Semisynthetic

Synonym: Partial synthesis

A semisynthetic chemical synthesis uses compounds isolated from natural sources (e.g. plant material or bacterial or cell cultures) as starting materials. These natural compounds are usually large and complex molecules. This is opposite to a classical chemical synthesis where large molecules are synthesized from a stepwise combination of small and cheap (petrochemical) building blocks.

Semisyntheses are usually used when the precursor molecules is too complex to be synthesized economically by a total synthesis.

One examples is the synthesis of LSD from ergotamine that is isolated from ergot fungus cultures.