Diazonamide studies. A direct synthesis of the indole bis-oxazole fragment from tri- and tetra-peptides using biomimetic oxidative cyclizations

The oxidation of several readily prepared tryptophan containing tri- and tetrapeptides with DDQ results in a biomimetic cyclization and direct formation of the indole bis-oxazole fragment of diazonamide A, establishing that such a transformation is a viable route when considering the biosynthetic formation of the heterocyclic core of the natural product.