4. Found in a wide variety of plants and in some animals.
*They are monoterpenes (С5Н8)2 biosynthesized from
isoprene.
*The iridoids are produced by plants primarily as a defense
against herbivores and infection by micro-organisms.
Chemically, the iridoids usually consist of a сyclopentane
ring fused to a six-membered oxygen heterocycle (Pyran).
The chemical structure is exemplified by iridomyrmecin, a
defensive chemical produced by the Iridomyrmex genus,
for which iridoids are named. iridomyrmecin
Monoterpenoids
(Iridoids)
5. Physical and chemical properties of iridoids
Colorless crystals,
Bitter compounds,
They are soluble in water, ethanol, acetone, methanol
They occur as glycosides or complex epoxides in plants
Aglycons of iridoids are non-stable: they are sensitive to
enzymes and acids, while acetylated iridoids to alkali.
When treated by acids or under the influence of enzymes in
presence oxygen, iridoids form colored (dark blue or violet-
blue) non-solved in water products.
6. Iridoids exhibit a wide range of bioactivities including:-
Bitter tonic e.g. Gentian
purgative,
antimicrobial, antiviral,
anti-inflammatory and analgesic e.g. Harpagophytum
immunomodulator,
sedative (valepotriates) e.g valeriana
Diuretic (catalpol и каталпозид),
antimutagenic,
antitumor (valtrate)
Cardiovascular,
hypoglycemic,
antispasmodic.
7. Test for identification
Trim and Hill’s test:
Iridoids + trim and hill’s reagent ( 1ml 0.2% aq. CuSO4 + 10 ml
acetic acid + 0.5 ml conc. HCl) Blue color
Classification:
Iridoid glycosides (e.g. aucubin, geniposide)
Secoiridoid glycosides (e.g. gentiopicroside)
Nonglycosidic iridoids (e.g. valeprotriates)
8. Iridoids are formed in plants by an alternative cyclization of geranyl
diphosphate. The structures of these compounds are based on a
cyclopentan-[C]-pyran skeleton, carbocyclic iridoids, and oxidative
cleavage at the 7,8-bond of the cyclopentane moiety affords the so
called secoiridoids.
On biogenetic grounds the iridoid formation may be considered to
startfrom iridodial cation and follow diversification through 27
differentroutes.
Iridoids have been used as chemical markers for the Corniflorae,
Gentianiflorae, Loasiflorae and Lamiiflorae superorders.
A B
1
O2
3
4
5
6
7
8
9
Сyclopentanpyran
Iridodial
9. Classification
2. Seco-iridoids. Cleavage of a bond in the cyclopentane ring gives rise toseco-
iridoids.
O
O Glu
HO
CH3
O
OH
CH2OH O Glu
Loganin Aucubin
O
O Glu
COOCH3
C
H
O
O
O O
O
O
O
O-Glu
COOCH3
OH
HO
Secologanin
O Glu
Gentiopicroside Oleuropeine
1. Cyclopentan types
According to number of C atom in skeleton of aglycon they could be divided on 4
types: С8, С9, С10 and С14.
O
O-R
OOO
OH
Iridodial
O-R
С10-Iridoid
O- R
С9- Iridoid С8- Iridoid
COOCH3
Iridoids are typically found in plants as
glycosides, most often bound to glucose.
10. Classification
4. Iridoids-alkaloids – complex of indole alkaloids,
containing as non-amine part iridoid (determine in
plants from family Rubiaceae,Apocynaceae)
3. Iridoids of plants from family Valerianaceae
Bicyclic monoterpenes or valepotriates (“Valeriana - Epoxy - triester”).
O
R O
2 O
OR1
CH2 O C CH3
O
O
R O
2 O
OR1
CH2 O C CH3
O
Valtrate
R1=R2 – Isovalerianic acid
Dihydrovaltrate
R1 – Isovalerianic acid;
R2 – Acetoxyisovalerianic acid
COOCH3
Indole alkaloids
Secoiridoids
11. I- Iridoids Glycosides
Aucubin
Source: from Aucuba japonica and plantago asiatica.
Properties:
Colorless needles, soluble in water, methanol and ethanol
On hydrolysis with β-glucosidase, it yields aucubigenin and
glucose.
Uses:
Aucubin has a Hepatoprotective while aglycone has antitumor
activity and antibacterial activity against Staph. Aureus.
Aucuba japonica
Plantago asiatica
12. Genioposide Harpagide and
Harpagoside
Gentiopicroside
(Gentipicrin)
Occurrence Gardenia jasminoides Harpagophytum
procumbens
Gentiana lutea
Chemical nature (1-Iridoid glycoside) (2-Secoiridoid glycoside)
Uses Anti-inflammatory and
analgesic
Anti-inflammatory, anti-
rheumatic and analgesic
Bitter Stomachic, Tonic,
antimicrobial and
antitumer
Chemical test + 10% HCl give
reddish violet color.
Structure
13. Valeprotriates Valtrate and Didovaltrate
Occurrence Valeriana officinalis
Chemical
nature
(3-Non-glycoside Iridoid )
EPOXYIRIDOID ESTERS OR TRIESTERS IRIDOIDS
Uses Sedative and
tranquilizer
Both Sedative and valtrate is
tranquilizer
Structure
14. Sesquiterpene Lactones
General Characters:
Biogenetically derived from farnesyl
pyrophosphate (FPP).
May be acyclic (linear), mono-, bi-,
tricyclic.
Colorless, bitter, toxic and relatively soluble
in water.
May be responsible for skin allergies.
May posses anticancer, antimicrobial and
antimalarial activities.
15. Germacranolides Eudesmanolides Guainolides Pseudoguainolides
Cnicin Parthenolide Santonin (Keto-type) Artabsin Ambrosin and damsin
Holy thistle
مبارك شوك
Feverfew
زهرةاألقحوان
Santonica flower
الشيحالخرسانى
Herba absinthii Damsissa (Ambrosia
maritima) نباتالدمسيسة
-Strong anti-
inflammatory
but is toxic.
-Stimulate
appetite
-Anti-
inflammatory,
arthritis,
migraine
Anthelmintic for round
worm
Antispasmodic in renal colic
16. Unusual-types of Sesquiterpene lactones
Artemisinin Gossypol
Artemisia annua Seeds of cotton (Gossypium species)
Endo-peroxide sesquiterpene Dimeric sesquiterpene
Antimalarial due to its Endo-peroxide
moiety.
Male contraceptive by alteration of
sperm maturation (L-form is only active)
17. Diterpenoids
Derived from four isoprene units.
Found in plant, animal and insect world.
Have antihypertensive, antitumor, antibiotic and Anti-HIV
activities.
Classification:
Monocyclic Bicyclic Tricyclic Tetracyclic Macrocyclic Diterpene
lactones
Zoapatanol -Labdane-type
(forskolin)
-Weight loss
-Pimarane-type.
-Abietane-type
-Aconitine
-Stevioside
(natural
sweetner)
-Taxol
-Tiglianes
-Ginkgolides
(Ginko biloba)
-Neuroprotective
-Anti-platelets
18. Triterpenoids (30C) Tetraterpenoids (40C)
-derived from squalene
-abundant in nature particularly in resin
- Most important among natural terpenoid are yellow,
orange red carotenoid pigments isolated from orange,
tomato, carrots, capsicum and brown algae.
1) Aliphatic e.g. squalene
2) Tetracyclic e.g. limonoids, cucurbitacins
(Ant-tumor activity)
3) Pentacyclic e.g. oleanolic acid,
glycyrrhetic acid.
4) Quassinoids.
*Test for identification
-CHCl3 soln of carotenoids+85% H2SO4 blue col.
-Carr-Price test:
(CHCl3 soln + Antimony trichloride gives
blue col.)
-with conc HCl gives dark blue col.
Lycopene
Β-carotene
