Two diastereomers of 24-O-methylmanoalide (1 and 2) and (6Z)-neomanoalide-24,25-diacetate (3) were isolated together with manoalide (4), seco-manoalide (5), (4E,6E)-dehydromanoalide (6) and manoalide-25-acetate (7) from a marine sponge Luffariella sp. collected in Palau. Two methyl ethers of manoalide (1 and 2) were revealed to be derived from manoalide, the main component of the extract, during the separation procedure. The stereochemistries of 1 (24R) and 2 (24S) were assigned based on the NOESY data for 2 and two 24,25-di-O-methylmanoalides (8 and 9), synthesized from 1 and 2. Although 3 has been chemically transformed from (6Z)-neomanoalide, this is the first report of the isolation of this compound from a marine sponge. Compounds 1, 2, 4, 5 and 7 showed an antibacterial activity against Staphylococcus aureus at 5-10 μg, while 3, 8 and 9 were not active at 50 μg.
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