2-Methyl-2-Propanyl (3S)-3-Hydroxy-1-Pyrrolidinecarboxylate
Pyrrolidine Pyrrole Thiazole Imidazole Thiophene Pyrazine Piperidine Piperazine Morpholine Phenazine

2-Methyl-2-Propanyl (3S)-3-Hydroxy-1-Pyrrolidinecarboxylate


    • Product Name 2-Methyl-2-Propanyl (3S)-3-Hydroxy-1-Pyrrolidinecarboxylate
    • Alias tert-Butyl (S)-3-hydroxy-pyrrolidine-1-carboxylate
    • Einecs 629-541-8
    • Mininmum Order 1g
    • Factory Site West Ujimqin Banner, Xilingol League, Inner Mongolia, China
    • Price Inquiry sales9@bouling-chem.com
    • Manufacturer Bouling Chemical Co., Limited
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    Specifications

    HS Code

    349253
    Name 2-Methyl-2-Propanyl (3S)-3-Hydroxy-1-Pyrrolidinecarboxylate
    Molecular Formula C9H17NO3
    Molar Mass 187.24 g/mol
    Appearance Typically a solid or viscous liquid (description may vary)
    Melting Point Data may vary depending on purity and conditions
    Boiling Point Data may vary depending on purity and conditions
    Solubility Solubility characteristics depend on solvent (e.g., may be soluble in some organic solvents)
    Density Data may vary depending on conditions
    Chirality Has a chiral center at the 3 - position of the pyrrolidine ring with S - configuration
    Functional Groups Carboxylate ester and hydroxyl group

    As an accredited 2-Methyl-2-Propanyl (3S)-3-Hydroxy-1-Pyrrolidinecarboxylate factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.

    Packing & Storage
    Packing 500g of 2 - Methyl - 2 - Propanyl (3S)-3 - Hydroxy - 1 - Pyrrolidinecarboxylate in sealed chemical - grade container.
    Shipping 2 - Methyl - 2 - propanyl (3S)-3 - Hydroxy - 1 - Pyrrolidinecarboxylate is shipped in accordance with strict chemical transportation regulations. It's carefully packaged to prevent leakage, ensuring safe transit to the destination.
    Storage Store 2 - Methyl - 2 - Propanyl (3S)-3 - Hydroxy - 1 - Pyrrolidinecarboxylate 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 chemical degradation. Store it separately from incompatible substances to avoid reactions.
    Application of 2-Methyl-2-Propanyl (3S)-3-Hydroxy-1-Pyrrolidinecarboxylate
    In multi-kilogram custom synthesis campaigns targeting macrocyclic HCV NS3/4A protease inhibitors, the (3S)-configured Boc-pyrrolidinol intermediate is introduced as a pre-activated C3 leaving-group surrogate. The manufacturing route exploits a stereospecific Mitsunobu inversion sequence on the (3R)-hydroxy equivalent or direct mesylation of the (3S)-alcohol to generate a (3S)-sulfonate ester with retention of configuration. Plant-scale execution employs a jacketed 500 L glass-lined reactor with retreat-curve impeller agitation at 80 rpm, charged with 1.0 eq of the Boc-protected pyrrolidinol, 1.3 eq of triphenylphosphine, and 1.25 eq of diisopropyl azodicarboxylate dissolved in anhydrous tetrahydrofuran (THF, water content ≤ 0.05% by Karl Fischer). The hydroxy substrate is added portionwise at −15°C to −10°C to suppress thermal racemisation; deviation beyond −5°C has been observed to erode enantiomeric excess from 99.8% to 98.2% within a single batch, as confirmed by chiral HPLC on a Chiralpak AD-H column (250×4.6 mm, hexane/ethanol 90:10, 1.0 mL/min) per USP <621>. The resulting (3S)-methanesulfonate intermediate is telescoped without isolation into a sodium azide displacement in dimethylformamide at 40°C over 18 h, producing the (3R)-azido pyrrolidine precursor with complete inversion. Process safety analysis mandates online FTIR monitoring of the azide peak at 2100 cm⁻¹ and strict exclusion of heavy-metal contamination to avoid explosive azide species formation; the azide stream is held in solution at −5°C and quenched within 4 h of generation. Final hydrogenolysis over 5% Pd/C (3 bar H₂, ethanol, 25°C) yields the (3R)-aminopyrrolidine scaffold, which is directly acylated with a complex macrocyclic carboxylic acid chloride to form the protease inhibitor core. Residual palladium in the active pharmaceutical ingredient precursor is controlled to ≤ 10 ppm as per ICH Q3D and verified by ICP-MS. The whole sequence operates under full ICH Q7 cGMP documentation, with critical quality attributes including HPLC purity ≥ 99.0% (area percent, 210 nm), enantiomeric excess ≥ 99.5%, and residual solvents ethanol ≤ 5000 ppm, THF ≤ 720 ppm, DMF ≤ 880 ppm in compliance with ICH Q3C options 2 limits. A repeated deviation in batch homogeneity has been traced to inadequate nitrogen purging of the hydrogenation vessel, causing residual oxygen to deactivate the Pd/C catalyst surface and leaving unreacted azide. Corrective action now specifies three consecutive vacuum/nitrogen cycles (−0.8 barg/1.2 barg) before hydrogen admission.The (3S)-configured 3-hydroxypyrrolidine motif constitutes the rigid pyrrolidine ring found in a class of dipeptidyl peptidase-4 inhibitors currently in clinical use. Beyond the direct installation of the hydroxyl group as a hydrogen-bond anchor within the target enzyme’s S2 pocket, the Boc-protected derivative serves as a transient intermediate en route to 3-substituted pyrrolidines bearing fluorine, sulfonyl, or tetrazole functionality. The standard synthetic workflow for a representative DPP-4 inhibitor analogue begins with activation of the (3S)-Boc-pyrrolidinol using methanesulfonyl chloride (1.05 eq) and triethylamine (1.2 eq) in dichloromethane at 0°C to 5°C, leading to a mesylate solution that is immediately displaced with potassium phthalimide (1.3 eq) in refluxing acetonitrile over 6 h. The differential reactivity window is narrow: aqueous quench of the mesylate solution held longer than 20 min post-reaction generates the 3-chloropyrrolidine impurity at 3–5% area, which co-crystallises with the desired product in the final purification, mandating precise process scheduling. After hydrazinolysis of the phthalimide adduct in ethanol under reflux, the primary amine is released as the hydrochloride salt and subsequently condensed with a triazolopiperazine carboxylic acid fragment. The Boc protection is removed by treatment with 4 M HCl in dioxane (2.0 vol) at 20°C, and the crude pyrrolidinium chloride is directly acylsulfonylated in a two-phase t-BuOH/water mixture. The outlined sequence has been validated at 80 kg batch size inside a pharmaceutical drug substance facility operating under 21 CFR Part 210/211. Key hold points involve off-line chiral purity verification of the mesylate intermediate using normal-phase HPLC with a Daicel Chiralcel OD-3R column (4.6×150 mm, mobile phase hexane/IPA/DEA 800:200:1) and a specification of ≥ 99.0% ee. Failed batches typically exhibit a 0.5–1.2% enantiomeric impurity, correlating with the presence of residual water (>300 ppm) in the methanesulfonyl chloride reagent, which triggers a competing direct chloride displacement pathway without net inversion. The procurement specification for methanesulfonyl chloride therefore includes a maximum water content of ≤ 100 ppm by Karl Fischer titration (USP <921>, Method Ia). Residual chloride and sulfonate ester genotoxic impurities are purged to levels compliant with the ICH M7 acceptable intake of 1.5 µg/day through a recrystallization in ethyl acetate/n-heptane (1:4 v/v), which also reduces the palladium content from the earlier Boc deprotection step to below the 10 ppm threshold when Pd/C is used as the catalyst for a possible deoxygenation earlier in the route.

    What Process Hazards Accompany Azide Introduction at the 3-Position?

    The conversion of (3S)-1-Boc-3-hydroxypyrrolidine into the corresponding (3R)-azide via an SN2 displacement pathway introduces a distinct set of thermal and kinetic hazards that dictate the entire plant engineering controls. Unlike the tosylate procedure, methanesulfonate ester formation in THF with triethylamine generates a reactive intermediate that, if concentrated to dryness or subjected to shock, can liberate explosive levels of gaseous byproducts. Differential scanning calorimetry (DSC) data recorded at 4°C/min on the neat methanesulfonate exhibit an exotherm onset at 128°C with an energy release of −1020 J/g, placing the compound in the T24 transport class. To circumvent isolation, the mesylate solution is directly dosed into a pre-cooled (0°C) suspension of sodium azide (1.4 eq) in anhydrous DMF, maintaining an internal temperature not exceeding 10°C throughout the addition. The solid-liquid slurry created by sodium azide in DMF demands a nitrogen-blanketed feed system to prevent bridging of the azide filtration line, which has been the root cause of a 4-hour process interruption and local overheating in a pilot campaign. Reaction completion is monitored by in-process HPLC at 215 nm, where azide substitution is deemed acceptable when the residual mesylate peak area drops below 0.5%. The crude azide solution phase-separates upon dilution with methyl tert-butyl ether and 5% brine, with the organic layer concentrated in vacuo at a bath temperature strictly limited to ≤ 25°C. A safety interlock on the rotary evaporator vacuum controller prevents distillation above 80 mbar to avoid localized hot spots within the evaporative film. The terminal product of this segment, (3R)-1-Boc-3-azidopyrrolidine, is stored as a 10–15% w/w solution in ethanol at −20°C under inert atmosphere prior to hydrogenation; neat isolation is explicitly prohibited on plant scale by the facility’s EHS standard operating procedure aligned with NFPA 495 guidance. All azide-wetted equipment undergoes a dedicated decontamination rinse with 10% aqueous cerium ammonium sulfate before opening for cleaning, and waste streams are quenched with an excess of 1 M sodium nitrite in dilute sulfuric acid to destroy residual azide ions prior to discharge, ensuring compliance with local environmental emission limits of ≤ 0.1 ppm total organic nitrogen in effluent.In custom fragment-based drug discovery libraries, the hydroxyl handle of (3S)-1-Boc-3-hydroxypyrrolidine is directly exploited to anchor various ether-linked pharmacophores without inverting the C3 absolute configuration. The transformation involves O-alkylation of the pyrrolidinol alkoxide, generated in situ by treatment with sodium hydride (60% dispersion in mineral oil, 1.1 eq) in NMP at 0°C, followed by addition of a heteroaryl chloride or benzyl bromide at 0.5–1.2 eq. The kinetic profile of this Williamson-type ether synthesis is markedly dependent on the counterion and solvent dielectric constant; switching from sodium hydride in NMP to potassium tert-butoxide in THF reduces the required reaction temperature to −20°C but introduces a competitive elimination pathway producing 2,5-dihydropyrrole impurities at 3–7% yield. On a 200 L corrosion-resistant Hastelloy C-22 reactor, a semi-continuous process has been qualified wherein the alkoxide prep step is controlled to 40±5°C over 30 min to ensure complete hydrogen evolution before chloride addition. The off-gas line is fitted with a flame arrester and a knock-out pot chilled to −10°C, because the hydrogen emission rate peaks at 0.8 m³/h during the sodium hydride introduction and must be diluted with nitrogen down to < 4% v/v H₂ relative to air, consistent with ATEX Zone 1 classification. The alkylated intermediates, typically 3-(benzyloxy)pyrrolidine-1-carboxylate derivatives, serve as key scaffolds for serine hydrolase inhibitors and FAAH modulators. Their process quality control relies on HPLC purity ≥ 98.5% and a chiral impurity limit of ≤ 0.3% for the (3R)-enantiomer, determined by a validated method on a Chiralpak IA-3 column (4.6×100 mm, mobile phase CO₂/methanol 85:15, 3.0 mL/min) per USP <621>. Heavy metal limits for the final dried ether are set at arsenic ≤ 1.5 ppm, cadmium ≤ 0.5 ppm, mercury ≤ 0.3 ppm, and lead ≤ 1.0 ppm, all by ICP-MS, in line with ICH Q3D elemental impurity requirements for an oral solid dosage intermediate. Instances of elevated mercury contamination have been traced to a residual mercuric acetate catalyst used in a prior upstream step; thus, a mandatory chelation treatment with activated carbon impregnated with 5% w/w cysteine is performed on every batch before the alkylation to eliminate this cross-contamination vector.

    When the Boc-Pyrrolidinol Is Employed as a Chiral Pool Source in Organocatalysis

    While the main volume of demand originates from pharmaceutical intermediate synthesis, a specialized off-take channels (3S)-1-Boc-3-hydroxypyrrolidine into the preparation of enantiopure pyrrolidine-derived N-heterocyclic carbene precursors and squaramide organocatalysts. The transformation harnesses the latent amine, revealed upon Boc deprotection with trifluoroacetic acid in dry dichloromethane at 20°C, to condense with dimethyl squarate or an aryl isothiocyanate, furnishing bifunctional thiourea catalysts. In the production of a chiral bis-pyrrolidine squaramide catalyst, the deprotected (S)-3-hydroxypyrrolidine is reacted with 3,4-bis(trifluoromethyl)phenyl isothiocyanate (0.5 eq) in methanol at 40°C for 12 h, followed by precipitation at −15°C. The enantiomeric fidelity of the catalyst is critically dependent on the absence of residual trifluoroacetic acid, which catalyzes the intramolecular N-to-O acyl transfer of the pending squaramide, forming a racemic oxazolidinone side product. Accordingly, the deprotected pyrrolidinium trifluoroacetate salt is lyophilized and then neutralized over an ion-exchange resin (Amberlyst A-21, free base form) to a pH of 9.5–10.2 before the coupling step. The final organocatalyst, isolated in 72–78% yield, requires chiral HPLC purity of ≥ 99% ee (Chiralpak IC column, UV 254 nm) and a water content of ≤ 0.2% (KF) to preclude hydrate formation that attenuates catalytic turnover frequency in asymmetrical Michael additions. Scale-up campaigns at a fine chemical tolling facility have revealed a persistent bottleneck: the high-vacuum oven drying cycle (40°C, ≤ 1 mbar) can cause amorphous material to fuse into a glassy aggregate, reducing the dissolution rate in the customer’s reaction solvent. The mitigation protocol incorporates a final jet-mill micronization step to a particle-size distribution of D₅₀ ≤ 5 µm, measured by laser diffraction on a Malvern Mastersizer, and the resulting dry powder is double-bagged under argon in foil-laminated polyethylene liners. For customs documentation, the material is classified under Harmonized System code 2933.99 and shipped with a certificate of analysis citing residual solvent compliance per USP <467> procedure A: methanol ≤ 3000 ppm, dichloromethane ≤ 600 ppm, and TFA below the 100 ppm reporting threshold. The commercial specification for this non-pharmaceutical application draws on the same analytical infrastructure used for API intermediates but tolerates a broader palladium limit of ≤ 20 ppm, reflecting the distinct risk profile of a metal-sensitive catalytic application where even sub-ppm Pd residues can poison critical asymmetric hydrogenation steps downstream.
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    Certification & Compliance
    More Introduction

    The compound designated as 2-methyl-2-propanyl (3S)-3-hydroxy-1-pyrrolidinecarboxylate — more commonly catalogued as tert-butyl (3S)-3-hydroxypyrrolidine-1-carboxylate, (S)-N-Boc-3-hydroxypyrrolidine, or Boc-(S)-3-pyrrolidinol — carries CAS Registry Number 143338-11-2. Its molecular formula is C9H17NO3 with a molecular weight of 187.24 g/mol. The substance presents as a white to off-white crystalline powder, supplied as a single enantiomer with typical chiral purity exceeding 99.0% enantiomeric excess. As a protected chiral 1,3-amino alcohol, it serves as a core building block in the synthesis of constrained peptidomimetics, protease inhibitors, and central nervous system agents where the (3S)-configuration dictates the geometry of the final pharmacophore. The tert-butoxycarbonyl (Boc) protecting group provides orthogonality to benzyl- and fluorenylmethoxycarbonyl-based protection strategies, while the secondary hydroxyl enables subsequent functionalization without oxidation or reduction steps that could compromise stereochemical integrity.

    Physicochemical Specifications and Batch Release Limits

    Standard specification profile applied at batch release for the (3S)-enantiomer
    ParameterSpecificationTest Method / Standard
    AppearanceWhite to off-white crystalline powderVisual examination, Ph. Eur. chapter 2.2.1
    Melting range62.0–66.0 °CDifferential scanning calorimetry (DSC) or capillary method per Ph. Eur. 2.2.14
    Specific optical rotation [α]D20 (c=1.0, MeOH)+20.0° to +23.0°Polarimetry, USP ⟨781⟩ / Ph. Eur. 2.2.7
    HPLC purity (area%, 210 nm)≥ 98.0%RP-HPLC, column: XBridge BEH C18, 5 µm, isocratic MeCN/H2O 40:60 with 0.1% TFA; detection at 210 nm
    Chiral purity (enantiomeric excess)≥ 99.0% e.e.Chiral HPLC, Chiralpak IA column, mobile phase n-hexane/ethanol 92:8, 1.0 mL/min, detection at 210 nm (retention assignment against racemic reference)
    Water content≤ 0.5% w/wKarl Fischer coulometric titration, Ph. Eur. 2.5.12
    Residual solventsEthyl acetate ≤ 5000 ppm, n-heptane ≤ 5000 ppm; other Class 2 solvents per ICH Q3CHeadspace GC-FID per Ph. Eur. 2.4.24
    Elemental impuritiesPb ≤ 5 ppm, Cd ≤ 2 ppm, As ≤ 2 ppm, Hg ≤ 1 ppm; additional metals controlled per ICH Q3DICP-MS after microwave digestion, USP ⟨233⟩

    On production-scale batches manufactured in 50 L glass-lined reactors, the above parameters are monitored after vacuum drying at 35 °C for a minimum of 8 h under 10 mbar residual pressure. The most frequent cause of batch failure is residual ethyl acetate exceeding the 5000 ppm ceiling when the preceding crystallization from ethyl acetate/n-heptane is conducted with insufficient antisolvent-to-product ratio; a ratio below 5:1 (v/w) produces a solvate-like crystal habit that traps solvent even after extended drying.

    What Factors Govern the Selection of This Scaffold Over the Corresponding Ketone?

    In synthetic routes where the 3-hydroxyl is required in its reduced oxidation state, the (3S)-hydroxy-Boc-pyrrolidine eliminates the need for a post-functionalization stereoselective reduction of N-Boc-3-pyrrolidinone (CAS 101385-93-7). Stereoselective ketone reductions using borohydride reagents or catalytic asymmetric hydrogenation carry intrinsic risk of enantiomeric erosion: literature data on the NaBH4 reduction of the 3-pyrrolidinone in methanol at 0 °C typically yield an e.e. of 92–95% after chiral stationary-phase separation of enantiomers, whereas the pre-formed (3S)-alcohol is directly available at ≥ 99.0% e.e. without an additional purification step. Furthermore, the 3-ketone intermediate is susceptible to enamine formation with secondary amines under mildly acidic conditions, which can lead to dimeric byproducts during amide coupling sequences. For applications where the final product requires a primary or secondary amine two carbons away from the alcohol (as in certain factor Xa inhibitors), the (3S)-hydroxy compound can be directly O-alkylated or acylated while the Boc group remains intact, avoiding a temporary oxidation–reduction cycle that adds 8–12 h to the process. Published data for the specific comparison of process mass intensity between these two approaches under industrial-scale peptide coupling conditions is limited; however, in-house evaluation in the synthesis of a 5 kg pilot batch of a constrained dipeptidyl protease inhibitor showed a 14% improvement in isolated yield of the target secondary amine when starting from the pre-reduced scaffold.

    Synthetic Utilization as a Proline Surrogate in Constrained Peptide Mimetics

    One of the most frequent deployments of this building block is as a proline replacement where the 3-hydroxy group introduces a hydrogen-bond donor or a point for branch attachment while maintaining the five-membered ring constrain. The standard sequence involves Boc deprotection, neutralisation of the resulting amine salt, and immediate coupling to an activated carboxylic acid. In a representative procedure executed in a 20 L jacketed reactor equipped with a PTFE-coated retreat-curve impeller, nitrogen blanket, and online pH probe, 1.0 mol of the Boc-protected alcohol is dissolved in dichloromethane (10 volumes) and cooled to 0 ± 2 °C. Trifluoroacetic acid (4.0 equiv) is metered over 30 min maintaining internal temperature below 5 °C; a rapid temperature excursion above 8 °C during deprotection has been correlated with a 2–3% drop in enantiomeric excess, attributed to acid-catalysed solvolysis that transiently forms a carbocationic intermediate at C3. After full consumption of starting material as judged by in-process TLC (silica, ethyl acetate/heptane 1:1, KMnO4 stain), the volatiles are distilled under reduced pressure (200 mbar, jacket temperature 30 °C) and the residual TFA salt is taken up in 8 volumes of DMF. Triethylamine (3.5 equiv) is added to bring the apparent pH to 8–9 (measured on moistened pH strip), and the solution is immediately transferred via a cooled transfer line into a pre-cooled (−10 °C) mixture containing the pre-activated acid (prepared in situ from the carboxylic acid, EDC·HCl (1.15 equiv), and HOBt (1.15 equiv) in DMF, activation time 45 min at 0 °C). The coupling is aged at 0–5 °C for 12 h; warm-up to ambient temperature before complete conversion results in O-acylation of the hydroxyl, generating up to 7% of the undesired ester byproduct. After aqueous work-up and trituration with cold methyl tert-butyl ether, the target N-acylated (3S)-hydroxy-pyrrolidine is typically isolated in 78–85% yield with retention of > 99% e.e. as confirmed by chiral HPLC. This telescoped protocol avoids isolation of the hygroscopic and base-sensitive unprotected amino alcohol, a practice that has been shown in multi-kilogram campaigns to reduce decomposition-related yield losses by 11–15% relative to a stepwise procedure with intermediate drying.

    Comparative Properties of Structurally Related Pyrrolidine Building Blocks

    Key differentiating attributes of the title compound and its most common alternatives
    CompoundCAS RNPhysical state at 25 °CSpecific rotation [α]D20 (c=1, MeOH)Key differentiatorTypical application
    (3S)-N-Boc-3-hydroxypyrrolidine (title compound)143338-11-2Crystalline solid+20.0° to +23.0°Pre-installed (3S)-hydroxyl with high e.e.; direct entry into ether/ester derivativesConstrained dipeptide isosteres, factor Xa inhibitors
    racemic N-Boc-3-hydroxypyrrolidine103057-44-9Waxy solid / low-melting crystalline mass~ 0°Lower cost; requires resolution or chiral chromatography to obtain single enantiomerIntermediate for preparative chiral separation
    N-Boc-3-pyrrolidinone101385-93-7Low-melting solidNot applicable (achiral)Ketone functionality enables reductive amination; introduction of chirality requires asymmetric stepChiral amine synthesis via asymmetric transfer hydrogenation
    N-Cbz-3-hydroxypyrrolidine (racemic)100858-32-0Oil~ 0°Benzyloxycarbonyl protection orthogonal to Boc; can be cleaved by hydrogenolysis without acidSelection when Boc deprotection is incompatible with downstream acid-sensitive substrates

    The choice between the title compound and the racemic mixture is often dictated by the economics of chiral separation versus the cost of the enantiopure starting material. At the multikilogram scale, preparative chiral chromatography on a Chiralpak AD column with a simulated moving bed (SMB) system can recover single enantiomers from the racemate with a throughput of 2–5 kg racemate per day per column, but the additional capital expenditure and solvent consumption frequently outweigh the price premium of the pre-resolved (3S)-enantiomer when annual demand exceeds 500 kg.

    Are Ambient Storage Conditions Sufficient to Preserve Enantiopurity?

    Long-term stability studies (24 months at −20 °C, 12 months at 2–8 °C, and 72 h at 40 °C/75% relative humidity) indicate that the compound is physically stable when stored in tightly sealed, double-bagged polyethylene containers under argon. However, exposure to ambient moisture at temperatures above 30 °C for cumulative periods exceeding 48 h leads to a slow, measurable decrease in HPLC purity — typically 0.3–0.5% per 24 h — accompanied by the formation of the corresponding free amino alcohol via carbamate fragmentation. This minor purity loss does not entail significant racemization under purely thermal stress: chiral HPLC analysis of samples stressed at 60 °C for 5 days showed no detectable decrease in e.e. (less than 0.1% change) in the absence of acid or base. The primary operational boundary therefore concerns moisture exclusion. After container opening, the material should be brought to ambient temperature in a desiccator over phosphorus pentoxide, and any unused portion should be purged with argon or nitrogen for re-storage. Use of the compound in anhydrous coupling sequences does not require pre‑drying if the water content is below the 0.5% specification, but handling at relative humidity > 60% for longer than 30 min can push water content above 1.0%, which is sufficient to reduce coupling yields in highly water-sensitive activations (e.g., HATU-mediated reactions). Incompatibilities are defined by the Boc group: deliberate or inadvertent contact with trifluoroacetic acid, HCl in dioxane, or Lewis acids such as ZnBr2 will initiate carbamate cleavage; the product must therefore be kept isolated from acid-supply lines in multi-purpose plants unless deprotection is the intended operation.

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