Polyhydroxylated 2-styrylchromones as potent antioxidants

Styrylchromones: Biological Activities and Structure-Activity Relationship

Styrylchromones (SC) are a group of oxygen-containing heterocyclic compounds, which are characterized by the attachment of a styryl group to the chromone core. SC can be found in nature or can be chemically synthesized in the laboratory. As their presence in nature is scarce, the synthetic origin is the most common. Two types of SC are known: 2-styrylchromones and 3-styrylchromones. However, 2-styrylchromones are the most common, being more commonly found in nature and which chemical synthesis is more commonly described. A wide variety of SC has been described in the literature, with different substituents in different positions, the majority of which are distributed on the A- and/or B-rings. Over the years, several biological activities have been attributed to SC. This work presents a comprehensive review of the biological activities attributed to SC and their structure-activity relationship, based on a published literature search, since 1989. The following biological activities are thoroughly revised and discussed in this review: antioxidant, antiallergic, antiviral, antibacterial, antifungal, anti-inflammatory, and antitumoral, affinity and selectivity for A3 adenosine receptors, neuroprotective, and α-glucosidase inhibition. In general, SC are composed by a promising scaffold with great potential for the development of new drugs.

A novel sulfonyl chromen-4-ones (CHW09) preferentially kills oral cancer cells showing apoptosis, oxidative stress, and DNA damage

Several functionalized chromones, the key components of naturally occurring oxygenated heterocycles, have anticancer effects but their sulfone compounds are rarely investigated. In this study, we installed a sulfonyl substituent to chromen-4-one skeleton and synthesized CHW09 to evaluate its antioral cancer effect in terms of cell viability, cell cycle, apoptosis, oxidative stress, and DNA damage. In cell viability assay, CHW09 preferentially kills two oral cancer cells (Ca9-22 and CAL 27), less affecting normal oral cells (HGF-1). Although CHW09 does not change the cell cycle distribution significantly, CHW09 induces apoptosis validated by flow cytometry for annexin V and by western blotting for cleaved poly(ADP-ribose) polymerase (PARP), and caspases 3/8/9. These apoptosis signaling expressions are partly decreased by apoptosis inhibitor (Z-VAD-FMK) or free radical scavenger (N-acetylcysteine). Furthermore, CHW09 induces oxidative stress validated by flow cytometry for the generations of reactive oxygen species (ROS) and mitochondrial superoxide (MitoSOX), and the suppression of mitochondrial membrane potential (MMP). CHW09 also induces DNA damage validated by flow cytometry for the increases of DNA double strand break marker γH2AX and oxidative DNA damage marker 8-oxo-2'-deoxyguanosine (8-oxodG). Therefore, our newly synthesized CHW09 induces apoptosis, oxidative stress, and DNA damage, which may lead to preferential killing of oral cancer cells compared with normal oral cells.

Synthesis of (E)-2-Styrylchromones and Flavones by Base-Catalyzed Cyclodehydration of the Appropriate β-Diketones Using Water as Solvent

A low cost, safe, clean and environmentally benign base-catalyzed cyclodehydration of appropriate β-diketones affording (E)-2-styrylchromones and flavones in good yields is disclosed. Water was used as solvent and the reactions were heated using classical and microwave heating methods, under open and closed vessel conditions. β-Diketones having electron-donating and withdrawing substituents were used to evaluate the reaction scope. The reaction products were isolated in high purity by simple filtration and recrystallization from ethanol, when using 800 mg of the starting diketone under classical reflux heating conditions.

Synthesis and Evaluation of Novel Fluorinated 2-Styrylchromones as Antibacterial Agents

A range of fluorinated 2-styrylchromones (5a–g) of which six were new (5a–f) were prepared in three steps using the Baker-Venkataraman rearrangement along with two methoxylated derivatives (5h-i) and a methylenedioxy derivative (5j) and screened for their antibacterial activity using Gram-positive bacteria (Staphylococcus aureus, sciuri, andxylosusas well asBacillus subtilis) and Gram-negative bacteria (Escherichia coli, Pseudomonas aeruginosa, andKlebsiella pneumonia). The compounds were most effective againstB. subtilisfollowed byS. aureusand a single strain ofE. coli(ATCC 25922). Difluorination on the phenyl ring was shown to enhance antibacterial activity, and fluorine substitution at the 6 position was shown to be far superior to substitution at the 7 position. In comparison to tetracycline, the activity indices of the fluorinated styrylchromones ranged from 0.50 to 0.75 againstB. subtilis. The crystal structure of 2′-fluoro-2-styrylchromone is also presented, and the molecule was shown to be planar.

Synthesis and antioxidant properties of new chromone derivatives

Nowadays, the recognition of the benefits of antioxidants is eliciting an increasingly interest in the search for new molecules with improved activity. The aim of the present work was to search for improved reactive oxygen species (ROS) and reactive nitrogen species (RNS) scavengers by testing new structures of 2-styrylchromones (2-SC) and 3-substituted flavones, which were synthesised by the Baker-Venkataraman approach. The new compounds were also tested for their metal chelating capacity and reducing activity. The obtained results showed that the methylation of hydroxyl groups decreases the scavenging of ROS and RNS by 2-SC. The decrease in the scavenging activities was, generally, more evident when the methylation occurred in B-ring, except for O2*- and (1)O(2). On the other hand, the introduction of a substituent, either hydroxyl or methoxyl, in position 8 was sometimes favourable and others unfavourable to the scavenging activities, depending on the reactive species. In conclusion, the study of the antioxidant properties of the new 2-SC and flavones allowed establishing new structure-activity relationships and brought out, in some cases, pharmacophores with improved activity.

2-Styrylchromones: novel strong scavengers of reactive oxygen and nitrogen species

2-Styrylchromones are a small group of naturally occurring chromones, vinylogues of flavones (2-phenylchromones). Natural and synthetic 2-styrylchromones have been tested in different biological systems, showing activities with potential therapeutic applications. In particular, the potential and hitherto understudied antioxidant behavior of these compounds has been raised as a matter of interest. Thus the present work consisted in the study of the in vitro scavenging activities for reactive oxygen species (ROS) and reactive nitrogen species (RNS) of various 2-styrylchromone derivatives and structurally similar flavonoids. Some of the studied 2-styrylchromones proved to be extremely efficient scavengers of the different ROS and RNS, showing, in some cases, IC(50)s under 1 microM. The hydroxylation pattern of 2-styrylchromones, especially in the B-ring but also in the A ring, modulates the activity of these compounds, the catecholic derivatives being the most effective scavengers. The styryl pattern also contributes to their observed outstanding antioxidant activity. In conclusion, the scavenging activities for ROS/RNS of 2-styrylchromone derivatives, here shown for the first time, provide novel and most promising compounds to be applied as antioxidants.