Provided herein are synthetic derivatives of combretastatin A-4 in which the aromatic rings are locked into a non-isomerisable active conformation, thus resulting in improved, stable compounds. The novel compounds are structurally related to combretastatin A-4 (CA-4) and lock the rings into the known active conformation by means of a four membered nitrogen containing heterocyclic ring, such as a beta-lactam ring, incorporated into the standard CA-4 structure. The compounds exhibit potent anti-cancer activity.
