Synthesis and biological evaluation of 4,6-diphenyl-2-(1H-pyrrol-1-yl)nicotinonitrile analogues of crolibulin and combretastatin A-4

A series of novel 4,6-diphenyl-2-(1H-pyrrol-1-yl)nicotinonitrile analogues of crolibulin and combretastatin A-4 (CA-4) were discovered using a 2-(1H-pyrrol-1-yl)pyridine ring as link-bridge to retain the cis-orientations of A-ring and B-ring. All the target compounds were synthesized and evaluated for their antiproliferative activity against five human Cancer cell lines. Compounds 6a-d exhibited superior potency, with IC₅₀ values at nanomolar levels. In particular, compound 6a exhibited antitumor activity similar to or higher than crolibulin and CA-4. Moreover, the inhibition of microtubule assembly by compound 6a was comparable to that by CA-4. A molecular modeling study of compound 6a was performed to elucidate its binding mode at the colchicine binding site in the tubulin dimer, which also provided a basis for further structure-guided design of novel colchicine binding site inhibitors.