Stereoselective Syntheses of Retro‐Isomers of N‐Glucoasparagine

Abstract

oxidation of the R u 2 + center is much more positive than that of the other complexes, but the peak reduction potentials remain remarkably constant. However, what is clear is that the electrochemical processes are chemically irreversible, showing almost no perceptible return upon scan reversals. There is only a hint of a return cathodic wave for Ru3+/Ru2+ at + 0.532 V, but none could be detected upon anodic reversal after reduction of the terpyridines.The reason for the observed chemically irreversible voltammetric responses is currently not well understood. It is possible to speculate that, due to the increased steric hindrance for 9< Ru > 12, either reduction or oxidation leads to sufficient destabilization. These redox processes occur in the vicinity of the metal center and could result in decomposition of the complex. Such a redox-driven "unlocking" of a complex could form the basis for a reversible formation-decomposition mechanism.This possibility, as well as the full characterization of the redox products, are currently under intense investigation.In summary, this construction concept allows the synthesis of specific polymacrocascade networks. as well as the incorporation of metal receptor units on or at a precise depth inside the macromolecule, to be controlled. We confirmed earlier that it is possible to encapsulate relevant molecules[211 randomly within a lipophilic region or to bind them covalently at a specific locus in the interior of cascades.'222' We now demonstrate the application of directed complex formation to generate the first stages in the construction of dendritic networks through metal-centered connectivity.

Partially Modified Retro-Inverso Peptides: Development, Synthesis, and Conformational Behavior

“…The retro concept has recently been applied to amide bonds other than those in simple peptides, that is in peptide nucleic acids (PNA) 216,217 and sugar-amino acid links. 218…”

“…The PMRI peptide concept constituted the arrival of the retro peptide bond as a true peptide bond surrogate, which has been widely applied in various biologically relevant peptides. The retro concept has recently been applied to amide bonds other than those in simple peptides, that is in peptide nucleic acids (PNA) , and sugar−amino acid links …”

Hypervalent Iodine and Carbohydrates – A New Liaison

“…Scheme 8 depicts some representative examples worked on in these laboratories. Studies by Sinaÿ and co-workers [28] and later by Kessler elimination of PhI, typically in a cis-fashion, to give enopyand Vasella et al [29] [30] showed that these compounds are ranoses 28, which are rapidly transformed into 2,3-dihydroideal precursors of anomeric lithio derivatives and hence 4H-pyran-4-ones 29 upon aqueous hydrolysis (Scheme 7a). Tributylstannyllithium adds in a 1,4-fashion to 2,3-dihydro-4H-pyran-4-ones such as disaccharide 11, affording glycosyl stannanes reactive primary intermediate usually undergoes reductive 36.…”

Design of superactive and selective integrin receptor antagonists containing the RGD sequence

“…An unnatural link between the sugar residue and the amino acid provides enzymatic stability. For this reason we synthesized O- glycopeptide analogues such as glycopeptides with 2-deoxy sugars [22], C-glycopeptides [23][24][25] or Sglycopeptides [26]. These modifications will not be treated here in detail.…”