Synthesis of novel macrolide derivatives with imidazo[4,5-b]pyridinyl sulfur contained alkyl side chains and their antibacterial activity

Imidazopyridine, a promising scaffold with potential medicinal applications and structural activity relationship (SAR): recent advances

Imidazopyridine scaffold has gained tremendous importance over the past few decades. Imidazopyridines have been expeditiously used for the rationale design and development of novel synthetic analogs for various therapeutic disorders. A wide variety of imidazopyridine derivatives have been developed as potential anti-cancer, anti-diabetic, anti-tubercular, anti-microbial, anti-viral, anti-inflammatory, central nervous system (CNS) agents besides other chemotherapeutic agents. Imidazopyridine heterocyclic system acts as a key pharmacophore motif for the identification and optimization of lead structures to increase medicinal chemistry toolbox. The present review highlights the medicinal significances of imidazopyridines for their rationale development as lead molecules with improved therapeutic efficacies. This review further emphasis on the structure-activity relationships (SARs) of the various designed imidazopyridines to establish a relationship between the key structural features versus the biological activities.Communicated by Ramaswamy H. Sarma.

Synthesis and biological evaluation of antibacterial activity of novel clarithromycin derivatives incorporating 1,2,3-triazole moieties at the 4''- and 11-OH positions

Bacterial infection is still one of the diseases that threaten human health, and bacterial drug resistance is widespread worldwide. As a result, their eradication now largely relies on antibacterial drug discovery. Here, we reveal a novel approach to the development of 14-membered macrolide antibiotics by describing the design, synthesis, and evaluation of novel clarithromycin derivatives incorporating 1,2,3-triazole moieties at the 4''- and 11-OH positions. Using chemical synthesis, 35 clarithromycin derivatives were prepared, and their antibacterial properties were profiled. We found that compounds 8e-8h, 8l-8o, 8v, and 19d were as potent as azithromycin against Enterococcus faecalis ATCC29212. Furthermore, compounds 8c, 8d, 8n, and 8o showed slightly improved antibacterial activity (2-fold) against Acinetobacter baumannii ATCC19606 when compared with azithromycin and clarithromycin. In addition, compounds 8e, 8f, 8h, 8l, and 8v exhibited excellent antibacterial activity against Staphylococcus aureus ATCC43300, Staphylococcus aureus PR, and Streptococcus pneumoniae ER-2. These compounds were generally 64- to 128-fold more active than azithromycin, and 32- to 128-fold more active than clarithromycin. The results of molecular docking indicated that compound 8f may bind to the nucleotide residue A752 through hydrogen-bonding, hydrophobic, electrostatic, or π-π stacking interactions. The predicted ClogP data suggested that higher values of ClogP (>6.65) enhanced the antibacterial activity of compounds such as 8e, 8f, 8h, 8l, and 8v. The determination of the minimum bactericidal concentration showed that most of the tested compounds were bacteriostatic agents. From this study of bactericidal kinetics, we can conclude that compound 8f had a concentration- and time-dependent effect on the proliferation of Staphylococcus aureus ATCC43300. Finally, the results of the cytotoxicity assay showed that compound 8f exhibited no toxicity at the effective antibacterial concentration.

Design, synthesis and antibacterial evaluation of novel C-11, C-9 or C-2'-substituted 3-O-descladinosyl-3-ketoclarithromycin derivatives

A novel series of 3-O-descladinosyl-3-keto-clarithromycin derivatives, including 11-O-carbamoyl-3-O-descladinosyl-3-keto-clarithromycin derivatives and 2',9(S)-diaryl-3-O-descladinosyl-3-keto-clarithromycin derivatives, were designed, synthesized and evaluated for their in vitro antibacterial activity. Among them, some derivatives were found to have activity against resistant bacteria strains. In particular, compound 9b showed not only the most significantly improved activity (16 µg/mL) against S. aureus ATCC43300 and S. aureus ATCC31007, which was >16-fold more active than that of CAM and AZM, but also the best activity against S. pneumoniae B1 and S. pyogenes R1, with MIC values of 32 and 32 µg/mL. In addition, compounds 9a, 9c, 9d and 9g exhibited the most effective activity against S. pneumoniae AB11 with MIC values of 32 or 64 µg/mL as well. Unfortunately, 2',9(S)-diaryl-3-O-descladinosyl-3-keto-clarithromycin derivatives failed to exhibit better antibacterial activity than references. It can be seen that the combined modification of the C-3 and C-11 positions of clarithromycin is beneficial to improve activity against resistant bacteria, while the single modification of the C-2'' position is very detrimental to antibacterial activity.

Studies on the novel pyridine sulfide containing SDH based heterocyclic amide fungicide

BACKGROUND

Succinate dehydrogenase (SDH) has been identified as one of the most significant targets for fungicide discovery. To date, 23 commercial SDH inhibitor (SDHI) fungicides have been approved for plant protection since the first launch of carboxin in 1966, and extensively applied to combat destructive plant fungi.

RESULTS

In this project, 20 novel pyridine sulfide derivatives containing SDH-based heterocyclic amide fungicide were designed, synthesized, and characterized by proton nuclear magnetic resonance (¹ H-NMR), carbon-13 (¹³ C)-NMR and high-resolution mass spectrometry (HRMS). In vitro fungicidal activity experiment, the target compound I-1 displayed excellent inhibitory rates against the common agricultural pathogens with half maximal effective concentration (EC₅₀ ) values of 5.2 to 39.8 μg mL^-1 . The in vivo fungicidal activities demonstrated that the compound I-1 could effectively prevent Botrytis cinerea from infecting tomato and cucumber leaves with the preventative rates of 67% and 50%. The mitochondrial membrane potential detection, SDH enzyme assay and the molecular docking simulation revealed that the mechanism of action of the compound I-1 and the relevant interactions with the target enzyme may be similar to those of the control fluopyram.

CONCLUSION

The biological activity screening and validation of mechanism of action indicated that the compound I-1 could be identified as a potential SDH inhibitor for further study. © 2020 Society of Chemical Industry.

Novel 3-O-carbamoyl erythromycin A derivatives (carbamolides) with activity against resistant staphylococcal and streptococcal isolates

A novel series of 3-O-carbamoyl erythromycin A derived analogs, labeled carbamolides, with activity versus resistant bacterial isolates of staphylococci (including macrolide and oxazolidinone resistant strains) and streptococci are reported. An (R)-2-aryl substituent on a pyrrolidine carbamate appeared to be critical for achieving potency against resistant strains. Crystal structures showed a distinct aromatic interaction between the (R)-2-aryl (3-pyridyl for 4d) substituent on the pyrrolidine and G2484 (G2505, Escherichia coli) of the Deinococcus radiodurans 50S ribosome (3.2Å resolution).

New macrolide, lincosaminide and streptogramin B antibiotics

IMPORTANCE OF THE FIELD

New antibiotics are needed to overcome microbial resistance and to improve on the therapeutic index and clinical effectiveness of existing agents.

AREA COVERED IN THIS REVIEW

This review covers the journal and patent literature published from about the mid-2000s to 2010 to provide an overview of the large diversity of new chemical entities in the macrolide, lincosaminide and streptogramin B (MLS(B)) class.

WHAT THE READER WILL GAIN

The review identifies areas of the greatest effort and recent results in pursuing structure-activity relationships among MLS(B) antibiotics and highlights preclinical and clinical candidates that have arisen from these diverse discovery programs.

TAKE HOME MESSAGE

Research on the MLS(B) class appears promising for the eventual registration and commercialization of several new antibiotics that improve the clinical effectiveness of existing agents and combat antibiotic-resistant pathogens.