Halichonadins A–D, new sesquiterpenoids from a sponge Halichondria sp.

A new dimeric sesquiterpenoid with two eudesmane skeletons through a urea linkage, halichonadin A (), as well as three new eudesmane sesquiterpenoids having a carbamate, an isonitrile, or an amino functionality, halichonadins B (), C (), and D (), respectively, have been isolated from a marine sponge Halichondria sp., and the gross structures and relative stereochemistry of were elucidated on the basis of spectral data and chemical means.