Ataa 2-(2-Aminothiazole-4-Yl) Acetic Acid

How Ceftazidime Side-Chain Acid Demands Strict Water Content Control During ATA Oximation

In the manufacture of the ceftazidime side-chain acid, (Z)-2-(2-aminothiazol-4-yl)-2-(1-carboxy-1-methylethoxyimino)acetic acid, 2-(2-aminothiazol-4-yl)acetic acid (ATA) undergoes sequential esterification, diazotization, hydrolysis, and a water-sensitive oximation. The ATA charge is first converted to ethyl 2-(2-aminothiazol-4-yl)acetate hydrochloride using anhydrous ethanol and thionyl chloride at 1.2 eq in a 2000 L glass-lined reactor with jacket control maintaining −5 °C to 0 °C. Following solvent displacement, the hydrochloride salt is diazotized with 1.05 eq of sodium nitrite at −3 °C ± 2 °C. Process control relies on online FTIR monitoring of the diazonium peak at 2280 cm⁻¹; deviation exceeding ±0.05 AU triggers automatic termination. The isolated diazonium intermediate must register a moisture content below 0.2 % w/w by Karl Fischer titration in accordance with ASTM D6304, because water ingress above this threshold promotes untimely hydrolysis and generates azo-tar impurities exceeding 0.15 % area by HPLC. Hydrolysis in chilled sulfuric acid yields 2-(2-oxothiazol-4-yl)acetic acid ethyl ester, which is then reacted with 1-aminooxy-2-methylpropanoic acid at 1.10 eq under strictly controlled pH 4.5–5.0 utilising a 316L stainless steel reactor equipped with a retreat-curve impeller. The subsequent saponification and acidification steps deliver the ceftazidime side-chain acid with ≥99.2 % purity, confirmed against EP 10.5 monograph for related substances. Regulatory compliance is maintained under ICH Q7 Sections 7 and 12 for starting material traceability; any ATA supplier must provide a Type II drug master file containing residual solvent data compliant with ICH Q3C and a nitrosamine risk assessment per EMA/CHMP/428286/2020. The terminal dosage form is ceftazidime pentahydrate sterile API, filled into vials after aseptic crystallisation and meeting USP 43 monograph 1092312. Operational boundary: if the ATA ester hydrochloride residual free moisture exceeds 0.15 % w/w, the entire batch is rejected before diazotization to avoid exothermic side-reactions leading to uncontrolled decomposition of the diazonium species.

Production of cefdinir’s acetoxyimino side chain, (Z)-2-(2-aminothiazol-4-yl)-2-acetoxyiminoacetic acid, begins with ATA as the core heterocyclic building block. The synthetic strategy circumvents the isolable diazonium route by directly introducing the pre-formed acetyloxyimino chloride, prepared in situ from acetylhydroxamic acid and phosphorus pentachloride in dichloromethane at −15 °C. The chlorooxime reagent is unstable and must be transferred within 30 min into the ATA coupling vessel, charged at a molar ratio of 1.03 eq acetyloxyimino chloride to ATA free acid previously suspended in anhydrous dichloromethane with 2.5 eq of triethylamine as acid scavenger. The reaction mass is held at −10 °C to −5 °C for 4 h, with continuous nitrogen purge to exclude moisture that would hydrolyse the acetyloxyimino group to the nitroso dimer impurity, which is monitored by HPLC and must not exceed 0.10 % area. After aqueous work-up and pH-controlled crystallization, the acetoxyimino acetic acid intermediate is activated as its 2-mercaptobenzothiazole (MBT) thioester for subsequent 7-AVNA coupling. Compliance demands are shaped by the fact that this side chain is a key starting material for an oral cephalosporin; the ATA certificate of analysis must include full impurity fate and purge data in line with ICH M7 for mutagenic impurities, and the manufacturer’s change-control protocol must forewarn of any alteration in the nitrite scavenging step that could raise N-nitrosamine levels above the acceptable intake of 26.5 ng/day. The downstream drug product is cefdinir formulated as capsules or granules, meeting dissolution specifications of ≥80 % in 30 min according to JP 18. A limitation observed at production scale is that when ambient relative humidity exceeds 60 %, the acetyloxyimino chloride generation step suffers yield loss due to premature quenching; dedicated dehumidified make-up air handling units are mandatory.

Methoxyimino Acetic Acid Side Chain Synthesis: Navigating the Exothermic Methylation of ATA Oxime

For the widely commercialised (Z)-2-(2-aminothiazol-4-yl)-2-methoxyiminoacetic acid side chain, ATA is first converted to ethyl 2-(2-aminothiazol-4-yl)acetate hydrochloride and transformed via the ketoester intermediate (2-oxothiazol-4-yl-acetic acid ethyl ester) into the oxime. Oximation is performed with methoxyamine hydrochloride at 1.3 eq in refluxing ethanol, maintaining pH between 3.8 and 4.2 to suppress the formation of the E-isomer, which must remain below 1.0 % of the API-label claim. The methylating agent, dimethyl sulfate (1.05 eq relative to oxime hydroxyl), is introduced by metered addition over 90 min while maintaining −12 °C to −8 °C in a 1500 L 316L stainless steel reactor with a jacket capable of 35 kW heat removal. The ester hydrolysis step is run with sodium hydroxide (2.2 eq) to give the sodium salt, which after acidification yields the side-chain acid. Traces of unreacted dimethyl sulfate are quenched with 0.5 % aqueous ammonia and reduced below the 1 ppm threshold by wiped-film evaporation—an essential operation to satisfy ICH Q3C guideline for class 2 solvents. The resulting methoxyimino acetic acid is then used to acylate 7-ACA, yielding ceftriaxone sodium, cefotaxime sodium, and cefetamet pivoxil. Compliance with 21 CFR 211 for sterile bulk pharmaceuticals is verified through bacterial endotoxin testing (USP <85>) and the absence of β-lactam polymer contaminants monitored via size-exclusion chromatography per EP 2.2.30. A documented processing bottleneck occurs during the methylation step: local overshoot of the set-point above −5 °C leads to rapid formation of dimethyl ether by-product and an irreversible drop in yield exceeding 12 %, limiting the maximum batch size to that which maintains a jacket approach temperature of ΔT ≤ 28 °C.

When the target API is ceftibuten dihydrate, the synthetic route exploits a Knoevenagel-type condensation between ethyl 2-(2-aminothiazol-4-yl)acetate and n-butyl glyoxylate to build the 4-carboxy-2-butenamide side chain directly without an oxime functionality. The ATA ester is charged at 1.0 eq into anhydrous toluene and treated with n-butyl glyoxylate (1.15 eq) in the presence of catalytic pyrrolidine (0.05 eq) and benzoic acid (0.03 eq). Process specifications mandate a continuous azeotropic removal of water at 110 mm Hg reduced pressure; the moisture content of the refluxing solvent must be maintained below 500 ppm by Karl Fischer titration (ASTM D6304) to avoid lactone by-product formation exceeding the critical impurity threshold of 1.5 % area. The reaction is aged at 20 °C to 25 °C for 16 h, conditions identified as the limited window where the desired (Z)-configuration remains above 98:2 Z/E ratio; excursions above 30 °C induce thermal isomerisation toward the E-isomer, which is difficult to purge in downstream crystallisations. Following aqueous wash and solvent swap, the intermediate ester is saponified with lithium hydroxide (2.4 eq) in tetrahydrofuran/water to release the ceftibuten side-chain acid. Residual pyrrolidine must be stripped to ≤290 ppm by nitrogen sparging at 45 °C to meet ICH Q3C class 2 limits before coupling with 7- amino - 3 - [( Z ) - 2 - (4 - methylthiazol - 5 - yl)vinyl] - 3 - cephem - 4 - carboxylic acid. The final dosage form is ceftibuten dihydrate finished as capsules or oral suspension, compliant with EP 11.0 monograph 1933. Process hazard analysis recorded a processing incompatibility: contact of n-butyl glyoxylate with traces of iron accelerates self-condensation; therefore, all post-reaction transfer lines must be constructed of electrophished 316L stainless steel with Ra ≤0.4 µm finish and passivated per ASTM A967.

Veterinary Cephalosporin Manufacturing and ATA-Derived Oxime: Residual Solvent Trade-offs

In the synthesis of cefquinome’s (Z)-2-(2-aminothiazol-4-yl)-2-methoxyiminoacetic acid side chain, process economics and animal-safety regulations drive the replacement of dimethyl sulfate with dimethyl carbonate as the methylating agent, used at 1.5 eq relative to the oxime. The ATA ketoester is initially oximated with methoxyamine hydrochloride in methanol, then the methylation is run at 40 °C to 50 °C in a 3000 L 316L reactor, avoiding the deep cooling needed for dimethyl sulfate routes. Residual dimethyl carbonate is removed by distillation under mild vacuum and controlled below 5 ppm to meet VICH GL18 guidance on residual new chemical entities. The resulting side-chain acid is converted to its MBT active ester and coupled with 7-ACA modified at C‑3 to form cefquinome sulfate. The API must comply with 21 CFR 556 tolerances for residues in edible tissues, with marker residue below 0.1 ppm as determined by LC‑MS/MS. Finished product takes the form of an injectable suspension. A production constraint specific to this veterinary oxime chain arises from the lower purity requirements on the methylating agent; commercially available dimethyl carbonate may contain 0.05 % water, requiring pre-drying over molecular sieves 3A for 24 h before use to prevent oxime ester hydrolysis during the extended methylation hold time.

Pre-Formed ATA Active Thioesters in 7-ACA Acylation: Bypassing In-Situ Activation Pitfalls

A number of API manufacturers elect to receive the isolated ATA-derived side-chain acid and perform the thioester activation with bis(2-mercaptobenzothiazolyl)disulfide and triphenylphosphine in acetonitrile at a molar ratio of side-chain acid : disulfide : triphenylphosphine = 1.0 : 1.05 : 1.10. The reaction is conducted at 0 °C to 5 °C under nitrogen, and the precipitated triphenylphosphine oxide is removed by filtration through a 0.5 µm PTFE membrane. The MBT-active ester solution, whose concentration is verified by HPLC assay to be within ±2 % of target, is then added to a solution of 7-ACA silyl ester in dichloromethane at −15 °C. The acylation proceeds for 2 h and is quenched with dilute HCl, furnishing intermediates for cefepime, cefpirome, or other expanded-spectrum cephalosporins. The entire operation falls under ICH Q7 Section 8.4 for controlled clean-room conditions when the API is intended for sterile filling. A documented incompatibility exists between the MBT-active ester and amine bases such as triethylamine, which can trigger premature β‑lactam ring opening; therefore, all acylation steps must maintain a free-amine concentration below 0.01 mmol/L. The resulting sterile API (e.g., cefepime hydrochloride meeting USP 43) is subjected to particulate matter testing per USP <788> before release. Operational boundary: the MBT-active ester solution loses 2.5 % of its titre per hour at 25 °C; hence, the holding time between activation and 7-ACA addition must not exceed 45 min within the validated jacketed vessel, otherwise the batch is reprocessed.