Analysis and identification of lignans in Phyllanthus urinaria by HPLC-SPE-NMR

HPLC-SPE-NMR has been applied to the analysis of a number of structurally similar lignans present in Phyllanthus urinaria. A reversed-phase HPLC system, using a C8 column eluted with tetrahydrofuran-water-methanol and detected at 225 nm was developed that gave good resolution for seven lignans from Phyllanthus urinaria. Coupling of this system with SPE-NMR provided clean 1H-NMR spectra for nine lignans present in 4 mg of a lignan-rich fraction, equivalent to ca. 1.0 g of dry plant material. The result demonstrates that HPLC-SPE-NMR is a very efficient and powerful tool for the unambiguous identification of natural products that have been previously characterised.