SYNTHESIS OF A 16-MEMBERED CYCLIC PEPTIDE MODEL OF THE BCF RINGS OF RISTOCETIN-A USING ARENE-RUTHENIUM CHEMISTRY COUPLED WITH CYCLOAMIDATION

A convergent synthetic approach to the cyclic peptide 4, which is a model for the B/C/F ring system of ristocetin B, is described. A key reaction is the coupling of the phenolic dipeptide 5, constructed from arylglycine subunits, with the chlorophenylalanine-RuCp cationic complex 6, followed by demetalation of the product to give the diaryl ether 7, without epimerization at any of the amino acid residues. Deprotection of 7 followed by cycloamidation affords the target molecule 4, produced as a mixture of atropdiastereomers which were separated and characterized by NMR spectroscopy.