12/10- and 11/13-Mixed Helices in α/γ- and β/γ-Hybrid Peptides Containing C-Linked Carbo-γ-amino Acids with Alternating α- and β-Amino Acids

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Abstract
New classes of α/γ- and β/γ-hybrid peptides have been synthesized with novel 12/10- and 11/13-mixed helical patterns, respectively. The α/γ-peptides were derived from the dipeptide repeats with alternating arrays of l-Ala and γ-Caa(l) (C-linked carbo-γ-amino acid from d-mannose), which generated a new 12/10-mixed helix, for the first time, without a β-amino acid. The β/γ-peptides made from an alternating arrangement of β-Caa(x) (C-linked carbo-β-amino acid) and γ-Caa(x) (C-linked carbo-γ-amino acid from d-xylose), on the other hand, resulted in an unprecedented 11/13-helix. The secondary structures in these peptides have been ascertained from detailed NMR studies, and CD spectroscopy and molecular dynamics investigations provided additional support for the structures derived.