Released under product code AZT-BOC-01P for oral solid dosage manufacturing and AZT-BOC-01I for injectable processing, 1-Boc-3-azetidinone (tert-butyl 3-oxoazetidine-1-carboxylate, CAS 398489-26-4) is a crystalline protected azetidinone supplied as a pharma-grade active pharmaceutical ingredient for tablet, capsule, granule, and injection dosage forms. The compound has molecular formula C8H13NO3 and molar mass 171.19 g/mol. The oral grade is packaged in double low-density polyethylene bags inside aluminium foil under vacuum; the injectable grade is supplied in sterile fluoropolymer bottles sealed under nitrogen. The product is intended for incorporation into oral solid dosage forms after deagglomeration and for injectable formulations after dissolution, pH adjustment, and aseptic filtration. Published data for the clinical pharmacokinetics of the unmodified protected ketone are limited because the Boc group is generally removed before final active pharmaceutical ingredient formation.

Specification release matrix and method designations

Release of AZT-BOC-01P and AZT-BOC-01I is performed against the following matrix. The HPLC assay method uses a C18 column, 150 mm × 4.6 mm, 5 μm particle size; mobile phase A is 0.1% phosphoric acid, mobile phase B is acetonitrile; gradient 10–90% B over 20 min; flow rate 1.0 mL/min; column temperature 30°C; injection volume 10 μL; detection at 210 nm. Residual solvents are determined by headspace gas chromatography using flame ionization detection according to USP <467> and ICH Q3C.

Method validation follows ICH Q2(R1). For the HPLC assay, linearity is established over 50–150% of the nominal concentration with a correlation coefficient >0.999; quantitation limit for the main peak is 0.05% relative to the nominal assay concentration. Forced degradation under oxidative, thermal, photolytic, acidic, and alkaline conditions is used to demonstrate peak purity. Mass balance across forced degradation is reported; acceptance is 95–105%. Across three oral-grade production campaigns, laser diffraction data displayed D50 values in the range 45–75 μm; however, published data for this exact product configuration is limited and the values are not a formal specification. Bulk density and tapped density are supplied on the certificate of analysis to support bin and blender load calculations. The powder is milled under nitrogen to avoid static retention and then sieved through a 1.0 mm security screen before packaging.

What happens to the Boc-protecting group during aqueous wet granulation?

During aqueous wet granulation, the Boc group is stable only within a relatively narrow pH window. The tert-butoxycarbonyl group undergoes acid-catalysed cleavage to yield free 3-azetidinone, isobutylene, and carbon dioxide. Granulating fluids buffered to pH 5.5–7.5 are used; citric acid and other acidic binders are avoided because even partial deprotection changes the impurity profile. Water addition above 12% w/w in high-shear mixers can produce overwetted masses and torque overload. Published data for this specific protected ketone in aqueous granulation is limited; process development batches require torque-rheometry profiling, residual moisture profiling by loss on drying, and HPLC purity testing before scale-up. The product is incompatible with primary amines in wet mass because the deprotected ketone can form Schiff-base adducts.

For high-shear wet granulation, mixers are operated with main impeller tip speed 4–8 m/s and chopper speed 1,500 rpm. Wet massing time is limited to 120–240 s; endpoint is controlled by impeller torque rather than time because water addition above 12% w/w can produce granule size D50 shifts greater than 18%. After drying in a fluid bed at inlet temperature 45°C and dew point below 8°C, granule moisture is 1.0–2.0% and granule friability is tested by sieve retention after tumbling.

Dry processing is retained for formulations that are moisture-sensitive or require rapid disintegration. The crystalline powder is deagglomerated through a conical mill with a 0.5 mm screen and blended in a diffusion mixer at 25 rpm for 15 min with microcrystalline cellulose, lactose, croscarmellose sodium, and colloidal silicon dioxide. Batch records from production-scale tableting indicate that lubrication with 0.5 wt% magnesium stearate for 3 min is sufficient to maintain ejection force below 5 kN. Extended lubrication beyond 15 min reduces tablet tensile strength due to hydrophobic film formation. On a rotary tablet press, weight variability is held below 2% at press speeds up to 40,000 tablets/h when the feed frame speed is matched to the granule flow. Capsule filling on an automatic encapsulator with tamping pins achieves fill weight relative standard deviation below 2% at machine speeds up to 75,000 capsules/h after adding 0.25% colloidal silicon dioxide to the blend.

Compression force is monitored across three regions of the tablet press; main compression force is set at 8–20 kN depending on tooling size. Tablet hardness is measured according to USP <1217>; disintegration is tested according to USP <701>. In one production configuration, use of F-type tooling with 10 mm round flat-faced bevel-edged punches produced tablet hardness 80–120 N at 15 kN force. Ejection force remained below 5 kN when magnesium stearate was added at 0.5% for 3 min; higher levels or longer times led to hardness reduction of 20–30%. Published data for this exact product in direct compression is limited; the cited values derive from development batches and require confirmation with the selected excipient system.

Roller compaction narrows the acceptable moisture window but improves blend uniformity

Roller compaction provides an alternative to wet granulation when the Boc group must be kept away from moisture. A roller compactor with hydraulic pressure 40–60 bar and roll diameter 25 mm produces ribbons with density 1.1–1.3 g/cm³; after milling, granules exhibit D50 180–300 μm. The process is limited by the low melting point of the crystalline material, so roll surface temperature is controlled below 60°C. Moisture is controlled below 2.0% before compaction because excess water plasticizes the powder and can cause ribbon delamination. Process analytical technology using near-infrared spectroscopy is applied at the ribbon outlet to verify density uniformity. Published data for this specific product in roller compaction is limited; the above ranges reflect installation qualification and process development runs, not a compendial requirement.

For injectable dosage forms, the AZT-BOC-01I grade is dissolved in a co-solvent system consisting of 10–20% v/v ethanol or propylene glycol in Water for Injection. The solution is pH-adjusted with sterile 0.1 M phosphate or acetate buffer to pH 5.0–6.5 and then passed through a 0.22 μm sterilizing-grade polyethersulfone filter. Terminal moist-heat sterilization at 121°C is not used without forced degradation confirmation because the Boc group is susceptible to hydrolytic deprotection. Aseptic filling is performed under ISO 14644-1 Grade A conditions with Grade B background. The final solution is tested for sterility per USP <71>, bacterial endotoxins per USP <85> with limit ≤0.25 EU/mg, and particulate matter per USP <788>. Container closure integrity is verified by vacuum decay according to USP <1207>. In-use holding times are confirmed by HPLC assay and pH monitoring because published reconstituted solution stability data for this protected ketone are limited.

When deprotected to 3-azetidinone for injectable conjugation, impurity and particulate burdens shift

When the Boc group is removed before injectable use, the deprotected species becomes the critical process intermediate. Acidic deprotection with 4 M hydrogen chloride in dioxane or trifluoroacetic acid is followed by solvent exchange and pH adjustment. Residual trifluoroacetic acid is controlled by ion chromatography with a reporting threshold of 0.1%; residual dioxane is controlled by gas chromatography. The salt conversion step can generate subvisible particles; the bulk solution is therefore passed through a 0.22 μm filter and held in a closed stainless steel or glass-lined vessel. For lyophilized formulations, the solution is frozen at −40°C and primary drying is performed at 0.1 mbar; collapse temperature is determined by freeze-drying microscopy. The deprotected ketone is more reactive than the Boc-protected form and requires inert gas overlay during holding.

Comparative product profile against related azetidinone derivatives

1-Boc-3-azetidinone differs from 3-azetidinone hydrochloride in protection, water affinity, and handling characteristics. The hydrochloride salt is directly soluble in water but is hygroscopic and may generate acidic chloride residues during drying. 1-Cbz-3-azetidinone requires hydrogenolysis over palladium on carbon and may introduce residual aromatic solvents; the Boc product releases isobutylene and carbon dioxide under acidic deprotection. 1-Boc-3-hydroxyazetidine is the reduced alcohol analogue and is not a direct substitute when the ketone is required for reductive amination or cycloaddition.

In solvent-based granulation or spray drying, the Boc derivative is soluble in acetone, ethyl acetate, and dichloromethane; the hydrochloride salt requires water or methanol. This solubility difference determines granulation solvent selection. The Cbz derivative often has higher crystallinity and may require hot filtration after hydrogenolysis, while the Boc derivative generates gaseous by-products that are removed under vacuum. These differences affect equipment selection: hydrogenolysis requires hydrogenation vessels with palladium recovery, whereas Boc deprotection requires acid-resistant reactors and scrubbers for isobutylene removal.

What evidence supports retest dating and primary packaging selection?

Stability studies follow ICH Q1A(R2) with long-term storage at 25°C/60% RH and accelerated storage at 40°C/75% RH. The oral grade is packaged in double low-density polyethylene bags inside aluminium foil with a silica gel desiccant; the injectable grade is packaged in sterile fluoropolymer bottles sealed under nitrogen. Storage is controlled at 2–8°C and protected from light. Because the product contains a Boc-protecting group, elevated temperature and high humidity are critical variables; forced degradation data show increased free 3-azetidinone when the powder is exposed to 0.1 M hydrochloric acid at 60°C for 24 h. The product is not stored with strong acids, alkalis, oxidizing agents, or primary amines.

Batch release documentation includes a certificate of analysis with the assay value, related substances, water, residual solvents, elemental impurities, particle size, and bioburden. For injectable grade, the certificate also includes endotoxin and sterility results, filter integrity test results, and container closure integrity data. Manufacturing is conducted under cGMP according to 21 CFR 210/211 and ICH Q7; the analytical laboratory operates under ISO 17025 for the methods listed on the certificate.