Antitumor agents. Part 215:: Antitubulin effects of cytotoxic B-Ring modified allocolchicinoids

N-Acetylcolchinol methyl ether 1 served as the starting material to prepare the chloroacetamide (3) and epoxide (5) analogues. Both 3 and 5 were potent inhibitors of tubulin polymerization in vitro. Compound 3 was also 4-fold more cytotoxic than colchicine against the 1A9 tumor cell line and showed a unique cross-resistance profile.