Accessible 6-O mono-detrimethylsilylation at per-O-TMS asymmetric disaccharides and their derivatization

Efficient mono-detrimethylsilylation at C-6 position of per-O-trimethylsilylated protected asymmetric disaccharides was achieved by an inexpensive reagent, ammonium acetate, at room temperature. The newly formed free hydroxyl at the non-reducing end of the product, 2, 3, 4, 2', 3', 4', 6'-heptakis-O-(trimethylsilyl)-d-lactose (2a), was coupled with azido, acetyl groups, and the modified intermediates represented potential precursors for the corresponding primary asymmetric modification of disaccharides. To broaden the usefulness of TMS-intermediates, the glycosylation and esterification occurred on the mono hydroxyl group of 2a simultaneously. Meaningfully trisaccharide derivative 7a was also obtained by utilizing the key intermediate 2a.