RAFANOMEZANTSOA

Chemical and biological investigation of the Madagascar endemic plant Saldinia proboscidea led to the isolation of an isomer of artemisinin, (−)-6-epi-artemisinin (2). Its structure was elucidated using a combination of NMR and mass spectrometry. The absolute configuration was established by chemical syntheses of compound 2 as well as a new stereoisomer (3). The comparable bioactivities of artemisinin (1) and its isomer (−)-6-epi-artemisinin (2) revealed that this change in configuration was not critical to their biological properties. Bioactivity was assessed using an apoptosis induction assay, a SARS-CoV-2 inhibitor assay, and a haematin polymerization inhibitory activity (HPIA) assay. This is the first report of an artemisinin-related compound from a genus not belonging to Artemisia and it is the first isolation of an artemisinin-related natural product that is the opposite enantiomeric series relative to artemisinin from Artemisia annua.

Senecio gossypinus Bakeris an endemic species encountered in the northern, southern, western and central parts of Madagascar. Phytochemical screening of the EtOH extract from the leaves revealed the presence of flavonoids, sterols and polysaccharides. Fractionation of the hexane and EtOAc extracts led to the isolation of the mixture of a-amyrin (1) and b-amyrin (2), and kaempferol-3-O-α-L-arabinopyranoside (3), respectively. Compound 3 exhibited potent antimicrobial activity in vitro against Pseudomonas aeruginosa, Proteus mirabilis, Streptococcus agalactiea, Staphylococcus aureus, Candida albicans with inhibition zones of 13mm, 19mm, 15mm, 12mm and 9mm, respectively, at a test dose of 10 µg/disk using the disk diffusion method. Moreover, compound 3 showed moderate antioxidant activity against the free radical DDPH with an IC50 value of 1.90mg/mL. These results gave support to the traditional uses of the studied plant for the treatment of colic, bronchitis and wounds.

New cardenolide 1 and two known compounds oleanan-3-one 2 and sucrose have been isolated from the aerial parts of Brachyleana Merana (Asteraceae) an endemic species from Madagascar. Structure elucidations of the compounds were elucidated through spectroscopic methods (1-D and 2-D NMR, ESI-MS) chemical methods and comparison with literature data.