CHEM 30B
Dr. R. Rinehart
Table of Carbohydrates
Names in bold represent sugars whose structures you should learn!
name
Fischer
projection
Haworth
projection
comments
D-glyceraldehyde
only cyclic sugars can have a Haworth projection
to determine whether a sugar is of the D- or L- type, look at the –OH group on the lowest chiral center in the Fischer projection
dihydroxyacetone
in the standard Fischer projection for carbohydrates, the aldehyde group is at the top; for ketoses, the ketone group is as close to the top as possible; for amino acids, the carboxyl group is at the top.
furan
cyclic unsaturated ether
---
sugars which form cyclic hemiacetals or hemiketals with 5-membered rings are called “furanoses” in analogy with furan
furanose:
basic depiction
the
standard orientation in the Haworth projection is with the ring oxygen at
the top, representing the back edge of the molecule. C-1 is at the right.
The ring atoms at the bottom are the front edge of the molecule. Shading
has been omitted from the structures below for clarity.
g-pyran
cyclic unsaturated ether
---
sugars which form cyclic hemiacetals or hemiketals with 6-membered rings are called “pyranoses” in analogy with pyran
pyranose:
basic depiction
the standard orientation in the Haworth projection is with the ring oxygen at the top right, representing the back edge of the molecule. C-1 is at the right. The ring atoms at the bottom are the front edge of the molecule. Shading has been omitted from the structures below for clarity.
D-ribose
only cyclic sugars can have a Haworth projection
one of eight possible aldopentoses, it’s the easiest to remember because all the –OH groups are on the right.
b-D-ribofuranose
In
RNA, the –OH at C-1 is replaced by N-1 of a pyrimidine base or N-9 of a
purine base; the –OH on C-3 and C-5 are converted to phosphate esters
The b-anomer
can be identified in the following manner: In the Fischer projection with
the ring O shown to the right of the vertical axis, the anomeric –OH is
on the left. In the Haworth projection, the anomeric –OH is on the same
side of the ring as the terminal –CH2OH group [up for
D-sugars]. For additional insight on going from Fischer to Haworth
projections, see Clarke Earley's [Kent State U, Stark campus] carbohydrate
page at
http://www.personal.kent.edu/~cearley/PChem/sugar/makering.htm
[or access from
http://www.personal.kent.edu/~cearley/PChem/pchem.htm ]
D-2-deoxyribose
found
in DNA; the lack of the –OH at C-2 makes DNA much more stable to
alkaline hydrolysis than RNA is.
D-glucose
---
the most common and most important of all the monosaccharides
a-D-glucopyranose
the
alpha-structure is conserved in maltose, sucrose, amylose, amylopectin,
and glycogen.
the Haworth
projection is closer to the actual shape of the molecule, but is
simplified to permit remembering the configuration of the -OH groups.
compare the Haworth structure above to the more accurate conformational
representation below.
b-D-glucopyranose
in solution, there is a mixture of ~⅔ b and ~⅓ a with <1% open-chain form present. The beta-structure is conserved in cellulose
L-glucose
only cyclic sugars can have a Haworth projection
L- sugars are the COMPLETE enantiomers [mirror images] of the corresponding D- sugar of the same name. You’d starve to death if this was the sugar you ate.
b-L-glucopyranose
L- sugars are the COMPLETE enantiomers [mirror images] of the corresponding D- sugar of the same name.
D-galactose
only cyclic sugars can have a Haworth projection
a common sugar in nature, it makes up half of the disaccharide lactose. A serious disorder called galactosemia results when some individuals have a hereditary inability to metabolize galactose. If not treated by total removal of galactose and lactose from the diet, irreversible mental retardation and even death can result.
compare the Haworth structure above to the more accurate conformational representation below.
b-D-galactopyranose
You can view
Dave Woodcock’s Chime structure of
b-D-galactopyranose at
http://www.molecularmodels.ca/molecule/modelfiles/al3073b.html
[or access from
http://www.molecularmodels.ca/molecule/Natural_Products.htm]
D-mannose
only cyclic sugars can have a Haworth projection
derived from ivory nuts and other sources.
D-fructose
only cyclic sugars can have a Haworth projection
the only ketohexose on this list; sweetest of all natural sugars
b-D-fructofuranose
note that C-1 is not part of the ring – the anomeric carbon is C-2
maltose
4-O-(a-D-glucopyranosyl)-b-D-glucose
D-glc(a1à4)b-D-glc
for clarity, unnecessary hydrogens are often not shown in Haworth structures. Maltose is produced by the breakdown of starch by enzymes in malted [sprouted] barley, and is fairly sweet.
lactose
4-O-(b-D-galactopyranosyl)-b-D-glucose
D-gal(b1à4)b-D-glc
milk sugar; almost tasteless, but helps keep Ca2+ in solution by complexing it.
sucrose
a-D-glucopyranosyl-b-D-fructofuranoside
D-glc(a1↔b2)D-fru
in
order to draw sucrose, either one of the rings has to be shown in
nonstandard orientation or the length of the glycosidic bonds has to be
exaggerated. I went for the latter option just to keep it simple. Since
both anomeric positions are tied up in acetal linkages, sucrose is not
capable of reducing Benedict’s reagent.
sucrose
alternate representations
this is what sucrose looks like when the standard ring orientation is sacrificed for more reasonable bond lengths or angles.
In the upper drawing, the furanose ring has been rotated 180o counterclockwise around an axis perpendicular to the paper, so C-2 of fructose ia now at its left side.
In the lower drawing, the furanose ring has been swiveled 180o around the C2-O glycosidic bond. Note that the fructose ring O and C-5 and C-6 are now at the front edge of the picture.
a very small portion of an amylose chain. all the subunits are a-D-glucose and all the acetal links connect C-1 of one subunit to C-4 of the next subunit. Thus the linkage abbreviation a(1à4). Amylose is responsible for the formation of a deep blue color in the presence of iodine.
very small portion of an amylopectin-type or glycogen-type polysaccharide showing two branch points [drawn closer together than they should be] Most linkages are still a(1à4), but the branch linkages are a(1à6). In glycogen, the branches occur at intervals of 8-10 glucose units, while in amylopectin the branches are separated by 10-12 glucose units. Natural starches are mixtures of amylose and amylopectin.
very small portion of a cellulose chain. . all the subunits are b-D-glucose and all the acetal links connect C-1 of one subunit to C-4 of the next subunit. Thus the linkage abbreviation b(1à4)
sorbitol
used as a noncaloric, noncarieogenic sweetener
mannitol
used as a laxative for babies and by drug dealers to cut heroin, etc.
xylitol
used as a noncaloric, noncarieogenic sweetener
glucosamine
component of many heteropolysaccharides, including some found in cartilage. You’ve seen it advertised on TV!
N-acetylglucosamine
the repeating unit in chitin, the structural material of arthropod exoskeletons
D-gluconic acid
the Haworth projection is of gluconolactone, the cyclic ester form
D-glucuronic acid
structure of a glucuronidate conjugate of “R”
the body “conjugates” [attaches by a glycosidic link] this compound to many foreign substances to render them more water-soluble and thus excretable in urine.
D-glucaric acid
---
it’s just here to torture you with completeness!
© Ronald W. Rinehart, 2002-6
Structures drawn with MDL IsisDraw® , ACD Labs
Chemsketch®
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