1 SHIKIMIC ACID PATHWAY 2 THE SHIKIMIC ACID PATHWAY This pathway (unique to plants) leads to the formation of the aromatic amino acids phenylalanine and tyrosine and to the formation of many other phenyl-C3 compounds. Phenylpropanoids Phenyl-C3 Cleavage of the C3 side chain leads to many phenyl-C1 compounds. Phenyl-C1 3 GLUCOSE ORIGINS OF THE SHIKIMIC ACID PATHWAY pentose phosphate pathway glycolysis PEP Erythrose-4-phosphate Phosphoenol pyruvate The pentose phosphate pathway is one that converts glucose into sugars of different sizes (different numbers of C) by acyl interchanges. Erythrose is a 4-carbon sugar. Acetyl-CoA Shikimic Acid 4 FORMATION OF SHIKIMIC ACID phosphoenol pyruvate B H erythrose-4-phosphate H H NADPH shikimic acid 5 FORMATION OF CHORISMIC ACID hydrolysis of PEP ATP H shikimic acid pyruvic acid nucleophilic addition to CO B - H3PO4 - H2O chorismic acid 6 PREPHENIC ACID chorismic acid Claisen Type Rearrangement prephenic acid pseudoaxial conformation Prephenic acid can be converted to phenylpyruvic acid or to 4-hydroxyphenylpyruvic acid NADP NADPH p-hydroxy- phenylpyruvic acid phenypyruvic acid - CO2 -H -H- - CO2 -H -OH phenylalanine tyrosine 7 CLAISEN REARRANGEMENT A THERMAL REARRANGEMENT H heat enolization an allyl ether an allyl phenol 8 PREPHENIC ACID TO PHENYLALANINE B-Enz - CO2 phenylpyruvic acid - H2O prephenic acid H transamination phenylalanine 9 PREPHENIC ACID TO TYROSINE B-Enz - CO2 4-hydroxyphenyl- pyruvic acid NAD prephenic acid transamination hydride transfer to NAD tyrosine 10 PHENYLALANINE AND TYROSINE COME FROM A COMMON SOURCE AND ARE NOT CONVERTED PREPHENIC ACID phenylpyruvic acid 4-hydroxyphenylpyruvic acid X tyrosine phenylalanine Although most plants could convert phenylalanine to tyrosine using hydroxylases this conversion is a minor pathway. Most plants make enough tyrosine without converting phenylalanine. 11 A PRELIMINARY OVERVIEW 12 SHIKIMIC ACID Shikimate Pathways CHORISMIC ACID ( acetogenin piece) PHENYL-C3 COMPOUNDS PREPHENIC ACID FLAVONOIDS CINNAMIC ACIDS TYROSINE PHENYLALANINE PHENYL-C1 COMPOUNDS ALKALOIDS ALKALOIDS 13 CINNAMYL COMPOUNDS 14 CINNAMYL COMPOUNDS The rings can have various numbers of hydroxyl or methoxyl groups (hydroxylases and SAM). NADPH cinnamaldehyde NADPH - H2O Enz-SH oxidative cleavage FADH2 cinnamic acid benzaldehyde hydrocinnamic acid 15 SOME NATURALLY-OCCURING CINNAMYL COMPOUNDS CINNAMIC ACID p-coumaric acid caffeic acid ferulic acid corresponding aldehydes are also found - see next
.. - H2O cinnamic acid RODENTICIDE (rat poison) dicoumarol causes internal bleeding in cows (sweet clover) Warfarin anti-coagulant 22 FLAVONOIDS Plant Pigments 23 PLANT PIGMENTS Flavonoids and anthocyanins are conspicuous plant pigments in nature that are responsible for the beauty and splendor of flowers fruits fruit tree blossoms and of the autumn leaves. Flavones are responsible for the yellow and orange colors and the anthocyanins are the source of red violet and blue colors. These compounds occur mainly in higher plants and are less common in the lower orders. You dont find them in algae fungi or bacteria. The flavonoids play a major role in attracting insects to feed and pollinate these plants. Some of them also have a bitter taste and repel harmful insects like caterpillars. 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 pathway and the acetogenin pathway - they are of hybrid origin. 24 shikimic acid pathway NARINGENIN found in grapefruit A different starter than acetyl-CoA. malonyl-CoA 3x acetogenin pathway
Michael addition internal Claisen and enolizations MIXED-ORIGIN COMPOUND A FLAVONE flavones are yellow or orange pigments naringenin 25 Anthocyanin Flower Pigments 26 Anthocyanin Leaf Pigments Autumn Leaves In Spring and Summer chlorophyll (green) masks the anthocyanin colors. 27 ANTHOCYANIDINS AND ANTHOCYANINS NADPH O2 naringenin (RH) O
- 2 H2O Anthocyanins are red violet or blue pigments. pelargonidin (RH) cyanidin (ROH) plant flower and leaf pigments cyanidin is blue pelargonidin is pink ANTHOCYANIDINS 28 SUMMARY REPEAT 29 ( acetogenin piece) SHIKIMIC ACID Shikimate Pathways FLAVONOIDS CHORISMIC ACID ANTHRANILIC ACID PHENYL-C3 COMPOUNDS PREPHENIC ACID CINNAMIC ACIDS TYROSINE TRYPTOPHAN PHENYLALANINE NEXT LECTURE PHENYL-C1 COMPOUNDS ALKALOIDS ALKALOIDS ALKALOIDS
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