Metabolites from Withania aristata with potential phytotoxic activity.

A series of apocarotenoids (1-8) and one carotenoid (9) were isolated from the leaves of Withania aristata. In addition, the tetraacetylated apocarotenoid glucosides 10-12 were obtained by acetylation, with derivative 9-hydroxymegastigma-4,6E-dien-3-one 9-O-beta-D-glucopyranoside tetraacetate (10) being described for the first time. The structures have been determined by spectroscopic and spectrometric means, mainly NMR and ESI-MS, and comparison with data reported in the literature. These metabolites were evaluated on a systematic phytotoxicity assay using the etiolated wheat coleoptile bioassay. Compounds 1-3, 9 and 12 were further assayed for their phytotoxicity on the target species Lepidium sativum, Lactuca sativa, Lycopersicum esculentum and Allium cepa. Among the assayed compounds, lutein (9) showed the most significant values for phytotoxicity, followed by the non-glycosylated apocarotenoids (6S, 9R)-vomifoliol (1) and 9-hydroxymegastigma-4,6E-dien-3-one (2).