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L. Iddon et al. / Bioorg. Med. Chem. Lett. 21 (2011) 3122–3127
Table 2
Copper wire catalysed experiments using alkyne 3a (analytical radiochemical yield by HPLC)
Reaction
temperature
pH
Solvents (v/v)
Pre-activation
time (min)
Other additives
Analytical yield (%) at:
5 min
15 min
30 min
1
2
3
4
5
6
7
8
9
10
80 °C
80 °C
rt
80 °C
80 °C
80 °C
rt
rt
rt
rt
5.0
5.0
5.0
6.0
4.0
8.0
5.0
5.0
5.0
5.0
DMF/AB (1:3)
DMF/AB (1:3)
DMF/AB (1:3)
DMF/PB (1:3)
DMF/FB (1:3)
DMF/TB (1:3)
DMF/AB (1:3)
DMF/AB (1:3)
DMF/AB (1:3)
DMSO/AB (7:3)
0
30
150
0
0
0
0
0
0
0
—
—
—
—
—
—
52
>98
0
4
3
2
67
0
35
0
95
—
7
—
—
—
>98
0
54
0
—
—
30
—
—
—
—
48
>98
0
40 mol % CuSO4, BPDS (9) (2 equiv)
40 mol % CuSO4,
BPDS (9) (2 equiv)
MonoPhos ligand (2 equiv)
All buffers are 250 mM concentrations. Sodium acetate buffer (AB) pH 5.0; sodium phosphate buffer (PB) pH 6.0; ammonium formate buffer (FB) pH 4.0; Tris buffer (TB) pH
8.0. Each experiment contained 100–120 mg of a copper wire coil, diameter 0.1 mm, and was used with out any treatment (rt = room temperature). All reactions carried out
using 100 l
l of [18F]fluoroethyl azide (8).
Table 3
Competitive binding assay IC50 values using 1a–5a and [19F]-1b–6b displacing [111In]-DTPA-octreotide on AR42J tumour cells and Log D values of [18F]-1b–6b
Peptides
Alkyne analogue (a) IC50 (nM)
Triazole analogue (b) IC50 (nM)
Control
Log D of 18F-triazole
1
2
3
4
5
6
5.3 0.75
5.1 2.1
1.4 0.1
1.8 0.8
1.0 0.3
—
10.8 5.9
13.2 7.8
4.0 1.4
2.9 1.3
1.6 0.2
>10.0 (mM)
—
—
—
—
—
—
—
À2.68
À2.77
À1.83
À1.5
À2.26
À1.14
—
Octreotide
—
14.7 7.7
N.B. (n = 4 for each concentration and assay repeated three times). Log D partition co-efficient measurements 1b–5b (n = 3), 6b (n = 6). IC50 values of AlF-NOTA-octreotide, Ga-
NOTA-octreotide found by Laverman et al.18 were 3.6 0.6, 13.0 3.0 nM, respectively. Literature IC50 value of octreotide = 0.5 nM used in a competitive binding assay with
125I-somatostatin-14.41
[
19F]-5b showed the highest affinity with an IC50 value of
References and notes
1.6 0.2 nM. PEGylation of the peptides, through the addition of
six sequential ethylene glycol groups, appeared not to significantly
affect the overall affinity of [19F]-1b and [19F]-2b giving IC50 values
of 10.8 5.9 nM and 13.2 7.8 nM, respectively. In comparison
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In conclusion, we have screened five novel alkyne functional-
ised octreotate analogues in the click reaction with [18F]2-fluoro-
ethyl azide. Our studies found the most reactive alkynes were
G-TOCA (3a) and bAG-TOCA (5a), showing complete conversion
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Supplementary data
Supplementary data associated with this article can be found, in