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2.12: Thioesters- Biological Carboxylic Acid Derivatives

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  • Introduction to thioesters and Coenzyme A

    In the metabolism of lipids (fats and oils), thioesters are the principal form of activated carboxylate groups. They are employed as acyl carriers, assisting with the transfer of acyl groups such as fatty acids from one acyl X substrate to another.

    The ‘acyl X group’ in a thioester is a thiol. The most important thiol compound used to make thioesters is called coenzyme A, which has the following structure:


    Coenzyme A is often abbreviated HSCoA, in order to emphasize that it is the thiol sulfur that provides the critical thioester linkage to acyl groups. When fuel (carbohydrate and fat) is broken down in your body, it is eventually converted to a simple two-carbon unit called acetyl CoA, which is essentially a thioester derivative of acetic acid:



    Reactivity of carboxylic acids, esters thioesters and acyl phosphates

    Thioesters are reactive among the biologically relevant acyl groups. However, thioesters are not as reactive as an acid chlorides or acid anhydrides. This property makes thioesters and acyl phosphates ideal reagents in biological systems, because they do not have the safety concerns related to using acid chlorides or acid anhydrides, which can only be used in the chemistry lab. 


    Relative reactivity of biologically relevant acyl groups

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