Isolated from the bacterium Streptomyces clavuligerus. The 1-proR hydrogen atom of geranylgeranyl diphosphate is lost in the reaction. The enzyme also produces hydropyrenol, isoelisabethatriene and traces of other diterpenoids. cf. EC 4.2.3.202, hydropyrenol synthase, and EC 4.2.3.203, isoelisabethatriene synthase.