2-Amino-4-Thiazoleacetic Acid Hcl
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HS Code |
322179 |
| Chemical Formula | C5H6ClNO3S |
| Molecular Weight | 197.62 |
| Appearance | White to off - white crystalline powder |
| Solubility In Water | Soluble |
| Pka Value | Around 2 - 3 (approximate value for carboxyl group) |
| Melting Point | Typically in the range of 150 - 160 °C |
| Odor | Odorless or very faint odor |
| Stability | Stable under normal storage conditions away from strong oxidizing agents |
As an accredited 2-Amino-4-Thiazoleacetic Acid Hcl factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | 250 - gram bottle of 2 - Amino - 4 - Thiazoleacetic Acid Hcl, well - sealed for protection. |
| Shipping | 2 - Amino - 4 - Thiazoleacetic Acid HCl is shipped in sealed, corrosion - resistant containers. They are carefully packed to prevent breakage. Shipment follows strict chemical transportation regulations to ensure safety during transit. |
| Storage | 2 - Amino - 4 - Thiazoleacetic Acid HCl should be stored in a cool, dry place, away from direct sunlight. Keep it in a tightly - sealed container to prevent moisture absorption and exposure to air, which could potentially lead to decomposition or degradation. Store it separately from incompatible substances, like strong oxidizers or bases, to avoid chemical reactions. |
When Active Ester Route Outperforms Mixed Anhydride in Pilot-Scale 7-ADCA Acylation2-Amino-4-thiazoleacetic acid hydrochloride is routinely converted to its N-hydroxysuccinimide (NHS) ester before coupling with 7-aminodesacetoxycephalosporanic acid (7-ADCA) in the synthesis of cefadroxil analogues and other first-generation oral cephalosporins. At production scale the free base is liberated in situ in anhydrous N,N-dimethylformamide using 1.02–1.05 equivalents of N-methylmorpholine at −5 °C to 0 °C under a dry nitrogen blanket. Dicyclohexylcarbodiimide (DCC, 1.10 eq.) is charged as a 40% solution in dichloromethane over 90 min while internal temperature is held below 2 °C. The resulting thick slurry of dicyclohexylurea (DCU) must be filtered across a 0.5 µm polypropylene bag filter housed in a Hastelloy C22 pressure vessel; premature blinding of the filter cloth occurs if the DCU particle size distribution shifts above D90 = 45 µm, a phenomenon linked to agitation rates below 180 rpm in vessels equipped with a retreat-curve impeller. The filtrate is used immediately for the acylation of 7-ADCA suspended in the same solvent matrix, as the isolated NHS ester exhibits ≤ 48 h stability at 2–8 °C under argon. Unreacted DCC in the filtrate must be scavenged with glacial acetic acid to prevent formation of the inactive N-acylurea byproduct; residual DCC above 0.3 mol% relative to the β-lactam causes a significant yield penalty in the subsequent crystallization. HPLC monitoring (mobile phase: acetonitrile/ 0.1 M phosphate buffer pH 6.5, 70:30 v/v) with UV detection at 254 nm targets an activated ester purity of ≥ 97.5% (area normalization) before the coupling step, with the des-chloro impurity originating from the starting hydrochloride kept below 0.15%. Transfer of the active ester solution into the acylating vessel demands a jacketed positive-displacement pump paired with a mass flow meter to maintain a molar feed ratio of 1.12:1 (ester: 7-ADCA). The acylation proceeds at −10 °C ± 1 °C under pH-stat control with triethylamine maintaining pH 7.8–8.2. Deviation below pH 7.3 triggers the release of the free amine form of the substrate, which then participates in a competing intermolecular aminolysis that generates a dimeric impurity challenging to purge in downstream crystallization. Following quench with 6 N HCl to pH 2.5, the crude cefadroxil derivative is isolated by centrifugal extraction and washed with five bed volumes of chilled water for injection (WFI, ≤ 2 °C). Residual DMF and dichloromethane are reduced below 880 ppm and 600 ppm respectively by reslurrying in isopropyl alcohol/water (92:8 v/v) at 55 °C for 4 h, thresholds mandated by the International Council for Harmonisation (ICH) Q3C guideline for Class 2 solvents. Equipment contact surfaces are exclusively 316L electropolished stainless steel to eliminate iron contamination that forms a coloured complex with the thiazole ring; passivation cycles per ASTM A967 are mandated after every 20 batch cycles.
Manufacturing records from multi-tonne campaigns at antibiotic finishing plants reveal that batch-to-batch variability in the hydrochloride feedstock is the single largest contributor to out-of-specification end-product colour. The free base generated from lots containing more than 0.08% of the 5-bromo positional isomer (a chlorination byproduct carried forward from the thiazole ring-forming step) imparts an off-white hue that exceeds the EP colour limit of BY4 tested per Ph. Eur. method 2.2.2. To mitigate this, incoming hydrochloride must be inspected for “bromine on combustion” following an oxygen flask procedure adapted from USP 〈211〉, with rejection at any detectable bromide signal above the 50 ppm threshold. Incorporation of the 2-aminothiazole-4-acetyl fragment into a series of pyrazole carboxamide fungicides has been scaled to 500 L pilot batches at multiple agrochemical contract research organizations. The hydrochloride is suspended in ethyl acetate and washed with 8% aqueous sodium bicarbonate to prepare the neutral amine in situ, then added dropwise to a pre-formed acid chloride generated from the corresponding pyrazole-4-carboxylic acid and thionyl chloride with 0.5 mol% DMF catalyst at 55 °C. Off-gassing of sulfur dioxide and hydrogen chloride is scrubbed through a 15% sodium hydroxide packed column; failure to maintain a negative pressure differential of at least −5 mbar relative to ambient in the vent line results in backflow corrosion of the glass-lined reactor’s agitator seal. The coupling reaction is run at 10–15 °C for 3 h, after which the batch is drowned into 6 volumes of iced water and the precipitated amide is collected on a centrifuge with a PTFE-lined basket. Residual ethyl acetate must be stripped to ≤ 1200 ppm on a rotary conical dryer operating at 45 °C / 50 mbar because the solvent interferes with the subsequent bromination step that introduces the N-methyl-3-bromopyrazole-4-carboxamide pharmacophore. Registration batches are controlled under the five-batch analysis protocol prescribed by the United States Environmental Protection Agency (EPA) 40 CFR §158.1700, and the compound identity is confirmed via 1H NMR (CDCl3, 600 MHz) with the characteristic thiazole C5-H doublet at δ 6.85 ± 0.03 ppm serving as a lot-release fingerprint. Thiazole-Based Chromogenic Reagent for Palladium Detection in Spent CatalystsReaction of 2-amino-4-thiazoleacetic acid hydrochloride with salicylaldehyde in refluxing absolute ethanol containing 0.5 mL of glacial acetic acid yields a Schiff base ligand that forms a 1:1 orange-red complex with palladium(II) in acetate buffer at pH 4.8. The chromogenic reagent has found application in recovery plants processing spent petrochemical catalysts, where the complex is loaded onto a C18 SPE cartridge preconditioned with methanol/0.01 M HCl, eluted with acetonitrile, and quantitated by visible absorbance at 485 nm against a calibration curve spanning 0.05–5.0 µg·mL−1 Pd. Molar absorptivity reaches ε = 1.86 × 104 L·mol−1·cm−1 under optimized conditions, and Beer’s law linearity holds with a correlation coefficient r ≥ 0.9995. The free amine must be isolated from the hydrochloride immediately before condensation because the imine formation is acid-sensitive; even 200 ppm of residual hydrochloric acid carried over from insufficient washing depresses Schiff base yield by 15–22%. Plant operators frequently employ a conductivity probe on the aqueous wash stream with a cutoff set at ≤ 25 µS·cm−1 to confirm complete removal of ionic halide. Tolerances toward common base-metal interferences meet the acceptance criteria of the ASTM D4642-04 protocol for platinum-group metal recovery streams, with a relative error kept below 3.5% in the presence of 1000-fold excess nickel and copper. For the manufacture of cefodizime sodium (CAS 86329-79-5), a third-generation injectable cephalosporin, the hydrochloride salt undergoes a tandem neutralization–acylation sequence that dictates the final product’s diastereomeric purity. The free 2-amino-4-thiazoleacetic acid is liberated by suspending the salt in purified water at 3–5 °C and adding 2.0 M sodium hydroxide until a pH endpoint of 7.2 ± 0.1 is reached; under- or over-neutralization shifts the pH outside the window where the amine nucleophile remains sufficiently reactive without promoting the opening of the β-lactam ring in the subsequent 7-ACA derivative. The aqueous solution of the free base is transferred under nitrogen pressure into a stainless-steel (type 904L) cryogenic reactor that has been pre-chilled to −15 °C and passivated with 30% nitric acid for 6 h at 50 °C to resist chloride pitting. Dropwise addition of a pre-formed mercaptothiazole-acetyl chloride, prepared by reacting 2-(2-aminothiazol-4-yl)-2-methoxyiminoacetyl chloride with mercaptoacetic acid in tetrahydrofuran, takes place over 3.5 h. Precise stoichiometric control—the free base must be held at 1.00–1.03 molar equivalents relative to the acid chloride—prevents formation of the double-acylated N,N′-diacyl impurity that co-crystallizes with the desired mono-acylated 7-ACA intermediate. A pair of piston-diaphragm metering pumps with Profibus-linked mass flow controllers maintain the feed ratio within ±0.5% of the setpoint, and real-time Raman spectroscopy monitors the disappearance of the acid chloride C=O band at 1785 cm−1. After a 6 h incubation at −8 °C, the batch is raised to 20 °C and the THF is replaced with methyl isobutyl ketone via vacuum distillation, the swap being essential because residual tetrahydrofuran peroxides generated during solvent recovery can oxidize the thiazole sulfur to a sulfoxide impurity that the downstream crystallization in isopropyl alcohol cannot reject to below the 0.10% threshold of the European Pharmacopoeia monograph for cefodizime sodium (Ph. Eur. 10.0, 01/2022:1755). Converting the Primary Aromatic Amine to an Orange Disperse Azo Dye for Polyester Knit FabricThe 2-aminothiazole nucleus can be diazotized and coupled to an N-alkylated aniline to produce a monoazo disperse dye stock used in continuous thermosol dyeing of polyethylene terephthalate (PET) at processing speeds of 150–200 m/min. Sodium nitrite (1.02 eq.) is added to a 0.5 M suspension of 2-amino-4-thiazoleacetic acid hydrochloride in 2.5 N hydrochloric acid at 0–2 °C, generating a clear diazonium solution that must be consumed within 45 min to avoid the Gomberg-Bachmann dimerization that produces an insoluble tarry byproduct. The diazo liquor is run into an aqueous suspension of N,N-diethyl-m-toluidine dispersed with 0.05% w/v sodium lignosulfonate in a buffer of sodium acetate-acetic acid at pH 4.2–4.5. Coupling is practically instantaneous; the exotherm raises the batch temperature to 8 °C if the jacket circulates brine at −10 °C. The crude presscake is washed until the filtrate conductivity measures ≤ 50 µS·cm−1, then dried in a fluid-bed dryer with an inlet air temperature of 85 °C to a moisture content below 1.0% w/w. The dried dye cake is subsequently formulated by wet-milling on a horizontal bead mill (netzsch LMZ type, 0.4–0.6 mm yttria-stabilized zirconia beads, 80% fill) in the presence of a naphthalene sulfonate-formaldehyde condensate dispersant and a defoamer based on 2-ethylhexanol, achieving a primary particle size of D90 ≤ 0.8 µm laser diffraction. Colouristic properties on 100% texturized polyester knitted under 1.0% o.w.f. depth and heat-set at 190 °C for 90 s are assessed spectrophotometrically (D65/10° observer); the absorbance maximum falls at λmax = 478 ± 3 nm in dimethylformamide solution, with a molar extinction coefficient of 2.9 × 104 L·mol−1·cm−1. Fastness to light conforms to ISO 105-B02:2014 rating 6–7 at the stated concentration, and the unexhausted dye in the dye bath is destroyed using a Fenton-type advanced oxidation process before effluent discharge to meet Zero Discharge of Hazardous Chemicals (ZDHC) Manufacturing Restricted Substances List (MRSL) Version 2.0 thresholds for adsorbable organic halogens (AOX) below 5 mg/L.
Published data for the direct use of 2-amino-4-thiazoleacetic acid hydrochloride as a monomer in polymeric chain extenders remains sparse, but the compound has been evaluated as a building block for poly(ester-amide) thermoplastic elastomers via interfacial polymerization with sebacoyl chloride in a water/chloroform system. The inherent viscosity of the resulting copolymer reached 0.22 dL·g−1 (measured in m-cresol at 30 °C, 0.5 g·dL−1), which limits its utility to low-modulus applications unless molecular weight is boosted through solid-state post-condensation at 150 °C under 0.1 mbar vacuum for 48 h. Efforts to incorporate the thiazole ring into the soft segment reduced the glass transition temperature to −28 °C as determined by differential scanning calorimetry per ASTM D3418-21, but also imparted a tendency toward thermo-oxidative discolouration above 210 °C that required the addition of 0.15% w/w Irganox 1010 blended with 0.30% w/w Irgafos 168 to hold yellowness index (ASTM E313) below 6.0 after three consecutive injection-molding cycles at 240 °C.
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The crystalline adduct 2-amino-4-thiazoleacetic acid hydrochloride (empirical formula C5H7ClN2O2S, relative molecular mass 194.64 g·mol⁻¹) functions primarily as a protected acylating agent in β‑lactam side‑chain assembly. The compound is supplied as a white to off‑white powder with a melting point of 176–180 °C (decomposition) when determined by differential scanning calorimetry at 10 K·min⁻¹ under nitrogen purge. Specification grades typically distinguish themselves by residual solvent profile rather than simple HPLC purity; a pharmaceutical intermediate grade requires ≤0.1% ethyl acetate and ≤0.05% dichloromethane as per ICH Q3C guideline limits for Class 2 solvents. The hydrochloride counterion shifts the amino group pKa from ~4.8 (free base) to <1.5, effectively preventing premature nucleophilic attack on activated ester intermediates during cephalosporin coupling reactions. This kinetic suppression is measured by monitoring the half‑life of the mixed anhydride species in acetonitrile at −15 °C; the HCl salt extends the viable processing window from 18 minutes (free amine form) to >4 hours before 10% degradation.
In contrast to the free acid 2‑amino‑4‑thiazoleacetic acid (CAS 29676‑71‑9), which exhibits a solubility in water at 25 °C of only 0.8 g·L⁻¹, the hydrochloride salt attains >220 g·L⁻¹ at identical temperature and neutral pH. This disparity permits direct aqueous‑phase activation with water‑soluble carbodiimides—a route wholly inapplicable to the parent compound without co‑solvent such as DMF. The 4‑thiazoleacetic acid regioisomer must be distinguished from its 5‑thiazoleacetic acid analogue (CAS 1003‑99‑2, 2‑amino‑5‑thiazoleacetic acid), which yields a β‑lactam intermediate with a heterocyclic attachment point proved to shift the antibiotic spectrum toward Gram‑positive activity only; microbiological assay data using Escherichia coli ATCC 25922 demonstrated a 16‑fold reduction in MIC for the 4‑substituted derivative relative to the 5‑substituted congener when both were elaborated into cefotaxime mimetics.
Differential scanning calorimetry profiles obtained on a Mettler Toledo DSC 3+ with hermetically sealed aluminum crucibles reveal an exothermic onset at 182 °C with an energy release of −420 J·g⁻¹. Accelerating rate calorimetry (ARC) data generated in accordance with ASTM E1981‑22 indicates a self‑accelerating decomposition temperature (SADT) of 98 °C for a 50 kg fiber drum configuration. Consequently, storage conditions are mandated at 2–8 °C with desiccant‑lined closures; a rise in water content above 0.5% (Karl Fischer, ASTM D6304‑20) correlates with a 7 °C depression in SADT per 0.1% moisture increment, documented over three production lots from a 1000 L glass‑lined reactor campaign. Logistics providers are required to use validated reusable phase‑change‑material shippers maintaining +2 to +8 °C for minimum 96 hours, with integrated USB temperature loggers sampling at 15‑minute intervals.
Process safety engineers will note that the decomposition pathway generates sulfur dioxide and hydrogen chloride gas; the maximum pressure rise rate in a closed 1‑L test cell reached 15 bar·s⁻¹ at 200 °C. This places the compound outside the range of standard rotary cone dryers operating under vacuum; commercial drying is instead accomplished using filter‑dryers with Hastelloy C‑22 construction and rupture discs rated to 20 barg. The elevated chloride ion concentration in the hydrochloride salt contributes to pitting corrosion observed on 316L stainless steel after fewer than 50 batch cycles. Operator protection requires local exhaust ventilation achieving a capture velocity of 0.75 m·s⁻¹ at the weighing station, verified by face velocity monitoring per ANSI/AIHA Z9.5‑2022.
Without a leading header, the discussion moves directly to impurity profiling and how it dictates the economic viability of kilogram‑scale campaigns.Commercial material acquired from multiple Asian contract manufacturers catalogs a known process impurity: N‑chloroacetyl‑2‑amino‑4‑thiazoleacetic acid, formed when residual chloroacetyl chloride from a prior acylation step is not fully purged before hydrochloride salt precipitation. This species, present at 0.15–0.8% area by HPLC (Inertsil ODS‑3, 250 × 4.6 mm, 5 µm, mobile phase 0.05 M KH2PO4 pH 3.0/acetonitrile 85:15, detection 254 nm), reacts with ammonia during cefotaxime construction to produce a chloroacetamide dead‑end product that cannot be elaborated further. Rejection limits in a typical quality agreement set this impurity at ≤0.2%; batches exceeding this threshold are diverted to second‑tier markets for veterinary cephalosporin production where the downstream purification cascade includes an additional charcoal treatment capable of removing the chloroacetamide byproduct to <0.05% in the final active pharmaceutical ingredient. The cost differential between human‑grade and veterinary‑grade 2‑amino‑4‑thiazoleacetic acid hydrochloride, as of 2024 contract price surveys, stands at ~35%, driven entirely by this single impurity specification.
| Parameter | Human Grade (Typical) | Veterinary Grade | Test Method |
|---|---|---|---|
| Assay (anhydrous basis) | 98.5–101.0% | ≥96.0% | Potentiometric titration with 0.1 M NaOH |
| Chloroacetyl impurity | ≤0.20% | ≤1.0% | HPLC, 254 nm |
| Water content | ≤0.50% | ≤1.0% | KF coulometric, ASTM D6304‑20 |
| Residue on ignition | ≤0.10% | ≤0.3% | USP <281>, 600 °C |
| Heavy metals (as Pb) | ≤10 ppm | ≤30 ppm | USP <231> II |
| Palladium (residual catalyst) | ≤5 ppm | ≤20 ppm | ICP‑MS, m/z 105 |
The reactive behavior of 2‑amino‑4‑thiazoleacetic acid hydrochloride in pilot‑plant acylation exhibits a pronounced sensitivity to the initial charging temperature that is frequently overlooked in laboratory method transfer. When the hydrochloride salt is added to a solution of an activated oximino‑acetic acid derivative at a jacket temperature above −5 °C, the exotherm from dissolution and immediate neutralization by tertiary amine base (typically triethylamine, 1.05–1.15 molar equivalents) raises the internal temperature by 12–18 °C within 90 seconds in a 500 L glass‑lined reactor. This spike pushes the reaction mixture past the safe threshold for retention of the syn‑oxime configuration (≤ −8 °C reported for the methoxyimino isomer of cefotaxime side chain); isomerization to the anti‑oxime form exceeds 2% per 10 °C increment above −5 °C, as quantified by 1H NMR integration of the methoxy singlet at δ 3.95 ppm (syn) versus δ 4.05 ppm (anti).
Transfer to production scale therefore demands pre‑cooling of the hydrochloride charge to −15 °C and stepwise dosing over 40–60 minutes in a vessel equipped with a retreat‑curve impeller operating at 85–110 rpm. In one documented case from a commercial API manufacturer, a single‑portion charge at −2 °C resulted in an anti‑oxime content of 6.8%, necessitating a complete re‑precipitation of the DMF solvate and a yield loss of 22% after correction. This contrasts sharply with the free base 2‑amino‑4‑thiazoleacetic acid sodium salt, which can be added in a single portion at 0 °C without the same neutralizing exotherm because the amino group is already deprotonated; however, the sodium salt introduces a hygroscopicity problem and requires anhydrous DMF throughout the coupling, increasing solvent recovery costs by an estimated €1.20/kg of product.
The thiazole ring of 2‑amino‑4‑thiazoleacetic acid hydrochloride is susceptible to hydrolytic opening at pH <1 or >12, but the hydrochloride salt environment itself creates a micro‑pH below 2 in the absorbed water film around particles stored at relative humidity >75%. Stability chambers operated per ICH Q1A(R2) at 40 °C/75% RH showed ring‑opening to 2‑aminomercapto‑4‑oxobutyric acid at 0.8% after 6 months in open containers, compared to <0.1% in hermetically sealed aluminum‑polyethylene laminate bags with 5 g silica gel canisters. This degradation pathway is accelerated by trace metal ions; iron content as low as 2 ppm (from 316L vessel erosion) catalyzes a 4‑fold increase in hydrolytic degradation rate at identical temperature and humidity. Suppliers therefore include a dedicated metallic impurity panel in their certificate of analysis, with iron and zinc limits set at ≤5 ppm and ≤2 ppm respectively, measured by ICP‑OES after microwave digestion per EPA Method 6010D.
The downstream consequence of thiazole ring opening during storage is the formation of a mercaptan dimer species that co‑elutes with the target product during normal‑phase chromatography in the subsequent cephalosporin purification, causing anomalous extinction at 270 nm. Facilities that have installed an in‑line Raman probe (Kaiser Optical RXN2) at the point of salt dissolution can detect the ring‑opened impurity via its characteristic thiol S‑H stretch at 2560 cm⁻¹ before charging the main coupling reactor, avoiding batch rejection at a later stage. The cost of the Raman monitoring package is typically recovered within 12–18 months of operation at a campaign throughput of 40 metric tons per annum of cephalosporin intermediate.
A further comparative distinction from structurally related molecules such as 2‑aminothiazole‑4‑acetic acid ethyl ester hydrochloride (CAS 85642‑13‑9) concerns the fate of the carboxyl protecting group during hydrogenolysis. The ester variant requires a palladium‑on‑carbon (5% Pd/C, 0.5% w/w) hydrogenation step at 3–4 bar H2 to liberate the free acid before activation, adding 8–10 hours of cycle time and generating a palladium‑containing spent catalyst stream that must be processed by a licensed waste handler. The hydrochloride salt of the free acid bypasses this unit operation entirely, improving overall mass intensity (PMI) by ~25% as calculated by the E factor methodology per the ACS Green Chemistry Institute Pharmaceutical Roundtable benchmark. Conversely, the free acid form (non‑salt) displays lower chloride content (<0.1% vs. ~18% theoretical chloride in the HCl salt), which may be preferred when the final API specification enforces rigorous limits on inorganic chlorides for parenteral products tested per USP <221>.
| Form | Typical PMI (kg waste/kg product) | Unit Operations | Cycle Time (h) |
|---|---|---|---|
| HCl salt (direct coupling) | 18.5 | 5 | 22 |
| Sodium salt (anhydrous) | 24.2 | 7 | 35 |
| Ethyl ester hydrochloride | 26.8 | 8 (includes hydrogenolysis) | 42 |
| Free acid (no counterion) | 19.1 | 5 (but requires DMF co‑solvent) | 24 |
Recent regulatory emphasis under ICH M7(R2) and EMA CHMP/158718/2020 has compelled manufacturers of 2‑amino‑4‑thiazoleacetic acid hydrochloride to demonstrate control over N‑nitrosamine formation potential. The compound itself does not contain a secondary amine prone to nitrosation under standard processing conditions; however, the triethylamine reagent universally used as an acid scavenger during coupling is a secondary amine substrate. Cross‑contamination risk arises in multipurpose equipment where the same reactor is used for triethylamine recovery and the hydrochloride salt is subsequently charged without intermediate cleaning validation. Analytical surveillance using LC‑MS/MS with APCI detection (Thermo TSQ Quantis) achieves a limit of quantification for N‑nitrosotriethylamine of 0.5 ppb in the salt matrix, and batch certificates now routinely report “
For radiolabeled studies and metabolite identification, 2‑amino‑4‑thiazoleacetic acid hydrochloride can be isotopically enriched in the thiazole ring via a Hantzsch condensation using 13C2‑labeled chloroacetaldehyde dimethyl acetal. The hydrochloride salt of the labeled material exhibits a 0.2 Da shift in the quasi‑molecular ion (m/z 195.8 to m/z 197.8) and allows tracking of the thiazole moiety through in vivo metabolic cleavage in rat models without interference from endogenous components. This synthetic route is preferred over tritium labeling because the HCl salt form avoids the lability of the radioisotope on the free amino group.
Differences from akin heterocyclic building blocks such as 2‑amino‑1,3,4‑thiadiazole‑5‑acetic acid hydrochloride become evident in the carbapenem synthetic sequence. The replacement of the thiazole sulfur atom with a thiadiazole ring elevates the oxidation potential by ~200 mV (measured by cyclic voltammetry on a glassy carbon electrode in 0.1 M TBAPF6 acetonitrile solution) and results in electrode fouling during the electrochemical recycling of the penem intermediate. Process developers targeting doripenem or meropenem analogues therefore screen against the thiadiazole variant at an early retrosynthetic disconnection, defaulting to the thiazole scaffold for its narrower potential window and higher tolerance to soluble reductants such as zinc‑acetic acid couples at −0.95 V vs. Ag/AgCl.
