Tert-Butyl (2S)-2-(Cyanomethyl)Pyrrolidine-1-Carboxylate

Production of sitagliptin phosphate monohydrate under US FDA ANDA pathways mandates strict control of the chiral starting material (2S)-2-(cyanomethyl)pyrrolidine-1-carboxylate tert-butyl ester. In a typical convergent synthesis, the Boc-protected nitrile is subjected to catalytic hydrogenation in a 500–2000 L Hastelloy C-276 autoclave equipped with a gas-inducing impeller and a sintered-metal hydrogen sparge ring. The reduction charge consists of the nitrile dissolved in anhydrous tetrahydrofuran (Karl Fischer titre < 0.05% w/w) to which a pre-conditioned slurry of Raney 2800 grade nickel catalyst is added at a loading of 8–12% w/w relative to substrate. The vessel is purged with nitrogen and then pressurized with hydrogen to 3.8–4.2 bar(g) while the internal temperature is ramped to 52±3 °C. Online FTIR monitoring of the 2245 cm⁻¹ C≡N stretching band is used to track conversion; the reaction is quenched when residual nitrile falls below 0.5 area%. After cooling and catalyst filtration through a 0.5 µm sintered metal candle, the clear THF solution is solvent-exchanged to ethyl acetate and treated with 5–6 N HCl in isopropanol at 0–5 °C to cleave the Boc group. The resulting (S)-2-(2-aminoethyl)pyrrolidine dihydrochloride is isolated by centrifugation, redissolved in water, and coupled with the triazolopiperazine fragment under phase-transfer conditions. Quality compliance: The starting nitrile is released per ICH Q7 § 7.30 after identity testing by optical rotation ([α]_D²⁰ −34.0±2.0°, c=1.0 MeOH) and chiral HPLC (Chiralpak AD-H, 250×4.6 mm, hexane/ethanol 90:10), limits for cyanide ion (≤10 ppm) per ICH M7 TTC, and residual palladium/nickel per ICH Q3D Option 2a. Formulation input ratio: The nitrile enters the hydrogenation step at a molar equivalence of 1.00 with respect to the subsequent triazolopiperazine acid; a 2–5 mol% excess is occasionally adopted to counter hold-up losses in the catalyst filtration train. Downstream unit operations: Hydrogenation is followed by cross-flow diafiltration, thin-film evaporation under 60 mbar, and final antisolvent crystallization of sitagliptin phosphate monohydrate from aqueous isopropanol. Terminal article: The API crystallizes as the monohydrate phosphate salt meeting USP monograph <2197>, with a particle size D₉₀ typically controlled to ≤150 µm on a Malvern Mastersizer 3000 for direct compression with metformin hydrochloride.

Table 1 compares impurity profiles recorded during manufacturing campaigns that substituted catalytic hydrogenation with a sodium borohydride–cobalt chloride chemical reduction, a route occasionally evaluated for sites lacking high-pressure infrastructure.

Operational experience on multiple 1200 kg batches reveals that moisture ingress above 60% RH in the catalyst charging glovebox elevates the des-cyano impurity above the 0.15% threshold, requiring a pre-drying protocol for the catalyst wet cake using molecular sieve-dried isopropanol.

When Does Enantiomeric Integrity Become the Rate-Limiting Parameter in Chiral Ligand Synthesis?

The title compound serves as a direct precursor to (S)-2-(aminomethyl)pyrrolidine, a C₂-symmetric or non-symmetric diamine building block used to construct salen-type and salan-type ligands. After Boc deprotection with 4.0 M HCl/dioxane, the free amine is reacted with 3,5-di-tert-butyl-2-hydroxybenzaldehyde at a precise molar ratio of 1.00 diamine : 2.05 aldehyde in anhydrous ethanol under a nitrogen atmosphere. The slight aldehyde excess compensates for competing imidazolidine formation. The resulting diimine is metallated with manganese(II) acetate tetrahydrate followed by aerial oxidation in the presence of lithium chloride to yield the Jacobsen-type Mn(III)-salen chloride complex. Regulatory framework: When the resultant catalyst is destined for the synthesis of an API intermediate, residual metal content must conform to ICH Q3D Option 1 (Mn oral PDE 130 µg/day); the ligand itself is released against an internal specification that includes enantiomeric excess by GC on a Chirasil-Dex CB column (≥99.5% ee). Usage ratio: In the asymmetric epoxidation of unfunctionalized olefins, the catalyst loading typically ranges from 2–5 mol% relative to the olefin substrate, with the chiral ligand being introduced as the pre-formed Mn complex. Process equipment: Ligand synthesis is performed in 50–200 L glass-lined reactors with anchor stirrers; stringent control of heating rate during the diimine formation step is mandatory—exceeding 2 °C/min towards reflux triggers Schiff-base oligomerization. Finished product: The terminal output is a dark brown microcrystalline Mn(III)-salen chloride, employed industrially for the Sharpless-type kinetic resolution of terminal epoxides or the enantioselective cyclopropanation of styrenes.

Incorporation of the (2S)-2-(cyanomethyl)pyrrolidine scaffold into conformationally constrained peptide mimics frequently targets the replacement of a Pro-Phe or Pro-Leu diad with a rigidified tertiary amide surrogate. The nitrile function is first reduced to the aminomethyl group and the resulting amine is protected as Fmoc-(S)-2-(aminomethyl)pyrrolidine hydrochloride for compatibility with Fmoc solid-phase peptide synthesis. On a CS Bio 136X automated peptide synthesizer operating at a 0.25 mmol scale, the resin-bound amino acid is coupled with 4.0 equivalents of Fmoc-amino acid derivative, activated in situ with HBTU (3.9 eq)/DIEA (8.0 eq) in DMF. Double coupling cycles of 40 min each at 50 °C are necessary to achieve an acylation yield above 99.0%, as monitored by online UV absorbance at 301 nm during Fmoc deprotection. Quality governance: Peptides produced for in vivo pharmacological evaluation are purified under ICH Q7 § 19 (non-GMP early-phase material) with LC-MS identity confirmation and TFA content <0.1%. Formula loading: The constrained amino acid is pre-dissolved to 0.3 M in DMF containing 0.05 M OxymaPure as a racemization suppressor; the volumetric addition is calibrated to deliver exactly 4.0 eq based on the resin substitution level determined by quantitative Fmoc assay. Manufacturing flow: The linear peptide is cleaved from the Rink amide resin with a TFA/TIS/water (95:2.5:2.5 v/v) cocktail, precipitated in cold diethyl ether, and lyophilized. For head-to-tail cyclization, the crude peptide is dissolved in DMF at 1 mM concentration and cyclized using PyBOP (3.0 eq)/DIEA (6.0 eq) overnight. End product: The chemotype is a 12- to 18-membered cyclic peptide bearing a chiral pyrrolidine tether, under investigation as a protease-resistant ligand for G protein-coupled receptors.

If the Mandated Qualified Impurity Reference Requires <0.10% Detection Limit in Sitagliptin Monograph

Pharmacopoeial impurity profiling under Ph. Eur. monograph 2983 and USP <2197> demands the synthesis and certification of the (R)-enantiomer of the nitrile intermediate, namely tert-butyl (2R)-2-(cyanomethyl)pyrrolidine-1-carboxylate. This substance is prepared from the parent (S)-compound via a racemic switch strategy: the nitrile is hydrolyzed to the corresponding carboxylic acid, subjected to dynamic kinetic resolution using D-(+)-tartaric acid in hot isopropanol, and the resolved R-acid is reduced back to the nitrile via the primary amide intermediate using trifluoroacetic anhydride and triethylamine. Compliance boundary: The reference standard is manufactured in an ISO/IEC 17025:2017 accredited laboratory under a cGMP quality system covering raw data integrity per 21 CFR Part 11. Each vial is assigned a certified value traceable to the SI unit through a mass-balance approach combining HPLC area% (≥99.7%), water content by Karl Fischer coulometry, residual solvents by headspace GC-MS (Ph. Eur. 2.4.24), and non-volatile residue. Material proportioning: In the preparative HPLC purification stage, a 50 mm ID × 250 mm Kromasil C18 column is loaded with 0.8–1.2 g of crude per injection, using a mobile phase of 0.1% TFA in water/acetonitrile (70:30) at 80 mL/min. The (R)-enantiomer elutes at a relative retention time of 1.11 versus the (S)-isomer. Process steps: Heart-cut collection triggers when the UV signal at 210 nm exceeds 50 mAU; fractions are pooled, rotary-evaporated below 35 °C to avoid Boc thermolysis, and lyophilized twice to reduce residual TFA. Final article: The deliverable is a 100 mg amber vial containing a lyophilized white powder, labeled as "(R)-Enantiomer Impurity Standard, Batch IS-2025-081, Lot 081-A, Expiry: 2028-03", stored at −20±5 °C with a desiccant insert.

Access to 1,4-dideoxy-1,4-imino-D-xylitol and related pyrrolidine alkaloids through the chiral pool route begins with the chemoselective partial reduction of the N-Boc nitrile. Instead of proceeding to the fully saturated amine, the nitrile is converted to the aldehyde by Raney nickel-catalyzed hydrogenation in the presence of semicarbazide (1.05 eq), creating a Boc-protected imino-sugar precursor in a single telescoped operation. Following Boc removal, the pyrrolidine is subjected to a stereoselective dihydroxylation protocol employing OsO₄ (1.5 mol%) and N-methylmorpholine N-oxide (1.2 eq) in acetone-water at −10 °C. Regulatory instrument: The polyhydroxylated pyrrolidine produced is evaluated as a pharmacological chaperone for lysosomal storage disorders; all in vivo batches comply with OECD Principles of Good Laboratory Practice (GLP, ENV/MC/CHEM(98)17), with a certificate of analysis listing endotoxin levels (<0.25 EU/mg, LAL test per Ph. Eur. 2.6.14). Formulation parameters: The substrate-to-osmium ratio is critical; at 0.5 mol% OsO₄ the conversion stops at approximately 60% after 24 h, while exceeding 3.0 mol% produces osmate ester byproducts that precipitate during workup. Production workflow: The oxidation is carried out in a 20 L jacketed glass reactor with a dry ice/IPA cooling loop, and the reaction progress is monitored by TLC (silica gel 60 F₂₅₄, ethyl acetate/methanol 4:1). After quenching with solid sodium sulfite, the crude mixture is desalted by ion-exchange chromatography on Amberlite IR-120 (H⁺). Resultant molecule: The isolated product is 1,4-dideoxy-1,4-imino-D-xylitol, a potent inhibitor of α-glucosidase with an IC₅₀ of 43 nM against the recombinant human enzyme, supplied as a ≥98% pure hydrochloride salt for structure-activity relationship studies.

Quaternary Ammonium Salts from Proline Analogs and the Enantioselective Alkylation Barrier

Derivatisation of the title compound into a C₂-symmetric quaternary ammonium bromide proceeds by exhaustive N-alkylation. After hydrogenolytic reduction of the nitrile and Boc deprotection, the resulting (S)-2-(aminomethyl)pyrrolidine is alkylated with 9-(chloromethyl)anthracene (2.05 eq) in the presence of anhydrous potassium carbonate (4.0 eq) in acetonitrile at reflux for 48 h. The resulting bis-ammonium salt is purified by hot filtration and recrystallization from ethanol/diethyl ether. Directive on standards: The catalyst falls under no pharmaceutical-specific regulation; however, when handling in a GMP production line, the material must be accompanied by a extended safety data sheet complying with Regulation (EC) No 1907/2006 (REACH) Annex II, and residual anthracene/methyl anthracene must be documented for occupational exposure limits (0.2 mg/m³ 8h-TWA). Addition stoichiometry: In the model asymmetric α-benzylation of N-(diphenylmethylene)glycine tert-butyl ester, the catalyst is employed at 10 mol% loading relative to the Schiff base, with cesium hydroxide monohydrate (5.0 eq) as the solid-liquid phase-transfer base. Substrate-to-alkylating agent molar ratio is fixed at 1.0:1.2 to suppress over-alkylation. Reaction engineering: The process is run in a 250 mL jacketed Schott reactor with a PTFE-coated magnetic stir bar at −20 °C; the cooling is maintained by a Lauda Ecoline thermostat. After 18 h, the organic phase is washed with water and analyzed by chiral HPLC (Chiralcel OD-H, hexane/i-PrOH 99:1, 1.0 mL/min) to determine enantiomeric excess. Deliverable product: The archetypal output—(R)-tert-butyl 2-amino-3-phenylpropanoate—is obtained in 85–92% yield and 88–94% ee after acid-base extraction, showcasing the utility of the proline-derived chiral pocket in the catalyst architecture.