Cyanoethylidene

JljHxgNOg 3,4,6-Tri-0-acetyl-l)2-0-(l-cyanoethylidene)-a-D-glucopy- ranose TACYEG 37 396... 

Cyanoethylidene derivatives can be prepared from the corresponding glycosyl halides by the treatment with KCN and n-Bu4NBr in CH3CN or from the corresponding peracetates and TMSCN in the presence of stannous chloride (Scheme 5.9). 

The 1,2-O-cyanoethylidene method also became the basis for a polycondensation reaction, which allowed the synthesis of many polysaccharides [37]. When both the O-trityl and cyanoethylidene groups are present in the same molecule as in 31, polycondensation takes place under glycosidation conditions giving a polysaccharide chain, for example 32 (Scheme 5.11). 

The trityl-cyanoethylidene polycondensation also permitted the synthesis of polysaccharides having functionalized aglycones for the production of neoglyco-conjugates. An alternative approach for preparation of neoglycoconjugates, which could be used for serodiagnosis of infectious diseases (such as... 

Group B type III Streptococcus was prepared by employing thioglycosyl. cyanoethylidene, and pentenyl glycosides (Scheme 4.15).3, 42 rrhe... 

Related to the above cyanoethylidene derivatives, thioorthoesters 231 also behave similarly, and can be activated with catalytic amounts of TrC104 to glycosylate trityl ethers [506,507]. By using the thioglycoside promoters NIS-TfOH [508] or I2 [254], glycosyl acceptors with free hydroxyls were glycosylated. 

SCHEME 4.46 Synthesis of Streptococcus pneumoniae type 14 polysaccharide using cyanoethylidene derivative. 

Activation of trisaccharide cyanoethylidene derivative 118 with catalytic trityl perchlorate in the presence of a stiochiometric amount of the 3,6-di-O-trityl ether 119 afforded the tetrasaccharide 120 in 55% yield, whereas carrying out the same reaction with a half-molar equivalent of the bis trityl ether gave the heptasaccharide 121 in 60% yield (Scheme 21). 

This ring is formed from the reaction of cyanoethylidene and acetyl functions by heating the compound with phosphoric acid. 

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