A correlation between plant growth and accumulation of naphthoquinones (shinanolone (1), 7-methyljuglone (2) and diospyrin (3)) was investigated in seeds and seedlings of Euclea natalensis A.DC. In this study, the seeds represented the first stage whereas the second seedling stage was defined as the stage, when the radicles were about 6 cm in length. The lengths of the seedlings at the third, fourth and fifth seedling stages were 9 cm, 12 cm and 16 cm respectively. Plant materials collected from the five seedling stages were separately extracted using chloroform and the naphthoquinones were then quantified by means of High Performance Liquid Chromatography (HPLC). Shinanolone (1), which was the only naphthoquinone detectible from seeds, accumulated at variable rates (P < 0.01) and no trend could be established between its synthesis and seedling growth. The content of shinanolone (1) ranged from 87.5 mg/kg in seeds (first stage) to a high mean value of 1047 mg/kg during the fourth seedling stage. A significant correlation (P < 0.01) was found between the mean concentrations of 7-methyljuglone (2) and seedling growth. 7-Methyljuglone (2) was quantified at a high mean level of 5003 mg/kg during the third seedling stage and was not detected from the seed samples. A positive correlation (P < 0.01) was established between the concentration of diospyrin (3) and seedling stages. Diospyrin (3) was detected at an elevated mean concentration of 6182 mg/kg during the fifth seedling stage, which was higher than the other quantified naphthoquinones.

The isolation and antimycobacterial activity of several naphthoquinones from Euclea natalensis were previously reported and initiated this study into the occurrence, chemistry and biological activity of this class of compounds. The structure activity relationship of the isolated naphthoquinones, and commercially available derivatives were also studied. Several plant species were investigated to establish a possible link between their traditional use for chest related symptoms (including tuberculosis infection) and the occurrence of 7-methyljuglone in these plants. The plants were extracted and tested qualitatively with the use of three analytical tools for the presence of 7-methyljuglone or related naphthoquinones. Due to its commercial unavailability, the chemical synthesis of two of these naphthoquinones, 7-methyljuglone and diospyrin, was attempted with varying degrees of success. The Friedel-Crafts acylation method was used to synthesise 7-methyljuglone from m-cresol and maleic anhydride as starting material. The optimisation of the synthesis was also investigated. Through a two-step pathway of epoxidation and steam distillation, diospyrin was successfully synthesised albeit in small quantities. During the attempts to synthesise diospyrin, two other related compounds were also synthesised. These compounds, neodiospyrin and mamegakinone, are structural isomers of diospyrin. The stability of some of the naphthoquinones was tested in various carriers in an attempt to explain the influence this will have on the obtained antituberculosis and toxicity data. The BACTEC vial solution, which is widely used to determine potency against Mycobacterium tuberculosis, was analysed with HPLC to determine the stability of these compounds in it. In addition the stability in organic solvents especially DMSO, was also tested as this is the solvent of choice for hydrophobic compounds in almost all bioassays. The antituberculosis activity and/or toxicity of 7-methyljuglone was investigated with three bioassays, to broaden our knowledge on the mechanism of action of naphthoquinones. Vero cells were employed to determine the inhibitory concentration (IC50) of most of the naphthoquinones. Mice experiments were carried out to determine the toxicity of 7-methyljuglone and diospyrin in vivo. In addition the lead compound, 7-methyljuglone, was tested on Musca domestica (house fly) to establish its toxicity on this organism. In order to find the pharmacophore of this class of compounds, a preliminary structure-activity relationship was conducted. During this study the active site in the compounds which confers potency and toxicity was partly established. The mode of action of some of the naphthoquinones was investigated and it was established that the compounds might interfere with the mycobacterial electron transport chain. A fluorinated 7-methyljuglone stops the production of menaquinone which transports electrons from the NADH dehydrogenase complex to the cytochrome bc complex and effectively kills the mycobacterium. / Thesis (PhD (Botany))--University of Pretoria, 2007. / Plant Science / unrestricted