Plakortides, Novel Cyclic Peroxides from the Sponge Plakortis halichondrioides: Activators of Cardiac SR-CA2+-Pumping ATPase

Abstract
As part of a search for novel activators of Ca2+ pumping activity of cardiac SR- (sarcoplasmic reticulum), the EtOAc extract of the Jamaican sponge Plakortis halichondrioides was shown to be active. Bioassay-guided fractionation of the extract followed by preparative TLC and HPLC yielded several known and novel compounds. Three of the novel cyclic peroxides, plakortides F, G, and H (3, 4, and 5) are the subject of this report. Their structures including relative stereochemistry were established by interpretation of spectral data. Micromolar concentrations of plakortides F−H (3−5) were found to significantly enhance Ca2+ uptake by SR.