Synthesis, spectroscopic analyses (FT-IR and NMR), vibrational study, chemical reactivity and molecular docking study and anti-tubercular activity of condensed oxadiazole and pyrazine derivatives

Novel Benzylamine Derivatives: Synthesis, Anti-Mycobacterium Tuberculosis Evaluation and Predicted ADMET Properties

Background:

Tuberculosis (TB), a disease caused by the bacillus bacteria Mycobacterium tuberculosis is one of the major contributors of ill health in the world. TB is ranked in the top 10 causes of death globally and it is the leading killer associated with a single infectious agent. According to the World Health Organization (WHO), global number of deaths associated with TB have been slowly declining with 1.3 million in reported 2016 and 2017, and 1.2 million reported in 2018 and 2019.

Objective:

The synthesis, characterisation, biological evaluations, and the prediction of ADMET properties of the novel benzylamine derivatives.

Methods:

Commercially available reagents and solvents were purchased from Sigma Aldrich and Merck (South Africa). All chemicals were used as received, unless otherwise stated. The synthesised crude compounds were purified by flash silica gel column chromatography (5 – 30% ethyl acetate in hexane). The successful formation and purity of the synthesised compounds was confirmed by NMR, HRMS and melting point.

Results:

The respective organic compounds were synthesised by treating 3-ethoxysalcyladehyde, 5-bromo-3-ethoxysalcyladehyde, 5-chloro-3-ethoxysalcyladehyde with various aromatic amines and the products were obtained in good to excellent yields. The 1H and 13C NMR spectra of all the products showed the appearance of the methylene signals ranging from 3.88 – 4.68 ppm and 42.25 – 52.57 ppm respectively. Additionally, most compounds showed anti-Mycobacterium tuberculosis activity that ranged between 20 and 28 µM.

Conclusion:

A total of 36 compounds were synthesised and successfully biologically evaluated against Mycobacterium tuberculosis (Mtb) H37RV strain. All compounds showed activity against Mtb at concentrations of > 20 µM < 28 µM with the exception of compound one that was active against Mtb at higher concentration (MIC90 > 125 µM).

Oxadiazole Schiff Base as Fe3+ Ion Chemosensor: "Turn-off" Fluorescent, Biological and Computational Studies

Compound, (E)-5-(4-((thiophen-2-ylmethylene)amino)phenyl)-1,3,4-oxadiazole-2-thiol (3) was synthesized via condensation reaction of 5-(4-aminophenyl)-1,3,4-oxadiazole-2-thiol with thiophene-2-carbaldehyde in ethanol. For the synthesis and structural confirmation the FT-IR, ¹H, ¹³C-NMR, UV-visible spectroscopy, and mass spectrometry were carried out. The long-term stability of the probe (3) was validated by the experimental as well as theoretical studies. The sensing behaviour of the compound 3 was monitored with various metal ions (Ca²⁺, Cr³⁺, Fe³⁺, Co²⁺, Mg²⁺, Na⁺, Ni²⁺, K⁺) using UV- Vis. and fluorescence spectroscopy techniques by various methods (effect of pH and density functional theory) which showing the most potent sensing behaviour with iron. Job's plot analysis confirmed the binding stoichiometry ratio 1:1 of Fe³⁺ ion and compound 3. The limit of detection (LOD), the limit of quantification (LOQ), and association constant (K_a) were calculated as 0.113 µM, 0.375 µM, and 5.226 × 10⁵ respectively. The sensing behavior was further confirmed through spectroscopic techniques (FT-IR and ¹H-NMR) and DFT calculations. The intercalative mode of binding of oxadiazole derivative 3 with Ct-DNA was supported through UV-Vis spectroscopy, fluorescence spectroscopy, viscosity, cyclic voltammetry, and circular dichroism measurements. The binding constant, Gibb's free energy, and stern-volmer constant were find out as 1.24 × 10⁵, -29.057 kJ/mol, and 1.82 × 10⁵ respectively. The cleavage activity of pBR322 plasmid DNA was also observed at 3 × 10^-5 M concentration of compound 3. The computational binding score through molecular docking study was obtained as -7.4 kcal/mol. Additionally, the antifungal activity for compound 3 was also screened using broth dilution and disc diffusion method against C. albicans strain. The synthesized compound 3 showed good potential scavenging antioxidant activity against DPPH and H₂O₂ free radicals.

Synthesis of novel quinoxaline-alkynyl derivatives and their anti-Mycobacterium tuberculosis activity

The study report on the synthesis of a series of novel quinoxaline-alkynyl derivatives that were evaluated for their activity against Mycobacterium tuberculosis (Mtb) H₃₇R_V strain. A total of 19 compounds bearing an alcohol, aldehyde, mesylate and ester groups on the alkynly group, and also containing a chloro and nitro groups at the 6-position, were prepared. Seven compounds (3c, 4a-b, 5a, 5c, 6c and 6i), were found to have MIC₉₀ < 10 µM, while five compounds (3b, 6a, 6b, 6d and 6h) had MIC₉₀ in the range 10-20 µM. Compounds bearing a nitro substituent in the 6-position were generally more active and demonstrated a better safety profile, when compared to the unsubstituted and 6-chloro derivatives. Of the seven most active compounds, four contained nitro group at the 6-position.

Oxadiazole scaffolds in anti-tuberculosis drug discovery

With the increasing number of cases of latent and drug resistant tuberculosis, there is an urgent need to develop new, potent molecules capable of combating this deadly disease. Molecules containing oxadiazoles are one such class that could be considered to fulfil this need. Oxadiazole regioisomers have been explored in drug discovery programs for their ability to act as effective linkers and also as pharmacophoric features. Oxadiazoles can act as bioisosteric replacements for the hydrazide moiety which can be found in first line anti-TB drugs, and some have been also reported to interact with newer anti-TB targets. In this context, the present review describes the potential of oxadiazoles as antituberculosis agents.