Preulithiacyclamide, a New Cyclic Peptide from the Ascidian Lissoclinum patella

Bioassay-guided fractionation of the ethyl acetate extract of the tunicate Lissoclinum patella, collected in the Republic of Palau, yielded six known compounds reported previously from L. patella plus a new cyclic peptide, preulithiacyclamide (2), whose structure was determined primarily by interpretation of spectral data. Of the seven compounds, ulithiacyclamide (1) was found to be the most potent inhibitor of the Macrophage Scavenger Receptor (MSR) with an IC50 of 98 nM.