Screening of natural products extracts for the presence of phosphodiesterase inhibitors using liquid chromatography coupled online to parallel biochemical detection and chemical characterization.

The ability to rapidly identify active compounds in a complex mixture (e.g., natural products extract) is still one of the major problems in natural products screening programs. An elegant way to overcome this problem is to separate the complex mixture by gradient liquid chromatography followed by online biochemical detection parallel with chemical characterization, referred to as high-resolution screening (HRS). To find and identify phosphodiesterase (PDE) inhibitors in natural products extracts using the HRS technology, the authors developed a continuous-flow PDE enzymatic assay. The suitability of the continuous-flow PDE enzymatic assay for natural products screening was demonstrated. After optimization of the continuous flow PDE assay, the limit of detection for 3-isobutyl-1-methyl-xanthine (IBMX) was 1 muM, with a dynamic range from 1 to 100 muM IBMX. The applicability of the HRS technology for the detection of PDE inhibitors in natural products extracts was demonstrated by the analysis of a plant extract spiked with 2 naturally occurring PDE inhibitors. The plant extract was analyzed with 2 assay lines in parallel, enabling background fluorescence correction of the sample. The simultaneous quantification of the active compounds using evaporative light-scattering detection allowed the estimation of the IC50 value of the active compounds directly in the crude extract.