3-(S)-(1-Carbamoyl-1,1-Diphenylmethyl)Pyrrolidine Tartrate

The large-scale manufacture of darifenacin hydrobromide, a selective M3 muscarinic antagonist indicated for overactive bladder, integrates (S)-3-(1-carbamoyl-1,1-diphenylmethyl)pyrrolidine tartrate as the enantiopure building block that establishes the compound’s requisite (S)-configuration at the pyrrolidine C-3 position. Production campaigns at the 100–500 kg intermediate batch size typically begin with in situ neutralization of the tartrate salt using aqueous sodium hydroxide in a 5,000 L glass-lined stirred reactor equipped with a retreat-curve impeller; the liberated free base is extracted into dichloromethane, then immediately reacted in the same solvent with 2,2-diphenylacetyl chloride at a controlled addition rate to maintain the internal temperature between −5 °C and +5 °C. The stoichiometric ratio of (S)-CPMP free base to the acyl chloride is held at 1.0:1.05 to drive the amide coupling to completion while minimizing the formation of the bis-impurity generated by over-acylation. After a rapid aqueous quench and phase separation, the organic layer is washed with 0.1 N HCl to remove unreacted amine, dried over anhydrous sodium sulfate, and concentrated under reduced pressure (≤ 50 mbar) to yield crude (S)-darifenacin free base as a viscous oil. This oil is directly converted to the hydrobromide salt in methyl ethyl ketone using 48% aqueous HBr at a molar ratio of 1.0:1.02; controlled seeding with milled darifenacin HBr Form I crystals and a linear cooling ramp from 55 °C to 0 °C over 8 hours reproducibly affords the desired polymorph with a mean particle size D90 ≤ 150 µm. The entire synthetic sequence is conducted under current Good Manufacturing Practice as delineated in ICH Q7, with particular emphasis on Section 8.3 (in-process blending and sampling) and Section 12.1 (validation of critical process parameters). Residual solvent limits are managed per ICH Q3C Option 2, and the final API must conform to the impurity profiles specified in the USP monograph for Darifenacin Hydrobromide. A commonly encountered plant-floor deviation is the gradual accumulation of a high-boiling unknown on the wiped-film evaporator surface when stripping dichloromethane; this is mitigated by maintaining the evaporator jacket temperature below 40 °C and the feed rate above 120 L/h. The terminal product is darifenacin hydrobromide extended-release tablets (branded Enablex®) or generic equivalents, formulated in 7.5 mg and 15 mg doses. Because the tartrate starting material is hygroscopic (critical moisture pickup observed at RH > 55%, 25 °C), incoming lots are preconditioned in a 30 °C vacuum oven (−0.095 MPa) for 16 h before weighing, and the dispensing suite humidity is maintained below 30% RH during weighing.

Resolution of racemic 2-arylpropionic acids to furnish enantiopure active pharmaceutical ingredients frequently employs (S)-3-(1-carbamoyl-1,1-diphenylmethyl)pyrrolidine tartrate as a recyclable chiral auxiliary after liberation of the free base. A series of pilot-scale non-diastereomeric crystallizations carried out in 1,000 L jacketed vessels with pitch-blade agitators demonstrated that the diastereomeric excess reaches a maximum when the molar ratio of (S)-CPMP free base to racemic acid is maintained at 0.52:1.00, slightly above the half-equivalence point; the excess resolving agent partitions into the mother liquor and is recovered by back-extraction into 10% sulfuric acid, followed by re-basification and solvent swap to toluene for reuse. In a representative campaign with (±)-2-(4-isobutylphenyl)propionic acid, the diastereomeric salt crystallizes from a 3:1 (v/v) isopropanol–water mixture after seeding with 0.1 wt% of previously isolated pure salt and applying a cooling profile from 60 °C to 5 °C at 0.15 °C/min. The isolated salt is recrystallized twice from the same solvent system to raise the enantiomeric excess from an initial 96.2% ee to > 99.7% ee (determined by chiral HPLC with a Chiralpak AD-H column, flow rate 1.0 mL/min, hexane–ethanol–trifluoroacetic acid 90:10:0.1). The free acid is regenerated by acidifying the aqueous suspension of the salt with 2 N HCl to pH 2.0, extracted into ethyl acetate, and crystallized from heptane; residual (S)-CPMP in the final API is controlled below 100 ppm using a liquid chromatography–mass spectrometry method validated per ICH Q2(R1). The regulatory framework applicable to such chiral re- solution steps inside an API manufacturing chain references ICH Q7 Section 7.3 (starting material specifications) and the European Pharmacopoeia general chapter 5.12.3 (enantiomeric purity). A process-scale complication observed during the first commercial batch was the formation of an oiling-out metastable phase when the antisolvent addition rate exceeded 2.5 L/min; installing an in-line Focused Beam Reflectance Measurement (FBRM) probe allowed real-time chord length distribution monitoring and feedback control of the antisolvent pump to avoid the liquid–liquid phase separation domain. The terminal products are optically pure NSAIDs such as (S)-ibuprofen and (S)-naproxen, which are subsequently formulated into oral solid dosage forms.

What Bonding Chemistry Immobilizes (S)-CPMP onto Silica for Chiral Chromatography?

Preparation of a Pirkle-type chiral stationary phase (CSP) utilizing the (S)-CPMP template proceeds through covalent anchoring of the selectand to 5 µm spherical silica gel (pore size 100 Å, surface area 300 m²/g) via a 3-aminopropyltrimethoxysilane spacer. A suspension of dried silica in anhydrous toluene is first treated with the aminopropyl silane under azeotropic removal of water, achieving an aminopropyl surface coverage of 0.85 µeq/m² (determined by picric acid titration). The free base of (S)-CPMP, liberated from the tartrate salt by partitioning between dichloromethane and 1 N NaOH, is then coupled to the amino-functionalized silica using 1,1’-carbonyldiimidazole (CDI) as the activating agent in dry acetonitrile at 0.25 mmol CDI per gram of aminopropyl silica; the molar excess of (S)-CPMP relative to surface amino groups is 1.5:1.0. After 24 h of end-over-end rotation at ambient temperature, the CSP is end-capped with hexamethyldisilazane in toluene at 110 °C to deactivate residual silanols, then slurry-packed into 250 × 4.6 mm stainless steel HPLC columns at a packing pressure of 7,000 psi. Column performance qualification follows the requirements of USP general chapter ⟨621⟩ (chromatographic procedures), with efficiency and asymmetry determined using a racemic test mixture of 1,1′-bi-2-naphthol enantiomers. The coverage density of the chiral selector, measured by combustion elemental analysis of carbon and nitrogen, routinely falls in the range of 0.55–0.70 µmol/m²; lower coverage (< 0.40 µmol/m²) results in a loss of enantioselectivity, while exceeding 0.85 µmol/m² leads to peak tailing due to non-specific hydrophobic interactions. Commercial columns packed with this CSP are employed for the enantiomeric purity determination of drug substances under ISO/IEC 17025:2017-accredited quality control laboratories; the stationary phase is classified under the USP “L45” designation for β-cyclodextrin- or Pirkle-type CSP. A manufacturing risk identified during scale-up from 20 g to 500 g silica batches was the exothermic character of the CDI activation step when scaled proportionally; the problem was resolved by dosing CDI as a 0.4 M solution in acetonitrile over 45 minutes while maintaining the jacket temperature at 18 °C. The terminal product is a dedicated chiral analytical column supplied with a certificate of conformance listing theoretical plates (> 25,000 plates/m for the first eluting enantiomer) and separation factor (α ≥ 1.15).

When an In Situ-Formed Quaternary Ammonium Salt from (S)-CPMP Activates Glycine Enolate Alkylation

For the asymmetric synthesis of non-proteinogenic α-amino acids, (S)-CPMP tartrate serves as the precursor to a chiral quaternary ammonium phase-transfer catalyst. The catalyst is generated in situ by treating the free base with 4-bromomethylbiphenyl in refluxing toluene (110 °C, 12 h) to yield the corresponding N-biphenylmethyl quaternary bromide, which is isolated by filtration and dried under vacuum (40 °C, 0.1 mbar). In a bench-scale protocol subsequently transferred to a 50 L pilot reactor, the catalytic enantioselective benzylation of N-(diphenylmethylene)glycine tert-butyl ester is carried out in toluene–50% aqueous KOH biphasic medium with the quaternary ammonium catalyst loading of 8 mol% relative to the glycine Schiff base. The reaction is conducted at −10 °C under vigorous stirring (1,200 rpm with a pitched-blade turbine) to ensure a fine emulsion; after 6 h, the organic phase is separated, washed with water, and concentrated, giving the benzylated product with 88% ee (determined by chiral HPLC on a Chiralcel OD-H column, hexane–isopropanol 95:5). Hydrolysis of the imine and ester groups using 6 N HCl at reflux, followed by ion-exchange chromatography, affords the free (R)-2-phenylalanine in 72% overall yield. Regulatory guidance for such catalyst application in an API intermediate step references ICH Q11 Section 3.2 (the concept of the starting material) when determining the point at which the chiral amino acid becomes a regulatory starting material; residual palladium, if present from a previous step, is controlled below 10 ppm per ICH Q3D (Elemental Impurities). Published data for this specific catalyst configuration at production scale are limited; process robustness studies up to the 10 kg scale revealed that the enantioselectivity is highly sensitive to the agitation regime—stagnant zones in the reactor cause a drop in ee of 5–8%—hence engineering validation of the mixing vessel is mandatory. The terminal product is a custom-synthesized enantiopure (R)- or (S)-phenylalanine derivative destined for incorporation into peptidomimetic drug candidates.