Transcript Slide 1

NH2
BOCHN
O
SBn
Ph
O
Ph
couple
Cy
+
O
O
O
O
O
O
N
H
N C N Cy
H
N
H
O
SBn
H
• Now, we need to attach the other AA (aminoadipic acid)
– First we need to selectively deprotect (at cys) to give the free
amine
NH3+
O
SH
-O2C
N
H
O
H
N
CO2-
Deprotection:
Ph
O
O
O
O
N
H
N
H
O
Ph
+
O
H+
O
O
H
O
N
H
N
H
O
SBn
SBn
free amine
Ph
O
O
Ph
O
N
H
NH2
O
H
O
N
H
SBn
+
N
H
O
stable cation
SBn
+
H
Note: You will not be required to know mechanism for
removal of BOC with acid.
You are req’d to know that H+ removes BOC to give
amine
H
O
O
-CO2
H
H
Ph
O
O
O
N
H
NH-PG
PG O
NH2
SBn
O
OH
O
DCC
SBn
NH-PG
O
PG O
N
H
O
H
N
O
O
deprotect
SH
NH2
HO
O
O
N
H
H
N
O
O
OH
O
Ph
• Solution-phase synthesis is very long
– Okay for small peptides (~2-4)
• For longer peptides, we use solid-phase supported
synthesis
– Similar to oligonucleotide solid-phase synthesis (CPG)
• Uses protection/activation strategy
• Molecule is attached to solid support
• The first peptide synthesis on a solid support was
performed by Merrifield (first reported in 1963; Nobel
Prize in 1984)
–
–
–
–
Polystyrene resin beads (support)
Support is functionalized for attachment
There have since been several modifications to the resin
Can make ~ 30 – long peptides with high efficiency
~99% / step
(0.99)30 = 75% yield
Overall synthesis
• Standard for proteingenic AA’s, but technique can be used for the
non-proteingenic AA’s
CH2Cl
Merrifield Resin
AA1
C AA 1
H2
AA2
AA3
AA4
C AA 1 AA 2 AA 3 AA 4
H2
O
CH2Cl
+
H
N boc
-O
R1
Resin
Attach protected amino acid to
resin as a benzyl ester
1
O
C O
H2
Remove BOC protecting group
2
H
N boc
R1
CF3CO2H, CH2Cl2
O
NH2
C O
H2
R1
O
Couple the second
BOC-protected amino acid
3
H
N boc , DCC
-O
R2
R2
O
C O
H2
H
N
R1
O
N boc
H
Amine is protected
prior to attachment
R2
O
C O
H2
H
N
O
R1
Remove BOC protecting group
4
R2
O
C O
H2
Repeat 3 - 4 cycle to build
the polypeptide chain. Last to
be attached is the N-terminal
AA
N boc
H
3
-
Cleave completed polypeptide
from resin
NH2
O
R1
4
R2
O
C O
H2
H
N
H
N
R1
5
O
R
N
H
polypeptide
O
HF
R2
O
CH2F
+
NH2
H
N
HO
R1
O
R
N
H
polypeptide
NH2
O