Synthesis and antinociceptive activity of 4-pyridyl and -dihydropyridyl analogues of meperidine and ketobemidone.

The synthesis and antinociceptive activity of 4-pyridylpiperdines (7 and 10) in which the phenyl group pf meperidine (1) or ketobemidone (3) is replaced by 2'-, 3'- or 4'-pyridyl is described. All were active in a rat writhing test, and the results showed that the point of attachment of the pyridyl ring to the 4-position was an important determinant of the activity; the relative potency order was 3'-pyridyl greater than 4'-pyridyl greater than 2'-pyridyl in each of the two series. The most potent compound (half the potency of meperidine) was 4-ethoxycarbonyl-4-(3'-pyridyl)-l-methylpiperidine (7b). This compound, and the corresponding 4'-isomer (7c), were further elaborated to provide 1'-phenyl, 1',6'-dihydropyridine (11), and 1'-phenyl, methyl or n-butyl. 1',2'-dihydropyridine (12) analogues containing an acyl function on the ring nitrogen. The most active compound in this series was 4-[4'-(1'-phenoxycarbonyl-2'-n-butyl-l',2'-dihydropyridyl)]- 4- ethoxycarbonyl-l-methylpiperdine (12k). Though less potent than the parent pyridyl compound (7c), it induced 70% inhibition in the writhing test at a dose of 8 mg/kg sc. [The ED50 for meperidine was 0.6 mg/kg sc.]