Lehualides E−K, Cytotoxic Metabolites from the Tongan Marine Sponge <i>Plakortis</i> sp.

Spectroscopy-guided chemical analysis of a marine sponge from the genus <i>Plakortis</i>, collected in Tonga, yielded seven new metabolites of polyketide origin, lehualides E−K (<b>5</b>−<b>11</b>), four of which incorporate various sulfur functionalities. The structures of compounds <b>5</b>−<b>11</b> were elucidated by interpretation of spectroscopic data and spectral comparison with model compounds. The biological activities of compounds <b>6</b>−<b>9</b> were investigated against human promyeloid leukemic HL-60 cells and two yeast strains, wild-type and a drug-sensitive mutant.