Contribution aux études phytochimique et biologique de Psorospermum aurantiacum Engl. (Hypericaceae) et Symphonia globulifera L.f (Clusiaceae).

Abstract

The work undertaken as part of this thesis focuses on the phytochemical and biological studies of two medicinal plants: the stems (bark and wood) of Psorospermum aurantiacum Engl. (Hypericaceae) and the leaves of Symphonia globulifera L.f. (Clusiaceae). Leaves of Symphonia globulifera have been harvested, dried, ground and extracted with methanol. Purification of the extract with a combination of chromatographic methods has led to fourteen (14) pure compounds, the structures of which have been obtained by spectrometric and spectroscopic methods (MS, NMR 1D and 2D). It is about: five flavonoids (5,7-dihydroxy-3(-4-hydroxyphenyl) chromen-4-one 86, 4-hydroxy-7-methoxyisoflavone 87, 5,7,4'- trihydroxy-2-phenylchromen-4-one 84, 3,5,7,4'-tetrahydroxy-2-phenylchromen-4-one 85 and (+)-epi-catechin 94), three biflavonoids (4',4''',5,5'',7,7''-hexahydroxy-2,2''-bis(4-hydroxyphenyl)-3',6''-bis(4H -1-benzopyran)-4,4'-dione 89, 4',4''',5,5'',7,-pentahydroxy-7''-Omethyl-3',6''-biflavone 96 and Amentoflavone 97), one xanthone (1,5-dihydroxyxanthone 88); one lanostane (3,15-dihydroxylanosta-7,9(11),24-triene 91), two polysteroids (stigmasterol glucoside 92 and β-sitosterol glucoside 93), friedelane 95 described for the first time and a new bisxanthone 90.Extraction of the stems of Psorospermum aurantiacum yielded a methanol extract and an ethyl acetate fraction. The ethyl acetate fraction left over gave after purification with combined chromatographic methods, six (6) pure compounds the structures of which were established using spectrometric and spectroscopic methods (MS, NMR 1D and 2D). They are: two xanthones (1,5,6-trihydroxy-7-methoxyxanthone 78 and 1,7-dihydroxyxanthone 79), three lupane-type triterpenes (betulin 80, lupeol 82 and betulinic acid 83), one new xanthonolignoid (cadensin H 81). The structure of known compounds has been confirmed by a comparison of their spectral data with literature. All the chemical constituents of Symphonia globulifera tested on bacterial strains have shown no antibacterial activity (MIC above 200 μg/mL). Compound 7''-Omethoxyrobustaflavone 96 was the only one to show antioxidant activity. The methanolic extract of Psorospermum aurantiacum showed antibacterial activity against Shigella flexneri, Staphylococcus aureus methicilline resistant, taphylococcus aureus, Salmonella typhi and Escherichia coli with MIC of 125 to 500 μg/mL and MBC of 500 μg/mL against Staphylococcus aureus, Salmonella typhi and Escherichia coli strains. The ethyl acetate fraction has activity against S. flexneri, S. aureus methicilline resistant, S. aureus, Salmonella typhi, Escherichia coli strains with MIC of 250 to 1000 μg/mL and MBC of 500 to 1000 μg/mL on S. flexneri, S. aureus and E. coli strains. Thèse de doctorat /Ph.D. de TENE Dénis-Grégoire 2022/2023 xxv Among all the compounds isolated from ethyl acetate fraction, only1,5,6-trihydroxy-7- methoxyxanthone 78 had an antibacterial activity on all strains mentioned above with MIC of 12.5 to 50 μg/mL and MBC of 25 μg/mL on S. aureus methicilline resistant and of 100 μg/mL on Escherichia coli. This same xanthone showed notable antioxidant activity. In view of these results, we can deduce that the multiple uses in traditional medicine of P. aurantiacum, would be due to the presence of this compound endowed with biological activities that we have just described. These findings could be exploited to justify the use of this plant in the treatment of infectious diseases in traditional medicine, especially against diarrhea and venereal infections.