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• A total of 13 compounds were identified from the leaves and twigs of Lobostemon fruticosus. • LC–LTQ-Orbitrap mass spectrometry method was established for identification and quantification of the constituents. • The anti-inflammatory activities of isolated compounds were assessed by measuring the levels of cytokines IL-1β, IL-2, IL-6, GM-CSF and TNF-α. • All the tested compounds and the extract decrease the release of the tested cytokines compared to LPS control. Lobostemon fruticosus is South Africa medicinal plant traditionally used in treatment of wounds and skin diseases. Nevertheless, there is no report on its phytochemical constituents. LC–LTQ-Orbitrap mass spectrometry was used for identification and quantification of its constituents. A total of 13 compounds were identified from the leaves and twigs of the plant using NMR, ESI-HRMS and reference substances. The identified compounds were p -hydroxybenzoic acid (1), lycopsamine-N-oxide (2), caffeic acid (3), loliolide (4), 3-indolcarbaldehyde (5), globoidnan B (6), rabdosiin (7), syringaresinol (8), pinoresinol (9), rutin (10), rosmarinic acid (11), keampferol-3- O -rutinoside (12) and globoidnan A (13). In addition, quantitative determination of 6 marker compounds in samples from 12 different locations in South Africa was established. Rosmarinic acid and globoidnan A were found in large amount in the leaves and flowers of the plant. Samples from West Cape contained relatively greater amount of the tested compounds per dry weight than the other samples. The anti-inflammatory activities of isolated compounds were assessed by measuring the levels of cytokines IL-1β, IL-2, IL-6, GM-CSF and TNF-α in the supernatant media of human peripheral blood mononuclear cells (PBMCs) stimulated by lipopolysaccharide (LPS). At a concentration of 100 μM, compounds 7, 8 and 11 significantly decreased secretion of IL-1β, IL-2 and IL-6 compared to the LPS treated control (0.76–57.6%). All compounds significantly reduced the production of TNF-alpha compared to the LPS treated control (0.17–12.2%) and reference drug ibuprofen. [ABSTRACT FROM AUTHOR]

• Chemical investigation on the leaves of Melianthus comosus resulted in the isolation of six bufadienolides. • The configurations were determined from single crystal X-ray crystallography and NOESY correlations. • The isolated compounds displayed strong cytotoxicity against MCF-7, CCRF-CEM, and CEM/ADR5000 cancer cell lines. • Compound 1 showed the strongest activity. From the leaves of South African medicinal plant Melianthus comosus , four previously undescribed bufadienolides, 16β-formyloxymelianthugenin (1), 2β-acetoxymelianthusigenin (2), 2β-hydroxy-3β,5β-di- O -acetylhellebrigenin (3), and 2β-acetoxy-5β- O -acetylhellebrigenin (4) were isolated together with two known bufadienolides. The structural elucidation of the compounds was based on 1D and 2D NMR spectroscopy, high-resolution mass spectrometry, and other spectroscopic methods. The relative configurations were determined by single-crystal X-ray crystallography analysis and NOESY correlations. The isolated compounds displayed strong cytotoxicity against MCF-7 breast cancer cells, sensitive CCRF-CEM and multidrug-resistant CEM/ADR5000 leukemia cells. Compound 1 showed the most potent activity, with IC 50 values of 0.07 μM towards CCRF-CEM, 0.06 μM towards CEM/ADR5000 and 0.36 μM towards MCF-7 followed by compound 4 with IC 50 values of 0.13 μM towards CCRF-CEM, 0.08 μM towards CEM/ADR5000 and 0.53 μM towards MCF-7. [ABSTRACT FROM AUTHOR]