Article · Wikipedia archive · Last revised Jun 13, 2026

AM-251 (drug)

AM-251 is an inverse agonist at the CB1 cannabinoid receptor. AM-251 is structurally very close to rimonabant; both are biarylpyrazole cannabinoid receptor antagonists. In AM-251, the p-chloro group attached to the phenyl substituent at C-5 of the pyrazole ring is replaced with a p-iodo group. The resulting compound exhibits slightly better binding affinity for the CB1 receptor (with a Ki value of 7.5 nM) than rimonabant, which has a Ki value of 11.5 nM, AM-251 is, however, about two-fold more selective for the CB1 receptor when compared to rimonabant. Like rimonabant, it is additionally a μ-opioid receptor antagonist that attenuates analgesic effects.

Last revised
Jun 13, 2026
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AM-251
Identifiers
  • 1-(2,4-Dichlorophenyl)-5-(4-iodophenyl)-4-methyl-N-(1-piperidyl)pyrazole-3-carboxamide
CAS Number
PubChem CID
IUPHAR/BPS
ChemSpider
UNII
ChEBI
ChEMBL
CompTox Dashboard (EPA)
ECHA InfoCard100.162.062
Chemical and physical data
FormulaC22H21Cl2IN4O
Molar mass555.24 g·mol−1
3D model (JSmol)
  • O=C(NN1CCCCC1)c4nn(c2ccc(Cl)cc2Cl)c(c3ccc(I)cc3)c4C
  • InChI=1S/C22H21Cl2IN4O/c1-14-20(22(30)27-28-11-3-2-4-12-28)26-29(19-10-7-16(23)13-18(19)24)21(14)15-5-8-17(25)9-6-15/h5-10,13H,2-4,11-12H2,1H3,(H,27,30) checkY
  • Key:BUZAJRPLUGXRAB-UHFFFAOYSA-N checkY
  (verify)

AM-251 is an inverse agonist at the CB1 cannabinoid receptor. AM-251 is structurally very close to rimonabant; both are biarylpyrazole cannabinoid receptor antagonists. In AM-251, the p-chloro group attached to the phenyl substituent at C-5 of the pyrazole ring is replaced with a p-iodo group. The resulting compound exhibits slightly better binding affinity for the CB1 receptor (with a Ki value of 7.5 nM) than rimonabant, which has a Ki value of 11.5 nM, AM-251 is, however, about two-fold more selective for the CB1 receptor when compared to rimonabant.1 Like rimonabant, it is additionally a μ-opioid receptor antagonist2 that attenuates analgesic effects.3

AM251 has shown an in vitro antimelanoma activity against pancreatic and colon cancer cells.4

See also

See also

References

References

  1. Lan R, Liu Q, Fan P, Lin S, Fernando SR, McCallion D, et al. (February 1999). "Structure-activity relationships of pyrazole derivatives as cannabinoid receptor antagonists". Journal of Medicinal Chemistry. 42 (4): 769–776. doi:10.1021/jm980363y. PMID 10052983.
  2. Seely KA, Brents LK, Franks LN, Rajasekaran M, Zimmerman SM, Fantegrossi WE, Prather PL (October 2012). "AM-251 and rimonabant act as direct antagonists at mu-opioid receptors: implications for opioid/cannabinoid interaction studies". Neuropharmacology. 63 (5): 905–915. doi:10.1016/j.neuropharm.2012.06.046. PMC 3408547. PMID 22771770.
  3. Seely KA, Brents LK, Franks LN, Rajasekaran M, Zimmerman SM, Fantegrossi WE, Prather PL (October 2012). "AM-251 and rimonabant act as direct antagonists at mu-opioid receptors: implications for opioid/cannabinoid interaction studies". Neuropharmacology. 63 (5): 905–915. doi:10.1016/j.neuropharm.2012.06.046. PMC 3408547. PMID 22771770.
  4. Carpi S, Fogli S, Romanini A, Pellegrino M, Adinolfi B, Podestà A, et al. (August 2015). "AM251 induces apoptosis and G2/M cell cycle arrest in A375 human melanoma cells" (PDF). Anti-Cancer Drugs. 26 (7): 754–762. doi:10.1097/CAD.0000000000000246. hdl:11568/750318. PMID 25974027. S2CID 205526223. Archived (PDF) from the original on July 2, 2021.