Super-Armed Thiomannopyranosides in the Synthesis of a Mannose-Capped Trisaccharide of <i>Mycobacterium tuberculosis</i> Lipoarabinomannan

Silylation of phenyl 1-thio-α-d-mannopyranoside, ethyl 1-thio-α- and β-d-mannopyranosides under different conditions was studied. Low-temperature NMR analysis revealed that the silylated products typically exist as an equilibrium of two chair conformations with a predominance of the axially rich 1 C 4 conformation. The dependence of the ratio of conformers on the anomeric configuration, the type of silyl groups and the nature of the aglycone was established. The fully silylated phenyl 1-thio-α-d-mannopyranoside, ethyl 1-thio-α- and β-d-mannopyranosides were tested as glycosyl donors in the synthesis of di- and trisaccharides, including one-pot synthesis. In all cases, only α-linked oligosaccharides as mixtures of conformers were formed. The obtained deprotected Man p -(1→2)-α-d-Man p- (1→5)-α-d-Ara f trisaccharide 2-azidoethyl glycoside, related to the non-reducing terminal fragment of the mannose-capped lipoarabinomannan (ManLAM) of Mycobacterium tuberculosis , can be used for further preparation of conjugates with proteins to provide antigens, which are important for development of new tuberculosis screening assays.