Involved in the biosynthesis of oryzalexin A-F phytoalexins. Catalyzes the conversion of ent-copalyl diphosphate to the phytoalexin precursor ent-sandaracopimaradiene. ent-copalyl diphosphate = diphosphate + ent-sandaracopimara-8(14),15-diene 9alpha-copalyl diphosphate = (12E)-9alpha-labda-8(17),12,14-triene + diphosphate Binds 3 Mg(2+) ions per subunit. Induced by UV irradiation. The Asp-Asp-Xaa-Xaa-Asp/Glu (DDXXD/E) motif is important for the catalytic activity, presumably through binding to Mg(2+). ent-sandaracopimaradiene is a precursor of the phytoalexins oryzalexins A-F. Phytoalexins are diterpenoid secondary metabolites involved in the defense mechanism of the plant and produced in response to attack (by a pathogen, elicitor or UV irradiation). Belongs to the terpene synthase family.