A New Ceramide (Rumexamide) and Other Chemical Constituents from <i>Rumex abyssinicus</i>Jacq (Polygonaceae): Isolation, Characterization, Antibacterial Activities and Chemophenetic Significance

The chemical study of Rumex abyssinicus Jacp (Polygonaceae) led to the isolation of a new ceramide named (R)-2'-hydroxy-N-[(2S,3S,4R,16E)-1,3,4-trihydroxyhexacos-16-en-2-yl]hexadecanamide (rumexamide) (1) together with sixteen known compounds: bis-(2-ethylhexyl) phthalate (2), chrysophanol (3), physcion (4), citreorosein (5), emodin (6), chrysophanein (7), physcionin (8), lupeol (9), 3β,28-dihydroxylup-20(29)-ene (10), 3β-dihydroxylup-20(29)-en-28-oic acid (11), oleanolic acid (12), ergosta-6,22-diene-3,5,8-triol (13), stigmastane-3,6-dione (14), a mixture of β-sitosterol (15) and stigmasterol (16), and stigmasterol 3-O-β-D-glucoside (17). Their structures were determined by interpretation of their spectroscopic 1D NMR (1H and 13C NMR), 2D NMR (COSY 1H-1H, HSQC and HMBC) data in conjunction with mass spectrometry (TOFESIMS and HR-TOFESIMS) and by comparison with those reported in the literature. Among all the known compounds, twelve (2, 5, 8-17) were firstly isolated from Rumex abyssinicus, seven (2, 10-14 and 17) from the genus Rumex and three (13, 14, 17) from family Polygonaceae. The in vitro antibacterial activities of extracts (MeOH, n-BuOH and EtOAc), as well as compounds 9, 11, 12, 15 + 16 and 17 against pathogenic bacteria (Staphylococcus aureus ATCC 43300, Shigella flexneri NR 518, Klebsiella pneumoniae ATCC 700603, Escherichia coli ATCC 25922), were performed using the broth microdilution method and the results show that, extracts were not active (MIC > 1000 μg/mL) while compounds were weakly or not active (MIC ≥ 500 μg/mL) against all bacteria strains. Furthermore, the chemophenetic relationships of the isolated compounds and their significances were discussed.