Conformational Analysis of Heteroannularly Substituted Ferrocene Oligoamides

Synthesis and structure analysis of ferrocene-containing pseudopeptides

Ferrocene with its aromaticity and facile redox properties is an attractive moiety to be incorporated into functional moieties. Medicinal applications of ferrocene are well known and ferrocene itself shows cytotoxic and antianemic properties. In this article, we will describe the synthesis and the structure analysis of two pseudopeptides containing a ferrocene moiety as N-terminal group. After purification, Fc-l-Phe-d-Oxd-OBn [l-Phel-phenylalanine; d-Oxd(4R,5S)-4-Methyl-5-carboxy-oxazolidin-2-one] appears as bright brown solid that spontaneously forms brown needles. The X-ray diffraction of the crystals shows the presence of strong π interactions between the ferrocenyl moiety and the phenyl rings, while no NH•••OC hydrogen bonds are formed. This result is confirmed by FT-IR and 1 H NMR analysis. In contrast, both FT-IR and 1 H NMR analysis suggest that Fc-(l-Phe-d-Oxd)2 -OBn forms a turn conformation stabilized by intramolecular NH•••OC hydrogen bonds in solution. Chiroptical spectroscopies (ECD and VCD) substantially confirmed the absence of a well-defined folded structure. The presence of the Fc moiety is responsible for specific ECD signals, one of which displayed pronounced temperature dependence and is directly related with the helicity assumed by the Fc core. Solid-state ECD spectra were recorded and rationalized on the basis of the X-ray geometry and quantum-mechanical calculations.

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.

Unusual carbamate-directed CH-activation at an annulated ferrocenophane framework

The tetrahydroazepine-annulated [3]ferrocenophane carbamate (4) was synthesized by two different linear routes starting from the readily available α-dimethylamino[3]ferrocenophane-ortho-carbaldehyde rac-6. The carbamate directed lithiation of 4 resulted in a selective attack at a (Cp)C-H bond at the higher substituted "lower" [3]ferrocenophane Cp-ring to eventually yield the respective ester (18) after treatment with ClCO(2)Me.