Total Synthesis and Structural Revision of (-)-ProtubonineA and (-)- Protubonine B

The proposed structures of (-)-protubonine A and (-)-protubonine B, which are pyrrolidinoindoline diketopiperazine alkaloids that were isolated from the marine-derived fungus Aspergillus sp. SF-5044, have been synthesized and correspond to diastereomers of the natural isolates. The total syntheses, herein, established the stereostructures of the alkaloids as the C-11 epimers of the purported structures.