Synthesis, physicochemical characterization and biological activity of novel pyrrole flavones

Abstract

Cancer remains one of the most significant health issues worldwide. By designing compounds with anticancer activity characterized by high selectivity towards cancer cells, medicinal chemistry focuses on the protection of healthy cells and tissues. In this study, we present the hybrid pharmacophore approach, which afforded a series of new pyrrole flavones. The synthetic strategy was based on the Paal-Knorr pyrrole synthesis, starting from aminoflavones through their condensation with 1,4-diketones and leading to 6- and 7-(pyrrol-1-yl) flavones. The isolated products underwent characterization using NMR and UV-VIS spectroscopy, mass spectrometry, TGA, DSC, and Microtox analyses. For all pyrrole flavones, single crystals were obtained and subjected to X-ray diffraction experiments. Their cytotoxic activity was assessed on two human bladder cancer cell lines (5637 and HT-1376) and one non-cancerous (MRC-5) cell line, showing the potential as anticancer agents. Flavone derivative with the 6-(2-methyl-5-phenylpyrrol-1-yl) moiety was active in the MTT assay towards 5637 and HT-1376 cancer cells after 24 h of incubation with IC₅₀ values of 2.97 µM and 5.89 µM, respectively. Notably, flavone derivative with 7-(2-methyl-5-phenylpyrrol-1-yl) revealed cytotoxic activity towards 5637 and HT-1376 cells with IC₅₀ values of 7.39 µM and 13.54 µM, respectively, without any effect on the viability of MRC-5 cells.

Keywords: Anticancer activity; Bladder cancer cell line; Flavonoids; Paal–Knorr synthesis; Pyrrole; X-ray structure.

Fig. 1

The flavone scaffold and pharmacological activities of flavone derivatives.

Fig. 2

The general workflow applied in the current study.

Scheme 1

Reagents and conditions: (i) trifluoroacetic acid, methanol, reflux, 24h.

Fig. 3

Percentage contribution of short contacts to the Hirshfeld surface area.

Fig. 4

Molecules connected with short intermolecular contacts. For one molecule, Hirshfeld surfaces mapped with d_norm are shown. Symmetry codes are given in Table S6.

Fig. 5

Molecules connected with short intermolecular contacts. For one molecule, Hirshfeld surfaces mapped with d_norm are shown. Geometrical parameters of short contact are given in Table S6.

Fig. 6

The decrease of Aliivibrio fischeri bioluminescence intensity upon exposition to the tested compounds 4a–c and 5a–c in different concentrations. Measurements were taken 5 and 15 min after adding of the pyrrolyl aminoflavones to the bacteria.

Fig. 7

Results of the preliminary experiment for the 6-aminoflavone derivatives 4a–c. Cell viability was determined using the MTT assay after incubation with compounds 4a (A), 4b (B), and 4c (C) at a concentration of 0.1 µM, 1 µM, and 10 µM for 24, 48, and 72 h. A one-way ANOVA with post-hoc Dunnett’s test was assessed statistical significance, with p < 0.05 considered significant. Asterisks indicate statistical significance: *p < 0.05, ** p < 0.01, *** p < 0.001, and ****p < 0.0001 vs. the control group. The figure also shows representative images of 5637 cells morphology after incubation with 4a–c at a concentration of 10 µM after 24, 48, and 72 h. The control cells were treated with DMSO at a concentration of 0.1% in a cell culture medium. The images were taken with a Nikon Eclipse TS100 microscope. The scale bar corresponds to 100 µm.

Fig. 8

Results of the preliminary experiment for 7-aminoflavone derivatives 5a–c. Cell viability after incubation with compounds 5a (A), 5b (B), and 5c (C) at a concentration of 0.1 µM, 1 µM, and 10 µM for 24, 48, and 72 h was determined using the MTT assay. One-way ANOVA with post-hoc Dunnett’s test was used to determine significance, with p < 0.05 considered significant. Asterisks indicate statistical significance *p < 0.05, ****p < 0.0001 versus the control group. The figure shows the representative images of 5637 cells morphology after incubation with 5a–c at a concentration of 10 µM after 24, 48, and 72 h. Control cells were treated with DMSO at a concentration of 0.1% in a cell culture medium. The images were taken with a Nikon Eclipse TS100 microscope. The scale bar corresponds to 100 µm.

Fig. 9

The dose–response curves for 5637, HT-1376, and MRC-5 cells after treatment with compounds 4b and 5b for 24 and 48 h. Data are presented as mean ± SD from at least three independent experiments.