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27.4 Synthesis of Amino Acids - PowerPoint PPT Presentation


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27.4 Synthesis of Amino Acids. O. O. CH 3 CHCOH. CH 3 CHCO. Br. N H 3. From a -Halo Carboxylic Acids. H 2 O. –. +. +. 2 N H 3. N H 4 Br. +. (65-70%). O. CH 3 CH. CH 3 CHC. N. N H 2. 1. H 2 O, HCl, heat. 2. HO –. O. –. CH 3 CHCO. +. N H 3. Strecker Synthesis.

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from a halo carboxylic acids

O

O

CH3CHCOH

CH3CHCO

Br

NH3

From a-Halo Carboxylic Acids

H2O

+

+

2NH3

NH4Br

+

(65-70%)

strecker synthesis

O

CH3CH

CH3CHC

N

NH2

1. H2O, HCl, heat

2. HO–

O

CH3CHCO

+

NH3

Strecker Synthesis

NH4Cl

NaCN

(52-60%)

using diethyl acetamidomalonate

O

O

C

C

C

OCH2CH3

CH3CH2O

CH3CNH

H

O

Using Diethyl Acetamidomalonate
  • Can be used in the same manner as diethyl malonate (Section 21.7).
example

O

O

CH3CH2OCCCOCH2CH3

H

CH3CNH

O

O

O

CH3CH2OCCCOCH2CH3

CH2C6H5

CH3CNH

O

Example

1. NaOCH2CH3

2. C6H5CH2Cl

(90%)

example6

O

O

CH3CH2OCCCOCH2CH3

CH2C6H5

CH3CNH

O

O

O

Example

HOCCCOH

CH2C6H5

H3N

+

HBr, H2O, heat

example7

O

O

CH3CH2OCCCOCH2CH3

CH2C6H5

CH3CNH

O

O

Example

(65%)

HCCOH

CH2C6H5

H3N

+

HBr, H2O, heat

acylation of amino group

O

O

O

+

H3NCH2CO

CH3COCCH3

O

O

CH3CNHCH2COH

Acylation of Amino Group
  • The amino nitrogen of an amino acid can be converted to an amide with the customary acylating agents.

+

(89-92%)

esterification of carboxyl group

O

+

H3NCHCO

CH3

O

Cl

Esterification of Carboxyl Group
  • The carboxyl group of an amino acid can be converted to an ester. The following illustrates Fischer esterification of alanine.

+

CH3CH2OH

HCl

+

H3NCHCOCH2CH3

(90-95%)

CH3

ninhydrin test

O

O

+

OH

H3NCHCO

OH

R

O

O

O

O

N

RCH

O

O

Ninhydrin Test
  • Amino acids are detected by the formation of a purple color on treatment with ninhydrin.

+

+

+

+

CO2

H2O

biosynthesis of l glutamic acid

O

HO2CCH2CH2CCO2H

HO2CCH2CH2CHCO2

+

NH3

Biosynthesis of L-Glutamic Acid
  • This reaction is the biochemical analog of reductive amination (Section 22.11).

+

NH3

enzymes and

reducing coenzymes

transamination via l glutamic acid

O

+

HO2CCH2CH2CHCO2

CH3CCO2H

+

NH3

Transamination viaL-Glutamic Acid

L-Glutamic acid acts as a source of the amine group in the biochemical conversion of a-ketoacids to other amino acids. In the exampleshown, pyruvic acid is converted to L-alanine.

transamination via l glutamic acid15

O

+

HO2CCH2CH2CHCO2

CH3CCO2H

+

NH3

O

CH3CHCO2

HO2CCH2CH2CCO2H

+

NH3

Transamination viaL-Glutamic Acid

enzymes

+

mechanism

O

+

HO2CCH2CH2CHCO2

CH3CCO2H

+

NH3

Mechanism

The first step is imine formation between theamino group of L-glutamic acid and pyruvicacid.

mechanism17

O

+

HO2CCH2CH2CHCO2

CH3CCO2H

+

NH3

Mechanism

HO2CCH2CH2CHCO2

N

CH3CCO2

slide18

HO2CCH2CH2CCO2

N

CH3CCO2

  • Formation of the imine is followed by proton removal at one carbon and protonation of another carbon.

H

slide19

HO2CCH2CH2CCO2

N

CH3CCO2

H

HO2CCH2CH2CCO2

N

CH3CCO2

H

slide20

HO2CCH2CH2CCO2

N

CH3CCO2

H

  • Hydrolysis of the imine function givesa-keto glutarate and L-alanine.
slide21

HO2CCH2CH2CCO2

N

CH3CCO2

H

+

NH3

HO2CCH2CH2CCO2

CH3CCO2

O

H

H2O

+

biosynthesis of l tyrosine

CH2CHCO2

+

NH3

Biosynthesis of L-Tyrosine

L-Tyrosine is biosynthesized from L-phenylalanine.

A key step is epoxidation of the aromatic ring to

give an arene oxide intermediate.

biosynthesis of l tyrosine23

CH2CHCO2

O

+

NH3

CH2CHCO2

+

NH3

Biosynthesis of L-Tyrosine

O2, enzyme

biosynthesis of l tyrosine24

CH2CHCO2

O

+

NH3

HO

CH2CHCO2

+

NH3

Biosynthesis of L-Tyrosine

enzyme

biosynthesis of l tyrosine25
Biosynthesis of L-Tyrosine
  • Conversion to L-tyrosine is one of the major metabolic pathways of L-phenylalanine.
  • Individuals who lack the enzymes necessary to convert L-phenylalanine to L-tyrosine can suffer from PKU disease. In PKU disease, L-phenylalanine is diverted to a pathway leading to phenylpyruvic acid, which is toxic.
  • Newborns are routinely tested for PKU disease. Treatment consists of reducing their dietary intake of phenylalanine-rich proteins.
decarboxylation

N

CH2CHCO2

NH

+

NH3

Decarboxylation
  • Decarboxylation is a common reaction of a-amino acids. An example is the conversion of L-histidine to histamine. Antihistamines act by blocking the action of histamine.
decarboxylation27

N

CH2CH2 NH2

NH

N

CH2CHCO2

NH

+

NH3

Decarboxylation

–CO2, enzymes

neurotransmitters

CO2

+

H3N

H

H

H

OH

Neurotransmitters
  • The chemistry of the brain and central nervous system is affected by neurotransmitters.
  • Several important neurotransmitters are biosynthesized from L-tyrosine.

L-Tyrosine

neurotransmitters29
Neurotransmitters

CO2

+

  • The common name of this compound is L-DOPA. It occurs naturally in the brain. It is widely prescribed to reduce the symptoms of Parkinsonism.

H3N

H

H

H

HO

OH

L-3,4-Dihydroxyphenylalanine

neurotransmitters30
Neurotransmitters

H

  • Dopamine is formed by decarboxylation of L-DOPA.

H2N

H

H

H

HO

OH

Dopamine

neurotransmitters31
Neurotransmitters

H

H2N

H

OH

H

HO

OH

Norepinephrine

neurotransmitters32
Neurotransmitters

H

CH3NH

H

OH

H

HO

OH

Epinephrine