Page 55 - Academic Press Encyclopedia of Physical Science and Technology 3rd BioChemistry

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Encyclopedia of Physical Science and Technology EN006P-81 June 29, 2001 21:48

Glycoconjugates and Carbohydrates 839

Glucose family
Amino sugars
CH 2 OH CH 2 OH CH 2 OH
CH 2 OH CH 2 OH
H O OH H O OH H O OH
H H H HO O OH H O OH
OH H OH H OH H H H
HO H HO H HO H OH H OH H 2 N
H H HO H
H OH H NH 2 H NH
H NH 2 H H
C O β -D-Galactosamine β -D-Mannosamine
CH 3
β -D-Glucose β -D-Glucosamine N-Acetyl-β -D-Glucosamine
Deoxy sugars
2 H H
CH 2 O PO 3 CH 2 OH CH 2 OH
H O OH H O OH H O OH CH 3 H O H HO O OH
H H H CH 3 CH 3
OH H R H R H R O C H H OH H H
HO H HO H HO H HO OH H H
COO
H OH H NH 2 H NH OH H OH OH
β -L-Fucose α -L-Rhamnose
C O
CH 3
β -D-Glucose 6-phosphate Muramic acid N-Acetylmuramic acid
Acidic sugars
O O CH 3 O O
R
C CH 2 OH CH 2 OH O C H C
H O OH H OH O H O HN O H C OH
H H C H O R
OH H OH H OH H H H H C OH
HO H HO O HO H OH
CH 2 OH
H OH H OH H OH OH H
β -D-Glucuronate D-Gluconate D-Glucono-δ -lactone N-Acetylneuraminic acid
(sialic acid)
FIGURE 12 Sugars related to D-glucose that occur in nature.

the carbonyl carbon and oxidizes the adjacent secondary tions are carried out elsewhere in the chain. This may be
hydroxyl (aldoses) or primary alcohol (ketoses) to al- achieved by formation of dithioacetals or, in the ring form,
low a second condensation. The resulting derivatives, by suitable substitution of the anomeric hydroxyl group
phenylosazones, are crystalline and were employed both (see below).
for identification and determination of stereochemistry.
Phenylhydrazine itself is a liver poison and it is gen- 2. Reaction at the Anomeric Hydroxyl Group
erally believed that Fischer suffered from liver damage
The hemiacetal nature of the anomeric hydroxyl group
due to this reagent (no longer employed). A simple ex-
makes it the most reactive of that type. Direct oxidation
ample of the utility of this conversion is the fact that
can be carried out with several reagents, most classically,
D-glucose, D-mannose, and D-fructose all give the same
hypoiodite. This results in rapid oxidation to the aldono-
phenylosazone showing that their relative stereochemistry
lactone and is only exhibited by aldoses. Alternatively,
at the remaining asymmetric centers (carbons 3,4,5) is
reaction with alcohols results in the formation of full ac-
identical (Fig. 13).
etals (glycosides). A very large variety of such structures
Certain transformations may dictate that the carbonyl
have been made.
function remain available for later chemistry while reac-
Control of stereochemistry at the anomeric center is
complex, involves the configuration at carbon two and ki-
CH NNHC 6 H 5 netic factors. In general, both alpha- and beta-glycosides
CHO CHO
C are formed. The configuration is very important in biologi-
H OH NNHC 6 H 5 HO H
HO H C 6 H 5 NHNH 2 HO H C 6 H 5 NHNH 2 HO H cal systems since enzymatic transformations are generally
H OH H OH H OH
H OH H OH H OH stereospecific with essentially all glycosidases having
CH 2 OH CH 2 OH CH 2 OH absolute specificity for either the alpha or beta form. Gly-
D-Glucose Same phenylosazone D-Mannose coside formation is generally carried out by reaction of the
FIGURE 13 Formation of phenylosazone from D-glucose or sugar with the appropriate alcohol in nonaqueous solution,
D-mannose. The loss of asymmetry at C-2 yields identical products. typically with an acid catalyst.