Application Domains for 3-Aminomethyl-Pyrrolidine-1-Carboxylic Acid Tert-Butyl Ester

In the construction of von Hippel-Lindau (VHL)-recruiting proteolysis-targeting chimeras (PROTACs) intended for androgen receptor degradation, the Boc‑protected 3‑aminomethylpyrrolidine functions as a rigidifying spacer module inserted between the polyethylene glycol chain and the cereblon‑binding moiety. The amine is unmasked in situ during flow‐chemistry protocols using 2.0 M hydrogen chloride in 1,4‑dioxane at a residence time of 45 seconds at 25 °C, then immediately neutralized with diisopropylethylamine and reacted with the activated ester of the linker‑warfarin conjugate. Molar input ratio of the deprotected amine relative to the terminal carboxylic acid of the PEG‑VHL ligand is maintained at 1.12 ± 0.05 eq. to compensate for competitive O‑acylation of the secondary alcohol generated during resin‑bound ester activation. Compliance with residual solvent and mutagenic impurity thresholds follows ICH M7(R2) addendum for cohort‑of‑concern compounds; the purge factor for tert‑butyl carbocation adducts is verified via spiking studies with LC‑MS/MS achieving a limit of quantification below 0.5 ppm relative to the final PROTAC mass. The downstream sequence proceeds through C‑18 reversed‑phase preparative HPLC with a mobile phase of 0.1 % trifluoroacetic acid in water/acetonitrile, lyophilisation, and salt metathesis to the hydrochloride form to ensure chemical stability during long‑term storage at −20 °C under argon. The terminal manufactured articles are sterile‑filtered, pre‑clinical grade heterobifunctional degraders such as ARV‑110 analogue series targeting the N‑terminal domain of the androgen receptor, supplied with a comprehensive certificate of analysis referencing USP <467> residual solvent testing and ICH Q3D elemental impurity profiling by ICP‑MS.

Coupling Efficiency in a Microwave‑Assisted Buchwald–Hartwig Amination Sequence Declines if Free Amine Equivalents Exceed 1.3

When the title compound serves as a precursor to 3‑aminomethyl‑N‑aryl‑pyrrolidines employed as selective histamine H3 receptor inverse agonists, the catalytic amination of aryl bromides is executed with palladium tris(dibenzylideneacetone)dipalladium(0) / XPhos precatalyst in tetrahydrofuran containing 1.4 eq. sodium tert‑butoxide. Deprotected amine molar input ratio must fall between 1.05 and 1.15 eq. relative to the aryl bromide; catalyst poisoning attributable to chelation by the liberated pyrrolidine nitrogen occurs above 1.30 eq., reducing conversion from 94 % to below 63 % in single‑mode microwave reactors operating at 110 °C with a power ceiling of 150 W. Manufacturing is performed under ISO 9001:2015 certified quality management systems augmented by ICH Q7 Section 12.5 for distribution of key starting materials; in‑process controls require diastereomeric purity measured by chiral supercritical fluid chromatography (SFC) in accordance with Ph. Eur. 2.2.45, using a Chiralpak IG‑3 column with a CO₂/isopropanol gradient. The downstream work‑up sequence involves quenching with aqueous ammonium chloride, extraction into 2‑methyltetrahydrofuran to replace dichloromethane per ICH Q3C class‑2 solvent minimization policy, filtration through a 0.2 μm polytetrafluoroethylene membrane, and crystallisation from methylcyclohexane/ethyl acetate to furnish the N‑arylated intermediate in enantiomeric excess exceeding 99.2 %. The resulting tertiary amine is further elaborated into clinical‑stage 1‑aryl‑pyrrolidine derivatives acting as functionally selective inverse agonists at the H3 histamine receptor, developed as cognition enhancers for mild cognitive impairment, with batch records referencing residual palladium limits below 10 ppm per USP <232> and <233>.

Deliberate omission of aqueous acid quenching after trifluoroacetic acid‑mediated N‑Boc cleavage generates a high‑temperature aging challenge. The free amine, left in neat trifluoroacetic acid at 50 °C for periods exceeding 30 minutes, undergoes an intramolecular aza‑Michael addition with deactivated alkenes present in the diaryl ether backbone, creating a spirocyclic amine impurity at levels up to 2.8 area % when the reaction mixture is subsequently basified. Purge factor determination for this spiro impurity, conducted per ICH M7(R2) Option 4 control strategy using design‑of‑experiment response surface modeling, indicates a required critical process parameter window of pH 7.8–8.2 during dichloromethane extraction and a maximum hold time of 15 minutes post‑neutralisation at 20 °C. Equipment specification calls for a GL‑lined steel reactor with an anchor agitator at 80 rpm tip speed to prevent vortex‑induced aeration, which otherwise promotes oxidative dimerization of the pyrrolidine ring. Terminal products are members of the N‑aryl‑3‑aminomethylpyrrolidine class that served as a key pharmacophore in clinical candidates evaluated for narcolepsy and attention deficit disorders.

What Purge Factors Are Adequate to Eliminate Genotoxic tert‑Butyl Cation Impurities During Scale‑Up of Trifluoromethylarylation Reactions?

3‑Aminomethyl‑pyrrolidine‑1‑carboxylic acid tert‑butyl ester is employed as the amine input in the manufacture of pyrrolidine‑containing hepatitis C virus NS5A replication complex inhibitors. The compound is treated with 2.5 eq. trifluoroacetic acid in dichloromethane at 0–5 °C for 2 hours to remove the Boc group. The consequential generation of genotoxic impurity PGI‑01 (tert‑butyl trifluoroacetate and isobutylene oligomers) mandates a risk assessment under ICH M7(R2) and EMA guideline CPMP/SWP/5199/02. Spiking experiments at pilot scale in a 100‑litre Hastelloy C‑22 reactor equipped with a triple‑distillation head established that a subsequent azeotropic distillation with n‑heptane at 40 mbar and pot temperature ≤ 45 °C achieves a purge factor greater than 3 × 10⁵, reducing the theoretical excess cancer risk below 1 × 10⁻⁶ for a daily dose of 100 mg of the final API precursor. The accepted addition ratio of the liberated amine to the trifluoromethyl‑substituted quinoline carboxylic acid in the subsequent EDCI·HCl/HOBt‑mediated amidation step is 1.02 ± 0.03 eq.; excess amine leads to homocoupling by‑products that are difficult to purge by crystallisation from methanol/water (solubility ratio approx. 1 : 8 at 20 °C). Production documentation references FDA 21 CFR 211.110 for sampling and testing of in‑process materials and ASTM E2500‑20 for application of a science‑ and risk‑based validation approach. The crystallised intermediate amide is further deprotected, sulfonylated, and converted to the terminal active pharmaceutical ingredient, a pan‑genotypic NS5A inhibitor currently in phase IIb trials, with full traceability along the supply chain per ICH Q11 Section 5.2.4.

Continuous processing of the free amine derived from 3‑aminomethyl‑pyrrolidine‑1‑carboxylic acid tert‑butyl ester for GMP radiolabeling with fluorine‑18 in a single‑use microfluidic cassette begins with the delivery of a 0.6 M solution of the Boc‑amine in anhydrous acetonitrile to a packed‑bed acidic resin column (Amberlyst 15‑Dry, sulfonic acid functionality) at a flow rate of 0.05 mL/min to effect deprotection without soluble acid carryover. The effluent is mixed with a stream of 2‑[¹⁸F]fluoroethyl tosylate freshly prepared via nucleophilic radiofluorination on a GE TRACERlab FXFN module, and the alkylation proceeds in a 250 μL PTFE coil at 85 °C for 5 minutes residence time. Stoichiometric ratio of amine to labeled alkylating agent is strictly controlled at 1.6 : 1 to compensate for adsorption losses on the microreactor walls and suppress formation of dialkylated side products. This process is conducted under an exploratory Investigational New Drug Application framework referencing 21 CFR 212 (cGMP for PET drugs) and USP <823> for positron emission tomography compounding. The downstream purification via semi‑preparative radio‑HPLC (Luna C18, 10 × 250 mm, ethanol/10 mM sodium phosphate pH 7.2) yields the ¹⁸F‑labeled pyrrolidine derivative in 28 ± 5 % decay‑corrected radiochemical yield with radiochemical purity exceeding 98 % and residual Boc‑amine below 5 μg/mL as verified by online UV detection. The final product is a sterile injectable solution of a novel metabotropic glutamate receptor subtype 5 (mGluR5) PET tracer used in clinical neuroimaging studies for amyotrophic lateral sclerosis, demonstrating that the batch‑mode to flow translation mitigates operator radiolytic dose and satisfies ISO 11137‑1:2019 for radiation sterilization of the consumable fluidic path.

Autoclave‑Free Enantioselective Reductive Amination Protocol for a Chiral Cyclic Secondary Amine

When 3‑aminomethyl‑pyrrolidine‑1‑carboxylic acid tert‑butyl ester is specified as the amine donor in the synthesis of (R)‑3‑aminomethyl‑1‑(2,2,2‑trifluoroethyl)pyrrolidine, a key synthon for heterocyclic LpxC zinc‑dependent amidase inhibitors targeting Gram‑negative pathogens, the deprotection is executed with 3.0 eq. trifluoroacetic acid in dichloromethane overnight at ambient temperature. The crude amine is subjected to reductive amination with 1.0 eq. trifluoroacetaldehyde ethyl hemiacetal in the presence of 2.5 eq. sodium triacetoxyborohydride and 0.5 eq. acetic acid in dichloromethane at 0 °C. Molar input ratio of the pyrrolidine amine to the aldehyde equivalent is fixed at 1.00 : 1.00; deviation beyond ± 0.03 eq. causes over‑alkylation that generates a quaternary ammonium impurity exceeding 1.5 area %, which cannot be removed without chiral simulated moving bed chromatography. The process operates in an ISO 13485‑certified environment for active implantable medical device excipients, with monitoring per ICH Q3A(R2) for qualification of novel impurities. The downstream isolation involves quenching with aqueous sodium bicarbonate, phase separation, distillation to replace dichloromethane with isopropanol, and fractional crystallisation at −10 °C to attain an enantiomeric excess of 99.5 % as determined by gas chromatography on a Chirasil‑Dex column (ASTM D6456‑10 analog). The isolated chiral amine is further elaborated into a lead LpxC inhibitor with MIC values below 0.06 μg/mL against multidrug‑resistant Acinetobacter baumannii, currently in preclinical development with toxicology batch release testing against Ph. Eur. 2.6.14 for bacterial endotoxins and ISO 10993‑5:2009 for in vitro cytotoxicity screening.

When Quaternary Ammonium Side‑products After N‑Alkylation Must Be Controlled Below 0.10 Area‑% for Photoredox Cross‑Coupling Feeds

Employment of the title compound as a latent amine source in the photoredox‑mediated Csp³–Csp² cross‑coupling with cyanopyridines requires liberation of the pyrrolidine base followed by formation of the corresponding N‑(trimethylsilyl)methylamine intermediate. The free amine is generated via hydrogen chloride in cyclopentyl methyl ether (4.0 M, 1.5 eq.) at 10 °C and directly alkylated with 1.1 eq. (trimethylsilyl)methyl triflate under rigorously anhydrous conditions. The addition stoichiometry of the silyl electrophile relative to the amine must be maintained within 1.08–1.14 eq.; overalkylation produces a quaternary ammonium impurity that acts as a deep eutectic solvent component, suppressing the quantum yield of the iridium(III) photocatalyst by forming a ground‑state complex evidenced by static quenching at λₐ₆₀ nm fluorescence spectroscopy. Quality assurance follows ICH Q7 Chapter 11 with 21 CFR 210.3(b) definitions for drug product intermediate, and residue limits for the silyl reagent are monitored by ICP‑OES for silicon per USP <233>. The downstream continuous‑flow photochemical reactor (Vapourtec UV‑150, 0.5 mm ID perfluoroalkoxy tubing) operates at 450 nm, 60 W, and a residence time of 90 seconds, producing the coupled C–C product in 76 ± 4 % isolated yield after flash chromatography. The terminal substance is a 4‑(pyrrolidin‑3‑ylmethyl)pyridine intermediate that undergoes further functionalisation to clinical‑stage selective JAK3/TEC family kinase inhibitors with covalent warhead functionality, fully characterized for mutagenic potential via Ames II assay compliant with OECD 471 and supplied under a technical package that includes glass transition temperature measurement by differential scanning calorimetry per ISO 11357‑2:2020.

Synthesis of the selective norepinephrine‑dopamine reuptake inhibitor intermediate (S)‑3‑(bis(4‑fluorophenyl)methoxy)methyl‑pyrrolidine‑1‑carboxylic acid tert‑butyl ester starts from optically pure (S)‑3‑aminomethyl‑pyrrolidine‑1‑carboxylic acid tert‑butyl ester. The amine is first condensed with 1.0 eq. 4,4′‑difluorobenzophenone imine in tetrahydrofuran containing titanium(IV) isopropoxide at 50 °C, followed by reduction with sodium cyanoborohydride at 0 °C. The molar ratio of reducing agent to imine is held at 2.0 with pH maintained at 4.0–4.5 by continuous addition of acetic acid, preventing over‑reduction of the aryl fluoride moieties that generates a dehalogenated impurity with very similar crystal habit. All operations are executed under a master batch record compliant with ICH Q7 Chapter 5 and ISO 14644‑1 Class 8 cleanroom. Downstream processing involves quenching in 2 M sodium hydroxide, extraction into diethyl ether, azeotropic drying with toluene, and salt formation with fumaric acid in acetone to precipitate the fumarate salt in 92 % yield with chemical purity exceeding 99.8 % quantified against a certified reference standard traceable to USP RS. The protected amine is a direct precursor to a dopamine transporter‑norepinephrine transporter dual ligand structurally related to current anti‑obesity agents, delivered with an elemental impurity risk assessment per ICH Q3D and a shelf‑life stability protocol per ICH Q1A(R2) Zone II conditions.