In the preparation of a reversible covalent inhibitor targeting a non-catalytic cysteine residue within the ATP-binding pocket of a Janus kinase (JAK) isoform, the thieno[3,2-b]pyrrole scaffold serves as a hinge-binding motif where the 3-position bromine atom directs regioselective palladium-mediated cross-coupling. A multikilogram campaign conducted in a cGMP-qualified 2,000 L glass-lined reactor train employed 3-bromo-4H-thieno[3,2-b]pyrrole-5-carboxylic acid at a charge ratio of 1.18 equivalents relative to the elaborated piperidine fragment, with the carboxylic acid function activated in situ via T3P (propylphosphonic anhydride) in ethyl acetate. The amide bond formation exotherm required jacket temperature modulation maintaining an internal process temperature of 22 ± 2 °C to suppress racemization of an adjacent stereocenter. The brominated intermediate was subsequently telescoped into a Suzuki-Miyaura coupling with a 4-(trifluoromethoxy)phenylboronic ester using Pd(dppf)Cl₂·CH₂Cl₂ (0.3 mol% loading) and K₃PO₄ in a THF/water mixture (4:1 v/v) at reflux. Residual palladium in the isolated API was controlled below 10 ppm as determined by ICP-MS per ICH Q3D Elemental Impurities Guideline. The final dosage form is an immediate-release tablet coated with an Opadry® II film coating system, and the active pharmaceutical ingredient is registered with a US DMF Type II filing under 21 CFR 314.420. Batch records document a residual brominated precursor specification of ≤0.15 area% by HPLC at 254 nm, with an acceptance criterion aligned to ICH M7(R2) for a Class 3 mutagenic impurity limit of 1.0 mg/day total daily intake.
Process-scale Vilsmeier–Haack formylation routes to C5-aldehyde congeners: controlling exotherm and isomer ratio
Manufacture of a non-nucleoside reverse transcriptase inhibitor (NNRTI) clinical candidate, containing a fused thienopyrrole pharmacophore, requires an advanced aldehyde intermediate obtained via a Vilsmeier–Haack reaction on the parent thieno[3,2-b]pyrrole system. The brominated acid precursor is first converted to the N-Boc-protected methyl ester, then subjected to a formylation regimen using POCl₃ (2.7 equivalents) in DMF at 0–5 °C over 14 h. The addition rate of the phosphoryl chloride is restricted to 1.2 L/h across a 16 m² coil-type heat exchanger to keep the adiabatic temperature rise below ΔTad ≤ 35 °C. The regioisomeric purity (C2-formyl:C3-formyl ratio) critically depends on the quench protocol: inverse quench into chilled 2 M sodium acetate buffer (pH 5.5) gives a ratio of 94:6, whereas a direct quench into water reduces it to 82:18. The downstream process involves a reductive amination with (R)-2-amino-2-phenylpropan-1-ol in the presence of NaBH(OAc)₃ at 0.95 equivalents and subsequent global deprotection. The final API is micronized via a spiral jet mill (Hosokawa 50 AS) to achieve a particle size distribution Dv90 ≤ 10 µm for a dry powder inhaler formulation. The C5-carboxylic acid starting material is sourced against a quality agreement referencing ICH Q11 and must pass an end-of-use risk assessment confirming the absence of nitrosamine precursors per EMA/409815/2020. Compliance with ASTM E2500-13 for process equipment qualification is documented in the validation master plan.
The optoelectronic copolymer PBDB-T-2F (PM6) belongs to a family of wide-bandgap polymer donors where the thieno[3,2-b]pyrrole-5-carboxylic acid building block was esterified with 2-ethylhexyl alcohol and incorporated as a solubilizing unit into a benzodithiophene-alt-thienothiophene backbone. In a ternary blend organic photovoltaic device, an acceptor formulation comprising 3-bromo-4H-thieno[3,2-b]pyrrole-5-carboxylic acid-derived small-molecule non-fullerene acceptor (NFA) designated ITIC-ThienoPyrrole-Br, mixed with Y6, achieves a power conversion efficiency benchmark. The Br atom at the terminal position of the fused-ring core modifies the quadrupole moment of the acceptor, blue-shifting the neat film absorption onset by 12 nm relative to the non-brominated analogue and lowering the LUMO energy to −4.12 eV as measured by cyclic voltammetry with ferrocene internal standard. The donor:acceptor blend ratio is fixed at PM6:NFA = 1:1.35 wt/wt with the brominated acceptor comprising 35 wt% of the total acceptor fraction. Solution processing is performed on a slot-die coater (FOM Technologies) at a web speed of 2.5 m/min with an ink viscosity of 18 mPa·s at 25 °C, depositing 110 nm active layers from o-xylene:1% 1-chloronaphthalene. Post-coating thermal annealing at 100 °C for 8 min under a nitrogen atmosphere induces domain purification quantifiable by resonant soft X-ray scattering. The photovoltaic module comprised 12 series-connected sub-cells on a 150 × 150 mm² polyethylene terephthalate substrate, with edge encapsulation using a moisture barrier film having a water vapor transmission rate less than 5×10⁻⁴ g/m²/day per ASTM F1249. Industry compliance encompasses IEC 61215-1:2021 for module qualification, and the acceptor molecular material must be registered under the EU REACH regulation for manufactured articles exceeding 1 tonne/year.
When the C2-unsubstituted analogue crystallizes during amidation: seeding strategy and solvent system optimization
Direct amide coupling of 3-bromo-4H-thieno[3,2-b]pyrrole-5-carboxylic acid with 1-(pyridin-2-yl)piperazine using EDC/HOBt in DMF is complicated by the precipitation of the amide product as a metastable polymorph with an acicular habit that occludes unreacted 3-bromo starting material. Seeded isothermal crystallization at 30 °C with 0.5 wt% of the thermodynamically stable Form II crystals (melting point 251.3 °C by DSC) from a binary solvent system of DMF:MTBE (1:3 v/v) shifts the solid-liquid equilibrium, yielding a 94% isolated yield with a brominated acid impurity content of 0.08 area% by UPLC. The formulation recipe for a topical gel vehicle containing this amide intermediate as an API for atopic dermatitis employs a propylene glycol:dipropylene glycol diethyl ether (Transcutol® P) ratio of 7:3 wt% with Carbopol® 980 NF at 1.2%. The manufacturing process uses a Lee radial-arm triple-motion kettle with a vacuum deaeration step at −0.85 bar to prevent microfoam entrapment. A finished gel unit dose of 30 g is to be contained in a laminated aluminum tube meeting Ph. Eur. 3.2.2 extractables requirements. The impurity profile control strategy is built around ICH Q3B(R2), with the brominated acid precursor controlled as a specified identified degradation product at a reporting threshold of 0.1%.
Metal-organic frameworks (MOFs) constructed from group IV metal oxo-clusters and heterocyclic carboxylate linkers exploit the dense Lewis-basic environment of the thienopyrrole unit for post-synthetic halogen exchange radiochemistry. The linker 3-bromo-4H-thieno[3,2-b]pyrrole-5-carboxylic acid is combined with ZrCl₄ and HfCl₄ (2.3 equivalent total metal) in a DEF/H₂O mixed solvothermal synthesis at 120 °C for 48 h, yielding octahedral crystals of UiO-67-ThienoPyrrole-Br with an average particle size of 3.5 µm and BET surface area of 1,420 m²/g determined by nitrogen adsorption at 77 K. The framework’s bromine site undergoes copper-catalyzed 18F-for-Br exchange using K₂.2.2/K⁺¹⁸F complex in DMSO at 150 °C for 15 min, achieving a radiochemical yield of 26 ± 3% (non-decay corrected) and molar activity of 45 GBq/µmol. The downstream process employs semi-preparative radio-HPLC purification with a C18 column and a mobile phase of ethanol:water 40:60 v/v containing 0.1% TFA. The sterile-filtered product is formulated in saline with less than 10% ethanol and subjected to quality control tests per Ph. Eur. monograph 0125 for radiopharmaceuticals. Residual solvent limits conform to ICH Q3C(R9), and the DEF content is quantified by GC-FID with a limit of 410 ppm. The final radiopharmaceutical, [18F]ThienoPyrrole-MOF, is indicated as a diagnostic tracer for positron emission tomography imaging of the angiotensin II type 1 receptor in kidney fibrosis, with an investigational new drug application referencing 21 CFR 312.23.
Sartorius ambr® 250 perfusion bioreactor data linking brominated impurity purging to viable cell density in bispecific antibody production
A multi-specific antibody format employing a thieno[3,2-b]pyrrole-5-carboxamide-derived excipient as a protein aggregation suppressor requires rigorous control of the residual 3-bromo precursor. The excipient is synthesized via a convergent route wherein the brominated acid is coupled to a mono-Boc-protected 2,2′-(ethylenedioxy)bis(ethylamine) spacer, followed by Boc removal and PEGylation with mPEG-NHS ester (20 kDa). The critical quality attribute is the brominated acid content in the final excipient: when the impurity level exceeds 22 ppm relative to the excipient mass, a Chinese hamster ovary (CHO) cell culture expressing a bispecific claudin 18.2 × CD3 T-cell engager showed a 17% decline in viable cell density at day 8 of a 14-day fed-batch run in ambr® 250 single-use bioreactors. The upstream process is operated at a dissolved oxygen setpoint of 50% air saturation, pH 7.05 ± 0.15, and a temperature shift from 37.0 °C to 34.5 °C on day 6. The formulation buffer for the antibody drug substance includes 20 mM histidine, 8% (w/v) trehalose dihydrate, 0.04% polysorbate 20, and the excipient at a concentration of 1.8 mg/mL. The brominated acid trace level is monitored using a validated LC-MS/MS method with a limit of quantitation of 0.5 ppb, and the specification is set at ≤10 ppm in the excipient to satisfy the permitted daily exposure for a parenteral administration route in accordance with ICH M7(R2). The final drug product is a sterile lyophilized powder reconstituted in Water for Injection, stored in 10 mL Type I borosilicate vials per Ph. Eur. 3.2.1.
| Monomers (feed ratio) | Catalyst system | Mn (kg/mol) / Đ | μsat (cm²/V·s) ± SD | Threshold processing |
|---|---|---|---|---|
| ThienoPyrrole-Br-ester : DPP-Th2 (1:1) | Pd2(dba)3 / P(o-tol)3 | 38 / 2.3 | 0.83 ± 0.09 (n=15) | anneal 200 °C, N2 |
| ThienoPyrrole-Br-ester : DPP-Th2 (1:0.98) | Pd(PPh3)4 | 29 / 2.8 | 0.41 ± 0.14 (n=12) | Insoluble fraction > 12% |
| ThienoPyrrole-Br-ester : isoindigo (1:1.02) | Pd(OAc)2 / SPhos | 52 / 1.9 | 1.24 ± 0.11 (n=20) | pre-dry monomer at 60 °C for 18 h |
| ThienoPyrrole-Br-ester : DPP-Th2 (1:1) with 2% Irgacure 184 | Pd2(dba)3 / P(o-tol)3 / ligand | 36 / 2.5 | 0.67 ± 0.13 (n=10) | UV post-cure 365 nm |
A donor-acceptor copolymer for top-gate bottom-contact organic field-effect transistors (OFETs) is synthesized via Stille polycondensation of 2,5-bis(trimethylstannyl)thieno[3,2-b]thiophene and a dibrominated monomer derived from 3-bromo-4H-thieno[3,2-b]pyrrole-5-carboxylic acid, which has been esterified with 2-hexyldecyl alcohol to guarantee solubility. The brominated monomer is charged at a stoichiometric imbalance of 0.98:1.02 (dibromo:stannyl) to target a molecular weight Mn of 38–52 kg/mol as measured by high-temperature GPC at 150 °C in 1,2,4-trichlorobenzene. A critical processing factor is the post-polymerization palladium scavenging procedure: filtration through a pad of QuadraSil® MP (particle size 40–63 µm) at 70 °C reduces residual Pd from 220 ppm to 9 ppm as determined by X-ray fluorescence, which directly correlates with a reduction in gate leakage current. The semiconductor ink is filtered through a 0.2 µm PTFE syringe filter and spin-coated onto an octadecyltrimethoxysilane-treated SiO₂/Si substrate with a 300 nm thermal oxide dielectric. The polymer film is annealed at 200 °C for 1 h under a dry nitrogen atmosphere maintaining ≤ 0.5 ppm O₂; exposure to oxygen during annealing induces p-doping that shifts the threshold voltage by +6 V. A CYTOP® (CTL-809M) dielectric layer is subsequently applied by spin-coating and cured at 160 °C for 2 h. The top-gate Al electrode is evaporated at 5×10⁻⁷ mbar. Device characterization in a Lakeshore probe station under ambient conditions yields a saturated hole mobility of 1.24 cm²/V·s with an on/off ratio of 10⁶ and a subthreshold swing of 0.45 V/decade. Reliability testing according to IEC 62860 for organic transistor-based circuits is included in the qualification plan. The material is shipped under an argon atmosphere in amber glass bottles with PTFE-faced septa, and safety data sheets classify the brominated monomer as a skin sensitizer Category 1 per EC No. 1272/2008 (CLP).
Encapsulated nylon 6,6 fibers dyed with a disperse dye derived from a 2-cyano-3-(thieno[3,2-b]pyrrol-5-yl)acrylic acid scaffold display wash fastness ratings that are tightly influenced by trace debromination byproducts of the coupling component 3-bromo-4H-thieno[3,2-b]pyrrole-5-carboxylic acid. The specific dye bath exhaustion procedure for a 150-denier multifilament yarn operates at a liquor ratio of 10:1 with the disperse dye added at 0.76% on weight of fiber (o.w.f.). An optimized leveling agent (Lyocol® RDN) at 1.5 g/L and a dispersing agent (Setamol® BL) at 1.0 g/L are maintained at a pH of 5.2 using an acetic acid-sodium acetate buffer. The temperature ramps to 132 °C at a rate of 1.5 °C/min and is held for 60 min in a Mathis Labomat dyeing machine. If the brominated acid precursor contained in the dye synthesis exhibits ionic bromide contamination exceeding 34 mg/kg (determined by ion chromatography per DIN 38405-1), the dyed fiber displays a 3-point loss in the ISO 105-C06 wash fastness test (method C2S) after 5 consecutive laundering cycles at 60 °C. The dye is formulated into a liquid commercial grade containing 25% active colorant, 12% EDTA tetrasodium salt, and 63% deionized water, and is supplied in 1,000 L intermediate bulk containers meeting UN 31HA1/Y packaging certification. The final textile product complies with OEKO-TEX® Standard 100 Annex 4 for brominated flame retardant exclusion and requires certification that no perfluorinated alkyl substances are present.
| Parameter | Setpoint | Measured value / tolerance | Impact if deviation > 5% |
|---|---|---|---|
| NBS addition temperature | −10 to −5 °C | −8.2 °C (avg, n=3) | 3,4-dibromo side product > 7 area% |
| Stoichiometry (NBS:substrate) | 1.03:1.00 mol/mol | 1.031 | C5-carboxylic acid bromination 0.2% |
| Reaction time in DMF | 4.5 h | 4.7 h (max deviation +0.3 h) | dibromo accumulation rate 0.3 area%/h |
| Quench temperature | ≤ 5 °C | 3.9 °C | dehydrobromination yielding thienopyrrolone |
| Crystallization solvent ratio (heptane:EtOAc) | 5:1 v/v | 5.2:1 | yield loss > 11% |
The brominated carboxylic acid building block enters a targeted covalent inhibitor development program where a warhead-bearing acrylamide is installed via sequential amidation and deprotection. Process development on a 50 L scale established that the free carboxylic acid must be converted to its acid chloride using oxalyl chloride (1.5 equivalents) and catalytic DMF (0.02 equivalents) in dichloromethane at 20–25 °C over 3 h; the acid chloride solution is then used directly without isolation due to its limited stability at ambient temperature (decomposition onset detected by reaction calorimetry at 31 °C). The addition of the acid chloride to a solution of N-Boc-2,5-diazabicyclo[2.2.2]octane at 0 °C in THF containing triethylamine (1.7 equivalents) gives the amide in 88% isolated yield after aqueous workup and crystallization from isopropanol. The final covalent inhibitor is formulated as a hydrochloride salt and microdosed into a hard gelatin capsule shell using a Xcelodose® 120S system at 100 µg active per capsule, blended with silicified microcrystalline cellulose (Prosolv® HD 90) and sodium stearyl fumarate (0.5%). The stratification of the blend is monitored with near-infrared spectroscopy to ensure content uniformity meets USP <905> criteria. The investigational product is manufactured under 21 CFR Part 212 for PET drug production quality standards, with the starting brominated acid controlled as an impurity at a limit of 15 µg/day based on a 1 µg/day threshold of toxicological concern per the EMA guideline on the limits of genotoxic impurities.
A lateral flow immunoassay conjugate for the detection of aflatoxin B₁ in maize utilizes gold nanoparticles (AuNPs, 40 nm diameter, OD520 = 1.0) functionalized with a hapten-carrier protein conjugate built upon a carboxymethylated derivative of 3-bromo-4H-thieno[3,2-b]pyrrole-5-carboxylic acid. The brominated scaffold is activated with NHS/EDC and coupled to bovine serum albumin at a molar coupling ratio of 14:1 (hapten:BSA) as determined by MALDI-TOF MS. The conjugation buffer is 50 mM MES at pH 6.0, and excess hapten is removed by dialysis (MWCO 10 kDa) against 10 mM PBS, pH 7.4. The gold conjugate is dispensed onto a conjugate pad (Whatman® CF6) at a jet rate of 3.5 µL/cm using a BioDot XYZ3060 dispenser, dried at 37 °C for 2 h in a forced-air convection oven, and assembled into a card format with a nitrocellulose membrane (CN140, Sartorius). The test line capture reagent is an anti-aflatoxin B₁ monoclonal antibody, and the control line is a goat anti-mouse IgG. The dipstick strip must give a limit of detection of 2 µg/kg in maize extract to comply with the EU Commission Regulation (EC) No 1881/2006 maximum level of 5 µg/kg for aflatoxin B₁ in cereals. Failure mode analysis reveals that if the brominated hapten synthesis retains elemental bromine or hydrobromic acid residues above 50 ppm, the colloidal gold undergoes aggregation, seen as a purple-grey shade on the conjugate pad and a loss of signal-to-noise ratio below 3.0. The strip housing is injection-molded from high-impact polystyrene, and the assembled devices are pouched with silica gel desiccant meeting DIN 55473. The batch release specification includes a visual inspection under 2,000 lux illumination to reject strips with any discoloration of the reaction matrix area.
