2-[3-Cyano-4-Isobutoxyphenyl]-4-Methylthiazole-5-Carboxylic Acid
|
HS Code |
178140 |
| Chemical Formula | C16H18N2O3S |
| Molecular Weight | 318.4 g/mol |
| Appearance | Solid (predicted) |
| Solubility In Water | Poor (predicted) |
| Logp | 3.6 (predicted) |
| Stability | Stable under normal conditions (predicted) |
As an accredited 2-[3-Cyano-4-Isobutoxyphenyl]-4-Methylthiazole-5-Carboxylic Acid factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | 100g of 2 - [3 - Cyano - 4 - Isobutoxyphenyl] - 4 - Methylthiazole - 5 - Carboxylic Acid in sealed plastic bags. |
| Shipping | The chemical 2 - [3 - Cyano - 4 - Isobutoxyphenyl] - 4 - Methylthiazole - 5 - Carboxylic Acid is shipped in sealed, properly labeled containers. It adheres to strict hazardous material shipping regulations to ensure safe transit. |
| Storage | Store 2-(3 - Cyano - 4 - Isobutoxyphenyl)-4 - Methylthiazole - 5 - Carboxylic Acid in a cool, dry place away from direct sunlight. Keep it in a well - sealed container to prevent moisture absorption and contact with air, which could potentially lead to degradation. Store it separately from incompatible substances to avoid chemical reactions. |
What Process Parameters Govern Content Uniformity in High-Shear Wet Granulation of Febuxostat?Tableting of 2-[3-cyano-4-isobutoxyphenyl]-4-methylthiazole-5-carboxylic acid via high-shear wet granulation demands strict control over particle engineering because the API exhibits poor aqueous solubility (BCS Class II) and a strong tendency for polymorphic interconversion. Micronisation to a Malvern Mastersizer‑determined volume-median diameter D90 < 20 µm is executed on a fluid‑bed opposed‑jet mill with classifier rotor speed calibrated to deliver a specific surface area exceeding 2.5 m²/g (BET nitrogen adsorption). The granulation charge combines the micronised acid (80.0 mg per tablet target), lactose monohydrate (210.0 mg), microcrystalline cellulose PH102 (100.0 mg), croscarmellose sodium (15.0 mg) and colloidal silicon dioxide (2.0 mg) in a 65‑L Frewitt PMA high‑shear mixer. Aqueous binder solution (purified water with pre‑dissolved povidone K30 at 4.2% w/w) is sprayed at 120–150 g/min through a binary nozzle under 1.5 bar atomising air, while the main impeller rotates at 200 ± 10 rpm and the side chopper at 1500 rpm. End‑point determination relies on a NIR probe integrated into the bowl lid: granulation is stopped when the in‑line moisture signal reaches 6.8–7.2% LOD (validated against a Sartorius MA160 moisture analyser at 105°C) because residual water content outside this window shifts the A‑form to the metastable G‑form — a transition detectable by the disappearance of the characteristic XRPD peak at 2θ = 12.8°. Wet mass is wet‑milled through a 1.5 mm screen and dried in a Glatt GPCG‑5 fluid‑bed drier with inlet air temperature maintained at 60 ± 2°C until LOD falls below 2.0%. Dried granules are sized through a 0.8 mm conical sieve and lubricated with magnesium stearate (3.0 mg/tablet, screened through 250 µm) in a bin blender operating at 12 rpm for 3 minutes — prolonged lubrication beyond 5 minutes increases the specific surface coverage of magnesium stearate and retards dissolution rate by > 12% at 15‑minute sampling in USP Apparatus 2 (75 rpm, 900 mL 0.5% sodium lauryl sulfate, 37.0 ± 0.5°C). Tablets are compressed on a Korsch XL400 rotary press fitted with 9.5 mm round concave tooling to a target hardness of 60–90 N (Schleuniger 8M tester, USP 〈1217〉) and a friability not exceeding 0.5% after 100 drops (USP 〈1216〉). Film‑coating applies an aqueous Opadry II Yellow dispersion at a pan speed of 4–6 rpm and an inlet temperature of 70°C until a weight gain of 3.5% w/w is achieved, yielding the finished dosage form Febuxostat Tablets 80 mg. Environmental controls are mandatory: when relative humidity inside the compression suite exceeds 60% RH (monitored at 25°C), pre‑conditioning of excipients and granule storage under nitrogen‑blanketed drums are required to prevent cohesive failure at the tablet surface due to amorphous content re‑crystallisation. Spray‑dried dispersions of 2-[3-cyano-4-isobutoxyphenyl]-4-methylthiazole-5-carboxylic acid with HPMCAS‑LF at a 20:80 drug‑to‑polymer ratio have been processed on a Buchi B‑290 mini‑spray dryer with inert loop, using a feed solution of acetone‑water 90:10 v/v at a total solids loading of 5% w/w. The nozzle atomising gas flow is set to 601 L/h, inlet temperature 105°C, outlet temperature 52–56°C, and the resulting powder passes through a cyclone separator. Secondary drying under vacuum at 40°C for 24 hours reduces residual acetone below the ICH Q3C limit of 5,000 ppm. Modulated differential scanning calorimetry confirms a single glass transition temperature (Tg) at 128 ± 2°C, indicative of molecularly dispersed API with no detectable crystallinity by XRPD (diffractogram shows only the amorphous halo, with absence of the characteristic sharp reflections at 2θ 11.4° and 12.8°). The solid dispersion can be directly filled into size 0 hard gelatin capsules — each containing 400 mg of spray‑dried powder equivalent to 80 mg of API — or blended with mannitol and crospovidone for tableting. Capsule disintegration time remains under 6 minutes in 0.1 N HCl (USP 〈2040〉), and comparative dissolution in USP Apparatus 2 at 75 rpm in pH 6.8 phosphate buffer demonstrates > 85% release within 30 minutes versus 38% for the physical mixture of micronised API and polymer. The amorphous product is hygroscopic at RH > 50% (confirmed by dynamic vapour sorption isotherms), mandating aluminium‑blister packaging with a desiccant containing molecular sieve 4A. Long‑term stability data under 25°C/60% RH (ICH Q1A) indicate no re‑crystallisation and impurity levels remaining within the 0.2% identification threshold for 12 months. Reference Standard Qualification Under ICH Q2(R1) — Purity Assignment by Mass BalanceWhen 2-[3-cyano-4-isobutoxyphenyl]-4-methylthiazole-5-carboxylic acid is applied as an in‑house primary reference standard or as a working standard traceable to the USP Febuxostat RS lot, the purity assignment follows the mass‑balance approach stipulated in ICH Q2(R1) and Ph. Eur. 5.12. A multi‑solvent recrystallisation from isopropanol:water 70:30 v/v with controlled cooling from 75°C to 5°C at 0.3°C/min produces exclusively the thermodynamically stable polymorph A in plate‑like crystals. HPLC‑UV purity on a Waters XBridge C18 column (250 × 4.6 mm, 5 µm) with mobile phase acetonitrile: 0.1% trifluoroacetic acid in water (60:40 v/v), flow rate 1.0 mL/min, and detection at 315 nm shows a main‑peak purity of 99.94% (area normalisation). Residual solvents are quantified by headspace GC‑FID against a dimethyl sulfoxide diluent blank; water content by Karl Fischer coulometric titration (Mettler Toledo C30) returns 0.08% w/w; residue on ignition is 0.01%. The assigned purity value — 99.82% (expanded uncertainty ±0.12%, k=2) — becomes the anchor for all subsequent content‑uniformity and dissolution‑profile quantification in finished product release. A solution of the standard at 0.1 mg/mL in diluent (acetonitrile:water 50:50) remains stable for 72 hours stored in amber volumetric flasks at 5 ± 3°C (assayed by peak‑area drift < 0.2%). Certified values are transferred to secondary working standards after identical chromatographic assessment, and every new lot is qualified against the primary batch using the system‑suitability mixture incorporating the 67M‑1 hydroxy metabolite impurity at 0.2% spike level (resolution minimum 2.0 between the main peak and the 67M‑1 peak). Serum Urate-Lowering Efficacy in Potassium Oxonate-Induced Hyperuricemic RatsPharmacodynamic evaluation of the acid employs the potassium oxonate‑challenged Sprague‑Dawley rat model, where hyperuricemia is established by intraperitoneal injection of oxonate at 300 mg/kg one hour before oral dosing. The test compound is suspended in 0.5% w/v sodium carboxymethylcellulose containing 0.1% v/v Tween 80 and administered by gavage at doses of 2.5, 5.0, and 10.0 mg/kg (dosing volume 10 mL/kg). Orbital sinus blood samples are drawn under isoflurane anaesthesia at 0, 1, 2, 4, 6, and 8 hours post‑dose; serum uric acid is measured using a colorimetric uricase‑peroxidase kit (BioAssay Systems DIUA‑250) calibrated against NIST‑traceable standards. The 10 mg/kg dose reduces serum urate by 62 ± 5% (mean ± SEM, n=10) at the 4‑hour nadir, corresponding to an ED50 of 3.8 mg/kg calculated by nonlinear regression. Urinary xanthine/hypoxanthine ratios concurrently increase 4.2‑fold, confirming mechanism‑based xanthine oxidase inhibition. All procedures are conducted under an IACUC‑approved protocol conforming to NIH Publication No. 86‑23 and OECD Principles of Good Laboratory Practice. Implications for human dosing extrapolation use allometric scaling with an exponent of 0.75, yielding a human equivalent dose of approximately 80 mg/day — the authorised therapeutic strength for chronic management of hyperuricemia in patients with gout. In broiler chickens developing spontaneous hyperuricemia induced by high‑calcium diets (layer‑type ration, 3.5% calcium), 2-[3-cyano-4-isobutoxyphenyl]-4-methylthiazole-5-carboxylic acid is administered via drinking water at 25 mg/L for 7 consecutive days. Plasma uric acid is monitored with a colorimetric endpoint assay; after three days, levels drop from a baseline of 8.2 ± 1.1 mg/dL to 3.9 ± 0.7 mg/dL (p< 0.01, Student’s t‑test). The finished veterinary product is an oral soluble powder composed of the micronised API (10 g), anhydrous dextrose q.s. 100 g, packed in sachets under nitrogen flush. Veterinary‑grade manufacturing complies with VICH GL1 (validation of manufacturing processes) and relevant monographs under Ph. Eur. The compound is not authorised for use in food‑producing animals in the EU, so withdrawal periods are determined by residue depletion studies in target species following EU Regulation 2019/6. The soluble powder must be dissolved within 2 hours of administration and protected from light to prevent photo‑degradation of the isobutoxy side chain (photolysis half‑life 45 minutes under simulated sunlight, ICH Q1B Option 2). Preparation of 67M-1 (4-Hydroxy Febuxostat) Metabolite Standard from the Parent AcidThe major human metabolite 2-[3-cyano-4-hydroxyphenyl]-4-methylthiazole-5-carboxylic acid (commonly coded 67M‑1) is synthesised from the parent isobutoxy phenyl compound by selective O‑dealkylation. A solution of the API (5.0 g, 15.8 mmol) in 48% aqueous hydrobromic acid (60 mL) is refluxed at 125°C under argon for 5 hours. Reaction progress is tracked by TLC on silica gel 60 F254 plates with ethyl acetate:hexane:formic acid 60:40:1; the starting material (Rf 0.72) disappears completely and the main spot at Rf 0.46 corresponds to the phenolic metabolite. The cooled mixture is quenched into ice‑water, extracted with ethyl acetate, washed with brine, and dried over anhydrous sodium sulfate. Crude product is recrystallised from ethanol‑water 80:20 to obtain off‑white needles of 67M‑1 in 73% yield with HPLC purity 99.5%. Identity is confirmed by ESI‑MS (m/z 261.0 [M+H]⁺) and ¹H NMR (DMSO‑d₆, 400 MHz): δ 2.65 (s, 3H), 6.95 (d, J=8.8 Hz, 2H), 7.65 (d, J=8.8 Hz, 2H), 11.0 (s, 1H), 13.2 (br s, 1H). This batch serves as the impurity marker for the related substances test in API release and is critical for bioanalytical LC‑MS/MS method development when quantifying systemic exposure to the active moiety. For stable‑isotope‑labelled internal standards, Febuxostat‑d₇ (with the isobutyl methyl groups fully deuterated) is obtained by reacting the phenolic intermediate with isobutyl‑d₇ bromide under Mitsunobu conditions (triphenylphosphine, diisopropyl azodicarboxylate, THF, 0°C to room temperature, 16 hours), providing an isotopic purity of 99.2 atom% D as determined by high‑resolution mass spectrometry.
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In the synthesis pathway of the xanthine oxidase inhibitor febuxostat, the compound 2-[3-cyano-4-isobutoxyphenyl]-4-methylthiazole-5-carboxylic acid (CAS 144060-53-7) functions as the principal penultimate intermediate, providing the complete thiazole ring scaffold bearing the critical 3-cyano and 4-isobutoxy substituents required for pharmacophore binding. Its molecular architecture pre-organizes the aromatic ring geometry such that a single amidation step with 2-(4-hydroxyphenyl)ethylamine in the presence of a carbodiimide coupling agent delivers the crude active pharmaceutical ingredient. Manufacturing-grade material is routinely supplied with a chromatographic purity exceeding 99.0% (HPLC, λ 315 nm) and a single maximum unknown impurity threshold of <0.10%, specifications that align with the related-substances criteria described in the febuxostat monographs of the USP and Ph. Eur. Anhydrous crystal forms exhibit a sharp endothermic melt at 198–202°C with decomposition; residual solvent profiles are controlled to meet ICH Q3C(R8) Option 1 limits for Class 2 solvents, with methanol typically held below 3000 ppm and dichloromethane below 600 ppm.
Routine lot release employs reversed-phase HPLC under conditions compliant with USP <621> for system suitability: a C18 column (250 × 4.6 mm, 5 µm), mobile phase consisting of 0.1% phosphoric acid and acetonitrile in gradient mode, column temperature 30°C, and injection volume 10 µL. Under these parameters, the retention time for the title compound is approximately 14.2 min, with relative retention for the des-cyano impurity analogue at 0.78 and for the isobutyl ether-cleaved phenol at 0.45. The limit of quantitation for the phenol species, a potential genotoxic structural alert, is validated at 75 ppm using a dedicated LC-MS/MS method with electrospray ionization in negative mode. Heavy metals are assessed by wet digestion and ICP-MS per USP <233>, with cadmium, lead, and arsenic each controlled to ≤ 5 ppm. Palladium content, a carryover risk when Suzuki coupling routes are employed for the biphenyl construction, is monitored by graphite furnace atomic absorption and limited to ≤ 10 ppm. Water content, determined by Karl Fischer coulometry, is maintained below 0.5% to mitigate hydrolytic instability.
For stereochemical purity, the compound is achiral; however, batch-to-batch consistency in polymorphic form is verified by X-ray powder diffraction against a reference pattern. Three principal diffraction peaks at 2θ = 9.8°, 14.2°, 18.7° are required with relative intensities within ±15% of the standard. Discrepancies in polymorphic ratios have been linked to residual amorphous content arising from rapid antisolvent precipitation, which accelerates nitrile hydration upon storage and reduces the coupling efficiency with the amine component by as much as 12%.
Upon scale-up from laboratory glassware to 1000 L glass-lined agitated reactors equipped with retreat-curve impellers, an observable processing bottleneck emerges during the final recrystallization from ethyl acetate/n-heptane. The metastable zone width narrows to less than 4°C when the cooling rate exceeds 0.3°C/min, promoting uncontrolled nucleation that entrains mother liquor rich in the previously mentioned des-cyano congener. Operators at pilot facilities have adopted seeded cooling crystallization protocols using 1.0–1.5 wt% micronized seed crystals (d90 < 20 µm) introduced at 52°C, followed by a 2-hour isothermal hold before linear ramp-down to –5°C. This practice improves the rejection factor for the des-cyano impurity from approximately 3.5 to over 8.0, as determined by mother liquor/seed partition analysis. Downstream isolation on a 0.6 m² Nutsche filter under nitrogen pressure of 0.2 bar and subsequent vacuum tray drying at 45°C and 5 mbar for 16 h consistently achieve the residual solvent thresholds cited earlier.
The amide bond formation between the title acid and 2-(4-hydroxyphenyl)ethylamine is most frequently executed with 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC·HCl) and 1-hydroxybenzotriazole (HOBt) in dry N,N-dimethylformamide. Under these conditions, the kinetic competition between desired amidation and nitrile hydration becomes critically sensitive to the proton activity of the medium. Trace water levels above 500 ppm in the reaction mixture shift the selectivity toward the corresponding primary amide, a path that generates febuxostat amide as a persistent impurity. Manufacturing batch records document that pre-drying of the carboxylic acid intermediate to a water content of ≤ 0.3% and the use of molecular sieve-dried DMF (4 Å sieves, 10% w/v) suppress the amide impurity below the 0.15% threshold specified in the final API. When coupling is performed on a 500 mL scale in a jacketed vessel with temperature control at 0–5°C during the first 30 minutes of reagent addition, the heat release rate of –ΔH = 210 ± 15 kJ/mol necessitates a jacket setpoint of –12°C to prevent localized overheating that would otherwise accelerate both racemization (not relevant here) and isobutoxy ether cleavage.
Process analytical technology (PAT) implementations on pilot lines have demonstrated that in-line ReactIR monitoring of the nitrile stretching band at 2230 cm⁻¹ provides real-time verification that the cyano group remains intact. A decrease in this absorbance by more than 4% over the 2-hour coupling window correlates with an amide impurity result above 0.3%, prompting immediate post-reaction aqueous work-up quenching. This zone of tight operational control—temperatures within ±3°C, water content below 500 ppm, and EDC addition over 45–60 minutes—constitutes the primary process conflict where batch failure risk is highest, and published data for the exact kinetic constants of nitrile hydrolysis under these specific coupling conditions is limited to the proprietary repositories of custom synthesis organizations.
Long-term stability studies conducted per ICH Q1A(R2) at 25°C/60% RH over 36 months reveal a predominant degradation route: hydrolysis of the nitrile group to the corresponding carboxylic acid, detectable at 0.08% after 12 months and reaching 0.22% at 36 months in poorly sealed polyethylene double-bag packaging. Transfer to aluminium-laminated foil bags with a heat-sealed closure reduces the 36-month hydrolysis level to 0.06%. Storage under refrigerated conditions (2–8°C) is required for retention periods longer than 12 months in regions where ambient humidity regularly exceeds 70% RH. The compound demonstrates incompatibility with strong bases—contact with sodium hydroxide in aqueous-organic biphasic systems at pH > 10 results in rapid nitrile hydrolysis and isobutyl ether cleavage within 30 minutes at 25°C. Additionally, exposure to direct light above 300 lux accelerates the formation of a dimeric impurity linked via a nitrile-to-nitrile condensation, a photo-degradant observed at 0.04% after 7 days under ICH Q1B confirmatory light exposure conditions. In manufacturing environments, amber glass or opaque HDPE containers and nitrogen-blanketed headspace are standard precautions.
| Attribute | Method Reference | Acceptance Criterion |
|---|---|---|
| Assay (anhydrous, solvent-free) | HPLC, external standard | 98.0–102.0% |
| Total impurities | HPLC area% | ≤ 1.0% |
| Single unknown impurity | HPLC area% | ≤ 0.10% |
| Phenol impurity (isobutyl cleavage) | LC-MS/MS, m/z 257 → 212 | ≤ 75 ppm |
| Water (Karl Fischer) | USP <921>, Method Ic | ≤ 0.5% |
| Residue on ignition | USP <281> | ≤ 0.1% |
| Palladium | GF-AAS | ≤ 10 ppm |
| Melting range | USP <741>, Class Ia | 198–202°C (dec.) |
Synthetic chemists evaluating alternative febuxostat intermediate scaffolds have occasionally explored structures where the 4-isobutoxy group is replaced by methoxy or n-butoxy motifs. The isobutoxy derivative demonstrates a pronounced advantage in crystal lattice energy, resulting in a melting point roughly 36°C higher than the 4-methoxy analogue (mp 162–165°C, dec.) and 14°C higher than the n-butoxy congener (mp 184–187°C, dec.). This difference translates directly into superior purification efficiency: the rejection of the des-cyano impurity in the isobutoxy system is enhanced by a factor of 1.8 relative to the methoxy variant during ethyl acetate/n-heptane recrystallization. Moreover, the steric branching of the isobutyl group slows the rate of ether cleavage under acidic conditions by approximately 40% compared to the linear n-butyl chain, as measured by the first-order rate constant for cleavage in 0.1 N HCl in dioxane/water (k₁ = 1.2 × 10⁻⁴ h⁻¹ for isobutoxy vs. k₁ = 2.0 × 10⁻⁴ h⁻¹ for n-butoxy at 60°C). A comparative summary of key differentiating properties is presented below.
| Structural Variant | Melting Point (°C, dec.) | Recrystallization Solvent | Cleavage Rate Constant (h⁻¹, 60°C) | Yield of Final Coupling Step (%) |
|---|---|---|---|---|
| 4-Isobutoxy (title compound) | 198–202 | Ethyl acetate/n-heptane | 1.2 × 10⁻⁴ | 85–90 |
| 4-Methoxy analogue | 162–165 | Methanol/water | 4.8 × 10⁻⁴ | 74–80 |
| 4-n-Butoxy analogue | 184–187 | Ethyl acetate/heptane | 2.0 × 10⁻⁴ | 80–84 |
| 4-Benzyloxy analogue | 211–214 | Toluene/acetonitrile | 0.8 × 10⁻⁴ | 78–83 |
The benzyloxy-protected intermediate, while offering the lowest hydrolytic lability, introduces a deprotection hydrogenolysis step that adds a palladium catalyst burden and risks over-reduction of the thiazole ring, making it less suitable for cost-sensitive generic API manufacturing. The isobutoxy variant therefore occupies a balanced position where steric protection of the ether linkage is sufficient to survive the downstream amidation and final recrystallization, yet the protecting group does not require an additional deprotection sequence. This balance is a primary reason it has become the standard intermediate for febuxostat routes filed in Drug Master Files across multiple regulatory jurisdictions.
When the free carboxylic acid form is substituted by the corresponding methyl ester, coupling with the amine requires harsher conditions (refluxing toluene or neat amine at 130°C), leading to elevated levels of the febuxostat dimer impurity (1.2–2.5%). Direct use of the carboxylic acid eliminates this side reaction and aligns with the synthetic strategy described in the original febuxostat patent literature. Thus, for generic API manufacturers targeting ANDA or 505(b)(2) applications, procurement of the title acid intermediate with the specified impurity profile constitutes a critical quality-by-design starting material decision.
Utilization in continuous flow setups is currently under evaluation at several contract manufacturing organizations, where residence time distribution in a Corning Advanced-Flow reactor may permit coupling at 20°C with a residence time under 5 minutes, a throughput improvement that could suppress the amide impurity formation by minimizing exposure time. Published data for this specific configuration is limited, though internal feasibility reports reference yields of 88–91% with amide below 0.08%.
