A FORMAL TOTAL SYNTHESIS OF THE ACE-INHIBITOR K-13 - AN APPLICATION OF ARENE-RUTHENIUM CHEMISTRY TO COMPLEX CHEMICAL SYNTHESIS

Stoichiometric ruthenium activation of 4-chlorophenylalanine derivatives toward nucleophilic substitution, using phenoxide nucleophiles that are derived from protected dipeptides, allowed the formation of isodityrosine derivatives that are synthetic precursors to the ACE inhibitor K-13. An evaluation of carboxyl blocking groups revealed that a 2-bromoethyl ester is the most useful in terms of its compatibility with ruthenium complexation and subsequent nucleophile addition but that its removal is problematic. Conversion to iodoethyl ester using Finkelstein reaction conditions, in the presence of the peptide and amino acid functionality, provided a solution to this problem, since the iodoethyl group was easily removed on treatment with samarium diiodide.