The work described in this thesis focuses on the development of inhibitors for two distinct types of proteins that act on carbohydrates: the galectins and O-GlcNAc transferase (OGT). Chapter 1 and 2 describe that these two types of protein can bind or convert certain carbohydrates to exhibit different functions in a wide variety of biological processes. Therefore, selective and potent inhibitors of these proteins would be valuable tools to investigate their biological functions.
Chapter 3 describes a synthesis of multivalent ligands inhibiting Gal-3, in which multiple lysine residues of albumin were chemically conjugated with “thiodigalactoside” epitopes to make neo-glycoproteins. The neo-glycoproteins were finally evaluated in binding studies with human Gal-1 and -3 to determine the binding properties.
Chapter 4 describes the synthesis of galectin inhibitors with a potential “chelate effect”, which are designed to bind to the two different binding sites on galectins simultaneously. In this chapter, a series of asymmetric “hybrid” compounds were prepared, that combine two galectin ligands, i.e., thiodigalactoside derivatives and calixarene 0118. Moreover, NMR spectroscopy was used to evaluate the interactions of these compounds with Gal-1 or -3. In addition, cellular experiments were conducted to compare the cytotoxic effects of the hybrids with those of calixarene 0118.
Chapter 5 describes our progress on OGT inhibition based on substrate peptides identified by array screening. Subsequently, bisubstrate inhibitors were prepared by conjugating these peptides to uridine in various ways. In parallel, an in silico fragment screening was conducted to obtain small molecules targeting the UDP binding pocket. After evaluation of the initial hits, one of these small molecules was elaborated into a novel OGT hybrid inhibitor, as the replacement of uridine. The novel compounds inhibit OGT activity with IC50values in the micromolar range.