Carbohydrate Analysis
249
Fortunately, although the analytical task
remains formidable, the full range of
monosaccharide ring size and linkage di-
versity is not found, with most glycans
being constructed out of a very limited sub-
set of possible molecular building blocks.
However, the analysis of polysaccharides
and glycans remains challenging and must
be tackled in a systematic manner. There
is no single method applicable to this anal-
ysis. Even for simple carbohydrates like
glucose, a number of methods are used
depending on the purpose of the analy-
sis. Complex carbohydrates may consist
of several monosaccharide moieties com-
bined in differing ways and proportions
and covalently attached to proteins or other
molecules. In these cases, it is necessary
to determine not only the relative amounts
of the carbohydrates present but also their
absolute con±guration (D or L), their ring
size (pyranose or furanose), the anomeric
con±guration of the linkages (
α
or
β
),
the linkage positions and sequence, and
the nature and location of any inorganic
groups or other nonsugar components.
Structures are sometimes determined or
con±rmed by the use of speci±c lectin
binding. Detailed structural analysis of the
carbohydrate moieties in glycoconjugates
enables the investigation and determina-
tion of biosynthetic pathways and biolog-
ical processes and may offer evidence for
the mechanism of metabolic disorders and
clinical behavior. As a ±nal re±nement, the
molecular conformation(s) may have to be
determined in order to fully understand
the biological relevance of the structure.
1.2
Monosaccharides
There are well-established standardized
methods, validated by the International
Commission for Uniform Methods of
Sugar Analysis (ICUMSA), for analyzing
individual low molecular weight carbohy-
drates in foodstuffs. These make use of
nonstoichiometric colorimetric assays for
reducing groups or physical methods such
Fig. 1
The commonest monosaccharides present in glycans, with their common abbreviations in
brackets. (1)
α
-D-glucose (Glc); (2)
β
-D-glucose (Glc); (3)
α
-D-galactose (Gal); (4)
β
-D-galactose
(Gal); (5)
α
-D-mannose (Man); (6)
β
-D-mannose (Man); (7)
α
-D-glucosamine (GlcN);
(8)
N
-acetyl-
β
-D-glucosamine (GlcNAc); (9)
N
-acetyl-
α
-D-galactosamine (GalNAc);
(10)
N
-acetyl-
β
-D-galactosamine (GalNAc); (11)
α
-L-fucose (Fuc); (12)
N
-acetyl-
α
-D-fucosamine
(FucNAc); (13)
α
-D-glucuronic acid (GlcA); (14)
α
-D-galacturonic acid (GalA); (15)
β
-D-glucuronic
acid (GlcA); (16)
β
-D-galacturonic acid (GalA); (17)
α
-L-arabinose (Ara); (18)
β
-L-arabinose (Ara);
(19)
α
-D-xylose (Xyl); (20)
β
-D-xylose (Xyl); (21)
α
-L-iduronic acid (IdoA); (22)
α
-L-rhamnose (Rha);
(23) 3,6-anhydro-
α
-D-galactose; (24) 3,6-anhydro-
α
-L-galactose; (25)
β
-D-fructose (Fru);
(26)
N
-acetyl-
β
-L-talosaminuronic acid; (27)
α
-L-galactose; (28)
β
-D-galactofuranose (Gal
f
);
(29) 3-deoxy-
β
-D-
manno
-oct-2-ulopyrasonic acid (Kdo); (30)
β
-L-arabinose (Ara);
(31)
β
-D-mannuronic acid (ManA); (32)
α
-L-guluronic acid (GulA); (33)
N
-acetyl-
α
-neuraminic acid
(NeuAc or sialic acid, SA). Compounds 17, 18, 25, and 28 are furanoses, the rest being pyranoses.
Compounds 1–6, 25, and 27–28 are hexoses, 7 an aminohexose, 8–10
N
-acetamidohexoses, 11, 12,
and 22 deoxyhexoses, 13–16, 21, and 31, 32 hexuronic acids, and 17–20 and 30 pentoses.
Compounds 2, 4–6, 8, 10–11, 14–15, 17, 20, 22, and 33 are relatively common, whereas compounds
7, 12, 16, 18, 23–24, 26 – 28, and 29–32 are rarely found, the remainder occurring occasionally.
Other monosaccharide residues (not shown) are found very rarely, with microorganisms in particular
producing a wide variety of rare monosaccharide units. Compounds are also found as derivatives
with some or all of sulfate, phosphate, or acetyl groups or as their methyl ethers.
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