Synthesis and bioactivity of novel amino-pyrazolopyridines

Here we describe the synthesis and biological activity of novel amino-pyrazolopyridines with anti-NF-κB and pro-apoptotic potential. α-Methylene ketones were used as a starting point for synthesis of amino-pyrazolopyridine 3. The alkylidene malononitriles 1 were obtained by the Knoevenagel reaction of ketones with malononitriles. Vilsmeier-Haack reaction allowed direct access to 2-chloro-3-cyanopyridines 2. Those products, by refluxing with hydrazine hydrate, allowed cyclization to amino-pyrazolopyridines 3a-g, which were not previously described in the literature. Bioactivity results indicated that amino-pyrazolopyridines 3a, 3b and 3g induced apoptotic cell death in K562 cancer cells with an IC₅₀ of 36.5 ± 3.9 μM, 27.6 ± 4.5 μM and 35.0 ± 2.3 μM, respectively, after 72 h. In addition, compounds 3a, 3b and 3g exerted NF-κB inhibition activity with an IC₅₀ of 4.7 ± 1.6 μM, 6.9 ± 1.9 μM and 39.8 ± 3.9 μM, respectively, after 8 h in K562 cells activated with TNFα. Compounds 3b and 3g showed interesting differential toxicity as viability of peripheral blood mononuclear cells (PBMCs) from healthy donors remained largely unaffected by this treatment.