Patchoulol (PA)

Patchoulol or patchouli alcohol (C15H26O) is a sesquiterpene alcohol found in Patchouli. The (−)-optical isomer is one of the organic compounds responsible for the typical patchouli scent. Patchoulol is also used in the synthesis of the chemotherapy drug Taxol.
Several mechanistic alternatives have been proposed for the enzyme-catalyzed, electrophilic cyclization of farnesyl pyrophosphate to the tricyclic sesquiterpene alcohol patchoulol, which is the characteristic component of the essential oil of Pogostemon cablin (patchouli). These alternatives include schemes involving deprotonation-reprotonation steps and the intermediacy of the monocyclic and bicyclic olefins germacrene and bulnesene, respectively, and involving a 1,3-hydride shift with only tertiary cationic intermediates and without any deprotonation-reprotonation steps.