Figure 1.

Molecular structure and formulation of allopregnanolone. (A) Chemical structure of allopregnanolone; molecular weight 318.49 g/mol. (B) Chemical structure of β-cyclodextrin derivatives, where R is hydrogen or 2-hydroxypropyl (CH₂CHOHCH₃) for HBCD or sulfobutylether ((CH₂)₄ SO₃ Na) for SBECD. HBCD has an average molecular weight ~1460 g/mol, with 0.7–3.15 average degrees of substitution for hydrogen. SBECD molecular weight ~2163 g/mol with average degrees of substitution estimated between 6.3–6.6. (C) The β-cyclodextrins form three-dimensional cyclic oligosaccharide toroidal structures comprised of 1,4-linked glucopyranose molecules with a hydrophilic outer surface and a hydrophobic inner surface. (D) Allopregnanolone in β-cyclodextrin formulation to render allopregnanolone water soluble for rapid release in vivo. Two or more molecules of β-cyclodextrin, represented as toroid-shaped hydrophilic caps, form an inclusion complex with each relatively insoluble Allo molecule.