Total Synthesis of Marine Sponge Bis(indole) Alkaloids of the Topsentin Class

The synthesis of four natural bis(indole) alkaloids of topsentin class 1 and 2 is described. Their bis(indole) α-carbonylimidazoline and subsequently bis(indole) α-carbonylimidazole moieties have been built via the condensation between indolic α-ketothioimidate salts 4 and 1-(indol-3‘-yl)-1,2-diaminoethane 3. This compound results from the β-amino indolic hydroxylamine 5 by a two-step sequence. This is the first total synthesis of compounds 1d, 2a, and 2b.