A Straightforward Approach to Protected (S)-Dolaphenine (Doe), the Unusual Amino Acid Component of Dolastatin 10

A short, four-step synthesis of Boc-protected (S)-dolaphenine is described, starting from protected phenylalanyl glycine. The key step is the cyclization of an endothiodipeptide to give a thiazolyl triflate, which can be subjected to a palladium-catalyzed reduction with formic acid.