Clozapine N-oxide
[CAS# 34233-69-7]

Identification

• Classification: API >> Other chemicals
• Name: Clozapine N-oxide
• Synonyms: 3-chloro-6-(4-methyl-4-oxidopiperazin-4-ium-1-yl)-11H-benzo[b][1,4]benzodiazepine
• Molecular Formula: C₁₈H₁₉ClN₄O
• Molecular Weight: 342.82
• CAS Registry Number: 34233-69-7
• EC Number: 636-446-3
• SMILES: C[N+]1(CCN(CC1)C2=NC3=C(C=CC(=C3)Cl)NC4=CC=CC=C42)[O-]

Properties

• Solubility: Soluble (48 g/L) (25 ºC), Calc.^*

^* Calculated using Advanced Chemistry Development (ACD/Labs) Software V11.02 (©1994-2014 ACD/Labs)

Safety Data

• Hazard Symbols: GHS06;GHS07 Danger
• Hazard Statements: H301-H315-H319-H335
• Precautionary Statements: P261-P264-P264+P265-P270-P271-P280-P301+P316-P302+P352-P304+P340-P305+P351+P338-P319-P321-P330-P332+P317-P337+P317-P362+P364-P403+P233-P405-P501

Hazard Classification

Hazard	Class	Category Code	Hazard Statement
Acute toxicity	Acute Tox.	3	H301
Skin irritation	Skin Irrit.	2	H315
Eye irritation	Eye Irrit.	2	H319
Specific target organ toxicity - single exposure	STOT SE	3	H335

Discovory and Applicatios

Clozapine N-oxide is a pharmacologically inert metabolite derived from clozapine, an atypical antipsychotic drug. It gained significant attention due to its role as a synthetic ligand in chemogenetics, particularly in the development of Designer Receptors Exclusively Activated by Designer Drugs (DREADDs). These engineered receptors are modified G protein-coupled receptors (GPCRs) that respond specifically to clozapine N-oxide, enabling precise control of cellular signaling pathways in research and therapeutic applications.

The discovery of clozapine N-oxide’s utility in chemogenetics emerged from efforts to create tools for selective modulation of neuronal and non-neuronal cell activity. Researchers found that clozapine N-oxide could activate modified muscarinic receptors without affecting endogenous receptors, allowing reversible and non-invasive control over cell functions. This approach provided a powerful method to study complex physiological processes in vivo, including neural circuits, behavior, and disease mechanisms.

Clozapine N-oxide is characterized by its high affinity and specificity toward DREADDs, which are engineered to be unresponsive to natural ligands but highly responsive to this compound. Upon binding, clozapine N-oxide activates the receptor to trigger downstream intracellular signaling cascades, typically modulating neuronal excitability or inhibition depending on the receptor subtype used. This property has made it an indispensable tool in neuroscience, enabling targeted activation or suppression of specific cell populations.

In addition to neuroscience, clozapine N-oxide is used in other biomedical fields to manipulate signaling pathways in immune cells, cardiac cells, and other tissues. Its reversible nature and ability to cross the blood-brain barrier facilitate in vivo experiments with temporal precision. This has expanded the understanding of physiological and pathological processes, including pain, addiction, metabolic regulation, and psychiatric disorders.

Despite its widespread use, clozapine N-oxide is not entirely pharmacologically inert. Some studies have reported that it can convert back to clozapine in vivo, which possesses a broad receptor binding profile and can cause off-target effects. This has led to ongoing research to develop alternative ligands with improved specificity and reduced side effects for chemogenetic applications.

Overall, clozapine N-oxide represents a milestone in chemical biology and neuroscience research. Its role as a selective DREADD agonist has revolutionized the ability to control cell signaling with high specificity and temporal resolution, facilitating advances in both basic and translational science. The compound’s continued optimization and application hold promise for novel therapeutic strategies and deeper insight into complex biological systems.

References

1993. Determination of clozapine, norclozapine, and clozapine-N-oxide in serum by liquid chromatography. Clinical Chemistry, 39(8).
DOI: 10.1093/clinchem/39.8.1656

1994. Decomposition of clozapine N-oxide in the qualitative and quantitative analysis of clozapine and its metabolites. Journal of Pharmaceutical Sciences, 83(10).
DOI: 10.1002/jps.2600831010

2024. Claustrum modulation drives altered prefrontal cortex dynamics and connectivity. Communications Biology, 7(1).
DOI: 10.1038/s42003-024-07256-5