Textbook Question
c. Under photochemical conditions, will ring closure be conrotatory or disrotatory?
d. Will the product have the cis or the trans configuration?
16. Conjugated Systems
Photochemical Electrocyclic Reactions
3:31 minutesProblem 21
Textbook Question
Chorismate mutase is an enzyme that promotes a pericyclic reaction by forcing the substrate to assume the conformation needed for the reaction. The product of the pericyclic reaction is prephenate that is subsequently converted into the amino acids phenylalanine and tyrosine. What kind of a pericyclic reaction does chorismate mutase catalyze?
Verified step by step guidance1
Step 1: Analyze the chemical structures of chorismate and prephenate. Chorismate contains a six-membered aromatic ring with substituents including a hydroxyl group, a carboxylate group, and an enol ether. Prephenate, the product, has a six-membered ring with a keto group and a rearranged substituent pattern.
Step 2: Recognize the type of reaction occurring. The transformation involves a rearrangement of bonds within the molecule, characteristic of a pericyclic reaction. Specifically, this reaction is a [3,3]-sigmatropic rearrangement, known as the Claisen rearrangement.
Step 3: Understand the role of chorismate mutase. The enzyme stabilizes the transition state and forces the substrate (chorismate) into a conformation that facilitates the pericyclic reaction. This ensures the reaction proceeds efficiently.
Step 4: Describe the mechanism of the Claisen rearrangement. In this reaction, the enol ether group in chorismate undergoes a concerted rearrangement, where bonds are broken and formed simultaneously, leading to the formation of prephenate.
Step 5: Relate the biological significance. Prephenate is a precursor for the biosynthesis of the amino acids phenylalanine and tyrosine, highlighting the importance of this enzymatic reaction in metabolic pathways.
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Video duration:
3mKey Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Pericyclic Reactions
Pericyclic reactions are a class of organic reactions that occur through a concerted mechanism, involving the cyclic rearrangement of electrons. These reactions typically involve the simultaneous breaking and forming of bonds in a cyclic transition state, which can lead to various products. Common types include cycloadditions, electrocyclic reactions, and sigmatropic rearrangements, each characterized by specific electron movement patterns.
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Properties and Types of Pericyclic Reactions
Chorismate Mutase Function
Chorismate mutase is an enzyme that catalyzes the conversion of chorismate to prephenate through a pericyclic rearrangement. This enzyme facilitates the necessary conformational change in the substrate, allowing the reaction to proceed efficiently. Understanding its mechanism is crucial for grasping how it influences the biosynthesis of aromatic amino acids like phenylalanine and tyrosine.
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Aromatic Amino Acid Biosynthesis
The biosynthesis of aromatic amino acids, such as phenylalanine and tyrosine, is a vital metabolic pathway in organisms. This process begins with chorismate, which is derived from the shikimic acid pathway. The conversion of prephenate into these amino acids involves additional enzymatic steps, highlighting the importance of chorismate mutase in the overall synthesis and regulation of these essential compounds.
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