Organic Chemistry

Problems 029

Key Terms

adrenal cortical steroids (p. 024)
anabolic steroids (p. 028)
androgens (p. 025)
angular methyl group (p. 024)
bile acids (p. 025)
carotenoid (p. 015)
cephalins (p. 008)
cerebroside (p. 010)
cholesterol (p. 024)
cis fused (p. 023)
dymethyl allyl pyrophosphate (p. 019)
essential oils (p. 015)
estrogens (p. 025)
fat (p. 005)
fatty acid (p. 002
hormone (p. 023)
isopentenyl pyrophosphate (p. 019)

isoprene rule (p. 014)

lecithins (p. 008)

lipid (p. 001)

lipid bilayer (p. 008)

leukotriene (p. 014)

membrane (p. 008)

mixed triacylglycerol (p. 004)

monoterpene (p. 015)

oil (p. 005)

phosphatidic acid (p. 008)

phosphoacylglycerol (p. 008)

phosphoglycerides (p. 008)

phospholipid (p. 008)

polyunsaturated fatty acid (p. 002)

prostacyclins (p. 012)

prostaglandin (p. 011)

sesquiterpene (p. 015)

simple triacylglycerol (p. 004)

sphingomyelins (p. 010)

sphingolipid (p. 010)

squalene (p. 015)

steroid (p. 023)

(p. 024)

(p. 024)

terpene (p. 014)

terpenoid (p. 014)

tetraterpene (p. 015)

thromboxanes (p. 012)

trans fused (p. 023)

triacylglycerol (p. 004)

triterpene (p. 015)

wax (p. 004)

b-substituent

a-substituent

(a terpene with six isoprene units), is a precursor of steroid
molecules. Lycopene and are tetraterpenes
called carotenoids. is cleaved to form two
molecules of vitamin A.
The five-carbon compound used for the synthesis of ter-
penes is isopentenyl pyrophosphate. The reaction of
dimethylallyl pyrophosphate(formed from isopentenyl
pyrophosphate) with isopentenyl pyrophosphate forms
geranyl pyrophosphate, a 10-carbon compound. Geranyl
pyrophosphate can react with another molecule of isopen-
tenyl pyrophosphate to form farnesyl pyrophosphate, a
15-carbon compound. Two molecules of farnesyl pyrophos-
phate form squalene, a 30-carbon compound. Squalene is
the precursor of cholesterol. Farnesyl pyrophosphate can
react with another molecule of isopentenyl pyrophosphate
to form geranylgeranyl pyrophosphate, a 20-carbon
compound. Two geranylgeranyl pyrophosphates join to

b-Carotene

b-carotene

form phytoene, a 40-carbon compound. Phytoene is the

precursor of the carotenoids.

Hormonesare chemical messengers. Many hormones

are steroids. All steroids contain a tetracyclic ring system.

The B, C, and D rings are trans fused. In most naturally

occurring steroids, the A and B rings are also trans fused.

Methyl groups at C-10 and C-13 are called angular methyl

groups. -Substituentsare on the same side of the steroid

ring system as the angular methyl groups; -substituents

are on the opposite side. Synthetic steroids are steroids that

are not found in nature.

The most abundant member of the steroid family in

animals is cholesterol, the precursor of all other steroids.

Cholesterol is an important component of cell membranes;

its ring structure causes it to be more rigid than other mem-

brane lipids. In the biosynthesis of cholesterol, squalene is

converted to lanosterol, which is converted to cholesterol.

A

B

Problems

26. An optically active fat, when completely hydrolyzed, yields twice as much stearic acid as palmitic acid. Draw the structure of the fat.


27. a. How many different triacylglycerols are there in which one of the fatty acid components is lauric acid and two are myristic acid?
    b. How many different triacylglycerols are there in which one of the fatty acid components is lauric acid, one is myristic acid, and
    one is palmitic acid?


28. Cardiolipins are found in heart muscles. Give the products formed when a cardiolipin undergoes complete acid-catalyzed hydrolysis.

CH 2 O

CHO CR^2

O−

OCH 2 CHCH 2 O

OH

a cardiolipin

P OCH 2

R^4 C OCH

O−

O

O O

O

P

R^3 C OCH 2

O

CH 2 OCR^1

O

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