Total Synthesis of Stephanotic Acid Methyl Ester

The methyl ester of the naturally occurring macrocyclic pentapeptide stephanotic acid, containing an unusual β-substituted α-amino acid with
a tryptophan C-6 to leucine β-carbon link, has been synthesized. The key steps include the formation of this amino acid through a thioxo-oxazolidine intermediate and a Horner−Wadsworth−Emmons reaction using a phosphonoglycine, derived by a dirhodium(II)-catalyzed N−H
insertion reaction, to give a dehydroamino acid and subsequent rhodium(I)-catalyzed asymmetric hydrogenation to introduce the modified
tryptophan residue.