3-(Hydroxyimino)imidazo[1,2-a]pyridin-2(3H)-ylidene)-1-arylethanones as new red heterocyclic dyes: Synthesis, spectral studies, quantum-chemical investigations, and antibacterial activities

The synthesis, optical properties, theoretical calculations, and antibacterial activities of a series of new red heterocyclic dyes derived from imidazo[1,2- a]pyridine are presented. 3-(Hydroxyimino)imidazo[1,2- a]pyridin-2(3 H)-ylidene)-1-arylethanones are obtained from the reaction of 3-nitroimidazo[1,2- a]pyridine with substituted acetophenone derivatives in good yields (65%–72%). The structures are confirmed by spectral and analytical data, and the optical properties of the dyes are characterized by spectrophotometry. Density functional theory calculations are performed to provide the optimized geometries and relevant frontier orbitals. Calculated electronic absorption spectra are also obtained by the time-dependent density functional theory method. Moreover, the antibacterial activities (minimum inhibitory concentration) of the new dyes against Gram-positive and Gram-negative bacterial species are determined (minimum inhibitory concentration: 5–200 μg mL−1).

Taheebo Polyphenols Attenuate Free Fatty Acid-Induced Inflammation in Murine and Human Macrophage Cell Lines As Inhibitor of Cyclooxygenase-2

Aim of study

Taheebo polyphenols (TP) are water extracts of Tabebuia spp. (Bignoniaceae), taken from the inner bark of the Tabebuia avellanedae tree, used extensively as folk medicine in Central and South America. Some anti-inflammatory drugs act by inhibiting both cyclooxygenase-2 (COX-2) and COX-1 enzymes. COX-2 syntheses prostaglandin (PG) E₂, which is a species of endogenous pain-producing substance, whereas COX-1 acts as a house-keeping enzyme. Inhibiting both COX-1 and -2 simultaneously can have side effects such as gastrointestinal bleeding and renal dysfunction. Some polyphenols have been reported for its selective inhibiting activity toward COX-2 expression. Our study aimed to demonstrate the potential and mechanisms of TP as an anti-inflammation action without the side effects of COX-1 inhibition.

Materials and methods

Free fatty acid-stimulated macrophage cell lines were employed to mimic macrophage behaviors during lifestyle-related diseases such as atherosclerosis and non-alcoholic steatohepatitis. Real-time polymerase chain reaction was used to detect expression of inflammatory cytokine mRNA. Griess assay was used to measure the production of nitric oxide (NO). ELISA was used to measure PG E₂ production. Molecular docking was adopted to analyze the interactions between compounds from T. avellanedae and COX-2.

Results

TP significantly suppressed the production of NO production, blocked the mRNA expression of iNOS, and COX-2 in both cell lines, blocked the mRNA expression of TNF-α, IL-1β, IL-6, and PGE₂ in the murine cell line. However, there was no inhibitory effect on COX-1. Molecular docking result indicated that the inhibitory effects of TP on COX-2 and PGE₂ could be attributed to acteoside, which is the main compound of TP that could bind to the catalytic zone of COX-2. After the interaction, catalytic ability of COX-2 is possibly inhibited, followed by which PGE₂ production is attenuated. COX inhibitor screening assay showed TP as a selective inhibitor of COX-2 enzyme.

Conclusion

The anti-inflammatory effects of TP can possibly regulate macrophages due to the targeted inhibition of COX-2 activity, without affecting COX-1 activity with other anti-inflammatory effects including suppression of iNOS and inflammatory cytokines. As such, TP is potentially useful in prevention and treatment of lifestyle-related disease by attenuating inflammation caused by macrophages infiltration.

Synthesis of New Dyes from Imidazo[1,2-a]Pyridine: Tautomerism, Spectroscopic Characterisation, DFT/TD-DFT Calculations, Atoms in Molecules Analyses and Antibacterial Activities

The synthesis, optical properties, theoretical calculations and antibacterial activity of a series of new heterocyclic dyes from imidazo[1,2-a] pyridine are described. The key intermediate 2-[3-(hydroxyimino)imidazo[1,2-a]pyridin-2(3H)-ylidene]malononitrile was obtained via the nucleophilic substitution of hydrogen in 3-nitroimidazo[1,2-a]pyridine with malononitrile in basic methanol solution. Tautomerism, oxidation and alkylation studies on the dye led to the synthesis of new heterocyclic indigo-coloured, purple, and orange dyes in good yields. The structures of all newly synthesised compounds were confirmed by spectral and analytical data. The optical properties of the dyes were spectrally characterised and shown to exhibit interesting photophysical properties including high extinction coefficients. Density functional theory calculations of the dyes were performed to provide the optimised geometries and relevant frontier orbitals. Calculated electronic absorption spectra were also obtained by the time-dependent density functional theory method. In addition, electrostatic potential maps and electron density maps of the dyes were evaluated by AIM (atoms in molecules) analysis. Moreover, the new dyes exhibited potent antibacterial activity and their antibacterial activities (MIC) against Gram-positive and Gram-negative bacterial species were determined.