New prospects for vinblastine analogues as anticancer agents.

Boger et al. synthesized a series of C20' urea derivatives of vinblastine that matched or exceeded the potency of vinblastine in cell growth inhibition assays. The studies demonstrated the importance of the H-bond donor on the C20' position and revealed the presence of a space surrounding the C20' substituent that tolerates a wide variety of substituents, remarkably enhancing potency of vinblastine analogues.