2,3-Seco-2,3-dioxo-lyngbyatoxin A from a Red Sea strain of the marine cyanobacterium <i>Moorea producens</i>

<div><p>Chemical investigation of the organic extract of a Red Sea strain of the cyanobacterium <i>Moorea producens</i> has afforded 2,3-seco-2,3-dioxo-lyngbyatoxin A (<b>1</b>). Five known compounds including lyngbyatoxin A (<b>2</b>), majusculamides A and B (<b>3</b> and <b>4</b>), aplysiatoxin (<b>5</b>) and debromoaplysiatoxin (<b>6</b>) were also isolated. Their structures were elucidated by using HR-FAB-MS, 1D and 2D NMR analyses. The compounds were evaluated for antiproliferative activity against HeLa cancer cells. Lyngbyatoxin A (<b>2</b>) showed potent activity, with an IC₅₀ of 9.2 nM, while <b>5</b> and <b>6</b> displayed modest activity with IC₅₀ values of 13.3 and 3.03 μM, respectively. In contrast, compounds <b>1</b>, <b>3</b> and <b>4</b> were inactive, with IC₅₀ values greater than 50 μM. The lack of cytotoxicity for 2,3-seco-2,3-dioxo-lyngbyatoxin A (<b>1</b>) demonstrates that the indole moiety in lyngbyatoxin (<b>2</b>) is essential for its cytotoxicity, and suggests that detoxification of <b>2</b> may be carried out by biological oxidation of the indole moiety to yield <b>1</b>.</p>