Interactions of Aminopropyl-Azithromycin Derivatives, Precursors in the Synthesis of Bioactive Macrozones, with E. coli Ribosome: NMR and Docking Studies

Antimicrobial macrozones interact with biological macromolecules via two-site binding mode of action: Fluorimetric, NMR and docking studies

Macrozones are novel conjugates of azithromycin and thiosemicarbazones, which exhibit very good in vitro antibacterial activities against susceptible and some resistant bacterial strains thus showing a potential for further development. A combination of spectrometric (fluorimetry, STD and WaterLOGSY NMR) and molecular docking studies provided insights into atomic details of interactions between selected macrozones and biological receptors such as E. coli ribosome and bovine serum albumin. Fluorimetric measurements revealed binding constants in the micro-molar range while NMR experiments provided data on binding epitopes. It has been demonstrated that both STD and WaterLOGSY gave comparable and consistent results unveiling atoms in intimate contacts with biological receptors. Docking studies pointed towards main interactions between macrozones and E. coli ribosome which included specific π - π stacking and hydrogen bonding interactions with thiosemicarbazone part extending down the ribosome exit tunnel. The results of the docking experiments were in fine correlation with those obtained by NMR and fluorimetry. Our investigation pointed towards a two-site binding mechanism of interactions between macrozones and E. coli ribosome which is the most probable reason for their activity against azithromycin-resistant strains. Much better activity of macrozone-nickel coordinated compound against E. coli ribosome compared to other macrozones has been attributed to the higher polarity which enabled better bacterial membrane penetration and binding of the two thiosemicarbazone units thus additionally contributing to the overall binding energy. The knowledge gained in this study should play an important role in anti-infective macrolide design in the future.

Screening of Novel Antimicrobial Diastereomers of Azithromycin-Thiosemicarbazone Conjugates: A Combined LC-SPE/Cryo NMR, MS/MS and Molecular Modeling Approach

A well-known class of antibacterials, 14- and 15-membered macrolides are widely prescribed to treat upper and lower respiratory tract infections. Azithromycin is a 15-membered macrolide antibiotic possessing a broad spectrum of antibacterial potency and favorable pharmacokinetics. Bacterial resistance to marketed antibiotics is growing rapidly and represents one of the major global hazards to human health. Today, there is a high need for discovery of new anti-infective agents to combat resistance. Recently discovered conjugates of azithromycin and thiosemicarbazones, the macrozones, represent one such class that exhibits promising activities against resistant pathogens. In this paper, we employed an approach which combined LC-SPE/cryo NMR, MS/MS and molecular modeling for rapid separation, identification and characterization of bioactive macrozones and their diastereomers. Multitrapping of the chromatographic peaks on SPE cartridges enabled sufficient sample quantities for structure elucidation and biological testing. Furthermore, two-dimensional NOESY NMR data and molecular dynamics simulations revealed stereogenic centers with inversion of chirality. Differences in biological activities among diastereomers were detected. These results should be considered in the process of designing new macrolide compounds with bioactivity. We have shown that this methodology can be used for a fast screening and identification of the macrolide reaction components, including stereoisomers, which can serve as a source of new antibacterials.

An Investigation of the Predominant Structure of Antibiotic Azithromycin in Chloroform Solution through NMR and Thermodynamic Analysis

Azithromycin (AZM) is a well-known macrolide-type antibiotic that has been used in the treatment of infections and inflammations. Knowledge of the predominant molecular structure in solution is a prerequisite for...