3-Bromo N -Alkyl Cyanamides as Versatile Building Blocks

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Rearrangement of 2-hydroxyalkylazetidines into 3-fluoropyrrolidines

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Diastereoselective ring cleavage of azetidines with cyanogen bromide

International audienceN-alkyl azetidines bearing a chiral substituent at the nitrogen atom, and a variable substituent at C-3 as a prochiral centre, react readily with cyanogen bromide even at low temperatures to produce the corresponding 3-bromo-N-cyanamides as diastereoisomeric mixtures via ring opening. This reaction was found to be diastereoselective (up to 80:20 dr). In one case, the major diastereomer could be isolated by recrystallization, and the configuration of the newly created stereocentre was determined by X-ray crystallography

Theoretical investigation of von Braun and von Braun‐like reactions

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Heterochiral Ala/(αMe)Aze sequential oligopeptides: Synthesis and conformational study

International audienceα‐Amino acid residues with a ϕ,ψ constrained conformation are known to significantly bias the peptide backbone 3D structure. An intriguing member of this class of compounds is (αMe)Aze, characterized by an Nα‐alkylated four‐membered ring and Cα‐methylation. We have already reported that (S)‐(αMe)Aze, when followed by (S)‐Ala in the homochiral dipeptide sequential motif ‐(S)‐(αMe)Aze‐(S)‐Ala‐, tends to generate the unprecedented γ‐bend ribbon conformation, as formation of a regular, fully intramolecularly H‐bonded γ‐helix is precluded, due to the occurrence of a tertiary amide bond every two residues. In this work, we have expanded this study to the preparation and 3D structural analysis of the heterochiral (S)‐Ala/(R)‐(αMe)Aze sequential peptides from dimer to hexamer. Our conformational results show that members of this series may fold in type‐II β‐turns or in γ‐turns depending on the experimental conditions

A novel peptide conformation: the γ-bend ribbon

International audienceUnlike the extensively investigated relationship between the peptide β-bend ribbon and its prototypical 310-helix conformation, the corresponding relationship between the narrower γ-bend ribbon and its regular γ-helix counterpart still remains to be studied, as the latter 3D-structures have not yet been experimentally authenticated. In this paper, we describe the results of the first characterization, both in the crystal state and in solution, of the γ-bend ribbon conformation using X-ray diffraction and FT-IR absorption, electronic CD and 2D-NMR spectroscopies applied to an appropriate set of synthetic, homo-chiral, sequential dipeptide oligomers based on (S)-Ala and the known γ-bend inducer, Cα-tetrasubstituted, N-alkylated α-amino acid residue (S)-Cα-methyl-azetidine-carboxylic acid

<i>N</i>‑Arylazetidines: Preparation through Anionic Ring Closure

We report herein an efficient synthesis of diversely substituted <i>N</i>-aryl-2-cyanoazetidines based on an anionic ring-closure reaction. These compounds can be prepared from β-amino alcohols in enantiomerically pure form through a three-step sequence involving (i) copper-catalyzed <i>N</i>-arylation, (ii) <i>N</i>-cyanomethylation of the secondary aniline, and (iii) one-pot mesylation followed by ring closure induced by a base. This high-yielding sequence gives access to azetidines with a predictable and adjustable substitution pattern and also with predictable diastereoselectivity. These compounds are susceptible to multiple further derivatizations through Suzuki coupling or nitrile transformation, thus appearing as valuable new scaffolds for medicinal chemistry. Their rigid shape, featuring an almost planar <i>N</i>-arylamine and a planar four-membered ring, was revealed by both AM1 calculations and X-ray crystallography