"Semisynthesis" or partial chemical synthesis's a type of chemical synthesis that uses compounds isolated from natural sources (for example plant material or bacterial or cell cultures) as starting materials. These natural biomolecules are usually large and complex molecules. This's opposed to a total synthesis where large molecules are synthesized from a stepwise combination of small and cheap (petrochemical) building blocks. Semisynthesis's usually used when the precursor molecule's too struct… (More on Semisynthesis)