2-Amino-N-(2-Chloro-6-Methylphenyl)-5-Thiazolecarboxamide

Supplied under part number TZ-5-CMP-001, 2‑Amino‑N‑(2‑chloro‑6‑methylphenyl)‑5‑thiazolecarboxamide (CAS 302964‑24‑5, molecular formula C₁₁H₁₀ClN₃OS, M_r 267.73 g·mol⁻¹) is a primary amine‑bearing thiazole scaffold that serves as the southern‑hinge binder in the convergent manufacture of ATP‑competitive tyrosine kinase inhibitors. The crystalline powder, routinely produced in 50‑kg campaigns using carbodiimide‑mediated amidation of 2‑aminothiazole‑5‑carboxylic acid with 2‑chloro‑6‑methylaniline, exhibits a typical HPLC area‑percent purity of 98.5 % at 254 nm (diluent: acetonitrile/water 1:1 v/v). Residual solvent profiles are quantified by headspace GC‑FID in accordance with USP ⟨467⟩ and consistently reported below 0.1 % w/w for acetone, ethyl acetate, and heptane; palladium content is maintained below 10 ppm via trimercaptotriazine‑functionalized silica scavenging. The product’s narrow melting interval (188–192 °C, USP ⟨741⟩) and low amorphous content (<2 % by X‑ray powder diffraction, USP ⟨941⟩) minimize batch‑to‑batch variability in subsequent coupling steps.

What spectroscopic fingerprints differentiate this intermediate from its position isomers?

Distinction from the 4‑chloro‑2‑methyl regioisomer and the 2‑amino‑N‑(2‑chlorophenyl) analog is routinely achieved by ¹H NMR at 400 MHz in DMSO‑d₆. The targeted compound displays a sharp two‑proton singlet at δ 7.22 for the thiazole‑bound –NH₂ group, while the aromatic region reveals the chloro‑methylphenyl pattern: a doublet for the C‑3 proton at δ 7.45 (J = 7.8 Hz), a triplet for C‑4 at δ 7.28, and a doublet for C‑5 at δ 7.32. The amide N–H resonates as a broad singlet at δ 10.15. In the 4‑chloro‑2‑methyl isomer, the C‑3 proton shifts downfield to δ 7.58 owing to altered ring current, providing a unambiguous handle even in crude reaction‑mixture assays. FT‑IR (KBr pellet) confirms the primary amine stretch at 3448 cm⁻¹ and the amide carbonyl at 1664 cm⁻¹; LC‑HRMS (ESI⁺) gives [M+H]⁺ at m/z 268.0312 (±2 ppm), which readily separates from the isobars of the 2‑chlorophenyl analog (m/z 254.0156).

On a 0.5 m² stainless‑steel nutsche filter equipped with a 10 μm polypropylene cloth, the filterability of a 15 % w/v slurry in methyl tert‑butyl ether chilled to 5 °C is governed by the particle‑size distribution attained during the final anti‑solvent crystallization. When laser‑diffraction analysis ( ASTM B822‑17 ) confirms D₅₀ between 15 and 35 μm and D₉₀ below 100 μm, the specific cake resistance measured at a pressure differential of 0.4 bar is 2.7 × 10¹⁰ m·kg⁻¹, translating to a filtration time of 12 min per 5‑kg charge. Deviations outside this PSD window — particularly fines accumulation below 5 μm when the anti‑solvent addition rate exceeds 2.5 L·min⁻¹ in a 100‑L glass‑lined reactor — elevate the cake resistance beyond 5 × 10¹⁰ m·kg⁻¹ and extend filtration beyond 25 min, after which evaporative cooling of the mother liquor initiates secondary nucleation and worsens blinding. Drying under vacuum at 40 °C (<50 mbar) in an agitated‑filter dryer with a jacket temperature deviation kept within ±2 °C reduces residual MTBE below 500 ppm within 8 h; process‑scale batches that underwent spray‑granulation before drying demonstrated a 35 % reduction in lump formation, as evidenced by sieve analysis (ASTM E11‑20).

When residual palladium levels above 10 ppm trigger downstream assay interference in kinase inhibitor conjugation

The convergent synthesis of dasatinib and related 2‑(pyrimidin‑4‑ylamino)‑thiazole‑5‑carboxamides relies on a late‑stage Buchwald‑Hartwig coupling that is exquisitely sensitive to palladium contamination carried through from earlier Suzuki steps on the thiazole ring. Even at levels of 15–20 ppm, residual Pd(0) catalyzes dehalogenation of the 2‑chloro‑6‑methylaniline moiety under the reductive conditions of the amide‑forming step, generating 2‑aminothiazole‑5‑carboxylic acid and 2‑chloro‑6‑methylaniline as assay‑skewing impurities. To meet the required ≤10 ppm threshold, the isolated intermediate is treated in a 20‑L glass‑lined vessel with 10 % w/w trimercaptotriazine‑functionalized silica (QuadraPure TMT) in tetrahydrofuran at 60 °C for 2 h. After decantation and a hot THF rinse, ICP‑MS analysis (USP ⟨730⟩) routinely shows Pd below 5 ppm, a limit validated across 15 consecutive production batches. Use of alternative scavengers such as activated carbon Ecosorb‑C resulted in incomplete capture (residual Pd 12–18 ppm) and introduced iron leachables that coloured the drug substance yellow; these lots were rejected under the customer’s ICH Q3D elemental‑impurity risk assessment.

Decomposition onset temperature as a function of heating rate under nitrogen atmosphere

Thermogravimetric analysis (ASTM D7582) at a heating rate of 10 K·min⁻¹ shows a clean, single‑step mass loss beginning at 238 °C with an onset extrapolated to 245 °C. At 20 K·min⁻¹, the onset shifts to 252 °C, while slow ramping at 2 K·min⁻¹ reveals a low‑temperature shoulder at 225 °C attributable to partial sublimation of the intact molecule before decomposition. Differential scanning calorimetry under nitrogen displays a sharp endothermic melt at 190.5 °C (peak) followed immediately by a broad exotherm (ΔH − 342 J·g⁻¹) corresponding to decomposition; in air, the exotherm shifts lower by 12 °C, indicating a radical‑promoted oxidative pathway. These data inform the maximum safe drying temperature (110 °C) and define the exclusion zone for melt‑based processing operations, where localized hot spots above 220 °C can generate hydrogen chloride gas and char the reactor headspace.

Exposure of the powder to relative humidity above 60 % at 25 °C initiates slow hydrolysis of the exocyclic amide bond; headspace GC‑MS detection of 2‑chloro‑6‑methylaniline after 72 h at 75 % RH confirms the degradation pathway. Lot‑to‑lot dissolution kinetics in anhydrous DMF (Karl Fischer water <100 ppm) exhibit a relative standard deviation of 3.2 % for time‑to‑complete‑dissolution, provided that the PSD D₅₀ remains within the 15–35 μm corridor. The product is therefore double‑bagged with a desiccant sachet under nitrogen and should not be stored in proximity to strong bases (favouring amide saponification) or oxidizing agents that may generate the sulfoxide derivative at the thiazole sulfur. Published data for chronic toxicology of this specific amine substitution pattern are limited; thus, operations involving aerosol‑generation require full enclosure with HEPA‑filtered exhaust.

A comparative survey of aryl substitution patterns in thiazolecarboxamide building blocks

The 2‑chloro‑6‑methyl substitution creates a bis‑ortho‑substituted anilide configuration that retards rotation around the amide C–N bond, giving rise to atropisomerism observable in chiral chromatography (Daicel CHIRALPAK IA column, n‑hexane/ethanol 80:20) at 5 °C. This steric rigidity, absent in the mono‑substituted analogs, translates into higher selectivity when the scaffold is elaborated into a kinase inhibitor; the active‑site DFG‑out pocket accommodates the twisted biaryl motif with an entropic penalty 3–5 kcal·mol⁻¹ smaller than that of the rotationally flexible de‑chloro congener, as inferred from isothermal titration calorimetry against Abl kinase domain constructs reported in the medicinal‑chemistry literature.

Quality‑control integration in multi‑tonne campaigns

All incoming batches are released against this specification after sampling according to ANSI/ASQ Z1.4‑2008 level S‑3. During scale‑up from 1‑kg to 50‑kg scale, a duplicate analysis scheme that cross‑references HPLC with quantitative ¹H NMR (ERETIC method) reduced outlier rejection events by 60 %, primarily by catching particulate contamination that selectively suppressed UV response. Long‑term stability data at 25 °C/60 % RH (ICH Q1A) covering 36 months show no purity drift beyond 0.3 % when the packaging seal integrity is maintained; any breach results in moisture ingress and the appearance of the hydrolysis product 2‑aminothiazole‑5‑carboxylic acid above the 0.5 % identification threshold within 45 days.