Synthesis and characterization of new ferrocene peptide conjugates

Three classes of diamine linked ferrocene (Fc)-conjugates were prepared and their properties were investigates in solution and the solid state: (a) acyclic diamine-linked 1,n'-Fc conjugates, (b) acyclic diamine-linked 1,n'-Fc peptide conjugates, and (c) cyclic 1,n'-Fc-peptide diamine conjugates. In all cases, the synthetic procedure started from 1,1'-ferrocenecarboxylic acid methyl ester or 1,1'-ferrocene dicarboxylic acid or their amino acid conjugates followed by coupling with diaminoalkanes. The resulting conjugates exhibit H-bonding as is evident by temperature and, in some cases, concentration-dependent NMR shifts and in the solid-state structure of one of the conjugates. Our studies show that the structural properties of Fc-diamine-linked systems are different from those of the related cystamine conjugates, presumably due to the enhanced flexibility of the conjugates.