Purine and Purine Isostere Derivatives of Ferrocene: An Evaluation of ADME, Antitumor and Electrochemical Properties

Ferrocenyl Azoles: Versatile N-Containing Heterocycles and their Anticancer Activities

The medicinal chemistry of ferrocene has gained its momentum after the discovery of biological activities of ferrocifen and ferroquine. These ferrocenyl drugs have been designed by replacing the aromatic moiety of the organic drugs, tamoxifen and chloroquine respectively, with a ferrocenyl unit. The promising biological activities of these ferrocenyl drugs have paved a path to explore the medicinal applications of several ferrocenyl conjugates. In these conjugates, the ferrocenyl moiety has played a vital role in enhancing or imparting the anticancer activity to the molecule. The ferrocenyl conjugates induce the cytotoxicity by generating reactive oxygen species and thereby damaging the DNA. In medicinal chemistry, the five membered nitrogen heterocycles (azoles) play a significant role due to their rigid ring structure and hydrogen bonding ability with the biomolecules. Several potent drug candidates with azole groups have been in use as chemotherapeutics. Considering the importance of ferrocenyl moiety and azole groups, several ferrocenyl azole conjugates have been synthesized and screened for their biological activities. Hence, in the view of a wide scope in the development of potent drugs based on ferrocenyl azole conjugates, herein we present the details of synthesis and the anticancer activities of ferrocenyl compounds bearing azole groups such as imidazole, triazoles, thiazole and isoxazoles.

Ferrocene-triazole conjugates: do we know why they are biologically active?

The bioorganometallic chemistry of ferrocene has been gaining significance in recent years. This review presents ferrocene-triazole conjugates displaying significant biological properties. The conjugates have been synthesized via azide-alkyne cycloaddition reactions. The data are summarized according to the type of activity (anticancer, antibacterial and/or antifungal, antiprotozoal, and other effects). The results of studies concerning the understanding of the role of the ferrocene core in their biological activity are highlighted. While generally the mode of action of these organometallic species remains unclear, the importance of redox properties of ferrocene has been postulated in several cases.

New Nucleic Base-Tethered Trithiolato-Bridged Dinuclear Ruthenium(II)-Arene Compounds: Synthesis and Antiparasitic Activity

Aiming toward compounds with improved anti-Toxoplasma activity by exploiting the parasite auxotrophies, a library of nucleobase-tethered trithiolato-bridged dinuclear ruthenium(II)-arene conjugates was synthesized and evaluated. Structural features such as the type of nucleobase and linking unit were progressively modified. For comparison, diruthenium hybrids with other type of molecules were also synthesized and assessed. A total of 37 compounds (diruthenium conjugates and intermediates) were evaluated in a primary screening for in vitro activity against transgenic Toxoplasma gondii tachyzoites constitutively expressing β-galactosidase (T. gondii β-gal) at 0.1 and 1 µM. In parallel, the cytotoxicity in non-infected host cells (human foreskin fibroblasts, HFF) was determined by alamarBlue assay. Twenty compounds strongly impairing parasite proliferation with little effect on HFF viability were subjected to T. gondii β-gal half maximal inhibitory concentration determination (IC₅₀) and their toxicity for HFF was assessed at 2.5 µM. Two promising compounds were identified: 14, ester conjugate with 9-(2-oxyethyl)adenine, and 36, a click conjugate bearing a 2-(4-(hydroxymethyl)-1H-1,2,3-triazol-1-yl)methyl substituent, with IC₅₀ values of 0.059 and 0.111 µM respectively, significantly lower compared to pyrimethamine standard (IC₅₀ = 0.326 µM). Both 14 and 36 exhibited low toxicity against HFF when applied at 2.5 µM and are candidates for potential treatment options in a suitable in vivo model.

Effect of Regiochemistry and Methylation on the Anticancer Activity of a Ferrocene-Containing Organometallic Nucleoside Analogue

Four new bis-substituted ferrocene derivatives containing either a hydroxyalkyl or methoxyalkyl group and either a thyminyl or methylthyminyl group have been synthesised and characterised by a range of spectroscopic and analytical techniques. They were included in a structure-activity-relationship (SAR) study probing anticancer activities in osteosarcoma (bone cancer) cell lines and were compared with a known lead compound, 1-(S,R_p ), a nucleoside analogue that is highly toxic to cancer cells. Biological studies using the MTT assay revealed that a regioisomer of ferronucleoside 1-(S,R_p ), which only differs from the lead compound in being substituted on two cyclopentadienyl rings rather than one, was over 20 times less cytotoxic. On the other hand, methylated derivatives of 1-(S,R_p ) showed comparable cytotoxicities to the lead compound. Overall these studies indicate that a mechanism of action for 1-(S,R_p ) cannot proceed through alcohol phosphorylation and that its geometry and size, rather than any particular functional group, are crucial factors in explaining its high anticancer activity.