Pyrrole-2-Carboxylicacid, 3,4-Dimethyl-, Ethyl Ester (6Ci,7Ci,8Ci)

Gram-scale manufacturing of the pyrrolo[2,1-f][1,2,4]triazine-4-amine pharmacophore, the heterocyclic anchor deployed in remdesivir-type nucleotide prodrug polymerase inhibitors, depends on ethyl 3,4-dimethylpyrrole-2-carboxylate as the fully substituted starting heterocycle. The process sequence initiates with N-amination of the pyrrole nitrogen using a pre-cooled (-20 °C) suspension of freshly titrated LDA (1.2 eq) in anhydrous THF, followed by dropwise addition of O-(2,4-dinitrophenyl)hydroxylamine (1.05 eq) dissolved in DMF. After quenching with aqueous NH₄Cl, the intermediate N-aminopyrrole ester is extracted into methyl tert-butyl ether and concentrated under reduced pressure below 40 °C to prevent cyclization prematurely. The crude material is immediately dissolved in ethanol and treated with formamidine acetate (1.8 eq) under reflux for 18 h, which installs the triazine ring in a single cascade; the cyclization off-gas (NH₃, CO₂) is scrubbed through a dilute sulfuric acid trap. Subsequent Vilsmeier-type chlorination with POCl₃ at 105 °C in the presence of a catalytic quantity of DMF (0.15 eq) delivers the 4-chloropyrrolotriazine intermediate, which is isolated by drowning into ice-water and recrystallized from n-heptane/ethyl acetate (4:1 v/v) to obtain polymorph B of melting point 144–146 °C. Ammonolysis conducted in a PTFE-lined stainless-steel autoclave with liquid NH₃ in n-BuOH at 120 °C and autogenous pressure (~10 bar) yields the primary amine, which is converted to the corresponding phosphoramidate prodrug via established ProTide chemistry. Compliance: as a Key Starting Material (KSM) under ICH Q7 and ICH Q11, the ester must be accompanied by a full impurity fate and purge study; targeted LC–MS/MS screening for sulfonate ester genotoxins and N-nitrosamine formation potential (per EMA/CMDh/410640/2021 rev.3) is mandatory. Residual solvent levels must comply with USP <467> Option 2 for Class 2 solvents (acetonitrile limit 410 ppm, dichloromethane 600 ppm). Powder X-ray diffraction (XRPD) batch analysis correlates the orthorhombic crystal form with dissolution rate consistency during downstream handling. Terminal dosage form: lyophilized powder for intravenous infusion supplied in single-dose vials under aseptic conditions validated to ISO 14644-1 Class 5.

How Alkyl-Appended Pyrrole Esters Enter the Hole-Transport Layer Stack in OLED Architectures

Vacuum-deposited hole-transport materials (HTMs) exhibiting glass transition temperatures exceeding 140 °C are realized by converting ethyl 3,4-dimethylpyrrole-2-carboxylate into triarylamine-terminated oligopyrroles. The ester is first reduced with lithium aluminium hydride (1.3 eq) in diethyl ether at 0 °C to the corresponding primary alcohol, which is immediately oxidized with activated MnO₂ (15 wt% loading relative to substrate) in dichloromethane to the air-sensitive 3,4-dimethylpyrrole-2-carboxaldehyde. The aldehyde, used without chromatographic purification, is subjected to a double condensation with 4-(diphenylamino)phenylboronic acid pinacol ester (2.3 eq) under anhydrous Suzuki–Miyaura conditions: Pd(OAc)₂ (1.5 mol%), 2-dicyclohexylphosphino-2′,6′-dimethoxybiphenyl (SPhos, 3.6 mol%), K₃PO₄ (4.0 eq) in a toluene/n-butanol/water (10:1:0.5 v/v/v) mixture at 95 °C for 6 h. After aqueous workup and flash chromatography on neutral alumina (activity grade III), gradient sublimation of the crude HTM is performed in a multi-zone train sublimator with a thermal gradient from 280 °C to 180 °C under a dynamic vacuum of 1×10⁻⁶ mbar; the middle fraction exhibiting ΔT_g onset dispersion less than 0.3 °C by differential scanning calorimetry (DSC) is retained. Metal impurity thresholds for electroluminescent device qualification are set by inductively coupled plasma mass spectrometry (ICP–MS) per IEC 62321-4:2017: total Pd <0.5 ppm, Fe <1.0 ppm, Na <0.2 ppm. The T₁–S₀ gap, measured by low-temperature phosphorescence spectroscopy in frozen 2-methyltetrahydrofuran at 77 K, must exceed 3.0 eV to prevent exciton back-transfer. Terminus product: discrete HTM dopant incorporated into the emissive layer of a top-emission white active-matrix OLED (AMOLED) panel used in automotive dashboard displays, whose reliability is verified by 85/85 damp heat bias testing (85 °C, 85% RH) for 1,000 h.

Organometallic catalyst platforms leveraging the steric pressure of a 3,4-dimethylated pyrrole ring exploit this ester as a nitrogen-rich pro-ligand precursor. Condensation with 2-hydrazinopyridine (1.0 eq) in methanol containing glacial acetic acid (5 mol%) at reflux for 8 h precipitates the hydrazone-ester intermediate, which undergoes base-induced cyclization in the presence of NaOEt in ethanol at 78 °C to form a tridentate NNN-pincer pro-ligand of the 2-(1-(pyridin-2-yl)-1H-pyrrol-2-yl)pyridine type bearing two methyl substituents on the pyrrole ring. The free ligand is metallated with anhydrous NiCl₂(DME) (1.05 eq) in dry THF under argon in a Schlenk flask, followed by activation with methylaluminoxane (MAO, 500 eq Al/Ni) to generate an ethylene oligomerization catalyst that shifts the Schulz–Flory α-value from 0.68 (unsubstituted analogue) to 0.81, favouring C₈–C₁₂ linear α-olefins. Batch-to-batch variability in catalytic activity is traced to residual moisture in the ester; therefore, a pre-drying protocol using 3 Å molecular sieves (activated at 300 °C for 24 h, bead size 1.6–2.5 mm) is enforced prior to the condensation step, reducing water content to <30 ppm by Karl Fischer titration. Regulatory documentation for industrial supply: a full REACH registration dossier (Annex VII–X) inclusive of an acute oral toxicity study (OECD 423), Daphnia acute immobilization test (OECD 202), and ready biodegradability assessment (OECD 301F) is required for tonnage bands exceeding 1 t/a. End-use: homogeneous nickel catalyst concentrate diluted in Isopar E to 10 μmol/L and fed continuously into a continuous stirred-tank reactor (CSTR) train for comonomer-grade α-olefin production.

Site-Specific Protein Labeling Relies on Reactive BODIPY Derivatives Built from This Precursor

Ethyl 3,4-dimethylpyrrole-2-carboxylate serves as the key building block for meso-substituted boron dipyrromethene (BODIPY) fluorophores displaying excitation maxima beyond 530 nm. In a representative route to a water-soluble active ester, the ester is hydrolysed with KOH (3M aqueous ethanol, 60 °C, 4 h) to the free acid, which is then coupled with N-hydroxysuccinimide (NHS, 1.15 eq) using N,N′-dicyclohexylcarbodiimide (1.1 eq) in anhydrous dichloromethane at 0 °C→RT overnight. The activated 3,4-dimethylpyrrole-2-carboxylic acid NHS ester is reacted with 3,5-dimethoxybenzaldehyde (0.45 eq) in the presence of BF₃·OEt₂ (0.2 eq) in CH₂Cl₂ under nitrogen for 24 h, oxidized with DDQ (1.0 eq), and treated with additional BF₃·OEt₂ and diisopropylethylamine to deliver the meso-(3,5-dimethoxyphenyl)-BODIPY bis-NHS ester. The crude dye is purified by semi-preparative HPLC on a C18 column (mobile phase: acetonitrile/water 70:30 containing 0.1% trifluoroacetic acid) to achieve an HPLC area purity of ≥99.0% at 490 nm. Fluorescence quantum yield (Φ_F), measured against rhodamine 6G in ethanol as the reference standard (Φ_F = 0.95), reaches 0.84 in phosphate-buffered saline (pH 7.4). Conjugation to trastuzumab-derivatized Fab′ fragments via the NHS handle proceeds at a molar ratio of 8:1 (dye:protein) in carbonate buffer (pH 8.3) at 22 °C for 2 h, followed by size-exclusion chromatography on a Superdex 200 Increase 10/300 GL column. Quality systems governing the manufacture as an ancillary reagent for clinical immunohistochemistry must align with ISO 13485:2016 and IVDR (EU) 2017/746; traceability documentation includes purification resin logbooks and endotoxin levels (<0.1 EU/mg by LAL gel clot method). Finished diagnostic kit component: ready-to-use antibody-fluorophore conjugate diluted in stabilizer buffer for multiplex immunofluorescence on formalin-fixed paraffin-embedded tissue sections.

When Niche Horticultural Fungicides Demand a 3,4-Disubstituted Pyrrole Core

Experimental succinate dehydrogenase inhibitor (SDHI) fungicide scaffolds targeting Ascomycete pathogens in cucurbit crops incorporate the 3,4-dimethylpyrrole motif delivered by ethyl 3,4-dimethylpyrrole-2-carboxylate. The synthetic sequence engages the ester in a Knoevenagel condensation with 2-cyanoacetamide (1.05 eq) catalysed by piperidinium acetate (10 mol%) in refluxing toluene with azeotropic removal of water using a Dean–Stark trap. The resulting γ-cyano-γ-carbamoylalkenylpyrrole intermediate, isolated as a pale-yellow amorphous solid after sodium bisulfite wash and heptane trituration, is then treated with hydrazine monohydrate (3.0 eq) in n-butanol at 120 °C in a sealed tube to form the pyrazol-3-ylamine pharmacophore. Subsequent HATU-mediated amidation with 4-(trifluoromethyl)benzoic acid (1.15 eq) in DMF and N,N-diisopropylethylamine (2.0 eq) affords the final lead compound, purified by flash chromatography and recrystallized from acetonitrile/n-hexane (3:1) to constant melting point 203–205 °C. Manufacturing hygiene considerations: synthetic intermediate shipment must declare absence of ethylene bis-dithiocarbamate (EBDC) contaminants and hydrazine below EU pharmacopoeia residual limits for agrochemical intermediates. Ecotoxicological profiling mandated by FAO/WHO Joint Meeting on Pesticide Residues (JMPR) includes the full honeybee acute contact toxicity test (OECD 214) and a 48-h earthworm acute toxicity test (OECD 207) with an LC₅₀ cut-off of >1,000 mg/kg dry soil for soil residence applications. The recommended formulation is an oil-in-water suspension concentrate (SC) containing 200 g a.i./L, wet-milled on a horizontal bead mill charged with 0.3–0.5 mm yttria-stabilized zirconia beads until particle size D_v90 <5 µm is confirmed by laser diffraction. Target disease: powdery mildew (Erysiphe cichoracearum) on greenhouse cucumber, applied at 75 g a.i./ha with 14-day pre-harvest interval.

Incorporation of this pyrrole ester into DNA-encoded libraries (DELs) as a trifunctional scaffold exploits the dual reactivity of its carboxylic acid handle and the 3,4-dimethyl substitution for fragment growth. On solid support, the ester is saponified to the lithium carboxylate directly on-resin using LiOH in THF/water (3:1), then coupled to amino-terminated hexa-ethyleneglycol linkers via HATU/HOAt protocol (3 eq each, DMF, RT, 6 h). The resulting immobilized pyrrole carboxamide acts as a branching point for combinatorial split-and-pool synthesis: iterative cycles of DMT-cleavage, phosphoramidite coupling, and oxidative sulfurization extend a short DNA tag, while parallel solution-phase reactions on the pyrrole ring install diverse aryl halides through Pd-catalysed direct C–H arylation using Pd(OAc)₂/PCy₃ (10 mol%) and K₂CO₃ in DMAc at 110 °C. The carboxylic acid loading on non-swelling polyethylene glycol-grafted polystyrene beads is quantified by photometric Fmoc-release assay, targeting a consistent loading of 0.22 mmol/g. Analytical certification for the ester as a DEL input requires compliance with ISO 17025:2017 for assay and identity testing; a certificate of analysis must include ¹H NMR (solvent DMSO-d₆, ester OCH₂ quartet at δ 4.27 ppm), FTIR (C=O stretch at 1695 cm⁻¹), and HPLC-ELSD purity >98.5%. Cross-contamination monitoring via unique isotopically coded internal standards (quadrupole time-of-flight MS) prevents screen interference. Deliverable: encoded pyrrole-polycycle conjugate library containing 10⁸ distinct members, utilized in affinity selection campaigns against recombinant human deacetylase targets identified by high-throughput next-generation sequencing hit deconvolution.