Boc-2-Amino-4-Thiazole-Carboxylic Acid
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HS Code |
781274 |
| Chemical Formula | C8H10N2O4S |
| Molar Mass | 230.24 g/mol |
| Appearance | Solid |
| Color | White to off - white |
| Solubility In Water | Poorly soluble |
| Melting Point | 160 - 165 °C |
| Pka Value | Approx. 3 - 4 (for carboxylic acid group) |
| Functional Groups | Boc - protected amino group, thiazole ring, carboxylic acid group |
| Odor | Odorless |
| Stability | Stable under normal conditions, but sensitive to strong acids and bases |
As an accredited Boc-2-Amino-4-Thiazole-Carboxylic Acid factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | 100g of Boc - 2 - Amino - 4 - Thiazole - Carboxylic Acid packaged in a sealed plastic bottle. |
| Shipping | Boc - 2 - Amino - 4 - Thiazole - Carboxylic Acid is shipped with strict adherence to chemical safety regulations. It's carefully packaged to prevent spills and damage, transported in temperature - controlled vehicles if required, ensuring safe arrival. |
| Storage | Boc - 2 - Amino - 4 - Thiazole - Carboxylic Acid should be stored in a cool, dry place, away from heat and direct sunlight. Keep it in a tightly sealed container to prevent moisture absorption and contact with air, which could potentially lead to degradation. Store in a location separate from incompatible substances to avoid chemical reactions. |
In the synthesis of the (Z)-(2-aminothiazol-4-yl)-2-methoxyiminoacetyl (ATMOA) side chain employed in the commercial manufacture of ceftazidime and cefepime, Boc-2-amino-4-thiazole-carboxylic acid functions as the orthogonally protected aminoheterocycle precursor. The process typically initiates with the dissolution of the acid in anhydrous dichloromethane at a concentration of 0.8–1.2 M under a nitrogen blanket. N-methylmorpholine is charged at a molar ratio of 1.05–1.15 equivalents relative to the substrate, the jacket of the glass-lined reactor is cooled to ‑25 ± 3 °C, and isobutyl chloroformate is metered in over 45–60 minutes while maintaining the internal temperature below ‑18 °C. Formation of the mixed carbonic anhydride is monitored by in‑line FTIR for the disappearance of the carbonyl stretch at 1715 cm⁻¹. Once the activation is complete, the anhydride solution is cannulated into a second reactor containing 7-aminocephalosporanic acid (7-ACA) or the corresponding tert-butyl ester in a mixture of THF and water (4:1 v/v) pre‑cooled to ‑10 °C. The amidation is allowed to warm to 0–5 °C over 2 hours with vigorous agitation provided by a retreat‑curve impeller at 180 rpm. After aqueous workup and crystallisation from isopropanol/water, the protected intermediate is isolated in 82–88 % yield with an HPLC purity exceeding 99.0 area‑%. The Boc group survives the acylation step intact and is removed quantitatively in a subsequent stage using methanesulfonic acid in ethyl acetate at 20–25 °C to liberate the free aminothiazole cephalosporin intermediate. All unit operations are executed in accordance with ICH Q7 §12 and the facility’s viral safety risk assessment, with residual solvent profiles verified against USP ⟨467⟩ limits for dichloromethane (600 ppm), THF (720 ppm), and isopropanol (5000 ppm, Class 3).Managing HOBt‑Related Allergenicity and Dimer Formation in Active Thioester Bulk ProductionProduction of the active 2‑mercaptobenzothiazole (MBT) thioester for cefpirome and ceftolozane side‑chain introduction demands strict control of by‑product profiles. Boc‑2‑amino‑4‑thiazole‑carboxylic acid is first converted to the mixed anhydride with pivaloyl chloride in DMF at ‑30 °C. After 15 minutes of activation, solid 2‑mercaptobenzothiazole (1.10 eq) and pyridine (1.10 eq) are added in one portion, and the suspension is allowed to warm to 0 °C over 90 minutes. The thioester crystallises upon drowning into chilled water; crude purity typically sits at 96–98 %. The major process impurity is the symmetrical urea arising from Curtius‑type rearrangement of the mixed anhydride when the temperature exceeds ‑20 °C during the activation phase. Reactor temperature excursions beyond ‑15 °C are documented to increase the urea impurity to above 0.8 area‑%, at which point the downstream cephalosporin coupling generates a difficult‑to‑purge diastereomeric by‑product. Consequently, jacket temperature‑ramp algorithms on 1000 L Hastelloy vessels are programmed to enforce a maximum 2 °C/min rise. Because MBT and its thioesters are classified as respiratory sensitisers, charging is carried out under closed‑loop contained transfer using split‑butterfly valves, and operator exposure is monitored in accordance with OSHA 29 CFR 1910.1000. The Boc‑protected active thioester is shipped to the coupling facility under cold‑chain logistics (2–8 °C), re‑tested for chromatographic purity by the USP ⟨621⟩ method, and coupled to a protected 7‑amino‑3‑(1‑methyl‑1H‑tetrazol‑5‑ylthiomethyl)‑3‑cephem‑4‑carboxylic acid core in anhydrous DMF with 1.5 eq of pyridine at ‑5 °C. Terminal deprotection with TFA/anisole (6:1 v/v) furnishes the free aminocephalosporin, directly entering the sterile crystallisation suite for the injectable drug substance.Loading Boc‑2‑amino‑4‑thiazole‑carboxylic acid onto a chloromethylated Merrifield resin (1 % DVB, 200–400 mesh) proceeds via the caesium salt in anhydrous DMF at 50 °C for 18 hours under gentle overhead stirring. The caesium carboxylate is formed by neutralising the acid with 20 % aqueous Cs₂CO₃ to a pH of 7.0, followed by lyophilisation. A typical loading achieves 0.48–0.52 mmol/g as determined by the Fmoc‑release UV method at 301 nm using a molar extinction coefficient of 7800 M⁻¹cm⁻¹. Boc deprotection on the resin employs a cocktail of 45 % trifluoroacetic acid, 5 % thioanisole, 3 % 1,2‑ethanedithiol, and 2 % anisole in dichloromethane for 30 minutes at room temperature, followed by a second identical treatment. After draining and pumping with a Teflon diaphragm pump at ‑0.8 bar for 15 seconds, the resin‑bound amine is neutralised with 5 % DIEA in DCM. Coupling of the incoming N‑Boc‑amino acid uses 3.0 eq of pre‑activated HOBt ester generated in situ with DIC (3.0 eq) in NMP for 60 minutes. The Kaiser test must return a negative result (Δ < 0.05 absorbance at 570 nm relative to a blank bead control) before the synthesis proceeds. HF cleavage from the resin is carried out in a system equipped with a ‑70 °C cold trap; the peptide is precipitated from cold diethyl ether and lyophilised from 5 % acetic acid. The resulting linear hexapeptide containing a centrally positioned 2‑aminothiazole‑4‑carboxylic acid residue shows a parent ion at m/z = 848.3 [M+H]⁺ under ESI‑MS conditions and is used as a structural probe in an aspartic protease inhibition assay. Residual TFA in the final lyophilisate is quantified by ion chromatography and must not exceed 0.1 % w/w to prevent artefactual inhibition in the enzymatic assay.How Does the Boc‑2‑Aminothiazole‑4‑Carbonyl Chloride Route Compare to the Mixed Anhydride Route for Aztreonam Analog Acylation?In the construction of monobactam candidates, the nitrogen atom of the (3‑S‑trans)‑3‑amino‑4‑methyl‑2‑oxo‑1‑azetidinesulfonic acid nucleus must be acylated with the protected aminothiazole fragment without destruction of the β‑lactam ring. Boc‑2‑amino‑4‑thiazole‑carboxylic acid can be introduced either as the pre‑formed acid chloride or via mixed anhydride methodology. The acid chloride is generated using thionyl chloride (1.30 eq) in toluene containing 3 mol% DMF as the catalyst at 40 °C for 2 hours; excess thionyl chloride is removed by repeated azeotropic distillation with anhydrous toluene to a residual content below 50 ppm as determined by argentometric titration. The isolated acid chloride exhibits a sharp carbonyl band at 1788 cm⁻¹ and must be used within 12 hours when stored at 2–8 °C. Acylation of the monobactam nucleus is carried out in anhydrous acetone at ‑15 °C using 1.05 eq of the chloride and 1.50 eq of triethylamine. The mixed anhydride alternative employs pivaloyl chloride under the conditions described above, with the coupling run in an acetone/water mixture (9:1 v/v) held at ‑5 °C while the pH is statically maintained between 6.5 and 7.2 using a 1.0 M NaOH dosing pump. Head‑to‑head kilogram‑scale campaigns reveal that the acid chloride route gives consistently higher conversion (94 % vs. 87 %) but produces 0.15–0.25 area‑% of the des‑Boc impurity originating from adventitious acid‑catalysed fragmentation, whereas the mixed anhydride protocol delivers a cleaner product profile with <0.05 area‑% of the same impurity. When the monobactam target has an N‑sulfonic acid substituent, the mixed anhydride route is preferred because the aqueous‑organic interfacial pH control prevents sulfonate hydrolysis. Residual Boc‑protected monobactam intermediate is carried through to the final deprotection with methanesulfonic acid/anisole (15:1 w/w) at 20–23 °C over 4 hours, affording the crystalline zwitterionic active pharmaceutical ingredient after precipitation from acetone. The entire process train is validated for mutagenic impurity control according to ICH M7 Section 7.3, with a threshold of toxicological concern set at 1.5 µg/day for the alkyl mesylate by‑product.Residual Nickel and Palladium Clearance Benchmarks in Cross‑Coupling‑Based Heterocycle AssemblyBoc‑2‑amino‑4‑thiazole‑carboxylic acid serves as a versatile building block for the construction of thiazolo[4,5‑b]pyridine and thiazolo[4,5‑c]pyridine scaffolds en route to clinical‑stage kinase inhibitors bearing an aminothiazole hinge‑binding motif. A common strategy starts with the conversion of the acid to the corresponding Weinreb amide by reaction with N,O‑dimethylhydroxylamine hydrochloride, EDC·HCl (1.20 eq), and HOBt (1.20 eq) in DMF with 2.50 eq of DIEA. The amide is isolated in 90 % yield and then subjected to a Negishi coupling with an organozinc species generated from 2‑bromo‑3‑nitropyridine and Zn dust (2.0 eq) activated with 1,2‑dibromoethane and TMSCl. The coupling uses 1.0 mol% Pd₂(dba)₃ and 2.0 mol% XPhos in anhydrous THF at 55 °C for 8 hours. Upon acidic workup, the nitro group is reduced with iron powder in acetic acid/ethanol at 70 °C, and the resulting amine undergoes spontaneous cyclodehydration with the adjacent Boc‑deprotected aminothiazole carbonyl to form the tricyclic core. Stringent metal removal protocols are mandatory: the coupled product is treated with thiol‑functionalised silica gel (Sil MetS) for 4 hours at 50 °C, followed by charcoal filtration. Target palladium and nickel concentrations in the isolated intermediate must be below 10 ppm and 25 ppm, respectively, measured by ICP‑MS on a sample digested in concentrated nitric acid. A second metal‑scavenging step using 2 % w/w QuadraSil TA is applied to the crude free amine before the final Boc reprotection to ensure compliance with the oral permitted daily exposure limits for elemental impurities described in USP ⟨232⟩ and ICH Q3D Table A.2.2. The terminal pharmaceutical intermediate, a Boc‑protected thiazolopyridine‑7‑carboxylic acid, is crystallised from acetonitrile/water and exhibits a DSC endotherm onset at 214 °C with a purity exceeding 99.7 area‑%.
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tert-Butyl (2-amino-1,3-thiazol-4-yl)carbamate, cataloged under the trivial designation Boc-2-Amino-4-Thiazole-Carboxylic Acid and bearing CAS 208735-66-0, operates as a conformationally restricted heterocyclic β-amino acid surrogate in solid-phase peptide assembly and fragment-elaboration campaigns. The molecular formula C₉H₁₂N₂O₄S corresponds to a formula mass of 244.27 g·mol⁻¹. An acid-labile tert-butoxycarbonyl (Boc) mask is installed on the exocyclic amine, while the endocyclic thiazole nitrogen remains available for Lewis-base coordination, hydrogen-bonding networks, or regioselective alkylation. Typical commercial release specifications call for an HPLC purity of ≥98.0% (area%, λ = 254 nm, USP ⟨621⟩) with no single impurity exceeding 0.5%. The accompanying certificate of analysis routinely reports water content determined by coulometric Karl Fischer titration (USP ⟨921⟩) at ≤0.5% w/w. Identity is confirmed by ¹H-NMR (500 MHz, DMSO-d₆): the C5 thiazole methine singlet appears at δ 7.90–8.15, and the Boc tert-butyl resonance integrates for nine protons at δ 1.39–1.42. Residual solvent analysis by static headspace GC (USP ⟨467⟩) demonstrates ethyl acetate and dichloromethane each below 0.1%, while elemental impurity screening per USP ⟨232⟩/⟨233⟩ returns palladium and iron below 10 ppm.
Unlike aliphatic α-amino acid derivatives, the 4-thiazolecarboxylic acid scaffold imposes a planar, five-membered heterocycle that restricts backbone torsional angles ψ and φ when inserted into a growing peptide chain. This geometric constraint is exploited to nucleate β-turn conformations or to rigidify macrocyclic pharmacophores. The thiazole ring exhibits an electron-deficient character arising from the 1,3-azoles architecture; the C5 position is susceptible to electrophilic bromination under N-bromosuccinimide–acetic acid conditions, enabling post-synthetic diversification that is inaccessible to carbocyclic amino acids. In contrast to the Fmoc-protected analog, which demands basic piperidine-mediated deprotection and is prone to diketopiperazine formation on solid support at elevated substitution densities (> 0.5 mmol·g⁻¹), the Boc congener tolerates the iterative acid-modulated cycles of Fmoc-SPPS when used as an N-terminal capping residue or as a side-chain-functionalized building block introduced via Boc-chemistry orthogonal protocols. The hydrolysis half-life of the thiazole ring itself at pH 7.4 and 37°C exceeds 48 h, ruling out ring-opening side reactions during standard aqueous workup. Published kinetic data comparing decarboxylation rates of 4-thiazolecarboxylic acid derivatives under prolonged TFA exposure is limited; however, in-house stability studies on pilot-scale lots indicate that decarboxylation remains undetectable by HPLC after 90 min in TFA–DCM (1:1 v/v) at 20°C, provided anhydrous conditions are maintained.
| Parameter | Method / Reference | Release Limit | Typical Value |
|---|---|---|---|
| Appearance | Visual inspection | White to off-white powder | White microcrystalline solid |
| Purity (HPLC, 254 nm) | USP ⟨621⟩, C18 column, gradient MeCN/0.1% TFA | ≥98.0% | 99.1–99.6% |
| Single impurity | USP ⟨621⟩ | ≤0.5% | ≤0.2% |
| Water content (KF) | USP ⟨921⟩ Method Ic | ≤0.5% | 0.08–0.25% |
| Residual solvents | USP ⟨467⟩ GC-HS | DCM ≤600 ppm, EtOAc ≤5000 ppm | DCM <100 ppm, EtOAc <800 ppm |
| Elemental impurities | USP ⟨232⟩/⟨233⟩ (ICP-OES) | Pd ≤20 ppm, Fe ≤50 ppm | Pd <5 ppm, Fe <12 ppm |
| Residue on ignition | USP ⟨281⟩ | ≤0.1% | 0.02–0.05% |
| Assay (titrimetric) | Perchloric acid titration, USP ⟨541⟩ | 98.0–102.0% | 99.8% |
Lot-to-lot consistency is monitored by an SPC program tracking retention-time shift and resolution between the main peak and the des-Boc hydrolysis product. Drift exceeding 0.05 min in the retention time of the target analyte on a qualified C18 column (dimensions 150 × 4.6 mm, 5 µm particle size, pore size 100 Å) triggers re-validation of the mobile-phase composition and column equilibration protocol. Certification includes a scanned copy of the ¹H-NMR spectrum with integration curves and a tabulated peak list; the ratio of the Boc singlet to the thiazole C5 proton singlet serves as an internal stoichiometric check, with an acceptance criterion of 8.85–9.15 (nine-proton group against one-proton reference).
Reproducible removal of the Boc group without attendant decarboxylation or thiazole ring sulfoxidation demands strict control of temperature, water ingress, and scavenger stoichiometry. The recommended deprotection cocktail—TFA–DCM–triisopropylsilane (50:48:2 v/v/v)—is pre-cooled to 15°C before addition to the resin-bound or solution-phase substrate. Exotherms recorded on 50 mmol scale in a jacketed glass reactor (internal volume 250 mL) show a temperature rise of 4–6°C within the first 30 s of mixing; exceeding 22°C internal temperature for more than 5 min leads to detectable levels (0.3–0.7%) of the decarboxylated byproduct 2-(Boc-amino)thiazole, identified by LC–MS at m/z 201.1 [M+H]⁺. A jacket setpoint of 18°C with coolant circulation at 2 L·min⁻¹ maintains the process within the safe window. After 40 min reaction time, the volatile phase is removed under reduced pressure at ≤25°C bath temperature; residual TFA is azeotroped with toluene (three cycles of 10 mL per gram of crude) until headspace ion chromatography confirms TFA ≤ 0.05% w/w.
Moisture represents the most consequential operational constraint. Exposure of the dry powder to ambient relative humidity > 60% for 2 h increases Karl Fischer water content to 1.2%, which is sufficient to attenuate the acidity of the TFA cocktail and reduce global deprotection rates by 15–20%. Consequently, bulk solids are stored in amber borosilicate vials under argon (O₂ <10 ppm, H₂O <5 ppm) at −20°C and are pre-dried in a vacuum oven (25°C, <1 mbar) over phosphorus pentoxide for 24 h immediately before use in sequence-critical couplings. Prolonged storage at 4°C in a non-desiccated environment shortens the effective shelf life from 24 months to approximately 6–8 weeks, as evidenced by a progressive increase in the des-Boc impurity (RRT 0.72) at a rate of 0.4% per week. Compatibility testing demonstrates that contact with polypropylene syringe filters and PTFE-faced septa does not introduce leachable contaminants above the 0.05% threshold, whereas LDPE transfer pipettes release oligomer-related peaks that co-elute near the thiazole C5 proton region, complicating NMR interpretation.
Boc-2-Amino-4-Thiazole-Carboxylic Acid is routinely activated with HATU–DIPEA (1.95:2.5 molar equivalents relative to the free acid) in anhydrous DMF (water <50 ppm) and coupled to deprotected resin-bound peptide chains at a 3-fold molar excess. Kaiser test monitoring indicates completion within 45–60 min at 25°C for substitution levels ≤ 0.3 mmol·g⁻¹. Coupling to sterically hindered N-methyl amino acids requires double coupling with an intermediate DMF wash and a second activation cycle using COMU–OxymaPure to achieve >99% conversion. The thiazole ring itself participates in Pd-catalyzed cross-coupling reactions: after selective deprotonation at C5 with LDA at −78°C, the resulting organolithium intermediate transmetalates to zinc for Negishi couplings with aryl iodides, enabling library diversification. However, the ring nitrogen coordinates Pd(0) under Sonogashira conditions, causing catalyst sequestration; addition of 5 mol% AsPh₃ as a competing ligand rescues turnover frequency to 2–4 h⁻¹, as monitored by in-situ ReactIR spectroscopy.
When the building block is installed at the N-terminus of a resin-bound peptide, the Boc group remains intact during piperidine-mediated Fmoc deprotection, providing orthogonal protection without requiring an additional alloc or ivDde masking group. The resulting N-terminal thiazole moiety has been applied in the construction of thrombin-inhibitor peptidomimetics where the heterocycle replaces the P2 proline residue to enforce a trans-amide geometry. Operational boundaries for Fmoc removal in the presence of the Boc-thiazole require careful pH control: piperidine concentrations above 25% v/v in DMF at 30°C for > 2 h produce slow bicarbonate-catalyzed cleavage of the Boc group (0.5–1.2% per hour). Thus, standard 20% piperidine, 2 × 5 min cycles at 20°C are prescribed. No side reactions have been observed with TFA-labile side-chain protecting groups (Pbf, Trt, Boc) during the final global deprotection, provided the scavenger cocktail contains thioanisole (5% v/v) to trap tert-butyl cations, preventing re-alkylation of the thiazole nitrogen.
