Ultra-short peptides have great promise in anticancer therapy due to their unique properties and recent progress in biotechnology that help overcome the limitations of peptides and realize their full potential. Short peptides combine the advantages of traditional small molecules and macromolecules, i.e. greater conformational rigidity, stability, bioactivity, bioavailability, tissue specificity, selectivity, permeability through cell membranes, faster biological effect, biocompatibility, biodegradability, lower toxicity, and immunogenicity, easier and cheaper for large synthesis scale. The main disadvantages of peptides include high conformational freedom, short half-life in vivo, and low bioavailability. Modulating intramolecular interactions forming pseudo-cyclic systems is an attractive approach to precisely control conformation and interaction with the appropriate receptor. These interactions increase both in vivo stability and permeability across cell membranes and into target cells. Our studies concentrate on the development of ultra-short peptides that are able to form pseudo-cyclic systems/synthons via intramolecular interactions. In addition, these systems can be stabilized by weak π-based intramolecular interactions. The interactions play a role in protecting the polar group (in this case - peptide bond). Thus, these compounds can be useful in research on molecules that can adapt the particles to the environment (molecular chameleons) - when the closed/cyclic form is preferred in an apolar environment, e.g. inside a cell membrane, and the open one - in an aqueous medium. On the poster, we will present the results of our studies on the development and characterization of these peptides in detail. We will focus on discussing the new synthons - pseudo-(bi)cyclic systems via intramolecular interactions in the rational design of a new generation of safe and effective theranostics.