Antibacterial geranylflavonoids from Paulownia tomentosa (Scrophulariaceae) fruits

Paulownia tomentosa (Thunb.) Steud. has been used as a traditional Chinese herbal medicine for the treatment of enteritis, tonsillitis, bronchitis and dysentery [1]. Previous phytochemical studies of this species identified several compounds, falling within iridoids, flavonoids, phenolic glycosides, furanofuran lignans and furanoquinones [2]. Our study was focused on isolation and identification of partly polar and non-polar compounds and aims to find bioactive substances with antibacterial activity. Eight geranylflavanones were isolated from ethanol extract of P. tomentosa fruit, four of which are described for the first time from a natural source. For isolation, liquid-liquid fractionation, column chromatography, flash chromatography and preparative HPLC were used. The compounds were described by spectrophotometric methods, and the structures of compounds were determined by mass spectrometry including HR-MS, and 1D and 2D NMR spectroscopy, absolute configuration was deduced from circular dichroism. Antibacterial activity against 6 G+, 3 G- human pathogenic bacteria and one yeast was determined by microdilution method. Seven compounds exhibited some degree of activity; however, any of the compounds was able to inhibit G- bacteria or the yeast. Six compounds were active against all G+ bacteria with MICs from 2 to 8µg/ml. Isolated antibacterial compounds from P. tomentosa may help with treatment of certain bacterial diseases.

Acknowledgements: IGA VFU 23/2004, Ministry of Education of the Czech Republic MSM0021622413, MSM 6046137305 and LC06030, Ministry of Health 1A8666.

References: [1] Jiang, T. et al. (2004) Chromatographia 59: 255–258. [2] Kang, H.K. et al. (1994) Arch. Pharm. Res. 17: 470–475