Total Syntheses of Epothilones A and B via a Macrolactonization-Based Strategy

The total syntheses of epothilones A (1) and B (2) and several analogues thereof are described. The reported strategy relies on a macrolactonization approach and features selective epoxidation of the macrocycle double bond in precursors 3 and 4 (Scheme ), respectively, as well as high convergency and flexibility. Building blocks 9−12 and 15 were constructed by asymmetric processes and coupled via Wittig, aldol, and macrolactonization reactions to afford the basic skeleton of epothilones and that of several of their analogues by a relatively short route. The utilization of intermediate 14, obtained via a stereoselective Wittig reaction and its Enders coupling to SAMP hydrazone 13 (Scheme ), in combination with a stereoselective aldol reaction with the modified substrate 69 (Scheme ) improved the stereoselectivity and efficiency of the total synthesis of these new and highly potent microtubule binding antitumor agents.