Pyroglutamic Acid (CAS 98-79-3)
Pyroglutamic Acid: Structure, Properties, and Applications
1. Introduction
Pyroglutamic acid, also known as 5-oxo-L-proline, pidolic acid, or 2-pyrrolidone-5-carboxylic acid (PCA), is a naturally occurring cyclic derivative of glutamic acid. It plays a crucial role in the gamma-glutamyl cycle (glutathione cycle) and is found in various biological systems. Pyroglutamic acid and its derivatives are widely used in the cosmetics industry as humectants and skin conditioners, as well as in biochemical and pharmaceutical research.
2. Chemical Structure and Nomenclature
IUPAC name: (2S)-5-Oxopyrrolidine-2-carboxylic acid
Synonyms: 5-Oxo-L-proline, pidolic acid, L-pyroglutamic acid, 2-pyrrolidone-5-carboxylic acid, PCA, glutimic acid
Molecular formula: C₅H₇NO₃
Molecular weight: 129.11 g/mol
CAS number: 98-79-3
EINECS number: 202-700-3
MDL number: MFCD00005222
Appearance: White to off‑white crystalline powder
Solubility: Soluble in water (approximately 1 g/3 mL), ethanol, methanol, and DMSO; slightly soluble in ethyl acetate; practically insoluble in ether.
Melting point: 160–165°C (decomposes)
3. Biological Role and Metabolism
Pyroglutamic acid is a key intermediate in the gamma‑glutamyl cycle, which is responsible for the synthesis and degradation of glutathione (GSH), one of the body's primary antioxidants. It is formed from glutamic acid by the enzyme gamma‑glutamyl cyclotransferase and is converted back to glutamic acid by the enzyme 5‑oxoprolinase. Accumulation of pyroglutamic acid can occur in certain metabolic disorders, such as 5‑oxoprolinuria (pyroglutamic aciduria), and in cases of acetaminophen overdose.
4. Physicochemical Properties
Appearance: White to off-white crystalline powder
Odor: Odorless or practically odorless
pH (1% solution): 2.0–2.5 (acidic)
Optical rotation [α]₂₀: −10 to −12° (c = 10 in water)
Stability: Stable under normal storage conditions
5. Synthesis Methods
Laboratory synthesis: Pyroglutamic acid is typically produced by heating glutamic acid or glutamine, resulting in intramolecular cyclization with loss of water.
Industrial production: Produced through controlled heating of glutamic acid or by enzymatic methods using specific cyclotransferases.
6. Applications
Cosmetics and personal care: Pyroglutamic acid and its salts (especially Sodium PCA) are widely used as humectants and skin conditioning agents in moisturizers, creams, lotions, serums, shampoos, and conditioners. It is a key component of the skin's Natural Moisturizing Factor (NMF), helping to attract and retain moisture, improve skin elasticity, and maintain barrier function.
Biochemical research: Used as a substrate in enzyme studies, particularly in research on the gamma‑glutamyl cycle and glutathione metabolism. Acts as an inhibitor of vitamin B6.
Pharmaceuticals: Used as an intermediate in the synthesis of various pharmaceutical compounds and studied for potential therapeutic applications.
Food industry: May be used as a flavor enhancer in some applications (subject to regulations).
7. Safety and Toxicology
Skin compatibility: Pyroglutamic acid and its sodium salt (Sodium PCA) are generally considered safe and well‑tolerated in cosmetic applications. They are classified as non‑irritating and non‑sensitizing at typical use concentrations.
Oral toxicity: Low acute oral toxicity; large doses may cause metabolic disturbances.
Environmental safety: Biodegradable and considered safe for the environment at typical use levels.
8. Conclusion
Pyroglutamic acid (5‑oxo‑L‑proline, CAS 98‑79‑3) is a naturally occurring cyclic amino acid derivative with important biological functions in glutathione metabolism and skin hydration. Its exceptional moisture‑binding properties make it a valuable ingredient in cosmetic formulations, where it helps maintain skin hydration, elasticity, and barrier function. In addition to its cosmetic applications, pyroglutamic acid is used in biochemical research and pharmaceutical synthesis. Its safety, biocompatibility, and natural origin make it a versatile and sustainable ingredient for a wide range of applications.