Bioguided fractionation of the antimalarial plant Argemone mexicana: isolation and quantification of active compounds from effective clinical batches

Despite major scientific advances and considerable health related efforts, malaria remains one of the world's leading killers in endemic countries, with an estimated 250 million cases every year, giving rise to an estimated 880 000 deaths, mostly among African children. For various reasons the access to safe and effective medicines such as artemisinin-based combined therapies is a major issue for a large proportion of the patients, especially those living in rural areas who use traditional medicinal plants for their primary healthcare [1]. Based on the promising clinical results of an Argemone mexicana L. (Papaveraceae) traditional preparation used to treat malaria in southern Mali [2], a bioguided fractionation of the decoction prepared with a clinical batch of the plant was performed in order to identify its active ingredients. Fractions were obtained by a combination of liquid-solid extraction and liquid-liquid partitions. From the active fraction, three alkaloids were isolated by semi-preparative HPLC and tested against P. falciparum in vitro: allocryptopine, berberine and protopine. A QNMR method was developed to quantify these three alkaloids within a mixture. The 1H NMR signal of the methylene dioxide group of each alkaloid was used for integration and anthracene was used as the internal standard. Allocryptopine was found to be the most concentrated alkaloid in the traditional decoction, with an antiplasmodial IC50 value of 1.46µg/ml. Qualitative and quantitative results are critically discussed in regard of the clinical efficacy of this traditional preparation. The outcome of the quantitative NMR measurements are compared to results obtained using other analytical methods.