A highly efficient stereocontrolled synthesis of (S)-2′,6′-dimethyltyrosine [(S)-DMT]

A new, practical and very convenient stereocontrolled synthesis of (S)-2′,6′-dimethyltyrosine (S)-Dmt] 4 was accomplished in a good yield, starting from the chiral synthon 1,4-N,N-(S)-phenylethyl]-piperazine-2,5-dione 1. The procedure, which is an extension of our original strategy and occurs with a high level of stereoselectivity (>98%), is simple and inexpensive allowing us to prepare the unnatural α-aminoacid (S)-Dmt also on a multi-gram scale.