N-Phenyl-N′-(2-chloroethyl)urea analogues of combretastatin A-4: Is the N-phenyl-N′-(2-chloroethyl)urea pharmacophore mimicking the trimethoxy phenyl moiety?

A series of novel N-phenyl-N′-(2-chloroethyl)urea derivatives potentially mimicking the structure of combretastatin A-4 were synthesized and tested for their cell growth inhibition and their binding to the colchicine-binding site of β-tubulin. Compounds 2a, 3a, and 3b were found to inhibit cell growth at the micromolar level on four human tumor cell lines. Flow cytometric analysis indicates that the new compounds act as antimitotics and arrest the cell cycle in G2/M phase. Covalent binding of 2a, 3a, and 3b to the colchicine-binding site of β-tubulin was confirmed also using SDS–PAGE and competition assays.