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BIOSYNTHESIS OF FLAVONOIDS
Anna Blázovics Dr. D.Sc.
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• OCCURRENCE
•  
• flavonoids are widely distributed in the flora
• they can be found in petals, crops, seeds,
  leaves, stems, roots and barks
• it is the reddish braunish - yellowish colour
  of heartwood
• flavonoids of ferns are C-methyl derivatives
• glycoflavonoids can be isolated from see-weeds
• inferior plants and mushrooms have them only very
  rarely
• microorganisms and algae species do not
  synthetize

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STRUCTURE OF FLAVONOIDS
Polyphenols, namely favonoids are low
molecular weight substances The skeleton can be
represented as the C6 - C3 - C6 system Three
main groups can be distinguished on the places of
phenyl ring.
The chemical structure of flavonoids are based on
a C15 skeleton with a chromane ring bearing a
second aromatic ring B in position 2, 3 or 4.
The oxidation state of propane chain means the
difference. Oxidation degree rises from 0 to 6.
(Tetrahedron, 8, 336, 1960.)
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SYNTHESIS OF FLAVONOIDS
Flavonoids are synthesized by the phenylpropanoid
metabolic pathway in which the amino acid
phenylalanine is used to produce 4-coumarate-CoA.
This can be combined with malonyl-CoA to yield
the true backbone of flavonoids, a group of
compounds called chalcones, which contain two
phenyl rings. Conjugate ring-closure of
chalcones results in the familiar form of
flavonoids, the three-ringed structure of a
flavone.
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The metabolic pathway continues through a series
of enzymatic modifications to yield flavanones ?
dihydroflavonols ? anthocyanins. Along this
pathway, many products can be formed, including
the flavonols, flavan-3-ols, proanthocyanidins
(tannins) and a host of other various
polyphenolics.
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ENZIMATIC CONVERSION OF NARINGENIN TO APIGENIN
EC 5.5.1.6 chalcone isomerase EC 1.14.11.22
flavone synthase
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ENZIMATIC CONVERSION OF TAXIFOLIN TO QUERCETIN
EC 1.14.11.23 flavonol synthase
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ENZYMATIC CONVERSION FROM DIHYDROKAEMPHEROL TO
LEUCOPELARGONIDIN
EC 1.1.1.219 dihydrokaempferol 4-reductase
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SYNTHESIS OF FLAVONOIDS
EC 1.1.1.219 dihydrokaempferol 4-reductase EC
1.14.11.9 flavanone 3-dioxygenase EC 1.14.11.22
flavone synthase EC 1.14.11.23 flavonol
synthase EC 1.14.13.21 flavonoid
3'-monooxygenase EC 1.14.13.88 flavonoid
3',5'-hydroxylase EC 1.17.1.3 leucoanthocyanidin
reductase EC 5.5.1.6 chalcone isomerase
http//www.chem.qmul.ac.uk/i
ubmb/enzyme/reaction/phenol/flavonoid.html
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FLAVONOIDS ARE DIVIDED INTO GROUPS According to
the IUPAC nomenclature, they can be classified
into
flavone 2-phenylchromen-4-one flavonol
(3-hydroxyflavone) 3-hydroxy-2-phenylchromen-4-on
e flavanone 2,3-dihydro-2-phenylchromen-4-one fl
avanonol (3-hydroxyflavanone) 3-hydroxy-2,3-dihyd
ro-2-phenylchromen-4-one
isoflavone anthocyanidin proantocianidin catechin
chalcone dihydrochalcone aurone
other flavonoids
Both the oxidation state of the heterocyclic ring
and the position of ring B are important in the
classification.
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ANTHOXANTHINES ARE THE REAL FLAVONOIDS
Natural derivatives from benzo-?-pyron stucture
are considered as flavonoids by certain
researchers. These molecules are anthoxantines.

benzo-?-pyron chromon
?-pyron
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BIOCHEMICAL PATHWAY OF THE FORMATION OF ROTENONE
SPECIAL FLAVON DERIVATIVES

• cumaroflavones
• isocumaroflavon
• furanoflavonoids
• biflavones
• coumestan derivatives
• rotenoids

blue carbons derived from methionine red
carbons derived from prenyl (isoprenoid).
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REASON FOR THEIR VARIETY

• OH groups
• number and position of
• O-methyl, O-alkil, O-glycosyl-groups
  
• variance of glycosyl groups, acylation
  grade
• with or without conjugated double bonds
• The most often occuring substituents can bond to
  C3 -, C5 , C7 -, C3 -, C4 atoms.
• Sugars can bond
• through oxygen atom (O-glycosides)
• directly to C-atom (C-glycosides)
• Antocyanides are always in their glycoside forms
  in vacuoles (in cell fluids)
• catechines and procyanidines can be stored in
  their aglycone forms
• (tannic acid holders, dissolved in essential
  volatile oils)

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THE ROLE OF FLAVONOIDS IN PLANTS

• Flavonoids are the secondary metabolites of
  plants, and they are providing the colour and
  flavour materials.
• protect against
• UV-radiation
• fungus- , insect- and snail pests
• they are signal for N-bound bacteria
• they modify enzyme reactions
• 75 of Angiospermae contain kaempferol and
  quercetin and 10 of them myricetin.

kaempferol
quercetin
myricetin
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THE MOST OFTEN OCCURING GLYCOSIDE rutin
Rutine can be found in 50 of Angiospermae.
Quercetin is the aglycone form of a number of
other flavonoid glycosides, such as rutin and
quercitrin, found in citrus fruits, buckwheat and
onions. Quercetin forms the glycosides
quercitrin and rutin together with rhamnose and
rutinose, respectively.
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BIOFLAVONOIDS HAVE BIOACTIVITY
flavone, flavonol, flavanone, flavanonol
2-phenyl-benzo-?-pyron
High concentration of quercetin in in vitro
experiments causes DNA mutations in spite of that
epidemiological studies declare that this
flavonoid consuming prevents atherosclerosis,
infarct and others Dunnick 1998, Williams 2004.

isoflavone 3-phenyl-benzo-?-pyron
catechin
anthocyanidin
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Recent in vitro examinations strenghten the
antiproliferative effects of prenylated
naringenin (Humulus lupulus L., hops) on
prostate tumour cell line culture. (Phytomedicine.
13 (9-10), 732-4. 2006.)
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• Oxygen of pyrane ring is quaterner.
• Oxoniumbases with acids form salines.

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20 dkg soylent contains ca. 300 mg izoflavones.
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CONDITIONS OF ANTIOXIDANT PROPERTY

• Fenolic antioxidants can function free radical
  scavengers and metal chelators.
• Flavonoids are highly effective scavengers of all
  types of oxidizing radicals.
• Rate constant of quercetin with superoxide anion
  is 0.9x105 at pH 7.5. The arised fenoxy radical
  is a relatively stable molecule.
• This molecule limits the metal catalysed
  degradation of hydroperoxides.

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CHELATING ABILITY OF FLAVONS AND FLAVANONS

• 3, 4- dihydroxy configuration
• carbonyl group at the position 4
• free OH-groups at 3- and 5 positions

Conditions of chelating property
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MESOMER STRUCTURE OF QUERCETIN AROXYL RADICAL
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PHYSIOLOGICAL ACTIVITY OF FLAVONOIDS
Flavonoids have been referred to as "nature's
biological response modifiers" because of strong
experimental evidence of their inherent ability
to modify the body's reaction

• antioxidant and /or scavenger activity
• immunomodulating and antiinflammatory effects
• anti-asthmatic and anti-allergic effects
• anti-viral and anti-bacterial and anti-fungal
  effects
• oestrogen activity (isoflavonoids)
• influencing effect on mutagenicity and
• carcinogenicity
• hepatoprotective effect
• effects on circulation, modification of
  permeability

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SILIBININ INCREASES SYNTHESIS OF RNA
POLIMERASE (Flavanolignane)
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BANNED!
Catechol-type antioxidant was used in cases of
alcoholic liver diseases.
CATERGEN
It was also available in Hungary, but became
banned because it caused haemolytic
anaemia. Depending on concentration, catergen
inhibits the activities of Mg ATP-ase and NaK
ATP-ase.
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METABOLISM OF FLAVONOIDS DEPENDS ON SEVERAL
FACTORS
Only 1 of the original form of flavonoids can
get into the circulation.

• stucture, oxidation state
• rate of glycosylation /acylation
• conjugation property
• rate of polymerisation
• antioxidant property
• rate of absorption
• bacterial enzyme activity
• effects of their derivatives are often
  different from natural
• molecules

(Hertog 1993, Hollman 1995, Breinholt 1999.)
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WHAT HAPPENS WITH FLAVONOIDS IN OUR SYSTEM?
Flavonoids are extensively metabolised, and their
metabolites arise on intestinal absorption.
Flavonoids are also transformed into phenolic
acids by the enzymes of colonised gut microbes.
These phenolic acids are also absorbed and
metabolised in the liver. Generally, flavonoids
may undergo conjugation, oxidation and
P450-related transformation intracellularly.
Glucuronide and sulfate conjugates are formed
with the majority of flavonoids in the small
intestine and in the liver.
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BIOTRANSFORMATION OF FLAVONOIDS IN MICROSOMES
The liver is the main detoxicating tissue, where
the elimination of exogenic toxic agents happen.
Mixed functioning oxidases are localised in the
endoplasmic reticulum and they can catalyse a lot
of oxidation reactions. They too have the main
role of decompositioning lipid peroxidation
endproducts.
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TRANSFORMATION OF LUTEOLIN BY BACTERIA AND
MICROSOME
Flavonoid glycosides can unergo changes because
of the effects of bacterial enzymes colonised in
the bowel in the terminal ileum and colon.
Mixed functioned monooxigenases are able to
modify flavonoids in the liver, bowel, kidneys
and skin.
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PLASMA LEVELS OF FLAVONOIDS
(mg/ttg)
(ug/ml) quercetin 65
lt0,1 Gungler (1975) () -
catechin 32 0,064
Lee (1995) 3-methoxycatechin
30 11 Hackett
(1985) diosmin 10
0,4 Cova (1992) rutin
1,4 0,09
Hollman (1997)
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REGULATION OF CELL CYCLE DEPENDS ON REDOX
HOMEOSTASIS
Flavonoids can influence the redox homeostasis in
several steps

• in PG-biosynthesis
• in leukotriene biosynthesis
• in NF-?B translocation to the
• nucleus
• in PKC activity and
• in PI3-kinase activity in signal
• transduction
• in MMP-ase activity in extra-
  cellular space in tumour

We can simply say that free radicals in small
concentrations may cause apoptosis, and in large
quantities necrosis.
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BIOSYNTHESIS OF PROSTAGLANDINS
Kempferol inhibits COX2-enzyme
?
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BIOSYNTHESIS OF LEUKOTRIENES
Quercetin inhibits the activities of
lipoxygenases, therefore they have
anti-inflammatory properties. Prenylated
flavonoids can inhibit the 15- lipoxygenase
activity.
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FLAVONOIDS AND SIGNAL TRANSDUCTION
The polyphenol like compounds inhibit signal
transduction pathways, the TNFamediated
activation of NF-?B pathway, partly through the
inhibition of I?B kinase and IL-1 ß activated
NF-?B pathway, which is a partly distinct route.
NF-?B activation by IL-1 requires an IL-1
receptor-associated protein kinase activity
Croson 1995.
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LOCATION OF FLAVONOIDS IN THE ACTIVE CENTRE OF
PI3-KINASE

• Flavonoids are the potential inhibitors of
  protein kinases.
• Glycosylation of aglicons moderate the
  inhibitory effect.
• Small molecular alterations can strenghten the
  inhibitory activity and selectivity.
• It is hard to predict between structure and
  function any better.

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FLAVONOIDS IN THE SIGNAL TRANSDUCTION
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PROLIFERATION AND SPREDING OF TUMOUR DEPENDS ON
ACTIVITIES OF MATRIX-METALLOPROTEINASES
In the formation of extracellular the matrix,
collagenes take part in the delimitation of
individual cell populations. Zn-containned
matrix metalloproteinases do the continous
renewal of the extracellular matrix. Tissue
inhibitors and alpha 2- macroglobuline inhibit
the MMP ases.
Flavonoids could also induce mechanisms that help
kill cancer cells and inhibit tumor invasion.
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BONDING OF FLAVONOIDS TO THE MATRIX
METALLOPROTEINASE-9

• Flavonoids are potent inhibitors of
  MMP-ases.
• There is small difference concerning the
  inhibitory effect
• in the case of flavonoid aglicons.
• Glycosylation increases the inhibitory
  effect.
• The connection between structure and
  function can be predicted well.

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FLAVONOIDS AND SIGNAL TRANSDUCTION
Flavonoids can modulate the activity of protein
kinase and lipid kinase signaling cascades.
Direct and indirect inhibitory actions of
flavonoids within ERK1/2 and Akt/PKB pathways
could initiate cell death, whereas inhibitory
actions within JNK pathways are more likely to be
protective. Agullo 1997, Gamet-Payrastre 1999,
NF-?B, JNK and p53 signaling proteins play an
important role in apoptotic death and free
radicals and metals are very important mediators
in the apoptotic process as well.
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DATA CONCERNING OF FLAVONOIDS

• Consuming vegetables and fruits containing one
  gram of flavonoid and polyphenol per day is
  advised.
• According to surveys in different countries,
  people consume flavonoids in the quantity of
  20-50 mgs per day.
• According to Dr. Lugasi and colleagues studies,
  the average flavonoid intake in our country is
• children 19,5 26,6 mg/person
• adults 18,8 28,9 mg/person
• Personal consumption
• children 0-179,3 mg,
• adults 0,5-309,7 mg

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CONCLUSION Flavonoids are required substances
from plant kingdom through animals to human, but
their type and concentrations are very
determined for healthy life.
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THANK YOU FOR YOUR ATTENTION!