Technology

Captisol Technology

Captisol^® is a beta cyclodextrin that has been derivatized to have an average of 6.5 sulfobutylether groups per cyclodextrin molecule.

Cyclodextrins are cyclic oligosaccharides typically containing 6(α-CD), 7(β-CD), or 8(γ-CD) glucopyranose units.  This cyclic orientation provides a truncated cone structure that is hydrophilic on the exterior and lipophilic on the interior.  Cyclodextrin complexes are formed when a guest molecule is partially or fully contained in the interior of the cavity, thereby improving the solubility and/or stability of the guest molecule. The parent α-, β-, and γ-cyclodextrins (particularly β) have limited aqueous solubility and show toxicity when given by injection.  Therefore, the parent cyclodextrin structure has been chemically modified to generate a parenterally safe CD-derivative.  The modifications are typically made at one or more of the 2, 3, or 6 position hydroxyls.

Captisol^® is unique because of its sulfobutylether groups. The very low pKa of the sulfonic acid groups results in Captisol® having multiple negative charges at physiologically compatible pH values. This greatly increases the solubility and safety of the cyclodextrin itself and provides another handle by which molecules can interact with Captisol^®. The four-carbon butyl chain coupled with repulsion of the end group negative charges allows for an "extension" of the cyclodextrin cavity. This often results in stronger binding to drug candidates than seen with other modified cyclodextrins.

Guest-host complexation is considered to be the major contributor in the interactions that lead to improved solubility and stability with cyclodextrins. It is important to keep in mind that these interactions are non-covalent, reversible interactions and typically occur in a 1:1 stoichiometry. This can be described by: