(1R,​3R)​-1-​(1,​3-​Benzodioxol-​5-​yl)​-​2,​3,​4,​9-​tetrahydro-1H-pyrido[3,​4-​b]​indole-​3-​carboxylic Acid Hydrochloride is an impurity of Tadalafil (T004500) and is a β-​carboline derivative. (1R,​3R)​-1-​(1,​3-​Benzodioxol-​5-​yl)​-​2,​3,​4,​9-​tetrahydro-1H-pyrido[3,​4-​b]​indole-​3-​carboxylic Acid Hydrochloride can be used to produce Tadalafil.