The coronavirus disease-2019 (COVID-19) pandemic started in early 2020 with the outbreak of a highly pathogenic human coronavirus. The world is facing a challenge and there is a pressing need for efficient drugs. Plants and natural compounds are a proven rich resource for new drug discovery. Considering the potential of natural products to manage the pandemic, this article was designed to provide an inclusive map of the stages and pathogenetic mechanisms for effective natural products on COVID-19. New drug discovery for the COVID-19 pandemic can encompass both prevention and disease management strategies. Preventive mechanisms that may be considered include boosting the immune response and hand hygiene in the preexposure phase; and blocking of virus binding and entry in the postexposure phase. Potential therapeutic target mechanisms include virus-directed therapies and host-directed therapies. Several medicinal plants and natural products, such as Withania somnifera (L.) Dunal and propolis for prevention; Tanacetum parthenium (L.) for treatment; and Ammoides verticillata (Desf.) Briq and Nigella sativa L. for both prevention and treatment have been found effective and are good targets for future research. The examples of phytochemical compounds that may be effective include aloin and terpenes as anti-septics; isothymol, dithymoquinone, and glycyrrhizin as inhibitors of virus binding and entry; glycyrrhizin, and berberine as replication suppressants; ginsenoside Rg1 and parthenolide as immunomodulators; and eriocitrin, rhoifolin, hesperidin, naringin, rutin, and veronicastroside as anti-complements. Recognizing different mechanisms of fighting against this virus can lead to a more systematic approach in finding natural products and medicinal plants for COVID-19 prevention and treatment.
Keywords: COVID-19; angiotensin-converting enzyme; coronavirus; new drug discovery; phytotherapy; plant extracts.