AS10 also inhibited biofilm formation of different bacteria as well as of fungi and bacteria in a mixed biofilm. In addition, AS10 does not affect the viability or functionality of different cell types involved in osseointegration of an implant, pointing to the potential of AS10 for further development as a lead peptide to coat implants.

A GFP promoter fusion library for the study of Salmonella biofilm formation and the mode of action of biofilm inhibitors

Salmonella, an important foodborne pathogen, forms biofilms in many different environments. The composition of these biofilms differs depending on the growth conditions, and their development is highly coordinated in time. To develop efficient treatments, it is therefore essential that biofilm formation and its inhibition be understood in different environments and in a time-dependent manner. Many currently used techniques, such as transcriptomics or proteomics, are still expensive and thus limited in their application. Therefore, a GFP-promoter fusion library with 79 important Salmonella biofilm genes was developed (covering among other things matrix production, fimbriae and flagella synthesis, and c-di-GMP regulation). This library is a fast, inexpensive, and easy-to-use tool, and can therefore be conducted in different experimental setups in a time-dependent manner. In this paper, four possible applications are highlighted to illustrate and validate the use of this reporter fusion library.

Synthesis, central nervous system activity, and structure-activity relationship of 1-aryl-6-benzyl-7-hydroxy-2,3-dihydroimidazo[1,2-a]pyrimidine-5(1H)-ones

A series of 24 1-aryl-6-benzyl-7-hydroxy-2,3-dihydroimidazo[1,2-a]pyrimidine-5(1H)-ones was designed as antinociceptive compounds acting through opioid receptors with additional serotoninergic activity. The compounds, similarly as previously published series, lack the protonable nitrogen atom which is a part of classical opioid receptor pharmacophore and is necessary to interact with the conserved Asp(3.32) in the opioid receptor binding pocket. The compounds were obtained in one-step cyclocondensation of 1-aryl-4,5-dihydro-1H-imidazol-2-amines diethyl 2-benzylmalonate or diethyl 2-(2-chlorobenzyl)malonate under basic conditions. Almost all the tested compounds exerted strong antinociceptive activity, but surprisingly, it was not reversed by naloxone; thus, it is not mediated through opioid receptors. It makes it possible to conclude that addition of one more aromatic moiety to the non-classical opioid receptor pharmacophore results in the compounds which are not opioid receptor ligands. The lack of activity of one of the tested compounds may be attributed to low blood–brain barrier permeation or unfavorable distribution of electrostatic potential and HOMO and LUMO orbitals.

Antimicrobial activity of the marine alkaloids, clathrodin and oroidin, and their synthetic analogues

Marine organisms produce secondary metabolites that may be valuable for the development of novel drug leads as such and can also provide structural scaffolds for the design and synthesis of novel bioactive compounds. The marine alkaloids, clathrodin and oroidin, which were originally isolated from sponges of the genus, Agelas, were prepared and evaluated for their antimicrobial activity against three bacterial strains (Enterococcus faecalis, Staphylococcusaureus and Escherichiacoli) and one fungal strain (Candida albicans), and oroidin was found to possess promising Gram-positive antibacterial activity. Using oroidin as a scaffold, 34 new analogues were designed, prepared and screened for their antimicrobial properties. Of these compounds, 12 exhibited >80% inhibition of the growth of at least one microorganism at a concentration of 50 µM. The most active derivative was found to be 4-phenyl-2-aminoimidazole 6h, which exhibited MIC₉₀ (minimum inhibitory concentration) values of 12.5 µM against the Gram-positive bacteria and 50 µM against E. coli. The selectivity index between S. aureus and mammalian cells, which is important to consider in the evaluation of a compound’s potential as an antimicrobial lead, was found to be 2.9 for compound 6h.

Regioselective synthesis of 3-benzyl substituted pyrimidino chromen-2-ones and evaluation of anti-microbial and anti-biofilm activities

Regioselective synthesis of a number of highly functionalized 3-benzylpyrimidino chromen-2-ones (4) were accomplished in a one pot three component reaction in acetic acid and determined their anti-microbial and anti-biofilm activities. Compounds 4o and 4p showed an excellent anti-microbial activity against Micrococcus luteus MTCC 2470 at a par with standard control (Ciprofloxacin) and exhibited best activity against Staphylococcus aureus MTCC 96 and Bacillus subtilis MTCC 121. Further, compounds 4h, 4i, 4m, 4n and 4q showed promising activity against Micrococcus luteus MTCC 2470, Staphylococcus aureus MTCC 96 and Bacillus subtilis MTCC 121. Whereas, compounds 4m showed very promising biofilm inhibition activity against Staphylococcus aureus MLS 16 MTCC 2940 and 4o, 4p showed very potent activity against Staphylococcus aureus MTCC 96 at a par with Ciprofloxacin used as standard control.

Microwave-assisted one-pot synthesis and anti-biofilm activity of 2-amino-1H-imidazole/triazole conjugates

A microwave-assisted protocol was developed for the construction of 2-amino-1H-imidazole/triazole conjugates with anti-biofilm activity.

The pseudo-Michael reaction of 1-aryl-4,5-dihydro-1H-imidazol-2-amines with ethyl ethoxymethylenecyanoacetate

Abstract

The pseudo-Michael reaction of 1-aryl-4,5-dihydro-1H-imidazol-2-amines with ethyl 2-cyano-3-methoxyprop-2-enoate (ethyl ethoxymethylenecyanoacetate) is investigated. At −10 °C reaction takes place on the exocyclic nitrogen atom, giving exclusively ethyl esters of 2-cyano-3-[(1-phenyl-4,5-dihydro-1H-imidazol-2-yl)amino]prop-2-enoic acid. The formation of isomeric enamines which may be a theoretical product of the reaction on N3 ring nitrogen atom is not observed. The N6 enamines, heated in boiling acetic acid, yield cyclic 1-aryl-5-oxo-2,3-dihydroimidazo[1,2-a]pyrimidine-6-carbonitriles. Heating of the enamines to the temperature of 120–140 °C without a solvent makes it possible to obtain a mixture of 1-aryl-5-oxo-2,3-dihydroimidazo[1,2-a]pyrimidine-6-carbonitriles and ethyl 1-aryl-5-imino-2,3-dihydroimidazo[1,2-a]pyrimidine-6-carboxylates. The reaction of the respective hydrobromides of 1-aryl-4,5-dihydro-1H-imidazol-2-amines with ethyl ethoxymethylenecyanoacetate in the presence of triethylamine gives selectively 1-aryl-5-oxo-1,2,3,5-dihydroimidazo[1,2-a]pyrimidine-6-carbonitriles.

Graphical Abstract

A flexible approach to 1,4-di-substituted 2-aminoimidazoles that inhibit and disperse biofilms and potentiate the effects of β-lactams against multi-drug resistant bacteria

The pyrrole-imidazole alkaloids are a 2-aminoimidazoles containing family of natural products that possess anti-biofilm activity. A library of 1,4-di-substituted 2-aminoimidazole/triazoles (2-AITs) was synthesized, and its anti-biofilm activity as well as oxacillin resensitization efficacy toward methicillin resistant Staphylococcus aureus (MRSA) was investigated. These 2-AITs were found to inhibit biofilm formation by MRSA with low micromolar IC50 values. Additionally, the most active compound acted synergistically with oxacillin against MRSA lowering the minimum inhibitory concentration (MIC) 4-fold.

Small molecule control of bacterial biofilms

Bacterial biofilms are defined as a surface attached community of bacteria embedded in a matrix of extracellular polymeric substances that they have produced. When in the biofilm state, bacteria are more resistant to antibiotics and the host immune response than are their planktonic counterparts. Biofilms are increasingly recognized as being significant in human disease, accounting for 80% of bacterial infections in the body and diseases associated with bacterial biofilms include: lung infections of cystic fibrosis patients, colitis, urethritis, conjunctivitis, otitis, endocarditis and periodontitis. Additionally, biofilm infections of indwelling medical devices are of particular concern, as once the device is colonized infection is virtually impossible to eradicate. Given the prominence of biofilms in infectious diseases, there has been an increased effort toward the development of small molecules that will modulate bacterial biofilm development and maintenance. In this review, we highlight the development of small molecules that inhibit and/or disperse bacterial biofilms through non-microbicidal mechanisms. The review discuses the numerous approaches that have been applied to the discovery of lead small molecules that mediate biofilm development. These approaches are grouped into: (1) the identification and development of small molecules that target one of the bacterial signaling pathways involved in biofilm regulation, (2) chemical library screening for compounds with anti-biofilm activity, and (3) the identification of natural products that possess anti-biofilm activity, and the chemical manipulation of these natural products to obtain analogues with increased activity.