A novel approach is presented in order to characterize new lead compounds from natural sources. Many natural products are pro-drugs that are metabolized and activated after oral administration. Nevertheless, this aspect is usually overlooked when searching for new therapeutic agents using classical approaches. In this project, Salix spp. (willow bark) and Filipendula ulmaria (meadowsweet) were selected as case studies for the characterization of new leads for anti-inflammatory drugs.