Antimicrobial azo molecules: a review

Discovery of Novel Nicotinamide Derivatives by a Two-Step Strategy of Azo-Incorporating and Bioisosteric Replacement

Azobenzene moieties can serve as active fragments in antimicrobials and exert trans/cis conversions of molecules. Herein, a series of novel nicotinamide derivatives (NTMs) were developed by employing a two-step strategy, including azo-incorporating and bioisosteric replacement. Azo-incorporation can conveniently provide compounds that can be easily optically interconverted between trans/cis isomers, enhancing the structural diversity of azo compounds. It is noteworthy that the replacement of the azo bond with a 1,2,4-oxadiazole motif through further bioisosteric replacement led to the discovery of a novel compound, NTM18, which made a breakthrough in preventing rice sheath blight disease. A control effect value of 94.44% against Rhizoctonia solani could be observed on NTM18, while only 11.11% was determined for boscalid at 200 mg·L-1. Further mechanism validations were conducted, and the molecular docking analysis demonstrated that compound NTM18 might have a tight binding with SDH via an extra π-π interaction between the oxadiazole ring and residue of D_Y586. This work sets up a typical case for the united applications of azo-incorporating and bioisosteric replacement in fungicide design, posing an innovative approach in structural diversity-based development of pesticides.

Insights into Two Novel Orthopalladated Chromophores with Antimicrobial Activity against Escherichia coli

Advanced chromophoric tools, besides being biologically active, need to meet the expectations of the technological demands including stability, colour retention, and proper solubility for their target. Many coordination compounds of conjugated ligands are antibacterial dyes, able to combine a strong dyeing performance with a useful biological activity. Specifically, palladium (II) complexes of Schiff base ligands are known for their relevant activity against common bacteria. In this article, we report the synthesis and comprehensive experimental and theoretical characterization of two novel Pd(II) chromophore complexes obtained from a cyclopalladated Schiff base as two different chelating azo dyes. The antibacterial response of these two novel complexes was tested against the ubiquitous Escherichia coli bacterium in an aqueous medium and revealed a noteworthy antimicrobial activity, higher than when compared with their uncoordinated biologically active ligands.

Azobenzene as Antimicrobial Molecules

Azo molecules, characterized by the presence of a -N=N- double bond, are widely used in various fields due to their sensitivity to external stimuli, ch as light. The emergence of bacterial resistance has pushed research towards designing new antimicrobial molecules that are more efficient than those currently in use. Many authors have attempted to exploit the antimicrobial activity of azobenzene and to utilize their photoisomerization for selective control of the bioactivities of antimicrobial molecules, which is necessary for antibacterial therapy. This review will provide a systematic and consequential approach to coupling azobenzene moiety with active antimicrobial molecules and drugs, including small and large organic molecules, such as peptides. A selection of significant cutting-edge articles collected in recent years has been discussed, based on the structural pattern and antimicrobial performance, focusing especially on the photoactivity of azobenzene and the design of smart materials as the most targeted and desirable application.

Triggered azobenzene-based prodrugs and drug delivery systems

Azobenzene-based molecules show unique trans-cis isomerization upon ultraviolet light irradiation, which induce the change of polarity, crystallinity, stability, and binding affinity with pharmacological target. Moreover, azobenzene is the substrate of azoreductase that is often overexpressed in many pathological sites, e.g. hypoxic solid tumor. Therefore, azobenzene can be a multifunctional molecule in material science, pharmaceutical science and biomedicine because of its sensitivity to light, hypoxia and certain enzymes, hence showing potential application in site-specific smart therapy. Herein we focus on the employment of azobenzene and its derivatives for engineering triggered prodrug and drug delivery systems, and provide an overview of photoswitchable azo-based prodrugs, the associated problems regarding ultraviolet light and reversible isomerization, as well as the potential solutions. We also present the advance of azo-bearing delivery vehicles wherein azobenzene act as the linker, capping agent, and building block, and discuss the corresponding mechanisms for controlled cargo release, endocytosis enhancement and sensitization of free radical cancer therapy.

Azo-incorporating Increases Inhibitory Activity of Succinate Dehydrogenase

Diversity of pesticide discovery provided a solution to resistance. Here, we presented a strategy of azo-incorporating to promote the diverse developments of fungicide. A series of novel fungicides were synthesized by incorporating azobenzene derivatives into fluxapyroxad. Much better in vitro fungicidal activity increases for compound 9d were observed compared to the positive control, fluxapyroxad against Botrytis cinerea and Rhizoctonia solani. Compound 9d (IC₅₀ = 0.03 μM) also had a great enzyme-inhibiting activity increase toward succinate dehydrogenase in comparison with fluxapyroxad (IC₅₀ = 4.40 μM). A comparatively equivalent biological activity was observed between compounds 8a and 9d. SEM analysis helped us to observe clearly the morphology of the fungi before and after active ingredient delivery. Our results of molecular docking analysis, fluorescence quenching analysis, and enzymatic assays demonstrated that compound 8a and 9d act on SDH. An increase in inhibitory activity could be occurring after incorporation of azobenzene, which provided a new strategy for molecular design in pesticide discovery.

Azo-Dyes-Grafted Oligosaccharides-From Synthesis to Applications

Azobenzenes are photochromic molecules that possess a large range of applications. Their syntheses are usually simple and fast, and their purifications can be easy to perform. Oligosaccharide is also a wide family of biopolymer constituted of linear chain of saccharides. It can be extracted from biomass, as for cellulose, being the principal constituent of plant cell wall, or it can be enzymatically produced as for cyclodextrins, having properties not far from cellulose. Combining these two materials families can afford interesting applications such as controlled drug-release systems, photochromic liquid crystals, photoresponsive films or even fluorescent indicators. This review will compile the different syntheses of azo-dyes-grafted oligosaccharides, and will show their various applications.