Synthesis and In vitro Leishmanicidal Activities of Six Quercetin Derivatives

Quercetin as a Promising Antiprotozoan Phytochemical: Current Knowledge and Future Research Avenues

Despite tremendous advances in the prevention and treatment of infectious diseases, only few antiparasitic drugs have been developed to date. Protozoan infections such as malaria, leishmaniasis, and trypanosomiasis continue to exact an enormous toll on public health worldwide, underscoring the need to discover novel antiprotozoan drugs. Recently, there has been an explosion of research into the antiprotozoan properties of quercetin, one of the most abundant flavonoids in the human diet. In this review, we tried to consolidate the current knowledge on the antiprotozoal effects of quercetin and to provide the most fruitful avenues for future research. Quercetin exerts potent antiprotozoan activity against a broad spectrum of pathogens such as Leishmania spp., Trypanosoma spp., Plasmodium spp., Cryptosporidium spp., Trichomonas spp., and Toxoplasma gondii. In addition to its immunomodulatory roles, quercetin disrupts mitochondrial function, induces apoptotic/necrotic cell death, impairs iron uptake, inhibits multiple enzymes involved in fatty acid synthesis and the glycolytic pathways, suppresses the activity of DNA topoisomerases, and downregulates the expression of various heat shock proteins in these pathogens. In vivo studies also show that quercetin is effective in reducing parasitic loads, histopathological damage, and mortality in animals. Future research should focus on designing effective drug delivery systems to increase the oral bioavailability of quercetin. Incorporating quercetin into various nanocarrier systems would be a promising approach to manage localized cutaneous infections. Nevertheless, clinical trials are needed to validate the efficacy of quercetin in treating various protozoan infections.

Sb(V) Kaempferol and Quercetin Derivative Complexes: Synthesis, Characterization and Antileishmanial Activities

Background

Recent studies on Leishmaniasis treatment have confirmed the antiparasitic effects of flavonols and organic antimony pentavalent [(Sb(V)] complexes.

Objectives

This study aimed to identify new Sb(V) complexes by combining the benefits of antimonials and flavonols as well as by optimizing their properties.

Methods

Kaempferol and quercetin peracetate were prepared using acetic anhydride in pyridine. By performing regioselective synthesis, 7-O-paramethylbenzyl as an electron-donating group and 7-O-paranitrobenzyl as an electron-withdrawing group were added to quercetin, and, then, the synthesis of Sb(V) kaempferol and quercetin derivative complexes were performed using SbCl₅ solution in glacial acetic acid. The structures were confirmed by UV, ESI mass, IR, 1H-, and ¹³C-NMR spectral data, and the Stoichiometry of the ligand-metal complex by the mole ratio method. Computational molecular modeling was conducted using the Gaussian program.

Results

The structures were confirmed based on the results from UV, nuclear magnetic resonance (NMR), and electrospray ionization (ESI) mass analyses (3-12). Among the produced compounds, 11 and 12 as newly described, and other compounds as pre-defined compounds were identified. According to the results from biological test, kaempferol triacetate with more lipophilicity showed the highest anti-promastigote activity with an IC₅₀ value of 14.93 ± 2.21 µM. As for anti-amastigote activity, despite the differences, all antimony complexes showed anti-amastigote effects in vitro with IC₅₀ values of 0.52 to 14.50 µM.

Conclusions

All flavonol Sb(V) complexes showed higher activity compared to meglumine antimonate in anti-amastigote effect. Inside the host macrophages, by breaking down the complex into antimony and quercetin or kaempferol analogs, the observed antiparasitic effects may have been related to both Sb(V)/Sb(III) conversion and flavonoid antileishmanial activities.

Structural Design, Synthesis and Antioxidant, Antileishmania, Anti-Inflammatory and Anticancer Activities of a Novel Quercetin Acetylated Derivative

Quercetin (Q) is a bioflavonoid with biological potential; however, poor solubility in water, extensive enzymatic metabolism and a reduced bioavailability limit its biopharmacological use. The aim of this study was to perform structural modification in Q by acetylation, thus, obtaining the quercetin pentaacetate (Q5) analogue, in order to investigate the biological potentials (antioxidant, antileishmania, anti-inflammatory and cytotoxicity activities) in cell cultures. Q5 was characterized by FTIR, ¹H and ¹³C NMR spectra. The antioxidant potential was evaluated against the radical ABTS^•+. The anti-inflammatory potential was evaluated by measuring the pro-inflammatory cytokine tumor necrosis factor (TNF) and the production of nitric oxide (NO) in peritoneal macrophages from BALB/c mice. Cytotoxicity tests were performed using the AlamarBlue method in cancer cells HepG2 (human hepatocarcinoma), HL-60 (promyelocytic leukemia) and MCR-5 (healthy human lung fibroblasts) as well as the MTT method for C6 cell cultures (rat glioma). Q and Q5 showed antioxidant activity of 29% and 18%, respectively, which is justified by the replacement of hydroxyls by acetyl groups. Q and Q5 showed concentration-dependent reductions in NO and TNF production (p < 0.05); Q and Q5 showed higher activity at concentrations > 40µM when compared to dexamethasone (20 µM). For the HL-60 lineage, Q5 demonstrated selectivity, inducing death in cancer cells, when compared to the healthy cell line MRC-5 (IC₅₀ > 80 µM). Finally, the cytotoxic superiority of Q5 was verified (IC₅₀ = 11 µM), which, at 50 µM for 24 h, induced changes in the morphology of C6 glioma cells characterized by a round body shape (not yet reported in the literature). The analogue Q5 had potential biological effects and may be promising for further investigations against other cell cultures, particularly neural ones.