Conformational Comparison of Cyclic á 3 â Tetrapeptide vs. á 3 â Pentapeptide

The a-turn inducing sugar â-amino acid plays an important role in the formation of well-defined secondary structures of cyclic tetra- and pentapeptide. Two tetra- and one novel pentapeptide were synthesized from a sugar â-amino acid and the conforma- tions of the compounds were established by NMR spectroscopy (EASY-ROESY) and compared with CD spectroscopic data. Although the a-turn conformation was dominant for both tetra- and pentapeptide according to NMR spectroscopic analysis in DMSO, the pentapeptide exhibited the presence of a second conformation. CD spectroscopic results in methanol showed that the tetrapeptides have a a-turn conformation, while the pentapeptide has a random structure.