Design and synthesis of novel constrained glycomimetics as inhibitors of galectins and galactosidases
Date
2023-10-10Author
Hever, Eoin
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Abstract
Chapter 1 gives a brief introduction to carbohydrate structure, discussing factors influencing
reactivity and conformation, such as the anomeric and exo-anomeric effect. Chapter 1 mentions
methods of structural analysis of carbohydrates. A description of the structure and biological
function of galectins, in diseases such as inflammation and cancer is next given. Natural
ligands for galectins are discussed, giving examples of published data obtained from affinity
measurements. A review of glycomimetic research is included and focuses particularly on work
from the Nilsson laboratory in Lund, Sweden with collaborators such as H. Leffler, H.
Blanchard and R. Pieters and industry partners Galecto Inc. The chapter concludes by
introducing C-glycosides and the concept of the conformational constraint, the hypothesis
investigated in this thesis work.
Chapter 2 describes the synthesis of five galactosidase inhibitors analogous to
isopropylthiogalactoside (IPTG), a galactosidase inhibitor, and also a molecular biology tool
used to induce protein expression in E.coli cell lines. The synthesised ligands had distinct
properties, including providing spatially different arrangements of the isopropyl group relative
to the galactopyranoside residue by using cyclic constraints or through influencing them via
the gauche effect. The synthetic C-glycosides were subjected to a galactosidase inhibition
study to explore the influence of the constraints or structural features on the inhibitory
properties of the ligands. Results of the assay showed that although the conformational
constraint improved inhibition relative to IPTG, an unconstrained C-galactose derivative,
isopropylmethylgalactoside (also known as isobutyl-C-galactoside, IBCG) was the best
inhibitor in the series of -galactosidase from E. Coli. The assay indicated the enzyme may
have the ability to accommodate several ligands with different presentations of the iPr group.
Other C-galactoside derivatives synthesised by Ashis Dhara and Dr. Saidulu Konda were also
tested. Molecular docking was performed to provide some rationalisation of the assay results.
Chapter 3 builds upon the galactosidase inhibitor synthesis described in chapter 2, altering the
structure of the compounds to generate galectin inhibitors. Synthesis is described, followed by
biological evaluation against galectins -1, -3, 8C, -8N, -9C, -9N, -4C and -4N using a
fluorescence polarization competitive inhibition assay. Derivatives synthesised by Ashis Dhara
were also evaluated. Inhibitors with the best results in the assay were in the high micromolar
range, with some ligands showing strong selectivity for certain galectins. Molecular docking of selected ligands was again performed, discussing conformational features of ligands and key
interactions with neighbouring amino acid residues in the galectin CRD which potentially
explain the measured galectin affinities.