Atypical McMurry cross-coupling reactions leading to a new series of potent antiproliferative compounds bearing the key [ferrocenyl-ene-phenol] motif

Ferrocifen stealth LNCs and conventional chemotherapy: A promising combination against multidrug-resistant ovarian adenocarcinoma

Ovarian cancer is one of the deadliest epithelial malignancies in women, owing to the multidrug resistance that restricts the success of conventional chemotherapy, carboplatin and paclitaxel. High grade serous ovarian carcinoma can be classified into two subtypes, the chemosensitive High OXPHOS and the Low OXPHOS tumour, less sensitive to chemotherapy. This difference of treatment efficacy could be explained by the redox status of these tumours, High OXPHOS exhibiting a chronic oxidative stress and an accumulation of reactive oxygen species. Ferrocifens, bio-organometallic compounds, are believed to be ROS producers with a good cytotoxicity on ovarian cancer cell lines. The aim of this study was to evaluate the in vivo efficacy of ferrocifen stealth lipid nanocapsules on High and Low OXPHOS ovarian Patient-Derived Xenograft models, alone or in combination to standard chemotherapy. Accordingly, two ferrocifens, P53 and P722, were encapsulated in stealth LNCs. The treatment by stealth P722-LNCs in combination with standard chemotherapy induced, with a concentration eight time lower than in stealth P53-LNCs, similar tumour reduction on a Low OXPHOS model, allowing us to conclude that P722 could be a leading ferrocifen to treat ovarian cancer. This combination of treatments may represent a promising synergistic approach to treat resistant ovarian adenocarcinoma.

Recent advances of carbonyl olefination via McMurry coupling reaction

McMurry coupling reaction utilizes the low-valent titanium reagents and carbonyl compounds to produce olefins. The wide synthetic application of McMurry reagents in intermolecular and intramolecular coupling reactions, tandem coupling reactions, and keto ester coupling reactions of carbonyl compounds for the last five years have been reviewed. The resulting coupling reaction produces natural and non-natural products, including strained olefins and unusual molecules as a candidate for nanomaterials, pharmaceuticals, electronic materials, and so forth. The advantages, scope, and limitations along with the improvement of the McMurry coupling reaction, including the addition of high functional group compatibility, McMurry reagents substitution, and several other treatments, have also been discussed.

McMurry coupling reaction utilizes the low-valent titanium reagents and carbonyl compounds to produce olefins.

Enantioselective Synthesis of Planar Chiral Ferrocifens that Show Chiral Discrimination in Antiproliferative Activity on Breast Cancer Cells

The design and first enantioselective synthesis of a series of chiral ferrocifens and ferrociphenols was realised by enantioselective palladium-catalysed intramolecular direct C-H bond activation followed by McMurry coupling. Biological evaluation revealed moderate anticancer activities on breast cancer cells and evidence of chiral discrimination between enantiomers. Treatment of the novel ferrocifens with Ag₂ O revealed that these systems are unable to form a neutral quinone methide, yet still demonstrate marked antiproliferative properties against both the hormone-dependent MCF-7 and hormone-independent MDA-MB-231 cell lines. This bioactivity arises from two mechanisms: Fenton-type chemistry and the anti-estrogenic activity associated with the tamoxifen-like structure.

Ferrocene-containing hybrids as potential anticancer agents: Current developments, mechanisms of action and structure-activity relationships

Cancer is one of the most fatal threatens to human health throughout the world. The major challenges in the control and eradication of cancers are the continuous emergency of drug-resistant cancer and the low specificity of anticancer agents, creating an urgent need to develop novel anticancer agents. Organometallic compounds especially ferrocene derivatives possess remarkable structural and mechanistic diversity, inherent stability towards air, heat and light, low toxicity, low cost, reversible redox, ligand exchange, and catalytic properties, making them promising drug candidates for cancer therapy. Ferrocifen, a ferrocene-phenol hybrid, has demonstrated promising anticancer properties on drug-resistant cancers. Currently, Ferrocifen is in pre-clinical trial against cancers. Obviously, ferrocene moiety is a useful template for the development of novel anticancer agents. This review will provide an overview of ferrocene-containing hybrids with potential application in the treatment of cancers covering articles published between 2010 and 2020. The mechanisms of action, the critical aspects of design and structure-activity relationships are also discussed.

Efficient synthesis of ferrocifens and other ferrocenyl-substituted ethylenes via a 'sulfur approach'

Stable and non-odorous alkyl ferrocenyl thioketones react with bis(4-methoxyphenyl)diazomethane according to the 'two-fold extrusion' reaction principles, and tetrasubstituted ethylenes obtained thereby can be demethylated to give (Fc,2OH)-ferrocifens in good yields. The method offers an alternative approach to this class of medically relevant compounds. A similar protocol with alkyl ferrocenyl thioketones and selected diaryldiazomethanes leads to ferrocenyl-substituted ethylenes including dibenzofulvenes. These products are of potential interest for electrochemical and photophysical studies.

Two Macrocycles in One Shot: Synthesis, Spectroscopy, Photophysics, and Tautomerism of 23-Oxahemiporphycene and 21-Oxacorrole-5-carbaldehyde

The synthesis of 23-oxahemiporphycene, the first monooxa analogue of hemiporphycene, a structural isomer of porphyrin, is reported. Its generation under McMurry reaction conditions is surprisingly accompanied by the appearance of a formyl derivative of oxacorrole, 21-oxacorrole-5-carbaldehyde. A mechanism for the formation of the latter is proposed, relying on pinacol rearrangement of titanium pinacolate. The structures of the most stable tautomeric forms are established for both compounds based on IR and NMR spectra combined with DFT calculations. Spectral and photophysical characteristics are compared with those of structurally similar macrocycles. Replacement of one nitrogen by oxygen in hemiporphycene has only a minor impact. In contrast, for corrole it leads to the enhancement of stability and to strongly reduced rates of nonradiative deactivation of the lowest excited singlet state. This is explained by the planarity of oxacorroles, achieved by removing one of the inner hydrogen atoms from the inner cavity. Unusual crystal packing is observed for the protonated form of 23-oxahemiporphycene, which exhibits a π-π stacked columnar alignment of positively charged macrocycle units.

Special issue: practical applications of metal complexes

In 1913 Alfred Werner received the Nobel Prize in Chemistry for his work that was of great importance for the development of coordination chemistry. In the years that followed numerous complexes consisting of metal ions and organic ligands were isolated, thus building a strong connection between inorganic and organic chemistry. Coordination compounds have many interesting properties which find diverse applications in numerous aspects of human life. Fourteeen contributions were received for this Special Issue covering very different aspects of metal complexes and their practical applications. The highest number of manuscripts deals with the biological activity of complexes which might potentially be used in the clinical practice. Authors have tested their cytotoxicity, antibacterial activity and enzyme inhibition. Their optical properties were studied in view of their potential use in photodynamic therapy. Moreover, optical properties could also be used for bioanalysis. It is also known that metal complexes are useful catalysts and a few such examples are also described herein. Many other interesting properties and facts about the isolated and described complexes are also reported (radioactivity, design of metal-organic frameworks, etc.).

Oxidative metabolism of ferrocene analogues of tamoxifen: characterization and antiproliferative activities of the metabolites

Ferrociphenols have been found to have high antiproliferative activity against estrogen-independent breast cancer cells. The rat and human liver microsome-mediated metabolism of three compounds of the ferrocifen (FC) family, 1,1-bis(4-hydroxyphenyl)-2-ferrocenyl-but-1-ene (FC1), 1-(4-hydroxyphenyl)-1-(phenyl)-2-ferrocenyl-but-1-ene (FC2), and 1-[4-(3-dimethylaminopropoxy)phenyl]-1-(4-hydroxyphenyl)-2-ferrocenyl-but-1-ene (FC3), was studied. Three main metabolite classes were identified: quinone methides (QMs) deriving from two-electron oxidation of FCs, cyclic indene products (CPs) deriving from acid-catalyzed cyclization of QMs, and allylic alcohols (AAs) deriving from hydroxylation of FCs. These metabolites are generated by cytochromes P450 (P450s), as shown by experiments with either N-benzylimidazole as a P450 inhibitor or recombinant human P450s. Such P450-dependent oxidation of the phenol function and hydroxylation of the allylic CH2 group of FCs leads to the formation of QM and AA metabolites, respectively. Some of the new ferrociphenols obtained in this study were found to exhibit remarkable antiproliferative effects toward MDA-MB-231 hormone-independent breast cancer cells.

Synthesis and redox activity of "clicked" triazolylbiferrocenyl polymers, network encapsulation of gold and silver nanoparticles and anion sensing

The design of redox-robust polymers is called for in view of interactions with nanoparticles and surfaces toward applications in nanonetwork design, sensing, and catalysis. Redox-robust triazolylbiferrocenyl (trzBiFc) polymers have been synthesized with the organometallic group in the side chain by ring-opening metathesis polymerization using Grubbs-III catalyst or radical polymerization and with the organometallic group in the main chain by Cu(I) azide alkyne cycloaddition (CuAAC) catalyzed by [Cu(I)(hexabenzyltren)]Br. Oxidation of the trzBiFc polymers with ferricenium hexafluorophosphate yields the stable 35-electron class-II mixed-valent biferrocenium polymer. Oxidation of these polymers with Au(III) or Ag(I) gives nanosnake-shaped networks (observed by transmission electron microscopy and atomic force microscopy) of this mixed-valent Fe(II)Fe(III) polymer with encapsulated metal nanoparticles (NPs) when the organoiron group is located on the side chain. The factors that are suggested to be synergistically responsible for the NP stabilization and network formation are the polymer bulk, the trz coordination, the nearby cationic charge of trzBiFc, and the inter-BiFc distance. For instance, reduction of such an oxidized trzBiFc-AuNP polymer to the neutral trzBiFc-AuNP polymer with NaBH4 destroys the network, and the product flocculates. The polymers easily provide modified electrodes that sense, via the oxidized Fe(II)Fe(III) and Fe(III)Fe(III) polymer states, respectively, ATP(2-) via the outer ferrocenyl units of the polymer and Pd(II) via the inner Fc units; this recognition works well in dichloromethane, but also to a lesser extent in water with NaCl as the electrolyte.