The product covered by this release specification is N-(2-Furoyl)piperazine, CAS 40172-95-0, molecular formula C₉H₁₂N₂O₂, molecular weight 180.20 g/mol, supplied as a white to off-white crystalline powder. It belongs to the supplier’s range of other active pharmaceutical ingredients designated Pharma Grade API for tablet, capsule, granule, and injectable dosage forms. The manufacturer’s model designations are NFP-API-PG-T for tableting, NFP-API-PG-C for capsule filling, NFP-API-PG-G for wet- or dry-granulation, and NFP-API-PG-I for injectable manufacturing campaigns. The base grade NFP-API-PG is manufactured under ICH Q7 GMP conditions, with release documentation covering identity, assay, related substances, residual solvents, elemental impurities, water content, and particle size.

The material has no dedicated pharmacopeial monograph. Release testing is performed against an internal specification aligned with Ph. Eur. and USP general chapters, and the impurity strategy follows ICH Q3A/Q3B for related substances, ICH Q3C for residual solvents, and ICH Q3D for elemental impurities. The product is not a research-grade reagent. The clinical indication and final excipient compatibility are controlled by the finished-product dossier and should be established by the downstream manufacturer. For finished-product production, applicable GMP requirements include FDA 21 CFR 210/211 or equivalent health authority regulations.

What Distinguishes a Furoylpiperazine Free Base From a Piperazine Salt in Oral Solid Dosage Formulation?

The 2-furoyl substituent at the piperazine N-1 position changes the protonation state relative to unsubstituted piperazine and piperazine dihydrochloride. The N-1 nitrogen is part of an amide and does not act as a free base; the N-4 nitrogen remains basic. This structural feature reduces the number of ionizable centers and alters pH-solubility behavior. Unlike piperazine dihydrochloride, this product is supplied as a free base and does not add a chloride counterion to a formulation. Compared with 1-benzoylpiperazine, the furan oxygen contributes an additional hydrogen-bond acceptor, which can shift dissolution at matched buffer pH. Published comparative solubility data for this specific configuration is limited.

For tablet development, the free-base character influences excipient selection. An acidic excipient such as citric acid or tartaric acid may form an in situ salt at the N-4 position; this interaction may change disintegration, dissolution, and physical stability. Therefore, excipient compatibility studies under ICH Q8 and Q9 should be performed before a commercial formula is fixed. In a high-speed rotary tablet press operating above 60 rpm, powder flow and bulk density become the main processing constraints. The supplier reports flow-related parameters using USP <1174> powder flow methodology and USP <616> bulk and tapped density. A compressibility index above 25% indicates that direct compression is unlikely to produce acceptable weight uniformity; roller compaction or slugging should be evaluated before compression.

For capsule filling, a dosator or tamping-pin machine typically requires a homogeneous powder bed with consistent bulk density. The oral solid grade is controlled by laser diffraction to limit oversized crystals that can segregate and fine particles that can stick to the dosator. The particle-size range is not a guarantee of a specific flow behavior; it is a release attribute that must be linked to a formulation-specific process model. Compared with other piperazine derivatives offered by the supplier, this product is a free-base amide rather than a salt or a substituted amine. This changes handling requirements: the powder has fewer hygroscopic salt-associated caking tendencies, but it may exhibit different compatibility with enteric coating polymers that rely on acidic microenvironments. Blending parameters developed for piperazine dihydrochloride or 1-benzylpiperazine should not be transferred directly.

Route-specific release data are summarized in Table 1. The oral solid and granule grade carries a wider total impurity limit than the injectable grade because parenteral products are subject to stricter regulatory thresholds under ICH Q3B(R2). The tighter moisture and endotoxin controls for NFP-API-PG-I reflect downstream requirements of USP <85> and Ph. Eur. 2.6.14. They do not indicate that the oral grade is chemically unstable. Batches that are milled or micronized after release should be re-tested for particle size and water content because mechanical size reduction can increase surface area and moisture uptake.

Particulate matter in the final injectable product is controlled by filtration and container inspection per USP <790> and Ph. Eur. 2.9.19; the dry API particle-size limit alone does not establish final particulate compliance. The injectable manufacturer should pass the solution through a 0.22 µm sterilizing-grade membrane; the API supplier does not supply a sterile product.

When a Parenteral Batch Requires Low Endotoxin and Controlled Particle Size

Injectable manufacturing requires NFP-API-PG-I, which is controlled for bioburden and endotoxin. The product is not sterile as supplied; terminal sterilization of the dry powder is not recommended because the furoyl amide may degrade under moist heat. The standard downstream route is aseptic filtration of the final solution through a 0.22 µm PVDF or PES membrane. Before filtration, complete dissolution should be confirmed in Water for Injection at 20–25 °C. If terminal autoclaving is considered, the formulation pH should be maintained within pH 4.0–7.0 during heat exposure; outside this range, the amide bridge can hydrolyze to 2-furoic acid and piperazine-related impurities. Published data for this specific configuration is limited; forced degradation under ICH Q1A(R2) should define the allowable holding time and final pH limits.

Lyophilization with mannitol or trehalose should be designed around the collapse temperature of the formulation, not the freezing point of the pure API. A formulation with a collapse temperature below −25 °C may require a lower shelf temperature and a longer primary drying phase. The injectable grade water limit of ≤0.5% reduces hydrolytic degradation during storage but does not eliminate the need for a stability study in the final container closure system.

Residual solvent control begins with the final crystallization. Ethanol and water are the preferred crystallization solvents; if dichloromethane is used as a processing solvent, the release limit is ≤600 ppm under ICH Q3C Class 2 requirements. For granulation, fine particles below 75 µm in excess of 30% can increase dusting in a high-shear granulator and reduce flow through a rotary press feed frame. Oversized particles above 250 µm can segregate in a V-blender and create weight variability. The oral solid grade release range is D10 ≥10 µm, D50 75–150 µm, and D90 ≤250 µm; values should be re-verified after any delumping or size-reduction step. Bulk and tapped density values are reported by USP <616>, and the compressibility index is calculated as the difference between tapped and bulk density divided by tapped density multiplied by 100.

Wet granulation with aqueous binder can be used if the granule moisture is dried to ≤2.0% before compression. High-shear granulator endpoint should be based on impeller torque or power consumption rather than fixed time; overwetting can generate hard agglomerates that are difficult to mill. The NFP-API-PG-G grade is supplied with a controlled bulk density range to support metering into high-shear mixers and fluid-bed dryers. Release testing for related substances uses a stability-indicating HPLC procedure. The method employs a reversed-phase C18 column, 5 µm particle size, 250 mm length, and UV detection at 254 nm. Mobile phase is a gradient of water containing 0.1% phosphoric acid and acetonitrile. The gradient is adjusted to resolve 2-furoic acid and piperazine-related impurities from the main peak. System suitability requires resolution between the main peak and the nearest related substance of at least 2.0; tailing factor not more than 2.0; relative standard deviation for replicate injections not more than 1.0%. This method is validated under ICH Q2(R2) for specificity, linearity, accuracy, precision, range, and robustness.

Furoyl Amide Degradation Pathways and pH-Dependent Stability in Aqueous Vehicles

The primary chemical degradation route expected in aqueous formulations is hydrolysis of the furoyl amide bridge, yielding 2-furoic acid and piperazine. Acid-catalyzed hydrolysis can become significant below pH 2.0; base-catalyzed hydrolysis can become significant above pH 8.0. The rate is also dependent on buffer species, ionic strength, and temperature. Phosphate and citrate buffers can exert catalytic effects, so stability data generated in unbuffered water should not be extrapolated to buffered formulations without additional studies. A forced degradation matrix under ICH Q1A(R2)/Q1B should include acidic, alkaline, oxidative, thermal, and photolytic stress conditions. The HPLC method should separate 2-furoic acid, piperazine, and the main peak; UV detection at 254 nm is typical for the furoyl chromophore. Mass balance should be reported with the stability results.

For solid oral dosage forms, the immediate environment is not aqueous, but residual moisture can facilitate surface degradation. The oral grade water limit of ≤1.0% is set to limit this route. The product should be stored in tightly closed containers at 15–25 °C, protected from light and humidity. When packaged in double LDPE bags inside an HDPE drum, a desiccant is recommended if storage humidity exceeds 60% RH. Residual solvents are analyzed by headspace gas chromatography with flame ionization detection. The vial equilibration temperature is typically 80–105 °C; the column is a 624-type capillary column with 1.0 µm film thickness. The method follows USP <467> for sample preparation as appropriate.

Elemental impurity risk assessment follows ICH Q3D. If a hydrogenation step using palladium on carbon or Raney nickel is applied during synthesis, the corresponding metal residuals are monitored by ICP-MS using USP <233> or Ph. Eur. 2.4.20. The release specification includes palladium ≤10 ppm and nickel ≤25 ppm where applicable; arsenic, cadmium, lead, and mercury are controlled at ICH Q3D Option 1 oral and parenteral limits. The product is not intended for inhalation; therefore inhalational limits do not apply. Packaging and transport should exclude strong oxidizing agents and prolonged exposure to temperatures above 40 °C. Each batch should be accompanied by a certificate of analysis listing assay, related substances, residual solvents, elemental impurities, water content, and the particle-size result relevant to the assigned grade. Oral solid grade is packed in double low-density polyethylene bags inside a sealed HDPE drum. Injectable grade is packed in a cleanroom-compatible double bag with an additional outer peelable bag; the outer bag can be removed in the controlled area. The headspace may be flushed with nitrogen to limit oxygen below 1.0% for storage periods longer than 24 months; this is not a substitute for controlled temperature and humidity. No additional downstream guarantee should be assumed outside a tripartite quality agreement between the API manufacturer, distributor, and finished-product manufacturer.