Synthesis and conformational analysis of optically active ferrocene containing macrocyclic peptides

Two macrocyclic peptides 3 and 4 were formed during lactamization of 1,1'-ferrocenylbis(alanine) 1. Isolation, structure determination, and conformational analysis of 3 and 4 are reported as well as a controlled stepwise synthesis of 4 also including an improved route to 1. On the basis of their H-1 NMR spectra recorded at 300 K in DMSO-d(6), the dimer 3 and trimer 4 were found to be C-2 and C-3 symmetric, respectively. As appeared from computational analysis, the low-energy conformations of the macrocyclic peptides were nonsymmetric. Cyclic voltammetry revealed that the ferrocenyl moieties in 3 or 4 are electrochemically equal to ferrocene.