Abstract
A new ganglioside, LLG-5 was purified from starfish Linckia laevigata by Higuchi group in 2005 and the structure was determined as 8-OMe-NeuGcα2→11NeuGcα2→11NeuGcα2→3Galβ1→4Glcβ1→1Cer. Moreover, LLG-5 displays neuritogenic activity toward rat pheochromocytoma PC-12 cells in the presence of nerve growth factor. The activity is greater than that of the mammalian ganglioside GM1. Therefore, LLG-5 is regarded as a potential drug to cure nervous system disease such as Parkinson's disease. In our synthetic approach toward LLG-5, D-lyxose was chosen as the starting material to efficiently construct three stereogenic centers of phytosphingosine, and the lipid chain was introduced via Wittig olefination. After coupling of D-lyxose with lipid Wittig reagent, the hydroxyl group on C2 of the resulting hydroxyl lipid was converted to azido group by Mitsunobu reaction. With the phytosphingosine acceptor in hand, different lactose donors were prepared to investigate their glycosylation with phytosphingosine. The GM3 derivative with Neu5NCbz was synthesized by enzymatic sialylation using CMP-Neu5NCbz and the above lactosyl lipid. By using enzymatic synthesis, we can obtain the exclusively α sialylated glycolipid. In conclusion, we have successfully synthesized the LLG-5 precursor in 12% yield with 5 steps (from lactose).