Catalyzes the cyclization of D-sedoheptulose 7-phosphate to 2-epi-5-epi-valiolone. Involved in cetoniacytone A biosynthesis. D-sedoheptulose 7-phosphate = 2-epi-5-epi-valiolone + phosphate Antibiotic biosynthesis. Belongs to the sugar phosphate cyclases superfamily. EEVS family.