3. LETS LEARN SOME GREEK!!!!
The name glucose comes from the Greek word
glykys (γλυκύς), meaning "sweet", plus the suffix
"-ose" which denotes a sugar
4 chiral centers give 24 = the 16 stereoisomer s
of hexose sugars. Chirality, or
"handedness", Greek, (χειρ), kheir: "hand”
chiral carbons are enantiomers
Alpha α and Beta β are letters in the Greek
alphabet
6. Carbohydrates
• Carbohydrates, or saccharides (saccharo is Greek for ―sugar)
are polyhydroxy aldehydes or ketones, or substances that yield such
compounds on hydrolysis.
• Carbohydrates include not only sugar, but also the starches that
we find in foods, such as bread, pasta, and rice.
• The term ―carbohydrate comes from the observation that when
you heat sugars, you get carbon and water (hence, hydrate of
carbon).
7. Carbohydrates and Biochemistry
•Carbohydrates are compounds of tremendous
biological importance:
–they provide energy through oxidation
–they supply carbon for the synthesis of cell
components
–they serve as a form of stored chemical energy
–they form part of the structures of some cells and
tissues
•Carbohydrates, along with lipids, proteins, nucleic
acids, and other compounds are known as
biomolecules because they are closely associated
with living organisms.
10. CLASSIFICATION:
1- Monosaccharides (simple sugars):
They can not be hydrolyzed into simpler units. E.g. glucose,
galactose,ribose
2- Oligosaccharides (oligo = few): contain from two to ten
monosaccharide units joined in glycosidic bonds. e.g.
• disaccharides (2 units) e.g. maltose and sucrose,
• trisaccharides (3 units).....etc.
3-Polysaccharides (poly = many): Also known as glycans.
They are composed of more than ten monosaccharide
units e.g. starch, glycogen, cellulose.....etc.
11. Monosaccharides
CLASSIFICATION OF MONOSACCHARIDES
1- According to the number of carbon atoms:
.Trioses, contain 3 carbon atoms.
• Tetroses, contain 4 carbon atoms.
• Pentoses, contain 5 carbon atoms.
• Hexoses, contain 6 carbon atoms.
• Heptoses, contain 7 carbon atoms.
• Octoses. contain 8 carbon atoms.
12. 2- According to the characteristic
carbonyl group (aldehyde or ketone
group):
- Aldo sugars: aldoses:
Contain aldehyde group e.g. glucose,
ribose, erythrose and glyceraldehydes.
- Keto sugars: ketoses:
Contain ketone group e.g. fructose, ribulose
and dihydroxy acetone.
19. It is aptly said that Glyceraldehyde is the
‘Reference Carbohydrate’
20. Cyanohydrin Formation and Chain Extension.
Kiliani-Fischer Synthesis- a series of reaction that
extends carbon chain in a carbohydrate by one carbon and one chiral
centre.
20
21. Determination of carbohydrate stereochemistry
1) HCN
2) H2, Pd/BaSO4
3) H2O
CHO
H
OH
H
OH
HNO3,
heat
CO2H
H
OH
H
OH
CH2OH
CO2H
D-(-)-erythrose
tartaric acid
CHO
H
OH
CH2OH
Killiani-Fischer
synthesis
D-(+)-glyceraldehyde
CHO
HO
H
1) HCN
2) H2, Pd/BaSO4
3) H2O
H
OH
CH2OH
HNO3,
heat
CO2H
HO
H
H
OH
CO2H
D-(-)-threose
D-(-)-tartaric acid
21
22. 1) HCN
CHO
2) H2, Pd/BaSO4
H
OH
3) H2O
H
OH
H
CO2H
HNO3,
heat
OH
H
OH
H
OH
H
OH
CH2OH
CO2H
D-(-)-ribose
ribonic acid
CHO
H
OH
H
OH
Killiani-Fischer
synthesis
CH2OH
D-(-)-erythrose
CHO
HO
H
H
1) HCN
2) H2, Pd/BaSO4
3) H2O
OH
H
OH
CH2OH
D-(-)-arabinose
CO2H
HNO3,
heat
HO
H
H
OH
H
OH
CO2H
arabonic acid
22
23. 1) HCN
2) H2, Pd/BaSO4
3) H2O
CHO
H
HO
H
OH
H
CO2H
HNO3,
heat
OH
H
HO
H
CH2OH
OH
H
OH
CO2H
D-(+)-xylose
xylonic acid
CHO
HO
H
H
OH
Killiani-Fischer
synthesis
CH2OH
D-(-)-threose
CO2H
CHO
HO
HO
1) HCN
2) H2, Pd/BaSO4
3) H2O
H
H
H
OH
CH2OH
D-(-)-lyxose
HNO3,
heat
HO
H
HO
H
H
OH
CO2H
lyxonic acid
23
25. Physical Properties of
Monosaccharides
• Most monosaccharides have a sweet taste (fructose
is sweetest; 73% sweeter than sucrose).
• They are solids at room temperature.
• They are extremely soluble in water:
• Despite their high molecular weights, the presence
of large numbers of OH groups make the
monosaccharides much more water soluble than
most molecules of similar MW.
• Glucose can dissolve in minute amounts of water to
make a syrup (1 g / 1 ml H2O).
28. The Stereochemistry of
Carbohydrates
• Two Forms of Glyceraldehyde
•Glyceraldehyde, the simplest
carbohydrate, exists in two isomeric forms
that are mirror images of each other:
10
29. Stereoisomers
• These forms are stereoisomers of each other.
• Glyceraldehyde is a chiral molecule — it
cannot be superimposed on its mirror image. The
two mirror-image forms of glyceraldehyde are
enantiomers of each other.
• Chirality and Handedness
• Chiral molecules have the same
relationship to each other that your left and
right hands have when reflected in a mirror.
•
11
30. Chiral Carbons
• Chiral objects cannot be superimposed on their mirror
images —e.g., hands, gloves, and shoes.
• Achiral objects can be superimposed on the mirror images
—e.g., drinking glasses, spheres, and cubes.
• Any carbon atom which is connected to four different
groups will be chiral, and will have two
nonsuperimposable mirror images; it is a chiral carbon or
a center of chirality.
• –If any of the two groups on the carbon are the same, the
carbon atom cannot be chiral.
• Many organic compounds, including
carbohydrates, contain more than one chiral carbon.
31. n rule
Van’t Hoff’s 2
When a molecule has more than one chiral carbon,
each carbon can possibly be arranged in either the
right-hand or left-hand form, thus if there are n
chiral carbons, there are 2n possible stereoisomers.
Maximum number of possible stereoisomers = 2n
Can you tell no. of possible stereoisomers of
CHOLESTEROL?
32. D and L isomers (Enantiomers)
Enantiomers :
They are the mirror image of each others.
CHO
H - C– OH
CH2OH
D-Glyceraldehyde
CHO
HO-C-H
CH2OH
L-Glyceraldehyde
33.
34. Carbohydrates are designated as D- or L- according to the
stereochemistry of the highest numbered chiral carbon of the
Fischer projection. If the hydroxyl group of the highest numbered
chiral carbon is pointing to the right, the sugar is designated as
D (Dextro: Latin for on the right side). If the hydroxyl group is
pointing to the left, the sugar is designated as L (Levo: Latin for
on the left side). Most naturally occurring carbohydrates are of
the D-configuration.
1 CHO
2
H
OH
3
HO
H
4 H
HO
6 CH2OH
highest numbered
"chiral" carbon
1 CHO
H 2 OH
3
HO
H
4
H
OH
5
H
OH
5 CH2OH
D-Glucose
highest numbered
"chiral" carbon
L-Arabinose
CHO
HO
H
highest numbered
"chiral" carbon
CHO
H
OH
HO
H
HO
H
H
OH
HO
H
H
OH
CH2OH
L- glucose
highest numbered
"chiral" carbon
CH2OH
34
D-Arabinose
35. What’s So Great About Chiral
Molecules?
Molecules which are enantiomers of each •
other have exactly the same physical
properties (melting point, boiling point,
index of refraction, etc.) but not their
interaction with polarized light.
•Polarized light vibrates only in one plane; •
it results from passing lights through
polarizing filter
36.
37. Optical Activity
A levorotatory(–) substance rotates polarized light to the left
[e.g., l-glucose; (-)-glucose].
•A dextrorotatory(+) substance rotates polarized light to the
right [e.g., d-glucose; (+)-glucose].
•Molecules which rotate the plane of polarized light are
optically active.
•Many biologically important molecules are chiral and
optically active. Often, living systems contain only one of the
possible stereochemical forms of a compound, or they are
found in separate system.
•
–D-lactic acid is found in living muscles; D-lactic acid is present in sour milk.
–In some cases, one form of a molecule is beneficial, and the enantiomer is a poison (e.g.,
thalidomide).
–Humans can metabolize D-monosaccharides but not L-isomers; only L-amino acids are used
in protein synthesis
•
•
•
•
•
•
38. The Aldotetroses. Glyceraldehyde is the simplest
carbohydrate (C3, aldotriose, 2,3-dihydroxypropanal). The next
carbohydrate are aldotetroses (C4, 2,3,4-trihydroxybutanal).
aldotriose
CHO
H
OH
CH2OH
D-glyceraldehyde
CHO
HO
H
CH2OH
L-glyceraldehyde
aldotetroses
highest numbered
"chiral" carbon
1 CHO
2
H
OH
3
H
OH
4 CH2OH
D-erythrose
1 CHO
HO 2
H
HO 3
H
4 CH2OH
L-erythrose
CHO
CHO
highest numbered
"chiral" carbon
HO
H
H
OH
CH2OH
D-threose
highest numbered
"chiral" carbon
H
HO
OH
H
CH2OH
L-threose
highest numbered
"chiral" carbon
39. Aldopentoses and Aldohexoses.
Aldopentoses: C5, three chiral carbons, eight stereoisomers
CHO
OH
OH
HO
H
H
OH
H
OH
HO
H
OH
H
OH
H
H
HO
H
H
OH
D-xylose
D-arabinose
OH
CH2OH
CH2OH
CH2OH
D-ribose
HO
H
H
H
CH2OH
CHO
CHO
CHO
D-lyxose
Aldohexoses: C6, four chiral carbons, sixteen stereoisomers
CHO
CHO
CHO
OH
HO
H
OH
H
OH
HO
H
OH
H
OH
H
OH
H
OH
HO
H
OH
H
OH
H
OH
H
OH
H
D-allose
CH2OH
D-altrose
H
CHO
H
CH2OH
H
CHO
OH
HO
H
H
OH
HO
H
HO
H
H
OH
H
CH2OH
D- glucose
CH2OH
D-mannose
H
OH
CH2OH
D-gulose
CHO
CHO
HO
H
H
H
CHO
OH
HO
H
OH
HO
H
HO
H
H
HO
H
HO
H
OH
CH2OH
D-idose
H
OH
H
OH
CH2OH
CH2OH
D-galactose
D-talose
40. Fischer Projections and the D-L Notation. Representation
of a three-dimensional molecule as a flat structure. Tetrahedral
carbon represented by two crossed lines:
horizontal line is coming
out of the plane of the
page (toward you)
vertical line is going back
behind the plane of the
paper (away from you)
substituent
carbon
(+)-glyceraldehyde
H C
CH2OH
HO
CHO
CHO
CHO
H
OH
H
OH
CH2OH
CH2OH
CHO
CHO
(-)-glyceraldehyde
CHO
HO C
CH2OH
H
HO
H
CH2OH
HO
H
CH2OH
40
41. Manipulation of Fischer Projections
1. Fischer projections can be rotate by 180° (in the plane of the
page) only!
CHO
180 °
H
CH2OH
OH
HO
H
CH2OH
CHO
(R)
(R)
CHO
180 °
HO
H
CH2OH
(S)
CH2OH
H
OH
CHO
(S)
180°
180°
Valid
Fischer
projection
Valid
Fischer
projection
41
42. a 90° rotation inverts the stereochemistry and is illegal!
90 °
OH
CHO
H
OH
CH2OH
(R)
°
OHC
CH2OH
H
(S)
90 °
90°
This is not the correct convention
for Fischer projections
Should be projecting toward you
Should be projecting away you
This is the correct convention
for Fischer projections and is
the enantiomer
42
43. 2. If one group of a Fischer projection is held steady, the other
three groups can be rotated clockwise or counterclockwise.
hold
steady
CHO
H
CHO
OH
HO
CH2OH
CH2OH
H
(R)
(R)
CHO
H
HO
hold
steady
H
OHC
CH2OH
CH2OH
(S)
Qu ickTime™ and a
TIFF (Uncompressed) de co mpressor
are need ed to see th is pi cture.
120°
(S)
Qu ickTi me™ and a
TIFF (Uncompressed) d ecompresso r
are nee ded to see th is pi ctu re.
hold
steady
hold
steady
Qu ickTime™ and a
TIFF (Uncompressed) de compressor
are need ed to see thi s pi cture.
120°
hold
steady
OH
120°
Qu ickTime™ and a
TIFF (Uncompressed) de compressor
are need ed to see thi s pi cture.
hold
steady
Qu ickTi me™ and a
TIFF (Uncompressed) decompressor
are nee ded to see this p icture.
120°
hold
steady
Qu ickTime™ and a
TIFF (Uncompressed) de co mpressor
are need ed to see th is pi cture.
hold
steady
43
44. Cyclic Forms of Carbohydrates: Furanose Forms.
O
H+
+
R1
H
R2OH
HO OR2
R1
H+, R2OH
H
R1
hemiacetal
O
OH
(Ch. 17.8)
H
acetal
OR
OH
H
H
R2O OR2
O
cyclic hemiacetal
H
H+, ROH
Ch. 25.13
O
mixed acetal (glycoside)
44
45. In the case of carbohydrates, cyclization to the hemiacet
creates a new chiral center.
* CHO
H
H
H
OH
OH
CH2OH
OH
O
H
H
OH
H
OH
H
*
H
H
O
H
+
H
OH
OH
OH
H
*
D-erythrose
Converting Fischer Projections to Haworth formulas
45
47. Cyclic Forms of Carbohydrates: Pyranose Forms.
H
5
H
CHO
H
H
H
H
4
1
2
HO
OH
3
H H H
OH
H
4
OH
H
5
H
HO
5
4
OH
H
1
H
3
OH
OH
OH
new chiral
center
1
2
3
HO
H
O
H
H
4
1
2
3
5
H
O
H
HO
H
H
OH
CHO
H OH OH OH
H
H
5
H
OH
H
H
4
D-ribose
OH
HO
HO
O
H
H
1
2
3
OH
OH
HO
O
H
H
4
1
2
3
H
H
H
5
OH
OH
ribopyranose
6
CH2OH
OH
H
H
4
OH H
HO
2
6
5
1
CHO
H
HO
H
HOH2C
6
2
3
HOH2C H OH H
4
OH
HO
5
H
D-glucose
H
5
4
3
H OH H
2
OH
4
HO
OH
1
H
3
H
OH
H
6
H
OH
1
3
OH
H
O
CH2OH
O
H
H
OH
5
OH
new chiral
center
1
CHO
6 CH
2OH
OH
5
H
4
H
OH
HO
3
H
6
H
H
1
H
2
OH
O
4
HO
CH2OH
O
H
H
OH
5
3
H
H
1
2
OH
OH
glucopyranose
47
48. Two types of pyranose form
Chair form
Boat form
48
49. CHAIR form is thermodynamically more
stable
Substituents on the ring carbons may be either axial (ax),
projecting parallel to the vertical axis through the ring, or
equatorial (eq), projecting roughly perpendicular to this
axis.
Two conformers such are these are not readily
Interconvertible without breaking the ring. However, when
the molecule is ―stretched‖ (by atomic force microscopy),
an input of about 46 kJ of energy per mole of sugar can
force the interconversion of chair forms.
Generally, substituents in the equatorial positions are
less sterically hindered by neighboring substituents,
and conformers with bulky substituents in equatorial
positions are favored.
• Another conformation, the “boat” is seen only in
derivatives with very bulky substituents.
50. Mutarotation and the Anomeric Effect. The hemiacetal
or hemiketal carbon of the cyclic form of carbohydrates is the
anomeric carbon. Carbohydrate isomers that differ only in the
stereochemistry of the anomeric carbon are called anomers.
Mutarotation: The - and -anomers are in equilibrium, and
interconvert through the open form. The pure anomers can be
isolated by crystallization. When the pure anomers are dissolved
in water they undergo mutarotation, the process by which they
return to an equilibrium mixture of the anomer.
HOH2C
HO
HO
H
HO
H
H
CHO
OH
H
OH
OH
CH2OH
D-glucose
O
HO
H
OH
Trans
HOH2C
H
O
O
-D-Glucopyranose (64%)
( -anomer: C1-OH and
CH2OH are cis)
H
OH
HO
HO
HO
HO
HOH2C
HO
HO
Cis
HOH2C
OH
HO
HO
O
H
HO
OH
-D-Glucopyranose (36%)
( -anomer: C1-OH and
CH2OH are trans)
50
52. Epimers:
• Two monosaccharides differ only in the
configuration around one specific carbon
atom.
• The D-glucose and D-mannose are
epimers with respect to carbon atom 2,
• D-glucose and D-galactose are epimers
with respect to carbon atom 4.
53.
54. Aldose-Ketose isomerism:
Two monosaccharides have the same
molecular formulae but differ in their
functionl groups.
• one has an aldehyde group (aldose e.g.
glucose)
• the other has a ketone group (Ketose e.g.
fructose).
57. 1-Pentoses:
* -D-ribose is a structural element of ribonucleic
acid (RNA)and coenzymes e.g. ATP, NAD,
NADP and others. D-ribose-phosphate and Dribulose-5-phosphate are formed from glucose in
the body (HMS).
* 2-deoxy D-ribose enters in the structure of DNA.
*D-lyxose: constituent of lyxoflavin in human
myocardium.Lot of experiments are going to
establish it as a potent myocardial infarction
marker.
58. 2-Hexoses:
1- D-glucose (grape sugar, Dextrose as Dglucose is dextrorotatory ).
• It is the sugar carried by the blood
(normal plasma level 70-100 mg/dL) and
the principal one used by the tissues.
• It is found in fruit juices
• obtained by hydrolysis of starch, cane
sugar, maltose and lactose.
59. 2- D-Fructose (honey sugar = levulose as
D-fructose is levorotatory).
• It is found in fruit juices (fruit sugar )
• Obtained from sucrose by hydrolysis.
• It is present in the semen in pyranose form
3- D-galactose:
• It is a constituent of galactolipids and
glycoprotein in cell membranes and
extracellular matrix.
61. Iodocompounds
Glucose when heated with conc. Hydroiodic
acid loses all its oxygen and converted to
Iodohexane.
This suggests that glucose has no branched
chain.
Glucose
conc.HI
Iodohexane
62. Ester Formation
The – OH groups of monosaccharides
can form esters with acids (phosphate
& sulfate).
Phosphate esters:
Glucose – 1 – phosphate
Glucose – 6 – phosphate
Sulfate esters:
Galactose – 3 – sulfate
62
64. Sugar as reducing agent
The monosaccharides and most of the disaccharides
are rather strong reducing agents, particularly at high
pH.
At alkaline pH aldehyde or keto group tautomerizes
to form highly reactive ENEDIOL group. This group
has strong reducing property.
H
C
OH
C
R
OH
1,2 enediol form
64
65. Trommer’s test-precursor of
BENEDICT’S test
CuSO4 + 2NaOH
Cu(OH)2 + Na2SO4
(bluish white)
2Cu(OH)2
2 CuOH + H2O + O
Cu2O + H2O
(red)
Trommer’s test is not convenient enough and later
Benedict’s test replaced it.
65
66. Benedict’s Reagent
(blue)
Copper(I) oxide
(red-orange ppt)
Benedict’s reagent contains CuSO4,sodium carbonate
and sodium citrate.
Ammoniac silver nitrate solution may be reduced to
metallic silver, producing a mirror-TOLLEN’s Test
Alkaline Bismuth solution, known as Nylander’s solution,
deposits black metallic bismuth on reduction.
Picric acid in alkaline medium is reduced to picramic
acid. Color changes from yellowish orange to mahogany
red.
In acid solution sugar reduces less vigorously.Barfoed’s
test utilizes this fact for distinguishing monosaccharides
66
67. Reaction with strong alkalis
The sugar caramelises and produces a
series of decomposition products,yellow
and brown pigments develop,salts may
form, many double bonds are formed
between C-atoms.
67
68. Action of strong acid on
monosaccharides
With conc. Mineral acids the
monosaccharides get decomposed.
Pentoses yield cyclic aldehyde
‘furfural’.
Hexoses are decomposed to
‘hydroxymethyl furfural’ which
decomposes further to produce
laevulinic acid,CO,CO2
68
69. The furfural products can condense with certain organic
phenols to form compounds having characteristic color.
It forms the basis of certain tests used for detection of
sugars.
Molisch’s Test: With alpha-naphthol (in alcoholic
solution)gives purple ring. A sensitive reaction but not
specific. It is used as Group test of carbohydrate.
Seliwanoff’s test:With resorcinol, a cherry red colour
is produced. It is characteristic of D-fructose.
Other tests are anthrone test, Bial-orcinol test
69
70. OSAZONE formation
Emil Fischer done this job to detect
various sugars.
Used to differentiate simple sugar by their varied
form of osazone and rate of osazone formation.
PREPARATION: they are obtained by adding a
mixture of phenylhydrazine hydrochloride and sodium
acetate to the sugar solution and heating in boiling
water bath for 30 to 45 mins.The solution is allowed
to cool slowly by itself.crystals are formed .A
coverslip preparation is made on a clean slide and
seen under microscope.
70
73. Principle
Free carbonyl group of sugars react eith
phenylhydrazine to form
phenylhydrazone
With excess phenylhydrazine, the
adjacent C-atom of carbonyl group
react with phenylhydrazine to form
yellow compounds called osazone.
73
76. Oxidation of sugar
1. Aldonic acid: oxidation of an aldoses with Br2-water
converts the aldehyde group to a carboxyllic group
D-Glucose
D-gluconic acid
2.Saccharic acid or aldaric acid: oxidation of aldoses
with conc.HNO3 under proper conditions convert both
aldehyde and primary alcohol group to –COOH
group,forming dibasic sugar acids, the Saccharic acid or
aldaric acid.
D-Glucose
D-Glucaric acid
D-Galactose
D-Mucic acid
76
77. 3. Uronic acid: When only the primary alcohol
group of an aldose is oxidized to –COOH group,
without oxidation of aldehyde group, a uronic
acid is formed.
D-Glucose
D-Glucuronic acid
D-galactose
D-Galacturonic acid
Due to presence of free –CHO group they
exert reducing action.
Biomedical importance
77
78. Reduction
Carbonyl groups can be reduced to alcohols (catalytic
hydrogenation)
H
O
R
H
[H]
H
OH
R
Sweet but slowly absorbed
Glucose is reduced to sorbitol (glucitol)
Xylose can be reduced to xylitol
Once reduced – less reactive; not absorbed
79.
Glceraldehyde & dihydroxyacetone to
Glycerol.
Ribose to Ribitol.
Glucose to Sorbitol.
Galactose to Dulcitol.
Mannose to Mannitol.
Fructose to Sorbitol & Mannitol
79
80.
Glycerol
Ribitol
Present in the structure of many lipids.
Enters in the structure of Riboflavin.
Myo-inositol
One of the isomers of inositol.
A hydroxylated cyclohexane.
Present in the structure of a phospholipid
termed phosphatidyl inositol.
80
81. Interconversion of sugars
Glucose, Fructose and Mannose differ
from each other only arrond C1- C3.So
they are interconvertible in weak
alkaline solution such as Ba(OH)2 or
Ca(OH)2.
This is due to same ENEDIOL formation during
tautomerization.
This is called Lobry de Bruyn-Van Ekenstein
Reaction
81
84. L – Ascorbic acid
O=C
HO – C
HO – C
O
H–C
HO – C - H
CH2OH
Due to lack of
enzymes it becomes a VITAMIN
for human beings
Glucuronic acid is reduced to L-Gulonic acid and then
converted through L-Gulonolactone to L-Ascorbic acid
in plants and most higher animals.
84
85. Phytic acid
The hexaphosphoric ester of inositol.
Forms insoluble salts with Ca2+, Mg2+,
Fe2+ & Cu2+
Prevent their absorption from diet in the
small intestine.
So it is better to avoid maize and legumes
in diet of anaemic patient with iron rich
diet or haematinic drugs.
85
88. Aminosugars
Formed from the corresponding
monosaccharide by replacing the –OH
group at C2 with an amino (NH2) group.
Are important constituents of GAGs &
some types of glycolipids eg gangliosides.
Are conjugated with acetic acid &/or
sulfate to form different derivatives.
88
90. Amino sugar
Glycosylamine
• Anomeric –OH group is
replaced by –NH2
• e.g glucosylamine
Glycosamine
• -OH group attached to
carbon atom other than
the anomeric one.
• e.g glucosamine
90
92. Aminosugars Acids
• Are formed of 6-C aminosugars linked
to 3-C acid.
• Examples:
– Neuraminic acid: (Mannosamine +
Pyruvic acid)
– N-acetylneuraminic acid (Sialic acid)
– Muramic acid (glucosamine + lactic acid)
92
93. Sialic Acid (NANA)
Enters in the structure of may glycolipids &
glycoproteins.
Forms an important structure of cell
membrane & has many important functions:
It is important for cell recognition & interaction.
It is an important constituent of cell membrane
receptors.
It plays an important role in cell membrane
transport systems.
93
95. Glycosides
Formed by a reaction between the anomeric
carbon (in the form of hemiacetal or
hemiketal) with alcohols or phenols.
Are named according to the reacting sugar.
Any glycosidic linkage is named according to
the type of parent sugar eg
glucosidic, galactosidic or fructosidic linkages.
95
96. Types of Glycosides
Monosaccharide units may condense in the
form of di-, oligo- & polysaccharides where
the second sugar reacts as an alcohol &
condenses with the anomeric carbon by
removal of H2O.
A sugar may also condense with a nonsugar radical (aglycon)
Nucleoside: (pentose sugar + nitrogenous
base)
96
97.
98.
99.
100. Biomedically important
Glycosides
• Cardiac glycosides: obtained from
digitalis
• They all contain steroids as aglycone.
• Digitalis glycosides include digitoxin,
gitoxin, gitalin and digoxin
• Digoxin is class V antiarrhythmic drug
according to Vaughan Williams
classification.
• Used in supraventricular arrhythmia
100
101. • Contraindicated in ventricular tachycardia.
• Chemically,
Digitonin
4Galactose
+Xylose+digitogenin
(aglycone)
OUABAIN: It gains interest as class 1C
antiarrhythmic drug that inhibit active transport of
sodium in myocardium in vivo.
It prevents paroxysmal atrial fibrillation.
102. PHLORIDZIN:
Obtained from the root and bark of apple tree.
It blocks transport of sugar across mucosal
cells of small intestine and renal tubular
epithelium.
Displaces Na+ from the binding site of carrier
protein and prevents the binding of sugar
molecule and produces glycosuria.
STREPTOMYCIN , the well known antibiotic is
also a Glycoside.
