Antifungal cyclic peptides from the marine sponge .

Screening natural product extracts from the National Cancer Institute Open Repository for antifungal discovery afforded hits for bioassay-guided fractionation. Using LC-MS analysis to generate chemical structure information on potentially active compounds, two new cyclic hexapeptides, microsclerodermins J () and K (), were isolated from the deep-water sponge , along with microsclerodermins A () and B (), previously isolated from an unidentified species. The structures of the new compounds were elucidated by spectroscopic analysis and chemical methods. In vitro antifungal testing showed that the four compounds possessed strong activities against the opportunistic fungal pathogens , C, and .