Novel quercetin and apigenin-acetamide derivatives: design, synthesis, characterization, biological evaluation and molecular docking studies

Abstract

Flavonoids exhibit essential but limited biological properties which can be enhanced through chemical modifications. In this study, we designed, synthesized, and characterized two novel flavonoid derivatives, quercetin penta-acetamide (1S3) and apigenin tri-acetamide (2S3). These compounds were confirmed using (¹H, ¹³C) NMR, UV-Vis, and FT-IR characterizations. Their interaction with fish sperm DNA (FS-DNA) at physiological pH was investigated by UV-Vis and fluorescence spectrophotometry. The binding constant (K _b) for the UV-Vis experiment was found to be 1.43 ± 0.3 × 10⁴ M^-1 for 1S3 and 2.08 ± 0.2 × 10⁴ M^-1 for 2S3. The binding constants (K _SV) for the fluorescence quenching experiment were 1.83 × 10⁴ M^-1 and 1.96 × 10⁴ M^-1 for 1S3 and 2S3, respectively. Based on molecular modeling and docking studies, the binding affinities were found to be -7.9 and -9.1 kcal mol^-1, for 1S3 and 2S3, respectively. The compound-DNA docked model correlated with our experimental results, and they are groove binders. Furthermore, mutagenicity potential was examined. 1S3 and its metabolites showed no mutagenic activity for both TA98 and TA100 strains. 2S3 did not show any mutagenic activity for the strain TA 98, while its metabolites were only active at high doses. Both 2S3 and its metabolites showed mutagenic activity in the TA100 strain.

Fig. 1. Structure of apigenin and quercetin.

Fig. 2. General structure of the flavonoids, the intermediates and the final products. R₃, R₅ and R₇ variables are shown in Table 1.

Scheme 1. Steps in the synthesis of 1S3 & 2S3 derivatives. Reagents and reaction conditions: step 1 (S0 → S1) ethyl chloroacetate, K₂CO₃ (excess), DMF, rt. Step 2 (S1 → S2) LiOH·H₂O, THF/H₂O, rt. Step 3 (S2 → S3) SOCl₂ (excess), reflux, 75 °C; NH₄OH (excess), 0 °C – rt.

Fig. 3. Absorption spectra of 10 μmol L⁻¹ 1S3 and 2S3 in Tris–HCl buffer (0.1 mol L⁻¹, pH 7.4).

Fig. 4. Absorption spectra of 10 μmol L⁻¹ 1S3 (a) and 10 μmol L⁻¹ 2S3 (b) in the presence of FS-DNA at different concentrations (a: 0.0, b: 1.94, c: 3.89 d: 5.84, e: 7.78, f: 9.73, g: 11.68, h: 13.63, i: 15.58, and j: 17.52 μmol L⁻¹ in Tris–HCl buffer (0.1 mol L⁻¹, pH 7.4)). The inset showing the plot of [DNA/(ε_a − ε_f)] versus [DNA].

Fig. 5. Quenched Fluorescence spectra of FS-DNA bound to the EtBr system with the addition of compounds 1S3 (a) and 2S3 (b). Inset: I₀/I versus [DNA] (μM).

Fig. 6. Comparison graphs showing the changes in revertant colony percentages in the presence (+S9) and absence (−S9) of the metabolic activation system for TA98 and TA100 strains of compounds 1S3 and 2S3.

Fig. 7. Molecular docked structure of 1S3 (a) and 2S3 (b) complexed with DNA. Surface representation showing the binding of 1S3 and 2S3 with the dodecamer duplex sequence, d(CGCGAATTCGCG)₂ (PDB ID: 1BNA).

Fig. 8. 2D plot of interaction between the 1S3 (a) and 2S3 (b) with the dodecamer duplex sequence, d(CGCGAATTCGCG)₂ (PDB ID: 1BNA).