Absolute Configuration of the New 3-epi-cladocroic Acid from the Mediterranean Sponge Haliclona fulva

The marine sponge Haliclona fulva (previously described as Reniera fulva) is widespread in the Mediterranean Sea. The chemical study of the sponge led to the isolation and identification of a new compound: 3-epi-cladocroic acid (1) alongside the previously reported cladocroic acid (2) and some other known compounds previously isolated. The structure was fully determined on the basis of extensive analysis by 1D and 2D NMR, as well as GC-MS/MS. The absolute configuration was determined by comparison of the experimental electronic circular dichroism (ECD) spectra with theoretically calculated spectra; these results may be extended to other asymetric cyclopropane carboxylic acids.