Plakortides, novel cyclic peroxides from the sponge Plakortis halichondrioides: Activators of cardiac SR-CA(2+)-pumping ATPase

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.