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 (3a3p) and pyrazolo[4,3-c]quinoline (6a6 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).