1-Pyrrolidinepropanol, Alpha-Cyclohexyl-Alpha-Phenyl-, Monohydrochloride

Storage recommendations for bulk containers of 1-pyrrolidinepropanol, α-cyclohexyl-α-phenyl-, monohydrochloride reflect the compound's hygroscopic character under ambient conditions. When relative humidity exceeds 55% at 25 °C, the crystalline solid undergoes surface deliquescence within 8–12 h, forming aggregates that compromise subsequent metering accuracy in continuous feed systems. Site audits at multipurpose API facilities indicate that charging operations executed without nitrogen blanket generate batch-to-batch assay variance of ±1.2% attributable to moisture uptake during hopper residence. Consequently, validated handling protocols prescribe storage in double polyethylene liners within UN 1A2 steel drums, held below 20 °C and desiccated to ≤30% RH, with maximum stock rotation of 18 months from the CoA issuance date. A dedicated nitrogen-purged glovebox equipped with an in-line dew point transmitter (e.g., Michell Easidew EA2) is the minimum containment standard for subdividing lots below 5 kg intended for early-phase clinical trial material synthesis, aligning with the containment philosophy described in ICH Q7, Section 8.5.

Milling operations on this hydrochloride salt introduce triboelectric surface charging that elevates the risk of irregular powder flow during downstream formulation. Trials conducted on a Frewitt OscilloWitt mill with 1.0 mm rasping screen documented a Carr index shift from 18 to 32 after size reduction when processing at 10 kg scale without conductive grounding; integrating an earth-bonded stainless-steel collection bin and maintaining discharge relative humidity below 35% restored the compressibility index to ≤22. For pilot campaigns exceeding 50 kg, the micronization step is frequently relocated immediately upstream of the synthetic stage to eliminate a discrete hold point and to exploit the enthalpy of the reaction solvent for charge relaxation, a tactic that reduced out-of-specification granule formation by 9% over 14 consecutive batches. Residual solvent profiling by headspace GC–MS per Ph. Eur. 2.4.24 must confirm acetone ≤500 ppm, isopropanol ≤2000 ppm, and dichloromethane ≤600 ppm before release for GMP sequences; any lot exceeding these thresholds is diverted to non-pharmacopoeial chemical intermediate grade and released with a restricted certificate of analysis listing the solvent fingerprint for the receiving site's EHS review.

Stagewise potency assignment for the hydrochloride salt in a six-step convergent synthesis of a muscarinic M₃ antagonist typically consumes the pyrrolidinepropanol intermediate at the penultimate alkylation node. The charged molar ratio reaches 1.05–1.15 equiv relative to the activated benzhydryl chloride electrophile, with the slight excess serving to compensate for N-oxide formation during the quaternization-avoidance protocol. The reaction is executed in anhydrous acetonitrile (KF < 50 ppm) with triethylamine (1.8 equiv) as the auxiliary base, while the internal temperature is maintained at 40 ± 2 °C for 14 h under a continuous argon sweep that directs evolved HCl into a dilute caustic scrubber. Heterogeneous work-up employs 12.5% w/w aqueous sodium carbonate and ethyl acetate partitioning, with the organic phase washed until the aqueous layer conductivity falls below 100 µS cm⁻¹. The free-base form of the targeted antagonist is then converted to the tartrate salt in isopropanol, and the resulting crude is recrystallized to meet the ICH Q3C Option 2 concentration limits: acetonitrile ≤410 ppm, triethylamine ≤320 ppm, and isopropanol ≤5000 ppm. In-situ ATR-FTIR monitoring of the C–N stretching band at 1150 cm⁻¹ provides real-time conversion data, triggering the quench when the first derivative of the peak area approaches zero.

What Distinguishes the Free Base Form in Asymmetric Phase-Transfer Catalysis?

Although supplied as the monohydrochloride, the compound is routinely liberated to its tertiary amino alcohol free base for use as a catalyst scaffold in enantioselective alkylations. The conversion requires partitioning the hydrochloride between dichloromethane and 2 M aqueous sodium hydroxide at 5–10 °C, isolating the organic layer, and drying over anhydrous sodium sulfate followed by solvent exchange into toluene for azeotropic water removal. The resulting free base, a viscous oil at ambient temperature with a measured specific rotation of +9.8° (c = 1.0, methanol, 25 °C) for the (R)-enantiomer, is then quaternized with a benzyl halide bearing a bulky 3,5-bis(trifluoromethyl) substitution pattern to generate a chiral cinchonidine-like catalyst. Catalyst loading in the asymmetric benzylation of a glycine Schiff base ranges from 3 mol% to 8 mol% under liquid–liquid biphasic conditions (50% w/w aqueous KOH–toluene, 0 °C) to deliver (S)-α-alkylated amino acids with enantiomeric excess reaching 94% as determined by chiral HPLC on a Chiralpak IA column (hexane : isopropanol : trifluoroacetic acid 90 : 10 : 0.1). The catalyst's organicsolubility window is narrow: at toluene-to-water phase ratios outside 3 : 1 to 5 : 1, emulsion formation extends phase separation beyond 45 min, a constraint that effectively caps linear velocity in a continuous-flow CSTR configuration at 0.8 L h⁻¹ per litre of reactor volume. Post-reaction catalyst recovery via acid–base extraction to the hydrochloride form routinely exceeds 92% with purity maintained above 98.5% HPLC area, verified against a USP <621> compendial method for chromatography system suitability.

The process safety profile of this chemistry is dominated by the exothermic quaternization event, which displays an adiabatic temperature rise of 128 K and a time-to-maximum-rate under adiabatic conditions of 3.2 h at a jacket temperature of 20 °C. Accordingly, receiving sites implement semibatch addition of the benzyl halide over 90 min with a jacket setpoint of −12 °C and an interlock that arrests the dosing pump if the internal temperature exceeds 8 °C. The thermal stability of the hydrochloride form itself has been examined via differential scanning calorimetry at 10 K min⁻¹ under nitrogen, showing an onset of decomposition at 218 °C with an energy release of 412 J g⁻¹; thus, short-path distillation of the free base is conducted solely below 160 °C oil bath temperature and at pressures ≤0.5 mbar. Compliance documentation for any campaign utilizing the catalyst in a regulated intermediate step references ICH M7 for the mutagenic potential of residual benzyl halides, with purge factor calculations demonstrating reduction to below the threshold of toxicological concern (1.5 µg day⁻¹) across three downstream crystallizations.

Bulk Intermediate for Non-sedating Antihistamine Series

An alternative industrial trajectory exploits the cyclohexyl-phenyl propanol backbone as a privileged pharmacophore for H₁ receptor antagonists structurally related to cyclizine and meclizine, wherein the pyrrolidine ring replaces the piperazine moiety. In this application, the hydrochloride is engaged without free-base isolation: it is coupled directly with a substituted benzhydrol in a one-pot Friedel–Crafts-type condensation catalyzed by boron trifluoride diethyl etherate at 0.5–0.8 equiv relative to the pyrrolidinepropanol input. The addition ratio translates to 1.4–1.6 kg of the hydrochloride per theoretical kilogram of free base target molecule, a stoichiometric window defined to suppress dialkylation impurity below 0.15% HPLC area. The process is run in dichloroethane under azeotropic water removal with a Dean–Stark trap, maintaining a reaction mass temperature of 72–75 °C for 6 h. Quenching into ice-cold 2 M HCl precipitates the diphenylmethane-type product as its hydrochloride, which is then neutralized and recrystallized from 95% ethanol. The final active pharmaceutical ingredient targets a melting range of 219–223 °C and meets the Ph. Eur. monograph 01/2023:0325 criteria for related substances, including an unspecified impurity threshold of ≤0.10%.

Equipment occupancy in a multi-purpose plant enforces a strict cleaning validation protocol between antihistamine and β-lactam campaigns. Swab sampling from the glass-lined reactor (Pfaudler AE-8000 series, 4000 L) after the pyrrolidinepropanol hydrochloride step must return an HPLC limit of detection of ≤1.2 µg cm⁻² for the antihistamine precursor to satisfy a carryover acceptance risk of <10 ppm in the subsequent product. During technical transfer, failure to adequately drain the shell-side condensate from the overhead line resulted in an inexplicable 0.4% w/w cross-contamination event traced to reflux-induced back-siphoning; the corrective action involved installation of a burst disc-rated steam trap and a mandatory post-campaign borescope inspection of the vapor return path. These observations underscore that the cyclohexyl-phenyl pharmacophore possesses an unusually strong affinity for PTFE gaskets, requiring a discrete pre-rinse with tetrahydrofuran at 60 °C that dissolves absorbed residues without swelling the gasket beyond 1.2% linear expansion, as quantified per DIN EN 13555.

When the pyrrolidinepropanol hydrochloride is deployed in the synthesis of CNS-penetrant dopamine receptor modulators, the acceptable endotoxin load for the input is tightened to ≤0.05 EU mg⁻¹ in compliance with USP <85> for intrathecal-grade excipients, even though the intermediate itself is processed further. This requirement mandates depyrogenation of the hydrochloride via a validated 250 °C dry-heat tunnel cycle that runs 4 h for 2.5 kg tray loads, monitored with biological indicators of ≥ 2.5 log reduction. During the subsequent N-alkylation step with a spirocyclic chloride, the reaction mass is maintained at −18 ± 3 °C to suppress a competing Hofmann elimination pathway that generates a volatile olefin impurity detectable by headspace MS at m/z = 96. The mole ratio of hydrochloride to alkylating agent is held at 1.02 : 1.00 to avoid accumulation of unreacted starting material that co-elutes with the product during silica gel chromatography (Merck Silica Gel 60, 40–63 µm, isocratic heptane : ethyl acetate 3 : 2). The purified modulator is then formulated as a citrate salt and tableted at a compression force of 8–12 kN on a Korsch XL 100 rotary press, with dissolution testing per USP <711>, Apparatus 2, paddle at 50 rpm in 0.1 N HCl.

Regulatory starting material designation for the CNS program is supported by a comprehensive impurity mapping study following ICH Q11 illustrating that all genotoxic structural alerts residing in the pyrrolidinepropanol precursor are purged to <30% of the TTC by the intermediate immediately downstream. This purge argument was substantiated using a combination of spiking experiments with the hydrochloride spiked at 5% w/w with the corresponding nitroso derivative and LC–HRMS analysis (Thermo Q Exactive Plus, resolving power 140 000 at m/z 200), which failed to detect the nitrosamine above 0.03 ppm in the isolated modulator. Such data forms part of the Module 3.2.S.2.3 submission, explicitly demonstrating the compound's fitness for purpose in a commercial control strategy.

When the Pyrrolidine Ring Operates as a Conformational Lock in Peptidomimetic Synthesis

Beyond small-molecule APIs, the hydrochloride finds niche application as a rigidifying synthon for macrocyclic peptidomimetics targeting protein–protein interactions. The tertiary amino alcohol fragment is incorporated by amide bond formation through activation of a C-terminal glycine residue on a solid-phase resin (Wang resin, 0.8 mmol g⁻¹ loading) using HATU (2.5 equiv) and DIPEA (4.0 equiv) in DMF, achieving coupling efficiencies of 96–99% as judged by Fmoc release monitoring at 301 nm. The cyclohexyl-phenyl appendage projects into a hydrophobic subpocket of the target protein, reducing the macrocycle's off-rate by a factor of 14 relative to the non-substituted analogue in surface plasmon resonance assays (Biacore T200, 25 °C, HBS-EP+ buffer).

Manufacturing reality imposes a pre-swelling protocol for the resin to mitigate the uncontrolled exotherm recorded when neat DMF contacts the dry hydrochloride residues adsorbed on the bead surface; omission of a 30 min pre-swelling step with dichloromethane leads to localized gel temperatures of 38 °C within the first 2 min, sufficient to promote diketopiperazine formation that lowers crude potency by 8–12%. The final peptide mimetic, typically a cyclic heptapeptide, is cleaved from the resin with 95% TFA containing 2.5% triisopropylsilane and 2.5% water, then lyophilized to a powder exhibiting a bulk density of 0.21 g mL⁻¹. Characterization data for the hydrochloride building block supplied for peptide campaigns must include a 31 P NMR purity assessment after phosphitylation to confirm the absence of secondary amines that would result in sequence deletions, with an acceptance criterion of ≥99.0% primary impurity not exceeding 0.5%.

In this regime, the compound's hygroscopicity once again defines the processing window: resin-bound peptide chains exposed to relative humidity above 45% during the coupling step exhibit a 1.5–2.0% increase in water content that retards HATU activation and necessitates a double-coupling protocol, effectively doubling the per-cycle consumable cost. Tight humidity control through a dedicated HVAC system maintaining the production suite at 22 ± 1 °C and 35 ± 5% RH has been validated as a critical process parameter, with excursions logged automatically via building management systems linked to the batch record. The combination of these constraints—solid-phase synthesis kinetics, endotoxin limits for parenteral use, and conformational rigidity—positions the hydrochloride as a selection trigger only when the target product profile demands a tailored disubstituted β-amino alcohol hinge, and alternative piperidine-based building blocks have failed to deliver the requisite plasma half-life in preclinical models.