Preparation and biodistribution of novel 99mTc(CO) 3-CNR complexes for myocardial imaging

Article abstract of DOI:10.1002/jlcr.1151

We evaluated lipophilicity and biodistribution of a series of ^99mTc(CO)₃-ether isonitrile complexes to determine whether different lipophilicity and structure of isonitrile ligands would improve the imaging properties of the radiopharmaceutical for the heart. Novel ^99mTc(CO)₃-MIBI analogs were prepared and analyzed by radio-HPLC, and their lipophilicity was determined. These new complexes could be bi- or tri-substituted in specified pH conditions like ^99mTc(CO) ₃-MIBI. These new complexes exhibited low liver, lungs and blood uptake compared with [^99mTc(CO)₃(MIBI)₃] ⁺ though their heart uptake was not so high. Among these complexes, [^99mTc(CO)₃(EPI)₂(OH₂)]⁺ showed higher target to non-target ratios at 5 and 30 min post-injection than that of [^99mTc(CO)₃(MIBI)₃]⁺. Copyright

Full text of DOI:10.1002/jlcr.1151

Journal of Labelled Compounds and Radiopharmaceuticals
J Label Compd Radiopharm 2007; 50: 13–18.
Published online in Wiley InterScience
JLCR
(www.interscience.wiley.com). DOI: 10.1002/jlcr.1151
Research Article
Preparation and biodistribution of novel 99mTc(CO)3-CNR
complexes for myocardial imaging
GUIYANG HAO1,2, JIANYING ZANG1 and BOLI LIU1,*
1 Department of Chemistry, Beijing Normal University, Beijing, People’s Republic of China
2 Molecular Imaging Center, National Institute of Radiological Sciences, Chiba, Japan
Received 20 September 2006; Revised 6 October 2006; Accepted 6 October 2006
Abstract: We evaluated lipophilicity and biodistribution of a series of 99mTc(CO)3-ether isonitrile complexes to
determine whether different lipophilicity and structure of isonitrile ligands would improve the imaging properties of
the radiopharmaceutical for the heart. Novel 99mTc(CO)3-MIBI analogs were prepared and analyzed by radio-HPLC,
and their lipophilicity was determined. These new complexes could be bi- or tri-substituted in specified pH
conditions like 99mTc(CO)3-MIBI. These new complexes exhibited low liver, lungs and blood uptake compared with
[
99mTc(CO)3(MIBI)3]+ though their heart uptake was not so high. Among these complexes, [99mTc(CO)3(EPI)2(OH2)]+
showed higher target to non-target ratios at 5 and 30 min post-injection than that of [99mTc(CO)3(MIBI)3]+. Copyright
# 2007 John Wiley & Sons, Ltd.
Keywords: Tc-99m; tricarbonyl; isonitrile; myocardial imaging
Introduction
with CO ligands expand the available range of com-
pounds significantly. There has been a lot of published
research work utilizing this new precursor to develop
new radiopharmaceuticals.3,4
Recently, Alberto1 reported the synthesis and
applications of the astonishing complex fac-
[
99mTc(CO)3(OH2)3]+. This simple complex combines a
99mTc-MIBI is widely used in myocardial perfusion
imaging and human tumor imaging. Therefore, pre-
paration and preliminary evaluations of 99mTc(CO)3-
MIBI as a myocardial imaging agent5–8 and a functional
probe of Pgp transport activity9 followed the intro-
duction of the attractive precursor of fac-
‘lower’ organometallic half with three carbonyl ligands
with an ‘upper’ Werner-type half with three water
molecules as ligands.2 It has favorable properties
mainly attributed to its unusual ligand set. The s-
bound water ligands are readily displaced by other
ligands, but in combination with other donor–acceptor
ligands, the carbonyl groups impart a high kinetic
stability on [Tc(CO)3]+ derivatives. In addition, a high
kinetic stability results from the d6 low-spin electron
configuration of the TcI complex. Although it was used
in hexakis(2-methoxyisobutyl isonitrile) 99mTc(I)
[
99mTc(CO)3(OH2)3]+. Our group independently de-
signed 99mTc(CO)3-MIBI as
myocardial imaging
a
agent which showed high potential both in mice
and dogs.
Examination of the uptake mechanism in myocardial
and carcinoma cells indicates that the lipophilicity,
cationic charge and the ligand of MIBI itself of 99mTc-
MIBI play a significant role in its accumulation and
retention. Moreover, it can be seen from our previous
research that 99mTc(CO)3-MIBI might be bi-, tri-sub-
stituted product or both in specified pH conditions.7 It
is still unknown whether this radiolabeling reaction
phenomenon is only specific for MIBI or not. Therefore,
we prepared novel 99mTc(CO)3-ether isonitrile com-
plexes to study this experimental phenomenon and
(
99mTc-MIBI), the oxidation state +1 is rather unusual
in 99mTc imaging agents and difficult to stabilize with
Werner-type ligands (typically with an N, O, or S donor
set) alone. In this respect, organometallic complexes
*Correspondence to: Boli Liu, Department of Chemistry, Beijing
Normal University, Beijing 100875, People’s Republic of China.
E-mail: liuboli@bnu.edu.cn
Contract/grant sponsor: National 211 Engineering Projects
Copyright # 2007 John Wiley & Sons, Ltd.

14 G. HAO ET AL.
the effects of different lipophilicity and ligand struc-
tures on biodistribution.
that appeared at the beginning of radiolabeling course
and would disappear quickly with the substitution
going on. When pH=9.0–10.0, all three H2O ligands of
was shown to be readily substituted by isonitrile
ligands. However, the sequential reaction would stop
at bi-substitution when pH=3.0–4.0. When pH lied
between the two scopes of 3.0–4.0 and 9.0-10.0,
tri-substitution only partially occurred and the ratios
of bi- to tri-complex were determined by the pH values.
These results above mentioned were same as that
Results and discussion
Synthesis
The general synthetic approach for the isonitrile
derivatives (CNR) is shown in Scheme 1. The isonitrile
derivatives could be prepared conveniently from com-
mercial available alkoxyl amines in a two-step synth-
esis (Table 1).10–12 The use of POCl3/pyridine for
dehydration of formamide was more convenient and
safer than other dehydration systems. The two steps
were both exothermic reactions, so the good cooling
conditions should be guaranteed. The Vigreux column
was necessary to collect the products with high purity,
though there would be a little loss in yields. All these
isonitriles could be stored at ꢀ208C under N2 for
radiolabeling.
of 99mTc(CO)3-MIBI,7 so it should be
a common
characteristic for ether isonitriles reacting with
[
99mTc(CO)3(OH2)3]+.
All complexes were stable within 6 h at room
temperature. Their lipophilicity was determined by
partition between 1-octanol and PBS (Table 3). Most
of them showed low lipophilicity because of the
hydrophilicity of 99mTc(CO)+3 core. The lipophilicity
turned higher when the substituent number changed
from two to three for the same isonitrile ligand. The
Table 2 Results of radiolabeling reaction in pH=3.0–4.0 and
9.0–10.0
Radiolabeling
The [99mTc(CO)3(OH2)3]+ precursor was prepared in
> 98% yield according to the method of Alberto et al.1
99mTc(CO)3-CNR complexes were prepared as de-
scribed in the experimental section (Table 1). They
were analyzed by radio-TLC and radio-HPLC, and the
results were shown in Table 2. Besides, there was one
radio-HPLC peak corresponding to the mono-complex
pH
condition
Complex HPLC elution
condition TETAa:
MeOH (v:v)
Rt (min) Yield (%)
1a
2a
3a
4a
5a
50:50
40:60
30:70
20:80
30:70
7.9
9.0
3.0–4.0
6.9
5.6
7.1
>98%
1b
2b
3b
4b
5b
50:50
40:60
30:70
20:80
30:70
9.5
10.7
10.0
7.9
R-NH2 + HCOOC2H5
R-NHCHO+ HOC2H5
9.0–10.0
>98%
R-N≡C+ PyHCl + PyHPO3
R-NHCHO + POCl3+ Py
9.2
a TETA: triethylamine phosphate buffer, 0.05 M, pH 2.25.
Scheme 1 Synthesis of isonitrile ligands.
Table 1 The isonitrile ligands and 99mTc(CO)3-CNR complexes
Ligand
Complex
No.
MEI
MPI
EPI
CH3OCH2CH2NC
[
[
[
[
[
[
[
[
99mTc(CO)3(MEI)2(OH2)]+
99mTc(CO)3(MEI)3]+
1a
1b
2a
2b
3a
3b
4a
4b
CH3OCH2CH2CH2NC
CH3CH2OCH2CH2CH2NC
(CH3)2CHOCH2CH2CH2NC
99mTc(CO)3(MPI)2(OH2)]+
99mTc(CO)3(MPI)3]+
99mTc(CO)3(EPI)2(OH2)]+
99mTc(CO)3(EPI)3]+
99mTc(CO)3(IPPI)2(OH2)]+
99mTc(CO)3(IPPI)3]+
IPPI
THFMI
MIBI
[
[
99mTc(CO)3(THFMI)2(OH2)]+
99mTc(CO)3(THFMI)3]+
5a
5b
N ≡ C
O
CH3OC(CH3)2CH2NC
[
[
99mTc(CO)3(MIBI)2(OH2)]+
99mTc(CO)3(MIBI)3]+
6a
6b
Copyright # 2007 John Wiley & Sons, Ltd.
J Label Compd Radiopharm 2007; 50: 13–18
DOI: 10.1002.jlcr

PREPARATION AND BIODISTRIBUTION OF NOVEL 99MTC(CO)3-CNR COMPLEXES 15
tri-substituted [99mTc(CO)3(IPPI)3]+ had the highest
lipophilicity, and the lipophilicity of
99mTc(CO)3
blood, liver, lungs, kidneys and spleen, were collected
at 5, 30, and 60 min post-injection. Ten complexes
showed distinct accumulation in heart, liver and lungs
etc. The heart uptake of the new complexes except
[
(MEI)2(OH2)]+ was the lowest. The lipophilicity
would increase with the number of carbon in ligands
increasing for MEI, MPI, EPI and IPPI. At the same
time, the sequences of lipophilicity of the correspond-
ing complexes were as below: 1a52a53a54a,
1b52b53b54b. Therefore, the structure of the
isonitriles strongly affects the lipophilicity of the
complexes.
[
99mTc(CO)3(EPI)2(OH2)]+ and [99mTc(CO)3(IPPI)2(OH2)]+
lay in a low level, and the activity in heart did not show
a good retention from 5 to 30 min post-injection. For
99mTc-MIBI and [99mTc(CO)3(MIBI)3]+ the heart uptake
at 30 min post-injection in mice could be 25 and
22%ID/g,13 respectively. However, clearance from liver,
lungs and blood was very fast for the new complexes
during the early stage post-injection, which resulted
in apparently low uptake of liver, lungs and blood at
30 and 60 min post-injection. Therefore, the new
complexes exhibited lower liver, lungs and blood
Biodistribution
Table 4 showed the tissue distributions of the novel
99mTc(CO)3-CNR complexes. Tissues, including heart,
Table 3 Partition coefficients of 99mTc(CO)3-CNR complexes
Complex
1a
0.09
1b
0.10
2a
0.31
2b
0.62
3a
0.58
3b
4a
4b
5a
0.14
5b
0.36
P
log P
1.58
0.20
2.79
0.44
10.86
1.04
ꢀ1.04
ꢀ1.00
ꢀ0.51
ꢀ0.21
ꢀ0.23
ꢀ0.87
ꢀ0.44
Table 4 Tissue distributions of all the complexes at 5, 30, and 60 min post-injection
Complex
Time(min)
%ID/g in tissues
Blood
Heart
Liver
10.24 ꢁ 1.64
Lungs
Kidneys
Spleen
5
1.29 ꢁ 0.16
0.39 ꢁ 0.02
0.31 ꢁ 0.01
2.32 ꢁ 0.20
0.87 ꢁ 0.11
0.39 ꢁ 0.02
1.09 ꢁ 0.24
0.36 ꢁ 0.01
0.20 ꢁ 0.02
2.08 ꢁ 0.27
0.44 ꢁ 0.07
0.21 ꢁ 0.02
1.44 ꢁ 0.10
0.42 ꢁ 0.03
0.26 ꢁ 0.02
3.66 ꢁ 0.67
0.75 ꢁ 0.01
0.42 ꢁ 0.02
1.63 ꢁ 0.19
0.47 ꢁ 0.07
0.94 ꢁ 0.89
6.65 ꢁ 0.74
1.18 ꢁ 0.04
0.63 ꢁ 0.08
0.60 ꢁ 0.06
0.14 ꢁ 0.02
0.08 ꢁ 0.01
1.00 ꢁ 0.13
0.23 ꢁ 0.01
0.11 ꢁ 0.06
3.04 ꢁ 0.34
2.10 ꢁ 0.02
1.63 ꢁ 0.25
7.74 ꢁ 1.31
4.32 ꢁ 0.48
2.02 ꢁ 0.82
11.44 ꢁ 2.14
10.35 ꢁ 1.14
7.54 ꢁ 2.18
15.39 ꢁ 1.04
9.71 ꢁ 2.24
5.26 ꢁ 0.15
28.87 ꢁ 3.19
19.48 ꢁ 1.96
12.39 ꢁ 0.59
15.98 ꢁ 6.61
7.14 ꢁ 1.12
4.71 ꢁ 1.58
17.03 ꢁ 4.45
17.08 ꢁ 3.90
14.99 ꢁ 3.09
5.77 ꢁ 1.34
1.99 ꢁ 0.27
1.18 ꢁ 0.28
4.68 ꢁ 0.53
2.55 ꢁ 0.20
2.16 ꢁ 0.18
5.00 ꢁ 1.02
4.67 ꢁ 0.78
2.52 ꢁ 0.73
2.16 ꢁ 0.22
1.27 ꢁ 0.12
1.34 ꢁ 0.19
3.60 ꢁ 0.37
2.10 ꢁ 0.12
1.25 ꢁ 0.20
2.64 ꢁ 0.40
1.70 ꢁ 0.36
1.19 ꢁ 0.37
4.72 ꢁ 0.82
1.70 ꢁ 0.14
0.97 ꢁ 0.04
6.56 ꢁ 0.40
2.98 ꢁ 0.30
1.96 ꢁ 0.26
7.12 ꢁ 1.65
2.15 ꢁ 0.37
0.99 ꢁ 0.14
6.01 ꢁ 1.86
2.46 ꢁ 0.30
1.96 ꢁ 0.73
9.83 ꢁ 0.96
1.69 ꢁ 0.22
1.01 ꢁ 0.34
1.50 ꢁ 0.25
0.59 ꢁ 0.05
0.61 ꢁ 0.25
1.78 ꢁ 0.32
1.06 ꢁ 0.16
0.73 ꢁ 0.15
28.11 ꢁ 7.05
9.85 ꢁ 2.04
4.58 ꢁ 0.37
34.22 ꢁ 1.58
11.19 ꢁ 1.15
6.03 ꢁ 0.62
31.71 ꢁ 4.19
9.19 ꢁ 1.77
5.36 ꢁ 0.25
41.42 ꢁ 1.74
10.12 ꢁ 1.35
6.53 ꢁ 0.21
62.91 ꢁ 16.95
16.91 ꢁ 1.28
9.44 ꢁ 0.69
112.35 ꢁ 26.3
42.14 ꢁ 6.71
17.78 ꢁ 3.98
70.61 ꢁ 19.65
50.95 ꢁ 9.11
46.60 ꢁ 12.76
71.78 ꢁ 9.51
26.36 ꢁ 5.89
14.53 ꢁ 3.80
18.00 ꢁ 3.90
3.18 ꢁ 0.46
2.53 ꢁ 0.03
22.49 ꢁ 6.27
7.75 ꢁ 1.75
4.36 ꢁ 0.60
0.85 ꢁ 0.03
0.44 ꢁ 0.12
0.43 ꢁ 0.04
1.65 ꢁ 0.23
0.97 ꢁ 0.18
0.62 ꢁ 0.23
1.72 ꢁ 0.42
1.18 ꢁ 0.13
0.81 ꢁ 0.19
2.93 ꢁ 0.18
1.29 ꢁ 0.09
1.02 ꢁ 0.23
3.99 ꢁ 1.34
2.40 ꢁ 0.31
1.22 ꢁ 0.17
7.37 ꢁ 1.22
2.60 ꢁ 0.76
1.40 ꢁ 0.38
5.70 ꢁ 1.03
3.99 ꢁ 0.54
1.61 ꢁ 0.04
7.74 ꢁ 1.63
2.72 ꢁ 1.39
0.92 ꢁ 0.10
0.70 ꢁ 0.15
0.29 ꢁ 0.06
0.29 ꢁ 0.11
0.97 ꢁ 0.36
0.61 ꢁ 0.23
0.45 ꢁ 0.06
1a
1b
2a
2b
3a
3b
4a
4b
5a
5b
30
60
5
30
60
5
30
60
5
30
60
5
30
60
5
30
60
5
30
60
5
30
60
5
6.80 ꢁ 0.85
7.06 ꢁ 0.63
14.00 ꢁ 1.92
8.39 ꢁ 0.38
5.82 ꢁ 1.02
11.62 ꢁ 1.24
5.26 ꢁ 0.71
4.99 ꢁ 2.64
14.67 ꢁ 1.02
4.34 ꢁ 1.17
2.48 ꢁ 0.05
8.60 ꢁ 1.30
5.35 ꢁ 0.45
5.08 ꢁ 0.49
57.06 ꢁ 15.74
13.00 ꢁ 4.17
5.77 ꢁ 1.27
14.41 ꢁ 0.74
8.53 ꢁ 0.68
9.77 ꢁ 1.45
104.10 ꢁ 8.39
19.07 ꢁ 2.98
11.23 ꢁ 4.66
7.67 ꢁ 1.98
1.95 ꢁ 0.12
1.57 ꢁ 0.08
6.03 ꢁ 1.30
2.48 ꢁ 0.14
1.09 ꢁ 0.09
30
60
5
30
60
Copyright # 2007 John Wiley & Sons, Ltd.
J Label Compd Radiopharm 2007; 50: 13–18
DOI: 10.1002.jlcr

16 G. HAO ET AL.
99mTc(CO)3(MIBI)3] +
99mTc(CO)3(MEI)3] +
99mTc(CO)3(MEI)2(H2O)] +
99mTc(CO)3(MPI)3] +
99mTc(CO)3(MPI)2(H2O)] +
99mTc(CO)3(EPI)3] +
99mTc(CO)3(EPI)2(H2O)] +
99mTc(CO)3(IPPI)3] +
99mTc(CO)3(IPPI)2(H2O)] +
99mTc(CO)3(THFMI)3] +
99mTc(CO)3(THFMI)2(H2O)] +
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
Heart / Liver
60 min
30 min
5 min
[
[
[
[
[
[
[
[
[
[
[
(a)
[
99mTc(CO)3(MIBI)3] +
99mTc(CO)3(MEI)3] +
99mTc(CO)3(MEI)2(H2O)] +
99mTc(CO)3(MPI)3] +
99mTc(CO)3(MPI)2(H2O)] +
99mTc(CO)3(EPI)3] +
99mTc(CO)3(EPI)2(H2O)] +
99mTc(CO)3(IPPI)3] +
99mTc(CO)3(IPPI)2(H2O)] +
99mTc(CO)3(THFMI)3] +
99mTc(CO)3(THFMI)2(H2O)] +
60 min
30 min
5 min
[
[
[
[
[
[
[
[
[
[
0
1
2
3
4
5
6
7
Heart /Lungs
(b)
[
99mTc(CO)3(MIBI)3] +
99mTc(CO)3(MEI)3] +
99mTc(CO)3(MEI)2(H2O)] +
99mTc(CO)3(MPI)3] +
99mTc(CO)3(MPI)2(H2O)] +
99mTc(CO)3(EPI)3] +
99mTc(CO)3(EPI)2(H2O)] +
99mTc(CO)3(IPPI)3] +
99mTc(CO)3(IPPI)2(H2O)] +
99mTc(CO)3(THFMI)3] +
99mTc(CO)3(THFMI)2(H2O)] +
60 min
30 min
5 min
[
[
[
[
[
[
[
[
[
[
0
5
10 15 20 25 30 35 40 45 50
Heart / Blood
(c)
Figure 1 The heart to non-target ratios of the 99mTc(CO)3-CNR complexes: (a) heart/liver; (b) heart/lungs; (c) heart/blood.
uptake compared with
[
99mTc(CO)3(MIBI)3]+, which
cardial imaging agents the new complexes chiefly
need to improve their heart uptake and retention
to a little higher level as 99mTc-MIBI and keep their
current high target to non-target ratios at the same
time.
made the target to non-target (T/NT) ratios of several
new complexes were higher than that of [99mTc(CO)3
(MIBI)3]+ (Figure 1). The heart to liver ratio of
[
99mTc(CO)3(EPI)2(OH2)]+ was 3.37 that was about
double ratio of [99mTc(CO)3(MIBI)3]+ at 5 min post
injection, and for 99mTc-MIBI this ratio was usually
[
99mTc(CO)3(IPPI)3]+ with highest lipophilicity also
had the highest liver, lungs and blood uptake at 5 min
post-injection, but it had low heart uptake. The
less than 1.0 within 1 h.
[
99mTc(CO)3(EPI)2(OH2)]+
exhibited almost the best performance in several
important aspects for myocardial imaging among
the new designed complexes. To be successful myo-
complex with the lowest lipophilicity, [
99mTc(CO)3
(MEI)2(OH2)]+, had low heart uptake though its liver,
lungs and blood uptake were also low. 99mTc(CO)3THFMI
Copyright # 2007 John Wiley & Sons, Ltd.
J Label Compd Radiopharm 2007; 50: 13–18
DOI: 10.1002.jlcr

PREPARATION AND BIODISTRIBUTION OF NOVEL 99MTC(CO)3-CNR COMPLEXES 17
with the greatest difference in ligand structure did
Animal Center of Peking University. Proton nuclear
magnetic resonance spectroscopy was performed
on Bruker Avance 500 MHz.Infrared spectrum was
performed on Nicolet-170SX. The automatic gamma
counts were carried out by WALLAC/WIZARD 1470,
not show good biodistribution. For 99mTc(CO)3-MIBI,
the tri-substituted product showed much better
performance in myocardial imaging than bi-complex.
On the contrary, for EPI and IPPI the bi-complex had
much more better imaging properties. Therefore, the
substituent number was not crucial factor in biodis-
tribution for 99mTc(CO)3-CNR.
Perkin Elmer Wallac. HPLC was performed on
a
SHIMADZU system (SCL-10Avp pumps and SPD-
10Avp UV detector) and Park Radioow detector. TLC
was run on polyamide film using acetonitrile as
mobile phase.
Usually, the biodistribution of homologous com-
plexes of complex is affected by their lipophilicity, size
and the ligand itself, etc. During the course of devel-
oping 99mTc-isonitrile complexes as myocardial
imaging agents, [99mTc(MIBI)6]+ showed much better
properties than others such as [99mTc(TBI)6]+ and
Synthesis of isonitriles (CNR)
[
99mTc(CPI)6]+. It proves that the ligand plays an
A solution of ethyl formate (8.0 ml, 100 mmol), pre-
cooled to approximately 08C, was added slowly to a
stirred solution of amine analogs (95 mmol) in an ice/
NaCl bath. After the slightly exothermic reaction
ceased, the solution was allowed to warm slowly to
room temperature and refluxed overnight. The solution
was distilled through a Vigreux column to give for-
mamide analogs determined by infrared spectroscopy.
50 mmol formamide was dissolved in methylene
chloride (45 ml). Triethylamine (20.1 ml, 0.25 mol)
was added and the clear solution was cooled in an
ice/water bath. Phosphorus oxychloride (2.75 ml,
30 mmol) was added dropwise to the cooled formamide
solution. The resulting suspension was stirred and
allowed to slowly warm to room temperature for 1 h,
and at reflux temperature for 15 min. 20 ml cold water
was added and the organic layer separated. The organic
layer was washed with a saturated solution of sodium
bicarbonate, water and dried with anhydrous sodium
sulfate. Evaporation of the methylene chloride left a
dark brown liquid. The dark brown liquid was distilled
through a Vigreux column under vacuum to give the
isonitrile analogs. They were determined by IR and
[1H]NMR.
important role to the biological behavior of the complex,
and MIBI is the best among the isonitrile analogs.
It might explain from one aspect why the new
complexes in this investigation did not exhibited the
same high heart uptake and retention as [99mTc(CO)3
(MIBI)3]+. In addition, the lipophilicity also showed
marked influence on the biodistribution. [99mTc(CO)3
(IPPI)3]+ and
[
99mTc(CO)3(MEI)2(OH2)]+ with highest
qand lowest lipophilicity, respectively, did not show
good biodistribution in mice. Therefore, there is a
most appropriate scope of lipophilicity to achieve
the good balance of high uptake in heart and fast
clearance from non-target tissues for 99mTc(CO)3-CNR
complexes. To get this scope, more 99mTc(CO)3-CNR
complexes should be prepared and studied in the
future.
Conclusion
Like 99mTc(CO)3-MIBI, there are bi- and tri-substituted
products when the five isonitriles react with fac-
[
99mTc(CO)3(OH2)3]+ in specified pH conditions. The
changes from lipophilicity and ligand itself did bring
great effects on the properties of the 99mTc(CO)3-CNR
complexes for myocardial imaging. Among these new
complexes, [99mTc(CO)3(EPI)2(OH2)]+ showed the most
favorable imaging characteristics in mice.
Preparation of 99mTc(CO)3-CNR
Experimental
The [99mTc(CO)3(OH2)3]+ precursor was prepared ac-
cording to the method of Alberto et al. 1.0 mg isonitrile,
dissolved in 0.5 ml water, was added to 1 ml
2-methoxyethaneamine, 3-ethoxypropaneamine, 3-iso
propoxypropan-1-amine, tetrahydro-furfurylamine were
purchased from Acros Organics Co. 3-methoxy-
propaneamine was purchased from Aldrich Chemical
Co. Other chemicals were purchased from Beijing
Chemical Reagents Company. Pure CO gas was pur-
chased from NRCCRM, China. 99Mo/99mTc generator
was obtained from the Beijing Syncor Medical Corpora-
tion. ICR mice, 18–20 g, female, were obtained from
[
99mTc(CO)3(OH2)3]+ solution which was adjusted to
pH=3.0–4.0 or 9.0–10.0 with 0.5 N HCl solution. The
solution was allowed in a boiling water bath for 15 min
and examined by TLC (Rf = 0.9–1.0 for [99mTc(CO)3(CN-
R)2(OH2)]+ and [99mTc(CO)3(CNR)3]+, Rf = 0–0.1 for
[
99mTc(CO)3(OH2)3]+ and Rf = 0.4–0.5 for 99mTcO4ꢀ)
and radio HPLC (Alltima C18 RP column,
250 ꢂ 4.6 mm, 5 mm, flow rate 1 ml/min).
Copyright # 2007 John Wiley & Sons, Ltd.
J Label Compd Radiopharm 2007; 50: 13–18
DOI: 10.1002.jlcr

18 G. HAO ET AL.
Peoples’s Republic of China’. The authors would like to
thank Lin Zhu for helpful assistance.
Stability
The labeled complexes were incubated at room tem-
perature for up to 6 h. Aliquots were taken and
analyzed by radio-HPLC to assess the stability.
Determination of the partition coefficient
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Acknowledgements
This work was supported financially by the ‘National
211 Engineering Project’ of ‘ Tenth-Five Year Plan of
Copyright # 2007 John Wiley & Sons, Ltd.
J Label Compd Radiopharm 2007; 50: 13–18
DOI: 10.1002.jlcr