Synthesis, structure and antiproliferative and optical activities of two new biphenyl-derived Schiff bases.

Two novel Schiff bases derived from indole and biphenyl have been designed and synthesized, namely 3-((E)-{(E)-[1-(biphenyl-4-yl)ethylidene]hydrazinylidene}methyl)-1-methyl-1H-indole (3-BEHMI) acetonitrile monosolvate, CHN·CHCN, and 3-((E)-{(E)-[1-(biphenyl-4-yl)ethylidene]hydrazinylidene}methyl)-1-methyl-1H-indole (3-BEHEI) acetonitrile monosolvate, CHN·CHCN. Their structures were characterized by elemental analysis, quadrupole time-of-flight MS, NMR and UV-Vis spectroscopy. The single-crystal packing structure of 3-BEHMI is largely dominated by C-H...π interactions and weak van der Waals interactions. The in vitro cytotoxicity of the two title compounds have been evaluated against two tumour cell lines (A549 human lung cancer and 4T mouse breast cancer) and two normal cell lines (MRC-5 normal lung cells and NIH 3T3 fibroblasts) by MTT assay. The results indicate that 3-BEHEI exhibits a slightly weaker antiproliferative capability (IC = ∼50 µM) than the previously reported similar Schiff base 3-BEHI (IC = ∼20 µM). This is in line with docking results. 3-BEHMI demonstrates a weak cytotoxic activity, with IC values around 110 µM, which disagrees with its docking results. Overall, the tested compounds manifest relevant cytotoxicities on the selected cancer cell lines and normal cell lines. The UV-Vis and fluorescence spectra were recorded and reproduced through the TD-DFT method with four types of hybrid density functionals, including B3LYP, M062X, PBE1PBE and WB97XD.