Involved in the biosynthesis of ent-kaurene diterpenoids natural products such as oridonin, miltiradiene, eriocalyxin B and nezukol, known to exhibit antitumor, anti-inflammatory and antibacterial activities (By similarity). Catalyzes the conversion of (2E,6E,10E)-geranylgeranyl diphosphate (GGPP) to (+)-copalyl diphosphate ((+)-CPP) (By similarity). (2E,6E,10E)-geranylgeranyl diphosphate = (+)-copalyl diphosphate Secondary metabolite biosynthesis; terpenoid biosynthesis. The Asp-Xaa-Asp-Asp (DXDD) motif is important for the catalytic activity, presumably through binding to Mg(2+). Belongs to the terpene synthase family. Tpsc subfamily.