Eine neue Strategie zur Festphasensynthese vonO-Glycopeptiden

Organic azides: an exploding diversity of a unique class of compounds

Since the discovery of organic azides by Peter Griess more than 140 years ago, numerous syntheses of these energy-rich molecules have been developed. In more recent times in particular, completely new perspectives have been developed for their use in peptide chemistry, combinatorial chemistry, and heterocyclic synthesis. Organic azides have assumed an important position at the interface between chemistry, biology, medicine, and materials science. In this Review, the fundamental characteristics of azide chemistry and current developments are presented. The focus will be placed on cycloadditions (Huisgen reaction), aza ylide chemistry, and the synthesis of heterocycles. Further reactions such as the aza-Wittig reaction, the Sundberg rearrangement, the Staudinger ligation, the Boyer and Boyer-Aubé rearrangements, the Curtius rearrangement, the Schmidt rearrangement, and the Hemetsberger rearrangement bear witness to the versatility of modern azide chemistry.

Glycopeptide synthesis and the effects of glycosylation on protein structure and activity

Despite the omnipresence of protein glycosylation in nature, little is known about how the attachment of carbohydrates affects peptide and protein activity. One reason is the lack of a straightforward method to access biologically relevant glycopeptides and glycoproteins. The isolation of homogeneous glycopeptides from natural sources is complicated by the heterogeneity of naturally occuring glycoproteins. It is chemical and chemoenzymatic synthesis that is meeting the challenge to solve this availability problem, thus playing a key role for the advancement of glycobiology. The current art of glycopeptide synthesis, albeit far from being routine, has reached a level of maturity that allows for the access to homogeneous and pure material for biological and medicinal research. Even the ambitious goal of the total synthesis of an entire glycoprotein is within reach. It is demonstrated that with the help of synthetic glycopeptides the effects of glycosylation on protein structure and function can be studied in molecular detail. For example, in immunology, synthetic (tumour-specific) glycopeptides can be used as immunogens to elicit a tumour-cell-specific immune response. Again, synthetic glycopeptides are an invaluable tool to determine the fine specificity of the immune response that can be mediated by both carbohydrate-specific B and T cells. Furthermore, selected examples for the use of synthetic glycopeptides as ligands of carbohydrate-binding proteins and as enzyme substrates or inhibitors are presented.

Synthesis of the glycosyl amino acids N alpha-Fmoc-Ser[Ac4-beta-D-Galp-(1-->3)-Ac2-alpha-D-GalN3p]-OPfp and N alpha-Fmoc-Thr[Ac4-beta-D-Galp-(1-->3)-Ac2-alpha-D-GalN3p]-OPfp and the application in the solid-phase peptide synthesis of multiply glycosylated mucin peptides with Tn and T antigenic structures

Two new glycosyl amino acids N alpha-Fmoc-Ser[Ac4-beta-D-Galp-(1-->3)-Ac2-alpha-D-GalN3p]-+ ++OPfp and N alpha-Fmoc-Thr[Ac4-beta-D-Galp-(1-->3)-Ac2-alpha-D-GalN3p]-+ ++OPfp were synthesized. Glycosylation of N alpha-Fmoc-Ser-OPfp or N alpha-Fmoc-Thr-OPfp with protected beta-D-Gal-(1-->3)-D-GalN3 donors afforded the glycosyl amino acids containing an activated C-terminus which could be utilized directly for solid-phase glycopeptide synthesis. The transformation of the 2-azido group into the acetamido derivative was achieved quantitatively at the end of the synthesis by treatment of the polymer-bound glycopeptide with thioacetic acid. The versatility of this strategy was demonstrated by the assembly of eight triply glycosylated mucin peptides which were synthesized simultaneously by multiple column techniques. The glycopeptides were prepared in order to investigate the substrate specificity of a galactosyltransferase.