The document describes the strategy and key steps of solid phase peptide synthesis using the Merrifield method. In this method, the C-terminus of the first amino acid is attached to an insoluble polystyrene resin support. Subsequent amino acids are then added step-wise through repetition of deprotecting the N-terminus, coupling with the next protected amino acid, and further deprotection until the full peptide is synthesized while still attached to the resin. The final peptide is then cleaved off the resin support to obtain the pure peptide product.
Mitsunubu reaction had been synthesised by Japanese scientist OYO Mitsunbu.
It involves the Conversion of primary, Secondary alcohol into the ester group.
It follows SN2 mechanism.
more chemistry contents are available
1. pdf file on Termmate: https://www.termmate.com/rabia.aziz
2. YouTube: https://www.youtube.com/channel/UCKxWnNdskGHnZFS0h1QRTEA
3. Facebook: https://web.facebook.com/Chemist.Rabia.Aziz/
4. Blogger: https://chemistry-academy.blogspot.com/
Organic Synthesis:
The Disconnection Approach
One Group C-C Disconnection of Alcohol and Alkene
When there are two functional groups of unequal reactivity within a molecule, the more reactive group can be made to react alone, but it may not be possible to react the less reactive functional group selectively.
A group the use of which makes possible to react a less reactive functional group selectively in presence of a more reactive group is known as protecting group.
A protecting group blocks the reactivity of a functional group by converting it into a different group which is inert to the conditions of some reaction(s) that is to be carried out as part of a synthetic route
Presented by Shikha Popali and Harshpal singh Wahi students from Gurunanak college of pharmacy, Nagpur in Department of pharmaceutical Chemistry. The explained topic is seful for every chemistry student and for others too
N-BROMOSUCCINAMIDE A REAGENT USED IN THE SYNTHESIS, IT IS ALSO A SYNTETIC REAGENT AND HERE IN THIS PRESENTATION THE MOLECULAR FORMULA ITS ALTERNATE NAME APLLICATION ARE DISCUSSED.
Mitsunubu reaction had been synthesised by Japanese scientist OYO Mitsunbu.
It involves the Conversion of primary, Secondary alcohol into the ester group.
It follows SN2 mechanism.
more chemistry contents are available
1. pdf file on Termmate: https://www.termmate.com/rabia.aziz
2. YouTube: https://www.youtube.com/channel/UCKxWnNdskGHnZFS0h1QRTEA
3. Facebook: https://web.facebook.com/Chemist.Rabia.Aziz/
4. Blogger: https://chemistry-academy.blogspot.com/
Organic Synthesis:
The Disconnection Approach
One Group C-C Disconnection of Alcohol and Alkene
When there are two functional groups of unequal reactivity within a molecule, the more reactive group can be made to react alone, but it may not be possible to react the less reactive functional group selectively.
A group the use of which makes possible to react a less reactive functional group selectively in presence of a more reactive group is known as protecting group.
A protecting group blocks the reactivity of a functional group by converting it into a different group which is inert to the conditions of some reaction(s) that is to be carried out as part of a synthetic route
Presented by Shikha Popali and Harshpal singh Wahi students from Gurunanak college of pharmacy, Nagpur in Department of pharmaceutical Chemistry. The explained topic is seful for every chemistry student and for others too
N-BROMOSUCCINAMIDE A REAGENT USED IN THE SYNTHESIS, IT IS ALSO A SYNTETIC REAGENT AND HERE IN THIS PRESENTATION THE MOLECULAR FORMULA ITS ALTERNATE NAME APLLICATION ARE DISCUSSED.
This powerpoint is about the swern oxidation...It is used for the oxidaton of alcohol and inorder to avoid the chromium reagent. Follow me through youtube
CHE-MYSTERY
Subscribe and press bell button for notfcation
THE DCC I.E. DICYCLOCARBODIIMDE IS A REAGENT AND HERE THE DETAIL ACCOUNT ON IT IS GIVEN INCLUDING MOLECULAR WEIGHT, STRUCTURE, SYNTHESIS AND PHYSICAL PARAMETERS AND APPLICATIONS FOR OTERS SYNTHESIS ARE ALSO DISCUSSED, THE DIFFERENT SYNTHESIS WITH DCC COMBINATION ARE ALSO MENTIONED
It includes the UGI reaction & Brook rearrangement.
mechanism & application also included that presentation.
student will be helpful for easilly available this reaction.
An approach for designing organic synthesis which involves breaking down of target molecule into available starting material by imaginary breaking of bonds (disconnection) and/or by functional group interconversion is known as disconnection approach or retrosynthesis or synthesis backward.
The C-X disconnection approach is mainly applicable to a carbon chain attached to any of the heteroatoms like O, N, or S. Here, a bond joins the heteroatom (X) to the rest of the molecule like a C-O, C-N, or C-S group. This point is good point to initiate a disconnection. This is called a ‘One-group’ C-X disconnection as one would need to identify only one functional group like ester, ether, amide etc. to make the disconnection.
How to choose a disconnection?
These are the few general strategy which are important points introduced which apply to the whole of synthetic design rather than one particular area. The main choice is between the various disconnection, even such a simple disconnection as the following alcohol can be disconnected.
We want to get back to simple starting materials and we shall do if we disconnect the bond which are:
Towards the middle of the molecule thereby breaking into two reasonably equal halves rather than chopping off one or two carbon atoms from the end and,
At a branch as this is more likely to give straight chain fragments and these are more likely to be available.
Disconnections very often take place immediately adjacent to, or very close to functional groups in the target molecule. This is pretty much inevitable, given that functionality almost invariably arises from the forward reaction.
A simple example is the weedkiller propanil used on rice fields. Amide disconnection gives amine obviously made from o-dichlorobenzene by nitration and reduction. All positions around the ring in o-dichlorobenzene are about the same electronically but steric hindrance will lead to dichloronitrobenzene being the major product
This compound was needed for some research into the mechanisms of rearrangements. We can disconnect on either side of the ether oxygen atom, but (b) is much better because (a) does not correspond to a reliable reaction: it might be hard to control selective alkylation of the primary hydroxyl group in the presence of the secondary one.
The disconnections we have made so far have all been of C–O, C–N, or C–S bonds, but, of course, the most important reactions in organic synthesis are those that form C–C bonds. We can analyze C–C disconnections in much the same way as we’ve analyzed C–X disconnections.
The Zeneca drug propranolol is a beta-blocker that reduces blood pressure and is one of the top drugs worldwide. It has two 1,2-relationships in its structure but it is best to disconnect the more reactive amine group first.
Arildone is a drug that prevents polio and herpes simplex viruses from ‘unwrapping’ their DNA, and renders them harmless.
What is a Heterocyclic Compound?
A heterocyclic compound has at least two different elements as a member of its ring.
The most common hetero atoms found on a cyclic ring are Oxygen (O), Nitrogen (N) and Sulphur (S).
Example:
Nucleic Acid that is present in the body responsible for storing and expressing genetic information, is an example of a Heterocyclic compound.
Essential micronutrient, Vitamins is also an example of a heterocyclic compound.
The majority of drugs, pesticides, dyes, and plastics are examples of heterocyclic compounds.
Classification of Heterocyclic Compounds
Based on the electronic arrangement, we can classify Heterocyclic compounds into two types:
Aliphatic Heterocyclic Compounds
Aromatic Heterocyclic Compounds
Aliphatic Heterocyclic Compounds
Aliphatic heterocyclic compounds are those cyclic heterocycles that do not contain any double bond.
The properties of aliphatic heterocyclic compounds are mainly affected due to ring strain.
Examples of aliphatic heterocyclic compounds are Aziridine, Ethylene Oxide, Thiirane, Oxetane, Azetidine, Thietane, Tetrahydrofuran (THF), Dioxane, Pyrrolidine, Piperidine, etc.
Aromatic Heterocyclic Compound
Aromatic heterocyclic compounds, as the name suggests, are cyclic aromatic compounds.
Aromatic Heterocyclic compounds obey Huckels Rule, i.e.
It should be cyclic.
It should be planar.
It should not contain any sp3 hybridised atoms.
It must have (4n+2) 𝛑 electrons.
Aromatic Heterocyclic compounds are analogous to Benzene.
Examples: Furan, Pyrrole, Thiophene, Indole, Benzofuran, Carbazole, Quinoline, Isoquinoline, Imidazole, Oxazole, Pyrazole, Pyridazine, Pyrimidine, Purine, etc.
Based on structure, we can classify Heterocyclic compounds into five types:
Three-Membered Heterocyclic Compounds
Four-Membered Heterocyclic Compounds
Five-Membered Heterocyclic Compounds
Six-Membered Heterocyclic Compounds
Condensed or Fused Heterocyclic Compounds
Three-Membered Heterocyclic Compounds
These heterocyclic compounds contain three atoms which may be saturated or unsaturated.
Based on the number of heteroatoms present, we can further classify them into two categories:
This powerpoint is about the swern oxidation...It is used for the oxidaton of alcohol and inorder to avoid the chromium reagent. Follow me through youtube
CHE-MYSTERY
Subscribe and press bell button for notfcation
THE DCC I.E. DICYCLOCARBODIIMDE IS A REAGENT AND HERE THE DETAIL ACCOUNT ON IT IS GIVEN INCLUDING MOLECULAR WEIGHT, STRUCTURE, SYNTHESIS AND PHYSICAL PARAMETERS AND APPLICATIONS FOR OTERS SYNTHESIS ARE ALSO DISCUSSED, THE DIFFERENT SYNTHESIS WITH DCC COMBINATION ARE ALSO MENTIONED
It includes the UGI reaction & Brook rearrangement.
mechanism & application also included that presentation.
student will be helpful for easilly available this reaction.
An approach for designing organic synthesis which involves breaking down of target molecule into available starting material by imaginary breaking of bonds (disconnection) and/or by functional group interconversion is known as disconnection approach or retrosynthesis or synthesis backward.
The C-X disconnection approach is mainly applicable to a carbon chain attached to any of the heteroatoms like O, N, or S. Here, a bond joins the heteroatom (X) to the rest of the molecule like a C-O, C-N, or C-S group. This point is good point to initiate a disconnection. This is called a ‘One-group’ C-X disconnection as one would need to identify only one functional group like ester, ether, amide etc. to make the disconnection.
How to choose a disconnection?
These are the few general strategy which are important points introduced which apply to the whole of synthetic design rather than one particular area. The main choice is between the various disconnection, even such a simple disconnection as the following alcohol can be disconnected.
We want to get back to simple starting materials and we shall do if we disconnect the bond which are:
Towards the middle of the molecule thereby breaking into two reasonably equal halves rather than chopping off one or two carbon atoms from the end and,
At a branch as this is more likely to give straight chain fragments and these are more likely to be available.
Disconnections very often take place immediately adjacent to, or very close to functional groups in the target molecule. This is pretty much inevitable, given that functionality almost invariably arises from the forward reaction.
A simple example is the weedkiller propanil used on rice fields. Amide disconnection gives amine obviously made from o-dichlorobenzene by nitration and reduction. All positions around the ring in o-dichlorobenzene are about the same electronically but steric hindrance will lead to dichloronitrobenzene being the major product
This compound was needed for some research into the mechanisms of rearrangements. We can disconnect on either side of the ether oxygen atom, but (b) is much better because (a) does not correspond to a reliable reaction: it might be hard to control selective alkylation of the primary hydroxyl group in the presence of the secondary one.
The disconnections we have made so far have all been of C–O, C–N, or C–S bonds, but, of course, the most important reactions in organic synthesis are those that form C–C bonds. We can analyze C–C disconnections in much the same way as we’ve analyzed C–X disconnections.
The Zeneca drug propranolol is a beta-blocker that reduces blood pressure and is one of the top drugs worldwide. It has two 1,2-relationships in its structure but it is best to disconnect the more reactive amine group first.
Arildone is a drug that prevents polio and herpes simplex viruses from ‘unwrapping’ their DNA, and renders them harmless.
What is a Heterocyclic Compound?
A heterocyclic compound has at least two different elements as a member of its ring.
The most common hetero atoms found on a cyclic ring are Oxygen (O), Nitrogen (N) and Sulphur (S).
Example:
Nucleic Acid that is present in the body responsible for storing and expressing genetic information, is an example of a Heterocyclic compound.
Essential micronutrient, Vitamins is also an example of a heterocyclic compound.
The majority of drugs, pesticides, dyes, and plastics are examples of heterocyclic compounds.
Classification of Heterocyclic Compounds
Based on the electronic arrangement, we can classify Heterocyclic compounds into two types:
Aliphatic Heterocyclic Compounds
Aromatic Heterocyclic Compounds
Aliphatic Heterocyclic Compounds
Aliphatic heterocyclic compounds are those cyclic heterocycles that do not contain any double bond.
The properties of aliphatic heterocyclic compounds are mainly affected due to ring strain.
Examples of aliphatic heterocyclic compounds are Aziridine, Ethylene Oxide, Thiirane, Oxetane, Azetidine, Thietane, Tetrahydrofuran (THF), Dioxane, Pyrrolidine, Piperidine, etc.
Aromatic Heterocyclic Compound
Aromatic heterocyclic compounds, as the name suggests, are cyclic aromatic compounds.
Aromatic Heterocyclic compounds obey Huckels Rule, i.e.
It should be cyclic.
It should be planar.
It should not contain any sp3 hybridised atoms.
It must have (4n+2) 𝛑 electrons.
Aromatic Heterocyclic compounds are analogous to Benzene.
Examples: Furan, Pyrrole, Thiophene, Indole, Benzofuran, Carbazole, Quinoline, Isoquinoline, Imidazole, Oxazole, Pyrazole, Pyridazine, Pyrimidine, Purine, etc.
Based on structure, we can classify Heterocyclic compounds into five types:
Three-Membered Heterocyclic Compounds
Four-Membered Heterocyclic Compounds
Five-Membered Heterocyclic Compounds
Six-Membered Heterocyclic Compounds
Condensed or Fused Heterocyclic Compounds
Three-Membered Heterocyclic Compounds
These heterocyclic compounds contain three atoms which may be saturated or unsaturated.
Based on the number of heteroatoms present, we can further classify them into two categories:
Introduction of poly-cyclic compounds, resonance, molecular orbital structure, physical properties, preparation, reaction and uses of napthalene, anthracene, phenanthrene, napthaquinone, napthol, napthylamine, 9,10 anthraquinone and phenanthrequinone.
More problems covering asymmetric synthesis. This time with examples of substrate control, chiral reagents, and chiral catalysis. Also another example of a synthesis.
The benzoin addition is an addition reaction involving two aldehydes. The reaction generally occurs between aromatic aldehydes or glyoxals. The reaction produces an acyloin. In the classic application benzaldehyde is converted to benzoin
HSSC Second year Chemistry course slides for Federal Board Pakistan, lectures by Dr. Raja Hashim Ali (also available on Youtube as a series of video lectures).
Similar to Solid Phase Peptide Synthesis(Rajendra Sonawane) (20)
This presentation by Morris Kleiner (University of Minnesota), was made during the discussion “Competition and Regulation in Professions and Occupations” held at the Working Party No. 2 on Competition and Regulation on 10 June 2024. More papers and presentations on the topic can be found out at oe.cd/crps.
This presentation was uploaded with the author’s consent.
Acorn Recovery: Restore IT infra within minutesIP ServerOne
Introducing Acorn Recovery as a Service, a simple, fast, and secure managed disaster recovery (DRaaS) by IP ServerOne. A DR solution that helps restore your IT infra within minutes.
0x01 - Newton's Third Law: Static vs. Dynamic AbusersOWASP Beja
f you offer a service on the web, odds are that someone will abuse it. Be it an API, a SaaS, a PaaS, or even a static website, someone somewhere will try to figure out a way to use it to their own needs. In this talk we'll compare measures that are effective against static attackers and how to battle a dynamic attacker who adapts to your counter-measures.
About the Speaker
===============
Diogo Sousa, Engineering Manager @ Canonical
An opinionated individual with an interest in cryptography and its intersection with secure software development.
Sharpen existing tools or get a new toolbox? Contemporary cluster initiatives...Orkestra
UIIN Conference, Madrid, 27-29 May 2024
James Wilson, Orkestra and Deusto Business School
Emily Wise, Lund University
Madeline Smith, The Glasgow School of Art
This presentation, created by Syed Faiz ul Hassan, explores the profound influence of media on public perception and behavior. It delves into the evolution of media from oral traditions to modern digital and social media platforms. Key topics include the role of media in information propagation, socialization, crisis awareness, globalization, and education. The presentation also examines media influence through agenda setting, propaganda, and manipulative techniques used by advertisers and marketers. Furthermore, it highlights the impact of surveillance enabled by media technologies on personal behavior and preferences. Through this comprehensive overview, the presentation aims to shed light on how media shapes collective consciousness and public opinion.
Have you ever wondered how search works while visiting an e-commerce site, internal website, or searching through other types of online resources? Look no further than this informative session on the ways that taxonomies help end-users navigate the internet! Hear from taxonomists and other information professionals who have first-hand experience creating and working with taxonomies that aid in navigation, search, and discovery across a range of disciplines.
3. •Making peptide bonds between amino acids is not
difficult: there are numerous methods to make
amides from amines and carboxylic acids.
•The challenge is connecting amino acids in the
correct sequence.
•Random peptide bond formation in a mixture of
phenylalanine and glycine, for example, will give four
dipeptides.
• Phe—Phe Gly—Gly Phe—Gly Gly—Phe
The Challenge of Peptide Synthesis
4. Amino Acids are Structurally Bifunctional
L-Phenylalanine
O
OH
N
H
H O
OH
N
H
H
H
Glycine
5. Possible Products from the Condensation of
Phenylalanine and Glycine
Phe-Phe
O
N
H
H2N
O
OH
N
H
H
Gly-Gly
OH
O
O
OH
H
N
H
O
H2N
O
H2N
O
OH
H
N
H
O
H2N
H
Phe-Gly
Gly-Phe
6. • 1.Limit the number of possible reactions by
"protecting" the nitrogen of one amino acid
and the carboxyl group of the other.
Step 1 of Peptide Synthesis: Protection
N-Protected
L-Phenylalanine
C-Electrophile
O
OH
N
H
O
O
N
H
H
H PG
PG
O-Protected
Glycine
N-Nucleophile
PG
protecting
group
7. • 2. Couple the two protected amino acids.
Step 2 of Peptide Synthesis: Coupling
O
OH
N
H
O
O
N
H
H
H PG
PG
O
N
H
N
H
H
PGPG
O
O
Peptide
Coupling
PG-Phe-Gly-PG
8. • 3.Deprotect the amino group at the N-terminus
and the carboxyl group at the C-terminus.
Peptide Synthesis, Step 3: Global Deprotection
Phe-Gly
O
N
H
N
H
H
PGPG
O
O
Deprotection
O
N
H
H3N
H
O
O
9. Does the Requirement for Three Extra Steps
Outweigh the Need to Purify a Mixture?
Phe-Phe
O
N
H
H2N
O
OH
N
H
H
Gly-Gly
OH
O
O
OH
H
N
H
O
H2N
O
H2N
O
OH
H
N
H
O
H2N
H
Phe-Gly
Gly-Phe
Yes - synthesis is easier than purification
11. What are we Trying to Achieve by Protecting
the Amino Group?
Amino groups can behave as nucleophiles and undergo reaction
with carboxylic acid derivatives. The nitrogen atom in amides is
much less nucleophilic. As a result, amide derivatives of amines
can be viewed as protecting groups.
O
OR
H2N
O
OR
H
NR2
O
Nucleophilic
Atom Non-Nucleophilic
Atom
Amine Amide Derivative
12. Peptide Synthesis: Amine Protecting Groups
1. Amino groups are normally protected by
converting them to amides. The nitrogen atom
in an amide does not behave as a nucleophile
and will not react with carboxyl groups.
2. Benzyloxycarbonyl (C6H5CH2O—) is a common
protecting group. It is abbreviated as Z or Cbz.
3. Cbz-protection is carried out by treating an
amino acid with benzyloxycarbonyl chloride.
13. Amine Protecting Groups: Benzyloxycarbonyl
O
O Cl
Benzyloxycarbonyl
chloride
(Cbz-Cl)
O
O N
H
R
Benzyloxycarbonyl
group
14. Amine Protecting Groups: Introduction of
Benzyloxycarbonyl Protecting Groups
O
O
H3N
H
O
O Cl
1. NaOH
H2O
2. H3O+
O
OH
H
N
H
O
O
(85%)
16. •An advantage of the benzyloxycarbonyl
protecting group is that it is easily removed by:
•a)catalytic hydrogenolysis under extremely mild
conditions
•b) cleavage with HBr in acetic acid
•Both reagents cleave the relatively weak
benzylic carbon-oxygen ether bond, albeit by
different mechanisms
Cleavage of Cbz Groups
17. Hydrogenolysis of Cbz Groups
O
N
H
H
N
H
O
O OEt
O
H2, Pd/C
solvent
O
N
H
H
N
H
O
HO OEt
O
Carbamic Acid
(Very Unstable)
H2C H
Toluene
(volatile)
ethyl ester is
stable to
hydrogenolysis
18. Hydrogenolysis of Cbz Groups
O
N
H
H
N
H
O
HO OEt
O
Spontaneous
decarboxylation
O
N
H
H2N
H
OEt
O
C
O
O
(100%)
19. Acid-Mediated Cleavage of Cbz Groups
O
N
H
H
N
H
O
O OEt
O
HBr
acetic acid
O
N
H
H3N
H
OEt
O
H2C Br
Benzyl
bromide
(volatile)
Br
C
O
O
(82%)
20. Amine Protecting Groups: tert-Butyloxycarbonyl
O
O O
Di-tert-butyl dicarbonate
(Boc 'anhydride')
O
O N
H
R
tert-Butyloxycarbonyl
group
O
O O
O
O
O Cl
tert-Butyl chloride
(instablity limits use)
22. Cleavage of Boc Groups
The tert-butyloxycabonyl protecting group is readily
removed by treatment wit strong, anhydrous BrØnsted
acids:
a) cleavage with trifluoroacetic acid in methylene
chloride
b) cleavage with HBr in acetic acid
Both reagents cleave the quaternary carbon-oxygen
ether bond by an acid-mediated elimination reaction.
23. Acid-Mediated Cleavage of Boc Groups
O
N
H
H
N
H
O
O OEt
O
O
N
H
H3N
H
OEt
O
Butene
(volatile)
C
O
O
(high yield)
CH3H3C
H H
O
OHF3C
trifluoroacetic
acid
O
OF3C
25. Peptide Synthesis: Carboxyl Protecting Groups
Carboxyl groups are normally protected as
esters.
Deprotection of methyl and ethyl esters is by
hydrolysis in base.
Benzyl esters can be cleaved by
hydrogenolysis.
26. Simultaneous Hydrogenolysis of Cbz
Group and Benzyl Ester
O
N
H
H
N
H
O
O O
O
H2, Pd/C
solvent
O
N
H
H
N
H
O
HO OH
O
Carbamic Acid
(Very Unstable)
H2C H
Toluene
(volatile)
27. Simultaneous Hydrogenolysis of Cbz
Group and Benzyl Ester
O
N
H
H
N
H
O
HO OEt
O
Spontaneous
decarboxylation
O
N
H
H2N
H
OEt
O
C
O
O
(87%)
29. Peptide Synthesis: Forming Peptide Bonds
The two major methods are:
1. coupling of suitably protected amino acids
using N,N'-dicyclohexylcarbodiimide (DCC)
2. via an active ester of the N-terminal amino
acid.
30. N,N'-Dicyclohexylcarbodiimide (DCC) is a
Powerful Dehydrating Agent
N C N
N,N'-dicyclohexylcarbodiimide
O
N
H
N
H
N,N'-dicyclohexylurea
'H2O'
O
OR1
H
H
N
R2H
O
NR1
R2
H
Amide
O
OR1
H
N
R2H
H
-H2OVery high
temps
31. • 2. Couple the two protected amino acids.
Peptide Coupling is a Condensation Reaction
O
OH
N
H
O
O
N
H
H
H PG
PG
O
N
H
N
H
H
PGPG
O
O
Peptide
Coupling -H2O
32. • 2. Couple the two protected amino acids.
DCC-Mediated Peptide Coupling
O
OH
N
H O
O
N
H
H
H
Et
O
N
H
N
H
Cbz
H
O
O
Et
DCC, CHCl3
(83%)
Cbz
33. Mechanism of DCC-Promoted Coupling
O
OH
N
H
H
Cbz N C N
O
O
N
H
H
Cbz N
H
N
1,2-Addition
O-Acylisourea
derivative
34. O-Acylisoureas are Powerful
Acylating Agents
The O-acylisourea
intermediate formed by
addition of the Cbz-
protected amino acid to
DCCI is similar in
structure to an acid
anhydride and acts as an
acylating agent.
O
O
N
H
H
Cbz N
H
N
O-Acylisourea
Derivative
H3C O
O
CH3
O
Acid
Anhydride
35. Attack by the
amine function of
the carboxyl-
protected amino
acid on the
carbonyl group
leads to
nucleophilic acyl
substitution.
Mechanism of DCC-Promoted Coupling
O
O
N
H
Cbz N
H
N
O
OEt
N
H
H
OH
O
N
H
Cbz N
H
N
N
H
OEtO
1,2-Addition
then
Proton Transfer
Unstable
Intermediate
36. Attack by the
amine function of
the carboxyl-
protected amino
acid on the
carbonyl group
leads to
nucleophilic acyl
substitution.
Mechanism of DCC-Promoted Coupling
OH
O
N
H
Cbz N
H
N
N
H
OEtO
Unstable
Intermediate
O
N
H
N
H
Cbz
OEt
OHO
N
H
N
H
N,N'-dicyclohexylurea
Dipeptide
Elimination
37. Peptide Synthesis: Forming Peptide Bonds
The two major methods are:
1. coupling of suitably protected amino acids
using N,N'-dicyclohexylcarbodiimide (DCCI)
2. via an active ester of the N-terminal amino
acid.
38. Peptide Synthesis: Active Ester Method
A p-nitrophenyl ester is an example of an "active
ester.”
p-Nitrophenyl is a better leaving group than methyl
or ethyl, and p-nitrophenyl esters are more reactive
in nucleophilic acyl substitution.
O
O
Alkyl
O
O
N+
O–
O
4-Nitrophenyl
(PNP) Ester
Alkyl Ester
is a more powerful
acylating agent than......
39. Peptide Synthesis: Active Ester Method
O
O
N
H
Cbz
O
OEt
N
H
H
OH
O
N
H
Cbz
N
H
OEtO
1,2-Addition
then
Proton Transfer
Unstable
Intermediate
NO2
NO2
40. Peptide Synthesis: Active Ester Method
Unstable
Intermediate
O
N
H
N
H
Cbz
OEt
OH
para-Nitrophenol Dipeptide
Elimination
OH
O
N
H
Cbz
N
H
OEtO
NO2
O2N OH
42. Solid Phase Peptide Synthesis
In solid-phase synthesis, the starting material is bonded
to an inert solid support.
Reactants are added in solution.
Reaction occurs at the interface between the solid and
the solution. Because the starting material is bonded to
the solid, any product from the starting material
remains bonded as well.
Purification involves simply washing the byproducts
from the solid support.
43. •The solid support is a copolymer of styrene and
divinylbenzene. It is represented above as if it
were polystyrene. Cross-linking with
divinylbenzene simply provides a more rigid
polymer.
Polystyrene is the Basis for the Solid Support
C
C
C
C
C
C
C
C
C
C
H H H H H H H H
HHHH
H H
44. Functionalization of Polystyrene
•Treating the polymeric support with
chloromethyl methyl ether (ClCH2OCH3) and
SnCl4 places ClCH2 side chains on some of
the benzene rings.
46. Solid Phase Peptide Synthesis
CH2 CH2
ClCl
The side chain chloromethyl group is a benzylic
halide, reactive toward nucleophilic substitution
(SN2).
47. 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.
Solid Phase Peptide Synthesis
CH2 CH2
ClCl
55. •Merrifield automated his solid-phase method.
•Synthesized a nonapeptide (bradykinin) in
1962 in 8 days in 68% yield.
•Synthesized ribonuclease (124 amino acids)
in 1969.
369 reactions; 11,391 steps
Merrifield Procedure