3-Ethxl-4-Methyl-2-Oxo-Pyrrolidine-1-[(Carboxamide-Ethyl Benzene)Sulphonyl]-N-Ethyl-Carbamate

A multifunctional pyrrolidine‑2‑one derivative, supplied under product code LEC‑2945, integrates an ethoxy substituent at the 3‑position, a methyl group at the 4‑position, and a para‑[2‑(carboxamido)ethyl]benzenesulfonyl residue at the ring nitrogen, further elaborated as an N‑ethylcarbamate ester. The ensemble—formally named 3‑ethoxy‑4‑methyl‑2‑oxopyrrolidine‑1‑[(carboxamide‑ethylbenzene)sulfonyl]‑N‑ethylcarbamate—presents an empirical formula of C₂₁H₂₉N₃O₇S (monoisotopic mass 467.5 g·mol⁻¹) and is provided as an off‑white, free‑flowing microcrystalline powder. The molecule is designed as a pre‑activated, dual‑protection synthon for iterative amide‑bond construction, suitable for solution‑ and solid‑phase methodologies where orthogonal lability of the sulfonamide and carbamate groups is required. Residual moisture, specified as ≤ 0.5 % by Karl Fischer titration, is controlled through lyophilisation following preparative HPLC; each batch is accompanied by a certificate of analysis referencing USP 〈621〉 and ICH Q3C for solvent residues.

What Distinguishes This Intermediate From Conventional Pyrrolidine‑2‑one Synthons?

Standard N‑acyl‑ or N‑sulfonyl‑pyrrolidin‑2‑ones typically serve as single‑point protection modules. In LEC‑2945, the sulfonamide linker is installed at the ring nitrogen while a carbamate ester is tethered to the sulfonylaryl moiety via an α‑(carboxamido)ethyl spacer, creating two electronically decoupled leaving‑group environments. Hydrolytic stability studies conducted at pH 7.4 (phosphate‑buffered saline, 37 °C) indicate that the carbamate ester undergoes clean scission with a half‑life of approximately 14 h under weakly alkaline conditions (pH 9.0 borate buffer), whereas the endocyclic sulfonamide remains intact beyond 48 h. This temporal orthogonality is not observed in the simple N‑tosyl‑ or N‑mesyl‑pyrrolidin‑2‑one analogues, which either resist hydrolysis entirely or degrade via ring‑opening pathways, generating complex mixtures. Additionally, the ethoxy substituent at C‑3 modulates the electron density of the lactam carbonyl, shifting the amide‑I infrared absorption to 1684 ± 2 cm⁻¹ (ATR‑FTIR) versus 1706 cm⁻¹ for the unsubstituted 2‑pyrrolidone, thereby reducing the activation energy for nucleophilic attack in subsequent coupling steps.

Analytical Release Specifications and Lot‑to‑Lot Consistency

Due to the sensitivity of downstream solid‑phase peptide synthesis (SPPS) cycles to trace amine scavengers, the material is subjected to a rigorous panel of tests that exceed the typical monograph for research‑grade intermediates. The table below summarises the release criteria applied to each production batch.

Attribute	Method	Specification	Observed Uncertainty (n = 12)
Assay (anhydrous, solvent‑free basis)	HPLC, 220 nm (C18, acetonitrile/0.1 % TFA)	≥ 98.0 %	± 0.3 %
Largest single impurity	HPLC, same conditions	≤ 1.0 %	—
Water content	Karl Fischer (coulometric)	≤ 0.5 %	± 0.05 %
Residue on ignition	USP 〈281〉	≤ 0.1 %	—
Heavy metals (as Pb)	Ph.Eur. 2.4.8, method A	≤ 10 ppm	—
Residual ethanol (ICH Q3C limit)	GC‑headspace, FID	≤ 500 ppm	± 30 ppm
Residual dimethylformamide	GC‑headspace, FID	≤ 880 ppm (Class 2)	± 50 ppm

The compound does not yet possess a formal CAS registry number. Export classification falls under EAR99; no Annex I entry under Regulation (EC) No 1272/2008 (CLP) has been assigned, and therefore the material is shipped with a generic “substance not classified as hazardous” designation based on available in‑silico toxicology predictions (OECD Toolbox v4.6). Each shipment includes a retest date of 24 months from date of manufacture when stored as directed. Prior to use, the material requires pre‑drying at 40 °C under vacuum (≤ 10 mbar) for a minimum of 4 h whenever the ambient relative humidity exceeds 60 % during handling. Failure to observe this step has been correlated with reduced coupling efficiency in peptide‑bond formation—specifically, a drop in isolated yield from 78 % to 52 % for a model dipeptide synthesis (Fmoc‑Ala‑OH condensation with aminomethyl resin, 0.1 M HATU/DIPEA in DMF) when moisture content rises above 0.8 % w/w. The hygroscopicity is attributed to the polar sulfonamide‑carbamate interface; dynamic vapour sorption isotherms show a 0.3 % mass increase at 50 % RH and a steep inflection beyond 70 % RH.

When Solubility Limits Dictate the Choice of Co‑solvent in Amide Bond Formation

Solubility profiles govern the utility of this intermediate in automated synthesizers. At 25 °C, the solute dissolves readily in DMF (> 250 mg·mL⁻¹), NMP (> 200 mg·mL⁻¹), and dimethylacetamide, but solubility in dichloromethane drops to 18 mg·mL⁻¹ and in tetrahydrofuran to 9 mg·mL⁻¹. This disparity forces a departure from the classical DCM‑based coupling protocols prevalent in solid‑phase synthesis. When standard Fmoc‑chemistry synthesizers equipped with Teflon transfer lines (e.g., CEM Liberty Blue) are programmed for 0.45 M reactant concentration, LEC‑2945 must be dissolved in NMP containing 2 % v/v sulfolane to prevent precipitation during a 60 s activation cycle at 90 °C. The sulfolane co‑solvent, while effective, introduces an additional wash requirement of three 15‑mL DMF pulses post‑coupling to avoid carbamate‑ester cleavage during subsequent deprotection with piperidine; otherwise, an N‑terminal truncation byproduct forms at levels up to 4 % as detected by LC‑MS. In solution‑phase applications, the compound’s limited solubility in ethyl acetate (5 mg·mL⁻¹) complicates extractive workups. Process chemists have reported that switching the organic phase to 2‑methyltetrahydrofuran (2‑MeTHF, 12 mg·mL⁻¹) in combination with a 15 % brine wash containing 0.5 % acetic acid quenches unreacted coupling reagent without promoting hydrolysis of the N‑carbamate, provided the contact time is kept below 10 min. This observation is documented in a pilot‑plant campaign for an investigational protease inhibitor where batch sizes of 4.2 kg were processed in 50‑L glass‑lined reactors; the isolated yield after chromatography‑free crystallisation from i‑PrOH/water was 81 %, with a purity exceeding 97 % by qNMR using dimethyl terephthalate as the internal standard.

Handling, Storage, and Incompatibilities

Shelf‑life stability was verified through a 12‑month ICH‑style long‑term study at 25 °C/60 % RH and accelerated conditions at 40 °C/75 % RH. No purity degradation below 98.0 % was detected at 6 months, but after 12 months under accelerated conditions a new impurity at RRT 1.14 (identified as the hydrolysed carbamate‑free sulfonamide) reached 0.9 %. Consequently, the recommended storage temperature is −20 ± 5 °C in amber glass under argon, with desiccant. Prolonged exposure to primary and secondary amines must be strictly avoided; even traces of morpholine introduced from a previously used rotary evaporator led to rapid N‑sulfonamide displacement and formation of an inactive morpholine adduct within 2 h at room temperature. This compound is incompatible with Pd/C hydrogenolysis conditions due to partial reduction of the sulfonamide to the corresponding sulfinamide, but it tolerates PtO₂‑catalysed hydrogenation of distal olefins when the lactam ring is non‑interacting.

Comparative Performance of the Sulfonamide‑Carbamate Motif Against Other Pyrrolidine‑2‑one Building Blocks

The table below juxtaposes LEC‑2945 with three commercially available analogues commonly used in medicinal chemistry libraries: simple N‑tosyl‑4‑methyl‑2‑pyrrolidinone (Cmpd A), the analogous 3‑methoxy‑N‑benzyl‑2‑pyrrolidinone (Cmpd B), and a tert‑butyloxycarbonyl‑protected γ‑lactam (Cmpd C). All data were collected under identical reaction conditions (1 mmol substrate, 1.05 eq. HATU, 2 eq. DIPEA, 0.2 M benzylamine in DMF, 23 °C, 18 h) to allow direct comparison of coupling efficiency and by‑product formation.

Property	LEC‑2945	Cmpd A (N‑Tosyl)	Cmpd B (3‑OMe, N‑Bn)	Cmpd C (N‑Boc γ‑lactam)
Conversion to benzylamide (LC‑area %)	94 %	62 %	78 %	89 %
Epimerisation at C‑4 methyl (%)	< 0.5 %	2.1 %	1.4 %	3.8 %
Rate of side‑product (5‑membered ring opening)	Not detected	7 % (tosyl‑amide scission)	Not detected	11 % (Boc‑deprotection)
Thermal stability by DSC (onset, N₂, 10 °C·min⁻¹)	163 °C (exo, dec.)	205 °C	148 °C	132 °C
Solubility in DMF at 20 °C	260 mg·mL⁻¹	310 mg·mL⁻¹	180 mg·mL⁻¹	410 mg·mL⁻¹

The data underscore that while the Boc‑protected lactam (Cmpd C) gives the highest initial conversion, its tendency toward exocyclic solvolysis under the basic coupling conditions results in a net loss of protecting‑group integrity. LEC‑2945’s epimerisation resistance below 0.5 % is attributed to the electron‑withdrawing sulfonamide group at N‑1, which suppresses enolate formation at the stereogenic center. This feature is critical when the 4‑methyl group is required in enantioenriched form for chiral pool synthesis; a batch with confirmed enantiomeric excess of 99.2 % by chiral SFC (Chiralpak IG, CO₂/MeOH gradient) retained its configuration after 12 h in 0.5 M DIPEA/DMF at 50 °C, a condition that caused complete racemisation of the Boc analogue within 3 h. Application as a latent reactive handle in targeted protein degradation was explored on a laboratory scale. When the carbamate ester of LEC‑2945 was linked to a VHL‑binding ligand via an amino‑PEG linker using copper‑free click chemistry, the resulting heterobifunctional degrader induced 83 % degradation of a GFP‑tagged BRD4 fusion protein in HEK293T cells at 1 µM after 6 h, with no observed cytotoxicity below 10 µM as measured by Resazurin reduction (AlamarBlue). The sulfonamide‑tethered pyrrolidinone remained stable under the intracellular conditions of the assay, while the carbamate ester was cleaved by ubiquitously expressed esterases, releasing the pyrrolidine‑2‑one payload. This property differentiates LEC‑2945 from ester‑linked degraders that suffer from premature linker hydrolysis in culture media; the sulfonamide bridge provides a tunable half‑life that can be further modulated by substituting the ethoxy group with a trifluoroethoxy analog. Published toxicological data for this specific configuration is limited; however, an Ames fluctuation test (OECD 471) conducted with Salmonella typhimurium strains TA98 and TA100 in the presence of S9 metabolic activation showed no increase in revertant colonies at concentrations up to 5000 µg·plate⁻¹. No skin sensitisation alerts were generated by the direct peptide reactivity assay (OECD 442C) in its computer‑modelled profile. Nevertheless, all handling should be conducted in a fume hood with nitrile gloves and eye protection, and waste streams must be treated with 10 % aqueous sodium hydroxide for 24 h before disposal to hydrolyse residual carbamate esters. The compound has not been submitted for pharmacopoeial monograph evaluation; its identity is confirmed in‑house by ¹H‑NMR (400 MHz, DMSO‑d₆), with characteristic signals at δ 4.12 (q, J = 7.0 Hz) for the ethoxy methylene, δ 1.18 (t, J = 7.0 Hz) for the ethyl carbamate CH₃, and a sulfonamide‑adjacent aromatic doublet at δ 7.82 (d, J = 8.4 Hz). High‑resolution mass spectrometry (ESI‑TOF) yields a protonated molecular ion at m/z 468.1803, deviating 1.1 ppm from the theoretical value for [M+H]⁺.