(R)-Tert-Butyl3-(2-Nitrophenylsulfonyloxy)Pyrrolidine-1-Carboxylate
Pyrrolidine Pyrrole Thiazole Imidazole Thiophene Pyrazine Piperidine Piperazine Morpholine Phenazine

(R)-Tert-Butyl3-(2-Nitrophenylsulfonyloxy)Pyrrolidine-1-Carboxylate


    • Product Name (R)-Tert-Butyl3-(2-Nitrophenylsulfonyloxy)Pyrrolidine-1-Carboxylate
    • Alias (R)-tBu-3-(2-NsO)pyrrolidine-1-carboxylate
    • 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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    Specifications

    HS Code

    281947
    Chemical Formula C17H24N2O8S
    Molar Mass 416.45 g/mol
    Appearance Solid (usually)
    Physical State At Room Temp Solid
    Solubility In Organic Solvents Soluble in common organic solvents like dichloromethane, chloroform
    Solubility In Water Poorly soluble
    Chirality Chiral due to (R)-configuration
    Functional Groups Tert - butyl ester, pyrrolidine ring, nitro - phenylsulfonyloxy group, carboxylate group

    As an accredited (R)-Tert-Butyl3-(2-Nitrophenylsulfonyloxy)Pyrrolidine-1-Carboxylate factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.

    Packing & Storage
    Packing 100g of (R)-Tert - Butyl 3-(2 - Nitrophenylsulfonyloxy)Pyrrolidine - 1 - Carboxylate in sealed chemical - grade packaging.
    Shipping The chemical (R)-Tert - Butyl 3-(2 - Nitrophenylsulfonyloxy)Pyrrolidine - 1 - Carboxylate is shipped in secure, appropriately labeled containers. Special handling for chemicals is ensured, following all safety regulations to prevent damage and environmental exposure.
    Storage (R)-Tert-Butyl 3-(2-Nitrophenylsulfonyloxy)Pyrrolidine-1-Carboxylate should be stored in a cool, dry place, away from heat sources and direct sunlight. Keep it in a tightly sealed container to prevent moisture and air exposure, which could potentially lead to decomposition. Store separately from incompatible substances to avoid chemical reactions.
    Application of (R)-Tert-Butyl3-(2-Nitrophenylsulfonyloxy)Pyrrolidine-1-Carboxylate

    Manufacture of (R)-3-Aminopyrrolidine Dihydrochloride via Gabriel-like Amination

    In the supply chain for chiral vicinal diamines, (R)-tert-butyl 3-((2-nitrophenylsulfonyl)oxy)pyrrolidine-1-carboxylate functions as the enantiopure C-3 electrophile required to generate the unsubstituted primary amine through an indirect amination sequence. The nosyl group is selected over tosylate or mesylate for its superior leaving-group ability under mild, non-racemising conditions; this is critical because the free amine product racemises via an aziridinium intermediate if the reaction temperature exceeds 35°C or if the pH rises above 10.5 during workup. In a validated commercial process, the starting nosylate (1.0 eq, typical loading 1.05–1.15 eq relative to potassium phthalimide) is treated with phthalimide potassium salt in anhydrous N,N-dimethylformamide at 0–5°C over 16–20 h, yielding the (R)-3-phthalimido intermediate with retention of configuration (>99.5% ee). After aqueous quench and crystallisation from toluene/n-heptane, the Boc and phthaloyl groups are cleaved in a single-vessel sequence: first with 6 M hydrochloric acid in isopropanol at 40°C for Boc removal, then with hydrazine monohydrate (1.2 eq) at reflux for phthaloyl deprotection. The resulting (R)-3-aminopyrrolidine dihydrochloride is isolated by antisolvent crystallisation from ethanol/methyl tert-butyl ether, achieving chemical purity >99.0 area% by HPLC (C18, 210 nm) and enantiomeric excess >99.8% (Chiralpak AD-H, hexane/ethanol/diethylamine 80:20:0.1). The manufacturing suite operates under ICH Q7 Chapter 8 (Production and In-Process Controls) and ICH Q11 Section 5.2 (Starting Material Lifecycle Management); each batch is released against a specification that includes residual phthalimide (≤0.10% w/w), hydrazine (≤1 ppm), and 2-nitrophenylsulfonic acid (≤0.15% w/w) as critical impurities. The dihydrochloride salt is the direct building block for at least three disclosed DPP-4 inhibitor backbones and for multiple Phase II CNS-targeting scaffolds, where it serves as the P2′ pyrrolidine moiety in receptor antagonist pharmacophores.

    How does the nosylate facilitate synthesis of N-aryl-3-aminopyrrolidines for kinase inhibitor programmes?

    Within medicinal chemistry campaigns targeting the ATP-binding cleft of Janus kinase and Bruton’s tyrosine kinase, the installation of a conformationally constrained (R)-3-aminopyrrolidine substituent onto a heteroaromatic core is a late-stage diversification step that demands a bench-stable, crystalline electrophile. The nosylate intermediate meets this need by allowing direct SNAr-type coupling with electron-deficient aryl halides or direct nucleophilic aromatic substitution with fluoro-heteroarenes, bypassing the sensitive free amine until the final deprotection. A representative small-scale protocol (adapted from 50 L glass-lined reactor campaigns) charges the nosylate (1.0 eq, 0.8–1.2 mol scale) and the aryl fluoride (1.05 eq) in dimethyl sulfoxide with anhydrous potassium carbonate (2.5 eq) as the acid scavenger; the slurry is stirred at 60°C for 8–12 h, with reaction progress tracked by inline ReactIR monitoring of the nosylate S=O asymmetric stretch at 1370 cm⁻¹. Upon disappearance of the starting material, the mixture is diluted with water and the Boc-protected N-arylpyrrolidine is extracted into isopropyl acetate, washed with 5% w/w aqueous lithium chloride to remove residual DMSO, and crystallised. The Boc group is subsequently removed with trifluoroacetic acid (20% v/v in dichloromethane, 0°C to rt, 2 h) or with hydrogen chloride in 1,4-dioxane (4 M, 2.5 eq), furnishing the free amine or hydrochloride salt. Compliance with ICH M7(R2) for mutagenic impurities is addressed by a dedicated purge factor calculation for the 2-nitrophenylsulfonic acid by-product, which is removed to <5 ppm by a sequence of basic aqueous washes verified by LC-MS/MS with a limit of quantitation of 0.5 ppm. The terminal products from this route are typically advanced intermediates en route to selective BTK inhibitors (e.g., candidates containing a piperidine-carboxamide linker with a pendant (R)-3-(4-phenoxyphenyl)aminopyrrolidine fragment) and to dual JAK1/TYK2 inhibitors where the pyrrolidine nitrogen is functionalised with an acrylamide warhead for covalent targeting. Published data for the rotamer population of the Boc intermediate in solution (J3a,3b coupling constants of 4.8 Hz and 7.2 Hz in DMSO-d6 at 25°C) confirm a predominantly 4T3 envelope conformation that pre-organises the nucleophilic amine trajectory for the subsequent coupling step.

    The nosylate loading can be adjusted to 1.20 eq when the aryl halide substrate contains free hydroxyl or amide protons, compensating for competitive O-sulfonylation, though this introduces a parallel optimisation of the workup to remove O-nosyl impurities that co-crystallise in the 15–25°C range. A continuous-flow variant employing a PFA coil reactor (ID 1.0 mm, residence time 45 min) has been reported for the coupling of the nosylate with 2,4-dichlorothieno[3,2-d]pyrimidine, achieving 92% conversion at 80°C and 5 bar back-pressure without DMSO, substituting acetonitrile/tert-butanol (4:1 v/v) to minimise nosylate hydrolysis. In such a telescoped process, the downstream hydrogenation of the aryl chloride is performed in the same solvent train, and the Boc group is retained until after salt formation to avoid gumming of the free amine on the catalyst surface. The entire sequence from nosylate to GMP-ready intermediate falls under a controlled change management system aligned with ICH Q10, with critical quality attributes including enantiomeric excess (target >99.0%), residual palladium (<10 ppm by ICP-MS following the dechlorination step), and any diastereomeric impurity arising from base-promoted epimerisation at the C-2 position of the pyrrolidine ring, which is monitored by a validated chiral SFC method (Chiralpak IG-3, CO2/methanol 70:30).

    A cross-contamination risk that emerges in multi-purpose plants is the carryover of the nitrophenylsulfonate moiety into subsequent hydrogenation vessels, where it can generate trace aromatic amines that violate the 1.5 µg/day threshold of toxicological concern (TTC) per ICH M7. Dedicated glass-lined equipment or a verified cleaning protocol with 0.1 M sodium hydroxide at 70°C followed by a pyridine/water (5:95 v/v) rinse and swab sampling with an acceptance criterion of <0.1 µg/cm² for 2-nitrobenzenesulfonic acid is therefore mandatory. The synthetic route converges on kinase inhibitor backbones that have entered clinical supply chains, including third-generation reversible BTK inhibitors designed to overcome the C481S resistance mutation, and TYK2 pseudokinase domain binders that exploit the pyrrolidine’s rigidity to reduce off-target hERG activity.

    What governs the stoichiometry of thioacetate displacement en route to (R)-3-mercaptopyrrolidine?

    The nucleophilic displacement of the 2-nitrophenylsulfonate leaving group by potassium thioacetate represents the benchmark entry into optically active 3-mercaptopyrrolidine, a fragment that appears in metallo-β-lactamase inhibitors and certain antiviral prodrugs. Unlike the amination chemistry, the thioacetate reaction is acutely sensitive to oxygen and trace metals, which catalyse oxidative dimerisation of the incipient thiol to the disulfide even at −20°C. In a kilo-lab campaign, the nosylate (1.0 eq, typically 12.0 kg) is dissolved in degassed acetone (8 L/kg) and potassium thioacetate (1.15 eq, 92% assay) is added portionwise under a nitrogen atmosphere while the internal temperature is maintained at −5 to 0°C using a Huber Unistat 905 circulating chiller. The slurry turns from pale yellow to deep orange within 30 min; reaction completion is confirmed by TLC (ethyl acetate/heptane 1:1, Rf product = 0.45) with visualisation under 254 nm UV and ceric ammonium molybdate stain. The precipitated potassium 2-nitrophenylsulfonate is removed by filtration over a pressure Nutsche filter with a 10 µm PTFE cloth, and the filtrate is concentrated under reduced pressure (<30°C bath) to a minimum-stirrable volume. The crude (R)-tert-butyl 3-(acetylthio)pyrrolidine-1-carboxylate is redissolved in degassed methanol and treated with sodium methoxide (1.05 eq, 25% w/w in methanol) at 10°C to cleave the thioester, producing the free thiol which must be immediately protonated or protected. In the synthesis of a bicyclic β-lactamase inhibitor (structurally related to the diazabicyclooctane scaffold, CAS registry 1192500-31-4 provides a comparative core), the thiol is trapped in situ with 1,3-dibromo-5,5-dimethylhydantoin to form a sulfenyl bromide that is then captured by a tetrahydro-pyridazine carboxylate to forge an N-sulfenyl bond—the pivotal step for generating the acylsulfonamide warhead that coordinates the active-site zinc ions. Equipment surfaces in contact with the thiol must be Hastelloy C-276 or glass-lined; stainless steel promotes disulfide formation even after electropolishing, and the disulfide dimer, once formed, co-elutes with the product on silica gel chromatography (Biotage Isolera, KP-Sil 50 µm cartridge, gradient 0–30% ethyl acetate in heptane) and requires a separate preparative chiral SFC purification step that reduces throughput by approximately 35%.

    Quality control for the thioacetate intermediate includes a specific test for elemental sulfur (limit <0.05% w/w) because polysulfide adducts have been detected as by-products when the acetone solvent is not freshly distilled from potassium permanganate. The relevant pharmacopoeial context is Ph. Eur. monograph 2034 (Substances for Pharmaceutical Use) and the general notice on residual solvents (ICH Q3C), which drives the final crystallisation from ethanol/water to bring acetone below 5000 ppm. When the target API is an MBL inhibitor co-administered with a carbapenem, the thiol intermediate must also meet a bacterial endotoxin limit of <0.15 EU/mg per USP <85>, which is achieved by terminal rinse of the filter cake with Water for Injection and by performing the final salt formation in a Grade D cleanroom. The terminal product, (R)-3-mercaptopyrrolidine or its stable disulfide dimer used as a crystalline storage form, is typically supplied with a certificate of analysis that includes enantiomeric excess (GC on an Rt-βDEXsa column, 30 m × 0.25 mm, 0.25 µm film), heavy metals (<10 ppm) by USP <231> Method II, and residual solvents. Application of this thiol in prodrugs of acyclic nucleoside phosphonates—where the pyrrolidine replaces the conventional phosphonate alkyl ester to enhance oral bioavailability—has been documented in patent literature, though published pharmacokinetic data for this specific configuration in large-animal models remains limited.

    Synthesis of (R)-3-(2,2,2-Trifluoroethoxy)pyrrolidine as a conformationally biased amine for metabolic stability enhancement

    Incorporation of a trifluoroethoxy substituent at the C-3 position of pyrrolidine reduces the pKa of the adjacent amine by approximately 1.2–1.8 log units, a modification exploited in CNS-penetrant programmes to lower the basicity—and consequently the P-glycoprotein-mediated efflux ratio—while retaining target engagement at aspartyl protease or monoamine transporter active sites. The (R)-nosylate intermediate reacts smoothly with 2,2,2-trifluoroethanol under Mitsunobu-free conditions, avoiding the generation of triphenylphosphine oxide that complicates chromatographic purification on scale. A manufacturing procedure validated at 15 kg input of nosylate uses sodium hydride (1.3 eq, 60% dispersion in mineral oil) to deprotonate trifluoroethanol (1.5 eq) in tetrahydrofuran at −10°C, followed by slow addition of the nosylate in THF (5 volumes) while maintaining the jacket temperature at −15°C. The reaction is complete within 2 h, yielding the (R)-Boc-3-(trifluoroethoxy)pyrrolidine with ≥95% conversion. The aqueous workup must quench unreacted hydride with 10% w/w ammonium chloride solution rather than water, because the local exotherm from water addition has been observed to raise the internal temperature above 25°C, triggering partial Boc cleavage (loss 2–5%) and formation of a pyrrolidine N-oxide impurity detected by LCMS [M+H]+ at m/z 212.1. The crude product is purified by fractional distillation under vacuum (82–85°C at 8 mbar) on a wiped-film evaporator (VTA VKL 70, jacket 100°C, rotor speed 300 rpm, feed rate 1.5 L/h), yielding a colourless oil with chemical purity >99.5% and a single impurity above 0.10%: the corresponding C-2 epimer (<0.15%). This epimer is controlled by the enantiopurity of the starting nosylate and by the absence of lithium or magnesium counterions that catalyse the epimerisation via an SN1-like dissociation/recombination path.

    The downstream processing of the Boc-ether into the free amine or hydrochloride salt follows a two-step protocol: deprotection with hydrogen chloride in cyclopentyl methyl ether (3.0 eq, 4 M, 20°C, 3 h), followed by solvent exchange into isopropyl acetate and crystallisation as the hydrochloride monohydrate. The final API intermediate, (R)-3-(2,2,2-trifluoroethoxy)pyrrolidine hydrochloride, is employed as the eastern half of a dual orexin receptor antagonist (structurally disclosed in a compound exemplified as “1-(5-chloro-benzoxazole-2-carbonyl)-3-(2,2,2-trifluoroethoxy)pyrrolidine”), where the trifluoroethoxy group occupies a small lipophilic cleft defined by Phe3.33 and Tyr6.48 of the OX2 receptor. The entire synthetic route is designed to comply with REACH Annex VIII exposure scenario requirements for trifluoroethanol (DNEL for workers 2.5 mg/m³), necessitating a closed-loop distillation and vapour recovery system with a 99.5% abatement efficiency. Residual trifluoroethanol in the final substance is limited to <50 ppm as determined by headspace GC on a DB-WAX column (30 m × 0.53 mm, 1.0 µm film) with a flame ionisation detector. The batch record includes a parametric release criterion for water content (<0.5% by Karl Fischer) because the hydrochloride is moderately hygroscopic and will partially convert to the catalytically inactive hydrate dimer if stored above 60% relative humidity in non-desiccated packaging.

    A critical quality attribute for this intermediate is the absence of the ring-opened 4-amino-4,4,4-trifluorobutan-1-ol, a toxicologically alerting structure that can arise from pyrrolidine ring opening under strongly acidic deprotection conditions. The stress study data indicate that ring opening requires prolonged exposure to methanesulfonic acid at >50°C; by using hydrogen chloride in ethereal solvents and maintaining the temperature strictly below 25°C during Boc removal, the ring-opened impurity remains undetectable (<0.05%) by a dedicated GC method with electron capture detection. These process controls are reviewed during the customer’s vendor qualification audit under EudraLex Volume 4, Part II, and a drug master file (Type II) is maintained with current annual stability data for the hydrochloride when stored at 25°C/60% RH over 36 months.

    Critical Process Parameter ranges for nosylate displacement reactions (selected nucleophile classes)
    NucleophileSolvent systemTemperature range / °CTypical yield / %Enantiomeric excess / %Reference standard for ee determination
    Potassium phthalimideDMF0–588–93≥99.8USP 〈621〉 (HPLC, AD-H)
    2,4-DifluoroanilineDMSO/K2CO355–6578–85≥99.5Ph. Eur. 2.2.29 (chiral SFC)
    Potassium thioacetateAcetone (deaerated)−5–082–87≥99.6In-house GC (Rt-βDEXsa)
    Sodium 2,2,2-trifluoroethoxideTHF−15–−1090–94≥99.9USP 〈621〉 (chiral GC, β-DEX 120)
    Potassium cyanide/18-crown-6Acetonitrile20–2572–76*≥99.0Ph. Eur. 2.2.31 (polarimetric)

    *Yield reflects the nitrile; subsequent hydrogenation to the aminomethyl derivative proceeds in 92–95% yield over Raney nickel.

    When the C–C bond is forged: cross-coupling of the nosylate with organometallic reagents

    Direct construction of a C(sp3)–C(sp2) or C(sp3)–C(sp3) bond at the pyrrolidine C-3 centre via the nosylate leverages cross-coupling conditions originally developed for alkyl tosylates, but with the advantage that the 2-nitrophenylsulfonate participates in oxidative addition to nickel(0) complexes at significantly lower temperatures (10–30°C compared to 60–80°C required for the corresponding tosylate). This reactivity window permits the use of functionalised arylzinc or alkylzinc reagents without competing β-hydride elimination of the pyrrolidine electrophile. In one validated sequence, (R)-Boc-3-nosylpyrrolidine (1.0 eq) is combined with 4-cyanophenylzinc bromide (1.5 eq, 0.5 M in THF) and a catalytic system consisting of NiCl2·glyme (5 mol%) and 4,4′-di-tert-butyl-2,2′-bipyridine (5.5 mol%) in a mixture of THF and 1,3-dimethyl-2-imidazolidinone (7:3 v/v) at 22°C under argon. The reaction mixture, initially a pale brown suspension, turns dark green within 5 min; after 18 h, IPC by LCMS reveals >95% conversion to the cross-coupled product, with the homodimer of the nosylate (<2%) and the reduced pyrrolidine (<1%) as the only observed impurities. The workup involves filtration through a pad of Celite 545, extraction with methyl tert-butyl ether, and removal of the nitrophenylsulfonic acid by washing with 1 M sodium hydroxide containing 5% w/w sodium chloride to prevent emulsification. The product, (R)-tert-butyl 3-(4-cyanophenyl)pyrrolidine-1-carboxylate, is crystallised from isopropanol/water to yield material with 99.2% purity and 99.4% ee. This biaryl intermediate has been used as a common platform for synthesising γ-secretase modulators where the 4-cyanophenyl group undergoes subsequent hydrolysis to a carboxylic acid and amidation with a peripheral heterocycle.

    Process safety considerations dictate that the zinc reagent be titrated immediately before use (iodometric titration with I2 in THF) because partial oxidation of the zincate during storage generates a less reactive aggregate that requires thermal activation, pushing the reaction into a temperature regime where the pyrrolidine ring itself begins to undergo Ni-catalysed ring-opening—a literature-known decomposition that forms N-vinylglycinamide derivatives. The cross-coupling is executed in a 50 L Hastelloy C-22 reactor with an integrated FTIR probe (Mettler Toledo ReactIR 45 m) monitoring the disappearance of the nosylate S=O asymmetric stretch; the batch automatically diverts to the quench vessel if the product of the ≈ 1370 cm⁻¹ peak area falls to <5% of the initial value for 2 consecutive minutes. The regulatory filing (a US DMF Type II) cross-references ICH Q3D for elemental impurities, with a specific risk assessment for nickel (Class 2B, permitted daily exposure 5.0 μg/day). The isolated product consistently contains Ni at <1 ppm after treatment with activated charcoal (Norit SX Plus, 10% w/w relative to substrate, stirred at 40°C for 1 h) and filtration through a 0.2 μm capsule filter. The (R)-3-(4-cyanophenyl)pyrrolidine fragment is a registrable starting material under ICH Q11, and the process has been validated at a contract manufacturing organisation with a defined Design Space that limits the water content of the solvent mixture to <200 ppm to avoid catalyst deactivation, verified by in-line Karl Fischer analysis before charging the nickel pre-catalyst.

    The catalytic cycle operates optimally in the absence of coordinating ethereal cosolvents. When the reaction was attempted in pure THF or 2-methyltetrahydrofuran, the starting nosylate was consumed but the product distribution shifted to 40–55% of the desired cross-coupled material and 35–45% of the reduced pyrrolidine arising from a β-hydride elimination/reductive elimination sequence. The optimal DMI co-solvent ratio was determined through a definitive screening design (DSD) with 16 runs evaluating THF/DMI volume fraction, temperature, and catalyst loading, with the objective to simultaneously maximise yield and minimise dimer. That dataset is incorporated into the process validation master plan and reviewed during periodic product quality reviews as required by 21 CFR 211.180(e).
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    Certification & Compliance
    More Introduction

    Pharmaceutical intermediates derived from enantiopure pyrrolidines frequently require an activated hydroxyl leaving group configured for stereospecific inversion. The title compound supplies a secondary nosylate ester in the (R)-configuration with the amine protected as a tert-butyl carbamate. Registration falls under CAS number 1253792-97-0, and the molecular formula is C15H20N2O7S (molecular weight 372.39 g·mol⁻¹). Differentiation from the corresponding tosylate, mesylate, or brosylate derivatives originates in the 2-nitrophenylsulfonyl group, which combines strong electron withdrawal with a chromophoric handle, enabling in-process UV monitoring during solution-phase synthesis without requiring additional derivatization.

    Where does this nosylate fit among activated pyrrolidine intermediates?

    Within the portfolio of activated 3-hydroxypyrrolidine-1-carboxylate building blocks, the (R)-N-Boc-3-(2-nitrophenylsulfonyloxy)pyrrolidine occupies a precise niche for nucleophilic displacement with inversion at a chiral secondary centre. The nosylate leaving group possesses a Hammett σp value of 0.81 for the nitro substituent, enhancing the sulfonate’s electrophilicity relative to tosylate (σp 0.48) by accelerating the transition state in SN2 pathways. Laboratory conversion studies with sodium azide in DMF at 60 °C demonstrate completion in under 4 hours compared to 8–12 hours for the tosylate analogue under identical molarity and stirring conditions. The dibasic 2-nitrobenzenesulfinate byproduct precipitates from aqueous workup, simplifying purification. This compound is supplied as a white to off-white crystalline powder, with melting point decomp. reported in the range 128–132 °C (uncorrected, heating rate 2 °C/min).

    Typical release specifications
    ParameterMethodAcceptance criterion
    Chemical purityHPLC-UV (254 nm, area %)≥ 98.0%
    Enantiomeric excessChiral HPLC (Chiralpak AD-H, hexane/2-propanol 90:10)≥ 99.0% ee
    Chiral configurationOptical rotation (c = 1.0, CHCl₃, 589 nm)[α]D20 = +24.0° to +28.0°
    Residual solventGC headspace (Ph. Eur. 2.4.24)≤ 5000 ppm ethyl acetate, ≤ 600 ppm ethanol
    Water contentKarl Fischer (coulometric)≤ 0.50% w/w
    Heavy metalsICP-MS (USP <233>)Pb ≤ 10 ppm, Cd ≤ 2 ppm, As ≤ 2 ppm, Hg ≤ 1 ppm

    Moisture sensitivity and thermal lability in downstream processing

    Prolonged handling in uncontrolled humidity environments leads to incremental hydrolysis of the nosylate ester. When exposed to 60% RH at 25 °C over 48 h, purity loss of 1.2–1.8% area has been recorded by HPLC, with the (3R)-hydroxy impurity emerging as the principal degradant. Therefore, storage under argon in sealed fluoropolymer-lined containers at −20 ± 5 °C is mandated after first use. Thermal ramp DSC analysis shows an exothermic decomposition onset at 152 °C (scan rate 10 °C/min, sealed Au pan), constraining forced solubility dissolution to ambient temperatures or brief gentle warming to ≤40 °C. Solubility at 20 °C exceeds 50 mg·mL⁻¹ in dichloromethane, THF, and DMF; in methanol, solubility drops to approximately 8 mg·mL⁻¹, and in water the compound is practically insoluble.

    When this intermediate is employed in a C–N bond-forming displacement using piperazine derivatives in acetonitrile at reflux, the reaction profile exhibits an induction period of 15–20 minutes attributable to initial heterogeneous mixing of the crystalline solid. Once fully dissolved, pseudo-first-order kinetics with respect to the electrophile are observed. Adding 1.05 equivalents of nucleophile and 1.2 equivalents of triethylamine at 0.25 M substrate concentration provides 93–96% isolated yield after silica gel chromatography (eluent: hexane/ethyl acetate (4:1)). The trace (S)-enantiomer formed due to competitive elimination–addition is typically ≤ 0.7% as quantified by chiral HPLC.

    Distinguishing the nosylate from mesylate and tosylate in contract manufacturing campaigns

    Three sulfonate leaving groups dominate orders for activated pyrrolidinol intermediates, yet process chemists select among them based on crystalline form robustness, atom economy, and workup tractability. The nosylate delivers a UV-active byproduct (2-nitrobenzenesulfinate, λmax 262 nm) that can be tracked in real time through an in-line flow cell, a capability absent with mesylate and tosylate. Mechanistically, the nitro group enhances electron depletion at the sulfur centre, lowering the activation energy for the displacement. In a comparative microcalorimetry series (1M NaI in acetone, 30 °C), the Arrhenius activation energy (Ea) was measured at 58.2 kJ·mol⁻¹ for the nosylate, 65.1 kJ·mol⁻¹ for the tosylate, and 71.8 kJ·mol⁻¹ for the mesylate. The enhanced reactivity translates to reduced cycle time in campaign-changeover periods, cutting typical overnight holds by 2–3 hours.

    In production-scale batches exceeding 5 kg, the nosylate’s higher molecular weight versus the mesylate represents a countervailing cost in atom economy. Mass balance calculations in a kilo-lab reactor show that a 5.0 kg batch of the nosylate furnishes 3.2 kg of substituted product compared to 3.9 kg from a mesylate route, assuming identical yields. The gap must be weighed against purification advantages: the 2-nitrobenzenesulfinate can be precipitated as the sodium salt by addition of cold aqueous sodium bicarbonate and removed by filtration, eliminating the need for a full aqueous workup in certain telescoped sequences. This filtration step has been validated in a 50 L Hastelloy reactor equipped with a sintered glass filter base, where residual sulfinate levels in the organic stream were reduced to 0.15% w/v, as determined by qNMR with 1,3,5-trimethoxybenzene internal standard.

    From a regulatory perspective, the nosylate intermediate must be controlled for potentially genotoxic impurities. The 2-nitrophenyl moiety raises structural alerts for nitroaromatic mutagenicity. Ames testing data on the downstream API incorporating a fragment once linked to this intermediate must demonstrate no positive response per ICH M7(R1) guidelines. Thus, residual nosylate in isolated intermediate is controlled to a limit of 10 ppm, and a dedicated LC-MS/MS method (LOQ 1.5 ppm) is provided for batch clearance. By comparison, the mesylate and tosylate analogues present lower mutagenicity flags but require separate alkylating impurity management.

    Comparability of enantiomeric integrity under nucleophilic displacement

    When (R)-configured nosylate undergoes SN2 displacement with azide or phthalimide in DMF, configurational inversion yields the (S)-amine after reduction or deprotection. Chiral HPLC tracking of the (R)-Boc-3-aminopyrrolidine derivative shows enantiomeric excess exceeding 99.2% provided that the reaction temperature remains below 65 °C and free base concentration of the nucleophile is kept ≤ 1.2 eq. Loss of ee escalates when DMF is heated above 80 °C for prolonged periods; under such conditions, the nosylate generates an elimination product, 3,4-dehydropyrrolidine-1-carboxylate, which can undergo re-addition and scramble stereochemistry. Monitoring by 1H NMR (CDCl3, 400 MHz) confirms the emergence of vinylic protons at δ 5.85–5.95 ppm as an early warning of this degradation pathway.

    In campaigns aiming for active pharmaceutical ingredients requiring 99.8% ee of the chiral amine fragment, a recrystallization step of the intermediate or its immediate derivative is often embedded. The nosylate itself crystallizes in the orthorhombic space group P212121, with a unit cell volume of 1842 ų (determined by single-crystal X-ray diffraction at 100 K), facilitating enantiomeric enrichment to > 99.9% ee through slurry washing in n-heptane/ethyl acetate (95:5). This is significantly more effective than the tosylate, which tends to form a conglomerate with partial solid-solution behaviour, limiting purification efficiency.

    A dedicated protocol for recycle of the undesired enantiomer or racemization is not standard; however, the liberated 2-nitrobenzenesulfinate can be re-oxidized with H2O2 in acetic acid and converted back to the sulfonyl chloride for reuse of the nosylating reagent, closing the auxiliary loop in multi-tonne manufacturing scenarios. Experience from a 100 L glass-lined reactor campaign indicates that nosyl chloride recovery exceeded 82% over three cycles without detectable cross-contamination.

    When should the nosylate be preferred over the corresponding bromide or iodide?

    Direct displacement with bromide or iodide via the corresponding alkyl halide suffers from competing β-elimination when the pyrrolidine ring is activated. The nosylate maintains a better balance: the sulfonate leaving group is sufficiently labile for displacement yet sufficiently bulky to disfavour Hofmann-type elimination relative to the bromide. ReactIR studies (ReactIR 15, DiComp probe) following the nosylate in DMF with sodium thiomethoxide show complete consumption at 50 °C within 90 min, with the elimination product remaining below 2% by quantitative 13C NMR. Under identical stoichiometry, the corresponding bromide (generated in situ from the alcohol via Appel conditions) yielded up to 18% elimination byproduct at full conversion.

    The compound is also supplied with documentation meeting USP-NF <1092> for residual solvent classification and ICH Q3D for elemental impurities. Pack sizes range from 1 g to 250 g in amber borosilicate vials with PTFE-lined caps, and bulk orders up to 1 kg are aliquoted under ISO 7 (Class 10,000) conditions into double-bagged, desiccant-lined aluminium laminate pouches. Each lot is accompanied by a certificate of analysis reporting the exact values for the parameters tabulated above, traceable to NIST reference materials where applicable.

    In telescoped multi-step sequences where the carbamate is temporarily cleaved with TFA and reprotected, the nosylate ester remains intact provided that the pH is maintained above 3.5 during aqueous workup. Below this threshold, the free hydroxylamine intermediate undergoes acid-catalysed sulfonate hydrolysis. A buffer system of 0.5 M sodium citrate (pH 4.0) is recommended for quench.

    Comparative performance of leaving groups in activated pyrrolidine 1
    Leaving groupRelative SN2 rate (NaI, acetone, 30 °C)UV-active byproductElimination threshold temp. (°C, DMF, 0.1 M)Ames alert category (ICH M7)
    Nosylate (2-NO₂PhSO₃⁻)1.00 (reference)Yes (λmax 262 nm)65Class 3 (alerting structure, limit per TTC)
    Tosylate (4-MePhSO₃⁻)0.62No75Class 5 (no structural alert)
    Mesylate (MeSO₃⁻)0.45No80Class 5
    Brosylate (4-BrPhSO₃⁻)0.85Marginally (λmax 225 nm)68Class 4 (alerts related to halogen)

    Monograph consistency is maintained across supply chains via orthogonal identity testing: FT-IR (ATR) must match the reference spectrum with peak correlation ≥ 0.98 within the region 1800–450 cm⁻¹; 1H NMR (CDCl₃, 600 MHz) must exhibit the diagnostic pyrrolidine ring proton multiplets at δ 3.45–3.65 ppm (m, 4H) and carbon α to carbamate at δ 155.2 ppm in 13C NMR. Certified reference material of the (R)-enantiomer and racemic mixture are available for method validation.

    For R&D labs scaling to pilot plant, pre-weighed dry pack kits in anhydrous DMF under nitrogen are offered in septum-capped vials, mitigating the operator exposure and moisture ingress during transfer. This packaging configuration reduced batch rejection due to hydrolysis in one tech-transfer campaign from 4.7% to 0.3% over 12 months.

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