7. Some facts:
Carbon atoms have a
characteristic tetrahedral
arrangement of their four single
bonds
Carbon-carbon single bonds
have freedom of rotation
Dr.
P.
ojola
8. When a carbon atom has
four different substituent
groups (A, B, X & Y), they
can be arranged in two
ways that represent non-
superimposable mirror
images of each other
(called "enantiomers")
Dr.
P.
ojola
9. Monosaccharides have several asymmetric ("CHIRAL")
carbon atoms
they occur in optically active isomeric
forms
The simplest aldose is glyceraldehyde
It contains one chiral center, and occurs
in two optical isomers or enantiomers:
BY CONVENTION:
one of them is called the D-isomer, the other the L-isomer
D-isomer: OH to the right (<Latin, Dexter)
L-isomer: OH to the left (<Latin, Laevus)
Dr.
P.
ojola
10. BY CONVENTION:
horizontal bonds project out of the plane of the paper,
vertical bonds project behind the plane of the paper.
Dr.
P.
ojola
11. The stereoisomers of
monosaccharides can
be devided into two
groups that differ in
the configuration at
the chiral center that is
most distant from the
carbonyl carbon.
The latter chiral center
is called the reference
carbon atom.
Reference carbon atom
Dr.
P.
ojola
12. D-Glucose L-Glucose
BY CONVENTION:
The sugar is called a D-sugar when the OH at the reference
carbon is on the right in the Fischer projection formula
The sugar is called an L-sugar when the OH at the reference
carbon is on the left in the Fischer projection formula
Most hexoses of living organisms are D-isomers.
Dr.
P.
ojola
13. Carbon atoms in red are chiral centers
Sugars in boxes are most common in nature
Dr.
P.
ojola
16. In aqueous solutions, sugars with four, five or more C-atoms in the
backbone predominantly occur as cyclic (ring) structures.
The formation of these ring structures is based on a general reaction
between aldehydes (ketones) and alcohols, to form resp.
hemiacetals (hemiketals):
These hemiacetals/hemiketals contain a new asymmetric carbon
atom, thus they can exist in two stereoisomeric forms
New chiral center
Dr.
P.
ojola
17. Anomeric
carbon atom
In solution, the ring structure
is in equilbrium with the
open (straight-chain) form.
The carbonyl carbon atom is
called the anomeric carbon
atom.
The stereoisomers are
designated the -(alpha)
and -(beta) anomers. The
interconversion of - and
-anomers is called
mutarotation.
Dr.
P.
ojola
18. Example:
D-glucose
1. Number the C-atoms in Fischer projection:
1
2
3
4
5
6
anomeric carbon atom (C1)
C2-5 are asymmetric
reference carbon atom (C5)
2. Check the position of the OH at the reference C-atom.
(You will need this information later)
Dr.
P.
ojola
19. 3. Convert the Fischer projection
into the Haworth projection
by starting to write down the
molecule in the following way:
tail
head
head
tail
i.e.:
reference carbon
anomeric carbon
heavy line, meaning
that this bond is
nearest to the
observer
Dr.
P.
ojola
20. 4. Place the OH groups at the correct positions (i.e. above or
below the plane of the emerging sugar ring), taking into account that:
5. Start counting from the anomeric carbon atom to trace the OH to be
used for ring closure.
This will be determined by the kind of ring (5-, or 6-ring) that will be formed.
6. Circularly permute the groups on the last carbon atom, in such a way that
the future ring oxygen is facing to the right:
Fisher projection Haworth projection
RIGHT UNDER
LEFT ABOVE
future ring oxygen,
if a 6-ring is to be
formed
Dr.
P.
ojola
21. 7. Close the ring, and rewrite the structure:
anomeric carbon
Dr.
P.
ojola
22.
23.
24. 8. Finally determine whether the OH group at the anomeric carbon
atom is above, or below the plane of the ring:
in an -sugar, the OH group is cis compared to the
OH group at the reference carbon atom*
in a -sugar, the OH group is trans compared to the
OH group at the reference carbon atom*
*Look back to the Fischer projection !!
Dr.
P.
ojola
25. Six-membered sugar rings are called PYRANOSES
Five-membered sugar rings are called FURANOSES
A six-membered aldopyranose ring is more stable than a five-membered
aldofuranose ring, and thus predominates in an aldohexose solution
Dr.
P.
ojola
26.
27. NO, because sugar rings are not planar
A pyranose ring tends to adopt a "chair" conformation in solution
Dr.
P.
ojola
28.
29.
30. Sucrose: prevalent in sugar cane and sugar beets, is composed
of glucose and fructose through an α-(1,2) glycosidic bond.
Disaccharides
• Bonds between sugar units are termed glycosidic bonds,
and the resultant molecules are glycosides.
• The linkage of two monosaccharides to form
disaccharides involves a glycosidic bond. The important
food disaccharides are sucrose, lactose, and maltose.
No reducing capacity
Reducing ends are not
exposed due to 1,2 bond
31. Lactose:
is found exclusively in the milk of mammals and consists of
galactose and glucose in a β-(1,4) glycosidic bond.
Both are reducing sugars…so we could do this in milk
32. Maltose:
Is the major degradation product of starch, and is composed
of 2 glucose monomers in an α-(1,4) glycosidic bond.
…and in starch hydrolysis reactions to monitor
glucose production in making corn syrup!
33.
34.
35.
36.
37.
38.
39.
40.
41.
42.
43.
44.
45.
46. Von Gierke disease is a condition in which the body cannot break down glycogen. Glycogen is a form of
sugar (glucose) that is stored in the liver and muscles. It is normally broken down into glucose to give you
more energy when you need it.
Von Gierke disease is also called Type I glycogen storage disease (GSD I).
Causes
Von Gierke disease occurs when the body lacks the protein (enzyme) that releases glucose from glycogen.
This causes abnormal amounts of glycogen to build up in certain tissues. When glycogen is not broken
down properly, it leads to low blood sugar.
Von Gierke disease is inherited, which means it is passed down through families. If both parents carry a
nonworking copy of the gene related to this condition, each of their children has a 25% (1 in 4) chance of
developing the disease.
Symptoms
These are symptoms of von Gierke disease:
•Constant hunger and need to eat often
•Easy bruising and nosebleeds
•Fatigue
•Irritability
•Puffy cheeks, thin chest and limbs, and swollen belly
47.
48.
49.
50.
51. Amylopectin + H2O (+)-maltose
(+)-maltose + H2O (+)-glucose
Also a polyglucose, but branched every 20-25 units:
52.
53.
54.
55.
56.
57.
58.
59.
60.
61.
62.
63.
64.
65.
66.
67.
68.
69.
70.
71.
72.
73.
74.
75.
76.
77.
78.
79.
80.
81.
82.
83.
84.
85.
86.
87.
88.
89.
90.
91.
92.
93.
94.
95. After being oxidised they cause the reduction of the other
substances and so known as reducing sugars.
Fehling’s solution and Benedict’s solution are carry out
the oxidation e.g.,
Reducing carbohydrate + Fehling’s solution (Deep blue) -
> Oxidised Carbohydrates + 2 Cu+
2Cu+ + 2OH -> 2CuOH (Light yellow or green) -> Cu2O
(Red) + H2O
C6H12O6 (Glucose) + 2Cu(OH)2-> C6H12O7 (Gluconic
acid) + Cu2O (Red) + H2O
96.
97.
98. Any carbohydrate capable of being oxidized and
causes the reduction of other
substances without having to be hydrolysed first is
known as reducing sugar, but
those which are unable to be oxidised and do not
reduce other substances are known
as non-reducing sugars.
Generally, all the free monosaccharides having free
aldehyde or hydroxyl ketonic group are capable of
being oxidised
99. Chemical Properties of Reducing Sugars
Reducing Sugars
• Some monosaccharides can act as Reducing Agents
(electron donators). (I.e. Glucose and Fructose)
– They reduce Fehling’s, Tollen’s, or Folin’s Reagents
We will use these properties of sugars for
understanding their physical properties.
101. • 3,5-DINITROSALICYLIC ACID reacts with reducing
sugars in alkali to form brown-red color that can
be measured on a spec
• RESORCINOL (a phenol) reaction is primarily
with ketoses to form a colored complex
• ORCINOL (a phenol) reacts with pentoses with
5X more color than hexoses
Chemical Methods
102. To the “extreme”
n Some methods detect the reaction of “going toooo far” with the
sugar hydrolysis
n PHENOL mixed with SULFURIC ACID and heated with “digest”
carbohydrates to create furans (furfural, 5-hydroxymethyl furfural,
furaldehyde) which condenses with phenol into a near pink color.
103. Carbohydrates: Indicator Tests
• Simple Sugars:
– Benedict’s solution
– Blue solution turns
orange/green/brown
• Complex Carbs:
– Lugol’s
solution/Iodine
– Turns from orange-
red-brown to black-
purple
