A phytochemical investigation of the roots and twigs of Penianthus zenkeri Diels led to the identification of twenty four compounds including one previously undescribed C-28 ecdysteroid (1) and previously described phytosteroids (2–5, 20, 22, 23), phenolic compounds (6–8, 12), diterpenoids (9–11), alkaloids (13,14, 18, 19), a dipeptide (15), ursane type triterpenoids (16–17), a carbohydrate (21) and a fatty alcohol (24). Three semi-synthetic derivatives (5b, 5a, 17a) obtained from acetylation and acetonidation of rubrosterone (5), and allylation of ursolic acid (17), respectively, are also reported. The chemical structures of the compounds were determined using 1D and 2D NMR spectral data, mass spectrometry and by comparison with the data reported in the literature. The absolute configuration of compound 9 was established using X-Ray and ECD analysis. Different extracts of the twigs and roots, compounds 2–4, 6–11, 15, and 17–21 were evaluated for their antibacterial, and cytotoxic activities. The twigs extract showed an antibacterial activity with an MIC of 62.5 μg/mol against Staphylococcus aureus ATCC 4300, while ursolic acid exhibited a moderate cytotoxicity with an IC50 of 50.9 μM. The chemotaxonomic relevance of the isolated compounds is discussed.
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