25CN-NBOH

25CN-NBOH (4-[2-[(2-hydroxyphenyl)methylamino]ethyl]-2,5-dimethoxybenzonitrile) is a synthetic phenethylamine of the N-benzyl-2-hydroxybenzyl (NBOH) structural class, first reported in 2014 by Hansen and colleagues at the University of Copenhagen as a potent and highly selective agonist of the serotonin 5-HT2A receptor. With a binding affinity (Ki) of approximately 0.81 to 1.32 nanomolar at the human 5-HT2A receptor and 52- to 100-fold selectivity over the closely related 5-HT2C receptor, 25CN-NBOH represents one of the most 5-HT2A-selective agonists described in the published literature and the most selective commercially available tool compound for interrogation of 5-HT2A receptor function in vitro and in vivo.

The compound occupies a distinctive pharmacological niche. Unlike psilocybin, lysergic acid diethylamide (LSD), and N,N-dimethyltryptamine, which activate multiple serotonin receptor subtypes and, in the case of LSD, dopamine and adrenergic receptors, 25CN-NBOH provides a pharmacological lever with which 5-HT2A-mediated effects can be isolated from confounding receptor contributions. Unlike the structurally related NBOMe series (25I-NBOMe, 25C-NBOMe, 25B-NBOMe), which carry an N-methoxybenzyl substituent and have been associated with serious toxicity and fatalities in recreational contexts, 25CN-NBOH carries an N-(2-hydroxybenzyl) group that confers a more favorable preclinical safety profile and improved metabolic stability.

The pharmacological characterization of 25CN-NBOH has advanced substantially since 2014. A tritiated radioligand ([3H]25CN-NBOH) has been synthesized and validated for equilibrium and kinetic binding assays and for autoradiography in rat brain, providing high-resolution mapping of 5-HT2A receptor distribution. The cryo-electron microscopy structure of 25CN-NBOH bound to the human 5-HT2A receptor in complex with a mini-Gaq heterotrimer, solved at 3.27 angstrom resolution by Kim et al. (2020) and published in Cell, provided the first atomic-resolution view of a hallucinogen-activated serotonin receptor and has become a foundational reference for structure-based drug design in the serotonergic psychedelic field. Structure-activity relationship studies have mapped the 2-prime and 3-prime positions of the N-benzyl ring as critical determinants of 5-HT2A agonist activity and have identified conformationally restrained analogs and beta-arrestin-biased derivatives that enable pathway-selective pharmacology.

Preclinical pharmacology in rodent models has characterized 25CN-NBOH across multiple behavioral and physiological endpoints. In mice, the compound produces a dose-dependent head-twitch response (the canonical 5-HT2A-mediated behavioral readout) with an inverted U-shaped dose-response curve peaking at 1.5 mg/kg and a half-maximal time of approximately 11 minutes, with both tachyphylaxis within sessions and tolerance across days consistent with 5-HT2A receptor desensitization. In rats, a single administration of 25CN-NBOH reduces immobility in the forced swim test with an effect size persisting without decrement for at least three months, paralleling the long-lasting antidepressant-like activity of psilocybin and supporting the hypothesis that 5-HT2A receptor activation underlies the enduring behavioral effects of serotonergic psychedelics. A single dose enhances cognitive flexibility in a reversal learning paradigm two to three weeks after administration. Additional preclinical findings include reduction of conditioned fear (blocked by the 5-HT2A inverse agonist MDL100907), reduction of marble burying behavior, cardiovascular effects including tachycardia and temperature-dependent modulation of carotid blood flow, and complex dual actions on medial prefrontal cortical neurons comprising 5-HT2A-dependent excitatory synaptic enhancement and 5-HT2A-independent M-current-mediated suppression of neuronal firing.

Pharmacokinetic characterization in mice demonstrates rapid brain penetration (free brain and plasma concentrations of approximately 200 nanomolar within 15 minutes after 3 mg/kg subcutaneous administration), high in vitro permeability (apparent permeability coefficient 29 times 10 to the negative 6 centimeters per second), and low P-glycoprotein-mediated efflux. The compound is metabolized more slowly than the NBOMe congeners and displays favorable physicochemical properties including aqueous stability of the hydrochloride salt at room temperature for weeks.

No human clinical trials of 25CN-NBOH have been conducted or registered as of the monograph date. The compound is not approved for any therapeutic indication in any jurisdiction and is classified as a controlled substance in the United Kingdom (Class A), Hungary, and Canada, and is potentially controlled in the United States under the Federal Analogue Act when intended for human consumption. This monograph reviews the chemistry, synthesis, receptor pharmacology, structural biology, pharmacokinetics, preclinical behavioral and physiological pharmacology, sourcing and handling considerations, and comparative assessment of 25CN-NBOH against five alternative 5-HT2A receptor agonists on five competency standards.