Inositol (Vitamin B8)

Inositol, often referred to as “vitamin B8,” is a naturally occurring cyclohexane‑hexol.

• It functions primarily as a structural component of phosphatidyl‑inositol (PI) and its phosphorylated derivatives (phosphoinositides).
• These lipid‑derived molecules serve as key second‑messenger precursors in cell‑signaling pathways.
• These pathways regulate hormone action, neurotransmission, and membrane dynamics.

• Inositol (C₆H₁₂O₆) is a cyclohexane ring bearing six hydroxyl groups (a hexahydroxycyclohexane).
• The most biologically active stereoisomer is myo‑inositol (IUPAC: (1R,2S,3R,4S,5R,6S)-cyclohexane‑1,2,3,4,5,6‑hexol).
• It is a polyol with a molecular weight of 180.16 g mol⁻¹, melting point ≈ 225 °C, and is highly soluble in water (≈100 g/L at 25 °C) but poorly soluble in non‑polar solvents.
• The molecule is achiral in its crystalline form due to rapid interconversion of axial/equatorial hydroxyls, but the stereochemistry determines its biological activity (e.g., d‑chiro‑inositol).
• In solution, it exists primarily as a neutral, non‑ionic, highly polar molecule, allowing rapid diffusion across cell membranes via carrier‑mediated transport (e.g., Na⁺‑dependent inositol transporters, SMIT1/2).

• Natural inositol is abundant in beans, nuts, whole grains, citrus fruits, and especially in high‑fiber foods like beans (≈1 g/100 g).
• Commercially, inositol is extracted from corn or wheat bran via aqueous extraction followed by crystallization.
• An alternative route uses the catalytic hydrogenation of glucose to produce myo‑inositol, which yields >99 % purity and is the standard for pharmaceutical‑grade products.
• Quality considerations include:
  • (i) verification of ≥ 99 % purity by HPLC;
  • (ii) absence of heavy metals and pesticides (especially for plant‑derived sources);
  • (iii) compliance with GMP and USP‑type monographs.
• Certified “pharmaceutical‑grade” inositol typically has a residual solvent profile < 10 ppm and is free of added sugars or fillers, ensuring consistent bioavailability.