The ferrocene moiety as a structural probe:: redox and structural properties of ferrocenoyl-oligoprolines Fc-Pron-OBzl (n=1-4) and Fc-Pro2-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-oligoprolines 1-4 adopt a helical polyproline II structure having all prolines in a mutually tl ans-conformation. This structure is maintained in MeCN and CHCl3 solutions, as was shown by NMR methods. Chemical and magnetic similarities among the proline residues render spectral assignment by conventional 1D H-1-NMR spectroscopy impossible. However, a combination of 2D NMR techniques allowed us to unequivocally assign all signals. The redox potential of the Fc-group attached to the oligoproline chain is sensitive to the sequence and length of the oligopeptide. With growing peptide length, the molecule becomes easier to oxidize. (C) 1999 Elsevier Science S.A. All rights reserved.