Transcript Solid Phase Combichem - San Diego Mesa College

Drug Discovery
The use of solid phase combinatorial
chemistry and parallel synthesis
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
Solid Phase Synthesis
• Technology adapted from Biochemistry and
peptide synthesis
• Addresses problem of purification steps
• Typically purifications involve such processes as
– Recrystallization
– Distillation
– Extraction
• All very time consuming and have losses that
lower yields
Solid Phase Synthesis
• First step is to attach
the starting molecule
to an inert solid.
– Typically inert
polymers or resins are
used.
– These are
commercially available
HO
Bead
O
NH2
Solid Phase Synthesis
• Since the molecule is attached to a solid, any other
chemicals added or products can be removed by
filtration.
– Typically reactions undertaken in vessels with frits at
the bottom (for filtration)
– “Tea bags” also used
• Here, solids are dipped into solutions containing subsequent
reagents.
• Next, they can be removed from the “dip” and placed into a
wash solution
Solid Phase Synthesis
• After all reactions are done the product is
still attached to the insoluble bead.
– Can be washed as in previous slide or, in the
case of a reaction well, excess solvent is
washed through
• Finally, the product is cleaved from the bead
and isolated.
Advantages of Solid Phase Synthesis
• Purification of each product can be
achieved in one step.
– Only purification technique is filtration
– Washing is simple
• Because all we do is change solution or
move a “tea bag” from solution to solution,
this process can be easily automated.
Disadvantages to Solid Phase
Synthesis
• Not all syntheses can be done solid phase
– Some molecules don’t attach well to beads
– Some chemistry just doesn’t work in this
fashion
– Removal of product from bead, can be
damaging to product if not careful
• Typically, kinetics not the same
– Reaction rates can be slower
Parallel Synthesis
• Method for making many molecules at the
same time.
• Reactions done “in parallel”
– Have to be analogous reactions
• Same basic chemistry
• Same conditions of temp, solvents, time etc.
• Reactions done at same time.
– Not all will give same yields as analogous is
NOT identical
Next Several Slides
• The slides below are an example or how we can
make several compounds at one time using
parallel synthesis and solid phase combinatorial
chemistry.
• Please look in the examples for the principles of
solid phase and parallel synthesis.
• Note that the number of reactions is significantly
fewer than the number of compounds.
– Number of reactions is additive
– Number of compounds multiplicative
12-well reaction block
12 well reaction block
• Again, this is an example
• This is simply a teflon block with wells
drilled in it.
– All of the reactions done in the block are done
at the same time.
• If the block is heated, all wells are heated etc
• Same solvents in each well etc.
Cross section of a well on the
reaction block
• Each well in the reaction
block has a frit on the
bottom
• If the wholc block is
placed on a vacuum,
liquids will go through the
frit
• Solids stay behind
• Can purify substances by
filtration
Frit. Plate
on vacuum
Scaffold
• A scaffold is a molecule on which the
structure of the final molecules is built
• Has a basic structure
• May have several reactive sites
– These are called points of diversity
– This is where other molecules are added
Example
• The molecule to the
right has 2 reactive
sites
• It is attached to a bead
for solid phase
synthesis
• For the next slides,
we’ll call this scaffold,
S
HO
Bead
O
NH2
Parallel Synthesis
• The Scaffold is now added to each well
• In this example, there are twelve wells, so
presently there are twelve copies of the
same molecule.
Add Scaffold to each well
S
S
S
S
S
S
S
S
S
S
S
S
Well after addition of scaffold
HO
Bead
Each well on
the plate has
the scaffold.
O
NH2
Diversity Groups
• For lack of a better term, these are the
things that will be reacted with the reactive
centers on the scaffold
• Remember “R” means the “rest” of the
molecule
– R groups can be methyl, ethyl, propyl,
isopropyl, benzyl etc
– The reaction takes place at the other end
Diversity Groups for our example
NH2
R
=A-D
O
=1-3
Cl
R
Reaction of First Reactant with
Scaffold
HO
NH2
R
O
R
H
N
O
+
Bead
NH2
Excess reagent and water
can be filtered out,
These R’s are A - D
NH2
Bead
+ H2O
Addition of First Reactant to
Scaffold
• Each reaction proceeds in the same fashion
• They are analogous
– Same chemistry
– Same other product (in this case, water)
– Same time
• Only difference will be the R groups
– Remember, in this example they are A - D
Well after first reaction, filtration
and washing
R
Bead
H
N
Each Column on
the plate has a
different R group (A – D).
O
NH2
The other products
were removed by
filtration.
Wells after addition of first
reagent
• There are now 4 different products
• There have been 4 different reactions
– However, though we added four different
reagents, all of the reactions were undertaken
simultaneously.
Wells after Addition of first
reagent
SA
SB
SC
SD
SA
SB
SC
SD
SA
SB
SC
SD
Addition of Second Reactant to
Scaffold
• Each reaction proceeds in the same fashion
• They are analogous
– Same chemistry
– Same other product (in this case, HCl)
– Same time
• Only difference will be the R groups
– Remember, in this example they are 1 - 3
Reaction of Second Reactant
with Scaffold
R
H
N
O
H
N
R
O
O
+
Bead
NH2
Cl
O
R
N
H
Bead
Excess reagent filtered through along
with HCl ions.
+
HCl
R
Wells after second reaction and
washing
R
H
N
Each Row on
the plate has a
different R group.
O
O
Bead
N
H
R
Excess reagent
and HCl removed
by filtration
Wells after addition of second
reagent
• There are now 12 different products
• There have been 7 different reactions
– However, though we added seven different
reagents, all of the reactions were undertaken
simultaneously.
There are now twelve different
products
SA1
SB1
SC1
SD1
SA2
SB2
SC2
SD2
SA3
SB3
SC3
SD3
Combinatorial Advantage
• Number of reactions is additive
– 4 + 3 = 7 reactions
• Number of products is multiplicative
– 4 X 3 = 12 products
• In this example, not a big deal, but imagine
if we did more steps
Isolation of Product
Product is cleaved from the bead
Solubilized product is filtered
through well into a small test
tube.
Contents of Test Tube
(Isolated compound)
Remember there are 12 different ones
R
H
N
O
O
N
H
R
Summary
• This example illustrates a couple of things
– Parallel synthesis
• Though there were 7 reactions, there were only 2 sets of
reactions.
• We had to add 7 different reagents, but there were only 2
events where we did the reactions
– Solid phase synthesis
• Original scaffold on a bead so excess reagents and other
products removed by filtration
• Intermediate products easily washed
– Combinatorial advantage
• Only did 7 reactions, but got 12 products
• Would be more pronounced if more steps