Frontiers in Natural Product Chemistry

Background Marine organisms are always considered as one of the richest sources of natural products. Historically, they are being used as medicines in diverse ailments. In recent years, researchers have reported several primary and secondary metabolites in marine organisms (few examples are macroalgae, sponges, seagrasses, bacteria, microalgae), which serve in numerous disorders, of which 20–25% have shown antiviral, antimicrobial, antifungal, anticancer or anti-inflammatory properties. According to the global pharmaceutical website, there are a total of nine approved pharmaceuticals from a marine source, and apart from this, thirty-one other compounds are currently in a clinical trial.

Objective Discovery of potent antiviral drugs is required currently to mitigate life-threatening viruses. Considerable research exploring the bioactivity of marine macroalgae has been documented, highlighting the immense biochemical diversity of its primary and secondary metabolites with a novel mechanism of action, making them perfect sources for novel antiviral bioactive compounds of pharmaceutical interest.

Methods Databases utilizing bibliographic databanks, such as PubMed, SpringerLink, Elsevier journal, Science Direct, Scopus databases, and Google search were surveyed using keywords anti-viral, seaweeds, antiviral drugs, seagrass, polyphenols, pharmacology, clinical trials.

Results Marine phytoplanktons are found to be the major source of several key medicinal agents (polyphenols, phenolic compounds), which are largely obtained from seaweeds and seagrasses and have shown promising antiviral activity in cell culture studies. This review explains recent developments regarding antiviral agents from seaweeds and seagrass.

Marine organisms produce numerous secondary metabolites that exhibit a wide range of biological activities, which have applications in pharmaceutical research. Numerous secondary metabolites have been discovered from various marine organisms and studied for their chemical and biological properties. Among the secondary metabolites of marine organisms, alkaloids constitute a versatile group of bioactive natural products with promising bio-activities. Several alkaloids, such as pyridoacridines, pyrroles, bisindole, isoquinolines, quinolizidines and bromotyrosines, etc., to name a few, have been isolated from marine organisms. The chemical diversity and bio-activities of marine alkaloids are reported in several research and review articles. Quinolizidine alkaloids (QAs) are a group of compounds that possess either a quinolizidine ring or its derivatives. They are isolated from terrestrial plants, animals and also from numerous marine organisms, such as sponges, tunicates, fungus, etc. Biological activities exhibited by QAs include ichthyotoxicity, chemical defense, antimicrobial, antiviral, and inhibition of nicotinic acetylcholine receptors. In the past years, a few scattered reviews appeared on the isolation of QAs from natural sources, mostly from terrestrial sources, but the reports skipped several QAs of marine origin. This chapter presents a comprehensive review of various quinolizidine and bis-1-oxaquinolizidine alkaloids isolated from marine organisms, detailing their chemical structures and reported biological properties. Further, the chapter highlighted synthesis of some marine-derived QAs, namely, petrosins, xestospongins, clavepictines, pictamine, citrinadins A and B.

Interest in psychoactive ethnobotanicals such as ayahuasca or Psilocybe mushrooms for clinical uses has increased over the last two decades. While clinical and experimental approaches have focused on using isolated compounds of interest (such as psilocybin), an emerging trend in drug discovery involves a more comprehensive approach. The polypharmacology paradigm, as it has been named, suggests that promiscuous drugs could be safer and more effective than highly selective ones. This is especially relevant with regards to complex diseases, like most mental health problems and neurodegenerative diseases, and for natural products, including psychoactive ethnobotanicals. Natural products not only show a multi-target profile, but they also contain several compounds capable of interacting with one another and producing synergistic effects. In this chapter, the use of whole natural products instead of isolated compounds is suggested in support of combining two recent paradigms: psychedelicassisted therapy on the one side and polypharmacology on the other.

Phenolic compounds, the bioactive phytochemicals, are abundantly found in a huge variety of food items, including fruits, vegetables, cereals, legumes, and herbs. Phenolic compounds are often called phenols, phenolics, and polyphenols. They are secondary metabolites of plants and are considered an integral part of both animal and human diet. Natural phenolic compounds have acquired increasing attention in the last few years because of their countless health-related therapeutic interventions. Biological activities of phenolic compounds include anti-oxidative, anti-inflammatory, antiallergic, and anti-hypertensive are found to play their role in neuroprotection. All of these above mentioned properties of different phenolic compounds play a critical and central role in preventing the progression of neurodegenerative, neurological disorders and brain injuries. A list of phenolic compounds including resveratrol, quercetin, rutin, curcumin, baiclein, luteolin, and (-) Epigallocatechin-3-gallateon have been discussed in detail in the context of their neuroprotective action. The present chapter describes a brief and comprehensive overview of the physiological activities of phenolic compounds along with their potential neuroprotective approach.

The growth of the average lifespan of the global population is accompanied by a progressive increase in the prevalence of neurodegenerative disease (NDD). Common NDDs such as Alzheimer’s, Parkinson’s, Huntington’s diseases, and others are known to be strongly related to aging. The prevalence of NDD is expected to increase steeply with the increment in life expectancy. The currently available therapeutic interventions are mainly symptomatic, and most have failed to reverse or slow down the disease progression. Hence, new treatments and preventive measures are urgently needed. Plants from the Lamiaceae family have reported several neuroprotective effects attributed to the abundance of secondary metabolites that could target multiple pathways of the cellular death mechanism. Owing to the multifactorial nature of NDDs, the abundance of secondary metabolites in plants has attracted the attention of researchersto the neuroprotective potentials of natural products. The neuroprotective effects and bioactive constituents of common herbs such as Perilla frutescens (Perilla), Sideritis scardica (Ironwort), Ocimum sanctum (Holy basil), Origanum syriacum (Lebanese oregano), Satureja bachtiarica (Bakhtiari savory), Orthosiphon stamineus (Cat whisker), Prunella vulgaris (Prunella), Pogostemon cablin (Patchouli) and Stachys sieboldii (Japanese artichoke) from the Lamiaceae family are discussed in this chapter. The neuroprotective property of these herbs relied on their ability to target the underlying mechanisms of neuronal cell death, such as aberrant protein aggregation, excessive oxidative stress, neurotransmission system dysfunction, neuroinflammation, and others. The multi-targeting ability of these plants is attributed to their complex chemical compositions with different bioactive compounds. Thus, the incorporation of these plants and herbs into the management of NDD should be further explored. Their role as dietary supplements to preserve the function of the nervous system is also strongly advocate.

The search for anti-inflammatory drugs is still challenging, even though recent advances in modern medicine have provided some relief. Coumarins, well known secondary metabolites widely distributed in plant kingdom, have successfully documented their candidature in the development of anti-inflammatory agents. Natural coumarins, including esculetin, umbelliferone, scopoletin and marmin showed potent anti-inflammatory activity through various targets, including COX-2, LOX, iNOS TNF-α, TXB2. Over the past decade, various synthetic modifications have been carried out on the scaffold of these natural products. The current review focuses on various synthetic and semi-synthetic modifications carried out on the coumarin nucleus with a primary focus on the evaluation of anti-inflammatory activity along with structureactivity relationship study.

Heterocycles have a crucial role in the design and discovery of active pharmaceutical ingredients. Chromenes are heterocycles containing oxygen that are abundantly found in nature and have attracted much attention because of their interesting drug activities. Chromene and its derivatives cover an extensive range of biological properties such as antibacterial, anti-inflammatory, anti-HIV, anti-cancer, anti-oxidant and antimicrobial properties. Regarding the numerous investigations conducted on these valuable compounds during the past few years, we have also pointed to the advances of the last five years in the field of the synthetic and biological importance of these compounds. Concerning the high importance of synthesis of chromene and its derivatives by synthesis methods of 2H-chromenes, 4H-chromenes, benzochromenes, benzopyrans and fused-chromenes, we mentioned that this issue includes the necessity of using various catalysts in mild conditions and/or in microwave conditions. In the following, concerning the very high biological importance of chromenes, we implied some biological properties, including anticancer, anti-inflammatory, anti-oxidant and antimicrobial activities, which indicated that the considered results could be promising and effective for the use of chromene derivatives in the field of drug design. Ultimately, we mentioned several vital methods and strategies include green synthesis and multi-component reactions in various categories for the general synthesis of various types of chromene derivatives. In economical, efficient, green and mild conditions, the above-said methods can synthesize high-efficiency products of chromene and its derivatives in a short period of time.