The interaction of ferrocenoyl peptides with 3-aminopyrazole

The syntheses of three ferrocenoyl peptides (Fc-GG-OEt (2), Fc-AA-OBzl (3), Fc-LF-OMe (4)) including their full spectroscopic characterization is reported. Titration of peptide solution with 3-aminopyrazole (APzl) in CDCl3 was followed by H-1-NMR spectroscopy and evaluated using Job's method and by non-linear regression. It was found that 4 showed the strongest interaction with APzl, followed by 3. The highly flexible 2 showed only a weak interaction. Association constants, derived from NMR measurements, are in the range of 9.4 +/- 1.0 to 21.4 +/- 0.5 M-1. Cyclic voltammetry shows that the redox potentials are sensitive to complex formation. The largest changes were observed for 4 (30 mV), followed by 3 (13 mV) and there was no observable change for 2. This sequence coincides with the ability of 3-APzl to form a complex with the Fc-peptide. (C) 1999 Elsevier Science S.A. All rights reserved.