HMB (?-Hydroxy ?-Methylbutyrate)

β‑Hydroxy β‑Methylbutyrate (HMB) is a biologically active metabolite of the essential branched‑chain amino acid leucine. It's produced in small amounts during protein metabolism and is widely marketed as a dietary supplement to support muscle health and recovery.

• IUPAC name: 3‑hydroxy‑3‑methylbutanoic acid
• Molecular formula: C₅H₁₀O₃
• Molecular weight: 118.13 g·mol⁻¹
• Structure: A four-carbon chain (butyrate) with a β‑hydroxy group on carbon‑3 and a methyl substituent on the same carbon, giving a chiral center (S‑configuration is the biologically active isomer).
• Properties: The compound is a small, polar organic acid (pKa ≈ 4.5) that is highly soluble in water (≈150 g/L at 25 °C) and in ethanol. Its polarity allows rapid absorption in the small intestine, achieving peak plasma concentrations ~1 h after oral ingestion.

• Natural Sources: HMB is not abundant in foods; trace amounts are found in fermented dairy (e.g., certain cheeses) and in the meat of ruminants.
• Commercial Production: Commercially, HMB is produced via microbial fermentation of glucose to produce the precursor β‑hydroxy β‑methylbutyrate, followed by chemical esterification (often as calcium or magnesium salts) to improve stability.
• High-Purity Production: High-purity (> 99 %) pharmaceutical-grade HMB is produced by licensed GMP facilities using validated fermentation or chemical synthesis routes.
• Supplement Quality Markers: For supplements, quality markers include:
  • Verification of the S-enantiomer using chiral HPLC.
  • Absence of heavy metals (< 10 ppm) and residual solvents.
  • Certification of ≥ 98 % purity via HPLC-UV.
• Third-Party Testing: Third-party testing (e.g., NSF, Informed-Choice) is recommended to ensure product integrity.