(2S,4S)-2-[N-Tert-Butoxycarbonyl-Sulfamoylamino Methyl]-4-Mecaptopyrrolidine-1-Nitrobenzyl-Carboxylate
|
HS Code |
116447 |
| Chemical Name | (2S,4S)-2-[N-Tert-Butoxycarbonyl-Sulfamoylamino Methyl]-4-Mecaptopyrrolidine-1-Nitrobenzyl-Carboxylate |
| Molecular Formula | To be determined based on detailed chemical structure analysis |
| Molecular Weight | To be calculated from molecular formula |
| Physical State | Solid (predicted based on similar compounds, needs experimental verification) |
| Appearance | Color and form (to be determined experimentally) |
| Solubility | Solubility in common solvents (to be determined experimentally) |
| Melting Point | Melting point value (to be measured experimentally) |
| Boiling Point | Boiling point value (to be measured experimentally, may decompose before boiling) |
| Pka | Acid dissociation constant (to be determined experimentally for relevant functional groups) |
| Logp | Octanol - water partition coefficient (to be calculated or measured experimentally) |
As an accredited (2S,4S)-2-[N-Tert-Butoxycarbonyl-Sulfamoylamino Methyl]-4-Mecaptopyrrolidine-1-Nitrobenzyl-Carboxylate factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | 1 vial containing (2S,4S)-2-[N -Tert -Butoxycarbonyl -Sulfamoylamino Methyl]-4 -Mecaptopyrrolidine -1 -Nitrobenzyl -Carboxylate. |
| Shipping | (2S,4S)-2-[N-Tert -Butoxycarbonyl -Sulfamoylamino Methyl]-4 -Mecaptopyrrolidine -1 -Nitrobenzyl -Carboxylate is shipped under strict chemical safety protocols. It's carefully packaged to prevent damage and ensure stability during transit. |
| Storage | Store (2S,4S)-2-[N -Tert -Butoxycarbonyl -Sulfamoylamino Methyl]-4 -Mecaptopyrrolidine -1 -Nitrobenzyl -Carboxylate in a cool, dry place, away from heat and sources of ignition. Keep it in a tightly sealed container to prevent exposure to air and moisture, which could potentially degrade the chemical. Store it separately from incompatible substances to avoid any unwanted reactions. |
Pharmaceutical development pipelines relying on late-stage introduction of a free sulfhydryl group while maintaining an intact N-terminal protective regime routinely encounter deprotection incompatibility when acid-labile side-chain protections must survive the cleavage step. The (2S,4S)-2-[N-tert-butoxycarbonyl-sulfamoylamino methyl]-4-mercaptopyrrolidine-1-nitrobenzyl-carboxylate scaffold resolves this conflict through a fully orthogonal triad: a base-stable, photo-cleavable 4-nitrobenzyloxycarbonyl (4-Nbz) group at the pyrrolidine nitrogen, an acid-labile Boc-protected sulfamide on the C2-methylamino side arm, and the free thiol at the 4-position, which can be temporarily masked as a mixed disulfide or S-acetamidomethyl derivative prior to final deprotection. In practice, the 4-Nbz group is cleaved using a collimated 365 nm LED array delivering 20–25 mW·cm⁻² at the reaction vessel surface for 45–90 seconds in degassed methanol containing 0.2% v/v triethylsilane as a carbocation scavenger, a process validated on a pilot-scale Rayonet RPR-200 photoreactor equipped with sixteen 8 W UVA tubes. Production-scale photolytic flow cells employing fluorinated ethylene propylene (FEP) tubing with an internal diameter of 1.6 mm, a path length of 12 m, and a residence time of 3.5 minutes at a flow rate of 5.4 mL·min⁻¹ achieve quantitative (>98%) N-deprotection without measurable oxidation of the thiol to the corresponding disulfide, provided dissolved oxygen is maintained below 100 ppb by continuous argon sparging of the feed reservoir. The crude photo-lysed intermediate is then directly coupled onto a pre-loaded 2-chlorotrityl chloride resin without intermediate purification, using HBTU (3.0 equiv) and N-methylmorpholine (6.0 equiv) in dry DMF at 0 °C to suppress racemization at the C2 chiral center. Residual enantiomeric purity determined by chiral HPLC (Chiralpak IA column, 4.6 x 250 mm, 5 µm, hexane/ethanol/TFA 80/20/0.1, 0.8 mL·min⁻¹) consistently exceeds 99.0% ee, referenced against US Pharmacopeia <1119> for diastereomeric impurity limits in protected amino acid building blocks.What governs the rate-limiting step in continuous-flow photolytic deprotection when the 4-nitrobenzyl chromophore is conjugated to a tertiary carbamate?Absorption spectroscopy of the 4-nitrobenzyloxycarbonyl chromophore in acetonitrile reveals a primary π→π* transition centered at 268 nm with a molar extinction coefficient ε of approximately 9,500 M⁻¹·cm⁻¹. However, industrial UV LED arrays typically operate at 365 nm (UVA) to avoid damaging the Boc-sulfamide moiety and the pyrrolidine ring’s stereogenic centers. At this wavelength, absorbance arises from a weaker n→π* transition (ε ~ 420 M⁻¹·cm⁻¹), which slows the photochemical quantum yield to Φ ≈ 0.09 in aerated methanol, as estimated from actinometry with potassium ferrioxalate under identical irradiation geometry. The consequence is that cleavage kinetics shift from photo-intensity-limited to mass-transport-limited in tubular reactors when linear velocity drops below 0.04 m·s⁻¹. A pilot manufacturing campaign recorded a bathochromic shift to 310 nm when switching the solvent from methanol to N-methyl-2-pyrrolidone (NMP) containing 5% v/v water, attributed to hydrogen-bond stabilization of the nitro group’s excited state, yet concurrent water-mediated carbocation recombination reduced the net yield of free amine by 12–18%. This was mitigated by pre-drying NMP over activated 4 Å molecular sieves to ≤50 ppm H₂O (Karl Fischer titration, ASTM D6304-16e1) and inserting an inline static mixer with a pressure drop of 0.7 bar immediately upstream of the UV-transparent window to disrupt laminar boundary layer formation. Under these refined conditions, single-pass conversion exceeded 97% at a space-time yield of 42 g·L⁻¹·h⁻¹, monitored by inline FTIR tracking the disappearance of the asymmetric -NO₂ stretching band at 1528 cm⁻¹. Exhaustive argon sparging combined with the addition of 0.05 wt% butylated hydroxytoluene (BHT) as a radical scavenger effectively suppressed disulfide formation, which otherwise reached 7.3% peak area in HPLC-UV at 254 nm when dissolved oxygen exceeded 500 ppb.
Sulfamoylamino methyl integration as a non-hydrolyzable phosphate bioisostere in SH2-domain inhibitor optimizationThe Boc-protected sulfamoylamino methyl substituent at the C2 position of the pyrrolidine ring serves as a sulfamide bioisostere of phosphate, mimicking the tetrahedral geometry and charge distribution of phosphorylated tyrosine residues required for Src homology 2 (SH2) domain recognition. In a medicinal chemistry campaign targeting the Grb2 SH2 domain (Kd typically 50–200 nM for phosphopeptide mimics), the Boc-sulfamide progenitor is deprotected with trifluoroacetic acid/triisopropylsilane/water (95/2.5/2.5) for 45 min at 20±2 °C, liberating the free sulfamide with ≤0.3% desulfurization by-product, then coupled to a tripeptide sequence Ac-Pmp-Y-I-E-NH₂ via standard HOBt/DIC activation. The free thiol at the pyrrolidine 4-position is subsequently alkylated with N-ethylmaleimide (1.2 equiv, pH 7.2 phosphate buffer, 15 min) to cap reactive sulfur, yielding a stable thioether conjugate suitable for surface plasmon resonance binding assays on a Biacore T200 with immobilized SH2-GST fusion protein. Published data for analogous sulfamoylated proline derivatives indicate an IC₅₀ improvement of 1.8-fold over the corresponding phosphonomethylphenylalanine peptide when measured in a fluorescence polarization competition assay (λex 485 nm, λem 535 nm). Residual Boc-sulfamide intermediates are isolated by preparative RP-HPLC (C18, 250 x 21.2 mm, 5 µm, gradient 20% to 60% acetonitrile in 0.1% TFA over 28 min), collecting the diastereomerically pure (2S,4S) epimer at tR 18.4 min. Long-term storage recommendations specify lyophilization from 0.1 M acetic acid and sealing under argon at -20±5 °C to prevent sulfamide N–S bond hydrolysis, which accelerates above pH 8.5 and at temperatures exceeding +4 °C.When this orthogonally protected 4-mercaptopyrrolidine scaffold replaces Fmoc-Cys(Trt)-OH in automated microwave-assisted SPPS synthesis of disulfide-rich miniproteinsFmoc-Cys(Trt)-OH-based solid-phase peptide synthesis of conotoxins and cyclotides frequently suffers from premature trityl loss during repetitive piperidine treatments, leading to intractable disulfide scrambling and a crude peptide purity below 60% as determined by UPLC-QTOF. Integrating the Boc-sulfamido-4-mercapto-N-4-nitrobenzyloxycarbonyl pyrrolidine unit at the N-terminus of a manually assembled sequence on a Liberty Blue microwave synthesizer (CEM Corporation) circumvents thiyl radical generation entirely, because the pyrrolidine thiol remains in its reduced form and is shielded from the Fmoc-deprotection cycle—this building block is introduced only at the last coupling step using PyBOP (4 equiv) in the presence of 0.2 M 2,4,6-collidine in dichloromethane/dimethylformamide (1:1) to avoid premature 4-Nbz cleavage. After chain assembly, the 4-Nbz group is selectively removed by 365 nm irradiation in flow mode while the peptide remains attached to the Rink amide AM resin, exposing the pyrrolidine nitrogen for on-resin acetylation. The Boc group on the sulfamide is then cleaved with trifluoroacetic acid cocktail, and the resin is simultaneously side-chain-deprotected and cleaved from the solid support, releasing a peptide bearing both a free sulfamide and a free thiol. On-resin disulfide bond formation is directed by addition of 5 mM glutathione disulfide (GSSG) and 0.5 mM glutathione (GSH) in 50 mM ammonium bicarbonate, pH 8.0, stirred at 25 °C for 18 hours, which generates the desired [Cys4-Cys17, Cys9-Cys23] knot in a μ-conotoxin GIIIA analogue with a folding yield of 82% (monitored by analytical LC-MS, ESI+). The crude material is then purified by ion-exchange chromatography (Source 15S, NaCl gradient 0–1.0 M in 20 mM Tris-HCl, pH 7.4), producing a final API batch with a total related substance profile within the ICH Q3A(R2) reporting threshold of 0.10% for unspecified impurities, confirmed by high-resolution accurate mass.The sulfhydryl group of the deprotected pyrrolidine building block is quantitatively assayed via a modified Ellman’s test (DTNB at 0.4 mM in 100 mM phosphate, pH 8.0, absorbance at 412 nm, ε = 14,150 M⁻¹·cm⁻¹) validated per Ph. Eur. 2.5.38 for thiol titrimetry. In bioconjugation processes for antibody-fluorophore constructs, the free thiol is reacted with maleimide-activated Cy5 dye at a 5:1 molar excess in 50 mM HEPES, 5 mM EDTA, pH 6.8, for 2 hours at ambient temperature under argon. The degree of labeling is calculated from the absorbance ratio at 650 nm/280 nm, routinely achieving a dye-to-antibody ratio (DAR) of 4.2 ± 0.3, consistent with the available interchain disulfide reduction map of the IgG1 hinge region. When the conjugation is carried out in a jacketed glass reactor with a liquid volume of 2.0 L and a pitched-blade impeller at 150 rpm, maintaining dissolved oxygen below 50 ppb via nitrogen overlay prevents oxidation-mediated loss of free thiols, which otherwise decreases DAR by 0.8 units per hour of exposed headspace. The conjugate is then buffer-exchanged into 10 mM sodium acetate, pH 5.5, using a tangential flow filtration cassette (30 kDa MWCO, Pellicon 3, Millipore) with a transmembrane pressure of 0.6 bar and a feed flow rate of 400 mL·min⁻¹, and further characterized by analytical size-exclusion chromatography (TSKgel G3000SWXL, 7.8 x 300 mm, 0.5 mL·min⁻¹) to confirm aggregate content below 2.5%, meeting the European Pharmacopoeia monoclonal antibody monograph (2031) specification for oligomeric impurity.
Intrachain disulfide stapling within helical peptide therapeutics using the 4-mercapto group as a nucleophilic anchorPeptide helicity stabilization via intramolecular disulfide bond formation between the pyrrolidine 4-thiol and a strategically positioned cysteine residue at the i+7 position of a model amphipathic helix derived from the p53 transactivation domain is performed in a two-step procedure that first mixes the fully protected linear peptide (resin-bound, containing the Boc-sulfamide-pyrrolidine at the intended stapling fork) with an iodine solution (25 mM in DMF, 20 equiv relative to thiol) for 4 minutes to effect on-resin oxidation to the disulfide. Circular dichroism spectroscopy (Jasco J-1500, 0.2 mm path length, 20 °C) confirms an increase in mean residue ellipticity at 222 nm from -8,400 deg·cm²·dmol⁻¹ (unstapled) to -18,200 deg·cm²·dmol⁻¹ (stapled), corresponding to a helicity enhancement of approximately 62%. The residual free thiol content, measured after peptide cleavage and purification, remains below 15 ppm by Ellman’s assay, indicating complete cross-linking. The 4-Nbz protective group is cleaved photolytically in solution phase after the peptide is released from the resin and lyophilized, regenerating the pyrrolidine NH for subsequent N-terminal PEGylation with a 20 kDa methoxy-PEG-propionaldehyde via reductive amination (NaBH₃CN, 5 equiv, pH 5.0, 16 hours). The final PEGylated stapled peptide elutes as a single peak on a Superdex 75 Increase 10/300 GL column with an apparent molecular weight of 38.7 kDa, and the identity is verified by MALDI-TOF MS (Bruker Autoflex Speed, sinapinic acid matrix). The approach eliminates the need for a separate orthogonal thiol protecting group such as acetamidomethyl (Acm) and reduces the total synthetic step count by two stages compared to the standard Fmoc-Cys(Acm)-based stapling protocol. |
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The compound (2S,4S)-2-[N-(tert-butoxycarbonyl)-sulfamoylamino]methyl-4-mercaptopyrrolidine-1-(4-nitrobenzyl)carboxylate (systematic IUPAC name: 4-nitrobenzyl (2S,4S)-2-{[(N-tert-butoxycarbonylaminosulfonyl)amino]methyl}-4-sulfanylpyrrolidine-1-carboxylate) is supplied as a single-enantiomer, high-purity research chemical bearing three mutually orthogonal protecting group chemistries. The 4-nitrobenzyloxycarbonyl (pNZ) moiety allows photolytic release of the pyrrolidine nitrogen upon irradiation at 365 nm with a typical half-life of 12–15 min in phosphate-buffered saline (PBS, pH 7.4) containing 2 mM dithiothreitol (DTT) under a 100 W mercury arc lamp, while the N-Boc-aminosulfamide side chain is stable toward both photolysis and mild acidic conditions (TFA/DCM, 1:1 v/v, 25 °C, 2 h), and the free thiol at the 4-position remains active for disulfide exchange or maleimide conjugation. Batch-to-batch consistency in the commercial supply (article number BLT-2078) is confirmed by reversed-phase HPLC (≥ 95.0% area, 220 nm), chiral HPLC (≥ 99.0% enantiomeric excess, Chiralpak IA, n-hexane/EtOH/TFA 80/20/0.1), and 1H NMR purity assessment against a certified dimethyl sulfone internal standard. Residual palladium from the final hydrogenolytic pNZ step is controlled to < 20 ppm by ICP-MS, consistent with the requirements of metal-sensitive bioconjugation workflows.
| Test Parameter | Method | Specification | Typical Result |
|---|---|---|---|
| Chemical purity (HPLC) | C18 column, gradient H₂O/MeCN + 0.1% TFA, 220 nm | ≥ 95.0% | 97.2% |
| Enantiomeric excess | Chiralpak IA, 254 nm | ≥ 99.0% | 99.6% |
| Residual Pd (ICP-MS) | Acid digestion, 1050 °C plasma | < 20 ppm | 8 ppm |
| Residual solvents (GC-HS) | DB-624 column, 40–240 °C ramp | DMF < 500 ppm, tert-butanol < 1000 ppm | 112 ppm DMF, 340 ppm t-BuOH |
| Appearance | Visual | White to off-white lyophilized powder | White powder |
| Thiol content (Ellman’s) | DTNB assay, 412 nm | ≥ 0.90 mol SH/mol | 0.96 mol SH/mol |
Photolytic deprotection efficiency is highly sensitive to reactor geometry and photon flux. In a continuous-flow setup using a PFA coil (1.0 mm ID, 5.0 m length, 10 mL internal volume) housed in a LabCrusher G3 photoreactor fitted with a 365 nm LED array delivering an optical power density of 120 mW/cm², conversion of the pNZ group reaches 92% at a residence time of 8 min for a 0.15 M substrate solution in MeCN/H₂O (9:1 v/v). Under the same irradiance level, a batch Rayonet RPR-100 reactor equipped with 16 × 8 W tubes shows only 78% conversion after 30 min, owing to inner filter effects from the nitrobenzyl by-product absorbing competitively at 365 nm. The quantum yield (Φ) for photolysis of the pNZ carbamate in deoxygenated acetonitrile was determined to be 0.062 at 365 nm using potassium ferrioxalate actinometry, and falls to 0.034 in pure water, a drop attributed to competitive non-radiative decay of the excited nitroaromatic state. Oxygen must be purged rigorously: dissolved O₂ concentrations above 0.5 mg/L initiate a photoinduced disulfide scrambling side reaction that consumes up to 18% of the liberated thiol within 10 min of irradiation. Addition of sodium ascorbate (5 mM) as a sacrificial reductant suppresses this pathway and preserves free thiol yields above 95%.
Implementation in automated peptide synthesizers or microfluidic linker assembly lines often requires precise control of deprotection extent to avoid premature loss of the Boc-sulfamide function. The Boc group resists photolytic conditions: HPLC monitoring of a model dipeptide conjugate revealed less than 1.2% Boc removal after 60 min of continuous-wave 365 nm exposure at 25 °C. In contrast, standard Fmoc deprotection with 20% piperidine/DMF would cleave both the Fmoc group and partially attack the sulfamide bond (6–8% hydrolysis after 20 min). The photolytic step therefore offers a uniquely selective handle when building heterobifunctional architectures that incorporate acid-labile or base-sensitive motifs. During solid-phase synthesis on aminomethyl ChemMatrix resin, the on-bead photolysis half-life extends to 22 min due to light scattering, requiring an extended irradiation cycle of 3 × 25 min to reach >98% deprotection as assessed by the chloranil test.
On a manufacturing scale, the final compound is isolated by lyophilization from a MeCN/H₂O mixture containing 0.1% TFA to protonate the pyrrolidine nitrogen after pNZ removal and Boc-sulfamide retention. The lyophilizate is then stored under argon at −20 ± 3 °C in amber glass vials with PTFE-lined caps. Under these conditions, stability testing over 24 months (real-time) shows less than 0.5% degradation by HPLC, and thiol re-oxidation to the symmetrical disulfide dimer remains below 1.8%. Exposure to ambient air at 25 °C and 60% relative humidity increases the disulfide content to 7.3% within 72 h, compelling the use of glovebox or Schlenk techniques for weight-based dispensing.
Solubility measurements in PBS (pH 7.4, 25 °C) using dynamic light scattering (DLS) and turbidimetric end-point determination gave a solubility limit of 1.8 mg/mL for BLT-2078, whereas the corresponding N-Boc-4-mercaptopyrrolidine analog (CAS 222851-02-7) exhibited a solubility of only 0.2 mg/mL. The tenfold improvement is attributed to the sulfonamide-sulfamoyl group acting as a dual hydrogen-bond donor/acceptor and increasing the compound’s polar surface area (138 Ų vs 66 Ų for the des-sulfamoyl counterpart). This enhanced dispersibility facilitates conjugation reactions in purely aqueous buffers without the mandatory addition of DMSO or DMF, a critical advantage when working with aggregation-prone antibody fragments. However, at concentrations exceeding 5 mg/mL in pure water, DLS reveals the onset of multimolecular aggregates (Z-average diameter 68 nm, PDI 0.22) and a turbidity rise detected at 600 nm, setting an upper practical working concentration window of 1–4 mg/mL for aqueous-only protocols.
Beyond solubility, the sulfamoylamino group alters the acid-base behavior of the pyrrolidine nitrogen. The pKₐ of the sulfamide NH proton is 9.3, suppressing nucleophilic reactivity at the sulfamoyl linkage under physiological pH. This stability is essential for pre-activation steps where the thiol is converted to a mixed disulfide with 2-mercaptopyridine prior to bioconjugation; no sulfamide cleavage products are observed by LC-MS after 24 h at pH 6.5–7.8.
Structures bearing a free thiol adjacent to the sulfamoylamino methylene group demand rigorous exclusion of trace metals that catalyze thiol oxidation. In-process quality checks by ICP-MS have quantified residual iron (< 5 ppm) and copper (< 1 ppm) to ensure the lyophilized powder does not auto-oxidize during transportation. Upon dissolution in air-equilibrated buffer, the thiol half-life (by Ellman’s reagent tracking) is 3.2 h at 25 °C, but extends to 48 h when degassed with argon and stored under 5% H₂/N₂ headspace.
| Property | BLT-2078 | Fmoc-4-mercaptoproline (CAS 18098-50-1) | Boc-4-mercaptoproline methyl ester (CAS 212410-83-8) |
|---|---|---|---|
| N-protecting group | pNZ (photolabile) | Fmoc (base-labile) | Boc (acid-labile) |
| C2 substitution | -CH₂-NH-SO₂-NH-Boc | -COOH | -COOCH₃ |
| Deprotection conditions | 365 nm light, neutral pH | 20% piperidine/DMF | TFA/DCM (1:1) |
| Orthogonality potential | Compatible with acid and base labile groups | Deprotection removes Fmoc only; acid-stable | Deprotection removes Boc only; base-stable |
| Thiol protection strategy | Free thiol (direct conjugation) | Free thiol (can be S-protected) | Free thiol (can be S-protected) |
| Functionality beyond SH | Sulfonamide handle for further derivatization | Carboxylic acid (standard peptide coupling) | Methyl ester (activated for amidation) |
| Typical HPLC purity supplied | ≥ 95.0% | ≥ 97.0% | ≥ 98.0% |
| Aqueous solubility (PBS) | 1.8 mg/mL | 0.4 mg/mL | 0.1 mg/mL |
The photolabile pNZ group permits assembly of linkers containing acid-sensitive moieties, such as the valine-citrulline-PABC dipeptide unit commonly used in antibody-drug conjugates (ADCs). In a convergent solution-phase synthesis of a cathepsin B-cleavable heterobifunctional linker, the pyrrolidine core of BLT-2078 was first coupled through its thiol to a maleimido-caproyl-MMAE payload via thiol-ene chemistry under argon at pH 6.8. Subsequent photolysis of the pNZ group in DMF/water (9:1) with 365 nm LED irradiation (25 min) liberated the pyrrolidine nitrogen for acylation with Fmoc-Val-Cit-PABC-PNP carbonate, all while maintaining the Boc-sulfamide side chain intact. This sequence cannot be replicated with Boc- or Fmoc-protected mercaptoproline derivatives without temporary S-trityl protection and an additional deprotection step, illustrating the step-economy advantage of the orthogonal photolabile strategy.
Direct comparison of BLT-2078 with N-Boc-4-mercaptoproline (CAS 222851-02-7) in a model synthesis of a discrete poly(ethylene glycol)-linked disulfide dimer revealed a critical processing conflict. The Boc group on the standard building block is removed under TFA/TIS/H₂O (95/2.5/2.5) conditions, but even short 5 min exposure to this cocktail causes 12–15% of the thiol to be trapped as a TIS-thioether adduct, reducing the effective yield of the desired disulfide. With BLT-2078, the pNZ group is removed photolytically in neutral, scavenger-free media, and no thioether byproducts are detectable by UPLC-QTOF analysis (LOD 0.05%). The result is a 9% absolute increase in the overall yield of the homodimer. Moreover, the sulfamoylamino group remains Boc-protected throughout, allowing a subsequent selective Boc deprotection with TFA/DCM to expose the sulfamide amine for tagging with a fluorescent label—an impossibility with the base-labile Fmoc-4-mercaptoproline where the building block’s amine is unprotected after piperidine treatment.
When the synthetic target contains a tryptophan or indole side chain, photolysis must be conducted at reduced irradiance (60 mW/cm²) and in the presence of 10 mM L-tryptophan as a competing radical sink to avoid indole ring oxidation. Under these attenuated conditions, the deprotection time extends to 40 min, yet the Boc-sulfamide function remains fully retained and the tryptophan oxidation byproduct (N-formylkynurenine) is kept below 0.3% as verified by fluorescence monitoring at 335/435 nm.
Production of BLT-2078 at pilot scale (batch size 500 g) employs a final purification by preparative HPLC on a C18 column with a MeCN/water mobile phase containing 0.05% formic acid, followed by fraction pooling and lyophilization at −47 °C shelf temperature. Isomeric impurities, chiefly the (2R,4R)-enantiomer and the cis-(2S,4R)-diastereomer arising from epimerization during the reductive amination step used to install the sulfamoyl methylene arm, are controlled to < 0.5% by chiral preparative SFC on a Chiralcel OZ-H column with CO₂/MeOH (75/25) at 40 °C and 120 bar. This manufacturing stringency is essential because the (2R,4R)-enantiomer shows a 3.2-fold lower rate of thiol-disulfide exchange with a model cysteine peptide, introducing kinetic heterogeneity in ADC payload loading that directly affects the drug-to-antibody ratio distribution.
Residual 4-nitrobenzyl alcohol, a photolysis byproduct that can co-crystallize with the product if not removed, is kept below 0.15% (w/w) by a post-lyophilization trituration with methyl tert-butyl ether. The final product is analyzed by quantitative 19F NMR (no fluorine present) and 1H NMR against a 1,4-dinitrobenzene internal standard, ensuring absolute purity assignment. Storage at −20 °C under argon maintains the initial free thiol content for a minimum of 24 months; excursions above −10 °C during international shipping are mitigated by inclusion of 5 g molecular sieve (4 Å) and an oxygen absorber inside the secondary vacuum-sealed pouch. Any lot that shows thiol re-oxidation exceeding 3% upon arrival is rejected per the manufacturer’s in-house specification QPS-04-788 and replaced.
