4-Piperidinecarboxylic acid, 4-((1-oxopropyl)phenylamino)-1-(2-(2-thienyl)ethyl)-, methyl ester 60771-38-2 BRN 0458457 Methyl 4-(N-(1-oxopropyl)-N-phenylamino)-1-(2-(2-thienyl)ethyl)-4-piperidinecarboxylate R 31826 Thiofentanil