Synthetic analgesics: N-(1-[2-arylethyl]-4-substituted 4-piperidinyl) N-arylalkanamides

The synthesis of several 4-arylamino-4-piperdinecarboxylic acids is reported. These acids were starting materials for the preparation of alpha-amino esthers, ethers and ketones. Different synthetic approaches are described. Suitable substitution on both nitrogen atoms afforded extremely potent analgesics. Thus, methyl 4-[N-(1-oxopropyl)-N-phenylamino]-1-(2-phenylethyl)-4-piperidinecarboxylate (22),N-(4-(methoxymethyl)-2-[2-(2-thienyl)ethyl]-4-piperidinyl)-N-phenylpropranamide (67) and N-[4-acetyl-1-(2-phenylethyl)-4-piperidinyl]-N-phenylpropanamide (82) were found to be respectively 7682, 3987 and 4921 times as potent as morfine. Both cis- and trans-3-methyl homologs of 22 have been prepared. As expected, analgesic activity resides mainly in the cis-isomer.