Synthesis of (9R,12S)- and (9S,12S)-Cycloisodityrosine and Their N-Methyl Derivatives

Full details of the synthesis of (9R,12S)- and (9S,12S)-cycloisodityrosine and their N-methyl derivatives are detailed based on an intramolecular nucleophilic aromatic substitution reaction for formation of the key biaryl ether with 14-membered ring macrocyclization. Their comparison with prior samples and the documentation of a facile C9 epimerization within the natural 9S series are described.