Antimicrobial constituents from the African medicinal plant Zanthoxylum capense

The genus Zanthoxylum, comprising approximately 250 species, is well known for its ethnobotanical uses among Rutaceae family [1]. Previous studies have demonstrated that plants belonging to this genus are rich sources of biologically active compounds, such as alkaloids, aliphatic and aromatic amides, coumarins, as well as lignans [2]. Zanthoxylum capense (Thunb.) Harv. is a medicinal plant indigenous to Zimbabwe, South Africa, and Mozambique. Traditional healers use the decoction of its roots for snakebites, and the decoction of its root barks to treat tuberculosis, paralysis, and relief of toothache. However, until date there have been relatively few phytochemical studies on this species [3, 4]. During our search for bioactive compounds from the methanolic extract of Z. capense roots, we have isolated a new benzophenanthridine alkaloid and two new 2-arylbenzofuran neolignans. In addition, several known compounds were also isolated, including six alkaloids with the benzophenanthridine scaffold, one furoquinoline-type alkaloid and a lignan. The structures of the compounds were elucidated by means of MS, extensive 1D and 2D-NMR analyses and by comparison of their physical and spectroscopic data with those reported in the literature. All the isolated compounds were evaluated for their in vitro antibacterial activity against Gram-positive and Gram-negative bacteria. Some compounds showed inhibitory activity mainly against Staphylococcus aureus ATCC 6538 with MIC values ranging from 12.5 to 50µg/mL. These compounds might be promising leads for the development of new antimicrobials.

Acknowledgement: This study was supported by a fellowship from FCT, Portugal (reference number SFRH/BPD/37179/2007).

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