Chemical and Enzymatic Synthesis of Sialylated Glycoforms of Human Erythropoietin.

Recombinant human erythropoietin (EPO) is the main therapeutic glycoprotein for the treatment of anemia in cancer and kidney patients. The in-vivo activity of EPO is carbohydrate-dependent with the number of sialic acid residues regulating its circulatory half-life. EPO carries three N-glycans and thus obtaining pure glycoforms provides a major challenge.

Natural Glycoforms of Human Interleukin 6 Show Atypical Plasma Clearance.

A library of glycoforms of human interleukin 6 (IL-6) comprising complex and mannosidic N-glycans was generated by semisynthesis. The three segments were connected by sequential native chemical ligation followed by two-step refolding. The central glycopeptide segments were assembled by pseudoproline-assisted Lansbury aspartylation and subsequent enzymatic elongation of complex N-glycans.

A Single Route to Mammalian N-Glycans Substituted with Core Fucose and Bisecting GlcNAc.

The occurrence of α1,6-linked core fucose on the N-glycans of mammalian glycoproteins is involved in tumor progression and reduces the bioactivity of antibodies in antibody-dependent cell-mediated cytotoxicity (ADCC). Since core-fucosylated N-glycans are difficult to isolate from natural sources, only chemical or enzymatic synthesis can provide the desired compounds for biological studies. A general drawback of chemical α-fucosylation is that the chemical assembly of α1,6-linked fucosides is not stereospecific.

Recognition of Complex Core-Fucosylated N-Glycans by a Mini Lectin.

The mini fungal lectin PhoSL was recombinantly produced and characterized. Despite a length of only 40 amino acids, PhoSL exclusively recognizes N-glycans with α1,6-linked fucose. Core fucosylation influences the intrinsic properties and bioactivities of mammalian N-glycoproteins and its level is linked to various cancers.

Breaking the Limits in Analyzing Carbohydrate Recognition by NMR Spectroscopy: Resolving Branch-Selective Interaction of a Tetra-Antennary N-Glycan with Lectins.

The biological recognition of complex-type N-glycans is part of many key physiological and pathological events. Despite their importance, the structural characterization of these events remains unsolved. The inherent flexibility of N-glycans hampers crystallization and the chemical equivalence of individual branches precludes their NMR characterization.

Synthetic Glycoforms Reveal Carbohydrate-Dependent Bioactivity of Human Saposin D.

The main glycoforms of the hydrophobic lysosomal glycoprotein saposin D (SapD) were synthesized by native chemical ligation. An approach for the challenging solid-phase synthesis of the fragments was developed. Three SapD glycoforms were obtained following a general and robust refolding and purification protocol.

NMR and Molecular Recognition of N-Glycans: Remote Modifications of the Saccharide Chain Modulate Binding Features.

Glycans play a key role as recognition elements in the communication of cells and other organisms. Thus, the analysis of carbohydrate-protein interactions has gained significant importance. In particular, nuclear magnetic resonance (NMR) techniques are considered powerful tools to detect relevant features in the interaction between sugars and their natural receptors.

Highly Efficient Synthesis of Multiantennary Bisected N-glycans Based on Imidates.

The occurrence of N-glycans with a bisecting GlcNAc modification on glycoproteins has many implications in developmental and immune biology. However, these particular N-glycans are difficult to obtain either from nature or through synthesis. We have developed a flexible and general method for synthesizing bisected N-glycans of the complex type by employing modular TFAc-protected donors for all antennae.

Selective oxidative debenzylation of mono- and oligosaccharides in the presence of azides.

When using benzyl ethers as permanent protecting groups in oligosaccharide synthesis selective oxidative debenzylation with NaBrO(3) + Na(2)S(2)O(4) under biphasic conditions is efficient and compatible with anomeric azides and many other functions.