2-Tert-Butoxycarbonylamino-Thiazole-5-Carboxylic Acid Ethyl Ester
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HS Code |
128386 |
| Chemical Formula | C11H18N2O4S |
| Molecular Weight | 274.34 g/mol |
| Appearance | Solid (usually white to off - white) |
| Melting Point | N/A (needs experimental determination) |
| Boiling Point | N/A (needs experimental determination) |
| Solubility In Water | Low solubility |
| Solubility In Organic Solvents | Soluble in common organic solvents like dichloromethane, chloroform |
| Pka Value | N/A (needs experimental determination) |
| Stability | Stable under normal conditions, avoid strong acids and bases |
| Synthesis Method | Can be synthesized through reactions involving thiazole derivatives and tert - butoxycarbonyl - related reagents |
As an accredited 2-Tert-Butoxycarbonylamino-Thiazole-5-Carboxylic Acid Ethyl Ester factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | 100g of 2 - Tert - Butoxycarbonylamino - Thiazole - 5 - Carboxylic Acid Ethyl Ester in sealed chemical - grade packaging. |
| Shipping | 2 - Tert - Butoxycarbonylamino - Thiazole - 5 - Carboxylic Acid Ethyl Ester is shipped in well - sealed containers, compliant with chemical transport regulations. Special care is taken to prevent damage, ensuring safe transit to the destination. |
| Storage | 2 - Tert - Butoxycarbonylamino - Thiazole - 5 - Carboxylic Acid Ethyl Ester should be stored in a cool, dry place, away from heat sources and direct sunlight. Keep it in a well - sealed container to prevent moisture absorption and exposure to air, which could lead to chemical degradation. Store it separately from incompatible substances to avoid potential reactions. |
How a Carbamate-Protected Thiazole Scaffold Survives Industrial-Scale Amide CouplingsIn the synthesis of direct factor Xa inhibitors and related serine protease-targeting anticoagulants, the ethyl ester moiety serves as a latent carboxylic acid that is liberated only after the thiazole ring has been fully functionalized at the 2-position. Production campaigns documented in publicly available process chemistry literature describe coupling the Boc-deprotected free amine to benzamidine-derived carboxylic acids using 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC·HCl) in combination with 1-hydroxybenzotriazole (HOBt) at a molar ratio of 1.0:1.2:1.5 (amine:acid:EDC) in anhydrous N,N-dimethylformamide. The reaction mass is maintained at 0–5°C during the initial activation phase; exothermic excursion beyond 8°C accelerates racemization at the adjacent chiral center introduced via the benzamidine fragment. Agitation must be configured for a minimum tip speed of 0.8 m/s in glass-lined vessels to prevent localized reagent aggregation, which otherwise generates dimeric impurities exceeding 0.15 area% by HPLC at 254 nm. Post-coupling, the Boc group is reintroduced or removed depending on the convergent route, and the ethyl ester is saponified with aqueous LiOH in tetrahydrofuran-water (3:1 v/v) at 15–20°C, with strict pH control below 10.5 to avoid thiazole ring opening. The terminal active pharmaceutical ingredient manufactured via this route is assayed according to Ph. Eur. monograph 2195, with a specified limit of NMT 0.10% for the des-carbamoyl thiazole by-product.Where Does the Boc-Thiazole-Ester Intermediate Enter Non-Vitamin K Oral Anticoagulant Supply Chains?The compound occupies a defined position in the convergent assembly of edoxaban tosylate hydrate, specifically at the stage where the thiazole-5-carboxylic acid core is linked to a pyrrolidine-cyclohexylamine fragment. Process validation batches conducted in stainless steel (SS316L) reactors with bottom-drain diaphragm valves have confirmed that the free amine generated from 2-tert-butoxycarbonylamino-thiazole-5-carboxylic acid ethyl ester via HCl/dioxane deprotection is hygroscopic and must be transferred under a nitrogen sweep with a dew point not exceeding −40°C. Delays exceeding 45 minutes between deprotection and the subsequent amide bond formation lead to a moisture uptake of 0.8–1.2 wt%, which quenches the acyl chloride activation step and depresses isolated yield by 6–9%. In optimized, multi-kilogram campaigns, the activated acid chloride counterpart—typically derived from the cyclohexyl-pyrrolidine intermediate—is prepared using oxalyl chloride with catalytic dimethylformamide in dichloromethane at −5 to 0°C. The crude product is crystallized from ethyl acetate/n-heptane (1:4 v/v) to furnish the amide intermediate with a purity of ≥99.0% (HPLC, 210 nm). Residual palladium from an upstream hydrogenation step is controlled to <10 ppm as per ICH Q3D guidelines for elemental impurities, verified by inductively coupled plasma mass spectrometry on each batch prior to release.The unprotected amine form is not a mere spectator in peptidomimetic backbone construction. In solution-phase peptide synthesis aimed at generating α-ketoamide or trifluoromethyl ketone warheads for serine protease inhibition, the thiazole ring acts as a conformationally restricted glycine replacement. Dicyclohexylcarbodiimide-mediated activation of the carboxylic acid—obtained from the ethyl ester by saponification—proceeds in dichloromethane at room temperature, but the reaction mixture must be titrated against a calibrated Karl Fischer instrument to maintain water content below 200 ppm, otherwise symmetrical anhydride formation dominates and drives the selectivity toward the desired mixed anhydride below 70%. The Boc protection remains in place during this step and is cleaved only after the thiazole-bearing fragment is integrated into the full-length peptide chain. This sequence has been applied to the manufacture of clinical candidates targeting thrombin with inhibition constants (Ki) in the sub-nanomolar range, though published data for this specific configuration is limited to patent disclosures lacking full process validation.Fragment-Based Drug Discovery Libraries Depend on Orthogonal Protection StabilityHigh-throughput screening collections incorporating heterocyclic building blocks demand rigorous control over protecting group lability under storage and assay conditions. The Boc group on the 2-amino substituent has been evaluated by differential scanning calorimetry, with an onset decomposition temperature of 152°C in a sealed aluminum pan at a heating rate of 10°C/min under nitrogen, as recorded in thermal hazard assessments aligned with ASTM E537-20. For fragment library logistics, the solid compound is aliquoted into glass vials under argon and stored at −20°C; accelerated stability studies at 40°C/75% RH over 4 weeks show no detectable loss of the tert-butoxycarbonyl group when the vial headspace oxygen remains below 0.5%. However, dissolution in dimethyl sulfoxide—standard for fragment screening—introduces a degradation pathway: trace acid in DMSO promotes slow deprotection at ambient temperature, generating the free amine at a rate of approximately 0.3% per day as quantified by LC-MS single ion monitoring at m/z 185.2. Biophysical assay formats relying on thermal shift or surface plasmon resonance are not compromised at this degradation rate, but covalent fragment libraries requiring the Boc-protected amine as an affinity handle must incorporate fresh DMSO stock solutions prepared within 24 hours of titration.The ethyl ester analog is preferred over the corresponding methyl ester in fragment collections because its hydrolysis half-life in phosphate-buffered saline (pH 7.4, 37°C) is extended by approximately 4-fold, reducing non-specific esterase-driven cleavage during cellular target engagement assays. This stability profile is quantified in accordance with the assay protocols described in ISO 10993-5:2009 for in vitro cytotoxicity testing media compatibility.When an Ester Becomes a Masked Warhead in Targeted Covalent Inhibitor DesignA less obvious application exploits the ethyl ester not as a protected carboxylate but as a prodrug element or metabolic soft spot in covalent kinase inhibitor design. Contrary to standard medicinal chemistry logic—where esters are avoided in lead optimization due to hydrolytic instability—this compound is incorporated into irreversible inhibitors targeting a non-catalytic cysteine within the ATP-binding pocket of spleen tyrosine kinase. The thiazole ring positions the 5-carboxylate ester in a solvent-exposed region where esterase-mediated hydrolysis in hepatocyte incubations (cryopreserved human hepatocytes, lot-specific metabolic activity verified by 7-ethoxycoumarin O-deethylation assay) generates the corresponding carboxylic acid at a rate of 12 ± 2 pmol/min/10⁶ cells. The acid metabolite retains sub-micromolar potency but is rapidly glucuronidated by UGT1A1, thereby creating a built-in clearance mechanism that prevents accumulation upon repeat dosing.The synthetic route to these investigational probes demands that the Boc-amine remain untouched through a sequence of palladium-catalyzed cross-couplings on the thiazole ring. Published process development accounts report a Suzuki-Miyaura coupling at the 4-position (requiring a brominated precursor not further described here) wherein the ethyl ester and Boc groups remain intact under standard tetrakis(triphenylphosphine)palladium(0) catalysis with aqueous sodium carbonate in dioxane at 85°C. The critical processing hazard is the exothermic CO₂ evolution upon thermal Boc cleavage if the reactor jacket temperature inadvertently exceeds 120°C during solvent swap distillation; a rupture disc rated to 1.5 bar and a thermal quench protocol are mandatory engineering controls documented in the batch record.The workhorse status of 2-tert-butoxycarbonylamino-thiazole-5-carboxylic acid ethyl ester across multiple anticoagulant programs obscures its equally significant role as a conformational probe in macrocyclic peptide engineering. When the thiazole replaces a native thiazoline or thiophene residue in cyclic heptapeptide scaffolds under investigation for integrin αIIbβ3 antagonism, the Boc protection permits selective on-resin acylation of a lysine side chain while the thiazole amine remains masked. Final global deprotection with trifluoroacetic acid/triisopropylsilane/water (95:2.5:2.5 v/v/v) simultaneously cleaves the resin link, removes Boc, and liberates the carboxylic acid from the ethyl ester, provided the cleavage cocktail is sparged with nitrogen for 15 minutes prior to use to eliminate dissolved oxygen that otherwise oxidizes the liberated thiazole to its N-oxide during the 2-hour cleavage time. Cyclization is accomplished in dilute solution (1 mM) using benzotriazol-1-yl-oxytripyrrolidinophosphonium hexafluorophosphate and N,N-diisopropylethylamine, with the crude product purified by reversed-phase preparative HPLC employing a C18 column and a 0.1% trifluoroacetic acid-modified acetonitrile/water gradient. The isolated macrocycle is lyophilized and stored with desiccant at −80°C to prevent diketopiperazine formation.
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2-tert-Butoxycarbonylamino-thiazole-5-carboxylic acid ethyl ester (CAS 365413-84-3, molecular formula C11H16N2O4S, molecular weight 272.32 g/mol) functions as a bifunctional, orthogonally protected heterocyclic building block in medicinal chemistry and fragment-based lead discovery. The tert-butoxycarbonyl (Boc) group at the 2-amino position presents acid-labile amine protection compatible with standard trifluoroacetic acid (TFA)/dichloromethane cleavage protocols, while the ethyl ester at the 5-carboxylate remains intact under acidic conditions yet undergoes selective hydrolysis with aqueous lithium hydroxide in tetrahydrofuran. This orthogonal reactivity profile permits sequential functionalization—amide bond formation at the liberated amine, followed by ester saponification to the free carboxylic acid or vice versa—without iterative protection/deprotection steps. Typical bulk syntheses performed in contract research organizations (CROs) yield white to off-white crystalline powder with HPLC purity (UV detection at 210 nm) consistently exceeding 97.0% area, confirmed against USP <621> system suitability criteria. The thiazole core provides a planar, electron-deficient heteroaromatic scaffold that mimics adenine or pyrimidine motifs in ATP-binding pockets, supporting its use in kinase inhibitor design.
| Test Parameter | Method/Standard | Acceptance Criterion |
|---|---|---|
| Appearance | Visual inspection under D65 illumination | White to off-white powder |
| Identity (¹H NMR) | Bruker 400 MHz, DMSO‑d6, δ reference 2.50 ppm | Characteristic triplets at δ 1.20 ppm (J = 7.1 Hz, –OCH₂CH3), singlet at δ 1.45 ppm (Boc t-Bu), quartet at δ 4.29 ppm (–OCH2–), singlet at δ 8.35 ppm (thiazole H‑4); ratio 3:9:2:1 |
| Identity (LC‑MS) | ESI positive, Agilent 1260/6130 | [M+H]+ 273.1 ± 0.2 Da |
| Purity (HPLC) | C18, 5 μm, 4.6×150 mm; gradient H2O/CH3CN + 0.1% TFA; USP <621> | Main peak area ≥ 97.0% (210 nm); single impurity ≤ 1.0% |
| Water (Karl Fischer) | Coulometric, USP <921>, Method Ic | ≤ 0.5% w/w |
| Residual Solvents | GC‑FID headspace, USP <467> | Ethyl acetate ≤ 0.5%, hexanes ≤ 0.029%, dichloromethane ≤ 0.06% |
| Heavy Metals | ICP‑MS, USP <233> | Sum of Class 1 and 2A elements ≤ 10 ppm |
| Storage Condition | Long‑term stability data (24 months) | 2–8°C, desiccated, under argon |
Inter‑lot variability monitored across 12 consecutive production campaigns at 500 g scale showed a mean purity of 98.2% (SD 0.3%). The primary impurity, identified as 2‑amino‑thiazole‑5‑carboxylic acid ethyl ester (the des‑Boc derivative), elutes at relative retention time (RRT) 1.12 and is controlled below 0.5% to prevent premature acylation events in downstream amide couplings. Water content above 0.8% has been observed to catalyze slow Boc cleavage during prolonged storage at 25°C, therefore vacuum‑sealed packaging inside a dry‑room (dew point ≤ ‑40°C) is applied for all research‑grade quantities above 1 g.
Whereas Fmoc‑amino‑thiazole congeners require basic conditions (usually 20% piperidine in DMF) for N‑deprotection, the 1,3-thiazole‑5‑carboxylic acid ethyl ester moiety is sensitive to ester hydrolysis and transesterification under those conditions. Monitoring by inline ReactIR during deprotection of the Fmoc‑protected analog at 1 mmol scale in DMF‑d7 revealed 8–12% loss of the ethyl ester within 30 min due to nucleophilic attack by piperidine. In contrast, Boc removal with 25% TFA in dichloromethane at 0°C proceeds to completion within 2 h with less than 1% ester cleavage, as quantified by 19F NMR using an internal 4‑fluorotoluene standard. The Boc group also introduces steric deactivation at the 2‑position that retards unwanted nucleophilic attack on the thiazole C‑2, a known side reaction when electron‑poor heterocycles are exposed to amine nucleophiles in peptide‑coupling mixtures. While published kinetic data for this specific substrate in solution‑phase amidation is limited, the empirical performance observed in parallel library syntheses across multiple CROs favors the Boc‑protected form for sequences requiring ester functionality to remain intact until the final step.
In medicinal chemistry programs targeting JAK3 and BTK inhibitors, the 5‑carboxylate ethyl ester acts as a masked carboxylic acid handle. After Boc deprotection, the free amine is acylated with acryloyl electrophiles or sulfonated with pyrrolidine sulfonyl chlorides using HATU/DIEA in DMF, generating focused covalent inhibitor libraries. The ethyl ester is then cleaved with 2 M LiOH in THF/H2O (3:1) at 0°C for 4 h, delivering the corresponding free acid with isolated yields consistently above 85% at 100 mmol input scale. This strategy minimizes protecting‑group interconversions and has been demonstrated in kilogram‑scale campaigns conducted under cGMP‑like controls.
| Compound | CAS RN | Molecular Weight (g/mol) | Typical HPLC Purity | Distinguishing Reactivity Feature |
|---|---|---|---|---|
| 2‑(tert‑Butoxycarbonylamino)‑thiazole‑5‑carboxylic acid ethyl ester | 365413-84-3 | 272.32 | ≥ 97.0% | 5‑COOEt is sterically accessible; HATU‑mediated couplings with 2,6‑dimethylaniline reach > 90% conversion in 2 h at 25°C |
| 2‑(tert‑Butoxycarbonylamino)‑thiazole‑4‑carboxylic acid ethyl ester | 848486-12-4 | 272.32 | ≥ 96.5% | 4‑COOEt in proximity to the Boc‑NH creates steric congestion; coupling with same aniline requires 12 h and 2.0 eq HATU |
| 2‑Amino‑thiazole‑5‑carboxylic acid ethyl ester | 103819-48-5 | 172.21 | ≥ 95.0% | Free amine susceptible to oxidation and acylation at both N‑ and C‑termini; unsuitable for iterative synthesis |
The superior coupling kinetics of the 5‑carboxylate regioisomer are attributed to reduced steric hindrance around the ester carbonyl, which lowers the activation energy for nucleophilic attack by deprotonated amine. In competitive experiments monitored by LC‑MS, the 5‑substituted ethyl ester reached 95% conversion to the amide in 1.5 h, whereas the 4‑analog plateaued at 72% under identical conditions (HBTU, NMM, DMF, 25°C). This rate advantage is exploited in the parallel synthesis of thiazole‑based PNA monomers, where the carboxylic acid derived from the 5‑ester has been employed with EDC/HOBt to couple to aminomethylglycine backbones, yielding monomers with crude purities acceptable for direct oligomerization. Published data for exhaustive kinetic profiling across a series of substituted anilines is limited, but the trend is reproducible across multiple contract synthesis labs.
At process scale (> 500 g), the crude ester obtained after Boc‑anhydride protection of 2‑amino‑thiazole‑5‑carboxylic acid ethyl ester typically contains 3–5% of the regioisomeric Boc‑migrated product and 1–2% of residual starting amine. Recrystallization from ethyl acetate/n‑heptane (1:3 v/v) with controlled cooling from 60°C to 5°C at ‑0.3°C/min yields a single polymorph (needles, melting onset 102–104°C by DSC) with a batch‑to‑batch residual solvent profile meeting ICH Q3C option 2 limits. Vacuum drying (≤ 10 mbar, 40°C, 16 h) is mandatory: residual ethyl acetate above 0.15% w/w has been associated with agglomeration during micronization for formulation studies. Attempts to dry at 50°C for shorter duration triggered partial Boc deprotection (up to 1.2% des‑Boc detected), illustrating the narrow thermal processing window. For campaigns exceeding 2 kg, a seeded cooling crystallization profile—holding the supersaturated solution at 45°C for 1 h before cooling—improved crystal size uniformity (D50 120 µm) and reduced filtration time from 4 h to 45 min on a 20 L Nutsche filter.
Exposure to strong bases, particularly NaOH or DBU, in the presence of the ethyl ester must be avoided if the Boc group is to be preserved; even amine bases such as N‑methylmorpholine at 1.5 eq can induce 3‑5% ester hydrolysis over 24 h at 25°C in aqueous THF. When downstream chemistry demands an aniline or aliphatic amine coupling partner, the use of pre‑formed active esters (e.g., pentafluorophenyl ester generated with DCC) at 0°C limits ester transamidation to less than 1%. For selective Boc removal without ester cleavage, a freshly prepared 4 M HCl in 1,4‑dioxane solution provides rapid deprotection (1 h, 20°C) yielding the hydrochloride salt directly, while TFA protocols require careful temperature control below 10°C to preserve the ester’s integrity. The compound is incompatible with primary and secondary amine‑based additives when used as a latent amine source in polyurethane formulations; premature crosslinking with isocyanates has been observed at loading levels as low as 0.5 phr in model MDI‑polyol systems. No REACH registration number has been assigned for this substance as of the filing date; all shipments within the EU are therefore limited to 1 tonne per annum per registrant under Article 17(2) of EC No 1907/2006.
