chapter 3
Protein Isolation and Determination of Amino Acid Sequence
Coupling of the
C-terminal residue
to the solid support
Removal of the protective
group by acidification
Covalent joining of two
amino acids by using the
condensing agent
Removal of the protective
Dipeptidal group anchored
to the resin and ready for
another cycle of amino
acid addition
Steps in the chemical synthesis of a polypeptide by the solid-phase technique.
Fmoc Solid-Phase Peptide Synthesis
Solid-phase polypeptide synthesis that uses the t-BOC
group to protect the N"-amino group is a major proce-
dure used by protein chemists. However, another solid-
phase procedure is frequently used for the chemical
synthesis of peptides and proteins of interest; this is the
9-fluorenylmethoxycarbonyl (Fmoc) procedure (Figure
3-15). The Fmoc method for solid-phase peptide synthesis
uses the Fmoc group for protecting the N“-amino group.
In contrast to the t-BOC group method which requires acid
for removal of the N“-amino protective group, the Fmoc
group can be removed by a mild base. A piperidine solution
in N,N-dimethylformamide or N-methylpyrrolidone is
generally used for the removal of the Fmoc group; an-
hydrous trifluoroacetic acid is used to remove the t-BOC
group. This Fmoc procedure is technically simpler and
chemically less complex than the t-BOC procedure. Be-
cause the Fmoc protecting group can be removed by base,
the linkage of the peptide to the resin support does not
have to be stable under acidic conditions as in the t-BOC
The Fmoc procedure offers more flexible reaction con-
ditions and more reagent options. Because of the milder
conditions of peptide synthesis, the Fmoc procedure
is widely used for the synthesis of modified polypep-
tides that are phosphorylated, sulfated, or glycosylated.
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