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 Terpenes are natural products that arestructurally related to isoprene.

H2C   C

CH3

CH CH2   or or 

Isoprene

(2-methyl-1,3-butadiene)

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Myrcene (isolated from oil of bayberry) isa typical terpene.

CH2

CH3

CH3C   CHCH2CH2CCH

CH2

or or 

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An isoprene unit is the carbon skeleton ofisoprene (ignoring the double bonds)

Myrcene contains two isoprene units.

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 The isoprene units of myrcene are joined "head-to-tail."

head tail

tailhead

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Class Number of carbon atoms

onoterpene ! #es$uiterpene !%

&iterpene '

#esterpene '%

 Triterpene

 Tetraterpene

Classifcation o Terpenes

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Representative Monoterpenes

α-Phellandrene

(eucalyptus)

Menthol

(peppermint)

Citral

(lemon grass)

 

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a-Selinene (celery)

 

RepresentativeSesquiterpenes

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Representative Diterpenes

itamin !itamin !

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Representative Triterpene

Squalene

(shark liver oil)

 

tail-to-tail linkage of isoprene units

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C15  sesquiterpenoids are derived from farnesyl diphosphate

!hich consists of three C5 "isoprene units# that are $oined

"head-to-tail#

OPP

C%& diterpenoids are derived from geranyl diphosphate

!hich consists of four C5 "isoprene units# that are $oined

"head-to-tail#

OPP

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C%5  sesterpenoids are derived from geranyl farnesyl

diphosphate !hich consists of five C5 "isoprene units# that

are $oined "head-to-tail#

C'& triterpenoids and steroids are derived from squalene

!hich consists of t!o C15 farnesyl units# that are $oined "tail-

to-tail#

C& tetraterpenoids are derived from phytocene !hich

consists of t!o C%& geranylgeranyl units# that are $oined "tail-

to-tail#

OPP

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he isoprene units in terpenes do notcome from isoprene*

hey come from isopentenyl pyrophosphate*

+sopentenyl pyrophosphate (5 car,ons)

comes from acetate (% car,ons) viamevalonate ( car,ons)*

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CH3C"H

"

3   H"CCH2CCH2CH2"H

CH3

"H

"

Me#alonic acid

H2C   CCH2CH2"$"$"H

CH3   " "

Isopentenyl pyrophosphate

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.imethylallyl pyrophosphate has a leaving group(pyrophosphate) at an allylic car,on/ it is reactiveto!ard nucleophilic su,stitution at this position*

Isopentenyl pyrophosphate is intercon#ertible to

dimethylallyl pyrophosphate.

Isopentenyl pyrophosphate Dimethylallyl pyrophosphate

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 The key process in*ol*es the doublebond of isopentenyl pyrophosphate 

acting as a nucleophile to+ard the allyliccarbon of dimethylallyl pyrophosphate.

%%

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 &OPP   %

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 The carbocationcan lose aproton to gi*e adouble bond.

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 The carbocationcan lose aproton to gi*e adouble bond.

H &  %

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 This compound is called geranylpyrophosphate. ,t can undergo hydrolysis ofits pyrophosphate to gi*e geraniol (rose oil).

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0eraniol

%2

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H &  %

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 This compound is called farnesylpyrophosphate.

ydrolysis of the pyrophosphateester gi*es the alcohol farnesol.

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arnesyl pyrophosphate is e/tendedby another isoprene unit by reaction

+ith isopentenyl pyrophosphate.

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0ings form by intramolecularcarbon-carbon bond formation.

E E  doubledouble

bondbondZ Z  doubledouble

bondbond

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H &  %

H2"

'imonene

α-erpineol

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 β -Pinene

%

α-Pinene

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CH3C"H

"

3   H"CCH2CCH2CH2"H

CH3

"H

"

Me#alonic acid

H2C   CCH2CH2"$"$"H

CH3   " "

Isopentenyl pyrophosphate

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,n a se$uence analogous to the earlysteps of fatty acid biosynthesis1 acetylcoen2yme A is con*erted to S-

acetoacetyl coen2yme A.

CHCH33CCHCCH22CCo!CCo!

""""

S S -!cetoacetyl-!cetoacetyl

coen*yme !coen*yme !

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,n the ne/t step1 #-acetoacetyl coen2yme Areacts +ith acetyl coen2yme A.

Nucleophilic addition of acetyl coen2yme A(probably *ia its enol) to the ketonecarbonyl of S-acetoacetyl coen2yme Aoccurs.

CHCH33CCo!CCo!

""

%%CHCH33CCHCCH22CCo!CCo!

""""

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CH3CCo!

"

CH3CCH2CCo!

CH2C"H

H"   "

"

%CH3CCH2CCo!

""

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Ne/t1 the acyl coen2yme A functionis reduced.

 The product of this reduction isme*alonic acid.

CH3CCH2CCo!

CH2C"H

H"   "

"

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CH3CCH2CCo!

CH2C"H

H"   "

"

CH3CCH2CH2"H

CH2C"H

H"

"

Me#alonic

acid

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 The t+o hydro/yl groups of me*alonicacid undergo phosphorylation.

CH3CCH2CH2"H

CH2C"H

H"

"

CH3CCH2CH2"$$

CH2C"H

"

"$"32&

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3hosphorylation is follo+ed by a no*elelimination in*ol*ing loss of C4' and 345.

CH3CCH2CH2"$$

CH2

"$"33&

CH3CCH2CH2"$$

CH2

"

"$"32&

C   "++

++++

 &

" C " 

Isopentenyl

Pyrophosphate