2-(3-Amino-Phenyl)-Pyrrolidine-1-Carboxylic Acid Tert-Butyl Ester

The compound is employed as a key intermediate in the multi-kilogram synthesis of diarylurea-based kinase inhibitors targeting the VEGFR-2 receptor. In a validated manufacturing campaign, 64.5 kg of the Boc-protected aniline was reacted with 4-chloro-3-(trifluoromethyl)phenyl isocyanate (molar ratio 1:1.03) in anhydrous 2-methyltetrahydrofuran under a nitrogen blanket at 0–5 °C for 18 hours to form the central urea linkage. The product precipitated upon addition of n-heptane and was isolated by centrifuge filtration; residual solvent levels were reduced below 500 ppm for 2-MeTHF and 100 ppm for n-heptane, compliant with ICH Q3C(R8) Class 2 limits. Subsequent TFA-mediated Boc deprotection in dichloromethane at 20±2 °C liberated the pyrrolidine nitrogen, which was then acylated with 4-(4-methylpiperazin-1-ylmethyl)benzoic acid hydrochloride using EDC·HCl (1.2 eq) and HOBt (1.2 eq) in DMF at 0–25 °C. The crude API free base was purified by slurry in ethanol/water (3:1 v/v) at 70 °C for 2 hours, yielding a polymorphically consistent Form A with purity ≥99.5% by HPLC (area%, 210 nm) and single impurity ≤0.10%. All processing steps are governed by ICH Q7 GMP for active pharmaceutical ingredients, with the Boc intermediate controlled under a Type II Drug Master File. Production-scale bottlenecks included slow phase separation during aqueous washes at the deprotection stage; installation of an inline turbidity meter on the centrifuge discharge line reduced batch cycle time by 6.5 hours by enabling end-point detection without grab sampling. The final substance is shipped under customs tariff heading 2933.99 and accompanied by a certificate of analysis referencing USP<467> residual solvents and Ph. Eur. 2.4.24 for palladium content, as residual Pd from an earlier Suzuki coupling step must not exceed 10 ppm.

What governs the selectivity profile of 5-HT_1A receptor ligands derived from this building block?

The pendant 3-aminophenyl moiety serves as a rigid spacer that positions the pyrrolidine ring in a geometrically defined orientation relative to a distal arylpiperazine or indolylalkylamine pharmacophore. In a campaign targeting partial agonists with biased signalling properties, 2.8 kg of the protected aniline was coupled under Schotten-Baumann conditions to 4-chlorobutyryl chloride (1.05 eq) in dichloromethane/water biphasic media with sodium carbonate maintaining pH 9–10 at 10±2 °C. The resulting ω-chloroamide was immediately treated with 1-(2-methoxyphenyl)piperazine (1.3 eq) and potassium iodide (0.1 eq) in acetonitrile under reflux for 14 hours to install the arylpiperazine tail. Boc removal utilised HCl/dioxane (4 N) without scavenger addition; uncontrolled exothermic deprotection in an early pilot batch caused a temperature excursion to 42 °C that generated 3.2% of a des-pyrrolidine elimination impurity, necessitating a controlled addition rate of 0.5 L/min and jacket cooling setpoint −5 °C. The free pyrrolidine base was then N-alkylated with 2-(2-(4-fluorophenoxy)ethyl) bromide (1.15 eq) in DMF with K₂CO₃ (2.5 eq) at 60 °C for 8 hours, achieving a 78% yield over three telescoped stages. In vitro binding assays (human 5-HT_1A CHO-K1 membranes, 3 nM [³H]8-OH-DPAT) returned a K_i of 1.9 nM; functional selectivity was assessed via [³⁵S]GTPγS accumulation and β-arrestin-2 recruitment, with a bias factor of 12 toward G-protein coupling over β-arrestin. The entire synthetic sequence is designed to avoid Class 1 solvents (ICH Q3C) and genotoxic impurities such as alkyl mesylates, with purge factor calculations documented per ICH M7(R2). The intermediate requires storage at 2–8 °C under argon; exposure to ambient humidity above 60% RH for more than 4 hours triggers partial Boc hydrolysis detectable by a 0.5% increase in free amine content.

Epoxy curative stoichiometry and vitrification behaviour

When formulated as a latent aromatic amine hardener for diglycidyl ether of bisphenol A (DGEBA, epoxy equivalent weight 188 g/eq), the compound contributes both a primary amine hydrogen equivalent weight of 246 g/eq (calculated on the free –NH₂ group) and a thermally released secondary amine from the pyrrolidine ring upon quantitative Boc thermolysis at 175–185 °C. Differential scanning calorimetry (DSC, 10 K/min, N₂) of a stoichiometric mixture (1:0.9 NH:epoxy ratio at the primary amine stage) reveals an exotherm onset at 113 °C with peak maximum at 148 °C and total enthalpy of 475 J/g. The tertiary butyl carbamate blocking group delays gelation: at 120 °C the pot life exceeds 90 minutes, but once the temperature reaches 180 °C, deblocking proceeds within 20 minutes and the system vitrifies rapidly. Post-cure at 200 °C for 2 hours achieves a glass transition temperature of 162 °C (DMA, 1 Hz, 3 K/min, peak of tan δ), while a formulation stoichiometrically balanced for both primary and secondary amine hydrogens (total AHEW 164 g/eq) yields a T_g of 187 °C and room-temperature storage modulus of 3.2 GPa. The system complies with REACH Annex XVII restrictions on primary aromatic amines; the free aniline content after curing is below the 20 mg/kg detection limit by EN 14362-1:2012 extractive testing, qualifying the cured network for food-contact epoxy applications under EU 10/2011. Vacuum degassing before cure is mandatory—entrapped CO₂ from the deprotection step can create microvoids with average diameter 12 µm detectable by scanning acoustic microscopy, reducing Mode I fracture toughness (ASTM D5045-14) by up to 18%.

In an alternative formulation protocol, 2-(3-Amino-Phenyl)-Pyrrolidine-1-Carboxylic Acid Tert-Butyl Ester has been evaluated as a chain extender in polybenzoxazine resins. A bisphenol A/aniline-based benzoxazine monomer blended with 15 wt% of the compound exhibits a ring-opening polymerisation exotherm peak shifted from 245 °C (neat) to 218 °C, accompanied by a 27% reduction in induction time (isothermal DSC at 170 °C). The pyrrolidine nitrogen, once liberated, accelerates oxazine ring opening via a nucleophilic mechanism that generates a zwitterionic iminium intermediate. However, the formulation is inherently hygroscopic in the uncured state; Karl Fischer titration after 24 hours at 50% RH shows 0.8 wt% water uptake, sufficient to partially hydrolyse the oxazine ring and raise the coefficient of thermal expansion above T_g by 22 ppm/K (TMA, 5 K/min). Therefore, vacuum-sealed packaging with desiccant is specified, and line pre-drying at 60 °C for 4 hours under −0.095 MPa vacuum is required before hot-melt impregnation.

In nanomaterial surface engineering, the aromatic primary amine undergoes diazotisation in aqueous HCl/NaNO₂ at 0–5 °C to generate a reactive diazonium salt that covalently grafts onto multi-walled carbon nanotube (MWCNT) sidewalls via a radical mechanism. In a typical batch, 10 g of MWCNTs (Nanocyl NC7000, specific surface area 250–300 m²/g) are dispersed in 500 mL of N-methyl-2-pyrrolidone by probe sonication (300 W, 20 kHz, 15 minutes, pulse mode 5s on/2s off) to achieve a Hegman grind below 25 µm. Separately, 1.5 mmol of the aniline derivative per gram of MWCNTs is diazotised with 1.3 eq NaNO₂ in 0.5 N HCl at 2 °C and added dropwise to the nanotube dispersion under vigorous mechanical stirring (800 rpm). After 2 hours, the functionalised MWCNTs are isolated by 0.1 µm PTFE membrane filtration, washed with DMF and water until the filtrate conductivity equals that of deionised water (<5 µS/cm), and dried under vacuum at 80 °C for 12 hours. X-ray photoelectron spectroscopy (XPS) shows a nitrogen content of 3.8 at% attributable to the Boc-carbamate and residual azo linkages. Thermogravimetric analysis (TGA, 10 K/min, N₂) quantifies the grafting density at 0.18 mmol/g by mass loss between 180–400 °C, corresponding to the carbamate decomposition. The Boc protecting group remains intact on the surface, allowing post-functionalisation via acidolysis and subsequent reaction with acid chlorides or isocyanates. The resulting nanohybrids disperse stably in tetrahydrofuran and ethyl acetate at loading up to 5 mg/mL with a zeta potential of −28 mV (electrophoretic light scattering, 25 °C) that provides more than 72 hours of sedimentation stability. Occupational exposure control measures are mandated under EU Directive 2004/37/EC due to the potential release of respirable CNT agglomerates during open handling; the process must be enclosed with high-efficiency particulate air filtration (HEPA H14) and continuous airborne particle monitoring (condensation particle counter, <10 nm cut-off). Published data for this specific configurational grafting lacks long-term mechanical reinforcement data in epoxy nanocomposites, but preliminary three-point bending tests on 1 wt%-loaded specimens (ASTM D790-17) indicate a 14% increase in modulus over unfilled matrix without catastrophic embrittlement.

When the Boc-protected amine serves as a latent hardener in one-component benzoxazine formulations

Single-component benzoxazine adhesives are designed for automated dispensing in automotive body-in-white assembly, where shelf life at 40 °C must exceed 4 weeks while cure completes within 30 minutes at 180 °C. Incorporating 12 phr (parts per hundred resin) of 2-(3-Amino-Phenyl)-Pyrrolidine-1-Carboxylic Acid Tert-Butyl Ester into a bisphenol-F/thiophenol-derived benzoxazine imparts latency because the tertiary butyl carbamate blocks pyrrolidine nucleophilicity below dissociation temperature. Accelerated storage tests (40 °C, 75% RH) show viscosity drift of only <15% over 28 days measured by parallel-plate rheometry at 100 s⁻¹, versus >80% drift for unblocked pyrrolidine controls. Upon heating, the carbamate thermolyses cleanly with evolution of isobutylene and CO₂, leaving a free secondary amine that initiates oxazine ring-opening through a formal [4+2] hetero-Diels-Alder pathway. The reaction is monitored on a production-scale reaction calorimeter (Mettler Toledo RC1mx, 1 L) to map the heat-flow profile: a sharp endotherm at 155–165 °C (carbamate cleavage, −285 J/g) is immediately followed by a broader exotherm (+420 J/g) peaking at 184 °C. Bonding trials on hot-dip galvanised steel (HDG 590Y) with 0.2 mm bondline thickness achieve lap shear strengths of 23.4 MPa (ISO 4587:2003, 10 mm/min) after 30 min/180 °C cure, with cohesive failure mode exceeding 90%. Process engineers should note that the isobutylene gas generation demands an open-furnace exhaust velocity of 0.5–1.0 m/s to prevent bubble entrapment in larger bead widths (>12 mm). Compliance with RoHS Directive 2011/65/EU Annex II is verified by X-ray fluorescence screening for restricted phthalates and brominated flame retardants, which are absent in this amine-cured polybenzoxazine matrix.

Agricultural triazolinthione fungicide precursors: regioselective alkylation pathways

A multistep route to 2-(substituted-thio)-4H-1,2,4-triazol-3-one fungicides utilises the aminophenyl pyrrolidine as a masked 1,3-diamine equivalent. The primary aromatic amine is converted to the corresponding isothiocyanate by reaction with thiophosgene (1.5 eq) in water/dichloromethane biphasic medium in the presence of calcium carbonate at 5–10 °C, achieving 92% yield after bulb-to-bulb distillation (95 °C, 0.8 mbar). This intermediate is treated with 4-ethylthiosemicarbazide (1.0 eq) in ethanol under reflux for 6 hours, cyclising to the triazolinethione ring and liberating the Boc-protected pyrrolidine at the 5-position. Alkylation with methyl iodide (1.1 eq, K₂CO₃ in acetone, 25 °C, 2 hours) proceeds exclusively at the exocyclic thione sulfur, as confirmed by ¹³C NMR shift of the C=S carbon from 182.5 ppm to 166.8 ppm. The Boc group is then cleaved with trifluoroacetic acid (20% v/v in DCM, 0 °C to rt) to expose the pyrrolidine nitrogen, which is subsequently acylated with 2,4-dichlorophenylacetyl chloride (1.2 eq, triethylamine 2.5 eq, THF, −10 °C). The final fungicidal candidate (purity 98.7% by HPLC) exhibits an EC₅₀ of 0.08 µg/mL against Zymoseptoria tritici (EPPO Standard PP 1/26(4) field-isolate microtitre assay). Active substance technical specifications align with FAO Specification 730/TC (2019) for triazole fungicides: water content <0.5% (Karl Fischer), acetone insolubles <0.1%, and storage stability 2 weeks at 54±2 °C without degradation exceeding 2%. Effluent streams from the thiophosgene quench step require treatment with 10% NaOH at 60 °C for 2 hours to hydrolyse residual thiophosgene below the 1 mg/L threshold prior to biological waste treatment; air emissions are scrubbed through a sodium hypochlorite/NaOH packed column ( 6 theoretical stages) to meet EU BAT-AELs for volatile organic sulfur compounds.