The Miraculous CD Spectra (and Secondary Structures?) ofβ-Peptides as They Grow Longer, Preliminary Communication

The recently improved conditions for solid-phase synthesis of β3-peptides by the Fmoc strategy were used to synthesize a β-tetracosapeptide (4, Scheme) composed of eight different β-amino acid residues; 11 of the 24 residues carry functionalized proteinogenic side chains (namely those of Glu, Lys, Ser, and Tyr). The highly H2O-soluble β-tetracosapeptide was identified by 1H-NMR spectroscopy (in MeOH), analytical HPL chromatography, and ESI-mass spectrometry (Fig. 1). The expected 314-helical secondary structure of the new β-peptide was designed to have one hydrophobic and two hydrophilic faces, and to be compared with other β-peptides (1 – 3), two of which are also of amphipathic character in this secondary structure (Fig. 2). In the absence of NMR-structural proof, the CD spectra of the four β-peptides were compared (Figs. 3 and 4). The β-tetracosapeptide exhibits an unprecedented CD pattern (in MeOH and in H2O solution) that may arise from a new type of secondary structure or from an unordered conformation.