Synthesis of a tetrasaccharide phosphate from the linkage region of the arabinogalactan–peptidoglycan complex in the mycobacterial cell wall

The synthesis of dibenzyl 6-O-naphthylmethyl-2,3,5-tri-O-benzoyl-β-d-galactofuranosyl-(1→5)-2,3-di-O-benzoyl-6-O-benzyl-β-d-galactofuranosyl-(1→4)-3-O-benzyl-2-O-pivaloyl-α-l-rhamnopyranosyl-(1→3)-2-acetamido-2-deoxy-4,6-di-O-benzoyl-α-d-glucopyranosyl phosphate (1), a protected form of the tetrasaccharide phosphate of the linkage region of the arabinogalactan–peptidoglycan complex in the mycobacterial cell wall, has been accomplished. Key steps include the coupling of four monosaccharide building blocks with complete stereoselectivity by glycosylations employing thioglycosides, 2′-carboxybenzyl glycosides, and glycosyl fluorides as glycosyl donors. The α-glycosyl phosphate linkage was also stereoselectively elaborated by reaction of a tetrasaccharide hemiacetal with tetrabenzyl pyrophosphate in the presence of a base.

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