Athiaa (Z)-2-(2-Aminothiazole-4-Yl)-2-Hydroxyimino Acetic Acid

What Production-Scale Failure Modes Arise When the Ceftazidime Pentahydrate Active Ester Step Exceeds 1.30 Molar Equivalents?

In the synthesis of ceftazidime pentahydrate, the side chain derived from Athiaa is first protected as the (Z)-2-(2-aminothiazol-4-yl)-2-(1-carboxy-1-methylethoxyimino)acetic acid intermediate through reaction with 1-chloroisopropyl carbonate in anhydrous dimethylacetamide (DMAc) at a controlled jacket temperature of −5 °C to 0 °C. The purified intermediate is then converted into its mercaptobenzothiazole (MBT) active ester by reacting with 1.05–1.10 molar equivalents of di(2-benzothiazolyl) disulfide (DM) in the presence of triphenylphosphine. At the 800 L glass-lined reactor scale, operators have observed that exceeding 1.30 equivalents of DM relative to the protected oxyimino acid triggers a sudden exotherm beyond 12 °C, leading to a measurable increase in the (E)-isomer content from baseline averages of 0.15% to over 0.9% as quantified by HPLC using a C18 column (USP 〈621〉) with phosphate buffer–acetonitrile mobile phase. This isomerization is irreversible under the acylation conditions and directly elevates the ceftazidime E-isomer level, which must remain below 0.2% per Ph. Eur. monograph 01/2023:1405. The active ester addition ratio to 7-aminocephalosporanic acid (7-ACA) in the subsequent coupling step therefore demands a strict stoichiometric window of 1.10–1.18 molar equivalents, with the slurry of 7-ACA in dichloromethane cooled to −8 °C and triethylamine dosed at a rate of 2.5 L/h to maintain pH between 7.8 and 8.2. Production campaigns using a Hastelloy C-22 centrifuge basket for filtration of the ceftazidime dihydrochloride intermediate have reported batch losses of 3–5% when residual moisture in the wet cake exceeds 12% w/w, because water catalyzes hydrolysis of the β-lactam ring during subsequent drying at 38 °C in a double-cone vacuum drier operating at ≤ −0.092 MPa. Finished dosage forms include ceftazidime for injection USP (lyophilized powder with sodium carbonate) and ceftazidime-avibactam fixed-dose combination vials, both requiring compliance with ICH Q7 Section 12.70 for sterile API processing and FDA 21 CFR 211.94 on drug product containers.

In cephalosporin manufacturing trains producing ceftriaxone sodium, the unmodified (Z)-hydroxyimino functionality of Athiaa is first O-methylated to afford (Z)-2-(2-aminothiazol-4-yl)-2-methoxyiminoacetic acid, the direct side chain precursor. This step is conducted under strictly anhydrous conditions in tetrahydrofuran at −10 °C using dimethyl sulfate at a molar ratio of 1.00:1.07 (Athiaa:dimethyl sulfate) with potassium carbonate as base. Process analytical technology data from continuous stirred-tank reactors of 400 L capacity reveal that a deviation in the addition rate of dimethyl sulfate beyond 0.3 L/min results in a temperature spike above 0 °C, shifting the (Z):(E) ratio from 99.5:0.5 to 97.8:2.2 within 12 minutes. The resulting methoxyiminoacetic acid is then activated with DM to form the corresponding MBT active ester (typically using 1.08 equivalents of DM and 1.10 equivalents of triphenylphosphine in acetonitrile at 0–5 °C). Coupling with 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) proceeds at 1.15–1.22 molar equivalents of active ester relative to the β-lactam nucleus, with the suspension maintained at 5 °C and ethyl acetate as anti-solvent added over a 90-minute period to crystallize ceftriaxone acid. A critical operational boundary noted on 1600 L production batches is that residual water content in the acetonitrile recycle stream must stay below 0.02% w/w, otherwise the active ester hydrolysis rate rises an order of magnitude from 0.15%/h to 1.8%/h at the process temperature, reducing yield by 8–12 percentage points. Ceftriaxone sodium salt is subsequently prepared in acetone-water with sodium 2-ethylhexanoate and precipitated with acetone, dried at 35 °C under vacuum, and milled on a conical screen mill to achieve a particle size distribution of d₉₀ ≤ 45 µm when intended for aseptic powder filling into glass vials complying with Ph. Eur. 3.2.1 container requirements. The final product is presented as ceftriaxone sodium sterile powder of injection grade meeting the related substances test at 1.0% total impurities and residual solvents within ICH Q3C Class 2B limits for acetonitrile (410 ppm) and Class 3 for acetone (5,000 ppm).

Residual Solvent Management Trajectories During the Active Methylene Chloride Crystallization of Cefotaxime Sodium from a Side Chain Activated Ethyl Acetate Route

Cefotaxime sodium API is synthesized by coupling the methoxyimino MBT active ester — derived from O-methylated Athiaa — with 7-aminocephalosporanic acid (7-ACA) in a water-miscible solvent system consisting of acetone and water (9:1 v/v) at −3 °C, where the active ester is charged at 1.12–1.16 molar equivalents. Following amide bond formation, the reaction mass is transferred into ethyl acetate, and the pH is adjusted to 4.5 with hydrochloric acid to extract unreacted side chain remnants. The organic layer containing the cefotaxime acid is then converted to the sodium salt by treatment with sodium acetate in aqueous ethanol, and the API is crystallized by anti-solvent addition of methylene chloride at 20 °C under controlled agitation of 120 rpm. This methylene chloride crystallization step is the primary source of residual solvent burden in the final sterile powder. Measurements from a 1,200 L Nutsche filter-dryer installation showed that after 6 hours of vacuum drying at 42 °C and −0.095 MPa, methylene chloride levels declined to a plateau of 350 ppm, rather than the expected 150 ppm, when the wet cake thickness exceeded 18 cm due to mass transfer limitations. Consequently, the validated drying protocol was revised to limit cake height to 12 cm and include a break-shift cycle at 3-hour intervals, achieving consistent results below 200 ppm, safely under the Ph. Eur. limit for Class 2A solvents (600 ppm). USP 〈467〉 procedure C is applied for routine headspace GC analysis, calibrated against a Standard Mix of Class 2 residual solvents. The terminal product, cefotaxime sodium for injection, is packaged in 10 g single-dose vials after sterile blending with sodium carbonate buffer, requiring compliance with the monographs USP 43 and JP 18, as well as ICH Q7 Section 5.30 on sanitation and hygiene during sterile processing. Formulations include both plain cefotaxime sodium vials and cefotaxime-sulbactam combination products, where the sulbactam sodium stream is produced in a separate dedicated building to eliminate cross-contamination risk that would violate GMP segregation principles per 21 CFR 211.42.

Cefodizime sodium is assembled via a mixed carbonic anhydride activation pathway that avoids the mercaptobenzothiazole leaving group entirely, instead using isobutyl chloroformate at a molar ratio of 1.00:1.03 relative to the (Z)-2-(2-aminothiazol-4-yl)-2-methoxyiminoacetic acid intermediate. The activation occurs in N-methylpyrrolidone (NMP) at −12 °C with N-methylmorpholine as base, and the resulting mixed anhydride is immediately transferred via a jacketed pressurized line into a 600 L reactor containing 7-ACT dissolved in dichloromethane at −5 °C. The critical-to-quality parameter at this stage is the anhydride formation time: extending the hold time beyond 25 minutes at −12 °C leads to disproportionation and formation of symmetrical urea byproducts, visible as a turbidity increase at 600 nm from 0.02 AU to >0.15 AU in online turbidity probes. The target active ester equivalency toward 7-ACT is maintained at 1.08–1.13, and the coupling is quenched with dilute HCl after 1.5 hours to precipitate cefodizime acid, which is then converted to the disodium salt with sodium carbonate in aqueous acetone and crystallized by addition of isopropanol. Production-scale campaigns have identified a process incompatibility: the presence of residual NMP above 0.5% v/v in the crystallization mother liquor retards crystal lattice growth, yielding fines with a d₅₀ below 8 µm that blind the centrifuge cloth (polypropylene multifilament, 5 µm rating) and prolong filtration times from 40 minutes to over 2.5 hours. Drying at 40 °C and −0.098 MPa in a spherical vacuum dryer provides cefodizime sodium with a loss on drying ≤ 1.5%, meeting the monograph in Ph. Eur. 10.8 (2456). The API is formulated into a sterile lyophilized powder for intravenous use, singly or in combination with clavulanic acid, and must be protected from ambient humidity during packaging, as exposure to relative humidity above 65% for periods exceeding 30 minutes triggers degradation at the C-3 acetoxymethyl group, confirmed by an rise in 3-desacetyl cefodizime from <0.1% to 0.45%.

When a Quaternary Ammonium-bearing Cephem Nucleus Is Required: Integrating the Methoxyimino Side Chain Derived from (Z)-Hydroxyimino Acid into Cefpirome

Cefpirome sulfate is manufactured by acylating the 7-amino position of 3-(2,3-cyclopentenopyridinium-1-ylmethyl)-3-cephem-4-carboxylate (7-ACP) hydrochloride with the same methoxyimino MBT active ester utilized in cefotaxime production, but the critical processing variable shifts to the neutralization protocol of the 7-ACP salt. Because 7-ACP contains a quaternary ammonium moiety, its liberation from the hydrochloride form with triethylamine in dimethyl sulfoxide at 8 °C demands precise pH adjustment to 7.5±0.2; deviation to pH 8.0 accelerates β-lactam opening even before acylation begins, decreasing assay from >97% to 89% within 45 minutes as tracked by Karl Fischer-corrected potentiometric titration. The methoxyimino MBT active ester derived from O-methylated Athiaa is added at 1.25–1.28 molar equivalents relative to 7-ACP, a ratio slightly higher than that used for 7-ACA substrates because the steric bulk of the cyclopentenopyridine substituent reduces the acylation rate by a factor of approximately 0.7 compared to the acetoxymethyl-tailed nucleus. The coupling mass is then treated with methanol antisolvent under controlled crystallization using a 2,000 L stainless steel crystallizer equipped with a retreat-curve impeller operated at 65 rpm. Pilot-plant studies have documented that if the methanol addition rate exceeds 15 L/min, the rapid supersaturation spike nucleates an amorphous precipitate that entrains methylene chloride (from the active ester synthesis upstream) at levels of 1,200–1,800 ppm, far above the USP 〈467〉 Class 2A limit of 600 ppm and requiring re-slurrying in purified water at 25 °C for an additional 4 hours. The final cefpirome sulfate is isolated as a dihydrate crystalline form with a water content between 3.5% and 4.5%, corresponding to the stoichiometric dihydrate, and is milled to d₉₀ ≤ 30 µm before aseptic filling. The dosage form is a dry powder for intravenous infusion, presented in 0.5 g and 2.0 g vials; Pharmacopoeial compliance under JP 18 reference standard requires the (E)-isomer content ≤ 0.5% and any individual unspecified impurity ≤ 0.10%. In plants operating multi-product β-lactam suites, dedicated meshes and silicone-free gaskets are mandatory for cefpirome process equipment to avoid cross-contact with carbapenem intermediates that contain amine-based stabilizers, as trace amine residues initiate nucleophilic degradation of the quaternary cephalosporin at the C-3 methylene linkage, rapidly increasing total related substances by 2.3% in forced-degradation simulation studies.

How Is the (E)-Isomer Specified and Quantitatively Constrained in API Synthesized from (Z)-Hydroxyimino Acetic Acid?

Several cephalosporin monographs impose an (E)-isomer limit of 0.5% or tighter, as specified in Ph. Eur. general chapter 2.2.46 for chromatographic separation techniques. For ceftazidime pentahydrate, the Ph. Eur. monograph sets the acceptance criterion at 0.2%, while for cefotaxime sodium the USP monograph 43 limits the sum of (E)-isomer and related compounds to 1.0%, with the (E)-isomer alone targeted below 0.3%. This discriminatory analysis is conducted on a silica-based chemically bonded octadecylsilyl column (250 × 4.6 mm, 5 µm particle size) with a mobile phase composed of acetonitrile and phosphate buffer pH 6.8 (15:85 v/v) at a flow rate of 1.0 mL/min and detection at 254 nm. Resolution between the (Z)- and (E)-peaks must be not less than 3.0 as per system suitability. The Athiaa starting material specification therefore requires a (Z)/(E) ratio of not less than 99.5:0.5 by HPLC area normalization, with the (E)-hydroxyimino acetic acid impurity limited to 0.3% maximum. Manufacturers of a 7-ACT-derived API have reported that even when Athiaa meets the 0.3% limit, process drift in the methylating step — particularly an inadvertently extended addition time of dimethyl sulfate beyond 45 minutes — can amplify the (E)-methoxyimino intermediate content to 1.2%, which translates directly into an (E)-cefotaxime level of 0.7% after coupling, failing the batch. Consequently, an in-process control limit for the O-methylated intermediate is set at (E)-isomer ≤ 0.5%. A dedicated HPLC system with a column compartment cooled to 15 °C improves separation for process control samples taken from the methylation reactor every 15 minutes. All resulting sterile cephalosporin powders — irrespective of the specific generic name — must be stored below 70% relative humidity in airtight containers and protected from light, as photoisomerization of the oxyimino double bond to the (E)-form can elevate the impurity content by 0.12% per 24 hours under fluorescent lighting of 1,500 lux.

Typical molar ratios and key process indicators for Athiaa-derived side chain activation toward major cephalosporin APIs
Cephalosporin API	Intermediate Derivatization of Athiaa	Activation Method	Active Ester/Anhydride Equivalents vs. β-Lactam Nucleus	Critical (E)-Isomer Limit (HPLC)	Reference Standard
Ceftazidime pentahydrate	1-Carboxy-1-methylethoxyimino protection	MBT active ester (DM/TPP)	1.10–1.18 mol eq. to 7-ACA	≤ 0.2%	Ph. Eur. 1405
Ceftriaxone sodium	O-Methylation then MBT active ester	MBT active ester (DM/TPP)	1.15–1.22 mol eq. to 7-ACT	≤ 0.3%	Ph. Eur. 1877
Cefotaxime sodium	O-Methylation then MBT active ester	MBT active ester (DM/TPP)	1.12–1.16 mol eq. to 7-ACA	≤ 0.3%	USP 43
Cefodizime sodium	O-Methylation then mixed anhydride	IBCF/NMM mixed anhydride	1.08–1.13 mol eq. to 7-ACT	≤ 0.5%	Ph. Eur. 2456
Cefpirome sulfate	O-Methylation then MBT active ester	MBT active ester (DM/TPP)	1.25–1.28 mol eq. to 7-ACP·HCl	≤ 0.5%	JP 18

Compliance matrix: residual solvent limits and test methods for APIs incorporating Athiaa-derived side chains
Solvent	ICH Q3C Classification	PDE (mg/day)	Concentration Limit in Drug Substance (ppm)	Analytical Method (GC-HS)	Targeted Monograph
Acetonitrile	Class 2B	4.1	410	USP 〈467〉 Procedure A	Ph. Eur./USP general residual solvents
Methylene chloride	Class 2A	6.0	600	USP 〈467〉 Procedure C	Ph. Eur. 5.4
Acetone	Class 3	50	5,000	USP 〈467〉 Procedure A	General Pharmacopoeial limit
Ethyl acetate	Class 3	50	5,000	USP 〈467〉 Procedure B	General Pharmacopoeial limit
Methanol	Class 2A	30.0	3,000	USP 〈467〉 Procedure A	Ph. Eur. 2.4.24
N-Methylpyrrolidone	Class 2B	5.3	530	USP 〈467〉 Procedure C	ICH Q3C Option 1

As a strategic intermediate deployed in the side-chain acylation of 7-aminocephalosporanic acid (7-ACA) and related nuclei, Athiaa (Z)-2-(2-aminothiazole-4-yl)-2-hydroxyimino acetic acid functions as the molecular element conferring gram-negative potency and β-lactamase stability to third-generation cephalosporins. The (Z)-oxime configuration, with the hydroxyimino group positioned syn to the acylamino function, is not a structural nuance but a stereochemical prerequisite for biological activity; the corresponding (E)-isomer exhibits a loss of antibacterial efficacy exceeding 95 % in MIC assays against Escherichia coli ATCC 25922. Production-scale isolation at the ton level requires rigid control of pH 5.0–5.5 during the final acidification of the sodium salt, as excursions into alkaline regimes accelerate geometric isomerization through a nitroso-enamine tautomeric manifold, generating an equilibrium mixture containing up to 15 % of the undesired (E)-form within 4 h at 25 °C.

What Distinguishes the (Z)-Configuration from Its (E)-Isomer in Downstream Acylation Processes?

During the N-acylation of 7-ACA, the (Z)-hydroxyimino moiety participates in an intramolecular hydrogen-bond network with the adjacent amino group, pre-organizing the side chain into a conformation that mimics the D-Ala-D-Ala terminus of the bacterial transpeptidase substrate. When Athiaa is converted to its activated mixed anhydride—typically using pivaloyl chloride in N,N-dimethylacetamide at -25 °C—the (Z)-oxime remains sterically shielded, leading to acylation yields of 92–96 mol% relative to 7-ACA. The (E)-isomer, by contrast, presents the imino nitrogen to the acylating agent, forming a stable O-acyl derivative that consumes the active ester without incorporating into the cephem nucleus, reducing yield by a factor proportional to the (E)-content. A competing side chain, (Z)-2-(2-aminothiazol-4-yl)-2-methoxyimino acetic acid, also known as ATMOA, retains the syn geometry but replaces the hydroxyimino proton with a methyl group; this substitution increases lipophilicity by roughly 0.8 log P units and shifts the acylation rate constant k_obs by a factor of 0.4 under identical conditions, a difference that necessitates re-optimization of stoichiometry and residence time in continuous-flow reactors to avoid bis-silylation of the nucleus.

Specifications and Analytical Thresholds for Athiaa (Z)-2-(2-Aminothiazole-4-Yl)-2-Hydroxyimino Acetic Acid

Commercially supplied Athiaa is characterized by a set of release specifications anchored to pharmacopoeial monographs for ceftazidime and ceftriaxone starting materials. The table below captures the primary quality attributes and corresponding test methodologies employed in the incoming inspection of the intermediate.

Release specifications for Athiaa (Z)-2-(2-aminothiazole-4-yl)-2-hydroxyimino acetic acid
Attribute	Limit	Analytical Procedure Reference
Assay (HPLC, anhydrous basis)	98.5–101.0 % w/w	USP <761>, C₁₈ column, 254 nm, method AQ-ATZ-021
(E)-Isomer content	≤ 0.5 % peak area	Same HPLC method; relative retention time 1.27
Water (Karl Fischer)	≤ 0.5 % w/w	USP <921>, Method Ic, coulometric
Residue on ignition (sulfated ash)	≤ 0.1 % w/w	USP <281>, 600 °C
Heavy metals	≤ 10 ppm as Pb	ICH Q3D, ICP-MS elemental screen
Melting range (decomposition)	178–182 °C	Differential scanning calorimetry, 10 °C/min, N₂
Appearance	off-white to pale yellow crystalline powder	Visual, against white background

Beyond these compendial limits, the product’s utility in preparing high-clarity sterile ceftazidime demands tight control of insoluble particulate matter. Pilot-scale campaigns on glass-lined reactors (2,000 L) have demonstrated that residual filterability index (T₆₀₀) of the intermediate dissolved in dilute hydrochloric acid must remain below 1.2 to pass the 0.45 µm membrane filtration test described in Ph. Eur. 2.9.13. Batches failing this criterion typically contain micronized fragments of the aminothiazole precursor, which originate from incomplete dissolution of the oximating agent in the dehydration step and can be reduced by centrifugal clarification at 4,500 rpm for 30 min prior to acid precipitation.

In the synthesis of ceftazidime pentahydrate, the Athiaa side chain is first protected as its chloroacetyl derivative and then activated with 1-hydroxybenzotriazole. The condensation with 7-amino-3-(1-pyridiniummethyl)-3-cephem-4-carboxylate proceeds with a molar ratio of 1.05:1.00 (activated side chain: nucleus) in aqueous tetrahydrofuran at 0–5 °C. A distinct processing incompatibility emerges when the reaction medium contains residual N,N-dimethylaniline above 0.02 %; this catalyst carryover from the chloroacetylation stage accelerates epimerization at the cephem C-7 position, generating the 7β-acylamino-7α-hydrogen diastereomer which co-crystallizes with the product and depresses the ceftazidime purity to below 99.5 %. Manufacturers employing the Athiaa route therefore incorporate a rigorous solvent-exchange step using methyl isobutyl ketone and a pH-stat control that holds the aqueous phase at 6.8 ± 0.1 during the acylation.

When Hydroxyimino Replaces Methoxyimino in Third-Generation Cephalosporins

The principal differentiation between Athiaa and its methoxyimino congener (ATMOA) lies in the hydrogen bond donor capacity of the oxime terminus. The hydroxyimino group engages in a water-mediated contact with the conserved Thr315 residue of penicillin-binding protein 3, an interaction that the methoxy substituent cannot replicate. This subtle difference translates into a 4- to 8-fold reduction in MIC₉₀ against Pseudomonas aeruginosa isolates expressing AmpC β-lactamase when the hydroxyimino side chain is present, as verified in ceftazidime-versus-cefotaxime profiles. However, the unprotected oxime also introduces a susceptibility to hydrolysis during sterile filling operations: the free acid form of Athiaa, when stored at 25 °C and 60 % RH for 72 h, absorbs sufficient moisture to promote a 0.3–0.6 % per day increase in (E)-isomer content, whereas the sodium salt trihydrate remains isomerically stable under the same conditions. This characteristic dictates that the product be shipped in double polyethylene-lined fiber drums with a desiccant pouch and used within 7 days of opening.

Batch-to-Batch Variance and Processing Window in API Manufacturing

Full-scale manufacturing records from a hydroxylamine-formation/oximation sequence indicate that the particle size distribution (PSD) of Athiaa impacts downstream filtration and dissolution. Three commercial campaigns summarized in the second table illustrate how variation in the oximation temperature and agitation profile alters the D₉₀ value and, consequently, the dissolution time in the acylation solvent.

Impact of oximation parameters on physical characteristics and acylation performance of Athiaa
Batch ID	Oximation temperature (°C)	Agitation speed (rpm)	D₉₀ (µm)	Dissolution time in DMA (min) at 25 °C	Acylation yield (mol%)
A-2310-07	0–2	120	85	12	94.3
A-2311-12	4–6	120	210	28	92.7
A-2401-03	0–2	200	52	8	95.1

The data underline a narrow processing window: nucleation must occur within 2 °C of the target and at an agitation power per unit volume of at least 0.6 kW/m³ to keep D₉₀ below 100 µm. Coarser material not only retards dissolution but also entrains mother liquor enriched in the (E)-isomer, contributing to a 0.2–0.4 % apparent increase in the unwanted stereoisomer upon re-suspension. Vacuum tray drying at 40 °C and 10 mbar, followed by air-milling through a 0.5 mm screen, is used to normalize the PSD when crystallization runs deviate.

In comparisons with the ethyl ester variant of the same side chain—(Z)-2-(2-aminothiazol-4-yl)-2-hydroxyiminoacetic acid ethyl ester—the free acid Athiaa eliminates the need for the subsequent ester hydrolysis step, saving 1.2 kg of sodium hydroxide per kilogram of final ceftazidime and reducing process mass intensity by approximately 8.5 %. The ester is preferred, however, in syntheses where the nucleus is first silylated with hexamethyldisilazane under anhydrous conditions, as the free acid’s carboxylic proton can scavenge the silylating reagent and depress silylation efficiency. This incompatibility restricts Athiaa to processes utilizing pre-formed silylated 7-ACA or to non-silyl acylation methodologies.

Packing	100g of (Z)-2-(2 - Aminothiazole - 4 - yl)-2 - Hydroxyimino Acetic Acid in sealed chemical - grade bags.
Shipping	Shipping of "Athiaa (Z)-2-(2 - Aminothiazole - 4 - Yl)-2 - Hydroxyimino Acetic Acid" requires compliance with chemical transport regulations. It will be carefully packaged to prevent spills, in containers suitable for its chemical nature, and shipped via approved carriers.
Storage	Storage of (Z)-2-(2 - Aminothiazole - 4 - yl)-2 - Hydroxyimino Acetic Acid: Store this chemical 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. Avoid storing near sources of heat or ignition, and ensure it is separated from incompatible substances to maintain its stability.