| Summary: | <i>Latrunculia</i> sponges represent a rich source of discorhabdin-type pyrroloiminoquinone alkaloids, a few of which comprise a dimeric structure. The anticancer-activity-guided isolation of the <i>n</i>-hexane subextract of the Antarctic deep-sea sponge <i>Latrunculia biformis</i> yielded the known compound (−)-(1<i>R</i>,2<i>R</i>,6<i>R</i>,8<i>S</i>,6’<i>S</i>)-discorhabdin B dimer (<b>1</b>) and two new derivatives, (−)-(1<i>S</i>,2<i>R</i>,6<i>R</i>,8<i>S</i>,6’<i>S</i>)-discorhabdin B dimer (<b>2</b>) and (−)-(1<i>R</i>,2<i>R</i>,6<i>R</i>,8<i>S</i>,6’<i>S</i>)-16’,17’-dehydrodiscorhabdin B dimer (<b>3</b>). The chemical structures of compounds <b>1</b>−<b>3</b> were elucidated by means of HR-ESIMS, NMR, [α]<sub>D</sub>, ECD spectroscopy, and a comparison with the previously reported discorhabdin analogs. Compounds <b>1</b> and <b>2</b> showed significant in vitro anticancer activity against the human colon cancer cell line (HCT-116), with IC<sub>50</sub> values of 0.16 and 2.01 µM, respectively. Compared to monomeric discorhabdins, dimeric discorhabdins are very rare in Nature. This study adds two new discorhabdin dimers (<b>2</b> and <b>3</b>) to this small pyrroloiminoquinone subfamily. This is also the first report of compound <b>1</b> as a natural product and the first assessment of its in vitro anticancer activity.
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