Synthesis of the β anomer of the spacer-equipped tetrasaccharide side chain of the major glycoprotein of the Bacillus anthracis exosporium

The β glycoside of the tetrasaccharide sequence β-Ant-(1→3)-α-l-Rhap-(1→3)-α-l-Rhap-(1→2)-l-Rhap, whose aglycon allows conjugation to proteins, was synthesized for the first time. A stepwise synthetic approach was applied with thioglycosides as glycosyl donors, and the β anomer of the compound was obtained equipped with a spacer group whose further transformation allows conjugation to suitable carriers. To synthesize the β-anthrosyl linkage with high stereoselectivity, a linker-equipped rhamnotriose derivative was glycosylated with ethyl 4-azido-3-O-benzyl-2-O-bromoacetyl-4,6-dideoxy-1-thio-β-d-glucopyranoside. Further functionalization of the tetrasaccharide thus obtained, followed by deprotection, gave the target substance.

Graphical abstractSynthesis of the tetrasaccharide side chain of the major glycoprotein of the Bacillus anthracis exosporium.Figure optionsDownload full-size imageDownload as PowerPoint slide