drugs of the fentanyl series ( 4-anilino-piperidines ) were potent displacers whereas agonists of the delta- ( enkephalin derivatives ) , sigma- ( phencyclidine , haloperidol , 3-hydroxyphenyl-propylpiperidine ) or k- ( u 50488 ) opiate sites had a low affinity ( ki greater than 0.5 microm ) for 3h-lofentanil specific binding sites .
C0031960
piperidines
C0031381
phencyclidine