Design, synthesis, crystal structure and in vitro cytotoxic properties of a novel Schiff base derived from indole and biphenyl

A novel and potentially active dihydroorotate dehydrogenase (DHODH) inhibitor, namely 3-({(E)-[(E)-1-(biphenyl-4-yl)ethylidene]hydrazinylidene}methyl)-1H-indole (BEHI) acetonitrile disolvate, C₂₃H₁₉N₃·2CH₃CN, has been designed and synthesized. The structure of BEHI was characterized by elemental analysis, Q-TOF (quadrupole time-of-flight) MS, NMR, UV-Vis and single-crystal X-ray diffraction. The antitumour activity of the target molecule was evaluated by the MTT method. Results indicated that BEHI exhibited rather potent cytotoxic activity against human A549 (IC₅₀ = 20.5 µM) and mouse breast 4T₁ (IC₅₀ = 18.5 µM) cancer cell lines. Meanwhile, to rationalize its potencies in the target, BEHI was docked into DHODH and the interactions with the active site residues were analyzed. Single-crystal structure analysis indicated that hydrogen bonds are present only between BEHI and acetonitrile solvent molecules in the asymmetric unit. The interplay of weak π-π stacking and weak C(N)-H...π interactions between neighbouring BEHI molecules play crucial roles in the formation of the final supramolecular frameworks.