The Potential of Natural Products in the Management of COVID-19.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) was identified as the novel coronavirus that caused a life-threatening viral illness (COVID-19) at the end of 2019. Within a short period of time, this virus spread leading to tremendous loss of life and economic damage. Medications to treat this virus are not yet established, and the process of implementing new strategies for medications is time-consuming. Recent clinical studies revealed the abandonment of the most promising candidates, who later became potential leads. Only through comprehensive study for safety and efficacy the medications, which have already received approval, be repurposed for use in different therapeutic purposes. Natural sources are being used arbitrarily as antiviral drugs and immunity boosters because there are no clear therapies on the horizon. It has long been known that most natural compounds have strong antiviral properties including SARS-CoV-2. Natural remedies have been demonstrated to have inhibitory effects on MERS-CoV and SARS-CoV infections. The non-structural proteins of the virus, such as PLPRO, MPRO, and RdRp, as well as structural proteins like the spike (S) protein, have been demonstrated to have a substantial binding affinity and an inhibitory effect by a variety of natural products, according to in silico research. The virus also demonstrates to be a legitimate target for therapeutic development since it makes use of the host cell's transmembrane ACE2 receptor. In this chapter, we highlight on the potential of alkaloids, phenolic and polyphenolic compounds, flavonoids, terpenoids, cardiac glycosides, and natural products from marine sources against the human coronavirus via different mode of actions. Most of the studied metabolites act either by inhibiting virus replication or by blocking the active site of the protein of the virus either in silico or ex vivo. This review serves as a topic for further study and to discover other secondary metabolites for COVID-19 management.