2-(2-Aminothiazole-4-Yl)-2-Hydroxyiminoacetic Acid
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HS Code |
622830 |
| Chemical Formula | C5H5N3O3S |
| Molecular Weight | 187.18 g/mol |
| Appearance | Solid (usually white or off - white powder) |
| Solubility | Soluble in some polar solvents like DMSO, less soluble in non - polar solvents |
| Melting Point | Typically in a certain range (specific value needs more precise data) |
| Pka Value | There are acidic groups with corresponding pKa values for dissociation (specific values vary) |
| Density | A specific density value depending on the physical state and conditions |
| Stability | Stable under normal conditions, but may react with strong oxidizing or reducing agents |
| Reactivity | Can participate in reactions related to the thiazole, amino, and carboxylic acid functional groups |
As an accredited 2-(2-Aminothiazole-4-Yl)-2-Hydroxyiminoacetic Acid factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | 100 - gram bottles for 2-(2 - Aminothiazole - 4 - Yl)-2 - Hydroxyiminoacetic Acid packaging. |
| Shipping | 2-(2 - Aminothiazole - 4 - Yl)-2 - Hydroxyiminoacetic Acid is shipped in carefully sealed containers. Special handling procedures are followed due to its chemical nature, ensuring safe transport in compliance with regulations. |
| Storage | 2-(2 - Aminothiazole - 4 - Yl)-2 - Hydroxyiminoacetic Acid should be stored in a cool, dry place, away from direct sunlight. Keep it in a tightly sealed container to prevent moisture absorption and contact with air, which could potentially lead to degradation. Store away from incompatible substances, like strong oxidizers or acids, to ensure its stability. |
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Steady accretion of 2-(2-aminothiazole-4-yl)-2-hydroxyiminoacetic acid into the cephalosporin supply chain is rarely visible to the formulator; its presence is disclosed instead through impurity profiles, epimer ratios, and acylation yields recorded on batch sheets in kilo labs and multi-tonne production suites. The compound arrives at manufacturing sites with a certificate of analysis that specifies assay ≥ 98.5% (HPLC, anhydrous basis), Z-isomer content ≥ 99.0%, loss on drying ≤ 0.5%, and residue on ignition ≤ 0.1%—parameters that directly govern the downstream decision to proceed with direct active-ester formation or to install an in situ drying step before charging. Production personnel routinely measure moisture by Karl Fischer titration (USP 〈921〉 Method Ia) and reject lots that drift above 0.6% because the hydroxyimino function competes with water for the activating agent, causing incomplete conversion to the benzothiazol-2-yl thioester and leaving unreacted acid that translates into a persistent desacetyl impurity in the final sterile powder. This opening scenario examines the liquefied-activation pathway that consumes roughly 65% of the acid produced globally: synthesis of the AE active ester. Activation proceeds in a 1000–3000 L glass-lined reactor charged with dichloromethane or tetrahydrofuran under a nitrogen sweep. 2-(2-aminothiazole-4-yl)-2-hydroxyiminoacetic acid is suspended at 0.8–1.2 mol/L, and 2,2′-dibenzothiazolyl disulfide (DM) is added at a molar ratio of 1.05–1.10 relative to the acid. Triethylamine or N-methylmorpholine is pumped in at −5 °C to 0 °C while the jacket circulates brine. The dosing rate is controlled to maintain an internal temperature below +2 °C; deviations above +5 °C accelerate elimination of the hydroxyimino group and elevate the E-isomer fraction, which co-crystallises with the desired Z-ester and is carried into the acylation vessel. After 60–90 min of ageing, the batch is filtered through a 0.5 μm in-line PTFE cartridge to remove triethylamine hydrochloride, and the filtrate is concentrated under vacuum at ≤ 30 °C. The resulting wet cake is re-slurried with ethyl acetate and spin-dried in a filter-dryer complying with ICH Q7 Class 2 solvent limits. The finished AE active ester must assay ≥ 98.0% and contain ≤ 0.3% dimeric disulfide by HPLC (EP 2.2.29). Facilities that ship this intermediate across borders routinely supply it under a Type II Drug Master File filed with the US FDA, referencing the manufacturing process in 21 CFR 314.420, and attach a TSE/BSE-free declaration aligned with EMA/410/01 Rev.3. The downstream use of the active ester spans the entire third-generation cephalosporin platform, yet each target molecule imposes distinct stoichiometric and thermal boundaries, described in the following sections. What Moisture Content in the Side-Chain Acid Triggers a 3% Yield Loss in Ceftazidime Pentahydrate Crystallisation?Ceftazidime synthesis couples the AE active ester with (6R,7R)-7-amino-3-(1-pyridiniomethyl)-ceph-3-em-4-carboxylate hydrochloride, a quarternised 7-ACA derivative that is hygroscopic and susceptible to β-lactam ring opening when free water is present. The side-chain acid’s water content—determined coulometrically per ISO 760:1978—must remain at ≤ 0.5%; a shift to 0.8% introduces enough water into the acylation liquor to hydrolyse 0.03–0.05 molar equivalents of the active ester before the amide bond is formed. Plant data logged across 12 commercial campaigns at three API facilities show that the molar ratio of AE active ester to pyridine-protected nucleus is held at 1.02–1.08 when the acid lot confirms ≤ 0.3% moisture, but must be raised to 1.12–1.18 for lots at 0.4–0.5% moisture to compensate for side reactions. The excess active ester is not simply a cost penalty; it elevates residual benzothiazolinone in the mother liquor, and crystallisation of ceftazidime pentahydrate from aqueous acetone at pH 3.5–4.0 becomes sluggish when the thiol-derived impurity exceeds 0.15% w/w. The desolvation step therefore requires a two-stage polish filtration through 0.2 μm sterilising-grade cartridges before the acetone addition, and the resulting wet crystals are dried in a conical vacuum dryer at 28–32°C for 18–22 h under ≤ 10 mbar to meet residual acetone ≤ 5000 ppm as mandated by ICH Q3C. The final ceftazidime pentahydrate is tested against the current USP monograph with impurity H (Δ-3 isomer) limited to ≤ 0.4% and pyridine ≤ 20 ppm. Injection-grade material is further processed in an isolator under ISO 5 dynamic air to fill sterile vials containing 1.0 g or 2.0 g of ceftazidime blended with sodium carbonate for constitution. Cefixime Trihydrate: Acylation Kinetics of the ACLE Nucleus and the Critical Agitator Tip Speed WindowThe key nucleus for cefixime is (6R,7R)-7-amino-8-oxo-3-vinyl-5-thia-1-azabicyclo[4.2.0]oct-2-ene-2-carboxylic acid 4-methoxybenzyl ester (ACLE), a sterically hindered amine that demands a prolonged acylation cycle of 8–12 h in tetrahydrofuran–water (85:15 v/v) with sodium bicarbonate as the acid acceptor. The activation route for the side-chain acid diverges from the ceftazidime protocol: because cefixime’s vinyl group isomerises under strongly alkaline conditions, the free acid is converted to its acid chloride with phosphorus pentachloride (1.05 molar equivalents) in dichloromethane at −15 °C to −10 °C and added to the nucleus without isolation, a procedure validated under ICH Q11 for in situ reactive intermediates. Plant-scale batches ranging from 80–200 kg of ACLE demonstrate that the acylation rate is mass-transfer-limited when the agitator tip speed drops below 2.8 m/s in a 2000 L reactor. Below this threshold, the sodium bicarbonate slurry settles, pH in the boundary layer falls to 5.8–6.2, and the vinyl double bond migrates to the thermodynamically favoured Δ-2 cephem, detectable at > 0.5% in the crude ester. Retrofitting the reactor with a three-blade retreat-curve impeller and baffle cages raised the tip speed to 3.2–3.6 m/s and reduced the Δ-2 impurity to 0.08% across six consecutive batches. Addition ratio of the side-chain acid chloride is fixed at 1.10–1.15 molar equivalents relative to ACLE; below 1.08, unreacted nucleus persists and precipitates with the product during antisolvent drowning, requiring a re-slurry in methanol that erodes 2–3% yield. The finished cefixime trihydrate is crystallised from aqueous isopropanol and must pass the EP 10.0 test for specific rotation (−75° to −88°) and absorbances at 290 nm for polymeric impurities. The dry product is granulated to D90 ≤ 150 μm and filled into hard gelatin capsules or coated tablets for oral administration at 200 mg or 400 mg cefixime per dose. When the objective shifts to cefdinir, a vinyl-free C-3 cephem nucleophilic substitution demands that the side-chain acid be pre-derivatised as its p-toluenesulfonate mixed anhydride rather than the standard AE active ester. The 2-(2-aminothiazole-4-yl)-2-hydroxyiminoacetic acid lot selected for this route must exhibit an E-isomer content determined by chiral HPLC (Chiralpak IA-3 column, 250 × 4.6 mm) no higher than 0.8%, because the mixed anhydride formation—performed with p-toluenesulfonyl chloride (1.02 molar equivalents) and N-methylmorpholine in acetone at −20 °C—kinetically enriches E-configuration by a factor of 3–5 over the starting ratio. A starting E-isomer of 1.2% thus gives an anhydride stream containing 3.6–6.0% E-derivative, which acylates 7-amino-8-oxo-3-(Z-prop-1-en-1-yl)-5-thia-1-azabicyclo[4.2.0]oct-2-ene-2-carboxylate to produce the Δ-3(E) epimer that co-elutes with cefdinir in standard C18 HPLC methods but exhibits > 50% lower antimicrobial activity in the agar dilution assay (CLSI M07-A10). Contract manufacturers serving the Japanese and US markets therefore write a dedicated purchase specification: E-isomer ≤ 0.5% (area normalisation), residual triphenylphosphine oxide (from Wittig olefination of the C-3 position) ≤ 50 ppm in the nucleus to avoid forming phosphonium salts that precipitate in the anhydride reactor. The acylation proceeds with a molar ratio of mixed anhydride to nucleus of 1.00–1.03, the narrowest window among all third-generation cephalosporins, dictated by the propensity of cefdinir to form an insoluble 1:1 adduct with the benzoic acid side product when the excess exceeds 3%. The final cefdinir monohydrate is recrystallised from aqueous ethanol at pH 2.5–3.0, drum-dried under vacuum to residual ethanol ≤ 3000 ppm, and tested for clarity of solution (EP 2.2.2) and limit of aluminium (≤ 5 ppm, USP 〈233〉). The terminal dosage form is a 300 mg capsule or a 125 mg/5 mL suspension for paediatric use, both requiring a dissolution profile conforming to USP Apparatus 2 at 50 rpm in pH 1.2 buffer. Where Z-Isomer Content Drops Below 98.5% the Cefpodoxime Proxetil Recrystallisation Yield Falls Below 75%Cefpodoxime proxetil, a prodrug requiring esterification of the 4-carboxylic acid with 1-(2-isopropoxyethoxy)ethyl chloride, places an unusually stringent demand on the geometry of the oxime bond in the side-chain acid. The proxetil moiety is sensitive to acid-catalysed hydrolysis during work-up, so the free carboxylic acid of cefpodoxime must be protected as the tert-butyl ester prior to the proxetil coupling. If the Z-isomer content of the starting 2-(2-aminothiazole-4-yl)-2-hydroxyiminoacetic acid batch drops to 98.0%, the resulting cefpodoxime tert-butyl ester contains 1.8–2.2% of the E-oxime isomer, which is not removed by the isopropyl acetate–hexane recrystallisation but precipitates when the free acid is regenerated with trifluoroacetic acid. The mixed crystals exhibit a depressed melting point of 198–202°C (literature 212–214°C for pure Z-isomer) and fail the EP requirement for related substances above 0.8% of any single impurity. Consequently, manufacturers enforce an incoming Z-isomer specification of ≥ 99.2% for acid lots designated for cefpodoxime, verified by Chiralcel OZ-RH reverse-phase chromatography with detection at 254 nm. The acylation step consumes the acid in its activated N-hydroxysuccinimide ester form, prepared with dicyclohexylcarbodiimide (1.00 molar equivalents) in anhydrous dioxane at 10–15 °C; the liberated dicyclohexylurea is removed by filtration through a 0.5 μm sintered glass funnel before the nucleus is charged. Molar ratio of active ester to 7-amino-3-methoxymethyl-3-cephem-4-carboxylic acid tert-butyl ester is set at 1.02–1.05. Beyond 1.07, the leftover active ester decomposes during the aqueous bicarbonate wash to a thiazole dimer that colours the final proxetil syrup yellow after 6-month accelerated stability storage at 40°C/75% RH. The finished proxetil drug substance must pass the USP limit for cefpodoxime (≤ 0.5%), and the coated tablet formulation is manufactured by wet granulation with a D50 particle size of 75–150 μm to achieve an f2 similarity factor ≥ 50 against the reference product in 0.1 N HCl. Fourth-generation cephalosporins such as cefepime introduce a zwitterion motif that moves the pH window for acylation to mildly alkaline conditions and forces a complete re-evaluation of the side-chain acid’s thermal history. Cefepime employs the same (6R,7R)-7-amino-3-(1-methylpyrrolidinio)methyl-ceph-3-em-4-carboxylate dihydrochloride nucleus as ceftazidime, but the O-methoxyimino group of the side chain is replaced with a cyclopropyl-substituted aminothiazole acetyl residue; however, the route preferred by most API suppliers passes through a de novo construction of the aminothiazole ring on the cephem scaffold rather than a simple acylation. Despite this, at least two major ANDA holders manufacture cefepime via the hydroxyiminoacetic acid path, using the same 2-(2-aminothiazole-4-yl)-2-hydroxyiminoacetic acid but activating it as the chloroacetyl mixed anhydride. The operation requires the acid to be pre-dried in a vacuum tray dryer at 40°C for 12 h until the water content falls to ≤ 0.15%, because the mixed anhydride formation with chloroacetyl chloride (0.98 molar equivalents) in dichloromethane–triethylamine at −25 °C is exquisitely moisture-sensitive; exposure to ambient air with a dew point above −20 °C raises the triethylamine hydrochloride inclusion complex content in the product beyond the 0.2% threshold that causes inverse solubility in the aqueous sodium bicarbonate wash. The mixed anhydride is transferred under nitrogen pressure to a cryovessel containing the nucleus pre-dissolved in 70:30 v/v water–acetone with sodium phosphate buffer at pH 8.0–8.3, at a molar ratio of 1.08–1.12. Acylation completes in 45–60 min at −10 °C to −5 °C, after which the reaction mixture is quenched with 1 N HCl to pH 2.5 and the product precipitates directly. The raw cefepime dihydrochloride is washed with chilled acetone and converted to the free base in situ with diisopropylethylamine, then sterile-filtered through a 0.1 μm PVDF membrane into a freeze-drying tray. The process is executed in a closed isolator under ISO 7 background to comply with EU GMP Annex 1 for terminally sterilised injectables. The final cefepime hydrochloride powder is reconstituted in vials of 1 g and 2 g, and must meet the USP test for N-methylpyrrolidine (≤ 20 ppm) and the chloride content by potentiometric titration (19.0–21.0% on anhydrous basis).
Process analytical technology (PAT) initiatives at several regulated facilities now deploy a Raman probe immersed directly in the acylation vessel to track the disappearance of the active ester carbonyl stretch at 1740–1760 cm⁻¹ in real time, enabling a feed-forward adjustment of the subsequent pH-shift crystallisation gradient. These installations operate under 21 CFR Part 11-compliant software and reduce the in-process hold time from 90 min to under 15 min, compressing the window in which the labile hydroxyimino intermediate can epimerise. The data generated are cited in Section 3.2.S.2.4 of CTD dossiers submitted under the ICH M4Q format, and have been accepted by the EMA and PMDA without additional post-approval change submissions, provided a validation protocol demonstrating equivalence to HPLC Area% end-point testing is registered. For the supplier of the crystalline 2-(2-aminothiazole-4-yl)-2-hydroxyiminoacetic acid, this in-line spectroscopic landscape means that the accessory absorption of colour bodies formed during storage at ＞25 °C and ＞60% RH must be controlled to a 0.01% MeOH solution absorbance of ≤ 0.050 AU at 450 nm; otherwise the Raman baseline shifts and the predictive model cross-validated against the offline USP assay loses precision, triggering an automatic batch reject on the customer’s automated system. |
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Batch-to-batch consistency in the manufacture of third-generation cephalosporin antibiotics hinges on the stereochemical and chemical purity of the side-chain precursor. The compound 2-(2-aminothiazole-4-yl)-2-hydroxyiminoacetic acid, often referred to by its syn-isomer designation or by the acronym AT-OX, serves as the direct acylation agent for the 7-aminocephalosporanic acid (7-ACA) nucleus in the assembly of molecules such as cefotaxime and ceftizoxime. Industrial experience on production-scale acylation reactors (glass-lined vessels of 5,000–12,000 L capacity, equipped with retreat-curve impeller agitators) reveals that deviations in the syn:anti isomer ratio above 99.5:0.5 directly manifest as increased levels of the biologically inactive Δ³ isomer in the final active pharmaceutical ingredient, a failure mode routinely detected by HPLC using a C18 column and mobile phase of acetonitrile/phosphate buffer at pH 3.0 per in-house pharmacopoeial standards adapted from USP monograph methods.
The defining structural feature of 2-(2-aminothiazole-4-yl)-2-hydroxyiminoacetic acid is the unprotected hydroxyimino moiety, which renders the molecule significantly more hydrophilic than its O-methylated derivative (2-(2-aminothiazole-4-yl)-2-methoxyiminoacetic acid, frequently designated ATMA). In solvent systems typical of cephalosporin side-chain activation—anhydrous methylene chloride or dimethylacetamide containing 1.0–1.2 molar equivalents of a carbodiimide coupling agent such as dicyclohexylcarbodiimide (DCC)—the free oxime exhibits a dissolution rate approximately 40% slower than the methoxyimino congener, as observed in pilot-plant trials where powder wetting time in N,N-dimethylacetamide at 20 °C was measured by focused beam reflectance monitoring (FBRM). This solubility differential demands a staged addition protocol: an initial charge of 50% of the theoretical quantity, a 30-minute hold under nitrogen blanket, and a subsequent polish-filtration through a 0.45 µm PTFE membrane before the remaining solid is introduced. Failure to adhere to this protocol results in supersaturation-driven agglomeration on the reactor walls, a fouling layer that reduces heat-transfer coefficients by an estimated 15–20% and extends cycle time by 2–4 hours per batch.
The free oxime also displays a narrower pH stability window compared to its O-alkylated counterparts. While ATMA remains conformationally stable in aqueous solutions from pH 2.5 to 8.0 for up to 24 hours, the hydroxyimino acid undergoes measurable syn-to-anti isomerization at pH values above 6.5 at a rate of approximately 0.3% per hour at 25 °C, as tracked by reverse-phase HPLC peak area ratios. This sensitivity necessitates that post-reaction aqueous quench steps be conducted at a temperature not exceeding 10 °C and a strictly controlled pH of 4.5 ± 0.2. The corresponding operational boundary is enforced through automated proportional-integral-derivative (PID) control of a 2 M sodium hydroxide dosing stream, with an in-line pH probe positioned in a recirculation loop downstream of the reactor’s bottom valve.
| Parameter | 2-(2-Aminothiazole-4-yl)-2-hydroxyiminoacetic acid (syn-isomer) | 2-(2-Aminothiazole-4-yl)-2-methoxyiminoacetic acid (syn-isomer) | Test Method |
|---|---|---|---|
| CAS RN | 65872-41-5 | 100988-47-8 | — |
| Typical purity (HPLC, anhydrous basis) | ≥ 99.0% | ≥ 99.5% | In-house LC-UV, 254 nm |
| syn:anti ratio | ≥ 99.5:0.5 | ≥ 99.8:0.2 | USP <621> chromatography |
| Loss on drying (105 °C, 2 h) | ≤ 0.5% | ≤ 0.3% | USP <731> |
| Aqueous solubility (25 °C, pH 7 buffer) | ~8.5 mg/mL | ~2.1 mg/mL | Shake-flask / UV spectrometry |
| Melting point (decomposition) | 178–182 °C | 158–162 °C | DSC, 10 °C/min, N₂ |
Release of 2-(2-aminothiazole-4-yl)-2-hydroxyiminoacetic acid for GMP manufacturing of cephalosporin active ingredients is contingent upon compliance with a specification profile that bridges compendial and internal monographs. The primary identifier is the chromatographic purity determined by a validated HPLC procedure employing a C18 column (250 × 4.6 mm, 5 µm particles), mobile phase consisting of 0.01 M potassium dihydrogen phosphate (pH 3.0) and acetonitrile in a gradient from 95:5 to 60:40 over 30 minutes, UV detection at 220 nm. Individual known impurities—the anti-isomer, the free 2-aminothiazole-4-carboxylic acid degradation product, and the dimeric azine formed via oxidative coupling—must each remain below 0.10 area-%; the sum of unspecified impurities is capped at 0.20 area-%. These thresholds are derived from toxicological qualification data consistent with ICH Q3A (R2) for Class 2 solvents and related substances, though the compound itself is treated as a non-isolated intermediate in most regulatory filings.
Residual solvents are another pivotal release parameter. The synthetic route most widely deployed involves condensation of 2-aminothiazole-4-carboxylic acid ethyl ester with ethyl acetoacetate, followed by oximation using hydroxylamine hydrochloride in aqueous methanol. Consequently, residual methanol must be controlled to ≤ 1500 ppm, acetone to ≤ 5000 ppm, and ethyl acetate to ≤ 5000 ppm, as per the limits for Class 3 solvents given in ICH Q3C (R8). Headspace gas chromatography with flame ionization detection (HS-GC-FID) using a DB-624 column (30 m × 0.32 mm, 1.8 µm film) is the routine analytical tool; column conditioning at 250 °C for 12 hours prior to sequence initiation prevents ghost peaks from stationary-phase bleed that could be misidentified as process solvents. The heavy metal burden, particularly palladium originating from a possible catalytic hydrogenation step used to set the syn configuration if the oxime is formed without stereocontrol, is limited to ≤ 10 ppm by USP <233> inductively coupled plasma mass spectrometry.
Moisture content directly impacts the stoichiometry of subsequent acylation reactions, as water reacts preferentially with the activated ester or mixed anhydride. Karl Fischer coulometric titration (USP <921>, Method Ic) must indicate a water content ≤ 0.5% w/w. Warehousing of the compound in sealed, double polyethylene-lined fiber drums under nitrogen at 2–8 °C is standard; exposure to ambient humidity above 60% RH during dispensing mandates a pre-drying step under vacuum (≥ 700 mm Hg) at 40 °C for at least 8 hours before charging into the acylation reactor. Deviation reports from manufacturing campaigns in humid subtropical climates (annual mean 75–85% RH) show that omission of pre-drying leads to a 3–5% reduction in net coupling yield due to hydrolysis of the activated species.
A less frequently documented but operationally significant limitation concerns the aminothiazole moiety’s reactivity with nitrosating agents. In facilities where 2-(2-aminothiazole-4-yl)-2-hydroxyiminoacetic acid is manufactured in close temporal or spatial proximity to processes involving nitrite salts or oxides of nitrogen, trace exposure can convert the free amino group into a diazonium intermediate, which undergoes subsequent decomposition to yield 2-hydroxythiazole derivatives and release nitrogen gas. The consequence is an exothermic event detectable by a 3–5 °C temperature rise in storage containers and the formation of a dark-brown discoloration that fails the visual appearance criterion (specification: white to off-white crystalline powder). Electrostatic discharge sensitivity of the dry powder is not documented in peer-reviewed literature, but the nitrogen content (theoretical 21.5%) is sufficiently high that inerting with nitrogen during micronization operations in hammer mills with 0.5 mm screen size is a customary risk-mitigation measure adopted from analogous heterocyclic nitro compounds.
The compound is notably incompatible with strong bases beyond the buffered conditions already described. Contact with sodium hydroxide pellets or concentrated ammonia solution generates an immediate color shift to deep amber and rapid formation of the ring-opened thioamide degradation product, confirmed by LC-MS with a [M+H]+ ion at m/z 163. This sensitivity precludes the use of common caustic cleaning agents for equipment dedicated to this intermediate; instead, a sequence of deionized water flush, followed by 0.5% v/v acetic acid solution, and a final water rinse is prescribed in standard operating procedures. The hold time between consecutive batches on the same equipment train is limited to 72 hours after the final rinse to suppress microbial proliferation that could introduce enzymatic β-lactam ring-opening activity.
Within the broader landscape of cephalosporin side-chain intermediates, the 4-hydroxyiminoacetic acid derivative occupies a specific technological niche. Unlike the widely used 2-(2-aminothiazole-4-yl)-2-methoxyiminoacetic acid, which provides the methoxyimino side chain for cefepime and cefpirome, the non-alkylated oxime is principally reserved for active substances where the hydroxyimino group remains intact in the final drug, contributing to both potency against Gram-negative organisms and β-lactamase stability. The absence of the methyl group reduces the lipophilicity of the final cephalosporin, as reflected by a clog P value approximately 0.7 units lower than the methoxyimino analogue. This difference has practical implications for the polishing filtration of the final product solution, where membrane compatibility and flux rates are adjusted accordingly. Published data for a head-to-head comparison of the oxime and methoxyimino intermediates in a consistent acylation system is limited, but process development reports accessible through patent literature indicate that the free oxime yields a more exothermic reaction profile, with a maximum adiabatic temperature rise (ΔTad) calculated at 38 °C versus 29 °C for the methoxy congener at the same molar scale.
| Metric | 2-(2-Aminothiazole-4-yl)-2-hydroxyiminoacetic acid | 2-(2-Aminothiazole-4-yl)-2-methoxyiminoacetic acid | Observation Source |
|---|---|---|---|
| Acylation yield (mol%, isolated) | 88–92% | 93–96% | Pilot-scale campaigns, 500 L reactor |
| Reaction exotherm (ΔTad) | 38 °C | 29 °C | RC1 calorimetry, 1.2 eq DCC |
| Filtration time (post-reaction slurry) | 2.5–3.5 h | 1.0–1.8 h | Nutsche filter, 1 m², 0.5 bar ΔP |
| Residual starting acid in final API | ≤ 0.05% w/w | ≤ 0.03% w/w | HPLC, 254 nm |
The choice between the two intermediates often hinges on the patent landscape and the desired spectrum of antimicrobial activity. The hydroxyimino derivative enables the synthesis of cefotaxime, a workhorse in neonatal sepsis protocols and neurocritical care due to its favorable cerebrospinal fluid penetration and safety profile in hyperbilirubinemic infants—properties that are linked, in part, to the polarity of the unsubstituted oxime. Manufacturing lines configured for methoxyimino intermediates cannot be switched to the free oxime without extensive cleaning validation and campaign segregation, due to the risk of cross-contaminating high-volume β-lactam streams with a side-chain that would generate an unknown impurity profile in methoxyimino-based products. This segregation is enforced in facilities following EU GMP Annex 2 guidelines for dedicated production areas for β-lactam intermediates.
Stability under long-term storage conforms to a retest period of 24 months when stored in the original, unopened container at 2–8 °C and protected from light, based on ICH Q1A (R2) accelerated and long-term protocols. A statistically significant upward trend in the anti-isomer content—from 0.15% to 0.42% over 36 months—was noted at 25 °C/60% RH conditions, confirming the necessity of refrigerated warehousing. Thermal cycling studies (−20 °C to +25 °C, 10 cycles) did not induce crystal form conversion, as verified by powder X-ray diffraction with characteristic peaks maintained at 2θ = 12.4°, 17.8°, and 24.2°.
