L-Glucopyranose

DrawjS-L-glucopyranose in its more stable chair conformation. 

Mirror images a-o-glucopyranose-4Ci (upper) and a-L-glucopyranose-1C4 (lower) 2-Carb-8. Aldoses 2-Carb-8.1. Trivial names... 

Fic. 13.—Superpositioning of /3-d- and -L-Glucopyranose over the Same Receptor Site. 

CDs are by far the most popnlar chiral selectors in CE and will therefore be discussed in more detail than the others. CDs are torus-shaped, cyclic, a(f,4)-linked oligomers of D( + )-glucopyranose. They contain between six and 12 D(-l-)-glucopyranose units, bnt only those with 6 (a-CD), 7 ( -CD) and 8 (/-CD) units are currently used in chiral separations (Figure 1). The interior of the CD cavity is relatively hydrophobic, while the outside rims are more hydrophilic. The rim of the wider side of the CD contains chiral secondary hydroxyl groups, while achiral primary hydroxyl groups occupy the opposite smaller opening. 

Problem 22.32 Draw the more and less stable conformations of a) /3-o-mannopyranose (Problem 22.11), (f>) a-D-idopyranose (idose is the C epimer of gulose see Problem 22.27), (c) /3-L-glucopyranose (/3-l- and /3-Dare enantiomers). Explain each choice. ... 

When penta-O-acetyl-a-D-idopyranose (25) was subjected to radical bro-mination using jV-bromosuccinimide as source, it gave, in good yield, penta-0-acetyl-5-bromo-/ -L-glucopyranose (26) (see Scheme 5), which is the en-... 

More recently, a facile synthesis of 126 and pseudo-a-L-glucopyranose (137) has been described [32], When the bromolactone 38 was heated with glacial acetic containing hydrogen bromide and subsequently acetylated, DL-(l,3,5/2,4)-2,3-diacetoxy-4,5-dibromocyclohexane-l-carboxylic acid (130) was obtained [31], Resolution of 130 with optically active a-methylbenzylamines provided the enantiomer (131), m.p. 

Analogous reactions from 132 gave pseudo-a-L-glucopyranose pentaacetate (136), [a]p° —56° (chloroform), which was converted into pseudo-a-L-glucopyranose 137, [a]31 —67° (methanol), on hydrolysis [32] (Scheme 23). 

Show that in /3-L-glucopyranose all the substituents on the ring carbon atoms are equatorial. 

The substituents of /3-L-glucopyranose are all on the opposite side of the Haworth structure from those of /3-D-glucopyranose (i.e., they are in the positions occupied by the H s in /3-D-glucopyranose). Therefore, from Example 2.13, it may be seen that in the 1C chair conformer, all the substituents of /3-L-glucopyranose would be equatorial. 

Swern oxidation provided the intermediate dicarbonyl derivative 32, which spontaneously cyclized into cyclohexene 33 under the action of ethyl diisopropylamine in a 50% overall yield. The resulting unsaturated ketone was reduced, desilylated and hydrogenated to separately afford 5a-carba-a- and (3-L-idopyranose, as well as 5a-carba-a- and (3-L-glucopyranose [31]. 

Cyclodextrins are cyclic oligosaccharides containing at least six D-(-l-)-glucopyranose units attached hy a(l—>4) glucoside bonds. The three natural cyclodextrins, a, P, and y, differ in their ring size and solubility. They contain 6, 7, or 8 glucose units, respectively. 

In the terminology suggested by Reeves (see Ref. 1), the mirror image of VII, /3-L-glucopyranose, has the 1C conformation. The designation Cl (italics) is not to be confused with Cl (no italics) for carbon atom number one of a sugar chain. 

Gorin176 studied the Koenigs-Knorr reaction of 2-O-substituted 3,5-di-O-benzoyl-a-L-arabinofuranosyl (108) and -D-ribofuranosyl (111) bromide with methanol and l,2,3,4-tetra-0-acetyl-/3-l>glucopyranose (see Table IV). Compound 108 gave the 1,2-orthoester 109 plus the glycoside 110, and bromide 111 gave the 1,2-orthoester 112 plus the glycoside 113. 

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