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 antagonist[2] that attenuates analgesic effects.

[3] AM251 has shown an in vitro antimelanoma activity against pancreatic and colon cancer cells.