Biosynthesis of flavonoids

Class Course presentation,
Department of Biochemistry and Molecular Biology
Obafemi Awolowo University, Ile ife
Nigeria.

1. BIOSYNTHESIS OF FLAVONOIDS BCH 614 (Natural Products) BY Omotosho Gbemiga O. SCP17/18/H/1049 and Oyelekan Esther Ibukunoluwa SCP18/19/R/0088 Lecturer: Dr. ( Akinpelu B.A

2. INTRODUCTION Flavonoids are a group of phenolic compounds with 15 carbon atoms; 2 benzene rings joined by a linear three carbon chain having a C6-C3-C6 carbon skeleton (Maria et al ., 2012). They act as antioxidants; and their anti-oxidative property depends on the molecular structure, presence of conjugated double bonds and the occurrence of functional groups in the rings . Flavonoids are polar and soluble in methanol and water. Widely distributed in different amounts, according to the plant species, organ, developmental stage and growth conditions.

3. Introduction Contd The antioxidant activities of flavonoids for example, present in tea, red wine, hops and beer, fruits vegetable e.t.c . They have been known to have antiviral, anti-allergic, anti-inflammatory and antitumor activities etc. They also provide stress protection.

4. Structure of Flavonoids Their basic structure is a skeleton of diphenylpropane , namely, two benzene rings (ring A and B) linked by a three carbon chain that forms a closed pyran ring (heterocyclic ring containing oxygen, the C ring) with benzenic A ring. Therefore, their structure is also referred to as C6-C3-C6. In most cases, B ring is attached to position 2 of C ring, but it can also bind in position 3 or 4; this, together with the structural features of the ring B and the patterns of glycosylation and hydroxylation of the three rings, makes the flavonoids one of the largest and more diversified groups of phytochemicals.

5. Schematic Diagram Adapted from Kuhn et al . (2011).

6. BIOSYNTHESIS OF FLAVONOIDS The biosynthesis of flavonoids start with the condensation of one P - coumaroylCoA molecule ( shikimate derived, B ring) with three molecules of malonyl -CoA ( polyketid origin, A ring) to give chalcone ( 2′, 4′, 6′, 4-tetrahydroxychalcone ) catalized by chalcone synthase (CHS) enzyme. Chalcone is subsequently isomerized by the enzyme chalcone flavanone isomerase (CHI) to flavanone From these central intermediates, the pathway diverges into several side branches, each yielding a different class of flavonoids

7. PAL: Phenylalanine lyase C4H: Cinnamate 4 hydroxylase 4CL: 4-Coumaryl lyase CHS: Chalcone synthase CHI: Chalcone isomerase DFR: Dihydroxyflavanone reductase ANS: Anthocyanidin synthase IFS: Isoflavonone synthase 3GT: 3-O glucosyltransferase FSI: Flavone synthase FHT: Flavanone 3b hydroxylase FLS: Flavonol synthase   Phenylalanine Cinnamic acid Caffeic acid Malonyl CoA Isoflavones Flavan-4-ols IFS DFR FHT, FLS FSI 3GT CHI CHS PAL C4H 4CL Acid CoA Complex BIOSYNTHESIS OF FLAVONOIDS 7 Adapted from Maria et al . (2012 ).

8. BIOSYNTHESIS OF FLAVONOIDS 8 Adapted from Martens et al . (2010 )

9. T he B ring formation is produced by a Shikimate pathway

10. Formation of A-Ring via Acetate pathway (Figure 2)

11. Simplified biosynthesis of Flavonoids pathway Phenylalanin PAL Figure 5

12. Biosynthesis of flavonoids continue Abbreviations of Enzymes ACTs = Acetyl transferases ANR = A nthocyanidin reductase ; ANS = A nthocyanidin synthase (also known as leucoanthocyanidin dioxygenase LDOX ) C4H = Cinnamate-4-hydroxylase CHI = Chalcone isomerase CHR = Chalcone reductase CHS = Chalcone synthase 4CL = 4-coumaroyl:CoA-ligase DFR = Dihydroflavonol 4-reductase DMID = 7,2'-dihydroxy, 4‘-methoxyisoflavanol dehydratase F3H = Flavanone 3-hydroxylase FNSI and FNSII , flavone synthase I and II F3’H and F3’5’H = Flavonoid 3’ and 3’5’ hydroxylase IOMT = Isoflavone O- methyltransferase IFR = Isoflavone reductase I2’H = I soflavone 2'- hydroxylase IFS = Isoflavone synthase LAR = Leucoanthocyanidin reductase OMTs = O- methyltransferase PAL = Phenylalanine ammonia- lyase GTs = Glucosyl transferases VR = Vestitone reductase .

13. REGULATORY MECHANISM T he synthesis of flavonoids begins from phenylalanine in the shikimate pathway, converting phenylalanine into 4-coumaroyl- CoA, which then enters the flavonoid biosynthesis pathway through chalcone intermediate (Maria et al., 2012 ). R egulatory enzyme specific for flavonoid pathway includes Phenylalanin Ammonia Lyase (PAL), C halcone synthase (CHS), the enzyme produces C halcone scaffolds from which all flavonoids derive, also Flavone 3-Hydroxylase (F3-H), which regulate the biosynthesis of Leucocyanidine in addition to these regulatory enzymes are Anthocyanidine synthase (ANS) (also known as Leucothocyanidin dioxygenase (LDOX)) that regulate the biosynthesis of Anthocyanidins and Glutathion S- Transferase (GST) that regulate the biosynthesis of Anthocyanins .

14. Scheme presentation of Regulation of Anthocyanins (Flavonoid) biosynthesis Figure : 6

15. Schematic presentation of Gene Regulation of Anthocyanin biosynthesis (A Flavonoid) Figure: 7

16. Conclusion Flavonoids are found in most plant tissues – where they provide brilliant colors that attract pollinators. The pigments act as antioxidants and sunscreens, absorbing UV radiation. Their biosynthesis appears to be ubiquitous in plants and evolved early in life, providing protection and signaling in plants . The regulatory mechanism is both genetic and subcellular localization of flavonoid pathways with C halcone synthase being the first regulatory enzyme specific for flavonoid biosynthesis.

17. References Dixon , R.A.; Pasinetti , G.M. (2010). Flavonoids and isoflavonoids : from plant biology to agriculture and neuroscience. Plant Physiology , 154 : 453-457. Iwashina , T . (2000). The structure and distribution of the flavonoids in plants. Journal of Plant Research , 113 : 287-299. Kuhn , B.M. , Geisler,M.,Bigler,L.,and Ringli,C .(2011). Flavonols accu mulate asymmetrically and affect auxin transportin Arabidopsis . PlantPhysiol . 156| 585–595. María , L. F. F., Sebastián , P. R. and Paula, C. (2012). Flavonoids: biosynthesis, biological functions,and biotechnological applications. Frontiers in plant science. 3(222):1-15. Martens , S., Preuss , A., and Matern , U. (2010). Multifunctional flavonoid dioxygenases : flavonols and antho-cyaninbiosynthesis in Arabidopsis thaliana L. Phytochemistry , 71: 1040–1049. Owens , D.K., Alerding , A.B., Crosby, K.C., Bandara , A.B., Westwood, J.H., and Winkel , B.S.J.(2008). Functional analysis of a predicted flavonol synthase gene family in Arabidopsis . Plant Physiol. 147: 1046–1061.

18. References contd. Martens S, Preuss A, Matern U. Multifunctional flavonoid dioxygenases : flavonols and anthocyanin biosynthesis in Arabidopsis thaliana L. Phytochemistry . 2010; 71 :1040-1049 . Markham K.R . Distribution of flavonoids in the lower plants and its evolutionary significance. In : Harborne JB, editor. The flavonoids: advances in research since 1980 (1st ed .). London : Chapman & Hall; 1988, pp. 427-464. Markham K.R , Porter L.J . Flavonoids in the green algae ( chlorophyta ). Phytochemistry . 1969; 8 :1777-1781 . Oh H, Kim DH, Cho JH, Kim YC. Hepatoprotective and free radical scavenging activities of phenolic petrosins , flavonoids isolated from Equisetum arvense . Journal of Ethnopharmacology . 2004; 95 :421-424. Vassao D, Kim KW, Davin LB, Lewis NG. Lignans ( neolignans ) and allyl / propenyl phenols: biogenesis, structural biology, and biological/human health considerations. In: Mander L, Liu H-WB, editors. Comprehensive natural products II (1st ed.). Oxford: Elsevier; 2010, pp. 815-928.

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