Catalyzes the conversion of (2E,6E)-farnesyl diphosphate (FPP) to yield a new 5-8 bicyclic (pristinane) sesquiterpenol (+)-(2S,3R,9R)-pristinol via a 1,11-cyclization, which requires the abstraction of the pyrophosphate from FPP to yield the humulyl cation. The only accepted substrate is farnesyl diphosphate (FPP). (2E,6E)-farnesyl diphosphate + H2O = (+)-(2S,3R,9R)-pristinol + diphosphate Binds 3 Mg(2+) ions per subunit. Secondary metabolite biosynthesis; terpenoid biosynthesis. The Asp-Asp-Xaa-Xaa-Asp (DDXXD) motif is important for the catalytic activity, presumably through binding to Mg(2+). Belongs to the terpene synthase family.