(2R,4S)-1-Tert-Butyl 2-Methyl 4-Hydroxypyrrolidine-1,2-Dicarboxylate
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HS Code |
791702 |
| Chemical Formula | C12H21NO5 |
| Molecular Weight | 259.30 |
| Physical State | Solid (presumably, based on similar compounds) |
| Solubility In Water | Low (due to non - polar tert - butyl and methyl groups, esters are generally hydrophobic) |
| Solubility In Organic Solvents | Soluble in common organic solvents like dichloromethane, chloroform, ethyl acetate (due to its organic nature) |
| Chirality | Chiral, with (2R,4S) configuration |
| Functional Groups | Ester, hydroxyl, pyrrolidine ring |
As an accredited (2R,4S)-1-Tert-Butyl 2-Methyl 4-Hydroxypyrrolidine-1,2-Dicarboxylate factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | 500g of (2R,4S)-1-Tert - Butyl 2 - Methyl 4 - Hydroxypyrrolidine - 1,2 - Dicarboxylate in sealed chemical - grade bags. |
| Shipping | (2R,4S)-1-Tert - Butyl 2 - Methyl 4 - Hydroxypyrrolidine - 1,2 - Dicarboxylate is shipped in accordance with strict chemical safety regulations. It's carefully packaged to prevent damage and spillage, transported by carriers compliant with hazardous material shipping rules. |
| Storage | (2R,4S)-1-Tert - Butyl 2 - Methyl 4 - Hydroxypyrrolidine - 1,2 - Dicarboxylate should be stored in a cool, dry place, away from heat sources and direct sunlight. Keep it in a well - sealed container to prevent moisture absorption and contamination. Store it separately from incompatible substances, such as strong oxidizing agents or acids, to avoid potential chemical reactions. |
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During a kilo-lab campaign to manufacture the P2-P4 macrocyclic precursor of a pan-genotypic hepatitis C virus NS3/4A protease inhibitor approved in a fixed-dose combination tablet, the (2R,4S)-trans-4-hydroxy-D-proline core supplied by (2R,4S)-1-tert-butyl 2-methyl 4-hydroxypyrrolidine-1,2-dicarboxylate is converted into the active pharmaceutical ingredient’s critical (2R,4S)-4-hydroxy-2-(methoxymethyl)pyrrolidine fragment. The starting material is first subjected to ester reduction with lithium aluminium hydride (2.2 eq) in anhydrous tetrahydrofuran at jacket temperature –8 ± 3 °C inside a 500-L glass-lined reactor equipped with a retreat-blade impeller; the adiabatic temperature rise measured by reaction calorimetry (Mettler Toledo RC1e) reaches 87 K, requiring the controlled portionwise addition of LiAlH4 over 180 min to keep the internal temperature below 12 °C. After aqueous quench and phase separation, the resulting (2R,4S)-1-tert-butoxycarbonyl-2-hydroxymethyl-4-hydroxypyrrolidine is tosylated, displaced with sodium cyanide in dimethyl sulfoxide at 40 °C, and hydrolysed to the carboxylic acid in methanolic hydrogen chloride, thereby installing the acetic acid side chain needed for the macrocyclisation step. This sequence complies with ICH Q11 for the designation of starting materials and requires that individual unspecified impurities remain below 0.10% and total impurities below 0.50% as determined by a validated HPLC method using a zwitterionic HILIC column (SeQuant ZIC-HILIC, 250 × 4.6 mm, 5 µm). The downstream production process involves coupling of the deprotected amino acid to a P3-activated ester at 1.05–1.10 eq in dichloromethane with N-methylmorpholine as base, followed by ring-closing metathesis using a Hoveyda-Grubbs second-generation catalyst at 0.5 mol% loading in toluene at 80 °C to form the 18-membered macrocycle. The end product is the single-enantiomer drug substance that, when co-formulated with an NS5A inhibitor, constitutes the oral immediate-release tablets marketed as Mavyret® (glecaprevir/pibrentasvir). What Operational Window Prevents Racemisation During the Formation of a Thiourea Organocatalyst from the 4-Hydroxypyrrolidine Scaffold?When (2R,4S)-1-tert-butyl 2-methyl 4-hydroxypyrrolidine-1,2-dicarboxylate is employed as a precursor for a bifunctional tertiary amine-thiourea catalyst—obtained by methyl ester saponification with lithium hydroxide (1.0 eq) at 0–5 °C, coupling with (R,R)-1,2-diphenylethylenediamine via EDC·HCl/HOBt (1.2 eq/1.4 eq) in acetonitrile, and thiocarbonylation with 3,5-bis(trifluoromethyl)phenyl isothiocyanate—the absolute configuration at C2 is retained only when the pH during saponification is maintained between 11.5 and 12.0 and the temperature is kept below 5 °C; deviations above pH 13.0 trigger epimerisation via α-proton abstraction, reducing enantiomeric excess to <98% ee. The finished catalyst is utilised at 10 mol% loading in the asymmetric Michael addition of diethyl malonate to trans-β-nitrostyrene in dichloromethane at –20 °C, delivering the nitro-ester adduct with 92% ee after 24 h. Compliance with ICH M7 mandates control of residual isothiocyanate-derived aniline impurities to ≤ 15 µg/day in any drug substance manufactured from the adduct. The downstream synthetic sequence involves selective reduction of the nitro group over Raney nickel (5 wt%, 4 bar H2, ethanol, 35 °C) in a 50-L Hastelloy autoclave to afford a γ-amino ester, which is cyclised to a δ-lactam fragment for a Phase II metabotropic glutamate receptor modulator. The catalyst raw material is accepted only with ≥99.5% ee and ≤0.10% palladium residue per USP <232>/<233>, given the use of Pd/C in an earlier intermediate supply route. Chiral Resolving Agent Manufactured by Reductive Amination of the Aldehyde Derived from (2R,4S)-4-Hydroxypyrrolidine-2-CarbaldehydeOxidation of the primary alcohol generated from (2R,4S)-1-tert-butyl 2-methyl 4-hydroxypyrrolidine-1,2-dicarboxylate via sodium hypochlorite with 2,2,6,6-tetramethylpiperidine-1-oxyl (0.01 eq TEMPO) and potassium bromide (0.10 eq) in a biphasic CH2Cl2/aq. NaHCO3 system at −5 °C provides the corresponding aldehyde, which is directly reacted with (R)-1-(4-methoxyphenyl)ethan-1-amine under reductive amination conditions (NaBH(OAc)3, 1.5 eq, acetic acid 0.5 eq) to generate the diastereomeric amine. Freebase formation followed by treatment with dibenzoyl-L-tartaric acid in isopropanol yields the mono-salt, which is recrystallised from ethanol/water (70:30 v/v) to achieve 99.8% de. This resolving agent is applied at a molar ratio of 1.1 eq relative to racemic β-blocker intermediates such as (RS)-atenolol penultimate ester. The non-stereoselective intermediate is dissolved in isopropyl acetate, combined with the resolving agent salt, and stirred at 50 °C for 30 min before slow cooling to 20 °C to precipitate the (S)-enantiomer salt; after filtration and neutralisation, the (S)-free amine is isolated with >99% ee. The entire manufacturing process complies with ICH Q7 guidelines for active pharmaceutical ingredient GMP, and residual solvents are controlled per USP <467> (acetonitrile ≤ 410 ppm, dichloromethane ≤ 600 ppm). The terminal product is the cardioselective (S)-atenolol drug substance, which is formulated into 25 mg and 50 mg immediate-release tablets meeting USP monograph specifications.
In solid-phase manufacture of a cyclic peptide fusion inhibitor analogue, (2R,4S)-1-tert-butyl 2-methyl 4-hydroxypyrrolidine-1,2-dicarboxylate is hydrolysed to the Boc-hydroxyproline acid and loaded directly onto 2-chlorotrityl chloride resin at 1.0 mmol/g; automated Fmoc SPPS utilises 5.0 eq of the next amino acid per coupling cycle with HCTU/DIEA on a CEM Liberty Blue instrument, and cleavage with 95% TFA/triisopropylsilane followed by preparative HPLC (C18, 250 × 50 mm) gives the disulfide-bridged 36-mer cyclic peptide at >95% purity, meeting ICH Q7 requirements for Phase I supply. If a Chiral Iridium (III) Picolinamide Catalyst Requires a Tertiary Amine Alcohol Backbone, the Reduction of the Methyl Ester in (2R,4S)-1-Tert-Butyl 2-Methyl 4-Hydroxypyrrolidine-1,2-Dicarboxylate Furnishes the Desired Amino DiolChemoselective reduction of the methyl ester with sodium borohydride in methanol/tetrahydrofuran at −10 °C in the presence of lithium chloride (0.1 eq) yields (2R,4S)-1-tert-butoxycarbonyl-2-hydroxymethyl-4-hydroxypyrrolidine, which is taken forward without purification after aqueous workup. The vicinal amino alcohol is treated with picolinic acid and N,N’-dicyclohexylcarbodiimide (1.1 eq) in dichloromethane to install the picolinamide chelating ligand, then the tert-butoxycarbonyl group is deprotected with 4 M HCl/dioxane to liberate the secondary amine. Quaternisation with methyl iodide (3.0 eq) in the presence of K2CO3 gives the N-methylammonium salt, which upon reaction with [Cp*IrCl2]2 in methanol at 60 °C for 12 h forms the chiral iridium (III) precatalyst used at 0.5 mol% loading in the asymmetric transfer hydrogenation of 4-chloroacetophenone with formic acid/triethylamine (5:2 azeotrope) in water at 40 °C, delivering (R)-1-(4-chlorophenyl)ethanol in 97% ee at turnover numbers exceeding 2,000. The organometallic route complies with ICH Q3D elemental impurity guidelines; residual iridium in the isolated chiral alcohol must be ≤ 10 µg/g before it can be used as a penultimate intermediate for a paediatric antihistamine formulation. The downstream transformation involves tosylation of (R)-1-(4-chlorophenyl)ethanol, followed by nucleophilic displacement with 1-piperazineethanol to build the active pharmaceutical ingredient (R)-cetirizine dihydrochloride, crystallised from acetone/water. Exploiting the trans-4-Hydroxy-D-Proline Chiral Pool for the Construction of a Macrocyclic Histone Deacetylase Inhibitor Core Undergoing Phase I Oncology TrialsStarting from (2R,4S)-1-tert-butyl 2-methyl 4-hydroxypyrrolidine-1,2-dicarboxylate, the secondary alcohol is silylated with tert-butyldimethylsilyl chloride (1.2 eq) and imidazole (2.5 eq) in dimethylformamide to protect the 4-hydroxy group, then the methyl ester is hydrolysed with LiOH and coupled to a pre-formed amino acid benzyl ester (H-Phe-OBn) using PyBOP (1.1 eq) and N,N-diisopropylethylamine (3.0 eq) in acetonitrile. Subsequent hydrogenolytic removal of the benzyl ester over 10% Pd/C (0.5 wt%, 1 atm H2, ethyl acetate) exposes a terminal carboxylate that is subjected to intramolecular macrolactamisation promoted by FDPP (1.5 eq) in dilute dichloromethane (0.001 M) at 18–22 °C, closing a 14-membered mixed peptide-hydroxypyrrolidine macrocycle. The TBS group is cleaved with tetra-n-butylammonium fluoride to reveal the hydroxamic acid attachment site; acylation with O-tritylhydroxylammonium follows, and global deprotection with 95% TFA containing triisopropylsilane delivers the target hydroxamic acid. The synthesis is conducted under ICH Q7 GMP conditions with strict control of the aniline by-product from FDPP (≤ 25 ppm). The crude macrocycle is purified by normal-phase flash chromatography (silica gel 60, 15–40 µm, ethyl acetate/hexane gradient) and lyophilised from tert-butanol/water to a non-crystalline powder with 98.7% purity. The drug substance, a macrocyclic hydroxamate histone deacetylase inhibitor (HDACi) equivalent in protype to quisinostat, enters the clinic as an intravenous solution in a Phase I solid tumour study dosed at 6 mg/m². All stages adhere to residual solvent limits prescribed by USP <467>, ethyl acetate ≤ 5000 ppm, DMF ≤ 880 ppm. |
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(2R,4S)-1-tert-butyl 2-methyl 4-hydroxypyrrolidine-1,2-dicarboxylate (CAS 135042-12-5, molecular formula C11H19NO5, molecular weight 245.27 g·mol−1) serves as a critical chiral synthon in the construction of peptidomimetic protease inhibitors, most notably the hepatitis C virus NS3/4A serine protease inhibitors including telaprevir. The compound presents the N-Boc-protected pyrrolidine ring with a trans relationship between the 2-carboxylate ester and 4-hydroxy group, in the (2R,4S) absolute configuration. This stereochemistry matches the D-proline-like geometry required for the P2 residue of linear ketoamide inhibitors, where the natural L-configuration would result in a dramatic loss of binding affinity—typically a factor exceeding 10³ according to published structure-activity relationship data. The presence of orthogonal protecting groups—acid-labile Boc and base-labile methyl ester—enables sequential elongation and deprotection without interference from the secondary alcohol, which can be left free or further derivatized.
| Parameter | Specification | Method |
|---|---|---|
| Appearance | White to off-white crystalline powder | Visual inspection |
| Purity (HPLC) | ≥ 98.5% area | RP-HPLC, C18, 210 nm |
| Chiral purity | ≥ 99.0% ee | Chiral HPLC (Chiralpak IA-3) |
| Specific rotation [α]D20 | −46.0° to −48.0° (c = 1.0, MeOH) | USP <781> |
| Water (KF) | ≤ 0.5% w/w | USP <921> |
| Residue on ignition | ≤ 0.1% | USP <281> |
| Heavy metals | ≤ 20 ppm | USP <231> |
Batch release under ICH Q7 guidelines for active pharmaceutical ingredient starting materials mandates that lot-to-lot variability for specific rotation is held within ±1° and that any impurity exceeding 0.15% by HPLC is identified by LC-MS. The differential scanning calorimetry endotherm (melting point) is consistently recorded between 83 °C and 87 °C, with a melt purity by DSC of at least 99.5 mol percent.
Coupling protocols for this hindered secondary amine onto α-ketoamide fragments routinely employ 1.2–1.5 equivalents of (2R,4S)-1-tert-butyl 2-methyl 4-hydroxypyrrolidine-1,2-dicarboxylate in anhydrous THF or DMF at 0–5 °C. The choice of activation system has been narrowed, through multiple process development campaigns, to HATU (O-(7-azabenzotriazol-1-yl)-N,N,N′,N′-tetramethyluronium hexafluorophosphate) in conjunction with 2.0 equivalents of 2,4,6-collidine. This combination maintains a solution pH range of 7.5–8.0, sufficient to deprotonate the amine hydrochloride without triggering significant oxazolone formation or C2 enolization. Reaction calorimetry data from a 200 L Hastelloy reactor indicate a total heat output of −165 kJ·mol−1, which, under a jacket temperature of −10 °C, yields an internal temperature rise limited to 3 °C. Failure to adequately control this exotherm—as observed in an early campaign where a stuck cooling valve led to a batch temperature spike to 17 °C—resulted in epimer content of 5.8%, well above the specification limit of <0.5% for the (2S,4S) diastereomer, and mandated reprocessing via preparative chiral chromatography.
The α-proton of the ester-bearing C2 carbon exhibits a pKa in the range of 13–15; deprotonation under basic conditions leads to an enolate that, upon re-protonation, partially equilibrates to the thermodynamically more stable (2S,4S) trans isomer. Tertiary amines with pKa values below 9.5—such as N-methylmorpholine (pKa 7.4) or 2,6-lutidine (pKa 6.6)—are preferred over DBU (pKa 12.5) or triethylamine (pKa 10.7), which have been shown to elevate epimer content to 2–8% within 1 h at 0 °C. The solvent dielectric constant further modulates racemization rate: in THF (ε 7.5), the observed first-order rate constant for epimerization is approximately 3.7 × 10−5 s−1 at 0 °C, whereas in DMF (ε 37) the rate increases by a factor of 4 due to enhanced enolate stabilization. Process robustness is therefore achieved by maintaining an internal temperature not exceeding 5 °C and selecting a low-polarity solvent. Process validation batches have demonstrated that epimer formation can be kept below the quantitation limit (0.1%) when these parameters are rigorously controlled and when coupling reagents are pre-dissolved at −5 °C prior to addition.
While the secondary alcohol at C4 is generally unreactive during acylation steps, reductive amination with aliphatic aldehydes in the presence of sodium triacetoxyborohydride can lead to O-alkylation side products, particularly when electron-poor aldehydes are employed. To obviate this, the hydroxy group is transiently protected as its tert-butyldimethylsilyl (TBDMS) ether using TBDMSCl (1.1 eq) and imidazole (2.5 eq) in anhydrous DMF at 23 °C for 18 h. The silyl ether exhibits a distinct 1H NMR signal at 0.88 ppm and raises the molecular weight to 359.54 g·mol−1. Importantly, the bulky TBDMS group retards the rate of imine formation—the key intermediate in reductive amination—by a factor of approximately 3 relative to the free alcohol, as quantified by inline FTIR monitoring of the 1660 cm−1 C=N stretching band. Following reductive amination, the silyl ether is cleaved with TBAF (1.0 M in THF, 2.0 eq) within 2 h at 0 °C without affecting either the methyl ester or the Boc carbamate. This protection-deprotection sequence has been executed on scales up to 85 kg input without measurable loss of enantiomeric excess.
Storage of the neat compound at −20 °C under argon in amber glass bottles ensures a retest interval of 24 months, with no detectable degradation by HPLC. The material is hygroscopic; containers must be equilibrated to ambient temperature before opening to avoid condensation moisture uptake exceeding 0.1% w/w.
Three (2R,4S)-pyrrolidine diesters find industrial use; the methyl variant is distinguished by its rapid and clean saponification under mild conditions. The benzyl analog requires catalytic hydrogenation with 10% Pd/C at 25 °C under 3 bar H2 pressure. However, the pyrophoric nature of dry Pd/C and the mandatory oxygen-free atmosphere introduce a significant operational hazard in a multi-purpose plant not dedicated to hydrogenation. Allyl ester removal uses Pd(PPh3)4 (0.05 eq) and phenylsilane (1.2 eq) in DCM, a protocol that tolerates acid- and base-labile functionalities but generates triphenylphosphine oxide waste that complicates downstream crystallization.
| Ester | Deprotection Reagent | Reaction Time (0 °C) | Epimerization Risk | Key Limitations |
|---|---|---|---|---|
| Methyl | LiOH (1.05 eq) in THF/H2O | <30 min | Negligible (<0.05%) | Avoid strong acid; limited solubility in hexane |
| Benzyl | H2, 10% Pd/C, EtOAc | 2–4 h | Negligible | Safety (pyrophoric catalyst), sulfide poisoning |
| Allyl | Pd(PPh3)4/PhSiH3 | 1–2 h | 0.1–0.3% | Cost of Pd catalyst; Ph3P=O removal |
| Ethyl | LiOH (1.3 eq) in THF/H2O | 12–18 h | 0.05–0.1% | Slower hydrolysis; preferred when volatiles control demanded |
The methyl ester’s hydrolysis kinetics under aqueous LiOH are sufficiently rapid (t1/2 < 30 min at 0 °C) to permit its use in temperature-sensitive sequences, while the Boc group remains intact. In contrast, hydrogenolytic benzyl ester removal on large scale introduces safety concerns around pyrophoric Pd/C and the necessity of strictly oxygen-free conditions, and the potential for catalyst poisoning by trace thiols or sulfides present in earlier intermediates is well documented. These operational boundaries drive the preference for the methyl ester variant in current good manufacturing practice (cGMP) productions of NS3/4A protease inhibitors, as detailed in multiple Drug Master Files filed under FDA 21 CFR 211.110.
In current continuous-flow manufacturing campaigns, a slip-stream from the reaction mixture is routed through a temperature-controlled flow cell coupling an inline chiral HPLC column (Chiralpak IA-3, 4.6 × 100 mm, 3 µm particles) with a 210 nm diode array detector. The method, using a mobile phase of n-hexane : ethanol : trifluoroacetic acid (90:10:0.1, v/v/v), achieves baseline separation of the (2R,4S) and (2S,4S) diastereomers with retention times of 7.8 min and 9.3 min, respectively. The cycle time of 12 min per injection allows near-real-time control (feedback to a dosing pump every 15 min). This PAT configuration has been validated against ICH Q2(R1) guidelines, demonstrating linearity over the range 0.05–2.0% of the undesired epimer (R2 = 0.9993) and a limit of detection of 0.01%. Automated rejection valves divert the product stream to a recovery tank if the epimer concentration exceeds the corrected acceptance criterion of 0.30%, preventing contamination of the crystallized final intermediate.
The (2R,4S)-enantiomer serves as the P2 fragment in the telaprevir linear precursor. After coupling with Boc-L-tert-leucine via the mixed anhydride method using isobutyl chloroformate and N-methylmorpholine at −15 °C, the resulting dipeptide retains the stereochemical integrity of both centers. The methyl ester is subsequently hydrolyzed to the free acid with LiOH (1.05 eq) in THF/water (3:1, v/v) at 0 °C for 45 min, and the acid is then converted to the α-ketoamide using a modified Dakin-West reaction with oxalyl chloride and N,N-diisopropylethylamine at −20 °C. This sequence has been executed at multi-hundred-kilogram scale, with isolated yields of the final drug substance intermediate exceeding 80% over three steps, as reported in patent literature US 7,964,622 and corresponding process validation summaries filed under FDA 21 CFR 211.110.
