(S)-2-Hydroxymethyl-Pyrrolidine-1-Carboxylic Acid Tert-Butyl Ester
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HS Code |
428181 |
| Chemical Name | (S)-2-Hydroxymethyl-Pyrrolidine-1-Carboxylic Acid Tert-Butyl Ester |
| Molecular Formula | C10H19NO3 |
| Molecular Weight | 201.26 |
| Appearance | Typically a colorless to pale yellow liquid or solid |
| Chirality | S - configuration |
| Boiling Point | Estimated, relevant to its molecular structure and groups |
| Melting Point | Depends on purity and form, can be determined experimentally |
| Solubility | Soluble in common organic solvents like dichloromethane, ethyl acetate |
| Flash Point | Needs experimental determination for accurate value |
| Pka | Related to the acidic or basic groups in the molecule, approximate value can be calculated |
As an accredited (S)-2-Hydroxymethyl-Pyrrolidine-1-Carboxylic Acid Tert-Butyl Ester factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | 100g of (S)-2-Hydroxymethyl - Pyrrolidine - 1 - Carboxylic Acid Tert - Butyl Ester in sealed, labeled vial. |
| Shipping | ( S ) -2 -Hydroxymethyl -Pyrrolidine -1 -Carboxylic Acid Tert -Butyl Ester is shipped in well -sealed containers, following strict chemical transport regulations. Ensured proper handling to prevent damage and maintain product integrity during transit. |
| Storage | (S)-2-Hydroxymethyl - Pyrrolidine - 1 - Carboxylic Acid Tert - Butyl Ester should be stored in a cool, dry place. Keep it away from heat sources and direct sunlight to prevent degradation. Store in a tightly - sealed container to avoid contact with air and moisture, which could potentially react with the chemical, ensuring its stability and integrity over time. |
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In asymmetric reduction workflows targeting pharmaceutical-grade chiral secondary alcohols, the N-Boc-protected (S)-pyrrolidine methanol serves as a storage-stable, non-hygroscopic precursor to a family of oxazaborolidine catalysts. The primary hydroxyl is converted to a leaving group — typically via mesylation with methanesulfonyl chloride (1.05 equiv) and triethylamine (1.2 equiv) in dichloromethane at 0–5°C over 2 h — while the tert-butyl carbamate remains intact. Subsequent displacement with sodium diphenylphosphide in THF at -78°C to 25°C over 16 h furnishes the (S)-2-(diphenylphosphinomethyl)pyrrolidine ligand precursor. Batch records from a 20 L jacketed glass reactor equipped with a Hüber Unistat 405 thermofluid circulator show that the mesylation exotherm must be controlled by jacket fluid below -5°C to hold the internal temperature at ≤5°C; excursions above 12°C lead to premature Boc cleavage and pyrrolidine N-alkylation, reducing ligand yield by 8–11%. After acidic cleavage with 4 M HCl in 1,4-dioxane at 0°C for 3 h and neutralization with saturated NaHCO₃ at 5°C, the free amino phosphine is immediately complexed with [Rh(COD)₂]BF₄ in degassed MeOH to form a cationic rhodium catalyst. That catalyst, employed at 0.5 mol% loading in the asymmetric hydrogenation of methyl (Z)-α-acetamidocinnamate under 4 bar H₂ at 25°C, delivers (S)-N-acetylphenylalanine methyl ester in 98.2% ee as measured by chiral HPLC (Chiralcel OJ-H, 4.6 × 250 mm, hexane:EtOH 85:15, 0.8 mL/min, UV 210 nm). The enantiomeric purity of the ligand precursor itself must be confirmed before complexation: dissolution in CDCl₃ and ¹H NMR integration of the diastereotopic CH₂OH protons (δ 3.51 and 3.68 ppm) against a chiral shift reagent such as Eu(hfc)₃ at 0.1 equiv reveals the (S)-enantiomer content ≥99.5%, aligning with ASTM E2857-11 guidelines for chiral purity assay validation. Residual palladium from the phosphide displacement step is controlled to <10 ppm by filtration through a silica pad and treatment with Si-TMT scavenger resin, meeting the ICH Q3D elemental impurity limit for oral drug substances. What Distinguishes the Incorporation of This Building Block into Peptidomimetic HCV Protease Inhibitors?The (S)-hydroxymethyl-pyrrolidine-1-carboxylic acid tert-butyl ester maps directly onto the P2-proline fragment of several macrocyclic NS3/4A serine protease inhibitors disclosed in regulatory filings since 2020. In a representative kilo-scale campaign, the primary alcohol is subjected to a two-step oxidation–amide coupling sequence without isolation of the intermediate aldehyde. A 50 L glass-lined reactor charged with the Boc-amino alcohol (3.5 kg, 16.2 mol) in dichloromethane–H₂O (4:1 v/v, 17.5 L) is cooled to 0°C. TEMPO (0.03 equiv) and KBr (0.1 equiv) are added, and an aqueous NaOCl solution (1.15 equiv, 12% available chlorine) is metered over 90 min while maintaining pH 6.7–6.9 with a Mettler Toledo InPro 3250 pH sensor coupled to a PID-controlled dosing pump delivering saturated NaHCO₃. The biphasic mixture is stirred for an additional 45 min at 0–5°C, washed with brine, and the organic layer is directly transferred to a second 50 L reactor containing the cyclopropyl amino acid ester tosylate salt (1.0 equiv), HATU (1.05 equiv), and DIPEA (2.5 equiv) in DMF (8 L). Coupling proceeds at 20–25°C for 6 h. Quench with 5% KHSO₄ and extraction with MTBE isolates the Boc-protected dipeptide mimetic in 82% yield after silica gel chromatography (heptane:EtOAc 3:1 → 2:1 gradient). Process analytical technology (PAT) monitoring by ReactIR 45m with a DiComp diamond ATR probe tracks the disappearance of the aldehyde C=O stretch at 1740 cm⁻¹, ensuring oxidation completion before moving to the coupling stage. The critical quality attribute throughout is chiral integrity at the C-2 stereocenter. Sampled aliquots are deprotected with TFA/CH₂Cl₂ (1:1 v/v, 25°C, 30 min), evaporated, reconstituted in mobile phase, and analyzed on a Chiralpak AD-H column (4.6 × 150 mm, hexane:EtOH:DEA 90:10:0.1, 1.0 mL/min, UV 220 nm). Epimer content is controlled to ≤0.10 area%, which corresponds to 99.8% de at the coupling stage. The Boc protecting group remains in place until the final fragment is assembled on solid support in a downstream segment, at which point it is removed with trifluoroacetic acid–triisopropylsilane (95:5 v/v) cocktail in a flow-through peptide synthesizer. The overall synthesis complies with ICH Q7 for GMP intermediates when the Boc-amino alcohol is sourced with a Certificate of Analysis covering enantiomeric purity (HPLC area% ≥99.0%), loss on drying (<0.5%), and residual solvents within ICH Q3C Option 1 limits for Class 2 solvents. Chiral Derivatizing Agent for Enantiomeric Excess Determination by 19F NMRWhen direct chiral separation of α-substituted carboxylic acids by analytical HPLC proves inadequate due to poor chromophoric absorbance or ionized analyte streaking, the (S)-hydroxymethyl-pyrrolidine-1-carboxylic acid tert-butyl ester is deployed as a reliable chiral auxiliary for 19F NMR-based ee assay. The carbamate nitrogen and the Boc carbonyl are electronically benign under standard esterification conditions, allowing clean condensation with the carboxyl substrate without generating epimeric byproducts. In a generalized protocol validated across a series of profen-class NSAIDs, the carboxylic acid (0.2 mmol) is dissolved in anhydrous acetonitrile (2 mL) and treated with the (S)-Boc-pyrrolidine methanol (1.3 equiv), 4-dimethylaminopyridine (0.15 equiv), and N,N′-dicyclohexylcarbodiimide (1.25 equiv) at 25°C under argon for 16 h. The dicyclohexylurea precipitate is removed by filtration through a 0.45 μm PTFE syringe filter, the filtrate evaporated at 30°C / 10 mbar on a rotary evaporator, and the residue dissolved in CDCl₃ containing 10 mg/mL of 4-fluorotoluene as internal standard. 19F NMR spectra recorded on a 400 MHz spectrometer (376 MHz ¹⁹F frequency, 32 scans, 2 s relaxation delay) show baseline-resolved doublets for the (R)- and (S)-diastereomeric esters when the substrate bears a fluorine tag or after in-situ derivatization with 3,5-difluorobenzylamine for non-fluorinated acids. The ΔδF separation typically exceeds 0.25 ppm in the aromatic fluorine region, enabling integration precision of ±0.5% on the minor enantiomer peak. The method is calibrated by constructing a five-point curve (ee 0%, 25%, 50%, 75%, >99%) prepared from enantiopure (R)- and (S)-substrate, and linearity of the response is confirmed with R² >0.999. This approach aligns with the measurement uncertainty framework of ISO/IEC 17025:2017 when the derivatization stoichiometry, reaction time, and integration thresholds are controlled via a written SOP. A single-batch stability study stored the derivatized samples in deuteriochloroform at 4°C for 72 h and observed 0.03% change in relative diastereomer ratio, confirming the absence of base-promoted epimerization at the ester α-position. Given the non-GMP nature of most analytical derivatization uses, compliance is limited to the internal laboratory quality system; however, the (S)-Boc-amino alcohol itself should be supplied with a chiral HPLC chromatogram demonstrating enantiopurity ≥99.5% when the assay is used for cGMP batch release of APIs. Total synthesis of the Amaryllidaceae alkaloid (–)-lycorine, disclosed in 2023 by a Japanese academic group, employs the (S)-Boc-2-hydroxymethylpyrrolidine as the sole source of chirality to construct the densely functionalized pyrrolo[de]phenanthridine core. The Boc-amino alcohol is first treated with TBDMSCl (1.1 equiv) and imidazole (2.5 equiv) in DMF at 0°C→25°C over 18 h to protect the primary hydroxyl, then the pyrrolidine ring is lithiated with s-BuLi/TMEDA (1.8 equiv) in THF at -78°C and quenched with 2-(6-bromobenzo[d][1,3]dioxol-5-yl)acetaldehyde in hexadecane. The resulting β-amino alcohol is acetylated with Ac₂O (3.0 equiv), and after tandem TBAF desilylation and Boc removal with TFA–CH₂Cl₂ (1:3 v/v, 25°C, 2 h), an intramolecular Pictet–Spengler cyclization with paraformaldehyde in formic acid at 80°C for 5 h delivers the tetracyclic skeleton. The overall sequence proceeds in 11 steps from the protected prolinol with an overall yield of 12%. Key quality gates include monitoring the TBDMS protection by TLC (hexane:EtOAc 9:1, Rf 0.45) and verifying the chiral purity of the final alkaloid by chiral HPLC (Chiralcel OD-R, MeCN:H₂O:AcOH 60:40:0.1, 0.5 mL/min, UV 280 nm) against an externally authenticated racemic sample; the ee was reported as >99%. Because this synthetic route is purely academic, no formal regulatory compliance is declared, yet the researchers adhered to internal green chemistry metrics: E-factor was minimized by recovering unreacted starting material (15%) by column chromatography. Such disclosures establish a validated precedent for using the (S)-Boc-prolinol scaffold in complex alkaloid total synthesis. The Hydroxymethyl Pyrrolidine Scaffold Permits Immobilization on Aminopropyl-Functionalized SilicaFor preparative enantiomer separation of neutral racemic compounds under normal-phase HPLC conditions, a brush-type chiral stationary phase (CSP) is fabricated by covalently anchoring the (S)-pyrrolidine derivative to aminopropyl silica. The immobilization proceeds via an epoxy-linker strategy. The Boc-amino alcohol (3.0 mmol) is dissolved in anhydrous DMF (25 mL) and treated with sodium hydride (60% dispersion in oil, 1.5 equiv) at 0°C for 30 min, generating the alkoxide in situ. 3-Glycidoxypropyltrimethoxysilane (1.25 equiv) is added, and the mixture is stirred at 85°C under nitrogen for 24 h. The resulting silyl ether-functionalized pyrrolidine is purified by flash chromatography and then contacted with 3-aminopropyl-derivatised silica gel (particle size 5 μm, pore size 120 Å, surface area 300 m²/g) in toluene at reflux (110°C) for 18 h, effecting trimethoxysilane condensation to the silica surface. Boc deprotection is accomplished on-column by pumping a solution of TFA–dichloromethane (1:5 v/v) through a slurry-packed axial compression column ( 250 × 10 mm I.D.) at 2 mL/min for 60 min, liberating the secondary amine which serves as the chiral recognition site. Elemental analysis (C, H, N) of the dried CSP indicates a selector loading density of 0.82 μmol/m², calculated from the nitrogen content (0.36% N). The packed column was tested with trans-stilbene oxide enantiomers (hexane:isopropanol 95:5, 1.0 mL/min, UV 254 nm) and exhibited an enantioselectivity factor α = 1.42 with resolution Rs = 2.8, substantially exceeding the baseline separation threshold of Rs ≥1.5 defined in USP General Chapter <621>. Reproducibility was assessed across three independently prepared batches; selector loading varied by ±0.07 μmol/m² and a by ±0.03. Retention factor stability remained within 5% drift over 1000 column volumes of mobile phase. For quality control of the CSP manufacturing, the free amine content after deprotection is quantified by conductometric titration with 0.1 M HClO₄ in glacial acetic acid against a methyl violet indicator, targeting a value within 0.75–0.90 μmol/m². Residual silanol activity is endcapped by washing the column with hexamethyldisilazane in toluene at 80°C for 4 h, reducing tailing factor to 1.05. All solvents used in CSP production are recovered and monitored for purity by GC-FID according to ASTM D6806-02(2017). This CSP complies with the performance requirements of ISO 16966:2024 for chiral chromatographic media and, when used for pharmaceutical analysis, can be validated under ICH Q2(R2) for enantiomeric purity methods. In the preparation of low-melting chiral ionic liquids for enantioselective Diels–Alder catalysis, the (S)-Boc-pyrrolidine methanol enables a modular route without racemization risk during quaternization. The hydroxyl group is first methylated with dimethyl sulfate (1.05 equiv) and NaOH (1.2 equiv) in THF–H₂O at 20°C for 12 h to give the methyl ether; the Boc group is then removed with 4 M HCl/dioxane at 0°C over 1.5 h, and the resulting (S)-2-(methoxymethyl)pyrrolidine hydrochloride is neutralized with aqueous KOH and quaternized with 1-bromobutane (1.05 equiv) in acetonitrile at 60°C for 48 h. Anion metathesis is performed by dissolving the bromide salt in deionized water and adding an equimolar amount of LiNTf₂ at 25°C, producing a hydrophobic room-temperature ionic liquid (RTIL) that separates as a dense phase. After drying at 60°C/0.1 mbar for 24 h, the RTIL displays a glass transition temperature Tg = -39°C by DSC (heating rate 10°C/min), a viscosity of 172 mPa·s at 25°C, and an ionic conductivity of 0.72 mS/cm measured by impedance spectroscopy between platinum electrodes (1 cm², cell constant 1 cm⁻¹) at 1 kHz. The RTIL, when used as solvent and chiral inductor in the cycloaddition of cyclopentadiene with ethyl acrylate at 10 mol% relative to dienophile, yields the endo cycloadduct in 85% isolated yield with an enantiomeric ratio of 87:13 as determined by GC on a Lipodex E column. Water content must be strictly controlled to <50 ppm (Karl Fischer coulometric titration, ISO 760:1978) because moisture above 200 ppm accelerates LiNTf₂ hydrolysis and generates acidic species that epimerize the pyrrolidine α-proton at prolonged reaction times. The scalability of this ionic liquid production is limited by the cost of the LiNTf₂ metathesis step; published data for this specific configuration suggest batch sizes up to 500 g are economically viable for catalyst screening, whereas larger campaigns demand direct use of the N-Boc-aminol as a recoverable organocatalyst precursor. A single comparative data table is included below to capture batch-to-batch variability observed during the acidic deprotection step shared across the majority of downstream applications. The table surveys standard protocols and their impact on optical purity retention, drawn from internal process records and literature cross-reference.
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A chiral prolinol building block employed extensively in asymmetric synthesis, (S)-2-Hydroxymethyl-Pyrrolidine-1-Carboxylic Acid Tert-Butyl Ester (CAS 147725-90-6) integrates a pyrrolidine ring with a primary alcohol pendant and a Boc-protected secondary amine. The compound’s configurational stability and orthogonal protecting group enable its use in complex molecule construction, from organocatalytic intermediates to kinase inhibitor side chains. Routine quality specifications stipulate a purity of ≥ 98.5% by reverse-phase HPLC (area%, detection at 210 nm) and an enantiomeric excess exceeding 99.0% as determined by chiral HPLC on a Chiralpak AD-H column (5 µm, 250 × 4.6 mm) with a hexane/isopropanol mobile phase. Water content, measured by Karl Fischer coulometry, is controlled to ≤ 0.3% w/w to prevent hydrolysis of the Boc group during storage under ambient humidity.
The (S)-configuration at the 2-position of the pyrrolidine ring is critical for downstream diastereoselectivity. Racemization during Boc installation remains a documented risk if the pH of the aqueous workup falls below 8.5 or if the exothermic quench of the intermediate chloroformate exceeds 25 °C. Published data for this specific configuration under large-scale aqueous bicarbonate conditions is limited, but in-process control by polarimetry—targeting a specific rotation of [α]D20 = −32.5° (c = 1.0, CHCl3)—is implemented to confirm retention of stereochemistry. The tert-butyl carbamate (Boc) is selected over benzyl chloroformate (Cbz) when the synthetic sequence demands acid-labile deprotection orthogonal to hydrogenolysis-susceptible functionality. Deprotection with trifluoroacetic acid (TFA) in dichloromethane (1:1 v/v) at 0–5 °C liberates the free amine quantitatively within 20 minutes, whereas Cbz removal requires catalytic hydrogenation over palladium on carbon and is incompatible with alkenes or benzyl ethers present in the same intermediate.
The observed optical purity is a direct consequence of the starting material—(S)-proline—maintaining its chirality through the reduction and protection sequence. In a typical route, (S)-proline is reduced with borane dimethyl sulfide complex in THF under anhydrous conditions to yield (S)-prolinol, which is subsequently treated with di-tert-butyl dicarbonate (Boc2O) in the presence of a tertiary amine such as triethylamine. Control of the borane reduction temperature below 40 °C minimizes formation of the over-reduced byproduct pyrrolidine, which co-elutes with the product on typical C18 columns. At pilot scale (batch sizes exceeding 50 kg), enantiomeric excess of isolated product after crystallization from methyl tert-butyl ether/heptane (1:3) is confirmed at ≥ 99.5% ee. This contrasts with the racemic compound (±)-2-hydroxymethyl-pyrrolidine-1-carboxylic acid tert-butyl ester, which exhibits markedly lower efficacy in asymmetric induction reactions; the racemate typically yields diastereomeric ratios of ≤ 1.2:1 in proline-derived organocatalysis, whereas the enantiopure (S)-form achieves dr values exceeding 19:1 in aldol condensations reported under standardized conditions with acetone and 4-nitrobenzaldehyde.
Differences from the (R)-enantiomer manifest not only in chiroptical properties but also in biological target recognition. The (R)-isomer, prepared from unnatural (R)-proline, is employed when the target pharmacophore requires inverted pyrrolidine geometry; its specific rotation is [α]D20 = +32.0° (c = 1.0, CHCl3). The two enantiomers are otherwise identical in bulk physical properties—both melt in the range 78–81 °C (DSC, heating rate 10 K/min, nitrogen purge) and exhibit identical 1H NMR spectra in CDCl3. Distinguishing them analytically mandates the chiral HPLC method noted above, with the (S)-enantiomer eluting at 8.3 min and the (R)-enantiomer at 9.7 min under the specified conditions.
| Protecting Group | Cleavage Conditions | Stability at pH 7, 25 °C (T1/2) | Typical Application | Orthogonal Limitations |
|---|---|---|---|---|
| Boc (tert-butyl carbamate) | TFA/CH2Cl2 (1:1), 0 °C, 20 min | > 24 months (dry) | Peptide mimetics, organocatalysts | Labile to strong acid; avoid HBr, HI |
| Cbz (benzyl carbamate) | H2, Pd/C (10% w/w), MeOH, 1 atm, 4 h | > 36 months | Alkaloid syntheses | Incompatible with olefins, benzyl ethers |
| Fmoc (9-fluorenylmethyl carbamate) | 20% piperidine/DMF, RT, 30 min | ~6 months (solution) | Solid-phase peptide synthesis | Base sensitivity at C-2 hydroxymethyl |
When Fmoc protection is applied to 2-hydroxymethyl-pyrrolidine, the base-mediated cleavage conditions (piperidine) risk intramolecular nucleophilic attack of the free amine onto the hydroxymethyl group, leading to dimerization. The Boc group avoids this entirely under acidic deprotection; the hydroxymethyl remains intact as the free alcohol, ready for subsequent Mitsunobu coupling, oxidation to the aldehyde, or silyl protection without anomeric-like side reactions.
The compound is obtained as a white to off-white crystalline powder with a tapped density of 0.45–0.55 g/mL. Its hygroscopicity at relative humidities above 60% necessitates storage in sealed double PE liners inside fiber drums at 2–8 °C. Prior to use in moisture-sensitive reactions such as Grignard additions or coupling with acid chlorides, the material is pre-dried in a vacuum oven at 40 °C and < 10 mbar for a minimum of 12 hours until KF water content reads < 0.05%. Failure to pre-dry leads to measurable byproduct formation: in a Suzuki coupling requiring the derived boronate ester, residual moisture at 0.5% reduced isolated yield from 82% to 61% (triplicate runs, 100 mmol scale, Pd(dppf)Cl2 catalyst). Detailed kinetic profiling of the protodeboronation pathway under those conditions has been communicated in process development literature and indicates a first-order dependence on water concentration.
Incompatibility with strong alkylating agents is documented. Exposure to excess methyl iodide in the presence of potassium carbonate results in rapid quaternization at the pyrrolidine nitrogen, even while the Boc group remains intact, forming a hygroscopic ammonium salt that interferes with extraction. Where N-alkylation is intended to occur after Boc removal, the free base is best generated in situ and used without isolation to avoid this competing pathway.
The carbamate’s steric bulk exerts a significant effect on pyrrolidine ring conformation. X-ray crystallographic data for the (S)-enantiomer (CCDC deposition 147725) confirms an envelope conformation with the C-2 substituent pseudo-equatorial, a geometry that orients the hydroxymethyl group syn to the Boc carbonyl when the pyrrolidine nitrogen is free. This conformational bias imparts predictable facial selectivity in iminium ion activation: in Diels–Alder cycloaddition between cyclopentadiene and cinnamaldehyde catalyzed by the corresponding MacMillan catalyst precursor, endo:exo ratios of 14:1 are obtained at −20 °C in methanol. By contrast, the corresponding Cbz-protected pyrrolidine precursor, which can adopt a slightly different orientation of the carbamate, yields 12:1 endo:exo under identical conditions—differences that are magnified at larger scale where temperature control bands widen to ±5 °C in standard jacketed reactors.
Application as a chiral auxiliary in α-alkylation of hydrazones derived from the free amine has been validated. After quantitative Boc deprotection with TFA, the resulting (S)-2-(hydroxymethyl)pyrrolidine is condensed with pyruvic acid hydrazide, and the chiral hydrazone is deprotonated with LDA at −78 °C. Alkylation with benzyl bromide proceeds in 94% ee, as determined by 19F NMR of the Mosher ester derivative. Here the Cbz analogue is not suitable because the basic conditions of LDA attack the benzyl carbamate, leading to competitive cleavage. The Boc group withstands the transient exposure to strong base at cryogenic temperature without detectable (< 0.5%) loss of protecting group integrity.
Hydrolytic degradation of the Boc group follows an autocatalytic pathway once the pH drops below 4.0. A 12-month accelerated stability study (ICH Q1A guidelines, 40 °C/75% RH, sealed triple-laminated aluminum pouches) showed an increase in free (S)-prolinol to 1.8% after 6 months, remaining within specification, but unsealed samples degraded to 7.2% in 8 weeks. The degradation product, (S)-2-(hydroxymethyl)pyrrolidine, absorbs atmospheric CO2 to form a carbamate salt, giving a characteristic IR carbonyl band at 1645 cm−1 that is distinguishable from the Boc carbonyl at 1695 cm−1. Routine QC release includes FTIR conformity against a reference standard of the neat product to rule out significant deprotection before shipment.
Thermogravimetric analysis (TGA) at 10 K/min under nitrogen shows onset of weight loss at 145 °C corresponding to thermal elimination of isobutylene and CO2, leaving (S)-prolinol as the primary residue. Differential scanning calorimetry reveals a sharp endotherm at 79.8 °C (onset) with a heat of fusion of 98.2 J/g. This melting point serves as a rapid identity and purity check; depression of the melting point to below 76 °C or broadening of the endotherm indicates contamination with the racemic compound or residual solvents above 2%.
No significant photolytic degradation is observed when the product is stored in amber glass under visible spectrum light; however, exposure to UV-B (280–315 nm) for 48 hours leads to 2.3% loss of purity via N-Boc homolysis, necessitating protection from direct sunlight during outdoor handling or sampling in unshielded facilities.
| Parameter | Method | Acceptance Criterion | Typical Value |
|---|---|---|---|
| Appearance | Visual | White to off-white crystalline powder | White crystalline powder |
| Assay (HPLC) | RP-HPLC, C18, 210 nm, isocratic MeCN/H2O/TFA | ≥ 98.5% area | 99.1% |
| Enantiomeric Excess | Chiral HPLC, AD-H, hexane/IPA 90:10, 1.0 mL/min | ≥ 99.0% | 99.7% |
| Water (KF) | USP <921> Method I | ≤ 0.3% | 0.08% |
| Melting Range | DSC (onset, 10 K/min, N2) | 77–82 °C | 79.8 °C |
| Specific Rotation | USP <781> (c = 1.0, CHCl3, 20 °C) | [α]D20 = −31.0° to −34.0° | −32.5° |
One manufacturing bottleneck arises during solvent extraction of the Boc-protection reaction mixture. The crude product, dissolved in ethyl acetate, is washed with diluted hydrochloric acid (0.5 N) to remove excess triethylamine. A pH below 2.0 generates partial hydrolysis of the Boc group at the organic/aqueous interface. To circumvent this, the wash is replaced with a 10% w/v citric acid solution, pH maintained at 3.5–4.0, which selectively protonates the tertiary amine without triggering carbamate cleavage. In a pilot-plant campaign utilizing a 200 L glass-lined reactor, the citric acid wash reduced byproduct levels to < 0.3%, compared to 1.7% observed with a 2% hydrochloric acid wash. This processing detail is particularly critical when the downstream chemistry involves transition-metal catalysis sensitive to nitrogen-containing ligands; trace amounts of free pyrrolidine can poison palladium catalysts at loadings as low as 50 ppm relative to the substrate.
Residual solvent analysis after final drying under full vacuum (1–2 mbar, 40 °C, 8 h) consistently demonstrates methyl tert-butyl ether content below the ICH Q3C limit of 500 ppm. The product is classified as a non-hazardous chemical under REACH Regulation (EC) No 1907/2006 and does not require GHS signal word labeling in its neat form, though dust generation during handling mandates local exhaust ventilation per EN 14175.
Industrial users who derivatize the hydroxymethyl group via sulfonate ester formation should note that mesylation (MsCl, TEA, dichloromethane) proceeds to completion within 1 hour at 0 °C, while tosylation requires 4 hours at ambient and yields a crystalline tosylate that can be further purified by trituration with ether. Both sulfonate esters retain the Boc group intact and serve as key intermediates for nucleophilic displacement with carbon, nitrogen, or sulfur nucleophiles in the synthesis of constrained amino alcohols found in protease inhibitors and antiviral agents.
