On the medicinal chemistry of ferrocene

Non-imidazole histamine H3 receptor ligands incorporating antiepileptic moieties

A small series of histamine H3 receptor (H3R) ligands (1-5) incorporating different antiepileptic structural motifs has been newly synthesized. All compounds exhibited moderate to high in vitro hH3R affinities up to a sub-nanomolar concentration range with pKi values in the range of 6.25-9.62 with varying preferences for this receptor subtype. The compounds (1-5) were further investigated in vivo on anticonvulsant effects against maximum electroshock (MES)-induced and pentylenetetrazole (PTZ)-kindled convulsions in rats having phenytoin (PHT) as the reference antiepileptic drug (AED). Surprisingly, animals pretreated with 1 mg/kg, i.p. of 5,5-diphenyl-3-(3-(piperidin-1-yl)propyl)imidazolidine-2,4-dione (4) were only moderately protected and no protection was observed for compounds 1-3 and 5 in three different doses (1 mg, 5 mg, and 10 mg/kg i.p.). Compound 4 (1 mg/kg, i.p.) failed to modify PTZ-kindled convulsion. However, a dose of 10 mg/kg significantly reduced convulsions in both models. In contrast, 5,5-diphenyl-3-(4-(3-(piperidin-1-yl)propoxy)benzyl)imidazolidine-2,4-dione (5) (1, 5, and 10 mg/kg, i.p.) showed proconvulsant effects in the MES model with further confirmation of these results in the PTZ model as no protection was observed against convulsion in the doses tested (1 and 10 mg/kg). In addition, compound 4 (10 mg/kg, i.p.) significantly prolonged myoclonic latency time and shortened total convulsion duration when compared to control, PHT or standard H3R inverse agonist/antagonist pitolisant (PIT). Our results showed that H3R pharmacophores could successfully be structurally combined to antiepileptic moieties, especially phenytoin partial structures, maintaining the H3R affinity. However, the new derivatives for multiple-target approaches in epilepsy models are complex and show that pharmacophore elements are not easily pharmacologically combinable.

6-Ferrocenoyl-7-(4-fluoro-phen-yl)spiro-[hexa-hydro-pyrrolo-[1,2-c][1,3]thia-zole-5,11'-indeno-[1,2-b]quinoxaline]

In the title compound, [Fe(C5H5)(C32H23FN3OS)], both the thia-zolidine ring and the pyrrolidine ring adopt a twist conformation on the N-C(H) bridging bond. Their mean planes are inclined to one another by 10.05 (10)°, and they make dihedral angles of 82.09 (10) and 89.67 (11)°, respectively, with the cyclo-pentane ring. The F atom deviates by -0.0238 (2) Å from the benzene ring to which it is attached. In the crystal, mol-ecules are linked by a pair of C-H⋯O hydrogen bonds, forming inversion dimers.

2-(4-Bromo-benzo-yl)-1-ferrocenyl-spiro-[11H-pyrrolidizine-3,11'-indeno-[1,2-b]quinoxaline]

In the title compound, [Fe(C₅H₅)(C₃₃H₂₅BrN₃O)], the fused four-ring system, 11H-indeno­[1,2-b]quinoxaline is essentially planar, with a maximum deviation of 0.087 (3) Å from the least-squares plane of the attached benzene ring. The pyrrolidine rings adopt envelope conformation and make a dihedral angle of 51.76 (19)° with each other. The cyclopentadiene rings of the ferrocenyl moiety have an eclipsed conformation. The Br atom deviates by 0.0190 (9) Å from the attached benzene ring. The mol­ecular structure features an intra­molecular C—H⋯N inter­action, which generates an S(8) ring motif. The crystal packing features C—H⋯O inter­actions, which generate R₂²(18) centrosymmetric dimers, as well as C—H⋯π inter­actions.

6-Ferrocenoyl-7-phenyl-spiro-[hexa-hydro-pyrrolo-[1,2-c][1,3]thia-zole-5,11'-indeno-[1,2-b]quinoxaline]

In the title compound, [Fe(C₅H₅)(C₃₂H₂₄N₃OS)], both the thia­zolidine ring and the pyrrolidine ring adopt an envelope conformation, with the S atom and the phenyl-bearing C atom, respectively, as the flaps. The thia­zolidine ring mean plane makes a dihedral angle of 59.08 (11)° with the pyrrolidine ring mean plane, which in turn makes a dihedral angle of 83.40 (10)° with the cyclo­pentane ring, indicating that the latter two rings are almost orthogonal to one another. In the crystal, a pair of C—H⋯O hydrogen bonds link the mol­ecules forming inversion dimers. The dimers are linked via π–π inter­actions [centroid–centroid distance = 3.7764 (10) Å] involving the quinoxaline moieties forming chains propagating along [1-10].

Synthesis, spectroscopic, coordination and biological activities of some organometallic complexes derived from thio-Schiff base ligands

Two series of mono- and binuclear complexes cyclic or acyclic thio-ferocine Schiff base ligands, derived from the condensation of 2-aminobenzenthiol (L) with monoacetyl ferrocene in the molar ratio 1:1 or in the molar ratio 1:2 for diacetyl ferocine have been prepared. The condensation reactions yield the corresponding Schiff Base ligands, HLa-Maf and H2Lb-Daf. The chelation of the ligands to metal ions occurs through the sulfur of the thiol group as well as the nitrogen atoms of the azomethine group of the ligands. HLa-Maf acts as monobasic bidentate or dibasic tetradentate, while H2Lb-Daf behaves as twice negatively cargend tetradentate ligand. The structures of these ligands were elucidated by elemental analysis, infrared, ultraviolet-visible spectra, as well as (1)H NMR spectra. Reactions of the Schiff bases ligands with ruthenium(III), oxovanadium(IV) and dioxouranium(VI) afforded the corresponding transition metal complexes. The properties of the newly prepared complexes were analyse by elemental analyses, infrared, electronic spectra, (1)H NMR as well as the magnetic susceptibility and conductivity measurement. The metal complexes exhibits different geometrical arrangements such as octahedral and square pyramidal coordination. Schiff base ligands and their metal complexes were tested against two pathogenic bacteria as Gram-positive and Gram-negative bacteria as well as one kind of fungi to study their biological activity. All the complexes exhibit antibacterial and antifungal activities against these organisms.

Functionalized ferrocenes: The role of the para substituent on the phenoxy pendant group

Six ferrocenecarboxylates with phenyl, 4-(1H-pyrrol-1-yl)phenyl, 4-fluorophenyl, 4-chlorophenyl, 4-bromophenyl, 4-iodophenyl as pendant groups were synthesized and fully characterized by spectroscopic, electrochemical and X-ray diffraction methods. The anti-proliferative activity of these complexes were investigated in hormone dependent MCF-7 breast cancer and MCF-10A normal breast cell lines, to determine the role of the para substituent on the phenoxy pendant group. The 4-fluorophenyl ferrocenecarboxylate is inactive in both cell lines while 4-(1H-pyrrol-1-yl)phenyl ferrocenecarboxylate is highly cytotoxic in both cell lines. 4-chlorophenyl and 4-bromophenyl ferrocenecarboxylates have moderate to good anti-proliferative activity in MCF-7 and low anti-proliferative activity on normal breast cell line, MCF-10A whereas the 4-iodophenyl analog is highly toxic on normal breast cell line. The phenyl ferrocenecarboxylate has proliferative effects on MCF-7 and is inactive in MCF-10A. Docking studies between the complexes and the alpha-estrogen receptor (ERα) were performed to search for key interactions which may explain the anti-proliferative activity of 4-bromophenyl ferrocenecarboxylate. Docking studies suggest the anti-proliferative activity of these ferrocenecarboxylates is attributed to the cytotoxic effects of the ferrocene group and not to anti-estrogenic effects.

A self-healing and multi-responsive hydrogel based on biodegradable ferrocene-modified chitosan

Here, we present a novel and facile method for constructing a self-healing hydrogel with multi-responses to external stimuli via the self-assemble of biodegradable ferrocene-modified chitosan (FcCS) in an acid aqueous solution.

5-Ferrocenyl-2,2′-bipyridine ligands: synthesis, palladium(ii) and copper(i) complexes, optical and electrochemical properties

Two 5-ferrocenyl-2,2′-bipyridine ligands were synthesised using the palladium(0) catalysed Suzuki–Miyaura cross-coupling reaction. Palladium(ii) and copper(i) complexes of these ligands were synthesised and the optical and electrochemical properties of the complexes were compared to those of the “free” ligands.

Ruthenium(ii) complexes containing functionalised β-diketonate ligands: developing a ferrocene mimic for biosensing applications

A novel ruthenium(ii) complex with electrochemical behaviour very similar to that of ferrocene was identified by variation of both the number and electronic demand of the substituted β-diketonato ligands bound to the metal centre.

Efficient continuous-flow synthesis of novel 1,2,3-triazole-substituted β-aminocyclohexanecarboxylic acid derivatives with gram-scale production

The preparation of novel multi-substituted 1,2,3-triazole-modified β-aminocyclohexanecarboxylic acid derivatives in a simple and efficient continuous-flow procedure is reported. The 1,3-dipolar cycloaddition reactions were performed with copper powder as a readily accessible Cu(I) source. Initially, high reaction rates were achieved under high-pressure/high-temperature conditions. Subsequently, the reaction temperature was lowered to room temperature by the joint use of both basic and acidic additives to improve the safety of the synthesis, as azides were to be handled as unstable reactants. Scale-up experiments were also performed, which led to the achievement of gram-scale production in a safe and straightforward way. The obtained 1,2,3-triazole-substituted β-aminocyclohexanecarboxylates can be regarded as interesting precursors for drugs with possible biological effects.

2-Ferrocenyl-3-nitro-2H-chromene

In the title compound, [Fe(C₅H₅)(C₁₄H₁₀NO₃)], the cyclo­penta­dienyl rings are in an eclipsed conformation and the pyran ring adopts a half-chair conformation. The mean plane of the pyran ring makes dihedral angles of 79.33 (1) and 80.73 (1)°, respectively, with the substituted and unsubstituted cyclo­penta­dienyl rings. In the crystal, pairs of C—H⋯O hydrogen bonds link the mol­ecules into inversion dimers with R₂²(16) motifs.

Novel ferrocenyl derivatives exert anti-cancer effect in human lung cancer cells in vitro via inducing G1-phase arrest and senescence

AIM

To investigate the effects of 7 novel 1-ferrocenyl-2-(5-phenyl-1H-1,2,4-triazol-3-ylthio) ethanone derivatives on human lung cancer cells in vitro and to determine the mechanisms of action.

METHODS

A549 human lung cancer cells were examined. Cell viability was analyzed with MTT assay. Cell apoptosis and senescence were examined using Hoechst 33258 and senescence-associated-β-galactosidase (SA-β-gal) staining, respectively. LDH release was measured using a detection kit. Cell cycle was analyzed using a flow cytometer. Intracellular ROS level was measured with the 2',7'-dichlorodihydrofluorescein probe. Phosphorylation of p38 was determined using Western blot.

RESULTS

Compounds 5b, 5d, and 5e (40 and 80 μmol/L) caused significant decrease of A549 cell viability, while other 4 compounds had no effect on the cells. Compounds 5b, 5d, and 5e (80 μmol/L) induced G1-phase arrest (increased the G1 population by 22.6%, 24.23%, and 26.53%, respectively), and markedly increased SA-β-gal-positive cells. However, the compounds did not cause nuclear DNA fragmentation and chromatin condensation in A549 cells. Nor did they affect the release of LDH from the cells. The compounds significantly elevated the intracellular ROS level, decreased the mitochondrial membrane potential, and increased p38 phosphorylation in the cells. In the presence of the antioxidant and free radical scavenger N-acetyl-L-cysteine (10 mmol/L), above effects of compounds 5b, 5d, and 5e were abolished.

CONCLUSION

The compounds 5b, 5d, and 5e cause neither apoptosis nor necrosis of A549 cells, but exert anti-cancer effect via inducing G1-phase arrest and senescence through ROS/p38 MAP-kinase pathway.

Alkyne-azide cycloadditions with copper powder in a high-pressure continuous-flow reactor: high-temperature conditions versus the role of additives

A safe and efficient flow-chemistry-based procedure is presented for 1,3-dipolar cycloaddition reactions between organic azides and acetylenes. This simple and inexpensive technique eliminates the need for costly special apparatus and utilizes Cu powder as a plausible Cu(I) source. To maximize the reaction rates, high-pressure/high-temperature conditions are utilized; alternatively, the harsh reaction conditions can be moderated at room temperature by the joint application of basic and acidic additives. A comparison of the performance of these two approaches in a series of model reactions has resulted in the formation of useful 1,4-disubstituted 1,2,3-triazoles in excellent yields. The risks that are associated with the handling of azides are lowered, thanks to the benefits of flow processing, and gram-scale production has been safely implemented. The synthetic capability of this continuous-flow technique is demonstrated by the efficient syntheses of some highly functionalized derivatives of the antifungal cispentacin.