The [3+2] cycloaddition of a variety of diazo compounds with o-(trimethylsilyl)aryl triflates in the presence of CsF or TBAF at room temperature provides a very direct, efficient approach to a wide range of potentially biologically and pharmaceutically interesting substituted indazoles in good to excellent yields under mild reaction conditions. Simple diazomethane derivatives afford N-unsubstituted indazoles or 1-arylated indazoles, depending upon the stoichiometry of the reagents and the reaction conditions, while dicarbonyl-containing diazo compounds undergo carbonyl migration to afford 1-acyl or 1-alkoxycarbonyl indazoles selectively.

Leishmaniasis is a major infectious disease with hundreds of thousands of new cases and over 20,000 deaths each year. The current drugs to treat this life-threatening infection have several drawbacks such as toxicity and long treatment regimens. A library of 1.8 million compounds, from which the hits reported here are publicly available, was screened against Leishmania infantum as part of an optimization program; a compound was found with a 2-aminobenzimidazole functionality presenting moderate potency, low metabolic stability and high lipophilicity. Several rounds of synthesis were performed to incorporate chemical groups capable of reducing lipophilicity and clearance, leading to the identification of compounds that are active against different parasite strains and have improved in vitro properties. As a result of this optimization program, a group of compounds was further tested in anticipation of in vivo evaluation. In vivo tests were carried out with compounds 29 (L. infantum IC50: 4.1 μM) and 39 (L. infantum IC50: 0.5 μM) in an acute L. infantum VL mouse model, which showed problems of poor exposure and lack of efficacy, despite the good in vitro potency.

The Fujiwara hydroarylation of alkynes was reinvestigated using the addition of indole to methyl or ethyl phenylpropiolate catalyzed by Pd(OAc)2 as a model reaction. Reactions were monitored by both 1H NMR spectroscopy and electrospray ionization mass spectrometry (ESI/MS), and also through reactions carried out in the gas phase using MS/MS experiments. Contrary to the original suggestion for exclusive heteroarene activation, the data supports the coexistence of both heteroarene activation (C–H activation) and alkyne activation (Friedel–Crafts‐type pathway). Under the reaction conditions used in this work, intermediates for both mechanisms were detected by NMR spectroscopy and MS, but alkyne activation seems to be predominant according to 1H NMR spectroscopic studies and theoretical predictions. Alkyne activation is promoted by the coordination of an electrophilic palladium species to the C–C triple bond, followed by nucleophilic attack of the heteroaryl counterpart. Two previously undetected equilibria in this reaction involving the vinylpalladium intermediates and the final products were also found to be critical to the stereoselectivity of the reaction.

Combination therapy drugs are considered a fundamental way to control malaria as it mimimizes the risk of emergence of resistance to the individual partner drugs. Consequently, this type of therapy constitutes a driving force for the discovery of new drugs with different modes of action, since this will provide options for combining different drugs to achieve the optimum antimalarial treatment. In this context, a 2,3,8-trisubstitued quinoline compound was found in a high throughput screen (HTS) to show an excellent inhibition of P. falciparum NF54 (IC50 = 22 nM) and low cytotoxicity. We performed a detailed evaluation of the substituents to improve the metabolic stability and solubility liabilities of the original hit and identified derivatives with enhanced physicochemical and/or PK properties and that maintained biological activity. However the high potency was not retained on testing against drug resistant plasmodium strains.

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