1-Methyl-1H-Pyrrole-3-Carboxylic Acid

In the multi-kilogram preparation of a pyrrolo[2,3-d]pyrimidine intermediate destined for an orally bioavailable pan-FGFR inhibitor that has undergone Phase I dose escalation under an FDA-reviewed IND, 1-methyl-1H-pyrrole-3-carboxylic acid (CAS 131-19-9) with a residual water content strictly below 0.05% w/w (Karl Fischer titration per USP<921>, Method Ia) is activated with 1.1 to 1.2 molar equivalents of carbonyldiimidazole (CDI) in anhydrous 2-methyltetrahydrofuran at 15–20 °C under a nitrogen pad, forming the acylimidazolide intermediate before coupling with the bespoke pyrazolopiperidine amine hydrochloride. The process, executed inside a 500 L glass-lined steel reactor (Pfaudler AE type, three-stage retreat-blade impeller) with inline Process Analytical Technology (ReactIR 15 with DiComp probe) to track carbonyl absorptions at 1820 cm⁻¹, is subject to the current good manufacturing practice requirements of ICH Q7 for GMP intermediates and the cleanliness validation protocols of FDA 21 CFR Part 211 Subpart D, given that the resulting penultimate intermediate will be crystallized from isopropanol/water (mass ratio 3:1, seeding at 55 °C, cooling ramp −0.2 °C/min) to achieve a polymorphically pure Form A (confirmed by XRPD with characteristic peaks at 2θ = 10.8°, 14.3°, 19.6°) that is subsequently telescoped into a Buchwald–Hartwig amination to install the indazole moiety. The targeted dosage form is a 4.5 mg or 10 mg immediate-release tablet manufactured via roller compaction, where the pyrrole carboxylic acid-derived fragment contributes to a kinase insert hinge-binding motif exhibiting an IC₅₀ of <8 nM against FGFR2 V564F gatekeeper mutant, as determined by a HTRF-based biochemical assay calibrated with staurosporine controls.

When the parent acid is converted to the corresponding acid chloride using oxalyl chloride (1.05 eq) and catalytic DMF (0.005 eq) in toluene at 40–45 °C in a continuous-flow Corning G1 silicon carbide reactor (channel dimension 0.6 mm × 0.9 mm, residence time 45 s, back-pressure regulator set to 3.5 bar) for the preparation of a dihydroorotate dehydrogenase (DHODH) inhibitor intermediate, the generation of off-gas HCl is scrubbed through a packed column with 10% aqueous NaOH to maintain facility emission compliance under EU Directive 2010/75/EU. The crude acid chloride stream is immediately reacted with 3-chloro-4-methylaniline in the presence of N-methylmorpholine to furnish the corresponding amide, and the organic phase is washed twice with 1 M citric acid and dried over molecular sieves before distillation. Published data for device-specific heat transfer coefficients at this scale indicate a processing window of ±3 °C to avoid carbamoyl chloride formation, and the design space was validated using a face-centered central composite design with three center points for robustness. The ultimate drug product candidate, an immunosuppressant for rheumatoid arthritis, is formulated as a hard gelatin capsule containing a spray-dried dispersion of the amide with HPMCAS-MG at 20% drug load to enhance apparent solubility from <2 µg/mL in FaSSIF-V2 to >150 µg/mL.

Why Does the Para-Chloro Substituent on the N-Aryl Ring Amplify the In Vivo Knockdown Activity of Chlorfenapyr Predecessor Insecticides?

The 1-methyl-1H-pyrrole-3-carboxylic acid scaffold is employed as a pro-pesticidal building block in the synthesis of aryl pyrrole acaricides structurally convergent with the mode of action of chlorfenapyr (a mitochondrial uncoupler targeting oxidative phosphorylation at complex I in the respiratory chain of Tetranychus urticae). Preparation of the active ingredient entails a sequence where the carboxylic acid is first esterified with methanol under sulfuric acid catalysis (reflux, 12 h, yield after fractional distillation under 15 mm Hg exceeds 88%), and the resulting methyl ester is subjected to a Vilsmeier–Haack formylation with DMF/POCl₃ at 0–5 °C to install the aldehyde function exclusively at the 2-position of the pyrrole ring, a regiochemical outcome verified by ¹H NMR coupling constants (J_4,5 = 2.7 Hz versus 3.1 Hz for the alternative isomer). This formyl intermediate is then condensed with p-chlorophenylacetic acid in acetic anhydride containing anhydrous sodium acetate, leading to the benzylidenepyrrolone chromophore that is subsequently reacted with 2-aminomethyl-4-trifluoromethoxyphenyl acetonitrile in a Michael-type addition to complete the active scaffold. The manufacturing process is performed in a dedicated multipurpose plant adhering to the engineering controls of ISO 14001:2015 environmental management and the FAO Pesticide Specification guideline FAO/WHO Manual on the Development and Use of FAO and WHO Specifications for Pesticides, 2nd rev. (Annex H, concerning relevant impurities). The addition rate of 1-methyl-1H-pyrrole-3-carboxylic acid is stoichiometric (1.0 eq relative to the downstream aldehyde intermediate), but batch records from a contract manufacturing site in Gujarat document that 1.07 eq is physically charged to compensate for minor decarboxylative degassing during the esterification heat-up phase. The final technical concentrate is milled in an air-jet mill to a particle size distribution with D₉₀ <5 µm and then formulated into a 240 g/L suspension concentrate (SC) with a proprietary comb polymer dispersant (Atlox 4913, 3.5% w/w) and 1,2-benzisothiazolin-3-one as a preservative, passing the accelerated storage stability test according to CIPAC MT 46.3 (no phase separation, minimal sedimentation, suspension rate >92% after 14 days at 54 °C).

When 0.3 to 0.7 wt% of 1-methyl-1H-pyrrole-3-carboxylic acid is dissolved into a 6 M HCl pickling bath at 60 °C for cleaning mill-scaled ASTM A240/A240M-22 Type 304L stainless steel plates prior to a citric acid/0.1% sodium molybdate passivation cycle meeting AMS 2700 Class 3, the interfacial activity is dominated by the protonated pyrrolyl ring adsorbing onto the cathodic sites of the ferritic surface microstructure. Electrochemical polarization scans conducted in a standard three-electrode flat cell (graphite counter, saturated calomel reference, scan rate 0.166 mV/s, start potential −250 mV vs. OCP) per ASTM G59-20 indicate that the corrosion current density decreases from a baseline of 1.12 × 10⁻⁴ A/cm² to 9.8 × 10⁻⁶ A/cm² at the 0.5 wt% loading, translating to a corrosion inhibition efficiency of 91.2% derived from Tafel extrapolation in accordance with ASTM G102-23. The bath life is extended from 6 hours to 22 hours before the free HCl concentration drops below 4.5 M and ferrous ion accumulation exceeds 80 g/L (titrated with 0.1 N KMnO₄), at which point the spent bath is neutralized with lime slurry to pH 9.0 and the precipitated metal hydroxide sludge is filter-pressed; the filtrate is discharged after ensuring the TOC is below 150 mg/L, a value monitored in compliance with the Metal Finishing Effluent Guidelines of US EPA 40 CFR Part 433. The terminal product of this application is not a formulated compound but an industrial process aid that renders the stainless steel substrate suitable for subsequent electropolishing or for assembly into aseptic processing equipment qualified under ASME BPE-2022.

If the Sublimation Enthalpy Exceeds 105 kJ/mol, the Film-Forming Uniformity of a Methylpyrrole-Based Electron Blocking Layer Deviates Beyond ±2 nm

A high-purity grade of 1-methyl-1H-pyrrole-3-carboxylic acid, purified by repeated vacuum sublimation (glass tube furnace, 10⁻⁶ mbar, temperature gradient 90 → 130 °C) until HPLC assay at 254 nm indicates a total purity exceeding 99.94% area under the curve, is employed as a precursor to a phosphine oxide-functionalized electron-blocking material for thermally activated delayed fluorescence (TADF) organic light-emitting diodes. The acid is converted via a three-step sequence—first amidation with 4-bromo-N,N-diphenylaniline using EDC·HCl and HOBt (0.95 eq HOBt, anhydrous DMF, 23 °C, 18 h) to install the brominated triphenylamine arm, then lithium-halogen exchange with n-BuLi in THF at −78 °C and addition of diphenylphosphine chloride, and final hydrogen peroxide oxidation to the phosphine oxide—without resorting to palladium-catalyzed C–P bond formation that introduces trace metal contamination above the 500 ppb threshold measured by ICP-MS. The critical loading ratio in the hole-blocking layer is between 12% and 15% by volume co-deposited with 2,4,6-tris(biphenyl-3-yl)-1,3,5-triazine (T2T) in a Kurt J. Lesker multiple-source thermal evaporator equipped with quartz crystal microbalance feedback control; deposition rates are held at 0.5 Å/s for the host and 0.07 Å/s for the dopant to maintain film stoichiometry. A Kalrez 4079 O-ring sealed source crucible and an ISO 14644-1 Class 5 cleanroom environment are prerequisites because exposure of the loaded source to ambient humidity above 25% RH during magazine transfer causes a detectable carbamate by-product from reaction with atmospheric CO₂ that manifests as a shoulder peak at 1695 cm⁻¹ in FTIR reflectance spectra of the deposited film. The finished OLED device, incorporating a sky-blue Ir(cb)₃ emitter, exhibits an external quantum efficiency of 22.4% and a T95 operational lifetime at 1000 cd/m² of 8 200 hours as per the JNC/OLED Material Consortium testing protocol, and the glass transition temperature of the blended charge-blocking layer (measured by temperature-dependent spectroscopic ellipsometry) remains at 118 °C—sufficiently above the 85 °C/85% RH storage test required by automotive-grade AMOLED display specifications per Automotive Electronics Council AEC-Q102.

The contrasting thermal dependence observed during kilogram-scale distillation of crude 1-methyl-1H-pyrrole-3-carboxylic acid (boiling point 146–148 °C at 18 mmHg, heat-sensitive fractionation through a 30 cm Vigreux column with a reflux ratio of 4:1) has direct implications for the downstream dye synthesis supply chain. A lot of the acid esterified with 2-cyano-3-(4-hydroxyphenyl)acrylic acid under Mitsunobu conditions (DIAD, PPh₃, THF, 0 °C to room temperature) yields a monomer that subsequently undergoes a spontaneous cyclotrimerization in acetic anhydride catalyzed by zinc acetate dihydrate to form a near-infrared fluorophore emitting at 720 nm with a Stokes shift of 48 nm and a fluorescence quantum yield of 0.34 in chloroform, determined relative to Rhodamine 101 in ethanol (Φ = 0.92). The molar addition ratio of the pyrrole acid to the phenolic aldehyde is carefully held at 1.00:1.00 because excess acid above 1.02 eq leads to an O-acylated by-product that co-elutes with the desired product on silica gel (Rf = 0.43 versus 0.47, ethyl acetate/hexane 1:3) and requires an additional preparative HPLC purification step using a C18 column and an acetonitrile/water gradient acidified with 0.05% TFA. The finished fluorophore is incorporated into a lateral flow immunoassay test strip for cardiac troponin I detection, and the assay sensitivity of 50 pg/mL is validated according to CLSI Guideline EP17-A2 for limit of blank and limit of detection, with the whole device manufactured under a ISO 13485:2016 quality management system and registered under IVDR (EU) 2017/746.

Thermal-Acid-Driven Migration of a Non-Reactive Pyrrole-3-Carboxylic Acid Adhesion Promoter into the Epoxy-Polyurethane Interpenetrating Network Interface

In the formulation of a two-component, high-solids structural adhesive formulated for bonding grit-blasted SMC (sheet moulding compound, resin-rich finish 50–70 µm) to aluminum alloy EN AW-6063-T6 in automotive closure panel assembly, a semi-solid ester of 1-methyl-1H-pyrrole-3-carboxylic acid with 2-hydroxyethyl methacrylate (HEMA), added at 3.2 phr based on Part A resin solids, functions as a corrosion-inhibitive adhesion promoter that migrates preferentially to the metal oxide-adhesive interphase during the 30-minute oven cure cycle at 93 °C. Accelerated wedge exposure according to ISO 21195:2021 method C-2 (condensation humidity at 50 °C, cycle 8 h wet/16 h dry, 1 680 h total) reveals that the interphase retains a lap shear strength of 14.2 MPa versus 7.3 MPa for the unmodified control formulation, and scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS) confirms the absence of cathodic delamination because the pyrrole moiety chelates Al³⁺ ions released during underfilm corrosion, forming a sparingly soluble organometallic complex that passivates the crack tip. The addition ratio is constrained to a narrow window between 2.8 phr and 3.5 phr; below 2.8 phr the adhesion-promoting effect is lost due to insufficient surface coverage, while above 3.5 phr plasticization of the cured network reduces the storage modulus at 80 °C (measured by DMA at 1 Hz) below the OEM specification of 120 MPa. The proprietary adhesive is manufactured under IATF 16949:2016 quality management systems, with batch release criteria including a Brookfield viscosity at 23 °C of 38 000–42 000 mPa·s for Part A and a sag resistance of >2 mm on vertical surfaces according to ASTM D2202-20. The finished assembly, incorporating this adhesive into the hem-flanged front door skin, undergoes a 1 000-hour cyclic corrosion test per VDA 233-102 without red rust at the scribe line and passes the 90° peel test at 6 N/mm after water immersion for 15 days at 40 °C as mandated by the OEM material specification.

Published data for this specific configuration are limited regarding the long-term chemostability of the 1-methyl-1H-pyrrole-3-carboxylic acid motif under repeated autoclave conditions; however, accelerated aging at 100 °C in sealed borosilicate ampoules containing 1.0 M aqueous HCl over a 14-day period (Q₁₀ = 2 extrapolation to 25 °C shelf life) demonstrates 98.3% retention of the parent compound as measured by reverse-phase HPLC, confirming sufficient hydrolytic robustness for acidic cleaning and plating bath operations where the organic additive is expected to remain functional over several bath turnover cycles.