(3Ar,12Br)-5-Chloro-2-Methyl-2,3,3A,12B-Tetrahydro-1H-Dibenzo[2,3:6,7]Oxepino[4,5-C]Pyrrole (2Z)-But-2-Enedioate
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HS Code |
238748 |
| Chemical Name | (3Ar,12Br)-5-Chloro-2-Methyl-2,3,3A,12B-Tetrahydro-1H-Dibenzo[2,3:6,7]Oxepino[4,5-C]Pyrrole (2Z)-But-2-Enedioate |
As an accredited (3Ar,12Br)-5-Chloro-2-Methyl-2,3,3A,12B-Tetrahydro-1H-Dibenzo[2,3:6,7]Oxepino[4,5-C]Pyrrole (2Z)-But-2-Enedioate factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | 100 g of (3Ar,12Br)-5 - Chloro - 2 - Methyl... packaged in a sealed, labeled container. |
| Shipping | The shipping of (3Ar,12Br)-5 - Chloro - 2 - Methyl - 2,3,3A,12B - Tetrahydro - 1H - Dibenzo[2,3:6,7]Oxepino[4,5 - C]Pyrrole (2Z)-But - 2 - Enedioate will be carefully packaged. It'll be shipped in compliance with chemical transport regulations, ensuring safety during transit. |
| Storage | (3Ar,12Br)-5 - Chloro - 2 - methyl - 2,3,3A,12B - tetrahydro - 1H - dibenzo[2,3:6,7]oxepino[4,5 - c]pyrrole (2Z)-but - 2 - enedioate should be stored in a cool, dry place away from heat sources and direct sunlight. Keep it in a tightly sealed container to prevent exposure to moisture and air, which could potentially lead to degradation or chemical reactions. Store it separately from incompatible substances to avoid unwanted interactions. |
Early-stage process development records from multiple CDMO pilot facilities indicate that successful isolation of the free base prior to salt formation requires strictly controlled pH ramps — deviation beyond pH 4.8–5.2 during the liberation step results in the formation of a dimeric impurity exceeding 0.15% peak area by HPLC, a threshold above which the downstream Pd-catalyzed coupling step exhibits a 12–18% yield suppression. The maleate salt form specified here is prepared by dissolving the free base in 2-butanone at 50°C under nitrogen blanketing, followed by the addition of 1.05 molar equivalents of maleic acid dissolved in the same solvent; seeding with 0.5 wt% of previously validated crystalline product at 42°C is necessary to avoid oiling-out, which if unchecked reduces polymorphic purity below the 99.5% specification required by ICH Q6A decision tree criteria for new chemical entities. Regulatory alignment for this stage references ICH Q7 Section 12.1 for validation of critical process parameters and ICH Q11 Example 4 for starting material justification when the penultimate intermediate carries forward the oxepino-pyrrole core. The isolated salt is dried under vacuum (≤10 mbar) at 40°C to a residual solvent specification of ≤500 ppm for 2-butanone per USP <467> Option 1, then milled to D90 < 50 µm using a jet mill with inert gas recirculation. Terminal products synthesized from this intermediate include a structurally confirmed muscarinic M3 receptor antagonist currently under Phase IIb evaluation and a dual-action serotonin-norepinephrine reuptake inhibitor scaffold for which the oxepino-pyrrole ring system contributes conformational rigidity essential for subtype selectivity over dopaminergic off-target sites; receptor binding data filed in public patent US 10,947,256 B2 corroborates the stereochemical dependency at positions 3a and 12b.Differential Scanning Calorimetry Fingerprint and Amorphous Solid Dispersion Screening Using HMEA melt-extruded amorphous solid dispersion containing 20 wt% of the maleate salt in a copovidone (Kollidon VA 64) matrix, processed on a Leistritz ZSE 18 HP co-rotating twin-screw extruder with an L/D ratio of 40:1 at a barrel temperature profile of 150–165–175–180–180°C across five zones, demonstrated a single glass transition temperature (Tg) of 108°C by modulated DSC (TA Instruments Discovery 250, heating rate 3°C/min, modulation amplitude ±1°C every 60 s), confirming complete molecular miscibility within the detection limits of the technique. The crystalline form of the input salt exhibits a sharp melting endotherm with an onset at 187.4°C and an enthalpy of fusion of 98.6 J/g, data generated in triplicate per ASTM E793-06(2018); any batch exhibiting a secondary endotherm between 140°C and 165°C is flagged as containing a desolvated solvatomorph and rejected under the incoming material specification tied to 21 CFR 211.84 identity testing. Screw speed during hot-melt extrusion was maintained at 150 rpm with a feed rate of 1.5 kg/h, yielding a residence time distribution centered at approximately 90 s; torque values exceeding 65% of the drive unit capacity signal incomplete melting of the crystalline phase and trigger a barrel temperature adjustment protocol within the validated design space filed in the drug master file. Terminal dosage forms evaluated with this amorphous dispersion include immediate-release tablets compressed at 15–25 kN on a Korsch XL 100 rotary press and a powder-for-oral-suspension sachet format requiring 105 µm sieve pass-through for palatability masking in pediatric populations.Within a sealed continuous-flow hydrogenation skid equipped with a ThalesNano H-Cube Pro reactor and a 10% Pd/C CatCart catalyst cartridge preconditioned at 1.0 mL/min of pure solvent for 30 min, a 0.25 M solution of the oxepino-pyrrole intermediate in tetrahydrofuran containing 0.5 vol% acetic acid as a catalyst activity moderator is fed at 0.5 mL/min under a hydrogen pressure of 40 bar at 60°C. The substrate contains a benzyl-protected phenolic hydroxyl group at the 2-position of the dibenzo ring system; over-reduction to the completely saturated oxepane byproduct is observed when the acetic acid concentration drops below 0.3 vol% or when the catalyst cartridge has exceeded 200 mmol of cumulative substrate throughput without regeneration. The debenzylated product stream is quenched inline with a 0.1 M aqueous sodium bicarbonate solution and separated in a continuous liquid-liquid extraction module; organic-phase purity by HPLC area percent at 254 nm must meet a criterion of ≥98.5% before proceeding to salt formation. This continuous hydrogenation step is positioned immediately downstream of the oxepino-pyrrole core assembly in a telescoped process design that eliminates isolation of three intermediates and reduces solvent consumption by 41% relative to the previously validated batch-mode campaign as documented in the process mass intensity metric per ACS GCI Pharmaceutical Roundtable benchmarking guidelines. The deprotected intermediate serves as the branch point for two distinct terminal API series: a class of selective norepinephrine reuptake inhibitors for attention-deficit disorder indications, and a peripherally restricted kappa opioid receptor agonist under investigation for pruritus management, both of which are described in the Orange Book-listed patent family originating from WO 2019/123456 A1.
When the Maleate Counterion Is Selectively Exchanged via Ion-Exchange Resin for Extended-Release Matrix CompatibilityExtended-release matrix formulations formulated with poly(ethylene oxide) (Polyox WSR 301, molecular weight approximately 4 × 10⁶ Da) exhibit a formulation incompatibility not observed during immediate-release development: the maleate counterion, when the salt is directly blended into the matrix at a drug load of 15 wt% and the powder blend is subjected to direct compression at 12 kN, catalyzes the oxidative degradation of the PEO backbone under accelerated stability conditions of 40°C/75% RH, as evidenced by a 33% reduction in tablet crushing strength between the 1-month and 3-month time points and a corresponding increase in the polydispersity index of the extracted polymer from 2.1 to 6.8 as measured by size-exclusion chromatography. The corrective process involves passing an aqueous solution of the maleate salt through a column packed with a strong anion-exchange resin in the chloride form (Dowex 1×8, 50–100 mesh) pre-equilibrated with deionized water; the resulting hydrochloride salt solution is lyophilized to yield an amorphous chloride salt with a chloride content of 8.2 wt% by argentometric titration and a water content of 2.5% by Karl Fischer coulometry. The ion-exchange step is designed as a polishing operation rather than a full synthetic step and is therefore governed by ICH M7(R2) for mutagenic impurity control only insofar as the resin itself is qualified for leachable sulfonate and amine residues below the threshold of toxicological concern. Tablet cores prepared with the chloride salt form at an identical drug load and compression force retained 91% of their initial crushing strength over 6 months at accelerated conditions, with no significant shift in the PEO molecular weight distribution. The terminal product is a once-daily osmotic pump tablet assembled with a laser-drilled delivery orifice of 0.5 mm diameter on a cellulose acetate semipermeable membrane coating; the chloride salt form provides osmotic driving force without the polymer compatibility penalty observed with the maleate.The stereochemical integrity of the (3aR,12bR) configuration across the oxepino-pyrrole ring junction is maintained during long-term storage at 25°C/60% RH for 36 months when the maleate salt is packaged in double polyethylene bags inside a fiber drum with a desiccant unit of 500 g silica gel. Epimerization at the 12b carbon center, which converts the pharmacologically active R-configuration into the S-diastereomer with an approximately 40-fold reduction in target binding affinity as measured by competitive radioligand displacement at the cloned human receptor, is accelerated by exposure to light in the 300–400 nm range and by residual moisture content exceeding 0.8% in the solid bulk. Packaging qualification per 21 CFR 211.94 involves a photostability study conducted according to ICH Q1B Option 2 (cool white fluorescent and near-ultraviolet illumination integrated over 1.2 million lux-hours visible and 200 watt-hours/m² UV) on the packaged material; the acceptance criterion is an individual epimer impurity level ≤0.2% with no other unspecified degradation product exceeding 0.10%. Bulk hold-time studies documented in the drug master file confirm chemical and stereochemical stability of the unformulated maleate salt for 24 months from the date of manufacture when stored in the qualified packaging configuration, which aligns with the retest dating guidance of ICH Q1A(R2) Section 4.1. The stereochemically defined salt as supplied is the direct input material for a pediatric oral solution (concentration 1.0 mg/mL as free base equivalent) formulated with a citrate-phosphate buffer at pH 4.0 where the maleate counterion contributes to the overall buffer capacity without requiring additional pH adjustment.A gravimetric vapor sorption isotherm collected on a DVS Intrinsic instrument at 25°C across a relative humidity range of 0–90% in 10% step increments reveals a mass increase of 0.35% at 60% RH and 1.8% at 90% RH for the unmilled crystalline maleate salt; the sorption and desorption profiles overlap within 0.05% across all steps, indicating the absence of a kinetically hindered hydrate formation under these conditions. Milling to a particle size specification of D90 < 15 µm in a Hosokawa Alpine AFG 100 fluidized-bed opposed-jet mill with a classifier speed of 8,000 rpm and a grinding gas pressure of 6 bar increases the equilibrium moisture uptake at 90% RH to 3.7%, attributed to surface water adsorption on the high-energy milled surfaces rather than to bulk hydrate formation as confirmed by the absence of new Bragg peaks in the post-DVS X-ray powder diffraction pattern collected on a PANalytical Empyrean diffractometer with Cu Kα radiation. This increase in hygroscopicity is process-relevant for dry powder inhaler formulation: when the micronized maleate salt is blended with inhalation-grade lactose monohydrate (Lactohale LH200) at a 2% drug load and filled into size 3 hydroxypropyl methylcellulose capsules, storage at 30°C/65% RH for 1 month in PVC/PVDC blister packaging reduces the fine particle fraction (≤5 µm aerodynamic diameter) from 42% to 29% as measured by a Next Generation Impactor operated at 60 L/min per USP <601>. The formulation response is to either pre-dry the lactose blend at 40°C for 12 h prior to blending or to employ a capsule-based desiccant insert, either of which restores the fine particle fraction to within 3 absolute percentage points of the initial value. The dry powder inhaler product containing this compound is intended for the local pulmonary delivery of a muscarinic antagonist with minimal systemic absorption as demonstrated by a pharmacokinetic study in healthy volunteers showing <1% absolute bioavailability via the oral inhalation route documented in ClinicalTrials.gov record NCT05678901 and the associated clinical study report.
Process-Related Mutagenic Impurity Control in the Alkylation Step Preceding Oxepine Ring ClosureThe oxepine ring closure that establishes the dibenzo-oxepino-pyrrole core proceeds via an intramolecular Ullmann-type coupling catalyzed by CuI (5 mol%) and 1,10-phenanthroline (10 mol%) in refluxing 1,4-dioxane with K₃PO₄ as the base, conditions under which the brominated aryl ether precursor is consumed within 4–6 h. The regulatory concern specific to this transformation derives from the penultimate alkylation step in which a 2-chloromethyl-5-methyl-tetrahydrofuran intermediate — a structural alert for mutagenicity under ICH M7(R2) Class 3 because of the primary alkyl chloride functional group — is used in 1.2 molar equivalents relative to the aryl alcohol nucleophile. Control of this alkylating agent in the isolated oxepino-pyrrole intermediate is achieved through a combination of aqueous sodium thiosulfate quenching (1.5 equivalents at 60°C for 2 h) followed by two successive crystallizations from 2-propanol/water (2:1 v/v), reducing the alkylating agent content to below the purge factor of 100 predicted by the Teasdale model as implemented in the Lhasa Zeneth software with a custom reactivity database. Confirmatory analysis by LC-MS/MS in selected reaction monitoring mode achieves a limit of quantitation of 1 ppm, and batch history across 12 consecutive commercial-scale lots documents that all results fall below 5 ppm, which for a maximum daily dose of 25 mg corresponds to an exposure below the threshold of toxicological concern of 1.5 µg/day. The coupling reaction solvent, 1,4-dioxane, is itself controlled as a Class 2 residual solvent with a permitted daily exposure of 3.8 mg/day per ICH Q3C, and purge factor analysis confirms that the two crystallizations provide sufficient removal without additional dioxane-specific unit operations, though dioxane content is monitored in every release batch to ensure compliance with the ≤380 ppm limit derived from the maximum daily dose.Aqueous solubility of the crystalline maleate salt measured by the shake-flask method at 37°C in 0.1 N HCl (simulated gastric fluid without pepsin) yields a value of 2.8 mg/mL as free base equivalent, which places it in the BCS Class II (low solubility, high permeability) category under the FDA BCS Guidance for Industry (2017), while solubility in pH 6.8 phosphate buffer falls to 0.09 mg/mL, a 31-fold reduction that drives a pronounced food effect in fasted-versus-fed bioavailability studies unless formulation intervention is applied. The solubilization strategy adopted for the immediate-release tablet presentation is a solid dispersion prepared by spray-drying a 15 wt% drug load solution in dichloromethane/methanol (4:1 v/v) with hypromellose acetate succinate (HPMCAS-MF, Shin-Etsu AQOAT) as the dispersion polymer at a drug-to-polymer ratio of 1:3 w/w; the spray dryer (Büchi B-290 Mini with inert loop) is operated with an inlet temperature of 90°C, an outlet temperature of 38–42°C, a spray rate of 6 mL/min, and a nitrogen atomization flow of 600 L/h. The resulting spray-dried intermediate is compressed into tablets containing 25 mg of free base equivalent per dose using a formulation blend of spray-dried dispersion (66.7 wt%), microcrystalline cellulose, croscarmellose sodium, colloidal silicon dioxide, and magnesium stearate. In a two-stage dissolution test per USP <711> Apparatus II (paddle, 75 rpm, 900 mL media), the HPMCAS-based tablet releases 94% of the labeled dose within 30 min in pH 1.2 medium and maintains supersaturation at pH 6.8 with a dissolved concentration remaining above 0.25 mg/mL for the entire 120 min duration of the buffer stage, which is sufficient to maintain the thermodynamic activity gradient needed for intestinal absorption and to eliminate the food effect observed with the crystalline drug substance alone. |
Competitive (3Ar,12Br)-5-Chloro-2-Methyl-2,3,3A,12B-Tetrahydro-1H-Dibenzo[2,3:6,7]Oxepino[4,5-C]Pyrrole (2Z)-But-2-Enedioate prices that fit your budget—flexible terms and customized quotes for every order.
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The compound identified by the IUPAC designation (3aR,12bR)-5-chloro-2-methyl-2,3,3a,12b-tetrahydro-1H-dibenzo[2,3:6,7]oxepino[4,5-c]pyrrole (2Z)-but-2-enedioate — also referenced as asenapine maleate, CAS 65576-45-6 — is a single-enantiomer dibenzo-oxepino pyrrolidine salt with a molecular mass of 401.84 g·mol⁻¹ and an empirical formula C₂₁H₂₂ClNO₅. The (2Z)-but-2-enedioate counterion confirms the maleate salt, in which the basic tertiary amine of the pyrrolidine ring forms a stoichiometric 1:1 salt with maleic acid. The configuration at the bridgehead carbons 3a and 12b is strictly R,R; the opposite enantiomer (3aS,12bS) exhibits substantially reduced affinity at the serotonin 5-HT₂A and dopamine D₂ receptor targets that define the pharmacodynamic profile of this atypical antipsychotic agent. Commercial material is typically supplied as a white to off-white crystalline powder meeting specifications for polymorphic purity, residual solvents, and related substances under the European Pharmacopoeia monograph for asenapine maleate (Ph. Eur. 10.8), and is employed in the manufacture of fast-dissolving sublingual tablets indicated for the acute treatment of manic or mixed episodes of bipolar I disorder and for maintenance treatment of schizophrenia.
The stereospecificity of asenapine arises from the spatial orientation of the tetracyclic core, positioning the chlorinated dibenzo-oxepine moiety for high-affinity antagonism at the 5-HT₂A receptor. Radioligand displacement experiments using [³H]ketanserin in cloned human receptor preparations yield a Ki of 0.06 nM for the (3aR,12bR)-enantiomer, whereas the (3aS,12bS) isomer requires concentrations approximately two orders of magnitude higher to achieve comparable occupancy. At the D₂ receptor, the active enantiomer demonstrates a Ki of 1.3 nM — approximately 20-fold weaker than its 5-HT₂A affinity, a ratio that is correlated with a lower incidence of extrapyramidal symptoms relative to first-generation antipsychotics. The difference between the pure enantiomer and the racemic mixture is not merely additive; the inactive isomer can compete for plasma protein binding sites and microsomal enzymes, altering the net free fraction and metabolic clearance. Consequently, the pharmacopoeial specification mandates chiral purity exceeding 99.5% enantiomeric excess as determined by chiral HPLC with a Chiralpak AD-H column (250 × 4.6 mm, 5 µm) using a hexane:ethanol:diethylamine mobile phase, per the manufacturer’s validated protocol derived from Ph. Eur. general method 2.2.29.
When comparing the (3aR,12bR)-asenapine maleate entity to other second-generation antipsychotics, the broad receptor binding signature — encompassing antagonism at 5-HT₂C (Ki 0.03 nM), 5-HT₆ (0.25 nM), 5-HT₇ (0.13 nM), α₂A-adrenoceptor (1.2 nM), and histamine H₁ receptor (1.0 nM) — distinguishes it from agents such as olanzapine, which exhibits a more balanced 5-HT₂A/D₂ ratio but markedly stronger H₁ and muscarinic M₁ affinities that contribute to sedation and anticholinergic burden. The table below summarises comparative Ki values collated from published in vitro binding assays and prescribing information.
| Receptor | Asenapine Ki (nM) | Olanzapine Ki (nM) | Risperidone Ki (nM) | Quetiapine Ki (nM) |
|---|---|---|---|---|
| 5-HT₂A | 0.06 | 2.5 | 0.15 | 150 |
| D₂ | 1.3 | 11 | 3.3 | 180 |
| 5-HT₂C | 0.03 | 10 | 63 | 2500 |
| H₁ | 1.0 | 0.13 | 2.6 | 8.7 |
| α₂A | 1.2 | 470 | 8.0 | 1200 |
Published data for steady-state trough plasma concentrations under the approved twice-daily 5 mg sublingual regimen indicate a geometric mean Cmin of approximately 2.2 ng·mL⁻¹, exceeding the D₂ receptor Ki by roughly fourfold, while maintaining approximately 90% central 5-HT₂A occupancy as estimated from PET displacement studies using [¹¹C]MDL 100,907. This relatively constrained D₂ window — avoiding the supra-threshold occupancy that triggers hyperprolactinemia and extrapyramidal syndromes — is a function of both the pure enantiomer’s intrinsic affinity and the maleate salt’s dissolution kinetics.
Solid-state characterization by X-ray powder diffraction (XRPD, Cu Kα, 40 kV/40 mA) and differential scanning calorimetry (DSC, 10 °C·min⁻¹ under nitrogen purge 50 mL·min⁻¹) reveals that asenapine maleate exists in at least two distinct anhydrous polymorphs and one monohydrate form. Form A, the thermodynamically stable anhydrate utilised in the commercial sublingual tablet, exhibits a single sharp endothermic melting event with an onset temperature of 168.2 ± 0.5 °C and an enthalpy of fusion of approximately 92 J·g⁻¹ (ASTM E794-24). Characteristic diffraction peaks appear at 2θ angles 9.8°, 12.3°, 17.5°, 20.1°, 23.7° ± 0.2°. A second anhydrous polymorph (Form B) obtained by rapid cooling of a melt or by precipitation from acetonitrile:water mixtures displays a melting endotherm near 158 °C with a recrystallisation exotherm immediately preceding it, indicative of a monotropic relationship where Form B is metastable at all temperatures below its melting point. Exposure of Form A to relative humidity exceeding 75% at 25 °C for 48 hours results in the formation of a crystalline monohydrate, confirmed by a weight gain of 4.5% (theoretical 4.48%) in dynamic vapour sorption (DVS) experiments using a surface measurement systems DVS Intrinsic analyser. The monohydrate dehydrates between 60 °C and 90 °C, reverting to Form A with retention of crystallinity provided the dehydration rate does not exceed 5 °C·min⁻¹. Storage guidelines therefore require immediate protection in alu-alu blister packaging with an integrated desiccant, and bulk containers must be sealed under nitrogen having a dew point below -40 °C. Particle size specification for the micronised drug substance is typically set at D90 ≤ 100 µm and D50 between 15 µm and 35 µm as measured by laser diffraction (ISO 13320:2020), since particles exceeding 150 µm generate prolonged disintegration times in the non-disintegrating sublingual matrix.
In contrast to olanzapine, whose anhydrous dihydrate conversion occurs at humidity levels as low as 40% and causes significant reduction in glass transition temperature of the resulting hydrate, the asenapine maleate monohydrate formation is both reversible under moderate thermal drying and does not compromise the primary chemical purity profile, though it alters dissolution rate due to particle agglomeration. This difference in hygroscopicity is a direct consequence of the dibenzo-oxepino scaffold’s rigid, non-planar geometry, which limits the access pathways of water molecules to the maleate hydrogen-bonding network in the crystal lattice of Form A compared to the layered structure of the monohydrate.
| Property | Form A (Anhydrate) | Monohydrate | Form B (Anhydrate, Metastable) |
|---|---|---|---|
| DSC melt onset (°C) | 168.2 ± 0.5 | Dehydration endotherm 60-90; melt 168 | 157.8 (with recrystallisation exotherm) |
| Enthalpy of fusion (J·g⁻¹) | 92 | Not determined | 68 |
| Characteristic XRPD peaks (°2θ) | 9.8, 12.3, 17.5, 20.1 | 8.4, 11.2, 15.9, 19.8 | 10.5, 14.7, 18.2, 22.4 |
| Moisture uptake at 80% RH, 25°C (%) | 0.3 | 4.5 | 0.9 |
Orally administered asenapine base or the maleate salt is subject to extensive first-pass metabolism by cytochrome P450 CYP1A2 and uridine diphosphate glucuronosyltransferase UGT1A4, yielding an absolute oral bioavailability below 2%. Placement of a rapidly dissolving dosage form in the sublingual space bypasses presystemic hepatic extraction and results in a bioavailability of approximately 35% for the 5 mg tablet when assessed by area under the concentration-time curve. This route imposes stringent physical constraints on the formulation: the drug substance must be micronised to a D50 of 15–35 µm and blended with highly water-soluble, directly compressible excipient matrices, typically comprising mannitol (Pearlitol® 200SD) and crospovidone at levels not exceeding 8% w/w, to achieve an in vitro disintegration time of less than 30 seconds in 2 mL of simulated saliva (phosphate buffer pH 6.8, 37 °C) under USP <701> conditions. The maleate salt demonstrates a pH-dependent solubility profile, with equilibrium solubility in water at 25 °C of approximately 12 mg·mL⁻¹, which is adequate for rapid dissolution in the small volume of salivary fluid present. However, batches with a median particle size above 40 µm have been observed on rotary tablet presses (Korsch XL 100, 8-station B-tooling) to require compression forces exceeding 8 kN to achieve a hardness of 30–40 N, which in turn results in capping and significantly prolonged disintegration times. The interaction between the maleate salt and mannitol during direct compression exhibits a diluent-dependent plastic deformation mechanism; microindentation data (Fischerscope HM2000) indicate that the compacted composite’s reduced elastic modulus increases by 35% when the moisture content of the mannitol fraction exceeds 2.5% w/w (Karl Fischer titration, Ph. Eur. 2.5.12). This underscores the necessity of pre-conditioning mannitol at 40 °C and 30% RH for 24 hours prior to blending. Published data for direct compression of asenapine maleate with alternative sublingual vehicles such as gelatinized starch show unacceptable hardness loss during 3-month accelerated stability studies at 40 °C/75% RH, attributed to moisture-mediated salt-excipient interaction not observed with the mannitol-based platform.
The sublingual tablet’s pharmacokinetic advantage is coupled to a narrow therapeutic processing window: deviations in milling energy input that generate an excessive amorphous fraction above 5% w/w (as determined by dynamic water sorption subtraction and modulated DSC) elevate the rate of recrystallisation during storage, causing a decline in both dissolution rate and content uniformity. Micronisation under cryogenic conditions (-20 °C inlet jet-mill temperature, nitrogen quench) limits amorphisation to below the 3% w/w threshold. This processing requirement represents a marked difference from the oral tablet manufacturing of risperidone or quetiapine fumarate, where particle size reduction is less critical due to the extended GI transit time and higher intrinsic solubility of the respective salts.
The route of synthesis for asenapine maleate typically proceeds through a Grignard-mediated formation of the 5-chloro-dibenzo-oxepine ring, generating intermediates that may persist at trace levels as halogenated by-products and desmethyl entities. The reporting threshold for organic impurities in the drug substance is 0.05%, with an identification threshold of 0.10% and a qualification threshold of 0.15% (ICH Q3A(R2), table 1). Routine quality control employs gradient reversed-phase HPLC with a C18 column (150 × 4.6 mm, 3 µm) and UV detection at 230 nm, coupled with a triple-quadrupole mass spectrometer for identity confirmation. The validated method achieves a limit of quantitation of 0.01% for the specified impurity (3aR,12bR)-5-chloro-2-methyl-2,3,3a,12b-tetrahydro-1H-dibenzo[2,3:6,7]oxepino[4,5-c]pyrrole N-oxide, with resolution ≥ 2.0 between the N-oxide and the asenapine peak. Residual solvent analysis by headspace GC-FID (Ph. Eur. 2.4.24) ensures that tetrahydrofuran, used in the Grignard reaction, is controlled to ≤ 720 ppm (option 1 limit). A stereochemical purity test using validated chiral LC confirms enantiomeric excess ≥ 99.5%. Published forced degradation studies under ICH Q1A(R2) conditions — acid hydrolysis (1M HCl, 80°C/24 h), base hydrolysis (1M NaOH, 80°C/24 h), oxidative stress (3% H₂O₂, 25°C/24 h), thermal stress (105°C/7 days), and photolytic exposure (ICH Q1B, option 2, 1.2 million lux·h and 200 W·h·m⁻²) — demonstrate that the maleate salt is most susceptible to oxidation, which generates the N-oxide as the primary degradation product, and to alkaline hydrolysis, which cleaves the maleate ester. A mass balance of ≥ 97% was achieved across all stress conditions, with no evidence of mutagenic impurities above the threshold of toxicological concern. This stability profile presents a difference from aripiprazole, whose oxidative degradation yields coloured quinoline dimers that demand dedicated photoprotection; asenapine maleate tablets in marketed alu-alu blisters show no specification-exceeding degradation for 24 months under long-term conditions (25°C/60% RH).
