Highly selective kappa-opioid analgesics. 3. Synthesis and structure-activity relationships of novel N-[2-(1-pyrrolidinyl)-4- or -5-substituted-cyclohexyl]arylacetamide derivatives.
This paper describes the chemical synthesis, mu/kappa opioid receptor selectivity and analgesic activity of 14 novel N-[2-(1-pyrrolidinyl)-4- or -5-substituted-cyclohexyl]arylacetamide derivatives. The prototype kappa-selective agonist, PD117302 (trans-N-methyl-N-[2-(1-pyrrolidinyl)cyclohexyl]benzo[b]thiophene-4- acetamide, 2) has been regio- and stereoselectively substituted in the C-4 and C-5 positions of the cyclohexyl ring with the methyl ether and spiro tetrahydrofuran groups. It is observed that optimal mu/kappa-receptor selectivity is obtained when the oxygen atom of the methyl ether or the tetrahydrofuran ring is joined to the equatorial C-4 position. Hence, (-)-(5 beta,7 beta,8 alpha)-N-methyl-N-[7-(1-pyrrolidinyl)-1- oxaspiro[4.5]dec-8-yl]benzo[b]furan-4-acetamide monohydrochloride (21) has exceptionally high kappa opioid receptor affinity and selectivity in vitro (kappa Ki = 0.83 nM, mu/kappa ratio = 1520) is the most potent kappa-selective analgesic ever reported. Compound 21 is 25 times more potent than morphine and 17 times more potent than U-62066 (spiradoline, 19) when assayed by the rat paw pressure test by intravenous administration (MPE50 = 0.024, 0.6, and 0.4 mg/kg, respectively).
Halfpenny
P R
PR
Parke-Davis Research Unit, Addenbrookes Hospital Site, Cambridge, UK.
Horwell
D C
DC
Hughes
J
J
Hunter
J C
JC
Rees
D C
DC
D000698:Analgesia; D000818:Animals; D055598:Chemical Phenomena; D002621:Chemistry; D003510:Cyclohexanes / Q000138:chemical synthesis* / Q000494:pharmacology; D015394:Molecular Structure; D009020:Morphine; D011759:Pyrrolidines / Q000138:chemical synthesis* / Q000494:pharmacology; D051381:Rats; D011957:Receptors, Opioid / Q000187:drug effects / Q000502:physiology*; D017473:Receptors, Opioid, kappa; D017450:Receptors, Opioid, mu; D013237:Stereoisomerism; D013876:Thiophenes / Q000138:chemical synthesis* / Q000494:pharmacology
D003510:Cyclohexanes; D011759:Pyrrolidines; D011957:Receptors, Opioid; D017473:Receptors, Opioid, kappa; D017450:Receptors, Opioid, mu; D013876:Thiophenes; D009020:Morphine