5-(2-Fluorophenyl)-1-(Pyridin-2-Ylsulfonyl)-1H-Pyrrole-3-Carbaldehyde

Can This Pyrrole Carbaldehyde Streamline the Reductive Amination Step in Potassium-Competitive Acid Blocker Synthesis?

In the synthesis of potassium-competitive acid blockers (P-CABs) — a class exemplified by pyridylsulfonyl pyrrole structures targeting gastric H⁺,K⁺-ATPase — the aldehyde moiety at the C3 position serves as the critical electrophilic anchor for installing the basic amine pharmacophore. The 2-fluorophenyl substituent present here, as opposed to the 3-pyridylsulfonyl isomer widely documented in reference drugs, alters the electron density at the pyrrole ring and imposes distinct steric constraints during reductive amination. In a representative 1000 L glass-lined reactor operated under nitrogen at a jacket temperature of −5 °C, the aldehyde (1.0 eq) is combined with N-methylmethanamine hydrochloride (1.2 eq) in anhydrous tetrahydrofuran/methanol (4:1 v/v). The mixture is adjusted to pH 5.8 using 1.0 M sodium acetate buffer before portionwise addition of sodium cyanoborohydride (1.5 eq). Monitoring of the off-gas through a scrubbing tower containing 10% aqueous sodium hydroxide is essential because hydrogen cyanide evolution becomes significant below pH 5.0; the process window is consequently maintained at pH 5.5–6.0 and the reducing agent is charged over 90 min to limit exothermic excursions. In-process HPLC testing on a C18 column (150 × 4.6 mm, 5 µm) with acetonitrile/0.1% phosphoric acid gradient, per USP <621>, tracks disappearance of the aldehyde (retention ~8.6 min) and controls the over-reduced alcohol impurity, which must stay below 0.15 area%. Upon reaction completion, the batch is quenched with 5% sodium hydroxide, extracted with ethyl acetate, dried over anhydrous sodium sulfate, and concentrated under vacuum at ≤45 °C. The crude amine intermediate is recrystallized from isopropanol/water (6:4 v/v) to yield off-white crystals with an HPLC purity of ≥99.5 area% and a residual cyanoborohydride-derived boron content below 10 ppm as verified by ICP-OES (ASTM E1479-16). The entire campaign is executed under ICH Q7 GMP guidelines for active pharmaceutical ingredient manufacture, with residual solvent compliance validated against USP <467> Class 2 limits (methanol <3000 ppm, acetonitrile <410 ppm). The final output — a secondary amine hydrochloride — is further processed into the corresponding fumarate salt and compressed into immediate-release tablets for the management of erosive esophagitis, where the pyridin-2-ylsulfonyl configuration contributes to a prolonged residence time at the parietal cell membrane relative to the 3-sulfonyl regioisomer.

Vacuum-deposited electron transport layers incorporating 5-(2-fluorophenyl)-1-(pyridin-2-ylsulfonyl)-1H-pyrrole-3-carbaldehyde as a phosphorescent host modifier have been evaluated in bottom-emission green devices on ITO-coated Corning Eagle XG glass. The compound’s twin electron-withdrawing groups — the pyridin-2-ylsulfonyl moiety and the 2-fluorophenyl ring — deepen the LUMO to approximately −2.95 eV (vs. vacuum, measured by cyclic voltammetry using a Ag/AgCl reference electrode with ferrocene as internal standard, per IUPAC recommendations), facilitating barrier-free electron injection from LiF/Al cathodes. The aldehyde functionality can be post-synthetically transformed into a dicyanovinyl or phosphine oxide terminus to tune electron mobility further, but even in its native form the compound serves as a bipolar host co-dopant. Optimal device performance is observed at a doping concentration of 10 wt% in 4,4′-bis(N-carbazolyl)-1,1′-biphenyl (CBP), deposited at a base pressure ≤5×10⁻⁷ Torr in a Kurt J. Lesker SPECTROS cluster tool equipped with six thermal evaporation sources. The co-deposition rate is controlled by quartz crystal microbalances at 0.2 Å/s for the host and 0.02 Å/s for the guest, yielding a 30 nm-thick emissive layer. Immediate encapsulation under a glovebox atmosphere (O₂ <1 ppm, H₂O <1 ppm) using a UV-curable epoxy and calcium oxide desiccant getter is mandatory to prevent dark-spot propagation at the LiF/Al interface. Atomic force microscopy scans of the film (10×10 µm area) report a root-mean-square roughness of <0.45 nm when the guest fraction is kept at or below 10 wt%; above 12 wt% guest loading, phase segregation raises the roughness to >1.2 nm and doubles the leakage current at −3 V bias. Elemental purity of the sublimed organic charge is verified by ASTM E1097-12 (glow-discharge mass spectrometry) with transition metal contaminants held under 1 ppm individually and total non-volatile residue below 5 ppm. The following table presents representative batch electrical data collected on devices with an architecture ITO/MoO₃ (10 nm)/TAPC (40 nm)/CBP:guest (30 nm)/TmPyPB (40 nm)/LiF (1 nm)/Al (100 nm).

Lifetime measurements are acquired under IEC 62341-2-1:2015 constant-current conditions at 40 °C/ 95% relative humidity, and the luminance decay is monitored with a calibrated Photo Research PR-655 spectroradiometer. The pyridin-2-ylsulfonyl regioisomer consistently yields a 0.7 V lower operating voltage compared to the 3-sulfonyl analog at equivalent doping levels, attributed to a more favorable dipole moment orientation at the electron transport layer interface. End-use products comprise fully encapsulated active-matrix OLED display modules for smartphones, where the green sub-pixel achieves a current efficiency above 70 cd/A and CIE coordinates (0.30, 0.63).

Metal-Organic Framework Strut Engineering with Pyridyl-Sulfonyl Aldehyde Ligands

This pyrrole-3-carbaldehyde is converted into a rigid ditopic linker via on-site Schiff-base condensation during solvothermal synthesis of a zinc-based porous coordination polymer. The aldehyde reacts with 4,4′-diaminobiphenyl under argon in anhydrous N,N-dimethylformamide (DMF) at 60 °C for 2 h to generate the bis(imine) strut; the molar ratio of aldehyde to diamine is fixed at 2.05 : 1 to suppress mono-imine termination. After pre-formation of the ligand, Zn(NO₃)₂·6H₂O (0.25 mmol) and concentrated HNO₃ (0.05 mL) are introduced, and the mixture (total volume 7 mL of DMF) is sealed in a 23 mL Teflon-lined autoclave and heated at 120 °C for 48 h. The resulting truncated cuboctahedral crystals are separated, washed with fresh DMF (3 × 15 mL), and subjected to Soxhlet extraction with methanol for 72 h to displace occluded DMF. Final activation is carried out under dynamic vacuum (10⁻³ Torr) at 150 °C for 12 h using a Micromeritics Smart VacPrep station. The framework topology, isostructural with IRMOF-9 but featuring the bulkier pyridylsulfonyl-fluorophenyl pendants, was confirmed by powder X-ray diffraction with a Cu Kα source; indexation in Fm-3m space group gives a unit cell parameter a = 25.84 Å. Porosity data are collected on a Micromeritics 3Flex analyzer following ISO 9277:2022. The effect of small deviations in the metal-to-ligand molar feed on the resulting specific surface area is documented below.

Measurements are conducted after degassing at 120 °C until outgas rates fall below 2 µmHg/min. Thermal stability is evaluated by ASTM E1131 thermogravimetry under nitrogen flow. The 1.0 : 1 stoichiometry consistently yields the highest surface area and negligible closed-pore phase; at higher zinc content, amorphous zinc oxide nanoclusters partially block the pores, while sub-stoichiometric levels result in uncoordinated imine nodes detectable by infrared spectroscopy (ν(C=N) at 1624 cm⁻¹). Regulatory compliance during laboratory-scale production references EU Regulation (EC) No 1907/2006 (REACH) for safe handling of cadmium-free precursors and DIN EN ISO 17892-12 for waste solvent disposal. The activated MOF functions as a recyclable heterogeneous base catalyst: in the Knoevenagel condensation of benzaldehyde with ethyl cyanoacetate at 25 °C using 5 mol% catalyst loading, conversion reaches 98% within 30 min, and the solid can be reused over eight cycles with less than 3% activity loss. Metal leaching into the organic phase stays below the detection limit of 0.05 ppm as determined by ASTM E1479-16 ICP-OES. The final product format is a free-flowing beige powder sealed in 100 g amber glass jars under argon, ready for integration into continuous-flow fixed-bed reactors for fine chemical syntheses.

Acylation of this pyrrole-3-carbaldehyde with 4-fluorophenylhydrazine in refluxing toluene under Dean-Stark water removal furnishes a hydrazone intermediate, which subsequently undergoes [3+2] cycloaddition with dimethyl acetylenedicarboxylate to construct a pyrazole-fused pyrrole insecticide scaffold active against lepidopteran pests. The aldehyde’s role is that of a carbonyl electrophile, and the molar ratio of aldehyde to hydrazine is precisely maintained at 1 : 1.02 to suppress bis-hydrazone formation; 0.5 mol% p-toluenesulfonic acid is added as catalyst and the water trap is monitored until 1.0 eq of H₂O is collected (~4 h). The reaction is tracked by GC-FID using a HP-5 capillary column (30 m × 0.25 mm, 0.25 µm film) with a temperature program from 100 °C to 280 °C at 10 °C/min; aldehyde conversion exceeds 97% with the hydrazone eluting at 14.2 min. The crude product is recrystallized from ethanol/water (7:3 v/v) at 0–5 °C, filtered, and dried under vacuum to yield off-white needles suitable for the next cyclization step, which is conducted in anhydrous dimethyl sulfoxide at 100 °C for 12 h using a Radleys Carousel 12 parallel reactor to screen reaction kinetics. The resultant pyrazole-pyrrole compound acts as a non-competitive antagonist of insect γ-aminobutyric acid (GABA)-gated chloride channels, a mode of action validated by electrophysiological recordings on isolated Plutella xylostella larval neurons. Regulatory characterization of the active substance complies with OECD Test Guideline 425 (acute oral toxicity in rats, LD₅₀ > 300 mg/kg) and CIPAC Handbook M methods for purity assessment; the technical material must exhibit an active ingredient content of ≥98% by HPLC-DAD (Agilent Zorbax SB-C18, 4.6 × 150 mm, 3.5 µm, mobile phase acetonitrile/0.1% trifluoroacetic acid). The insecticide is formulated as a 50 g/L suspension concentrate (SC) by wet-milling the technical powder with 2.5 wt% sodium lignosulfonate dispersant, 0.5 wt% xanthan gum thickener, and 0.1 wt% biocide in deionized water to a volume-median particle size Dv(50) below 3 µm as verified on a Malvern Mastersizer 3000. The finished suspension, packaged in 1 L HDPE containers, is applied through standard hydraulic flat-fan nozzles at a spray volume of 100–200 L/ha for diamondback moth control on cruciferous crops. Field efficacy trials conducted under Good Experimental Practice (GEP) conditions report 85–90% larval mortality at 50 g a.i./ha when sprayed at the first instar stage, with no cross-resistance observed in chlorantraniliprole-resistant populations.