On the medicinal chemistry of ferrocene

Ferrocenyl chalcone difluoridoborates inhibit HIV-1 integrase and display low activity towards cancer and endothelial cells

We report here the discovery of a potent series of HIV-1 integrase (IN) inhibitors based on the ferrocenyl chalcone difluoridoborate structure. Ten new compounds have been synthesized and were generally found to have similar inhibitory activities against the IN 3' processing and strand transfer (ST) processes. IC(50) values were found to be in the low micromolar range, and significantly lower than those found for the non-coordinated ferrocenyl chalcones and other ferrocene molecules. The ferrocenyl chalcone difluoridoborates furthermore exhibited low cytotoxicity against cancer cells and low morphological activity against epithelial cells.

Ferrocenyl-substituted curcumin: can it influence antioxidant ability to protect DNA?

The antioxidant capacities of ferrocenyl-substituted curcumin derivatives including 1,7-bis(p-hydroxy-m-methoxyphenyl)-4-ferrocenylidene-hepta-1,6-diene-3,5-dione (FCU), 1-(p-hydroxy-m-methoxyphenyl)-3-hydroxy-7-ferrocenyl-hepta-1,4,6-trien-5-one (FFT), and 1-(p-hydroxy-m-methoxyphenyl)-5-ferrocenyl-penta-1,4-dien-3-one (FDZ) were evaluated in 2,2'-azobis(2-amidinopropane hydrochloride) (AAPH), Cu2+/glutathione (GSH), and hydroxyl radical (.OH)-induced oxidation of DNA, and in trapping 2,2'-diphenyl-1-picrylhydrazyl (DPPH), 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonate) cationic radical (ABTS+), and galvinoxyl radicals. FCU, FFT, and FDZ protected DNA against Cu2+/GSH-induced oxidation, but promoted .OH-induced oxidation of DNA. FCU, FFT, and FDZ scavenged 9.5, 5.7, and 4.7 radicals in protecting DNA against AAPH-induced oxidation. FCU can trap more DPPH and ABTS+ than FDZ and FFT, whereas FCU, FFT, and FDZ cannot react with galvinoxyl radical. Both phenolic hydroxyl groups and iron atom in ferrocenylidene curcumin derivatives play antioxidant role in this case.

New potential anticancer agent of carborane derivatives: selective cellular interaction and activity of ferrocene-substituted dithio-o-carborane conjugates

The large diversity of structures and unique bonding modes of organometallic complexes make them possible to act as promising candidate therapeutic agents. In this study, the new type of ferrocene-substituted dithio-o-carborane conjugates (FcSB1, FcSB2, and FcSBCO) has been synthesized, and their in vitro antineoplastic activities have been explored by means of the electrochemical study, the real time cell electronic sensing (RT-CES) system, and biological assays. The conjugate-cell interactions were first monitored by electrochemistry, and the results show different cell uptake efficiency for FcSB1, FcSB2, and FcSBCO toward target cells. Both the highly hydrophobic ferrocenyl and carboranyl groups render the conjugates able to rapidly enter cells and exert acute cytotoxicity after 4 h incubation in serum-free media. However, FcSB1, FcSB2, and FcSBCO display different inhibition efficiencies toward SMMC-7721 and HepG2 cancer cells via the G(0)/G(1) arrest mechanism in a physiological environment. The anticancer activity is in the order FcSB2 > FcSB1 > FcSBCO, which is parallel to the order of the redox potentials of the ferrocenyl groups in the three complexes. In particular, FcSB1 and FcSB2 display a potent selective inhibition effect on the proliferation of the cancer cell lines SMMC-7721 and HepG2, but almost no effect on the normal cell line, the human embryonic lung fibroblast (HELF) cells. Thus, these results may provide some clues for use of the ferrocene-carborane conjugates in developing anticancer drugs.

19-Ferrocenyl-18-oxa-8,16-diaza-penta-cyclo-[8.6.3.0.0.0]nona-deca-2(7),3,5-triene-9,17-dione

In the title compound, [Fe(C(5)H(5))(C(21)H(19)N(2)O(3))], both pyrrol-idine rings of the pyrrolizine substructure show an envelope conformation. In the ferrocenyl moiety, the unsubstituted cyclo-penta-dienyl ring is disordered over two orientations with site occupancies of 0.64 (2) and 0.36 (2). In the pyrrolizine ring, one C atom is disordered over two positions, with site occupancies of 0.71 (1) and 0.29 (1). Intra-molecular C-H⋯O inter-actions occur. The crystal packing is established through weak inter-molecular C-H⋯O and N-H⋯O inter-actions.

Biotin as acylating agent in the Friedel-Crafts reaction. Avidin affinity of biotinyl derivatives of ferrocene, ruthenocene and pyrene and fluorescence properties of 1-biotinylpyrene

(D)-Biotin was used for Friedel-Crafts acylation of electron-rich aromatic molecules--ferrocene, ruthenocene and pyrene. The reaction carried out in the presence of trifluoroacetic anhydride and trifluoromethanesulfonic acid afforded the corresponding biotinylarenes in moderate yields. These compounds, although lacking an amide bond, exhibited high affinity for avidin, with the ability to displace 2-(4'-hydroxyphenylazo)-benzoic acid (HABA) in its complex with avidin. Their affinity for avidin was determined by a solid-phase competitive enzymatic assay, which gave IC(50) values in the range of 33-58 nM (under the same conditions biotin showed IC(50) = 24 ± 7 nM). 1-Biotinylpyrene (1c) excited at 355 nm displayed fluorescence emission in aqueous solutions with λ(max) = 461 nm. The fluorescence maximum was shifted to 425 nm upon binding of 1c to avidin. Formation of the avidin-1c complex was also evidenced by quenching of the fluorescence from the protein tryptophan residues (342 nm) and appearance of the emission band of the avidin-bound 1c at 430 nm as a result of a Förster resonance energy transfer (FRET) phenomenon.

1,1′-Bis[1-(Hydroxyimino)Alkyl]Ferrocenes and their Antioxidant Activity

Condensation reactions of 1,1′-diacylferrocenes with hydroxylamine afford a series of 1,1′-bis[1-(hydroxyimino)alkyl]ferrocenes, [2(a–d)] which have antioxidant activity towards DPPH· This is enhanced with an increase of the compound concentration, but reduced as the bulkiness of the α-substituent hydroximino group increases. The antioxidant activity of [2(a–d)] is much higher than that of diacylferrocenes.

Novel organometallic cationic ruthenium(II) pentamethylcyclopentadienyl benzenesulfonamide complexes targeted to inhibit carbonic anhydrase

Cationic ruthenium(II) pentamethylcyclopentadienyl benzenesulfonamide sandwich complexes have been synthesized and screened for enzymatic inhibition of the physiologically dominant carbonic anhydrase (CA) isozymes: human CA I and II, mitochondrial isozymes VA and VB, and the cancer-associated isozyme IX. The complexes demonstrated weaker binding to CAs compared with typical aromatic sulfonamides, inhibiting the enzyme at high nanomolar concentrations. An in vitro cytotoxic evaluation of the complexes was also undertaken against a range of tumorigenic cell lines and a healthy human cell line. Complexes inhibited the growth of cancerous cells at low micromolar concentrations while expressing lower levels of toxicity towards the normal human cell line. Factors influencing the synthesis, cytotoxicity, and enzyme affinity for this series of organometallic complexes are discussed.

Synthesis, structure, electrochemistry, and cytotoxic properties of ferrocenyl ester derivatives

A series of ferrocenyl ester complexes, varying the lipophilic character of the pendant groups, was prepared and characterized by spectroscopic and analytical methods. The syntheses of Fe(C₅H₄CO₂CH₃)₂, Fe(CpCOOCH₃) (CpCOO CH₂CH₃), and Fe(CpCOOCH₂CH₃)₂ are reported. The solid-state structure of Fe(C₅H₄CO₂CH₃)₂ has been determined by X-ray crystallography. Fe(C₅H₄CO₂CH₃)₂ has the cyclopentadienyl rings virtually in an eclipsed conformation with the pendant groups not completely opposite to each other. Cyclic voltammetry characterization showed that the functionalized ferrocenes oxidize at potentials, E_pa, higher than ferrocene as a result of the electro withdrawing effect of the pendant groups on the cyclopentadienyl ligand. The cytotoxicities of Fe(C₅H₄CO₂CH₂CH₂OH)₂, Fe(C₅H₄CO₂CH₂CH=CH₂)₂, Fe(C₅H₄CO₂CH₃)₂, Fe(CpCOOCH₃)(CpCOOCH₂CH₃), and Fe(CpCOOCH₂CH₃)₂ in colon cancer HT-29 and breast cancer MCF-7 cell lines were measured by the MTT biological viability assay and compared to ferrocene and ferrocenium. Fe(C₅H₄CO₂CH₂CH=CH₂)₂ showed the best IC₅₀ values, 180(10) μM for HT-29 and 190(30) μM for MCF-7 cell lines, with cytotoxicities similar to ferrocenium. The cytotoxic data suggest that as we increase the lipophilic character of the functionalized ferrocene, the cytotoxicity improves approaching to the cytotoxic activity of ferrocenium.

Ferrocenylbutadiyne

The title compound, [Fe(C₅H₅)(C₉H₅)], crystallizes in a form of a π–π-stacked assembly formed as a result of strong inter­molecular π–π inter­actions between (a) the triple bonds of two neighboring butadiyne substituents overlapping in a ‘head-to-tail’ fashion [characterized by C⋯C short contacts of 3.622 (5), 3.567 (6) and 3.556 (6) Å] and (b) the triple bonds of the butadiyne substituent and substituted cyclo­pendadiene ring of neighboring mol­ecules [C⋯C = 3.474 (5) and 3.492 (6) Å]. The linear butadiyne substituent has alternating C—C triple and single bonds, while the unsubstituted cyclo­penta­diene ring is slightly positionally disordered (although the structure reported here was solved as non-disordered) and retains a close to eclipsed conformation.