Immunosuppressive agent and process of producing the same

A method for effecting immunosuppression in a subject, which comprises administering to a subject in need of immunosuppression, an amount of a .delta.-opioid receptor antagonist, or a pharmaceutically acceptable salt thereof, in an amount sufficient to effect immunosuppression in said subject chlorine, bromine, amino, nitro, C.sub.1 -C.sub.5 alkyl, C.sub.1 -C.sub.5 alkoxy or R.sub.4 and R.sub.5 together represent benzo.

• wherein said .delta.-opioid antagonist is a compound represented by the formula (1):
• ##STR7## wherein R.sub.1 represents C.sub.1 -C.sub.5 alkyl, C.sub.3 -C.sub.6 cycloalkylalkyl, C.sub.5 -C.sub.7 cycloalkenylalkyl, aryl, aralkyl, C.sub.4 -C.sub.5 trans-alkenyl, allyl or furan-2-ylalkyl, R.sub.2 represents hydrogen, hydroxy or C.sub.1 -C.sub.5 alkanoyloxy, R.sub.3 represents hydrogen, C.sub.1 -C.sub.5 alkyl or C.sub.1 -C.sub.5 alkanoyl, X represents oxygen, sulfur or nitrogen to which a radical Y is attached, wherein Y represents hydrogen or C.sub.1 -C.sub.5 alkyl, R.sub.4 and R.sub.5 individually represent hydrogen, fluorine,