Jumat, 05 Oktober 2012

Flavonoid

Abstract

          Flavonoids are a group of polyphenolic compounds, diverse in chemical structure and characteristics, found ubiquitously in plants. Therefore, flavonoids are part of the human diet. Over 4,000 different flavonoids have been identified within the major flavonoid classes which include flavonols, flavones, flavanones, catechins, anthocyanidins, isoflavones, dihydroflavonols, and chalcones. Flavonoids are absorbed from the gastrointestinal tracts of humans and animals and are excreted either unchanged or as flavonoid metabolites in the urine and feces. Flavonoids are potent antioxidants, free radical scavengers, and metal chelators and inhibit lipid peroxidation. The structural requirements for the antioxidant and free radical scavenging functions of flavonoids include a hydroxyl group in carbon position three, a double bond between carbon positions two and three, a carbonyl group in carbon position four, and polyhydroxylation of the A and B aromatic rings. Epidemiological studies show an inverse correlation between dietary flavonoid intake and mortality from coronary heart disease (CHD) which is explained in part by the inhibition of low density lipoprotein oxidation and reduced platelet aggregability. Dietary intake of flavonoids range between 23 mg/day estimated in The Netherlands and 170 mg/day estimated in the USA. Major dietary sources of flavonoids determined from studies and analyses conducted in The Netherlands include tea, onions, apples, and red wine. More research is needed for further elucidation of the mechanisms of flavonoid absorption, metabolism, biochemical action, and association with CHD.

Introduction

The flavonoids are polyphenolic compounds possessing 15 carbon atoms; two benzene rings joined by a linear three carbon chain.
The skeleton above, can be represented as the
C6 - C3 - C6 system.
Flavonoids constitute one of the most characteristic classes of compounds in higher plants. Many flavonoids are easily recognised as flower pigments in most angiosperm families (flowering plants). However, their occurence is not restricted to flowers but include all parts of the plant.
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.
In a few cases, the six-membered heterocyclic ring C occurs in an isomeric open form or is replaced by a five - membered ring.

AURONES (2-benzyl-coumarone)
The oxygen bridge involving the central carbon atom (C2) of the 3C - chain occurs in a rather limited number of cases, where the resulting heterocyclic is of the FURAN type.
Various subgroups of flavonoids are classified according to the substitution patterns of ring C. Both the oxidation state of the heterocyclic ring and the position of ring B are important in the classification.
Examples of the 6 major subgroups are:
1. Chalcones
2. Flavone (generally in herbaceous families, e.g. Labiatae, Umbelliferae, Compositae).
Apigenin (Apium graveolens, Petroselinum crispum).
Luteolin (Equisetum arvense)
3. Flavonol (generally in woody angiosperms)
Quercitol (Ruta graveolens, Fagopyrum esculentum, Sambucus nigra)
Kaempferol (Sambucus nigra, Cassia senna, Equisetum arvense, Lamium album, Polygonum bistorta).
Myricetin ().
4. Flavanone
5. Anthocyanins
6. Isoflavonoids
Most of these (flavanones, flavones, flavonols, and anthocyanins) bear ring B in position 2 of the heterocyclic ring. In isoflavonoids, ring B occupies position 3.
A group of chromane derivatives with ring B in position 4 (4-phenyl-coumarins = NEOFLAVONOIDS) is shown below.
The Isoflavonoids and the Neoflavonoids can be regarded as ABNORMAL FLAVONOIDS.




CHALCONE

Chalcone is derived from three acetates and cinnamic acid as shown below.

ANTHOCYANIDIN

Anthocyanidin is an extended conjugation made up of the aglycone of the glycoside anthocyanins. Next to chlorophyll, anthocyanins are the most important group of plant pigments visible to the human eye.
The anthocyanodins constitute a large family of differently coloured compounds and occur in countless mixtures in practically all parts of most higher plants. They are of great economic importance as fruit pigments and thus are used to colour fruit juices, wine and some beverages.
The anthocyanidins in Hydrangea, colours it RED in acid soil and BLUE in alkali soil.
They will chelate with metal ions like Ca2+ and Mg2+ under alkali conditions.
This extends the conjugation as shown below.


ISOFLAVONOIDS

In contrast to most other flavonoids, isoflavonoids have a rather limited taxonomic distribution, mainly within the Leguminosae. Most of our knowledge about the biosynthesis of isoflavonoids originates from studies with radioactive isotopes, by feeding labelled 14C cinnamates.
The isoflavonoids are all colourless. It has been established that acetate gives rise to ring A and that phenylalamine, cinnamate and cinnamate derivatives are incorporated into ring B and C-2, -3, and -4 of the heterocyclic ring.
Since chalcones and flavanones are efficient precursors of isoflavonoids, the required aryl migration of ring B from the former 2 or beta position to the 3 or alpha position of the phenylpropanoid precursor must take place after formation of the basic C15 skeleton.


Example of a BIOLOGICALLY ACTIVE ISOFLAVONOID
Rotenone comes from Derris root and Lonchocarpus species leaf (Family: Leguminosae)
It is an insecticide and also used as a fish poison.
* (blue): carbons derived from methionine.
(red): carbons derived from PRENYL (isoprenoid).
Biochemical pathway to the formation of rotenone.
Six rotenoid esters occur naturally and are isolated from the plant Derris eliptica found in Southeast Asia or from the plant Lonchocarpus utilis or L. urucu native to South America.
Rotenone is the most potent. It is unstable in light and heat and almost all toxicity can be lost after two to three days during the summer. It is very toxic to fish, one of its main uses by native people over the centuries being to paralyze fish for capture and consumption. Crystalline rotenone has an acute oral LD50 of 60, 132 and 3000mg/kg for guinea pigs, rats, and rabbits (Matsumura, 1985). Because the toxicity of derris powders exceeds that of the equivalent content of rotenone, it is obvious that the other esters in crude preparations have significant biologic activity.
Acute poisoning in animals is characterized by an initial respiratory stimulation followed by respiratory depression, ataxia, convulsions, and death by respiratory arrest (Shimkin and Anderson, 1936). The anesthetic-like action on nerves appears to be related to the ability of rotenone to block electron transport in mitochondria by inhibiting oxidation linked to NADH2, this resulting in nerve conduction blockade (O'Brien, 1967; Corbett, 1974). The estimated fatal oral dose for a 70kg man is of the order of 10 to 100g.
Rotenone has been used topically for treatment of head lice, sacbies, and other ectoparasites, but the dust is highly irritating to the eyes (conjunctivitis), the skin (dermatitis), and to the upper respiratory tract (rhinitis) and throat (pharyngitis).

8 komentar:

  1. What is the relationship of the Examples of the 6 major subgroups are Chalcones, Flavone, Flavonol, Flavanone, Anthocyanins, and Isoflavonoids , tell me please... thanks

    BalasHapus
    Balasan
    1. oke thanks for your problem lina
      the answer is >>
      Flavonoids are water soluble polyphenolic molecules containing 15 carbon atoms. Flavonoids belong to the polyphenol family. Flavanoids can be visualized as two benzene rings which are joined together with a short three carbon chain. One of the carbons of the short chain is always connected to a carbon of one of the benzene rings, either directly or through an oxygen bridge, thereby forming a third middle ring, which can be five or six-membered. The flavonoids consist of 6 major subgroups: chalcone, flavone, flavonol, flavanone, anthocyanins and isoflavonoids.
      Together with carotenes, flavanoids are also responsible for the coloring of fruits, vegetables and herbs.

      Hapus
  2. actually i still confused how can a flavonoid be an antioxidant? please explain that mecanism. Thank you

    BalasHapus
    Balasan

    1. I'll try to answer your question about antioxidants
      Phenolic Compounds >> is one natural ingredient compounds having biological activity of anti-free radicals that can capture reactive oxygen compounds. Flavonoids are phenolic compounds that have activity capture hydroxyl radicals and superoxide ion radicals. Flavonoid structure having C = O group at position C-4 and the hydroxyl group in C-5 can prevent the formation of hydroxyl radicals in the fenton reaction that can form complexes with metal ions Fe2 + (Cos, et al. 1998). The presence of hydroxyl at position C-7, C-3, C-4 ', and the double bond at C-2 would increase the activity of anti-free radicals. Anti-free radical activity will decrease or completely inactive if the hydroxyl group substituted with a methoxy group or another. The relationship between the structure of flavonoids with anti-free radical activity seen that with increasing number of hydroxyl groups, the higher the anti-free radical activity. Kaempferol compounds having a hydroxyl substituent at C-7, C-5, C-4 ', and the double bond at C-2 also causes the compound has anti-free radical activity.
      Measurement of antioxidant activity can be done by several methods, including the method of DPPH, β-carotene method, measurements of Ferric Tio cyanate (FTC), Fremy salt reduction, and measurement of Trolox Equivalent Antioxidant Capacity (TEAC), and others. DPPH method to determine antioxidant activity of isolates obtained.

      Hapus
  3. havis,why The Isoflavonoids and the Neoflavonoids can be regarded as ABNORMAL FLAVONOIDS?and how about the reactivity from isoflavonoids? please explain ... thx

    BalasHapus
    Balasan
    1. THANKS CHITRA
      the answer >> Because the majority of B (flavanones, flavones, flavonols, and anthocyanins) bear ring in position 2 of the heterocyclic ring. In isoflavonoids, ring B position 3.
      A group chromane derivatives with ring B in position 4 (4-phenyl-coumarin = NEOFLAVONOIDS) for which they can be considered as "ABNORMAL"

      Hapus
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    BalasHapus
  5. Great tips regrading flavonoids. You provided the best information which helps us a lot. Thanks for sharing the wonderful information.

    BalasHapus