Object-oriented synthetic approach toward angular and linear fused pyrazoloquinolines of biological importance with InCl₃ catalyst

A simple and short approach for the synthesis of pyrazolo[3,4-b]quinoline (3a-3p) and pyrazolo[4,3-c]quinoline (6a-6 h) using various Lewis acid catalysts was developed. InCl₃ was found to be more effective in providing greater yield of products compared to Yb(OTf)₃, Sc(OTf)₃, SnCl₄, AlCl₃, TiCl₄, ZnCl₂, FeCl₃, and BF₃ · Et₂O. Moreover, a comparison of conventional and microwave methods has revealed that the latter method is more efficient compared to former one. Structures were confirmed by Fourier transform infrared, mass spectrometry, ¹H and ¹³C NMR, X-ray crystallography, and elemental analyses. All of the synthesized compounds were evaluated for α-glucosidase inhibitory activity. Compounds 3a, 3p, 3i, 3 h, 3k, 3o, and 3 g exhibited anti α-glucosidase inhibitory activity with IC₅₀ values of 57.5, 60.3, 65.9, 71.9, 80.8, 123.7, and 126.4 μM, respectively, which is quite comparable to the standard drug acarbose (IC₅₀ = 115.8 μM).