Total Synthesis of Sialylgalactosylgloboside: Stage-Specific Embryonic Antigen 4.
A versatile total synthesis of sialylgalactosylgloboside (SGG, 1), carrying the stage-specific embryonic antigen 4 (SSEA-4) is reported, illustrating a more general strategy for the synthesis of complex globo-series glycosphingolipids. Starting from readily available building blocks 7, 8, and 10, two different approaches to the synthesis of the key tetrasaccharide 6 have been developed in a highly convergent manner. Further glycosylations with galactosyl trichloroacetimidate (5) and sialyl phosphite (2) donors successively afforded the penta- and hexasaccharides 3 and 11. The latter was finally converted into the target molecule (SGG, 1) with the help of a azidosphingosine glycosylation procedure, favored in this case by the stereocontrolling properties of the 2a-O-pivaloyl protecting group. Valuable intermediates 6 and 3, having the oligosaccharidic skeletons of Gb(4) and Gb(5) (SSEA-3), respectively, were obtained in the course of the synthesis.
Lassaletta
José M.
JM
Fakultät für Chemie, Universität Konstanz, Postfach 5560 M 725, D-78434 Konstanz, Germany.
Carlsson
Karin
K
Garegg
Per J.
PJ
Schmidt
Richard R.
RR