3-Piperazinyl-1,2-Benzisothiazole Hydrochloride

What stoichiometric constraints govern the N‑alkylation step in ziprasidone freebase assembly?

In the commercial manufacture of ziprasidone hydrochloride monohydrate—an atypical antipsychotic formulated as intramuscular suspension and oral capsules—the hydrochloride salt of 3-piperazinyl‑1,2‑benzisothiazole serves as the nucleophilic coupling partner in a convergent route. The reaction with 5‑(2‑chloroethyl)‑6‑chloro‑1,3‑dihydro‑2H‑indol‑2‑one proceeds under anhydrous alkaline conditions, typically in refluxing acetonitrile or DMF containing finely milled potassium carbonate. The molar input ratio of 3‑piperazinyl‑1,2‑benzisothiazole hydrochloride (as free base equivalent) to the chloroethyl oxindole fragment is maintained at 1.0:1.02–1.05, the slight excess of the alkylating agent compensating for moisture‑mediated hydrolysis. Process‑scale deviations beyond this window are known to generate a dimeric bis‑alkylated impurity above the 0.10% threshold specified in the USP monograph for ziprasidone hydrochloride, requiring additional hot acetone trituration cycles that reduce overall yield below the economically viable 72% benchmark. The compliance framework is anchored to ICH Q7 Section 7.3 (Cleaning Validation) and Section 12.1 (Validation of API Processes), enforced through a Drug Master File structure conforming to 21 CFR 314.420. Downstream, the crude ziprasidone freebase is isolated by drowning the reaction mixture into deionized water at 2°C–5°C, followed by vacuum filtration on a 316L stainless‑steel Nutsche filter and two sequential reslurries in isopropanol/water (70:30 v/v) to purge residual benzisothiazole‑related substances. The terminal API crystallisation as the hydrochloride monohydrate from aqueous methanol yields a polymorph designated as Form I, confirmed by XRPD, with a particle size d₉₀ target below 100 µm to ensure content uniformity in capsule filling on a Zanasi LZ‑64 dosator machine.

Lurasidone key intermediate: coupling the cyclohexane dimethanol ditosylate lobe at sub‑ambient temperature

For lurasidone hydrochloride—a benzisothiazole piperazine‑derived antipsychotic administered as oral tablets of 20 mg, 40 mg, 80 mg, and 120 mg strengths—the hydrochloride salt of 3‑piperazinyl‑1,2‑benzisothiazole is employed in a S_N2 displacement on (1R,2R)‑cyclohexane‑1,2‑dimethanol ditosylate. This step is carried out under strictly controlled temperature conditions: the reactor jacket is charged with a ‑15°C ethylene glycol/water mixture to keep the bulk reaction mass at ‑10°C ± 2°C. The stoichiometry requires 2.20–2.25 molar equivalents of the benzisothiazole piperazine nucleophile relative to the ditosylate substrate; using fewer than 2.15 equivalents consistently generates the mono‑substituted tosylate intermediate at levels above 2.5 area% by HPLC, an impurity that co‑crystallises with the final product in the subsequent mesitylene recrystallisation step. The reaction solvent is dry THF with free‑base generation performed in situ using freshly titrated sodium hydride (60% dispersion in mineral oil) to liberate the piperazine nitrogen; residual mineral oil removal is achieved via filtration through a 0.2 µm hydrophilic PTFE cartridge filter before addition of the ditosylate. All process operations adhere to EMA Guideline EMA/CHMP/CVMP/QWP/496873/2018 for mutagenic impurity control, specifically with regard to the benzyl chloride analogue potentially arising from thermal degradation of the ditosylate at local hot spots exceeding 40°C. Production‑scale execution frequently employs a glass‑lined Pfaudler reactor of 2,000‑gallon capacity fitted with a retreat‑curve impeller rotating at 85–95 rpm to prevent vortex formation and to ensure adequate heat transfer during the exothermic quench step into 5% aqueous ammonium chloride. The terminal product is lurasidone hydrochloride, crystallised from a ternary solvent system of methanol, water, and ethyl acetate with a Hall flow meter compressibility index below 25%, directly compressed into tablets using a Korsch XL 400 rotary press with compression force maintained between 8 kN and 14 kN to achieve tablet hardness of 6–8 kp.

Integrating the benzisothiazole piperazine moiety into perospirone hydrochloride hydrate involves a reductive amination sequence where the hydrochloride salt of 3‑piperazinyl‑1,2‑benzisothiazole is first neutralised in methanol using a stoichiometric amount of sodium methoxide (1.05 eq.), then reacted with 4‑chlorobutanal dimethyl acetal under a hydrogen atmosphere of 30 psi in a Hastelloy C‑22 autoclave charged with 5% platinum on carbon (sulfided). The molar ratio of the benzisothiazole piperazine free base to the chloro‑acetal is precisely 1.00:1.00, because any deviation results in the formation of a quaternary ammonium salt of the piperazine that precipitates as an adherent crust on the agitator shaft, demanding a lengthy CIP cycle with 10% citric acid at 60°C. Addition of the acetal is conducted over 90 minutes via a calibrated peristaltic pump; the internal temperature is maintained at 25°C ± 1°C to suppress undesired acetal hydrolysis, which would liberate free aldehyde and trigger premature imine reduction. The compliance boundary encompasses the Japanese Pharmaceutical and Medical Device Act (PMD Act) and the JP XVIII monograph for perospirone hydrochloride hydrate, with the residual platinum level mandatorily below 10 ppm as determined by ICP‑MS per JP general test 2.61. Work‑up after catalyst filtration through a 0.5 µm sintered metal candle involves distillation to one‑third volume under 50 mbar and addition of 2‑propanol to precipitate the crude perospirone; recrystallisation from ethyl acetate/hexanes (3:2) yields the hemihydrate in a polymorphic form that is micronised to a volume‑weighted mean diameter of 5–8 µm for uniform dispersion in orally disintegrating tablet matrices.

When a multi‑kilogram GMP campaign for tiospirone must accommodate the acetonitrile solvate transition at 34% relative humidity

Tiospirone, a serotonin 5‑HT_1A partial agonist and dopamine D₂ antagonist explored for generalised anxiety disorder, relies on the benzisothiazole piperazine intermediate as the core scaffold to which the azaspiro[4.5]decanedione fragment is appended. The synthetic step is a nucleophilic substitution in refluxing acetonitrile (82°C) between the free amine of 3‑piperazinyl‑1,2‑benzisothiazole and the mesylate ester of 3‑(trifluoromethyl)benzenepropanol; the hydrochloride salt of the piperazine is converted to the free base in situ with 1.02 eq. of DIPEA, and the mesylate is added in a single portion at the boiling point. The feed ratio mesylate:piperazine free base is fixed at 0.98:1.00 to minimize the carry‑over of unreacted benzisothiazole piperazine into the DMF‑antisolvent crystallisation, where it otherwise co‑precipitates as a contaminant exhibiting a DSC endotherm at 168°C. A unique process hazard arises during the primary isolation: if the relative humidity in the filter‑dryer chamber exceeds 34%, the initially formed anhydrate crystals convert to a needle‑like acetonitrile hemisolvate that retains 7.2% w/w residual solvent even after 18 hours of drying at 50°C under 10 mbar. This forces a second vacuum drying cycle at 65°C that causes partial degradation to a ring‑opened amide impurity exceeding the ICH Q3A qualification threshold of 0.15%. Consequently, the production facility is equipped with a Munters desiccant dehumidifier coupled to the Rosenthal suction dryer, maintaining the chamber atmosphere at 25°C/22% RH. The regulatory submission is structured per ICH M4 CTD Module 3.2.S.2.6, and the residual solvent profile is validated against USP 467 using a DB‑624 capillary column (30 m × 0.32 mm × 1.8 µm) with FID detection. The final dosage form is a hard gelatin capsule containing tiospirone hydrochloride blended with pregelatinised starch NF and magnesium stearate, manufactured under 21 CFR 211 subpart F production controls.

‘Developer kits’ for CNS receptor occupancy studies: radio‑tracer precursor and cold reference standard convergence

Positron emission tomography (PET) studies of dopamine D₂ and serotonin 5‑HT_2A receptor occupancy by benzisothiazole piperazine‑derived antipsychotics require ¹¹C‑ or ¹⁸F‑labelled analogues, and the 3‑piperazinyl‑1,2‑benzisothiazole hydrochloride serves as the immediate precursor for on‑site radiosynthesis modules such as the GE Healthcare TRACERlab FX_FN. The hydrochloride salt is dissolved in anhydrous DMSO (water content by Karl Fischer <100 ppm) at a concentration of 2.0 mg/mL and reacted with [¹¹C]methyl iodide delivered via a heated platinum tube from the cyclotron target. The addition ratio of base‑treated precursor to [¹¹C]CH₃I is determined by real‑time radiation monitoring; quenching with 0.1 N HCl occurs when the plateau activity reaches 3.7 GBq. Semi‑preparative HPLC purification on a Waters XBridge C18 column (10 × 250 mm, 5 µm) using 35:65 acetonitrile:ammonium formate (0.1 M, pH 4.0) yields the labelled product with radiochemical purity exceeding 99.5% per the European Pharmacopoeia chapter 0125 guidelines for radiopharmaceutical production. The cold reference standard, prepared from the identical batch of benzisothiazole piperazine precursor via stoichiometric methylation with unlabelled methyl iodide (1.05 eq.) in THF at 0°C, is co‑injected to confirm chemical identity by retention time matching. The entire process is enclosed in a lead‑shielded hot cell, and the precursor batch is release‑tested per a Certificate of Analysis that includes endotoxin levels (LAL test, limit <0.5 EU/mg) and residual DMSO solvent (headspace GC, limit <0.2%).

3‑Piperazinyl‑1,2‑benzisothiazole hydrochloride is utilised as a synthetic building block for a series of N‑substituted sulfenamide fungicides in development for leather and textile preservation, where the benzisothiazole ring replaces the conventional dichlorophenyl nucleus in tetraconazole structural mimics. The hydrochloride is suspended in dichloromethane, treated with 1.05 eq. triethylamine, and reacted with p‑toluene sulfenyl chloride at ‑5°C to afford the sulfenamide intermediate, which is then immediately subjected to a copper(I)‑catalysed Ullmann coupling with 2‑chloro‑4‑nitroimidazole to install the antifungal pharmacophore. The feed ratio of benzisothiazole piperazine free base to sulfenyl chloride is held at 1.00:1.02; an excess beyond 1.05 produces a disulfide by‑product that precipitates as a sticky gum interfering with the basket centrifuges used for solid isolation. The process is governed by the Biocidal Products Regulation (EU) 528/2012 Active Substance Approvals and the ISO 11930:2019 challenge test methodology for evaluating preservation efficacy. Manufacturing is performed in a multipurpose GMP suite with dedicated glass‑lined equipment that is cleaned using a validated protocol of 2% aqueous acetic acid rinses, monitored to a 1 ppm swab limit for the active intermediate via LC‑MS/MS. The resultant N‑(4‑nitroimidazol‑2‑yl)‑3‑piperazinyl‑1,2‑benzisothiazole sulfenamide is formulated at 0.15–0.40 wt% in a polyurethane‑based aqueous dispersion applied to full‑grain leather hides using an automatic spray line (Carrara 88‑P), providing a protection index of Grade 2 or better against Aspergillus niger ATCC 16404 in the ASTM E2180‑18 agar slurry test. The terminal preservation product is a wet‑blue or crust leather article classified under EU Ecolabel criteria, requiring the active substance concentration to be documented on the Safety Data Sheet per Annex II of REACH Regulation 1907/2006.

When loaded into a continuous twin‑screw wet granulation‐compression line for antipsychotic tablets, particle morphology variance of the 3‑piperazinyl‑1,2‑benzisothiazole hydrochloride intermediate itself becomes a critical quality attribute for the downstream API manufacturing step. Batches with acicular particle habit—typically resulting from uncontrolled cooling rates below 0.5°C/min during recrystallisation from toluene/cyclohexane—exhibit a Carr’s compressibility index exceeding 35%, causing severe arching in the conical hopper of the GEA NICA M6 small‑scale feeder used to meter the reagent into the alkylation vessel. This leads to oscillation in the local molar excess of the chloroethyl oxindole, generating intermittent excursions of the dimer impurity above the 0.15% alert limit. The mitigation strategy involves a WAB Turbula shaker‑mixer that pre‑de‑lumps the hydrochloride powder through a 500 µm screen, followed by a laser diffraction measurement (Malvern Mastersizer 3000) to confirm a volume median diameter d₅₀ between 90 µm and 180 µm. The material of construction contact surface for the feeder is specified as 316L with a Ra ≤ 0.8 µm electropolished finish to minimise triboelectric charging, which is monitored using a Faraday pail electrometer with a pass criterion of <5 µC/kg. These control strategies are embedded in the process performance qualification protocol according to ASTM E2500‑20 and are reviewed during pre‑approval inspections under ICH Q8(R2) principles of enhanced design space verification.