Oligosaccharide synthesis disaccharides

This procedure has been demonstrated to provide moderate yields and anomeric selectivity in oligosaccharide synthesis. For instance, the disaccharide 110 was obtained in 50% yield as a 1 2 a p ratio. The reaction side products were mainly the self-condensed donor (10-25%) and unreacted hemiacetal (5-10% or higher). Alternatively, the a-linked glycosides were favored with diethyl ether solvent. In this way, trisaccharide 111 was prepared from the disaccharide hemiacetal donor in 49% yield, favoring the a-anomer by 4 1. 

It has long been recognized that polymeric supports for oligosaccharide synthesis do not need to be insoluble.33 Wang et al. applied the sulfoxide glycosylation method to the synthesis of disaccharide 79 (Scheme 3.14). The key feature of this work was the base-labile linker. Sulfoxide 74 was used to glycosylate polyethylene glycol... 

This method has been successfully extended to the iterative synthesis of oligosaccharides. The disaccharides, derived from selective activations of unprotected MOP donors and partially esterified MOP acceptors, can be converted into reactive donors simply by deacylation. The newly generated unprotected MOP disaccharide donor can be subjected to another cycle of glycosylation by repeating the same process. Schemes 7 and 8 illustrate... 

Koichi Fukase et al. reported an example of oligosaccharide synthesis by combining microreactors and an isolation strategy called synthesis based on affinity separation (SAS) [72, 73], The glycosylation was carried out under continuous flow, and the mixture was directly sent to the stainless steel affinity column, and the flow channel was switched to wash the column with CH2C12. The labeled disaccharide was trapped in the column later to be eluted with a mixture of CH2C12 and methanol to obtain the isolated oligosaccharide product. 

Given the complexity of the field and the vast amount of approaches used, this chapter does not attempt to cover aU aspects of oligosaccharide synthesis. Instead, the basic concept of oligosaccharide synthesis is demonstrated on the preparation of a simple disaccharide. Furthermore, strategies and selected techniques for the synthesis of higher and structurally more complex oligosaccharides are discussed. 

It was also found that introduction of any protecting group on the unprotected MOP glycosyl donors resulted in a significant decrease of the reactivity. This deactivation was considerable whenp-fluorobenzoates (FBz) were used as protecting groups, and it was applied to the synthesis of disaccharides, and to iterative oligosaccharide synthesis (O Scheme 80). 

In situ preactivation of thioglycosides with BSP/Tf20, initially developed by Crich for the synthesis of /i-mannosides 21 was applied to expeditious oligosaccharide synthesis by van der Marel and co-workers.20 For a representative example, see the synthesis110 of 106 depicted in Scheme 19. The thiogalactosyl donor 102 was preactivated with BSP/Tf20 and then allowed to react with thiomannoside 103 to yield disaccharide 104 in 73% yield. The latter then reacted with glycosyl acceptor... 

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