Glycosyl Imidates, 74. Synthesis of Ganglioside GM1 via a GM3 Intermediate

The synthesis of GM1 (1) via GM3 intermediate 7 was based on lactose building‐block 5, sialyl donors 6, and a Galß(1–3)‐GalN3 donor 13α. Reaction of donor 13α with acceptor 7 in the presence of TMSOTf as catalyst afforded GM1 pentasaccharide 30. Azido group reduction, N‐acetylation, hydrogenolytic O‐debenzylation, and O‐acetylation furnished O‐acyl‐protected GM1 pentasaccharide 34. Chemoselective 1a‐O‐deacetylation and generation of O‐(pentaosyl)trichloro‐acetimidate 36 provided the required glycosyl donor for the application to azidosphingosine glycosylation procedure affording GM1 (1).