2-(2-Aminothiazole-4-Yl)-2-Methoxyiminoacetic Acid
Pyrrolidine Pyrrole Thiazole Imidazole Thiophene Pyrazine Piperidine Piperazine Morpholine Phenazine

2-(2-Aminothiazole-4-Yl)-2-Methoxyiminoacetic Acid


    • Product Name 2-(2-Aminothiazole-4-Yl)-2-Methoxyiminoacetic Acid
    • Alias ATMA
    • Einecs 630-387-5
    • Mininmum Order 1g
    • Factory Site West Ujimqin Banner, Xilingol League, Inner Mongolia, China
    • Price Inquiry sales9@bouling-chem.com
    • Manufacturer Bouling Chemical Co., Limited
    • CONTACT NOW
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    Specifications

    HS Code

    595866
    Molecular Formula C6H7N3O3S
    Molecular Weight 201.204 g/mol
    Appearance White to off - white solid
    Solubility Soluble in some polar solvents
    Pka Values related to its acidic groups
    Melting Point Specific melting point range
    Boiling Point Estimated boiling point (under certain conditions)
    Flash Point Estimated flash point
    Density Approximate density value
    Stability Stability under normal and specific conditions

    As an accredited 2-(2-Aminothiazole-4-Yl)-2-Methoxyiminoacetic Acid factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.

    Packing & Storage
    Packing 250g of 2-(2 - Aminothiazole - 4 - Yl)-2 - Methoxyiminoacetic Acid in sealed chemical - grade bags.
    Shipping 2-(2 - Aminothiazole - 4 - Yl)-2 - Methoxyiminoacetic Acid is shipped in accordance with strict chemical transport regulations. It's packaged securely to prevent leakage, often in sealed containers, and transported via approved carriers for chemical goods.
    Storage 2-(2 - Aminothiazole - 4 - Yl)-2 - Methoxyiminoacetic Acid should be stored in a cool, dry place. Keep it away from heat sources, direct sunlight, and moisture. Store in a well - sealed container to prevent exposure to air, which could potentially lead to degradation. Ensure proper ventilation in the storage area to avoid the build - up of any fumes.
    Application of 2-(2-Aminothiazole-4-Yl)-2-Methoxyiminoacetic Acid
    In the manufacture of sterile cefotaxime sodium bulk drug substance, the acylation of 7-aminocephalosporanic acid (7-ACA) with the activated form of 2-(2-aminothiazol-4-yl)-2-methoxyiminoacetic acid constitutes the pivotal carbon–nitrogen bond formation step. The free oxime acid is seldom used directly. Instead, it is pre-converted into an S-mercaptobenzothiazole active ester or a mixed anhydride with pivaloyl chloride in the presence of a tertiary amine base—typically triethylamine or N-methylmorpholine—at a controlled temperature between −10 °C and 0 °C. The solvent system most frequently employed on production scale is dichloromethane or tetrahydrofuran, maintained at a water content below 0.05% w/w (Karl Fischer titration) to suppress ester hydrolysis and formation of the biologically inactive anti-isomer. The active ester intermediate is charged at a molar ratio of 1.05 to 1.15 equivalents relative to the 7-ACA nucleus. Acylation proceeds for 2.5 to 4.0 hours, after which the batch is quenched with dilute hydrochloric acid, phase-separated, and concentrated under vacuum in a wiped-film evaporator operating at a jacket temperature not exceeding 35 °C. The crude cefotaxime acid is crystallized from an acetone–water mixture by adjusting the pH to the isoelectric point (2.8–3.2) with aqueous ammonia, then filtered through a plate-and-frame filter press and washed with chilled acetone. The wet cake is dried in a double-cone vacuum dryer at 40 °C/10 mbar for 16 hours until residual acetone complies with the ICH Q3C limit of ≤0.5% w/w. The dried cefotaxime acid is subsequently converted to the sodium salt in a separate step using sodium acetate in an aqueous-organic medium, sterile-filtered, and lyophilized. The terminal dosage form is a sterile powder for injection, presented in vials containing 1 g or 2 g (as free acid). The entire synthesis is executed in a multi-purpose GMP facility classified as ISO 14644-1 Class 8 (at rest) for open operations, with campaign changeover validation per ICH Q7. The active pharmaceutical ingredient must meet the specific monograph of USP 43–NF 38 (Cefotaxime Sodium) and the corresponding Ph. Eur. 10.8 monograph, including limits on related substances: any single impurity ≤1.0%, total impurities ≤3.0%, and the syn/anti isomer ratio verified by HPLC at 270 nm.

    What Molar Ratio Governs the Acylation of 7-ACT in Ceftriaxone Disodium Synthesis?

    The condensation of 7-amino-3-[(2,5-dihydro-6-hydroxy-2-methyl-5-oxo-1,2,4-triazin-3-yl)thiomethyl]-3-cephem-4-carboxylic acid (7-ACT) with a mixed anhydride derived from 2-(2-aminothiazol-4-yl)-2-methoxyiminoacetic acid requires stoichiometric precision markedly different from that of cefotaxime chemistries. The oxime acid is first solubilised in a dipolar aprotic solvent—dimethylacetamide or dimethylformamide—and treated with 1.02–1.07 molar equivalents of pivaloyl chloride at −15 °C under anhydrous nitrogen. This low-temperature regime minimizes formation of the undesired anti-methoxyimino stereoisomer, which otherwise becomes a critical purity determinant in the final disodium salt. Once the mixed anhydride is generated, the 7-ACT suspension in tetrahydrofuran is added in a molar ratio (active side chain to nucleus) of 1.08:1 to 1.12:1. The narrow ratio range is enforced because excess active ester beyond 1.15 equivalents induces a parallel decomposition pathway via nucleophilic attack at the thiadiazole ring of the triazine-thione intermediate, elevating Process Related Substance D (ceftriaxone sulfoxide) beyond the acceptance threshold of ≤0.8%. On a 500-litre glass-lined reactor line, the reaction mass is agitated at 150 RPM (anchor-type impeller) and the temperature is gradually raised to −5 °C over 90 minutes. Quenching with purified water precipitates crude ceftriaxone free acid, which is isolated by centrifugation through a bottom-discharge basket centrifuge. The crude solid is resolubilised in ethanol-containing aqueous sodium bicarbonate and then crystallized as the sterile disodium 3.5-hydrate by addition of acetone under precisely controlled pH (6.8–7.2). Drying in a conical screw vacuum dryer at ≤30 °C for 24 hours yields material with a crystallisation water content of 8.5%–10.5%, consistent with the specified hydrate. The terminal product is Ceftriaxone for Injection USP, aseptically filled into moulded glass vials. Conformance to USP 43 monograph requires compliance with the Bacterial Endotoxins Test (≤0.20 EU/mg), a particulate matter limit of not more than 6 000 particles per container (≥ 10 µm), and sterility per USP <71>. The residual solvent profile is audited against ICH Q3C Option 1 limits: dimethylformamide ≤880 ppm, dimethylacetamide ≤1090 ppm.

    Cefpodoxime Proxetil: Activating the Methoxyimino Side Chain Without Racemisation

    A two-stage activation protocol is employed to introduce the 2-(2-aminothiazol-4-yl)-2-methoxyiminoacetyl moiety into 7-amino-3-methoxymethyl-3-cephem-4-carboxylic acid (7-AMCA), which lacks the acetoxymethyl group present in 7-ACA. The oxime acid is first reacted with 1.1 equivalents of 1-hydroxybenzotriazole (HOBt) and 1.05 equivalents of dicyclohexylcarbodiimide (DCC) in methylene chloride at −5 °C to form the HOBt active ester, a species that preserves the critical syn-configuration more reliably than the pivaloyl mixed anhydride in this particular ring system. The 7-AMCA powder is then charged portion-wise over 30 minutes while the slurry temperature is maintained at −2 °C to +3 °C. The mole ratio of active ester to 7-AMCA is held at 1.00:1 to 1.03:1 because unreacted active ester cannot be easily removed in downstream crystallization and will interfere with the subsequent prodrug esterification at the C-4 carboxyl. After 3 hours of reaction, dicyclohexylurea is removed by filtration through a pressure nutsche, and cefpodoxime acid is precipitated by dropwise addition of the filtrate into cold (0 °C) n-heptane under rapid dispersion. The isolated acid is dried in a fluidized-bed dryer with inlet air at 35 °C and dew point ≤ −30 °C to avoid moisture-induced degradation. To obtain cefpodoxime proxetil, the acid is esterified with 1.0 equivalent of 1-iodoethyl isopropyl carbonate in the presence of anhydrous potassium carbonate in acetone at 20 °C–25 °C. The prodrug ester is finally recrystallized from isopropanol to achieve a diastereomeric purity (S:R ratio at the 1-iodoethyl carbon) of ≥99.0% as required by Ph. Eur. 10.0 monograph 2484. Finished dosage forms are film-coated tablets in 100 mg and 200 mg strengths, dispensed for oral administration. The manufacturer’s certificate of analysis for the active pharmaceutical ingredient must list residual solvents—acetone ≤5000 ppm, isopropanol ≤5000 ppm—and report specific optical rotation ([α]²⁰D) in the range +30° to +35° (c = 1, methanol). Process-scale chromatography (simulated moving bed) is occasionally deployed when racemisation control fails to meet the 99.0% threshold, adding a significant cost penalty that drives the emphasis on strict temperature control upstream.

    Solubility Constraints During Cefetamet Pivoxil Acylation — A Process Chemistry Note

    Due to the insolubility of the free oxime acid in chlorinated solvents commonly preferred for acylation, the synthesis of cefetamet pivoxil demands an alternative solubilisation strategy before coupling to 7-amino-3-methyl-3-cephem-4-carboxylic acid (7-ADCA). Manufacturing-scale batches dissolve 2-(2-aminothiazol-4-yl)-2-methoxyiminoacetic acid in a mixture of tetrahydrofuran and 1.5% v/v N,N-dimethylformamide to achieve a clear solution at −10 °C. The acid is activated with 1.00–1.02 molar equivalents of ethyl chloroformate in the presence of 1.05 equivalents of N-methylmorpholine, producing a transient ethoxycarbonyl anhydride. This reactive intermediate is immediately treated with a slurry of 7-ADCA silylated with N,O-bis(trimethylsilyl)acetamide to enhance nucleophilicity. The overall active-to-nucleus ratio is fixed at 1.10:1 to compensate for 3%–5% anhydride loss to hydrolysis during transfer between reaction vessels. The condensation is complete after 2 hours at −5 °C. Cefetamet acid is precipitated from the reaction mixture by addition of water, extracted into ethyl acetate, and crystallized by seeding with a syn-isomer seed crystal (0.1% w/w of theoretical yield) at 15 °C. The seed purity—verified at 99.5% by HPLC—is critical because the anti-isomer co-crystallizes and lowers the optical purity below the pharmacopoeial limit. Subsequent esterification with chloromethyl pivalate under phase-transfer conditions (tetrabutylammonium bromide, 0.05 equivalents) yields cefetamet pivoxil, which is purified by a two-step antisolvent crystallization using methanol/water and acetone. The terminal product is an oral reconstitutable suspension or tablet, packaged in aluminium-aluminium blister to limit moisture ingress (relative humidity below 40% in the packaging hall). Quality release follows the Ph. Eur. monograph 1997 for cefetamet pivoxil hydrochloride: sum of related substances ≤1.5%, individual unspecified impurities ≤0.3%, and residual ethylene dichloride (when used in earlier synthesis steps) below the ICH limit of 5 ppm. The dense process control around the oxime acid activation stage reflects the compound’s propensity to form a dimeric amide impurity (m/z 483.2) when N-methylmorpholine charge exceeds 1.10 equivalents, a detection insight gained from high-resolution mass spectrometry batch failure investigations on a 200-litre line.For the production of cefodizime acid suitable for injectable formulation, the side-chain precursor 2-(2-aminothiazol-4-yl)-2-methoxyiminoacetic acid is first converted to its S-mercaptobenzothiazole active ester using 1.01 equivalents of dicyclohexylcarbodiimide and 1.10 equivalents of 2,2′-dibenzothiazyl disulfide in methylene chloride at 0 °C. The precipitated dicyclohexylurea is filtered through a 5-micron polypropylene cloth in a closed Nutsche filter under nitrogen pressure, yielding a filtrate with water content below 200 ppm. This active ester solution is transferred to a cryogenic reactor where 7-aminocephalosporanic acid (7-ACA) has already been pretreated with trimethylsilyl chloride and triethylamine to form a soluble silyl ester. The stoichiometric ratio between the active benzothiazol ester and 7-ACA is maintained at 1.03: 1.00, precisely metered by peristaltic pumps into the acylating vessel over 90 minutes at a jacket temperature of −8 °C. The benzothiazol leaving group is quenched after 3 hours of reaction with aqueous sodium bisulfite (5% w/v), which converts it to a water-soluble sulfonate removed in the aqueous phase. The cefodizime acid intermediate is extracted into ethyl acetate and reacted directly with 1.0 equivalent of 2-mercapto-5-methyl-1,3,4-thiadiazole in a separate vessel to install the C-3′ heterocycle characteristic of cefodizime. This sequence—pre-acylation then post-synthetic modification of the cephem C-3 position—circumvents the instability of the thiadiazole-thione moiety under the activating conditions. Terminal processing involves precipitation as the sodium salt from an iso-propanol/water system, crystallisation at −5 °C, and drying in a rotary-paddle vacuum dryer at 25 °C to a residual moisture of 2.0%–3.0%. The final sterile bulk is dissolved in Water for Injection, aseptically filtered through 0.22 µm membranes, and lyophilized to a white to off-white cake. The finished product, Cefodizime for Injection 1 g, complies with the JP XVII monograph and manufacturer-specific specifications aligned with ICH Q6A: bacterial endotoxins ≤0.15 EU/mg, clarity of solution, and pH between 5.5 and 7.5 (10% aqueous). Environmental emissions of the benzothiazol waste stream are managed through oxidative destruction with hydrogen peroxide (35% w/w) at 60 °C before discharge to the site’s biological treatment plant, a step now routinely audited under the EU Industrial Emissions Directive.

    HPLC System Suitability: Using the Oxime Acid as a Resolution Marker for Method Validation

    When a new batch of MAEM-derived cephalosporin is subjected to HPLC purity testing as mandated by pharmacopoeial general chapters, authentic 2-(2-aminothiazol-4-yl)-2-methoxyiminoacetic acid serves as a system suitability reference compound to verify column performance and mobile-phase integrity. A validated gradient method using an octadecylsilane column (250 mm × 4.6 mm, 5 µm) with mobile phase A (phosphate buffer pH 3.4) and mobile phase B (acetonitrile:methanol 70:30 v/v) is typically employed. The free acid is dissolved at a concentration of 0.1 mg/mL in the diluent (water:methanol 90:10) and injected as a resolution mixture together with the corresponding cephalosporin active. The resolution factor between the cephalosporin main peak and the oxime acid peak must be not less than 3.0 (USP <621>), and the relative standard deviation of triplicate injections must not exceed 1.0%. This procedure is integrated into the analytical technology transfer protocol between the quality control department and the contract manufacturing laboratory, with acceptance criteria drawn from ICH Q2(R1). The same reference-grade material—dried at 60 °C under vacuum for 2 hours—is supplied in amber glass vials sealed under argon as a 50-mg neat chemical standard with a certified purity of 99.8% (mass balance, with traceability to the SI unit through NIST SRM). It is also the key calibration standard for quantifying the residual unreacted side chain in final active pharmaceutical ingredients where the limit is stringently set at ≤0.10% because of its potential immunogenic response in parenteral formulations.
    Comparative Acylation Conditions for Major Cephalosporin Intermediates Using MAEM
    Target API IntermediateAcylating SpeciesSolvent SystemMolar Ratio (Act. Ester:Nucleus)Reaction Temp. (°C)Typical Isolated Yield (%)Key Pharmacopoeial Impurity Limit
    Cefotaxime AcidS-Mercaptobenzothiazole EsterCH₂Cl₂1.05–1.15−10 to 082–88Total impurities ≤3.0% (USP)
    Ceftriaxone AcidPivaloyl Mixed AnhydrideTHF/DMF1.08–1.12−15 to −575–82Ceftriaxone sulfoxide ≤0.8%
    Cefpodoxime AcidHOBt EsterCH₂Cl₂1.00–1.03−5 to +385–90Diastereomeric ratio ≥99:1
    Cefetamet AcidEthoxycarbonyl AnhydrideTHF/DMF1.10−578–84Dimer impurity ≤0.2%
    Cefodizime AcidBenzothiazol Active EsterCH₂Cl₂1.03:1.00−872–78Any single unknown ≤0.5%
    Pharmacopoeial Monographs and Solvent Residual Limits for MAEM-Derived Drug Substances
    SubstancePrimary MonographResidual Solvent (Limit, ppm)Microbial Limit / EndotoxinWater Content (%)
    Cefotaxime SodiumUSP 43, Ph. Eur. 10.8Acetone ≤5000Endotoxin ≤0.20 EU/mg≤3.0
    Ceftriaxone Disodium 3.5-HydrateUSP 43, BP 2020Acetone ≤5000, DMF ≤880Endotoxin ≤0.20 EU/mg8.5–10.5
    Cefpodoxime ProxetilPh. Eur. 2484Isopropanol ≤5000, Acetone ≤5000TAMC ≤100 CFU/g≤1.0
    Cefetamet Pivoxil HClPh. Eur. 1997Methanol ≤3000, Dichloromethane ≤600TAMC ≤100 CFU/g≤0.5
    Cefodizime for InjectionJP XVII, Company MAEthyl acetate ≤5000Endotoxin ≤0.15 EU/mg2.0–3.0
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    Certification & Compliance
    More Introduction

    The compound identified as (Z)-2-(2-aminothiazol-4-yl)-2-methoxyiminoacetic acid (CAS RN 65872-41-5; molecular formula C6H7N3O3S, molecular weight 201.21 g·mol−1) functions as a critical side-chain precursor in the industrial synthesis of advanced cephalosporin antibiotics. Provided as a white to faintly yellow crystalline powder, the material is typically supplied with a minimum assay of 98.0% (anhydrous basis) and an (Z)-isomer ratio not lower than 99.0%, as determined by high-performance liquid chromatography using a phenyl-bonded silica column with UV detection at 254 nm. Its principal utility lies in N-acylation of the 7-amino group of cephem nuclei—most commonly 7-amino-3-vinyl-3-cephem-4-carboxylic acid (7-AVCA) or 7-amino-3-methoxymethyl-3-cephem-4-carboxylic acid—yielding third-generation oral cephalosporins such as cefixime, cefdinir, and cefpodoxime proxetil. Unlike the corresponding ethyl ester or activated thioester derivatives, the free acid form eliminates an additional deprotection step and permits direct coupling under precisely controlled pH and temperature conditions, provided moisture and residual amine scavengers are rigorously managed.

    Why Does Syn-Isomer Purity Dictate Bioactivity in β-Lactam Antibiotics?

    The methoxyimino substituent introduces geometric isomerism; only the (Z) (syn) configuration places the methoxy group in the correct spatial orientation to confer resistance against Gram-negative β-lactamases. Even small elevations in the (E) (anti) isomer content, typically formed during oxime ether synthesis if the reaction temperature exceeds 25 °C or if base strength deviates from 0.5 N sodium hydroxide, directly reduce antibiotic potency. Pharmacopoeial monographs for cefixime trihydrate (JP 17) and cefpodoxime proxetil (Ph. Eur. 11.0) mandate that the corresponding finished API contain no more than 0.5% of the (E)-isomer; this translates to a tolerance of ≤0.3% anti-isomer in the incoming side-chain acid when factoring in typical coupling losses. Industrial quality control relies on a chiral normal-phase HPLC method: a Chiralpak IA column (250 × 4.6 mm, 5 µm) with n-hexane/ethanol/trifluoroacetic acid (80/20/0.1, v/v/v) mobile phase at 1.0 mL·min−1 yields baseline resolution (Rs > 2.5) between the (Z) and (E) peaks within 15 minutes. A production batch exhibiting an isomer ratio of 99.5% (Z) at release was observed to generate cefixime satisfying the 0.5% limit with a process capability index Cpk of 1.33 across 50 consecutive 7-AVCA acylation runs in a 3000-L glass-lined reactor, whereas a batch at 99.0% (Z) required secondary purification via pH-controlled recrystallization, increasing cycle time by 8 hours.

    Industrial Specification and Release Criteria

    Typical batch release parameters for 2-(2-aminothiazol-4-yl)-2-methoxyiminoacetic acid; test methods align with general chapters of Ph. Eur. and JP.
    ParameterAcceptance LimitTest Method
    AppearanceWhite to pale yellow crystalline powderVisual inspection (Ph. Eur. 2.2.1)
    Assay (anhydrous basis)98.0–102.0%HPLC (JP General Tests <2.01>, C18 column, 0.1% H₃PO₄/MeCN gradient)
    (Z)-Isomer ratio≥99.0%Normal-phase HPLC, Chiralpak IA, n-hexane/EtOH/TFA
    Water content≤0.5%Karl Fischer coulometric titration (Ph. Eur. 2.5.12)
    Residue on ignition≤0.10%Ph. Eur. 2.4.16, 600 ± 50 °C
    Heavy metals (as Pb)≤10 ppmPh. Eur. 2.4.8, Method A
    Palladium (Pd)≤5 ppmICP-MS, microwave digestion
    Residual solventsMethanol ≤3000 ppm, THF ≤720 ppmHeadspace GC-FID (Ph. Eur. 2.4.24, Class 2 solvents)
    Particle size (D90)≤200 µmLaser diffraction (ISO 13320:2020), dry dispersion

    The product is hygroscopic; a lot exposed to 60% relative humidity at 25 °C for 4 hours gained 0.3% water, elevating the end-of-drying cycle moisture in a 7-AVCA coupling charge beyond the critical threshold if not pre-dried. Consequently, bulk packaging employs double polyethylene liners inside fibre drums with desiccant pouches, and material is stored at 2–8 °C under nitrogen. Prior to charging, a vacuum drying step at 40 °C and ≤10 mbar for 6 hours reduces water content to ≤0.1% for moisture-sensitive acylation protocols.

    The compound is introduced directly into cephalosporin coupling chemistry without protection of the aminothiazole nitrogen, relying on the low nucleophilicity of the thiazole amine under the chosen reaction conditions. In a representative production-scale protocol, 52.0 kg (approximately 258 mol) of the acid is dissolved in 260 L of anhydrous N,N-dimethylacetamide (DMAc) at −5 °C under a nitrogen sweep. A slight molar excess of a carbodiimide coupling agent—typically dicyclohexylcarbodiimide (1.05 eq) or 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (1.1 eq when used with 0.1 eq of N-hydroxybenzotriazole)—activates the carboxyl group as the O-acylisourea or active ester. The resulting activated species is added over 45–60 minutes to a solution of the 7-amino cephem nucleus (e.g., 55.0 kg 7-AVCA, 239 mol) in DMAc/water (10/1 v/v) maintained at −5 to 0 °C and pH 7.5–8.0 by automated addition of 20% aqueous triethylamine. In-process HPLC monitoring (sampling every 15 minutes) tracks residual 7-AVCA; typical endpoint is reached at <2.0% unreacted nucleus. Under these conditions, the formation of the Δ3-isomer by-product is held below 0.8%, a critical quality attribute for cefixime manufacture. The isolated crude API after pH adjustment to 4.0 and filtration yields 85–88% of theory prior to recrystallization.

    If Residual Palladium Exceeds 10 ppm in API Synthesis

    The methoxyiminoacetic acid side chain is itself synthesized via a palladium-catalyzed route that may leave trace palladium in the bulk intermediate if the final recrystallization solvent (typically methanol/water 1:1) and charcoal treatment are not optimized. Palladium content above 5 ppm in the side chain correlates with Pd carryover into the crude cephalosporin API at levels exceeding the ICH Q3D (Guideline for Elemental Impurities) permitted daily exposure limit of 10 µg/day for oral administration. In one production campaign, a side-chain lot assaying 12 ppm Pd resulted in cefdinir crude containing 18 ppm Pd after a single crystallization. Reducing Pd to ≤2 ppm required an additional EDTA-chelation wash and two recrystallizations, raising solvent consumption by 40% and reducing overall yield by 5 percentage points. Therefore, the side-chain supplier’s specification tightened to ≤5 ppm Pd, enforced by inductively coupled plasma mass spectrometry (ICP-MS) analysis of every production batch according to Ph. Eur. 2.4.20. This limit eliminates the need for a dedicated metal scavenger step in downstream API manufacturing, which is incompatible with the acid-labile β-lactam ring.

    Comparative Reactivity Against Activated Ester and Protected Derivatives

    Key process attributes of different 2-(2-aminothiazol-4-yl)-2-methoxyiminoacetyl derivatives in cephalosporin acylation.
    Derivative FormActivation RequiredTypical Coupling Yield (crude)Critical Impurity ControlDeprotection Step
    Free acid (this product)In situ carbodiimide or mixed anhydride85–88%Moisture ≤0.1%, (Z)-isomer ratioNone
    Ethyl ester (CAS 60845-81-0)Saponification to acid prior to coupling80–84%*Ester hydrolysis by-productsAlkaline hydrolysis, 2 h
    1-Hydroxybenzotriazole (HOBt) active esterPre-formed isolated ester90–94%HOBt removal from waste streamNone
    N-Trityl-protected acidAcid deprotection, then coupling78–82%Triphenylmethanol removalFormic acid or HCl/dioxane deprotection

    *Based on overall two-step yield after ester hydrolysis and coupling.

    The free acid offers the shortest synthetic sequence and eliminates a deprotection step that contributes up to 15% of the total process mass intensity in routes employing the N-trityl-protected derivative. However, the acid requires stringent anhydrous conditions during activation to prevent hydrolysis of the O-acylisourea intermediate, which regenerates the starting acid and releases dicyclohexylurea. A comparison run in a 2000-L reactor using the free acid with 0.05% water achieved 87.2% yield, whereas intentionally spiking moisture to 0.5% dropped yield to 67% and produced a dicyclohexylurea partition coefficient requiring additional filtration on a 0.5 µm bag filter. By contrast, the pre-formed HOBt active ester tolerates moisture up to 0.3% with only 3% yield loss, but its commercial supply chain is less reliable and generates a hazardous waste stream containing benzotriazole, classified as a Substance of Very High Concern (SVHC) under REACH. Thus, for API manufacturers with in-house moisture control capability, the free acid remains the preferred intermediate.

    The solubility profile of 2-(2-aminothiazol-4-yl)-2-methoxyiminoacetic acid in common aprotic solvents also dictates reactor loading. At −5 °C, solubility in DMAc exceeds 200 g/L, permitting a reactant concentration of 1.0 M, but in acetonitrile the solubility drops below 50 g/L, forcing a larger solvent volume and longer distillation times during work-up. Manufacturers using a continuous processing set-up with a microreactor for activation (Corning Advanced-Flow G1, 0.45 mL internal volume) report residence times of 30 seconds at −10 °C for mixed anhydride formation with pivaloyl chloride, compared to 45 minutes in a semi-batch stirred-tank configuration. Published data for this specific microreactor configuration is limited, but early adoption suggests a yield improvement of 4–6% due to suppressed isomerization.

    The product differs from 2-(2-aminothiazol-4-yl)-2-methoxyiminoacetyl chloride hydrochloride, a reactive intermediate occasionally employed, in that the acid generates no corrosive hydrogen chloride upon activation, protecting stainless steel reactor components (316L) from chloride-induced pitting corrosion when process temperatures fluctuate between −10 °C and 25 °C. Avoid combination with strong amine bases like 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) prior to activation, as rapid deprotonation of the carboxylic acid leads to an insoluble ammonium salt that aggregates and resists re-dissolution, causing mass-transfer limitations in the acylation step.

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