Organic Chemistry

Section 21.11 Biologically Important Heterocycles 911

3-D Molecule:

Chlorophyll a

The ring system in chlorophyll a, the substance responsible for the green color of
plants, is similar to porphyrin but contains a cyclopentanone ring, and one of its pyrrole
rings is partially reduced. The metal atom in chlorophyll ais magnesium

Vitamin also has a ring system similar to porphyrin, but one of the methine
bridges is missing. The ring system of vitamin is known as a corrin ring system.
The metal atom in vitamin is cobalt The chemistry of vitamin is dis-
cussed in Section 25.7.

PROBLEM 26

Is porphyrin aromatic?

PROBLEM 27

Show how the last two porphobilinogen molecules are incorporated into the porphyrin

ring.

NH 2

NH 2

NH 2

CH 3

CH 3

CH 3

CH 3

CH 3

CH 2 OH

H 3 C

H 3 C

H 3 C

H 2 N

H 2 N

H 2 N

CH 3

H 3 C

H 3 C

O

O

O

O

O

O

O

OH

H

H

H

H

H

H

H

H

CN

N

N

N

O

N

N

N

O

HN

O

−O O

P

CoIII

vitamin B 12

B 12 (Co^3 +). B 12

B 12

B 12

H 3 C

MgII

CH 2

H 3 C

CH 2 CH 3

CH 3

HC CH 3

chlorophyll a

N

H

H

NN

N

C

OCH 3

O O

O

O

(Mg^2 +)

3-D Molecule:

Vitamin B 12