Design and chemoenzymatic synthesis of thiooligosaccharide inhibitors of 1,3:1,4-β-D-glucanases

A successful chemoenzymatic synthesis of oligosaccharides with an interglucosidic sulfur atom as inhibitors of 1,3:1,4-β-D-glucanases is described. The key compound 3a was synthesized from acetylated 1-thio-β-laminaribiose 4 and the methyl 4'-O-triflyl-lactoside 5. After de-O-acylation, the tetrasaccharide 3b was used as an acceptor and glucose-1-P as a donor in a phosphorolytic elongation catalysed by cellodextrin phosphorylase from Clostridium thermocellum. The expected pentasaccharide 2a and hexasaccharide 1 were isolated in 56% and 13% yield, respectively. As expected, the thiooligosaccharides 1, 2a, and 3b were resistant to enzymatic cleavage by 1,3:1,4-β-D-glucanase isolated from Bacillus licheniformis. Furthermore, they have been shown to act as competitive inhibitors of the hydrolysis of the chromophoric trisaccharide substrate 11 by this enzyme.