Potential affinity labels for the opiate receptor based on fentanyl and related compounds

Abstract
Derivatives of fentanyl, 3-methylfentanyl, sufentanil and lofentanil, possessing chemo- or photoaffinity functionalities, were synthesized as potential affinity reagents for the opiate receptor. Opiate receptor binding constants (IC50 [median inhibitory concentration]) were determined in competition experiments with [3H]naloxone and [3H]naltrexone [in rat brain]. Affinity-labeling experiments were generally unsuccessful, although some irreversible attachment was achieved with .alpha.-diazoamide 17 [cis-2-diazo-N-phenyl-N-[1-(2-phenylethyl)-3-methyl-4-piperidinyl]acetamide] and aryl azide 23 [N-[1-[2-(4-azidophenyl)ethyl]-4-(methoxymethyl)-4-piperidinyl]-N-phenylpropanamide].