2S,3S,4R) 3-Ethyl-4-Hydroxypyrrolidine-2-Carboxylic Acid Methyl Ester P-Toluenesulfonate
|
HS Code |
996570 |
| Chemical Formula | C15H23NO6S |
| Molecular Weight | 345.41 g/mol |
| Appearance | Solid (usually) |
| Melting Point | Varies, needs experimental determination |
| Solubility In Water | Low solubility, organic solvents are more favorable |
| Solubility In Organic Solvents | Soluble in common organic solvents like dichloromethane, ethyl acetate |
| Chirality | Chiral molecule with multiple chiral centers |
| Pka | For the carboxylic acid group (if relevant), around 4 - 5 approximately |
As an accredited 2S,3S,4R) 3-Ethyl-4-Hydroxypyrrolidine-2-Carboxylic Acid Methyl Ester P-Toluenesulfonate factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | 10 - gram vial of (2S,3S,4R)-3 - Ethyl - 4 - Hydroxypyrrolidine - 2 - Carboxylic Acid Methyl Ester P - Toluenesulfonate. |
| Shipping | The chemical (2S,3S,4R)-3 -Ethyl-4 -Hydroxypyrrolidine-2 -Carboxylic Acid Methyl Ester P -Toluenesulfonate will be shipped in accordance with strict chemical handling protocols. Packaging ensures stability, and it will be transported via approved carriers suitable for such substances. |
| Storage | Store (2S,3S,4R)-3 - Ethyl - 4 - Hydroxypyrrolidine - 2 - Carboxylic Acid Methyl Ester P - Toluenesulfonate in a cool, dry place away from heat sources and direct sunlight. Keep it in a tightly sealed container to prevent moisture absorption and exposure to air, which could potentially lead to degradation. Avoid storing near incompatible substances. |
In the synthesis of chiral secondary amine organocatalysts of the Hayashi–Jørgensen type, the crystalline p‑toluenesulfonate salt of (2S,3S,4R)-3‑ethyl‑4‑hydroxypyrrolidine‑2‑carboxylic acid methyl ester is first partitioned between dichloromethane and 10% aqueous sodium carbonate to liberate the free base, which is dried and concentrated at ≤35°C. The resulting oil is dissolved in anhydrous tetrahydrofuran and cooled to −20°C; a Grignard reagent, typically 4‑chlorophenylmagnesium bromide in THF, is added at a molar ratio of 2.2:1.0 relative to the pyrrolidine ester to ensure complete nucleophilic addition while suppressing reductive side reactions. After quenching with saturated ammonium chloride and extraction, the crude diaryl carbinol intermediate is purified by silica‑gel plug and silylated with chlorotrimethylsilane (1.5 equiv) in the presence of imidazole (2.0 equiv) in dimethylformamide at 0–5°C, delivering the O‑TMS‑protected organocatalyst in 72–78% overall yield with an enantiomeric ratio exceeding 99:1 as determined by chiral SFC on a Daicel CHIRALPAK AD‑H column with CO₂/methanol 90:10. The entire campaign is governed by ICH Q11 starting‑material requirements, and the supplier provides a full purging assessment per ICH M7 for potential genotoxic impurities, confirming residual palladium ≤10 µg/g and zinc ≤25 µg/g. The final organocatalyst is applied in enantioselective α‑amination and Michael addition steps that yield advanced intermediates for cardiovascular APIs, and the tosylate salt carries an active REACH registration as a transported isolated intermediate under strictly controlled conditions.Table 1. Representative release specifications for the p‑toluenesulfonate salt.| Test Parameter | Method / Standard Reference | Acceptance Criterion || --- | --- | --- || Appearance | Visual | White crystalline powder || Assay (anhydrous, solvent‑free) | HPLC‑DAD, in‑house validated | ≥ 99.0% w/w || Chiral purity | HPLC on CHIRALPAK IA; Ph. Eur. 2.2.31 | ≥ 99.5% ee || Loss on drying | USP 〈731〉 | ≤ 0.5% || Total heavy metals | ICH Q3D via ICP‑MS | ≤ 20 µg/g || Palladium | ICP‑MS | ≤ 10 µg/g || Residual toluene | HS‑GC‑FID, USP 〈467〉 | ≤ 890 µg/g |Conformationally Restricted Peptidomimetics Incorporating 4‑Hydroxy‑3‑ethylpyrrolidine ScaffoldsIn solid‑phase peptide synthesis, the 3‑alkyl‑4‑hydroxyproline motif introduces conformational rigidity into bioactive linear and cyclic pentapeptides, improving plasma stability and target‑binding kinetics. Before loading, the p‑toluenesulfonate salt is suspended in water and treated with 2 M lithium hydroxide at 10–15°C to hydrolyse the methyl ester; the mixture is neutralized to pH 7–8 with 1 M hydrochloric acid and extracted with ethyl acetate to give zwitterionic (2S,3S,4R)‑3‑ethyl‑4‑hydroxypyrrolidine‑2‑carboxylic acid. For 2‑chlorotrityl chloride resin (loading 1.2 mmol/g), 3.0 equivalents of the amino acid and 6.0 equivalents of N,N‑diisopropylethylamine are stirred in dichloromethane for 2 hours, achieving a substitution level of 0.85–1.05 mmol/g. Chain elongation follows an Fmoc/t‑Bu protocol; the sterically hindered pyrrolidine acid requires extended double‑coupling cycles of 16 hours with HBTU/DIEA activation, reaching >99% incorporation by the Kaiser test. Large‑scale peptide‑API manufacture is operated under ICH Q7 GMP for Phase II/III material, with strict control of residual solvents per ICH Q3C and an endotoxin limit of ≤0.25 EU/mg (USP 〈85〉) for parenteral products. The p‑toluenesulfonate counterion is fully removed before lyophilisation, and the final cyclic peptidomimetic—typically a CXCR4 antagonist or a proteasome inhibitor under clinical investigation—is processed as a sterile lyophilised powder. Supply‑chain qualification ensures that the starting material complies with EU GMP Part II and holds a valid CEP for intermediates destined for sterile medicinal products.During the construction of peptidomimetic inhibitors targeting the SARS‑CoV‑2 3CL protease (Mpro), a 3‑ethyl‑4‑hydroxypyrrolidine‑2‑carboxylic acid ester moiety occupies the S2 hydrophobic pocket, forming additional van der Waals contacts that sharpen inhibitory activity in FRET enzymatic assays relative to unsubstituted proline—an observation documented in patent exemplifications focused on oral pan‑coronavirus agents. The crystalline tosylate salt is the preferred input form because it avoids the need for chromatographic purification of the hygroscopic free amine prior to coupling. In a scaled‑up sequence, 100 kg of the salt is neutralized with 10% aqueous ammonia in ethyl acetate at 0–5°C; the liberated amine is immediately condensed with (S)‑2‑((tert‑butoxycarbonyl)amino)‑4‑((S)‑1‑(benzyloxy)‑1‑oxopropan‑2‑yl)amino)butanoic acid using propanephosphonic acid anhydride (T3P, 50 wt% in EtOAc, 1.5 equiv) and pyridine (3.0 equiv) at 0–10°C for 4 hours, delivering 95–97% coupling efficiency by LC‑MS. After solvent exchange into tetrahydrofuran, the product is cyclized under Mitsunobu conditions with diisopropyl azodicarboxylate (1.2 equiv) and triphenylphosphine (1.3 equiv) at 0°C to furnish the bicyclic lactam core. Subsequent hydrogenolysis of the benzyl ester and sulfonamide formation with 4‑cyanobenzenesulfonyl chloride under Schotten‑Baumann conditions afford the advanced intermediate. Throughout the campaign, purge factors for DNA‑reactive impurities are calculated in accordance with ICH M7 and the additive approach described in EMA/CHMP/CVMP/QWP/672980/2018; the supplier of the tosylate salt provides a full ICH Q3D elemental analysis with a nickel limit of ≤15 µg/g. Residual toluene is controlled to 890 µg/g (USP 〈467〉) and methanol to 3000 µg/g. The final antiviral drug substance is formulated as an immediate‑release tablet containing 300 mg of the free‑base equivalent, and the intermediate’s manufacturing process is validated under a process‑development dossier that couples ISO 9001 quality management with ICH Q11 starting‑material designation.What Makes the PTSA Salt Preferable for Quaternization in Chiral Phase‑Transfer Catalyst Manufacturing?The crystalline p‑toluenesulfonate salt eliminates batch‑to‑batch moisture variation, a persistent issue when handling the corresponding free amino ester as a viscous oil, and thereby ensures reproducible stoichiometry in the N‑alkylation step that generates quaternary ammonium phase‑transfer catalysts. In an optimized protocol, the salt is suspended in acetonitrile with anhydrous potassium carbonate (2.5 equiv) at 60°C for 30 minutes to generate the free pyrrolidine in situ; 1‑bromooctane (1.05 equiv relative to the pyrrolidine) is then added and the mixture heated at reflux (82°C) for 18 hours. After cooling, filtration of inorganic salts and concentration, the crude N‑octylammonium tosylate is crystallized from ethyl acetate/n‑heptane (1:3 v/v) to provide analytically pure product in 84–88% yield. The quaternary ammonium salt is subsequently evaluated as a chiral catalyst in the enantioselective alkylation of glycine Schiff‑base esters under O’Donnell conditions (50% aq. NaOH, PhMe, 0°C), a process that supplies non‑proteinogenic α‑amino acids used in antidiabetic API routes. Quality specifications for the p‑toluenesulfonate salt in this application align with the general monograph Ph. Eur. 2034 and include a limit for benzylic halide impurities of ≤0.1% (GC area). The alkylation campaign operates at 200‑kg batch scale under an ISO 9001‑certified quality system, and the supplier’s technical dossier confirms that toluene is excluded from the synthetic pathway to avoid poisoning the downstream palladium‑catalysed deprotection steps. The terminal catalyst, after conversion to the bromide salt, delivers enantiomeric ratios up to 96:4 in model glycine benzophenone imine alkylations, with the validated batch history demonstrating consistent performance across 12 consecutive production runs.When the Application Demands Sub‑0.5 µmol/m² Chiral Selector Bonding on HPLC SilicaDevelopment of brush‑type chiral stationary phases for liquid chromatography often requires a linker‑arm architecture that positions hydrogen‑bonding and steric features at a controlled distance from the silica surface. The methyl ester tosylate salt is first neutralized with triethylamine (2.2 equiv) in dichloromethane at 0°C, and the free amine is reacted with 3‑(triethoxysilyl)propyl isocyanate (1.02 equiv) to form the corresponding silylated carbamate. After removal of triethylammonium tosylate by filtration and evaporation, the ligand is combined with spherical silica gel (particle size 5 µm, pore size 120 Å, surface area 300 m²/g) in refluxing anhydrous toluene under nitrogen for 24 hours. To achieve a target surface coverage of 0.28–0.32 µmol/m², a ratio of 0.16 g of ligand per 1.0 g of silica is employed; this leaves roughly half of the aminopropyl sites accessible for end‑capping. After bonding, the material is treated with hexamethyldisilazane in toluene at 120°C for 4 hours, then washed and dried. The bonded silica is slurry‑packed into 250 mm × 4.6 mm i.d. stainless steel columns and evaluated with racemic 1,1′‑bi‑2‑naphthol under normal‑phase conditions: n‑hexane/2‑propanol 90:10 at 1.0 mL/min yields an enantioselectivity α of 1.8–2.2 and a column efficiency exceeding 60,000 plates per meter. Quality control of the tosylate salt in this application follows ISO 15382 for chromatographic reagents, with additional limits on non‑volatile residue (≤0.05%) and UV transmittance at 210 nm (≥90% for a 1 mg/mL solution). The resulting custom CSP columns are used for preparative‑scale separation of protected β‑lactam enantiomers destined for carbapenem antibiotic manufacture, where optical purity ≥99.5% ee is required by generic‑drug application guidance.Table 2. Bonding parameters and column evaluation for the pyrrolidine‑derived CSP.| Parameter | Value / Specification || --- | --- || Silica substrate | 5 µm, 120 Å, 300 m²/g || Ligand‑to‑silica ratio | 0.16 g ligand per 1.0 g silica (coverage 0.30 µmol/m²) || Bonding medium | Anhydrous toluene, reflux 110°C, 24 h || End‑capping agent | Hexamethyldisilazane, 120°C, 4 h || Column format | 250 mm × 4.6 mm i.d. || Test racemate | 1,1′‑Bi‑2‑naphthol || Mobile phase | n‑Hexane/2‑propanol 90:10, 1.0 mL/min || Enantioselectivity (α) | 1.8–2.2 || Plate count per meter | ≥60,000 |Assembling the highly constrained P4 pyrrolidine fragment found in next‑generation oral Factor Xa inhibitors demands a stereochemically defined 3,4‑disubstituted proline ester, and the (2S,3S,4R)‑3‑ethyl‑4‑hydroxypyrrolidine‑2‑carboxylic acid methyl ester tosylate salt delivers both the required absolute configuration and a crystalline form that permits large‑scale purification without chromatography. In a typical manufacturing campaign, the salt is Fmoc‑protected under Schotten‑Baumann conditions (10% aq. Na₂CO₃, THF, 0–5°C) using Fmoc‑OSu at a molar ratio of 1.2:1.0 relative to the free amine. The resulting Fmoc‑protected ester is hydrolysed with lithium hydroxide in THF/water at 10–15°C to give the carboxylic acid, which is then coupled with a meta‑substituted benzamidine derivative employing EDCI/HOBt in DMF. The synthesis sequence is risk‑assessed under ICH Q3D for palladium and nickel; Pd content is verified at ≤10 µg/g by ICP‑MS because transition‑metal catalysis is typically used in earlier supply‑chain steps. After global deprotection and salt formation, the final drug substance is formulated as an immediate‑release tablet of 60 mg dose strength. The tosylate salt supplier maintains a Type II US DMF and a CEP under EU GMP Part II, in addition to undergoing periodic ISO 14001 environmental performance audits. The entire downstream process is monitored by in‑process controls prescribed in the registered drug‑master file, guaranteeing batch‑to‑batch optical purity and compliance with the pharmacopoeial monograph for the finished anticoagulant. |
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The pyrrolidine ester (2S,3S,4R)-3-ethyl-4-hydroxypyrrolidine-2-carboxylic acid methyl ester p-toluenesulfonate, supplied as a white crystalline powder with a molecular weight of 361.43 g·mol⁻¹ (free base C₉H₁₇NO₃, tosylate C₇H₈O₃S), functions as a pivotal chiral building block in the convergent synthesis of dipeptidyl peptidase-4 (DPP-4) inhibitors. The compound crystallizes as a single-configuration salt from 2-propanol/n-heptane mixtures, exhibiting a sharp melting endotherm with an onset at 148–152°C determined by differential scanning calorimetry at a heating rate of 10 K·min⁻¹ under nitrogen (method ASTM E794). Typical batches, analyzed on a Rudolph Autopol IV polarimeter at 25°C and a concentration of c=1 in methanol, show a specific optical rotation [α]ᴅ²⁵ of +12.8° to +14.1°. This narrow range corresponds to a diastereomeric excess exceeding 99.0% as quantified by isocratic HPLC on a Chiralpak IA column (250 × 4.6 mm, 5 µm) with a mobile phase of n-hexane/ethanol/diethylamine (90:10:0.1 v/v/v) at 1.0 mL·min⁻¹ and UV detection at 210 nm. Residual inorganic content, assessed by ICP-MS on a PerkinElmer NexION instrument, stays below 10 ppm for each of the regulated elements Pb, Cd, Hg, and As, well within the limits of ICH Q3D.
| Stereoisomer | [α]ᴅ²⁵ (c=1, MeOH) | Chiral HPLC purity | DSC onset (°C, ASTM E794) |
|---|---|---|---|
| (2S,3S,4R)-p-toluenesulfonate | +13.5° (typical) | >99.0% ee | 148–152 |
| (2R,3R,4S)-p-toluenesulfonate | −13.2° | >99.0% ee | 147–151 |
| (2S,3R,4R)-p-toluenesulfonate | −8.7° | 97% | 130–135 (broad, multi-peak) |
| (2S,3S,4S)-p-toluenesulfonate | +5.2° | 94% | 141–146 (shouldered peak) |
The (2S,3S,4R) arrangement places the 3-ethyl group on the same face as the 4-hydroxyl, creating a contiguous hydrophobic surface that mimics the side chain of L-isoleucine. Molecular docking studies of the derived β-amino acid fragment into the S1 pocket of DPP-4 show that the (3S)-ethyl substituent occupies a sterically restricted sub-pocket lined by residues Tyr547 and Trp629, while the (4R)-hydroxyl forms a hydrogen bond with Glu205/Glu206. The (2S,3R,4R) epimer, by contrast, forces the ethyl group into a clashing orientation with the Tyr547 phenyl ring, resulting in a >45° deviation from the bioactive torsion angle and a measured IC₅₀ shift of three orders of magnitude in fluorogenic substrate assays. Process-wise, the target isomer crystallizes as a single-phase material with a narrow melting range, whereas the (2S,3R,4R) salt yields broad endotherms and often entrains 2–3% of the trans-hydroxy diastereomer that co-elutes during chiral HPLC using a Chiralpak IC column (mobile phase methyl tert-butyl ether/acetonitrile 95:5 with 0.05% trifluoroacetic acid, flow 0.8 mL·min⁻¹). This co-elution masks incomplete stereochemical purity and can propagate into late-stage intermediates, where the epimeric impurity depresses coupling yields by 12–15% as documented in batch records of a 50-L pilot plant campaign using a Büchi GlasUster reactor equipped with a retreat-curve impeller at 150 rpm.
The methyl ester remains inert under reductive amination conditions that employ sodium triacetoxyborohydride in 1,2-dichloroethane at 0–5°C, and it survives catalytic hydrogenolysis of a Cbz group with 10% Pd/C at 3 bar H₂ for 4 hours. In contrast, the corresponding free acid undergoes partial N-alkylation of the carboxylate and forms lactone byproducts when exposed to carbodiimide coupling reagents at ambient temperature. A head-to-head comparison of coupling with 2,4,5-trifluorophenylacetic acid using EDC·HCl/HOBt in DMF at 0°C revealed that the methyl ester achieves 91% isolated yield of the trifluorophenylacetamide intermediate (purity 98.7% by HPLC at 254 nm) versus 73% for the free acid under identical stoichiometry; the free acid reaction generated a diketopiperazine dimer as a major side product identified by HRMS (Q-TOF, positive ion mode). The ester also demonstrates superior solubility in DMF — >220 mg·mL⁻¹ at 25°C compared to 48 mg·mL⁻¹ for the zwitterionic free base — allowing coupling at higher concentration and reducing solvent volume by 35% in 100-L glass-lined vessels, which has direct implications for large-scale throughput. Saponification to the carboxylic acid is accomplished with LiOH·H₂O in THF/water (4:1) at 5°C over 2 hours with <0.2% epimerization at the α-center, as confirmed by derivatization with Marfey’s reagent and subsequent LC-MS analysis.
Headspace GC-FID on an Agilent 7890B system equipped with a DB-624 column (30 m × 0.32 mm, 1.8 µm film) detects residual methanol at ≤0.15%, ethyl acetate at ≤0.08%, and n-heptane at ≤0.07% across three consecutive production lots. All values sit below the 5,000 ppm (Class 3, methanol) and 5,000 ppm (Class 3, ethyl acetate) thresholds of ICH Q3C (R6). Acetone, occasionally present from the final trituration step, is measured at <0.05%. Water content, determined by coulometric Karl Fischer titration (Metrohm 851 Titrando) on 200 mg samples dissolved in anhydrous methanol, is maintained at ≤0.5% w/w. The salt shows no detectable THF or dioxane, Class 2 solvents that would exceed the 3,800 ppm and 380 ppm concentration limits respectively. Manufacturers running continuous vacuum drying in a BSR conical dryer at 40°C and 5 mbar achieve these residual levels within 8 hours without sign of ester solvolysis, as confirmed by online FTIR monitoring of the carbonyl stretch at 1,735 cm⁻¹ using a Mettler Toledo ReactIR probe. The tosylate counterion offers an additional benefit: during vacuum drying it suppresses the base-catalyzed transesterification that can occur when trace methanol is present alongside the free amine, a side reaction that degraded 3.4% of an early hydrochloride salt batch stored under similar conditions.
| Parameter | Method | Limit |
|---|---|---|
| Assay (anhydrous) | HPLC-UV, 210 nm, C18 column (USP <621>) | ≥98.5% |
| Chiral purity | Chiral HPLC, Chiralpak IA, n-hexane/EtOH/DEA | ≥99.0% ee |
| Water | Karl Fischer | ≤0.5% w/w |
| Residue on ignition | USP <281> | ≤0.1% |
| Heavy metals (Pb,Cd,Hg,As) | ICP-MS (USP <233>) | ≤10 ppm each |
| Residual methanol | GC-HS, ICH Q3C | ≤3,000 ppm |
| Microbial limits | USP <61>, <62> | TAMC <100 CFU/g, TYMC <10 CFU/g |
Protonation of the pyrrolidine nitrogen with p-toluenesulfonic acid yields a salt that is physically and chemically distinct from the corresponding hydrochloride or trifluoroacetate. Dynamic vapour sorption analysis (Surface Measurement Systems DVS-Intrinsic) at 25°C indicates that the tosylate adsorbs less than 0.3% moisture across a 10–80% RH ramp, while the hydrochloride gained 4.8% mass at 60% RH and deliquesced above 75% RH. This low hygroscopicity eliminates the requirement for controlled humidity packaging and permits direct filling into amber glass vials under ambient conditions (22°C, 45% RH), significantly reducing operational costs on a semi-automated coater line. The tosylate’s bulky aromatic anion also spaces chiral chains in the crystal lattice, preventing the solid-state dimerization observed for the mesitylenesulfonate salt, which developed 2.1% dimer content after 12 weeks at 40°C/75% RH as per SEC-MALS analysis (Wyatt DAWN HELIOS-II). Bench-scale coupling with EDC/HOBt in dichloromethane shows no anion interference; the tosylate dissociates rapidly and p-toluenesulfonic acid is removed by an aqueous bicarbonate wash, leaving no detectable 1H NMR signals in the final product. Competing salts such as the camphorsulfonate exhibit higher molecular weight and reduce stoichiometric density, leading to 8–12% lower product per gram of starting material in parallel syntheses, a loss that becomes costly when scaling to multi-kilogram campaigns.
Without a distinct header, the following constraints for storage and handling complete the regulatory profile. The product ships in sealed, nitrogen-flushed Type I borosilicate glass vials with PTFE-lined caps and should be stored at −20°C ± 5°C in the dark; under these conditions, accelerated aging data (ICH Q1A, 25°C/60% RH for 6 months) show less than 0.1% assay drop and no detectable epimerization. Re-packaging into polyethylene bags leads to static charge buildup that causes particle adhesion and 2–5% product loss during transfer, a phenomenon reported in micronized grades and remedied by antistatic chute linings in GMP dispensing suites compliant with ISO 14644-1 Class 8. Prior to use, the container should be equilibrated to room temperature in the sealed septum vial to avoid condensation; once opened, the material must be stored with a desiccant pouch containing silica gel activated at 120°C and consumed within 72 hours to keep water content below 0.5%.
