Modular synthesis of diphospholipid oligosaccharide fragments of the bacterial cell wall and their use to study the mechanism of moenomycin and other antibiotics

Abstract

We present a flexible, modular route to GlcNAc-MurNAc-oligosaccharides that can be readily converted into peptidoglycan (PG) fragments to serve as reagents for the study of bacterial enzymes that are targets for antibiotics. Demonstrating the utility of these synthetic PG substrates, we show that the tetrasaccharide substrate lipid IV (3), but not the disaccharide substrate lipid II (2), significantly increases the concentration of moenomycin A required to inhibit a prototypical PG-glycosyltransferase (PGT). These results imply that lipid IV and moenomycin A bind to the same site on the enzyme. We also show the moenomycin A inhibits the formation of elongated polysaccharide product but does not affect length distribution. We conclude that moenomycin A blocks PG-strand initiation rather than elongation or chain termination. Synthetic access to diphospholipid oligosaccharides will enable further studies of bacterial cell wall synthesis with the long-term goal of identifying novel antibiotics.

SEDS proteins are a widespread family of bacterial cell wall polymerases

“…4). Importantly, the PGT activity was resistant to moenomcyin at concentrations that inhibit PBP1A 28 as well as SgtB, a PGT from Staphylococcus aureus (Fig. 4b–c), suggesting the activity was not due to aPBP contamination.…”

Positive cooperativity between acceptor and donor sites of the peptidoglycan glycosyltransferase

“…Two main strategies are being followed to identify novel pharmacophore lead molecules for the design and synthesis of new GT inhibitors that could be developed as antibiotics: high throughput screening of chemical libraries [2][3][4] and rational synthesis of substrate and moenomycin (GT inhibitor) analogs [5][6][7][8]. The second strategy requires a deep understanding of the GT mechanism and structural data on protein-ligand complexes.…”

Bioactive oligosaccharide natural products

“…It is proposed that the phosphoglycerate and lipid portion of moenomycin mimics the diphospholipid leaving group of the donor substrate. 76 …”