Characterization of salvianolic acid B and verbascoside cyclodextrin complexes by innovative NMR methods. Evaluation of their stability

Salvianolic acid B is a potent antioxidant with anti-thrombotic, anti-hypertensive and hepatoprotective activities obtained from Salvia miltiorrhiza L. root [1]. Verbascoside is a phenylpropanoid glycoside widely spread in nature with remarkable antioxidant, neuroprotective and hepatorpotective properties [2]. Both constituents are very water-soluble but unstable in aqueous solutions at pH >5 [3]. In the present study both substances were enclosed in β-cyclodextrin in order to increases their water stability and the complexes were characterised by ¹H-NMR complexation shifts analysis, ¹H-NMR diffusion measurements, ROESY, NMR titration study and Job's plot. Diffusion ordered spectroscopy (DOSY) has been used extensively to study supramolecular aggregates and solubilisation processes in order to determine diffusion coefficients for the individual signals in a spectrum [4]. The DOSY spectra demonstrated that in the presence of β-CyD the translational diffusion of verbascoside and salvianolic acid B are sizably slowed down with respect to the free drugs. In the case of salvianolic acid B induced shifts and intermolecular ROE signals demonstrated that two caffeoyl moieties are deeply inserted in the cyclodextrin cavity, while one caffeoyl moiety hangs out from the wider rim. The Job's plots confirmed the 3:2 inclusion complex. In the case of verbascoside induced proton shifts and intermolecular ROE signals demonstrated that the caffeoyl moiety is deeply inserted in the cyclodextrin cavity. The Job's plots confirmed the 1:1 inclusion complex. Stability studies made by qNMR showed that both complexes increased the stability of the molecules.

References: 1. Lin, YL et al. (2006)J. Ethnopharm. 105: 215–222.

2. Guangmiao, F. et al. (2008) Cur. Med. Chem.15: 2592–2613.

3. Meng, W. et al. (2009) Nat. Prod. Comm. in press.

4. Bilia, AR. et al. (2002)J. Pharm. Sci 91: 2265–2270.