may seem like a trivial subject because differences between
stereoisomers are usually subtle. In nature, however, and
most importantly, in biological systems such as the human
body, these subtle differences have sweeping implications.
Most drugs for example, are often composed of a single stereoisomer
of a compound, and while one stereoisomer may have positive
effects on the body, another stereoisomer may be toxic. Because
of this, a great deal of work done by synthetic organic chemists
today is in devising methods to synthesize compounds that
are purely one stereoisomer.
below, for example, is the binding of Ibuprofin, a common
pain reliever. While one stereoisomer of the compound has
the right three-dimensional shape to bind to the protein receptor,
the other does not and can not bind, and is therefore ineffective
as a pain reliever.
Shown above: Only one stereoisomer of Ibuprofin has the
correct three-dimensional shape to bind to the receptor, so
only one isomer actively relieves pain.
Another example of the significance of stereochemistry was
demonstrated by Thalidomide (shown below). Thalidomide was
a drug used during the 1950s to suppress morning sickness.
The drug, unfortunately, was prescribed as a racemic mixture
-- that is, it contained a 50:50 mixture of its mirror
images -- and while one stereoisomer of the drug actively
worked on controlling morning sickness, the other stereoisomer
caused serious birth defects. Ultimately the drug was pulled
from the marketplace.
a drug once used to surpress morning sickness
of stereochemistry in biological systems extends to more than
just drugs: our bodies, for example, can only create and digest
carbohydrates and amino acids of a certain stereochemistry.
Thus, all of our proteins that make up our hair, skin, organs,
brain, and tissues, are composed of a single stereoisomer
of amino acids. Additionally, our bodies can make and digest
starch (found in potatoes and bread) but not cellulose (found
in wood and plant fibers), even though both are just polymers
of glucose of different stereochemistry. These are just a
few of numerous examples of the important role stereochemistry
plays in our everyday lives.