Total Synthesis of (-)-Clavicipitic Acid via γ,γ-Dimethylallyltryptophan (DMAT) and Chemoselective C-H Hydroxylation.

The first total synthesis of natural (-)-clavicipitic acid from γ,γ-dimethylallyltryptophan (DMAT), its biosynthetic precursor, is described. This is done by regio- and chemoselective, remote, nondirected C(sp3)-H hydroxylation followed by aminocyclization. This study also features regio- and chemoselective Pd(0)-catalyzed linear prenylation at C4 of l-tryptophan boronic pinacol ester derivate, the latter obtained by a Lewis acid-promoted aziridine amino acid ring opening with 4-boronated indole. In addition, these results support the hypothesis that oxidative cyclization between amino acid nitrogen and the prenyl chain during clavicipitic acid biosynthesis can occur through the transient hydroxylated intermediate.