1
Glycosides
Definition:
Glycosides are (usually) non-reducing compounds, on hydrolysis by
reagents or enzymes yield one or more reducing sugars among the
products of hydrolysis.
non-sugar
(genin)
glycosidic
linkage
sugar
(glycone)
1- Alcoholic or phenolic (aglycone): e.g., O-Glycoside
CH2 OH
CH2OH
O-C6 H11 O5
OH
C6 H12 O6 +
-H2O
Glycosidic linkage
Sugar
Salicin
2- Sulphur containing compounds: e.g., S-Glycoside
Glycosidic linkage
SH
C6H12O6
Sugar
+ CH2
CH
CH2
C
CH2
N
CH
CH2
OSO3 K
Sinigrin
S
C6 H11 O5
N
OSO3 K
C
2
3- Nitrogen containing compounds: e.g., N-Glycoside
NH2
OHCH2
NH2
OH
O
H
+
H
N
N
N
OH OH
N
H
N
N
N
OHCH2
N
O
Glycosidic linkage
H
H
OH OH
Adenine
4- C-Glycoside
HO
C6 H12 O6
O
HO
OH
O
OH
+
CH2 OH
CH2 OH
Glycosidic
linkage
C6 H11 O5
Barbaloin
1- Sugars exist in isomeric α and β forms. Both α and β Glycosides
are theoretically possible.
2- All natural glycosides are of the β Type.
3- Some α linkage exists in sucrose, glycogen and starch. Also the
glycoside K-strophanthoside (strophanthidin-linke to
strophanthotriose (Cymarose + β-glucose + α- glucose).
3
1- According to the type of glycosidic linkage: α- glycoside (α-sugar)
and β-glycosides (β-sugar).
2- According to the chemical group of the aglycone involved into
the acetal union:
a. O-glycoside (OH group)
b. S-glycoside (SH group).
c. N-glycoside (NH group).
d. C-glycoside (C group).
3- According to the nature of the simple sugar component of the
glycoside:
a. Glucosides (the glycone is glucose).
b. Galacosides (the glycone is galacose).
c. Mannosides (the glycone is mannose).
d. Arabinosides (the glycone is arabinose).
4- According to the number of the monosaccharides in the sugar
moiety:
a. Monoside (one monosaccharide) e.g., salicin.
b. Biosides (two monosaccharide) e.g., gentobioside.
c. Triosides (three monosaccharide) e.g., strophanthotriose.
5- According to the physiological or pharmacological activity
‘therapeutic classification)
a. Laxative glsycosides.
4
b. Cardiotonic glycosides.
6- according to the correlation to the parent natural glycoside:
a. primary glycosides e.g., amygdalin, purpurea glycoside A,
b. Secondary glycosides e.g., prunasin, digitoxin.
7- According to the plant families.
8- According to the chemical nature of the aglycone:
a. Alcoholic and phenolic glycosides (aglycones are alcohols
or phenols)
b. Aldehydic G (aglycones are aldehydes).
c. Cyanogenic G (aglycones are nitriles or derivatives of
hydrocyanic acid).
d. Anthracene or anthraquinone G (aglycones are anthracene
der.).
e. Steroidal G (aglycones are steroidal in nature, derived from
cyclopentanoperhydrophenanthrene) .
f. Coumarin G (aglycones are derivative of benzo α-pyrone).
g. Chromone glycosides (aglycones are derivatives of benzoδ-pyrone)
h. Flavonoidal G (aglycones are 2-phenyl chromone
structure).
i. Sulphur containing or thioglycosides (aglycones are
contain sulphur).
j. Alkaloidal glycosides (aglycone is alkaloidal in nature) e.g.,
glucoalkaloids of solanum species.
5
Sugars in glycosides:
1- Monosaccharide (glucose in salicin, rhamnose in ouabain)
2- Disaccharides (gentiobiose in amygdalin).
3- Trisaccharides (strophanthotriose).
4- Tetrasaccharides (purpurea glycosides)
5- Rare sugers (deoxy sugers)
6- Sugar linked in one position to the aglycone rarely in 2 positions as
sennosides.
A- 6-deoxy sugars
e.g., 1- methylpentoses
CHO
H C OH
H C OH
HO C H
HO C H
CH3
2- α-L-rhamnose.
O OH
HO CH3
OH OH
6
B- 2,6-deoxy sugars (called rare sugars)
e.g.,
1- D.digitoxose
2- D.cymarose
3- diginose
CHO
CHO
CHO
C H2
C H2
C H2
C OH
C OCH3
C
OH
C
OH
C
OH
C
OH
CH3
CH3
H3 CO C
HO C
H
C
OH
CH3
C- 2-deoxy sugars
e.g.,
2-deoxy-D-ribose
HOH2 C
H
O
H
OH
OH H
Characteristic of 2-deoxy sugers:
1- Give positive Schiff’s test for aldehydes.
2- Positive Keller-Kelliani test.
Diversity in structure makes it difficult to find general physical and
chemical properties:
7
1- A- Most glycosides are water soluble and soluble in alcohols.
B- Either insoluble or less soluble in non polar organic solvents.
C- More sugar units in a glycoside lead to more soluble in polar
solvents.
2- Glycosides do not reduce Fehling’s solution, but when are
susceptible to hydrolysis give reducing sugars (C-glycosides are
exceptions).
1- Acid hydrolysis:
a- Acetal linkage between the aglycon and glycone more unstable than
that between two individual sugars within the molecule.
b- all glycosides are hydrolysable by acids non specific (except Cglycosides).
c- Glycosides containing 2-deoxy sugars are more unstable towards acid
hydrolysis even at room temperature.
d- C-glycosides are very stable (need oxidative hydrolysis).
2- Alkali hydrolysis:
1- mild alkali
2- strong alkali
3- Enzyme hydrolysis:
1- Enzymatic hydrolysis is specific for each glycoside there is a specific
enzyme that exerts a hydrolytic action on it.
8
2- The same enzyme is capable to hydrolyze different glycosides, but α
and β sterio-isomers of the same glycoside are usually not hydrolysed by
the same enzyme.
3- Emulsin is found to hydrolysed most β-glycoside linkages, those
glycoside are attacked by emulsin are regarded as β-glycosides.
4- Maltase and invertase are α-glycosidases, capable of hydrolyzing αglycosides only.
1- Water mixed with different proportions of methanol or ethanol
(most suitable extracting solvent).
2- Non-polar organic solvents are generally used for de-fating
process.
3- Glycosides are not precipitate from aqueous solutions by lead
acetate.
1- Destruction of hydrolysing enzymes.
a. Drying for 15-30 min. at 100 C˚.
b. Place plant in boiling water or alcohol 10-20 min.
c. Boiling with acetone.
d. Cold acid pH treatment.
e. Extract at very low temperature.
2- De-fating or purification of the plant material (in case of seeds).
3- Extraction of the glycosidal constituents by alcohol, water or
dilute alcohols. Some times ether saturated with water for dry
material.
9
4- Concentrate the alcoholic extract (to get rid of the organic solvent).
Add water (or hot water)→ filter any precipitate.
5- Purify aqueous extract:
a- Extract non glycosidal impurities by org solvent.
b- Water soluble impurities precipitate by lead acetate.
6- Precipitate excess lead salts.
7- Isolation of the glycosides from the purified aqueous solution, by
crystallization.
They do not themselves reduce Fehling’s. but reducing sugars upon
hydrolysis.
To test for the presence of glycosides
Estimate reducing sugars before and after hydrolysis. (by acids or
enzymes)
1- Steroidal or cardiac glycosides:
Give positive Liebermann’s test (steroidal structure).
2- Anthraquinone glycosides and/or aglycone:
Give positive Borntrager’s test, characteristic reddish coloration with
alkalies.
10
3- Flavonoidal glycosides and/or aglycones:
Characteristic color with, NH4OH, AlCl3, FeCl3.
4- Cyanogenetic glycosides give upon hydrolysis hydrocyanic acid
can be easily tested by change Na bikrate paper (yellow) to red
color.
5- Sulphur containing glycosides give black precipitate of silver
sulphate upon treatment with AgNO3 solution.
1- Keller Killiani’s test for 2-deoxy sugers:
Specificity of action of the hydrolyzing enzymes is often applied for the
identification of the sugar moieties of glycosides or even the glycoside as
alcohol.
1- Scillarin A [acid hydrolysis] →→→ Scillaridine A + Scillabiose
Scillabiose [Scillabiase] →→→ Rhamnose + glucose.
CHO
2- Prunasin [Prunase] →→→ glucose + HCN +
H
O C 6 H 11 O 5
C
CN
3- Amygdalin [amygdalase] → Prunasin
+ glucose
4- Myrosin enzyme is specific for thio D- glucosides e.g., Sinigrin and
sinalbin.
11
Determination of the glycosidic linkages:
1- By the use of α and β glycosidases.
2- By acid hydrolysis of glycosides, immediate optical activity
measurement of the resulting solution.
Color reactions based on the sugar moiety [2-deoxy sugars]:
1- Keller Killiani:
glacialacetic acid containing + FeCl3 + H2SO4 → brown ring free from
red (acetic acid a quire blue).
2- Xanthydrol:
xanthydrol in glacial acetic containing 1% HCl + glycoside [heat]→
red color.
N.B. Stability indicating after extraction. U.S.P.
Medicinal importance of glycosides:
1- Cardiac drugs: cardiotonic glycosides e.g., digitalis glycosides,
strophanthus, squill.
2- Laxatives e.g., anthraquinone glycosides of senna, aloes, rhubarb,
cascara, frangula.
3- Counter irritants e.g., thioglycosides and their hydrolytic
products ‘allylisothiocyanate’
4- Analgesics e.g., methylsalicylate ‘a hydrolytic product of
gaultherin.
5- Anti rheumatic e.g., salicin.
12
6- Some glycosides are claimed to reduce the capillary fragility e.g.,
flavonoidal glycosides, rutin, hisperidin.
7- Anti-inflamatory: e.g., the glycoside glycyrrhizin has a
demulcent, expectorant and antispasmodic action.
8- More recently as an anticancer agent e.g., amygdalin known in
the U.S. as Laetrile.
13
1-The genins of all cardiac glycosides are steroidal in nature, that act as cardiotonic
agents.
2-They are characterized by their highly specific action cardiac muscle, increasing
tone, excitability and contractility of this muscle, thus allowing the weakened heart
to function more efficiently.
Lactone ring
12
11
1
2
R
O
9
4
16
14
8
10
5
17
13
3
Sugar
CH3
OH
15
7
6
All cardio active glycosides are characterized by the
following structural features:
1- The presence of β-OH at position C-3, which is always involved in
a glycosidic linkage to a mono, di, tri, OR tetra saccharide.
2- The presence of another β-OH group at C-14.
3- The presence of unsaturated 5 or 6- membered lactone ring at
position C-17, also in the β configuration.
4- The A/B ring junction is usually (cis), while the B/C ring junction
is always (trans) and the C/D ring junction is in all cases (cis).
5- Additional OH groups may be present at C-5, C-11 and C-16.
14
1- Cardiac glycosides that α-β unsaturated 5-membered
lactose ring in position C-17 are known as cardenolides. These
are represented by the digitalis and straphanthus group.
2- Digitalis glycosides contain angular methyl group at C-10,
while strophanthus glycoside are characterized by presence of
either an aldehydic (CHO) or primary alcoholic (C`H2OH)
group at C-10.
O
OH 12
11
1
2
O
5
4
14
8
10
3
Sugar
17
13
9
R
CH3
O
OH
16
15
7
6
Cardenolides
Digitalis glycosides
R=CH3
Strophanthus glycosides
R=CHO OR CH2OH
3- Cardiac agents that have doubly unsaturated 6-membered
lactone ring in position C-17 are referred to as Bufadienolides.
4- This group includes the squill glycosides and the toad
venom, Bufotoxin.
15
O
O
OH 12
11
1
2
13
9
O
5
4
15
8
10
16
14
3
Sugar
17
R1
7
R2
6
Bufadienolides
Squill glycosides
Bufotoxin
R1=OH, R2=H
R1 & R2 = ester group
5- The glycone portion at position C-3 of cardiac glycosides
may contain four monosaccharide molecules linked in series.
Thus, from a single genin one may have a monoside, a bioside, a
trioside or a tetroside.
6- With the exception of D-glucose and L-rhamnose, all the
other sugars that are found in cardiac glycosides are uncommon
deoxy-sugars e.g., Digitoxose, Cymarose, Thevetose.
16
CHO
CHO
C H2
C H2
C OH
C OCH3
CHO
C
OH
C
OH
C
OH
C
OH
CH3 O C H
H
C
OH
H
C
OH
CH3
CH3
Cyamarose
Thevetose
CH3
Digitoxose
HC OH
Isolation difficulties:
1- Major difficulty in the isolation of 1ry glycosides from the
crude drug.. why? because 1ry glycosides are converted
into secondary glycosides by hydrolysable enzymes.
2- Other difficulty is the existence of several closely related
glycosides in the same drug, which are extremely difficult
to separate and purify.
Origin: D. purpurea, D. lanata, D. lutea and D. thapsi
The structures of the common aglycones of the digitalis
group are indicated below:
17
O
O
R1
12
11
1
2
16
9
14
8
10
3
H
Compounds
O
5
4
17
13
OH
R2
15
7
6
R1
R2
Digitoxigenin
H
H
Gitoxigenin
H
OH
Digoxigenin
OH
H
DX = Digitoxose, DX (AC)=Acetyldigitoxose,G = Glucose.
1- Glycosides derived from Digitoxigenin:
a- Lanatoside A = Digitoxigenin---DX---DX----DX(AC)---G.
b- Acetyl-digitoxin = Digitoxigenin---DX---DX----DX---(AC).
c- Digitoxin = Digitoxigenin------DX---DX----DX.
d- Purpurea gly A = Digitoxigenin---DX---DX----DX---G
2- Glycosides derived from Gitoxigenin:
a- Lanatoside B = Gitoxigenin---DX---DX----DX(AC)---G.
b- Acetyl-gitoxin = Gitoxigenin---DX---DX----DX---(AC).
c- Gitoxin = Gitoxigenin------DX---DX----DX.
d- Purpurea gly B = Gitoxigenin---DX---DX----DX---G
18
3- Glycosides derived from Digoxigenin:
a- Lanatoside C = Digoxigenin---DX---DX----DX(AC)---G.
b- Acetyl-digoxin = Digoxigenin---DX---DX----DX---(AC).
c- Digoxin = Digoxigenin------DX---DX----DX.
d- Deslanoside = Digoxigenin---DX---DX----DX---G
1- The 1ry glycosides Lanatoside A, Lanatoside B,
Lanatoside C are acted by specific enzyme which split
the
terminal
acetyldigitoxin,
glucose,
give
acetylgitoxin
the
and
2ry
glycosides
acetyldigoxin
respectively.
2- The deacetyl-lanatosides A, B and C can be obtained by
the alkaline hydrolysis of the corresponding lanatosides.
3- Digitoxin, gitoxin and digoxin are obtained by the action
of alkali on their acetyl-derivatives.
Lanatoside A
purpurea gly. A
Specific
enzyme
Alkaline
hydrolysis
Specific
enzyme
Digitoxin
Acetyldigitoxin
Alkaline
hydrolysis
Acid hydrolysis
Digitoxigenin + 3 digitoxose
19
1- The
glycoside
K-strophanthoside
(a
trioside),
K-
strophanthin B (bioside) and cymarin (a monoside) were
isolated from different strophanthus species.
2- The 1ry glycoside K-strophanthoside gives by hydrolysis
one
molecule
of
glucose
and
the
2ry
glycoside
K-
strophanthoside B or K- strophanthin B.
3- The later gives by hydrolysis one molecule of glucose and the
tertiary glycoside cymarin, which on turn hydrolyze into the
genin K-strophanthidin and the deoxysugar cymarose.
O
11
1
2
O
Cymarose
B-glucose
a-glucose
4
OH 6
17
K- strophanthidin
13
16
CHO 9
10
5
3
12
O
14
8
OH
7
15
Cymarin
K- strophanthin B
K- strophanthoside
20
The seeds of Strophanthus gratus contains another glycoside
named Ouabain or (G-strophanthin), which yield on
hydrolysis rhamnose and the aglycone ouabagenin.
Ouabagenin differs from K-strophanthidin in having 2
additional (OH) groups at C-1 and C-11 and having a 1ry
alcoholic group at C-10 instead of the aldehydic group.
O
O
OH
OH
OH
1
2
11
CH2 9
O
5
4
17
13
16
14
8
10
3
Rhamnose
12
OH
15
7
6
OH
Ouabain (G-strophanthin)
This group of cardioactive agents includes the squill glycosides
(the scillarins) and the Toad poison (Bufotoxin).
21
The genins of squill glycosides differ from those
of the cardenolides in two important aspects:
1- They have six membered doubly unsaturated lactone
ring in position C-17.
2- They have at least one double bond in the steroid nucleus.
O
O
OH
Glucose-Glucose-Rhamnose
O
Scillaridin A
Proscillaridin A
Scillarin A
Glucoscillarin A
The Bufadienolides of Squill
Name of glycosides
Structure
Glucoscillarin
Scillaridin A ---RH—G---G
Scillarin A
Scillaridin A ---RH—G
Proscillaridin A
Scillaridin A ---RH
22
* The different cardiac glycosides show different solubilities in
aqueous and organic solvents. They are usually soluble in water
or aqueous alcohol and insoluble in the fat solvents with
exception of chloroform and ethylacetate.
* The higher number of sugar units in the molecule, the greater
solubility in water but lower soluble in chloroform.
*
Alcohols are good solvents for both the glycosides and the
aglycones. Therefore, they are considered as the solvents of
choice for the extraction of all CG from drugs.
* pet.ether and ether are used for defatting process of drug, they
do not dissolve CG.
1- Acid hydrolysis cleavage of the glycosides into aglycones
and sugar residues.
23
2- Specific enzyme usually coexist with CG in plants, which
may split the primary G into G with less sugar units. Thus,
CG deteriorate during drying and storage unless special
precautions are taken.
3- So it is required by many pharmacopoeias that CG
containing drugs must contain not more than specified moisture
content and that these drugs should be stored in sealed
containers over dehydrating agents.
4- It is recommended to heat stabilize these CG, by destroying
the enzymes at higher temperatures. At higher temperature, the
tertiary OH gp at C-14 may split off as water, leading to
formation of an inactive anhydro-form of CG.
O
12
11
1 R
2
9
O
8
10
5
4
14
OH
11
16
-H2O
1
15
2
R
Sugar
O
5
16
9
14
15
8
10
4
17
13
3
7
6
CH3
12
17
13
3
Sugar
CH3
O
O
7
6
5- The gitoxin has in addition to tertiary OH at C-14 another
secondary OH at C-16. Both OH gps split as water by the
action of H2SO4 with the formation of two additional double
bonds. These with the double bond of the lactone ring from a
O
24
conjugated double bond system that makes the compound
fluorescent in UV light.
O
12
11
1
2
R
9
O
8
10
5
4
14
11
OH
16
OH
-2H2 O
1
15
2
R
Sugar
O
5
16
9
14
15
8
10
4
7
6
The detection of gitoxin in other digitalis G is based on the
above mentioned reaction.
1- CGs are steroidal in nature, give +Ve with Liebermann’s
and Salkoviski’s test.
2- CG that contain deoxy-sugars are distinguished by Keller
Kiliani’s test, e.g., digitoxose and cymarose.
3- Cardenolides are distinguished from the scillarins by a
group of color reagents, that are all alkaline solutions of
aromatic nitro compounds, namely,
17
13
3
7
6
CH3
12
17
13
3
Sugar
CH3
O
O
O
25
Kedde’s reagent, 3,5 dinitrobenzoic,
Raymond’s reagent, metadinitrobenzene,
Baljet’s reagent, picric acid,
Legal’s test, alkaline solution of sodium nitroprusside.
4- All these nitrocompounds react with the active
methylene of the five membered lactone ring (in alkaline
medium) to give characteristic colors.
1- Cardiotonics,
CHF,
rheumatic
heart
disease,
atherosclerosis, HTN.
2- Diuretics (capillary of the kidneys are dialated).
1- The glycone part displays a great influence on the
solubility and the rate of absorption and distribution of the
glycosides to the site of action.
2- Small change in the molecules such as a change of the
location of the OH gp, modify the cardiac activity or even
eliminate it completely.
26
3- The saturation and/or cleavage of the lactone ring,
destroys the cardiac activity.
Therefore, the closely related CG, differ greatly in the rate
of absorption, duration of action and their cumulative effect.
1- digitalis leaf (digitalis tablets)
2- digitoxin tablets 200μg/tablet
3- digoxin injection contain 0.0025% digoxin
4- digoxin tablets contain 250μg/tablet
5- gitalin,
lanatoside
C,
deslanoside,
strophanthin, ouabain and squill.
strophanthus,
27
Anthraquinone
Anthrone
O
Anthranol
O
1
8
OH
1
8
7
9
2 4H
7
9
2
6
10
3
6
10
3
5
5
4
H
H
4
O
H
O
2H
1
8
7
9
2
6
10
3
5
H
OH
4
Oxanthrone
1-
O-glycosides
where
the
aglycone
moiety
is
1,8
dihydroxyanthraquinone derivatives, e.g.,
Gl O
O
8
9
OH
1
2
10
5
4
O
Aloe-emodin-8-glycoside
Gl O
O
8
9
OH
1
2
10
CH2 OH
5
Gl O
O
8
9
O
Rhein-8-glycoside
2
10
COOH
4
OH
1
5
CH3
4
O
Chrysophanol-8-glycoside
28
2- O-glycoside where the aglycone moiety partially reduced 1,8
dihydroxy anthraquinone, e.g., Oxanthrone-type.
Gl
OH
H
1
9
8
7
OH
O
6
2
3
10
5
4
O
Emodin-oxanthrone-9-glucoside
3- C-glycoside where the aglycone structure (anthrone der.)
O
OH
8
7
6
5
OH
9
1
2
10
4
3
H
CH2 OH
C6 H11 O5
Barbaloin
4- O-glycosides where the aglycone moiety is di-anthrone der.
(i.e., dimmer) e.g., Sennosides where there is C-C bridge
between the anthranol units. Sennoside A&B
Gl
7
O
O
8
6
5
OH
9
1
2
10
4
3
H
COOH
H
COOH
Gl
O
O
OH
29
The most widely used drugs that contain anthracene
compounds are:
Consists of the dried leaflet of Alexandrian or Khartoum
senna,
Cassia
senna
(C.acutifolia),
Tinnevelly
senna
(C.angustifolia).
Constituents:
Dimeric anthracene glycosides derived from two anthrones
moieties which may be:
OH
8
O
OH
1
9
OH
2
10
5
4
Aloe-emodin anthrone
O
OH
1
9
8
CH2 OH
2
10
5
COOH
4
Rhein anthrone
1- Similar anthrone moiety (Homo-dianthrones) i.e., 2 rhein
anthrone moieties condensate through two C-10 atomes.
Thus it can be exist in two optical forms, Sennoside A (Lform) & Sennoside B (meso form).
30
Gl
7
O
O
8
6
5
OH
9
1
2
10
4
3
COOH
H
H
COOH
Gl
O
OH
O
Sennosides A &B
2- Or different (Hetero-dianthrones) i.e., one rhein-anthrone
& one emodin anthrone, Sennoside C (L- form) and
Sennoside D (meso form).
Gl
7
O
O
8
6
5
OH
9
1
2
10
4
3
H
CH2 OH
H
COOH
Gl
O
O
OH
Sennoside C&D
31
The dried bark of Rhamnus purshiana Family Rhamnaceae.
B. P. specified that the collection must be made at least one
year before the bark is used (fresh bark contains an emetic
principle).
Constituents:
A- Four primary glycosides:
1- cascarosides A&B (glycosides of barbaloin)
2- cascarosides C&D (glycosides of chrysaloin)
O
OH
H
OH
Gl
O
O
CH2 OH
Gl
CH2 OH
H
Gl
Barbaloin
O
OH
H
OH
Cascaroside A& B
OH
Gl
CH3
Gl
Chrysaloin
O
O
H
OH
CH3
Gl
Cascaroside C & D
B-Two aloins (secondary glycosides):
Barbaloin derived from (C-10-C-glycoside) of aloe-emodin
anthrone and chrysaloin derived from (C-10-C-glycoside) of
chrysophanol anthrone.
32
C- A number of O- glycosides:
e.g., derived from emodin, emodine oxanthrone, aloe emodin
and chrysophanol.
OH
O
OH
O
OH
OH
CH2 OH
CH3
O
O
Aloe emodin
Chrysophanol
E- Free anthraquinones:
Aloe emodin, chysophanol and emodin.
1- Frangulin (frangula emodin rhamnoside).
2- Glucofrangulin (frangula emodin glucorhamnoside).
OH
O
RO
OH
CH3
O
Frangulin
Glucofrangulin
R= Rhamnose
R= Rhamnose-glucose
33
3- hydrolysis of glucofrangulin yields frangulin and glucose.
4- Hydrolysis of frangulin gives frangula emodin and
rhamnose.
1- Consist
of
glycoside
of
rhein,
rhein
anthrone,
chrysophanol and aloe emodin.
2- Dianthrones of heteroanthrone types are palmidin A, B, C,
Rheidins, sennosides A&B and their oxalate esters
(sennosides E&F).
3- The presence of tannins in rhubarb makes the drug
constipating. So in small doses, rhubarb exerts no
purgative action but acts only as intestinal astringent, but
large doses cause purgation.
Cascara is a purgative, mainly in the form of liquid extract,
elixir or as tablets prepared from a dry extract.
The laxative action of the crude drugs is always higher
than from their content of anthracene der. The different
34
anthracene der. contained by the crude drug are said to
exert a synergistic action.
Thus, the naturally occurring anthracene glycosides were
found superior to the synthesis of numerous hydroxyl
anthracene der.
Some of these synthetic compounds act too drastically and
also caused kidney damage.
The only compound which is used to some extent in
current medicine is danthrone. It is also used as a
standared in colorimetric assays of anthraquinone
glycosides.
OH
O
OH
O
Danthrone
Note:
1- The 1ry glycosides are more active than the aloins while
the free anthraquinon have little purgative activity.
2- C-C glycosides, aloins are very resistance to hydrolysis
and are not easily hydrolysed (like other anthrones and
anthranols) to corresponding anthraquinones.
35
3- Aloin type glycosides are present in aloes and other
anthracene bearing drugs of the family liliaceae.
1- Glycosilation:
The purgative action of anthracene bearing drugs is owed to
their anthracene glycosidal content rather than their content
of free anthracene aglycones (i.e., glycosylation is the main
requirement for activity, as the sugar moiety serve to
transport the aglycone to the site of action in the large
intestine).
2- Hydroxylation:
Hydroxylation of C-1, C-8 is essential for activity. Increase
hydroxylation leading to increase solubility.
3- Oxidation level:
The degree of oxidation at positions C-9 & C-10 plays an
important role in the pharmacological activity. Higher
oxidation level at C-9 & C-10 caused lowering of activity.
i.e., anthrones and anthranols are more potent than their
corresponding oxanthrones, which in turn more active than
their corresponding anthraquinones. Complete reduction of
C-10 &C-9 lead to complete loss of activity.
36
4- The nature of substances at C-3:
Derivative with CH2OH (as in aloe emodin) are more active
than those with CH3 substitution. The latter more active than
derivative with COOH substitution at C-3.
Anthraquinone glycosides containing adimer more active than
a monomer.
5- Effect of storage on the active of anthracene glycosides:
a- Prolonged storage of anthracene bearing drugs may bring
oxidation of anthranols and anthrones to give the less
active anthraquinones. Thus, the activity of drugs
decreases by time. However, anthraquinone glycosides
do not cause any griping action (like anthranol and
anthone), thus no antispasmodic such as belladonna is
prescribed with them.
b- Drugs as senna, Aloe and cascara preparations retain
their activity for a long time.
c- Cascara and frangula must be aged for one year before it
is used for medicinal preparation.WHY?
37
Stability is achieved as follows:
1- In senna, there is dimeric glycoside in which a C-C bridge
between two anthrone units is formed (the C-10 position of
one anthrone is involved in a C-C-covalent bonding with C10 of the other anthrone). Thus, the C-10 position can not be
easily oxidized and the anthrone structure is stabilized.
2- In the aloe, the aloins (barbaloin & chrysaloin) contain CC glycosidic linkage (anhydroglycosides) stabilise the
anthrone structure.
4- In cascara, cascarosides have an additional O-glycosidic
linkage (beside the C-10-C glycosidic linkage. The
solubility of cascarosides is increased and thus, produce
higher pharmacological activity.
The glycosides are extracted and hydrolyzed by boiling the drug
with acids.
The aglycones are extracted from the acidic solution with ether
or benzene. Upon shaking the ether or benzene layer with
aqueous alkali or ammonia solution, the aqueous layer assumes
a deep red color, because of the formation of anthraquinone
salts.
38
Borntrager’s reaction can distinguish anthraquinones from
anthrones and anthranols which do not give the test unless they
are converted to anthraquinone by oxidation with mild oxidants
such as hydrogen peroxide or ferric chloride.
Official anthraquinone drugs in B.P and U.S.P.:
1- Senna leaf & senna fruit (pod).
2- Aloes.
3- Cascara tablets, elixir, dry exract, liquid extract.
4- Rhubarb powdered, tincture.
5- Danthrone
6- Frangula bark
39
- Flavonoidal compounds are considered as the largest
group of naturally occurring phenols.
- Flavonoidals constitute the majority of the yellow
colored plant pigments.
- Many flavonoidal compounds present as a glycosidic
or as a free forms.
- All derived from the same parent nucleus, 2-phenylbenzopyran (flavan), thus they have a basic C-15
skeleton.
Flavonoidal compounds are classified according to the
oxidation level of central pyran ring they are classified into
flavones,
isoflavones,
flavonols,
flavanones,
(true
flavanoids) anthocyanidins, chalcones and aurones.
True
flavones,
are
2-phenyl
chromones
(2-phenyl
benzopyrone), while isoflavones are 3-phenyl chromones
der.
Flavonols are 3-hydroxyflavones, while flavanones are 2,3dihydro der. of flavones (2,3-double bond is lacking).
40
(2-phenylbenzopyran)
8
9
7
3'
2'
1
O
(2-phenylbenzopyrone)
O
1'
4'
2
6
5
10
4
3
6'
5'
Flavan
O
Flavone
O
O
OH
O
O
Flavonol
Isoflavone
O
H
H
O
Flavanone
Anthocyanidines, chalcones and aurones are lack the typical
flavone
structure.
Anthocyanidins
and
its
glycosides
(anthecyanins) are ionic oxonium salts. This is responsible
for the permanent blue, purple, violet, mauve, and red color
of flower, fruits and leaves of higher plants.
Anthocyanidins and anthecyanins are soluble in polar
solvents.
41
Cyanidin chloride is an example of anthocyanidines .
8
9
2'
+
O
3'
R
4' OH
6
5
3
10
8
OH
1'
7
6'
X
5'
R
-
9
Cl
+
O
2'
OH
1'
7
4' OH
6
5
Anthocyanidins
3'
10
3
OH
6'
5'
Cyanidin chloride
OH
Chalcones, have no central pyrone ring, so they are not true
flavonoidal compounds. The parent compound chalcone, is
chemically
phenyl-styryl
ketone,
or
benzylidene
acetophenone.
Aurones are oxidized forms that are obtained by enzymatic
oxidation. Instead of the central pyrone ring of the normal
flavonoidal structure, aurones have five membered ring.
O
CH
O
Chalcon
O
Aurone
42
Flavonoids dissolve in alkalis give intense yellow color
solution, on the addition of acid become colorless.
Flavonoids exhibit strong fluorescence under UV light.
Flavonoidal glycosides are soluble in water and alcohol.
Ethylacetate is the solvent of choice for the extraction of
flavonoids from aqueous solution.
Flavonoids compounds may be characterized through the
investigation of their UV Spectra, that usually show two
main bands,
1- Band at higher wavelength (band I) which is attributed
to the cinnamoyl fraction of the flavonoidal structure Why?.
2- Band at lower wavelength (band II) which is due to the
benzoyl fraction of the flavonoidal structure.
43
Benzoyl
O
B
A
R
Cinnamoyl
O
A
I
Band
II
Band
200
Wave length
Hypsochromic shift
400
Bathochromic shift
Band I >> 300 nm
If R= H
R=OH
R=O-substitution
Flavones
flavonols
3-sub flavonol
Band I: 304-350 nm
Band I: 352-385
Band I: 328-357
Band II << 300nm
(250-280 nm)
Note:
More OH in ring A: Bathochromic shift in band II.
More OH in ring B: Bathochromic shift in band I.
Shift reagents:
Back to lab.
44
1- Diosmin: flavone glycoside
Occurance: buchu leaves, Barosma crenulata F. Rutaceae.
Uses: diuretic and diaphoretic action of the leaves is owed in
part to diosmin, and in part to diosphenol, the main
constituent of the volatile oil of the leaf.
OH
Rha-Gl
O
O
B
A
OCH3
OH
O
Diosmin
Upon hydrolysis, diosmin yields rhamnose, glucose and
diosmetin.
2- Rutin and quercetrin: are examples of flavonol
glycosides
a- Rutin occurs in the leaves of buckwheat. It is the 3rhamnoglucoside (called rutinose) of the genin quercitin.
It gives on hydrolysis the aglycone (quercitin) beside one
molecule of glucose, and one molecule of rhamnose.
45
Rutin is used to
1- Decrease capillary fragility.
2- It is a biflavonoids that plays a true vitamin function.
b- Quercitrin is quercitin 3-O-rhamnoside.
It occurs in the bark of Quercus tinctoria.
Quercitrin yield upon acid hydrolysis rhamnose and
quercetin.
The aglycone quercetin occurs in bearberry leaves (Uva
Ursi) and has a diuretic action of the leaves.
OH
O
HO
B
A
OH
OR
OH
O
Quercetin: R=H
Quercetrin: R= rhamnosyl
Rutin:
R=rutinosyl
3- Hesperidin: it is an example of flavanones. It is the main
flavonoidal glycoside of citrus fruits.
46
OH
R
O
O
B
A
OCH3
OH
O
Hesperitin R:H
Hesperidin R:rutinosyl
Upon hydrolysis by acid, hesperidin gives
rhamnose,
glucose and hesperitin.
Uses:
1- Hesperidin appears to be identical to vitamin P (citrin).
2- It is necessary for absorption and retention of vit C that
lead to decrease capillary fragility.
3- Decrease CVD and HTN.
Uses of flavonoids:
1- Increase capillary resistance and decrease vitamins C & P
deficiency.
2- They are recommended in the treatment of thrombopenia
(blood coagulation).
3- They are reported of value in the treatment of influenza,
when given with ascorbic acid.
47
Isoflavone:
1- Genistein show significant oestrogenic activity.
O
HO
OH
O
OH
2- Rotenoids employed as insecticide.
O
O
O
O
Flavono-lignans
Coupling of a flavonoid moiety with hemi-lignan molecule
by oxidative coupling.
48
O
OH
B
A
OR
OH
+
OH
OH
O
Hemi-lignan moiety
Flavonoid moiety
O
OH
B
A
O
OH
O
OH
O
OCH3
OH
Flavonolignan
The leaves and fruits of Silybum marianum family
Compositae contain silymarin (silybin).
O
OH
B
A
OH
OH
O
O
O
OH
OCH3
Silybin
OH
49
1- Silymarin is a very effective lipotropic and hepato protective
therapy.
2- It is a free radical scavenger.
3- Supportive treatment of acute and chronic alcoholic
poisoning and toxin induce hepatitis.
4- It is used for treatment of liver cirrhosis caused by plant
toxins (mushroom, amanita), silymarin is applied as intravenous
injection.
5- Silymarin is available in the market in the form of tablets,
effervescent granules. Trade name legalon, silyhexal,
silirex…etc.
Synthetic flavonoids
Flavoxate:
O
O
N
O
B
A
CH3
O
Flavoxate
Uses:
To remove pain (anti-spasmodic) and anti-inflammatory of the
genitor urinary tract.
Flavoxate tablets are available under several names: Urispas,
Uronid, Spasurit, Genurin).
50
* Saponins are a group of amorphous colloidal glycodides
which is wiedly distributed in the higher plants.
* Have ability to form lasting foam when shaking in aqueous
solution.
* They are excellent emulsifying agents (modify surface
tension).
* Formerly used as detergents to replace soap (e.g., quillaia).
* Saponins are colorless and optical active. They form colloidal
solution with water and are soluble in alcohol and dilute
alcohols.
* Saponins have haemolytic properties, they precipitate the
cholesterol and lethisins that exist in the memberanes of the
red blood cells and thus haemoglobin is liberated. So,
saponins are extremely toxic when injected into the blood
stream. However, they are not harmful when taken orally.
*
Saponins
are
difficult
to
purify.
However,
they
precipitated from solutions containing them by the addition
of a solution of the sterol, filtering off the insoluble sterolsaponin compound and boiling it with toluene which resolves
the compound again into sterol (which is soluble in toluene)
and saponin (which is insoluble in toluene).
51
Chemically:
Saponins are classified according to the genin part into:
1- Steroidal type C25.
2- Triterpinoidal type C30.
Both types of saponins have the glycosidic linkage at position 3.
O
O
COOH
R2
HO
HO
R1
Diosgenin
Quillaic acid: R1=CHO, R=OH
Olianolic acid R1=CH3, R2=H
Medicinal importance of saponins:
1- The steroidal saponins are structurally related to modern
synthetic compounds that have a therapeutic significance,
such as adrenocortecoids and the sex hormones. So, they
are a suitable precursors in the partial synthesis of these
hormones, e.g., Diosgenin (sapogenins) isolated from the
rhizome of Dioscoria species.
52
CH3
OH
O
CO
OH
O
O
O
Testosterone
Progesterone
O
CH2 OH
O
O
CO
OH
O
HO
Cortisone
Diosgenin
2- Saponins increase the rate of absorption of many
pharmacological
active
substances
(e.g.,
cardiac
glycosides).
3- Many saponin-containing drugs are used as expectorants
(e.g., Ipeca, Senaga and liquorice) as their contents of
saponins stimulate bronchial secretion and also activate
the ciliary epithelium of the bronchi.
a-The triterpenoidal saponin glycoside, glycyrrhizin, is the
main sweet principle of liquorice. It is calcium and
potassium salts of glycyrrhizic acid, which in tern is the
diglucuronic acid glycoside of glycyrrhitinic acid.
53
COOH
O
Glucuronic-glucuronic
O
B-Glycyrrhitinic
Glycyrrhizic acid
Glycyrrhizin =Ca, K
b- Beside being a valuable flavouring and sweetening agent,
liquorice has demulcent, expectorant and antispasmodic
action. All these activities attributed to the saponin,
glycyrrhizin.
c- Recently, glycyrrhizin was shown to be effectively in
gastric ulcer treatment and have a cortisone like action in
rheumatic arthritis and other inflammatory diseases.
Saponins drugs officially in the B.P and U.S.P:
1- Quillaia bark: used as emulsifier.
2- Liquorice root: used as flavouring agent and expectorant.
54
1- Tannins are widely distributed phenolic plant constituents.
It is characterized by being able to combine with proteins of
animal hides thus preventing their putrefaction and
converting them into leather (true tannins).
2- Tannins are detected qualitatively by Goldbeater’s skin
test (a tanning test), and can be quantitatively estimated by
absorption
on standard
hide
powder.
Only
high
molecular weight tannins that are capable of tanning hide.
It is more acceptable to define true tannins as those high
molecular weight phenolic plant constituents that can be
detected by Glodbeater’s skin tanning test.
3- True tannin solutions have the ability of precipitating
soluble proteins (gelatine), heavy metals, alkaloids and
glycosides.
4- This will exclude simple molecular weight compounds
such
as
gallic
acid,
catechin,
flavan-3,4-diol
and
chlorogenic acid, that usually coexist with true tannins.
55
These simpler tannins like compounds are referred to as
pseudotannins.
HO
HO
OH
HO
OH
HO
COOC6 H11 O5
COOH
Glucogallin
Gallic acid
OH
CH=CH-COO
HO
OH
HO
HO
O
OH
Chlorogenic acid
OH
OH
Flavan-3,4-diol
Hydrolysable tannins
Condensed tannins
OH
56
1- Hydrolysable tannins:
a- These can be hydrolyzed by acids or enzymes to give
phenolic acids (gallic or ellagic) and glucose, so called
phenolic acid glycosides.
b- Tannins of gallic acid are called gallitannins and those of
ellagic acid is called ellagitannins.
c- Dry distillation of hydrolysable tannins gives pyrogallol.
This class is named pyrogallol tannins.
d- Gallitannins and ellagitannins react with ferric salts to give
bluish color precipitate.
2- Condensed tannins:
a- These are more resistant to hydrolysis upon prolonged
heating with acids.
b- They undergo decomposition (not hydrolysis) to give a
red soluble compound (phlobaphane).
c- Condensed tannins are derived from catechin and flavan,
3,4-diol.
d- Dry distillation of condensed tannins gives catechol. This
class is named catechol tannins.
e- Being phenolic, it reacts with ferric salts to give greenish
color precipitate.
57
1- Salicin:
Salicin is classified as:
1- Alcoholic glycoside, as it contains free primary alcoholic
group.
2- A phenolic glycoside, as its aglycone is phenolic in
nature.
CH2 OH
Gl O
Salicin
1- Salicin is obtained from different species of Salix, the
principle commercial source is Salix fragilis.
2- Salicin is used for many years as a remedy in the
treatment of fever and rheumatism.
3- It is now used as an analgesic-antipyretic in case of
periodic fever. It is better tolerated in the stomach than
sodium salicylate, asprin and other antipyretics and antiinflammatory agents, which have largely displaced in
medical practice.
58
4- Salicin is hydrolyzed by the enzyme emulsin into
saligenin (Salicyl alcohol) and glucose.
5- Acid hydrolysis of salicin gives glucose and a phenolic
ether called saliretin which is a condensation product of
two molecules of saligenin.
CH2 OH
Gl O
Acid
Enzyme
CH2 OH
CH2 OH
HO
+ Glucose
Saligenin
O
+ Glucose
CH2 OH
Saliretin
6- Oxidation of saligenin gives salicylic acid and this
accounts for the medicinal value of salicin.
1- Arbutin is a phenolic glycoside that occurs in bearberry
leaves Arectostaphyllos uva ursi.
2- When hydrolysed with acids or with emulsin it yields glucose
and hydroquinone.
59
3- It is used as diuretic and also has bactericidal action. This
activity is due to the hydroquinone given by hydrolysis.
3- Uva ursi leaf contains also methylarbutin (the methyl ether
of arbutin), that also contributes to the diuretic and urinary
antiseptic action of the leave.
OH
OCH3
O-Gl
O-Gl
Arbutin
Methylarbutin
1- Glucovanillin is a glycosidal constituent of green vanilla
pods.
2- The fruits of the plant (pods) are collected and carefully
cured. To permit enzymatic action on the glycoside with
the liberation of vanillin (the aglycone) which is the
principal flavouring constituent of the pods.
60
3- Vanillin is widely used as a flavouring agent. It may be
obtained from vanilla pod or prepared from the glycoside
coniferin, lignin or from the phenolic volatile oil
constituents eugenol.
CHO
CHO
OCH3
OCH3
O-Gl
OH
Glucovanillin
Vanillin
1- From Coniferin and lignin
CH=CH-CH2 OH
CH=CH-CH2 OH
Hydrolysis
CHO
Oxidation
OCH3
OCH3
OCH3
OH
O-Gl
Coniferin
OH
Coniferyl alcohol
Vanillin
2- From Eugenol
CH2 -CH=CH2
CH=CH-CH3
KOH
Oxidation
OCH3
OH
Eugenol
CHO
OCH3
OH
isoeugenol
OCH3
OH
Vanillin
61
The bulk of vanillin which is produced commercially is
prepared from lignin, which gives upon hydrolysis coniferyl
alcohol.
Hydrolysis
Lignin
coniferyl alcohol
Lignin is obtained in extremely large amounts as a by product
of timber industry.
1- These are glycosides that are yield hydrocyanic acid as one
of their hydrolytic products.
2- Plant containing these glycosides are toxic.
3- The aglycone part is cyanohydrin of a carbonyl compound
(condensation product of HCN with an aldehyde or keton).
4- The majority of cyanogenic glycosides are derived of
benzaldehyde cyanohydrin.
O
OH
HCN
Sugars
C
CH
H
CN
Benzaldehyde
Mandilonitrile
CH3
C
CH3
Acetone
Mandilonitrile glycosides
O
HCN
CH3
OH
C
CH3
O-Gl
CH3
Sugars
CN
Acetone cyanohydrin
C
CH3
CN
Linamarin
62
D-Mandelonitrile gentiobioside
1- Amygdalin is the most widely distributed cyanophore
glycoside.
2- It occurs in several Prunus species, and is obtained from
bitter almonds (Prunus amygdalus Var. amara Family
Rosaceae).
3- Amygdalin is considered as gentiobioside of Dmandelonitrile. Gentiobioside is a reducing disaccharide
consisting of two molecules of β-glucose linked by β-1,6
linkage.
CN
C
O
O
6
CH2 OH
H
O
5
H
O
5
2
3
2
3
1
6
CH2
1
4
4
Amygdalin
CN
C
O
1
6
CH2 OH
5
3
4
H
O
2
Prunasin
63
4- Acid hydrolysis of amygdalin split two molecules of
glucose and one molecule of mandelonitrile. The latter
decomposes spontaneously to form benzaldehyde and
HCN.
5- Different enzymes act upon amygdalin in different ways:
Amygdalase
Gl-Gl-O
C
CN
Prunase
Glocose + Prunasin
Prunase
Glucose + HCN +Benzaldehyde
Gentiobiose + Benzaldehyde + HCN
H
Amygdalin
Emulsin
or acid
Glucose + Benzaldehyde + HCN
The plant material is cutted into small fragments and then a
filter paper moistened with sodium picrate is then suspended in
the neck of the flask, the flask is stoppered and incubated in a
warm place (40˚C) for about 30-60 min. By this time, the
coexisting enzymes act upon the glycosides with the liberation
of HCN which turns, the sodium picrate paper convert to brick
red color.
64
Thioglycosides
1- A number of plants of the family Cruciferae yield glycosides
containing sulphur.
2- Hydrolysis of these, yield volatile genins of thiocyanate
structure e.g., mustard oils.
3- The best known compounds Sinigrin and Sinalbin, two
glycosides occurring in black mustard and white mustard seed
respectively.
4- The glycosides and their specific enzymes are found in
different cell in the seeds. They donot interact until they are
brought together by the distruction of the cell walls.
5- The general structure of thioglycosides is:
S-GL
X
R C
+
N-OSO3
6- The anion is called the glucosinolate ion, R may be aliphatic
or aromatic. The cation (X) may be a simple metal ion or a
complex organic cation, e.g., sinapine ion of sinalbin.
65
S-GL
S-GL
CH2
HO
CH-CH2 -C
CH2 C
N-OSO3 - Sinapine+
N-OSO3 K
Sinigrin
6- Sinigrin
Sinalbin
gives
allylisothiocyanate
upon
(volatile
hydrolysis,
oil
of
glucose,
mustard)
and
potassium acid sulphate.
7- Hydrolysis of the glycoside sinalbin gives a phenolic
isothiocyanate (Acrinyl isothiocyanate), glucose and the
acid sulphate of a quaternary alkaloid, sinapine.
+
CH3 O
HO
CH-CH-COO-CH2 -CH2 -N
CH3
CH3
CH3
CH3 O
Sinalpine cation
8- Black and white mustard seeds are used as rubefacients
and counter irritants. These effects are attributed to their
contents of thioglycosides.
66
Aglycone 1- coumarin (benzo-α-pyrane).
2-coumarin derivative (hydroxyl and methoxy coumarins).
3- Umbelliferone [7-hydroxy coumarin] is the lactone of
umbellic acid which occurs both in the free state and in the
form of glycosides in some resins of the Umbelliferae
(Asafetida and galbanum).
O
O
O
a-pyrone
O
HO
coumarin
O
O
umbelliferone
4- Coumarin and its derivatives give blue or violet
fluorescence in aqueous ammonical solutions (conjugated
double bond system). This is made use of in qualitative
testing for coumarin, coumarin derivatives and coumarin
glycosides and drugs containing them.
5- The
oleo
gum
resin
galbanum
that
contains
umbelliferone in a free state is distinguished from
asafoetida that contains only combind umbelliferone, by
the addition of ammonia to its aqueous alcoholic extract,
when the characteristic blue fluorescence is given.
Asafetida responds positive to the fluorescence test only
after acid hydrolysis.