Chemical structures of principal compounds examined.
A, tiopronin ((2-mercaptopropanoyl)aminoacetic acid). Tiopronin is the condensation product of glycine and thiolactic acid. B, mercaptosuccinic acid (thiomalic acid, 2-sulfanylbutanedioic acid). C, demethyl tiopronin ((2-mercaptoethanoyl)aminoacetic acid). D, dimethyl tiopronin ((2-mercapto-2-methylpropanoyl)aminoacetic acid). Tiopronin and mercaptosuccinic acid were tested as the racemate.