A new phenanthrene derivative from Entada abyssinica with antimicrobial and antioxidant properties

Entada abyssinica Steud. Ex A. Rich (Leguminosae) is a medicinal plant used traditionally for the treatment of infections. A phytochemical investigation of the methanol extract of E. abyssinica root bark led to the isolation of a new phenanthrene derivative named phenentada (1), together with seven known compounds (8 S, 13 E)-kolavic acid 15-methyl ester (2) and 8 S-kolavic acid 15-methyl ester (3) obtained as mixture, 8 S-kolavic acid 15-methyl ester (3), 8 S-kolavic acid 18-methyl ester (4), 13,14,15,16-tetranorclerod-3-ene-12,18-dioic acid (5), 1′,26′-bis-[(S)-2,3-dihydroxypropyl] hexacosanedioate (6), campesterol (7) and 3-O-β -d-glucopyranosylstigmasterol (8). Their structures were determined by NMR spectroscopy (1D and 2D), mass spectrometry (HRESIMS) and by comparison with previously reported data. The crude extract and some isolated compounds were evaluated for their in vitro antimicrobial activities by the microdilution method while, the antioxidant activity was evaluated by the DPPH methods. Regarding the antimicrobial activity, the crude extract showed significant inhibitory activities against bacteria strains (MIC 7.81–31.3 μg mL⁻¹) and yeasts (MIC 15.6–31.3 μg mL⁻¹) whereas all compounds tested exhibited significant activity against Staphylococcus epidermidis. Moreover, compounds 4, 5 and 6 and the mixture 2/3 showed significant antimicrobial activity on Candida parapsilosis strain (MIC = 3.12 μg mL⁻¹), as well as selected antifungal property against candida pathogenic fungi strains. On the other hand, compounds (1) demonstrated the best bioactivities against Candida albicans and Salmonella enterica with MIC = 3.12 μg mL⁻¹ while the mixture 2/3 appeared to have the highest inhibition on gram (+) bacteria strain S. epidermidis with MIC of 0.78 μg mL⁻¹ and compound 5 (MIC = 1.56 μg mL⁻¹) against the gram (−) bacteria strain. Furthermore, the SC₅₀ values measured by the antioxidant test for all samples varied between 47.21 and 52.44 μg mL⁻¹ for DPPH. These results support the traditional uses of E. abyssinica in the management of several diseases including the claim in the skin disease treatment. Additionally, here is reported the first time isolation of a phenanthrene derivative in the Fabaceae family to the best of our knowledge.