Euryjanicin A: a new cycloheptapeptide from the Caribbean marine sponge Prosuberites laughlini.

A new proline-containing cycloheptapeptide, euryjanicin A (1), has been isolated from the marine sponge Prosuberites laughlini indigenous to Puerto Rico, and its structure established by an X-ray crystal structure determination. The absolute configuration of each amino acid residue was determined by Marfey's method.