Catalyzes the intramolecular carbocycle formation from D-glucose-6-phosphate to 2-deoxy-scyllo-inosose (DOI). D-glucose 6-phosphate = 2-deoxy-L-scyllo-inosose + phosphate Binds 1 Co(2+) ion per subunit. Metabolic intermediate biosynthesis; 2-deoxystreptamine biosynthesis; 2-deoxystreptamine from D-glucose 6-phosphate: step 1/4. Antibiotic biosynthesis; ribostamycin biosynthesis. Belongs to the sugar phosphate cyclases superfamily. DOI synthase family.