Encapsulation of adefovir bis(l-leucine propyl)ester pro-virucide in cucurbit[7]uril and its activity against tobacco mosaic virus

The interaction of cucurbit7]uril (Q7]) with a pro-virucide, adefovir bis(l-leucine propyl)ester (PMEA-Leu) in aqueous solutions and in solid state was studied by ¹H NMR, UV absorption spectroscopy, fluorescence and IR spectroscopy. The ¹H NMR revealed that the leucine propyl moiety of the compound could be entrapped in the cavity of the host Q7], and the other moiety except for leucine propyl moieties, including aminopurine, was probably located at the portal area of Q7]. Absorption and fluorescence spectroscopy proved that the interaction of Q7] with PMEA-Leu led to the formation of host–guest inclusion complexes (2:1) that were controlled by the concentration of the host Q7]. Formation of the inclusion complex between Q7] and PMEA-Leu was confirmed by IR spectroscopy in solid state. In addition, deliquescent stability studies indicated that the moisture stability of the host–guest complex was significantly enhanced. The phenomenon was explained by the fact that the formation of solid inclusion complexes can prevent the compounds from absorbing water. Finally, bioactivity of PMEA-Leu and its inclusion complex against tobacco mosaic virus (TMV) was tested. The compound PMEA-Leu and its inclusion complexes showed some inhibitory activity against TMV at 500 μg/ml in vivo.