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Asam amino^ Samuel Budi Ph.D

Synthesis of AminoSynthesis of AminoSynthesis of AminoSynthesis of Amino Acids

AcidsAcidsAcids:

S2 reaction of an α-halo carboxylic acid with a large excess of NHN

3

1.1.1.1. SSSSNNNN Good yields because the amino group in the product is both less basic and moresterically crowded than other 1° amines.

222 2 Reaction of αReaction of αReaction of αReaction of α-

• --Halo Acids with NHHalo Acids with NHHalo Acids with NHHalo Acids with NH

3.3.3.3. StreckerStreckerStreckerStrecker Synthesis

SynthesisSynthesisSynthesis

-^ Reaction of aldehyde with NaCN and NH

Cl into an amino acid that adds 4

one carbon atom to the aldehyde carbonyl.

α-amino nitrile

Synthesis of Amino AcidsSynthesis of Amino Acids:Synthesis of Amino AcidsSynthesis of Amino Acids

:::

Nucleophilic addition of NH

to form an imine, followed by addition 3

of cyanide to the C––N bond forming the α-amino nitrile.

1. Nucleophilic attack of NH

followed by proton transfer and loss of H 3

O 2

forms an imine. Loss of H

O occurs forms an imine 2

3.3.3.3. StreckerStreckerStreckerStrecker Synthesis

SynthesisSynthesisSynthesis

Synthesis of Amino AcidsSynthesis of Amino Acids:Synthesis of Amino AcidsSynthesis of Amino Acids

:::

2. Protonation of the imine followed by nucleophilic attack of –CN gives the α-amino nitrile.

Separation of Amino AcidsSeparation of Amino AcidsSeparation of Amino AcidsSeparation of Amino Acids •^ Synthesize an amino acid usually yield a racemic mixture.^ Resolution is separation of a racemic mixture into its component enantiomers. Enantiomers have : •^ the same physical properties

^ cannot be separated by common physical methods

-^ the same chemical properties

^ cannot be separated by chemical reactions.

But diastereomers have

different physical properties.

(distillation or chromatography)

A racemic mixture can be resolved by:1. Convert a pair of enantiomers intoa pair of diastereomers2. Separate the diastereomers.3. Re-convert each diastereomer intothe original enantiomer

Separation of Amino AcidsSeparation of Amino AcidsSeparation of Amino AcidsSeparation of Amino AcidsResolving a racemic mixture of (R)- and (S)-alanine: •^ The racemate is treated with acetic anhydride to form N-acetyl amino acids (amides). •^ Each of these amides contains one stereogenic center and they are still enantiomers, sothey are still inseparable.

Kinetic Resolution of Amino Acids Using EnzymesKinetic Resolution of Amino Acids Using EnzymesKinetic Resolution of Amino Acids Using EnzymesKinetic Resolution of Amino Acids Using Enzymes^ Enantiomers react differently with chiral reagents like an enzyme^ •^ Acylases enzymes hydrolyze amidebonds of only N-acetyl L-alanine togenerate L-alanine, but not amidesof D-amino acids.^ •^ mixture now consists of one aminoacid and one N-acetyl amino acid

can be physically separated.

Enantioselective Synthesis of Amino AcidsEnantioselective Synthesis of Amino AcidsEnantioselective Synthesis of Amino AcidsEnantioselective Synthesis of Amino Acids •^ Synthesis amino acid using chiral reagent •^ For example using enantioselective (or asymmetric) hydrogenation reactions: •^ Addition of H

to the double bond forms an N-acetyl amino acid with a new 2 Drawback of prevous method: half of the reaction product is useless because ithas the undesired configuration, costly and time-consuming.stereogenic center on the α carbon to the carboxy group. With a chiral catalyst,only the S configuration can be obtained • Rh* = Rhodium metal complexed to a chiral molecule containing one or more phosphorus atoms. • This catalyst is synthesized from a rhodium salt and a phosphorus compound, 2,2’-bis(diphenylphosphino)-1,1'-binaphthyl (BINAP). It is the BINAP moiety that makes the catalyst chiral.

Soal1.^ Which of the following amines can be used to resolve a racemic mixture of amino acids?2.^ Draw the organic products formed in the following reaction.3.^ What alkene is needed to synthesize each amino acid by an enantioselective hydrogenationreaction using H2 and Rh*: (a) alanine; (b) leucine; (c) glutamine?

-^ Reaksi dengan gugus amina:^ ^ Ninhidrin^ ^ Reagen sanger (FDNB)^ ^ Dansil klorida •^ Reaksi dengan gugus karboksilat •^ Reaksi dengan gugus samping

ReaksiReaksiReaksiReaksi kimia

kimiakimiakimia asam

asamasamasam amino

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