Unnatural C6-Substituted d-Galactosides as Attenuated Substrates of Glycosyl Hydrolases

The covalent attachment of pendant groups to the carbons of d-pyranosides can influence their ability to be recognized by proteins that bind natural sugars. These carbon-modified sugars have received only limited attention, and systematic investigations on their ability to act as substrates of glycosyl hydrolases have not been reported. Here, C6-substituted β-d-galactosides are synthesized and evaluated as putative substrates of β-glycosyl hydrolases. The results indicated that the size of the group at C6-methyl vs. di-methyl vs. phenyl-attenuated their ability to act as substrates. The C6-methyl derivative was a weak substrate, but the C6-dimethyl and C6-phenyl compounds were not. The new β-galactosides can be leveraged as tool compounds in the search for glycosidases with novel activity and as starting points for enzyme-engineering campaigns.