p–nitrobenzyl-substituted N–heterocyclic carbene in Silver(I) and Gold(I) complexes and their antibacterial activities

An organometallic hybrid antibiotic of metronidazole with a Gold(I) N-Heterocyclic Carbene overcomes metronidazole resistance in Clostridioides difficile

Antimicrobial resistance (AMR) has been emerging as a major global health threat and calls for the development of novel drug candidates. Metal complexes have been demonstrating high efficiency as antibacterial agents that differ substantially from the established types of antibiotics in their chemical structures and their mechanism of action. One strategy to exploit this potential is the design of metal-based hybrid organometallics that consist of an established antibiotic and a metal-based warhead that contributes an additional mechanism of action different from that of the parent antibiotic. In this communication, we describe the organometallic hybrid antibiotic 2c, in which the drug metronidazole is connected to a gold(I) N-heterocyclic carbene warhead that inhibits bacterial thioredoxin reductase (TrxR). Metronidazole can be used for the treatment with the obligatory anaerobic pathogen Clostridioides difficile (C. difficile), however, resistance to the drug hampers its clinical success. The gold organometallic conjugate 2c was an efficient inhibitor of TrxR and it was inactive or showed only minor effects against eucaryotic cells and bacteria grown under aerobic conditions. In contrast, a strong antibacterial effect was observed against both metronidazole-sensitive and -resistant strains of C. difficile. This report presents a proof-of-concept that the design of metal-based hybrid antibiotics can be a viable approach to efficiently tackle AMR.

Structure-Activity Relationships in NHC-Silver Complexes as Antimicrobial Agents

Silver has a long history of antimicrobial activity and received an increasing interest in last decades owing to the rise in antimicrobial resistance. The major drawback is the limited duration of its antimicrobial activity. The broad-spectrum silver containing antimicrobial agents are well represented by N-heterocyclic carbenes (NHCs) silver complexes. Due to their stability, this class of complexes can release the active Ag⁺ cations in prolonged time. Moreover, the properties of NHC can be tuned introducing alkyl moieties on N-heterocycle to provide a range of versatile structures with different stability and lipophilicity. This review presents designed Ag complexes and their biological activity against Gram-positive, Gram-negative bacteria and fungal strains. In particular, the structure-activity relationships underlining the major requirements to increase the capability to induce microorganism death are highlighted here. Moreover, some examples of encapsulation of silver-NHC complexes in polymer-based supramolecular aggregates are reported. The targeted delivery of silver complexes to the infected sites will be the most promising goal for the future.

Phthalimide-tethered imidazolium salts: Synthesis, characterization, enzyme inhibitory properties, and in silico studies

A series of new imidazolium salts were prepared in good yield by the reaction between 1-alkylimidazole and a variety of alkyl halides. The structures of the compounds were identified by FT-IR, ¹ H NMR, and ¹³ C NMR spectroscopy, elemental analysis, and mass spectrometry. The crystal structure of 1b was determined by the single-crystal X-ray diffraction method. The phthalimide-tethered imidazolium salts exhibited inhibition abilities toward acetylcholinesterase (AChE) and human carbonic anhydrases (hCAs) I and II, with K_i values in the range of 24.63 ± 3.45 to 305.51 ± 35.98 nM for AChE, 33.56 ± 3.71 to 218.01 ± 25.21 nM for hCA I and 17.75 ± 0.96 to 308.67 ± 13.73 nM for hCA II. The results showed that the new imidazolium salts can play a key role in the treatment of Alzheimer's disease, epilepsy, glaucoma, and leukemia, which is related to their inhibition abilities of hCA I, hCA II, and AChE. Molecular docking and in silico absorption, distribution, metabolism, excretion and toxicity studies were used to look into how the imidazolium salts interacted with the specific protein targets. To better visualize and understand the binding positions and the influence of the imidazolium salts on hCA I, hCA II, and AChE conformations, each one was subjected to molecular docking simulations.