SOLID PHASE CHEMISTRY

SOLID PHASE CHEMISTRY 1 Contents-Introduction Solid SupportLinkers, AnchorsProtecting GroupsCoupling ReagentsDeprotecting GroupsApplication In peptide synthesisAdvantages Disadvantages2IntroductionSolid 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 dipeptideZ-NH-CH-COOH + Cl-CH2

RZ-NH-CH-COO-CH2 R

NH2-CH-COO-CH2

R

Z-NH-CH-COX + NH2-CH-COO-CH2 R1 R

4CONT.Z-NH-CH-CO-NH-CH-COO-CH2 R1 R

NH2-CH-NH-CH-COOH + R1 R

solid support Z protecting group 5

Problems with Traditional Synthesis1 chemist 1 moleculeCan only make one molecule at a time.

Each synthesis very time consumingMultistep syntheses have loss at each stepPurification of products very time-consuming between steps.

Yields can be low and produces very few molecules at a time for testing.6Solid SupportResin 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. 7TypesCrosslinked Polystyrene -Styrene+Divinylbenzene -Most widely used -Hydrophobic8

9PEG Grafted Supports -Tentagel - 1-2% crosslinked polystyrene - More flexible -Hydrophilic

Inorganic Supports- -Glass beads as a inorganic supports - High mechanical strength -Negligible swelling

10Properties:-

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.11Linker, Anchors

The linker that is bound to the resin is called anchor.

Remains at the resin after cleavage. Resin LinkerResinAnchor12linkerBifunctional 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.

13AnchorsTypes :

1) Benzylic Halide Type Resin- i. Merrifield resin.

=

14Anchorii. Trityl chloride resin.

15Anchor 2) Benzylic alcohols Type Resin -

16Wang resinAnchor3)Benzylic amines Type Resin-

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Rink amide resin17Anchor4) Aromatic aldehyde Type Resin-

18Bal resinProtecting GroupsA fragment bound to functional group that blocks the reactivity of that group.

Good protecting groups are easily attached and removed using mild reaction condition.

19Protecting Groups20

Acid Protection The most common acid protecting group used is the methyl ester. It is stable in most coupling reaction and deprotection reaction conditions. 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.

Alanine methyl esterAlanine allyl ester

2121Protecting Groups

Amine Protection22

There are two standard types of N-protecting groups used, the Boc and Fmoc group.N-Fmoc cleavage

N-Boc cleavage2323Protecting Groups Protection of the R-group

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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).

25Coupling ReagentsIn 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.

2627 Coupling Reagents 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 27

Deprotecting GroupsIt 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.28Deprotecting GroupsMild Acids : e.g. Trifluoroacetic acid. Hydrochloric acid. Methanesulfonic Acid.

Alkaline condition : e.g. Piperidine in dimethylformamide.29Solid Phase Synthesis Mechanism & Application

R. Bruce Merrifield

7/15/19215/14/2006

Nobel prize in chemistry 198430Peptide SynthesisCH2CH2CH2CH2CHCHCHCH

Treating the polymeric support with chloromethyl methyl ether (ClCH2OCH3) and SnCl4 places ClCH2 side chains on some of the benzene rings.31Peptide SynthesisCH2CH2CH2CH2CHCHCHCH

CH2ClThe side chain chloromethyl group is a benzylic halide, reactive toward nucleophilic substitution.32Peptide SynthesisCH2CH2CH2CH2CHCHCHCH

CH2Cl The chloromethylated resin is treated with the Boc-protected C-terminal amino acid. Nucleophilic substitution occurs, and the Boc-protected amino acid is bound to the resin as an ester.33Peptide SynthesisCH2CH2CH2CH2CHCHCHCH

CH2ClRO BocNHCHCO34Peptide SynthesisCH2CH2CH2CH2CHCHCHCH

CH2Next, the Boc protecting group is removed with HCl. BocNHCHCOR O35Peptide Synthesis H2NCHCO RCH2CH2CH2CH2CHCHCHCH

CH2OHOBt-promoted coupling adds the second amino acid36Peptide SynthesisNHCHCOROCH2CH2CH2CH2CHCHCHCH

CH2 BocNHCHC R' ORemove the Boc protecting group.37Peptide SynthesisCH2CH2CH2CH2CHCHCHCH

CH2 NHCHCO R O H2NCHC R' OAdd the next amino acid and repeat.38Peptide SynthesisCH2CH2CH2CH2CHCHCHCH

CH2NHCHCO R ONHCHC R' OCO+H3NpeptideRemove the peptide from the resin with HBr in CF3CO2H39Peptide Synthesis

CH2CH2CH2CH2CHCHCHCH

CH2BrNHCHCORONHCHCR'OCO+H3Npeptide40Advantages of Solid Phase SynthesisSynthetic intermediates dont have to be isolated.

Quick process.

Reagents simply washed away each step.

Can be automated with robots!!

41Disadvantages to Solid Phase SynthesisAll the synthesis cant 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.42REFERENCESwww.google.co.inwww.discoveryofsps.comwww.wikipedia.orgIntroduction to medicinal chemistry 3rd edition by Patric.

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