22
Bioorganic Chemistry
catalytic activity of the type desired. This
approach has proven successful in a range
of systems.
4.4
Solid-phase Peptide Synthesis
Solid-phase peptide synthesis (SPPS) is a
technique that allows the semi- or fully
automatic synthesis of relatively long pep-
tides without the need for puriFcation of
reaction intermediates. The basic strategy
of SPPS is outlined in ±ig. 17. The Frst
amino acid of the peptide is tethered to
a derivatized resin via its carboxyl group.
The amino terminus of this Frst amino
acid is freed from its protecting group by
an appropriate cleaving system and then
treated with the activated carboxyl of the
nex
tam
inoac
idtobeaddedtothecha
in
.
The amino group of this newly added
amino acid is also protected to prevent
condensation with the activated carboxyl.
After the new peptide bond is formed, the
new terminal amino group is deprotected
and the cycle of condensation followed by
deprotection can continue. In addition to
protection of the alpha amino group of the
newly added amino acid, the chemically
reactive side chains of the peptide (such as
the amino group of lysine and the carboxyl
group of aspartic acid) are also protected
with groups that will not be cleaved until
after the peptide synthesis is complete. A
major advantage of SPPS is that after each
of these steps, the reaction by-products can
be flushed from the container holding the
resin. The peptide that is attached to the in-
soluble resin will remain in the container.
The alternative to SPPS is solution-phase
peptide synthesis, which, as with most
organic synthesis, requires the isolation
and puriFcation of reaction intermediates,
usually after each condensation reaction.
Thus, making a peptide of even modest
length becomes a major undertaking. In
addition to removing a large amount of the
puriFcation from the process, SPPS lends
itself very well to automation. A modern
automatic solid-phase peptide synthesizer
can make a peptide of 20 residues in length
in about a day. The equivalent synthesis by
solution methods would typically be on
the order of months. Since each interme-
diate is not isolated and puriFed, the key to
making SPPS a viable technique was the
O
R
1
O
H
N
O
O
Link to
resin
Protecting group
TFA
Protecting group
cleavage
O
R
1
O
NH
2
Acylation
X
R
2
O
H
N
O
O
Activated
ester
O
R
1
O
H
N
O
R
2
N
H
O
O
(1) Further rounds of
deprotection and acylation
(2) Side-chain deprotection
and resin cleavage
Deprotection
Fig. 17
Strategy of solid-phase peptide synthesis using BOC chemistry.
previous page 696 Encyclopedia of Molecular Cell Biology and Molecular Medicine read online next page 698 Encyclopedia of Molecular Cell Biology and Molecular Medicine read online Home Toggle text on/off