Phorbol is a diterpenoid with the structure of tigliane hydroxylated at C-4, -9, -12(beta), -13 and -20, with an oxo group at C-3 and unsaturation at the 1- and 6-positions. It is a tetracyclic diterpenoid, an enone, a cyclic ketone, a tertiary alcohol and a tertiary alpha-hydroxy ketone. It derives from a hydride of a tigliane.