Trichloroacetimidates method

This review covers the recent advances in the use of O-glycosyl imidates in oligosaccharide and glycoconjugate synthesis, with emphasis on literature published between 1999 and 2006. However, because of the large volume of work in this area, only the most representative applications will be presented. One can refer to the similar preceding review [381] published in 2000 and another quite comprehensive review [375] on trichloroacetimidate method published in 1994 for earlier application of glycosyl trichloroacetimidates. Trifluoroacetimidate method will be discussed separately in this review in the light of its less popularity in carbohydrate chemistry. 

The trichloroacetimidate method has also been used to prepare bivalent Lex oligosaccharides to study the conformational details of carbohydrate clusters by NMR spectroscopy [437] TWo Le trisaccharides were covalently linked through... 

The trichloroacetimidate method has also found wide applications in the synthesis of various complex oligosaccharides. In the course of the development of chemically defined glycoconjugate vaccines against shigellosis, a decasaccharide, corresponding to two consecutive repeating units of the O-specifk polysaccharide of Shigella... 

Another series of GSL mimics with oligo-ethylene glycol as spacer have also been obtained successfully using trichloroacetimidate method [482]. In addition, fluorescence-labeled sLex glycosphingolipids have also been chemically synthesized as targets for investigating microdomain formation in membranes [483]. 

Scheme 3.52), whereas the corresponding acetyl-protected donor gave little product under the same reaction conditions [512], Additionally, the trichloroacetimidate method has also been applied to synthesize other natural products, such as bupres-tin A and B [517], macrophylloside D [518] and neomycin mimetics [519]. 

In addition, a novel fluorous support has been developed recently as an alternative to traditional polymer supports and applied successfully to oligosaccharide synthesis in combination with the trichloroacetimidate method [541]. Each intermediate in the fluorous oligosaccharide synthesis [542,543] could be obtained by simple fluorous-organic solvent extraction, and the reactions could be monitored by TLC, NMR and MS, in contrast to solid-phase reactions. Moreover, the new liquid-phase technique is anticipated to be easily applicable to the large-scale synthesis. 

ANOMERIC-OXYGEN ACTIVATION FOR GLYCOSIDE SYNTHESIS THE TRICHLOROACETIMIDATE METHOD... 

The trichloroacetimidate method for glycoside synthesis extended its versatility right at the outset (51,52a) by exhibiting an especially smooth reaction of 0-(glycosyl)trichloroacetimidates with Bransted acids. Without the addition of any catalyst, simple Bransted acids are able to substitute the trichloroacetimidate group at room temperature in high yields, as shown (17) for la-a in Scheme 6. Because of anomerization of possible / products... 

The requirements for new glycosylation methods outlined at the beginning of this chapter, namely convenient diastereocontrolled anomeric O-ac-tivation (first step) and subsequent efficient diasterecontrolled glycosylation promoted by genuinely catalytic amounts of a catalyst (second step), are essentially completely fulfilled by the trichloroacetimidate method. This is clearly shown by the many examples and references given in this article. In terms of stability, reactivity, and applicability toward different acceptors, the... 

Anhydrous hydrogen fluoride, application of for the structural analysis of polysaccharides, 47, 167-202 Anomeric and exo-anomeric effects in carbohydrate chemistry, 47, 45-123 Anomeric-oxygen activation for glycoside synthesis, trichloroacetimidate method, 50,21-123... 

Glycopeptides containing glycosyl L-aspara-gine, L-serine, and L-threonine, developments in, 50,277-310 Glycoside hydrolases, mechanistic information firm studies with reversible and irreversible inhibitors, 48, 319-384 Glycoside synthesis, anomeric-oxygen activation for (trichloroacetimidate method), 50,21 -123... 

Trichloroacetimidate method, anomeric-ox-ygen activation for glycoside synthesis, 50,21-123... 

II. THE TRICHLOROACETIMIDATE METHOD A. Trichloroacetimidate Formation (Activation Step)... 

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