Structural Biochemistry/Natural Products

Overview
Natural products are chemical compounds or substances produced by a living organism that are found in nature and usually has a pharmacological or biological activity for use in pharmaceutical drug discovery and drug design. A natural product can be considered even if it can be prepared by total synthesis. The natural products provide the source or inspiration for the majority of FDA-approved agents and continue to be one of the major sources of inspiration for drug discovery. In particular, these compounds are important in the treatment of life-threatening conditions.

Problems with total synthesis
Not all natural products can be fully synthesized and many natural products have extremely complex structures that are way too difficult and expensive to synthesize on an industrial scale. These include drugs such as penicillin, morphine, and paclitaxel (Taxol). Such compounds can only be harvested from their natural source - a process which can be tedious, time consuming, and expensive, as well as being wasteful on the natural resource. For example, one yew tree would have to be cut down to extract enough paclitaxel from its bark for a single dose. Furthermore, the number of structural analogues that can be obtained from harvesting is severely limited.

Reference
http://en.wikipedia.org/wiki/Natural_product