Q40E - Organic Chemistry (Mcmurry)

Question

One of the steps in metabolism of fats is the reaction of an unsaturated acyl coA with water to give a $\beta$ - hydroxyacyl CoA. Propose a mechanism.

Step-by-Step Solution

Answer

The first step of the mechanism is-

Step1: Introduction

The reactant given in the reaction is an $\alpha , \beta$  unsaturated type of aldehyde/ketonic compound. To this water can be added reversibly to an unsaturated acyl CoA to give a  $\beta$- hydroxyacyl CoA. This is one of the steps in the metabolism of fats and also an example of Conjugate nucleophilic addition to an unsaturated aldehyde or ketone.

Step 2: Mechanism

In the first step of the reaction, the OH adds to the C=C or $\alpha$ carbon (carbon atom next to carbonyl carbon is $\alpha$ carbon while next to the $\alpha$ carbon is the $\beta$ carbon). Initially, an enolate ion is obtained which then undergoes a protonation to yield finally _$\beta$

-hydroxyacyl-CoA. This is also known as 1,4 addition. The mechanism can be represented as-