4-(N-Phenylamino)-4-carboxypiperidine is an intermediate in the synthesis of Remifentanil Ester Hydrochloride (R143515), a controlled substance, an Opioid. Remifentanil Esters are used as intermediates in the synthesis of isothiocyanate derivatives of carfentanils and (methoxymethyl)fentanyls which are opioid δ receptor irreversible inhibitors.
