Pyranoids sugars

As it has been revealed that replacement of the ring-oxygen atom in a pyranoid sugar by a CH2 group is not detrimental to its sweetness, 6a-carba- -D-fructopyranose may have the same intense sweetness as D-fruc-tose. To substantiate this prediction, the following two reaction routes have been successfully developed for 6a-carba-y -DL-fructopyranose, as well as for the enantiomers. 

While the broad mission of the National Bureau of Standards was concerned with standard reference materials, Dr. Isbell centered the work of his laboratory on his long interest in the carbohydrates and on the use of physical methods in their characterization. Infrared spectroscopy had shown promise in providing structural and conformational information on carbohydrates and their derivatives, and Isbell invited Tipson to conduct detailed infrared studies on the extensive collection of carbohydrate samples maintained by Isbell. The series of publications that rapidly resulted furnished a basis for assigning conformations to pyranoid sugars and their derivatives. Although this work was later to be overshadowed by application of the much more powerful technique of nuclear magnetic resonance spectroscopy, the Isbell— Tipson work helped to define the molecular shapes involved and the terminology required for their description. 

The symbols CA and CE, appended to the names of the structures shown, follow an improved system for indicating the principal conformations of pyranoid sugars and derivatives [H. S. Isbell and R. S. Tipson, J. Ret. Natl. Bur. Sid., 64A, 171 (I860)]. Through the use of symbols, a precise specification of all of the principal pyranoid conformers can be made. 

In this context, pyranoid sugar enolones of type 8, or 9, i. e. those that carry chiral centers on either side of the enolone structural element, are even more powerful building blocks stereoselectivities in addition reactions. They are accessible in various substituted forms from the respective hydroxyglycal esters in another, preparatively delightful reaction channel, a chlorination - hydrolysis elimination sequence (27, 28). 

An interesting example of a branched trimer containing (1 6)- and /3(1 2)-amide-linked sugars was supplied by Sicherl and Wittmann who devised mimetics of amino glycosides [37]. Pioneered by the group of Kessler [38] pyranoid sugar amino acid templates were described to represent turn mimetics and model peptides [39,40] including cyclic peptides [41,42]. As... 

P. L. Durette and D. Horton, Conformational studies on pyranoid sugar derivatives by NMR spectroscopy. Correlations of observed proton-proton coupling constants with the generalized Karplus equation, Org. Magn. Reson., 3 (1971) 417-427. 

For pyranoid sugars, the Whiffen-Brewster rules were reduced to four rotational parameters. These are based on pairwise gauche relationships between carbon... 

Bond Lengths and Angles in Pyranoid Sugars and Derivatives... 

Pyranoid sugar or sugar residue Derivative studied Bond length (A.) Angles degrees) At carbon At in rings Or References... 

By integration of the signals for the anomeric protons of pyranoid sugars the relative amounts of the anomeric forms were measured and compared with values obtained by other methods (Table II). The... 

The synthesis of pyranoid sugar derivatives having an episulfide group fused to the ring involves requirements of molecular geometry more critical than for episulfides on an acyclic chain. Conversion of an epoxide in a locked-ring system to an episulfide by the action of thiourea or thiocyanate ion is diflicult, because reactions of this type involve a trans-fused, cyclic intermediate (91), formation of which requires a [Pg.179]

Pyranoid Sugar Derivatives Having Fused Rings.114... 

The first application to pyranoid sugars of the Sachse-Mohr theory of puckered rings was made by Sponsler and Dore in 1926 in their... 

The study of the conformations of cyclic sugars was developed more fully by Reeves in a series of papers, beginning in 1949, dealing with the formation of complexes of sugars and their derivatives in cuprammonia solution. Reeves was able to provide experimental evidence to indicate that some pyranoid sugars indeed adopt chair conformations in solution, and that, in such cases, one chair form usually appeared to preponderate over the other. Boat or skew conformations were considered possible if the nonbonded interactions between the substituents in the chair conformation became too large. " Reeves s investigations have formed the basis of much subsequent work in the conformational analysis of cyclic carbohydrate... 

A notable exception has been the application of i.r. spectroscopy by Isbell and Tipson to the analysis of the conformations of methyl aldopyranosides," acetylated methyl aldopyranosides," " and fully acetylated aldopyranoses in the solid state. Their approach was based on (J) the assumption that the pyranoid sugar derivatives predicted by Reeves to exist in only one of the chair conformations in solution would adopt that same conformation in the crystalline state, and (2) the observation that axially and equatorially attached groups at the anomeric carbon atom give rise to different vibrations. 

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