Phytochemical investigation and antidiabetic activity of cissampelos capensis and strychnos henningsii the Eastern Cape medicinal plants

Diabetes mellitus is recorded as a significant health crisis in South Africa and various medicinal plants are used for the management of diabetes. However, the chemistry and bioactivity associated with these plants' antidiabetic activity are still lacking. Cissampelos capensis L.f. and Strychnos henningsii Gilg are among the plants utilised to manage diabetes in the Eastern Cape Province, South Africa. C. capensis and S. henningsii are known for their isoquinoline – and indole alkaloids, respectively. Other phytochemical groups associated with antidiabetic activity are the phenols, flavonoids, and terpenes. Thus, this study aimed to evaluate in-depth the phytochemical profiling, alkaloidal identification, and structural characterisation of phytochemicals isolated from these plants. Also, subsequent in vitro antidiabetic screening of the crude extracts and isolated compounds from both plants was done. The phytochemical profiling was performed by employing a qualitative and quantitative approach through high-performance thin layer chromatography (HPTLC) and UV-spectrometry. Further analysis for the identification of alkaloids was done by using LCMS. Fractionation and purification of crude extracts were achieved through crystallisation and various chromatographic techniques. NMR, HRMS, UV/Vis, FTIR, and XRD spectroscopic techniques were used to characterise isolated compounds. In vitro antidiabetic activity screening involved the investigation of cytotoxicity, antioxidant activity, alpha-amylase – and/or alpha-glucosidase inhibition (particular to type II diabetes). C. capensis and S. henningsii extracts tested positive for alkaloids, phenolics, flavonoids, and terpenes through HPTLC screening. Quantitative estimation by UV spectrometry of these phytochemical groups detected the highest concentration of alkaloids, followed by flavonoids, phenolics, and terpenes content. The in vitro antidiabetic biological screening of the various crude extracts suggested that the presence of alkaloids, flavonoids, phenolics, and terpenes fostered favourable biological activity. The LCMS of the known alkaloidal constituents from C. capensis detected the presence of ten alkaloids, including glaziovine, lauroscholtzine, pronuciferine and vi salutardine. Seven known alkaloids and one triterpene were detected from S. henningsii, including holtsiine, 23-hdroxyspermostrychnine, henningsiine, and the triterpene, friedelin. These findings suggest that C. capensis and S. henningsii have similar phytochemical constituents compared to the species reported in literature. However, the distribution of the phytochemicals in the various plant parts differed from previous accounts.Thesis (PhD) -- Faculty of Science,School of Biomecular and Chemical Sciences , 202