Total synthesis of (±)-dragmacidin E; Problems solved and lessons learned

(±)-Dragmacidin E was synthesized in 25 steps from commercially available 7-(benzyloxy)indole. Key transformations in the preparation of this sponge metabolite include (a) a Witkop cyclization to establish the bridging indole core, (b) cyclo-dehydrative pyrazinone formation to unite the two indole-bearing components, and (c) late-stage guanidine installation through chemoselective carbonyl activation. 1 Introduction 2 Results and Discussion 2.1 Model System Synthesis 2.2 (±)-Dragmacidin E Synthesis 3 Conclusions.