Palladium-catalysed synthesis of arylnaphthoquinones as antiprotozoal and antimycobacterial agents

Selective electrophilic cyclization of ortho-carbonylarylacetylenols for the synthesis of cyclopenta[a]naphthalenol and 2-phenylnaphthalen-1-ol analogs

This work demonstrates a new method for the synthesis of cyclopenta[a]naphthalenol and 2-phenylnaphthalen-1-ol analogs via selective cyclization. ortho-Alkynylarylkenones were employed as the common substrates that could be prepared by Sonogashira coupling between 2-haloarylacetophenone and pent-4-yn-1-ol derivatives. These precursors were used without purification to construct 2-phenylnaphthalen-1-ol intermediates by treating with (+)-CSA under heating conditions. Selective cyclization occurred when the reaction was conducted in methyl trimethylacetate solvent which predominantly produced the 2-phenylnaphthalen-1-ol product through 6-endo-dig cyclization without elimination or the formation of cyclopenta[a]naphthalenol via shutting down the 5-exo-dig mode of cyclization. Switching the acid from a Brønsted acid to Bi(OTf)3 led to smooth reactions, providing the cyclopenta[a]naphthalenol products in moderate to good yields. Moreover, we also demonstrated the utilization of 2-phenylnaphthalen-1-ol to prepare naphthoquinone, which is an important core structure of bioactive and natural product compounds.

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.

Efficient Oxidative Dearomatisations of Substituted Phenols Using Hypervalent Iodine (III) Reagents and Antiprotozoal Evaluation of the Resulting Cyclohexadienones against T. b. rhodesiense and P. falciparum Strain NF54

Quinones and quinols are secondary metabolites of higher plants that are associated with many biological activities. The oxidative dearomatization of phenols induced by hypervalent iodine(III) reagents has proven to be a very useful synthetic approach for the preparation of these compounds, which are also widely used in organic synthesis and medicinal chemistry. Starting from several substituted phenols and naphthols, a series of cyclohexadienone and naphthoquinone derivatives were synthesized using different hypervalent iodine(III) reagents and evaluated for their in vitro antiprotozoal activity. Antiprotozoal activity was assessed against Plasmodium falciparum NF54 and Trypanosoma brucei rhodesiense STIB900. Cytotoxicity of all compounds towards L6 cells was evaluated and the respective selectivity indices (SI) were calculated. We found that benzyl naphthoquinone 5c was the most active and selective molecule against T. brucei rhodesiense (IC₅₀ = 0.08 μM, SI = 275). Furthermore, the antiprotozoal assays revealed no specific effects. In addition, some key physicochemical parameters of the synthesised compounds were calculated.

Novel Formula of Antiprotozoal Mixtures

Antimicrobial resistance (AMR) is becoming more common in both bacteria and pathogenic protozoa. Therefore, new solutions are being sought as alternatives to currently used agents. There are many new ideas and solutions, especially compounds of natural origin, including essential oils. In the present study, the antiprotozoal activity of a mixture of essential oils (eucalyptus, lavender, cedar and tea tree), organic acids (acetic acid, propionic acid and lactic acid) and metal ions (Cu, Zn, Mn) were tested. As a model, protozoans were selected: Euglena gracilis, Gregarina blattarum, Amoeba proteus, Paramecium caudatum, Pentatrichomonas hominis. The tested concentrations of mixtures were in the range of 0.001-1.5%. The analyses show unexpected, very strong protozoicidal activity of combinations, presenting the synergy of compounds via determination of LD50 and LD100 values. Obtained mixtures showed significantly higher activity against protozoans, compared to chloramphenicol and metronidazole. Most of the analyzed samples show high antiprotozoal activity at very low concentration, in the range of 0.001-0.009%. The most effective combinations for all analyzed protozoans were the cedar essential oil and tea tree essential oil with a mixture of acids and manganese or zinc ions. Innovative combinations of essential oils, organic acids and metal ions are characterized by very high antiprotozoal activity at low doses, which, after further investigation, can be applicable for control of protozoan pathogens.

The seven-step, one-pot regioselective synthesis of biologically important 3-aryllawsones: scope and applications

3-Aryllawsones are well known for their wide range of applications in medicinal chemistry, but their synthesis has always remained challenging as no comprehensive protocol has been outlined to date. Owing to their structural importance, we synthesized various 3-aryllawsones with high regioselectivity from simple lawsone and aldehydes in a seven-step double-cascade one-pot reaction through the combination of organocatalytic Ramachary reductive coupling and Hooker oxidation reactions. The commercial availability of the starting materials, diverse substrate scope, possibility of a one- or two-pot approach, regioselectivity of alkyl transfer (with mechanistic proof provided via X-ray crystal structure analysis), and numerous medicinal applications of 3-aryllawsones are the key attractions of this work.