Fundamentals of Medicinal Chemistry

H

CH 3

O

N

N

O

H

N

N

H

N NH 2

O

N

H

O

H

HH

OH

H

HOCH 2

OH

N

N

N

N

NH 2

O

H

HH

OH

H

HOCH 2

OH

N

N

N

O

NH

NH 2

Guanine (G)

N

N

H

NH 2

N

N

Adenine (A)

1

2

3

7

8

9

6

5

4

Cytosine (C)

H

N

NH 2

N

O

6 1

5

4

3

2

Thymine (T)

Purines Pyrimidines

(c)

Uracil (U)

(b)

1'

3' 2'

4'

5'

1'

5'

3' 2'

4'

H

HH

OHH

H

HOCH 2 N

NH 2

N

O

Adenosine Guanosine Deoxycytidine

O P

O

O

O−

SUGAR

BASE

O P

O

O

SUGAR

P BASE

O

O

O

O− O−

SUGAR

BASE

O P

O

O

O−

SUGAR

BASE

(d)

(a)

C5'' C3''

H

O

O

N

H

N

Figure 1.28 (a) The general structure of a nucleotide. (b) A schematic representation of a section

of a nucleic acid chain. (c) The bases commonly found in DNA and RNA. These bases are

indicated by the appropriate letter in the structures of Nucleic acids. Thymine is not found in

RNA; it is replaced by uracil, which is similar in shape and structure. (d) Examples of nucleosides

found in DNA and RNA

asnucleosidesare linked, through the 3’and 5’carbons of their sugar residues,

by phosphate units to form the nucleic acid polymer chain (Figure 1.28(d) ).

Nucleotides can exist as individual molecules with one or more phosphate or

polyphosphategroupsattachedtothesugarresidue.Thenamesofthesemolecules

are based on those of the correspondingnucleosides. Ribosenucleosidesare named

after their bases (Figure 1.28(c) ) but with either the suffix-osineor-idine. Nucleo-

sides based on deoxyribose use the name of the corresponding RNA nucleoside

prefixed bydeoxy- (Figure 1.28(d) ). The purine and pyrimidine rings are

numbered in the conventional manner (Figure 1.28(c) ) whilst primes are used for

thesugar residuenumbers(Figure1.28(d) ). Numbersarenot includedinthe name

if the phosphate unit is at position 5’(Figure 1.29). The positions of phosphates

attached at any other position are indicated by the appropriate locants.

NUCLEIC ACIDS 27