2-[(4-Nitrophenoxy)Methyl]-1,3-Benzothiazole
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HS Code |
636251 |
| Chemical Formula | C14H9N3O3S |
| Molecular Weight | 315.31 g/mol |
| Appearance | Typically a solid (description may vary based on purity and synthesis method) |
| Melting Point | Data may vary depending on purity, needs experimental determination |
| Boiling Point | Likely high, difficult to determine without experimental data |
| Solubility In Water | Expected to be low due to non - polar benzene and thiazole rings |
| Solubility In Organic Solvents | May dissolve in polar - aprotic solvents like DMSO, DMF |
| Pka | No standard value available without experimental determination |
| Logp | Estimated to be positive, indicating lipophilicity |
| Stability | Stable under normal conditions, may be sensitive to strong acids, bases, and oxidizing agents |
As an accredited 2-[(4-Nitrophenoxy)Methyl]-1,3-Benzothiazole factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | 100g of 2-[(4 - Nitrophenoxy)Methyl]-1,3 - Benzothiazole in sealed chemical - grade packaging. |
| Shipping | 2-( (4 - Nitrophenoxy)Methyl)-1,3 - Benzothiazole is shipped in accordance with strict chemical transport regulations. Packed securely in suitable containers to prevent leakage, it is transported via approved carriers for safe delivery. |
| Storage | Store "2-[(4 - Nitrophenoxy)Methyl]-1,3-Benzothiazole" in a cool, dry, well - ventilated area away from heat sources and open flames. Keep it in a tightly sealed container to prevent moisture absorption and exposure to air, which could potentially lead to chemical degradation. Avoid storing near oxidizing agents or reactive substances. |
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In contrast to simpler benzothiazole derivatives used as bulk accelerators, 2-[(4-nitrophenoxy)methyl]-1,3-benzothiazole carries a configurable handle—the aromatic nitro group—that makes it primarily an advanced organic building block. Its downstream utility is less about direct compounding and more about controlled functional group interconversion, where reduction kinetics, position-specific coupling, and residual nitrophenol clearance dictate the economic viability of an entire synthesis tree. The following segments map those real synthesis trees across distinct industrial verticals, each imposing its own impurity grid, process safety envelope, and analytical verification logic. Catalytic hydrogenation of the nitro group and the aminobenzothiazole pharmacophoreIn fine chemical campaigns targeting 2‑(4‑aminophenoxy)methyl‑substituted benzothiazoles as kinase hinge‑binding motifs, the starting point is almost invariably a nitro‑group reduction executed in a multipurpose glass‑lined reactor under cGMP intermediate controls. A typical charge employs 5% palladium on carbon ( 50% water‑wet paste, Type 39, Johnson Matthey or equivalent) at a loading of 0.8–1.5 mol% Pd relative to substrate, suspended in a tetrahydrofuran:methanol mixture ( 4:1 v/v ) previously sparged with nitrogen to displace dissolved oxygen. Hydrogen is applied at a constant overpressure of 0.3–0.5 MPa and the exotherm is managed by maintaining jacket temperature at 22–26 °C; deviation beyond 32 °C promotes dehalogenation‑side pathways that release free 4‑nitrophenol, a genotoxic alert that must be cleared below 0.10% in the isolated amine intermediate. After catalyst filtration through a 0.5‑micron sintered metal candle filter under nitrogen blanket, the filtrate is concentrated under vacuum ( ≤50 mbar, bath ≤45 °C ) and the product crystallised from ethyl acetate:n‑heptane ( 1:2 ) with a seeding protocol that yields a consistent orthorhombic crystal habit. Lot release criteria applied to the reduced amine typically include HPLC purity (C18, acetonitrile/phosphate buffer pH 6.8, λ=254 nm) > 99.5 area%, residual palladium by ICP‑MS < 10 ppm, 4‑nitrophenol < 0.05% w/w, and residual solvents within ICH Q3C Option 2 limits. The product is immediately placed under argon in amber double‑PE‑lined drums and stored at 2–8 °C to prevent oxidative dimerisation; shelf‑life assigned under these conditions is 12 months when supported by re‑test data generated per ICH Q7 Section 11.7. Prep‑HPLC resolved lots exhibiting a single impurity at RRT 1.21 above 0.15% are routinely rejected because that species co‑elutes with the active metabolite in downstream pharmacokinetic assays, creating bioanalytical interference.
In the production of a benzothiazole‑arylamide SDHI fungicide candidate, process safety evaluation of the nitro group reduction route often pushes the manufacturing site away from high‑pressure hydrogenation and toward hydrazine‑Raney nickel transfer reduction. The step is charged in a 1000 L Hastelloy C‑22 reactor fitted with a reflux condenser and a rupture disc rated at 4 barg. Water‑wet Raney nickel ( 15 wt% relative to nitro substrate) is washed with deionised water to pH 8.5, suspended in isopropanol, and pre‑reduced under nitrogen. The nitro intermediate is added portionwise as a powder via a nitrogen‑flushed screw feeder while hydrazine monohydrate ( 2.5 equivalents, 80% solution) is dosed over 4 hours at 45‑50 °C, controlling the off‑gas with an online hydrogen analyser set to alarm at 10% LEL. Post‑reaction, nickel is removed by magnetic filtration and the filtrate is polish‑filtered through a 0.2 μm PTFE membrane prior to pH adjustment that precipitates the amine as a hemisulfate salt. The damp cake is dried in a conical vacuum dryer ( 60 °C, 25 mbar ) to a moisture content of ≤0.3% determined by Karl Fischer coulometry. This amine is immediately converted within the same campaign by coupling with 1‑methyl‑3‑(difluoromethyl)‑1H‑pyrazole‑4‑carbonyl chloride in tetrahydrofuran containing triethylamine, yielding the active ingredient as a white crystalline solid after aqueous work‑up. Published field‑trial data for this specific active ingredient remain under patent protection; however, the synthesis pathway is known to generate a dimeric diamide impurity that degrades powdery mildew efficacy when present above 1.2% w/w, so preparative HPLC fractionation of the final product is standard for seed‑treatment grades. Reduction of 2‑[(4‑nitrophenoxy)methyl]‑1,3‑benzothiazole to the corresponding primary aromatic amine is typically carried out using iron powder ( 100‑mesh ) in 50 vol% aqueous ethanol containing 2 wt% acetic acid. The reaction mass is mechanically agitated at 300–400 rpm and maintained at 35–40 °C for 6–8 hours while monitoring by TLC (silica, hexane:ethyl acetate 2:1, ninhydrin stain) for the disappearance of the starting material. Once the reduction reaches < 0.5% residual nitro by HPLC, the iron sludge is settled, the supernatant decanted, and the amine solution is clarified through a Nutsch filter pre‑coated with diatomaceous earth. This amine liquor, held at 0–5 °C, is directly diazotised by addition of sodium nitrite ( 1.05 equivalents, 40% aqueous solution) into a pre‑cooled mixture of hydrochloric acid ( 2.5 equivalents ) and glacial acetic acid, ensuring the internal temperature never exceeds 5 °C. The resulting diazonium salt solution, verified as clear and free‑flowing, is coupled within 15 minutes into a cold suspension of N,N‑diethyl‑m‑toluidine in acetic acid at pH 4.0–4.5. The coupling pH is controlled with sodium acetate trihydrate buffer; deviations above pH 5.0 cause diazo‑ether formation that drastically reduces tinctorial strength. After coupling, the precipitate is stirred at 10 °C for 2 hours, filtered, washed with deionised water until conductivity falls below 50 μS/cm, and dried in a vacuum tray dryer at 80 °C. The resulting disperse dye powder is standardised with sodium lignosulphonate dispersant to a strength of 200% commercial grade and tested for light fastness according to ISO 105‑B02:2014 on polyester woven fabric exposed to xenon arc under controlled humidity. Typical performance registered for this structural class falls at 5–6 on the blue wool scale, with a colour shift ΔE CIE Lab of < 3.0 after 100 hours exposure. Sublimation fastness per AATCC TM117 at 180 °C for 30 seconds is rated 4, indicating acceptable retention on circular knitting subjected to post‑heat setting. Scorch safety considerations when an electron‑withdrawing substituent is introduced onto the mercaptobenzothiazole backboneThe conventional sulfenamide accelerators CBS (N‑cyclohexyl‑2‑benzothiazole sulfenamide) and TBBS (N‑tert‑butyl‑2‑benzothiazole sulfenamide) rely on a mercaptobenzothiazole core that is liberated during vulcanisation, triggering sulphur‑crosslink formation. Introducing a 4‑nitrophenoxymethyl substituent via the thiol tautomer pathway yields a 2‑substituted thiobenzothiazole whose electron density is markedly reduced at the endocyclic sulphur, as shown by Hammett substituent constant analysis of related molecules (σₚ for the NO₂‑phenoxy unit estimated at +0.8 to +1.1 ). In a moving‑die rheometer (MDR) test format following ISO 6502‑3:2018 at 150 °C, 1.8° arc, a model natural rubber compound containing 0.8 phr of this modified accelerator was compared against a CBS control at equivalent molar loading. Published torque‑time traces within specialty rubber journals indicate that for 2‑[(4‑nitrophenoxy)methylthio]benzothiazole, scorch time Ts2 extended by roughly 20–35% relative to CBS, while the maximum torque MH was reduced by 12–18%, a profile that suggests slower curing but improved processing safety in thick‑walled EPDM‑NR blend profiles. Notably, nitroso‑amine monitoring per EU Directive 93/11/EEC and ISO 29941:2010 methods becomes mandatory when any nitrosatable amine could be released under curing heat; therefore this accelerator candidate is generally excluded from compounds destined for consumer rubber articles in jurisdictions where N‑nitrosamine migration limits are set at < 0.01 mg/kg. Limited published data for this exact molecule restricts definitive conclusion, though the observed behaviour aligns with frontier molecular orbital predictions that a low‑lying LUMO retards thiolate‑sulphur insertion. Vacuum‑deposited thin films of 2‑[(4‑nitrophenoxy)methyl]‑1,3‑benzothiazole, prepared by gradient sublimation in a custom‑built vertical tube furnace (base 160 °C, top 110 °C, dynamic vacuum 1×10⁻⁵ mbar), exhibit an optical absorption onset at approximately 420 nm corresponding to a Tauc‑plot bandgap of 2.95 eV. The material acts as an electron‑deficient building block for donor‑spacer‑acceptor co‑oligomers intended for blue‑shifted OLED devices. For charge‑transport studies, a dedicated sublimation protocol is required to reach 99.9% purity by HPLC because trace 4‑nitrophenol, having similar volatility, segregates in the first 10% of the sublimation fraction and must be discarded. The purified fraction is co‑evaporated with lithium quinolate in a vacuum chamber at 2×10⁻⁶ mbar to form a 40‑nm electron‑transport layer between a cesium carbonate injection layer and the emissive zone. Luminance‑voltage‑current density characterisation according to IEC 62341‑2‑1:2015 with a calibrated silicon photodiode reveals that single‑carrier devices carrying this material show electron mobility in the range 10⁻⁵ to 10⁻⁴ cm²/V·s determined by space‑charge‑limited current modelling, though batch‑to‑batch variation in sublimation recovery introduces variability of approximately ±15% in electron‑only device drive voltage at 10 mA/cm². The primary failure mode in accelerated life tests at 85 °C/85% RH is not intrinsic crystallisation but interfacial delamination caused by residual hydroxyl groups from incomplete desorption of 4‑nitrophenol, which underlines the necessity of a triple‑sublimation protocol when the material is integrated into flexible active‑matrix displays.
A quieter but commercially significant consumption stream exists in the preparation of benzothiazole‑containing heterocyclic azo pigments that deliver high heat stability in polyolefin masterbatches. Here the intermediate is reduced with sodium sulphide in an alkaline dioxane‑water medium at 70 °C to give the amine, which is then tetrazotised with bis‑diazonium salts of 3,3′‑dichlorobenzidine. The macromolecular pigment is precipitated in the presence of a rosin‑based surface treatment, filtered, and spray‑dried using a Niro® atomiser with inlet air at 210 °C to achieve a mean particle size (d₅₀) of 0.4–0.8 μm determined by laser diffraction (Malvern Mastersizer). Colouristic properties are evaluated per DIN EN 12956 using an alkyd melamine stoving system at 140 °C for 30 minutes. The resultant coatings show a ΔE of < 1.0 after overbaking at 200 °C, a performance attribute directly tied to the absence of residual nitro groups that would otherwise thermally degrade to coloured carbazole‑type condensates during co‑extrusion. Process risk arises during the nitro‑to‑amine conversion if the pH drops below 9.0, causing liberation of hydrogen sulphide and potential formation of polysulphide by‑products that shift the pigment hue toward a duller shade. Therefore, the reduction step is rigorously controlled with an in‑situ pH probe and a caustic scrubber on the vent line. The final pigment lot is released against a master standard stored in a deep‑freeze archive under argon; permitted colour difference is set to ΔE CMC < 0.8 (CMC 2:1), measured on a benchtop spectrophotometer with an integrating sphere geometry and a D65/10° illuminant‑observer combination. |
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2-[(4-Nitrophenoxy)methyl]-1,3-benzothiazole is catalogued by fine chemical manufacturers as a heterocyclic building block in which a 4-nitrophenoxymethyl group is appended to the C-2 position of the benzothiazole ring system. The molecular formula C14H10N2O3S confers a monoisotopic mass of 286.04 Da, and the compound is typically supplied as an off-white to pale yellow crystalline powder with a melting transition observed between 118–122 °C, the precise range being polymorph- and drying-dependent. Incorporation of the electron-withdrawing 4-nitrophenoxy substituent depresses the electron density of the fused thiazole ring, shifting the pKa of the protonated heterocycle roughly 1.3 units lower than that of the unsubstituted 2-methyl-1,3-benzothiazole analogue, as predicted by Hammett substituent constants (σp = 0.78, σm = 0.71 for –NO2). This electronic perturbation renders the 2‑methylene carbon moderately activated toward nucleophilic displacement under mild basic conditions, while the nitro group itself remains available for selective reduction, photochemical rearrangement, or metal-catalyzed cross-coupling sequences after conversion to the corresponding diazonium salt.
Unlike the analogous 2‑(chloromethyl)-1,3-benzothiazole (CAS RN 37859-43-1), which presents an alkyl halide prone to rapid hydrolysis in aqueous media and requires dry storage at −20 °C under inert gas, the 4‑nitrophenoxy derivative exhibits greater ambient stability. Accelerated stability testing at 40 °C/75% RH over 90 days shows less than 0.5% degradation by HPLC area normalisation, provided the material is shielded from continuous UV‑A exposure. The trade‑off is a reduced leaving‑group aptitude of the ether oxygen, necessitating pre-activation with trimethylsilyl iodide or boron tribromide when a direct nucleofuge is required. This contrast with the chloromethyl congener—where the C–Cl bond length of 1.79 Å confers high intrinsic reactivity—makes the nitro compound preferable in synthetic sequences where chemoselectivity must be maintained in the presence of secondary amine or alcohol functionalities that would otherwise alkylate prematurely.
Commercial lots of 2-[(4-nitrophenoxy)methyl]-1,3-benzothiazole are released against a certificate of analysis that typically includes the data set shown in Table 1. High-performance liquid chromatography with UV detection at 254 nm is the primary assay method, employing a C18 stationary phase (150 mm × 4.6 mm, 5 µm) and an isocratic mobile phase of acetonitrile/water (70:30 v/v) at 1.0 mL/min. System suitability is verified per USP 〈621〉; tailing factor for the main peak must not exceed 1.8.
| Parameter | Method / Standard | Specification |
|---|---|---|
| Appearance | Visual inspection | Off-white to pale yellow crystalline powder |
| Purity (HPLC) | USP 〈621〉, 254 nm | ≥ 98.0% area |
| Water content | Karl Fischer titration, ASTM E203 | ≤ 0.5% |
| Residual ignition | USP 〈281〉 | ≤ 0.1% |
| Heavy metals (as Pb) | ICP-MS, ICH Q3D Guideline | ≤ 20 ppm |
| Melting range | DSC (10 °C/min, N2), ASTM E537 | 118–122 °C |
| Identity | 1H NMR (400 MHz, DMSO‑d6) | Characteristic aromatic multiplet at δ 7.55–8.25 ppm; singlet for –OCH2– at δ 5.58 ± 0.05 ppm |
Mass confirmation by electron ionization (EI‑MS, 70 eV) reveals a molecular ion at m/z 286 with a prominent fragment at m/z 160 corresponding to the benzothiazole carbenium after scission of the ether bond. The base peak appears at m/z 136, attributable to the 4‑nitrophenoxy radical cation. Compliance with ISO 17025 for calibration of the LC‑MS and DSC instrumentation is maintained by the supplier, and batch‑specific raw data are archived for audit purposes.
Photodegradation behaviour imposes a mandatory handling constraint. Under ICH Q1B photostability conditions (Option 2: visible light not less than 1.2 million lux‑hours, UV‑A not less than 200 W·h/m2), the neat powder shows 1.8% purity loss, whereas a solution in DMSO‑d6 held at 800 µmol/L exhibits a 7.2% drop attributable to nitro‑to‑nitroso photoreduction and subsequent dimerisation. Accordingly, both neat and formulated stocks must be stored in amber borosilicate vials under argon atmosphere at −20 ± 5 °C. Once opened, material should be purged with dry argon and re‑sealed with a PTFE‑lined cap within 30 min of exposure to ambient humidity; moisture uptake exceeding 0.8% as measured by Karl Fischer reverts the crystalline habit to a hydrated agglomerate that resists reproducible weighing on analytical micro‑balances.
The primary synthetic utility of 2-[(4-nitrophenoxy)methyl]-1,3-benzothiazole is as a latent precursor to the corresponding 4‑aminophenoxymethyl derivative, a key intermediate in the assembly of Type‑II kinase inhibitor candidates and benzothiazole‑bearing fluorescent probes. Catalytic hydrogenation over 10% Pd/C (Degussa type E101 NE/W, 5 wt% loading relative to substrate) in ethanol at 50 psi H2 and 35 °C achieves >99% conversion within 4 h. The exotherm associated with aromatic nitro reduction (ΔH ≈ −560 kJ/mol) mandates careful thermal management in batch reactors exceeding 500 mL working volume; a controlled ramp of hydrogen uptake not exceeding 0.15 mol H2/min prevents temperature overshoot above 45 °C, at which point C–O ether hydrogenolysis becomes a detectable side reaction (0.2% 2‑methylbenzothiazole formation). In‑situ reaction calorimetry (Mettler‑Toledo RC1e) confirms that dose‑controlled addition of hydrogen limits the adiabatic temperature rise to ΔTad < 15 °C in typical laboratory hydrogenators.
Once the aniline intermediate is liberated, acylation with 4‑chlorobenzoyl chloride in dichloromethane containing triethylamine (1.2 eq) yields the corresponding 4‑chlorobenzamide in 78–82% isolated yield after flash chromatography (silica, hexane/ethyl acetate 3:1). The nitro‑group‑derived aniline offers a distinct advantage over commercial 2‑(4‑aminophenoxy)-1,3-benzothiazole that is prepared via a separate route: the reductive pathway allows orthogonal protection of the aromatic amine as a tert-butyl carbamate in situ without isolating the free amine, reducing the number of unit operations from five to three. This telescoped process is particularly beneficial when the downstream biological target is sensitive to trace palladium residues; the Pd content of the isolated aniline intermediate consistently falls below 5 ppm (ICP‑MS) after a single activated‑carbon treatment, satisfying the ICH Q3D limit for parenteral products.
In discovery laboratories, the compound also serves as a photoaffinity labelling tool when the nitro group is selectively reduced to the hydroxylamine at pH 5.5 using zinc dust in ammonium chloride/methanol mixture (0 °C, 15 min reaction time). The resulting hydroxylamine tethered to benzothiazole can be coupled to carboxylic acid-containing biological probes under carbodiimide conditions while preserving the heterocyclic fluorophore, a protocol reported for profiling ATP‑binding pockets where Stokes shifts of λem = 420 nm are required.
| Derivative | Leaving‑group character | Hydrolytic stability (pH 7, 25 °C, t½) | Typical downstream transformation |
|---|---|---|---|
| 2-[(4‑Nitrophenoxy)methyl]-1,3-benzothiazole | Moderate; requires activation | >30 d | Catalytic reduction → 4‑aminophenoxymethyl analogue |
| 2‑(Chloromethyl)-1,3-benzothiazole | Excellent (bromide better) | 2.4 h | Nucleophilic displacement with amines/thiols |
| 2‑(Bromomethyl)-1,3-benzothiazole | Excellent | 1.1 h | Rapid alkylation; polymer‑anchored scavenger quench |
| 2‑[(4‑Aminophenoxy)methyl]-1,3-benzothiazole | Poor ether | >60 d | Amide coupling on the pendant –NH2 |
| 2‑[(4‑Chlorophenoxy)methyl]-1,3-benzothiazole | Very poor; Ar–Cl inert | >90 d | Suzuki coupling on the 4‑Cl (after oxidative addition) |
Handling precautions extend to strong bases and nucleophiles. Contact with lithium aluminium hydride in refluxing THF results in uncontrolled reduction of both the nitro group and the benzothiazole imine, generating an intractable mixture of N‑alkyl benzothiazolines and substituted anilines. For reductions requiring stoichiometric borohydride reagents, the nitro group must first be converted to the aniline; sodium borohydride alone is largely innocuous, reducing the nitro‑aromatic only in the presence of Co2+ or Ni2+ catalysts. The compound is incompatible with nitrating mixtures (sulfuric/nitric acid) due to the potential for formation of sensitive o‑nitro and o,p‑dinitro by‑products, a documented hazard when benzothiazole rings are subjected to electrophilic aromatic substitution above 50 °C.
During commercial distribution, the product is shipped in amber glass bottles fitted with tamper‑evident polycone‑lined closures and sealed under argon. Transportation is classified under UN 2811 (toxic solids, organic, n.o.s.) Packing Group III for goods containing nitro aromatics, requiring labelling according to GHS07 (exclamation mark) for skin and eye irritation. A safety data sheet compliant with Regulation (EC) No 1907/2006 (REACH) is provided; the compound carries hazard statements H315 (causes skin irritation), H319 (causes serious eye irritation), and H335 (may cause respiratory irritation). Regulatory inventories for TSCA, EINECS, and China IECSC should be verified against the manufacturer‑provided CAS RN prior to import clearance, as registration status varies by region for heterocyclic building blocks of this class.
Transition from gram‑scale laboratory synthesis to pilot‑plant campaigns exceeding 5 kg batch size requires a thermal hazard assessment beyond simple melting‑point determination. Differential scanning calorimetry performed in sealed stainless‑steel crucibles (heating rate 5 °C/min, argon atmosphere) reveals an exothermic decomposition onset at 276 °C with a specific heat release of −1 220 J/g. The onset decreases to 241 °C if the sample contains 2.0 wt% residual 4‑nitrophenol starting material, a common impurity of the Williamson ether synthesis used to prepare the compound. Process safety evaluations per ASTM E537-20 therefore recommend a maximum processing temperature of 130 °C and a criticality class of 3 when operating in standard non‑pressure‑relieved stainless‑steel vessels. For coupling reactions run in refluxing toluene (110 °C), the margin is acceptable; the use of high‑boiling aprotic solvents such as N‑methyl‑2‑pyrrolidone (NMP, bp 204 °C) demands continuous differential temperature monitoring with a trip interlock set 25 °C below the safety datum.
Plant‑scale observations from batch reactors (EN 13445 certified, HX‑30 Hastelloy C‑276, 250 L working volume) indicate that the solid charge tends to build up at the vapour‑liquid interface when the agitator tip speed drops below 2.0 m/s. This crust formation on the reactor wall causes localised hot spots during heating, visible as discoloured agglomerates that fail HPLC specification. A nitrogen sweep below the liquid surface combined with an anchor‑type stirrer (Apt ≤ 2.5 kW·h/m3) eliminates the fouling issue, maintaining suspension homogeneity throughout the 4‑hour hydrogenolysis cycle. Post‑campaign cleaning requires a methanol/acetone (50:50) reflux under mild vacuum to remove adsorbed nitro‑aromatic residues, verified by wipe tests with conductivity limits ≤ 10 µS/cm.
In combinatorial libraries targeting the hinge‑binding region of kinases, direct comparison of 2‑[(4‑nitrophenoxy)methyl]-1,3-benzothiazole against its 4‑amino and 4‑bromo siblings reveals divergent structure‑activity relationships. The nitro derivative engages the conserved glycine‑rich loop through favourable dipole‑dipole interactions with the aromatic –NO2 group, as evidenced by a 0.23‑kcal/mol lower predicted binding free energy relative to the 4‑amino analogue in docking simulations using the crystal structure of Aurora kinase A (PDB 8DFC). However, the same –NO2 moiety imparts a ca. 1.5‑log‑unit increase in clogP (calculated 2.97 vs. 1.45 for the 4‑amino), frequently translating into reduced aqueous solubility (12 µM in phosphate‑buffered saline, pH 7.4, versus 580 µM for the amino congener). This dichotomy forces a careful balance between target affinity and pharmacokinetic developability when the nitro compound is included in hit‑to‑lead progression sets.
For peptide‑mimetic modifications where a traceless linker is required, the nitro‑aromatic ether outperforms the corresponding 4‑chlorophenoxy derivative in on‑bead photocleavage protocols. Irradiation at 365 nm in a Rayonet photoreactor (RPR‑100, 16 lamps × 8 W) releases the free benzothiazole carboxylic acid with 92% conversion after 30 min, while the chlorinated derivative yields only 11% under identical conditions due to the dominant photohomolysis of the C–Cl bond generating non‑productive radical recombination products. These performance differentials have led to the product’s adoption as a preferred building block in probe synthesis contracts outsourced under ISO 9001:2015 quality management systems, where batch‑to‑batch photosensitivity must remain within a ±3% coefficient of variation to guarantee consistent biolabeling efficiency. Published data for long‑term storage of the conjugate formed from the nitro precursor in live‑cell imaging media is limited, and users are advised to confirm lysosomal accumulation kinetics for each cell line independently.
