The hydrochloride addition salt of (2R,3S/2S,3R)-3-(4-Chloro-5-fluoro-6-pyrimidinyl)-2-(2,4-difluorophenyl)-1-(1H-1,2,4-triazol-1-yl)-2-butanol is a racemic pharmaceutical active ingredient for tablet, capsule, granule, oral liquid, and injectable formulations. The neutral free base has the empirical formula C16H13ClF3N5O; the monohydrochloride salt corresponds to C16H14Cl2F3N5O and has a calculated molecular weight of 420.24 g/mol. The stereochemical notation lists two enantiomers, (2R,3S) and (2S,3R); therefore, the product is a racemic mixture rather than a single enantiomer. This chiral identity must be confirmed by a validated enantiomeric method and cannot be inferred from optical rotation alone. The API is manufactured as a crystalline powder and should be assigned separate grades for non-sterile oral processing and sterile injectable use because the injectable grade requires additional controls for bacterial endotoxin, bioburden, particulate matter, and aseptic handling.

Release testing should align with ICH Q6A and compendial methods

Specifications should be designed using the ICH Q6A decision tree for new drug substances and the pharmacopoeial chapters relevant to salt identity, water content, residue on ignition, chromatographic purity, and particulate control. Table 1 lists the minimum release attributes to be included in a certificate of analysis when the material is intended for oral or injectable formulation. Because the compound is a hydrochloride salt, the drying endpoint should be evaluated not only by loss on drying but also by chloride content; nonstoichiometric HCl loss can generate free-base domains that may alter dissolution rate and stability under humid storage. For injectable use, the release panel should additionally include bacterial endotoxin per USP <85> and particulate matter per USP <788> or USP <787> where applicable to the finished formulation.

Release attributes and reference procedures

Attribute	Procedure / standard	Control boundary
Appearance	Visual inspection	White to off-white crystalline powder, free from visible extraneous matter
Identification	USP <197>; HPLC retention time	IR spectrum matches reference; retention time matches standard
Assay	HPLC per USP <621>	98.0–102.0% on anhydrous, solvent-free basis
Enantiomeric ratio	Chiral HPLC per USP <621>	(2R,3S):(2S,3R) ratio 0.95–1.05 unless a single-isomer claim is filed
Chloride content	USP <221> or ion chromatography	Consistent with monohydrochloride stoichiometry
Water content	Karl Fischer per USP <921>	Limit based on stability data; typical hydrochloride salts require ≤0.5% for solid oral
Residue on ignition	USP <281>	≤0.1%
Residual solvents	Headspace GC per ICH Q3C	Class 1 solvents not detected; Class 2 solvents within Option 2 limits
Elemental impurities	ICP-MS per ICH Q3D	Permitted daily exposure limits based on finished-product dose
Bacterial endotoxins	USP <85>	Required for injectable grade; limit set by finished product
Particle size	Laser diffraction per ISO 13320:2020 / USP <429>	d90 target determined by dissolution and blend uniformity studies

Method qualification for the release tests should follow ICH Q2(R2) for specificity, linearity, accuracy, precision, and range. The assay method should be linear over at least 80–120% of the nominal concentration, with accuracy demonstrated by spike recovery at 80%, 100%, and 120% levels. The racemic method should be validated for limit of detection and limit of quantitation for the minor enantiomer if the specification uses a ratio rather than an assay. If the API is released for injectable use, endotoxin method suitability should be demonstrated by inhibition and enhancement testing per USP <85>, and particulate matter limits should align with the final compounded solution. Direct compression and dry granulation require the powder characteristics of the hydrochloride salt to be matched to the process equipment. A production-scale rotary tablet press using 8–12 mm round concave tooling is normally screened in compression force ranges from 5 to 20 kN, with precompression below 2 kN for brittle formulations to reduce capping. For a drug load of 5–25% w/w, particle-size reduction to d90 below 100 µm by laser diffraction per ISO 13320:2020 can be a starting point, but the final d90 must be justified by dissolution and blend uniformity data. If a jet mill is used, grinding pressure from 0.7 to 1.2 MPa with nitrogen and a controlled dew point can reduce moisture uptake; micronized hydrochloride salts may retain static charge at relative humidity below 30%, causing poor die filling and blend segregation. In such cases, a low-shear bin blender at 50–65% fill volume and a blend uniformity assessment per USP <905> are used to establish mixing time and sampling points. Capsule filling with dosator machines requires bulk density and Carr index data; if the Carr index exceeds 25, a flow aid such as colloidal silicon dioxide at 0.1–0.5% w/w may be considered, but alkaline lubricants should be evaluated because local pH at the particle surface can influence salt disproportionation.

What limits wet granulation and aqueous film coating for this racemate?

Wet granulation is limited by the electron-deficient pyrimidine ring and the chlorine substituent under alkaline conditions. If water is used as the granulating fluid, the pH should be controlled on the acidic side through hydrochloric acid or citrate buffer; prolonged exposure to hydroxide can promote nucleophilic displacement of the 4-chloro group and generate a hydroxypyrimidine degradant. Process mapping should include granulation time, water amount, impeller speed, and inlet air temperature. For a high-shear granulator with bowl volume between 25 and 65 L, initial screening may set wet massing time from 2 to 6 min at impeller speeds below 300 rpm; published data for this specific configuration is limited, so these values are screening points rather than release limits. Drying should maintain product temperature below 60 °C, and the final granulation should be milled through a screen of 0.8–1.25 mm. Water content after equilibration should be verified by Karl Fischer per USP <921>. Aqueous film coating may be used if the tablet core retains a moisture-protective subcoat; otherwise, organic or hydroalcoholic coating systems should be tested for edge splitting and moisture ingress. In comparison with single-isomer (2R,3S)-2-(2,4-difluorophenyl)-3-(5-fluoropyrimidin-4-yl)-1-(1H-1,2,4-triazol-1-yl)butan-2-ol, the 4-chloro-5-fluoro-6-pyrimidinyl substitution in the racemic product increases the calculated base molecular weight from 349.31 g/mol to 383.57 g/mol and changes the attachment point from the 4-position to the 6-position of the pyrimidine ring. This alteration modifies hydrogen-bonding capacity, crystal packing, and chromatographic retention. Regulatory equivalence with single-isomer triazole antifungal monographs should not be assumed; the racemic designation and the chloro substitution require a product-specific reference standard and a stability-indicating method. Differences from other hydrochloride salts of fluorinated pyrimidinyl butanols should be documented by differential scanning calorimetry, X-ray powder diffraction, and moisture-sorption isotherms per USP <941>.

If the finished presentation is a sterile injectable, aseptic processing enters a risk-based control strategy

Injectable manufacture requires the API to meet microbiological and particulate specifications before formulation. Handling should follow EU GMP Annex 1 and FDA 21 CFR Part 211 with an environmental classification appropriate to the open-powder transfer step; an API dispensing room at ISO 14644-1 ISO Class 8 is commonly used, with local unidirectional airflow for open transfers. Dissolution in Water for Injection should be evaluated at the target concentration and pH; because the hydrochloride salt can depress solution pH, pH adjustment with hydrochloric acid or sodium hydroxide may be required before sterile filtration. Filter validation should include a bacterial retention study per ASTM F838-20 and a product-wetted integrity test using a 0.22 µm PVDF or PES membrane. Adsorption of the halogenated aromatic active to polysulfone or nylon should be evaluated because hydrophobic membrane binding can reduce assay recovery. For aseptic filling of vials, the sterilizing filter should be placed close to the filling needle, and the pre-filtration bioburden should be controlled at ≤10 CFU/100 mL per EU GMP Annex 1 guidance. Lyophilized products require freeze-drying microscopy and differential scanning calorimetry to determine the collapse temperature and glass transition temperature of the maximally freeze-concentrated solute; published data for this specific configuration is limited, so cycle design should not rely on surrogate thermograms from different hydrochlorides. Terminal sterilization may be considered only if aqueous stability and degradation kinetics support it; otherwise, aseptic filtration is the boundary condition for sterility assurance.

Degradation markers and stability-indicating method readiness

A stability-indicating HPLC method should be developed under ICH Q1A(R2) and ICH Q1B conditions to separate the two enantiomers, the free base, process impurities, and oxidative or hydrolytic degradants. Typical forced degradation conditions include 0.1 N HCl, 0.1 N NaOH, 3% hydrogen peroxide, dry heat at 80 °C, and photostability per ICH Q1B. The electron-deficient pyrimidine ring may generate the corresponding hydroxy displacement product under alkaline stress; therefore, the method should include a resolution check between the parent and the hydroxypyrimidine degradant. Mass balance across stress conditions should be reported and should fall within 90–110% unless co-elution is demonstrated. For a racemic API, chiral HPLC should be monitored on accelerated stability batches to verify that the enantiomeric ratio remains unchanged. System suitability for the chiral method should require resolution not less than 1.5, tailing factor not more than 2.0, and injection repeatability below 2.0% relative standard deviation per USP <621>. For oral liquid formulations, the hydrochloride salt should be dissolved at an acidic pH below the pKa-driven solubility minimum, and the solution should be protected from light if photolytic degradation is identified in ICH Q1B studies. A vehicle containing propylene glycol, glycerin, and purified water may be screened, but solubility and stability of the chloro-substituted pyrimidine ring in the presence of nucleophilic buffer species should be confirmed. Preservative efficacy should be tested per USP <51>, and antioxidant addition should be justified only after forced oxidation studies show a measurable peroxide sensitivity. The oral liquid grade is not automatically interchangeable with injectable grade; endotoxin and particulate controls differ, and the dissolution vehicle may expose the API to moisture for longer durations than solid oral forms. Dissolution testing for solid oral forms should be conducted in 900 mL of 0.1 N HCl at 37 °C using USP Apparatus 2 at 50 rpm for immediate-release products. The hydrochloric acid medium is preferred because the salt is likely to exhibit higher solubility under gastric pH; however, if the drug product is intended for modified release, a pH-shift method or USP Apparatus 4 may be required. Reported dissolution values should be tied to HPLC assay rather than UV alone because process impurities and the pyrimidine chromophore can interfere.

Bulk packaging and controlled storage for the hydrochloride salt

Bulk API should be double-bagged in low-density polyethylene inside an aluminum-laminated outer bag, with desiccant where moisture uptake exceeds 0.1% in open stability studies. A moisture-sorption isotherm per USP <941> should be generated at 25 °C from 10 to 90% RH; if water uptake exceeds 0.5% at 60% RH, the packaging should contain desiccant and the retest period should be shortened accordingly. Storage should be controlled at 15–25 °C with protection from light and humidity, unless the stability protocol supports wider excursions. Each container should be labeled with the batch number, gross and net weight, manufacturing date, retest date, and the racemic identity. Temperature-controlled shipping should be validated by a thermal mapping profile over the distribution route; if the material is used for sterile injectables, the supply chain should maintain chain-of-custody for microbiological attributes. Incompatibility with strong bases, oxidizing agents, and nucleophilic amines should be stated in the packaging insert because these agents can stress the pyrimidine ring and complicate release testing.