Synthesis of Ruthenium‐Labelled Tripeptoids with Alternating Amide and Diaryl Ether Bonds

Free‐amino forms of 4‐O‐methyldopamine and 4‐O‐methyltyramine react as nucleophiles in a chemoselective manner with [RuCp]+‐complexed p‐substituted chloroarenes. As a consequence, it is not necessary to use protecting groups for the synthesis of peptoids with alternating amide and diaryl ether bonds. [RuCp]+‐labelled diaryl ether tripeptoids containing DOPA‐ and tyrosine‐derived subunits have been assembled as model compounds. The purification of the charged complexes was conveniently achieved employing aminopropyl‐functionalised silica as a stationary phase. The free‐amino form of tripeptoid 2 resembles the ABB′ partial structure of the macrocyclic bastadins, biologically active natural products from the marine sponge Ianthella. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)