Object-oriented synthetic approach toward angular and linear fused pyrazoloquinolines of biological importance with InCl<sub>3</sub> catalyst

<p>A simple and short approach for the synthesis of pyrazolo[3,4-b]quinoline (<b>3a</b>–<b>3p</b>) and pyrazolo[4,3-c]quinoline (<b>6a</b>–<b>6 h</b>) using various Lewis acid catalysts was developed. InCl<sub>3</sub> was found to be more effective in providing greater yield of products compared to Yb(OTf)<sub>3</sub>, Sc(OTf)<sub>3</sub>, SnCl<sub>4</sub>, AlCl<sub>3</sub>, TiCl<sub>4</sub>, ZnCl<sub>2</sub>, FeCl<sub>3</sub>, and BF<sub>3</sub> · Et<sub>2</sub>O. 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, <sup>1</sup>H and <sup>13</sup>C NMR, X-ray crystallography, and elemental analyses. All of the synthesized compounds were evaluated for α-glucosidase inhibitory activity. Compounds <b>3a, 3p, 3i, 3 h, 3k, 3o,</b> and <b>3 g</b> exhibited anti α-glucosidase inhibitory activity with IC<sub>50</sub> 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 (IC<sub>50</sub> = 115.8 µM).</p>