854055-80-4Relevant academic research and scientific papers
Highly stereoselective peptide modifications through Pd-catalyzed allylic alkylations of chelated peptide enolates
Deska, Jan,Kazmaier, Uli
, p. 6204 - 6211 (2008/02/13)
Deprotonation of peptides in the presence of zinc chloride gives rise to highly reactive nucleophiles that can be subjected to palladium-catalyzed allylic alkylation reactions. Excellent diastereoselectivities are obtained that are nearly independent of the allylic substrate used. By using this protocol, highly functionalized side chains can also be incorporated in excellent yields and selectivities. The stereochemicaloutcome of the reaction is exclusively controlled by the peptide chain as long as terminal π-allyl-palladium complexes are involved. Probably, there is a threefold coordination, at least, ofthe deprotonated peptide chain to the chelating zinc ion. In such metal peptide complexes, one face of the generated enolate is shielded by the side chain of the adjacent amino acid, thus directing the electrophilic attack onto the opposite face. This behavior explains why an S amino acid always generates an R amino acid (and the other way round).
Preferred conformations of peptides containing tert-leucine, a sterically demanding, lipophilic α-amino acid with a quaternary side-chain C β atom
Formaggio, Fernando
, p. 2395 - 2404 (2007/10/03)
Terminally protected homopeptides of tert-leucine, from the dimer to the bexamer, co-oligopeptides of tert-leucine in combination with α-aminoisobutyric acid or glycine residues up to the hexamer level, and simple dipeptides representing known scaffolds for catalysts in asymmetric organic reactions were prepared by solution methods and fully characterized. The results of conformation analysis, performed by use of FT-IR absorption, NMR, CD, and X-ray diffraction techniques, indicate that this Hydrophobic α-amino acid with tetrasubstitution at the Cβ atom is structurally versatile. We show that it prefers extended or semiextended conformations, but can also be accommodated in folded structures, pro vided that these are biased by the presence of helicogenic residues. The current large-scale production of Tle, combined with its conformational preferences unravelled in this work, should make this bulky, hydrophobic, C α-trisubstituted α-amino acid a regular building block of any strategy seeking to tailor peptides with improved catalytic and pharmacological properties.
