RESEARCH PROJECTS Iminoalditols as Diagnostics and Therapeutics Iminoalditols for structure activity relationship studies of glycosyl hydrolases and their application as diagnostics and therapeutics Iminosugars including iminoalditols and related bicyclic alkaloids are the most prominent family of low molecular weight competitive glycosidase inhibitors. Paradigmatic examples such as compounds 1 and 2 and quite a few of their derivatives have found important roles as diagnostic compounds for example in the investigation of glycoprotein trimming glycosidases or as pharmaceutical substance such as in the treatment of diabetes type II symptoms and hereditary enzyme deficiency diseases. Other significant biological activities associated with their glycosidase inhibitory properties are anti-viral, anti-cancer and anti-metastatic, anti-infective as well as insect anti-feedant and plant growth regulatory effects. In this context, a substantial collection of various iminosugars, differently substituted at position C-1 (3), as well as N-alkylated structures were synthesized and biologically evaluated. The synthesised collection of iminoalditols served as tools for structure activity relationship studies of paradigmatic glucosidases and revealed information as to the biological interaction of this compound class influenced by the pattern of substitution. The obtained SARS gave ride to the design of an "inhibitory activity ruler" based on competitive displacement reactions of non-fluorescent inhibitors by fluorescent ones and vice versa. Furthermore, research was conducted towards the use of iminosugars, such as compound 4, for building up microarrays and their application for enzyme fishing and tracking. In a proof-of-concept study three potent glycosidase inhibitors were spotted on an amino dendrimer surface thus constructing a first generation iminoalditol chip designed as a glycosidase scavenging and detecting device. Incubation of the chip employing three typical glucosidases nicely reflected the characteristic properties of the inhibitors in solution and confirmed the viability of the concept for the detection and characterisation of proteins with glycosidase functions. Likewise, inhibitor profiling can conveniently be achieved. It can be expected that suitable inhibitors for other glycosidases such as D-galactosidases, glucocerebrosidases and hexosaminidases can be exploited accordingly, which will add sophistication and versatility to extend the scope of iminoalditol glycosidase inhibitor arrays to a wide range of applications, for example as diagnostic tools for lysosomal storage diseases in order to prevent irreversible damage by identification of the type of this disease in the very early embryonic phase. Furthermore, adequate derivatives of iminoalditol structures will find use as therapeutical tools in chaperone mediated therapy of the same diseases. A Novel Synthetic Concept for Neoglycoconjugates: Syntheses via an Amadori rearrangement Method for site-selective protein modification Glycoconjugates are structures where carbohydrates and oligosaccharide moieties are covalently attached to biomolecules such as lipids, proteins or peptides. The oligosaccharide components chosen by nature are exclusive and specific for a particular species, cell type and development status. Glycoproteins consist of monosaccharides or complex oligosaccharides covalently bound in an O- or N-glycosidic linkage. Despite the obvious importance of carbohydrates in a variety of biological processes, progress towards understanding their specific functions has been limited by their complexity and heterogeneity. The only way to access glycoconjugates of defined structure, in a pure form and sufficient quantities is through demanding and challenging multistep chemical and enzymatic synthesis. Furthermore, synthetic glycoconjugates are believed to show potential for developing therapeutic agents. The Amadori rearrangement of selected aldoses, such as D-glycero-L-mannose 5 with suitable amines or peptides can be performed in acidic aqueous solution and is clearly suitable for building up glycoconjugates. The formed hemiacetal function in the rearrangement product can either undergo, if necessary, reduction leading to a real C-glycosidic linkage of the amino component to the sugar moiety 7 or can be stabilised via ring closure to a cyclic carbamate 6. The developed method will be investigated for side selective glycation of peptides and proteins, insulin being a prominent target for this study with three potential sites for this modification method. Furthermore, the synthesised neoglycoconjugates can be used as building blocks for peptide synthesis allowing for incorporation into the peptide backbone. The carbohydrate part of the obtained glycopeptides can further be modified leading to more complex glycoforms of the peptide. For such glycosylation events glycosynthases have become useful tools allowing excellent yields for syntheses of oligosaccharides and complex glycan structures. Strategies towards the synthesis of complex carbacyclic oligosaccharide Structures for the investigation of glycoside hydrolases Carbacyclic polyols are important constituents of many biologically active molecules exhibiting important effects such as cellular regulation or selective inhibition of certain enzymes. One representative of this compound class is the designer drug Oseltamivir or Tamiflu today a considered blockbuster for a contingent pandemic outbreak of the avian flu. Furthermore, carbacyclic structures are constituents of pharmacologically interesting compounds, for example valienamine being the unit at the nonreducing end of acarbose, arguably the most studied inhibitor of -amylase, which is on the market (Glycobay) for the treatment of Diabetes type II. The Sina cyclisation and Ferrier II reaction are complementary in their outcome concerning the aglycon moiety. Both reactions lead to carbacyclic structures employing similar starting material but due to the difference of mechanism, the resulting pseudosugars can be distinguished by their aglycon which is kept in the Sina cyclisation (9) and lost in the Ferrier II reaction (8). This difference can be utilized for the synthesis of differently glycosylated carbacyclic structure. Employing selected starting materials for the two reactions together with appropriate follow up chemistry interesting structure types will be approachable, glycosylated carbacyclic structures bearing O- or N-linkage between the carbohydrate moieties which are pseudosubstrates (10) or inhibitors (11) for exo glycoside hydrolases such has -amylase. The carbasugar moiety in compounds such as 10 prevents a cleavage of the substrate at this particular glycosidic linkage. By constructing larger oligomers placing sugars and carbasugars together in defined patterns, the enzyme activities are directed by these non-natural substrates. Such structures give ideal tools for subsite mapping as well as investigation of the mechanism of endo glycosidases. Stepwise elongation of the immobilized ligands creates tri-, tetra- and pentamaltose on an array and subsequent investigation of the interactions with each substrate would give an idea of the contribution of individual pocket to the overall binding affinities. Carbacyclic structures with exocyclic nitrogen to the next sugar such as 11 residue are inhibitors for glycosyl hacdrolases by mimicking the valienamine subunit in acarbose. Step by step elongation will allow Inhibition studies of the change in kinetics providing information about the structure activity relationship of the inhibitors and enzyme system under investigation.
|Effective start/end date||1/06/99 → 31/08/03|
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