Chemistry of renieramycins. Part 11: Total synthesis of (±)-cribrostatin 4

A 19-step synthesis of (±)-cribrostatin 4 (1) from readily available piperazine-2,5-dione derivative 6 is described. The synthesis features the concise construction of a pentacyclic framework, followed by the base-catalyzed epimerization of the C-1 stereo center of aldehyde (11). The results of cytotoxicity studies are also presented.