BOC-L-Alaninol is the common commercial designation for tert-butyl N-[(2S)-1-hydroxypropan-2-yl]carbamate, a chiral N-protected amino alcohol with the molecular formula C8H17NO3 and a molecular weight of 175.23 g/mol. The substance is registered under CAS 79069-13-9 and is traded as a laboratory reagent, custom synthesis intermediate, and bulk pharmaceutical intermediate. The white to off-white crystalline solid carries a free primary hydroxyl and a tert-butoxycarbonyl-protected amine; the hydroxyl remains available for esterification, sulfonate formation, oxidation, and displacement, while the Boc group suppresses competing amine nucleophilicity. The stereochemical descriptor at C-2 is (S); the opposite enantiomer is supplied as BOC-D-Alaninol. Commercial packaging ranges from amber glass bottles to fluoropolymer-lined fibre drums, with a nitrogen or argon headspace and desiccant. The product is not a formulated pharmaceutical; it is an intermediate whose lot-specific certificate of analysis must be checked against the intended chemistry because no harmonized model number or pharmacopeial monograph is assigned.

Which Release Tests and Pharmacopeial Limits Govern Commercial Acceptance of BOC-L-Alaninol?

Bulk acceptance is controlled by certificate-of-analysis parameters that include assay, chiral purity, water content, residue on ignition, residual solvents, and specific rotation. Because no dedicated monograph exists, release methods are typically compendial adaptations. Organic purity is determined by gas chromatography with flame ionization detection on a 5% phenyl methylsiloxane capillary column; a common release criterion is ≥ 98.0% area. Chiral purity is assessed by normal-phase high-performance liquid chromatography on a polysaccharide-based Chiralpak AD-H column 250 mm × 4.6 mm, with an acceptance threshold of ≥ 99.0% enantiomeric excess. Water content is measured by coulometric Karl Fischer titration according to ASTM E203-16; residue on ignition is controlled below 0.10% using USP <281> or Ph. Eur. 2.4.14. Residual solvent screening against USP <467> focuses on tert-butanol and dichloromethane; the typical release limits are ≤ 0.5% and ≤ 0.06%, respectively. Optical rotation is measured in chloroform at 20 °C with a specification interval of −22.0° to −25.0° at c = 1; the value is solvent-dependent and cannot be compared directly with methanol or aqueous measurements. Method validation for non-compendial HPLC and GC procedures often follows ICH Q2(R1), with forced-degradation data used to establish peak purity and specificity.

Because BOC-L-Alaninol has a weak chromophore, HPLC with charged aerosol detection or evaporative light scattering detection is used for non-volatile impurities; gas chromatography is used for volatile impurities such as L-alaninol and tert-butanol. The absence of a strong UV signal means that simple UV area-percent HPLC can under-report non-chromophoric process impurities. Release methods therefore combine GC-FID, Karl Fischer titration, residue on ignition, and chiral HPLC. In QC laboratories, direct Karl Fischer injection of hygroscopic solids can bias the result high; an oven method coupled to the titrator is used for routine batch release to avoid surface-moisture interference.

For kilogram-scale processing, BOC-L-Alaninol is charged into a glass-lined reactor or Hastelloy C-22 vessel for sulfonate formation; methanesulfonyl chloride in dichloromethane at 0–5 °C with triethylamine converts the hydroxyl to the mesylate. The addition is controlled over 30–60 min, and the jacket is kept below 10 °C to prevent heat accumulation. The resulting N-Boc-2-aminopropyl methanesulfonate is not typically isolated; it is quenched with 1 M hydrochloric acid, washed with saturated sodium bicarbonate and brine, and concentrated below 25 °C. The sulfonate is then displaced with nitrogen, sulfur, or carbon nucleophiles to generate protected 1,2-diamines, β-aminothioethers, or longer-chain amino alcohol derivatives. The C-2 stereocentre is generally retained under SN2 displacement, but inversion is possible with certain nucleophiles; chiral HPLC after derivatization is used to confirm that the enantiomeric excess remains ≥ 99.0% before further processing. When the required intermediate is N-Boc-L-alaninal, oxidation with Dess-Martin periodinane in dichloromethane at 20–25 °C is preferred over Swern conditions when acid-sensitive groups are absent, because the workup is simpler; the aldehyde is used immediately to avoid α-epimerization. In peptide and peptidomimetic routes, the Boc group is retained through coupling steps and removed later with trifluoroacetic acid or HCl in dioxane; cleavage in dichloromethane at 0–25 °C is generally complete within 1–4 h at 1–2 M acid strength. Residual tert-butanol from incomplete solvent stripping can depress the apparent assay by 1–3%; vacuum stripping at 40–45 °C and 10–20 mbar before release is therefore applied to bulk lots.

Solid-State Handling Constraints in Double-Cone Vacuum Drying of the Bulk Solid

In a 500 L double-cone rotary vacuum dryer, charging BOC-L-Alaninol at ambient relative humidity above 60% has been observed to produce surface moisture and clumping that increase drying time. Pre-drying the dryer with nitrogen and limiting the open-charge interval to less than 30 min are practical countermeasures. Drying at 40–45 °C under 10–20 mbar typically reduces water content to ≤ 0.3% within 6–12 h, but milled material with a fine fraction may require longer cycles. Exposure to jacket temperatures above 80 °C for prolonged periods is not recommended because the Boc group eliminates isobutylene and carbon dioxide, generating L-alaninol and oligomeric impurities. The product is incompatible with strong aqueous acids, acid chlorides under heating, and prolonged exposure to formaldehyde; acid residues from previous trifluoroacetic acid campaigns must be verified absent by rinse testing. Storage stability is improved by sealing the dried solid under nitrogen with desiccant and maintaining the warehouse at 2–8 °C for long-term inventory; drum-level retest intervals are usually 12 or 24 months, depending on the supplier stability programme.

When BOC-L-Alaninol Replaces N-Cbz-L-alaninol in Hydrogenolysis-Sensitive Routes

If a route contains a benzyl ester, benzyl ether, or alkene that cannot tolerate hydrogenolysis, BOC-L-Alaninol is selected instead of N-Cbz-L-alaninol because the Boc group remains intact under catalytic hydrogenation. The protecting-group mass contribution is lower: the Boc group adds 100.12 g/mol to L-alaninol, whereas the Cbz group adds 134.13 g/mol. At the same molar loading, this difference improves process mass intensity and reduces the final deprotection load. The Boc derivative lacks the strong UV chromophore of the Cbz group; therefore TLC and HPLC monitoring at 254 nm is less sensitive, and charged aerosol detection or low-wavelength detection at 205–210 nm is used. Boc is removed cleanly with 4 M HCl in dioxane or trifluoroacetic acid, while Cbz requires hydrogenolysis or more forcing acidic conditions. In multiproduct plants, residual benzyl chloroformate or benzyl alcohol from Cbz processing can contaminate Boc-destined batches; dedicated glass-lined equipment and verified cleaning with an HPLC rinse test are used when switching campaigns. The opposite enantiomer BOC-D-Alaninol is differentiated by chiral HPLC retention time inversion on a Chiralpak AD-H column and by the sign of optical rotation; a batch with unintended enantiomer contamination below the release limit is not suitable for diastereoselective steps.

Unlike unprotected L-alaninol, which is a colourless viscous liquid with high aqueous solubility and a free-amine odour, BOC-L-Alaninol is a crystalline solid handled through solids addition hoppers under nitrogen. The narrow melting range of commercial material is typically 57–61 °C; molten charging is possible but requires heated transfer lines and care to avoid thermal deprotection. The product is not used in aqueous alkaline solutions above pH 10 at elevated temperature; short aqueous washes are maintained below pH 9 to limit slow Boc hydrolysis. The crystalline solid is also easier to isolate by pressure filtration or centrifugation than unprotected L-alaninol, but residual solvent entrapment in the crystal lattice requires longer vacuum cycles than for the liquid analogue. Published data for continuous large-scale production of this specific amino alcohol is limited; most industrial use is batch-mode laboratory or kilo-scale manufacture, where the main process risks are residual solvent retention, enantiomeric drift, and premature deprotection caused by thermal or acidic excursions.