Contents Introduction
 Solid Support
 Linkers, Anchors
 Protecting Groups
 Coupling Reagents
 Deprotecting Groups
 Application In peptide synthesis
 Advantages
 Disadvantages
2
Introduction
 Solid phase synthesis was developed by B. Merrifield, It
is of the particular interest in the field of Peptide
synthesis.
 Solid-Phase Synthesis focuses on chemical reactions of
substrates attached to solid supports.
 Including methods for attachment and detachment from
the supports.
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Eg.
Solid phase Synthesis of a dipeptide
Z-NH-CH-COOH + Cl-CH2
R
Z-NH-CH-COO-CH2
R
NH2-CH-COO-CH2
R
Z-NH-CH-COX + NH2-CH-COO-CH2
R1
R
4
CONT…….
Z-NH-CH-CO-NH-CH-COO-CH2
R1
R
NH2-CH-NH-CH-COOH +
R1
R
Z
solid support
protecting group
5
Problems with Traditional
Synthesis
 1 chemist 1 molecule
 Can only make one molecule at a time.
 Each synthesis very time consuming
 Multistep syntheses have loss at each step
 Purification of products very time-consuming between
steps.
 Yields can be low and produces very few molecules at a
time for testing.
6
Solid Support
 Resin act as a solid support for a solid phase synthesis.
 The term solid support used to denote the matrix upon
which chemical reaction is performed.
 It is a copolymer of styrene and divinylbenzene.
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Types
 Crosslinked Polystyrene
-Styrene+Divinylbenzene
-Most widely used
-Hydrophobic
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•PEG Grafted Supports
-Tentagel
- 1-2% crosslinked polystyrene
- More flexible
-Hydrophilic
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• Inorganic Supports-
-Glass beads as a inorganic supports
- High mechanical strength
-Negligible swelling
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Properties: Chemical stability
 Mechanical stability
 It must swell extensively in the solvents used for the
synthesis;
 Peptide-resin bond should be stable during the synthesis;
 Peptide-resin bond can be cleaved effectively at the end
of the synthesis.
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Linker, Anchors
 The linker that is bound to the resin is called anchor.
 Remains at the resin after cleavage.
Resin
Linker
Resin
Anchor
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linker
 Bifunctional spacer molecules which contain on one end
a functional group for attachment to the solid support and
on the other end a selectively cleavable group onto which
the starting molecule is attached.
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Anchors
Types :
1) Benzylic Halide Type Resini. Merrifield resin.
Cl
Cl
=
Cl
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Anchor
ii. Trityl chloride resin.
Cl
15
Anchor
2) Benzylic alcohols Type Resin -
OH
O
Wang resin
16
Anchor
3)Benzylic amines Type Resin-
NH2
O
MeO
Rink amide resin
OMe
17
Anchor
4) Aromatic aldehyde Type Resin-
CHO
MeO
OMe
O
Bal resin
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Protecting Groups
 A fragment bound to functional group that blocks the
reactivity of that group.
 Good protecting groups are easily attached and removed
using mild reaction condition.
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Protecting Groups
Acid Protection
R
OH
H2N
O
20
•
The most common acid protecting group used is the methyl ester.
•
It is stable in most coupling reaction and deprotection reaction
conditions.
O
H2N
Alanine methyl ester
O
•
Depending on what type of coupling reaction and with what
amino acids will be used other acid protecting groups can be used,
such as the allyl ester.
O
H2N
O
Alanine allyl ester
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Protecting Groups
Amine Protection
R
OH
H2N
O
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• There are two standard types of N-protecting groups used,
the Boc and Fmoc group.
O HC
3
O
CH3
N-Boc cleavage
CH3
50% TFA in DCM
BocHN
H 2N
COOH
COOH
Glycine
N-Fmoc cleavage
O
O
20% Piperidine in DMF
FmocHN
COOH
H2N
COOH
Glycine
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Protecting Groups
Protection of the R-group
R
OH
H2N
O
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•
Some of the different R-groups that must be protected
before coupling are
hydroxyl groups (Ser), thiol groups (Cys), amines (Lys) and
carboxylic acids (Asp).
COOH
HO
COOH
HS
NH2
NH2
Serine (Ser)
H2N
Cysteine (Cys)
COOH
COOH
HOOC
NH 2
Lysine (Lys)
NH 2
Aspartic Acid (Asp)
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Coupling Reagents
 In the coupling reactions of peptide synthesis the
carboxyl group of the acylating amino acid is activated.
 The care should be taken in selecting the activation
method to avoid racemization.
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Coupling Reagents
N
N
N
HOBt
N
N
N
N
OH
HOAt
N
N
N
OH
N
N
O
Me2N
PF6 (BF4 )
N
N
O
NMe2
HBTU (TBTU)
PF6
Me2N
NMe2
HATU
HOBt- (N- Hydroxy benztriazole)
HOAt- (1- Hydroxy-7-aza- benztriazole)
HBTU- (O-benztriazole-N,N,N’,N’-tetramethyl-uronium-hexafluoro
phosphate)
HATU- 2-(1H-7-Azabenzotriazol-1-yl)--1,1,3,3-tetramethyl uronium
hexafluorophosphate
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Deprotecting Groups
 It is the cleavage of the side-chain protecting groups.
 For protecting group such as Boc using
Trifluoroacetic acid (TFA) the deprotecting groups
like HF and Trifluoromethanesulfonic acid (TFMSA)
have been used.
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Deprotecting Groups
 Mild Acids :
e.g. Trifluoroacetic acid.
Hydrochloric acid.
Methanesulfonic Acid.
 Alkaline condition :
e.g. Piperidine in dimethylformamide.
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Solid Phase Synthesis Mechanism &
Application
R. Bruce Merrifield
7/15/1921–5/14/2006
Nobel prize in chemistry 1984
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Peptide Synthesis
CH2
CH
CH2
CH
CH2
CH
CH2
CH
Treating the polymeric support with chloromethyl
methyl ether (ClCH2OCH3) and SnCl4 places ClCH2
side chains on some of the benzene rings.
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Peptide Synthesis
CH2
CH
CH2
CH
CH2
CH
CH2
CH
CH2Cl
The side chain chloromethyl group is a benzylic
halide, reactive toward nucleophilic substitution.
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Peptide Synthesis
CH2
CH
CH2
CH
CH2
CH
CH2
CH
CH2Cl
The chloromethylated resin is treated with the Bocprotected C-terminal amino acid. Nucleophilic
substitution occurs, and the Boc-protected amino acid is
bound to the resin as an ester.
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Peptide Synthesis
CH2
CH
CH2
CH
CH2
CH
CH2
CH
CH2Cl
O
BocNHCHCO
–
R
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Peptide Synthesis
CH2
CH
CH2
CH
CH2
O
CH
CH2
CH
CH2
BocNHCHCO
R
Next, the Boc protecting group is removed with HCl.
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Peptide Synthesis
CH2
CH
CH2
CH
CH2
O
CH
CH2
CH
CH2
H2NCHCO
R
HOBt-promoted coupling adds the second amino acid
36
Peptide Synthesis
CH2
CH
CH2
CH
CH2
O
BocNHCHC
R'
O
CH
CH2
CH
CH2
NHCHCO
R
Remove the Boc protecting group.
37
Peptide Synthesis
CH2
CH
CH2
CH
CH2
O
H2NCHC
R'
O
CH
CH2
CH
CH2
NHCHCO
R
Add the next amino acid and repeat.
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Peptide Synthesis
CH2
CH
CH2
O
CH
CH2
O
O
+
H3N peptide C NHCHC NHCHCO
R'
CH
CH2
CH
CH2
R
Remove the peptide from the resin with HBr in CF3CO2H
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Peptide Synthesis
CH2
CH
CH2
CH
CH2
CH
CH2
CH
CH2Br
+
H3N peptide
O
O
C
NHCHC
R'
O
NHCHCO
R
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Advantages of Solid Phase
Synthesis
 Synthetic intermediates don’t
have to be isolated.
 Quick process.
 Reagents simply washed away
each step.
 Can be automated with robots!!
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Disadvantages to Solid Phase
Synthesis
 All the synthesis can’t be done on solid phase.
 Typically, kinetics not the same.
 Unsuitable for solvent assisted chemical reaction.
 High viscosity in reactant system.
 Insufficient purity if reaction steps are incomplete.
42
REFERENCES

www.google.co.in

www.discoveryofsps.com

www.wikipedia.org

Introduction to medicinal chemistry 3rd
edition by Patric.
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