2 THE SHIKIMIC ACID PATHWAY This pathway (unique to plants) leads to the formation of thearomatic amino acids phenylalanine and tyrosine and to theformation of many other phenyl-C3 compounds.PhenylpropanoidsPhenyl-C3Cleavage of the C3 side chain leads to many phenyl-C1 compounds.Phenyl-C1
3 GLUCOSE ORIGINS OF THE SHIKIMIC ACID PATHWAY PEP Acetyl-CoA pentosephosphatepathwayglycolysisErythrose-4-phosphatePEPPhosphoenol pyruvateThe pentose phosphatepathway is one thatconverts glucose intosugars of different sizes(different numbers of C)by acyl interchanges.Erythrose is a 4-carbonsugar.Acetyl-CoAShikimic Acid
4 FORMATION OF SHIKIMIC ACID phosphoenol pyruvateB:H+erythrose-4-phosphateH+H+NADPHshikimic acid
5 FORMATION OF CHORISMIC ACID hydrolysisof PEPATPH+shikimic acidpyruvic acidnucleophilicaddition to C=O:B- H3PO4- H2Ochorismic acid
6 PREPHENIC ACID phenylalanine tyrosine p-hydroxy- phenypyruvic chorismic acidClaisen TypeRearrangementprephenic acidpseudoaxial conformationPrephenic acid can be converted to phenylpyruvic acidor to 4-hydroxyphenylpyruvic acid:NADPHNADP+p-hydroxy-phenylpyruvicacidphenypyruvicacid-H+- CO2-H--H+- CO2-OHphenylalaninetyrosine
7 CLAISEN REARRANGEMENT A THERMAL REARRANGEMENTH+heatenolizationan allyl etheran allyl phenol
8 PREPHENIC ACID TO PHENYLALANINE :B-Enz- CO2phenylpyruvic acid- H2Oprephenic acidH+transaminationphenylalanine
10 PHENYLALANINE AND TYROSINE COME FROM A COMMON SOURCE AND ARE NOT CONVERTEDPREPHENIC ACIDphenylpyruvic acid4-hydroxyphenylpyruvic acidXtyrosinephenylalanineAlthough most plants could convert phenylalanine to tyrosineusing hydroxylases, this conversion is a minor pathway. Mostplants make enough tyrosine without converting phenylalanine.
14 CINNAMYL COMPOUNDS The rings can have various numbers of hydroxyl or methoxyl groups (hydroxylases and SAM).NADPHcinnamaldehydeNADPH- H2OEnz-SHoxidativecleavageFADH2cinnamic acidbenzaldehydehydrocinnamic acid
15 SOME NATURALLY-OCCURING CINNAMYL COMPOUNDS CINNAMICACIDp-coumaric acidcaffeic acidferulic acidcorrespondingaldehydes arealso found -see next slidep-coumarylalcoholconiferylalcoholsinapylalcoholsinapic acid
23 PLANT PIGMENTSFlavonoids and anthocyanins are conspicuous plant pigments in nature thatare responsible for the beauty and splendor of flowers, fruits, fruit tree blossomsand of the autumn leaves.Flavones are responsible for the yellow and orange colors; and the anthocyaninsare the source of red, violet and blue colors. These compounds occur mainly inhigher plants and are less common in the lower orders. You don’t find them inalgae, fungi or bacteria.The flavonoids play a major role in attracting insects to feed and pollinate theseplants. Some of them also have a bitter taste and repel harmful insects likecaterpillars.Flavonoids are thought to be antioxidants, and play a major role in our diet,preventing the ravages of aging caused by free-radicals.These compound have their biosynthetic origin in both the skimic acid pathwayand the acetogenin pathway - they are of hybrid origin.
24 NARINGENIN found in grapefruit : MIXED-ORIGIN COMPOUND shikimic acid pathwayNARINGENINA different starterthan acetyl-CoA.found in grapefruitmalonyl-CoA3xacetogeninpathway:Michaeladditioninternal Claisenand enolizationsMIXED-ORIGINCOMPOUNDA FLAVONEflavones are yellowor orange pigmentsnaringenin