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Chapter 26 811
Copyright © 2017 Pearson Education, Inc.
Solutions to Problems
1.
The most basic atom in the ring is protonated. In the case of a purine, this is the nitrogen at the 7-position.
In the next step, the bond between the heterocyclic base and the sugar breaks, with the anomeric carbocation
being stabilized by the ring oxygen’s nonbonding electrons.
N
N N
N
NH
2
O
HO
HO OH
H B
+
N
N N
N
NH
2
O
HO
HO OH
+
H
N
N N
H
N
NH
2
O
HO
HO OH
+
H
2
O
The mechanism is exactly the same for pyrimidines, except that the initial protonation takes place at the
3-position.
N
N
NH
2
O
HO
HO OH
HN
N
NH
2
O
HO
HO OH
+
H
2
O
O
HN
N
NH
2
O
HO
HO OH
+
O
O
H B
+
2.
a.
O
N
N
NH
2
O
HO
−
O
−
O
dCDP
O
P
O
−
O O
P
O
b.
O
N
HN
O
O
HO
dTTP
CH
3
−
O
−
O O
P
O
−
O
P
O
O
−
O O
P
O