(6R)-N~6~-Propyl-4,5,6,7-Tetrahydro-1,3-Benzothiazole-2,6-Diamine

Product Name (6R)-N~6~-Propyl-4,5,6,7-Tetrahydro-1,3-Benzothiazole-2,6-Diamine
Alias Pramipexole
Einecs 629-397-9
Mininmum Order 1g
Factory Site West Ujimqin Banner, Xilingol League, Inner Mongolia, China
Price Inquiry sales9@bouling-chem.com
Manufacturer Bouling Chemical Co., Limited
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In terms of specification, (6R)-N~6~-Propyl-4,5,6,7-Tetrahydro-1,3-Benzothiazole-2,6-Diamine is supplied with ≥98% enantiomeric excess and ≥95% chemical purity (HPLC), making it suitable for use as a chiral reference standard in pharmaceutical impurity profiling.

Specifications

HS Code	364230
Chemical Formula	C10H17N3S
Molar Mass	211.33 g/mol
Physical State	Solid (predicted)
Appearance	White to off - white powder (predicted)
Solubility In Water	Poorly soluble (predicted)
Melting Point	Unknown (no data available)
Boiling Point	Unknown (no data available)
Pka	Unknown (no data available)
Logp	Predicted to be lipophilic
Density	Unknown (no data available)

As an accredited (6R)-N~6~-Propyl-4,5,6,7-Tetrahydro-1,3-Benzothiazole-2,6-Diamine factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.

Packing & Storage

Packing	100g of (6R)-N⁶-Propyl-4,5,6,7 - Tetrahydro - 1,3 - Benzothiazole - 2,6 - Diamine in sealed chemical vial.
Shipping	(6R)-N⁶-Propyl-4,5,6,7 - Tetrahydro - 1,3 - Benzothiazole - 2,6 - Diamine is shipped in well - sealed containers, following strict chemical transport regulations. Packing ensures protection from environmental factors during transit.
Storage	(6R)-N⁶-Propyl-4,5,6,7 - Tetrahydro - 1,3 - benzothiazole - 2,6 - diamine should be stored in a cool, dry place, away from direct sunlight. Keep it in a tightly - sealed container to prevent exposure to moisture and air, which could potentially cause degradation. Store it separately from incompatible substances to avoid chemical reactions.

Application of (6R)-N~6~-Propyl-4,5,6,7-Tetrahydro-1,3-Benzothiazole-2,6-Diamine

When the (R)-Enantiomer Defines Pharmacopoeial System Suitability in Pramipexole Dihydrochloride Analysis

In quality control laboratories across finished-dose manufacturing sites, the (6R)-N⁶-propyl-4,5,6,7-tetrahydro-1,3-benzothiazole-2,6-diamine free base—frequently designated as Pramipexole Related Compound B or Enantiomeric Impurity A—is not employed as a bulk active ingredient but as a chromatographic discrimination probe. A solution at a concentration of **0.1 % (w/v)** relative to the test solution, prepared by dissolving approximately **10 mg** of the (R)-isomer in diluent composed of ammonium formate buffer (pH **4.5 ± 0.05**) and methanol in a **70:30** volumetric ratio, is injected into a liquid chromatograph fitted with a **150 × 4.6 mm** octadecylsilane column of sub-**3 µm** particle size and maintained at a column compartment temperature of **40 °C ± 0.5 °C**. The isocratic mobile phase consists of **985 mL** of a solution containing **3.45 g/L** sodium 1-octanesulfonate monohydrate and **1.5 mL/L** triethylamine adjusted to pH **3.0** with phosphoric acid, mixed with **15 mL** of acetonitrile; the flow rate is kept at **1.0 mL/min**, and detection is performed at **262 nm** using a UV-Vis diode array detector. The system is deemed suitable only when a resolution factor of at least **2.0** between the (S)-enantiomer principal peak and the (R)-enantiomer peak is observed, and the relative standard deviation for replicate injections remains below **2.0 %**. The downstream process is the batch release testing of pramipexole dihydrochloride monohydrate tablets—dosage strengths **0.125 mg**, **0.25 mg**, **0.5 mg**, **0.75 mg**, **1.0 mg**, and **1.5 mg**—against the acceptance criterion NMT **0.3 %** of the (R)-isomer specified in the current harmonized monograph aligned with ICH Q3A (R2) and the general chromatography chapter <621>. Compliance documentation references the European Pharmacopoeia monograph **2417** and the corresponding USP Pramipexole Hydrochloride monograph, where the identity of the (R)-enantiomer is confirmed by comparative retention time against a certified reference standard stored at **2–8 °C** in a desiccated environment under nitrogen overlay to prevent oxidative degradation of the aminothiazole ring. The whole analytical cycle—from dissolution and filtration through **0.22 µm** PVDF syringe filters to injection sequence bracketing—is conducted under GLP conditions with full data integrity audit trails, and the terminal output is a certified Certificate of Analysis accepting or rejecting a commercial batch of pramipexole hydrochloride destined for blister-packed tablet cards.

What Stoichiometric Constraints Emerge When the Chiral Diamine Is Used as a Building Block for D₃ Receptor Ligand Libraries?

Medicinal chemists constructing structure–activity relationship arrays around the 2-aminothiazole scaffold utilize the (6R)-N⁶-propyl diamine as an enantiomerically pure synthon whose ring-locked (R)-configuration at the 6-position directs receptor subtype selectivity away from D₂ and toward D₃ dopamine receptors in in vitro binding assays. A typical synthetic sequence begins with the free base dissolved in anhydrous tetrahydrofuran under argon, to which a substituted benzoyl chloride—most commonly 4-iodobenzoyl chloride or 3-methoxy-4-methylbenzoyl chloride—is added at a molar ratio of **1.00:1.05** (amine:acyl chloride) in the presence of triethylamine at **0–5 °C** with vigorous overhead stirring at **400 rpm** in a jacketed glass reactor. After warming to ambient temperature over **90 minutes**, the amide intermediate is isolated via precipitation in deionized water, filtered through a Büchner funnel, and recrystallized from absolute ethanol until HPLC purity exceeds **99.0 area%**. This intermediate is subsequently engaged in a Buchwald-Hartwig cross-coupling reaction with a suitable aryl bromide in toluene at **110 °C** for **16 hours**, catalyzed by tris(dibenzylideneacetone)dipalladium(0) at **2.5 mol%** loading and (±)-2,2'-bis(diphenylphosphino)-1,1'-binaphthyl (BINAP) as the ligand. The reaction mass is quenched with ammonium chloride solution, extracted with ethyl acetate, and purified by flash chromatography on silica gel **60** (particle size **40–63 µm**) with a step gradient of hexane/ethyl acetate from **4:1** to **1:1**. The final deprotection of the benzyl-protecting group—where present—is executed via catalytic hydrogenolysis in methanol at **50 psi** hydrogen pressure over **10 % Pd/C (50 % water wet)** for **4 hours** at **25 °C**. The terminal product classes are highly selective dopamine D₃ receptor partial agonists and antagonists, formulated as hydrochloride or mesylate salts and submitted for microsomal stability testing in human liver microsomes (HLM) at a substrate concentration of **1 µM** and an incubation time of **60 minutes** at **37 °C**. All compounds intended for in vivo study must meet internal specifications requiring >**95 %** purity by a two-channel HPLC-ELSD/UV method and are accompanied by a certificate citing compliance with the OECD Principles of Good Laboratory Practice ENV/MC/CHEM(98)17 for non-clinical safety studies.

Manufacturing Salts of the (R)-Isomer as Impurity Markers for Forced Degradation Studies

Beyond the parent compound, regulatory submissions for pramipexole abbreviated new drug applications mandate identification and quantification of process-related and degradation impurities beyond the simple enantiomer; consequently, the (R)-diamine is deliberately derivatised into N-alkylated, oxidized, and dimeric side products that are isolated, characterised, and supplied as impurity marker batches. The addition ratio in a typical propylation side-reaction simulation involves treatment of the (R)-diamine with 1-bromopropane at a molar excess of **3.0 equivalents** in dimethylformamide containing anhydrous potassium carbonate at **60 °C** for **8 hours**, yielding the N,N,N-tripropyl quaternary ammonium species after preparative HPLC purification on a **250 × 21.2 mm** C18 column with a mobile phase of **0.1 % formic acid** in water and acetonitrile running in gradient mode from **5 %** to **40 %** organic over **20 minutes**. The downstream production protocol for the N-oxide impurity marker involves stirring the free base in dichloromethane with **3.0 equivalents** of meta-chloroperoxybenzoic acid (m-CPBA, **<77 %** purity) at **0 °C** for **24 hours**; the crude product is washed with saturated sodium bicarbonate, dried over anhydrous sodium sulfate, and purified by recrystallization from a mixture of diethyl ether and hexane. Each isolated impurity is characterized by high-resolution mass spectrometry (Q-TOF, resolution >**30,000** FWHM) and ¹H, ¹³C, DEPT-135, COSY, HSQC, and HMBC NMR spectroscopy at **400 MHz** or higher in DMSO-d₆. The terminal outputs are individually sealed in USP Type III glass vials under argon, assigned a batch-specific retest date based on a stability protocol with storage at **−20 °C ± 5 °C** and monitored for purity at **0, 3, 6, 12, 24 months** by the same HPLC method. These impurity lots ship with a comprehensive analytical dossier conforming to the requirements of ICH M7(R1) for mutagenic impurity assessment and the data integrity expectations of 21 CFR Part 11 for electronic records. The downstream user integrates these markers into forced degradation cocktails applied to pramipexole tablets under stress conditions—acidic hydrolysis in **0.1 N HCl** at **80 °C** for **24 hours**, oxidative stress with **3 % H₂O₂** at ambient temperature for **6 hours**, photolytic exposure per ICH Q1B Option 2 at **1.2 × 10⁶ lux·h** and **200 W·h/m²**—and the resulting chromatograms establish relative retention times for impurity profile identification.

Selective scavenging of residual palladium during the late-stage deprotection of (R)-6-propyl intermediates has introduced an application niche in metal-scavenging functionalized silica fabrication, wherein the free amine anchors onto activated silica gel. The immobilization sequence proceeds by suspending silica gel **60** (particle size **63–200 µm**, pore diameter **60 Å**) in dry toluene, adding **3-aminopropyltriethoxysilane** at **2.0 mmol/g** of silica, and refluxing for **18 hours** under nitrogen; after filtration and washing, the amine-functionalized silica is reacted with glutaraldehyde ( **25 %** aqueous solution) at pH **7.0** in phosphate-buffered saline for **2 hours** at room temperature, creating a Schiff base terminal that reacts with the primary amine of the (6R)-propyl diamine added at **1.5 mmol per gram** of wet support and reduced in situ with sodium cyanoborohydride at **20 mmol/L** final concentration over **12 hours**. The washed and vacuum-dried scavenger powder exhibits a palladium-binding capacity measured by inductively coupled plasma mass spectrometry of **1.2 mmol Pd(II) per gram** under dynamic column flow conditions at a linear velocity of **30 cm/h** using a simulated reaction stream containing **500 ppm** palladium acetate in ethyl acetate at **25 °C**. This application is driven by commercial-scale producers of pramipexole intermediates operating in 2000 L glass-lined reactors who require final crude active pharmaceutical ingredient with residual Pd below **10 ppm** before recrystallization, in compliance with the ICH Q3D Guideline for Elemental Impurities and the oral permissible daily exposure limit of **100 µg/day** for palladium. The spent scavenger beds, after exhaustion indicated by breakthrough palladium concentration exceeding **5 ppm** at the column outlet, are returned for metal reclamation through aqua regia digestion and electrowinning.

**Table 1.** Gradient Program for (R)-Enantiomer Quantitation in Pramipexole Tablets per In-House Validated LC Method
Time (min)	Mobile Phase A (%)*	Mobile Phase B (%)**	Flow Rate (mL/min)	Elution Profile
0.0	90	10	1.0	Initial isocratic hold
15.0	90	10	1.0	Isocratic
25.0	50	50	1.0	Linear gradient
30.0	50	50	1.0	Isocratic wash
30.1	90	10	1.0	Return to initial
40.0	90	10	1.0	Re-equilibration

*Phase A: 0.01 M Sodium 1-Octanesulfonate + 0.15% Triethylamine pH 3.0; **Phase B: Acetonitrile

What governs the recovery of non-racemic (R)-enantiomer from mother liquors of pramipexole resolution that would otherwise be discarded has led to a parallel reprocessing pathway operated by contract manufacturing organisations holding Drug Master Files. The input stream—an acetonitrile/water mother liquor containing approximately **4–6 % (w/w)** of the (R)-enantiomer alongside **85–90 %** of diastereomeric resolving agent L-(+)-tartaric acid by-products—is first concentrated under reduced pressure at **45 °C** bath temperature until turbidity, then cooled to **−5 °C** with seeding of pure (R)-diamine crystals at **0.05 % (w/w)** to induce primary nucleation. The crystal slurry is filtered using a 0.5 m² agitated Nutsche filter-dryer operated at a pressure differential of **0.2–0.3 bar** across the filter cloth; the wet cake is displacement-washed with pre-chilled **2-propanol** at **−10 °C** in three portions totalling **7.5 m³** per metric ton of wet cake and subsequently dried under vacuum at **35 °C** for **12 hours** with intermittent agitation at **20 rpm** to prevent agglomeration. Chiral purity determined by the validated HPLC method must exceed **99.5 % ee** and chemical purity surpass **99.8 %** before the recrystallised free base is released from quarantine. This reprocessed material is not introduced into the primary pramipexole synthesis chain but instead is supplied as a dedicated starting material for several clinical-stage pipeline compounds—most notably peripherally-restricted D₃ antagonists intended for metabolic syndrome indications—where only the (R)-configuration delivers the desired pharmacokinetic profile of low brain penetration. The process is executed under an ICH Q7-compliant quality management system for active pharmaceutical ingredients, and each shipped drum (UN-approved fibre drums with double polyethylene inner liners) carries a certificate of analysis referencing the specific optical rotation [α]²⁰_D measured at **1.0 %** concentration in methanol as **−58.0° ± 1.5°**, ensuring lot-to-lot batch traceability for the end-user synthetic chemistry team.

N-Sulfonylation into a Chiral Auxiliary for Diastereoselective Alkylation of Enolate Equivalents

A limited but technically rigorous application of the (R)-diamine involves its conversion into a camphor-derived sulfonamide chiral auxiliary; while the majority of auxiliary-based methodologies have migrated toward catalytic approaches, a cluster of patent-protected processes for the manufacture of a specific β₂-adrenoceptor agonist intermediate still employs this stoichiometric approach at the decagram to kilogram scale. The synthetic protocol requires the (R)-N⁶-propyl diamine to be chemoselectively tosylated at the exocyclic primary amine by slow addition of p-toluenesulfonyl chloride (1.05 eq.) in dichloromethane at −15 °C over 3 hours in the presence of 2.5 eq. of pyridine, thereby preserving the endocyclic secondary amine for subsequent acylation. The resultant N-tosyl intermediate is recrystallised to >99.5 % ee and then condensed with phenylacetic acid activated by 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride and 1-hydroxybenzotriazole monohydrate in dimethylformamide at 0–22 °C over 16 hours. The key diastereoselective alkylation is performed by deprotonating this N-acyl sulfonamide with lithium hexamethyldisilazide (1.1 eq.) at −78 °C in tetrahydrofuran under a rigorous nitrogen atmosphere (O₂ < 5 ppm in glovebox-dried solvent) and adding benzyl bromomethyl ether (2.0 eq.) dropwise via a syringe pump at a rate of 0.5 mL/min. The diastereomeric ratio determined by ¹H NMR of the crude reaction mixture typically reaches 98:2 under these conditions, a value that directly influences the downstream enantiomeric excess of the liberated chiral alcohol obtained after reductive cleavage with sodium borohydride in tetrahydrofuran/water at 25 °C. The entire batch production occurs in a 100 L glass-lined reactor equipped with a multi-stage Rushton turbine agitator and a cryogenic jacket capable of maintaining internal temperatures to ±2 °C of setpoint; process analytical technology using ReactIR 45m monitors the disappearance of the isocyanate intermediate band at 2275 cm⁻¹. The terminal product is the (R)-configured phenylethanolamine fragment, isolated as its hydrochloride salt with a chiral purity of 99.8 % ee, which is then elaborated into the final respiratory therapeutic by an approved abbreviated new drug application filing referencing FDA guidance for process validation under 21 CFR 820.75. For this application, the (R)-diamine must be supplied with a certificate of analysis proving water content by Karl Fischer titration below 0.3 % and a residual solvent profile showing single-digit ppm levels of dichloromethane and acetonitrile by headspace GC-FID per USP <467>.

**Table 2.** Specification Profile for (6R)-N⁶-Propyl-4,5,6,7-Tetrahydro-1,3-Benzothiazole-2,6-Diamine Used in Chiral Auxiliary Synthesis
Parameter	Method	Acceptance Criterion
Appearance	Visual inspection against white standard	White to off-white crystalline powder, free of visible extraneous matter
Identification	FTIR (ATR), 4000–400 cm⁻¹	Spectrum concordant with reference spectrum; characteristic bands at 3350, 1650, 1560 cm⁻¹
Chiral Purity	HPLC, Chiralpak AD-H, 250×4.6 mm, hexane/ethanol/diethylamine 80:20:0.1	≥ 99.5 % ee, S-enantiomer ≤ 0.25 %
Chemical Purity	HPLC, C18, gradient method per Table 1	≥ 99.0 area%, total impurities ≤ 1.0 %, largest single unknown impurity ≤ 0.10 %
Water Content	Karl Fischer, coulometric	≤ 0.3 % w/w
Residue on Ignition	Sulfated ash, 800 °C	≤ 0.1 %
Heavy Metals	ICP-MS (Method per USP <233>)	Pb ≤ 1 ppm, Cd ≤ 1 ppm, As ≤ 1 ppm, Hg ≤ 0.1 ppm, Pd ≤ 2 ppm
Assay (anhydrous basis)	Perchloric acid titration, non-aqueous, potentiometric	98.0–102.0 %

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Certification & Compliance

(6R)-N~6~-Propyl-4,5,6,7-Tetrahydro-1,3-Benzothiazole-2,6-Diamine is manufactured under an ISO 9001 quality system and complies with relevant regulatory requirements.
COA, SDS/MSDS, and related certificates are available upon request. For certificate requests or inquiries, contact: sales9@bouling-chem.com.

More Introduction

The compound (6R)-N⁶-propyl-4,5,6,7-tetrahydro-1,3-benzothiazole-2,6-diamine (free base, CAS 104632-27-1; molecular formula C₁₀H₁₇N₃S, molecular weight 211.33 g·mol⁻¹) is supplied as a crystalline, off-white to pale-yellow solid with a characteristic amine odour. The molecule constitutes the R-enantiomer of the 2,6-diamino-4,5,6,7-tetrahydrobenzothiazole N6-propyl intermediate central to the industrial synthesis of pramipexole dihydrochloride monohydrate. In pharmaceutical quality control, this enantiomer is listed as Impurity R in the European Pharmacopoeia monograph for pramipexole dihydrochloride monohydrate (Ph. Eur. 01/2017:2417) and is employed as a chiral reference marker for the validation of chromatographic methods intended to discriminate between the R- and S-forms. Beyond its role as a reference impurity, the diamine scaffold serves as a nucleophilic building block in asymmetric ligand synthesis, exploiting the fixed stereogenic centre at C6 to induce chirality in metal-catalysed transformations.

When Enantiomeric Purity Becomes a Critical Method Validation Parameter

Quantification of the undesired R-enantiomer in pramipexole active pharmaceutical ingredient relies on a chiral high-performance liquid chromatography procedure aligned with Ph. Eur. 2.2.29 (liquid chromatography). The separation is achieved on a polysaccharide-based chiral stationary phase — typically a Chiralcel OJ-RH (150 × 4.6 mm, 5 µm) column thermostatted at 40°C. The mobile phase consists of acetonitrile and 25 mM potassium dihydrogen phosphate buffer adjusted to pH 7.0 (60:40 v/v), delivered isocratically at a flow rate of 0.8 mL·min⁻¹. Detection at 264 nm yields a retention time for the (R)-enantiomer of approximately 9.5 min, while pramipexole (S-enantiomer) elutes at roughly 10.5 min, providing a resolution factor R_s > 3.0 under optimised conditions. The limit of quantification (signal-to-noise ratio ≥ 10) for the (R)-form is established at 0.03% area relative to the main peak, enabling compliance with the acceptance threshold of ≤ 0.3% prescribed by the monograph. System suitability is verified by injecting a resolution solution containing both enantiomers at 5 µg·mL⁻¹ and confirming a tailing factor ≤ 1.5 for the (S)-enantiomer peak. Deviations in column temperature exceeding ±2°C can distort the baseline separation, while traces of water in the injection solvent above 0.5% v/v reduce retention time reproducibility due to alteration of the chiral recognition mechanism on the cellulose tris(4-methylbenzoate) phase. Calibration curves constructed from triplicate injections at five concentration levels (range 0.05–2.0 µg·mL⁻¹) routinely exhibit coefficients of determination r² ≥ 0.999.

Specification and routine quality control parameters for (6R)-N⁶-propyl-4,5,6,7-tetrahydro-1,3-benzothiazole-2,6-diamine (free base, Research Grade).
Parameter	Acceptance Criterion	Analytical Method
Appearance	Off-white to pale-yellow crystalline powder	Visual inspection against Pharmacopoeial colour standards
Identity	IR spectrum concordant with reference; proton NMR spectra match structure	FT-IR (ATR, 4000–400 cm⁻¹), ¹H-NMR (400 MHz, DMSO-d₆)
Chiral purity (enantiomeric excess)	≥ 99.5% (area %)	Chiral HPLC-UV per Ph. Eur. 2.2.29; Chiralcel OJ-RH, 264 nm
Purity (achiral HPLC)	≥ 98.0% (area %)	RP-HPLC, C18 column, acetonitrile/phosphate buffer pH 3.0, 220 nm
Water content	≤ 0.5%	Karl Fischer coulometric titration (Ph. Eur. 2.5.32)
Residue on ignition	≤ 0.1%	Sulphated ash method (Ph. Eur. 2.4.14)
Heavy metals	≤ 20 ppm	Method D of Ph. Eur. 2.4.8

How Does the (R)-Enantiomer’s Pharmacological Activity Compare with Pramipexole at Dopamine Receptors?

Pramipexole [(S)-enantiomer] acts as a full agonist at dopamine D₂ and D₃ receptor subtypes with sub-nanomolar affinity; reported equilibrium dissociation constants (K_i) are 3.9 nM (D₂) and 0.5 nM (D₃) in radioligand displacement assays using ³H-spiperone. The (R)-enantiomer exhibits a dramatically reduced binding profile: K_i values exceed 10,000 nM at both receptor subtypes, confirming that the stereochemistry at C6 is the principal determinant of agonist activity. Consequently, the (R)-propyl-diamine is used as a negative control in cell-based cAMP accumulation assays to verify that signal attenuation observed in D₂/D₃-expressing CHO cells is enantioselective. In toxicological impurity qualification, the compound is evaluated per ICH Q3A guidelines; batch data demonstrating levels below the qualification threshold of 0.15% (or the identification threshold of 0.10% for a 2.0 g/day daily dose) support the absence of a dedicated genotoxicity assessment for the R-impurity. The (R)-diamine is employed as a starting fragment for C₂-symmetric bis(oxazoline) and phosphoramidite ligand families. Condensation with 2,6-difluorobenzoyl chloride in anhydrous dichloromethane under argon, catalysed by 4-dimethylaminopyridine (5 mol%) at 0°C to room temperature over 12 h, yields the corresponding diamide. Subsequent cyclisation with methane sulfonic anhydride and base generates the bis(oxazoline) with retention of the (R)-configuration. Copper(I) complexes of these ligands catalyse asymmetric allylic alkylation reactions with enantioselectivities reaching 94% ee when the ligand is derived from a chiral diamine with ≥ 99% ee. The same diamine also reacts with chlorodiphenylphosphine to afford N-diphenylphosphino derivatives that serve as P,N-ligands in ruthenium-catalysed asymmetric transfer hydrogenation of acetophenone, delivering (S)-1-phenylethanol in 88% ee at a substrate-to-catalyst ratio of 500:1.

Impurity R Profiling Under Forced Degradation and LC–MS/MS Conditions

Stability-indicating methods that resolve (R)- and (S)-enantiomers are mandatory for finished product shelf-life justification. Forced degradation of pramipexole tablets under oxidative stress (3% H₂O₂, 70°C, 4 h) generates up to 1.2% of the (R)-enantiomer via a radical-mediated racemisation pathway that is suppressed by the inclusion of 0.1% w/w sodium metabisulphite as an antioxidant excipient. Simultaneous detection by tandem quadrupole mass spectrometry (MRM transition m/z 212.1 → 126.0 for the propyl-diamine nucleus) allows unambiguous assignment even when co-elution with an unknown degradation product challenges the UV-based method. Collision energy of 28 eV provides optimal fragment ion intensity; the method achieves a detection limit of 0.01 ng on-column.

Comparative properties of (6R)- and (6S)-N⁶-propyl-4,5,6,7-tetrahydro-1,3-benzothiazole-2,6-diamine free bases.
Property	(R)-Enantiomer (this product)	(S)-Enantiomer (Pramipexole base)
Specific optical rotation [α]_D²⁰ (c=1, methanol)	− 67° to − 71°	+ 67° to + 71°
Melting point (DSC onset, 10 K·min⁻¹, N₂)	125–128°C (polymorph I)	126–129°C
Chiral HPLC relative retention to pramipexole	0.90	1.00
Solubility in water (free base, 25°C)	18 mg·mL⁻¹	20 mg·mL⁻¹
Dopamine D₃ K_i	> 10,000 nM	0.5 nM

Handling Anhydrous and Oxygen-Sensitive Diamine Hydrochlorides

The free base exhibits moderate hygroscopicity and undergoes colour darkening upon exposure to atmospheric oxygen over extended periods, forming coloured oxidative coupling products that absorb at 420 nm. Storage under dry argon in sealed, septum-capped amber vials at −20°C preserves a purity of ≥ 98.5% for at least 24 months. When the material is to be used in moisture-sensitive amidations or phosphitylations, residual water is removed by vacuum drying (10 mbar) at 35°C for 12 h immediately before use; Karl Fischer analysis post-drying confirms water content below 0.1%. Combination with strong oxidising agents such as concentrated nitric acid or peroxides is contraindicated due to rapid degradation with gas evolution. The amine groups are reactive toward electrophilic halocarbons — contact with dichloromethane under prolonged reflux in the presence of base leads to quaternary ammonium salt formation that complicates product isolation; therefore, tetrahydrofuran or toluene is preferred for alkylation reactions. In a multi-kilogram production setting, vacuum tray drying at 40°C with a nitrogen bleed of 0.5 L·min⁻¹ avoids the formation of a static charge that otherwise causes powder adherence to polypropylene container walls, a phenomenon documented during batch campaigns exceeding 5 kg. Sieving through a 60-mesh (250 µm) screen eliminates agglomerates that form after storage at −20°C and improves flowability for automated solid dispensing systems operating under positive nitrogen pressure. The optical rotation should be verified after any thermal processing step; exposure to temperatures above 80°C for more than 6 h in the absence of an acid scavenger can induce partial racemisation (≤ 2% decrease in enantiomeric excess), attributed to reversible imine formation via amine oxidation. Therefore, isolation of the free base from its hydrochloride salt by aqueous alkaline extraction and subsequent drying must be conducted at ≤ 25°C under reduced pressure.