Resumen:
enzyl 3-deoxy-4-S-(B-D-galactopyranosyl)-4-thio-B-D-threopentopyranoside is a potent inhibitor of the B-galactosidase from Escherichia coli synthesized in our laboratory. The 2´,3´,4´,6´-tetra-O-acetyl derivative of this thiodisaccharide was oxidized with m-chloroperoxybenzoic acid to give a 2:1 diastereomeric mixture of sulfoxides S and R. The absolute configurations of their sulfur stereocenters were determined by using NMR techniques and by taking into account the anisotropic effects of the S=O group in the major conformers. O-Deacetylation of S and R afforded the free thiodisaccharide S-oxides, which were evaluated as inhibitors of the above-mentioned enzyme. The kinetic studies showed that S and R are competitive inhibitors of the enzyme with Ki values of 0.19 and 0.45 mM, respectively. Further enzymatic reactions demonstrated that the S isomer is also a substrate of the B-galactosidase, as it was diastereoselectively hydrolyzed, while the R isomer remaining unchange