2-Phenylthiazole-4-Carboxylic Acid

In the manufacturing train for a small-molecule cathepsin K inhibitor currently under Phase II evaluation, 2-Phenylthiazole-4-Carboxylic Acid serves as the heterocyclic warhead precursor that introduces the critical thiazole-phenyl pharmacophore. The acid is activated via a mixed anhydride strategy using isobutyl chloroformate and N-methylmorpholine in anhydrous tetrahydrofuran at -15 °C to -5 °C, then coupled to a constrained (S)-proline-derived amine intermediate. Stoichiometric loading of the acid is tightly controlled at 1.00–1.03 equivalents relative to the amine; excursions beyond 1.05 eq. consistently generate a dimeric byproduct that precipitates during the subsequent aqueous work-up and occludes the 50 μm filter cloth in the agitated nutsche filter-dryer, causing batch losses of 11–14%. The downstream process stream passes through two sequential solvent swaps into isopropyl acetate and is polished via hot filtration at 55–60 °C before crystallization. Regulatory compliance is maintained under ICH Q7 for active pharmaceutical ingredient starting materials, with the acid classified as a GMP starting material under a Designated Starting Material justification filed in the US Type II Drug Master File. Residual palladium from an earlier Suzuki coupling is controlled to <10 ppm by IPC before the amidation step because the thiazole nitrogen acts as a ligand and retains metal ions at levels that would otherwise exceed the ICH Q3D parenteral permitted daily exposure for Pd. The terminal drug substance is an orally bioavailable inhibitor of the collagenolytic cysteine protease cathepsin K, formulated as a 50 mg film-coated tablet for osteoporotic fracture risk reduction.

What governs the amidation selectivity of 2-Phenylthiazole-4-Carboxylic Acid in agrochemical lead optimization?

During the synthesis of fluorinated thiazole carboxamide fungicides intended for leaf blotch control in winter wheat, selectivity between the primary amide pathway and the undesired heterocyclic ring-opening side-reaction is determined by base strength and temperature ramping profiles. The acid is converted to the corresponding acid chloride using oxalyl chloride and catalytic dimethylformamide in dichloromethane at 0–5 °C, with the addition rate of oxalyl chloride not exceeding 1.2 mL·min⁻¹·kg⁻¹ of substrate to prevent a runaway exotherm that accelerates decarboxylation. The crude acid chloride is held at -5 °C for no longer than 4 hours before being added dropwise to a precooled solution of 2,6-difluoroaniline in methyl tert-butyl ether containing 1.1 eq. of triethylamine. An excess of the acid chloride relative to aniline at 1.03:1 is maintained; inversion of this ratio results in bis-acylation on the thiazole ring at the 5-position, producing an impurity that co-elutes with the target amide on a C18 column under USP <621> conditions and requires preparative chromatography for removal. The formulated a.i. is registered according to FAO Specification 540/TC principles, and the technical concentrate is manufactured in an ISO 9001-certified plant with an established threshold for the acid intermediate of 98.5% purity by GC-FID area normalization. Scale-up experience on 100 L glass-lined steel reactors indicates that the shear rate during the quench step must be kept below 80 s⁻¹ to avoid emulsification that extends phase separation beyond 45 minutes. The end-use product is a suspension concentrate containing 200 g/L active ingredient for application at 125 g/ha on cereal crops.

Metal-Organic Framework Node Engineering with 2-Phenylthiazole-4-Carboxylate Linkers

In the solvothermal construction of zirconium-based UiO-type metal-organic frameworks for post-combustion CO₂ capture, the bent carboxylate donor of the thiazole acid provides a coordination angle that deviates from linear terephthalate analogues, leading to framework defects that enhance accessible pore volume at the expense of structural rigidity. A typical synthesis loads 2.0 mmol of ZrCl₄ and 2.0–2.4 mmol of 2-Phenylthiazole-4-Carboxylic Acid in 30 mL of N,N-dimethylformamide with 4.8 mL of formic acid as modulator, sealed in a 100 mL PTFE-lined autoclave and held at 120 °C for 48 hours. The acid-to-metal molar ratio window is critically narrow: at ratios below 1.0, amorphous gelation occurs within 6 hours, while ratios above 1.2 cause the acid to self-assemble into a non-porous hydrogen-bonded organic framework that competes with MOF nucleation. After synthesis, solvent exchange with anhydrous methanol over 72 hours is necessary because residual DMF coordinates to Zr₆ nodes and reduces the BET surface area by 32–38% when the material is activated at 150 °C under vacuum. BET specific surface area is measured following ISO 9277:2022 using argon at 87 K; published data for this specific configuration is limited, although analogous phenyl-carboxylate UiO derivatives typically fall in the range of 600–1100 m²/g depending on defect density. Filter-cake cracking during the filtration of the microcrystalline product on a 2 μm polypropylene membrane is a recurrent processing failure, mitigated by adding 0.5 wt% of poly(ethylene glycol) with a molecular weight of 400 g/mol to the slurry before transfer. The resulting MOF is pelletized with 5 wt% polyvinyl alcohol binder and loaded into a 0.5 m³ fixed-bed adsorption column for breakthrough measurements.

When trace metal detection demands ratiometric fluorescence turn-off in aqueous media, the acid undergoes a modified Hantzsch-type condensation on solid support to generate a molecular probe that selectively complexes Cu²⁺ ions. The synthesis loads the carboxylic acid at 1.0 mmol per gram of Wang resin, using diisopropylcarbodiimide and 4-dimethylaminopyridine as coupling agents in dimethylformamide, with an acylation time of 16 hours. Cleavage with 95% trifluoroacetic acid in dichloromethane yields the free sensor molecule in 82–88% crude purity before reversed-phase flash chromatography. In a typical assay, the compound is dissolved in a 70:30 v/v acetonitrile/HEPES buffer mixture (pH 7.4, 10 mM) to prepare a 10 µM stock. Upon incremental addition of Cu(NO₃)₂, the emission band centered at 455 nm decreases in intensity with a Stern-Volmer quenching constant of 9.8×10³ M⁻¹, while the band at 380 nm remains static as an internal reference. The relative standard deviation of the ratiometric signal across 5 independent preparations is 2.3%, and the sensor does not respond to physiological levels of Na⁺, K⁺, Mg²⁺, or Fe³⁺. Compliance with optical sensor validation protocols references ASTM E1335-08 for steady-state fluorescence measurements and ISO/IEC 17025:2017 for calibration laboratory competence. The downstream embodiment is a lateral-flow test strip on a nitrocellulose membrane where the acid-derived probe is deposited as a 0.5 µL spot from a 1 mM methanolic solution and dried under nitrogen; the strip exhibits a visual detection limit of 5 ppb Cu²⁺ in drinking water, correlating with the US EPA secondary maximum contaminant level of 1.0 ppm.

Modulating β-turn geometries via thiazole-based amino acid surrogates

In solid-phase peptide synthesis of cyclic antimicrobial peptidomimetics, 2-Phenylthiazole-4-Carboxylic Acid substitutes for a dipeptide unit (Phe-Gly) in the turn region, enforcing a 105° dihedral angle between the phenyl and thiazole planes that stabilizes a type I′ β-turn conformation. The acid is pre-converted to its N-hydroxysuccinimide ester using EDC·HCl and NHS in dimethylformamide, isolated by precipitation from diethyl ether, and used immediately at 1.1 eq. per resin-bound amine. Coupling is carried out on a 0.1 mmol scale using an automated microwave peptide synthesizer operating at 75 °C for 10 minutes, with double couplings mandated for all residues following the thiazole surrogate to compensate for steric hindrance that reduces subsequent coupling efficiency by 18–22%. Fmoc deprotection is monitored by the dibenzofulvene-piperidine adduct absorbance at 301 nm; a persistent elevation of this signal beyond 0.05 AU after the second deprotection wash indicates incomplete removal and risks epimerization in the following cycle. Cleavage from the resin employs a cocktail of trifluoroacetic acid, triisopropylsilane, and water at 95:2.5:2.5 v/v/v for 2.5 hours at room temperature. The crude peptide is precipitated in cold diethyl ether, centrifuged at 5000 rpm, and lyophilized before preparative HPLC purification with a mobile phase of 0.1% trifluoroacetic acid in water/acetonitrile. Quality attributes are assessed per Ph. Eur. monograph 01/2023:1170 for peptide content and related substances, with the target cyclic peptide exhibiting a purity of ≥95.0% by area at 220 nm. The finished lyophilized product is a sterile, single-dose vial containing 10 mg of the peptide matching the molecular weight of 1387.6 Da, intended for intravenous treatment of multidrug-resistant Acinetobacter baumannii infections.

Electron-transport monolayer assembly on SnO₂ for inverted perovskite photovoltaics

Solution-processed interfacial layers in p-i-n perovskite solar cells demand compact, chemically robust anchor groups that shift the work function of tin oxide while resisting desorption during subsequent dimethylformamide-based perovskite deposition. 2-Phenylthiazole-4-Carboxylic Acid forms a self-assembled monolayer on SnO₂-coated indium tin oxide when substrates are immersed in a 1 mM ethanolic solution of the acid at 25 °C for 12 hours inside a nitrogen-filled glovebox with H₂O < 0.1 ppm and O₂ < 1 ppm. The immersion time is critical: durations below 8 hours leave pinholes in the monolayer detectable by cyclic voltammetry as faradaic leakage currents above 10⁻⁴ A·cm⁻². Excess physisorbed molecules are removed by sonication in anhydrous ethanol for 3 minutes, followed by drying under a stream of dry nitrogen. The modification reduces the contact angle of water on the SnO₂ surface from 62° to 38°, consistent with outward-facing carboxylate groups, and shifts the valence band edge by -0.23 eV as measured by ultraviolet photoelectron spectroscopy. Device fabrication proceeds by spin-coating a 1.55 eV bandgap perovskite composition of Cs₀.₀₅FA₀.₈₅MA₀.₁Pb(I₀.₉₇Br₀.₀₃)₃ at 5000 rpm, depositing a hole-transport layer of spiro-OMeTAD doped with Li-TFSI, and thermally evaporating a 100 nm gold counter electrode. Encapsulated cells are characterized under standard test conditions per IEC 61215-2:2021; published data for this specific configuration is limited, but analogous carboxyphenyl-thiazole monolayers have been reported to boost power conversion efficiency by 1.2–2.5% absolute through reduced non-radiative recombination at the buried interface. The long-term stability is assessed under damp-heat conditions at 85 °C and 85% relative humidity, with the requirement that the cell retains 80% of initial efficiency after 1000 hours to meet basic industrial qualification benchmarks.