Zanthoxylum rhoifolium (Rutaceae) is a plant alkaloid that grows in South America and has been used in Brazilian traditional medicine for the treatment of different health problems. The present study was designed to evaluate the antimicrobial activity of the steam bark crude methanol extract, fractions, and pure alkaloids of Z. rhoifolium. Its stem bark extracts exhibited a broad spectrum of antimicrobial activity, ranging from 12.5 to 100 µg/mL using bioautography method, and from 125 to 500 µg/mL in the microdilution bioassay. From the dichloromethane basic fraction, three furoquinoline alkaloids (1–3), and nine benzophenanthridine alkaloids (4–12) were isolated and the antimicrobial activity of the benzophenanthridine alkaloids is discussed in terms of structure-activity relationships. The alkaloid with the widest spectrum of activity was chelerythrine (10), followed by avicine (12) and dihydrochelerythrine (4). The minimal inhibitory concentrations of chelerythrine, of 1.50 µg/mL for all bacteria tested, and between 3.12 and 6.25 µg/mL for the yeast tested, show this compound to be a more powerful antimicrobial agent when compared with the other active alkaloids isolated from Z. rhoifolium. To verify the potential importance of the methylenedioxy group (ring A) of these alkaloids, chelerythrine was selected to represent the remainder of the benzophenanthridine alkaloids isolated in this work and was subjected to a demethylation reaction giving derivative 14. Compared to chelerythrine, the derivative (14) was less active against the tested bacteria and fungi. Kinetic measurements of the bacteriolytic activities of chelerythrine against the bacteria Bacillus subtilis (Gram-positive) and Escherichia coli (Gram-negative) were determined by optical density based on real time assay, suggesting that its mechanism of action is not bacteriolytic. The present study did not detect hemolytic effects of chelerythrine on erythrocytes and found a protective effect considering the decrease in TBARS and AOPP (advanced oxidized protein products) levels when compared to the control group.
Two new dihydrobenzophenanthridine-type alkaloids, 6-methoxy dioxolo[4',5':4,5]benzo[c] dioxolo[4,5- j]phenanthridine (1) and 2,3,13-trimethoxy-5,11a-dihydro dioxolo[4',5':4,5]benzo[c]phenanthridine (2) were isolated from the stem bark of Zanthoxylum rhoifolium, together with four other previously known benzophenanthridine alkaloids, 6-acetonyldihydronitidine (3) [= 8-acetonyldihydronitidine], 6-acetonyldihydroavicine (4) [= 8-acetonyldihydroavicine], 6-acetonyldihydrochelerythrine (5) and xanthoxyline (6). The structures were elucidated mainly by spectroscopic methods, including 1D and 2D NMR spectroscopy. For alkaloids 1 and 2 we propose the trivial names rhoifolines A and B. The crude plant extracts and the alkaloids 3, 4 and 6 showed activity against Gram (+/-) bacteria, while the new alkaloids 1 and 2 were inactive.
The essential oils from the aerial parts of leaves, fruits and flowers of Zanthoxylum rhoifolium of Southern Brazil (Rio Grande do Sul), were analysed by GC, GC/MS, and chiral phase gas chromatography (CPGC). Forty-eight compounds were identified from the essential oils. The major constituents of the essential oil of the leaves were germacrene D (34 %) and bicyclogermacrene (23 %) and of the fruits, menth-2-en-1-ol (46.2 %), beta-myrcene (30.2 %), (-)-linalool (15 %) and (-)-alpha-terpineol (8.45 %). beta-Myrcene (65 %) and menth-2-en-1-ol (5.4 %) dominate the essential oil of the flowers. The oils of the leaves and fruits were bioactive with antibacterial activity against Staphylococcus aureus (Gram positive), and Klebsiella pneumoniae and Salmonella setubal bacteria (Gram negative) microorganisms, while the essential oil of the flowers was inactive.
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