Microsclerodermins F–I, Antitumor and Antifungal Cyclic Peptides from the Lithistid Sponge Microscleroderma sp

Four new cyclic peptides, microsclerodermins F–I (6–9), were isolated from the deep water lithistid sponge Microscleroderma sp. from Palau. Their structures, which incorporate an unusual long chain β-amino acid, were elucidated using spectroscopic methods and chemical degradation.