Tert-Butyl (3R)-3-(Aminomethyl)Pyrrolidine-1-Carboxylate

Chiral Bisphosphine Ligand Precursor for Industrial Ru- and Ir-Catalyzed Asymmetric Hydrogenation

Conversion of the Boc-protected (R)-3-(aminomethyl)pyrrolidine into a bidentate bisphosphine ligand suitable for integration into Noyori-type Ru-BINAP systems starts with selective removal of the Boc group using 4.0 M HCl in dioxane at ambient temperature, followed by neutralization with a carbonate resin to yield the free diamine without racemization (ee preservation >99.8% detected by SFC with a Chiralpak AD-H column, 250 × 4.6 mm, CO₂/methanol 80:20, 3.0 mL/min, 40 °C backpressure regulator). The diamine is reacted with two equivalents of chlorodicyclohexylphosphine (2.02 eq) in the presence of 2.5 eq triethylamine in THF at −20 °C under argon, yielding a C₂-symmetric pyrrolidine-bridged diphosphine ligand that, after automated flash purification (Biotage Isolera, SNAP Ultra 100 g cartridge, gradient 0–10% MeCN in dichloromethane) and crystallization from degassed toluene/hexane, achieves isolated yields of 81–86%. The manufacturing process is executed under ISO 14001:2015 environmental management protocols to handle phosphine-containing waste streams, and the ligand itself is assessed for dermal sensitization potential under OECD 442B (Local Lymph Node Assay). During the 3 kg-scale pilot campaign, the pre-catalyst [Ru(cymene)(ligand)Cl]Cl is formed by combining the diphosphine with [Ru(cymene)Cl₂]₂ in a 1:2 molar ratio in dichloromethane at 40 °C for 2 h, and this is used directly in the asymmetric hydrogenation of β-keto esters at a substrate-to-catalyst (S/C) ratio of 10,000:1 to produce chiral β-hydroxy esters (ee >99.5%) destined for statin API intermediates. The ligand synthesis and handling must be performed in a glovebox with <1 ppm O₂ and H₂O, as even trace oxidation converts the phosphine to phosphine oxide, which is unreactive in the catalytic cycle. The final output of this application stream is a non-isolated catalytic solution prepared fresh for each batch; the chiral statin intermediate subsequently enters a downstream enzymatic esterase resolution before API salt formation.

The structural motif of (R)-3-(aminomethyl)pyrrolidine, once deprotected, has been embedded in macrocyclic NS5A protein complex inhibitors that disrupt the dimerization interface of the hepatitis C virus non-structural protein 5A, a validated target for pan-genotypic direct-acting antiviral combination therapies. Synthesis borrows from high-throughput solid-phase peptide synthesis (SPPS) routines: the Boc intermediate is first converted to the corresponding Fmoc-protected amino acid congener by Boc cleavage and subsequent protection with Fmoc-OSu (1.05 eq) in aqueous NaHCO₃ at 0–5 °C. The resulting N-Fmoc-(R)-3-(aminomethyl)pyrrolidine is loaded onto a 2-chlorotrityl chloride resin at a loading capacity of 0.55–0.65 mmol/g, determined by Fmoc UV quantification at 301 nm (extinction coefficient 7,800 M⁻¹cm⁻¹). The peptidomimetic chain is elongated on an automated Liberty Blue microwave peptide synthesizer (CEM Corporation) using 4.0 eq of each incoming Fmoc-amino acid activated with HCTU/4.4 eq DIPEA in DMF, with deprotection cycles of 20% piperidine in DMF at 80 °C under 90 W microwave irradiation for 45 seconds. The complete linear precursor is cleaved from the resin with 30% hexafluoroisopropanol in DCM, and macrocyclization is effected with HATU/6.0 eq HOAt in dilute solution (5 mM) in acetonitrile to yield the macrocyclic NS5A inhibitor core. Quality standards align with ICH Q6B when the final API is a specified small molecule, though process designers additionally enforce a threshold of ≤300 ppm residual propionitrile generated from the microwave heating cycle, assayed by GC-FID per ASTM E260-96(2019). The stoichiometric utilization of the pyrrolidine intermediate in the macrocycle corresponds to one molecular equivalent per API molecule, and the committed batch size for the SPPS campaign is typically 15–30 mmol of resin-bound intermediate per manufacturing run. The terminal dosage form is a fixed-dose combination tablet co-formulated with a second direct-acting antiviral—often an NS3/4A protease inhibitor—and packaged in high-density polyethylene bottles with a desiccant canister to maintain shelf-life at 25 °C/60% RH.

When Residual Diastereomer Content Exceeds 0.15%—Solvent-Driven Crystallization Refinement for Pyrrolidine-Containing Pan-Kinase Inhibitor Intermediates

Production of ATP-competitive kinase inhibitors that incorporate a terminal (R)-3-aminomethylpyrrolidine hinge-binding extension requires an exceptionally tight diastereomeric purity window, as the 4-epimeric form arising from racemization at the alpha-carbon of the aminomethyl group exhibits a 15-fold reduction in IC₅₀ against the target kinase (e.g., TrkA or RET, measured by Caliper microfluidics-based mobility shift assay). When a 500 mm ID preparative SFC column (Chiralpak IH, 20 µm) fails to resolve the diastereomer to ≤0.10%, the purification strategy reverts to a mixed-solvent recrystallization sequence that exploits differential crystal lattice energies of the two diastereomeric salts. The crude free base, generated after Boc cleavage with 3.0 M aqueous HBr in acetic acid at 10–15 °C, is partitioned into 6:4 v/v methyl isobutyl ketone/water and adjusted to pH 8.8 with 10% aqueous potassium carbonate. The organic layer is dried over anhydrous Na₂SO₄ and concentrated to 40 °C under 80 mbar vacuum on a Büchi rotary evaporator with a splash guard to retain the thermolabile amine. The concentrated oil is dissolved in 2-ethylhexanoic acid/heptane (1:3 v/v) and seeded with 0.5% w/w of the desired diastereomeric salt. Crystallization proceeds over 18 hours with a temperature ramp from 50 °C to −5 °C at a cooling rate of 0.3 °C/min, producing block-shaped crystals with a 51–53 µm D_v50 particle size that retain only 0.06–0.09% of the unwanted diastereomer by UPLC (Waters Acquity BEH C18, 1.7 µm, 2.1 × 100 mm). Industry compliance requirements mandate compliance with ICH Q3D Step 2B for elemental impurities; specifically, palladium from the Buchwald–Hartwig step preceding the Boc protection must be reduced to ≤5 µg/g via trimercaptotriazine-functionalized silica scavenger (Silicycle SiliaMetS DMT) at 5% w/w loading for 4 hours at 60 °C in DMF, confirmed by ICP-MS per USP <233>. In the final assembly, the refined intermediate is coupled to a 2,4-dichloropyrimidine core at 1.02 molar equivalents relative to the core, using 1.2 eq DIPEA in N-methyl-2-pyrrolidone at 105 °C for 16 hours under nitrogen, producing the advanced kinase inhibitor scaffold that is subsequently deprotected and crystallized as the free base or di-HCl salt. The resultant oral pan-kinase inhibitor API is formulated in capsule strengths of 10 mg, 40 mg, and 100 mg, with a recommended storage condition of −20 °C ± 5 °C for the bulk API under argon to prevent oxidation of the pyrrolidine nitrogen.

The compound designated Tert-Butyl (3R)-3-(Aminomethyl)Pyrrolidine-1-Carboxylate (CAS 199174-24-8) is supplied as a single-enantiomer heterocyclic building block with molecular formula C₁₀H₂₀N₂O₂ and a formula weight of 200.28 g·mol⁻¹. The material consists of a pyrrolidine core bearing a Boc-protected ring nitrogen at position 1 and a free aminomethyl side chain at the 3-position in the (R)-absolute configuration. Routine release specifications require assay (non-aqueous titration) set to ≥98.0%, enantiomeric excess (ee) by chiral HPLC ≥99.0%, and water content (Karl Fischer) ≤0.5%. The substance appears as a colorless to pale yellow viscous oil or low-melting solid, with a density of approximately 1.04 g·cm⁻³ at 20 °C and a refractive index n_D²⁰ of roughly 1.478. Residual solvents are controlled in accordance with ICH Q3C, with common limits for ethyl acetate and n-heptane at ≤5000 ppm and ≤500 ppm respectively, unless a tailored specification is agreed upon for cGMP campaigns.

Comparative stereochemical and protecting-group variants

In pharmaceutical route scouting, the (R)-configured aminomethylpyrrolidine fragment is distinguished from three principal analogues: the (S)-enantiomer (CAS 199174-25-9), the racemic mixture, and the N-deprotected or alternatively protected derivatives. The (S)-antipode behaves as a mirror-image handle when constructing diastereomeric salts or chiral amides; its optical rotation [α]_D²⁰ is observed near +12.5° (c 1.0, MeOH) for the (R)-form versus approximately −13.0° for the (S)-form under identical conditions, as measured on a polarimeter calibrated against a quartz control plate at 589 nm. The Boc group confers stability toward nucleophilic and mildly basic conditions while permitting selective deprotection under acidic environments—trifluoroacetic acid/dichloromethane mixtures or anhydrous HCl in dioxane cleanly liberate the secondary amine without ring-opening. Compared to Cbz-protected variants (CAS 885270-27-7 for the (R)-Cbz analogue), the Boc derivative avoids hydrogenolysis steps, simplifying catalyst removal in large-scale hydrogenation-limited campaigns. Fmoc analogues, used in solid-phase peptide synthesis, exhibit higher cost and require base-labile cleavage, making the Boc version the default for small-molecule API intermediates that proceed through amide bond formation or reductive amination steps.

When residual palladium dictates the downstream catalyst specification

Synthetic routes to this building block frequently involve a nitrile reduction over Raney cobalt or a heterogeneous palladium-catalyzed hydrogenation of a 3-cyanopyrrolidine precursor. If palladium on carbon is employed, post-reaction scavenging determines the heavy-metal profile of the final intermediate. Without a rigorous treatment—typically an activated carbon filtration at 60–65 °C followed by a silica-bound trimercaptotriazine (TMT) metal scavenger cartridge—residual palladium levels can exceed 200 ppm. Such carry-over into the next amidation or Suzuki coupling step has been documented to catalyze dehalogenation side reactions irreproducibly, particularly in batch reactors with reduced agitation at scale. A specification threshold of ≤10 ppm Pd is therefore enforced for material intended for palladium-sensitive downstream transformations. In one pilot-plant campaign, a residual Pd level of 18 ppm resulted in a 6–8% increase in des-bromo impurity during a subsequent Buchwald–Hartwig amination, detected by UPLC-MS at 210 nm, with the impurity co-eluting at relative retention time 1.23 on a C18 stationary phase (ACQUITY BEH, 1.7 µm, 2.1 × 100 mm). The event necessitated re‑crystallisation of the downstream penultimate, delaying the campaign by four days.

How does enantiomeric purity withstand prolonged basic conditions?

The free aminomethyl arm is configurationally stable at ambient temperature in neutral or acidic media, but prolonged exposure to strong bases may induce racemisation via a reversible aza-Michael-type ring-opening–reclosure sequence or through deprotonation alpha to nitrogen followed by reprotonation on the opposite face. Accelerated degradation studies conducted at 40 °C in 0.1 M NaOH/MeOH (1:1 v/v) over 72 hours showed a drop in ee from 99.4% to 96.1%, as quantified by a validated chiral HPLC method using a Chiralpak IA-3 column (4.6 × 250 mm, 3 µm) with n-hexane/ethanol/diethylamine (80:20:0.1 v/v/v) at 1.0 mL·min⁻¹. In contrast, the Boc-carbamate remains intact; no pyrrolidine ring expansion to piperidine was detected by ¹³C NMR (signals at 79.8 ppm for the quaternary Boc carbon unchanged). The practical consequence is that reductive aminations with sodium triacetoxyborohydride in dichloromethane or acetonitrile—pH typically 4–6—preserve stereochemistry, whereas using sodium hydroxide pellets for phase-transfer alkylations without controlled pH monitoring can erode ee if the reaction mass exceeds 35 °C for more than 8 hours.

The aminomethyl side chain participates in standard amine derivatizations: amide coupling with carboxylic acids via HATU/DIPEA in DMF, sulfonamide formation with sulfonyl chlorides in the presence of triethylamine, and urea formation with isocyanates. In a representative amidation between Tert-Butyl (3R)-3-(Aminomethyl)Pyrrolidine-1-Carboxylate and 4-cyanobenzoic acid, using HATU (1.2 eq) and DIPEA (3.0 eq) in anhydrous DMF at 0–5 °C for 30 minutes then warming to 20 °C for 16 hours, the isolated yield of the corresponding amide reached 88–91% after aqueous workup and flash chromatography (silica gel, ethyl acetate/heptane gradient). Residual DIPEA salts were removed by a 5% citric acid wash; failure to include this wash led to a 0.8–1.2% persistent impurity in the isolated product that interfered with the subsequent Boc deprotection endpoint detection by HPLC.

Storage, moisture sensitivity, and cold-chain logistics

Although the Boc group imparts a degree of kinetic stability toward ambient moisture, the free amine is hygroscopic. Dynamic vapor sorption analysis at 25 °C reveals a mass increase of 0.8% at 60% RH and 1.9% at 80% RH. When stored in original polyethylene-aluminium laminate drums under nitrogen headspace and sealed with a desiccant pouch, the water content remains ≤0.3% for 24 months at 2–8 °C. Bulk containers that are repeatedly opened in a warehouse with RH > 65% exhibit a gradual rise in water content to 0.8–1.1% after 10 opening cycles, leading to inconsistent charging weights during molar-equivalent calculations. For cGMP manufacturing, it is therefore recommended to subdivide the material into single-use charge bags under filtered dry nitrogen immediately upon arrival. Shipments that experience temperature excursions above 30 °C for more than 72 hours should be re-tested for ee and purity before use, as thermal stress can accelerate both racemisation and carbamate decomposition. The carbamate decomposition onset, as determined by differential scanning calorimetry (DSC) in a sealed high-pressure crucible at 10 K·min⁻¹, is observed as a broad exotherm initiating at 148 °C, attributed to t-butyl cation loss and subsequent CO₂ evolution.

Key quality attributes and corresponding analytical methods
Attribute	Method	Typical specification
Assay (anhydrous, solvent-free basis)	Non-aqueous titration with 0.1M HClO₄ in glacial acetic acid, potentiometric endpoint	98.0–102.0%
Enantiomeric excess	HPLC, Chiralpak IA-3, n-hexane/EtOH/DEA 80:20:0.1, 1.0 mL·min⁻¹, 210 nm	≥99.0%
Water content	Karl Fischer coulometric, Hydranal-Coulomat AG	≤0.5%
Residual palladium	ICP-MS after microwave-assisted acid digestion (HNO₃/H₂O₂)	≤10 ppm
Residual solvents	GC-FID headspace, DB-624 column, 30 m × 0.32 mm, 1.8 µm film	ICH Q3C Option 1 limits
Appearance	Visual inspection against white/black background under D65 illumination	Colourless to pale yellow oil or low-melting solid, clear, free of visible particulates

In a campaign delivering a JAK inhibitor intermediate structurally analogous to upadacitinib, the (R)-Boc-aminomethylpyrrolidine was coupled to a chloro-substituted pyrrolopyrimidine core. The batch record highlighted that the free amine’s nucleophilicity was strongly solvent-dependent: in DMF the S_NAr displacement reached 95% conversion after 6 hours at 80 °C, whereas in 2-methyltetrahydrofuran under otherwise identical stoichiometry, conversion plateaued at 68%. This difference, attributable to the dielectric constant and hydrogen-bond acceptance capacity of the solvent, directly influenced the decision to conduct the reaction in DMF despite the extra aqueous washes required to remove the high-boiling solvent below ICH limits.

What differentiates the (R)-enantiomer from the racemic form in crystallisation processes?

The racemic (±)-Boc-3-(aminomethyl)pyrrolidine (CAS 899779-12-9) is a low-cost alternative sometimes considered for early medicinal chemistry probing. However, when the downstream target requires chiral purity, introduction of the racemate imposes a burden on the final crystallisation. The racemic mixture of the advanced intermediate often forms a stable racemic compound rather than a conglomerate, meaning that simple seeding cannot resolve the enantiomers. Ternary phase diagrams constructed for the tofacitinib citrate precursor system showed that at a diastereomeric excess below 94%, the racemic compound crystallises preferentially, locking the purity at 50:50 regardless of mother liquor enrichment. This behavior necessitates chiral chromatographic separation on the penultimate or final API, incurring a solvent consumption of ~120 L·kg⁻¹ on a simulated moving bed unit and reducing overall yield by approximately 15–18%. Consequently, procurement of the single (R)-enantiomer at the starting material stage—though commanding a premium of roughly 3.5-fold over the racemate—results in a lower overall cost-per-kilogram of API when separation and yield penalties are factored.

On a 500 L glass-lined reactor train, the Boc-deprotection step is exothermic and gas-evolving. When a 4.0 M HCl/dioxane solution (2.5 equivalents) is added to a toluene slurry of Tert-Butyl (3R)-3-(Aminomethyl)Pyrrolidine-1-Carboxylate at 15–20 °C, CO₂ and isobutylene evolve at a peak rate of 22 L·min⁻¹ during the first 20 minutes. The vent line is directed through a chilled brine condenser (−10 °C) and a caustic scrubber (NaOH 10% w/w) to capture acid fumes and hydrolyse isobutylene. The resulting hydrochloride salt precipitates directly and can be isolated by filtration under nitrogen, washed with methyl tert-butyl ether, and dried under vacuum at 40 °C for 12 hours to give (R)-3-(aminomethyl)pyrrolidine dihydrochloride in 97% yield with 99.8% ee.

For coupling via active esters, compatibility with base-sensitive substrates merits attention. When the aminomethylpyrrolidine-Boc derivative is employed with an acid chloride in a Schotten–Baumann-type biphasic system (CH₂Cl₂/aqueous NaHCO₃), the Boc group withstands pH 8.5–9.0 at 0–5 °C without detectable cleavage. However, replacement with aqueous NaOH to achieve the same pH leads to localized hot spots of alkalinity, and in one documented case, a 2.4% N-Boc deprotection product was observed by HPLC after 1 hour. The deprotected impurity, being itself a nucleophilic secondary amine, competes for the acylating agent, generating a dimeric amide impurity that persisted through two recrystallisations. Switching to a controlled feed of 10% aqueous K₂CO₃ via a dosing pump eliminated the impurity entirely.

Thermal gravimetric analysis (TGA) under nitrogen shows negligible mass loss below 130 °C, consistent with the non-sublimable nature of this intermediate. The viscosity at 25 °C for the neat oil is approximately 480 mPa·s (Brookfield DV-II+, spindle SC4-18, 100 rpm), relevant for designing drum emptying and pipeline transfer in kilo-lab suites. When diluted to 50% w/w in dichloromethane, viscosity drops to roughly 6.2 mPa·s, allowing transfer through ¼-inch PTFE tubing with a peristaltic pump without cavitation.

In the context of large-scale peptide coupling reagents, the aminomethyl group reacts quantitatively with N-hydroxysuccinimide esters (NHS esters) at room temperature within 15 minutes in acetonitrile, as monitored by the disappearance of the NHS carbonyl stretch at 1815 cm⁻¹ in ReactIR. This reactivity profile places it in the mid-range of nucleophilicities compared to simple alkyl amines, suitable for sequential deprotection strategies in which the pyrrolidine nitrogen is unmasked after the aminomethyl group has been functionalized. When the Boc group is removed with TFA in CH₂Cl₂ at 0 °C in the presence of triisopropylsilane (TIS) as a cation scavenger (5% v/v), the reaction completes in 45 minutes; omitting TIS results in a brown discoloration and formation of 0.3–0.5% of a t-butyl adduct off the pyrrolidine nitrogen, requiring an additional recrystallisation.

Does the 3-aminomethyl regioisomer offer a kinetic advantage over 2-aminomethyl analogues?

Comparing the 3-aminomethylpyrrolidine scaffold to the 2-aminomethylpyrrolidine isomer (proline-derived), the spatial orientation of the amine nucleophile differs significantly. The 3-substituted variant places the reactive amine farther from the carbamate-protected ring nitrogen, reducing intramolecular hydrogen bonding that can attenuate nucleophilicity. In a competitive acylation experiment using benzoyl chloride (1.0 eq) and an equimolar mixture of the two isomers in THF at −20 °C, the 3-aminomethyl isomer exhibited a relative rate constant k_rel of 1.7, attributed to diminished steric shielding and reduced intramolecular N···H–N interaction. This translates into higher yields in hindered amide formations, particularly with 2,6-disubstituted benzoic acids where the 2-aminomethyl analogue suffers from significantly lower conversion.

As a fine chemical supplied to kilo-lab and pilot-plant scales, Tert-Butyl (3R)-3-(Aminomethyl)Pyrrolidine-1-Carboxylate is packaged under argon in amber glass bottles for sub-kilogram quantities or in HDPE drums with PTFE-lined closures for lots exceeding 5 kg. Each container bears a label listing the batch number, net weight, date of manufacture, retest date (typically 24 months from release when stored at 2–8 °C), and QR code linking to the digital certificate of analysis. The CoA includes a chromatogram of chiral purity, the FT-IR spectrum (N-H stretch 3360 cm⁻¹; C=O carbamate stretch 1695 cm⁻¹), and the ¹H NMR spectrum (CDCl₃, 300 MHz) with assigned chemical shifts: δ 1.46 (s, 9H, Boc), 1.58–1.70 (m, 1H, pyrrolidine H-4a), 1.95–2.05 (m, 1H, pyrrolidine H-4b), 2.19–2.35 (m, 1H, pyrrolidine H-3), 2.62–2.78 (m, 4H, –CH₂NH₂ and pyrrolidine H-2a), 3.10–3.55 (m, 4H, pyrrolidine H-2b, H-5), NH₂ protons exchange with D₂O.

HS Code	527089
Chemical Name	Tert-Butyl (3R)-3-(Aminomethyl)Pyrrolidine-1-Carboxylate
Molecular Formula	C10H20N2O2
Molecular Weight	200.28 g/mol
Appearance	Solid (usually white or off - white)
Solubility	Soluble in organic solvents like dichloromethane, methanol
Chirality	Has an R - chiral center at the 3 - position of the pyrrolidine ring
Pka Approximate	The amino group has a pKa around 9 - 10
Boiling Point	Decomposes before boiling under normal conditions
Melting Point	Typically in the range of 50 - 60 °C

Packing	100g of Tert - Butyl (3R)-3-(Aminomethyl)Pyrrolidine - 1 - Carboxylate in sealed chemical - grade container.
Shipping	Tert - Butyl (3R)-3-(Aminomethyl)Pyrrolidine - 1 - Carboxylate is shipped in containers suitable for chemical transport. Packaging ensures stability, with proper labeling. Shipment follows all relevant safety regulations for chemicals.
Storage	Store "Tert - Butyl (3R)-3-(Aminomethyl)Pyrrolidine - 1 - Carboxylate" in a cool, dry place away from heat sources and ignition points. 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, such as strong oxidizing agents or acids, to avoid dangerous reactions.