In a step in the degradation if the amino acid isoleucine, the intermediate compound 2-methyl-3-keto-butyryl \(CoA\) undergoes a retro-Claisen cleavage. Draw curved arrows for the carbon-carbon bond-forming step in mechanism for this condensation reaction between two fatty acyl-thioester substrates. Because esters can contain α hydrogens they can undergo a condensation reaction similar to the aldol reaction called a Claisen Condensation. Chemistry 328N t-Butyl esters. You should look back at the general mechanism for a forward Claisen condensation and convince yourself that the retro-Claisen mechanism illustrated aboveis a step-by-step reverse process. Unless otherwise noted, LibreTexts content is licensed by CC BY-NC-SA 3.0. Claisen Condensation Lecture 21 April 9, 2019. The reaction proceeds when a strong base is present and the product of the reaction is a beta-keto ester or a beta-diketone. An illustration of this reaction is provided below. Is a decarboxylation/Claisen condensation step also likely to be metabolically relevant in the 'retro' direction? The major points to recall are that a nucleophile attacks a carboxylic acid... Biochemical Claisen condensation examples. (, is the compound that is primarily responsible for the distinctive yellow color of turmeric, a spice used widely in Indian cuisine. The Claisen condensation reaction is an organic coupling reaction that results in the formation of a C-C bond between either a single ester and one carbonyl compoundor between two esters. You have already seen that ethyl acetoacetate‑type compounds are very useful in organic syntheses. Missed the LibreFest? For a given Claisen reaction, there is essentially one suitable base that can be used. For more information contact us at info@libretexts.org or check out our status page at https://status.libretexts.org. Meanwhile, a transthioesterification reaction occurs (steps a and b) to free the enzyme's cysteine residue, regenerating a fatty acyl CoA molecule which is two carbons shorter than the starting substrate. Other than that, the reaction looks just like the Claisen condensation reactions we saw earlier. The Claisen Condensation between esters containing α-hydrogens, promoted by a base such as sodium ethoxide, affords β-ketoesters. The main difference in the products is that, in Claisen reaction, both molecules retain their carbonyl group , and this is due to the presence of the alkoxy group which serves as a leaving group after the nucleophilic addition: Then the resulting tetrahedral intermediate collapses (step 3), expelling the thiol leaving group and leaving us with a \(\beta\)-keto thioester product (a thioester with a ketone group two carbons away). Mixed Claisen Condensation Like mixed aldol reactions, mixed Claisen condensations are useful i differences in reactivity exist between the two esters as for example when one of the esters has no α-hydrogen. Chemistry 328N t-Butyl esters. When your body 'burns' fat to get energy, it is a retro-Claisen cleavage reaction (EC 2.3.1.16) that is responsible for breaking the carbon-carbon bonds in step IV of the fatty acid degradative pathway. Draw a mechanism for this step. Legal. In a typical retro-Claisen reaction, a thiol (or other nucleophile such as water) attacks the carbonyl group of a \(\beta\)-thioester substrate (step 1), and then the resulting tetrahedral intermediate collapses to expel an enolate leaving group (step 2) - this is the key carbon-carbon bond-breaking step. Example of a Claisen condensation: This is an example of an intramolecular Claisen reaction, called a Dieckmann condensation. Claisen rearrangement is an organic chemical reaction that offers a powerful method in the formation of carbon-carbon bonds.The reactant of this reaction – allyl vinyl ether, is converted into a gamma, delta-unsaturated carbonyl compound when subjected to heat or a Lewis acid.. A simple example of a Claisen condensation is the reaction of ethyl ethanoate which is shown below in two representations. A major difference with the aldol reaction is the fact that hydroxide cannot be used as a base because it could possibly react with the ester. Missed the LibreFest? In step 1, the \(\alpha\)carbon of one thioester substrate is deprotonated to form an enolate, which then goes on to attack the second thioester substrate (step 2). C 2 H 5 ONa, undergo self condensation to produce β-keto esters.. CH 3 COCH 2 COOC 2 H 5. Try to identify the enolate portion … Chemistry 328N t-Butyl ester hydrolysis condensation step also likely to be metabolically relevant in the 'retro' direction? An α-hydrogen in an ester is weakly acidic than the α-hydrogen of aldehydes or ketones, because the carbonyl group helps accommodate the negative charge of the carbanion to a lesser extent. We also acknowledge previous National Science Foundation support under grant numbers 1246120, 1525057, and 1413739. Recall the general mechanism for a nucleophilic acyl substitution mechanism, which we studied in chapter 10: The major points to recall are that a nucleophile attacks a carboxylic acid derivative, leading to a tetrahedral intermediate, which then collapses to expel the leaving group (X). During the reaction a new carbon-carbon bond is formed. One example (EC 3.7.1.2) occurs in the degradation pathway for tyrosine and, 13.3: An Overview of Fatty Acid Metabolism, Biochemical Claisen condensation examples, Organic Chemistry With a Biological Emphasis. Play. Predict the products. The reaction is named after its discoverer, the German chemist Rainer Ludwig Claisen. What is Claisen Rearrangement? Example of Claisen condensation Claisen condensation. A typical nucleophilic acyl substitution reaction might have an alcohol nucleophile attacking a thioester, driving off a thiol and producing an ester. Explain. The driving force is the formation of the stabilized anion of the β-keto ester. [ "article:topic", "Claisen condensation", "mechanism", "authorname:soderbergt", "showtoc:no", "license:ccbyncsa", "Decarboxylation", "Retro-claisen cleavage" ], Emeritus Associate Professor of Chemistry, Draw curved arrows for the carbon-carbon bond-forming step in mechanism for this condensation reaction between two fatty, can be hydrocarbon chains of various lengths. write a detailed mechanism for a Claisen condensation reaction or its reverse. Have questions or comments? PATTERNSPATTERNS R CH2 C OH R CH C R O R R CH2 C C C R O RR 3-hydroxyaldehyde or 3-hydroxyketone (H) (H) β-hydroxy to C=O α,β-unsaturated C=O 2-propen-1-al or 2-propen-1-one ALDOL ALDOL CLAISENR CH2 C O CH C OR O R β-keto ester Type of Condensation Reaction -H2O (with loss of H2O) 43. This video shows you the step by step reaction mechanism including why the reaction is reversible only till the final step. Dr. Dietmar Kennepohl FCIC (Professor of Chemistry, Athabasca University), Prof. Steven Farmer (Sonoma State University). Now, we can finally understand the fatty acid chain-elongation step that we heard about in the chapter introduction in the context of the Lorenzo's oil story, which is a decarboxylation/Claisen condensation between malonyl-ACP (the donor of a two-carbon unit) and a growing fatty acyl CoA molecule. Watch the recordings here on Youtube! One example (EC 3.7.1.2) occurs in the degradation pathway for tyrosine and phenylalanine: Organic Chemistry With a Biological Emphasis by Tim Soderberg (University of Minnesota, Morris).

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