Design and enantioselective synthesis of a peptidomimetic of the turn in the helix-turn-helix DNA-binding protein motif

A peptidomimetic of the turn in the helix-turn-helix (HTH) motif of DNA-binding proteins was designed and synthesized, Conformational constraint was achieved by an unusual linking of two amino acids with a side chain carbon-carbon bond, A phenyl ring provides the potential for new hydrophobic contacts with the hydrophobic core of the HTH motif. In the mimic, the peptide backbone and the central residue were retained in native form within a 12-membered cyclic tripeptide, The target compound Ib was synthesized by two sequential Horner-Wittig couplings followed by enantioselective hydrogenation with Rh(MeDuPHOS) in eight steps and 35% overall yield. The stereochemical outcome of the key hydrogenation was determined by aromatic ring oxidation with RuO2/NaIO4 to give 2 equiv of Boc-Asp-OMe.