A solid-phase approach to the phallotoxins: Total synthesis of [Ala ⁷]-phalloidin

Herein we report a solid-phase synthetic approach to [Ala ⁷]-phalloidin (1). Prior syntheses of phallotoxins were carried out using solution-phase routes that required large scale and preclude library production. The route presented here consists of solution-phase preparation of key orthogonally protected amino acid building blocks, followed by a solid-phase peptide synthesis sequence, featuring two resin-bound macro-cyclization reactions. The final product mixture was composed of two atropisomeric compounds, one designated "natural" (1) and the other designated "non-natural" (1′). The structures of these species were modeled using restrained energy minimization with NMR-derived restraints.