Q28-16E - Organic Chemistry (Mcmurry)

Question

The final step in DNA synthesis is deprotection by treatment with aqueous ammonia. Show the mechanisms by which deprotection occurs at the points indicated in the following structure:

Step-by-Step Solution

Answer

The hydrolysis mechanism for the guanine to xanthine conversion is,

Mechanism of hydrolysis

The guanine hydrolysis can occur by the catalytic guanine deaminase. It also occurs when the reaction of water happens due to the reaction of nucleophilic addition. Water will add due to the nucleophilic addition to the bond of CN. This is followed by the ammonia removal using a substitution reaction.

Diagram of mechanism for guanine hydrolysis

The hydrolysis mechanism of guanine can be drawn as,

The guanine hydrolysis will give raise to xanthine.

In the first step addition of the water takes place and then the removal of amine occurs which leads to the formation of Xanthine.