New bioactive cyclic peroxides from the Caribbean marine sponge Plakortis zyggompha

The new plakortide Q () has been isolated from the little studied marine sponge Plakortis zyggompha, together with the six new cyclic peroxide analogues in their methyl ester forms . Their structure was fully elucidated through NMR and MS analyses and the relative stereochemistry of the 1,2-dioxane ring was established after interpretation of the coupling constant values and the NOESY data. The carboxylic acid function of these compounds was proved to be very reactive and methylation was found to take place during the purification process. The non-esterified peroxides exhibited more cytotoxic activity against human tumor cell lines than their corresponding methyl esters.