The serotonin 2A
receptor (5-HT
2A
R) is the mediator
of the psychedelic effects of serotonergic psychedelics, which have
shown promising results in clinical studies for several neuropsychiatric
indications. The 5-HT
2A
R is able to signal through the
Gα
q
and β-arrestin effector proteins, but it
is currently not known how the different signaling pathways contribute
to the therapeutic effects mediated by serotonergic psychedelics.
In the present work, we have evaluated the subtype-selective 5-HT
2A
R agonist 25CN-NBOH and a series of close analogues for biased
signaling at this receptor. These ligands were designed to evaluate
the role of interactions with Ser159
3×36
. The lack
of interaction between this hydroxyl moiety and Ser159
3×36
resulted in detrimental effects on potency and efficacy in both
βarr2 and miniGα
q
recruitment assays. Remarkably,
Gα
q
-mediated signaling was considerably more affected.
This led to the development of the first efficacious βarr2-biased
5-HT
2A
R agonists
4a–b
and
6e–f
, βarr2 preferring, relative to lysergic acid diethylamide
(LSD).