Clavatadines C-E, guanidine alkaloids from the Australian sponge Suberea clavata.

Three new marine alkaloids, clavatadines C-E (1-3), together with the three known compounds aerophobin 1 (4), purealdin L (5), and aplysinamisine II (6) were isolated from extracts of the sponge Suberea clavata by bioassay-guided fractionation using a serine protease factor XIa assay. Their structures were determined by 1D and 2D NMR spectroscopy. Compounds 1-6 exhibited weak inhibition of factor XIa.