Eight new ent-beyerane metabolites, 5-8, 12, and 14-16, and four new ent-kaurane metabolites, 3, 10, 11, and 13, together with two known metabolites, 4 and 9, were isolated from the microbial transformations of steviol-16α,17-epoxide using Streptomyces griseus ATCC 10137 and Cunninghamella bainieri ATCC 9244. The structures of the metabolites were characterized by IR, HRFABMS, and 1D and 2D NMR data. In addition, a GRE (glucocorticoid response element)-mediated luciferase reporter assay was used to initially screen for the biological activity of the 11 metabolites and stevioside. Steviol (1), steviol-16α,17-epoxide (2), ent-11α,13, 16α,17-tetrahydroxykauran-19-oic acid (3), ent-17-hydroxy-16-ketobeyeran- 19-oic acid (4), ent-9α,13-dihydroxy-16β,17-epoxykauran-19-oic acid (10), ent-9β,17-dihydroxy-16-ketobeyeran-19-oic acid (12), ent-1β,17-dihydroxy-16-ketobeyeran-19-oic acid (14), and stevioside showed significant effects; in particular, stevioside showed almost equal potency as dexamethasone.
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