Organic Chemistry

Leopold Stephen Ru i ka
(1887–1976)was the first to
recognize that many organic
compounds contain multiples of five
carbons. A Croatian, Ru i ka
attended college in Switzerland
and became a Swiss citizen in 1917.
He was a professor of chemistry at
the University of Utrecht in the
Netherlands and later at the Federal
Institute of Technology in Zürich.
For his work on terpenes, he shared
the 1939 Nobel Prize in chemistry
with Adolph Butenandt (p. 25).

zMcM

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014 CHAPTER 26 Lipids

Arachidonic acid can also be converted into a leukotriene. Because they induce

contraction of the muscle that lines the airways to the lungs, leukotrienes are implicat-

ed in allergic reactions, inflammatory reactions, and heart attacks. Leukotrienes also

bring on the symptoms of asthma and are implicated in anaphylactic shock, a poten-

tially fatal allergic reaction. There are several antileukotriene agents available for the

treatment of asthma.

PROBLEM 10

Treating with a strong base such as sodium tert-butoxide followed by addition of

acid converts it to Propose a mechanism for this reaction.

26.6 Terpenes

Terpenesare a diverse class of lipids. More than 20,000 terpenes are known. They

can be hydrocarbons, or they can contain oxygen and be alcohols, ketones, or

aldehydes. Oxygen-containing terpenes are sometimes called terpenoids. Certain

terpenes and terpenoids have been used as spices, perfumes, and medicines for many

thousands of years.

After analyzing a large number of terpenes, organic chemists realized that they

contained carbon atoms in multiples of 5. These naturally occurring compounds con-

tain 10, 15, 20, 25, 30, and 40 carbon atoms, which suggests that there is a compound

with five carbon atoms that serves as their building block. Further investigation

showed that their structures are consistent with the assumption that they were made by

joining together isoprene units, usually in a head-to-tail fashion. (The branched end of

isoprene is called the head, and the unbranched end is called the tail.) Isoprene is the

common name for 2-methyl-1,3-butadiene, a compound containing five carbon atoms.

That isoprene units are linked in a head-to-tail fashion to form terpenes is known as

the isoprene rule.

head

tail tail

carbon skeleton of two isoprene units with a bond

between the tail of one and the head of another

head

OH

HO

menthol

peppermint oil

geraniol

geranium oil

zingiberene

oil of ginger

-selinene

oil of celery

PGC 2.

PGA 2

OH OH

arachidonic acid a leukotriene

COOH COOH

Pg number to be fixed