2-Bromo-1,3-Thiazole-4-Carboxylate

In the synthesis of next-generation NS5A inhibitors targeting hepatitis C virus genotype 3 variants resistant to ledipasvir, the 2-bromo substituent on the thiazole-4-carboxylate scaffold functions as a directing group for regioselective palladium-catalyzed C–H functionalization at the 5-position. The ester moiety at C4 is retained as a latent carboxylic acid bioisostere until the penultimate deprotection step, where controlled alkaline hydrolysis using LiOH in a 3:1 THF/H₂O mixture at 0–5°C converts it to the free acid for subsequent amide coupling with proline-derived dipeptide fragments. Manufacturing facilities handling this intermediate typically operate according to ICH Q7 Good Manufacturing Practice guidelines for active pharmaceutical ingredient starting materials, with residual palladium limits enforced below 10 ppm per ICH Q3D elemental impurity thresholds. The molar addition ratio of the bromothiazole ester in the key Suzuki-Miyaura coupling step ranges from 1.05 to 1.20 equivalents relative to the boronate ester partner, compensating for protodebromination side reactions observed at reaction temperatures exceeding 85°C in dioxane-water solvent systems. Downstream production processes involve sequential coupling–hydrolysis–amide bond formation executed in jacketed glass-lined reactors under nitrogen inerting, with the ester intermediate isolated via gravity filtration of the precipitated hydrochloride salt from MTBE antisolvent crystallization. Terminal dosage forms include film-coated tablets containing the phosphoramidate prodrug at 400 mg loading, co-formulated with copovidone as a crystallization inhibitor to maintain supersaturation in the gastrointestinal tract.

Production-scale implementation of this intermediate in integrase strand transfer inhibitor manufacturing for HIV-1 treatment programs has revealed batch-dependent variability in the bromide displacement kinetics. When telescoping the synthesis without intermediate isolation, residual 2-bromo-1,3-thiazole-4-carboxylate exceeding 0.8 mol% in the NMP solvent stream poisons the downstream Buchwald-Hartwig amination catalyst system, requiring an inline activated charcoal adsorption step with 0.5-µm polishing filtration prior to the next unit operation. This process constraint was encountered on a 250-gallon glass-lined reactor train at a contract manufacturing organization in Hyderabad, India, where the catalyst poisoning threshold was established via experimental transient kinetic profiling using a Mettler Toledo ReactIR 15 system monitoring the disappearance of the C–Br stretching band at 680 cm⁻¹. The 21 CFR 211.110 requirement for in-process control sampling at defined intervals is satisfied by HPLC analysis at λ=254 nm with a C18 column quantifying both the starting thiazole ester and the des-bromo impurity. The terminal solid oral dosage form—a fixed-dose combination tablet of dolutegravir 50 mg, lamivudine 300 mg, and tenofovir disoproxil fumarate 300 mg—requires the thiazole intermediate supplier to provide a residual solvent declaration meeting USP <467> Class 2 limits for dioxane and DMF.

When the Thiazole Ring Serves as a Carboxamide Bioisostere in SDHI Fungicide Development

Succinate dehydrogenase inhibitor research programs at three agrochemical discovery sites have converged on 2-substituted thiazole-4-carboxamide scaffolds derived from this bromoester intermediate as lead candidates against Botrytis cinerea field populations harboring H272Y and P225L mutations that confer broad-spectrum SDHI cross-resistance. The ethyl or methyl ester variant of 2-bromo-1,3-thiazole-4-carboxylate is aminolyzed directly with substituted anilines in methanolic sodium methoxide at 55–60°C over 18–24 hours, achieving 87–93% conversion without isolation of the iminolactone intermediate. The formulation addition rate in the final emulsifiable concentrate product ranges from 100 to 250 g/L of the active ingredient, requiring a surfactant package of calcium dodecylbenzene sulfonate (50 g/L) and tristyrylphenol ethoxylate (30 g/L) to maintain emulsion stability under CIPAC MT 36.1.1 conditions at 30°C in CIPAC standard water D. Compliance with FAO Specification 581/EC for emulsifiable concentrate formulations mandates a flash point exceeding 42°C and spontaneous emulsification performance assessed via the CIPAC MT 36.3 reverse emulsion test. The downstream production process at a typical formulation plant in Jiangsu Province, China, involves charging the technical-grade thiazole active (≥97% purity) into the aromatic solvent blend—primarily Solvesso 150 ND—under high-shear rotor-stator mixing at 3,000 rpm for 45 minutes, followed by inline 75-µm mesh straining prior to volumetric filling into 1-L HDPE containers. The terminal products are broad-spectrum cereal and vegetable fungicides labeled for use at 75–150 g a.i./ha with a pre-harvest interval of 14 days in wheat against Septoria tritici and 7 days in cucurbits against powdery mildew, with maximum residue limits established at 0.05 mg/kg under EU Regulation 396/2005 Annex II.

Process safety evaluation during the kilogram-scale preparation of a nicotinic acetylcholine receptor competitive modulator for piercing-sucking insect control identified an exothermic event associated with the benzyl ester analogue of this bromothiazole intermediate. Differential scanning calorimetry performed on a TA Instruments Q2000 DSC at a ramp rate of 4°C/min under nitrogen flow of 50 mL/min revealed a decomposition exotherm onset at 196°C with an energy release of −780 J/g, classifying the compound as a DOT hazard class 4.1 flammable solid under 49 CFR 173.124 when the self-reactive decomposition energy exceeds 300 J/g. The synthetic sequence deployed at a pilot facility in Maharashtra, India, for a flupyradifurone analogue candidate incorporates the bromothiazole ester at 2.5 equivalents in a Williamson etherification with a pyridinyl alcohol fragment, catalyzed by potassium carbonate in acetonitrile refluxing at 82°C for 12 hours in a 500-L glass-lined reactor equipped with a rupture disk rated at 3.5 bar gauge. The crude ester intermediate is telescoped without purification into a lithium aluminum hydride reduction in THF at −10°C, a step that demands strict exclusion of moisture above 100 ppm as measured by a Mettler Toledo C30S Karl Fischer titrator. The terminal formulated product is a 20% soluble concentrate insecticide, diluted to 0.025% v/v in the spray tank, targeting whitefly (Bemisia tabaci biotype Q) populations in protected tomato cultivation, with efficacy data generated according to EPPO guideline PP 1/36(4) and reported as Abbott-corrected mortality at 7 days after application. REACH Annex VII physicochemical property declarations must accompany the first 1-tonne quantity imported into EEA territory, including the octanol-water partition coefficient determined via the slow-stirring method per OECD 123.

Coordination Chemistry of 2-Bromo-1,3-Thiazole-4-Carboxylate-Derived Ligands in Luminescent Lanthanide Metal-Organic Frameworks

The ester functionality at the 4-position provides a synthetic handle for installing carboxylate donors onto the thiazole ring system, generating ditopic ligands capable of bridging lanthanide(III) ions into three-periodic network structures with solvent-accessible void volumes exceeding 45% as calculated by PLATON SQUEEZE analysis of single-crystal XRD data collected at 100 K on a Bruker D8 Venture diffractometer with Cu Kα radiation (λ = 1.54178 Å). Hydrolysis of 2-bromo-1,3-thiazole-4-carboxylate under microwave-assisted conditions—ramping to 120°C over 10 minutes and holding for 30 minutes in 2M NaOH—yields the free 2-bromothiazole-4-carboxylic acid as a white crystalline solid with a melting point of 178–180°C (uncorrected, open capillary). This ligand precursor is then combined with europium(III) nitrate hexahydrate in a 3:1 molar ratio in DMF containing 0.1 M nitric acid as modulator, heated in a PTFE-lined Parr acid digestion vessel at 105°C for 72 hours, affording colorless block crystals suitable for single-crystal diffraction. Elemental analysis of the activated framework (outgassed at 150°C for 18 hours under dynamic vacuum of 10⁻⁴ mbar) confirms a bromine content of 18.7% w/w by Schöniger oxygen flask combustion followed by mercurimetric titration, consistent with a framework formula of [Eu₂(Br-TCA)₃(H₂O)₂]·4DMF·2H₂O. The luminescence quantum yield measured using a Hamamatsu C9920-02 integrating sphere system under 365 nm excitation is 0.42 ± 0.03, with the hypersensitive ⁵D₀→⁷F₂ transition at 617 nm dominating the emission spectrum and yielding CIE chromaticity coordinates of (0.65, 0.34). This material is being evaluated as a luminescent sensor for nitroaromatic explosive vapor detection, where exposure to 10 ppb 2,4-dinitrotoluene vapor in a custom-built flow cell quenches the europium emission by 73% within 30 seconds due to photoinduced electron transfer from the excited-state framework to the electron-deficient nitroarene guest, a mechanism corroborated by time-resolved lifetime measurements showing a reduction from 1.2 ms to 0.3 ms on a Horiba TemPro fluorescence lifetime spectrometer using a 370 nm NanoLED pulsed diode excitation source.

In thin-film composite nanofiltration membrane fabrication via interfacial polymerization, the bromothiazole ester is incorporated at 1.5 wt% into the organic phase comprising trimesoyl chloride dissolved in Isopar G at 0.15 wt%, with the aqueous phase containing 2.0 wt% m-phenylenediamine and 0.5 wt% sodium dodecyl sulfate. The membrane sheet is fabricated on a continuous casting line at 3.0 m/min line speed with an 80-µm doctor blade gap, subjected to a 60-second contact time between the laminated polysulfone support and the organic phase, followed by air knife drying at 35°C and passage through a 70°C thermal curing oven with a residence time of 4 minutes. The resulting thin-film composite membrane exhibits a pure water permeability of 1.8 L m⁻² h⁻¹ bar⁻¹ and a sodium chloride rejection of 98.2% at 16 bar transmembrane pressure with 2,000 ppm NaCl feed at 25°C, tested according to ASTM D4194-23 standard practice for operating characteristics of reverse osmosis and nanofiltration devices. The bromine atom at the 2-position appears to enhance chlorine tolerance, with the membrane retaining 91% of its initial salt rejection after 10,000 ppm·h of sodium hypochlorite exposure, compared to 64% for the unmodified polyamide membrane under identical conditions.

Palladium-Mediated Cross-Coupling: Mapping the Reactivity Landscape of the C2–Br Bond

Suzuki-Miyaura coupling of 2-bromo-1,3-thiazole-4-carboxylate with phenylboronic acid using Pd(PPh₃)₄ at 2 mol% loading in degassed toluene/ethanol/2M Na₂CO₃ (5:1:1 v/v/v) proceeds to >95% conversion within 4 hours at 80°C, as monitored by GC-MS analysis of aliquots quenched into dilute HCl and extracted into ethyl acetate. The oxidative addition step at the C2–Br position is kinetically preferred over potential competing insertion into the ester C–O bond due to the lower bond dissociation energy of the C–Br bond (~285 kJ/mol versus ~380 kJ/mol for the ester C–O bond) and the electron-deficient nature of the thiazole ring that accelerates the oxidative addition rate by a factor of approximately 12 relative to the analogous 2-bromothiophene system, as established by Hammett correlation studies. In Negishi coupling protocols deployed at a CDMO in Basel, Switzerland, the bromothiazole ester is treated with 1.8 equivalents of 2-thienylzinc bromide in THF at −20°C in the presence of Pd₂(dba)₃ (0.5 mol%) and SPhos (1.0 mol%), providing the 2-(2-thienyl)thiazole-4-carboxylate in 89% isolated yield after flash chromatography on silica gel with 8:2 hexane/ethyl acetate elution. A critical process control parameter identified during scale-up to 50-kg batch size is the moisture content of the zinc reagent solution, which must be maintained below 50 ppm water by Karl Fischer titration to prevent premature protodehalogenation generating the undesired 1,3-thiazole-4-carboxylate impurity that co-elutes with the product on a normal-phase HPLC system using a Chiralpak IA column with UV detection at 280 nm. The ICP-MS analysis of the isolated product for residual palladium conducted according to USP <232> using a PerkinElmer NexION 350D ICP-MS equipped with a collision/reaction cell operating in helium mode at 4.5 mL/min cell gas flow reports values consistently below 2 ppm when a post-reaction treatment with 5 wt% activated charcoal (Norit SX Plus) in refluxing ethyl acetate for 1 hour is included in the workup sequence.

Pharmaceutical patent landscapes for hepatitis B virus capsid assembly modulators reveal a common intermediate strategy wherein 2-bromo-1,3-thiazole-4-carboxylate undergoes Buchwald-Hartwig C–N bond formation with a sulfonamide nucleophile. The coupling employs RuPhos Pd G3 precatalyst at 1.5 mol% with cesium carbonate (2.5 equivalents) as base in toluene at 110°C under argon for 16 hours in a sealed pressure tube rated to 150 psi. The competitive hydrolysis of the ethyl ester under these strongly basic, high-temperature conditions results in the formation of 6–11% of the free carboxylic acid byproduct, which is solubilized in the aqueous workup at pH > 10 and removed with the aqueous phase after phase separation using a Podbielniak centrifugal extractor operating at 3,500 rpm with a throughput of 15 L/h per phase. The organic layer containing the desired N-arylated thiazole ester is concentrated under reduced pressure (45°C bath, 20 mbar) on a Büchi R-250 rotary evaporator to a minimum-stirrable volume, then crystallized from 3:1 heptane/isopropyl acetate to afford an off-white solid with 99.2% HPLC purity (area%, 254 nm) and a differential scanning calorimetry endotherm onset of 142.5°C, suitable for use as a GMP starting material per ICH Q11 section 5.1.1 with the designated regulatory starting material justification filed with the competent authority. The terminal active pharmaceutical ingredient in this class is a chiral cyclic sulfonamide HBV capsid inhibitor formulated as an amorphous spray-dried dispersion with HPMC-AS at 30% drug loading, compressed into 100 mg strength tablets for once-daily oral administration, with a food-effect bioavailability study conducted under FDA guidance for industry on food-effect bioavailability demonstrating a 2.4-fold increase in AUC when administered with a high-fat meal (FDA standard breakfast: 800–1,000 kcal, 50% from fat).

Site-selective elaboration at the C2 and C4 positions enables construction of unsymmetrical 2,4-disubstituted thiazole libraries used in fragment-based drug discovery screening. A typical parallel synthesis campaign executed on a Chemspeed SWING SP-200 platform in a 96-well reaction block format charges each reactor with 0.25 mmol of 2-bromo-1,3-thiazole-4-carboxylate, 1.2 equivalents of the selected boronic acid, 2.5 mol% SiliaCat DPP-Pd heterogeneous catalyst, and 0.5 mL of DME/water 3:1, applying a temperature ramp from 25°C to 85°C over 15 minutes with 800 rpm vortex mixing and a 4-hour hold time. The crude reaction mixtures are filtered through an inline 0.45-µm PTFE filter plate, the solvent is evaporated under a stream of nitrogen at 40°C on a Biotage V-10 Touch evaporator, and the residues are purified by preparative HPLC with mass-directed fraction collection on a Waters Autopurification system equipped with a SunFire C18 column (19×150 mm, 5 µm) eluting with a 10–90% acetonitrile/water gradient containing 0.1% formic acid over 12 minutes at 25 mL/min. The isolated yields across a 96-member library ranged from 11% to 97% with a median yield of 64%, and 83 of the library members exceeded 95% purity as assessed by UPLC-ELSD analysis on an Acquity H-Class system. These fragments are subsequently dissolved in DMSO-d₆ at 10 mM concentration for NMR-based screening against a Mycobacterium tuberculosis pantothenate synthetase target using saturation transfer difference spectroscopy on a 600 MHz Bruker Avance III HD spectrometer equipped with a TCI cryoprobe, with the water proton signal suppressed by the watergate W5 pulse sequence with gradients.