Synthesis and structure–activity relationship of dicationic diaryl ethers as novel potent anti-MRSA and anti-VRE agents

Small Molecules Incorporating Privileged Amidine Moiety as Potential Hits Combating Antibiotic-Resistant Bacteria

The continuing need for the discovery of potent antibacterial agents against antibiotic-resistant pathogens is the driving force for many researchers to design and develop such agents. Herein, we report the design, synthesis, and biological evaluation of amidine derivatives as new antibacterial agents. Compound 13d was the most active in this study against a wide range of antibiotic-resistant, and susceptible, Gram-positive, and Gram-negative bacterial strains. Time-kill assay experiments indicated that compound 13d was an effective bactericidal compound against the tested organisms at the log-phase of bacterial growth. Docking simulations were performed to assess in silico its mode of action regarding UPPS, KARI, and DNA as potential bacterial targets. Results unveiled the importance of structural features of compound 13d in its biological activity including central thiophene ring equipped with left and right pyrrolo[2,3-b]pyridine and phenyl moieties and two terminal amidines cyclized into 4,5-dihydro-1H-imidazol-2-yl functionalities. Collectively, compound 13d represents a possible hit for future development of potent antibacterial agents.

Novel tetrahydropyrimidinyl-substituted benzimidazoles and benzothiazoles: synthesis, antibacterial activity, DNA interactions and ADME profiling

A series of tetrahydropyrimidinyl-substituted benzimidazoles attached to various aliphatic or aromatic residues via phenoxymethylene were synthesised to investigate their antibacterial activities against selected Gram-positive and Gram-negative bacteria. The influence of the type of substituent at the C-3 and C-4 positions of the phenoxymethylene linker on the antibacterial activity was observed, showing that the aromatic moiety improved the antibacterial potency. Of all the evaluated compounds, benzoyl-substituted benzimidazole derivative 15a was the most active compound, particularly against the Gram-negative pathogens E. coli (MIC = 1 μg mL^-1) and M. catarrhalis (MIC = 2 μg mL^-1). Compound 15a also exhibited the most promising antibacterial activity against sensitive and resistant strains of S. pyogenes (MIC = 2 μg mL^-1). Significant stabilization effects and positive induced CD bands strongly support the binding of the most biologically active benzimidazoles inside the minor grooves of AT-rich DNA, in line with docking studies. The predicted physico-chemical and ADME properties lie within drug-like space except for low membrane permeability, which needs further optimization. Our findings encourage further development of novel structurally related 5(6)-tetrahydropyrimidinyl substituted benzimidazoles in order to optimize their antibacterial effect against common respiratory pathogens.

Recent Advances in Therapeutic Applications of Bisbenzimidazoles

Nitrogen-containing heterocycles are one of the most common structural motifs in approximately 80% of the marketed drugs. Of these, benzimidazoles analogues are known to elicit a wide spectrum of pharmaceutical activities such as anticancer, antibacterial, antiparasitic, antiviral, antifungal as well as chemosensor effect. Based on the benzimidazole core fused heterocyclic compounds, crescent-shaped bisbenzimidazoles were developed which provided an early breakthrough in the sequence-specific DNA recognition. Over the years, a number of functional variations in the bisbenzimidazole core have led to the emergence of their unique properties and established them as versatile ligands against several classes of pathogens. The present review provides an overview of diverse pharmacological activities of the bisbenzimidazole analogues in the past decade with a brief account of its development through the years.

Synthesis and structure-activity relationship of novel bisindole amidines active against MDR Gram-positive and Gram-negative bacteria

A series of novel diamidines with N-substituents on an amidine N-atom were synthesized and evaluated for their cytotoxicity and in vitro antibacterial activity against a range of Gram-positive and Gram-negative bacterial strains. Based on structure-activity relationship, N-substituents with a branched chain and a shorter carbon chain on the amidine N-atom exhibited more promising activity against Gram-negative and MDR-Gram-positive bacteria; compounds 5c and 5i were the most powerful candidate compounds. Compound 5c showed greater efficacy than levofloxacin against most drug-resistant Gram-positive bacteria and exhibited broad-spectrum antibacterial activity against Gram-negative bacteria, with MIC values in the range of 2-16 μg/mL. Slightly more potent antibacterial activity against Klebsiella pneumoniae, Acinetobacter calcoaceticus, Enterobacter cloacae, and Proteus mirabilis was observed for 5i in comparison with 5c. Compound 5i also showed remarkable antibacterial activity against NDM-1-producing Gram-negative bacteria, with MIC values in the range of 2-4 μg/mL, and was superior to the reference drugs meropenem and levofloxacin. Effective antibacterial activity of 5i was also shown in vivo in a mouse model of Staphylococcus aureus MRSA strain, with an ED₅₀values of 2.62 mg/kg.

meso-Dihydroguaiaretic acid derivatives with antibacterial and antimycobacterial activity

Thirty-three meso-dihydroguaiaretic acid (meso-DGA) derivatives bearing esters, ethers, and amino-ethers were synthesized. All derivatives were tested against twelve drug-resistant clinical isolates of Gram-positive and Gram-negative bacteria, including sensitive (H37Rv) and multidrug-resistant Mycobacterium tuberculosis strains. Among the tested compounds, four esters (7, 11, 13, and 17), one ether (23), and three amino-ethers (30, 31, and 33) exhibited moderate activity against methicillin-resistant Staphylococcus aureus, whereas 30 and 31 showed better results than levofloxacin against vancomycin-resistant Enterococcus faecium. Additionally, nineteen meso-DGA derivatives displayed moderate to potent activity against M. tuberculosis H37Rv with minimum inhibitory concentration (MIC) values ranging from 3.125 to 50µg/mL. Seven meso-DGA derivatives bearing amino-ethers (26-31 and 33) exhibited the lowest MICs against M. tuberculosis H37Rv and G122 strains, with 31 being as potent as ethambutol (MICs of 3.125 and 6.25µg/mL). The presence of positively charged group precursors possessing steric and hydrophobic features (e.g. N-ethylpiperidine moieties in meso-31) resulted essential to significantly increase the antimycobacterial properties of parent meso-DGA as supported by the R-group pharmacophoric and field-based QSAR analyses. To investigate the safety profile of the antimycobacterial compounds, cytotoxicity on Vero cells was determined. The amino-ether 31 exhibited a selectivity index value of 23, which indicate it was more toxic to M. tuberculosis than to mammalian cells. Therefore, 31 can be considered as a promising antitubercular agent for further studies.

Triaryl Benzimidazoles as a New Class of Antibacterial Agents against Resistant Pathogenic Microorganisms

A new class of nontoxic triaryl benzimidazole compounds, derived from existing classes of DNA minor groove binders, were designed, synthesized, and evaluated for their antibacterial activity against multidrug resistant (MDR) Gram-positive and Gram-negative species. Molecular modeling experiments suggest that the newly synthesized class cannot be accommodated within the minor groove of DNA due to a change in the shape of the molecules. Compounds 8, 13, and 14 were found to be the most active of the series, with MICs in the range of 0.5-4 μg/mL against the MDR Staphylococci and Enterococci species. Compound 13 showed moderate activity against the MDR Gram-negative strains, with MICs in the range of 16-32 μg/mL. Active compounds showed a bactericidal mode of action, and a mechanistic study suggested the inhibition of bacterial gyrase as the mechanism of action (MOA) of this chemical class. The MOA was further supported by the molecular modeling study.

Bis-benzimidazole hits against Naegleria fowleri discovered with new high-throughput screens

Naegleria fowleri is a pathogenic free-living amoeba (FLA) that causes an acute fatal disease known as primary amoebic meningoencephalitis (PAM). The major problem for infections with any pathogenic FLA is a lack of effective therapeutics, since PAM has a case mortality rate approaching 99%. Clearly, new drugs that are potent and have rapid onset of action are needed to enhance the treatment regimens for PAM. Diamidines have demonstrated potency against multiple pathogens, including FLA, and are known to cross the blood-brain barrier to cure other protozoan diseases of the central nervous system. Therefore, amidino derivatives serve as an important chemotype for discovery of new drugs. In this study, we validated two new in vitro assays suitable for medium- or high-throughput drug discovery and used these for N. fowleri. We next screened over 150 amidino derivatives of multiple structural classes and identified two hit series with nM potency that are suitable for further lead optimization as new drugs for this neglected disease. These include both mono- and diamidino derivatives, with the most potent compound (DB173) having a 50% inhibitory concentration (IC50) of 177 nM. Similarly, we identified 10 additional analogues with IC50s of <1 μM, with many of these having reasonable selectivity indices. The most potent hits were >500 times more potent than pentamidine. In summary, the mono- and diamidino derivatives offer potential for lead optimization to develop new drugs to treat central nervous system infections with N. fowleri.

In vitro screening of pentamidine analogs against bacterial and fungal strains

A series of linear pentamidine analogs exhibiting low cytotoxicity, active against Pneumocystis carinii, were evaluated for in vitro activities against bacterial and fungal strains. The majority of the tested bis-amidines exhibited marked activities against Gram-positive strains. In view of the fact that the highest potency was found for 1,5-bis(4-amidinophenoxy)-3-thiapentane dihydrochloride 1j with the S atom in the middle of the aliphatic linker, four new pentamidines bearing S atoms were synthesized and also evaluated against MRSA strains. N,N'-Dialkylated pentamidines with S atoms in the linker are the promising lead structures for antimicrobials development.

The therapeutic journey of benzimidazoles: a review

Presence of benzimidazole nucleus in numerous categories of therapeutic agents such as antimicrobials, antivirals, antiparasites, anticancer, anti-inflammatory, antioxidants, proton pump inhibitors, antihypertensives, anticoagulants, immunomodulators, hormone modulators, CNS stimulants as well as depressants, lipid level modulators, antidiabetics, etc. has made it an indispensable anchor for development of new therapeutic agents. Varied substitutents around the benzimidazole nucleus have provided a wide spectrum of biological activities. Importance of this nucleus in some activities like, Angiotensin I (AT(1)) receptor antagonism and proton-pump inhibition is reviewed separately in literature. Even some very short reviews on biological importance of this nucleus are also known in literature. However, owing to fast development of new drugs possessing benzimidazole nucleus many research reports are generated in short span of time. So, there is a need to couple the latest information with the earlier information to understand the current status of benzimidazole nucleus in medicinal chemistry research. In the present review, various derivatives of benzimidazole with different pharmacological activities are described on the basis of substitution pattern around the nucleus with an aim to help medicinal chemists for developing an SAR on benzimidazole derived compounds for each activity. This discussion will further help in the development of novel benzimidazole compounds.

Bis[2-(4-amino-phen-yl)-4,5-dihydro-1H-imidazol-3-ium] dichloride monohydrate

The asymmetric unit of the title compound, 2C₉H₁₂N₃⁺·2Cl⁻·H₂O, comprises two mol­ecules, two chloride anions and one mol­ecule of crystal water. In the imidazolinium ring, the protonation contributes to delocalization of the positive charge over the two C—N bonds. Both chloride anions are acceptors of four hydrogen bonds in a flattened tetra­hedron environment. The donors are NH₂ groups, the NH groups of the imidazolinium rings and the water mol­ecule. These hydrogen bonds and N—H⋯O(H₂O) hydrogen bonds form a three-dimensional network.

Unprecedented C-2 arylation of indole with diazonium salts: Syntheses of 2,3-disubstituted indoles and their antimicrobial activity

A novel reaction of indole with aryldiazonium salts leading to the formation of 2-aryl-3-(arylazo)indoles was discovered. The products were found to possess potent anti-MRSA and anti-LLVRE activities. The SAR studies indicate that the potentially metabolically labile azo functionality can be replaced with ether oxygen and thioether sulfur atoms without any loss of activity.

4-(5-Hydroxymethyl-2-methoxyphenoxy)benzoic acid

The title compound, C₁₅H₁₄O₅, crystallizes with two independent mol­ecules in the asymmetric unit in which the benzene rings are inclined at dihedral angles of 79.4 (1) and 84.2 (1)°. In the crystal, inter­molecular O—H⋯O hydrogen bonds link the mol­ecules into double chains propagating in [001].