Construction of the Pentacyclic Core and Formal Total Synthesis of ()-Renieramycin T.

A formal total synthesis of the antitumor marine natural product ()-renieramycin T, which possesses a characteristic ecteinascidin-type A ring in the renieramycin-saframycin core skeleton, was elaborated. The key steps in the synthesis of ()-renieramycin T are a modified Pictet-Spengler cyclization of dialkylated oxomalonate derivatives and decarboxylation via a monocarboxylic acid derivative followed by stereocontrolled protonation of the enol intermediate. A key intermediate in our previous synthesis of renieramycin T was used, and the formal synthesis was accomplished in 21 steps from a known piperazine-2,5-dione derivative.