Solvent-free Povarov reaction for synthesizing ferrocenyl quinolines: Antioxidant abilities deriving from ferrocene moiety

Synthesis and Antioxidant Properties of Psoralen Derivatives

Five psoralen derivatives were synthesized and the structures of them were characterized by 1 H-NMR, 13 C-NMR, and IR. The antioxidant properties of the compounds were tested by inhibiting the free radical-initiated DNA oxidation and scavenging the radical reaction. The results showed that the effective stoichiometric factors (n) of the compounds V and IV could reach 2.00 and 2.11 in the system of inhibiting the DNA oxidation reaction initiated by 2,2'-Azobis(2-methylpropionamidine) dihydrochloride (AAPH). In the inhibition of ⋅OH-oxidation of the DNA system, compounds I~V showed antioxidant properties. The thiobarbituric acid absorbance (TBARS) percentages of compounds IV and V were 76.19 % and 78.84 %. Compounds I~V could also inhibit Cu2+ /GSH-oxidation of DNA, and all compounds exhibited good antioxidant properties except compound II (94.00 %). All the five compounds were able to trap diammonium 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonate) salt radical (ABTS+ ⋅), 2,2-diphenyl-1-picrylhydrazyl radical (DPPH⋅) and 2,6-di-tert-butyl-alpha-(3,5-di-tert-butyl-4-oxo-2,5-cyclohexadien-p-tolylox radical (galvinoxyl⋅). The ability of compounds I~V to scavenge those free radicals can be measured by the k values. The k values ranged from 0.07 to 0.82 in scavenging ABTS+ ⋅, galvinoxyl, and DPPH radicals, respectively.

The Povarov Reaction: A Versatile Method to Synthesize Tetrahydroquinolines, Quinolines and Julolidines

The multicomponent Povarov reaction represents a powerful approach for the construction of substances containing N-heterocyclic frameworks. By using the Povarov reaction, in addition to accessing tetrahydroquinolines, quinolines and julolidines in a single step, it is possible to form the following new bonds: two Csp 3–Csp 3 and one Csp 3–Nsp 3, two Csp 2–Csp 2 and one Csp 2–Nsp 2, and four Csp 3–Csp 3 and two Csp 3–Nsp 1, respectively. This short review discusses the main features of the Povarov reaction, including its mechanism, the reaction scope by employing different catalysts and substrates, as well as stereoselective versions.

1 Introduction

2 Mechanism of the Povarov Reaction

3 Tetrahydroquinolines

4 Quinolines

5 Julolidines

6 Concluding Remarks

Effect of hydroxyl on antioxidant properties of 2,3-dihydro-3,5-dihydroxy-6-methyl-4H-pyran-4-one to scavenge free radicals

It is well known that 2,3-dihydro-3,5-dihydroxy-6-methyl-4H-pyran-4-one (DDMP) is usually formed in the Maillard reaction and it contributes to the antioxidant properties of Maillard reaction intermediates. A series of hydroxyl group protected DDMP derivatives were synthesized to further understand the source of antioxidant activity. Antioxidant abilities of the DDMP derivatives were evaluated by scavenging the 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonate) cationic radical (ABTS˙+), 2,2'-diphenyl-1-picrylhydrazyl radical (DPPH), and galvinoxyl radical, respectively. It was found that the introduction of protecting groups to the free hydroxyl groups of DDMP decreases their reducing abilities. In particular, the hydroxyl group at the olefin position exhibited a remarkable impact on the antioxidant activity of DDMP, indicating that the unstable enol structure in the DDMP moiety is the key factor for its antioxidant activity.

Multicomponent Reactions for Integrating Multiple Functional Groups into an Antioxidant

A large number of convincing evidences has revealed the correlation of the pathogeny of diseases with the oxidative damages of DNA, protein, biomembrane, and other biological species, while supplementation of antioxidants is demonstrated to be a promising way to avoid, at least, rectify the unbalance redox status in vivo. Although many endeavors have focused on synthesis of antioxidants, a main hurdle still hinders the wide usages of synthetic antioxidants because of low bioavailability and potential cytotoxicity. The search for antioxidants with multiple functional groups being recognized by different receptors becomes a much sought by researchers, and multicomponent reactions (MCRs) provide with powerful tools for the construction of multifunctional antioxidants. Presented herein is a personal account on the application of MCRs for the synthesis of multifunctional antioxidants, while radical-induced oxidation of DNA acts as the experimental system for evaluating antioxidative effect. Concretely, the Biginelli three-component reaction (3CR) affords such a dihydropyrimidine scaffold that the tautomerization between C=S and C-SH leads to antioxidative effect. The Povarov 3CR is able to integrate multiple antioxidative groups, i. e., ferrocenyl and -N(CH₃ )₂ , into a quinoline scaffold, while the Groebke 3CR provides with imidazo[1,2-a]pyridine skeleton for inhibiting DNA oxidation. Additionally, the Knoevenagel-related MCRs also become efficient strategies for achieving radical-scavengers. On the other hand, the Ugi 4CR and Passerini 3CR result in the dipeptide and α-acyloxycarboxamide, respectively, with the benefit for the integration of antioxidative features by aliphatic chains. Therefore, MCRs have emerged as efficient tools for integrating multiple antioxidative features into one molecule in order to meet with complicated requirements from various biological surroundings.

Anti-Oxidant in China: A Thirty-Year Journey

Anti-oxidant refers to such a kind of endogenous or exogenous compound that is able to retard or even prohibit in vivo or in vitro oxidation with only small amount being used. The study of anti-oxidants starts nearly 30 years ago, and the research on this topic in China almost begins simultaneously with that in the world. Gratifyingly, contributions on anti-oxidants from China researchers have rapidly increased in the recent decade as anti-oxidants have become a hot topic in biochemistry, pharmacology, food science, chemistry as well as other related disciplines. Anti-oxidants provide a specific viewpoint for clarifying pharmacological effects of Chinese medicinal herbs. For example, as a traditional Chinese medicinal herb, Panax ginseng C. A. Meyer is found to be a natural anti-oxidant resource. Meanwhile, some signaling pathways such as nuclear factor-[Formula: see text]B (NF-[Formula: see text]B), nuclear factor erythroid 2 related factor 2 (Nrf2), and Kelch-like ECH associated protein 1 (Keap1) are regarded to play an important role in anti-oxidant responses. These findings provide a substantial basis for understanding the pharmacological behaviors of Chinese medicinal herbs in view of regulating the aforementioned signaling pathways. Moreover, inhibition of reactive oxygen species (ROS) by supplementation of anti-oxidant becomes a popularly accepted idea in keeping health and treating diseases. Isolations of antio-xidative ingredients from medicinal herbs and foods lead to set up a large range of anti-oxidative compound libraries, and intake of anti-oxidants from foods may be the most efficient way for supplementing exogenous anti-oxidants. On the other hand, designing anti-oxidants with novel structures motivates organic and medicinal chemists to explore the structure–activity relationship, and then, to find novel structural features with anti-oxidative properties. Therefore, it is reasonable to believe that China researchers will donate more endeavors to obtain more achievements on anti-oxidants in the future.

Ferrocene-Containing Polymer via the Biginelli Reaction for In Vivo Treatment of Oxidative Stress Damage

Small molecule antioxidants have little impact on oxidative stress in vivo because of their poor bioavailability. To explore an antioxidant for in vivo applications, a polymeric antioxidant containing a ferrocene moiety was developed. The ferrocene-containing monomer was synthesized through the robust tricomponent Biginelli reaction with a high yield. The corresponding water-soluble copolymer was conveniently prepared via radical polymerization. Both the ferrocene moiety and the Biginelli structure (dihydropyrimidin-2(H)-one) contributed to the remarkable radical scavenging ability of this highly biocompatible copolymer. It was more efficient than traditional small molecule antioxidants at protecting cells against fatal oxidative stress. This copolymer also showed clear therapeutic activity in counteracting oxidation-induced acute liver damage in a live mouse model. Our study into functional organometallic polymers resulted in a promising polymeric biomaterial that may find therapeutic applications and have important implications in the fields of organic chemistry and polymer chemistry.

Enhancing Antioxidant Effect against Peroxyl Radical-Induced Oxidation of DNA: Linking with Ferrocene Moiety!

As a major member in the family of reactive oxygen species, peroxyl radical is able to abstract hydrogen atom from 4-position of ribose, leading to the collapse of DNA strand. Thus, inhibiting oxidative stress with exogenous antioxidants acts as a promising strategy to protect the integrity of DNA structure and is thereby suggested to be a pathway against developments of related diseases. Ferrocene as an organometallic scaffold is widely applied in the design of organometallic drugs, and redox of Fe(II)/Fe(III) in ferrocene offers advantage for providing electron to radicals. Presented herein are our ongoing studies on ferrocene-appended antioxidants, including McMurry reaction applied to construct ferrocifen; Aldol condensation used to prepare ferrocenyl curcumin; Povarov reaction employed to prepare ferrocenyl quinoline; Biginelli reaction used to construct ferrocenyl dihydropyrimidine; Groebke reaction used to synthesize ferrocenyl imidazo[1,2-a]pyridine; and Passerini three-component reaction as well as Ugi four-component reaction applied to synthesize α-acyloxycarboxamide and bisamide, respectively. It is found that ferrocene moiety is able to enhance antioxidative effect of the aforementioned scaffolds even without the aid of phenolic hydroxyl group. The role of ferrocene in enhancing antioxidative effect can be attributable to trapping radicals, decreasing oxidative potential, and increasing the affinity toward DNA strand. Therefore, ferrocene is worthy to be taken into consideration in the design of drugs in relation to DNA oxidation.

Synthesis and biological evaluation of ferrocene-based cannabinoid receptor 2 ligands

Ferrocene analogs of known fatty acid amide hydrolase inhibitors and CB2 ligands have been synthesized and characterized spectroscopically and crystallographically. The resulting bio-organometallic isoxazoles were assayed for their effects on CB1 and CB2 receptors as well as on fatty acid amide hydrolase. None had any fatty acid amide hydrolase activity but compound 3, 5-(2-(pentyloxy)phenyl)-N-ferrocenylisoxazole-3-carboxamide, was found to be a potent CB2 ligand (Ki = 32.5 nM).

An efficient and green synthesis of ferrocenyl-quinoline conjugates via a TsOH-catalyzed three-component reaction in water

An efficient and green synthesis of 4-ferrocenylquinoline derivatives through a TsOH-catalyzed three-component reaction of aromatic aldehydes, amines and ferrocenylacetylene in water has been successfully developed. This strategy is a powerful method for the construction of diverse ferrocenyl-quinoline conjugates from simple available starting materials as it minimized the use of metal catalyst and organic solvent in the reaction process. The conjugates feature unique structures and excellent electronic properties. Moreover, a plausible mechanism for this TsOH-catalyzed three-component reaction was proposed and assessed.

Synthesis of substituted 4-hydroxyalkyl-quinoline derivatives by a three-component reaction using CuCl/AuCl as sequential catalysts

A new method to construct 4-hydroxyalkyl-quinoline derivatives is described via Cu(i) and Au(i) sequential catalyzed cyclization of anilines with aldehyde derivatives and aliphatic alkynes, respectively.

Coumarin-fused coumarin: antioxidant story from N,N-dimethylamino and hydroxyl groups

Two coumarin skeletons can form chromeno[3,4-c]chromene-6,7-dione by sharing with the C ═ C in lactone. The aim of the present work was to explore the antioxidant effectiveness of the coumarin-fused coumarin via six synthetic compounds containing hydroxyl and N,N-dimethylamino as the functional groups. The abilities to quench 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonate) cationic radical (ABTS(+•)), 2,2'-diphenyl-1-picrylhydrazyl radical (DPPH), and galvinoxyl radical revealed that the rate constant for scavenging radicals was related to the amount of hydroxyl group in the scaffold of coumarin-fused coumarin. But coumarin-fused coumarin was able to inhibit DNA oxidations caused by (•)OH, Cu(2+)/glutathione (GSH), and 2,2'-azobis(2-amidinopropane hydrochloride) (AAPH) even in the absence of hydroxyl group. In particular, a hydroxyl and an N,N-dimethylamino group locating at different benzene rings increased the inhibitory effect of coumarin-fused coumarin on AAPH-induced oxidation of DNA about 3 times higher than a single hydroxyl group, whereas N,N-dimethylamino-substituted coumarin-fused coumarin possessed high activity toward (•)OH-induced oxidation of DNA without the hydroxyl group contained. Therefore, the hydroxyl group together with N,N-dimethylamino group may be a novel combination for the design of coumarin-fused heterocyclic antioxidants.