Seasonal variation of naphthoquinones in Euclea natalensis subspecies natalensis

Seasonal variation of naphthoquinones was investigated from eleven wild plants of Euclea natalensis A.DC. subsp. natalensis belonging to the same population. The study was carried out in Tembe National Park, KwaZulu-Natal, South Africa. Quantitative analysis of bioactive naphthoquinones (shinanolone, 7-methyljuglone, diospyrin, isodiospyrin and neodiospyrin) from the root extracts was conducted using High Performance Liquid Chromatography (HPLC). All these naphthoquinones have potent antituberculosis activity. The concentration of the best antituberculosis compound 7-methyljuglone, ranged from 0 g/kg to 3.77 g/kg between individuals of a population and among seasons. Highest amount of 7-methyljuglone was found in winter in most of the trees. Accumulation of isodiospyrin and neodiospyrin varied significantly with seasonal changes (P < 0.05). Maximum levels of isodiospyrin and neodiospyrin recorded per individual plant were 1.72 g/kg in summer and 0.48 g/kg in winter respectively. A statistically significant variation (P < 0.05) was established between the mean levels of diospyrin and seasonal changes. Diospyrin was detected at a mean concentration of 3.19 g/kg during spring, which was the highest mean value quantified in all the four seasons. The highest amount of diospyrin quantified per individual plant was 6.79 g/kg during spring. The study showed that there is tremendous variation in the accumulation of naphthoquinones by natural populations of E. natalensis subsp. natalensis. Depending on the requirement of a particular naphthoquinone for research, one could harvest the roots from a given population in seasons recommended from this study.