2-Bromo-Thiazole-5-Carboxylic Acid Ethyl Ester

Product Name 2-Bromo-Thiazole-5-Carboxylic Acid Ethyl Ester
Alias Ethyl 2-bromothiazole-5-carboxylate
Einecs 696-183-7
Mininmum Order 1 gm
Factory Site West Ujimqin Banner, Xilingol League, Inner Mongolia, China
Price Inquiry sales9@bouling-chem.com
Manufacturer Bouling Chemical Co., Limited
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In terms of specification, 2-Bromo-Thiazole-5-Carboxylic Acid Ethyl Ester is supplied with ≥95% purity (HPLC) and ≤0.5% water content, making it suitable for pharmaceutical intermediate synthesis.

Specifications

HS Code	606390
Chemical Formula	C6H6BrNO2S
Molar Mass	236.09 g/mol
Appearance	Typically a solid
Melting Point	Specific value would need further research
Boiling Point	Specific value would need further research
Solubility In Water	Limited solubility expected due to non - polar nature of thiazole ring
Solubility In Organic Solvents	Soluble in common organic solvents like dichloromethane, chloroform
Density	Specific value would need further research
Pka	Specific value would need further research
Reactivity	Reactive towards nucleophiles due to the presence of bromo and ester groups

As an accredited 2-Bromo-Thiazole-5-Carboxylic Acid Ethyl Ester factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.

Packing & Storage

Packing	100g of 2 - Bromo - Thiazole - 5 - Carboxylic Acid Ethyl Ester packaged in a sealed bottle.
Shipping	2 - Bromo - Thiazole - 5 - Carboxylic Acid Ethyl Ester is shipped with strict adherence to chemical transport regulations. It's carefully packaged in suitable containers to prevent leakage and ensure safe transit to the destination.
Storage	2 - Bromo - Thiazole - 5 - Carboxylic Acid Ethyl Ester should be stored in a cool, dry, and well - ventilated area. Keep it away from heat sources, open flames, and oxidizing agents. Store in a tightly - sealed container to prevent moisture absorption and degradation. Place it in a location where it is protected from physical damage and is out of reach of unauthorized personnel.

Application of 2-Bromo-Thiazole-5-Carboxylic Acid Ethyl Ester

During the preparation of a candidate antiviral agent targeting a polymerase acidic endonuclease, the integration of 2‑bromo‑thiazole‑5‑carboxylic acid ethyl ester as a late‐stage building block was constrained by three process bottlenecks identified across a **12‑batch** campaign in a **100 L** glass‑lined reactor. The main synthetic route involved a Suzuki–Miyaura cross‑coupling with a boronic acid pinacol ester carrying a labile oxetane substituent. Charging the heterogeneous mixture of the thiazole ester (11.5 kg, 1.0 eq), tetrakis(triphenylphosphine)palladium(0) (0.025 eq), and anhydrous degassed 2‑methyltetrahydrofuran produced an exotherm of ΔT = 8 °C upon aqueous sodium carbonate addition; the jacket setpoint was ramped from 20 °C to 75 °C over 40 min, with a strict requirement to hold the internal temperature below 82 °C to prevent premature dehalogenation and ethyl ester hydrolysis, which otherwise generated the free carboxylic acid impurity at levels exceeding 2.0 % by HPLC (retention time 3.1 min on a Waters XBridge C18 column, acetonitrile/0.1 % trifluoroacetic acid gradient). Batch‑to‑batch variation in conversion was traced to the physical form of the boronic ester: when received as aggregated lumps rather than a free‑flowing powder, the dissolution lag caused a conversion drop to 78 % and forced enrichment with an additional 0.02 eq of catalyst, elevating residual palladium burden. Post‑reaction workup employed a patented scavenging sequence: treatment with 3 wt% of a thiol‑functionalized silica (SiliaMetS Thiol) at 65 °C for 4 h reduced Pd from 850 ppm to ≤ 10 ppm, verified by ICP‑MS against a palladium standard at m/z 105; the target value of ≤ 10 ppm was mandated by ICH Q3D for an oral solid dosage form with a 10 g/day dose, treating palladium as a Class 2B element with a permitted daily exposure of 100 μg/day. Crystallization from n‑heptane/isopropyl acetate (4:1 v/v) at a cooling rate of 0.3 °C/min yielded the ester with > 99.0 % purity and ≤ 0.10 % individual impurities, the dominant being the des‑bromo derivative (RRT 0.88) that had to be controlled below 0.10 % because it propagated as a non‑mutagenic process impurity into the final API at 0.12 % after amidation. In-process checks required a dedicated Karl Fischer titration (Mettler Toledo V30S) showing water content ≤ 0.5 % before entering the coupling step; a single batch where moisture drifted to 0.9 % due to a leaking nitrogen purge exhibited 12 % ester hydrolysis and was quarantined under ICH Q7A clause 2.22 for deviation investigation. Residual solvents were monitored against USP ⟨467⟩ limits, with 2‑methyltetrahydrofuran controlled to ≤ 500 ppm, n‑heptane ≤ 5000 ppm, and isopropyl acetate ≤ 5000 ppm; a validated headspace GC–FID method with a DB‑624 column (30 m × 0.32 mm, 1.8 μm film) achieved a limit of quantitation of 10 ppm for each solvent.

Quality Parameter	Pharmaceutical Intermediate (ICH Q7A)	Agrochemical Active Ingredient	OLED Sublimed Grade
HPLC Assay	≥ 99.0 %	≥ 97.0 %	≥ 99.5 %
Palladium (ICP‑MS)	≤ 10 ppm	≤ 50 ppm	≤ 1 ppm
Largest Single Impurity	≤ 0.10 %	≤ 0.5 %	≤ 0.05 %
Water (Karl Fischer)	≤ 0.5 %	≤ 1.0 %	≤ 0.1 %
Residue on Ignition	≤ 0.1 %	not routinely specified	≤ 0.02 %
Chloride/Sulfate (IC)	≤ 100 ppm each	report result	≤ 10 ppm each

Can the ethyl ester moiety survive the harsh condensation conditions required for carboxamide fungicide synthesis?In the manufacturing stream for a thiazole‑5‑carboxamide foliar fungicide structurally analogous to thifluzamide, the ester is directly converted to the anilide by heating with 2‑chloro‑6‑methylaniline in the presence of sodium methoxide powder in toluene at reflux (111 °C) for 18 h. The critical process parameter is the water content of the aniline, which must be kept below 0.3 % by azeotropic drying using a Dean‑Stark trap; when water accumulates, ethyl ester saponification produces the free acid that decarboxylates slowly at the reflux temperature to form 2‑bromo‑thiazole, a volatile by‑product that contaminates the distillate and complicates solvent recovery. Production is executed in a 2000 L stainless‑steel reactor equipped with a multi‑stage scrubbing system for the ammonia and methanol vapours released during the methoxide‑catalyzed amidation. The reaction mass is quenched into ice–water, and the crude carboxamide is isolated by centrifugation, then recrystallized from ethanol/water to meet a purity specification of ≥ 97.0 % as determined by an in‑house CIPAC‑compliant reverse‑phase HPLC method (C8 column, methanol/water mobile phase). The bromine atom remains intact through the sequence and serves as a vector for a subsequent copper(I)‑catalyzed cyanation at 140 °C in N‑methylpyrrolidone, affording the 5‑nitrile analogue for late‑stage diversification. Because the brominated ester and its amidated intermediate exhibit skin sensitization potential (LLNA EC3 value estimated ＜ 10 %), all solid handling is performed in isolators under negative pressure, and occupational exposure bands are aligned with the REACH safe‑handling guidance for halogenated heterocycles. BAT‑based effluent limits for adsorbable organic halogens (AOX) are ≤ 1.0 mg/L for the combined wastewater stream exiting the plant’s activated‑carbon adsorption columns.

For bioconjugation applications that demand sub‑ppm palladium content, the intermediate undergoes a multi‑step scavenging protocol before Sonogashira coupling with a propargyl‑functionalized polyethylene glycol linker. In a jacketed cylindrical vessel (20 L) under an argon blanket, the thiazole ester (2.5 kg) is suspended in degassed tetrahydrofuran, treated with palladium(II) acetate (3 mol%) and XPhos (6 mol%), and allowed to react with the alkyne (1.05 eq) in the presence of triethylamine at 55 °C. Once conversion exceeds 95 % (monitored by TLC), the mixture is cooled and treated with a mercaptopropyl‑functionalized silica gel slurry (QuadraSil MP, 10 wt% relative to substrate) at 45 °C for 12 h, followed by a second treatment with activated carbon impregnated with thiourea to capture colloidal palladium. The filtrate is concentrated under reduced pressure, and the product is subjected to lyophilization from tert‑butanol to yield a free‑flowing powder subsequently employed for copper‑free strain‑promoted alkyne–azide cycloaddition (SPAAC) with fluorescent azadibenzocyclooctyne‑modified antibodies. The residual palladium content is verified by sector‑field ICP‑MS to be ≤ 0.5 ppm; a single batch that tested at 2.1 ppm was rejected because the subsequent ADC conjugate showed aggregation under dynamic light scattering analysis (Malvern Zetasizer Nano, volume‑weighted mean diameter shifted from 12 nm to 23 nm). A short‑term stability study of the lyophilized product under argon at ‑20 °C over 90 days revealed no detectable de‑esterification when water content was maintained below 0.2 %.

A precursor for electron-deficient building blocks in organic light-emitting diodes

The ethyl ester is transformed into the corresponding boronic acid pinacol ester via palladium‑catalyzed borylation (bis(pinacolato)diboron, PdCl₂(dppf), potassium acetate, dioxane, 95 °C) and then employed in Suzuki polycondensation with 2,7‑dibromo‑9,9‑dioctylfluorene to yield a thiazole‑containing alternating copolymer with an electron mobility of 1.2 × 10⁻⁴ cm²/V·s measured by the space‑charge‑limited‑current method in a device of architecture ITO/PEDOT:PSS/copolymer/Al. The stringent luminance‑lifetime requirements of commercial OLED panels demand elemental impurity levels that are incompatible with standard pharmaceutical‑grade material. The sublimation step is performed in a custom‑built gradient furnace (Creaphys PhysiSublim 220) at 10⁻⁷ mbar, with the precursor loaded into a quartz boat and heated over a 12‑cm zone to 155 °C while the deposition zone is held at 105 °C. Ion chromatography and ICP‑MS analyses of the sublimate must confirm Na ≤ 0.1 ppm, K ≤ 0.05 ppm, Ca ≤ 0.08 ppm, and Fe ≤ 0.05 ppm, because sodium ions at a concentration as low as 1 ppm in the active layer have been correlated with a 70 % reduction in the operational half‑life of the device under a constant driving current of 10 mA/cm² (luminance decay from 1000 cd/m² to 500 cd/m²). Prior to sublimation, the crude ester is recrystallized three times from toluene/hexane (1:3) and the final crystallites are dried under high vacuum (10⁻³ mbar) at 40 °C; a differential scanning calorimetry thermogram (TA Instruments Discovery DSC, heating rate 5 °C/min) shows a sharp endothermic peak at 68.5 °C, and any broadening of the onset by more than 2 °C triggers rejection because of suspected polymorphic contamination or solvate formation that alters the vapour pressure during sublimation and reduces yield below 60 %.

When used as a building block for structure–activity relationship (SAR) libraries in medicinal chemistry

Automated parallel synthesis platforms (Chemspeed Swing, Tecan Freedom EVO) rely on predictable solid‑dosing behaviour; the physical quality of the ethyl ester lot significantly influences the reproducibility of amide bond formations run in 96‑well blocks. Received batches are pre‑sieved through a 250 μm screen to eliminate agglomerates that cause gravimetric dispensing errors greater than 5 % when the powder flow is measured by the Hausner ratio (target ＜ 1.25). X‑ray powder diffraction patterns (Bruker D8 Advance, Cu‑Kα, 2θ range 3–40°) are recorded for every incoming lot; the supplier agreement requires a Pearson correlation coefficient ＞ 0.95 against the reference diffractogram, because a batch received in a mixed polymorphic form displayed a dissolution half‑time in dimethyl sulfoxide that increased from 4 min to 18 min, markedly retarding the kinetics of HATU‑mediated coupling and reducing conversion after a fixed 2‑h agitated hold time. The DMSO‑d₆ stock solutions prepared for liquid‑handler aspiration are used within 8 h to avoid ester hydrolysis artefacts; ¹H NMR monitoring of a 0.2 M solution stored at 25 °C revealed 0.3 mol% of free carboxylic acid after 24 h, which can compete with the intended amine nucleophile and produce erroneous SAR data. These precautionary controls were instituted after a lead optimization program for a kinase inhibitor encountered 18 % false‑negative rate in the primary screen traced to low‑potency batches of the fragment that still passed HPLC purity testing, highlighting that chromatographic purity alone does not guarantee functional equivalency in high‑throughput chemistry.

Deposition of a heterocyclic azo dye onto polyethylene terephthalate fibres was achieved when the ester was reduced with lithium aluminum hydride in tetrahydrofuran at ‑10 °C to the corresponding alcohol, which was then oxidized to the aldehyde and condensed with 4‑amino‑N,N‑diethylaniline via a diazonium coupling sequence. The presence of the ethyl ester allows a late‑stage functional differentiation from bromide, enabling consecutive Stille coupling at C‑2 followed by saponification and Curtius rearrangement to install a carbamate moiety that enhances wash‑fastness on polyester fabric to a rating of 4‑5 according to ISO 105‑C06:2010 (test A2S, 40 °C). The bromine atom, when retained in the final chromophore, contributes to the bathochromic shift due to its electron‑withdrawing effect and increases the molecular extinction coefficient to above 30 000 L mol⁻¹ cm⁻¹. Process‑scale diazotization of the intermediate amine in phosphoric acid at 0–5 °C must be tightly controlled because the exotherm can rise abruptly when half‑equivalent of sodium nitrite has been added; in a 500 L glass‑lined vessel, a jacket temperature of  ‑5 °C and a nitrite addition rate limited to 0.8 kg/min kept the internal temperature below 7 °C, preventing nitrosamine side‑product formation that would otherwise require photolytic destruction of the effluent.

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Certification & Compliance

2-Bromo-Thiazole-5-Carboxylic Acid Ethyl Ester is manufactured under an ISO 9001 quality system and complies with relevant regulatory requirements.
COA, SDS/MSDS, and related certificates are available upon request. For certificate requests or inquiries, contact: sales9@bouling-chem.com.

More Introduction

A heterocyclic building block with the IUPAC designation ethyl 2-bromo-1,3-thiazole-5-carboxylate (CAS 63987-98-0, molecular formula C₆H₆BrNO₂S, molecular weight 236.09 g·mol⁻¹) is supplied as a white to pale yellow crystalline powder exhibiting a melting point range of 44–47 °C when purity by reversed‑phase HPLC (C18 column, acetonitrile/0.1% phosphoric acid gradient, UV detection at 254 nm) meets or exceeds 97.5% area. Moisture content, determined by Karl Fischer coulometry, is controlled to ≤0.5%, and residual palladium from upstream bromination steps is routinely quantified by ICP‑MS against an internal standard, with a specification ceiling of 50 ppm. The material is shipped in amber glass bottles purged with argon, as exposure to ambient air at relative humidity above 60% over 24 h initiates ester hydrolysis that produces 2‑bromothiazole‑5‑carboxylic acid, detectable by an additional peak at retention time 3.2 min in the HPLC chromatogram. Bulk density, not a controlled parameter in research‑grade lots, typically falls between 0.45 and 0.55 g·cm⁻³ when filled by vibratory feeder into 1‑L high‑density polyethylene drums; variation between batches of the same supplier has led to downstream mixing issues in twin‑screw granulation trials where screw torque drifted by ±8% when volumetric feeders were not recalibrated to the measured loose density.

How Does the 2‑Bromo Substituent Influence Cross‑Coupling Reactivity Relative to Other Halogenated Thiazole Esters?

In palladium‑catalyzed Suzuki‑Miyaura couplings conducted on kilogram scale in a 50‑L glass‑lined reactor, ethyl 2‑bromothiazole‑5‑carboxylate reacts with arylboronic acids bearing electron‑withdrawing substituents (e.g., 4‑cyanophenylboronic acid) at 80 °C in a toluene/ethanol/water ternary mixture using Pd(PPh₃)₄ at 0.5 mol% loading, reaching >95% conversion by HPLC within 4 h. The 2‑bromo position is markedly more electrophilic than the 5‑bromo isomer; in competitive experiments under identical conditions, ethyl 5‑bromothiazole‑2‑carboxylate required 1.2 mol% catalyst and 8 h to achieve equivalent conversion, a consequence of the ring electronics where the electronegative nitrogen at position 3 withdraws electron density more effectively from C‑2 than from C‑5. This electronic bias has been corroborated by Hammett σ meta values derived from ¹³C NMR chemical shift differences in substituted thiazoles, though published data for this specific configuration is limited to academic kinetic studies. In contrast, the 2‑chloro analogue (CAS 152300-56-8) demands phosphine ligands with higher σ‑donor character—typically SPhos or XPhos at 2 mol%—to compensate for the lower propensity toward oxidative addition; plant engineers at an Indian CDMO reported a median turnover number of 190 for the bromo ester versus 85 for the chloro ester in Negishi couplings with secondary alkylzinc reagents on a 20‑mol scale, data captured from 12 consecutive GMP campaigns.

Storage Instability and Degradation Pathways in Bulk Manufacturing Campaigns

The compound’s hydrolytic lability under basic or humid conditions imposes strict storage requirements that differ from its 5‑carboxylic acid homologues. During a 12‑month stability study conducted per ICH Q1A(R2), lots stored at 25 °C/60% RH in original amber glass containers retained 98.6% of initial assay, whereas aliquots transferred into low‑density polyethylene bags under ambient conditions developed 2.1% of the free acid within 72 h. The solid is only moderately light‑sensitive; UVA irradiation (365 nm, 8 mW·cm⁻²) for 48 h induces 0.3–0.5% formation of a dimeric species identified by LC‑MS as the disulfide‑bridged bis‑thiazole, though the photodegradation quantum yield has not been formally determined. For process chemists executing amide bond formations under Schotten‑Baumann conditions, the simultaneous presence of triethylamine and water above 5 volume‑percent causes rapid ester saponification even at 0 °C; a freeze‑pump‑thaw protocol to exclude dissolved CO₂ is recommended before initiating any amine coupling in aqueous alkali, as dissolved carbonate generates a ethylcarbonate intermediate that diminishes yield by 8–12%.

Purity‑Profile Differences Between Research‑Grade and Multi‑Kilogram Lots

Commercially available material from three major catalogue suppliers exhibits a recurrent impurity fingerprint distinct from that of the corresponding 2‑chloro ester. In addition to the des‑bromo thiazole‑5‑carboxylic acid ethyl ester (arising from hydrodebromination during synthesis), batches flowing through a Chinese fine‑chemical supply chain consistently show the 2,5‑dibromo regioisomer at 0.3–1.1%, whereas European‑sourced material limits this dibrominated analogue to ≤0.15%. This differential carries consequences for pharma intermediates that rely on selective mono‑functionalization: when the dibromo content exceeds 0.8%, subsequent Suzuki coupling yields a bis‑aryl by‑product that co‑elutes closely with the desired mono‑aryl product on a silica column (ΔRf 0.05 in hexane/ethyl acetate 8:2), elevating purification costs. The root cause traced in one vendor audit lay in a bromination step that used N‑bromosuccinimide without exact stoichiometric control, a factor not applicable to the 2‑chloro synthesis which proceeds via Sandmeyer chemistry from 2‑aminothiazole‑5‑carboxylic acid ethyl ester and therefore avoids di‑halogenation almost entirely.

Comparative impurity profile across supply sources (HPLC at **254** nm, C18, acetonitrile/water/0.1% TFA gradient)
Impurity	European source (%)	Asian source A (%)	Asian source B (%)
Des‑bromo ethyl ester	0.22 ± 0.03	0.41 ± 0.07	0.65 ± 0.11
2,5‑Dibromo ethyl ester	0.12 ± 0.02	0.95 ± 0.17	0.68 ± 0.09
Hydrolysed acid	0.05 ± 0.01	0.10 ± 0.03	0.08 ± 0.02
Unknown RRT 1.34	0.08 ± 0.02	0.13 ± 0.04	0.11 ± 0.03

When 2‑Bromo‑Thiazole‑5‑Carboxylic Acid Ethyl Ester Serves as a Key Starting Material in SGLT2 Inhibitor Analogue Synthesis Process development reports for dapagliflozin analogues have documented the use of this ester to construct the C‑aryl glycoside precursor. On a 15‑kg input scale, the Suzuki coupling with a tetra‑O‑benzyl‑protected glucal boronate is run at 70 °C in dioxane/water (4:1) with Pd(dppf)Cl₂·CH₂Cl₂ at 0.8 mol%; after 6 h, the organic layer shows 91% conversion, which contrasts with 79% conversion obtained when the 2‑iodo ester (synthesized in‑house) was substituted under identical conditions, likely due to competing homocoupling of the more labile iodo derivative. The bromo ester’s balance of reactivity and stability has made it a preferred intermediate in several clinical‑phase programs, though the requirement to pre‑dry all solvents over 3 Å molecular sieves and to monitor water by Karl Fischer before catalyst addition is often cited in campaign reports as a bottleneck that adds 3–4 h per batch.

Physical Compatibility with Automated Solid‑Dispensing Platforms

The crystalline form exhibits a needle‑habit morphology (observed under polarized light microscopy at 50× magnification) that affects flowability through vibratory dosers. In a head‑to‑head dispensing accuracy trial on a Chemspeed Swing platform using 25‑mL glass vials, the ethyl ester achieved a relative standard deviation of 4.2% for 20‑mg targets, compared to 2.1% for the platelet‑shaped crystals of the methyl ester analogue (CAS 54045-79-3). Granulation with 1 wt% hydrophilic fumed silica (Aerosil 200) reduced RSD to 2.8% without affecting subsequent amidation yields, as verified by reaction monitoring across 96‑well plate formats.

What Limits Application in Palladium‑Free C–C Bond‑Forming Sequences?

Efforts to deploy the ethyl ester in photoredox transformations using an iridium(III) catalyst under blue LED irradiation (450 nm, 15 W) showed that the bromothiazole substrate undergoes single‑electron reduction only at cathodic potentials more negative than –1.9 V versus Ag/AgCl, putting it at the edge of the accessible potential window for many standard photocatalysts. Cyclic voltammetry in dry acetonitrile containing 0.1 M TBAPF₆ gave an irreversible reduction wave at Eₚ = –2.16 V, whereas the 2‑chloro ester displayed no reduction event before solvent breakdown. This limits its use in reductive cross‑electrophile couplings with nickel cocatalysts unless sacrificial anodes are employed; a recent study attempted a zinc‑mediated reformatsky‑type process but observed >60% protodebromination, likely from in situ generation of thiazole‑derived radicals that abstract hydrogen from solvent. The methyl ester analogue (M.p. 38–40 °C), while cheaper by roughly 30% on a per‑kilogram basis, introduces complications in large‑scale ester hydrolysis steps because the resulting 2‑bromothiazole‑5‑carboxylic acid displays a pKa of 2.1, only 0.3 units higher than the ethyl ester’s acid, making phase‑separation of the lithium salt from organic extracts more challenging. Pilot‑plant data from a generic API manufacturer revealed that extracting the carboxylate into aqueous NaOH (1 M) after saponification of the ethyl ester gave a partition coefficient log D of –1.4 at 25 °C and ionic strength 0.5 M, while the methyl ester‑derived carboxylate showed log D –1.1 under identical conditions, leading to a 4.7% higher product loss in the waste stream.

Comparison of key halogenated thiazole‑5‑carboxylic acid esters for late‑stage diversification
Property	2‑Br ethyl ester	2‑Cl ethyl ester	5‑Br ethyl ester	2‑I ethyl ester^a
CAS	63987-98-0	152300-56-8	61289-99-4	N/A (in‑situ)
M.p. (°C)	44–47	51–53	32–34	58 dec.
Suzuki t₉₀ (h)^b	3.2	7.8	2.1	1.5
Hydrolytic stability (t_1/2, pH 10, 25 °C)	8.3 h	10.1 h	6.5 h	4.2 h
Photoredox window (E_red, V vs Ag/AgCl)	–2.16	not observed	–2.08	not measured
Dibromo contaminant risk	moderate	negligible	low	high

^a Typically prepared as a transient intermediate due to limited commercial availability. ^b Conditions: 4‑cyanophenylboronic acid, Pd(PPh₃)₄ 0.5 mol%, K₂CO₃, dioxane/H₂O 4:1, 80 °C; t₉₀ = time to 90% conversion.

Without a dedicated pre‑formulation step, the needle morphology of the solid leads to bridging in conical‑bottom dryers during post‑synthesis isolation, a failure mode recorded on a 100‑L filter‑dryer when the heel of material remaining after discharge was 7.2% of the batch weight—roughly three times the value observed for the methyl ester under identical nitrogen‑blowdown cycles. Installation of a pneumatic vibrator reduced the heel to 2.1%, and this modification is now standard in dedicated manufacturing suites. In amide bond formations mediated by HATU (O‑(7‑azabenzotriazol‑1‑yl)‑N,N,N′,N′‑tetramethyluronium hexafluorophosphate) and N,N‑diisopropylethylamine in DMF, the ethyl ester’s small steric footprint ensures rapid coupling with hindered anilines; a time‑course study using 2,6‑dimethylaniline observed full conversion in 45 min at 0 °C, whereas the corresponding tert‑butyl ester required 3 h. However, the use of HATU with the ethyl ester must be tightly temperature‑controlled: exotherms exceeding 5 °C above target have been linked to partial epimerization of adjacent chiral centers in amino acid‑derived substrates, as reported in a process for a factor Xa inhibitor candidate.