I. Physicochemical Properties
Appearance and Solubility
Appearance: Typically a white to off-white crystalline powder with a regular crystal structure. It exhibits hygroscopicity due to polar functional groups (e.g., amino and carboxyl groups).
Solubility: Readily soluble in polar solvents (e.g., water, methanol, ethanol), with solubility increasing with temperature in water. Sparingly soluble in nonpolar solvents (e.g., diethyl ether, chloroform). This behavior arises from hydrogen bonding between polar groups (amide, carboxyl, amino) and water, while the hydrophobic benzene ring in the benzyl group limits solubility in nonpolar media.
Melting and Boiling Points
Melting Point: Approximately 155–160°C (decomposition). Decomposes upon heating rather than melting, attributed to the thermal instability of the amide bond and benzyloxycarbonyl group.
Boiling Point: Not definitively determined (decomposes before reaching boiling). Thermal decomposition involves cleavage of the benzyloxycarbonyl group and degradation of the amino acid backbone.
Acid-Base and Dissociation Properties
Amphoteric Nature: Contains both acidic (–COOH) and alkaline (–NH₂) groups, acting as an amphoteric compound. Its isoelectric point (pI) is slightly lower than that of L-lysine (free L-lysine pI ≈ 9.74) due to reduced dissociation of the protected amino group.
Dissociation Behavior: Under acidic conditions (low pH), the amino group protonates; under alkaline conditions (high pH), the carboxyl group deprotonates. The protected amino group in the benzyloxycarbonyl moiety exhibits significantly reduced dissociation.
Optical Activity
Exhibits optical activity due to the chiral center at the α-carbon of lysine (L-configuration). Specific rotation [α]ᴅ²⁰ (in water) is approximately +10° to +15°, depending on purity.
II. Stability Study
Thermal Stability
Room Temperature: Stable under dry conditions at 20–25°C for extended storage. At elevated temperatures (e.g., >80°C), the benzyloxycarbonyl (–Cbz) group may hydrolyze or undergo deprotection, releasing benzyl (C₆H₅CH₂–) and free amino groups, reducing product purity.
Decomposition Temperature: Above 150°C, thermal decomposition of the amide bond and carboxyl group occurs, generating CO₂, amines, and benzyl derivatives. Avoid high-temperature processing (e.g., baking, strong heating).
Acid-Base Stability
Acidic Conditions: In dilute acids (e.g., HCl, acetic acid), the Cbz group hydrolyzes 逐步，yielding L-lysine and benzyl benzoate. Reaction rate increases with acid concentration and temperature (e.g., reflux in 6 M HCl rapidly removes the Cbz group).
Alkaline Conditions: The carboxyl group neutralizes in strong bases (e.g., NaOH, KOH), while the Cbz group remains relatively stable. Prolonged exposure to high-temperature alkaline conditions may hydrolyze the amide bond, liberating the amino group.
Oxidative and Photostability
Antioxidation: The benzene ring provides some resistance to oxidation, but amino and carboxyl groups may be oxidized by strong oxidants (e.g., KMnO₄, H₂O₂), leading to structural degradation.
Photostability: The benzyl benzene ring is sensitive to UV light. Prolonged exposure (especially to UV) may induce photolysis, cleaving the Cbz group to form free amino groups and benzaldehyde. Store in amber vials to avoid light exposure.
Hydrolytic and Enzymatic Stability
Hydrolysis: In neutral aqueous solutions, amide bond hydrolysis is slow but accelerates under prolonged storage (especially in hot and humid conditions), forming L-lysine and benzyloxycarboxylic acid. Acidic or alkaline conditions enhance hydrolysis.
Enzymatic Degradation: Proteases (e.g., trypsin) may hydrolyze the peptide (amide) bond, but the Cbz group reduces enzymatic efficiency, making N6-Cbz-L-lysine less susceptible to cleavage than free L-lysine.
Impact of Storage Conditions
Optimal storage: Avoid light，dry, cool (0–4°C or sealed at room temperature). Avoid contact with acids, bases, and oxidants. Hygroscopicity may promote aggregation or hydrolysis in humid environments; use desiccants for long-term storage.
III. Conclusion
The physicochemical properties of N6-Cbz-L-lysine are determined by its amino acid backbone and Cbz protecting group, combining water solubility from polar groups with hydrophobicity from the benzene ring. It exhibits good stability under room temperature，neutral, and avoid light conditions but is prone to structural changes under high temperature，strong acids/bases, light, or oxidants—particularly deprotection of the Cbz group. In practical applications (e.g., organic synthesis, pharmaceutical intermediate storage), control reaction and storage conditions to maintain product purity and activity.
Note: Ensure consistency with your original references for citation accuracy. Chemical structures and stability mechanisms are described using standard IUPAC terminology.
