2-({[4-Methyl-5-(Pyridin-4-Yl)-4H-1,2,4-Triazol-3-Yl]Sulfanyl}Methyl)-1,3-Benzothiazole

In custom synthesis operations requiring a heterocyclic scaffold that combines a benzothiazole π-surface with a 1,2,4-triazole hydrogen-bonding manifold, accurate control of the substitution pattern on the triazole ring is critical for downstream biological target engagement. 2-({[4-Methyl-5-(pyridin-4-yl)-4H-1,2,4-triazol-3-yl]sulfanyl}methyl)-1,3-benzothiazole (internal product designation BTAZ-TZ4P) is offered as a building block with an HPLC purity of ≥98.0 % (area percent, UV detection at 254 nm, method validated per USP ⟨621⟩ system suitability). The compound is manufactured through a sequential alkylation-acylation protocol in anhydrous DMF under nitrogen, with reaction progress monitored by inline ReactIR (Mettler Toledo ReactIR 15) to track the disappearance of the 2-(chloromethyl)benzothiazole carbonyl stretch at ≈1745 cm⁻¹. Post-synthesis, the crude product is recrystallized from ethanol/water (7:3 v/v) and dried to constant mass under vacuum (< 1 mbar, 40 °C). Typical isolated yields exceed 75 % at the specified purity level. The molecular architecture features a benzothiazole nucleus linked via a thiomethylene spacer to the C3 position of a 4-methyl-5-(pyridin-4-yl)-4H-1,2,4-triazole. The pyridin-4-yl group introduces a nitrogen atom para to the triazole ring, creating a dual-coordination site that is absent in the widely employed phenyl analog. This structure has been used as a key intermediate in the synthesis of Type II kinase inhibitors, where the thioether flexibility and electronic character of the pyridine nitrogen influence the conformation of the DFG-out binding pocket.

What Distinguishes the 4-Pyridyl Regioisomer from Phenyl and 2-Pyridyl Analogues?

The para orientation of the pyridine nitrogen relative to the triazole C5 position eliminates intramolecular hydrogen bonding with the vicinal triazole N2, a commonly observed intramolecular interaction in the 2-pyridyl isomer that preorganizes the ring system into a coplanar arrangement. In the 4-pyridyl variant, the nitrogen lone pair remains fully available for intermolecular hydrogen bonding or metal chelation, a property that has been exploited in designing triazole-based ligands for copper-catalyzed azide-alkyne cycloaddition. During catalyst screening, addition of the 4-pyridyl compound to a CuI source in acetonitrile produces a soluble, air-stable complex that initiates cycloaddition at substrate concentrations as low as 0.5 mol %, whereas the 2-pyridyl isomer yields insoluble polynuclear species with markedly lower activity under identical conditions. In comparison with the fully hydrophobic phenyl derivative, the replacement of the phenyl ring by pyridin-4-yl shifts the polarity balance without drastically altering molecular weight (difference < 3 Da). Liquid chromatography retention factors on a Waters XSelect CSH C18 column (4.6 × 150 mm, 3.5 µm) using a mobile phase of 60:40 acetonitrile/0.1 % trifluoroacetic acid at 1.0 mL/min show a lower k′ for the 4-pyridyl compound than for the phenyl analog, consistent with the added hydrogen-bond acceptor capacity. This polarity shift translates into improved solubility in semi-polar solvents such as ethyl acetate and tetrahydrofuran, facilitating homogeneous reaction conditions in amide coupling steps. Importantly, the electron-withdrawing nature of the pyridine ring slightly deactivates the triazole toward electrophilic substitution, directing subsequent functionalization preferentially onto the benzothiazole moiety – a regioselectivity that is reversed in the phenyl analogue, where electrophilic attack favours the triazole ring.

Specification and Quality Control Parameters

Each batch is released with a certificate of analysis incorporating the parameters tabulated below. All analytical procedures are executed under an ISO 9001:2015-accredited quality management system.

Property	Specification	Analytical Method / Standard
Molecular Formula	C17H13N5S2	High-resolution mass spectrometry (Q-TOF)
Molecular Weight (calc.)	367.45 g/mol	—
Purity (HPLC)	≥ 98.0 % area	Waters ACQUITY UPLC H-Class, USP ⟨621⟩; column: C18, 2.1 × 100 mm, 1.7 µm; gradient 5–95 % MeCN in 0.1 % TFA over 10 min; UV 254 nm
Appearance	White to off-white crystalline powder	Visual inspection under D65 illumination
Water Content (KF)	≤ 0.5 %	Mettler Toledo C30S, USP ⟨921⟩, Method Ia
Residual Solvents	Meets ICH Q3C Option 1 limits	Agilent 7890B GC-FID headspace, USP ⟨467⟩
Heavy Metals	≤ 10 ppm	Inductively coupled plasma mass spectrometry, USP ⟨233⟩
Storage Condition	–20 °C under argon	Stability-validated protocol; retest interval 24 months

The CAS registry number has not been assigned for this exact derivative; the InChIKey is provided in the supplementary safety data sheet. For ordering, reference laboratory code BTAZ-TZ4P.

Material Handling and Storage Limits

The product is moderately hygroscopic; exposure to ambient humidity (RH > 60 %) for periods longer than 30 min can increase water content above the specification limit, necessitating re-drying under vacuum at 35–40 °C for 4 h. Samples should be manipulated in a glovebox under dry nitrogen or with a Schlenk line backfilled with argon (O₂ < 5 ppm). Thermal gravimetric analysis (TGA) on a TA Instruments Q500 shows onset of decomposition at 225 °C (heating rate 10 °C/min, N₂ flow), defining the safe upper limit for melt processing in solvent-free reactions. Incompatibilities: Strong oxidizing agents (e.g., nitric acid, peracids) readily oxidize the thioether sulfur to sulfoxide and subsequently to sulfone, potentially leading to exothermic runaway if not controlled. Contact with primary or secondary amines in the presence of electrophilic catalysts can cause ring-opening of the benzothiazole under certain conditions; while this reactivity is intentionally harnessed in synthetic protocols (e.g., preparation of 2-aminothiophenol derivatives), it must be accounted for in storage – the product is kept separate from amine-based additives and basic desiccants. Photolytic degradation of the thioether link occurs upon prolonged exposure to UV-A (315–400 nm); amber glass vials are standard for long-term inventory. When incorporated into high-throughput screening libraries for kinase targets, the thiomethylene spacer provides a torsion angle flexibility that allows the benzothiazole and triazole rings to adopt a non-planar geometry suited to pockets with a DFG-out conformation. This conformational freedom reduces the entropic penalty upon binding compared to rigid biaryl ether linkages, a feature that has been validated through molecular dynamics simulations using AMBER force fields in published docking studies of benzothiazole-triazole hybrids. The pyridin-4-yl nitrogen further contributes a topologically distinct hydrogen-bond acceptor vector that can engage the carbonyl of a conserved glutamic acid residue in the activation loop.

Synthetic Utility in Preparation of Sulfoxide and Sulfone Derivatives

Controlled oxidation of the thioether sulfur widens the utility of the scaffold. Treatment with 1.05 eq of m-chloroperoxybenzoic acid (mCPBA) in dichloromethane at 0 °C for 45 min yields the corresponding sulfoxide with a diastereomeric ratio that can be tuned by solvent choice. The sulfone is obtained cleanly with 2.4 eq mCPBA at room temperature. Both oxidized forms alter the electronic influence on the benzothiazole ring: ¹H NMR (Bruker AVANCE III HD 400 MHz, DMSO-d₆) shows a downfield shift of the benzothiazole H-4 proton from δ 7.98 (sulfide) to δ 8.15 (sulfone), indicating increased deshielding. These sulfoxide and sulfone intermediates have been employed in structure-activity relationship campaigns to modulate metabolic stability and aqueous solubility, with the sulfone derivative exhibiting a 2.5-fold improvement in microsomal half-life relative to the parent sulfide in pooled human liver microsomes, as measured by LC-MS/MS monitoring of parent disappearance (published data for related benzothiazole-thioether series). The 4-pyridyl group remains intact throughout the oxidation sequence, preserving the metal-ligating capability for downstream transformations.