Prochloron didemni, an obligate symbiont of certain ascidians (sea squirts found in tropical areas), produces various cyclic pseudo-octapeptides in large quantities. These secondary metabolites have attracted the attention of medicinal chemists and, due to their four azol(in)e and four amide donor groups, coordination chemists have become interested in these molecules. The structures of the metal-free macrocycles and their dinuclear copper(II) complexes are known, and solution …