Practical and Green Synthesis of Combretastatin A-4 and Its Prodrug CA4P Using Renewable Biomass-Based Starting Materials

A practical and green protocol for the synthesis of vascular disrupting agent combretastatin A-4 (CA4) and its water soluble prodrug CA4P is described. Starting from the biomass-based compound anethole, which is abundantly and sustainably available from Chinese star anise (Illicium verum Hook. f.), the key intermediate 3-hydroxy-4-methoxyphenylacetic acid can be obtained within five steps. Perkin condensation between this acid and another naturally derived compound 3,4,5-trimethoxybenzaldehyde, followed by decarboxylation gives combretastatin A-4 in good overall yield. The phosphate produrg CA4P can be prepared under simple and mild conditions in a sequential one-pot two-step reaction.