Evaluation of C-(β-d-galactosyl) and C-2(2-deoxy-d-lyxo-hex-1-enopyranosyl) (d-galactal type) derivatives as inhibitors of β-d-galactosidase from Escherichia coli

C-(2-Deoxy-d-lyxo-hex-1-enopyranosyl)formamide was prepared from acetylated C-(β-d-galactopyranosyl)formamide by a radical-mediated bromination—zinc/N-methylimidazole-induced reductive elimination—Zemplén deacetylation reaction sequence. The preparation of acetylated 5-(2-deoxy-d-lyxo-hex-1-enopyranosyl)tetrazole was improved. Methyl C-(2-deoxy-d-lyxo-hex-1-enopyranosyl)formimidate was transformed by benzylamine into N-benzyl-C-(2-deoxy-d-lyxo-hex-1-enopyranosyl)formamidine and, after hydrolysis to methyl C-(2-deoxy-d-lyxo-hex-1-enopyranosyl)formate, into N-benzyl-C-(2-deoxy-d-lyxo-hex-1-enopyranosyl)formamide. A series of C-(β-d-galactopyranosyl) and C-(2-deoxy-d-lyxo-hex-1-enopyranosyl) derivatives was comparatively investigated for E. coli β-d-galactosidase inhibitory activity. N-Benzyl-C-(2-deoxy-d-lyxo-hex-1-enopyranosyl)formamidine was the best inhibitor and had Ki = 6 μM (on the basis of its free base concentration, Ki = 8.3 nM was obtained). Basicity and hydrophobicity of the aglycon proved to be more important factors for the inhibition than the conformation of the sugar ring.