Based on the pharmacophoric features of the natural product combretastatin A-4 (CA-4) and its synthetic analogues that inhibit tubulin polymerization, a series of novel 2-aryl-3-arylamino-imidazo-pyridines/pyrazines as potential antitubulin anticancer agents were designed. They were synthesized by a one-pot method involving preparation of isocyanides from the anilines via formylation and subsequent dehydration followed by their reactions with heterocyclic-2-amidines and aldehydes. Compounds 1, 2,14, and 15 were found to exhibit significant tubulin polymerization inhibition and disruption of tubulin– microtubule dynamics similar to that of CA-4. They showed potent anticancer activities in kidney, breastand cervical cancer cell lines, and relatively low toxicity to normal cells, compared to CA-4. Thecompounds induced DNA and chromosomal damage, and apoptosis via cell cycle arrest in the G2/Mphase.
The molecular docking and molecular dynamics (MD) simulation studies revealed that disruptionof microtubule dynamics might occur by interaction of the compounds at the colchicine binding site ofthe a,b-tubulin heterodimer interface, similar to that of CA-4. Molecular modelling analysis showed thattwo of the three methoxy groups at ring A of all four potent compounds (1, 2, 14, and 15) were involvedin bifurcated hydrogen bonding with Cysb241, an important molecular recognition interaction to showtubulin inhibitory activity. In comparison to CA-4, the bridging NH and the imidazo-pyridine/pyrazinemoieties in the title compounds provide flexibility for attaining the required dihedral relationship of twoaryls and additional pharmacophoric features required for the interaction with the key residues of thecolchicine binding site.