Capsidiol is a terpenoid compound that accumulates in tobacco Nicotiana tabacum and chili pepper Capsicum annuum in response to fungal infection.

[1] Capsidiol is categorized under the broad term of phytoalexin, a class of low molecular weight plant secondary metabolites that are produced during infection.

Capsidiol is produced in the pepper fruit Capsicum annuum or tobacco Nicotiana tabacum after infection by the oomycete water-mold Phytophthora capsici.

[citation needed] Capsidiol is a bicyclic terpene that is biosynthetically derived from the mevalonate pathway via farnesyl pyrophosphate (FPP).

[5]  Crystal structures of recombinant tobacco 5-epi-aristolochene synthase (TEAS), alone and also complexed with two FPP analogues have been reported and analyzed to suggest the following mechanism of biosynthesis.