Netamines H–N, Tricyclic Alkaloids from the Marine Sponge <i>Biemna laboutei</i> and Their Antimalarial Activity

Chemical examination of the CH₂Cl₂–MeOH (1:1) extract of the Madagascar sponge <i>Biemna laboutei</i> resulted in the isolation of seven new tricyclic alkaloids, netamines H–N (<b>1</b>–<b>7</b>), along with the known netamine G and mirabilins A, C, and F. Their structures were elucidated by interpretation of 1D and 2D NMR spectra and HRESIMS data. All compounds were evaluated for their cytotoxicity against KB cells and their antiplasmodial activity. Netamine M (<b>6</b>) was found to be cytotoxic, with an IC₅₀ value in the micromolar range, and netamine K (<b>4</b>) exhibited activity against <i>Plasmodium falciparum</i> with an IC₅₀ value of 2.4 μM