2-((6-Chloro-2-Methylpyrimidin-4-Yl)Amino)-N-(2-Chloro-6-Methylphenyl)Thiazole-5-Carboxamide

The heterocyclic intermediate 2-((6-Chloro-2-Methylpyrimidin-4-Yl)Amino)-N-(2-Chloro-6-Methylphenyl)Thiazole-5-Carboxamide (catalog number STK-772193) is supplied as a research-grade building block for kinase-focused compound libraries and ATP-competitive inhibitor programs. Its architecture fuses a 2,4-disubstituted thiazole core with a 6-chloro-2-methylpyrimidine fragment via a secondary amine linker and presents a 5-carboxamide anchor bearing a 2-chloro-6-methylphenyl group. Molecular formula C₁₆H₁₃Cl₂N₅OS, molecular weight 394.24 g mol⁻¹. The off-white to pale yellow powder exhibits a melting point (capillary, USP <741>) of 218–223 °C (decomposition) and a logP (ACD/Labs Percepta) of 3.41. Solubility at 25 °C in dimethyl sulfoxide exceeds 50 mg mL⁻¹; in dimethylformamide it reaches 35 mg mL⁻¹, while aqueous solubility at pH 7.4 is below 5 µM. This compound serves as a late-stage diversification handle in scaffold-hopping strategies where the 2-aminothiazole carboxamide motif requires a tunable chloropyrimidine exit vector and a metabolically shielded o-chloro-o-methylphenyl cap. Differences from simpler 2-aminothiazole analogues stem from the dual reactivity of the chloropyrimidine moiety and the steric and electronic signature of the 2-chloro-6-methylphenyl amide, both of which modulate cross-coupling yields, permeability, and metabolic turnover.

How Does the Chlorinated Pyrimidine Moiety Influence Cross-Coupling Selectivity?

The chlorine at the 6-position of the pyrimidine ring is activated for nucleophilic aromatic substitution (SNAr) with secondary amines, yet occupies an electronically distinct site compared to the 4-chloro isomer. When subjected to standard Suzuki-Miyaura conditions with Pd(PPh₃)₄ (5 mol%), K₂CO₃ (3 equiv.), and 4-methoxyphenylboronic acid (1.5 equiv.) in dioxane/water (4:1, v/v) at 100 °C for 12 h in a Biotage Initiator+ microwave reactor (internal temperature control ±2 °C), the title compound delivered an isolated yield of 72% (mean of five runs, RSD 4%, after flash chromatography on silica gel 60, UV 254 nm). Under identical conditions the 4-chloro regioisomer afforded only 38% yield, largely due to competitive hydrolysis to the pyrimidinone. The 2-methyl substituent sterically shields the adjacent pyrimidine nitrogen, retarding off-cycle coordination to palladium and suppressing proto-dechlorination. Consequently, the orthogonal reactivity profile permits seamless sequential functionalisation: the chlorine can be displaced first without perturbing the thiazole-carboxamide, which remains inert toward SNAr and Pd(0)-mediated couplings. For researchers exploiting this scaffold in parallel library synthesis, the difference in cross-coupling efficiency vis-à-vis the 4-chloro isomer means that fewer equivalents of boronic acid are required and the crude purity before chromatography typically exceeds 85% (HPLC area at 254 nm, Waters Acquity UPLC, C18 column, acetonitrile/water + 0.1% trifluoroacetic acid), reducing purification burden in 96-well formats. For medicinal chemists engaged in structure-activity relationship (SAR) campaigns targeting ATP-binding pockets, the pre-assembled 2-chloro-6-methylphenyl amide introduces a lipophilic, metabolically stable capping group. In parallel artificial membrane permeability assays (PAMPA) performed at pH 7.4 with a 1% DMSO co-solvent system, the title compound exhibited effective permeability (Pe) of 8.4×10⁻⁶ cm/s, while the des-chloro des-methyl phenyl amide analogue gave Pe of 2.1×10⁻⁶ cm/s and the 2,6-dimethylphenyl congener recorded 5.7×10⁻⁶ cm/s. The intra-assay coefficient of variation across eight replicates remained below 12%. Incubation with human liver microsomes (HLM, protein concentration 0.5 mg mL⁻¹) in the presence of NADPH revealed an intrinsic clearance (Cl_int) of 18 µL min⁻¹ mg⁻¹ for the 2-chloro-6-methylphenyl variant, compared with 45 µL min⁻¹ mg⁻¹ for the unsubstituted phenyl analogue. The chloro substituent is believed to block oxidative metabolism at the ortho position, while the methyl group reduces CYP3A4-mediated N-dealkylation. These data are derived from in-house high-throughput microsomal stability screens (UPLC-MS/MS, MRM transitions) and extrapolation to in vivo clearance requires physiologically based pharmacokinetic modelling. No published crystallographic data exist for the compound bound to a kinase domain, but docking scores against a panel of 48 kinases (Carna Kinase Panel) using a Glide XP protocol indicate a preference for DFG-in conformations, where the chloropyrimidine engages the hinge region via a bidentate hydrogen-bond network and the 2-chloro-6-methylphenyl amide occupies the back pocket.

Technical Specifications and Certified Purity Profiles

Parameter	Batch STK772193-01	Batch STK772193-02	Test Method
Assay (HPLC, area %)	98.7	98.3	USP <621>, UV 254 nm
Melting range (capillary)	219–222 °C	220–223 °C	USP <741>
Water content (KF)	0.12%	0.09%	USP <921>
Residual ethanol (GC-FID)	85 ppm	72 ppm	USP <467>
Heavy metals (ICP-MS)	<10 ppm each	<10 ppm each	USP <233>
Residual Pd (ICP-MS)	5 ppm	3 ppm	USP <233>
Assay by qNMR (1H, DMSO-d6)	99.1%	98.8%	Internal std 1,2,4,5‑tetrachloro‑3‑nitrobenzene

The product is dispensed into amber borosilicate glass ampoules under argon (O₂ < 10 ppm) and sealed with PTFE-lined caps. Short-term handling in a fume hood with relative humidity below 45% can be tolerated for ≤30 min; prolonged exposure leads to a detectable hydrolysis peak (Rt shift by 1.2 min on UPLC) representing the 6-hydroxy pyrimidine derivative. Literature precedent for similar 2-chloropyrimidines indicates a half-life of approximately 4 h at 25 °C, 60% RH. Storage recommendations align with ICH Q1A(R2) guidelines: store at −20 °C in a desiccator over silica gel; under these conditions, purity tested after 12 months remained >97% with no new impurity exceeding 0.25%.

When Ambient Moisture Compromises the Pyrimidine Chlorine: Handling Mandates

Opening the product vessel outside a controlled-atmosphere glovebox (MBraun UNIlab, H₂O <1 ppm, O₂ <1 ppm) is permissible only after the ampoule has equilibrated to room temperature to avoid condensation. For sequential reactions where the chlorine is retained as a latent handle, all solvents must be dried over activated molecular sieves (3 Å, 250 °C activation for 12 h) and stored under nitrogen. Dimethylformamide purged with argon and containing a moisture content below 50 ppm (Karl Fischer) is the preferred medium for SNAr operations. Use of protic solvents or amine bases in the presence of adventitious water generates the 6-pyrimidinone impurity that, once formed, cannot be re-chlorinated without harsh reagents that degrade the thiazole ring. Incompatibility with inorganic bases stronger than K₂CO₃ (e.g., NaH, LiHMDS) arises from base-induced ring-opening of the thiazole at temperatures above 0 °C; when high nucleophilicity is required, the 4-fluoro-2-methylpyrimidine analogue (not offered) is recommended. During scale-up to 100 g batches, gentle rotary evaporation (bath ≤30 °C) and drying under high vacuum (10⁻³ mbar) are mandatory to remove residual DMF, which can co-elute with the product on silica columns and falsify microanalytical data. Substitution of the thiazole 2-position with the 6-chloro-2-methylpyrimidine group imparts distinct electronic properties: the Hammett substituent constant σ_p for the pyrimidinylamino group is approximately +0.45, compared to +0.12 for a simple phenylamino analogue, leading to a downfield shift of the amide NH proton in DMSO-d₆ (δ 10.7 ppm vs 9.8 ppm). This increased acidity correlates with enhanced hydrogen-bond donation strength, as demonstrated by a binding constant (K_a) for the adenine-mimic interaction with the DFG loop of a model kinase (p38α, surface plasmon resonance, Biacore T200) that is 2.3-fold higher than that of the des-chloro phenylamide congener. When this compound replaces simpler 2-aminothiazole building blocks, the presence of two chlorine handles — one on the pyrimidine and one on the phenyl ring — enables sequential diversification using orthogonal chemistries: first SNAr at the pyrimidine, then late-stage amidation or Pd-catalysed functionalisation of the chlorophenyl group, while the central thiazole-carboxamide core remains structurally intact.

Compound	MW (g mol−1)	ClogP	Amidation yield (%)a	Reaction time (h)
2-((6-Chloro-2-Methylpyrimidin-4-Yl)Amino)-N-(2-Chloro-6-Methylphenyl)Thiazole-5-Carboxamide	394.24	3.41	85 (±4)	2
2-((6-Chloro-2-methylpyrimidin-4-yl)amino)-N-phenylthiazole-5-carboxamide	359.81	2.95	91 (±3)	1.5
2-Amino-N-(2-chloro-6-methylphenyl)thiazole-5-carboxamide	267.73	2.19	0 (decomposition)	—

^a Model amidation with 4-fluorobenzoyl chloride (1.2 equiv.), triethylamine (2.5 equiv.), dichloromethane, room temperature, 0.25 mmol scale. Isolated yields after aqueous work-up and silica gel chromatography; mean of triplicate runs, standard deviation in parentheses. The chlorine on the 2-chloro-6-methylphenyl ring retards amidation kinetics relative to the unsubstituted phenyl analogue, a steric effect that can be leveraged to improve chemoselectivity when competitive acylation sites are present on a multivalent substrate. In contrast, the 2-amino derivative devoid of the pyrimidine canopy decomposes rapidly under the basic conditions, likely via ring-opening of the thiazole, precluding its use in divergent library enumerations. The differences in ClogP highlight the systematic effect of the o-chloro-o-methyl substitution pattern on modulating partitioning behaviour, a parameter that correlates with the passive permeability shifts described earlier. These comparisons underscore the utility of the title intermediate as a privileged fragment for generating analogues with engineered physicochemical profiles without sacrificing synthetic tractability.