Discovery of Kebanmycins with Antibacterial and Cytotoxic Activities from the Mangrove-Derived sp. SCSIO 40068.

Mangrove derived actinomycetes are a rich reservoir of bioactive natural products and play important roles in pharmaceutical chemistry. In a screen of actinomycetes from mangrove rhizosphere sedimental environments, the isolated strain sp. SCSIO 40068 displayed strong antibacterial activity. Further fractionation of the extract yielded four new compounds kebanmycins A-D (-) and two known analogues FD-594 () and the aglycon (). The structures of - were determined based on extensive spectroscopic data and single-crystal X-ray diffraction analysis. - featured a fused pyranonaphthaxanthene as an integral part of a 6/6/6/6/6/6 polycyclic motif, and showed bioactivity against a series of Gram-positive bacteria and cytotoxicity to several human tumor cells. In addition, the kebanmycins biosynthetic gene cluster () was identified in sp. SCSIO 40068, and KebMT2 was biochemically characterized as a tailoring sugar--methyltransferase, leading to a proposed biosynthetic route to -. This study paves the way to further investigate as a potential lead compound.