The ferrocene moiety as a structural probe: redox and structural properties of ferrocenoyl-oligoprolines Fc-Pro(n)-OBzl (n=1-4) and Fc-Pro(2)-Phe-OBzl

The preparations of the five ferrocenoyl-oligopeptides, Fc-Pro-OBzl (1), Fc -Pro(2)-OBzl (2), Fc-Pro(3)-OBzl (3), Fc-Pro(4)-OBzl (4) and Fc-Pro(2)-Phe- OBzl (5) are described. Crystallographic studies show that the Fc-oligoprol ines 1-4 adopt a helical polyproline II structure having all prolines in a mutually tl ans-conformation. This structure is maintained in MeCN and CHCl 3 solutions, as was shown by NMR methods. Chemical and magnetic similaritie s among the proline residues render spectral assignment by conventional 1D H-1-NMR spectroscopy impossible. However, a combination of 2D NMR technique s allowed us to unequivocally assign all signals. The redox potential of th e Fc-group attached to the oligoproline chain is sensitive to the sequence and length of the oligopeptide. With growing peptide length, the molecule b ecomes easier to oxidize. (C) 1999 Elsevier Science S.A. All rights reserve d.