GLYCOSIDES - PowerPoint PPT Presentation

Loading...

PPT – GLYCOSIDES PowerPoint presentation | free to download - id: 43deb1-MTc2M



Loading


The Adobe Flash plugin is needed to view this content

Get the plugin now

View by Category
About This Presentation
Title:

GLYCOSIDES

Description:

By : - Jaspreet Rekhi www.rhombnet.com www.ppt.rhombnet.com is an organic compound, usually of plant origin, that is composed of a sugar portion linked to a non-sugar ... – PowerPoint PPT presentation

Number of Views:1140
Avg rating:5.0/5.0
Slides: 41
Provided by: mac202
Learn more at: http://www.ppt.rhombnet.com
Category:

less

Write a Comment
User Comments (0)
Transcript and Presenter's Notes

Title: GLYCOSIDES


1
GLYCOSIDES
By - Jaspreet Rekhi www.rhombnet.com
www.ppt.rhombnet.com
2
  • is an organic
    compound, usually of plant origin, that is
    composed of a sugar portion linked to a non-sugar
    moiety. The sugar portion is called glycone,
    while the non-sugar portion is called aglycone or
    genin .

A glycoside
3
OH on the anomeric carbon is replaced by an OR
group, such acetal is called glycoside
4
  • The linkage between the sugar and the aglycone
    is an acetal linkage.
  • Types of Glycosides
  • I- According to atoms involved in the
    glycosidic linkage
  • 1- O-glycosides
  • 2- C-glycosides
  • 3- S-glycosides
  • 4- N-glycosides

5
(No Transcript)
6
(No Transcript)
7
  • II- According to the configuration of the
    glycosidic linkage
  • 1- ?-glycosides
  • Here the sugar involved has the ? configuration
    at the hemiacetal carbon.
  • The majority of plant glycosides isolated are
    ?-glycosides.

8
2- ? -glycosides
  • Here the sugar involved has the ? configuration
    at the hemiacetal carbon the sugar is usually of
    the L-series e.g. L-rhamnose. There are only few
    medicinal ?-glycosides known, especially the
    rhamnosides.

9
(No Transcript)
10
III- According to the sugar moiety
  • 1-Glucosides
  • 2- Ribosides
  • 3- Rhamnosides
  • IV- According to the aglycone
  • 1-Cardiac glycosides
  • 2- Flavonoid glycosides
  • 3- Anthracene glycosides

11
  • 4- Saponin glycosides
  • 5-Thioglycosides
  • 6- Cyanogenic glycosides
  • 7- Phenolic glycosides possessing phenolic
    aglycones e.g. arbutin.
  • 8- Alcohol glycosides, with alcoholic aglycones
    e.g. salicin.
  • 9-Antibiotic glycosides
  • e.g, Amino-glycoside antibiotics

12
10- Ester glycosides, such as the glycosides of
methyl salicylate e.g gaultherin 11- Aldehyde
glycosides, with an aldehyde aglycone e.g.
glucovanillin . 12- Terpene glycosides a-
Monoterpene glycosides e.g. gentiopicrin and
loganin. b- Triterpene saponin glycoside.
13
  • 13- Glycoalkaloids
  • These are the glycosidal alkaloids i.e. They
    possess a glycosidic
  • linkage and a cyclic nitrogen in the aglycone.
    e.g steroidal alkaloids of Solanum species e.g.
  • solanine.

14
  • 14- Complex glycosides
  • These include a number of complex secondary
    carbohydrates e.g. gums, mucilage pectin a
    number of glycosidal resins e.g. Jalap resin as
    well as a number of glycosidal tannins e.g.
    glucogallin in Rhubarb.

15
Sugars in glycosides
  • The sugar portion
  • 1- It may be molecule of a monosaccharide e.g.
    D-glucose or L-rhamnose.
  • - or composed of 2 or more sugars, forming a
    di-or oligosaccharide chain e.g. purpurea
    glycoside A has a tetrasaccharide attached to
    digitoxigenin e.g. Digitoxigenin
  • -O-(digitoxose)3-O-glucose .

16
(No Transcript)
17
  • 2- In certain cases, the oligosaccharide portion
    is branched as in the
  • steroidal saponin, digitonin where there is a
    branched pentasaccharide chain.
  • 3- Sometimes, two monosaccharide units are
    attached at two different
  • positions in the aglycone molecule, so we are
    dealing with a diglycoside e.g.

18
(No Transcript)
19
The sugars involved
  • 1- b-D-glucose is the most common sugar in
    glycosides.
  • 2- Other sugars include
  • i - Other hexoses e.g. galactose
  • ii - Pentoses e.g. ribose, xylose and
    arabinose.
  • iii - 6-Deoxyhexoses e.g. rhamnose and
    digitalose.

20
  • iv - 2,6-Dideoxysugars e.g. sarmentose,
    digitoxose and cymarose (rare sugars)
  • The 6-Deoxy sugars and 2,6-Dideoxy sugar are
    common in
  • Cardiac glycosides.

21
  • vi - A uronic acid e.g. glucuronic acid found
    in glycyrrhizin .

22
Effect of the sugar portion on solubility of the
glycoside
  • Ex. salicin, with one glucose unit, is soluble in
    ether, while glycosides with a larger sugar
    portion are more soluble in alcohol or aqueous
    alcoholic solvents .

23
Effect of the sugar on susceptibility of the
glycoside to acid hydrolysis
  • Generally 2-deoxy sugars can be hydrolyzed easier
    than 6-deoxysugars, and the latter more easily
    than normal sugars . Thus milder conditions can
    be chosen to hydrolyze the glycoside involving
    2-deoxysugars, without affecting the others .

24
Solubility of glycosides
  • The presence or absence of various polarity
    contributing functional groups in the structure
    of the aglycone portion, would contribute to the
    degree of solubility in a given solvent e.g.
    thioglycosides are soluble in water partly
    because of the ionic sulfate residue.

25
  • The number and kind of monosaccharide units
    present in the sugar portion would contribute a
    certain polar character and thus contributing to
    the degree of solubility in polar solvents.

26
Hydrolytic cleavage and stability
  • 1-Acid Hydrolysis
  • Glycosides can be hydrolyzed by heating with a
    dilute acid, where by the glycosidic linkages
    are cleaved.
  • Glycosidic linkages involving different kinds of
    sugars are hydrolyzed with different degrees by
    acid hydrolysis

27
  • e.g. 2-deoxysugars are hydrolyzed easier than
    6-deoxy-sugars, which is still easier than normal
    sugars.
  • - If there is a di-or an oligosaccharide unit in
    the molecule, it is practically impossible to
    cleave one unit of sugar at a time with acid
    hydrolysis.

28
When stepwise cleavage of monosaccharide units is
needed, specific enzyme hydrolysis must be used.
  • C-glycosides are more resistant to acid
    hydrolysis than O-glycosides
  • i.e. they do require more vigorous conditions.

29
2- Enzymatic Hydrolysis
  • Glycosides can be hydrolyzed by appropriate
    enzymes, which are usually found in the same
    plant, in separate compartments.
  • The glycosidic linkages involving b-D-glucose as
    well as most b-glycosides can be hydrolyzed by
    various b-glycosidases.

30
  • - Stepwise hydrolysis of monosaccharide units is
    possible using specific enzyme.
  • a- Digitalidase, in Digitalis purpurea
  • b- Lanatosidase present in D. lanata
  • c-Strophanthibiase acts upon K-strophanthoside to
    give cymarin.
  • It is thus clear that enzymatic hydrolysis is
    specific .

31
  • N.B
  • During extraction or isolation of glycosides
    appropriate measures should be taken to prevent
    the cleavage of glycosides by the
  • enzymes that may be present in the same plant.

32
3- Effect of Alkali
  • - Alkalies do not , generally, cleave glycosidic
    linkages.
  • - Ester groups in the glycosides may be cleaved
    e.g. the acetyl-
  • group in lanatosides or the sulfate group in
    thioglycosides ... etc.
  • - Degradation may occur in the aglycone or in the
    sugar portion by alkali.

33
  • The lactone ring at C17, in cardiac aglycones is
    opened by strong alkalies, with subsequent loss
    of the cardiotonic activity, this change is
    irreversible on addition of acids.

34
Extraction and Isolation
  • 1- Acidic conditions should be avoided during
    extraction.
  • 2- Inactivation of the enzymes
  • a- Boiling alcohol for 10-20 minutes.
  • b- Boiling with acetone.
  • c- Low temperature i.e. in the cold.
  • d- precipitates the enzymes with ammonium
    sulfate.

35
  • e- Freeze-drying.
  • f-A special drying procedure such as a short
    heat treatment.
  • Extraction Procedures
  • Generally, the glycoside is extracted from the
    crude drug with
  • Alcohol.
  • -Adding basic lead acetate to the alcoholic
    extract causes the impurities to precipitate.

36
After filteration, the alcoholic extract is
concentrated, and the glycosides may
crystallize ( oily seeds should be defatted).

37
Pharmacological or Therapeutic Activity
  • 1- cardiac glycosides of Digitalis, Strophanthus,
    and squill are cardiotonic agents useful in
    congestive heart failure.
  • 2- Anthracene glycosides of cascara, Frangula,
    senna, Rhuharb, Aloes have a laxative effect.

38
  • 3- Flavonoid glycosides e.g. rutin and hesperidin
    are used to decrease capillary fragility and
    permeability.
  • 4- In case of cyanogenic or thioglycosides, that
    the aglycone is the active component used. The
    aglycone from the former (e.g. HCN
    Benzaldehyde) is useful as a sedative and
    flavoring agent

39
  • aglycone from the latter (e.g. allyliso-
    thiocyanate) is useful as a rubifacient and
    counterirritant.
  • Generally the pharmacological action of the
    glycoside is due to the aglycone. However, the
    sugar portion is necessary to carry the aglycone
    to the site of action.

40
Thanks for downloadingDo Comment plz.
By - Jaspreet Rekhi www.rhombnet.com
www.ppt.rhombnet.com
About PowerShow.com