4-[2-[(4-Ethyl-3-Methyl-5-Oxo-2H-Pyrrole-1-Carbonyl)Amino]Ethyl]Benzenesulfonyl Chloride

Designated as Item No. BC‑S‑2409 in the company’s specialty electrophile portfolio, 4‑[2‑[(4‑ethyl‑3‑methyl‑5‑oxo‑2H‑pyrrole‑1‑carbonyl)amino]ethyl]benzenesulfonyl chloride is supplied as a pale‑yellow to off‑white crystalline solid with a minimum purity of 98.0 % (HPLC, 210 nm, area normalization per USP ⟨621⟩). The molecular architecture integrates a γ‑lactam‑terminated acyl‑aminoethyl spacer into the para‑position of a benzenesulfonyl chloride core, yielding a reagent whose reactivity profile is neither that of a conventional aromatic sulfonyl halide nor that of a simple aliphatic sulfonamide precursor. Its systematic construction modulates electrophilicity at sulfur through both electron‑withdrawing character of the 2‑oxopyrroline ring and steric compression from the ethyl and methyl substituents at C4 and C3 of the heterocycle. The compound carries a formula weight of 384.88 g·mol⁻¹, a predicted logP_ow of approximately 2.8, and is stored under argon at ‑20 °C with desiccant, as adventitious moisture leads to hydrolysis of the sulfonyl chloride functionality with a half‑life of less than 6 h at 25 °C and 60 % relative humidity (accelerated stability chamber data, internal protocol based on ICH Q1A(R2)).

What Distinguishes This Sulfonyl Chloride from Aromatic Sulfonyl Halides in Acylation Kinetics?

When benchmarking against the commonly employed para‑toluenesulfonyl chloride (tosyl chloride, TsCl), the pyrrolinone‑linked reagent exhibits a measurable attenuation of intrinsic reactivity that cannot be assigned solely to electronic effects. Stopped‑flow UV‑vis monitoring of the reaction with n‑butylamine in anhydrous DMF at 0.0 ± 0.2 °C reveals a pseudo‑first‑order rate constant k_obs of approximately 1.8 × 10⁻³ s⁻¹, compared with 4.6 × 10⁻³ s⁻¹ for TsCl under identical conditions (amine concentration 10 mM, reagent concentration 1 mM, background electrolyte tetrabutylammonium hexafluorophosphate 0.1 M). The 2.5‑fold deceleration arises predominantly from steric shielding: the gauche‑preferred conformation of the ethyl‑methyl‑substituted γ‑lactam projects a van der Waals volume that frustrates nucleophilic approach to the sulfonyl center along the Bürgi‑Dunitz trajectory. This steric imposition becomes advantageous when selective sulfonylation of a primary amine in the presence of a less hindered secondary amine is required, a common challenge in divergent oligomer assembly. Moreover, the non‑planar lactam ring reduces π‑stacking interactions that can cause crystallisation‑driven side‑product precipitation in aromatic sulfonyl chlorides, thereby maintaining solution homogeneity during prolonged additions over 6–8 h in reactor vessels equipped with overhead stirring at 250 rpm.

For pre‑column derivatization of primary aliphatic amines in reversed‑phase HPLC workflows, the compound is dissolved in acetonitrile containing 1 % (v/v) N‑methylmorpholine and reacted with the sample at 50 °C for 20 min in a sealed 1.5‑mL polypropylene microcentrifuge tube. The resultant sulfonamide derivatives exhibit λ_max centered at 263 nm with a molar absorptivity of around 8 200 L·mol⁻¹·cm⁻¹, enabling detection limits of 0.1 µM on a standard C18 column (150 × 4.6 mm, 5 µm) using a methanol‑water gradient. No chromatographic interference from the hydrolysis by‑product, 4‑[2‑[(4‑ethyl‑3‑methyl‑5‑oxo‑2H‑pyrrole‑1‑carbonyl)amino]ethyl]benzenesulfonic acid, is observed, as it elutes in the solvent front at t₀ < 2.0 min. Published data for this specific configuration is limited to in‑house validation studies across a panel of 16 biogenic amines; repeatability expressed as RSD of peak area was ≤ 1.7 % (n = 6) at the 5 µM level.

When Hydrophobicity Governs Extraction Efficiency in Aqueous Work‑up Schemes

Because the product bears a substantial alkyl‑heterocyclic tail, its sulfonamide conjugates partition into ethyl acetate or methyl tert‑butyl ether with distribution coefficients (log D at pH 7.4) exceeding those of tosylamide analogues by roughly 1.2 log units. In a typical parallel synthesis campaign targeting a library of tertiary sulfonamides for kinase inhibition screening, the use of BC‑S‑2409 instead of TsCl reduced the number of back‑extraction cycles required to recover the crude product from three to one while maintaining an average isolated yield of 87 % (n = 48 compounds). This shift directly cuts processing time on a liquid‑handling platform fitted with a 96‑well phase separator membrane by 40 min per plate. However, the elevated log D brings a corresponding limitation: sulfonamide derivatives with a total carbon count below 14 may display insufficient aqueous solubility for direct biological assay at concentrations above 50 µM in phosphate‑buffered saline containing 0.1 % DMSO, necessitating the addition of 0.01 % Tween‑80 as solubiliser.

In the preparation of surface‑active sulfonate esters for emulsion polymerisation, the reagent is first converted to the sulfonyl azide intermediate via sodium azide in acetone‑water at 0 °C to circumvent the hydrolytic lability of the parent sulfonyl chloride. The azide is then thermally decomposed at 120 °C in toluene in the presence of poly(ethylene glycol) monomethyl ether (M_n = 750 g·mol⁻¹), generating a non‑ionic surfactant with a critical micelle concentration of 2.8 × 10⁻⁴ M determined by surface tensiometry (Wilhelmy plate method). Compared with the surfactant derived from benzene sulfonyl chloride, the larger hydrophobic domain lowers the cloud point by 13 °C, an outcome that can be exploited to engineer thermoresponsive latex stabilisation without co‑surfactant.

Polyetherimide Crosslinking and Dynamic Mechanical Performance

A less conspicuous but industrially relevant utilisation involves the compound as a thermally activated crosslinker for amine‑terminated polyetherimides (PEI, Ultem™ 1000 series). The reagent was dry‑blended at 2.0 wt% with PEI powder that had been oven‑dried at 120 °C for 12 h under vacuum, and the mixture was processed in a co‑rotating twin‑screw micro‑compounder (Xplore MC 15, L/D = 18, screw speed 100 rpm, barrel temperature 320 °C, residence time 90 s). During processing, the sulfonyl chloride reacts with the terminal amine groups of the PEI chains, forming stable sulfonamide crosslinks that raise the glass transition temperature from 217 °C (neat resin) to 231 °C as measured by DMA (single cantilever, 1 Hz, 3 K·min⁻¹, ASTM D7028). The storage modulus at 250 °C increased by a factor of 1.7, while the melt viscosity at 100 s⁻¹ and 350 °C rose from 870 Pa·s to 2 400 Pa·s, a processor‑relevant thickening that demands attention to injection moulding clamp force margins. Gel fraction after 24‑h Soxhlet extraction with dichloromethane was 48 ± 3 %, confirming covalent network formation. The crosslinking efficiency is, however, acutely sensitive to residual moisture; the pre‑drying regime is mandatory, and the compound’s handling must occur under a dry nitrogen blanket with dew point ‑45 °C or lower to prevent premature deactivation to sulfonic acid. In direct contrast, maleic anhydride‑grafted PEI crosslinking under identical barrel conditions produced a Tg increase of only 6 °C and gel fractions below 20 %, underscoring the higher nucleophilic specificity of the sulfonyl chloride electrophile toward the PEI amine terminus.

The reagent’s acyl‑aminoethyl spacer allows an additional functional handle: the amide carbonyl can engage in hydrogen‑bond‑directed pre‑organisation with a substrate carrying a complementary H‑bond donor. When applied to the selective sulfonation of the ε‑amino group of lysine in a peptide bearing a free N‑terminal serine, the reaction proceeds with >95 % regioselectivity at pH 9.0 and 4 °C in borate buffer‑acetonitrile (1:1), provided the serine hydroxyl is positioned within 4 Å of the intended sulfonamide nitrogen. Molecular mechanics simulation (MMFF94) of the pre‑transition‑state assembly suggests that the pyrrolinone oxygen accepts a hydrogen bond from the serine OH, orienting the sulfonyl chloride toward the lysine side chain. No comparable selectivity is attainable with TsCl under these conditions, where random modification of both serine and lysine is observed by MALDI‑TOF peptide mapping. This feature has not been exploited in published synthetic procedures, and in‑house robustness across diverse peptide sequences remains under evaluation; current observations are drawn from a series of 11 model pentapeptides. Process‑scale deployment requires additional validation of the intramolecular H‑bond hypothesis via ¹H‑¹⁵N HSQC titration data, which are not yet publicly available.

From a regulatory perspective, the compound is not listed in Annex XIV of REACH and holds a pre‑registration number under the 1–10 tonnes per annum band. Its hazard classification according to Regulation (EC) No 1272/2008 (CLP) includes Skin Corr. 1B (H314) and Eye Dam. 1 (H318), requiring impermeable butyl rubber gloves tested to EN 374 and indirect‑vent goggles. Work in a fume hood with face velocity ≥ 0.5 m·s⁻¹ is standard. For shipment, double‑sealed aluminised polyester bags inside a screw‑cap HDPE container are validated for 72 h excursion to ambient temperature during transport, provided the external humidity indicator remains below 20 % RH.