L-Carnitine (Levocarnitine)

L‑Carnitine (also called levocarnitine) is a quaternary ammonium compound that functions primarily as a carrier molecule for long‑chain fatty acids. In humans it is synthesized from the amino acids lysine and methionine and is essential for transporting these fatty acids across the inner mitochondrial membrane where they undergo β‑oxidation to generate ATP.

• L‑carnitine is a zwitterionic molecule with the formula C₇H₁₅NO₃ and a molecular weight of 161.20 g·mol⁻¹.
• IUPAC Name: Its IUPAC name is (3R)-3‑hydroxy‑4‑trimethylazaniumylbutanoate.
• Structure: The structure features a quaternary ammonium (‑N⁺(CH₃)₃) group attached to a 2‑hydroxy‑4‑carboxylic acid chain, giving it both a positive charge (on the nitrogen) and a negative charge (on the carboxylate).
• Solubility: This confers high water solubility (≈1 g mL⁻¹) and a pKa of ~9.5 for the carboxyl group.
• Stereochemistry: The stereochemistry is R‑configuration at C‑3, essential for biological activity; the S‑enantiomer (D‑carnitine) is inactive in humans.

• Natural Sources: Naturally, L‑carnitine is abundant in red meat, dairy, and fish (≈30–50 mg per 100 g).
• Commercial Production: Commercially, it is produced either by extraction from animal tissues (e.g., bovine kidney) or via microbial fermentation (e.g., Corynebacterium glutamicum), which yields a highly pure, racemic‑free L‑enantiomer.
• Synthetic Routes: Synthetic chemical routes (e.g., condensation of β‑hydroxy‑γ‑butyrolactone with trimethylamine) are also used.
• Supplement Grade: For supplements, pharmaceutical‑grade L‑carnitine is typically produced by fermentation, providing >98 % purity and minimal contaminants.
• Quality Considerations: Quality considerations include verification of enantiomeric purity (R‑form), absence of heavy metals, and compliance with GMP or USP monographs for dietary supplements.