A Nonpeptidic Reverse Turn that Promotes Parallel Sheet Structure Stabilized by CH⋅⋅⋅O Hydrogen Bonds in a Cyclopropane γ‐Peptide

Abstract

Kehrt, marsch! Ein von einer Aminosäure abgeleiteter Alkohol und ein Arylamid wurden zu einem Kehrenbaustein für Peptidkonformationen kombiniert. Cyclopropananaloga von Tetra‐ und Hexapeptiden bilden parallele Faltblattstrukturen, die durch CH⋅⋅⋅O‐Wasserstoffbrücken stabilisiert werden (siehe Schema). NMR‐spektroskopische Studien bestätigen das Vorliegen von Wasserstoffbrücken.

Plagiarizing Proteins: Enhancing Efficiency in Asymmetric Hydrogen‐Bonding Catalysis through Positive Cooperativity

“…Herein we generate conformationally well‐defined but flexible thiourea catalysts10, 11 that benefit from cooperative ligand binding, and we demonstrate the utility of this phenomenon in catalytic asymmetric synthesis. We have constructed a simple and effective turn mimetic that populates a well‐defined hairpin conformation in solution and in the solid state stabilized by intramolecular hydrogen bonds 12…”

α‐Halogenoacetanilides as Hydrogen‐Bonding Organocatalysts that Activate Carbonyl Bonds: Fluorine versus Chlorine and Bromine

“…[5b] Weak nonconventional CÀH···O interactions were recently highlighted in natural and artificial systems that offer complementary interactions useful for structure and function (protein folding, enzyme activity, advanced materials, organic synthesis). [6] Concerning their contribution to organocatalysis, the N + ÀCH moiety within quaternary ammonium groups has been exploited in asymmetric CÀC bond formations [7] and ROP, [8] whereas less activated CH groups were reported in a few examples as probable participants in the stereocontrol of such reactions. [9] Taking advantages of the H-bonding properties of anilides and keeping in mind the need for an adjustable activation of C=O bonds even in the presence of a cocatalyst or a second substrate, [3,4] we envisioned that a-halogenoacetanilides possessing a second activated H-bond donor group such as HÀ CX n (n = 1-2), should be attractive catalysts (Scheme 1).…”