First Synthesis of a Pentasaccharide Moiety of Ganglioside GAA‑7 Containing Unusually Modified Sialic Acids through the Use of N‑Troc-sialic Acid Derivative as a Key Unit

The pentasaccharide part of the potent neuritogenic ganglioside GAA-7 has been synthesized for the first time. The unique branched terminus constituting partially modified sialic acids and N-acetylgalactosamine was successfully established by stereoselective double-sialylation using 8-O-methyl-N-Troc-sialic acid as a donor. The final 4 + 1 coupling reaction provided a high yield of pentasaccharide, which was deprotected to deliver the target molecule.