Given below are three projects that are representative examples of the research that is currently being undertaken at Simon Fraser University.
Sialic acid (N-acetylneuraminic acid) is a common constituent of the glycolipids and glycoproteins produced by animal cells and is frequently used to 'cap' the non-reducing ends of the oligosaccharide moieties of these glycoconjugates. The prominence of sialic acid on the surface of cells and macromolecules gives it great importance in cellular and molecular recognition. The process of sialic acid residue addition and removal from complex oligosaccharides, requires that animal cells produce sialyltransferases and sialidases. Notably, a variety of sialidases are also encoded by viruses and bacteria, some of which are known to be important determinants of pathogenicity. The influenza virus, for example, produces a sialidase that is essential for the release of progeny virus particles from infected host cells. Such relationships between sialidases and pathogenicity have given rise to a widespread interest in sialidase mechanisms and in the development of specific sialidase inhibitors.
We have recently shown that the influenza type A viral sialidase is an effective catalyst for the hydrolysis of pyridinium a-D-sialosides (manuscript number 42: collaboration with Thor Borgford). Furthermore, the efficiency at which various bacterial sialidase enzymes hydrolyze this class of non-natural substrates is greatly reduced relative to aryl a-D-sialosides substrates (work currently in progress). We are continuing our efforts to pinpoint the critical mechanistic features for this particular class of biological catalysts. For example, using site-directed mutagenesis, we have made the E277D mutant influenza sialidase (A/Tokyo/3/67) which contains a Glu®Asp mutation in the active site.
We reported the first synthesis of a glycosidase inhibitor (2,6-anhydro-1-deoxymanno-nojirimycin) based on the bicyclo[2.2.2]octane skeleton (manuscript number 36). Presently, our synthetic efforts are concentrated on making bicyclo[4.1.0]heptane analogues of various carbohydrates. One of the first two bicyclic compounds made (see structures) is the tightest binding inhibitor for yeast a-glucosidase reported to date (manuscript number 45). The results from this manuscript were recently reviewed in the May 2001 issue of Modern Drug Discovery.