compound barbiturate barbituric acid CHEBI:29745 UPa:UPC00813 KEGG:C00813 CHEBI:16294 compound C4H4N2O3 InChI=1S/C4H4N2O3/c7-2-1-3(8)6-4(9)5-2/h1H2,(H2,5,6,7,8,9)