An efficient microwave-assisted Suzuki cross-coupling reaction of imidazo[1,2-a]pyridines in aqueous medium

8-Aryl-6-chloro-3-nitro-2-(phenylsulfonylmethyl)imidazo[1,2-a]pyridines as potent antitrypanosomatid molecules bioactivated by type 1 nitroreductases

Based on a previously identified antileishmanial 6,8-dibromo-3-nitroimidazo[1,2-a]pyridine derivative, a Suzuki-Miyaura coupling reaction at position 8 of the scaffold was studied and optimized from a 8-bromo-6-chloro-3-nitroimidazo[1,2-a]pyridine substrate. Twenty-one original derivatives were prepared, screened in vitro for activity against L. infantum axenic amastigotes and T. brucei brucei trypomastigotes and evaluated for their cytotoxicity on the HepG2 human cell line. Thus, 7 antileishmanial hit compounds were identified, displaying IC50 values in the 1.1-3 μM range. Compounds 13 and 23, the 2 most selective molecules (SI = >18 or >17) were additionally tested on both the promastigote and intramacrophage amastigote stages of L. donovani. The two molecules presented a good activity (IC50 = 1.2-1.3 μM) on the promastigote stage but only molecule 23, bearing a 4-pyridinyl substituent at position 8, was active on the intracellular amastigote stage, with a good IC50 value (2.3 μM), slightly lower than the one of miltefosine (IC50 = 4.3 μM). The antiparasitic screening also revealed 8 antitrypanosomal hit compounds, including 14 and 20, 2 very active (IC50 = 0.04-0.16 μM) and selective (SI = >313 to 550) molecules toward T. brucei brucei, in comparison with drug-candidate fexinidazole (IC50 = 0.6 & SI > 333) or reference drugs suramin and eflornithine (respective IC50 = 0.03 and 13.3 μM). Introducing an aryl moiety at position 8 of the scaffold quite significantly increased the antitrypanosomal activity of the pharmacophore. Antikinetoplastid molecules 13, 14, 20 and 23 were assessed for bioactivation by parasitic nitroreductases (either in L. donovani or in T. brucei brucei), using genetically modified parasite strains that over-express NTRs: all these molecules are substrates of type 1 nitroreductases (NTR1), such as those that are responsible for the bioactivation of fexinidazole. Reduction potentials measured for these 4 hit compounds were higher than that of fexinidazole (-0.83 V), ranging from -0.70 to -0.64 V.

Switch in Site of Inhibition: A Strategy for Structure-Based Discovery of Human Topoisomerase IIα Catalytic Inhibitors

A study of structure-based modulation of known ligands of hTopoIIα, an important enzyme involved in DNA processes, coupled with synthesis and in vitro assays led to the establishment of a strategy of rational switch in mode of inhibition of the enzyme's catalytic cycle. 6-Arylated derivatives of known imidazopyridine ligands were found to be selective inhibitors of hTopoIIα, while not showing TopoI inhibition and DNA binding. Interestingly, while the parent imidazopyridines acted as ATP-competitive inhibitors, arylated derivatives inhibited DNA cleavage similar to merbarone, indicating a switch in mode of inhibition from ATP-hydrolysis to the DNA-cleavage stage of catalytic cycle of the enzyme. The 6-aryl-imidazopyridines were relatively more cytotoxic than etoposide in cancer cells and less toxic to normal cells. Such unprecedented strategy will encourage research on "choice-based change" in target-specific mode of action for rapid drug discovery.

Aqueous microwave chemistry: a clean and green synthetic tool for rapid drug discovery

The development of "Greener Organic Chemistry" is due to the recognition that environmentally friendly products and processes will be economical in the long term as they circumvent the need for treating 'end-of-the-pipe' pollutants and by-products generated by conventional synthesis. The fundamentals and significant outcomes of microwave-assisted organic synthesis in aqueous medium are summarized in this tutorial review, which have resulted in the development of relatively sustainable and environmentally benign protocols for the synthesis of drugs and fine chemicals.