Stereoselective syntheses of the O,N-protected subunits of the tunicamycins

The synthesis of the title compounds is described, i.e. coupling of the ylide, generated from the iodophosphonium salt of protected N-phthaloyl-d-galactosamine with 2,3-O-isopropylidene d-ribo-aldehyde afforded an undecose in high yield. Hydroboration-oxidation reaction of the olefinic linkage in the undecose led to the desired tunicamine, as the predominant product. After conversion of the latter to a glycosyl acceptor, this was assembled with the fully protected 2-oxyimino-2-deoxy-α-d-arabino-hexopyranosyl bromide, leading to a trehalose-type α,β-disaccharide.