Nitrosobiotin [4-keto-4-(6-(5-(311-(3,5-dihydroxyphenyl)-balanyl)-1-tetrahydro-2H-thiopyran-3-yl)amino)-2,4,6trihydroxyphen-1-yl]-is a cyclic monomeric lactone. It contains three carbonyl groups (one on each carbon) but without ethanol functionalities to connect a third thiol group.