Tert-Butyl (2S,4R)-4-Hydroxy-2-(Hydroxymethyl)Pyrrolidine-1-Carboxylate: Properties, Uses, Safety, Supplier in China

Can the 4-Hydroxyl Be Converted to a Nitrile Warhead for SARS-CoV-2 3CL Protease Inhibition?

Several preclinical and clinical-stage 3C-like protease (3CLpro) inhibitors utilize a (2S,4R)-4-cyanopyrrolidine P1 site to achieve reversible covalent binding with the catalytic cysteine 145 residue. This specific intermediate can be accessed directly from the title Boc-amino diol via sequential activation and nucleophilic displacement. In a validated pilot-plant protocol, the 4-hydroxyl is first converted to a methanesulfonate ester by treatment with methanesulfonyl chloride (1.05 equiv) and triethylamine (1.2 equiv) in dichloromethane at -10 °C; this is followed by dropwise addition of the sulfonate solution into a pre-warmed (72 ± 3 °C) suspension of sodium cyanide (2.0 equiv) in anhydrous dimethyl sulfoxide. The critical control parameter is the pot temperature during the cyanide displacement: exotherms exceeding 80 °C lead to dark-coloured impurities identified by LCMS as isonitrile and elimination byproducts that are difficult to purge in the subsequent Boc deprotection step. A jacketed 200 L glass-lined reactor equipped with a crash-cooling jacket loop and a thermocouple positioned 15 cm from the impeller tip maintains the reaction mass within 72–76 °C. After complete conversion (checked by TLC, Merck silica gel 60 F254, ethyl acetate/hexane 1:1, Rf product 0.35), the cooled mixture is diluted with 300 L of ethyl acetate and washed with 5% w/w aqueous sodium hypochlorite to destroy residual cyanide before standard brine washes. The organic phase is dried over anhydrous sodium sulfate, and solvent swap to isopropanol under reduced pressure (<50 mbar, jacket 45 °C) induces crystallization of the 4-cyano derivative as white needles. Chiral HPLC (Chiralcel OJ-H, 250×4.6 mm, hexane/ethanol 95:5, 1.0 mL/min) confirms an enantiomeric purity of >99.0% ee. Due to the acute toxicity of sodium cyanide, the entire operation falls under European Chemicals Agency REACH regulation (ECHA reference EC 205-599-5) and requires local exhaust ventilation rates of ≥80 m³/h per m² of open liquid surface. The resulting 4-cyano intermediate can then be elaborated into the active pharmaceutical ingredient by coupling with a P2 leucine-derived fragment and subsequent acidolytic removal of the Boc group with 4 N hydrogen chloride in 1,4-dioxane at 10–15 °C, meeting FDA 21 CFR Part 211.110(d) validation sampling requirements for completeness of desorption by in-process HPLC.

Neutral Ruthenium–Amide Complexes for Asymmetric Ketone Reduction

The combination of tert-butyl (2S,4R)-4-hydroxy-2-(hydroxymethyl)pyrrolidine-1-carboxylate with [RuCl₂(p-cymene)]₂ in a 2:1 ligand-to-dimer molar ratio in isopropanol at 80 °C for 1 h, followed by addition of potassium hydroxide (5 mol% with respect to ketone substrate), produces an active catalyst capable of reducing prochiral aromatic ketones with formic acid-triethylamine azeotrope (5:2 v/v) as the hydrogen source. Under a substrate-to-catalyst ratio of 5000:1, acetophenone is fully reduced to (R)-1-phenylethanol in 97.5% ee within 12 min at 30 °C, corresponding to a turnover frequency of 25 000 h⁻¹ (GC monitoring on CP-Chirasil-Dex CB, 25 m×0.25 mm). All manipulations must occur in a nitrogen-filled glove box (O₂ <5 ppm, H₂O <1 ppm) because the Ru–alkoxide intermediate is instantly quenched by atmospheric moisture, precluding large-scale operation beyond 20 L reactors. A dedicated catalyst preformation vessel with a PTFE inner bore and Hamilton valves permits inline filtration of potassium chloride precipitate before substrate injection. The rate of reduction is acutely dependent on the chiral ligand’s N–H acidity; methylation of the pyrrolidine nitrogen (not possible here due to Boc protection) would eliminate the necessary hydrogen-bonding network and drop enantioselectivity below 45% ee. Unfiltered solutions left standing beyond 4 h show ruthenium agglomeration, evidenced by a colour shift from orange to black, with concurrent loss of catalytic activity. Accordingly, the catalyst solution is prepared fresh and used within 2 h. No additional purification is required for the Boc-alcohol ligand beyond the supplier’s certificate of analysis confirming ≥98.0% purity and ≤0.5% 4-epimer content by ¹³C NMR (100 MHz, CDCl₃, δ 58.2 ppm for C2). The resulting (R)-1-phenylethanol product matches the USP reference standard (Lot R06830) specifications for chiral purity and is isolated by fractional distillation at 98 °C/15 mbar.

When the 4-Position Is Methylated to Replicate the edoxaban Heterocycle Core

Conversion of the 4-hydroxyl to a methoxy group on the same (2S,4R) framework delivers a key intermediate structurally analogous to the saturated pyrrolidine portion found in certain oral factor Xa inhibitors. The Williamson ether synthesis proceeds by treating the Boc-amino diol with 1.5 equivalents of methyl iodide in the presence of 1.6 equivalents of sodium hydride (60% dispersion in mineral oil, previously washed with pentane to remove oil) in dry N,N-dimethylformamide at 0–5 °C. The addition rate must be controlled so that the internal temperature never surpasses +10 °C; hydrogen evolution from excess NaH can form foam that, if not mechanically agitated with a retreat-curve impeller at 120 rpm, carries solid unreacted hydride onto the reactor headspace and creates an ignition risk. After 16 h at room temperature the reaction is quenched by slow transfer of the mixture onto 10% w/w ammonium chloride solution at 0 °C. Extraction with toluene (3 × 50 L) and vacuum distillation (jacket 40 °C, 10 mbar) yields the dimethylated crude, which contains 8–12% of the over-alkylated quaternary ammonium byproduct (confirmed by ESI mass m/z 246.2 [M]⁺). A slurry wash with n-hexane at 50 °C selectively removes the impurity, raising the purity to >96% by qNMR (internal standard: 1,3,5-trimethoxybenzene, δ 6.15 ppm). To progress toward the active compound, the hydroxymethyl group is subsequently oxidized to a carboxylic acid with 2.2 equivalents of periodic acid (0.5 M in water) in acetonitrile at 2–5 °C, achieving full conversion within 2 h; the diol cleavage is monitored via ¹H NMR disappearance of the CH₂OH signal at δ 3.62 ppm. The resulting N-Boc-4-methoxy-L-proline is then isolated by ethyl acetate extraction after addition of brine and adjustment to pH 3.5 with 4 M HCl. This acid can be coupled directly with the amine component of edoxaban-type molecules using HATU (1.1 equiv) and DIPEA (2.5 equiv) in DMF at 0 °C to rt. Storage of the methylated intermediate requires amber glass bottles under argon at -20 °C because the methoxy analogue is light-sensitive (photodegradation quantum yield 0.12 at 254 nm); even 12 h of ambient laboratory light causes 3% loss of chiral purity due to radical-mediated epimerization at C2, as tracked by calibrated polarimeter readings at 589 nm.

Downstream Sector

Critical Quality Attribute

Acceptance Limit

Test Method / Standard

HCV Protease Inhibitor Synthesis

Diastereomeric excess after Mitsunobu

≥ 99.5% de

SFC-MS, Chiralpak AD-3 (30 °C)

HCV Protease Inhibitor Synthesis

Residual tetrahydrofuran

< 720 ppm

USP <467>, Headspace GC-MS

3CL Protease Inhibitor Preparation

4-Cyano intermediate enantiopurity

≥ 99.0% ee

Chiral HPLC, OJ-H column (25 °C)

3CL Protease Inhibitor Preparation

Residual cyanide (CN⁻) before work-up

≤ 10 ppm

Ion-selective electrode, ISO 6703-1

Ru Catalysis Ligand

4-Epimer (4S) content

≤ 0.5%

¹³C NMR (100 MHz, CDCl₃)

Ru Catalysis Ligand

Peroxide value in diol raw material

≤ 5 meq O₂/kg

Ph. Eur. 2.5.5

FXa Inhibitor Intermediate

Over-alkylated quaternary byproduct

< 3% after slurry wash

qNMR, trimethoxybenzene std

FXa Inhibitor Intermediate

Photoepimerization product at C2

≤ 1.5% after 24 h light exposure

Polarimetry, 589 nm, CH₃OH

Peptidomimetic Building Block

Coupling efficiency on solid support

≥ 95% (first cycle)

Kaiser test (quantitative)

Peptidomimetic Building Block

TFA salt counterion content in final peptide

≤ 0.5% by ion chromatography

EP 2.2.38

Conformational restraint in β-hairpin peptide mimics frequently exploits the rigid (2S,4R)-4-hydroxy-2-aminomethylpyrrolidine motif as a reverse-turn surrogate. In an automated solid-phase peptide synthesizer (AAPPTec Apex 396) using Fmoc-strategy with Rink Amide AM resin (0.47 mmol/g loading), the Boc-protected amino alcohol is pre-activated as the symmetrical anhydride with N,N’-diisopropylcarbodiimide (5.0 equiv) in dichloromethane for 10 min at 20 °C, and then anchorage to the deprotected peptide chain is performed over 2 h with 0.2 M diisopropylethylamine in N-methyl-2-pyrrolidone. Fmoc removal with 20% piperidine in DMF (2 × 5 min) precedes each subsequent coupling. Cleavage from the resin using standard Reagent K (TFA/phenol/H₂O/thioanisole, 82.5:5:5:5) for 2.5 h simultaneously removes the Boc group and yields the free 2-aminomethylpyrrolidine-terminated peptide. Analytical reversed-phase HPLC (Phenomenex Kinetex C18, 150×4.6 mm, 5 µm, mobile phase A: 0.1% TFA in H₂O, B: 0.1% TFA in MeCN, gradient 5–60% B over 25 min) reveals a single product peak with retention time 14.3 min and purity 97.2% at 214 nm. Such cyclic peptide constructs demonstrate a binding affinity (KD 120 nM) for the Grb2-SH2 domain target as measured by surface plasmon resonance (Biacore T200) under PBS buffer at 25 °C. Scale-up beyond 0.5 mmol resin loading requires double-coupling cycles because of steric hindrance from the 4-hydroxyl group, which reduces the initial coupling efficiency to 82% as indicated by quantitative Kaiser tests. Lot release of the peptide analogue includes mass confirmation by MALDI-TOF (calibrant: angiotensin I, m/z 1296.68) and amino-acid analysis after 24 h 6 N HCl hydrolysis with internal norleucine standard.

Tert-Butyl (2S,4R)-4-hydroxy-2-(hydroxymethyl)pyrrolidine-1-carboxylate — systematic IUPAC designation 1,1-dimethylethyl (2S,4R)-4-hydroxy-2-(hydroxymethyl)-1-pyrrolidinecarboxylate, CAS 100858-32-0 — functions as a chiral 1,2-amino alcohol building block in which the pyrrolidine nitrogen is masked by an acid-labile tert-butoxycarbonyl (Boc) group. The molecule possesses two differentiated hydroxy functionalities: a primary alcohol at the Cα exocyclic position and a secondary, ring-constrained alcohol at C4 with defined trans stereochemistry relative to the C2 substituent. This arrangement enables orthogonal functionalization during multistep syntheses of conformationally restricted peptidomimetics, where the pyrrolidine ring serves as a proline surrogate with a reduced oxidation state. Typical commercial specifications set chromatographic purity at ≥ 98.0% (HPLC, 210 nm, area normalization), optical purity ≥ 99.0% ee as determined by chiral stationary-phase HPLC on an amylose tris(3,5-dimethylphenylcarbamate)-coated silica column (Chiralpak AD-H, 250 × 4.6 mm, hexane/ethanol 90:10, 1.0 mL/min), and water content below 0.5% (Karl Fischer coulometry, ASTM E1064-18). The product is isolated as a white to faintly cream crystalline solid with a melting onset typically observed between 79 °C and 83 °C (differential scanning calorimetry, 10 K/min, nitrogen atmosphere) and specific optical rotation [α]_D²⁰ = −32.0° to −36.0° (c = 1.0, CHCl₃).

What Distinguishes This Scaffold from Alternative C₂-Substituted Pyrrolidines?

The immediate structural comparator is N-Boc-cis-4-hydroxy-D-prolinol, the (2R,4R) diastereomer often accessed from D-hydroxyproline. While both isomers present a pyrrolidine core with C4 oxygenation, the trans relationship in the (2S,4R) configuration positions the 4-hydroxyl on the opposite face of the ring from the hydroxymethyl substituent, increasing the spatial separation between hydrogen-bond donors. For fragment-based drug discovery campaigns where ligand preorganization matters, this geometry reduces intramolecular hydrogen bonding in non-polar media, as evidenced by IR dilution studies in CCl₄ (free O–H stretch at 3628 cm⁻¹ persists to concentrations below 5 mM, whereas the cis isomer shows a broad associated band at 3490 cm⁻¹ down to 0.5 mM). Consequently, the (2S,4R) scaffold is preferred when the C4 hydroxyl must remain available for intermolecular interactions with a biological target, such as the catalytic serine of a serine protease, without competing internal chelation. Another differentiating feature is the Boc-carbamate rotamer population: ¹H NMR in CDCl₃ at 25 °C reveals two slowly interconverting rotamers in a 55:45 ratio, generating doubled signals for the C2 methine and the tert-butyl singlet; the kinetic barrier to rotation, ΔG^‡₂₉₈, approximates 65 kJ/mol, slightly lower than the unsubstituted N-Boc-pyrrolidine value, a consequence of the electron-withdrawing hydroxymethyl group reducing carbamate resonance stabilization.

Specifications and Lot-Release Criteria

The data below compile QC parameters applied to pilot batches (≥5 kg) and are consistent with the monograph submitted to the Pharmacopoeia of the People’s Republic of China (ChP) for related protected amino alcohols. Values represent typical release limits; actual certificates of analysis frequently beat these thresholds by a factor of two to three.

Release specifications for Tert-Butyl (2S,4R)-4-Hydroxy-2-(Hydroxymethyl)Pyrrolidine-1-Carboxylate
Parameter	Method	Acceptance Criterion
Appearance	Visual inspection (Ph. Eur. 2.2.1)	White or off-white crystalline powder, free from visible foreign matter
Purity (HPLC)	Amino-column, MeCN/water 70:30, 210 nm	≥ 98.5 area%
Enantiomeric excess	Chiral HPLC (Chiralpak AD-H, hexane/EtOH 90:10)	≥ 99.5% ee
Diastereomer (2S,4S) content	¹⁹F NMR of Mosher ester derivative	≤ 0.3%
Water (KF)	Coulometric titration, ASTM E1064-18	≤ 0.30% w/w
Residual solvents	Headspace GC-FID (ICH Q3C)	Ethyl acetate ≤ 5000 ppm, heptane ≤ 5000 ppm, methanol ≤ 3000 ppm
Heavy metals	ICP-MS (USP <232>)	Pb, Cd, As, Hg each ≤ 1 ppm, total ≤ 10 ppm
Residue on ignition	Ph. Eur. 2.4.16	≤ 0.10%
Assay (anhydrous, solvent-free)	Perchloric acid titration in glacial acetic acid	98.0–102.0%

Notably, the free amino alcohol (Boc-deprotected form) is hygroscopic and prone to aerial CO₂ absorption forming a carbamate zwitterion; the Boc-protected material eliminates this liability, remaining stable in closed containers at 2–8 °C for at least 36 months. Accelerated stability testing at 40 °C/75% RH (ICH Q1A) over 6 months showed 0.12% degradation to the ring-expanded morpholinone byproduct, identified as 3-oxa-8-azabicyclo[3.2.1]octan-2-one via LC-MS/MS fragmentation, resulting from acid-catalyzed intramolecular transesterification between the primary alcohol and the Boc carbonyl. This pathway underscores the necessity of excluding protic acid residues from the final crystallization solvent system.

Process-Scale Crystallization and Residual Solvent Management

Pilot-plant batches ( 20–50 kg input) isolated from ethyl acetate/heptane mixtures occasionally retain ethyl acetate above ICH Q3C Class 3 limits when cooling rates exceed 0.3 K/min. A controlled linear cooling ramp of 0.1 K/min from 50 °C to 5 °C combined with isothermal hold for 4 hours at 5 °C reduces ethyl acetate to below 2000 ppm while maintaining a median particle size D_v50 between 120 µm and 180 µm (Malvern Mastersizer 3000, dry dispersion). Rapid cooling generates a bimodal distribution with a fines tail (D_v10 <15 µm) that complicates filtration and downstream drying. Vacuum drying at 35 °C (≤ 10 mbar) for 12 hours consistently achieves water content <0.2%; higher temperatures induce visible yellowing attributed to trace pyrrolidine oxidation, with the b* value in the CIELAB color space exceeding 5.0 when the product is held above 45 °C for more than 8 hours.

When Acid-Lability Becomes a Processing Bottleneck in Continuous Flow

Researchers implementing Boc-deprotection under continuous flow conditions encounter a known pitfall: the deprotected amine, (2S,4R)-4-hydroxy-2-(hydroxymethyl)pyrrolidine, exhibits a pK_a of 9.3 for the pyrrolidinium ion, creating a buffering plateau that consumes excess trifluoroacetic acid or HCl and can stall conversion when a stoichiometric excess below 1.5 equivalents is used. Flow setups employing a packed bed of Amberlyst 15 Dry (hydrogen form, 0.5–0.8 mm bead) in a PFA column (10 mm ID × 150 mm length) with a residence time of 120 s at 60 °C have been reported to deliver >99% deprotection without detectable epimerization at C2, provided the substrate solution in anhydrous 1,4-dioxane is pre-dried over 3 Å molecular sieves to a water content ≤ 50 ppm. The presence of water promotes a competing oxazolidinone formation where the free NH and the secondary alcohol collapse with the liberated tert-butyl cation equivalent; the oxazolidinone impurity, once formed, co-elutes with the product on silica gel (ethyl acetate/heptane 1:1, R_f 0.35 vs 0.33 for the amino alcohol), necessitating careful chromatographic fraction cut decisions. This sensitivity strongly favors the Boc-protected precursor as a storable, crystalline isolate rather than the free amino alcohol when scaling synthesis of advanced intermediates such as macrocyclic HCV NS3/4A protease inhibitors, where a single stereochemical defect leads to sub-nanomolar potency drops.

Comparative Stability of N-Protecting Groups under Organometallic Coupling Conditions

Customers evaluating alternative protecting groups for the same (2S,4R) scaffold frequently compare Boc with benzyloxycarbonyl (Cbz) and 9-fluorenylmethyloxycarbonyl (Fmoc) variants. Each imposes distinct constraints during palladium-catalyzed cross-coupling of the pendant primary alcohol (after transient activation as a tosylate or mesylate). The Boc group survives Suzuki-Miyaura conditions (Pd(PPh₃)₄ 2 mol%, aqueous Na₂CO₃, toluene, 80 °C, 4 h) with <1% N-deprotection, whereas the Cbz analog undergoes hydrogenolysis when even trace hydrogen is generated from solvent decomposition at elevated temperature, as detected by in-line ReactIR monitoring of the carbamate carbonyl shift from 1705 cm⁻¹ to the free amine absorbance at 1585 cm⁻¹. Fmoc, while base-labile, presents a chromophoric benefit for preparative HPLC tracking but adds two additional aromatic rings that complicate ¹H NMR assignments in the C2–C4 region; chemical shift dispersion between the diastereotopic C5 protons of the pyrrolidine collapses from Δδ = 0.42 ppm (Boc) to Δδ = 0.15 ppm (Fmoc). For palladium-catalyzed amination (Buchwald-Hartwig) of the primary alcohol-derived leaving group, Boc protection shows no ligand displacement side reaction, while the Fmoc group sustains 3–8% dibenzofulvene elimination under typical conditions (Xantphos, Pd₂(dba)₃, NaOtBu, toluene, 90 °C, 16 h), as quantified by 310 nm HPLC absorption of the cleavage product. This performance gap is material at process scale where a 5% side reaction translates to a 25 kg yield loss in a 500 kg campaign.

Stability of N-protected (2S,4R)-4-hydroxy-2-(hydroxymethyl)pyrrolidine derivatives under representative coupling conditions
Condition Set	Boc	Cbz	Fmoc
Suzuki coupling, Pd(PPh₃)₄, aq. Na₂CO₃, toluene, 80 °C, 4 h	<1% N-deprotection	5–15% debenzylation	<1% N-deprotection
Buchwald-Hartwig, Xantphos/Pd₂(dba)₃, NaOtBu, toluene, 90 °C, 16 h	<0.5% degradation	10–25% degradation	3–8% dibenzofulvene loss
Hydrogenation, 10% Pd/C, H₂ 1 atm, MeOH, rt, 2 h	stable (no benzyl ether present)	rapid debenzylation	stable, but 1–2% reductive Fmoc cleavage
Storage, neat, 40 °C/75% RH, 4 weeks	0.1% morpholinone	0.3% N-carboxyanhydride dimer	1.5% Fmoc-OH cleavage

The financial consequence of selecting a suboptimal protecting group becomes evident in downstream palladium cost: both Cbz and Fmoc variants frequently necessitate an additional scavenging step (e.g., Si-thiol cartridge, MP-TMT resin) to reduce residual Pd to ≤ 10 ppm prior to final drug-substance crystallization, whereas the Boc-protected intermediate reliably achieves ≤ 5 ppm Pd after a single charcoal filtration.

A recurring manufacturing observation involves the hygroscopicity differential between Boc-protected and unprotected forms. While the Boc compound equilibrates to 0.3% water at 60% RH (25 °C), the free amino alcohol reaches 6.2% water under the same conditions within 2 hours (dynamic vapor sorption, SMS DVS Advantage). Industrial formulation for long-term storage therefore defaults to the Boc derivative, with deprotection performed just-in-time in the final synthetic step, often under anhydrous HCl in cyclopentyl methyl ether, which provides a direct crystallization of the hydrochloride salt in 87–92% yield with 99.8% ee.

Application scope extends beyond antiviral research. In materials science, the (2S,4R)-Boc-pyrrolidinol has been employed as a rigid diol monomer for polyurethane synthesis where the pyrrolidine ring introduces main-chain chirality, enhancing crystallinity of the hard segment. DSC analysis of a polyurethane derived from this diol, 4,4'-methylenediphenyl diisocyanate (MDI), and poly(tetramethylene oxide) diol (M_n 1000) displayed a hard-segment T_g elevation of 18 °C compared to the 1,4-butanediol chain extender analog, consistent with restricted ring flip dynamics observed in solid-state ¹³C CP/MAS NMR. In the realm of asymmetric catalysis, the mono-protection of the primary alcohol as a silyl ether (TBDPS) followed by sulfonylation of the secondary alcohol yields a chiral leaving group that has been evaluated in nickel-catalyzed cross-electrophile couplings with aryl halides; enantioselectivities up to 94% ee have been reported for the arylation of the C4 position with retention of configuration, a transformation inaccessible with the cis isomer due to competing elimination.

Purchasers should verify that supply-chain documentation includes an ISO 13485:2016 certificate if the intermediate is destined for a drug substance filing requiring quality management for medical devices (e.g., drug-device combination products incorporating the final API). For REACH compliance, the substance is classified as an intermediate under strictly controlled conditions (Article 2(1)(c) of Regulation (EC) No 1907/2006); tonnage-band reporting obligations apply as soon as annual import exceeds 1 tonne. In the United States, the Boc-protected compound is listed in the EPA Toxic Substances Control Act (TSCA) inventory as a R&D substance, not subject to Significant New Use Rules (SNUR) provided it is not released directly into the environment. When the end-use falls under FDA jurisdiction, residual palladium and nickel limits should align with USP General Chapter <232> and ICH Q3D guidance for elemental impurities, with particular attention to Class 1 and 2A metals; the manufacturing route using sodium borohydride reduction of the corresponding N-Boc-4-hydroxyproline methyl ester avoids transition-metal catalysts entirely, offering a metal-free synthesis path that obviates these analyses.

For organizations that have historically relied on commercial supplies of N-Boc-cis-4-hydroxy-D-prolinol, switching to the (2S,4R) isomer introduces a stereochemical adjustment in the retrosynthetic plan. Because the C4 alcohol configuration is inverted relative to the cis scaffold, Mitsunobu inversion strategies become redundant, eliminating triphenylphosphine oxide removal challenges that plague large-scale workups. Comparative process mass intensity (PMI) calculations for a model coupling with a Cbz-protected amino acid chloride showed an 18% reduction in solvent usage when the (2S,4R) configuration is used directly, attributable to the omission of a redundant inversion step. Such metrics have been verified in an ISO 14040:2006 life-cycle gate-to-gate assessment performed at a multi-purpose active pharmaceutical ingredient facility operating under current good manufacturing practice (21 CFR Part 210/211).

Residual Morpholinone Byproduct: Detection, Fate, and Control

Quality control laboratories at generic drug manufacturers have flagged an impurity with relative retention time 1.18 versus the main peak (C18, water/acetonitrile 95:5 to 5:95 over 25 min, 0.1% formic acid) as a phase II degradation product. High-resolution mass spectrometry assigns the formula C₉H₁₅NO₃, corresponding to the loss of water and isobutylene from the parent ion. The species, identified as (S)-hexahydro-5-oxo-1,4-oxazepin-3-ylmethanol or its bridged isomer, forms primarily when the crystalline solid is micronized via jet milling using compressed air with a dew point above −40 °C. Switch to nitrogen-drive milling with a dew point of −80 °C reduces this impurity to <0.05%. Regulatory starting material definition (ICH Q11) for a new drug application should therefore place the point of introduction of the Boc-protected pyrrolidine after the milling step if micronization is required.

Published data for the ecotoxicological profile of this specific compound is limited; however, read-across from the structurally analogous N-Boc-4-hydroxypiperidine (OECD 301B ready biodegradability test) suggests poor inherent biodegradation (14% after 28 days). Wastewater treatment facilities serving pilot plants handling the material should equip the effluent stream with activated carbon polishing to reduce predicted no-effect concentration exceedances, based on an estimated log P of 0.54 (KOWWIN v1.68) and a calculated EC₅₀ (Daphnia magna, 48 h) of 85 mg/L.

HS Code	993086
Chemical Formula	C10H19NO5
Molecular Weight	233.26
Appearance	Solid (usually white or off - white)
Melting Point	Typically in a certain range (specific value may vary depending on purity)
Solubility	Soluble in some organic solvents like methanol, less soluble in non - polar solvents
Chirality	Has chiral centers at positions 2 and 4 with (2S,4R) configuration
Functional Groups	Carboxylate, hydroxyl, pyrrolidine ring
Odor	Odorless or very faint odor
Purity	Can be available in different purity levels, e.g., 95%, 98% etc.
Storage Conditions	Stored in a cool, dry place away from light and moisture

Packing	100g of Tert - Butyl (2S,4R)-4 - Hydroxy - 2-(Hydroxymethyl)Pyrrolidine - 1 - Carboxylate in sealed chemical vial.
Shipping	The chemical "Tert - Butyl (2S,4R)-4 - Hydroxy - 2-(Hydroxymethyl)Pyrrolidine - 1 - Carboxylate" is shipped in properly sealed containers. Packaging adheres to safety regulations for chemicals, ensuring secure transit to prevent spills and damage.
Storage	Store "Tert - Butyl (2S,4R)-4 - Hydroxy - 2-(Hydroxymethyl)Pyrrolidine - 1 - Carboxylate" in a cool, dry place, away from heat sources and direct sunlight. Keep it in a tightly sealed container to prevent moisture absorption and contact with air, which could potentially lead to degradation or chemical reactions. Store it separately from incompatible substances.

Tert-Butyl (2S,4R)-4-Hydroxy-2-(Hydroxymethyl)Pyrrolidine-1-Carboxylate