| Summary: | Four new chlorinated cycloaromatized enediyne compounds, jejucarbosides B–E (<b>1</b>–<b>4</b>), were discovered together with previously-identified jejucarboside A from a marine actinomycete strain. Compounds <b>1</b>–<b>4</b> were identified as new chlorinated cyclopenta[<i>a</i>]indene glycosides based on 1D and 2D nuclear magnetic resonance, high-resolution mass spectrometry, and circular dichroism (CD) spectra. Jejucarbosides B and E bear a carbonate functional group whereas jejucarbosides C and D are variants possessing 1,2-diol by losing the carbonate functionality. It is proposed that the production of <b>1</b>–<b>4</b> occurs via Bergman cycloaromatization capturing Cl<sup>-</sup> and H<sup>+</sup> in the alternative positions of a <i>p</i>-benzyne intermediate derived from a 9-membered enediyne core. Jejucarboside E (<b>4</b>) displayed significant cytotoxicity against human cancer cell lines including SNU-638, SK-HEP-1, A549, HCT116, and MDA-MB-231, with IC<sub>50</sub> values of 0.31, 0.40, 0.25, 0.29, and 0.48 μM, respectively, while jejucarbosides B–D (<b>1</b>–<b>3</b>) showed moderate or no cytotoxic effects.
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