Zeitschrift für Naturforschung. B, A journal of chemical sciences
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... reof, contained in this work. The citation of registered names, trade names, trademarks, etc. in this work does not imply, even in the absence of a specific statement, that such names are exempt from laws and regulations protecting trademarks etc. and therefore free for general use. PRINTING Franz X. Stückle Druck und Verlag e. K., Ettenheim COVER ILLUSTRATION Front Cover: The cyclic nonapeptides cyclo(Val-Leu-Pro-Ile-Leu-Leu-Leu-Val-Leu) (I) and cyclo(Val-Leu-Pro-Ala-Leu-Leu-Leu-Val-Leu) (II) were identified as promising candidates for the development as potential anti-cancer drugs. Their crystal structures were re-refinement of deposited single-crystal X-ray diffraction data with aspherical scattering factors from the invariom database by this issue). The sequences differ only in residue 4, Ile in (I) and Ala in (II). Since the anti-tumor potency is reduced for the Ala peptide (II), the causes for the differences seen in activity between (I) and (II) were examined from a structural and from an electron density (ED) point of view. The exchange at residue 4 does not lead to significant changes in molecular geometry (blue circles above). Molecular Hirshfeld surfaces and electrostatic potential (ESP) isosurfaces show accumulations of intermolecular interactions in regions adjacent to the Ile/Ala residues indicating preferred interactions with a potential receptor in these regions (blue circles below).