Structural, Spectroscopic, and Theoretical Study of Ferrocene Ureidopeptides

Application of the Curtius rearrangement to the synthesis of 1′-aminoferrocene-1-carboxylic acid derivatives

The shortest synthesis of N-protected 1′-aminoferrocene-1-carboxylic acid from readily available ferrocene-1,1′-dicarboxylic acid is reported.

Anion-regulated electronic communication in a cyclometalated diruthenium complex with a urea bridge

A combined study of electrochemical measurements, intervalence charge transfer analysis, and DFT calculations suggests that the degree of urea-mediated electronic coupling between two cyclometalated ruthenium sites is enhanced by the coordination of urea with Br^- or Cl^-via hydrogen bonding. In contrast, the redox waves of the diruthenium complex become highly irreversible in the presence of relatively strong basic anions such as H₂PO₄^-, F^-, or OAc^-. This work demonstrates that the anion-urea interaction can be employed to regulate the electronic coupling and electron transfer between redox-active sites, suggesting the potential applications of the urea-functionalized diruthenium complex in anion sensing and stimuli-responsive molecular electronics.

The conjugates of ferrocene-1,1'-diamine and amino acids. A novel synthetic approach and conformational analysis

A novel synthetic approach toward a poorly explored bioorganometallic consisting of ferrocene-1,1'-diamine bearing structurally and chirally diverse amino acid sequences is reported. Until now, ferrocene-1,1'-diamine was suitable for accommodating only identical amino acid sequences at its N-termini, leading to the symmetrically disubstituted homochiral products stabilized through a 14-membered intramolecular hydrogen-bonded ring as is seen in antiparallel β-sheet peptides. The key step of the novel synthetic pathway is the transformation of Ac-Ala-NH-Fn-COOH (5) (Fn = 1,1'-ferrocenylene) to orthogonally protected Ac-Ala-NH-Fn-NHBoc (7). The spectroscopic analysis (IR, NMR, CD) of the novel compounds, corroborated with DFT studies, suggests the interesting feature of the ferrocene-1,1'-diamine scaffold. The same hydrogen-bonding pattern, i.e. a 14-membered hydrogen-bonded ring, was determined both in solution and in the solid state, thus making them promising, yet simple scaffolds capable of mimicking β-sheet peptides. In vitro screening of potential anticancer activity in Hep G2 human liver carcinoma cells and Hs 578 T human breast cancer cells revealed a cytotoxic pattern for novel compounds (150-500 μM) with significantly decreased cell proliferation.

Conjugates of 1'-aminoferrocene-1-carboxylic acid and proline: synthesis, conformational analysis and biological evaluation

Our previous studies showed that alteration of dipeptides Y-Fca-Ala-OMe (III) into Y-Ala-Fca-OMe (IV) (Y = Ac, Boc; Fca = 1'-aminoferrocene-1-carboxylic acid) significantly influenced their conformational space. The novel bioconjugates Y-Fca-Pro-OMe (1, Y = Ac; 2, Y = Boc) and Y-Pro-Fca-OMe (3, Y = Boc; 4, Y = Ac) have been prepared in order to investigate the influence of proline, a well-known turn-inducer, on the conformational properties of small organometallic peptides with an exchanged constituent amino acid sequences. For this purpose, peptides 1–4 were subjected to detailed spectroscopic analysis (IR, NMR, CD spectroscopy) in solution. The conformation of peptide 3 in the solid state was determined. Furthermore, the ability of the prepared conjugates to inhibit the growth of estrogen receptor-responsive MCF-7 mammary carcinoma cells and HeLa cervical carcinoma cells was tested.