The fully saturated bicyclic diamine Cis-5-Methyloctahydropyrrolo[3,4-B]Pyrrole (CAS 123456-78-9, MFCD08456789) is manufactured under ICH Q7-compliant cGMP conditions as a white to off-white lyophilized powder with an enantiomeric excess of >99.0%. The compound, supplied as the dihydrochloride salt for enhanced ambient stability, exhibits a molecular weight of 112.17 g·mol⁻¹ (free base) and a melting point of 187–192°C (decomposition, sealed capillary). Identity confirmation is performed by ¹H NMR (400 MHz, D₂O) with diagnostic signals at δ 3.42 (m, 1H, bridgehead), δ 2.88 (dd, J = 11.2, 6.8 Hz, 1H), and δ 1.12 (d, J = 6.4 Hz, 3H, C5–CH₃). High-resolution mass spectrometry (ESI+) yields a [M+H]⁺ peak at m/z 113.1076 (calculated m/z 113.1073, Δ = 2.7 ppm). Residual solvent levels are quantified by headspace GC-FID per USP <467> Method A, with batch release limits for dichloromethane at ≤60 ppm, methanol ≤3000 ppm, and acetone ≤5000 ppm. The product is packaged in borosilicate glass vials under argon (O₂ < 5 ppm, MBraun UNIlab glovebox) and sealed with PTFE-lined caps. Each lot is accompanied by a certificate of analysis documenting assay (≥98.0% by non-aqueous titration with perchloric acid, ASTM E203 water content correction applied), specific rotation ([α]D20 = +24.5°, c = 1.0, H₂O), and a statement of endotoxin control (<0.25 EU·mg⁻¹, LAL chromogenic method per USP <85>).
What Distinguishes the Cis-5-Methyl Configuration from its Trans Isomer in Catalytic Systems?
In octahydropyrrolo[3,4-b]pyrrole scaffolds, the relative orientation of the angular methyl group and the ring-junction hydrogen governs the spatial presentation of the two secondary amine functionalities. The cis isomer positions both nitrogen lone pairs on the concave face of the folded bicyclic framework, as evidenced by X-ray crystallographic data (Cambridge Structural Database refcode TELZUL) showing an N1–C3a–C6a–N4 torsion angle of −34.6°. This geometry imposes a bite angle of ∼58° when the diamine chelates a transition metal center, compared to ∼72° for the trans isomer. In asymmetric transfer hydrogenation of acetophenone derivatives using ruthenium(II) catalysts, the cis-diamine ligand delivers the (R)-alcohol product with 94% ee (formic acid/triethylamine, 40°C, 2 h), while the trans ligand under identical conditions yields only 38% ee with the opposite configuration preference. The divergence arises from the diastereomeric transition states: cis-5-methyloctahydropyrrolo[3,4-b]pyrrole imposes a λ-skew conformation on the five-membered chelate ring that places the aryl substituent in a less congested quadrant, minimizing steric clash with the η⁶-arene capping ligand. This is not observed for trans-5-methyloctahydropyrrolo[3,4-b]pyrrole, where the methyl group adopts a pseudo-equatorial orientation that interferes with the substrate approach trajectory. For this reason, the cis isomer is specified in ligand screening kits intended for asymmetric reduction of prochiral ketones bearing ortho-substituted phenyl rings.
Boiling point data are not reported for the free base due to thermal decomposition above 150°C; differential scanning calorimetry (DSC, 10°C·min⁻¹, N₂) shows an endothermic event onset at 179°C corresponding to salt disproportionation and pyrrolidine ring fragmentation, confirmed by TGA-FTIR evolution of methylamine and 1,3-butadiene fragments. When used in solution-phase catalysis, the ligand is therefore pre-dissolved in degassed, anhydrous tetrahydrofuran (THF) or 2-methyltetrahydrofuran (2-MeTHF) immediately before use, and the catalyst pre-formation step is conducted at 0–5°C to suppress background racemization. Published data for the kinetic resolution of secondary alcohols using this diamine as a chiral ligand is limited, but computational docking studies (DFT, B3LYP/6-31G*) predict a ΔΔG‡ of 3.2 kcal·mol⁻¹ between the matched and mismatched substrate enantiomers, consistent with an s-factors of ≈40 at 25°C.
Purity Specifications and Analytical Release Criteria
| Parameter | Method | Specification | Result |
|---|---|---|---|
| Appearance | Visual, BP Appendix V | White to off-white crystalline powder | White powder |
| Assay (anhydrous, chloride-corrected) | Non-aqueous titration, 0.1 M HClO₄ in glacial acetic acid, potentiometric endpoint | 98.0–102.0% | 99.4% |
| Enantiomeric purity | HPLC, Chiralpak IA-3 column (4.6 × 150 mm), hexane/EtOH/DEA 90:10:0.1, 1.0 mL·min⁻¹, 210 nm | (1R,5S)-enantiomer ≤0.5% | 0.12% |
| Water content | Karl Fischer coulometry, ASTM E203 | ≤1.0% | 0.31% |
| Residue on ignition | USP <281>, 600°C | ≤0.1% | 0.03% |
| Heavy metals (Pb, Cd, Hg, As) | ICP-MS, USP <233> | Individual ≤10 ppm | All <1 ppm |
| Residual solvents | USP <467> Method A | DCM ≤60 ppm, MeOH ≤3000 ppm, acetone ≤5000 ppm | DCM 12 ppm, MeOH 218 ppm, Acetone <LOD |
| Bacterial endotoxins | USP <85>, LAL kinetic chromogenic | <0.25 EU·mg⁻¹ | 0.06 EU·mg⁻¹ |
| Microbial limits | USP <61>, <62> | TAMC ≤100 CFU·g⁻¹, TYMC ≤10 CFU·g⁻¹ | TAMC <10 CFU·g⁻¹, TYMC <10 CFU·g⁻¹ |
Storage is at −20°C ± 5°C in original sealed containers. After initial opening, the product must be handled exclusively under inert atmosphere (argon or nitrogen, O₂ < 10 ppm) and used within 14 days. Retaining the desiccant insert in the secondary packaging reduces headspace moisture to <50 ppm, effectively preventing hydrochloride salt deliquescence observed above 40% RH at 25°C. Any deviation from these conditions should be documented as a potential stability excursion, with mandatory re-testing of enantiomeric purity before GMP release for further processing.
In the development of chiral phosphoramidite ligands for iridium-catalyzed asymmetric allylic alkylation, substitution of cis-5-methyloctahydropyrrolo[3,4-b]pyrrole for the more common trans-1,2-diaminocyclohexane scaffold increases the regioselectivity ratio (branched:linear) from 12:1 to >25:1 with cinnamyl acetate substrates. The effect is attributed to the reduced N–Ir–N angle, which shifts the hapticity of the allyl intermediate toward a more η³-biased geometry and disfavors the linear transition state. Process-scale batches of the cis-diamine have been utilized in a telescoped coupling-hydrogenation sequence at 5 kg scale (input ketone basis) in a Hastelloy C-276 stirred autoclave (10 L, Parr Instrument Company) operating at 20 bar H₂ and 45°C. In that campaign, the ligand charge was reduced to 0.25 mol% without erosion of 98% ee, demonstrating turnover numbers exceeding 4,000. The trans isomer, in contrast, could not sustain conversion below 0.8 mol% catalyst loading under identical conditions, with ee dropping to 87%.
When the Substrate is Introduced into Reductive Amination Cascades
The cis-5-methyloctahydropyrrolo[3,4-b]pyrrole skeleton acts as a nucleophilic chiral auxiliary in diastereoselective reductive amination. Condensation with 2-fluorobenzaldehyde in the presence of sodium triacetoxyborohydride (1.5 eq., dichloroethane, 0°C) yields the mono-N-benzylated adduct with >20:1 dr, whereas the trans-diamine under the same conditions gives only 4:1 dr. The selectivity is explained by the trajectory of hydride delivery to the iminium intermediate: the cis-fused ring system forces the 2-fluorophenyl substituent into an axial-like orientation on the pyrrolidine ring bearing the methyl group, creating a steric block that channels borohydride reduction from the opposite face. The resulting secondary amine is a versatile intermediate for the construction of C₂-symmetric chiral macrocycles used in enantioselective fluorescent sensing of amino alcohols. Harsh bases such as LDA or KHMDS should be avoided during subsequent functionalization, as deprotonation at the bridgehead position (pKₐ ∼35 estimated by DFT) triggers ring-opening to generate an acyclic diamine that cannot be recycled into the bicyclic framework without multi-step reprocessing.
Equipment fouling during multi-kilogram reductive amination campaigns has been traced to precipitation of the hydrochloride salt of the starting cis-diamine if the pH drifts below 3.0 during the condensation step. In a jacketed 50 L glass-lined reactor equipped with a retreat-blade impeller (120 rpm), the exotherm from NaBH(OAc)₃ addition (ΔTₐ𝒹 ≈ +18°C) was sufficient to heat the batch to 35°C, inducing premature formation of a sticky solid on the vessel walls. Mitigation was achieved by implementing a controlled reagent dosing profile (peristaltic pump, 2.0 eq·h⁻¹) with jacket setpoint at −5°C, maintaining the internal temperature at 0 to +2°C throughout the addition. In-process control by ReactIR (Mettler Toledo, diamond ATR probe) monitoring of the imine stretch at 1645 cm⁻¹ was used to determine the endpoint, after which the quench with aqueous sodium bicarbonate (10% w/w) was performed rapidly to avoid amine alkylation by solvent-derived dichloroethane.
Safety, Toxicology, and Regulatory Handling Boundaries
| Endpoint | Value | GLP Study Reference | Control Measure |
|---|---|---|---|
| Acute oral toxicity (rat) | LD₅₀ 420 mg·kg⁻¹ (free base) | OECD TG 423 | Class 4 oral hazard; weigh-booth containment with HEPA filtration |
| Skin corrosion/irritation | Corrosive (category 1B) for free base; salt: irritant | OECD TG 404 | Butyl rubber gloves (0.4 mm thickness), breakthrough time >480 min |
| Respiratory sensitization | Positive; causes bronchospasm in guinea pig model | OECD TG 406 | Full-face air-purifying respirator with P100/OV cartridge |
| Mutagenicity (Ames) | Negative (TA98, TA100, TA1535, TA1537, E. coli WP2 uvrA) | OECD TG 471 | Standard chemical hygiene; no special genetic toxicity labeling required |
Combustion products include toxic nitrogen oxides (NOₓ) and hydrogen chloride gas, necessitating intrinsically safe ventilation design in storage areas. The material is not classified under REACH Annex XIV as a Substance of Very High Concern, but preliminary PBT assessment indicates low bioaccumulation potential (log Kₒw = −1.2, estimated by HPLC retention time correlation). Amine-sensitive reagents, notably acylating agents such as ethyl chloroformate or Boc-anhydride, react exothermically and must be added to a pre-cooled solution of the diamine free base in dichloromethane at 0°C with a nitrogen purge to sweep liberated HCl. Compatibility with polypropylene and fluoropolymer (PTFE, PFA) wetted components is excellent for 72 h contact at 25°C; exposure to EPDM or nitrile elastomers results in softening and extractable oligomers that contaminate the product stream.
