Phenolic compounds are the most abundant antioxidants in the human diet. They have a considerable structural diversity, characterized by the hydroxyl groups on aromatic rings. According to the number of phenol rings and the structural elements that bind rings to one another, such compounds are grouped and classified as simple phenols, phenolic acids, flavonoids, xanthones, stilbenes, and lignans. Each group has different mechanisms of action correlated to a structural specificity, which confer the antioxidant properties to the compounds. They act mainly in scavenging reactive species of oxygen, nitrogen, and chlorine or can also chelate metal ions, acting in both the initiation stage and in the propagation of the oxidative process. The most common in vitro methods used to evaluate antioxidant activity of phenolic compounds are in vitro methods which are based on single electron transfer reaction or single hydrogen atom transfer reaction.

Phenolic Compounds: Structure, Classification, and Antioxidant Power

Anti-inflammatory effects of flavonoids.

Flavonoids are phytochemical compounds present in many plants, fruits, vegetables, and leaves, with potential applications in medicinal chemistry. Flavonoids possess a number of medicinal benefits, including anticancer, antioxidant, anti-inflammatory, and antiviral properties. They also have neuroprotective and cardio-protective effects. These biological activities depend upon the type of flavonoid, its (possible) mode of action, and its bioavailability. These cost-effective medicinal components have significant biological activities, and their effectiveness has been proved for a variety of diseases. The most recent work is focused on their isolation, synthesis of their analogs, and their effects on human health using a variety of techniques and animal models. Thousands of flavonoids have been successfully isolated, and this number increases steadily. We have therefore made an effort to summarize the isolated flavonoids with useful activities in order to gain a better understanding of their effects on human health.

https://www.mdpi.com/1420-3049/25/22/5243/pdf

Important Flavonoids and Their Role as a Therapeutic Agent.

Spike glycoprotein, a class I fusion protein harboring the surface of SARS-CoV-2 (SARS-CoV-2S), plays a seminal role in the viral infection starting from recognition of the host cell surface receptor, attachment to the fusion of the viral envelope with the host cells. Spike glycoprotein engages host Angiotensin-converting enzyme 2 (ACE2) receptors for entry into host cells, where the receptor recognition and attachment of spike glycoprotein to the ACE2 receptors is a prerequisite step and key determinant of the host cell and tissue tropism. Binding of spike glycoprotein to the ACE2 receptor triggers a cascade of structural transitions, including transition from a metastable pre-fusion to a post-fusion form, thereby allowing membrane fusion and internalization of the virus. From ancient times people have relied on naturally occurring substances like phytochemicals to fight against diseases and infection. Among these phytochemicals, flavonoids and non-flavonoids have been the active sources of different anti-microbial agents. We performed molecular docking studies using 10 potential naturally occurring compounds (flavonoids/non-flavonoids) against the SARS-CoV-2 spike protein and compared their affinity with an FDA approved repurposed drug hydroxychloroquine (HCQ). Further, our molecular dynamics (MD) simulation and energy landscape studies with fisetin, quercetin, and kamferol revealed that these molecules bind with the hACE2-S complex with low binding free energy. The study provided an indication that these molecules might have the potential to perturb the binding of hACE2-S complex. In addition, ADME analysis also suggested that these molecules consist of drug-likeness property, which may be further explored as anti-SARS-CoV-2 agents. Communicated by Ramaswamy H. Sarma.

Targeting SARS-CoV-2 spike protein of COVID-19 with naturally occurring phytochemicals: an in silico study for drug development.

The impact of pulsed electric field (PEF) treatment on orange, pomelo, and lemon in aqueous media was studied. Whole fruits and stack of peels were PEF treated at electric field strength of 3 kV/cm and 10 kV/cm, respectively. The PEF induced damage of the whole fruit was evaluated by different disintegration indexes. The PEF treatment increased the yield of juice obtained after pressing by 25% for orange, 37% for pomelo, and 59% for lemon. The effect of PEF on different parts of each fruit was studied. Flavedo and albedo were separated from the untreated fruit or PEF treated fruit and solvent extraction (1/1 ethanol/water solution) of polyphenols was conducted. The quantification and characterization of polyphenols in each part was compared for untreated and PEF treated fruit. The application of high electric field strength on orange peels enhanced the extraction of polyphenols up to 22 mg GAE/g DM. Industrial relevance Citrus fruits are valuable sources of bioactive compounds (vitamins, antioxidants, carotenoids and flavonoids) and their processing represents an industrial importance. An application of PEF to whole fruits may be useful for improving the efficiency of juice extraction from different citrus fruits. The concentration of polyphenols in the extracted juice could be significantly enhanced by the treatment of citrus peels with PEF at high electric field strength.

Kai shun Bi

Papers

Bioactive flavonoids in medicinal plants: Structure, activity and biological fate.