Darigabat’s 2026 Phase 2 Results: Route Chemistry and Positional-Isomer Control

Results posted in 2026 provide a timely reason to revisit darigabat’s disclosed chemistry. The public route uses 3,5-dichloropyridazin-4-amine (CAS 53180-76-0), while a same-formula positional isomer shows why CAS, structure and analytical identity must agree.

Clinical results do not have to be positive to provide useful direction for medicinal chemistry and sourcing. Results posted on May 7, 2026, from a Phase 2 panic-disorder trial of darigabat offer a timely example. They also provide a reason to revisit the publicly disclosed route from 3,5-dichloropyridazin-4-amine (CAS 53180-76-0)—and the identity controls required for a building block that has a same-formula positional isomer.

Darigabat, also known as PF-06372865 or CVL-865, is an investigational positive allosteric modulator of GABA_A receptors containing α2, α3 and α5 subunits. It is not an approved medicine. Public patent and scientific sources connect CAS 53180-76-0 to a disclosed route to darigabat, but they do not identify Rlavie as a supplier to any clinical or commercial program.

Why the market still follows subtype-selective GABA chemistry

The World Health Organization estimates that 359 million people were living with an anxiety disorder in 2021 and that only about one in four people in need receives treatment. Panic disorder is one of the conditions within this broader burden.

At the same time, the U.S. FDA requires a boxed warning across the benzodiazepine class for risks including abuse, addiction, physical dependence and withdrawal. These realities help explain continued interest in GABA_A modulators designed to separate therapeutic effects from α1-associated sedation.

This is a research and treatment-need signal—not a market-size forecast for CAS 53180-76-0. Demand for a particular building block depends on program decisions, route selection, inventory and qualification status, none of which can be inferred from disease prevalence or a patent.

What the 2026 Phase 2 results showed

ClinicalTrials.gov lists 80 participants in the randomized, double-blind trial NCT05941442: 40 received placebo and 40 received darigabat, titrated before maintenance treatment at 25 mg twice daily. The sponsor terminated the study because of significant enrollment and study-design challenges.

The primary endpoint was the proportion of participants free of panic attacks during the final two maintenance weeks. In the evaluable primary-analysis set, 8 of 25 placebo recipients and 5 of 19 darigabat recipients were panic-attack free. The estimated between-group difference was −0.06 (95% CI, −0.33 to 0.23; p=0.7488), so superiority was not demonstrated.

No deaths or serious adverse events were reported in either group. Other adverse events affected 20 of 40 placebo participants and 21 of 40 darigabat participants. Dizziness and somnolence were more frequent with darigabat in the posted tables.

The distinction matters: the trial did not establish efficacy on its primary endpoint, while the stated termination reason was enrollment and design—not a declared safety or efficacy stop. The small evaluable set and early termination also limit interpretation. The results should not be described as clinical success, but neither should the termination reason be rewritten as something the registry does not say.

How CAS 53180-76-0 enters the disclosed route

Pfizer patent US8952008B2, corresponding to WO2014/091368, discloses an imidazo[4,5-c]pyridazine series. Its Preparation 4 produces 3,5-dichloropyridazin-4-amine, and Preparation 7 subjects that material to ethylamine substitution. Cyclization with triethyl orthoformate then builds the fused imidazopyridazine core, after which aryl-functionalization steps lead to Example 4. Public chemical databases and the peer-reviewed discovery paper identify that example as PF-06372865, now known as darigabat.

A separate Pfizer PCT application published in 2025 describes solid forms of the same molecule. That later filing illustrates how a discovery route can eventually intersect with crystal-form and CMC work. It does not prove commercialization, current manufacturing demand or use of the original patent route.

Same formula does not mean same material

PubChem identifies CAS 53180-76-0 as 3,5-dichloropyridazin-4-amine, with formula C₄H₃Cl₂N₃, molecular weight 163.99 and InChIKey RPFJGTZUJUOCCL-UHFFFAOYSA-N. CAS 823-58-5 is 3,6-dichloropyridazin-4-amine. It has the same formula and molecular weight but a different connectivity and InChIKey.

Consequently, formula, nominal mass or a generic “dichloroaminopyridazine” name cannot establish identity. For route development, a fit-for-purpose package may include:

agreement among the CAS number, drawn structure and systematic name;
structure-confirming NMR, supported where appropriate by a reference standard;
a chromatographic method capable of detecting the relevant positional isomer and process impurities;
control of unreacted or over-substituted material before cyclization;
water, residual-solvent and route-relevant elemental-impurity assessment; and
batch traceability plus notification of material process changes.

These controls should be set for the buyer’s intended use. A research-screening specification is not automatically suitable for later regulated development.

What this means for sourcing

The darigabat record shows both sides of CNS development: a large treatment need and sophisticated receptor-selective chemistry, alongside difficult clinical translation. For sourcing teams, that makes chemical identity, flexible quantities and route-aware documentation more valuable than promotional claims about a compound’s eventual market.

Rlavie lists 3,5-dichloropyridazin-4-amine, CAS 53180-76-0. Teams evaluating the material for route scouting, medicinal chemistry or custom synthesis can contact Rlavie to discuss current availability, batch-specific analytical documentation, specifications and scale requirements.

This review is based solely on public clinical, patent and scientific sources. It does not imply that Rlavie supplied Pfizer, Cerevel, AbbVie, any clinical trial or any darigabat manufacturing program. It also does not establish that the catalog material is qualified for a particular pharmaceutical application.

Sources

This article is an industry and process-chemistry overview. It does not constitute medical, regulatory or investment advice.