Synthesis of potential metal-binding group compounds to examine the zinc dependency of the GPI de-N-acetylase metalloenzyme in Trypanosoma brucei

Michael D Urbaniak,Michael A.J Ferguson,Arthur T Crossman,Nuha Z Abdelwahab

doi:10.1016/j.carres.2011.02.004

Abstract

A small zinc-binding group (ZBG) library of deoxy-2-C-branched-monosaccharides, for example, 1,5-anhydroglucitols, consisting of either monodentate ligand binding carboxylic acids or bidentate ligand binding hydroxamic acids, were prepared to assess the zinc affinity of the putative metalloenzyme 2-acetamido-2-deoxy-α-d-glucopyranosyl-(1→6)-phosphatidylinositol de-N-acetylase (EC 3.5.1.89) of glycosylphosphatidylinositol biosynthesis. The N-ureido thioglucoside was also synthesised and added to the ZBG library because a previous N-ureido analogue, synthesised by us, had inhibitory activity against the aforementioned de-N-acetylase, presumably via the N-ureido motif.

Highlights

Glycosylphosphatidylinositol (GPI) acts as a membrane anchor for a small but significant proportion of higher eukaryote cellsurface glycoproteins that are abundant in protozoan parasites such as Trypanosoma brucei, the causative agent of African sleeping sickness in humans and the related disease Nagana in cattle.[1]
A key early step in the biosynthesis of the GPI anchors is the de-N-acetylation of 2-acetamido-2-deoxy-a-D-glucopyranosyl(1?6)-phosphatidylinositol10 [a-D-GlcpNAc-PI (1, Fig. 1)] to form a-D-GlcpNH2-PI (2, Fig. 1)
De-N-acetylation is a prerequisite for subsequent processing of 2 that leads to mature GPI anchor precursors.[11]

Summary

Introduction

Glycosylphosphatidylinositol (GPI) acts as a membrane anchor for a small but significant proportion of higher eukaryote cellsurface glycoproteins that are abundant in protozoan parasites such as Trypanosoma brucei, the causative agent of African sleeping sickness in humans and the related disease Nagana in cattle.[1]. We have shown[14] that mammalian and trypanosomal a-D-GlcpNAc-PI de-N-acetylases are zinc metalloenzymes, proposed a mechanism of action similar to that of zinc peptidases and postulated that known zinc binding motifs[15,16] such as the N-hydroxyurea analogue 3 (Fig. 1),[17] could act as inhibitors. The hydroxamic acid 7 was resynthesised and included in the compound library because 7 was shown to be a potent inhibitor of LpxC,[19] presumably via zinc chelation, and could serve as the standard by which to compare the potency of the other analogues in the library. Compounds 9–11 were synthesised to supply potential glycosyl donors for another project but might exhibit some degree of inhibition towards the trypanosome de-N-acetylase enzyme. Chem. 2000, 275, 11002–11009, no preparative details are given therein

Results and discussion

General methods

Synthesis of the ZBG library