The Potential Use of Cyclodextrins in Separation at Scale in Process Chemistry

I had occasion to read a review, Past, Present and Future of Cyclodextrin Research, Jozsef Szejtii, Pure Appl. Chem. 76(10) 1825-1845 (2004).

I did not realize the use of cyclodextrins for separation could be so practical. β-cyclodextrin only costs $2-5 dollars per kilogram. β-cyclodextrin has a molecular weight of 1,134 and if it forms a 1:1 complex with a drug substance (mw about 500), a kilogram would complex about 500 gm of API.  That is the cyclodextrin cost to complex a kilogram of such API would be between 4 and 10 US dollars .

 Nor did I realize that cyclodextrin can form very strong complexes which will take an insoluble drug into aqueous solution.  Β-cyclodextrin forms a strong complex with cholesterol which then crystallizes.

A cyclodextrin complex may be quite stable while in water solution but, when it is dried completely, the stability of the complex vanishes, because as water is removed the basis for the stabilization is removed and one gets just an intimate powder mixture.

One would anticipate therefore that slurrying a mixture of two essentially water insoluble compounds, one of which forms a stabilized inclusion complex and another that does not, would partition the former into aqueous solution and leave the latter undissolved.

Solvent switching to an organic solvent should cause the organic that had been complexed to move into the organic layer and a complex of the new organic solvent (if that solvent forms a complex)  and cyclodextrin to precipitate.