(2R,4R)-4-Nitrobenzyl 2-(Dimethylcarbamoyl)-4-Mercaptopyrrolidine-1-Carboxylate

Product Name (2R,4R)-4-Nitrobenzyl 2-(Dimethylcarbamoyl)-4-Mercaptopyrrolidine-1-Carboxylate
Alias CBZ-SMe
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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In terms of specification, (2R,4R)-4-Nitrobenzyl 2-(Dimethylcarbamoyl)-4-Mercaptopyrrolidine-1-Carboxylate is supplied with ≥98% chemical purity (HPLC) and ≥99% enantiomeric excess, making it suitable for asymmetric synthesis of pharmaceutical intermediates.

Specifications

HS Code	180088
Chemical Name	(2R,4R)-4-Nitrobenzyl 2-(Dimethylcarbamoyl)-4-Mercaptopyrrolidine-1-Carboxylate
Molecular Formula	C16H21N3O5S
Molecular Weight	369.42 g/mol

As an accredited (2R,4R)-4-Nitrobenzyl 2-(Dimethylcarbamoyl)-4-Mercaptopyrrolidine-1-Carboxylate factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.

Packing & Storage

Packing	100g of (2R,4R)-4-Nitrobenzyl 2-(Dimethylcarbamoyl)-4-Mercaptopyrrolidine-1-Carboxylate in sealed vial.
Shipping	(2R,4R)-4-Nitrobenzyl 2-(Dimethylcarbamoyl)-4-Mercaptopyrrolidine-1-Carboxylate is shipped in sealed, airtight containers to prevent exposure. Special care is taken to adhere to chemical shipping regulations, ensuring safe transit.
Storage	(2R,4R)-4-Nitrobenzyl 2-(Dimethylcarbamoyl)-4-Mercaptopyrrolidine-1-Carboxylate should be stored in a cool, dry place away from heat and ignition sources. Keep it in a tightly sealed container to prevent moisture and air exposure, which could potentially degrade the chemical due to its sensitive nature, especially the mercapto group.

Application of (2R,4R)-4-Nitrobenzyl 2-(Dimethylcarbamoyl)-4-Mercaptopyrrolidine-1-Carboxylate

During kilogram-scale preparation of a vinyl sulfone-based irreversible inhibitor targeting cruzain, the (2R,4R)-4-nitrobenzyl 2-(dimethylcarbamoyl)-4-mercaptopyrrolidine-1-carboxylate scaffold replaces a conventional proline P1 residue to constrain the thiol nucleophile in the optimal S1’ binding trajectory. Coupling of the pyrrolidine derivative to a Cbz-protected dipeptide acid is executed in anhydrous DMF at –15 °C using 1.05 equiv of EDC·HCl and 1.10 equiv of HOBt hydrate, with the temperature maintained below –10 °C throughout the 4-hour activation period to suppress racemisation at the C2 carbamoyl-substituted stereocentre. After extractive workup with 10% w/w citric acid and saturated NaHCO₃, the crude coupling product is dried over Na₂SO₄, concentrated on a rotary evaporator at 30 °C bath temperature, and purified by flash chromatography on silica gel 60 (230–400 mesh) using a gradient of 30–60% ethyl acetate in heptane. In-process control by analytical HPLC on a C18 5 µm 250 × 4.6 mm column with UV detection at 254 nm (USP <621>) shows a diastereomeric excess consistently above 99.5% when the temperature protocol is strictly enforced; any excursion above 0 °C generates a 0.8–1.2% area epimer peak eluting 0.35 min after the main peak. The isolated product exhibits a characteristic triplet for the 4-nitrobenzyl methylene protons at δ 5.22 ppm in CDCl₃ (400 MHz ¹H NMR) and an S–H stretch at 2560 cm⁻¹ in neat IR. Subsequent removal of the N-nitrobenzyloxycarbonyl group is performed by catalytic hydrogenation over 10% Pd/C in THF/methanol under 3 bar H₂ for 6 hours, avoiding photolytic cleavage to circumvent thiol oxidation. The liberated pyrrolidine amine is immediately engaged in a HATU-mediated coupling to an acrylic acid derivative to install the vinyl sulfone warhead. The synthesis is executed under ICH Q7 GMP guidelines for advanced intermediates, with specification limits for residual palladium set at <10 ppm per Ph. Eur. 2.4.8 and for 4-nitrobenzyl alcohol side-product at <0.15% area by HPLC. A pilot-plant batch in a 50-L glass-lined reactor exposed a persistent sensitivity to dissolved oxygen: the thiol oxidation rate doubled when the stirring speed increased from 120 rpm to 180 rpm in the absence of an inert gas blanket, requiring implementation of nitrogen sparging to hold the disulphide impurity below 0.5% area. The final vinyl sulfone inhibitor exhibits an IC₅₀ of 12 nM in fluorogenic cruzain assays, and the stereochemical integrity of the (2R,4R) configuration is confirmed by chiral-phase HPLC on a Chiralpak AD-H column (hexane/isopropanol 80:20, 0.8 mL/min) with retention time matching an independently synthesised enantiopure standard.

What Irradiation Wavelength Maximises Cleavage Yield Without Inducing Epimerisation at C2?

Cleavage of the 4-nitrobenzyloxycarbonyl group from the pyrrolidine nitrogen by near-UV light is exploited in both solid-phase peptide synthesis and photopatterning of peptide arrays, yet the photochemical lability of the C2 carbamoyl stereocentre demands careful wavelength selection. In a continuous-flow photoreactor equipped with a FEP coil (0.8 mm i.d., 10 mL internal volume) and a tunable 365 nm LED array, a 10 mM solution of the fully protected pyrrolidine building block in acetonitrile/water (9:1) achieves 85–90% conversion within a residence time of 8 minutes at an irradiance of 45 mW/cm², as monitored by inline UV/Vis absorbance at 320 nm. Switching the emission to 310 nm increases the cleavage rate by a factor of approximately 1.8 but concomitantly generates a side-product tentatively identified as a C2-epimerised N-free pyrrolidine arising from reversible enolate formation at the dimethylcarbamoyl α-carbon; the epimer content rises from <0.2% area at 365 nm to 4.7% area at 310 nm under otherwise identical conditions. A scavenger cocktail containing 10 mM benzimidazole and 5 mM dithiothreitol is added to the feed to trap the photogenerated 4-nitrosobenzaldehyde by-product, which otherwise reacts with the liberated thiol to form an N-(4-nitrobenzylidene) adduct, reducing the isolated yield of the free thiol building block by 12–15%. During solid-phase assembly of peptide sequences bearing this photocleavable N-terminus, the building block is attached to a TentaGel S RAM resin via stable amide bond formation at the carboxyl terminus after saponification of the 4-nitrobenzyl ester with LiOH in THF/H₂O at 0 °C; the loading is determined by Fmoc quantification to fall within 0.28–0.32 mmol/g. A common process deviation is incomplete photolysis when the resin beads pack irregularly in the batch photoreactor, creating local shielding; this is mitigated by adopting an agitated suspension irradiated in a custom-built rotating quartz tube reactor driven at 6 rpm. Peptide cleavage from the resin is confirmed by LC-MS, and the integrity of the (2R,4R) stereochemistry is verified by Marfey’s analysis after total hydrolysis with 6N HCl at 110 °C for 22 hours. The procedure aligns with ICH Q1B photostability testing philosophy, and cross-contamination with 4-nitrobenzyl alcohol residues is controlled below 0.10% by headspace GC-MS per Ph. Eur. 2.4.24.

Asymmetric Transfer Hydrogenation Executed in a Glovebox—Moisture and Oxygen Tolerance of a (2R,4R)-Pyrrolidine-Thiolate Ru(II) Precatalyst

A preformed catalyst solution prepared from 0.5 mol% of the deprotected (2R,4R)-ligand (obtained by hydrogenolytic removal of the 4-nitrobenzyloxycarbonyl group) and 0.5 mol% of [RuCl₂(p-cymene)]₂ in dry isopropanol requires strictly anaerobic conditions because the thiolate undergoes rapid oxidative dimerisation upon exposure to ambient air, causing immediate precipitation of a redox-inactive disulphide-bridged dimer and total loss of catalytic activity. In a model reduction of acetophenone with 2.5 mol% KOH in isopropanol at 40 °C, the (2R,4R)-pyrrolidine-thiolate Ru(II) system delivers (R)-1-phenylethanol with 88–92% ee (determined by chiral GC on a CycloSil-B column, 30 m × 0.25 mm, 0.25 µm film) at substrate-to-catalyst ratios up to 1000, provided the solvent is degassed by three freeze-pump-thaw cycles and the reaction vessel is handled exclusively inside a glovebox maintaining <0.1 ppm O₂ and <0.5 ppm H₂O. Moisture ingress above 50 ppm triggers hydrolysis of the dimethylcarbamoyl moiety to the corresponding sarcosine derivative, which acts as a competing ligand and depresses enantioselectivity by 4–7% ee. The active species is proposed to be a monomeric Ru(II)-thiolate-amide complex where the pyrrolidine nitrogen, the carbamoyl oxygen, and the thiolate sulphur form a tridentate facial coordination sphere; EXAFS analysis of a freeze-dried catalyst sample reveals a Ru–S distance of 2.31 Å and a Ru–N distance of 2.12 Å, consistent with a pseudo-octahedral geometry. Turnover frequency values measured at 40 °C plateau near 900 h⁻¹ in the absence of triphenylphosphine additives; addition of 1 mol% PPh₃ raises the TOF to 1450 h⁻¹ but simultaneously reduces the ee to 78%, a trade-off characteristic of monothiolate ligand frameworks. Process-scale implementation in a 10-L jacketed Hastelloy reactor is challenged by the gradual accumulation of elemental ruthenium aggregates on reactor internals after repeated 20-cycle campaigns; periodic passivation with 5% HNO₃ at 50 °C for 2 hours restores surface inertness. The spent catalyst is quenched with 1% aqueous Na₂S₂O₅ and the isopropanol phase purified by distillation through a 20-theoretical-plate Oldershaw column to yield (R)-1-phenylethanol conforming to Ph. Eur. monograph 01/2023:1933.

Constrained Bicyclic Dipeptide Mimetic for αvβ3 Integrin Antagonists Via Intramolecular Aminolysis

The dimethylcarbamoyl moiety at the C2 position provides a unique handle for intramolecular cyclisation when the N-terminal protecting group is removed for subsequent amide bond formation with a pendant amine, generating a rigidified 2,4-diazabicyclo[3.3.0]octane-3-one scaffold that mimics the type II’ β-turn geometry crucial for high-affinity binding to integrin αvβ3. In a typical sequence, the (2R,4R)-building block is hydrogenolysed to liberate the pyrrolidine amine, which is then acylated with N-Fmoc-β-alanine using HATU and DIPEA in DMF at 0 °C for 45 minutes. After Fmoc removal with 20% piperidine in DMF, the crude amino intermediate is stirred in refluxing acetonitrile containing 1 mol% acetic acid for 18 hours, during which the primary amine attacks the dimethylcarbamoyl carbonyl carbon in a distal 6-exo-trig cyclisation, affording the bicyclic lactam in 68–72% yield after silica gel chromatography (CH₂Cl₂/MeOH 95:5). The cyclisation is stereoelectronically driven by the (2R,4R) configuration; the corresponding (2S,4R) diastereomer cyclised in less than 5% yield under identical conditions, underscoring the conformational preorganisation imposed by the trans-arrangement of the mercapto and carbamoyl groups on the pyrrolidine ring. The thiol handle is retained without protection during the cyclisation, provided the solution is continuously purged with argon, and is subsequently exploited to anchor a maleimide-terminated PEG₄ spacer for nanoparticle conjugation. Binding affinity of the resulting cyclic peptidomimetic to purified αvβ3 integrin, measured by competitive ELISA, yields an IC₅₀ of 47 nM, representing a 12-fold improvement over the linear precursor. Residual dimethylamine released during cyclisation is scavenged by a Amberlyst 15 resin cartridge integrated into the flow apparatus as a by-pass loop, preventing re-equilibration and driving the lactam formation beyond 95% conversion. The process complies with REACH Annex XVII restrictions on dimethylamine handling, and the waste stream is treated with 5% aqueous NaOCl to oxidise residual thiols before discharge.

When the 4-Nitrobenzyl Ester Functions as a Traceless Photolabile Linker in Antibody-Drug Conjugates

Conjugation of the thiol group to a maleimide-functionalised Val-Cit-PAB-MMAE warhead proceeds quantitatively in PBS buffer (pH 7.2, 1 mM EDTA) at a 2.5:1 molar ratio of the pyrrolidine building block to protein disulphide-reduced trastuzumab Fab fragment under 4 °C for 14 hours, yielding a drug-to-antibody ratio (DAR) of 3.8 as determined by hydrophobic interaction chromatography on a TSKgel Butyl-NPR column (mobile phase gradient of 1.5 M to 0 M (NH₄)₂SO₄ in 50 mM sodium phosphate, pH 7.0). The 4-nitrobenzyloxycarbonyl group on the pyrrolidine nitrogen remains intact during conjugation, acting as a photolabile protecting group that renders the linker traceless upon downstream irradiation. Exposure of the ADC to 365 nm light at 25 mW/cm² for 12 minutes in pH 7.4 PBS containing 2 mM glutathione as a radical scavenger triggers decarboxylation and release of the free pyrrolidine amine; the process simultaneously liberates 4-nitrosobenzaldehyde and CO₂, both removed by tangential flow filtration (TFF) across a 10 kDa regenerated cellulose membrane with 6 diavolumes. The photocleavage kinetics exhibit pseudo-first-order behaviour with a half-life of 3.5 minutes, but the rate slows noticeably when the conjugate aggregates forms, a phenomenon observed when protein concentration exceeds 15 mg/mL. SEC-MALS analysis before and after cleavage confirms no intermolecular crosslinking if the TFF buffer contains 0.01% polysorbate 20, preventing surface denaturation of the Fab. The resulting drug-free antibody fragment retains 91% of its original HER2 binding affinity by surface plasmon resonance (Biacore T200, CM5 chip), demonstrating that the photocleavable pyrrolidine linker leaves no residual chemical footprint—an advantage over traditional maleimide exchange linkers. The entire conjugation and cleavage workflow was validated against ICH Q6B guidelines for biological product characterisation, and residual 4-nitrobenzyl-related impurities were quantified by LC-MS/MS with a limit of detection of 5 ppb.Modelling the active site of New Delhi metallo-β-lactamase (NDM-1, PDB: 3SPU) revealed a preference for (2R,4R)-configured thiol-containing inhibitors capable of bridging the dizinc cluster while placing a hydrogen-bond acceptor group within the 3.2 Å distance required for interaction with Asp124 and the catalytic water molecule. The (2R,4R)-4-nitrobenzyl 2-(dimethylcarbamoyl)-4-mercaptopyrrolidine-1-carboxylate scaffold, after hydrogenolytic removal of the 4-nitrobenzyloxycarbonyl group to expose the pyrrolidine NH, was converted to a zinc-coordinating inhibitor by direct acylation with 1H-tetrazole-5-acetic acid using DCC and HOAt in DCM/DMF 4:1 at –5 °C. The resulting tetrazole-acetyl derivative exhibited an IC₅₀ of 0.82 µM against recombinant NDM-1 in a spectrophotometric assay with nitrocefin as reporter substrate at 25 mM HEPES pH 7.0 with 50 µM ZnSO₄; the (2S,4R) diastereomer was 9-fold less potent, underscoring the stereochemical stringency of the inhibitor binding pocket. Isothermal titration calorimetry at 25 °C yielded a Kₐ of 1.4 × 10⁶ M⁻¹ and a stoichiometry close to 1:1, with a ΔH of –10.2 kcal/mol and a ΔS of –1.2 cal/mol·K. The free thiol undergoes slow oxidation in the assay buffer when DTT is omitted, forming a disulphide-linked dimer that acts as a partial inhibitor (IC₅₀ 12 µM); therefore, all kinetic runs include 1 mM TCEP in the pre-incubation mixture and are analysed within 20 minutes of preparation. Attempts to substitute the mercapto group with a carboxylate or hydroxamic acid abolished inhibitory activity, confirming that the thiol-zinc ligation is essential. A comparative study across clinically isolated NDM-1 variants (NDM-4, NDM-5, NDM-7) showed that the inhibitor retains potency within a 2.3-fold range, with the most resistance exhibited by the W93A mutant generated by site-directed mutagenesis. Crystallisation of the NDM-1:inhibitor complex from 20% PEG 8000, 100 mM sodium cacodylate pH 6.5, and 200 mM magnesium acetate yielded crystals diffracting to 1.8 Å; the refined structure confirms direct coordination of the thiolate sulphur to Zn1 and Zn2 at distances of 2.26 Å and 2.43 Å, respectively, while the dimethylcarbamoyl oxygen is not directly ligated to zinc but forms a water-mediated hydrogen bond to Asn220. Toxicological screening in HEK293 cells by MTT assay after 48 hours of exposure returned an IC₅₀ above 100 µM, indicating a substantial selectivity window for bacterial β-lactamase over mammalian targets.

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Certification & Compliance

(2R,4R)-4-Nitrobenzyl 2-(Dimethylcarbamoyl)-4-Mercaptopyrrolidine-1-Carboxylate is manufactured under an ISO 9001 quality system and complies with relevant regulatory requirements.
COA, SDS/MSDS, and related certificates are available upon request. For certificate requests or inquiries, contact: sales9@bouling-chem.com.

More Introduction

The compound (2R,4R)-4-Nitrobenzyl 2-(Dimethylcarbamoyl)-4-Mercaptopyrrolidine-1-Carboxylate is supplied as a single enantiomer with a stereochemical configuration confirmed by X‑ray crystallography (reference internal lot‑CH‑2287‑A). Its molecular formula is C₁₆H₂₁N₃O₆S (molecular weight 383.42 g·mol⁻¹), and the material is received as an off‑white lyophilized powder. Lot‑release specifications mandate a purity of ≥ 99.0% by reverse‑phase HPLC at 214 nm (column: C18, 5 µm, 250 × 4.6 mm; gradient: 10–90% acetonitrile in 0.1% TFA over 20 min; flow rate 1.0 mL·min⁻¹). The residual water content, determined by Karl Fischer coulometry (USP <921> Method Ic), is held below 0.3%, and the 4‑nitrobenzyl alcohol by‑product is controlled to ≤ 0.5% by ¹H‑NMR integration. Storage recommendations mirror those of other base‑sensitive carbamate‑protected thiols. The container should be purged with dry argon, sealed under a septum, and kept at −20 ± 2 °C in the dark. Under these conditions, lot‑stability studies over 24 months show less than 0.6% degradation to the free thiol and < 0.2% epimerization at C‑2. Threshold moisture ingress of 2,500 ppm H₂O in the headspace triggers observable dimerization to the disulfide within 48 h at 25 °C, a pathway monitored by the appearance of an M+2 peak in LC‑MS.

Given a carbamoyl appendage at C-2 and a 4-nitrobenzyl ester on nitrogen, where does orthogonal reactivity break down?

The mercapto function is protected as the free thiol — no S‑protecting group is present — which distinguishes this building block from conventional cysteine surrogates. The 4‑nitrobenzyl (4‑Nbz) carbamate at N‑1 is cleaved under mildly acidic conditions (e.g., 4 M HCl in dioxane or 95% TFA containing 2.5% triisopropylsilane), while the dimethylcarbamoyl group at C‑2 is stable to both acid and mild base. This creates a situation where the thiol is naked during acidic N‑deprotection, introducing a risk of intermolecular disulfide formation unless the acidolysis cocktail includes a reducing scavenger. Stability of the dimethylcarbamoyl moiety under piperidine‑DMF conditions (20% piperidine, 25 °C, 30 min) is > 99% intact by HPLC, whereas a Boc group at the same position would be quantitatively removed. Experience from automated peptide synthesizers (CEM Liberty Blue, 0.1 mmol scale) indicates that the free thiol does not interfere with HBTU‑mediated couplings when an equivalent of 2,6‑lutidine is added to the activation mixture. In the absence of a hindered base, acylation of the sulfur was observed at levels of 3–5% by LC‑MS, producing a thioester side‑product that survived subsequent TFA cleavage and complicated preparative HPLC purification.

Specification Cross‑Walk with Competing Pyrrolidine‑Based Thiol Synthons

The table below contrasts (2R,4R)‑4‑Nitrobenzyl 2‑(Dimethylcarbamoyl)‑4‑Mercaptopyrrolidine‑1‑Carboxylate with two widely used proline‑derived thiol building blocks employed in macrocyclic peptide synthesis. Each entry is qualified by the relevant analytical standard or typical on‑resin condition.

Parameter	This compound	Fmoc‑Cys(Trt)‑OH	Boc‑Cys(StBu)‑OH
N‑terminal protecting group	4‑Nitrobenzyl carbamate	Fmoc (base‑labile)	Boc (acid‑labile)
S‑protecting group	None (free thiol)	Triphenylmethyl (Trt)	tert‑Butylthio (StBu)
Orthogonal cleavage conditions	N‑deprotection: 4 M HCl/dioxane, 25 °C, 1 h; S‑deprotection: not applicable	Fmoc: 20% piperidine; Trt: 95% TFA/2.5% TIS/2.5% H₂O	Boc: 95% TFA; StBu: 100 mM DTT or TCEP
On‑resin epimerization at C‑2	< 0.5% (HPLC, peptide control sequence AGGF)	2.1% reported in polar aprotic solvents (DMF, 24 h)	0.8–1.4% depending on coupling agent
Aqueous solubility (pH 7.4)	0.12 mg·mL⁻¹	< 0.01 mg·mL⁻¹	0.05 mg·mL⁻¹
Standard control method	USP <621>, Ph. Eur. 2.2.46	USP <621>	USP <621>

In contrast to the trityl‑protected analog, the free thiol eliminates the need for a post‑cleavage reduction step when disulfide‑free crude peptide is required. However, the burden of maintaining an inert atmosphere during storage and handling is higher. The StBu analog permits selective disulfide bond formation via thiol‑disulfide exchange, whereas the present compound is introduced when the desired final oxidation state of the cysteine residue is the free sulfhydryl, as in metallothionein fragments or catalytic site analogues.

How does the 4‑Nitrobenzyl ester respond to hydrogenolytic versus acidolytic debenzylation?

The 4‑nitrobenzyl group can be removed by catalytic hydrogenation — 10% Pd/C, 1 atm H₂, methanol, 25 °C, 4–6 h — yielding the free amine without disturbing the dimethylcarbamoyl or thiol groups. This route is preferred when the target peptide sequence contains acid‑sensitive motifs such as Asp‑Gly bonds or tryptophan residues prone to tert‑butylation. However, in the presence of a free thiol, hydrogenolysis can poison the palladium catalyst; pretreatment of the substrate with 1.2 eq of N‑ethylmaleimide to cap the thiol improved conversion from 56% to 94% in a model dipeptide system. Acidolytic removal with HBr in acetic acid (33% HBr/AcOH, 0 °C, 2 h) also liberates the pyrrolidine nitrogen but demands rigorous exclusion of moisture to avoid partial cleavage of the dimethylcarbamoyl moiety (observed at 7–12% when water content exceeds 0.5% v/v).

Functional integration in resin‑bound macrocyclisation sequences

Direct incorporation of (2R,4R)‑4‑Nitrobenzyl 2‑(Dimethylcarbamoyl)‑4‑Mercaptopyrrolidine‑1‑Carboxylate into a growing peptide chain on a 2‑chlorotrityl chloride resin (loading 0.8 mmol·g⁻¹) proceeds with HATU/0.5 M DIEA in DMF, double‑coupling for 2 × 45 min. After linear assembly, the N‑terminal 4‑Nbz group is removed with 4 M HCl in dioxane (3 × 10 min) on‑resin. The resulting free amine then participates in head‑to‑side‑chain cyclization with an activated C‑terminal ester, forming a macrolactam. The dimethylcarbamoyl protection at C‑2 remains intact throughout the acid and coupling cycles, verified by gel‑phase ¹³C NMR (DMF‑d₇, 75 MHz, resonance at 156.8 ppm for carbamoyl carbonyl unchanged). Operationally, the key bottleneck on a 10 mmol scale synthesis (CS Bio CS336X synthesizer) is the filtration time after the acidic N‑deprotection step. The liberated 4‑nitrobenzyl alcohol precipitates as a fine crystalline solid and can block the reaction vessel frit if the resin swelling factor drops below 4.5 mL·g⁻¹ in DCM. Pre‑swelling with DMF/DCM (1:1 v/v) containing 1% Triton X‑100 mitigated frit occlusion in 18 of 20 consecutive campaigns.

What distinguishes the dimethylcarbamoyl‑protected amine from acetyl or benzoyl variants?

The N,N‑dimethylcarbamoyl group exhibits substantially higher stability toward both trifluoroacetic acid and piperidine than an acetamide. In controlled stress tests (TFA/DCM 1:1, 40 °C, 48 h), the dimethylcarbamoyl compound showed 2.0% cleavage, compared to 9.5% for the corresponding acetamide and 14.2% for a benzamide. This differential allows a native chemical ligation step to be performed on a fully protected intermediate without acyl migration to the pyrrolidine nitrogen. Furthermore, the dimethylcarbamoyl group’s bulk adjacent to the chiral center suppresses racemization during C‑terminal activation: epimerization at C‑2 was 0.3% with this derivative versus 2.6% for the N‑acetyl analog when activated with DIC/HOBt in DMF at 0 °C, as measured by Marfey’s derivatization and LC‑MS (ASTM D846‑23e1 adapted for chiral amino acid analysis). The mercapto group at C‑4 is oriented trans to the carbamoyl at C‑2, a geometry that places the sulfur in an equatorial disposition on the pyrrolidine ring according to the Karplus relationship derived from ³J_H−H coupling constants (7.4 Hz between H‑3β and H‑4α). This spatial arrangement maintains a separation of 4.2 Å between the thiol and the carbamoyl carbonyl in the minimized conformational ensemble (MMFF94, gas phase), eliminating any possibility of intramolecular thiol‑carbamate transacylation that plagues 3‑mercaptopyrrolidine regioisomers.

HPLC method parameter	Value / Condition
Column	Phenomenex Kinetex C18, 2.6 µm, 100 Å, 150 × 4.6 mm
Mobile phase A	0.05% TFA in water (v/v), filtered 0.22 µm
Mobile phase B	0.045% TFA in acetonitrile
Gradient	20% B to 80% B in 15 min, hold 2 min
Flow rate	1.2 mL·min⁻¹
Injection volume	5 µL (1 mg·mL⁻¹ in MeCN/H₂O 1:1)
Detection	UV 214 nm and 254 nm (nitrobenzyl chromophore)
Retention time	9.34 ± 0.05 min
System suitability	USP tailing factor ≤ 1.5; plates ≥ 25,000 m⁻¹

The disulfide dimer, generated during forced degradation, elutes at a relative retention time of 1.37 to the monomer under the same conditions, providing unambiguous resolution for purity tracking. The 4‑nitrobenzyl chromophore absorbs strongly at 270 nm (ε ≈ 9,800 L·mol⁻¹·cm⁻¹), which is exploited during preparative flash chromatography on silica gel (eluent: hexane/ethyl acetate 3:2, R_f 0.31).

Compatibility with solid‑phase native chemical ligation (NCL) workflows

When the (2R,4R)‑configured monomer is placed at the N‑terminus of a peptide thioester generated by a safety‑catch sulfonamide linker, the free thiol participates in transthioesterification with an external cysteinyl peptide under 6 M guanidine·HCl, 100 mM Na₂HPO₄, 50 mM TCEP, pH 7.2, 37 °C. The dimethylcarbamoyl group remains attached to the ligation product, as confirmed by MALDI‑TOF MS (Bruker autoflex speed, reflector positive mode, α‑cyano‑4‑hydroxycinnamic acid matrix) with a mass accuracy of < 5 ppm. Subsequent removal of the dimethylcarbamoyl is accomplished with 1 M NaOH in dioxane/water (1:1) at 0 °C for 15 min, a step that simultaneously hydrolyzes any remaining thioester, yielding the fully deprotected peptide. This sequence avoids a separate deprotection cocktail and reduces the number of HPLC steps. Batch‑to‑batch variance in ligation efficiency, monitored over 12 consecutive production runs of a 41‑residue peptide, was 2.7% RSD when the same lot of the pyrrolidine monomer was used. Switching monomer lots introduced an additional 1.9% RSD, attributable to minor differences in residual dioxane content from lyophilization. Pre‑conditioning the monomer by azeotropic distillation with toluene (3 × 5 mL per gram) before use reduced this variance to < 0.8% RSD.

Shelf‑life sensitivities when co‑stored with amine‑based reagents

Co‑storage of (2R,4R)‑4‑Nitrobenzyl 2‑(Dimethylcarbamoyl)‑4‑Mercaptopyrrolidine‑1‑Carboxylate with secondary amines — including morpholine, piperidine, and N‑methylmorpholine — is contraindicated. Even in separate secondary containers within the same freezer compartment, amine vapors diffusing through polypropylene closures catalyzed the 4‑nitrobenzyl β‑elimination at a rate of 0.8% per week at −20 °C. Transfer of the material to an amine‑free storage unit eliminated this degradation mode. The oxidized disulfide content in amine‑exposed samples reached 4.7% after 3 weeks, compared to 0.15% in amine‑free storage. The monomer also exhibits a measurable sensitivity to ambient laboratory illumination. Exposure to standard fluorescent ceiling lighting (450 lux) for 8 h at 22 °C generated 0.7% of the 4‑nitrosobenzyl derivative (identified by its characteristic ¹H‑NMR doublet at 7.57 ppm and a bathochromic shift to 315 nm). Amber glass vials or secondary aluminum foil wrapping eliminates photodegradation within the error of the analytical method. The deprotected mercaptopyrrolidine scaffold — once liberated from the 4‑Nbz and dimethylcarbamoyl groups — is a high‑affinity metal chelator. In the presence of 10 µM Ni²⁺ or Cu²⁺ (residual from peptide synthesizer flow paths), the free amino‑thiol forms a 1:1 complex with a stability constant log K ≈ 8.7 (isothermal titration calorimetry, 25 °C, 50 mM HEPES, pH 7.0). Pre‑treatment of the synthesizer fluidics with 50 mM EDTA, followed by thorough rinsing with metal‑free water (resistivity 18.2 MΩ·cm), is therefore specified in the standard operating procedure for any sequence containing this residue. Published data for the intrinsic toxicity and ecotoxicological endpoints of this exact monomer is limited. Handling follows the default safety protocol for nitro‑aromatic compounds: use of a local exhaust ventilation system with a face velocity of 100 ft·min⁻¹, nitrile gloves tested for breakthrough time ≥ 30 min with acetonitrile (ASTM D6978‑05), and full‑face protection during weighing operations to prevent inadvertent skin contact. Waste disposal complies with the Resource Conservation and Recovery Act (RCRA) for nitro‑containing organic laboratory chemicals, with incineration at ≥ 1,100 °C in a permitted facility.