Chemistry Reference
In-Depth Information
HO
O
N
ssON
O
O
O
ssON
N
oligonucleotide
synthesis
OH
7
8
O
O
single-stranded ON = 5'-UCACUUACAGGAUCUAUAA
N
N
N
siRNA
O
siRNA
O
18
F
O
O
N
3
CuSO
4,
TBTA
Na ascorbate
H
2
O/DMSO/
t
BuOH
H
H
+
18
F
OH
OH
81
8
2
8
18
F
O
N
3
84
18
F
O
N
N
N
siRNA
O
O
H
85
OH
SCHEME 7.16
CuAAC in the labeling of siRNA using aryl- and benzyl-azides as prosthetic
groups.
7.4 OTHER METHODS
Several methods relevant of click chemistry and specific to carbohydrate chemistry
have been investigated to couple a sugar and a biomolecule suitable to provide a
radiotracer. The unique reactivity of the anomeric center is a key element in these
researches. The aldehydic form has been used in the Maillard reaction and oxime
formation whereas the reactivity of the anomeric alcohol has been used in the gly-
cosylation reaction. Thiosugars have also been used for unsymmetrical disulfides
formation.
7.4.1 Maillard Reaction
Radiotracers based on somatostatin receptor ligands are useful for cancer imaging
of somatostatin receptor (SR) positive neuroendocrine tumors. Octreotide is a cyclic
eight amino acid peptide which binds to the SRs overexpressed on the surface of
neuroendocrine tumors. Several octreotide analogs have been developed as potential
radiotracers [79, 80]. Carbohydration of octreotide has been investigated as a means
to reduce lipophilicity of the peptide and to limit its elimination by the liver.
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