Transcript Shikimic acid - coercingmolecules

8. Shikimates and
Phenylpropanoids
RA Macahig
FM Dayrit
O
H
CO 2 H
O
HO
HO
OH
OH
O
H
shikimic acid
O luteolin
O
H
Introduction
Shikimic acid is the key intermediate of a large group
aromatic natural products. The isolation of shikimic acid was
first reported from aniseed (Illicium anisatum) and the fruit of
I. religiosum, whose Japanese name was “shikimi-no-ki” (shi 
four; kimi  seasons; no  of; ki  tree, literally “tree of four
seasons”). Shikimic acid has since been found in many plants,
bacteria, yeasts and moulds.
It is estimated that this group accounts for 35%
CO 2 H
of plant dry mass, and that one-fifth of the
carbon fixed by plants is channeled to shikimic
acid metabolites, such as the lignins.
HO
Shikimic acid is the precursor of three important
aromatic amino acids: phenylalanine, tyrosine,
and tryptophan.
8.0 Shikimates & phenylpropanoids (Dayrit)
OH
OH
shikimic acid
2
Overview
OP
H+
_
O2C
phosphoenol pyruvate
glycolysis
O
_
O2C
D-glucose
H
pentose
phosphate
cycle
OH
H
H-O
PO
O
H
HO
OH
OH
heptulose
D-erythrose-4-phosphate
Shikimic acid is produced directly
from two D-glucose metabolites:
phosphoenol pyruvate (C3) and Derythrose-4-phosphate (C4) condense
to form the seven carbon heptulose.
Heptulose cyclizes to form 5dehydroquinate which loses water to
form shikimic acid.
H H
_
CO2
O
HO
_
CO2
O
OH
OH
OH
OH
5-dehydroquinate
3-dehydroshikimate
_
CO2
HO
OH
OH
shikimate
8.0 Shikimates & phenylpropanoids (Dayrit)
3
HOCH2
O
H
H
HO
Shikimic acid is converted to 5-enolpyruvylshikimate-3-phosphate,
which loses phosphate to yield chorismic acid and prephenic acid.
Chorismic acid is the branch point to a group of benzoic acid
metabolites and tryptophan. Prephenic acid leads to the phenyl
propanoids (C6-C3) and the flavonoids (C6-C3-C6), and the amino
acids phenylalanine and tyrosine.
OH
OH H H
H
OH
D-glucose
CH3
CO2H
O
CO2H
1
CO2H
3
EPSPS
HO
OH
OH
shikimic acid
CO2H
benzoic acids,
tryptophan
5
PO
O
CO2H
OH
5-enolpyruvylshikimate
-3-phosphate
O
CO2H
OH
chorismic acid
EPSPS: 5-enolpyruvyl
shikimate-3-phosphate
synthase
phenylalanine,
tyrosine
O
HO2C
lignans,
lignins
CO2H
+ (3 x Ac-CoA)
flavonoid
phenyl propanoids
OH
phenols
prephenic acid
8.0 Shikimates & phenylpropanoids (Dayrit)
4
styrenesbenzoic acids
In microorganisms:
[O]
polyketide
aromatic compound
quinone
In plants:
[O]
Overview of
biosynthesis of
quinones. Depending
on the organism,
quinones can arise via
the polyketide or
shikimate pathways.
polyketide
aromatic compound
quinone
quinone
shikimate
aromatic compound
+ terpene
[O]
quinone
(mixed metabolite)
quinone from shikimate:
OH
quinones from shikimate + terpene:
OH
O
OH
O
H
OH
CO2H
OH
homogentisic acid
alkarinin
O
R
H
5. Polyketides (Dayrit)
O
n
ubiquinones: R = H, CH3 ; n = 4-13
5
Shikimates comprise a large group of aromatic natural products.
CO2H
CO2H
R
NH2
O
phenylalanine, R=H
tyrosine, R=OH
cinnamic acid
O
coumarin
CO2H
O
CO2H
phenylacetic acid
benzoic acid
O
flavonoid
O
O
lignan
8.0 Shikimates & phenylpropanoids (Dayrit)
6
Shikimic acid picks up three carbons from of phosphoenol pyruvate to
form chorismic acid and prephenic acid. Chorismic acid is converted to
prephenic acid via a concerted [3,3]-sigmatropic shift.
_
CO2
_
CO2
_
CO2
H
H
HO
1. ATP
OH
PO
OH
2. PEP
shikimate
_
CO 2
_
CO2
O
OH
3
2
_
1
HO
2
1
OH
CO2
O2C
O
3
[3,3]sigmatropic
shift
_
CO2
_
_
CO2
2
_
CO2
3
O
3
3
2
3
1
_
CO2
OH
chorismate
5-EPSP
1
_
O2C
PO
O
H
1
O
2
1
OH
2
_
CO2
OH
p-hydroxybenzoic acid
prephenate
o-aminobenzoic acid,
p-aminobenzoic acid
phenylpropanoids
8.0 Shikimates & phenylpropanoids (Dayrit)
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a
_
O
_
_
CO2
O
Prephenate is
the precursor of
phenylalanine
and tyrosine.
NH2
O
CO2
CO2H
O
a
-CO2,
-H2O
Pyridoxamine
transaminase
OH
phenylalanine
prephenate
b [O]
_
_
O2C
CO2
NH2
O
_
CO2
CO2H
O
-CO2
Pyridoxamine
transaminase
O
OH
OH
tyrosine
8.0 Shikimates & phenylpropanoids (Dayrit)
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C6, C6-C1 and C6-C2
The shikimate metabolites can be grouped according to the
number of carbons atoms in the side chain.
• C6: phenols and quinones
• C6-C1: benzoic acid derivatives, including tannins
• C6-C2: phenyl ethyl compounds
8.0 Shikimates & phenylpropanoids (Dayrit)
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Routes to benzoquinones:
A. Polyketides
Hydroxybenzoic acids
B. Shikimatic acid
Benzoquinones
Homogentisic acid
Benzoquinones
Chroismic acid
p-Hydroxybenzoic acid
Benzoquinones
Phenylalanine
From p-Hydroxybenzoic acid:
CO 2H
CO 2H
R=
1. -CO 2
2. [O]
3. O-methylation
n
from terpenes
R
MeO
OH
OH
O
O
Me
Me
MeO
MeO
O
Ubiquinone
n
R
O
5-Demethoxy
ubiquinone
[O]
C6 Metabolites
Quinones are
formed mainly from
the polyketide and
shikimate pathways,
although other
groups may produce
quinones from
extensive
modification. The
biosynthesis of
R
OH
ubiquinone, the
1. [O]
compound which
2. C-methylation
assists in biological
electron transfer, is
OH
Me
shown.
MeO
R
OH
10
C6-C1. Tannins are a group of benzoic acid plant metabolites which precipitate
proteins. The gallotanins, which are hydrolyzable tannins, contain glucose and
gallic acid joined by ester linkages.
HO
O
HO
OH
O
HO
HO
O
O
OH
OH
corilagin
OO
HO
O
O
OH
OH
O
HO
HO
O
OH
OH
OH
O
O
OH
OH
O
HO
O
OH
HO
O
O
OH
O
HO
O
HO
O
OH
OH
O
O
HO
HO
O
OH
Turkish tannin
HO
OH
8.0 Shikimates & phenylpropanoids (Dayrit)
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Two benzoic acid derivatives of some interest are gallic acid and ellagic acid.
Gallic acid and ellagic acid are constituents of hydrolyzable tannins but these are
found in many other natural products. These compounds are natural antioxidant in
aqueous and micellar environments. Ellagic acid is also a naturally-occuring
phytochemical pesticide and antimicrobial.
O
H
O
H
H
O
O
O
H
H
O
H
O
H
O
O
H
O
H
H
O
H
O
O
Gallic acid
O
O
O
O
O
H
O
H
O
O
H
H
O
O
H
Ellagic acid
8.0 Shikimates & phenylpropanoids (Dayrit)
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Ellagitannins are hydrolyzable
tannins which are formed from
the condensation of a sugar
core and ellagic acid units.
Ellagitannis from banaba,
Lagerstroemia speciosa, were
shown to increase uptake of
adipocytes in rats, and could be
responsible for lowering the
blood glucose level. (Hayashi, et
al., “Ellagitannins from Lagerstroemia
speciosa as Activators of Glucose
Transport in Fat Cells,” Planta Med.,
2002, 68, 173-5.)
OH
HO
OH
OH
OH
R1
HO
O
R2
H
O
O
H
H
O
H
O
O
O
HO
HO
HO
O
OH
OH
OH
OH
CH 2
O
O
HO
O
HO
HO
O
O
O
O
Lagerstroemin : R 1 =OH; R 2 =H
Flosin B : R 1 =H; R 2 =OH
8.0 Shikimates & phenylpropanoids (Dayrit)
OH
OH
13
-o xidation
PAL
The benzoic
and cinnamic
acids are
biosynthesized
in a metabolic
grid. These
compounds
occur widely in
plants.
CO 2H
CO 2H
CO 2H
NH2
cinnamic acid
phenylalanine
[O]
[O]
CO 2H
NH2
HO
be nzoic acid
[O]
CO 2H
TAL
HO
p-hydroxybenzoic acid
[O]
[O]
HO
CO 2H
HO
[O]
CO 2H
-o xidation
NH2
HO
HO
HO
CO 2H
de carbo xylase,
-CO2
CO 2H
pro tocatechuic acid
OH
gallic acid
[CH3]
CH3O
HO
HO
HO
caffe ic acid
3,4-dihydroxyphenylalanine (DOPA)
HO
chorismic
acid
HO
4-hydroxycinnamic acid
(p-c oumaric acid)
tyrosine
CO 2H
-o xidation
[CH3]
CO 2H
CH3O
CO 2H
-o xidation
NH2
HO
HO
HO
ferulic acid
do pamine
vanillic acid
1. [O]
2. [Me]
1. [O]
2. [Me]
1. [O]
2. [Me]
OH
CH3O
HO
CH3O
CO 2H
CO 2H
-o xidation
NH(CH3)
HO
adrenaline
HO
HO
OCH3
sinapic acid
14
OCH3
syring ic acid
Cyanogenic glycosides: C6-C2
• A cyanogenic glycoside has an
aglycone with a cyanide group and
an attached sugar. Cyanogenic
glycosides release the poisonous
hydrogen cyanide enzymatically.
• Cyanogenic glycosides are found in
cassava, and the fruits and wilting
leaves of the rose family (including
cherries, apples, plums, almonds,
peaches, apricots, and raspberries).
Sorghum (Sorghum bicolor)
expresses cyanogenic glycosides in
its roots and thus is resistant to pests
such as rootworms.
• The dotted arrow is a metabolic link
to aromatic glucosinolates.
(Jorgensen et al., Curr Opinion in Plant Biol 2005, 8:280–291)
8.0 Shikimates & phenylpropanoids (Dayrit)
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Glucosinolates
OH
O
HO
HO
HO
HO
• The glucosinolates are found in
Brassicales and contain sulfur,
nitrogen and a group derived from
OSO3
glucose.
S
N
• About 120 glucosinolates are known
in plants, where the R group is alkyl,
derived from methionine, alanine,
(R group
variable)
leucine, or valin; aromatic, derived
from phenylalanine and tyrosine; or
indolic derived from tryptophan.
• Glucosinolates act as natural pesticides and defense against
herbivores. These substances are also responsible for the bitter
or sharp taste of many common foods such as mustard, radish,
horseradish, cress, cabbage, Brussels sprouts, cauliflower,
broccoli, and turnip.
8.0 Shikimates & phenylpropanoids (Dayrit)
16
Phenyl propanoids: C6-C3
• The phenylpropanoid metabolism is unique to plants.
• Many intermediates and end products of the phenylpropanoid
pathway play important roles in plants as phytoalexins,
antioxidants, antiherbivory compounds, UV protectants, pigments,
and aroma compounds. Phenylpropanoids polymerize to form
lignins, which are essential components of the cell wall stability.
• Phenylpropanoid biosynthesis is one of the best-studied pathways
in plants. The enzymes of the phenylpropanoid pathway are
organized in multi-enzyme complexes and there is evidence for
the coordinated expression of genes and enzymes. Genes
encoding enzymes of this pathway are developmentally and
tissue-specifically regulated and may be induced by
environmental stresses such as nutrient deficiency, exposure to
cold, UV light, and pathogen attack.
8.0 Shikimates & phenylpropanoids (Dayrit)
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Phenylalanine and tyrosine are deaminated by phenylalanine ammonia lyase
(PAL) or tyrosine ammonia lyase (TAL) to cinnamic acids. The cinnamic acids
(C6-C3) are the precursors to the phenyl propanoids, coumarins, styrenes,
benzoic acids, phenols, and flavonoids. A multi-enzyme complex enables
coordinated action of PAL and cinnamate-4-hydroxylase (C4H) which control
the flux of intermediates in phenylpropanoid biosynthesis.
NH2
CO2H
CO2H
CO2H
Ar - C3: cinnamaldehydes
cinnamyl alcohols
aryl propanes
PAL
or
TAL
Ar - C3: coumarins
C4H
R
R1
R3
R
phenylalanine, R=H
tyrosine, R=OH
R2
+ 3 x Ac
cinnamic acids
Ar - C2: styrenes
acetophenones
flavonoids
Ar: phenols
quinones
Ar - C1: benzoic acids
benzyl aldehydes
benzyl alcohols
8.0 Shikimates & phenylpropanoids (Dayrit)
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HO CO2H
Examples of
cinnamic acids
and the C6-C3
derivatives.
Cinnamic acids
themselves do
not usually
occur in the
free form but
are isolated as
glycosides.
Cinnamic acids
are precursors
of lignans and
lignins.
O
OH
HO
O
3-caffeoylquinic acid (chlorogenic acid).
First isolated in 1846 from coffee, it has since
been found to be a common plant compound.
It functions as an allelopathic substance in
sunflower.
OH
OH
OH
HO
O O
OH
HO
HO
OC
CH3O
OH
RO
OH
coniferyl alcohol, R=H
coniferin, R=glucosyl
O
2-caffeoylarbutin
CH3O
eugenol
Eugenol and saffrole are well-known
constituents of flavor and spice plants.
They are precursors to lignins and lignans.
HO
O
saffrole
O
8.0 Shikimates & phenylpropanoids (Dayrit)
19
Examples of cinnamic acids and the C6-C3 derivatives. Rosmarinic acid is
a dimer of two different C6-C3 units.
C
O
H
2
H
O
C
O
H
2
O
N
H
2
H
O
O
H
H
O
O
tyrosine
caffeic acid H
O
C
H
C
H
C
O
H
2
2
O
H
H
O
H
O
C
O
H
2
C
O
H
2
O
H
N
H
2
H
O
phenylalanine
rosmarini
Rosmarinic a
anti-histamine
tsaang
Ehretia
gubat
). m
Coumarins are aromatic lactone C6-C3 derivatives. They are widely
distributed in plants, particularly the Umbelliferae and Rutacea families.
C
O
H
2
[O]
R
O
C
O
H
2
C
O
H
2
R
O
glucose
O
H
O
g
lu
R
O
E
R1R2
umbelliferone R
H
H
2
4
herniarin
H
CH
5
3
6
3
skimmin
glu
H
7
2
1
aesculetin8.0 Shikimates & phenylpropanoids
H
OH
8
(Dayrit)
R
1
O CH
O O
scopoletin
OCH
R
O
3
3
Z
C
O
H 20
2
O
g
lu
Examples of coumarin compounds.
O
O- H
O
C
O
H
2
O
H
O
O
O
C
H
O
H
O
H
O
O- H
O
O
O
O
Some microorganisms
Aspergillus
(such)fumigatus
as
C
H
2
transform coumarin from plants (such as grass)
to produce dicoumarol. Dicoumarol is a powerful
blood anticoagulant and can cause fatal hemmorages
in cattle that eat the hay.
O O
O
O
dicoumarol
O
H
O
H
H
O
H
Furobinorden
O
O
O
HO
OH
8.0 Shikimates & phenylpropanoids (Dayrit)
21
Lignans are phenylpropanoid dimers. They can be rationalized by formation by
coupling of resonance-stabilized by radicals with the assistance of “dirigent” proteins.
OH
oxidase with guiding (dirigent) protein
oxidase only
OCH3
OH
H
OH
.
O
CH3O
HO
CH3O
OH
H
O
O
OH
.
OCH3
OCH3
OH
H
Proposed coupling intermediate
(+/-)-Dehydrodiconiferyl alcohols
+
OCH3
OCH3
OH
OH
O
O
H
H
O
O
HO
HO
OCH3
(+/-)-Pinoresinols
OCH3
(+)-Pinoresinol
+ Other dimers
8.0 Shikimates
& phenylpropanoids
(Dayrit)
(N.G. Lewis,
et al. in
Science, 275, 362 (1997);
Plant Physiol.
, 123, 453 (2000);Chem. Biol.
, 6, 143 (1999))
22
The diversity of lignan structures can be rationalized by bond formation via
different radical sites.
CH2OH
CH2OH
CH2OH
.
[O]
CH3O
CH3O
CH2OH
O
CH2OH
CH3O
O.
OH
CH3O
O
OCH3
O
H+
O
[H]
HO
OCH3
OCH3
HO
O
CH3O
CH2OH
HO
CH2OH
OH
O
OCH3
O
H+
OCH3
OCH3
HO
(+)pinoresinol
O
H+
CH3O
CH2OH
HO
CH2OH
8.0 Shikimates & phenylpropanoids (Dayrit)
OCH3
OH
(+)isolariciresinol
23
The diversity of lignan structures can be rationalized by bond formation via
different radical sites.
H
.
C
H
O
3
.
C
H
O
3
O
O
O
O
C
H
3
(from
C
H
O
3
O
O
C
H
3
+
H
H
O
O
O
C
H
3
licarin
eugenol)
8.0 Shikimates & phenylpropanoids (Dayrit)
24
A
Lignins
 The majority of carbon in the
phenylpropanoid group is channeled
toward the synthesis of lignin, a
complex three-dimensional polymer
that is a principal structural
component of plant cell walls.
(/www.scielo.cl)
 Lignin has far-reaching impacts on agriculture, industry and
the environment, making phenylpropanoid metabolism a
globally important part of plant biochemistry.
 Lignin is the second most abundant polymer on earth, next to
cellulose. Lignin is a major carbon sink in the biosphere,
accounting for about 30% of the more than 1.4 × 1012 kg of
carbon sequestered into terrestrial plant material each year.
8.0 Shikimates & phenylpropanoids (Dayrit)
25
O
OH
CH3O
O
HO
OCH3
O
Ph. + Ph.
O
OCH3
alkyl. + alkyl.
O. + alkyl.
HO
O
O
OCH3
OH
Ph. + alkyl.
HO
OCH3
OH
HO
Lignins are
extensively
crosslinked
phenylpropanoid
polymers. Similar to
the lignans, they are
formed by coupling
between different
radicals arising from
phenylpropanoids.
Lignins contribute to
the strength and
robustness of plants
and as a protective
barrier against
biochemical
degradation by
microorganisms.
CH3O
O
8.0 Shikimates & phenylpropanoids (Dayrit)
26
Intermediates and enzymes of the lignin pathway.
4CL, 4-(hydroxy)cinnamoyl CoA ligase
C3H, p-coumarate 3-hydroxylase
C4H, cinnamate 4-hydroxylase
CAD, cinnamyl alcohol dehydrogenase
CCoAOMT, caffeoyl CoA O-methyltransferase
CCR, cinnamoyl CoA reductase
COMT, caffeic acid/5-hydroxyferulic acid O-methyltransferase
CQT, hydroxycinnamoyl CoA:quinate hydroxycinnamoyltransferase
CST, hydroxycinnamoyl CoA:shikimate hydroxycinnamoyltransferase
F5H, ferulate 5-hydroxylase
PAL, phenylalanine ammonia-lyase
pCCoA3H, p-coumaryl CoA 3-hydroxylase
SAD, sinapyl alcohol dehydrogenase.
8.0 Shikimates
& phenylpropanoids
Humphreys
and Chapelle, (Dayrit)
Current Opinion in Plant Biology 2002,27
5:224–229.
Flavonoids
 The flavonoids are a very widely occurring group of natural
products. There are over 5,000 flavonoids identified in plants.
 Most flavonoids, except for the catechins, are naturally found
in their glycosylated form. Flavonoids are universally
distributed among vascular plants and are found throughout
the plant- roots, bark, fruit, seeds, leaves and flowers—where
they play important functions.
 Flavonoids are physiologically important because of their
many antioxidant properties.
O
H
4’
Flavonoids have a characteristic “C6-C3C6” structure, with three rings: an aromatic
A and B ring, and a -pyrone C ring.
1
O
HO 7
8.0 Shikimates & phenylpropanoids (Dayrit)
B
1’
H
3’ O
A
C
5
4
O
H
O luteolin
28
O
H
O
HO
Flavonoids
O
H
O
H
O luteolin
Flavonoids have attracted wide interest due to the following:
a. Distribution of flavonoids. The flavonoids are one of the
most numerous and widespread groups of secondary
metabolites. They are present in most parts of the plant,
often in various methylated and glycosylated forms.
b. Functions of flavonoids in plants. The colored pigments in
flowers of angiosperms (blues, purples, reds, and yellows)
are produced by the flavonoid group known as the
anthocyanidins. In leaves, the chlorophylls mask these
colors. The highly oxygenated flavonoids are UV-active
and are thought to protect the plant against UV radiation.
Various flavonoids are believed to play specific roles in the
physiology of plants. A number of flavonoids, for example,
are known to be antifungal, antibacterial, and allelopathic.
8.0 Shikimates & phenylpropanoids (Dayrit)
29
O
H
O
HO
Flavonoids
O
H
O
H
O luteolin
c. Biological activity of flavonoids. A number of flavonoids
have been shown to protect cells against oxidative attack.
This is thought to explain its anti-inflammatory and cancerprotective properties. In addition, flavonoids have been
shown to strengthen blood capillaries, and have found use in
protection against weak arteries, strokes and hemorrhoids.
• Flavonoids are formed from the condensation of a
phenylpropanoid + triketide. The flavonoids can be
subdivided according into oxidation level and position at the
rings.biosynthetic studies have been carried out using
• three
Extensive
tissue culture of parsley. Chalcone is the entry point to the
flavonoids. Further oxidation and methylation occur after
flavonoid ring formation.
8.0 Shikimates & phenylpropanoids (Dayrit)
30
R
R
1. PAL / TAL
2. CoA ligase
CoA -S
-O C
2
NH2
O
CO 2-
phenylalanine, R=H
tyrosine, R=OH
-
1.
R
O
*
CoA -S
2. -CO 2, -CoASH
R
1. NADPH
2. -CO 2, -CoASH
benzal acetone
Overview of the
condensation of
phenylpropanoid
+ (3 x acetyl
CoA).
O
CoA -S
*
R
O
O
CO 2-
-CoASH
O
O
-
*
1.
O
*
CoA -S
2. -CO 2, -CoASH
OH
dihydropyrone
R
R
CoA -S
O O
*
O
O
-CoASH
*
*
O
*
styryl pyrone
CO 2 -
1.
*
O
CoA -S
2. -CO 2, -CoASH
R
R
OH
HO
to the
flavonoids
*
*
-CoASH
O
*
O
*
O
chalcone
S -CoA
*
O
*
OH
chalcone
synthase
O
31
R
R
1. PAL / TAL
2. CoA ligase
CoA -S
-O C
2
NH2
O
CO 2-
phenylalanine, R=H
tyrosine, R=OH
-
1.
R
O
*
CoA -S
2. -CO 2, -CoASH
R
1. NADPH
2. -CO 2, -CoASH
benzal acetone
O
CoA -S
R
*
O
O
CO 2-
-CoASH
O
O
-
*
1.
*
O
CoA -S
2. -CO 2, -CoASH
OH
dihydropyrone
R
R
CoA -S
O O
Flavonoids arise from
condensation of a
phenylpropanoid, (C6C3), with three acetyl
CoA units (3 x C2).
The addition of acetyl
CoA probably occurs
stepwise yielding
intermediates with the
following structures:
(C6-C3) + C2;
(C6-C3) + C4;
(C6-C3) + C6.
The first member of the
flavonoid group is
chalcone.
*
O
O
-CoASH
*
*
O
*
32
styryl pyrone
CO 2 -
2. -CO 2, -CoASH
benzal acetone
O
CoA -S
*
R
O
O
CO 2-
-CoASH
O
O
-
*
1.
O
*
CoA -S
2. -CO 2, -CoASH
OH
dihydropyrone
R
R
CoA -S
O O
Flavonoids arise
from
condensation of
phenylpropanoid
+ triketide. The
first member
formed is
chalcone.
*
O
O
-CoASH
*
*
O
*
styryl pyrone
CO 2 -
1.
*
O
CoA -S
2. -CO 2, -CoASH
R
R
OH
HO
to the
flavonoids
*
*
-CoASH
O
*
O
*
O
chalcone
S -CoA
*
O
*
OH
chalcone
synthase
(polyketide
cyclization)
O
33
5'
Oxidation
Level
1
8
9
7
1
4'
6'
O
2
3'
1'
2'
6
3
10
5
4
flavone
O
2
OH
O
dihydrochalcone
flavan-3-ol (catechin)
O
O
3
The principal
structural feature
of the flavonoids
is C6-C3-C6. The
flavonoids can be
subdivided by
oxidation level
and oxidation
position.
O
O
chalcone
O
flavanone
isoflavanone
+
O
O
OH
OH
flavan-3,4-diol
(leucoanthocyanidinin)
flavylium
8.0 Shikimates & phenylpropanoids (Dayrit)
34
Oxidation
level
O
O
4
O
O
isoflavone
O
flavone
aurone
+
O
O
OH
O
OH
anthocyanidin
flavanonol
(dihydroflavonol)
The principal
structural
feature of the
flavonoids is
C6-C3-C6.
Flavonoids can
be subdivided
by oxidation
level at the C
ring.
O
5
OH
O
flavonol
8.0 Shikimates & phenylpropanoids (Dayrit)
35
Six flavonoid subgroups
1. Flavones:
Apigenin
Luteolin
Kaempferol
Quercetin
2. Flavonols:
3. Flavanones:
Naringenin
8.0 Shikimates & phenylpropanoids (Dayrit)
36
Six flavonoid subgroups
4. Isoflavones:
5. Flavan-3-ols:
Epicatechin
Epigallocatechin
6. Anthocyanidins:
Cyanidin
8.0 Shikimates & phenylpropanoids (Dayrit)
37
OH
OH
B
O
HO
OH
HO
7
OH
O
4'
A
C
5
4
O naringenin
(flavanone)
OH
chalcone
flavones
flavonols
4'
4'
O
HO
5
4
O apigenin
(flavone)
5
4
OH
OH
O
kaempferol
(flavonol)
anthocyanin
OH
OH
4'
3'
O
OH
2
7
5
OH
OH
luteolin
O
HO
OCH3
2
7
5
OH
O
OH
O
quercetinin
2
7
OH
4'
3'
O
HO
5
4
4
[Me]
OH
4'
3'
OH
2
7
5
[Me]
4'
3'
O
HO
4
O
OH
OH
[O]
[O]
HO
O
7
7
OH
OCH3
4
OH
8.0 Shikimates
& phenylpropanoids (Dayrit)
chrysoeriol
4'
+
HO
O
HO
7
5
OH
OH
OH
OH
Biosynthetic
studies in tissue
culture of parsley:
Chalcone is the
entry to the
flavonoids.
Flavonoids can be
further grouped
according to the
specific position
of oxidation at the
three rings. Note
that further
oxidation and
methylation occur
after flavonoid
ring formation.
O
isohamnetin
38
Occurrence of flavonoids
in various plants (Wink,
Biochemistry of Secondary
Metabolites 2010). There
are
some taxonomic patterns
but many questions remain.
OH
HO
OH
Glc-O
O
O
OH
OH
OH
UDP-glucose
O
UDP
OH
O
UDP-glucose
UDP
OH
OH
Glc-O
HO
O
OH
OH
O-Glc
O
O
2x CoASH
O
O
2x malonyl CoA
OH
O
Numerous
flavonoids are
formed by further
modifications of
the basic
flavonoid rings.
For example,
glycosylation and
acetylation are
commonly
observed
modifications.
O
O
CO2
OH
-
O
-
CO2
O
O
O
HO
OH
HO
bismalonyl isorhamnetin-3,7-bisglucoside
8.0 Shikimates & phenylpropanoids (Dayrit)
40
Isoflavonoids
Isoflavonoids are formed from flavonoids by 1,2-migration
of the B-ring from the 2- to the 3-position. Studies using
labeled phenylalanine are consistent with the proposed origin
of the isoflavonoids.
A.
Labeling
studies
on
isoflavonoid
O
H
H
O
*
^
#
H
O
C N
H
2
2
H
O
O
*
^
#
O
*
^
#
O
O
8.0 Shikimates & phenylpropanoids (Dayrit)
O
C
H
3
form onon
41
H
O
Isoflavonoids
O
O
O
C
H
3
• The isoflavonoids, which are produced in legumes, are
essential for plant-microbe interactions, such as chemoattractants and signal molecules for symbiotic Rhizobium
bacteria. The nodD gene-encoded proteins of Rhizobia
have been shown to physically bind to flavonoids and
isoflavonoids, and this ligand association initiates
transcription of the nod operon leading to root nodule
formation.
• Different isoflavonoids are also either precursors to, or are
themselves the major phytoalexins in legumes, which play
key roles in non-specific plant defense against bacterial
and fungal pathogens. The activation of isoflavonoid
synthesis during the disease resistance response is
important for providing these many defense compounds.
8.0 Shikimates & phenylpropanoids (Dayrit)
42
H
O
Isoflavonoids
O
O
O
C
H
3
• Isoflavonoid synthesis is a branch of the general
phenylpropanoid pathway that exists in all higher plants.
An enzyme found almost exclusively in the legumes,
isoflavone synthase (IFS), converts the phenylpropanoid
pathway intermediates tetrahydroxy-chalcone (naringenin)
and trihydroxy-chalcone (isoliquiritigenin) into the
isoflavones genistein and daidzein, respectively.
• Isoflavones are produced at significant levels only in
tissues where the phenylpropanoid pathway activity is
elevated, such as in floral tissues, in UV-treated tissues,
and in tissues where expression of a heterologous
transcription factor was used to activate genes of the
phenylpropanoid pathway.
8.0 Shikimates & phenylpropanoids (Dayrit)
43
O
O
Flavonoids
are converted
pterocarpan
enzymatically
to the
isomeric
isoflavonoids.
dehydropterocarpan
The
isoflavonoids
are found
mostly in the
coumestan
Leguminosae
family.
isoflavanone
O
O
O
O
isoflavone
O
O
O
O
O
O
3-arylcoumarin
O
O
O
O
O
rotenoid
dehydrorotenoid
O
O
8.0 Shikimates & phenylpropanoids (Dayrit)
44
B. Biosynthesis of rotenone
OPP
[O]
HO
1. [O]
2. ATP
H3C
O
O
isoflavone
HO
H2C
O
O
O
O
OCH3
OCH3
[H-]
OCH3
OCH3
NADPH
H
HO
H
O
HO
O
O
O
OPP
H
H
O
O
OCH3
OCH3
OCH3
OCH3
Rotenone is one
of the best
known of the
isoflavonoids.
Rotenone is
found in
mangrove
plants and is a
fish poison, but
is considered
safe for
mammals.
another closely related compound: milletone
H
O
O
s
s
H
O
O
O
O
H
O
OCH3
rotenone
OCH3
H
O
8.0 Shikimates & phenylpropanoids (Dayrit)O
O
45
Anthocyanins are the sugar- derivatives of the anthocyanidins (the
aglycone). Anthocyanins are water-soluble pigments in flowers,
leaves and fruits. They also impart many of the colors of fruit
juices and wines.
A. List of the best-known anthocyanins and anthocyanidins;
A.
Substituents
and
Color
R:
3
5 3'
5' Name
Color
R
5
'
H
H
O
H
H
H
+
H
O
O
H
H
R
3
'
Glc
Glc
O
R
3
O
R
5
8.0 Shikimates & phenylpropanoids (Dayrit)
46
B. Anthocyanin color is produced in compounds which can
achieve a planar conformation which gives maximum
delocalization.
B. Structure and Color
R
5'
H
O
+
O
R
5
'
+
O
H
O
H
R
3
'
H
O
O
H
H
O
R
3
O
R
3
O
R
5
R
3
'
O
R
5
extended
reso
non-planar conformation
is colorle
this
conformat
this form predominates if R3 is lar
8.0 Shikimates & phenylpropanoids (Dayrit)
47
Anthocyanins and flower color
(“The Big Bloom: Birth of
Flowering Plants, National
Geographic, July 2002)
• The yellow day lily has a near uniform hue in the visible
spectral range. However, in the UV range which is invisible
to most animals but visible to bees, the lily has a two-toned
pattern.
• The UV pattern of many flowers is due to anthocyanins.
8.0 Shikimates & phenylpropanoids (Dayrit)
48
Leaf color is due to several
Anthocyanins and autumn leaves compounds:
Why do leaves turn yellow, orange, • Chlorophyll, which is green, gives
leaves its predominant color. It is
red, purple and magenta during
responsible for photosynthesis. As
autumn?
the temperature drops and the days
shorten, it is destroyed
enzymatically, revealing the
presence of the other leaf pigments.
• Carotenoids are responsible for the
yellow, orange and gold hues.
Different species of trees contain
various types of carotenoids.
• Anthocyanins give rise to the reds,
purple and magenta hues. In contrast
to the carotenoids, which are always
present, anthocyanins are actively
formed in the leaves during autumn.
8.0 Shikimates & phenylpropanoids (Dayrit)
49
Anthocyanins and autumn leaves
Why do leaves turn yellow, orange, What is the special role of
anthocyanins?
red, purple and magenta during
autumn?
It is hypothesized that
anthocyanins protect the leaf from
free radicals which are produced
by the destruction of the
photosynthetic system.
They provide some
environmental protection from
UV radiation and nutrient
deficiency.
The net effect is that
anthocyanins slow down leaf
death and abscission.
8.0 Shikimates & phenylpropanoids (Dayrit)
50
A.
OH
+
O
HO
Catechins are
OH
HO
O
OH
OH
OH
catechin
anthocyanidin
OH
B.
HO
O
OH
HO
O
OH
OH
OH
OH
OH
OH
(-)-epicatechin
(-)-catechin
OH
HO
O
OH
HO
O
OH
OH
OH
OH
OH
OH
(+)-epicatechin
(+)-catechin
8.0 Shikimates & phenylpropanoids (Dayrit)
flavan-3-ols which
are believed to be
biosynthetically
related to the
anthocyanidins and
may be produced
during the
extraction of
anthocyanidins.
The best known
catechins are ()catechin and ()epicatechin which
are major
constituents of tea.
51
Condensed tannins are polymeric compounds made up of
catechin monomers.
OH
R
HO
O
OH
OH
OH
OH
OH
HO
O
OH
n x
HO
O
OH
OH
OH
OH
OH
OH
(-)-epicatechin
HO
O
OH
OH
OH
8.0 Shikimates & phenylpropanoids (Dayrit)
R
52
8.0 Shikimates & phenylpropanoids (Dayrit)
53
MK biosynthetic pathways. (A) Classical pathway. Chorismate is converted into
isochorismate by MenF (isochorismate synthase) and then into 2-succinyl-6-hydroxy-2,4cyclohexadiene-1-carboxylate by MenD. This compound is dehydrated by MenC to osuccinylbenzoate, followed by the attachment of coenzyme A to yield o-succinylbenzoylCoA by MenE. o-Succinylbenzoyl-CoA is then converted into 1,4-dihydroxy-2-naphthoate
by MenB. In the last two steps of the pathway, MK is converted by MenA and MenG,
which catalyze prenylation and methylation, respectively. Red and black bold lines show
carbons originated from erythrose-4-phosphate and phosphoenolpyruvate, respectively.
MK biosynthetic pathways. (B) Alternative pathway. Green and blue bold lines indicate
two carbon units derived from C-5 and C-6 of glucose via different metabolic pathways.
Based on the annotation of the open reading frames of S. coelicolor A3(2), we presumed
that SCO4491 (prenylation), SCO4556 (methylation), SCO4490 (decarboxylation), and
SCO4492 (decarboxylation) would be involved in the late step of the MK biosynthetic
pathway.
Metabolons of Phenylpropanoid Genes
• A metabolon is a temporary functional
complex of several sequential enzymes
held together by noncovalent interactions
in a given metabolic pathway.
• Organization of the branched pathways
of phenylpropanoid metabolism within
separate individual metabolons.
• Enzymes that participate in multiple
branches are shown in red and blue, whereas
enzymes that are thought to be unique to
specific pathways are shown in other colors.
• Enzymes that are known to be present as
multiple isoforms are marked with an asterix.
Jorgensen et al., Curr Opinion in Plant Biol 2005, 8:280–291
4CL, 4-(hydroxy)cinnamoyl CoA ligase
C3H, p-coumarate 3-hydroxylase
C4H, cinnamate 4-hydroxylase
CAD, cinnamyl alcohol dehydrogenase
CCoAOMT, caffeoyl CoA O-methyltransferase
8.0
CCR, cinnamoyl CoA reductase
COMT, caffeic acid/5-hydroxyferulic acid O-methyltransferase
CQT, hydroxycinnamoyl CoA:quinate hydroxycinnamoyltransferase
CST, hydroxycinnamoyl CoA:shikimate hydroxycinnamoyltransferase
F5H, ferulate 5-hydroxylase
PAL, phenylalanine ammonia-lyase
Shikimates
phenylpropanoids
(Dayrit)
pCCoA3H&
, p-coumaryl
CoA 3-hydroxylase
SAD, sinapyl alcohol dehydrogenase.
56
Metabolons and the Biosynthesis of Natural Products
• Metabolon formation and metabolic channeling in plant secondary
metabolism enable plants to effectively synthesize specific natural
products and to avoid metabolic interference.
• Channeling can involve different cell types, take advantage of
compartmentalization within the same cell or proceed directly within a
metabolon. New experimental approaches document the importance of
channeling in the synthesis of isoprenoids, alkaloids,
phenylpropanoids, flavonoids and cyanogenic glucosides.
• Metabolon formation and metabolic channeling in natural-product
synthesis facilitate attempts to genetically engineer new pathways into
plants to improve their content of valuable natural products. They also
offer the opportunity to introduce new traits by genetic engineering to
produce plant cultivars that adhere to the principle of substantial
equivalence. (Jorgensen et al., Curr Opinion in Plant Biol 2005, 8:280–291)
8.0 Shikimates & phenylpropanoids (Dayrit)
57
Metabolic channeling of
biosynthesis: flavonoids 
isoflavonoids  phytoalexins
Biosynthesis of O-methylated
isoflavonoids in licorice, and
conversion to phytoalexins. (Jorgensen et
al., Curr Opinion in Plant Biol 2005, 8:280–291)
IFS: 2-hydroxyisoflavanone synthase
HI4’OMT: 2,7,4’-trihydroxyisoflavone 4’-Omethyltransferase
D7OMT: daidzein 7-O-methyltransferase
HID: 2-hydroxyisoflavanone dehydratase
8.0 Shikimates & phenylpropanoids (Dayrit)
58
Summary
Many of the aromatic compounds found in higher plants belong
to the shikimates. The shikimates have for a diverse range of
properties and functions in plants, ranging from structural
(lignins), flower and leaf coloration (anthocyanins and
flavonoids), scent (some aryl propanes), and plant defense
(flavonoids and isoflavonoids).
The shikimates can be grouped by C6-Cn classification:
 C6: phenols and quinones
 C6-C1: benzoic acids; benzaldehydes; benzyl alcohols
 C6-C2: phenylethyl amines; styrenes; acetophenones
 C6-C3: phenyl propanoids: cinnamaldehydes; aryl propanes;
lignins; lignans
 C6-C3-C6: flavonoids; isoflavonoids; catechins
8.0 Shikimates & phenylpropanoids (Dayrit)
59
glucose
shikimic acid
Summary of
the shikimates
C6-C1: p-hydroxybenzoic acid
chorismic acid
C6-C1: o-hydroxybenzoic acid
(salicylic acid)
C6-C1: p-aminobenzoic acid
prephenic acid
phenylalanine,
tyrosine
C6-C2: phenylethylamines
C6-C3: cinnamic acids
C6-C3: cinnamaldehydes
C6-C3: cinnamic alcohols
C6-C1: o-aminobenzoic acid
(anthranilic acid)
indole,
tryptophan
+3 x (C2)
C6: phenols,
quinones
C6-C3-C6: flavonoids
isoflavonoids
catechins
C6-C3: coumarins
C6-C3: arylpropanes
C6-C1: benzoic acids,
C6-C2: styrenes,
benzaldehydes,
benzyl alcohols
acetophenones
condensed
tannins