N-(2-(Diethylamino)Ethyl)-5-((Z)-(5-Fluoro-1,2-Dihydro-2-Oxo-3H-Indol-3-Ylidene)Methyl)-2,4-Dimethyl-1H-Pyrrole-3-Carboxamide

Malate Salt Crystallization Stoichiometry and the Impact of Residual Solvent on Tablet Formulation Uniformity

Conversion of the free base to sunitinib malate for direct compression tablet manufacture proceeds through a strictly controlled acid-base pairing in hydroalcoholic medium. A molar ratio of free base to L-malic acid of 1:1.02 is charged into a 7:1 (v/w) mixture of anhydrous ethanol and purified water relative to base mass. The slurry is heated to 62 ± 2 °C under nitrogen blanket until complete dissolution, treated with 0.5% (w/w) activated carbon, and filtered through a 0.45 µm polypropylene membrane into a pre‑heated crystallization vessel. The clear filtrate is cooled at a controlled ramp of −3 °C/h to 0–2 °C and aged under low‑shear stirring (80–100 rpm) for 3 hours. The resulting white crystalline suspension is centrifuged in a peeler centrifuge, washed twice with chilled anhydrous ethanol (2 × 2 volumes), and dried in a double‑cone vacuum dryer at 40 °C, jacket pressure −0.095 MPa, until loss on drying by Karl Fischer titration falls below 0.3%. Terminal particle size control employs a conical sieve mill (Quadro Comil 197, screen 032R) at 1500 rpm. The dried salt complies with USP Sunitinib Malate monograph specifications: assay 98.5–101.5% on anhydrous basis, Z‑isomer (Related Compound G) ≤0.10%, total impurities ≤0.50%. Batch records link residual ethanol ≤5000 ppm and water 0.2–0.5% to superior flowability (Carr’s index ≤18) during direct compression with microcrystalline cellulose and croscarmellose sodium into 12.5 mg, 25 mg, and 50 mg hard gelatin capsules. ICH Q7 GMP principles for active pharmaceutical ingredients and 21 CFR 211 subpart E control of components are integrated throughout the manufacturing directive.

For HPLC system suitability testing under USP Sunitinib Malate monograph procedure, the free base form is dissolved alongside the malate reference standard to generate a resolution mixture that discriminates the target component from the late‑eluting Z‑isomer. A stock solution is prepared by weighing precisely 10.0 mg of N-(2-(Diethylamino)Ethyl)-5-((Z)-(5-Fluoro-1,2-Dihydro-2-Oxo-3H-Indol-3-Ylidene)Methyl)-2,4-Dimethyl-1H-Pyrrole-3-Carboxamide and 10.0 mg of Sunitinib Malate RS into a 100 mL volumetric flask, adding 70 mL of diluent (acetonitrile:water 50:50 v/v), sonicating for 10 minutes, and diluting to volume. Chromatographic separation uses a stainless steel column (150 × 4.6 mm, 5 µm octadecylsilane, pore size 100 Å) maintained at 30 °C with a gradient mobile phase of phosphate buffer pH 2.5 and acetonitrile at 1.0 mL/min flow rate, injection volume 20 µL, and UV detection at 254 nm. The resolution factor between the free base peak and the Z‑isomer peak (relative retention approximately 1.12) must be not less than 2.0 for system qualification. The method is validated according to ICH Q2(R1) guidelines for specificity, linearity (range 0.05–0.15 mg/mL, r² ≥0.999), and precision (RSD ≤0.85% for six replicate injections). This base‑spiked reference solution serves as a working standard for release testing of both drug substance and finished dosage forms, enabling identification, assay, and related substances determinations compliant with USP General Chapter 〈621〉 and European Pharmacopoeia monograph 01/2024:2945.

What Photolytic Stress Conditions Under ICH Q1B Reveal About the (E)-Isomer Threshold

Forced degradation of the solid‑state free base under ICH Q1B Option 2 exposes the photolability of the exocyclic double bond, generating an impurity profile dominated by the (E)‑geometric isomer. A thin layer not exceeding 2 mm of micronized compound (D90 < 15 µm) is evenly distributed in a quartz petri dish and placed in a photostability chamber (Atlas SUNTEST XLS+ equipped with a xenon lamp and daylight ID65 filter). The irradiance is calibrated to deliver an overall illumination of not less than 1.2 × 10⁶ lux·h and an integrated near‑ultraviolet energy of not less than 200 W·h/m² at the sample plane. Dark control samples wrapped in aluminum foil are concurrently exposed to temperature effects. Following exposure, the sample is dissolved in acetonitrile:water (50:50) to a concentration of 0.5 mg/mL and analyzed by the same HPLC method described in USP Sunitinib Malate Related Compounds test. Chromatograms of photodegraded specimens consistently show a new peak at relative retention time 0.89 corresponding to the (E)‑isomer, typically reaching 0.35–0.50% area, while the unchanged free base remains the principal component (purity loss < 0.2% under dark conditions). The (E)‑isomer is not a specified impurity in the drug substance at levels above 0.15%; therefore, quality agreements for the base as an intermediate require a photolability information panel and storage under amber light (≤100 lux) in laminated aluminum foil bags. These data are integrated into the impurity specification justification in Module 3.2.S.3.2 of the CTD, directly referencing ICH Q1B and Q3A thresholds.

Stock solutions for in vitro kinase inhibition profiling are prepared by dissolving the anhydrous free base in anhydrous dimethyl sulfoxide (DMSO) to achieve a 10 mM primary stock, which is stored in single‑use aliquots at −80 °C under argon to prevent oxidative degradation. Serial dilutions are executed in kinase reaction buffer (50 mM HEPES, pH 7.5, 0.01% Brij‑35, 10 mM MgCl₂, 1 mM EGTA) so that the final DMSO concentration in the assay well does not exceed 1% (v/v). A typical dose‑response assay against the recombinant human VEGFR2 (KDR) cytoplasmic domain uses a 12‑point dilution series spanning 0.1 nM to 1 µM, incubated with 0.2 µg/mL kinase and 2 µM substrate peptide in a total volume of 25 µL for 60 minutes at 30 °C. Phosphorylation is quantified by a europium‑labeled anti‑phosphotyrosine antibody time‑resolved fluorescence resonance energy transfer (TR‑FRET) readout on a PerkinElmer EnVision plate reader. The calculated IC₅₀ against VEGFR2 is routinely observed in the range of 5–15 nM under these conditions, with inter‑run variability ≤15% CV validated using staurosporine as a reference inhibitor. The compound is concurrently screened against PDGFRβ, c‑KIT, and FLT3 kinases in a panel assay format compliant with the NIH Assay Guidance Manual and Eurofins DiscoverX KINOMEscan protocol for selectivity scoring. For cell‑based mechanistic studies, freshly diluted working solutions are added to culture medium (RPMI‑1640, 10% fetal bovine serum) at a final DMSO concentration ≤0.1% to assess target modulation via western blotting of phospho‑ERK and phospho‑AKT pathways in HUVEC or A498 renal carcinoma cell lines. The compound is classified as a potent multi‑target inhibitor exclusively for laboratory research use; any disposition for human administration requires full GMP manufacture of the malate salt and relevant clinical trial authorization.

When HPMCAS-MG Replaces Copovidone in Twin-Screw Extrusion: Process Torque and Amorphization Limits

Amorphous solid dispersion of the poorly water‑soluble free base (aqueous solubility <1 µg/mL at pH 6.8) by hot melt extrusion addresses the dissolution‑limited absorption of the crystalline form. Formulation screening evaluates polyvinyl acetate/polyvinylpyrrolidone copolymer (PVP‑VA 64) and hypromellose acetate succinate (HPMCAS‑MG) at drug loads of 25%, 30%, and 35% w/w. Thermal stability by modulated DSC confirms that the free base melts with decomposition onset near 230 °C, demanding processing temperatures well below this ceiling. The blend (500 g batch) is fed into a co‑rotating twin‑screw extruder (Thermo Fisher Pharma 11 mm, L/D 40) with a screw configuration incorporating two kneading zones with 60° forward and 90° neutral mixing elements. Barrel temperatures from feed to die are set at 120/135/155/160/160/160/155/150 °C, screw speed at 150 rpm, and feeder rate at 0.5 kg/h. Under these conditions, the specific mechanical energy input for the 30% drug‑loaded HPMCAS‑MG grade is 0.28–0.35 kWh/kg, with die pressure < 30 bar and torque 45–50% of motor capacity, indicative of a fully molten and low‑viscosity process window. In contrast, the copovidone‑based extrudate at the same drug load exhibits torque fluctuations exceeding 65% and localized darkening, evidencing phase separation and partial chemical degradation. The pale‑yellow extrudate strands are air‑cooled on a belt conveyor, pelletized, and milled through a 0.8 mm screen in a pin mill to obtain a free‑flowing powder with bulk density 0.32–0.38 g/mL. Polarized light microscopy and bench‑top PXRD (Cu Kα, 5–40° 2θ) confirm full amorphization for the HPMCAS‑MG 30% formulation, whereas the 35% variant shows residual crystallinity peaks at 8.2° and 16.4° 2θ. The 30% loaded dispersion is encapsulated into size 2 hypromellose capsules, each containing 25 mg free base equivalent. USP Apparatus 2 dissolution (900 mL, pH 6.8 simulated intestinal fluid, paddle speed 75 rpm) yields release profiles that exceed 80% of label claim within 30 minutes, versus 12% for the crystalline base over the same interval, qualifying the dispersion as a bioequivalent candidate for therapeutic product development subject to ANDA 206838 reference standards.

Screening for the stable polymorph of N-(2-(Diethylamino)Ethyl)-5-((Z)-(5-Fluoro-1,2-Dihydro-2-Oxo-3H-Indol-3-Ylidene)Methyl)-2,4-Dimethyl-1H-Pyrrole-3-Carboxamide is conducted through parallel slurry conversion experiments in a Crystal16 multiple reactor system. Suspensions of 25 mg of micronized base in 0.6 mL of each solvent (methanol, ethanol, isopropanol, acetonitrile, ethyl acetate, toluene, and acetone) are loaded into 1.5 mL glass vials with cross‑shaped magnetic stir bars. The temperature program cycles between 5 °C and 50 °C at 0.5 °C/min for 48 hours, then holds at 2 °C for 4 hours before isolation. Solids are recovered by vacuum filtration, dried under a stream of nitrogen at 25 °C, and immediately characterized by powder X‑ray diffractometry. A needle‑shaped crystalline form designated Form I crystallizes from alcohol solvents and exhibits characteristic diffraction peaks at 8.2°±0.1°, 12.9°±0.1°, 16.4°±0.1°, and 22.3°±0.1° 2θ. Form II, a plate‑type morphology obtained from ethyl acetate and toluene, displays a distinct pattern with main reflections at 7.8°, 13.6°, and 19.1° 2θ. DSC thermograms of Form I show a single endothermic melting peak with an onset at 222.5 °C and an enthalpy of 116 J/g, while Form II undergoes an exothermic solid‑solid transition to Form I at 178 °C before melting at the same temperature, confirming an enantiotropic relationship. Competitive slurry experiments in isopropanol at 20 °C for 72 hours result in complete conversion of Form II to Form I, establishing Form I as the thermodynamically stable polymorph at room temperature. In accordance with ICH Q6A decision tree #4 for polymorphism, this thermodynamic relationship requires that the polymorphic form of the free base used as a starting material for malate salt synthesis be specified by a control of PXRD pattern or DSC melting endotherm to ensure batch‑to‑batch consistency in downstream salt formation kinetics and eventual tablet dissolution performance.

Apparent Permeability Across Caco‑2 Cell Monolayers and Transporter‑Mediated Efflux Ratios

Bidirectional transport of the free base is investigated in Caco‑2 cell monolayers to evaluate the contribution of intestinal efflux transporters to net absorption. Caco‑2 cells (clone C2BBe1, passage 40–60) are seeded at 6 × 10⁴ cells/cm² onto polyethylene terephthalate Transwell inserts (0.4 µm pore size, 0.33 cm² growth area) and cultured for 21–24 days in Dulbecco’s modified Eagle medium supplemented with 10% fetal bovine serum and 1% non‑essential amino acids. Monolayer integrity is verified by transepithelial electrical resistance (TEER) measurement using an EVOM2 voltohmmeter; inserts with TEER <300 Ω·cm² are discarded. The donor chamber receives HBSS‑HEPES buffer (pH 7.4 for apical, pH 7.4 for basolateral) containing the test compound at 10 µM with a final DMSO concentration of 0.5% (v/v). The receiver chamber is supplemented with 4% bovine serum albumin to minimize non‑specific binding. Sampling is performed at 30, 60, and 90 minutes from both receiver compartments under sink conditions maintained by replacing withdrawn volumes with fresh buffer. Concentrations are quantified by a validated LC‑MS/MS method using a C18 column and multiple reaction monitoring transitions, with a lower limit of quantification of 0.5 ng/mL. The calculated apparent permeability (P_app) in the apical→basolateral direction is 2.3 × 10⁻⁶ cm/s, while the basolateral→apical P_app is 15.6 × 10⁻⁶ cm/s, yielding an efflux ratio of 6.8. Upon co‑administration of 50 µM elacridar (GF120918), a potent P‑glycoprotein and BCRP inhibitor, the efflux ratio collapses to 1.2, confirming that the compound is actively secreted by ABCB1 transporter. These data align with FDA Guidance for Industry on drug interaction studies (2020) and position the free base as a BCS Class II compound with permeability limited by P‑gp‑mediated efflux, a critical parameter for predicting food‑effect and inter‑subject variability in bioequivalence trial designs. The Caco‑2 assay is executed under GLP principles as per OECD Series on Principles of Good Laboratory Practice No. 1, and the report is formatted for inclusion in Investigational New Drug application toxicology modules.