base base base :B О :0-Н nucleophilic catalyst -0-P=0 -0-P-0: P. base Н-B+ base a 2',3'-cyclic phosphodiester НО base О ОН О ОН О Он ↑

Organic Chemistry
9th Edition
ISBN:9781305080485
Author:John E. McMurry
Publisher:John E. McMurry
Chapter30: Orbitals And Organic Chemistry: Pericyclic Reactions
Section30.SE: Something Extra
Problem 41AP: In light of your answer to Problem 30-40, explain why a mixture of products occurs in the following...
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The 2′,3′-cyclic phosphodiester that is formed when RNA is cleaved, forms a mixture of nucleotide 2′- and 3′-phosphates when it reacts with water. Propose a mechanism for this reaction.

base
base
base
:B
О :0-Н
nucleophilic catalyst
-0-P=0
-0-P-0:
P.
base
Н-B+
base
a 2',3'-cyclic phosphodiester
НО
base
О ОН
О ОН
О Он
↑
Transcribed Image Text:base base base :B О :0-Н nucleophilic catalyst -0-P=0 -0-P-0: P. base Н-B+ base a 2',3'-cyclic phosphodiester НО base О ОН О ОН О Он ↑
Expert Solution
Step 1

This is the reaction in which the phosphodiester bond in the sugar phosphate of the RNA backbone is cleaved. The hydroxyl group present at the 2' position makes it susceptible for base catalyzed hydrolysis. This is the reason why RNA is less stable when compared to DNA.

 

Step 2

There are four steps involved in the mechanism:

1. Deprotonation of the hydroxyl group present on the 2' position:There is a removal of proton from the hydroxyl group due to the catalyst which results in the formation of nucleophile O-.

2. Nucleophilic attack of the deprotonated hydroxyl group on the adjacent phosphorous:The nucleophile thus formed in the first step attacks the phosphorous present adjacent to it.This results in the formation of a transition state.

3. Transition state:This results in the formation of a transition state which is highly unstable.

4. Formation of 2',3'-cyclic phosphodiester which hydrolyzes to give either 2' or 3' phosphate:Since the transition state is unstable it undergoes hydrolysis in the presence of water to give either 2' or 3' phosphate.

 

 

 

 

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