Authors: Fausto Queda, Sérgio R. Filipe, Maria Manuel Marques
Peptidoglycan (PGN) is a major component of bacteria cell walls. The composition of PGN, or enzymes involved in its synthesis, is often linked with the development of bacterial infections. The limited access to pure, chemically defined, amounts of specific PGN fragments hampers the research of processes where PGN has an important role. This work aimed to develop straightforward and sustainable synthetic routes to access PGN fragments that could be valuable for biological studies. Two approaches were developed that rely on the use of chitin or chitosan as starting materials. The first approach involved an acetolysis reaction of chitin to give a peracetylated disaccharide, in a gram scale, which, through protecting group orthogonal synthesis, gave an advanced PGN intermediate in five synthetic steps. This molecule possesses all the functional groups in the correct positions as the PGN fragments, considered a high-value synthetic intermediate. In the second approach, chitosan was used as the starting material in a chemoenzymatic synthesis. Through an orthogonal protecting group strategy, it was possible to modify a high molecular weight chitosan polymer to produce a PGN surrogate. Using commercially available PGN hydrolases, we were able to hydrolyze this surrogate and identify the oligosaccharides that are present in the surrogate PGN sugar backbone.