Collect. Czech. Chem. Commun. 1992, 57, 614-620

Melanin Concentrating Hormone Analogs: Contraction of the Cyclic Structure. III. CD Spectroscopic Study

Ivo Friča, Michal Lebla and Victor J. Hrubyb

a Institute of Organic Chemistry and Biochemistry, Czechoslovak Academy of Sciences, 166 10 Prague 6
b Department of Chemistry, The University of Arizona, AZ 857 21, U.S.A.


A comparison of the CD spectra of MCH analogs differing in length but containing a heterodetic ring of the same size (compounds I, IV and VII or III, VI and IX) reveals that a conformational change occurs upon elongating the peptide chain from thirteen to seventeen amino-acid residues. The 5-17 fragments appear to prefer a β-turn conformation, whereas the 1-17 full-sequence peptides prefer α-helical conformation. Peptides containing seventeen-membered ring exhibit greater conformational adaptability (the incorporation of their cyclic moiety into an ordered conformation being easier) than those containing a twenty-six-membered ring. Spectral properties of the twenty-three-membered heterodetic ring in peptides II and V indicate that they do not possess highly ordered conformation.