A cyclic organic compound which comprises 16 amino acids or 17 amino acids and has no carboxyl group C-terminally and/or no amino group N-terminally. Optionally, one of the amino acids is a nonnatural amino acid. The ring closure is formed between a side chain of one amino acid and the C-terminus of another amino acid, or the ring closure is effected with the aid of a nonnatural amino acid. A process for producing and using the compound for regulating vectorial ion channels, for treating diseases associated with the lung function and for treating oedemas is provided.
