1) Combinatorial chemistry techniques allow for the parallel synthesis of multiple chemical compounds. This involves dividing chemical reactions into separate vessels to allow many reactions to occur simultaneously, saving time over sequential synthesis. 2) Some key developments in parallel synthesis techniques include Merrifield's solid phase peptide synthesis using resin beads, Stabchen's use of polyethylene rods for parallel peptide synthesis, and Lam's split-mix method which uses repetition of dividing, reacting, and recombining steps to efficiently generate compound libraries. 3) Combinatorial chemistry relies on solid supports like polystyrene or polyethylene glycol resin beads that are insoluble and compatible with reagents. Linkers attach initial building blocks like amino acids to these supports, and parallel

1. COMBINATORIAL
CHEMISTRY
Prof. S. A Waghmare
JSPM’s Charak College of Pharmacy and Research,
Wagholi, Pune
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2. History of Combinatorial
Chemistry
Structure
1. Solid-phase synthesis Merrifield
2. Multiple solid-phase synthesis Stäbchen Synthese
3. Split-mix-method Lam
4. Arrays Fodor
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3. Solid-Phase Synthesis
Who get it started
Merrifield 1963 – solid-phase
– Revolution in synthesis
– Reducing of temporial and technical effort
– Nobel prize in 1985
– Base of automation and Combinatorial Chemistry
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4. Multiple solid-phase synthesis
Stäbchen
Development of parallel synthesis
• Polyethylene skewer with a amino function carrier
• 40 mm lenght; 4 mm diameter
• 96 Skewers in 8 rows fits in a microtiterplate
• Coupling of aminoacids in the plate
• Chemistry analog merrifield
• Peptides stay on the skewers
• Method for investigation of antibodies
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5. Split-Mix-Synthesis
Lam, 1991
 Method to eliminate the problems with the coupling
tendency of aminoacids
 The polymere are little beads, diameter 100-200 μm
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7. Arrays
Fodor, 1991
• Solid phase synthesis + Photo Lithography and Photocemistry
• Synthesis on a functionalised glass plates
• Photolabile α-amino protecting group
• Masks + light with a specific wavelenght
• Control of the sequence
• Screening with antibodies
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8. Introduction
1) Solid Supports
 Insoluble in solvents
 Not to react with the reagents
 Form of small resin beads, polymer or glass beads, rods, sheets
etc ( that may or may not swell in the solvents)
Composed of two parts
1. The core
2. The linker
CORE Linkers Start compound
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9. The core
1) Crosslinked polystyrene
2) Polyethylene glycol (PEG) grafted supports
3) Inorganic supports
4) Non-bead form supports
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10. 1) Crosslinked polystyrene
• Most commonly used supports
• Synthesized from styrene and divinylbenzene
• By suspension polymerization in the form of small beads
• The ratio of divinylbenzene to styrene determines the density
of cross links.
 Higher crosslink density
 Increases the mechanical stability of the beads
 Lowering the crosslink density
• Increases swelling
• Increases the accessibility of the functional groups
Ratio: 1-2% divinylbenzene
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11. Specification of bead
Functional groups can be introduced into the resin
• Post functionalization of the aromatic rings of polystyrene
• functionalized styrene in polymerization
The reactions are faster when small beads are used
• Diameter of the Beads or by the inversely proportional mesh
size
• 200-400 mesh (35-75micron)
• 100-200 mesh (75-150 micron)
• Narrow bead size distribution is advantageous
• Capacity of the Polystyrene beads is around 0.5 mmol/g.
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12. 2) Polyethylene glycol (PEG) grafted supports
Structure:
Tentagel
Where X is Br, OH, SH or NH2 for attachment of the substrate
• Aromatic rings & polyethylene glycol chains are covalently
attached
• Ratio: 1-2% crosslinked polystyrene
Advantage
• flexible
• chain is more accessible to reagents
• behaves like being in a solution-like environment
• gives a hydrophilic character to the resin
• swells well in water and methanol 12

13. 3) Inorganic supports
Glass beads
 functionalized
 controlled pore size
 Commercially available
 mechanical stability
 do not swell in solvents
 Functionalized ceramics can also be used as supports
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14. 4) Non-bead form supports
 Microscopic beads
 Surface of macroscopic objects can be functionalized with
groups
 Can serve as anchors to hold the substrate
 Styrene or polyolefin chains can be grafted by radiation into
the Surface of the objects
 The chains can be functionalized
 SynPhase lanterns are commercially available in different sizes
at Mimotopes
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15. Linkers
 Covalently attached to the solid support
 Bifunctional molecule
 One functional group for irreversible attachment to the core
resin
 Second functional group for forming a reversible covalent
bond with the initial building block of the product
 Also called anchor
+ =Resin Linker Resin Linker
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16. 1) Merrifield resin
 Used to attach carboxylic acids to the resin
 cleaved from the resin in carboxylic acid form using HF
2) Trityl chloride resin
 much more reactive than the Merrifield resin
 used for attachment of a vide variety of compounds like
carboxylic acids, alcohols, phenols, amines & thiols.
 cleaved under mild conditions using a solution of
trifluoroacetic acid (TFA) in varying concentrations (2-50%)
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17. 3) Hydroxymethyl resin
 Applied for attachment of activated carboxylic acids
 Cleavage conditions resemble that of the Merrifield resin (HF)
4) Wang resin
 Used to bind carboxylic acids
 Ester linkage formed has a good stability
 Cleavage by 95% TFA is applied
 Frequently used in peptide synthesis
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18. 5) Aminomethyl resin
 Carboxylic acids in their activated form can be attached to the
resin
 Formed amide bond is resistant to cleavage
 Resin is used when the synthesized products are not cleaved
from the support
6) Rink amide resin
 Designed to bind carboxylic acids
 Cleave the product in carboxamide form under mild conditions
 Amino group in the resin is usually present in protected form
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19. 7) Photolabile anchors
• Photolabile anchors have been developed that allow cleavage
of the product from the support by irradiation without using
any chemical reagents
• 2-nitrobenzhydrylamine
• Usually contain nitro group that absorbs UV light
8) Traceless anchors
• Block of a multi-step solid phase synthesis
• It may happen that In the end product this group is
unnecessary and needs to be removed
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20. Parallel synthesis
• Synthesis of compound arrays based on saving reaction time
• food cooking processes
• She is doing different activities in parallel in order to be more
effective
Standard microtiter plate: 8 rows and 12 columns 20

21. Principle of Parallel Synthesis
• Chemical reactions takes time
• During that time not only one but a series of reactions can be
realized
• Each synthetic reaction is started in a different reaction vessel
• All the necessary operations are executed in parallel
Ex. Tripeptides in parallel 21

22. • Number of reaction vessels is the same as the number of
compounds
• Number of operations is practically the same
• Solvents and reagents have to be serially transported into each
reaction vessel
• The real advantage is that the reaction time for the in
synthesizing the 5 compounds is about the same as preparing a
single one
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23. Advantages
 Each compound is substantially pure in this location
 Define location provides the structure of certain compound
 Easier biological evaluation
 No Deconvolution is required
 No risk of synergistic effect
Disadvantages
 Applicable only for medium libraries
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24. Types of Parallel Synthesis
1. The multipin metod of Geysen
2. The Spot technique of Frank
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25. The multipin metod of Geysen
• The first example of parallel synthesis was published by
Geysen and his colleagues
• Synthesized series of peptide
• Used the microtiter plate
• Cover plate with mounted polyethylene rods
• End of polyethylene rods (pins) were coated with derivatized
polyacrilic acid
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26. The Spot technique of Frank
• The synthesis is carried out on cellulose paper membranes
• Small droplets of solutions of protected amino acids dissolved
in low volatility solvents
• Coupling reagents are pipetted onto predefined positions of the
membrane
• The spots thus formed can be considered as reaction vessels
where the conversion reactions of the solid phase synthesis
take place
• Many as 2000 peptides can be made on an 8x12 cm paper
sheet
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27. The temperature of the reaction mixtures could be controlled by
heating or cooling the reaction block
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28. The split-mix synthesis
• Based on Merrifield's solid phase procedure
• Using only three different protected amino acids as building blocks
• by red, yellow and blue circles
• The synthesis is executed by repetition of the following three simple
operations that form a cycle
1. Dividing the solid support into equal portions;
2. Coupling each portion individually with only one of the different amino
acids
3. Mixing and homogenizing the portions.
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30. In the first round
 The amino acids are coupled to equal portions of the resin
 The final product - after recombining and mixing the portions -
is the mixture of the three amino acids bound to resin.
In the second cycle
 This mixture is again divided into three equal portions
 The amino acids are individually coupled to these mixtures
 In each coupling step three different resin bound dipeptides are
formed, so the end product is a mixture of 9 dipeptides
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35. THANK YOU
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