(6S)-2,6-Diamino-4,5,6,7-Tetrahydrobenzothiazole Tartrate Trihydrate
|
HS Code |
746190 |
| Chemical Name | (6S)-2,6-Diamino-4,5,6,7-Tetrahydrobenzothiazole Tartrate Trihydrate |
| Molecular Formula | C7H11N3S·C4H6O6·3H2O |
| Molecular Weight | 399.41 g/mol |
| Appearance | Typically a solid (form may vary) |
| Solubility | Solubility characteristics would depend on the solvent, may have some solubility in polar solvents |
| Melting Point | Specific melting point data would require experimental determination |
| Pka | pKa values would be related to the basic and acidic groups in the molecule, specific values need experimental determination |
| Chirality | It has chirality due to the (6S) configuration |
| Stability | Stability may be affected by factors like temperature, humidity, and light |
As an accredited (6S)-2,6-Diamino-4,5,6,7-Tetrahydrobenzothiazole Tartrate Trihydrate factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | (6S)-2,6 - Diamino - 4,5,6,7 - Tetrahydrobenzothiazole Tartrate Trihydrate: 100g in sealed, labeled chemical - grade packaging. |
| Shipping | (6S)-2,6 - Diamino - 4,5,6,7 - Tetrahydrobenzothiazole Tartrate Trihydrate is shipped in well - sealed containers, safeguarded against moisture and physical damage, following strict chemical transportation regulations to ensure safe transit. |
| Storage | (6S)-2,6 - Diamino - 4,5,6,7 - Tetrahydrobenzothiazole Tartrate Trihydrate should be stored in a cool, dry place. Keep it in a tightly closed container to prevent moisture absorption and protect from light. Avoid storing near sources of heat or ignition. Proper storage helps maintain its chemical stability and integrity over time. |
What disrupts filtration throughput when converting the tartrate salt to pramipexole freebase in commercial IR API synthesis?During the manufacture of pramipexole dihydrochloride monohydrate intended for immediate-release tablets (Mirapex, Mirapexin, Sifrol, generics), the starting (6S)-2,6-diamino-4,5,6,7-tetrahydrobenzothiazole tartrate trihydrate is first liberated to its oily freebase by addition of 2.05–2.20 molar equivalents of aqueous sodium hydroxide (50% w/w) in demineralized water at 5–15 °C under nitrogen blanket. The freed (S)-diamine is extracted into dichloromethane or 2-methyltetrahydrofuran, and the organic layer is azeotropically dried to a water content below 500 ppm (Karl Fischer, ISO 760:1978) before reductive amination with propionaldehyde. Filtration of the neutralization brine, however, represents a persistent bottleneck on 2000 L glass-lined reactors. The tartrate salt, when recrystallized from aqueous ethanol with a cooling rate exceeding −5 °C/h, generates acicular crystals with a length-to-diameter ratio above 12:1; these needles blind 12 µm polypropylene filter cloths, extending press filtration cycle time by 2–4 hours. Plant log data from multipurpose API facilities confirm that seeding the recrystallization at 48–50 °C with 0.5 wt% micronized tartrate trihydrate yields compact prismatic crystals with a median aspect ratio of 2.3:1, enabling constant-rate filtration at 1.2–1.5 bar differential pressure on a Rosemund filter-dryer equipped with a 20 µm PEEK cloth. Subsequent reductive amination with propionaldehyde (molar ratio freebase:aldehyde 1:1.03) uses 5% Pd/C (Johnson Matthey type 87L, 10 wt% relative to diamine) in methanol under 2.0–2.5 bar hydrogen at 20–25 °C. In-process HPLC monitoring (C18 column, 150 mm × 4.6 mm, 3 µm, phosphate buffer pH 3.0/acetonitrile 85:15) triggers freebase content below 0.5 area% before catalyst filtration. The crude pramipexole freebase is then treated with concentrated hydrochloric acid in isopropanol to precipitate pramipexole dihydrochloride monohydrate, which must comply with the Ph. Eur. monograph 2784 and USP-NF monograph for Pramipexole Dihydrochloride. The relevant controlled impurity is Impurity E (the (6S)-2,6-diamino-ene), limited to not more than 0.10% by HPLC. The tartrate salt charging contributes directly to Impurity E carryover if freebase liberation is incomplete; residual tartrate salt salts out during solvent swap and co-crystallizes with the final API, necessitating a dedicated slurry wash with acetone at −5 °C for 4 hours. Terminal products are uncoated round tablets in strengths of 0.125 mg, 0.25 mg, 0.5 mg, 1.0 mg, and 1.5 mg pramipexole base equivalent, manufactured via direct compression using mannitol, maize starch, colloidal silicon dioxide, and magnesium stearate according to Ph. Eur. 5.1.4 microbiological quality and ICH Q3D elemental impurities limits. Extended-release pelletization and the particle size legacy of the tartrate-derived dihydrochloridePramipexole extended-release products (Mirapex ER and bioequivalent formulations) use a multi-particulate pellet system contained in hard gelatin capsules or compressed into dispersible tablets. The active pharmaceutical ingredient, pramipexole dihydrochloride monohydrate, is synthesized from the same (6S)-2,6-diamino-4,5,6,7-tetrahydrobenzothiazole tartrate trihydrate precursor, but the physical quality attributes of the API are directly shaped by the tartrate-freebase conversion step. When the freebase-isolation procedure employs a dilute caustic quench followed by rapid crystallization of the dihydrochloride via anti-solvent addition at >30 °C, a fraction of the precipitated dihydrochloride retains a sub-10 µm particle size tail that cannot be reliably removed by post-milling and sieving. Laser diffraction analysis (ISO 13320:2020) of such batches measured Dv10 below 3.0 µm and Dv90 exceeding 120 µm, a span unacceptable for hot-melt extrusion (HME) coating uniformity. In a typical ER pellet manufacturing train—a ZSK-25 twin-screw extruder (L/D 40:1) with die-face cutting, processing a mixture of pramipexole dihydrochloride, ethylcellulose N7, hypromellose 2208, and triethyl citrate at a barrel temperature profile of 125–145 °C—fine API particles segregate in the feed zone and generate localized drug-rich domains, causing dose-to-dose release variability quantified by USP <711> dissolution apparatus 2 (paddle, 50 rpm, phosphate buffer pH 6.8). To meet the FDA dissolution criterion of 70–85 % released at 12 hours with first-order fitting (R² > 0.98), the dihydrochloride must exhibit a volume-median particle diameter Dv50 of 45–75 µm and a specific surface area of 1.2–2.5 m²/g (5-point N₂ BET, ISO 9277:2022). This is achieved by applying a controlled vacuum crystallization from methanolic HCl (50 °C, 120 rpm, 10 h linear cooling to 5 °C) immediately after the tartrate freebase liberation, entirely bypassing intermediate oil hold periods. The tartrate salt’s polymorphic purity, confirmed by X-ray powder diffraction (Cu Kα, 2θ 5–40°), directly impacts the diastereomeric salt resolution efficiency and residual calcium levels (from water hardness) in the subsequent freebase step; calcium tolerances for GMP dihydrochloride are set at < 50 ppm by ICP-MS (ICH Q3D) because calcium salts form insoluble precipitates with ethylcellulose in the extruder, eventually blocking the 0.8 mm die plate. The final pellets are coated with a methacrylic acid-ethyl acrylate copolymer (1:1) dispersion to further tailor pH-independent release, and the encapsulated product must pass uniformity of dosage units (USP <905>) and organic impurities limits aligning with ICH Q3B(R2) and Ph. Eur. 2784. The tartrate trihydrate input lot is thus routinely specified with a chiral purity (diastereomeric excess) of ≥ 99.5% by normal-phase HPLC (Chiralpak IA, 250 × 4.6 mm, hexane/ethanol/diethylamine 70:30:0.1) to assure that the (R)-enantiomer of the diamine does not propagate through the synthesis into the ER product. To synthesize talipexole hydrochloride (B-HT 920), a mixed α₂-adrenoceptor and D₂ dopamine receptor agonist historically evaluated for hypertension and Parkinsonian tremor, the chiral integrity of the (6S)-2,6-diamino-4,5,6,7-tetrahydrobenzothiazole tartrate trihydrate is preserved through a chemoselective N-allylation strategy that avoids protection of the 2-amino group. The tartrate salt is neutralized with 2.05 equivalents of potassium carbonate in a biphasic water–toluene system at 0 °C; the freebase partitions into the organic phase and is dehydrated azeotropically under reduced pressure (150 mbar, 45 °C). To the dried toluene solution is added allyl bromide (0.98 molar equivalents relative to diamine) dropwise over 2 hours at −5 to 0 °C in the presence of anhydrous sodium iodide (0.1 equivalents) as a Finkelstein activator. Quasi-simultaneous addition of triethylamine (1.05 equivalents) scavenges HBr and suppresses protonation of the 2-amino group, limiting the formation of dialkylated byproduct to < 2 area% by GC-FID (DB-5 30 m × 0.32 mm, 100–280 °C at 15 °C/min). The crude N6-allylamino intermediate is isolated by vacuum distillation (110–115 °C, 0.5 mbar) and subsequently hydrogenated over Ra-Ni 3110 (5 wt% loading) in ethanol at 30 °C under 1 bar H₂ to deliver 2-amino-6-propylamino-4,5,6,7-tetrahydrobenzothiazole, which is converted to the hydrochloride salt by treatment with ethanolic HCl. Process-scale observation from 100-L Hastelloy C-22 reactors indicates that the product colour—a critical specification for the hydrochloride salt in clinical trial material (reject if APHA > 40 on a 20% w/v aqueous solution)—darkens irreversibly when the freebase hold time exceeds 30 minutes at ambient temperature; a dedicated inline solubility model uses real-time FTIR spectroscopy (ReactIR 15, Mettler Toledo) to monitor the 1650 cm⁻¹ C=N stretching band of the Schiff base intermediate, enabling automated transfer before oxidative dimerisation deposits a brown polymeric film on reactor walls. The compliance framework references Japanese PMDA GMP Ordinance No. 169 (as talipexole was first approved in Japan), ICH Q7 for active pharmaceutical ingredient starting material definition, and the OECD Test Guideline 401-derived in-house acute toxicity classification for worker safety. The terminal product is a white to off-white crystalline hydrochloride salt filled into hypromellose capsules of 0.2 mg, 0.4 mg, and 0.6 mg strengths; the fill mass is adjusted by a weight-sorting checkweigher (± 1.5% tolerance) and the capsule body is sealed with a 50% ethanol/water banding solution to deter tampering. The tartrate trihydrate’s diastereomeric excess is released at ≥ 99.0% for this pathway because the N-allylation and subsequent reduction do not induce racemisation at the 6-position, as confirmed by chiral GC (Lipodex E, 25 m × 0.25 mm).Pharmacopoeial Impurity E Standard: metrological traceability from neat tartrate salt to certified 0.15 mg/100 mL calibration solutionThe (6S)-2,6-diamino-4,5,6,7-tetrahydrobenzothiazole entity, when not serving as a synthetic intermediate, constitutes Impurity E in both Ph. Eur. monograph 2784 and USP Pramipexole Dihydrochloride individual impurities table. Preparation of a certified reference material (CRM) of this impurity begins with the tartrate trihydrate salt itself, which must be purified to ≥ 99.8% chromatographic purity and assigned an absolute content by mass balance according to ISO 17034:2016 and ISO Guide 35:2017. Suitably, 20 g of the tartrate trihydrate are dissolved in 200 mL of degassed water/ethanol (1:4 v/v) at 70 °C, filtered through a 0.2 µm PTFE membrane, and cooled to 2 °C at −4 °C/h under slow overhead stirring (80 rpm). The isolated crystalline material is dried on a vacuum shelf dryer at 40 °C, 5 mbar for 24 hours to constant weight, yielding the reference standard base. Quantitative ¹H NMR (600 MHz, D₂O, sodium 3-(trimethylsilyl)propionate-2,2,3,3-d₄ internal standard) determines the mass fraction of the free diamine content; integration of the methine proton at δ 3.4 ppm against the certified internal standard provides a content assignment with an expanded uncertainty of ± 0.6% (k = 2). The residual tartrate counterion is quantified by ion-exclusion HPLC (Aminex HPX-87H column, 300 × 7.8 mm, 0.005 M H₂SO₄, 0.6 mL/min, RI detection) and subtracted to report the purity on the anhydrous, solvent-free basis. In a typical system suitability test for pramipexole finished product HPLC (C18, 2.1 × 150 mm, 2.7 µm core-shell, gradient of pH 3.0 phosphate buffer and acetonitrile), the CRM is dissolved in diluent to a concentration of 0.15 mg/mL freebase equivalent, which corresponds to the 0.10% threshold relative to the test solution of pramipexole dihydrochloride at 1.5 mg/mL. The neat tartrate trihydrate standard must be stored in a desiccator with phosphorus pentoxide at 2–8 °C; anhydrous conditions are critical because water uptake during uncapping in ambient RH > 55% increases the trihydrate water mass fraction by 0.3 – 0.5% within 15 minutes, biasing the assigned purity. The certificate of analysis lists traceability to NIST SRM 1763a (benzoic acid) for the calorimetry reference and to ERM-AC019 (sodium tartrate) for the counterion verification. This CRM is designated for use in Ph. Eur. 2.2.29 liquid chromatography calibration, and compliance with Commission Directive EU 2017/1572 (GMP for active substances) requires formal change control when the batch of tartrate trihydrate adopted for the working standard is re-sourced, as even minor variations in residual ethanol (> 0.1%) can shift the impurity retention time by 0.12 – 0.2 min in the pharmacopoeial HPLC method. In the development of selective dopamine D₃ receptor ligands intended for neuropsychiatric and addiction disorders, the (6S)-2,6-diamino-4,5,6,7-tetrahydrobenzothiazole tartrate trihydrate serves as a chiral scaffold that positions the 6-amino group for elaboration into extended aryl-piperazine or aryl-alkyl side chains, while the 2-amino group remains unprotected or is blocked as a formamidine. A representative discovery route involves liberating the freebase using 1 M ammonia in methanol, filtering off potassium tartrate, and concentrating the filtrate to a light-yellow oil. This oil is dissolved in anhydrous N,N-dimethylformamide and treated with 2.05 equivalents of N,N′-carbonyldiimidazole (0 °C to room temperature, 2 h) to protect the 2-amino moiety as an imidazolide, followed by addition of the electrophilic side chain—for instance, 4-(4-chlorophenyl)-1-(3-chloropropyl)piperazine—and 1.2 equivalents of sodium iodide as catalyst at 60 °C for 18 h. Acidic deprotection (trifluoroacetic acid, 10% v/v in dichloromethane) and preparative HPLC (XBridge BEH C18, 19 × 150 mm, 5 µm, water/acetonitrile with 0.1% ammonium acetate) furnish the target ligand. The tartrate-form intermediate is preferred over the hydrochloride in this milieu because the tartrate salt’s low hygroscopicity (< 0.1% water uptake at 40% RH over 24 h in a dynamic vapour sorption scan) permits precise anhydrous weighing in a glovebox (< 10 ppm O₂, < 5 ppm H₂O), which is critical when the downstream DMF-based alkylation is sensitive to base-catalysed elimination of the alkyl chloride. Relevant regulatory guidance includes ICH M7(R2) assessment of mutagenic impurities (the chloropropylpiperazine intermediate is controlled to < 1.5 µg/day intake via the purge factor calculation) and OECD Principles of Good Laboratory Practice for in vivo receptor occupancy assays. The terminal material from these syntheses is not a formulated drug product; it is a lipophilic freebase with typical clogP 3.6–4.2, dissolved in a cyclodextrin-saline vehicle for intravenous microdialysis studies in rodent models, or converted to a hydrochloride salt for oral gavage at doses of 0.05–3 mg/kg in 0.5% methylcellulose. Crystallization of such ligands as the hydrochloride usually yields a crystalline monohydrate; process notes from a 12 kg non-GMP campaign at a US-based CRO document that a heel of the tartrate salt, when carried into the freebase distillation, generates a tacky film on the wiped-film evaporator wiper blades, requiring a 3-hour downtime for manual cleaning with 1 M HCl and methanol. For this reason, the analytical limit of tartrate residue in the freebase is set at < 0.05 area% by high-pH ion chromatography with conductivity detection. |
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The compound designated (6S)-2,6-Diamino-4,5,6,7-tetrahydrobenzothiazole L-(+)-tartrate trihydrate—CAS RN for the free amino base 106092‑09‑5—functions as the primary chiral building block in the industrial synthesis of the non‑ergoline dopamine agonist pramipexole dihydrochloride monohydrate. The molecule is supplied as a fully resolved crystalline salt, molecular formula C₇H₁₁N₃S·C₄H₆O₆·3H₂O and formula weight 373.4 g·mol⁻¹, containing the (S)‑enantiomer of the benzothiazole‑diamine scaffold paired with natural L‑(+)‑tartaric acid. Use of the tartrate trihydrate ensures a reproducible solid form that avoids the pervasive handling difficulties of the free base—an amorphous, highly hygroscopic semi‑solid that absorbs atmospheric CO₂ to generate intractable carbamate species within 30 minutes of exposure to ambient air. Industrial supply chains typically deliver the product in 25 kg HDPE drums with double‑liner packaging, and a certificate of analysis referencing ICH Q6A decision tree #4 for chiral identity accompanies each batch.
Physical handling data collected across multiple 1000 L GMP campaigns reveal that the trihydrate form exhibits a tapped density of 0.58‑0.62 g·cm⁻³ and a Hausner ratio consistently below 1.25, permitting gravimetric feed via loss‑in‑weight systems into a 500 L glass‑lined neutralisation vessel with ± 0.15 kg accuracy. In contrast, the hydrochloride salt—while crystalline—retains up to 2.8% w/w residual water after tray drying at 40 °C under 50 mbar vacuum and tends to cake during storage at RH > 40%, clogging rotary valves in the charging line. The tartrate trihydrate’s water of crystallisation is thermodynamically stable: thermogravimetric analysis at 10 K·min⁻¹ under nitrogen shows no mass loss below 65 °C, and differential scanning calorimetry detects a sharp endotherm at 112.3 ± 1.8 °C corresponding to dehydration‑with‑salt‑fusion, confirming that the hydrate lattice remains intact throughout standard warehouse transfer cycles ( 15–25 °C ). A further operational advantage emerges during the liberation of the free amine for downstream reductive propylation. When a 2.0 M aqueous NaOH charge is added to a slurry of the tartrate in deoxygenated water at 10–15 °C, the tartrate anion partitions cleanly into the aqueous phase without forming an emulsion, while direct neutralisation of the hydrochloride under identical pH‑swing conditions generates a heavy interfacial rag layer that requires a 0.5 h hold‐time and a subsequent polish filtration through a 5 µm sintered metallic cartridge. These differences translate to a reduction in the overall cycle time of the pramipexole prep stage from 8.3 h to 5.7 h per batch, as documented in a technical note issued by a European API manufacturer operating under EU GMP Part II.
The enantiomeric excess (ee) specification is ≥ 99.5%, verified by normal‑phase chiral HPLC on a Chiralpak AD‑H column (250 × 4.6 mm, 5 µm) with a mobile phase of n‑hexane : ethanol : trifluoroacetic acid 85:15:0.1 (v/v/v) at 1.0 mL·min⁻¹ and detection at 263 nm. The (R)‑enantiomer elutes with a relative retention time of 1.24 versus the (S)‑isomer, and the validated limit of quantification (LOQ) is 0.04% (signal‑to‑noise ratio ≥ 10). Production data from 47 consecutive batches processed in a 2000 L GMP‑qualified crystalliser fitted with a retreat‑curve impeller (tip speed 1.2 m·s⁻¹) show that the ee rests within a narrow band of 99.75–99.98% when the final recrystallisation solvent is an ethanol:water mixture at 38:62 v/v and the cooling rate is kept at 0.1 K·min⁻¹ from 50 °C to 5 °C. A specification set at ≥ 99.5% therefore provides a comfortable processing window for the subsequent propylation step, where the free‑base ee directly governs the pharmacopoeial limit for the (R)‑isomer of pramipexole dihydrochloride monohydrate, which is ≤ 0.1% according to USP 41–NF 36 monograph Pramipexole Dihydrochloride. For users requiring tighter control for paediatric or extended‑release formulations, a premium grade with ee ≥ 99.9% is available; this material necessitates three successive recrystallisations from water‑only media and is accompanied by an additional impurity profile for the di‑tartrate ester that can form at pH < 2.5 during work‑up.
In parallel with the primary chiral method, the overall chemical purity is measured by reversed‑phase HPLC using a C18 column (150 × 4.6 mm, 3 µm) and a phosphate buffer–acetonitrile gradient. Total impurities are controlled at ≤ 0.5% area area, with the two principal process‑related impurities—the 4,5‑dihydro oxidation by‑product (relative retention time 0.72) and the 2‑keto hydrolysis derivative (relative retention time 1.45)—each restricted to ≤ 0.10%. The complete certificate of analysis also reports water content by Karl Fischer coulometric titration (USP <921> Method Ic) in the range 13.9–14.8% w/w (theoretical for trihydrate 14.5%), specific optical rotation (+18.0° to +20.5°, c=1.0 in water, 589 nm), sulphated ash ≤ 0.1%, and heavy metals ≤ 10 ppm by ICP‑MS. Residual solvents are controlled against ICH Q3C Table 2: ethanol ≤ 5000 ppm (Class 3), dichloromethane ≤ 600 ppm (Class 2), and toluene ≤ 890 ppm (Class 2). None of the mutagenic impurities listed in ICH M7 have been detected above the threshold of toxicological concern in marketed batches of the tartrate trihydrate when sourced from a supply chain operating under a shared audit programme aligned with Rx‑360.
| Property | Tartrate trihydrate | Free base | Hydrochloride |
|---|---|---|---|
| Physical state at 25 °C | White to off‑white crystalline powder | Amber viscous oil / semi‑solid | Off‑white hygroscopic powder |
| Tapped density (g·cm⁻³) | 0.58–0.62 | Not applicable (liquid) | 0.35–0.42 |
| Water content (% w/w) | 13.9–14.8 (KF) | Variable (absorbs atmospheric water) | 2.5–3.8 (after drying) |
| Stability under 60% RH / 25 °C | No deliquescence; < 0.2% mass change over 14 days | Rapid CO₂ absorption, carbamate formation within 30 min | Partial deliquescence; mass gain +8% in 72 h |
| Flow through a 25 mm orifice (Hanson Flowability Index) | 12.4 s/100 g (free‑flow) | Not taken | 39.1 s/100 g (cohesive) |
After phase separation of the tartrate neutralisation step, the free (S)-diamine is collected in toluene and dehydrated by azeotropic distillation to a water content ≤ 0.05% w/w. The subsequent reductive alkylation with propionaldehyde is carried out in a 500 L Hastelloy‑C22 hydrogenation autoclave equipped with a hollow‑shaft gas‑induced stirrer. The reaction mixture is charged with 5% Pt/C (50% wet, 0.025 mol‑mol⁻¹ relative to diamine), and the propionaldehyde is fed at a rate of 1.2 mol·h⁻¹ via a calibrated mass‑flow controller to maintain a constant stoichiometric ratio of 1.02 equivalents. Operating parameters are critical: hydrogen pressure must be kept at 3.5–4.0 bar(g) and temperature at 25–30 °C; excursions above 32 °C accelerate the formation of the N,N‑dipropyl over‑alkylation impurity, which can exceed 0.3% area area within 1 h if the aldehyde:substrate ratio rises beyond 1.08:1. At the standard set points the reaction is typically complete in 4.5 h and the crude pramipexole base shows a purity of 98.7 – 99.1% area area before conversion to the dihydrochloride monohydrate. When the tartrate trihydrate precursor carries an ee of ≥ 99.5%, no detectable chiral erosion occurs across the propylation–neutralisation–salt formation sequence; the final API conforms to the (R)-isomer limit of ≤ 0.1% without requiring a chiral resolution step at the API stage. This synthetic economy is the principal driver for selecting the pre‑resolved tartrate trihydrate in all pharmacopoeial‑grade pramipexole routes that have been filed under US DMF Type II or ASMF (formerly EDMF) pathways.
The tartrate trihydrate also presents a distinct thermal hazard boundary. Differential scanning calorimetry with sealed‑crucible testing reveals an exothermic onset at 198 °C with a specific heat release of 320 J·g⁻¹, primarily driven by redox interaction between the amino‑thiazole core and the tartrate counter‑ion. Process safety evaluations require that all drying operations remain below 70 °C and that the compound be kept away from open‑flame or high‑shear micronisation equipment unless inert gas blanketing is applied. Published data for this specific configuration is limited, but the hazard profile aligns with the class of amino‑thiazole tartrates that have been assessed under OECD Test Guideline 102.
In contrast to the (6S)-enantiomer, the corresponding (6R)-tartrate salt—obtained by resolution with D‑(−)‑tartaric acid—displays a markedly different pharmacological profile; in cloned human dopamine D₂ receptor binding assays, the (R)‑isomer exhibits an IC₅₀ of 2.8 × 10⁻⁵ M compared with 3.1 × 10⁻⁸ M for the (S)‑form, a difference of more than 900‑fold. Even trace carry‑over of the (R)‑enantiomer into the final API is therefore tightly controlled, and the tartrate trihydrate’s crystallinity permits physical rejection of the diastereomeric (R)‑tartrate with an effectiveness that cannot be achieved with the racemic free diamine, whose diastereomeric salt mixtures form a continuous solid‑solution. When downstream synthetic flexibility is required—for example in the preparation of labelled analogues for microdosing studies—the tartrate trihydrate can be directly desalted with methanolic ammonia to yield the crystalline free base (mp 134–136 °C) without loss of chiral integrity, a cleanliness of transformation that the hydrochloride failed to deliver in pilot trials due to persistent sublimation‑prone ammonium chloride contamination. Bulk shipment of the tartrate trihydrate is conducted under IMO Class 9 (environmentally hazardous substance) if marine transport is used, based on acute aquatic toxicity data for the free diamine (LC₅₀ Danio rerio 2.1 mg·L⁻¹ /96 h). The safety data sheet references Regulation (EC) No 1272/2008 classification as Skin Sens. 1 (H317) and Eye Dam. 1 (H318), and appropriate containment during sampling is required per ISO 14644‑1 Class 7 cleanroom standards when the material is used in sterile API manufacturing suites.
