A comparison investigation on the solubilization of betulin and betulinic acid in cyclodextrin derivatives

Betulin (BET) and betulinic acid (BA) are naturally occurring pentacyclic lupane triterpenes, exhibit great promise as bioactive agents for the treatment of many diseases. The poor solubilities of BET and BA in water have limited their applications. In the present work, BET and BA were selected as guest molecules, three hydrophilic gamma-cyclodextrin (CD) thioethers were synthesized and selected as host molecules. beta-, Hydroxypropyl-beta-CD, (HP-beta-CD), gamma-CD and HP-gamma-CD were also investigated as hosts in order to compare the solubilization abilities of these host molecules. The solubilities of BET and BA were estimated from 1H NMR measurements by comparing the relative integral areas of the proton signals between CDs and guests. gamma-CD thioethers 5-7solubilized BET and BA to much higher extends than other host molecules. The obtained maximal solubilities of BET and BA were 5.2 and 4.5 mM, respectively. The topographies of the inclusion compounds were determined by ROESY NMR spectroscopy.