Fifteen new stilbenoids including 11 phenylbenzofurans, the stemofurans A-K (1-11), and four dihydrostilbenes, the stilbostemins A (15), C (17), E (19), and F (20), were isolated and identified from a methanolic extract of Stemona collinsae roots together with five known derivatives, the stilbenes pinosylvin (13) and 4'-methylpinosylvin (14), the dihydrostilbenes, stilbostemins B (16) and D (18), and the dihydrophenanthrene racemosol (12) as well as (+)-sesamin, coniferyl alcohol, and stigmasterol. Bioautographic tests with Cladosporium herbarum displayed antifungal activity for stilbenoids of all four structural types. Ten derivatives were tested against five microfungi using the microdilution technique linked with digital image analysis of germ tubes.

ᮀ In plants, accumulation in specific compartments and huge structural diversity of secondary metabolites is one trait that is not understood yet. By exploring the diverse abiotic and biotic interactions of plants above-and belowground, we provide examples that are characterized by nonlinear effects of the secondary metabolites. We propose that redox chemistry, specifically the reduction of reactive oxygen species (ROS) and, in their absence, reduction of molecular oxygen by the identical secondary metabolite, is an important component of the hormetic effects caused by these compounds. This is illustrated for selected phenols, terpenoids, and alkaloids. The redox reactions are modulated by the variable availability of transition metals that serve as donors of electrons in a Fenton reaction mode. Low levels of ROS stimulate growth, cell differentiation, and stress resistance; high levels induce programmed cell death. We propose that provision of molecules that can participate in this redox chemistry is the raison d'être for secondary metabolites. In this context, the presence or absence of functional groups in the molecule is more essential than the whole structure. Accordingly, there exist no constraints that limit structural diversity. Redox chemistry is ubiquitous, from the atmosphere to the soil.

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Eight flavaglines, six cyclopenta[b]benzofurans, a cyclopenta[bc]benzopyran, and a benzo[b]oxepine, together with an aromatic butyrolactone were isolated from Aglaia odorata, A. elaeagnoidea, and A. edulis (Meliaceae) and tested against the three plant pathogens Pyricularia grisea, Fusarium avenaceum, and Alternaria citri for antifungal properties. Using the microdilution technique linked with digital image analysis of germ tubes, the benzofurans displayed strong activity, whereas the benzopyran, benzoxepine, and butyrolactone were inactive at the highest concentration tested. P. grisea, responsible for rice blast disease, was the most susceptible fungus against all benzofurans, with rocaglaol as the most active derivative. Based on EC(50), EC(90), and MIC values, the antifungal activity of rocaglaol was clearly higher than of the reference compounds, blasticidin S and Benlate.