Ten-membered rings as key interaction motifs in folding of desmuramyl di-, tri-, and tetrapeptides

Structural Chemistry - Muropeptides are fragments of polymeric peptidoglycan, unique constituent of bacterial cell walls, acting as immunostimulators (adjuvants). The smallest biologically active...     

1′-Acetylferrocene amino acid esters and amides. A simple model for parallel β-helical peptides

In this study we present a synthesis and conformational analysis of 1′-acetylferrocene amino acid derivatives of type Ac–Fn–CO–AA–Y (Fn=ferrocene-1,1-diyl; AA=Gly, Ala or Val; Y=OMe or NHMe) as a simple model for parallel β-helical peptides. Derivatives with only one amino acid adopt a reduced number of total conformations and allow a more exact analysis of intramolecular hydrogen bonds (IHB) close to the ferrocene unit. Conformational analysis of these bioconjugates was performed by a combination of spectroscopic techniques (IR, NMR and CD) and corroborated by solution-phase DFT calculations. The investigation of ester conjugates 1–3 indicates the coexistence of non-bonded (an open forms) and hydrogen bonded NH_a group forming a 7-membered ring (γ-turn). The amide derivatives 4–6 with an additional NH_b hydrogen bond donor are mostly constituted of conformers with a 10-membered ring (β-turn) as a single IHB pattern or the β-turn accompanied by a 7-membered ring (γ-turn) containing NH_a group. The exchange of the amino acid side-chain does not significantly affect the conformational properties and IHB pattern of the studied conjugates 1–6.     

Ferrocene-dipeptide conjugates derived from aminoferrocene and 1-acetyl-1′-aminoferrocene: synthesis and conformational studies

In this study we present the synthesis and conformational analysis of mono- and disubstituted ferrocene bioconjugates bearing dipeptide chains (Boc-AA-AA-Fn-X, AA=Gly, l-Ala, l-Val). The conformational preferences of novel aminoferrocene derived conjugates with X=H, as well as their 1-acetyl analogues (X=COMe), were investigated by spectroscopic techniques (IR, NMR and CD) and corroborated by DFT calculations. Chirally organized structures, stabilized through intrachain hydrogen bonds, prevail in solution when X=H. The resulting 10-membered hydrogen-bond ring is destabilized by heteroannular introduction of an acetyl group when X=COMe.