Synthesis and Antibacterial Evaluation of Bis-thiazolium, Bis-imidazolium, and Bis-triazolium Derivatives

Antibacterial quaternary ammonium agents: Chemical diversity and biological mechanism

Bacterial infections have seriously threatened public health especially with the increasing resistance and the cliff-like decline of the number of newly approved antibacterial agents. Quaternary ammonium compounds (QACs) possess potent medicinal properties with 95 successfully marketed drugs, which also have a long history as antibacterial agents. In this review, we summarize the chemical diversity of antibacterial QACs, divided into chain-like and aromatic ring, reported over the past decade (2012 to mid-2022). Additionally, the structure-activity relationships, mainly covering hydrophobicity, charges and skeleton features, are discussed. In the cases where sufficient information is available, antibacterial mechanisms including biofilm, cell membrane, and intracellular targets are presented. It is hoped that this review will provide sufficient information for medicinal chemists to discover the new generation of antibacterial agents based on QACs.

Functionalized Cyclopentenones and an Oxime Ether as Antimicrobial Agents

Several naturally occurring cyclopentenones, such as palmenones and nigrosporiones, exhibit antimicrobial activity. Herein we describe the antimicrobial activity of cyclopentenones and derivatives that can be easily accessed from biomass derivatives furfural and 5-hydroxymethylfurfural. Upon screening a range of functionalized trans-diamino-cyclopentenones (DCPs) and δ-lactone-fused cyclopentenones (LCPs), an oxime ether derivative of DCP was identified that exhibited remarkable antimicrobial activity against Gram-positive bacteria, including resistant strains such as methicillin-resistant S. aureus (MRSA) and vancomycin-resistant E. faecalis (VRE) strains.

Using Slippage to Construct a Prototypical Molecular "Lock & Lock" Box

We report a new slippage system based on p-tert-butylbenzyl-terminated imidazolium ions and di(ethylene glycol)-containing macrocycles and their use as linking units for the construction of a prototypical molecular "Lock & Lock" box from a resorcinarene-based cavitand "bowl" and a porphyrin "cover". The multivalent structure with four slippage linkers provided the molecular box with high stability, yet the system dissociated into its two components upon application of suitable external stimuli.

Electrosynthesis of 1,2,4-Triazolium Tetrafluoroborates

The synthesis of 1,2,4-triazolium tetrafluoroborates under electrochemical conditions is reported. The reaction is performed with stoichiometric amounts of HBF₄, which converts starting materials to their corresponding cationic forms due to protonation. As a result, sufficient conductivity is gained in MeOH, CD₃OD, and EtOH, and no additional supporting electrolyte is required. Agrochemical fungicide, (±)-triticonazole (1), is transformed in this manner into 2a, an O-methylated potential intermediate involved in the metabolism of 1, in 42% yield on a gram scale.

Quaternary Ammonium Compounds (QACs) and Ionic Liquids (ILs) as Biocides: From Simple Antiseptics to Tunable Antimicrobials

Quaternary ammonium compounds (QACs) belong to a well-known class of cationic biocides with a broad spectrum of antimicrobial activity. They are used as essential components in surfactants, personal hygiene products, cosmetics, softeners, dyes, biological dyes, antiseptics, and disinfectants. Simple but varied in their structure, QACs are divided into several subclasses: Mono-, bis-, multi-, and poly-derivatives. Since the beginning of the 20th century, a significant amount of work has been dedicated to the advancement of this class of biocides. Thus, more than 700 articles on QACs were published only in 2020, according to the modern literature. The structural variability and diverse biological activity of ionic liquids (ILs) make them highly prospective for developing new types of biocides. QACs and ILs bear a common key element in the molecular structure-quaternary positively charged nitrogen atoms within a cyclic or acyclic structural framework. The state-of-the-art research level and paramount demand in modern society recall the rapid development of a new generation of tunable antimicrobials. This review focuses on the main QACs exhibiting antimicrobial and antifungal properties, commercial products based on QACs, and the latest discoveries in QACs and ILs connected with biocide development.

1,2,4-Triazoles as Important Antibacterial Agents

The global spread of drug resistance in bacteria requires new potent and safe antimicrobial agents. Compounds containing the 1,2,4-triazole ring in their structure are characterised by multidirectional biological activity. A large volume of research on triazole and their derivatives has been carried out, proving significant antibacterial activity of this heterocyclic core. This review is useful for further investigations on this scaffold to harness its optimum antibacterial potential. Moreover, rational design and development of the novel antibacterial agents incorporating 1,2,4-triazole can help in dealing with the escalating problems of microbial resistance.

Ammonium-Charged Sterically Hindered Phenols with Antioxidant and Selective Anti-Gram-Positive Bacterial Activity

The increase in the resistance of pathogens, in particular Staphylococcus aureus, to the action of antibiotics necessitates the search for new readily available and non-toxic drugs. In solving this problem, phenolic acylhydrazones have high potential. In this communication, the synthesis of quaternary ammonium compounds containing a differently substituted phenolic moiety has been performed. An initial study of antimicrobial activity showed that these compounds are highly selective against S. aureus and B. cereus. The highest activity (MIC 2.0 μm) was shown by hydrazones containing a catechol fragment. These compounds are more than 3-fold more active against S. aureus and 3-10-fold more active against B. cereus than norfloxacin. Low hemolytic and high antioxidant activities of all new compounds were also established.