Germacrenes are a group of naturally occurring volatile organic hydrocarbons of the sesquiterpene and cycloalkene class. They are typically produced in plants and have antimicrobial and insecticidal properties, though they also play a role as insect pheromones. Two prominent molecules are germacrene A and germacrene D.
Structures Germacrene has five structural isomers.
+ Germacrene isomers (–)-Germacrene A Germacrene B Germacrene C Germacrene D Germacrene E Germacrene A is chiral and both the (–)-(S) and (+)-(R) forms are found naturally. Germacrene D is also known in both enantiomeric forms.
Natural occurrences The essential oils of deadnettles (genus Lamium), hedgenettles (genus Stachys), and Clausena anisata are characterized by their high contents of germacrene D. Germacrene B is a major component of patchouli oil.
Metabolism in plants The germacrenes are precursors to sesquiterpene lactones. For example, the enzyme germacrene A hydroxylase in chicory converts (+)-germacrene A to a carboxylic acid which is the starting material for costunolide synthase, which converts it to costunolide:
References
Further reading Germacrene A
Germacrene D