2,6-dioxo-3H-pyrimidine-4-carboxylate 2,6-diketo-3H-pyrimidine-4-carboxylate 50887-69-9 73-97-2 ZINC00895161 2,6-dioxo-1,2,3,6-tetrahydropyrimidine-4-carboxylate CHEBI:30839