2. Are the simplest of shikimic-acid-derived
biosynthetic subunit. These secondary
metabolites are consist of purely of an
aromatic ring (C6), with an unsaturated 3-
carbon chain (C3), attached to the ring.
3.
4. Lignans are low molecular weight polymers
formed by the coupling of two phenylpropene
units through their C3 side-chains and
between the aromatic ring and the C3 chain.
A common precursor of lignans is cinnamyl
alcohol,which can readily form free radicals
and enzymatically dimerize to form
aryltetralin-type lignans.
5.
6. is the major compound found in podophyllum
hexandrum (Indian podophyllum) is used in
treatment of warts (abnormal cell growth).
I t s cytotoxic effect was then demonstrated, The
compound was found to be very toxic.
the major active cytotoxic principle,
podophyllotoxin, being isolated in the 1940s and
much work has been done on the
podophyllotoxin (structure modification)) class of
lignans since that time.
This compound inhibits the enzyme tubulin
polymerase which is needed for the synthesis of
tubulin, a protein that is a vital component of cell
division (mitosis).
7.
8.
9. The coumarins are shikimate-derived
metabolites formed when phenylalanine is
deaminated and hydroxylated to trans-
hydroxycinnamic acid (Fig. 6.18).
The double bond of this acid is readily converted
to the cis form by light-catalysed isomerization,
resulting in the formation of a compound that
has phenol and acidic groups in close proximity.
These may then react intramolecularly to form a
lactone and the basic coumarin nucleus, typified
by the compound coumarin itself, which
contributes to the smell of hay (Melilots).
10.
11. Coumarins have a limited distribution in the
plant kingdom and have been used to classify
plants according to their presence (chemo-
taxonomy).
They are commonly found in the plant families
Apiaceae, Rutaceae, Asteraceae and Fabaceae
and, as with all of the natural products
mentioned so far, undergo many elaboration
reactions, including hydroxylation and
methylation and, particularly, the addition of
terpenoid-derived groups ( C5 and C10 units)
12.
13. Coumarins act as antimicrobial; for example,
scopoletin which is synthesized by the potato
(Solanum tuberosum) following fungal
infection.
Khellin is an isocoumarin (chromone) natural
product from Ammi visnaga (Apiaceae) and
has activity as a spasmolytic and vasodilator.
14. It has long been known that animals fed
sweet clover (Melilotus officinalis, Fabaceae)
die from hemorrhage.
The poisonous compound responsible for this
adverse effect was identified as the
bishydroxycoumarin (hydroxylated coumarin
dimer) dicoumarol (Fig. 6.21).
15.
16. The flavonoids are derived from a C6-C3
(phenylpropane) unit which has as its source
shikimic acid (via phenylalanine) and a further C6
unit that is derived from the polyketide pathway.
This polyketide fragment is generated by three
molecules of malonyl-CoA, which combine with
the C6-C3 unit (as a CoA thioester) to form a
triketide starter unit .
Flavonoids are, therefore, of mixed biosynthesis,
consisting of units derived from both shikimic
acid and polyketide pathway.
The triketide starter unit undergoes cyclization by
the enzyme chalcone synthase to generate the
chalcone group of flavonoids.
17.
18.
19.
20. The flavonoids contribute to many colours
found in nature, particularly the yellow and
orange of petals
Anthocyanins contribute to the brilliant blues
of flowers and the dark colour of red wine
Even the colourless flavonoids absorb light in
the UV spectrum (due to their extensive
chromophores) and are visible to many insect
that they have high ecological importance in
nature as colour attractants to insects and
birds as an aid to plant pollination.
21. Certain flavonoids also markedly affect the taste
of foods, for example, some are very bitter and
asrtringent such as the flavanone glycoside
naringin which occure in the peel of grapefruit
(Citrus paradisi )
While the closely related compound naringin
dihydrochalcone which lacks the pyranone ring of
naringin is exceptionally sweet, being 1000 times
sweeter than table sugar (sucrose).
22. Its likely that the flavonoids have important
dietary significance because being phenolic
compounds, they are strongly antioxidant
Many disease states are known to be
exacerbated by the presence of free radicals
such superoxide and hydroxyl, and flavonoids
have the ability to scavenge these damaging
oxidizing species
23. Foods rich in this group have therefore been
proposed to be important in ameliorating
diseases such as cancer and heart disease
( which can be worsen by oxidation of low
density lipoprptein LDL)
For example quercetin is a strong antioxidant
flavonoid that present in many food stuffs
24. Parsley, both fresh and dried, contains
flavone and have antispasmodic activity
Blueberries contains anthocyanine
Tea contains flavan-3-ol
Citrus fruit contains hesperidine
Red grape and dark chocolate also contain
flavonoids
25. isoflavones along with lignans belong to a
class of substances known as non-steroidal
phyto-oestrogens
Both structurally and functionally similar to
oestradiol and related sex hormones and
exert weak oestrogenic effects
Foods containing isoflavones are soya beans
and other legume crops, red clover (Trifolium
pratense) and broomtops (Cytisus scoparius)
27. Components of milk thistle (Silybum marianum),
Milk thistle's extract by an organic solvent is known
as silymarin, which is a mixture of about 75%
flavolignan and trace content of flavonoid (mainly
taxifolin), other ingredients involve fatty acids and
polyphenolic compounds. The major flavolignans are
silybin, isosilybin, silydianin, and silychristin
silymarin, are antihepatotoxins and are used to
reduce the effects of poisoning by fungi of the genus
Amanita, which produces the deadly peptide toxins
amanitine that it protect liver cells by reducing entry
of the toxic peptides through the cell membrane and
by acting as broad-spectrum antioxidants by
scavenging the free radicals that can lead to
hepatotoxicity.
28.
29. Sometimes referred to as bisbenzyls or
stilbenoids
They are related to the flavonoids and have
the basic structure C6-C2-C6 arising from
the loss of one carbon (as CO2) from the
triketide starter unit.
The simplest member of this class is stilbene
30. There is a much interest in this class of
compounds, especially in resveratrol, a
component of red wine that has anticancer,
antioxidant and anti-inflamatory activity
31. Stilbenoid derived from Combretum caffrum
it’s a potent inhibitor of microtubule
assembly and thought to have antitumor
activity as a result of specifically targeting the
vasculature of tumors therefore it consider as
an important cytotoxic drug lead
