Flavones as isosteres of 4(1H)-quinolones: discovery of ligand efficient and dual stage antimalarial lead compounds

Photocatalytic acceptorless dehydrogenation of flavanones by cationic Eosin Y as a bifunctional catalyst

We report the first example of photocatalytic acceptorless dehydrogenation using cationic Eosin Y as a bifunctional photocatalyst, without metal catalysts or HAT reagents. Under Bayesian optimized conditions, a wide range of flavones were synthesized in moderate to excellent yields, many of which were reported with biological activities. Mechanistic studies suggest that flavones likely form through two HAT processes, with hydrogen release occurring via photoredox.

Application of Quinoline Ring in Structural Modification of Natural Products

Natural compounds are rich in pharmacological properties that are a hot topic in pharmaceutical research. The quinoline ring plays important roles in many biological processes in heterocycles. Many pharmacological compounds, including saquinavir and chloroquine, have been marketed as quinoline molecules with good anti-viral and anti-parasitic properties. Therefore, in this review, we summarize the medicinal chemistry of quinoline-modified natural product quinoline derivatives that were developed by several research teams in the past 10 years and find that these compounds have inhibitory effects on bacteria, viruses, parasites, inflammation, cancer, Alzheimer's disease, and others.

Amino-Acid-Conjugated Natural Compounds: Aims, Designs and Results

Protein is one of the essential macronutrients required by all living things. The breakdown of protein produces monomers known as amino acids. The concept of conjugating natural compounds with amino acids for therapeutic applications emerged from the fact that amino acids are important building blocks of life and are abundantly available; thus, a greater shift can result in structural modification, since amino acids contain a variety of sidechains. This review discusses the data available on amino acid–natural compound conjugates that were reported with respect to their backgrounds, the synthetic approach and their bioactivity. Several amino acid–natural compound conjugates have shown enhanced pharmacokinetic characteristics, including absorption and distribution properties, reduced toxicity and increased physiological effects. This approach could offer a potentially effective system of drug discovery that can enable the development of pharmacologically active and pharmacokinetically acceptable molecules.

Biological Evaluation and Mechanistic Studies of Quinolin-(1H)-Imines as a New Chemotype against Leishmaniasis

Leishmaniasis is one of the most challenging neglected tropical diseases and remains a global threat to public health. Currently available therapies for leishmaniases present significant drawbacks and are rendered increasingly inefficient due to parasite resistance, making the need for more effective, safer, and less expensive drugs an urgent one. In our efforts to identify novel chemical scaffolds for the development of antileishmanial agents, we have screened in-house antiplasmodial libraries against axenic and intracellular forms of Leishmania infantum, Leishmania amazonensis, and Leishmania major. Several of the screened compounds showed half-maximal inhibitory concentrations (IC₅₀s) against intracellular L. infantum parasites in the submicromolar range (compounds 1h, IC₅₀ = 0.9 μM, and 1n, IC₅₀ = 0.7 μM) and selectivity indexes of 11 and 9.7, respectively. Compounds also displayed activity against L. amazonensis and L. major parasites, albeit in the low micromolar range. Mechanistic studies revealed that compound 1n efficiently inhibits oxygen consumption and significantly decreases the mitochondrial membrane potential in L. infantum axenic amastigotes, suggesting that this chemotype acts, at least in part, by interfering with mitochondrial function. Structure-activity analysis suggests that compound 1n is a promising antileishmanial lead and emphasizes the potential of the quinoline-(1H)-imine chemotype for the future development of new antileishmanial agents.

A novel one-pot synthesis of flavones

In this paper, a one-pot facile route for the BiCl₃/RuCl₃-mediated synthesis of functionalized flavones is described, including: (i) intermolecular ortho-acylation of substituted phenols with cinnamoyl chlorides, and (ii) intramolecular cyclodehydrogenation of the resulting o-hydroxychalcones. The reaction conditions are discussed herein.

A one-pot facile route for the BiCl₃/RuCl₃-mediated synthesis of functionalized flavones is described, including: (i) ortho-acylation of phenols with cinnamoyl chlorides, and (ii) cyclodehydrogenation of the resulting o-hydroxychalcones.

Flavonoids as efficient scaffolds: Recent trends for malaria, leishmaniasis, Chagas disease, and dengue

Endemic in 149 tropical and subtropical countries, neglected tropical diseases (NTDs) affect more than 1 billion people annually with over 500,000 deaths. Among the NTDs, some of the most severe consist of leishmaniasis, Chagas disease, and dengue. The impact of the combined NTDs closely rivals that of malaria. According to the World Health Organization, 216 million cases of malaria were reported in 2016 with 445,000 deaths. Current treatment options are associated with various limitations including widespread drug resistance, severe adverse effects, lengthy treatment duration, unfavorable toxicity profiles, and complicated drug administration procedures. Flavonoids are a class of compounds that has been the subject of considerable scientific interest. New developments of flavonoids have made promising advances for the potential treatment of malaria, leishmaniasis, Chagas disease, and dengue, with less toxicity, high efficacy, and improved bioavailability. This review summarizes the current standings of the use of flavonoids to treat malaria and neglected diseases such as leishmaniasis, Chagas disease, and dengue. Natural and synthetic flavonoids are leading compounds that can be used for developing antiprotozoal and antiviral agents. However, detailed studies on toxicity, pharmacokinetics, and mechanisms of action of these compounds are required to confirm the in vitro pharmacological claims of flavonoids for pharmaceutical applications. HIGHLIGHTS: In the current review, we have tried to compile recent discoveries on natural and synthetic flavonoids as well as their implication in the treatment of malaria, leishmaniasis, Chagas disease, and dengue. A total of 373 (220 natural and 153 synthetic) flavonoids have been evaluated for antimalarial, antileishmanial, antichagasic, and antidengue activities. Most of these flavonoids showed promising results against the above diseases. Reports on molecular modeling of flavonoid compounds to the disease target indicated encouraging results. Flavonoids can be prospected as potential leads for drug development; however, more rigorously designed studies on toxicity and pharmacokinetics, as well as the quantitative structure-activity relationship studies of these compounds, need to be addressed.

A Strength-Weaknesses-Opportunities-Threats (SWOT) Analysis of Cheminformatics in Natural Product Research

Cheminformatics-based techniques, such as molecular modeling, docking, virtual screening, and machine learning, are well accepted for their usefulness in drug discovery and development of therapeutically relevant small molecules. Although delayed by several decades, their application in natural product research has led to outstanding findings. Combining information obtained from different sources, i.e., virtual predictions, traditional medicine, structural, biochemical, and biological data, and handling big data effectively will open up new possibilities, but also challenges in the future. Strategies and examples will be presented on how to integrate cheminformatics in pharmacognostic workflows to benefit from these two highly complementary disciplines toward streamlining experimental efforts. While considering their limits and pitfalls and by exploiting their potential, computer-aided strategies should successfully guide future studies and thereby augment our knowledge of bioactive natural lead structures.

Antibiotics in malaria therapy: which antibiotics except tetracyclines and macrolides may be used against malaria?

Malaria, a parasite vector-borne disease, is one of the most significant health threats in tropical regions, despite the availability of individual chemoprophylaxis. Malaria chemoprophylaxis and chemotherapy remain a major area of research, and new drug molecules are constantly being developed before drug-resistant parasites strains emerge. The use of anti-malarial drugs is challenged by contra-indications, the level of resistance of Plasmodium falciparum in endemic areas, clinical tolerance and financial cost. New therapeutic approaches are currently needed to fight against this disease. Some antibiotics that have shown potential effects on malaria parasite have been recently studied in vitro or in vivo intensively. Two families, tetracyclines and macrolides and their derivatives have been particularly studied in recent years. However, other less well-known have been tested or are being used for malaria treatment. Some of these belong to older families, such as quinolones, co-trimoxazole or fusidic acid, while others are new drug molecules such as tigecycline. These emerging antibiotics could be used to prevent malaria in the future. In this review, the authors overview the use of antibiotics for malaria treatment.

Anticoccidial efficacy of naringenin and a grapefruit peel extract in growing lambs naturally-infected with Eimeria spp

The current study aimed to determine the anti-Eimeria efficacy of an extract of grapefruit peels (GF) and commercial naringenin (NAR) in naturally-infected lambs, as well as the influence of these flavonoids on the oxidative status during ovine coccidiosis. Pharmacokinetic profiles were also determined. Extracts were administered per os to Eimeria naturally infected growing lambs during 90 consecutive days. The commercial anticoccidial drug toltrazuril (TTZ) was included in this trial as a standard. Twenty-four lambs were divided into four groups: NAR, lambs given a daily dose of 5mg of a commercial naringenin extract of 98% higher purity per kg body weight; GF, lambs that recived a daily dose of 5mg of ethanolic extract of grapefruit peels per kg body weight; TTZ, lambs treated with 20mg of toltrazuril/kg body weight on days 0 and 15 of the experiment; and CTRL, untreated lambs that received daily dose of 30ml of water. Daily doses of GF and NAR were dissolved in 30ml of water and orally given to animals; whereas toltrazuril was administered as a single dose of an undiluted suspension to lambs of the TTZ group. The CTRL group received 30ml of water; as well as the TTZ group for the period after the single dose administration. Fecal and serum samples were collected from all lambs. Anticoccidial efficacy was estimated by coprological techniques. Generation of nitric oxide levels and the antioxidant capacity of the experimental compounds were determined by the Griess and ABTS assays, respectively. The pharmacokinetic parameters of NAR and the GF extract were obtained. On day 30 post-ingestion, anticoccidial efficacy was 91.76% (NAR) and 89.65% (GF); whereas 99.63% of efficacy was achieved with TTZ 15days after treatment. NAR, GF and TTZ significantly reduced oxidative stress in infected animals. The mean daily weight gain for each group was 122g (NAR), 122g (GF), 143g (TTZ) and 98g (CTRL). Following the oral administration of NAR and GF, values in plasma approached maximum concentrations within 2.1 to 2.5h. In conclusion, the administration of NAR and the GF extract reduced Eimeria oocyst output, oxidative stress and promoted higher mean daily weight gains in infected lambs.

Reinvestigating Old Pharmacophores: Are 4-Aminoquinolines and Tetraoxanes Potential Two-Stage Antimalarials?

The syntheses and antiplasmodial activities of various substituted aminoquinolines coupled to an adamantane carrier are described. The compounds exhibited pronounced in vitro and in vivo activity against Plasmodium berghei in the Thompson test. Tethering a fluorine atom to the aminoquinoline C(3) position afforded fluoroaminoquinolines that act as intrahepatocytic parasite inhibitors, with compound 25 having an IC50 = 0.31 μM and reducing the liver load in mice by up to 92% at 80 mg/kg dose. Screening our peroxides as inhibitors of liver stage infection revealed that the tetraoxane pharmacophore itself is also an excellent liver stage P. berghei inhibitor (78: IC50 = 0.33 μM). Up to 91% reduction of the parasite liver load in mice was achieved at 100 mg/kg. Examination of tetraoxane 78 against the transgenic 3D7 strain expressing luciferase under a gametocyte-specific promoter revealed its activity against stage IV-V Plasmodium falciparum gametocytes (IC50 = 1.16 ± 0.37 μM). To the best of our knowledge, compounds 25 and 78 are the first examples of either an 4-aminoquinoline or a tetraoxane liver stage inhibitors.

Investigation of Ugi-4CC derived 1H-tetrazol-5-yl-(aryl) methyl piperazinyl-6-fluoro-4-oxo-1,4-dihydroquinoline-3-carboxylic acid: synthesis, biology and 3D-QSAR analysis

Novel series of 7-piperazinylquinolones with tetrazole derivatives were synthesized and evaluated for their antibacterial activity against various strains of Staphylococcus aureus. All the synthesized compounds showed significant in vitro antibacterial activity against Gram-positive bacteria whereas some compounds displayed moderate activity against Gram-negative bacteria. Among all the synthesized compounds, compounds (6a-c, 6e-g, 6i-k, 6m, 6'f and 6'm) were found to be more effective with MIC ranging from (0.78-3.12 μg/mL) against S. aureus (ATCC-29213) than the control; ciprofloxacin (MIC = 25 μg/mL). Moreover, these analogues displayed no toxicity up to MIC = 0.39 μg/mL against mammalian cell line L-929. Furthermore, to correlate the biological activities of synthesized compounds with their 3D conformation, we attempted 3D-QSAR study.