| Summary: | The mangrove ecosystem is a rich resource for the discovery of actinomycetes with potential applications in pharmaceutical science. Besides the genus <i>Streptomyces</i>, <i>Micromonospora</i> is also a source of new bioactive agents. We screened <i>Micromonospora</i> from the rhizosphere soil of mangrove plants in Fujian province, China, and 51 strains were obtained. Among them, the extracts of 12 isolates inhibited the growth of human lung carcinoma A549 cells. Strain 110B exhibited better cytotoxic activity, and its bioactive constituents were investigated. Consequently, three new isoflavonoid glycosides, daidzein-4′-(2-deoxy-<i>α</i>-<span style="font-variant: small-caps;">l</span>-fucopyranoside) (<b>1</b>), daidzein-7-(2-deoxy-<i>α</i>-<span style="font-variant: small-caps;">l</span>-fucopyranoside) (<b>2</b>), and daidzein-4′,7-di-(2-deoxy-<i>α</i>-<span style="font-variant: small-caps;">l</span>-fucopyranoside) (<b>3</b>) were isolated from the fermentation broth of strain 110B. The structures of the new compounds were determined by spectroscopic methods, including 1D and 2D nuclear magnetic resonance (NMR) and high-resolution electrospray ionization mass spectrometry (HR-ESIMS). The result of medium-changing experiments implicated that these new compounds were microbial biotransformation products of strain <i>M. aurantiaca</i> 110B. The three compounds displayed moderate cytotoxic activity to the human lung carcinoma cell line A549, hepatocellular liver carcinoma cell line HepG2, and the human colon tumor cell line HCT116, whereas none of them showed antifungal or antibacterial activities.
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