Catalyzes the conversion of sedoheptulose 7-phosphate to 2-epi-valiolone, which may serve as an alternative precursor for aminocyclitol biosynthesis. D-sedoheptulose 7-phosphate = 2-epi-valiolone + phosphate Binds 1 divalent metal cation per subunit. Co(2+) is the preferred cofactor. kcat is 2.0 min(-1). Belongs to the sugar phosphate cyclases superfamily. EVS family.