Frontiers in Natural Product Chemistry

The emergence of SARS-CoV-2 in late 2019 and the subsequent COVID-19 pandemic have highlighted an urgent global demand for developing potent antiviral therapies with minimal side effects. Despite advances in current treatments, they remain limited and non-specific medications. Natural phytochemicals, particularly flavanones, a subclass of flavonoids with diverse biological properties, have emerged as promising antiviral candidates. This review explores flavanones’ potential against SARS-CoV-2, focusing on their chemistry, occurrence, mechanism of action, key active compounds, challenges to their application, and structure-activity relationships (SARs). A comprehensive literature review was conducted using multiple electronic databases, including Scopus, PubMed, Google Scholar, and ScienceDirect. Evidence from previous computational, cellular, and animal models underscores flavanones’ multifaceted mechanisms, including direct viral enzyme inhibition and immunomodulation to mitigate cytokine storms. Flavanones such as hesperidin, naringin, and their aglycones exhibit significant potential for combating the COVID-19 pandemic, though challenges such as poor solubility and insufficient clinical data remain. SAR insights showed how structural modifications, specifically glycosylation, could enhance potency and bioavailability. These findings could position flavanones as valuable scaffolds for developing novel anti-COVID-19 agents and optimizing current therapeutic protocols. Further studies are warranted to transform these research insights into clinical applications.

In the marine environment, it is estimated that numerous fungal species on our planet range from 1.5-5.0 million, however, to date, only 10% of fungi have been identified. In the marine ecosystem, the most widely found fungi belong to Aspergillus genus. Apart, from the coastal ecosystem and open-ocean, fungi are also found in the deep sea and demonstrated the ability to adapt to extreme environmental conditions. Marine fungi have developed chemical defenses for their survival to combat extreme conditions like variations in pressure, temperature, salinity, desiccation, and pH, resulting in the production of chemically diverse scaffolds. Different strains of genus Aspergillus settle on various marine substrates like fauna (sponge, softcoral, tunicates, fish etc.), plants (algae), and with the environment (sediments, seawater), have been known to produce numerous secondary metabolites. Bioactive compounds, namely, butyrolactones & terrein (anti-inflammatory), kojic acid (skin whitening agent), pyrrolidinedione, AD0157 (angiosuppressive), asperxanthone (Antiviral), aspergiolide A (cytotoxic), methylhydroquinone (antibacterial), etc. from marine Aspergillus make them a valuable source for pharmaceutical applications. This chapter gives a comprehensive survey of metabolites isolated from marine Aspergillus in the last two decades beginning from 2001, including their occurrence, structural information and biological activities.

Sensory analysis of virgin olive oil, organoleptic assessment, or panel test (PT), is one of the most important techniques for evaluating the quality of virgin olive oil. Sensory analysis of olive oil is based on the International Olive Council (IOC) standards. It is carried out by trained panelists to evaluate and calculate median values of the positive and negative attributes. This chapter is aimed to discuss the sensory analysis of virgin olive oil, sensory methodology, positive and negative (defects) attributes, classification of virgin olive oils, test conditions, and impact factors on sensory quality.

Melatonin production and release in the brain are related to the light and dark cycles. The synthesis of melatonin occurs in the pineal gland. The night-time melatonin production is stimulated by neural input from a structure called the suprachiasmatic nucleus, which acts as a master circadian clock for the brain. Tryptophan is an essential amino acid that is used to produce the monoamine neurotransmitter serotonin and the hormone melatonin. In the process of converting tryptophan into serotonin and melatonin, several important cofactors are used, including tetrahydrobiopterin, s-adenosyl methionine (SAM), and co-enzymes. Molecular models have indicated that any disruption in the circadian rhythm of melatonin production or release can cause nocturnal activity and daytime quiescence. Convincing evidence supports the presence of melatonin in plants and foods. The intake of such foods affects circulating melatonin levels in humans. Melatonin dietary supplements have been studied for sleep disorders, such as jet lag, disruptions of the body's internal “clock,” insomnia, and problems with sleep among people who work night shifts. The normal melatonin cycle can diminish with age and be disrupted by exposure to electromagnetic pollution and blue-wavelength light. Supplemental melatonin contributes to restoring normal, healthy sleep patterns. The highest melatonin-containing food groups in animals are eggs and fish. Dietary melatonin is absorbed in the gastrointestinal tract and transported into the bloodstream. The ingestion of medicinal and plant foods by mammals as a source of melatonin may be conceived as a key step in serum melatonin modulation and may even cross the blood brain barrier, promoting health. Literature reviews have reported mixed views regarding melatonin supplementation and dosage.

Since the ancient period, various plants have been used for dietary consumption for their tastes as well as beneficial effects on health. Among them, the tea plant (Camellia sinensis) is a notable one. Brewed tea is amongst the top most consumed beverages around the globe. Tea leaves undergo different processes and fermentations to produce tea powder from which brew is prepared. Depending upon its processing, it is divided into various varieties like green, oolong, white, and black tea. Fermentation processes also affect the phytochemical contents in each variety which further determines its dietary significance. Among various phytochemicals present in tea leaves, polyphenolic catechins are the most abundant ones among which epigallocatechin-3-gallate is the dominant catechin. At the time of fermentation, most contents of catechins are found in green tea as oxidation of catechins takes place. Black tea undergoes the most extensive fermentation process and hence catechins get reduced. Most of the catechins in black tea bind with each other and form polymeric structures (e.g. theaflavins and thearubigin) which also exhibit prominent health benefits. Theaflavins, one of the categories of polymeric catechin compounds, are antioxidants and also have various medicinal properties. Apart from the entire polyphenolic compound present in tea, various other non-polyphenolic compounds like enzymes, and non-protein amino acids like L-theanine, pigments, etc. can also be found that exhibit beneficial properties. A detailed study of polyphenolic green tea catechins mainly EGCG, polyphenolic black tea compound theaflavins, and non-protein Ltheanine are described in this chapter containing physical properties, chemical, and biosynthesis process, isolation process, pharmacokinetic study, analytical process, toxicity study, and health beneficial studies.