B. Teng et al. / Bioorg. Med. Chem. Lett. 17 (2007) 3440–3444
3443
Table 2. The radiochemical yields of Tc-99m-labeled thymidine analogs obtained by using tricine as coligand
Compound
Radiochemical yield (%)/temperature (°C)
50 °C/time (min)
25 °C/time (min)
100 °C/time (min)
5
15
30
5
15
30
5
15
30
11
31
32
23
19
34
37
31
24
43
45
35
29
42
32
26
15
50
45
37
27
51
52
59
31
43
31
28
19
57
46
50
25
62
67
71
35
15a
15b
15c
Table 3. The radiochemical yields of Tc-99m-labeled thymidine analogs obtained by EDDA/tricine exchange labeling
Compound
Radiochemical yield (%)/temperature (°C)
50 °C/time (min)
25 °C/time (min)
100 °C/time (min)
5
15
30
5
15
30
5
15
30
11
45
30
36
24
48
45
45
25
52
54
61
31
86
60
72
39
75
65
74
43
79
74
81
42
88
79
84
59
95
89
94
63
95
92
90
62
15a
15b
15c
x-amino acids (Scheme 3). First, 30-amino-30-deoxy-50-O-
(4,40-dimethoxytrityl)-thymidine reacted with Boc-pro-
tected x-amino acids to give compound 12a–c, following
that DMTr and Boc protecting groups were removed in
one pot by addition of TFA at 0 °C for 30 min to give
compound 13a–c. And then, thymidine analogs with dif-
ferent chain lengths were conjugated with Boc-HYNIC-
NHS to give compound 14a–c. Finally, the deprotection
of compound 14a–c was performed with the same proce-
dure of HYNIC-thymidine to give 30-{[(hydrazinopyri-
dine-3-carbonyl-amino)-1-oxobutyl]-amino} thymidine
(compound 15a), 30-{[(hydrazinopyridine-3-carbonyl-
amino)-1-oxohexyl]-amino}thymidine (compound 15b),
and 30-{[(hydrazinopyridine-3-carbonyl-amino)-1-oxoun-
decanyl]-amino} thymidine (compound 15c).
It has been shown that the choice of chelating system
has profound influence upon the radiochemistry and
labeling conditions. EDDA/tricine exchange labeling
could produce better radiochemical yield than the other
labeling methods. With increase in reaction temperature,
the radiochemical yield obviously increased in the radio-
labeling experiments. The best radiochemical yields
(95%, 89%, 94% and 63%) were obtained by using com-
pounds 11, 15a–c, respectively, as precursors when the
reaction temperature was set at 100 °C. The optimized
labeling time was 15 min when the reaction temperature
was 100 °C; the prolonged reaction time could not
increase obviously the radiochemical yield. On the
other hand, the spacer is an important factor which
influences the radiochemical yield. Overlong spacer
decreased obviously the radiochemical yield in labeling
experiment.
These HYNIC-thymidine analogs were conjugated with
technetium-99m to give compounds 16, 16a–c. We ex-
plored two different labeling methods including direct
labeling with N-(2-hydroxy-1,1-bis(hydroxymethyl)
ethyl)glycine (tricine) and Ethylenediamine-N,N0-diace-
tic acid (EDDA)/tricine exchange labeling.
In summary, we have synthesized several novel thymi-
dine analogs which could be labeled easily with techne-
tium-99m. We suggested that it is advisable when the
length of alkyl spacers was set as n = 3, 5 or none spacer.
Additionally, we have explored the technetium-99m-la-
beled conditions of these thymidine analogs and found
that the optimized labeling conditions were the reaction
temperature 100 °C and reaction time 15 min. The bio-
distribution and imaging of these labeled thymidine ana-
logs in tumor-bearing mice are underway in our
laboratory. The effect of different spacers between thy-
midine analogs with HYNIC on biological function of
these labeled thymidine analogs will also be published
elsewhere.
The reaction time (5–30 min) and temperature (25–
100 °C) were varied to optimize the labeling reaction con-
ditions. The amount of thymidine analogs (compounds
11, 15a–c) (10 lg), tricine (40 mg) and EDDA (1.5 mg),
Na99mTcO4 (150 MBq) were kept constant. The labeled
mixture was passed through a Sep-Pak Plus C18 cartridge
and then the final labeling product was eluted by alcohol.
The radiochemical yields and radiochemical purity of
technetium-99m-labeled thymidine analogs were deter-
mined by TLC on three systems and the Rf values of tech-
netium-99m-species are listed in Table 1.
Acknowledgments
The radiochemical purity of all labeled thymidine ana-
logs was over 97% through purification using Sep-Pak
Plus C18 cartridge. The radiochemical yields obtained
by different labeling methods are, respectively, shown
in Tables 2 and 3.
This study in part was supported by the National Center
NanoScience and Technology (China 90406024-8),
National Natural Science Foundation of China
(30600154). The radiochemical data were acquired at