Tiopronin
Tiopronin is an acylated sulfhydryl-containing derivative of glycine with reducing and complexing properties. Tiopronin breaks the disulphide bond of cystine and binds the sulfhydryl group of the resultant cysteine monomers to form a soluble tiopronin-cysteine-mixed disulfide, which is more water-soluble than cystine and is readily excreted. This leads to a reduction in urinary cystine concentration and subsequently reduces cystine stone formation.