The definition of natural products is usually restricted to purified organic compounds isolated from natural sources. For instance, Quercetin-3-O-[2-O-(6-O-p-hydroxyl-E-coumaroyl)-D-glucosyl]-(1-2)-L-rhamnoside is a flavonoid compound isolated from Ginkgo biloba L. Also, Ginsenoside Rd is a natural triterpenoid compound found in the roots of Panax ginseng C. A. Mey.
What makes natural compounds different from other synthetic compounds is their therapeutic benefits. Since ancient times they have presented themselves in traditional medicines for treating various diseases. As we enter the new millennium, there are greater demand for knowledge to derive active components as lead compounds for drug discovery.
Although natural products have made contributions in giving birth to numerous U.S. Food and Drug Administration-approved drugs, they have received declining attention from pharmaceutical companies in regard to drug discovery. The possible reasons may partly include:
Unreliable access and supply,
Intellectual property concerns,
Seasonal or environmental variability of composition,
Loss of sources due to rising extinction rates.