9/11 Mixed Helices in α/β Peptides Derived from C‐Linked Carbo‐β‐Amino Acid and L‐Ala Repeats

Synthesis and Analysis of the Conformational Preferences of 5‐Aminomethyloxazolidine‐2,4‐dione Scaffolds: First Examples of β2‐ and β2, 2‐Homo‐Freidinger Lactam Analogues

“…A variety of secondary structures have been reported, stabilized by 10-to 15-membered hydrogen-bonded rings in both orientations of the backbone direction, whereas nine-membered hydrogenbonded rings of type 27 !1 have been described less often. [49] More recently, the 27 !1 nine-membered hydrogen-bond ring was described by Sanjayan and Rajamohanan [47] in oligopeptide foldamers consisting of the repeating building blocks l-Pro and anthranilic acid, the latter as a rigid b-amino acid (Figure 7 d). [33f] In contrast, the peptide Boc-[(R)-Phe-(R)-b 3 -homo-Val] 2 -(R)-PheOMe (Figure 7 c), [46] 'heterochiral' because the b 3 -residues derived from l-a-residues, was shown to adopt a mixed structure characterized by one classic 11-membered i7 !i + 3 hydrogen bond, and a distinct ninemembered 27 !1 hydrogen-bond with opposite orientation.…”

Heterogeneous H-Bonding in a Foldamer Helix

“…Thus, for example, an α/β-peptide contains H-bond accepting groups (C=O) and donating groups (N-H) from both α and β residues. Different types of H-bonds are found also in foldameric helices in which H-bond directionality alternates along the backbone, whether the backbone is homogeneous (as in the β-peptide 10/12-helix 7 and 18/20-helix 8 ) or heterogeneous (as in the α/β-peptide 11/9-helix 9 and 18/16-helix 10 ). These systems raise a fundamental question: are the different types of intrahelical H-bonds comparably favorable?…”

The Design of α/β‐Peptides: Study on Three‐Residue Turn Motifs and the Influence of Achiral Glycine on Helix and Turn

“…On exposure to CF 3 COOH for 2 h, ester 12 gave the salt 12a , which, on reaction with acid 13 14 in the presence of EDCI, HOBt, and DIPEA in CH 2 Cl 2 , gave the tetrapeptide 2 in 54 % yield. Peptide 13a 6a on treatment with base (aq. 4 n NaOH) gave the acid 13b , which, independently upon reaction with 12a and 12b in the presence of EDCI, HOBt, and DIPEA in CH 2 Cl 2 , furnished the heptapeptides 2a (55 %) and 2b (67 %), respectively.…”

“…The α/β‐peptide series with alternating proteinogenic α‐ and cyclic β‐residues, disclosed by Gellman et al.,4a showed the propensity of an 11‐helix and 14/15‐helix 7. Sharma et al 6a. have observed that α/β ‐ peptides with alternating L ‐Ala and C‐linked carbo‐β‐amino acid (β‐Caa) that contain ‘α–β–α’ residues at the C terminus display a robust 11/9‐mixed helix.…”