Synthesis and evaluation of inhibitors of E. coli PgaB, a polysaccharide de-N-acetylase involved in biofilm formation

Many medically important biofilm forming bacteria produce similar polysaccharide intercellular adhesins (PIA) consisting of partially de-N-acetylated β-(1 → 6)-N-acetylglucosamine polymers (dPNAG). In Escherichia coli, de-N-acetylation of the β-(1 → 6)-N-acetylglucosamine polymer (PNAG) is catalysed by the carbohydrate esterase family 4 deacetylase PgaB. The de-N-acetylation of PNAG is essential for productive PNAG-dependent biofilm formation. Here, we describe the development of a fluorogenic assay to monitor PgaB activity in vitro and the synthesis of a series of PgaB inhibitors. The synthesized inhibitors consist of a metal chelating functional group on a glucosamine scaffold to target the active site metal ion of PgaB. Optimal inhibition was observed with N-thioglycolyl amide (K_i = 480 μM) and N-methyl-N-glycolyl amide (K_i = 320 μM) glucosamine derivatives. A chemoenzymatic synthesis of an N-thioglycolyl amide PNAG pentasaccharide led to an inhibitor with an improved K_i of 280 μM.