Mycobacterium tuberculosis is the cause of the deadly human disease tuberculosis. In studies over the last 40 years it has been revealed that this organism possesses a complex cell wall including glycophospholipids such as the phosphatidylinositiol mannosides (PIMs), lipomannan (LM) and lipoarabinomannan (LAM). These glycolipids all contain a common α-1,6-linked mannoside core, and the higher PIMs and LAM possess α-1,2-linked mannosyl residues. It has been shown that simple α-1,6-linked oligomannosides can act as substrates for α-1,6-mannosyltransferases in mycobacteria. Here we report a simple iterative synthesis of a series of hydrophobic octyl α-1,6-linked oligomannosides from mono- through to tetrasaccharides. We have utilized a single thioglycoside donor and alcohol acceptor. Further, we have developed conditions for the conversion of each of these compounds to the 6-deoxy congeners. Deoxygenation of the 6-position of the terminal mannosyl residue should prevent these compounds acting as substrates for the abundant α-1,6-mannosyltransferases in mycobacteria and should permit detection of the elusive α-1,2-mannosyltransferase activity responsible for elaboration of LM to mature LAM and the biosynthesis of the higher PIMs.
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