Organic Chemistry

950 CHAPTER 22 Carbohydrates

HEPARIN

Heparin is an anticoagulant that is released to

prevent excessive blood clot formation when an

injury occurs. Heparin is a polysaccharide made up of glu-

cosamine, glucuronic acid, and iduronic acid subunits. The C-6

OH groups of the glucosamine subunits and the C-2 OH groups

of the iduronic acid subunits are sulfonated. Some of the amino

groups are sulfonated and some are acetylated. Thus, heparin is

a highly negatively charged molecule, found principally in cells

that line arterial walls. Heparin is widely used clinically as an

anticoagulant.

O O

−O

3 SNH

OSO 3 −

HO

HO

HO

HO

CH 2 OSO 3 −

O

O

O

O

O

CH 2 OSO 3 −

CO 2 −

CH 3 CNH

O

CO 2 −

OSO 3 −

O

heparin

O

3-D Molecule:

Gentamicin

Inamino sugars, one of the OH groups is replaced by an amino group. N-Acetyl-

glucosamine—the subunit of chitin and one of the subunits of certain bacterial cell

walls—is an example of an amino sugar (Sections 22.18 and 24.9). Some important

antibiotics contain amino sugars. For example, the three subunits of the antibiotic gen-

tamicin are deoxyamino sugars. Notice that the middle subunit is missing the ring oxy-

gen, so it really isn’t a sugar.

CHNHCH 3

CH 3

HO

gentamicin

an antibiotic

NH 2

NH 2

O

O

O

HO

NH 2

CH 3

CH 3

NH

OH

O

L-Ascorbic acid (vitamin C) is synthesized in plants and in the livers of most verte-

brates. Humans, monkeys, and guinea pigs do not have the enzymes necessary for the

biosynthesis of vitamin C, so they must obtain the vitamin in their diets. The biosyn-

thesis of vitamin C involves the enzymatic conversion of D-glucose into L-gulonic

acid—reminiscent of the last step in the Fischer proof. L-Gulonic acid is converted

into a by the enzyme lactonase, and then an enzyme called oxidase oxidizes

the lactone to L-ascorbic acid. The L-configuration of ascorbic acid refers to the con-

figuration at C-5, which was C-2 in D-glucose.

g-lactone