Papuamides E and F, cytotoxic depsipeptides from the marine sponge Melophlus sp.

Two known papuamides C (1) and D (2) together with two new depsipeptides, papuamides E (3) and F (4), were isolated from an undescribed sponge of the genus Melophlus collected in the Solomon Islands. The planar structures of the compounds were elucidated on the basis of spectroscopic studies. Papuamides C–F (1–4) showed cytotoxicity against brine shrimp with LD50 values between 92 and 106 μg/mL.