Synthesis of Bis-Strychnos Alkaloids (-)-Sungucine, (-)-Isosungucine, and (-)-Strychnogucine B from (-)-Strychnine

It was developed a concise synthetic route resulting in the first syntheses of bis-Strychnos alkaloids(-)-sungucine,(-)-isosungucine, and (-)-strychnogucine B from commercially available (-)-strychnine. Employing a highly convergent synthetic strategy, it was demonstrated that both Strychnos monomers could be efficiently prepared from commercially available (-)-strychnine. The venerable Mannich reaction was enlisted to join the two Strychnos monomers in a biomimetic fashion. Subsequent epimerization and olefin isomerization yielded (-)-strychnogucine B. Functional group manipulation transformed (-)-strychnogucine B into (-)-sungucine and (-)-isosungucine. Computational chemistry was employed to rationalize the regiochemical course of key steps en route to the bis-Strychnos targets.