New 3‐Substituted‐2‐(4‐hydroxyanilino)pyridine Derivatives: Synthesis, Antitumor Activity, and Tubulin Polymerization Inhibition

A series of new pyridine derivatives 4a–c, 5a–d, 6a–d, 7a–f, and 8a–f structurally related to ABT-751 were synthesized and characterized by spectroscopic means and elemental analysis. All the synthesized compounds were tested for their cytotoxic activity in vitro against the HCT-116 and HepG-2 cancer cell lines using the MTT assay. The results showed that compound 8d has higher cytotoxic activity than the reference antimitotic agent colchicine, against both tested cell lines, with IC50 = 0.52 and 1.40 μM, respectively. The three most active compounds, 5d, 8b, and 8d, were further screened in vitro for inhibition of tubulin and showed remarkable results in comparison to colchicine.