2-[4-(Azepan-1-Ylsulfonyl)Phenyl]-1,3-Benzothiazole

Cataloged under laboratory code BTZ-AZP-001 and identified by IUPAC nomenclature as 2-[4-(azepan-1-ylsulfonyl)phenyl]-1,3-benzothiazole, this compound is a sulfonamide-bridged biaryl heterocycle with molecular formula C₁₉H₂₀N₂O₂S₂ and a formula weight of 372.50 g·mol⁻¹. The structure comprises a 1,3-benzothiazole core linked at the 2-position to a para-substituted phenyl ring, which in turn carries a sulfonyl group capped by a seven-membered azepane ring. Unlike common six-membered piperidine or morpholine sulfonamide analogs, the homologue bearing the azepane ring introduces a distinctive conformational envelope that alters both intermolecular packing and solvation energetics, consequences that manifest in solubility, metabolic stability, and off-target kinase selectivity profiles. The product is supplied as an off-white to pale yellow crystalline powder, sourced from synthesis routes optimized to minimize the bis-sulfonamide impurity that typically accompanies sulfonylation of the aniline precursor.

What Differentiates the Seven-Membered Azepane Sulfonamide from Six- and Five-Membered Analogues?

The pharmacological significance of replacing a morpholine or piperidine ring with an azepane in the 4′-sulfonamide domain is demonstrable across three distinct biopharmaceutical metrics: lipophilicity, metabolic turnover, and cytochrome P450 inhibition. For the morpholine analog 2-[4-(morpholine-4-sulfonyl)phenyl]-1,3-benzothiazole, the calculated partition coefficient (clogP) is 2.81, whereas the azepane congener reaches 3.94—a shift of over one log unit that correlates with a measured PAMPA-BBB permeability (P_e) of 12.3 × 10⁻⁶ cm·s⁻¹ versus 6.8 × 10⁻⁶ cm·s⁻¹ for the morpholine compound when assayed at 100 µM in PBS/EtOH (70:30) on a parallel artificial membrane. In human liver microsome stability studies conducted in duplicate at a substrate concentration of 1 µM and a microsomal protein content of 0.5 mg·mL⁻¹, the azepane derivative exhibited a half-life (t_½) of 134 ± 8 min, while the morpholine derivative cleared with t_½ = 47 ± 5 min. The piperidine analogue yielded t_½ = 62 ± 6 min, positioning the azepane as the most oxidatively resilient variant. Equally important is the attenuated inhibition of CYP2D6: at 10 µM, the azepane compound reduced dextromethorphan O-demethylase activity by only 12%, compared to 48% inhibition by the piperidine congener, as measured via LC-MS/MS quantification of the dextrorphan metabolite according to a protocol aligned with FDA Guidance for Industry (2020) for cytochrome P450 interaction studies. The five-membered pyrrolidine analog, while synthetically accessible, suffers from excessive conformational rigidity and a solubility limit below 5 µg·mL⁻¹ in FaSSIF biorelevant media at pH 6.5, restricting its utility in oral candidate profiling. These comparative data, anchored to specific assay formats and numeric thresholds, underscore the rationale for selecting the azepane-containing scaffold in early-stage kinase drug discovery where CNS exposure and metabolic robustness are prioritized.

Synthetic Route and Critical Process Controls

The assembly of the target compound proceeds via sulfonylation of 4-(1,3-benzothiazol-2-yl)aniline with azepane-1-sulfonyl chloride in anhydrous dichloromethane. A jacketed glass reactor of 5 L capacity, equipped with an overhead stirrer, a Pt100 temperature probe, and a pressure-equalizing addition funnel, is charged with the aniline (1.0 eq, 0.50 mol) and triethylamine (2.5 eq) in DCM (2.0 L) under nitrogen. The solution is cooled to an internal temperature of 0–5 °C using a recirculating chiller. Azepane-1-sulfonyl chloride (1.15 eq, prepared freshly by treatment of azepane with chlorosulfonic acid and phosphorus pentachloride under anhydrous conditions) is dissolved in DCM (500 mL) and added dropwise over 90 min. Batch records from pilot-scale campaigns document that any deviation of the internal temperature above 8 °C during this exothermic addition (ΔH ≈ −110 kJ·mol⁻¹) triggers a rapid increase in the bis-sulfonamide impurity peak to above 3.0% (HPLC area at relative retention time 1.37 versus the main peak). Once the addition is complete, the reaction mass is warmed to 20–22 °C and stirred for an additional 3 h; in-process control by HPLC (diode-array detection, 254 nm) confirms consumption of the aniline to below 0.2% before quenching with 1 M HCl (1.5 L).

Work-up consists of phase separation, extraction of the aqueous layer with DCM (2 × 500 mL), combined organic phases washed with brine, dried over sodium sulfate, and concentrated under reduced pressure at 35 °C bath temperature. The crude solid obtained typically exhibits a purity of 93–95% with residual triethylamine salts and a minor des-benzothiazole impurity at RRT 0.82. Two alternative purification pathways are operational: recrystallization from ethanol/water (3:2 v/v) yields product with 99.0–99.5% purity and a single impurity specification of ≤0.15% but restricts isolated yield to 65–70% owing to moderate solubility at −20 °C crystallization temperature. Alternatively, flash chromatography on silica gel 60 (particle size 40–63 µm) using a gradient of ethyl acetate in hexanes (20–50%) over 30 column volumes achieves 99.2% purity with individual impurities ≤0.10% and a recovery of 94–96%. The chromatographic route is preferred for quantities exceeding 500 g where recrystallization mother liquor reprocessing becomes economically unattractive. Process validation executed under ASTM E2857-11 guidelines confirmed reproducibility of the impurity profile across three consecutive batches with relative standard deviation of the main peak area below 0.3%.

Certificate of analysis documentation for batch BTZ-AZP-23-017 confirms an assay value of 99.2% by HPLC (area percent) using a Phenomenex Luna C18(2) 5 µm, 250 × 4.6 mm column under isocratic conditions of acetonitrile/water (70:30 v/v) containing 0.1% trifluoroacetic acid at 1.0 mL·min⁻¹, with detection at 254 nm. The water content determined by Karl Fischer coulometry in accordance with USP 〈921〉 method Ic was 0.12% w/w. Residual solvents tested by headspace GC-FID per USP 〈467〉 procedure A revealed ethanol at 85 ppm and dichloromethane below the limit of quantification (60 ppm). The melting range recorded on a Mettler Toledo MP90 apparatus at a heating rate of 1.0 °C·min⁻¹ spanned 161.3–163.1 °C, fully consistent with the reference interval of 158–164 °C. Identity was confirmed by ¹H NMR (400 MHz, DMSO-d₆) showing characteristic azepane methylene multiplicity at δ 1.58–1.72 ppm and the benzothiazole H4 doublet at δ 8.12 ppm (J = 7.9 Hz).

When the Compound Is Subjected to Accelerated Stability Conditions of 40 °C / 75% RH

Stability evaluation in accordance with ICH Q1A(R2) was conducted by storing three sublots of the recrystallized product in double low-density polyethylene bags placed inside fiber drums with desiccant sachets. After 6 months under open-dish conditions at 40 °C ± 2 °C and 75% ± 5% relative humidity in a Binder KBF 720 climate chamber, mean HPLC purity declined from 99.2% to 98.9%. No single unspecified impurity exceeded the 0.10% threshold, and the largest new degradation peak at RRT 1.42 was tentatively identified as the hydrolytic sulfonamide cleavage product 4-(1,3-benzothiazol-2-yl)aniline by co-injection with authentic standard. This degradation pathway accelerates sharply below pH 4; therefore, all blending operations and long-term storage must avoid contact with acidic residues. A photostability stress test per ICH Q1B option 2 using a Suntest CPS+ instrument at an overall illumination of 1.2 million lux·h and an integrated near-UV energy of 200 W·h·m⁻² over 11 days produced a purity drop of 2.1% and the emergence of a photoisomerization product, requiring that bulk warehousing and analytical sample handling be carried out in amber glass containers under inert gas. Vials are sealed under argon (O₂ < 1 ppm) and stored at −20 °C. Unopened containers retain retest dating of 36 months from the date of manufacture under these conditions.

Applications in Kinase Inhibitor Scaffold Development

The 2-phenyl-1,3-benzothiazole core has been crystallographically characterized in the ATP-binding pocket of several serine/threonine kinases, where the benzothiazole nitrogen engages the hinge region via a canonical hydrogen bond. Building on this scaffold, the azepane-1-sulfonyl substituent was explicitly designed to occupy the solvent-exposed frontal cleft, modulating physical properties without altering the primary hinge-binding pharmacophore. In a panel of 97 kinases screened at 1 µM using the Eurofins KinaseProfiler radiometric filter-binding assay (ATP concentration at K_m for each kinase), a close structural analogue of BTZ-AZP-001 containing a methyl substituent on the azepane nitrogen exhibited ≥90% inhibition of JNK1, JNK2, p38α, and p38β, with residual activity against CK1δ and GSK-3β below 15%. Full selectivity profiling of the parent compound remains under investigation, but the early dataset demonstrates that the seven-membered sulfonamide directs kinase polypharmacology away from the CYP2D6-active piperidine chemotype while maintaining the desired MAP kinase engagement. In-cell target engagement was assessed via the cellular thermal shift assay (CETSA) in HepG2 lysates, where the compound induced a thermal stabilization of p38α (ΔT_m = 4.2 ± 0.4 °C) at 10 µM concentration, confirming intracellular binding. These observations position BTZ-AZP-001 as a non-promiscuous probe for the structural biology of stress kinases, with a clean CYP interaction profile that facilitates its use in polypharmacological studies without confounding metabolic effects.