Escherichia coli β‐Galactosidase Inhibitors through Modifications at the Aglyconic Moiety: Experimental Evidence of Conformational Distortion in the Molecular Recognition Process

Abstract

Herein, we describe the use of thioglycosides as glycosidase inhibitors by employing novel modifications at the reducing end of these glycomimetics. The inhibitors display a basic galactopyranosyl unit (1→4)-bonded to a 3-deoxy-4-thiopentopyranose moiety. The molecular basis of the observed inhibition has been studied by using a combination of NMR spectroscopy and molecular modeling techniques. It is demonstrated that these molecules are not recognized by Escherichia coli β-galactosidase in their ground-state conformation, with a conformational selection process taking place. In fact, the observed conformational distortion depends on the chemical nature of the compounds and results from the rotation around the glycosidic linkage (variation of Φ or Ψ) or from the deformation of the six-membered ring of the pentopyranose. The bound conformations of the ligand are adapted in the enzymatic pocket with a variety of hydrogen-bond, van der Waals, and stacking interactions.

Thiodisaccharide Sulfoxides: Absolute Configuration of the SO Sulfur Atom and Influence on the Biological Activity towards the β‐Galactosidase from E. coli

“…[17] It was mentioned above that the pentopyranose ring can be conformationally described as an equilibrium between the 1 C 4 and 4 C 1 chairs, in accordance with the fact that this ring has a higher flexibility and a lower conformational barrier than the hexopyranose ring. [17] Furthermore, the replacement of one sulfur lone pair in 3 by an oxygen atom, as in sulfoxides 4S and 4R, is expected to restrict the rotation of the interglycosidic linkage as a result of electronic and steric changes around the sulfur atom. The flexibility of the pentopyranose ring may be modified by replacement of the glycosyl sulfide group at C-4 of 3 by a glycosyl sulfoxide group, as in 4R or 4S, and the rotation of the thioglycosidic linkage could be restricted in the sulfoxides due to the presence of the additional S=O bond.…”

“…[15] The oxidation of the sulfur atom of 1 with m-chloroperoxybenzoic acid (mCPBA) at 0°C led to a diastereomeric mixture of thiodisaccharide Soxides 2 (Scheme 1). [17] The experimental and calculated J values are shown in Scheme 1. The absolute stereochemistry of the sulfur stereocenter was assigned as S and R, respectively, as described below.…”

“…The stereoselective oxidation of chiral substrates, such as thiosugars, with mCPBA has been reported previously. [17] The NOESY spectrum of thiodisaccharide 1 shows an intense NOE interaction between 1Ј-H and 4-H, which indicates a highly populated syn φ/syn ψ conformation of the interglycosidic linkage ( Figure 2). The coupling constants (J) observed for the vicinal protons of the 4-thio-3-deoxy-pentopyranose ring of 1 suggest an equilibrium between the 1 C 4 and 4 C 1 conformations.…”

“…This enzyme has been widely used by us and many other research groups as a model enzyme for kinetic studies. This flexibility is an important factor as we have demonstrated, [17] by using a combination of NMR spectroscopy and molecular modeling techniques, that thiodisaccharide 3 undergoes conformational distortion, by deformation of the pentopyranose ring or by rotation of the thioglycosidic linkage, to adapt to the enzymatic pocket. [19] Moreover, 4-thiolactoside analogues, like 3, have already been tested as inhibitors of this enzyme, and the interactions of the amino acids of its active site with this type of thiodisaccharide have been established.…”

Synthesis of Thiodisaccharide Sulfoxides and Sulfones – Determination of the Configuration of the Sulfur Stereocentre

“…The replacement of the interglycosidic oxygen atom by a sulfur atom in thiooligosaccharides generally gives stability to the thioglycosidic linkage towards hydrolysis by glycosidases, and increases the potential of such molecules to act as inhibitors of these enzymes. [8] The sulfur atom of thiosugars can be oxidized to the corresponding sulfoxides or sulfones. [3][4][5][6][7] The molecular basis of the inhibition of the β-galactosidase from E. coli by selected S-disaccharides has been studied by using a combination of NMR spectroscopy and molecular modelling techniques.…”