The products of three terpene synthases from two social amoebae, Dictyostelium discoideum and Dictyostelium purpureum, were identified, showing sesquiterpene synthase activity for one and diterpene synthase activity for the other two enzymes. Site-directed mutagenesis experiments revealed the importance of a newly identfied highly conserved residue for catalytic activity. For one of the enzyme products, β-araneosene, a bromonium ion induced transannular cyclisation was investigated, yielding the first brominated derivatives of this diterpene.