carfentanil4-((1-Oxopropyl)phenylamino)-1-(2-phenylethyl)-4-piperidinecarboxylic acid methyl esterMethyl 1-phenylethyl-4-(N-phenylpropionamido)isonipecotateMethyl 4-(N-(1-oxopropyl)-N-phenylamino)-1-(2-phenylethyl)-4-piperidinecarboxylateMethyl 4-(N-propionyl-N-phenylamino)-1-(2-phenylethyl)-4-piperidine-carboxylatecarfentanyl