Preparation and cyclodextrin solubilization of the antibacterial agent benzoyl metronidazole.

A one-pot method for the preparation of benzoyl metronidazole was achieved by using N,N'-carbonyldiimidazole as a coupling reagent. Moreover, it was found that the byproduct imidazole as the catalyst promoted the reaction. In addition, the β-cyclodextrin solubilization of benzoyl metronidazole was investigated by phase-solubility method. The phase-solubility studies indicated that the solubility of benzoyl metronidazole (S = 0.1435 g/L) was substantially increased 9.7-fold (S' = 1.3881 g/L) by formation of 1 : 1 benzoyl metronidazole/β-cyclodextrin complexes in water, and the association constant K(a) value was determined to be 251 (±23) dm(3)/mol. Therefore, β-cyclodextrin can work as a pharmaceutical solubilizer for benzoyl metronidazole and may improve its oral bioavailability.