HPLC in the comparative study of the content of naphthoquinones (quinonoid constituents) in Euclea species of South Africa

Four naphthoquinones namely 7-methyljuglone, diospyrin, neodiospyrin and isodiospyrin present in Euclea natalensis subsp. natalensis (Ebenaceae), have been found to have potent antituberculosis activity. A comparative study of these naphthoquinones was conducted in the different species of Euclea found in South Africa, in order to select a plant species with the highest concentration of naphthoquinones for preclinical studies. High performance liquid chromatography was used to quantify the concentration of each naphthoquinone. Isodiospyrin showed the best interday values with a relative error of 2.4% and diospyrin the lowest reproducibility with a relative error value of 13%. The intraday determination showed that isodiospyrin had the lowest reproducibility with a relative error of 13.6%, in contrast to 7-methyljuglone which exhibited satisfactory reproducibility with a relative error of 4.64%. The most potent antituberculosis compound, 7-methyljuglone was found in almost all species studied and the concentration ranged between 20 and 1,300 mg kg-1. The concentration of 7-methyljuglone was found to be the highest in E. pseudebenus. Of all the plants studied, only one of the E. pseudebenus specimens showed the presence of all four compounds in significant quantities. Variation observed with regard to the concentration of the four compounds in the different Euclea species could be due to the age of the roots harvested, wound, and environmental and/or other stress factors.