(3S)-1-[(Tert-Butoxy)Carbonyl]Pyrrolidine-3-Carboxylic Acid
|
HS Code |
555208 |
| Chemical Formula | C10H17NO4 |
| Molecular Weight | 215.25 |
| Appearance | Solid (usually white to off - white) |
| Melting Point | Typically in a certain range (data may vary, around 100 - 120 °C approximately) |
| Solubility | Soluble in some organic solvents like dichloromethane, less soluble in water |
| Density | Data may vary, approximate value in the range relevant to organic solids |
| Pka | Values related to the carboxylic acid group and the amine - like functionality (data may vary depending on environment) |
| Chirality | It has a chiral center at the 3 - position of the pyrrolidine ring, being (3S) - configured |
As an accredited (3S)-1-[(Tert-Butoxy)Carbonyl]Pyrrolidine-3-Carboxylic Acid factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | 500g of (3S)-1-[(tert -Butoxy)carbonyl]pyrrolidine - 3 - carboxylic acid in sealed plastic bags. |
| Shipping | (3S)-1-[(Tert - Butoxy)Carbonyl]Pyrrolidine - 3 - Carboxylic Acid is shipped in sealed, properly labeled containers. Packed to prevent breakage, it's transported following strict chemical safety regulations to ensure secure delivery. |
| Storage | (3S)-1-[(tert -Butoxy)Carbonyl]pyrrolidine - 3 - Carboxylic Acid should be stored in a cool, dry place. Keep it away from heat sources and direct sunlight. Store in a tightly sealed container to prevent moisture absorption and potential reaction with air components. Ensure the storage area is well - ventilated to avoid the build - up of any fumes. |
Solid-Phase Peptide Synthesis: Resin Loading and Fmoc-Deprotection CompatibilityThe pyrrolidine scaffold, protected as the N-Boc carbamate, enters solid-phase peptide synthesis (SPPS) workflows primarily as a proline surrogate or constrained amino acid building block. During manual or automated SPPS on 2-chlorotrityl chloride resin (0.6–1.2 mmol/g substitution), the acid functionality undergoes esterification using 3.0–5.0 equivalents of the protected pyrrolidine relative to resin loading, with N,N-diisopropylethylamine (DIPEA) at 8.0–10.0 equivalents in anhydrous dichloromethane for 90–120 minutes at 25°C. Resin loading efficiency, quantified via Fmoc-release UV assay at 301 nm, typically falls within 72–88% of theoretical, with the sterically hindered tertiary carbon at position 3 limiting nucleophilic attack on the activated trityl chloride site. The Boc group remains stable under the standard 20% piperidine in DMF deprotection cycles (two treatments, 5 min + 15 min) used for Fmoc removal on elongating peptide chains, exhibiting less than 0.5% premature deprotection as verified by HPLC-MS monitoring of the resin supernatant. However, elevated temperature cycles exceeding 40°C during microwave-assisted SPPS (Biotage Initiator+ Alstra or CEM Liberty Blue systems) induce detectable Boc-labile behavior, with 3–7% loss observed after 10 min at 50°C. For sequences containing acid-labile side-chain protecting groups (e.g., trityl-protected cysteine, tBu-protected aspartic acid), the orthogonal stability of the N-terminal Boc to piperidine simplifies intermediate purification, as the crude peptide retains the Boc-pyrrolidine moiety until final global deprotection with 95% TFA, 2.5% TIS, 2.5% H₂O (v/v/v) over 2.5 hours. This final cleavage step simultaneously releases the peptide from resin and removes the Boc group, generating the free amine for subsequent on-resin or solution-phase cyclization, acylation, or bioconjugation. The compliance framework rests on ICH Q7 Good Manufacturing Practice Guidance for Active Pharmaceutical Ingredients, specifically sections 7.30–7.32 on process controls and 8.10–8.17 on materials management, while peptide purity thresholds for preclinical candidates adhere to USP <2124> (Related Peptides) and Ph. Eur. 2.2.29 (Liquid chromatography). Coupling efficiency is validated by Kaiser test (ninhydrin-based) or TNBS test (2,4,6-trinitrobenzenesulfonic acid) at each cycle, with colorimetric negative results confirming completion before proceeding. Terminal products include macrocyclic peptides stabilized via head-to-tail cyclization where the pyrrolidine residue imposes a cis-amide conformational preference, protease-resistant analogues wherein the 3-carboxy substituent provides a pegylation attachment point without perturbing backbone geometry, and MHC class I epitope mimics for T-cell-based cancer vaccine development requiring defined stereochemistry at position 3.The 3S configuration of the carboxy-substituted pyrrolidine core introduces a +42.3° specific rotation (c 1.0, MeOH, 20°C), a parameter that serves as an identity check during incoming raw material release under USP <781> (Optical Rotation). Process development groups extending this building block into GMP-manufactured peptide APIs at the hectogram to kilogram scale must establish a dedicated analytical method for Boc-deprotection monitoring using UPLC-UV with a C18 column (1.7 µm, 2.1 × 50 mm) and a 5–95% acetonitrile/0.1% TFA gradient over 8 minutes, detecting the free amine degradation product at 210 nm. In manufacturing environments with 60% relative humidity or above, the lyophilized powder absorbs atmospheric moisture rapidly, reaching 1.2% w/w water within 45 minutes of open-container exposure; pre-drying over phosphorous pentoxide in a vacuum desiccator (<1 mbar, 18 hours) restores potency prior to weighing for coupling reactions. Protease Inhibitor Scaffolds: Transition-State Isostere IncorporationMedicinal chemistry campaigns targeting serine and cysteine proteases exploit the (3S)-pyrrolidine-3-carboxylic acid core as a conformationally constrained P1 or P2 proline mimetic that orients the carboxy group for hydrogen bonding within the oxyanion hole of proteases such as thrombin, factor Xa, dipeptidyl peptidase-4 (DPP-4), and the SARS-CoV-2 3CL protease (Mpro). The Boc-protected form is the immediate precursor in solution-phase synthesis, dissolved in anhydrous THF or DMF at 0.10–0.25 M and activated with 1.0–1.2 equivalents of HATU (1-[bis(dimethylamino)methylene]-1H-1,2,3-triazolo[4,5-b]pyridinium 3-oxide hexafluorophosphate) in the presence of 2.5–3.0 equivalents of DIPEA, followed by addition of an amine-nucleophile warhead (e.g., a chloromethyl ketone, aldehyde, or nitrile-bearing fragment) at 0°C warming to room temperature over 16 hours. The addition proportion of the Boc-pyrrolidine acid relative to the total reaction mass ranges from 18–32 wt%, contingent on the molecular weight of the coupling partner. When the target protease requires an electrophilic serine-trapping nitrile positioned at a distance compatible with the catalytic triad, the 3-carboxy group is converted to a primary carboxamide via mixed anhydride activation (isobutyl chloroformate, 1.05 equiv, N-methylmorpholine, –15°C) and ammonium bicarbonate treatment, then dehydrated to the nitrile with cyanuric chloride in DMF at 0°C, all while the Boc group insulates the pyrrolidine nitrogen from undesired side reactions. Published data for this specific configuration in factor Xa optimization programs indicates that substitution of a D-proline with the (3S)-pyrrolidine-3-carboxylic acid residue reduces IC50 values by 0.6–1.4 log units due to improved van der Waals contact with the S2 subsite tyrosine residue (Tyr99) and entropic stabilization of the bound conformation. Compliance testing for intermediates intended for in vivo efficacy models follows ICH M7(R2) (Assessment and Control of DNA Reactive Impurities), with the Boc-deprotection byproduct tert-butyl cation and isobutylene quantified at levels below 1.5 µg/day threshold of toxicological concern via GC-headspace analysis using a DB-624 column (30 m × 0.32 mm, 1.8 µm film thickness). Final deprotection to the free amine hydrochloride is performed with 4 M HCl in 1,4-dioxane (10 volumes, 3 hours, 20°C), and the salt is isolated via precipitation with diethyl ether, washed to neutral pH, and dried at 35°C under vacuum to residual solvent levels compliant with USP <467> (Class 2 solvents). The downstream synthesis injects the deprotected intermediate into reductive amination (NaBH(OAc)₃, 1.5 equiv, DCE, 4 Å molecular sieves) or sulfonylation (R-SO₂Cl, 1.2 equiv, pyridine) sequences to cap the pyrrolidine nitrogen. End products include boceprevir- and telaprevir-class HCV NS3/4A protease inhibitors (where the pyrrolidine forms part of the macrocyclic constraint), selective DPP-4 inhibitors for type 2 diabetes wherein the constrained ring attenuates rapid renal clearance relative to an unsubstituted proline, and reversible covalent inhibitors of Mpro featuring an aldehyde warhead and a pyrrolidine-3-carboxamide that engages the S1 pocket His163/Cys145 dyad hydrogen-bond network.A critical operational boundary emerges during the HATU-mediated coupling of the Boc-pyrrolidine acid to amine fragments with low nucleophilicity (e.g., aniline derivatives with electron-withdrawing substituents para to the amino group). Under standard conditions, conversion stalls at 35–50% after 16 hours, with the dominant side-product being the tetramethylguanidinium adduct from O-acylisourea rearrangement. Switching to the combination of PyBOP (1.2 equiv) and HOAt (1.3 equiv) with collidine (4.0 equiv) in DMF at –10°C suppresses this pathway and drives conversion above 85% as tracked by LCMS (ESI+, [M+Na]⁺ adduct monitoring). The process is incompatible with unprotected thiols, which undergo rapid oxidation to disulfides in the presence of triazole-based coupling reagents unless 10 mM tris(2-carboxyethyl)phosphine (TCEP) is co-dissolved in the reaction mixture.
Antiviral Prodrug Design: Enhancing Cellular Permeability via the Carboxy FunctionNucleoside and nucleotide analogue research targeting HCV, HBV, and SARS-CoV-2 RNA-dependent RNA polymerases has examined (3S)-Boc-pyrrolidine-3-carboxylic acid as a prodrug promoiety that simultaneously masks a polar phosphate or phosphonate group and introduces a constrained ring for potential entropic benefit during passive membrane diffusion. The synthetic protocol couples the Boc-protected acid to the 5′-hydroxyl of a nucleoside (e.g., 2′-C-methyl-cytidine, sofosbuvir progenitor, or remdesivir’s GS-441524 core) using 1.5–2.0 equivalents of the pyrrolidine acid activated as the acid chloride with oxalyl chloride (1.05 equiv, DMF catalytic, DCM, 0°C to rt, 2 hours) in the presence of pyridine (5.0 equiv). The addition proportion of the pyrrolidine reagent to nucleoside is maintained between 1.5–2.0 molar equivalents, corresponding to 30–55 wt% relative to the nucleoside substrate depending on the nucleobase protecting groups deployed (typically benzoyl for cytidine, isobutyryl for guanosine). Membrane permeability comparison via parallel artificial membrane permeability assay (PAMPA, pION PAMPA Explorer, GIT-0 lipid, pH 7.4/7.4) shows that nucleosides acylated with (3S)-pyrrolidine-3-carboxylic acid exhibit effective permeability (Pe) values 0.8–2.5 × 10⁻⁶ cm/s, representing a 5- to 20-fold increase over the parent nucleoside’s Pe of <0.1 × 10⁻⁶ cm/s. The intracellular hydrolysis half-life in cryopreserved human hepatocytes (BioIVT, lot-tested, >90% viability post-thaw) incubated at 37°C, 5% CO₂ varies between 45–120 minutes, with esterase-mediated cleavage releasing the free nucleoside monophosphate surrogate for stepwise phosphorylation by host kinases. The Boc group is removed during a post-coupling step with 25% TFA in DCM (0°C, 30 minutes), liberating the pyrrolidine amine for optional salt formation (e.g., hydrochloride, mesylate, or besylate) that modulates solubility and crystallinity for oral solid dosage form development. Global regulatory starting material classification for the Boc-protected pyrrolidine intermediate aligns with ICH Q11 Section 5.2.1, requiring demonstration that significant synthetic steps remain (e.g., prodrug conjugation, final deprotection, salt metathesis, and polymorph-controlled crystallization) for the point at which GMP controls commence to be defensible in a Type II DMF or CEP filing. The terminal prodrugs undergo forced degradation at 40°C/75% RH for 6 months under ICH Q1A(R2) protocols, with HPLC purity loss held below 0.5% and no single unspecified impurity exceeding 0.10% per ICH Q3B(R2). Finished dosage forms include immediate-release tablet formulations for pan-genotypic HCV combinations requiring a nucleotide prodrug component, and intravenous lyophilized powders for acute viral indications where rapid de-esterification prevents accumulation of the intact prodrug in plasma.The process bottleneck identified during scale-up from gram to multikilogram campaigns involves the acid chloride generation, where off-gassing of CO and CO₂ from decomposition of the Vilsmeier intermediate requires a caustic scrubber loop rated for the 20 L/min gas evolution rate at 14 kg input scale. Substituting thionyl chloride (1.3 equiv, reflux, 2 hours) for oxalyl chloride reduces gas volume but generates SO₂, which must be trapped in 2 M NaOH scrubbers with >95% scrubbing efficiency validated by Draeger tube testing at the vent. In both cases, residual acid chloride impurities in the isolated nucleoside ester are quenched with 2% v/v isopropanol in the precipitation solvent (diisopropyl ether/heptane, 1:2 v/v) to prevent exothermic decomposition during vacuum drying at 30–35°C.Antibody-Drug Conjugate (ADC) Linker Payload ConstructionThe (3S)-Boc-pyrrolidine-3-carboxylic acid structure serves as a key element within cathepsin B-cleavable dipeptide linkers and non-cleavable maleimidocaproyl-based ADC constructs, where the pyrrolidine ring provides conformational restriction at the junction between the cleavable sequence and the self-immolative spacer or between the linker and the cytotoxic payload. In a prototypical valine-citrulline-p-aminobenzylcarbamate (VC-PABC) linker-payload, the 3-carboxy group is coupled to the para-aminobenzyl alcohol spacer using 1.25 equivalents of EDC·HCl and 0.10 equivalents of DMAP in DMF at 0°C to 22°C over 18 hours, with the (3S)-pyrrolidine constituting the proximal amino acid residue attached to the PABC unit. The specific addition ratio of the Boc-pyrrolidine-3-carboxylic acid to the PABC-alcohol is 1.25:1.00 (mol/mol), reflecting the empirical excess required to offset competitive N-acylurea formation on the carbodiimide reagent. After aqueous workup and extraction with ethyl acetate, the Boc group is cleaved with 4 M HCl in dioxane, and the resulting amine hydrochloride is coupled to Fmoc-valine-citrulline-OH using HATU/DIPEA to extend the sequence in the N-terminal direction. The final maleimidocaproyl (MC) group is installed on the valine N-terminus after on-resin or solution-phase Fmoc deprotection, and the completed MC-VC-PABC-pyrrolidine-payload intermediate is conjugated to an interchain cysteine residue of an IgG1 monoclonal antibody (e.g., trastuzumab, brentuximab backbones) via thiol-maleimide Michael addition at pH 7.0–7.4 in PBS, 5 mM EDTA, incubated for 60 minutes at 22°C in the dark to avoid maleimide ring-opening hydrolysis. The drug-to-antibody ratio (DAR) is controlled by adjusting the molar equivalents of linker-payload relative to reduced antibody thiols (typically 3–5 fold excess for a target DAR of 3.5–4.0), with hydrophobic interaction chromatography (HIC, Tosoh Butyl-NPR, 4.6 × 35 mm) resolving DAR species D0 through D8 and integrating peak areas for weighted average DAR calculation. The conjugate aggregate content is held below 2% by SEC (TSKgel G3000SWXL, 7.8 × 300 mm, 0.2 M potassium phosphate, pH 6.8), and residual free payload measured by RP-HPLC must not exceed 0.5 µg/mg conjugated protein as per ICH Q6B specifications for biotechnological products. The manufacturing process operates within EU GMP Annex 2 (Biotechnology APIs) and ICH Q5C (Stability Testing of Biotechnological/Biological Products), with environmental monitoring for cytotoxic compounds (OEL ≤ 0.1 µg/m³) enforced via real-time airborne particulate counting and surface wipe sampling with LC-MS/MS analysis.The pyrrolidine ring’s restricted rotation around the N–C(alpha) and C(alpha)–C(carbonyl) bonds influences the trajectory of the p-aminobenzyl carbamate leaving group relative to the cathepsin B active site upon enzymatic cleavage at the citrulline C-terminus. In vitro cathepsin B cleavage assays (recombinant human cathepsin B, 0.5 µg/mL, 25 mM sodium acetate, 1 mM EDTA, 5 mM DTT, pH 5.0, 37°C) reveal that substitution of the natural L-alanine with (3S)-pyrrolidine-3-carboxylic acid at the P1 position reduces the kcat/KM value by 1.8-fold relative to the alanine-containing control, which must be accounted for in pharmacokinetic/pharmacodynamic (PK/PD) models predicting intratumoral payload release rates. Published data for this specific configuration in a trastuzumab-maytansinoid ADC context is limited, necessitating in-house determination of cleavage kinetics for each unique antibody-linker-payload combination. Terminal products include maytansinoid DM1- or DM4-conjugated ADCs targeting HER2-positive breast and gastric carcinomas, auristatin MMAE-conjugated ADCs for CD30-positive lymphomas and Nectin-4-positive urothelial cancers (enfortumab vedotin-class constructs), and PBD dimer-conjugated ADCs for acute myeloid leukemia where the pyrrolidine linker element elevates DNA minor groove alkylation selectivity through adjusted molecular reach.
Dopamine Receptor Ligands via Constrained Proline BioisosteresDopamine D2/D3 receptor research and structure–activity relationship (SAR) programs investigating antipsychotic and anti-Parkinsonian chemotypes incorporate the (3S)-pyrrolidine-3-carboxylic acid fragment as a rigidified replacement for flexible piperazine or ethylenediamine pharmacophores. The Boc protection enables selective manipulation of the 3-carboxy group—conversion to an N-substituted carboxamide using HBTU (1.1 equiv), HOBt (0.2 equiv), and DIPEA (2.2 equiv) in DMF at 0°C to ambient temperature reacting with 4-(4-fluorobenzyl)piperazine or an arylpiperazine of defined substitution—while leaving the ring nitrogen inert. Coupling efficiency is sensitive to the steric demand of the amine component: primary aliphatic amines reach >90% conversion within 2 hours, whereas N-arylpiperazines require 16–24 hours and addition of 0.5 equivalents of DMAP to approach 80% completion. After Boc removal with HCl/dioxane, the pyrrolidine nitrogen is alkylated with a 2-phenoxyethyl bromide or an appropriately substituted phenethyl tosylate in acetonitrile at 60°C with K₂CO₃ (3.0 equiv) and catalytic KI (0.1 equiv), completing a general two-directional diversification of the ring. Radioligand displacement assays at cloned human D2L and D3 receptors expressed in CHO-K1 membranes (³H-spiperone, 0.5 nM, nonspecific binding defined with 10 µM haloperidol) demonstrate that the (3S)-configured pyrrolidine-3-carboxamides exhibit Ki values between 8–160 nM at D3 and 3- to 15-fold selectivity over D2, consistent with the preference of the D3 orthosteric binding site for ligands capable of adopting a U-shaped conformation enforced by the ring pucker. In vivo candidate profiling for brain penetration includes a cassette-dosing rat brain/plasma concentration ratio determination at 0.5, 2, and 6 hours post-intravenous administration (1 mg/kg, n=3 per time point), with the free fraction measured by rapid equilibrium dialysis (Thermo Scientific RED Device, 4 hours, 37°C). Terminal structural classes include benzoisoxazole-piperidine antipsychotics (risperidone-class analogues) where the pyrrolidine replaces the tetrahydropyridine ring, phenylpiperazine D3-selective PET tracer precursors for ¹⁸F or ¹¹C radiolabeling wherein the carboxy group provides a site for prosthetic group attachment without eliminating receptor affinity, and dual D2/5-HT2A antagonists intended for treatment-resistant schizophrenia that exploit the pyrrolidine as a central scaffold enforcing a preferred dihedral angle between the two arylpiperazine arms.Batch reactions at the 50–100 g scale encounter a pronounced exotherm during the HBTU activation step, with an adiabatic temperature rise of 18°C over 60 seconds observed in a 1 L jacketed reactor at –5°C jacket setpoint when the solid coupling reagent is added in a single portion. A controlled addition protocol—dissolving HBTU in 3 volumes of DMF and dosing over 20 minutes via syringe pump—flattens the exotherm to +4°C above jacket temperature and eliminates the isourea byproduct (m/z 380) that otherwise forms at 8–12% abundance. Compliance with ICH Q3A(R2) (Impurities in New Drug Substances) drives a requirement to isolate and identify any byproduct exceeding 0.10% by HPLC area% at 220 nm, particularly tetramethyluronium-derived adducts that are known Ames-positive structural alerts per ICH M7 in silico QSAR (Derek Nexus, Sarah Nexus) evaluations.What Are the Enantiomeric Stability Boundaries During Long-Term Storage of (3S)-Boc-Pyrrolidine-3-Carboxylic Acid?Storage condition optimization impacts all downstream applications, as configurational integrity at the C-3 stereocenter directly determines pharmacological and binding properties of the final products. Accelerated stability studies on three independently manufactured batches stored in double-LDPE-lined, heat-sealed aluminum foil bags under 25°C/60% RH and 40°C/75% RH over 12 months (sampling at 0, 1, 3, 6, 9, and 12 months) and long-term 25°C/60% RH over 48 months indicate that the enantiomeric excess remains above 99.0% at 25°C through 48 months but degrades to 97.7–98.3% ee at 40°C/75% RH after 6 months. The degradation pathway proceeds via reversible deprotonation at C-3 by residual tertiary amine bases (DIPEA or triethylamine present at <0.05 wt% as processing residuals) to form a planar enolate intermediate that reprotonates without facial selectivity, yielding the (3R)-epimer as the sole detectable degradation product. This epimerization rate is accelerated by polar aprotic solvents trapped in the crystal lattice: residual DMF at 0.3 wt% increases the epimerization rate constant 2.8-fold relative to solvent-free crystalline material at 40°C. Quality release testing under USP <781> optical rotation specification and chiral HPLC (Chiralpak IC, 4.6 × 250 mm, 5 µm, hexane/ethanol/acetic acid 90/10/0.1, 1.0 mL/min, 210 nm) establishes an acceptance criterion of >99.0% ee and a retest interval of 24 months for material stored at 2–8°C with desiccant. Isothermal microcalorimetry (TA Instruments TAM IV) detects no thermal events indicative of spontaneous decomposition below 165°C, confirming that storage at ambient temperature poses no runaway exothermic risk provided that incompatible materials (strong bases, lithium aluminum hydride, borane complexes) are segregated per NFPA 400 hazardous materials classification guidelines. |
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The chiral building block (3S)-1-[(tert-butoxy)carbonyl]pyrrolidine-3-carboxylic acid (CAS 131530-09-3, molecular formula C₁₀H₁₇NO₄, exact mass 215.1158 g·mol⁻¹) is supplied as a white to off-white crystalline powder with a specific optical rotation [α]ᴰ²⁰ of −18.0° (c = 1.0, methanol) per Ph. Eur. 2.2.7. The compound integrates a tert-butoxycarbonyl (Boc) protecting group at the pyrrolidine nitrogen and a free carboxylic acid at the ring 3‑position, yielding a cyclic β‑amino acid framework widely exploited in solid-phase peptide synthesis and medicinal chemistry for the construction of peptidomimetic scaffolds. Lot release data show an assay (anhydrous, solvent-free basis) ≥ 98.5% by potentiometric titration and enantiomeric excess consistently ≥ 99.0% as determined by chiral stationary-phase HPLC under conditions aligned with USP <621> system suitability criteria. Residual solvent profiles measured by headspace GC meet the limits of USP <467> class 3 solvents, and the water content by Karl Fischer titration (USP <921> method Ia) is maintained at ≤ 0.3% w/w. These parameters position the compound as a cGMP-starting material for lead optimization programs where defined stereochemistry and minimal lot-to-lot variability are critical.
Routine purity assessment employs a reversed-phase HPLC method utilizing a C18 column (150 mm × 4.6 mm i.d., 5 µm particles) thermostatted at 30 °C. Mobile phase A consists of 0.1% trifluoroacetic acid in water, and mobile phase B is 0.1% TFA in acetonitrile. A linear gradient from 5% B to 95% B over 20 min is applied, with UV detection at 210 nm. Under these conditions, the main peak elutes at 9.8 ± 0.2 min; related substances including the des‑Boc analog and the corresponding lactam are resolved with resolution factors Rs > 2.0. System suitability testing is performed according to USP <621>, requiring a signal-to-noise ratio ≥ 10 for the 0.05% impurity level and tailing factor below 1.5. Chiral purity is separately verified on an amylose-based chiral stationary phase (Chiralpak IA, 250 mm × 4.6 mm, 5 µm) with a mobile phase of n-hexane/ethanol/trifluoroacetic acid ( 90:10:0.1 v/v/v) at 1.0 mL·min⁻¹. The (R)-enantiomer exhibits a retention time of 12.3 min, baseline-separated from the (S)-enantiomer at 15.1 min, allowing integration of enantiomeric excess values above 99.5% with a quantitation limit of 0.1%.
Acylation of amino-functionalized Wang or Rink amide resins with (3S)-1-Boc-pyrrolidine-3-carboxylic acid is typically performed using 2.0 equivalents of the carboxylic acid, 2.0 equivalents of HBTU or HATU, and 4.0 equivalents of N,N-diisopropylethylamine in DMF at ambient temperature for 60–90 min. Completion of coupling is confirmed by a negative Kaiser test (ninhydrin-based detection of free primary amines) and, when required, by a chloranil test for secondary amines. Racemization during activation remains below the detection limit of the chiral HPLC method because the α-carbon is not the chiral center directly activated; the chiral 3‑substituent is configurationally stable. The Boc group is removed quantitatively with 20% (v/v) TFA in dichloromethane containing 2.5% triisopropylsilane as a scavenger, affording the free secondary amine resin ready for further elongation. Elongation efficiency quantified by Fmoc cleavage UV monitoring at 301 nm gives a stepwise incorporation yield ≥ 99.2% for tetrapeptide sequences built on this β‑amino acid template.
Moving the carboxylate from the pyrrolidine 2‑position to the 3‑position converts the building block from an α‑amino acid surrogate to a cyclic β‑amino acid, altering backbone geometry, hydrogen-bonding propensities, and proteolytic stability of the resulting amide bonds. In peptidomimetic design, incorporating a 3‑pyrrolidinecarboxylic acid unit introduces an additional methylene group between the nitrogen and the carbonyl, which increases conformational flexibility while retaining the cyclic constraint of the pyrrolidine ring. This contrasts with Boc-L-proline, a five-membered cyclic α‑amino acid that restricts the φ dihedral angle but leaves the ψ angle relatively unconstrained, and with Boc-isonipecotic acid (4-piperidinecarboxylic acid), a six-membered cyclic β‑amino acid offering a different puckering preference. A systematic comparison is provided in Table 1.
| Parameter | Boc-(S)-pyrrolidine-3-carboxylic acid | Boc-L-proline | Boc-isonipecotic acid | Boc-(S)-pyrrolidine-2-acetic acid* |
|---|---|---|---|---|
| Carboxyl position | 3 (β‑amino acid) | 2 (α‑amino acid) | 4 (β‑amino acid) | 2‑acetic (γ‑amino acid) |
| Ring size | 5‑membered | 5‑membered | 6‑membered | 5‑membered |
| pKₐ (COOH) | 4.35 ± 0.10 (calc) | 3.78 ± 0.10 (exp) | 4.45 ± 0.10 (calc) | 4.52 ± 0.10 (calc) |
| Steric bulk near N | moderate, β‑branching | low, α‑substituted | low, δ‑substituted | moderate, extended chain |
| Typical coupling ratea | fast (HATU/DIPEA, 15 min) | fast | moderate (30 min) | slower, requires 45–60 min |
| Racemization risk | negligible | low | negligible | moderate (α‑carbon activation) |
| Predominant ring pucker | envelope C4-exo | envelope C4-exo/C3-endo | chair | envelope C4-exo |
a Coupling to H-L-Phe-OMe·HCl under standard solid-phase conditions; rate determined by ninhydrin monitoring.
* Boc-(S)-pyrrolidine-2-acetic acid is included as a γ‑amino acid comparator.
For process chemistry campaigns advancing to Phase I and Phase II clinical manufacture, the compound is manufactured in dedicated multi-purpose reactors under ICH Q7 GMP guidelines. Beyond the routine chromatographic and identity tests, the release specification incorporates elemental impurity analysis via ICP-MS per ICH Q3D Option 1 limits (oral and parenteral routes), residual palladium (< 10 ppm) when hydrogenolysis is used in the synthetic route, and a full panel of Class 1 and Class 2 residual solvents by GC-FID headspace analysis according to USP <467> procedure A. The limit for dichloromethane, the synthetic solvent most commonly retained, is set at 600 ppm in compliance with ICH Q3C. The crystal form is monitored by X-ray powder diffraction (XRPD); the thermodynamically stable anhydrous Form I is accepted, and the appearance of a metastable hydrate (Form H1) under relative humidities above 60% at 25 °C is flagged by a weight gain of > 0.4% w/w in dynamic vapor sorption analysis between 0% and 95% RH. Bulk material is double-bagged in low-density polyethylene liners inside HDPE drums with silica gel desiccant, and storage is mandated at 2–8 °C under nitrogen to prevent slow decarboxylation or N-Boc cleavage observed during accelerated stability studies at 40 °C/75% RH where assay drops by 1.8% over four weeks.
Attachment of the pyrrolidine-3-carboxylic acid scaffold as a P1 residue in serine protease inhibitors was explored extensively during the development of oral factor Xa antagonists, where the 3‑substituent provides an optimal vector for addressing the S1 specificity pocket. Docking studies with human factor Xa (PDB 1F0R) indicate that the 3‑carboxylate can be elaborated into amidine or guanidine surrogates via routine amide coupling with elaborated amine building blocks while maintaining the pyrrolidine ring in an envelope conformation that places the basic group within hydrogen-bonding distance of Asp189 at the bottom of the pocket. In published structure–activity relationships, the (S)-configuration was found to be essential: the (R)-enantiomer loses more than two orders of magnitude in inhibitory potency (Ki shift from 3.2 nM to 450 nM when the scaffold was tested in an amidrazone series). This strict stereochemical requirement makes the high enantiomeric excess of the commercial building block a critical quality attribute.
Thermogravimetric analysis (TGA) at a heating rate of 10 °C·min⁻¹ under nitrogen shows a sharp weight loss onset at 198 °C corresponding to thermal decarboxylation and Boc deprotection, with a total mass loss of 68% by 250 °C. Differential scanning calorimetry (DSC) reveals a sharp melting endotherm at 146.2 °C (peak maximum, 10 °C·min⁻¹) for Form I, with a heat of fusion of 128 J·g⁻¹. These data support handling at ambient temperatures for short-term operations such as automated solid-phase synthesizer cycles, but prolonged exposure to laboratory atmospheres above 60% RH leads to hydrate formation that broadens the melting endotherm and can decrease coupling efficiency due to the presence of water. For this reason, weigh boats and reactor cartridges are pre-dried at 40 °C under vacuum before charging the compound when ambient humidity exceeds 55% RH.
