L-Alanyl-L-Tyrosine is a dipeptide compound formed by the linkage of L-alanine and L-tyrosine through a peptide bond. Its structure combines the characteristics of two natural amino acids, conferring unique physicochemical properties and biological activities. The following provides a detailed overview from three aspects: properties, functional features, and applications.

I. Basic Properties

1. Physical Properties

Appearance and Form: Typically appears as a white to off-white crystalline powder, odorless or with a faint amino acid-like smell, and exhibits good flowability.

Solubility: Moderately soluble in water (better than free tyrosine, due to improved hydrophilicity from the peptide bond and alanine residue), easily soluble in dilute acid or base solutions, and poorly soluble in organic solvents like methanol, ethanol, or ether. Solubility slightly increases with temperature.

Molecular Formula and Weight: Molecular formula is C₉H₁₄N₂O₄, with a molecular weight of 214.22 (formed via condensation of L-alanine C₃H₇NO₂ and L-tyrosine C₉H₁₁NO₃, eliminating one molecule of water).

Melting Point and Stability: Decomposes upon heating at around 220–230°C (no clear melting point). Stable under dry, dark, room-temperature conditions. May agglomerate under moisture but retains chemical stability.

2. Chemical Properties

Optical Activity: Due to both amino acid residues being in the L-configuration, the molecule is optically active. Specific rotation $[α]^D$ is generally negative (e.g., around −20° to −25° in water, depending on solvent and concentration).

Hydrolysis: The peptide bond is susceptible to cleavage under strong acidic (e.g., boiling 6 M HCl) or basic conditions, yielding L-alanine and L-tyrosine. In vivo, it can be enzymatically hydrolyzed by dipeptidases.

Reactivity: Retains typical amino acid functional groups: the amino group (–NH₂) can undergo acylation or alkylation; the carboxyl group (–COOH) can undergo esterification or amidation; the phenolic hydroxyl group (–OH) of tyrosine can react with diazonium compounds or be oxidized by oxidants like hydrogen peroxide.

Stability: Relatively stable under neutral or mildly acidic conditions. The phenol group makes it sensitive to strong oxidants, potentially leading to oxidation into quinone-like structures (causing discoloration).

II. Functional Characteristics

Excellent Biocompatibility and Safety: Composed of natural L-amino acids, highly compatible with human metabolism. Once absorbed, it is hydrolyzed into alanine and tyrosine, which participate in protein synthesis and metabolic processes. Non-toxic under appropriate doses, suitable for use as a bioactive component.

Improved Stability over Free Tyrosine: Free tyrosine is prone to oxidation due to its phenolic hydroxyl group, whereas the dipeptide form reduces exposure of this group. The inclusion of alanine enhances chemical stability, making it more suitable for liquid formulations.

Sustained Release & Efficient Absorption: As a dipeptide, it is absorbed through specific intestinal peptide transporters (e.g., PEPT1), offering higher bioavailability than free amino acids. Slow enzymatic hydrolysis enables sustained amino acid release, avoiding rapid spikes in plasma levels.

Tyrosine Precursor Function: The released tyrosine is a precursor for vital bioactive compounds such as dopamine, epinephrine, thyroid hormones, and melanin.

Low Bitterness: Compared to the slight bitterness of free tyrosine, the dipeptide form has a milder taste and better palatability, making it suitable for food and supplement applications.

III. Applications

1. Pharmaceutical and Clinical Nutrition

Foods for Special Medical Purposes (FSMPs): Used in nutritional formulations for post-operative recovery, malnutrition, or patients with impaired digestion/absorption. It provides sustained release of alanine (involved in gluconeogenesis and energy metabolism) and tyrosine (for neurotransmitter synthesis).

Support for Neurological and Mental Health: As a tyrosine precursor, it may alleviate neurotransmitter deficiencies caused by tyrosine shortage (e.g., during stress), and is used in cognitive support supplements (often combined with other nutrients).

Nutritional Support for Liver and Kidney Dysfunction: Compared to free amino acids, dipeptides place a lower metabolic burden, making them suitable for amino acid supplementation in patients with compromised liver/kidney function.

2. Sports Nutrition and Dietary Supplements

Performance Supplements: Alanine is a precursor of carnosine (which buffers muscle acidity), while tyrosine can enhance focus and endurance. Therefore, this dipeptide is added to sports drinks and energy bars to support performance and recovery.

Anti-Fatigue Supplements: Gradual tyrosine release helps maintain neurotransmitter levels, reducing mental fatigue and stress—suitable for high-stress populations like students or cognitive workers.

3. Cosmetics and Skincare

Skin Repair and Brightening: Tyrosine is a precursor for melanin synthesis, and its dipeptide form may mildly regulate local tyrosinase activity, helping maintain pigmentation balance. Its good biocompatibility also minimizes skin irritation, suitable for gentle brightening or repair products (e.g., serums, creams).

Antioxidant Protection: The phenolic hydroxyl group helps scavenge free radicals, inhibits lipid peroxidation in skin, and delays skin aging. It works synergistically with antioxidants like vitamins C and E.

4. Biochemistry and Research

Model Dipeptide: Used to study peptide bond hydrolysis kinetics, intestinal peptide transport mechanisms, and peptidase substrate specificity—informing the design of peptide-based drugs.

Culture Media Additive: Provides specific amino acid precursors (especially for neural or melanocyte cultures), supporting growth and functional studies of target cells or microorganisms.

IV. Precautions

Storage: Keep sealed, away from light, in a cool and dry place. Avoid contact with strong oxidizers (e.g., peroxides) to prevent oxidation of the phenolic group.

Usage in Pharma or Food: Purity must be strictly controlled (avoid racemization or impurities). Adhere to regulatory dosage limits, as excessive intake may increase metabolic burden (e.g., accumulation of tyrosine metabolites).

L-Alanyl-L-Tyrosine, with its excellent biocompatibility, good stability, and amino acid sustained-release functionality, has broad application prospects in medical nutrition, sports supplementation, and cosmeceuticals. It is a naturally derived dipeptide with both functional and safety advantages.

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