Synthesis and Structural Analysis of Ruthenium-bound Norvaline Peptides

A series of norvaline (Nva) peptides possessing ONO-pincer ruthenium complexes, Boc-{l-[Ru(pydc)(t-Bu-terpy)]Nva}n-OMe (n = 2–6), were synthesized successfully by solution-phase peptide synthesis. Efficient coupling of equimolar amounts of N-free Ru-bound norvaline peptides, H-{l-[Ru(pydc)(t-Bu-terpy)]Nva}n-OMe, and C-free Ru-bound norvaline, Boc-l-[Ru(pydc)(t-Bu-terpy)]Nva-OH, was achieved by using the 2-chloro-4,6-dimethoxy-1,3,5-triazine-based method. Structural analysis by means of CD and NMR spectroscopy revealed the formation of stable helical conformations in peptides more than three residues.