glycolipids) constitute important cell surface macromolecules that are important drug
targets and antigens central to immune-mediated disease fighting systems. In addition,
carbohydrates may themselves constitute drugs. Heparin, a polysulphated polysacccha-
ride, is used as a therapeutic to prevent blood clotting. Streptomycin (8.7) is an important
carbohydrate antibiotic.
8.1.6 HeterocyclesHeterocyclic compounds, or heterocycles, are molecules with rings that contain more than
one type of atom; they are to be distinguished from carbocycles, which are molecules
with rings that contain only carbon atoms. The heterocyclic compounds of greatest
interest to medicinal chemists have carbon rings containing one or two heteroatoms—
atoms other than carbon.
ENDOGENOUS MACROMOLECULES 477Figure 8.4 Structures of common carbohydrates.