Hydroxypropyl ß-Cyclodextrin

2-Hydroxypropyl-beta-Cyclodextrin are non-toxic solubilizers. The solubility of drugs increases linearly with the concentration of 2-Hydroxypropyl-b-cyclodextrin in aqueous buffer. The formation of drug/cyclodextrin complexes is a rapidly reversible reaction and complexes exist both in solution and crystalline states. Solutions of many such complexes may be lyophilized to produce freely soluble powders which may be compressed into tablets. Bio-effects are only slightly affected by cyclodextrin complexation. Cells in serum supplemented medium can be grown in up to 1-2%. In serum-free medium, concentrations of 0.5-1% are acceptable. Hydroxypropyl-b-cyclodextrin has been found to be non-toxic in mice and rabbits. 2-hydroxypropyl-g-cyclodextrin with its 8 glucose units, has a slightly larger cavity and can accomodate larger substrates than the beta form. The use of cyclodextrins in receptor binding assays in not recommended.

Cyclodextrins are cyclic oligosaccharides consisting of 6, 7, or 8 glucopyranose units, usually referred to as α-, β-, or γ-cyclodextrins, respectively. These compounds have rigid doughnut-shaped structures making them natural complexing agents. The unique structures of these compounds owe their stability to intramolecular hydrogen bonding between the C2- and C3-hydroxyl groups of neighboring glucopyranose units. The molecule takes on the shape of a torus with the C2- and C3-hydroxyls located around the larger opening and the more reactive C6-hydroxyl aligned around the smaller opening. The arrangement of C6-hydroxyls opposite the hydrogen bonded C2- and C3-hydroxyls forces the oxygen bonds into close proximity within the cavity, leading to an electron rich, hydrophobic interior. The size of this hydrophobic cavity is a function of the number of glucopyranose units forming the cyclodextrin.