Sugars cyclic

Monosaccharide (simple sugar) + cyclic nitrogenous base yields nucleoside ... 

This has led to an inversion at the C3 center of the sugar backbone. Kiessling et al. (94TL7335 95JOC6254) realized the poor reactivity of cyclic sulfites against oxygen nucleophiles and therefore activated sugar cyclic... 

Some sugar cyclic sulfites are also opened with sodium thiocyanate. Interestingly, they gave exclusively cis-fused 1,2-oxazolidine 2-thione, 221 (95TL5347) [Eq. (41)]. 

Ring expansion products of deamination reactions of amino-sugar cyclic diethioacetals are mentioned in Chapter 8. 

Texts published this year of general interest to carbohydrate chemists have included issues in the Advances in Carbohydrate Chemistry and Biochemistry series, which are prefaced by appreciations of the late Professors E. J. Bourne and E. L. Hirst these texts include review articles on 1,6-anhydro sugars, cyclic acetals of aldoses and aldosides, the Koenigs-Knorr reaction, carbohydrate boronates, and the biosynthesis of sugars in antibiotics. Extensive surveys of carbohydrate derivatives are also included in several books devoted to antibiotics. ... 

Finally, sugar 1,2-cyclic sulfites have been investigated as glycosyl donors. Preliminary studies exploited these compounds for the introduction of reactive nucleophiles, such as azide or benzoate, on the anomeric position [156]. EflFective P-O-glycosylations with sugar cyclic sulfites were then reported, under catalysis of lanthanide(III) triflates. However, the reactions required high temperatures (from 80 to 100 °C), limiting their application only to simple alcohols [157]. 

Lactam (Section 20 15) A cyclic amide Lactone (Section 19 15) A cyclic ester Lactose (Section 25 14) Milk sugar a disacchande formed by a p glycosidic linkage between C 4 of glucose and C 1 of galactose... 

CAP controls a number of operons, all of which are involved in the breakdown of sugar molecules and one of which is the lac operon. When the level of the breakdown products of lactose is low, the concentration of cyclic AMP in the cell increases and CAP is switched on, binds to its specific operators, and increases the rate of transcription of adjacent operons. 

Alkylation of enamines with epoxides or acetoxybromoalkanes provided intermediates for cyclic enol ethers (668) and branched chain sugars were obtained by enamine alkylation (669). Sodium enolates of vinylogous amides underwent carbon and nitrogen methylation (570), while vicinal endiamines formed bis-quaternary amonium salts (647). Reactions of enamines with a cyclopropenyl cation gave alkylated imonium products (57/), and 2-benzylidene-3-methylbenzothiazoline was shown to undergo enamine alkylation and acylation (572). A cyclic enamine was alkylated with methylbromoacetate and the product reduced with sodium borohydride to the key intermediate in a synthesis of the quebrachamine skeleton (57i). 

In a similar manner, ketones can react with alcohols to form hemiketals. The analogous intramolecular reaction of a ketose sugar such as fructose yields a cyclic hemiketal (Figure 7.6). The five-membered ring thus formed is reminiscent of furan and is referred to as a furanose. The cyclic pyranose and fura-nose forms are the preferred structures for monosaccharides in aqueous solution. At equilibrium, the linear aldehyde or ketone structure is only a minor component of the mixture (generally much less than 1%). 

Nucleosides are compounds formed when a base is linked to a sugar via a gly-cosidic bond (Figure 11.10). Glycosidic bonds by definition involve the carbonyl carbon atom of the sugar, which in cyclic structures is joined to the ring... 

Jager and coworkers have used the TBAF catalyzed-stereoselective niho-aldol reaction for the synthesis of cyclic amino alcohols such as iminopolyols, imino sugars, and cyclic amino acids. They are important classes of compounds and have the potential utility as anh-diabetic. 

The well-known reaction leading to ring expansion of cyclic ketones has been applied to derivatives of oxo sugars in an attempt to develop a new route to novel deoxy sugars. By treatment with diazomethane both a five-membered (42) and a six-membered (26) sugar ring have been expanded by insertion of a methylene group. 

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). 

Easily prepared from the appropriate monosaccharide, a glycal is an unsatu-rated sugar with a C1-C2 double bond. To ready it for use in potysaccharide synthesis, the primary -OH group of the glycal is first protected at its primary -OH group by formation of a silvl ether (Section 17.8) and at its two adjacent secondary - OH groups by formation of a cyclic carbonate ester. Then, the protected glycal is epoxidized. 

The following cyclic structure is that of allose. Is this a furanose or pyranose form Is it an a or /3 anomer is it a D or L sugar ... 

Cyclic adenosine monophosphate (cyclic AMP), a modulator of hormone action, is related to AMP (Problem 29.24) but has its phosphate group linked to two hydroxyl groups at C3 and C5 of the sugar. Draw the structure of cyclic AMP. 

Anomers (Section 25.5) Cyclic stereoisomers of sugars that differ only in their configuration at the hemiacetal (anoineric) carbon. 

Glycoside (Section 25.6) A cyclic acetal formed by reaction of a sugar with another alcohol. 

There is another aspect of the structure of glucose and fructose. They, like other simple sugars, can exist as a straight chain but this form is in equilibrium with a cyclic structure. In solutions the latter form prevails. Reaction (2) shows both forms of glucose. 

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