Branched trisaccharide synthesis

Scheme 2.13 Synthesis of a branched trisaccharide via thioethyl donors.

S. Valverde, M. Garcia, A. M. Gomez, and J. C. Lopez, A combined intramolecular-intermolecular one-pot glycosylation approach for the synthesis of a branched trisaccharide, Chem. Commun., (2000) 813-814. 

Mechanism of the Enzymic Synthesis of a Branched Trisaccharide Containing the a-l 2-Glucosidic Linkage, E. J. Bourne, J. Hartigan, and H. Weigel,/. Chem. Soc., 2332-2337 (1959). 

This latent-active glycosylation strategy was also applied by Boons to the synthesis of libraries of both linear [31] and branched trisaccharides [32]. 

Among other insoluble promoters proposed for mannoside synthesis van Boeckel s porous silver silicate [84] has emerged as a most efficient activator [85, 86], This catalyst even promotes p-selective mannosylation by donor 15 at 0-4 of the disaccharide 16 to afford the 4,6-branched trisaccharide 17 that corresponds to an Asn-linked core structure (Scheme 6) [86]. 

The nature of the protecting groups employed in the preparation of disaccharide discussed above does not permit the extension of the synthesis to the branched type of KDO trisaccharide shown in Fig. 1. To obtain another model compound for the structure elucidation of the natural KDO trisaccharide by spectroscopic and immunochemical methods, a route was devised which would permit the synthesis of the model trisaccharide 12. 

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