7. MONOSACCHARIDES AND OLIGOSACCHARIDES
325
L. URONIC ACIDS
The uronic acids are acidic derivatives of monosaccharides in which
the terminal carbon (bearing the highest number) is a carboxyl group;
only six-carbon uronic acids ("hexuronic acids") have so far been found
in nature. These free monosaccharide acids, like their parent hexoses,
can form a- and ß-glycosidic linkages and are, of course, "reducing"
substances. In addition, being carboxylic acids, they can form anions,
esters, etc. (LXXIX-LXXXI).
CHO
C0 2 H
C0 9 -CH
Aldehydohexuronic
acid
(LXXIX)
HOH
a/ß- Hexopyranuronate
ion
(LXXX)
OCH 3
Methyl-O-0-hexo
pyranuronoside
methyl ester
(LXXXI)
Six hexuronic acids are known in glycosidic combination (LXXXIILXXXVII), one of these, D-galacturonic acid has been found free in
detectable amounts in fruits (156).
(
•—
(
DHO
—·
—·
:O 2 H
(
•—
•—
(
}HO
—·
UO2H
D-Glucuronic
D-Galacturonic
acid
acid
(LXXXII)
(LXXXIII)
CHO
•—
•—
(
L-Idi
a
(LX.
—·
—·
:O 2 H
uronic
cid
XXV)
CHO
•—
•—
•—
(
L-(
(L
jrU
a
x:
—·
U0 2 H
[uronic
cid
XXVI)
•—
•—
CHO
1—NH 2
C0 2 H
D-Galactosaminuronic
acid
(LXXXIV)
CHO
•—1
•—
c
D-Man
a<
(LXX
—·
;O 2 H
nuronic
3id
XVII)
1. Ό-Glucuronic Acid
Derivatives of this acidic monosaccharide are widely distributed
throughout the plant, animal, and microbiological kingdoms. In animals
O-glycosidic derivatives of phenolic and other cyclic foreign chemicals
are generated in the liver, kidney, and possibly other tissues (156a).