Sugars displacement reactions

Another deviation from the normal displacement reaction of primary tosylates occurs in nucleoside derivatives (39, 81) where cyclonucleosides and anhydronucleosides are formed by participation of a nitrogen atom (as in purine nucleosides) and oxygen atom (as in pyrimidine nucleosides ), respectively. Iodonucleosides can result from these reactions only if these cyclic compounds are prone to attack by iodide ion. Several new examples of unexpected reactions during the solvolysis of sulfonate esters in sugar derivatives have been recorded in the past few years (2, 4,5,7,15,44,62,63,94). 

Two branched-chain sugars, methyl 3-azido-4,6-0-benzylidene-2,3,-dideoxy-3-C-(fluoromethyl)-a-D-flraZ)/ o-hexopyranoside and methyl 2-azido-4,6-0-benzylidene-2,3-dideoxy-2-C-(fluoromethyl)-) -D-r/to-hexo-pyranoside have been prepared through the usual displacement reactions. 

Internal-displacement reactions to give sugar anhydrides are well known, and anhydro derivatives of sucrose have been prepared by treatment of the respective sulfonates or chlorides with a base. Buchanan and coworkers described the synthesis of 3, 6 -anhydrosucrose by treating 2,3,4,6,l, 3, 4 -hepta-0-acetyI-6 -0-(p-ni-trophenylsulfonyl)sucrose with sodium ethoxide in ethanol for 2 h under reflux.18 Similar treatment of 2,3,4,l, 3, 4, 6 -hepta-0-acetyl-6-chloro-6-deoxysucrose (46) with sodium methoxide in methanol, followed by acetylation, gave crystalline 2,4,l, 3, 4, 6 -hexa-0-acetyl-3,6-anhydrosucrose (47) in 83% yield.81 The H n.m.r. spectrum of 47... 

Bimolecular, nucleophilic-displacement reactions of sugar sulfonates have been reviewed in this Series.58,59 The value of these reactions in the preparation of deoxyhalo sugars has been emphasized by Hanessian.92... 

Azidodeoxy sugars are useful intermediates in the synthesis of aminodeoxy sugars. Nucleophilic-displacement reactions of sulfonate and deoxyhalo derivatives of sucrose with sodium azide have been used for the preparation of sucrose azides. The reaction of... 

Nucleophilic-displacement reactions constitute some of the earliest known methods for the preparation of deoxyhalogeno sugars. A variety of leaving groups have been used, including sulfonyloxy (usually jP-tolylsulfonyloxy or methylsulfonyloxy), halide, triphenyl-methoxy (trityloxy), acetoxy, phosphate, and nitrate. As Barnett has surveyed the reactions in Volume 22 of this Series,1 this subject will not be discussed comprehensively in the present Chapter instead, only some general comments will mainly be made that will also be relevant to later discussions. 

A diamino sugar, 2,4-diamino-2,3,4,6-tetradeoxy-D-arafomo-hexo-pyranose (kasugamine), is a component of the antibiotic kasugamycin. Two key steps in a synthesis182 of this sugar were the preparation of a bromodeoxy sugar and a subsequent displacement reaction by azide... 

By far, the most challenging task in bond-forming reactions with sugar derivatives is to effect C—C branching. The 2 nucleophilic displacement reactions with carbon nucleo-... 

One of the compounds formed from UDP-GlcNAc is UDP-N-acetylmuramic acid. The initial step in its synthesis is an unusual type of displacement reaction on the a-carbon of PEP by the 3-hydroxyl group of the sugar (Eq. 20-6, step a).40410 Inorganic phosphate is... 

Several efficient methods for the preparation of amino sugars have been developed57 and the following general methods can be identified nucleophilic displacement reactions, epoxide opening, additions to glycals, reduction of oximes and intramolecular substitutions. 

---