Fundamentals of Medicinal Chemistry

Key:

A = Abequose
G = D-Galactose
H = Heptose
K = 2-Keto-3-deoxyoctanoate (KDO)
M = Mannose
N = N-Acetylglucosamine (NAG)
P = Phosphate unit
R = Rhamnose

P

N K H

etc

etc

P

O G

K

K

H

N

G

G N

N

G R

M

A

G R

A

M

G R

A

M

G

P

P

O

PP

O

CH 3

OH

HO

H

H

H

H

H

H

(A)

O

OH

HO

H

H

OH

CHOH

H

H

COO−

CH 2 OH

O

OH

HO

H

OH

H

H

H

CH OH

3

H

(K) (R)

n

n

Core oligosaccharide

O

HO

OH

OH

H

CHOH

H

OH

H

CH 2 OH

H

(H)

Figure A2.5 The structure of the surface lipopolysaccharides of Gram-negative bacteria

These lipopolysaccharides often contain monosaccharide units such as abequose

(Abe) and 2-keto-3-deoxyoctanoate (KDO) that are rarely found in other

organisms. The repeating units, which are known asO-antigens, are unique to

a particular type of bacterium. Experimental evidence suggests that they play a

part in the bacteria’s recognition of host cells. It is also believed that they enable

the host’s immunological system to identify the invading bacteria and produce

antibodies that destroy the bacteria. However, a particular bacterial cell can

have a number of different O-antigens and it is this diversity that allows some

bacteria to evade a host’s immune system.

APPENDIX 2 BACTERIA 243