Organic chemistry with biological applications

John E. McMurry

Chapter 23

Biomolecules: Lipids and Their Metabolism - all with Video Answers

Educators

Chapter Questions

Problem 1

Carnauba wax, used in floor and furniture polishes, contains an ester of a $\mathrm{C}_{32}$ straight-chain alcohol with a $\mathrm{C}_{20}$ straight-chain carboxylic acid. Draw its structure.

Kevin Zaborsky

Kevin Zaborsky

Numerade Educator

Problem 2

Draw structures of glyceryl tripalmitate and glyceryl trioleate. Which would you expect to have a higher melting point?

Kevin Zaborsky

Numerade Educator

Problem 3

Draw the structure of magnesium oleate, a component of bathtub scum.

Kevin Zaborsky

Numerade Educator

Problem 4

Write the saponification reaction of glyceryl dioleate monopalmitate with aqueous $\mathrm{NaOH}$.

Kevin Zaborsky

Numerade Educator

Problem 5

Write the equations for the remaining passages of the $\beta$ -oxidation pathway following those shown in Figure 23.5 .

Pahk Thepchatri

Pahk Thepchatri

Numerade Educator

Problem 6

How many molecules of acetyl CoA are produced by catabolism of the following fatty acids, and how many passages of the $\beta$ -oxidation pathway are needed?
(a) Palmitic acid, $\mathrm{CH}_{3}\left(\mathrm{CH}_{2}\right)_{14} \mathrm{CO}_{2} \mathrm{H}$
(b) Arachidic acid, $\mathrm{CH}_{3}\left(\mathrm{CH}_{2}\right)_{18} \mathrm{CO}_{2} \mathrm{H}$

Pahk Thepchatri

Pahk Thepchatri

Numerade Educator

Problem 7

Write a mechanism for the dehydration reaction of $\beta$ -hydroxybutyryl ACP to yield crotonyl ACP in step 7 of fatty-acid synthesis.

Pahk Thepchatri

Pahk Thepchatri

Numerade Educator

Problem 8

Evidence for the role of acetate in fatty-acid biosynthesis comes from isotopelabeling experiments. If acetate labeled with ${ }^{13} \mathrm{C}$ in the methyl group $\left({ }^{13} \mathrm{CH}_{3} \mathrm{CO}_{2} \mathrm{H}\right)$ were incorporated into fatty acids, at what positions in the fattyacid chain would you expect the ${ }^{13} \mathrm{C}$ label to appear?

Julia Fontana

Numerade Educator

Problem 9

Does the reduction of acetoacetyl ACP in step 6 occur on the Re face or the Si face of the carbonyl group?

Julia Fontana

Numerade Educator

Problem 10

Assign $R$ or $S$ configuration to each chirality center in prostaglandin $\mathrm{E}_{2}$ (Figure 23.10 ), the most abundant and biologically potent of mammalian prostaglandins.

Kevin Zaborsky

Numerade Educator

Problem 11

Studies of the conversion of mevalonate 5 -phosphate to isopentenyl diphosphate have shown the following result. Which hydrogen, pro-R or pro-S, ends up cis to the methyl group, and which ends up trans?

Kevin Zaborsky

Numerade Educator

Problem 12

Propose mechanistic pathways for the biosynthesis of the following terpenoids:

Kevin Zaborsky

Numerade Educator

Problem 13

Draw the following molecules in chair conformations, and tell whether the ring substituents are axial or equatorial:

Kevin Zaborsky

Numerade Educator

Problem 14

Lithocholic acid is an A-B cis steroid found in human bile. Draw lithocholic acid showing chair conformations as in Figure $23.16,$ and tell whether the hydroxyl group at $\mathrm{C} 3$ is axial or equatorial.

Kevin Zaborsky

Numerade Educator

Problem 15

Compare the structures of lanosterol and cholesterol, and catalog the changes needed for the transformation.

Kevin Zaborsky

Numerade Educator

Problem 16

Identify the following fatty acid, and tell whether it is more likely to be found in peanut oil or in red meat:

Kendrick Buford

Kendrick Buford

Numerade Educator

Problem 17

The following model is that of cholic acid, a constituent of human bile. Locate the three hydroxyl groups, and identify each as axial or equatorial. Is cholic acid an A-B trans steroid or an A-B cis steroid?

Kendrick Buford

Kendrick Buford

Numerade Educator

Problem 18

Propose a biosynthetic pathway for the sesquiterpene helminthogermacrene from farnesyl diphosphate:

Kendrick Buford

Kendrick Buford

Numerade Educator

Problem 19

Cold-water fish like salmon are rich in omega-3 fatty acids, which have a double bond three carbons in from the noncarboxyl end of the chain and have been shown to lower blood cholesterol levels. Draw the structure of eicosa- 5,8,11,14,17 -pentaenoic acid, a common example. (Eicosane $=\mathrm{C}_{20} \mathrm{H}_{42}$ )

Kendrick Buford

Kendrick Buford

Numerade Educator

Problem 20

Fats can be either optically active or optically inactive, depending on their structure. Draw the structure of an optically active fat that yields 2 equivalents of stearic acid and 1 equivalent of oleic acid on hydrolysis. Draw the structure of an optically inactive fat that yields the same products.

Kendrick Buford

Kendrick Buford

Numerade Educator

Problem 21

Spermaceti, a fragrant substance from sperm whales, was much used in cosmetics until it was banned in 1976 to protect the whales from extinction. Chemically, spermaceti is cetyl palmitate, the ester of cetyl alcohol $\left(n-C_{16} H_{33} O H\right)$ with palmitic acid. Draw its structure.

Kendrick Buford

Kendrick Buford

Numerade Educator

Problem 22

The plasmalogens are a group of lipids found in nerve and muscle cells. How do plasmalogens differ from fats?

Kendrick Buford

Kendrick Buford

Numerade Educator

Problem 23

What products would you obtain from hydrolysis of a plasmalogen (Problem 23.22) with aqueous $\mathrm{NaOH}$ ? With $\mathrm{H}_{3} \mathrm{O}^{+}$ ?

Ronald Prasad

Numerade Educator

Problem 24

Cardiolipins are a group of lipids found in heart muscles. What products would be formed if all ester bonds, including phosphates, were saponified by treatment with aqueous $\mathrm{NaOH}$ ?

Kendrick Buford

Kendrick Buford

Numerade Educator

Problem 25

Show the products you would expect to obtain from reaction of glyceryl trioleate with the following reagents:
(a) Excess $\mathrm{Br}_{2}$ in $\mathrm{CH}_{2} \mathrm{Cl}_{2}$
(b) $\mathrm{H}_{2} / \mathrm{Pd}$
(c) $\mathrm{NaOH} / \mathrm{H}_{2} \mathrm{O}$
(d) $\mathrm{LiAlH}_{4},$ then $\mathrm{H}_{3} \mathrm{O}^{+}$
(e) $\mathrm{CH}_{3} \mathrm{MgBr}$, then $\mathrm{H}_{3} \mathrm{O}^{+}$

Kendrick Buford

Kendrick Buford

Numerade Educator

Problem 26

How would you convert oleic acid into the following substances?
(a) Methyl oleate
(b) Methyl stearate
(c) Pentatriacontan-18-one, $\mathrm{CH}_{3}\left(\mathrm{CH}_{2}\right)_{16} \mathrm{CO}\left(\mathrm{CH}_{2}\right)_{16} \mathrm{CH}_{3}$

Kendrick Buford

Kendrick Buford

Numerade Educator

Problem 27

Without proposing an entire biosynthetic pathway, draw the appropriate precursor, either geranyl diphosphate or farnesyl diphosphate, in a conformation that shows a likeness to each of the following terpenoids:

Lottie Adams

Numerade Educator

Problem 28

Indicate by asterisks the chirality centers present in each of the terpenoids shown in Problem 23.27 . What is the maximum possible number of stereoisomers for each?

Kendrick Buford

Kendrick Buford

Numerade Educator

Problem 29

Assume that the three terpenoids in Problem 23.27 are deriv biosynthetically from isopentenyl diphosphate and dimethylal diphosphate, each of which was isotopically labeled at the diphc phate-bearing carbon atom (C1). At what positions would the t penoids be isotopically labeled?

Kendrick Buford

Kendrick Buford

Numerade Educator

Problem 30

Assume that acetyl CoA containing a ${ }^{14} \mathrm{C}$ isotopic label in the carboxyl carbon atom is used as starting material for the biosynthesis of mevalonate, as shown in Figure 23.12 . At what positions in mevalonate would the isotopic label appear?

Kendrick Buford

Kendrick Buford

Numerade Educator

Problem 31

Assume that acetyl CoA containing a ${ }^{14} \mathrm{C}$ isotopic label in the carboxy carbon atom is used as starting material and that the mevalonate pathway is followed. Identify the positions in $\alpha$ -cadinol where the label would appear.

Kendrick Buford

Kendrick Buford

Numerade Educator

Problem 32

Assume that acetyl CoA containing a ${ }^{14} \mathrm{C}$ isotopic label in the carboxyl carbon atom is used as starting material and that the mevalonate pathway is followed. Identify the positions in squalene where the label would appear.

Kendrick Buford

Kendrick Buford

Numerade Educator

Problem 33

Assume that acetyl CoA containing a $14 \mathrm{C}$ isotopic label in the carboxyl carbon atom is used as starting material and that the mevalonate pathway is followed. Identify the positions in lanosterol where the label would appear.

Kendrick Buford

Kendrick Buford

Numerade Educator

Problem 34

Propose a mechanistic pathway for the biosynthesis of caryophyllene, a substance found in clove oil.

Kendrick Buford

Kendrick Buford

Numerade Educator

Problem 35

Stearolic acid, $\mathrm{C}_{18} \mathrm{H}_{32} \mathrm{O}_{2}$, yields stearic acid on catalytic hydrogenation and undergoes oxidative cleavage with ozone to yield nonanoic acid and nonanedioic acid. What is the structure of stearolic acid?

Kendrick Buford

Kendrick Buford

Numerade Educator

Problem 36

How would you synthesize stearolic acid (Problem 23.35) from dec-1-yne and 1 -chloro-7-iodoheptane?

Kendrick Buford

Kendrick Buford

Numerade Educator

Problem 37

Show the product of each of the following reactions:

Allison Krajewski

Allison Krajewski

Numerade Educator

Problem 38

Draw a Fischer projection of sn-glycerol 1 -phosphate (Section $23-4$ ), and assign $R$ or $S$ configuration to the chirality center. Do the same for sn-glycerol 2,3 -diacetate.

Ricajoy Montero

Ricajoy Montero

Numerade Educator

Problem 39

Flexibilene, a compound isolated from marine coral, is the first known terpenoid to contain a 15 -membered ring. What is the structure of the acyclic biosynthetic precursor of flexibilene? Show the mechanistic pathway for the biosynthesis.

Kendrick Buford

Kendrick Buford

Numerade Educator

Problem 40

Suggest a mechanism by which $\psi$ -ionone is transformed into $\beta$ -ionone on treatment with acid.

Kendrick Buford

Kendrick Buford

Numerade Educator

Problem 41

Draw the most stable chair conformation of dihydrocarvone.

Kendrick Buford

Kendrick Buford

Numerade Educator

Problem 42

Draw the most stable chair conformation of menthol, and label each substituent as axial or equatorial.

Kendrick Buford

Kendrick Buford

Numerade Educator

Problem 43

As a general rule, equatorial alcohols are esterified more readily than axial alcohols. What product would you expect to obtain from reaction of the following two compounds with 1 equivalent of acetic anhydride?

Tom Rutherford

Numerade Educator

Problem 44

Propose a mechanistic pathway for the biosynthesis of isoborneol. A carbocation rearrangement is needed at one point in the scheme.

Kendrick Buford

Kendrick Buford

Numerade Educator

Problem 45

Isoborneol (Problem 23.44 ) is converted into camphene on treatment with dilute sulfuric acid. Propose a mechanism for the reaction, which involves a carbocation rearrangement.

Kendrick Buford

Kendrick Buford

Numerade Educator

Problem 46

Digitoxigenin is a heart stimulant obtained from the purple foxglove Digitalis purpurea and used in the treatment of heart disease. Draw the three-dimensional conformation of digitoxigenin, and identify the two
- OH groups as axial or equatorial.

Kendrick Buford

Kendrick Buford

Numerade Educator

Problem 47

Eleostearic acid, $\mathrm{C}_{18} \mathrm{H}_{30} \mathrm{O}_{2}$, is a rare fatty acid found in the tung oil used for finishing furniture. On ozonolysis followed by treatment with zinc, eleostearic acid furnishes one part pentanal, two parts glyoxal $\left.$ (OHC-CHO), and one part 9-oxononanoic acid [OHC(CH $\left.\left._{2}\right)_{7} \mathrm{CO}_{2} \mathrm{H}\right] .$ What is the structure of eleostearic acid? (Note that alkenes undergo ozonolysis followed by treatment with zinc to give carbonyl compounds in which each of the former $\mathrm{C}=\mathrm{C}$ carbons becomes a $\mathrm{C}=\mathrm{O}$ carbon.

Kendrick Buford

Kendrick Buford

Numerade Educator

Problem 48

Diterpenoids are derived biosynthetically from geranylgeranyl diphosphate (GGPP), which is itself biosynthesized by reaction of farnesyl diphosphate with isopentenyl diphosphate. Show the structure of GGPP, and propose a mechanism for its biosynthesis from FPP and IPP.

Kendrick Buford

Kendrick Buford

Numerade Educator

Problem 49

Diethylstilbestrol (DES) has estrogenic activity even though it is structurally unrelated to steroids. Once used as an additive in animal feed, DES has been implicated as a causative agent in several types of cancer. Show how DES can be drawn so that it is sterically similar to estradiol.

Kendrick Buford

Kendrick Buford

Numerade Educator

Problem 50

How many chirality centers are present in estradiol (Problem 23.49 ) Assign configurations to all.

Dalton Hilovsky

Dalton Hilovsky

Numerade Educator

Problem 51

Cembrene, $\mathrm{C}_{20} \mathrm{H}_{32}$, is a diterpene hydrocarbon isolated from pine resin. Cembrene has a UV absorption at $245 \mathrm{nm}$, but dihydrocembrene $\left(\mathrm{C}_{20} \mathrm{H}_{34}\right),$ the product of hydrogenation with 1 equivalent of $\mathrm{H}_{2},$ has $\mathrm{no}$ UV absorption. On exhaustive hydrogenation, 4 equivalents of $\mathrm{H}_{2}$ react and octahydrocembrene, $\mathrm{C}_{20} \mathrm{H}_{40}$, is produced. On ozonolysis of cembrene, followed by treatment of the ozonide with zinc, four carbonylcontaining products are obtained:
Propose a structure for cembrene that is consistent with its formation from geranylgeranyl diphosphate (Problem 23.48 ).

Anupa Sharad Medhekar

Anupa Sharad Medhekar

Numerade Educator

Problem 52

$\alpha$ -Fenchone is a pleasant-smelling terpenoid isolated from oil of lavender. Propose a pathway for the formation of $\alpha$ -fenchone from gerany diphosphate. A carbocation rearrangement is required.

Kendrick Buford

Kendrick Buford

Numerade Educator

Problem 53

Propose a mechanism for the biosynthesis of the sesquiterpene trichodiene from farnesyl diphosphate. The process involves cyclization to give an intermediate secondary carbocation, followed by several carbocation rearrangements.

Kendrick Buford

Kendrick Buford

Numerade Educator