Isolated from the bacterium Streptomyces clavuligerus. The 1-proR hydrogen atom of geranylgeranyl diphosphate is lost in the reaction. The enzyme also produces hydropyrene, isoelisabethatriene and traces of other diterpenoids. cf. EC 4.2.3.201, hydropyrene synthase, and EC 4.2.3.203, isoelisabethatriene synthase.