The cyanobacterium Prochloron didemni, an obligate symbiont of different species of colonial ascidians, occurring in the Pacific and Indian Oceans, produces a variety of cyclic peptides. These patellamide-type macrocycles lead to relatively stable dicopper(II) complexes that are extremely efficient carbonic anhydrase mimics, the most active model systems known so far. Importantly, it recently was shown that copper(II) is coordinated to patellamide derivatives in Prochloron cells. An …