Synthesis and biological evaluation of fatty acids conjugates bearing cyclopentadienyl-donors incorporated [99mTc/Re(CO)3] + for myocardical imaging

Article abstract of DOI:10.1016/j.ejmech.2013.11.015

Four ^99mTc-labeled fatty acid analogs, 1b, 2b, 3b, 4b were synthesized by a double ligand transfer reaction and theirs potential were investigated. The radiochemical yield of the radiotracers was from 11.7% to 30.3% (no decay corrected). Those compounds were found to be chemically stable when incubated in SD rat serum for 3 h at 37 C. The biodistribution studies in mice showed that high radioactivity accumulated of Tc-99m complexes were observed, followed by moderate clearance from the heart. The maximum heart/blood ratio was 5.7 at 15 min postinjection of 1b. Metabolite analysis showed 1b was not metabolized by β-oxidation in the heart. These results suggest that 1b may be a promising radiotracer for evaluation of myocardial viability.

Full text of DOI:10.1016/j.ejmech.2013.11.015

European Journal of Medicinal Chemistry 72 (2014) 10e17
Contents lists available at ScienceDirect
European Journal of Medicinal Chemistry
journal homepage: http://www.elsevier.com/locate/ejmech
Original article
Synthesis and biological evaluation of fatty acids conjugates bearing
cyclopentadienyl-donors incorporated [99mTc/Re(CO)3]þ for
myocardical imaging
,
,
Huahui Zeng a b, Huabei Zhang a
*
a Key Laboratory of Radiopharmaceuticals of Ministry of Education, College of Chemistry, Beijing Normal University, Beijing 100875, China
b Department of Nuclear Medicine, Second Affiliated Hospital of Zhejiang University School of Medicine, Hangzhou 310009, China
a r t i c l e i n f o
a b s t r a c t
Four 99mTc-labeled fatty acid analogs, 1b, 2b, 3b, 4b were synthesized by a double ligand transfer reaction
and theirs potential were investigated. The radiochemical yield of the radiotracers was from 11.7% to
30.3% (no decay corrected). Those compounds were found to be chemically stable when incubated in SD
rat serum for 3 h at 37 ꢀC. The biodistribution studies in mice showed that high radioactivity accumu-
lated of Tc-99m complexes were observed, followed by moderate clearance from the heart. The
maximum heart/blood ratio was 5.7 at 15 min postinjection of 1b. Metabolite analysis showed 1b was
Article history:
Received 3 July 2013
Received in revised form
11 November 2013
Accepted 14 November 2013
Available online 22 November 2013
not metabolized by
tracer for evaluation of myocardial viability.
b-oxidation in the heart. These results suggest that 1b may be a promising radio-
Keywords:
Fatty acid
Technetium-99m
Myocardial imaging
Tissue distribution
Ó 2013 Elsevier Masson SAS. All rights reserved.
1. Introduction
tracers. In addition, the cyclotron-produced C-11 and I-123 have
inherent economic and logistic disadvantages, particularly in nu-
clear medicine centers located far away from the cyclotron. A
technetium-99m-labeled fatty acid analog would be highly desir-
able since the ideal nuclear properties of radiotechnetium (141 keV,
t1/2 ¼ 6 h) and its availability through the 99Mo/99mTc generator
system whenever needed.
Fatty acids act as the most important energy sources in the
normal myocardium, accounting for 60e90% of aerobic meta-
bolism, via the beta-oxidation pathway [1]. Disturbances in fatty
acid metabolism often reflect myocardial damage, such as
myocardial ischemia and cardiomyopathy [2]. Accordingly, radio-
labeled fatty acid analogs have been utilized for diagnosis of
myocardial ischemia and other heart diseases using single-photon
emission computed tomography (SPECT) or positron emission to-
mography (PET). Reported PET myocardical imaging agent 1-[11C]
Palmitate showed biexponential clearance in heart with rapid
washout via beta-oxidation and slow washout for slow turnover of
the intracellular lipid pool [2], which were unfavorable for myo-
cardical imaging. Two types of iodinated tracers, 123I-iodophe-
nylpentadecanoic acid (IPPA) and its beta-methyl-branched
derivative 15-(p-[123I]iodophenyl)-3-methylpentadecanoic acid
(BMIPP), have been reported as successful SPECT radiopharma-
ceuticals for the estimation of myocardial fatty acid metabolism
[3,4]. However, shedding radioiodine and easy deiodination were
disadvantageous to the application and preparation of those
Recently, various Tc-99m complexes incorporating fatty acid
analogs have been developed, but no compound has potential use
in clinical practice due to poor myocardial uptakes and rapid
clearance from heart. Among these analogs (Fig. 1), [99mTc]-MAMA-
hexadecanoic acid
(
99mTc-MAMA-HDA) [5], 99mTc(CO)3-15-[N-
(Acetyloxy)-2-picolylamino]pentadecanoic acid [6], 99mTc-CpTT-PA
[7] and 99mTc-CpTT-16-oxo-HDA [8] showed higher initial heart
uptakes than early 99mTc-labeled fatty acid analogs, such as 99mTc-
BAT-pentadecanoic acid, 99mTc-labeled DTPA or EDTA fatty acid
[9,10]. Those Tc-99m-labeled fatty acid analogs were all analyzed
using the metabolites in rodent heart or urine samples to elucidate
whether those analogs are recognized and metabolized by heart via
beta-oxidation. 99mTc-MAMA-HDA was a milestone as part of the
strategy to develop 99mTc-labeled long-chain fatty acid analogs,
which demonstrated that the fatty acid was metabolized to 99mTc-
MAMA-butyric acid via beta-oxidation in myocardium. In addition,
99mTc(CO)3-15-[N-(Acetyloxy)-2-picolylamino]pentadecanoic acid,
99mTc-CpTT-PA and 99mTc-CpTT-16-oxo-HDA were primarily
* Corresponding author. Tel.: þ86 10 58802961; fax: þ86 10 58800567.
E-mail addresses: huahuizeng@gmail.com, hhzeng@qq.com (H. Zeng),
hbzhang@bnu.edu.cn (H. Zhang).
0223-5234/$ e see front matter Ó 2013 Elsevier Masson SAS. All rights reserved.
http://dx.doi.org/10.1016/j.ejmech.2013.11.015

H. Zeng, H. Zhang / European Journal of Medicinal Chemistry 72 (2014) 10e17
11
a significantly delayed myocardial tracer washout. Another beta-
oxidation-inhibiting approach is the intrachain replacement of a
methylene group by a p-phenylene. Many similar fatty acids
showed that phenyl groups were tolerated by myocytes and the p-
phenylene group located close to the carboxyl group enhanced the
retention of the radioactivity, such as IPPA, BMIPP and [123I]-PHIPA
3e10 [14]. The increase in retention was as well attributed to the
hypothetical mitochondrial trapping mechanism [14].
In this study, [99mTc]CpTT was introduced at the
u-position of
the fatty acids and alkyl groups or heterocyclic groups (similar to
phenyl group with the aromatic properties) were inserted in the
beta-position of the chain to hinder fatty acids metabolize and
enhance the retention of the radioactivity. We synthesized 15-
Cyclopentadienyl Tricarbonyl technetium-99m 15-oxo-pentadeca-
noyl Thiopheneacetic Acid ([99mTc]CpTT-15-oxo-PTA, 1b), 15-
Cyclopentadienyl Tricarbonyl technetium-99m 15-oxo-pentadeca-
noic Acid ([99mTc]CpTR-15-oxo-PA, 2b), 5-Cyclopentadienyl Tri-
carbonyl technetium-99m 3-methyl 5-oxo-valeric Acid ([99mTc]
CpTR-5-oxo-MVA, 3b), and 6-Cyclopentadienyl Tricarbonyl
technetium-99m 6-oxo-hexanoic Acid ([99mTc]CpTR-6-oxo-HA, 4b)
and tested their in vitro stability, electronic properties, partition
coefficient and biodistribution of radioactivity in mice. The
myocardium metabolism of [99mTc]-CpTT-oxo-PTA in rats was
evaluated by a simple extraction method.
2. Material and methods
2.1. Chemistry
Chemicals and solvents were obtained from commercial sup-
pliers and used without further purification. Na99mTcO4 was ob-
tained by elution with saline from a 99Mo-99mTc generator (Beijing
Atomic High-tech Co., Beijing). All reactions were monitored by
TLC, using silica gel plates with fluorescence F254 and UV light
visualization. Flash column chromatography employed silica gel 60
(230e400 mesh). High-performance liquid chromatography
(HPLC) was performed on a Shimadzu SCL-10AVP System equipped
Fig. 1. Representative 99mTc-labeled fatty acids analogs reported recently that showed
higher initial heart uptakes.
metabolized to 99mTc(CO)3-[N-(acetyloxy)-2-picolylamino]penta-
noic acid, 99mTc-CpTT-propionic acid and 99mTc-CpTT-4-oxo-butyric
acid via beta-oxidation in myocardium, respectively. According to
the metabolism mechanism, fatty acids for myocardial imaging
require suitable modification in order to increase the residence
time of the tracers in the myocardium. And the Tc-99m core with
high stability and relative small molecular size is more favorable to
decrease the negative influences on the property of radiolabeled
fatty acids [11].
The diminutive and lipophilic cyclopentadienyl tricarbonyl Tc-
99m cores (99mTc-CpTT) is expected to only minimally perturb
biological activity of fatty acid. 99mTc-CpTT complexes were syn-
thesized by a double ligands transfer reaction between the
carbonyl-ferrocene ligand and the fac-99mTc(CO)3(H2O)3þ complex
[12]. In the chelating groups of 99mTc-CpTT-PA and 99mTc-CpTT-16-
oxo-HDA, cyclopentadienyl long-chain fatty acids were chosen to
chelate the fac-99mTc(CO)3(H2O)þ3 complex, which showed the
tracers had high chemical stability in vitro and high initial radio-
activity accumulation but with rapid myocardial washout and
higher blood background than [125I]IPPA. Consequently, structur-
ally modified radiolabeled fatty acids are feasible to overcome the
problems of rapid clearance from heart and high blood background.
9-[123mTe]-telluraheptadecanoic acid (9-THDA) reported by Knapp
group [13] exhibits that this model agent is rapidly extracted from
the blood and concentrates in the myocardium in significant levels
by an unusual mitochondrial trapping mechanism, which the
tellurium heteroatom has been inserted in the alkyl chain to
interfere with metabolism. The radioiodinated BMIPP with the
with
a
semipreparative column (Venusil MP C-18,
5
m
m
,
,
10 mm ꢁ 250 mm) or an analytical column (Alltima C-18, 5
4.6 mm ꢁ 250 mm) with a UV detector (254 nm) and a radioisotope
detector. 1H NMR spectra were obtained on a Bruker ARX-400
spectrometer and 13C NMR spectra at 400 MHz with deuterated
dimethyl sulfoxide (DMSO-d6) or CDCl3 as a solvent. Chemical shifts
were reported in parts per million (ppm,
d units) downfield from
tetramethylsilane. Mass spectra (EI-MS) were obtained with a
Trance MS-2000 mass spectrometer (Finnigan, America). Radioac-
tivity was measured in a dose calibrator (Beijing Nuclear Instru-
ment Factory) and tissue radioactivity in a Bioscan-g-detector B-FC
3200. All animal experiments were carried out by using normal
Kunming mice (Peking University, China), and in compliance with
the relevant national laws, as approved by the local committee on
the conduct and ethics of animal experimentation.
2.2. Synthesis
2.2.1. Synthesis of methyl 15-ferrocenyl-15-oxo-pentadecanoate (9)
Thionyl chloride (15 mL, 206 mmol) was added dropwise to
pentadecanedioic acid (3 g, 11 mmol), and heated at 90 ꢀC over-
night. After thionyl chloride had been removed in vacuo, the
resulting 1,15-pentadecanoyl dichloride (5) was obtained without
further purification. The reaction flask was charged with ferrocene
(2.16 g, 11 mmol) and 1,15-pentadecanoyl dichloride in dichloro-
methane (30 mL) and chilled in ice bath. Anhydrous aluminum
chloride (1.5 g, 11.2 mmol) was added to this solution carefully over
30 min using a spatula under N2. The reaction mixture, which
substitution of b-methylene hydrogen by one methyl group showed

12
H. Zeng, H. Zhang / European Journal of Medicinal Chemistry 72 (2014) 10e17
turned to deep-violet color, was stirred for 1 h in an ice bath and
then allowed to stand for 16 h at room temperature. At the end of
the reaction, the resulting of 15-Ferrocenyl-15-oxo-pentadecanoyl
chloride (6) without further purification was slowly added with
methanol (10 mL) and triethylamine (2 mL) in ice bath. The mixture
was refluxed vigorously for another 1 h, then most of the solvent
was removed under reduced pressure, the crude mixture was
diluted with hydrochloric acid (30 mL 1 mol/L) and extracted with
dichloromethane (3 ꢁ 15 mL). The organic layer was washed with
saturated sodium chloride solution (3 ꢁ 15 mL) and dried over
anhydrous Na2SO4, and the solvent was removed in vacuo. The
residue obtained was purified by flash column chromatography
(10:90 ethyl acetateehexane) to give 9 (2.5 g, 50.0%) as a brownish
51.46, 69.36, 69.40, 69.83, 72.28, 76.72, 77.04, 77.35, 79.36, 173.09,
203.37. MS (ESI) m/z: 328.07 (Mþ), 329.06 ([M þ H]þ).
2.2.4. Synthesis of methyl 6-ferrocenyl-6-oxo-hexanoate (16)
Adipic acid (1.6 g, 11 mmol) was dissolved in 10 mL of thionyl
chloride. The mixture was refluxed overnight. Then the solvent was
evaporated to provide the crude product of adipoyl chloride, which
was used without further purification. The reaction flask was
charged with ferrocene (4.63 g, 24.88 mmol) and adipoyl chloride
in dichloromethane (30 mL) and chilled in ice bath. To this solution
was added anhydrous aluminum chloride (1.5 g, 11.2 mmol) care-
fully over 30 min. The reaction mixture, which turned a deep-violet
color, was stirred for 1 h in ice bath and then allowed to stand for
16 h at room temperature. At the end of the reaction, the flask was
placed again in an ice bath, then methanol (10 mL) and triethyl-
amine (2 mL) were slowly added. The mixture was refluxed
vigorously for 1 h, and after solvent had been removed under
reduced pressure, the crude mixture was diluted with hydrochloric
acid (30 mL, 1 mol/L) and extracted with dichloromethane
(3 ꢁ 15 mL). The organic layer was washed with saturated sodium
chloride solution (3 ꢁ 15 mL) and dried over anhydrous Na2SO4. The
organic layer was treated similarly as described above for com-
pound 10, to give 16 (2.7 mg, 75.0%) as a brownish red solid. 1H
red solid. 1H NMR (400 MHz, CDCl3)
2.27 (t, 2H), 2.65 (t, 2H), 3.57 (s, 3H), 4.21 (s, 5H), 4.57 (s, 2H), 4.77 (s,
2H); 13C NMR (400 MHz, DMSO-d6)
30.02, 34.84, 37.86, 52.06,
d 1.26 (m, 18H), 1.56 (m, 4H),
d
68.98, 69.42, 71.90, 79.07, 128.68, 132.77, 143.16, 144.55, 170, 193,
203.36; MS (ESI) m/z: 454.8 (Mþ), 455.4 ([M þ H]þ).
2.2.2. Synthesis of methyl 15-ferrocene-15-oxo-pentadecanoyl
thiopheneacetate (10)
Thionyl chloride (5 mL, 68 mmol) was added dropwise to
methanol (30 mL) at 0 ꢀC. then 2-(thiophen-2-yl)acetic acid (3 g,
19 mmol) was added to this solution, and refluxed vigorously for
4 h. After the solvent was removed under reduced pressure, the
resulting methyl thiopheneacetate (8) was obtained without
further purification.
NMR (400 MHz, CDCl3)
(s, 3H), 4.20 (s, 5H), 4.49 (s, 2H), 4.78 (s, 2H). 13C NMR (400 MHz,
CDCl3) 23.89, 24.77, 33.92, 39.21, 51.47, 51.53, 69.02, 69.28, 69.74,
d 1.73 (m, 4H), 2.38 (t, 2H), 3.73 (t, 2H), 3.68
d
The flask was charged with 8 (1.72 g, 11 mmol) and 6 (as
described above to prepare 6) in ice bath. To this solution was
added anhydrous aluminum chloride (1.5 g, 11.2 mmol) carefully
over 10 min using a spatula under N2. The mixture was stirred for
1 h in an ice bath and then allowed to stand for 16 h at room
temperature. After most of the solvent was removed under reduced
pressure, the crude mixture was diluted with hydrochloric acid
(30 mL, 1 mol/L) and extracted with dichloromethane (3 ꢁ 15 mL).
The organic layer was washed with saturated sodium chloride so-
lution (3 ꢁ 15 mL) and dried over anhydrous Na2SO4. When the
solvent was evaporated, the residue was subjected to chromatog-
raphy (10:90 ethyl acetateehexane) to give 10 (3.8 g, 58.7%) as a
69.78, 72.17, 76.76, 77.08, 77.40, 79.07, 173.86, 203.91. MS (ESI) m/z:
328.07 (Mþ), 329.06 ([M þ H]þ).
2.2.5. Synthesis of 15-Cyclopentadienyl Tricarbonyl rhenium 15-
oxo-pentadecanoyl Thiopheneacetic Acid (CpTR-15-oxo-PTA, 1a)
A mixture of the ester 10 (121 mg, 0.21 mmol), NH4ReO4 (20 mg,
0.07 mmol), Cr(CO)6 (85 mg, 0.385 mmol) and CrCl3 (20 mg,
0.13 mmol) were placed in a pressure tube containing a magnetic
stir bar. Dry methanol (300
mL) was added to the vial that was
sealed and heated at 160e170 ꢀC for 1 h. At the end of the reaction,
the mixture was cooled in an ice bath for 10 min and the solvent
was removed in vacuo. The residue was dissolved in CH2Cl2, passed
through a short silica plug, and the solvent was removed. The
residue was added in 3 mL of 0.3 M NaOH and methanol (1:3) and
heated at 70e80 ꢀC for 40 min. After removing methanol under
reduced pressure, the solution was cooled and acidified with 0.1 M
HCl in an ice bath. The reaction mixture was then extracted with
dichloromethane, and the organic layer was dried over anhydrous
Na2SO4 and concentrated. The crude products were purified by
flash column chromatography (30:70 ethyl acetateehexane) to
afford the 1a (9.0 mg, 18.0%) as a gray solid. 1H NMR (400 MHz,
pale brownish red solid. 1H NMR (400 MHz, DMSO-d6)
d 1.25 (m,
18H), 1.57 (m, 4H), 2.71 (t, J ¼ 14.1 Hz, 2H), 2.88 (t, J ¼ 14.2 Hz, 2H),
3.65 (s, 3H), 4.03 (s, 2H), 4.22 (s, 5H), 4.55 (s, 2H), 4.79 (s, 2H), 7.07
(d, 1H), 7. 79 (d, 1H), 13C NMR (400 MHz, DMSO-d6)
d 23.89, 24.21,
28.93, 28.96, 34.84, 52.06, 71.90, 79.09, 128.68, 132.77, 143.16,
144.55, 170, 193, 203.36; MS (ESI) m/z: 578.8 (Mþ), 579.4
([M þ H]þ).
2.2.3. Synthesis of methyl 5-ferrocenyl-5-oxo-(3-methyl)valerate
(13)
3-Methylglutaric anhydride (1.41 g, 11 mmol) was dissolved in
methanol (5 mL), and the mixture was stirred vigorously at 100 ꢀC
for 90 min. After most of the solvent was removed in vacuo, thionyl
chloride (2.5 mL, 34 mmol) was added dropwise, and stirred at
room temperature overnight. After thionyl chloride was removed in
vacuo, ferrocene (2.16 g, 11 mmol) in dichloromethane (30 mL),
followed by anhydrous aluminum chloride (1.5 g, 11.2 mmol) were
added carefully over 30 min in ice bath. The reaction mixture,
which turned a deep-violet color, was stirred for 1 h in ice bath and
then allowed to stand for 16 h at room temperature. The mixture
was diluted with hydrochloric acid (30 mL 1 mol/L) and extracted
with dichloromethane (3 ꢁ 15 mL). The organic layer was treated
similarly as described above for compound 10, to give 13 (2.6 g,
CDCl3)
J ¼ 7.04 Hz, 2H), 3.75 (s, 2H), 5.39 (s, 2H), 5.98 (s, 2H), 6.83 (d, 2H),
7.50 (d, 2H); 13C NMR (400 MHz, CDCl3)
24.48, 24.72, 29.58, 29.67,
d
1.25 (s, 18H), 1.68 (m, 4H), 2.57 (t, J ¼ 6.68 Hz, 2H), 2.69 (t,
d
38.89, 39.81, 69.39, 69.74, 72.13, 85.14, 87.89,192.12,195.46, 202.86;
MS (ESI) m/z: 712.4 (Mþ, 185Re), 714.5 (Mþ, 187Re).
2.2.6. Synthesis of 15-Cyclopentadienyl Tricarbonyl rhenium 15-
oxo-pentadecanoic Acid (CpTR-15-oxo-PA, 2a)
Prepared analogously as described above for compound 1a. 2a
(8.3 mg, 20.0%) as a gray solid was obtained from 9. 1H NMR
(400 MHz, CDCl3)
d
1.26 (m, 18H), 1.66 (m, 4H), 2.33 (t, J ¼ 5.96 Hz,
2H), 2.58 (t, J ¼ 7.28 Hz, 2H), 5.39 (t, 2H), 5.98 (t, J ¼ 2.21 Hz, 2H); 13
C
70.0%) as a brownish red solid. 1H NMR (400 MHz, CDCl3)
3H), 2.33e2.82 (m, 5H), 3.67 (s, 3H), 4.22 (s, 5H), 4.52 (s, 2H), 4.83
(s, 2H). 13C NMR (400 MHz, CDCl3)
20.23, 26.92, 40.88, 45.94,
d
1.06 (d,
NMR (400 MHz, CDCl3) d 20.16, 24.47, 24.73, 29.05, 29.11, 29.20,
29.38, 29.52, 38.89, 85.12, 87.84, 96.32, 175.57, 191.71, 195.37; MS
d
(ESI) m/z: 589.2 (Mþ, 185Re), 591.2 (Mþ, 187Re).

H. Zeng, H. Zhang / European Journal of Medicinal Chemistry 72 (2014) 10e17
13
2.2.7. Synthesis of 5-Cyclopentadienyl Tricarbonyl rhenium 3-
treated with 0.3 M NaOH (50
m
L) at 70e80 ꢀC for 10 min. The so-
methyl 5-oxo-valeric acid (CpTR-5-oxo-MVA, 3a)
lution was cooled, acidified with 0.1 M HCl (150
with CH2Cl2. The reaction mixture was purified by reversed phase
HPLC (Venusil MP C-18, 5
using 80:20 methyl cyanide with 0.09% phosphoric acid (aq) and 1b
was eluted with the retention time 16.45 min.
mL), and extracted
The same procedure as described above to prepare 1a was used,
and 5.4 mg of 3a as a pale yellow solid was obtained in a 16.0% yield
m
, 10 mm ꢁ 250 mm) at a flow 2 mL/min
from 13. 1H NMR (400 MHz, CDCl3)
d
1.04 (s, 3H), 2.44e2.76 (m, 5H),
5.39 (s, 2H), 6.04 (s, 2H); 13C NMR (400 MHz, CDCl3)
d
21.67, 28.68,
28.96, 38.71, 45.30, 47.90, 68.52, 68.86, 71.34, 78.28, 177.40, 189.10,
The same reaction as described above to prepare 1b was used for
radiochemical synthesis of 15-Cyclopentadienyl Tricarbonyl
technetium-99m 15-oxo-pentadecanoic Acid (CpTR-15-oxo-PA,
2b), 5-Cyclopentadienyl Tricarbonyl technetium-99m 3-methyl 5-
oxo-valeric Acid (CpTR-5-oxo-MVA, 3b), and 6-Cyclopentadienyl
Tricarbonyl technetium-99m 6-oxo-hexanoic Acid (CpTR-6-oxo-
HA, 4b) (Schemes 1 and 2).
202.92; MS (ESI) m/z: 462.6 (Mþ, 185Re), 464.1 (Mþ, 187Re).
2.2.8. Synthesis of 6-Cyclopentadienyl Tricarbonyl rhenium 6-oxo-
hexanoic acid (CpTR-6-oxo-HA, 4a)
The same procedure as described above to prepare 1a was used,
and 6.8 mg of 4a as a pale yellow solid was obtained in a 21.0% yield
from 16. 1H NMR (400 MHz, CDCl3)
d 1.25 (m, 4H), 2.40 (t,
J ¼ 7.08 Hz, 2H), 2.63 (t, J ¼ 6.76 Hz, 2H), 5.40 (t, J ¼ 2.28 Hz, 2H, Cp),
5.99 (t, J ¼ 2.28 Hz, 2H, Cp). MS (ESI) m/z: 462.4 (Mþ, 185Re), 464.4
(Mþ, 187Re).
2.4. In vitro stability
The radiotracer (1b, 2b, 3b or 4b) (100
tube (5.0 mL) containing Kunming rat serum (900
mixture was incubated at 37 ꢀC for 3 h. The mixture was filtered
with a 0.2 m Millipore filter and the radiochemical purity was
m
L) was added to a test
mL). The resulting
2.3. Radiochemical synthesis
m
15-Cyclopentadienyl Tricarbonyl technetium-99m 15-oxo-pen-
tadecanoyl Thiopheneacetic Acid (CpTT-15-oxo-PTA, 1b) was syn-
thesized as described in synthesis of 1a with some modification
(Scheme 1). A solution of Na99mTcO4 (740 MBq, 0.2 mL) eluted from
a generator was placed in a pressure tube and dried at 70 ꢀC under a
analyzed by radio-HPLC.
2.5. Determination of partition coefficient
The partition coefficients of the radiotracers were measured by
mixing 0.1 mL of radiotracers (1b, 2b, 3b or 4b) with n-octanol
(5 mL) and phosphate buffer (PBS, 4.9 mL) (0.1 M, pH 7.4) in a test
tube. The test tube was vortexed for 3 min at room temperature,
followed by centrifugation for 5 min at 3500 rpm. Weighted sample
from the n-octanol and buffer layers were counted. The partition
coefficient was expressed as the logarithm of the ratio of the counts
per gram from n-octanol versus that of PBS. Sample from n-octanol
layer was repartitioned until consistent partition of coefficient
stream of N2. Ester 10 (2.5 mg), Cr(CO)6 (2.1 mg, 9.64
mmol), CrCl3
(0.5 mg, 3.21 mol), and methanol (300 L) were then added, and
m
m
the reaction mixture was sealed with a Teflon cap/O-ring and
heated at 160e180 ꢀC (oil bath) for 1 h. At the end of the reaction,
the mixture was cooled in an ice bath and methanol was then
removed under a stream of N2. The residue was dissolved in CH2Cl2,
passed through a 0.2
mm Millipore filter, and the solvent was
removed. The residue was redissolved in methanol (200
mL) and
Scheme 1. Synthetic procedure for [99mTc]CpTT-15-oxo-PTA and CpTR-15-oxo-PTA, [99mTc]CpTT-15-oxo-PA and CpTR-15-oxo-PAa.

14
H. Zeng, H. Zhang / European Journal of Medicinal Chemistry 72 (2014) 10e17
Scheme 2. Synthetic procedure for [99mTc]CpTT-5-oxo-MVA and CpTR-5-oxo-MVA, [99mTc]CpTT-6-oxo-HA and CpTR-6-oxo-HAa.
value was obtained. The measurement was done in triplicate and
repeated three times.
postinjection. Heart samples were homogenized in a 2:1:1 mixture
of CHCl3eMeOH-0.03 M NaOH and centrifuged and the organic and
aqueous fractions and residual tissue pellets were counted.
Aqueous fractions were then analyzed by HPLC with an analytical
2.6. Paper electrophoresis
column (Alltima C-18, 5
m, 4.6 mm ꢁ 250 mm) at a flow rate of 1 mL/
min using an 80:20 mixture of methyl cyanide and 0.09% phos-
phoric acid (aq) for 30 min. 1b was also analyzed by HPLC under the
same conditions.
Electrophoresis was used to determine the charge on radio-
tracers. Studies were performed using paper chromatography
(Xinhua No.1 chromatographic paper) in 20 mM phosphate buffer
The Re complex 1a as a surrogate for 1b was injected into the SD
rats via a tail vein, and heart samples were homogenized and
centrifuged at 30 min postinjection as described above to analyze
metabolites of 1b. The aqueous fractions were passed through a
(pH ¼ 7.4). Each 1
mL sample was spotted and developed in elec-
trophoresis containers with a constant potential of 220 V for 2 h.
After drying the strips, three separate parts cut from the center of
the paper were counted.
0.2 mm Millipore filter and concentrated. The residual was dissolved
in ethanol and centrifuged, the solution were passed through a
solid phase extraction column (Whatman, 60 mg/3 mL) and sub-
sequently washed with water and methanol. After concentration,
the metabolites were characterized with mass spectrometry.
2.7. Biodistribution
Female Kunming mice (18e20 g) were housed for a week under
a 12 h light/12 h dark cycle with free access to food and water for
subsequent tissue distribution studies. Animals were fasted before
experiments for 12 h. The radiotracer (1b, 2b, 3b or 4b) (0.1 mL,
3. Results and discussion
10 mCi) was injected via the tail vein. At the indicated time points (1,
The synthesis of the Re/99mTc-labeled fatty acid analogs is out-
lined in Schemes 1, and 2. The four precursors (9, 10, 13, and 16)
were prepared by FriedeleCrafts acylation from ferrocene and
aliphatic acyl chloride using AlCl3. A double ligand transfer reaction
between the precursors and NH4ReO4/Na99mTcO4 in the presence of
CrCl3 and Cr(CO)6 and subsequent methyl ester hydrolysis were
carried out to afford compounds 1a, 2a, 3a, and 4a or radiotracers
1b, 2b, 3b, and 4b, respectively. In the reaction, the ReOꢂ4 /99mTcO4ꢂ is
reduced and carbonylated, which underwent a quantitative trans-
fer reaction with the ferrocenyl precursor [15]. Hydrolysis of the
Re/99mTc-labeled compound was attempted in 0.3 M NaOH (aq) and
methanol (volume, 1:3) at 70e80 ꢀC, which gave a maximal yield of
5, 15, 30, and 60 min), mice (n ¼ 5) were sacrificed by exsangui-
nation, and samples of whole organ and tissue (blood, heart, brain,
lung, liver, spleen, kidney, intestine, muscle, and bone) were
collected, weighed and counted. Data are expressed as the percent
injected dose per gram of tissue (%ID/g). All experiments were
carried out following the principles of laboratory animal care and
the Chinese law on the protection of animals.
2.8. Analysis of metabolites
Sprague Dawley (SD, 210 e250 g) rats were injected with 1b (37
MBq) via a tail vein, and heart tissue were collected at 30 min

H. Zeng, H. Zhang / European Journal of Medicinal Chemistry 72 (2014) 10e17
15
Table 1
the desired product. Subsequent HPLC purification furnished the
four radiotracers in overall radiochemical yield (11.7e30.3%, no
decay corrected) and with a high radiochemical purity (91e99%).
Total synthesis time including HPLC purification was 160e200 min.
The radiochemical identity of the 99mTc complex was verified by
comparative HPLC using the corresponding Re complex as a sur-
rogate for the similar chemical properties between 99mTc and Re
complexes. The retention times of 99mTc-labeled fatty acid analogs
were similar to their nonradioactive rhenium counterparts on HPLC
HPLC retention times of Re/99mTc-labeled fatty acids.a
Compd
Retention
Compd
Retention
time (min)
time (min)
CpTR-15-oxo-PTA, 1a 15.50
CpTR-15-oxo-PA, 2a 18.15
CpTR-5-oxo-MVA, 3a 16.21
[
[
[
[
99mTc]CpTT-15-oxo-PTA, 1b 16.45
99mTc]CpTT-15-oxo-PA, 2b
19.09
99mTc]CpTT-5-oxo-MVA, 3b 16.52
99mTc]CpTT-6-oxo-HA, 4b
13.85
CpTR-6-oxo-HA, 4a
13.06
a
HPLC analysis was conducted using a semipreparative column (Venusil MP C-18,
5
m
, 10 mm ꢁ 250 mm) and a NaI(Tl) radioactivity detector.
(Venusil MP C-18, 5
m, 10 mm ꢁ 250 mm), which were summarized
in Table 1. The proximate retention times between 99mTc-labeled
tracers and the corresponding Re complexes suggested that the
desired 99mTc-labeled fatty acid analogs were successfully synthe-
sized. The proligands and Re complexes were characterized using
1H and 13C NMR spectroscopy and mass spectrometry, and the
spectra were all in accordance with the predicted structures, which
further corroborated the successful synthesis of desired complexes.
Paper electrophoresis confirmed that the 99mTc complexes were
neutral; the 99mTc complexes almost gathered in the center of the
paper, and few moved towards the anode, and tiny moved towards
the cathode (Table 2).
Table 2
Eletrophoresis pattern, in vitro stability and partition coefficient of 99mTc-labeled
fatty acids.
Compd
Position of radioactive counts (%)
In vitro
stability
log P
Cathode
Origin
Anode
1b
2b
3b
4b
1.2
1.7
2.2
2.3
97.0
95.6
94.7
93.1
1.8
2.7
3.1
4.6
94%
98%
99%
98%
1.10 ꢃ 0.03
1.21 ꢃ 0.03
1.13 ꢃ 0.03
1.05 ꢃ 0.01
Table 3
The biodistribution of 99mTc-labeled fatty acids in normal mice (%ID/g, x ꢃ s; n ¼ 5).
Tissue
1 min
5 min
15 min
30 min
60 min
[
99mTc]CpTT-15-oxo-PTA, 1b
Blood
Brain
Heart
Liver
Spleen
Lung
Kidney
Muscle
Bone
4.47 ꢃ 0.61
0.18 ꢃ 0.06
9.39 ꢃ 1.10
10.27 ꢃ 1.36
2.47 ꢃ 0.96
5.13 ꢃ 3.90
2.54 ꢃ 0.18
0.46 ꢃ 0.34
0.93 ꢃ 0.41
0.73 ꢃ 0.09
0.83 ꢃ 0.07
0.08 ꢃ 0.04
4.47 ꢃ 0.145
11.92 ꢃ 3.31
2.19 ꢃ 0.45
1.77 ꢃ 0.27
1.69 ꢃ 0.04
0.55 ꢃ 0.12
0.41 ꢃ 0.03
0.27 ꢃ 0.07
0.56 ꢃ 0.02
0.05 ꢃ 0.01
3.19 ꢃ 0.18
15.96 ꢃ 1.49
1.81 ꢃ 0.44
1.82 ꢃ 0.24
1.8 ꢃ 0.02
0.42 ꢃ 0.02
0.04 ꢃ 0
0.31 ꢃ 0.02
0.03 ꢃ 0
1.48 ꢃ 0.14
13.65 ꢃ 1.67
1.63 ꢃ 0.53
0.96 ꢃ 0.05
1.76 ꢃ 0.10
0.36 ꢃ 0.11
0.33 ꢃ 0.13
0.06 ꢃ 0.05
0.93 ꢃ 0.08
9.91 ꢃ 1.03
1.00 ꢃ 0.09
0.86 ꢃ 0.38
1.48 ꢃ 0.19
0.23 ꢃ 0.02
0.36 ꢃ 0.08
0.06 ꢃ 0.01
0.48 ꢃ 0.18
0.8 ꢃ 0.23
Intestine
0.08 ꢃ 0.01
[
99mTc]CpTT-15-oxo-PA, 2b
Blood
Brain
Heart
Liver
Spleen
Lung
Kidney
Muscle
Bone
5.62 ꢃ 0.59
0.09 ꢃ 0.05
7.85 ꢃ 0.66
26.80 ꢃ 1.81
1.79 ꢃ 0.18
4.16 ꢃ 0.21
6.48 ꢃ 0.53
0.12 ꢃ 0.07
0.86 ꢃ 0.35
1.78 ꢃ 0.18
2.12 ꢃ 0.11
0.06 ꢃ 0.02
3.74 ꢃ 0.14
28.31 ꢃ 1.06
1.3 ꢃ 0.08
1.66 ꢃ 0.06
0.03 ꢃ 0.01
2.32 ꢃ 0.17
30.41 ꢃ 2.20
0.76 ꢃ 0.05
1.24 ꢃ 0.09
9.16 ꢃ 0.07
0.43 ꢃ 0.03
0.55 ꢃ 0.05
0.41 ꢃ 0.02
0.34 ꢃ 0.03
0.01 ꢃ 0.02
1.2 ꢃ 0.09
0.28 ꢃ 0.03
0.01 ꢃ 0.00
0.64 ꢃ 0.03
11.20 ꢃ 0.90
0.03 ꢃ 0.00
0.06 ꢃ 0.00
11.78 ꢃ 0.23
0.67 ꢃ 0.01
0.24 ꢃ 0.01
0.12 ꢃ 0.09
33.50 ꢃ 3.12
0.33 ꢃ 0.01
0.32 ꢃ 0.00
14.67 ꢃ 0.43
0.56 ꢃ 0.00
0.23 ꢃ 0.01
0.25 ꢃ 0.02
2.34 ꢃ 0.10
7.71 ꢃ 0.32
0.31 ꢃ 0.06
0.65 ꢃ 0.01
1.13 ꢃ 0.10
Intestine
[
99mTc]CpTT-5-oxo-MVA, 3b
Blood
Brain
Heart
Liver
Spleen
Lung
Kidney
Muscle
Bone
0.58 ꢃ 0.14
0.08 ꢃ 0.01
0.46 ꢃ 0.11
2.84 ꢃ 0.58
0.28 ꢃ 0.07
0.75 ꢃ 0.15
1.88 ꢃ 0.32
0.29 ꢃ 0.09
0.15 ꢃ 0.11
0.14 ꢃ 0.12
0.32 ꢃ 0.05
0.06 ꢃ 0.01
0.73 ꢃ 0.45
3.02 ꢃ 0.88
0.16 ꢃ 0.03
0.39 ꢃ 0.12
1.64 ꢃ 0.52
0.1 ꢃ 0.06
0.21 ꢃ 0.02
0.03 ꢃ 0.01
1.48 ꢃ 0.71
3.92 ꢃ 1.81
0.27 ꢃ 0.2
0.11 ꢃ 0.04
0.03 ꢃ 0.02
0.95 ꢃ 0.53
8.74 ꢃ 8.91
0.11 ꢃ 0.1
0.07 ꢃ 0.04
0.01 ꢃ 0.01
0.08 ꢃ 0.07
4.51 ꢃ 1.08
0.05 ꢃ 0.03
0.15 ꢃ 0.08
3.4 ꢃ 2.26
0.03 ꢃ 0.02
0.1 ꢃ 0.12
0.01 ꢃ 0.00
0.28 ꢃ 0.12
2.77 ꢃ 1.13
0.10 ꢃ 0.04
0.42 ꢃ 0.25
0.07 ꢃ 0.00
0.18 ꢃ 0.06
10.28 ꢃ 5.87
0.09 ꢃ 0.06
0.08 ꢃ 0.08
0.07 ꢃ 0.01
0.14 ꢃ 0.04
0.12 ꢃ 0.08
Intestine
[
99mTc]CpTT-6-oxo-HA, 4b
Blood
Brain
Heart
Liver
Spleen
Lung
Kidney
Muscle
Bone
0.51 ꢃ 0.08
0.04 ꢃ 0.01
0.35 ꢃ 0.07
1.79 ꢃ 0.51
0.33 ꢃ 0.3
0.43 ꢃ 0.07
2.18 ꢃ 0.54
0.1 ꢃ 0.07
0.12 ꢃ 0.88
0.17 ꢃ 0.01
0.26 ꢃ 0.02
0.03 ꢃ 0.00
0.17 ꢃ 0.02
1.96 ꢃ 0.16
0.17 ꢃ 0.03
0.23 ꢃ 0.02
2.07 ꢃ 0.12
0.1 ꢃ 0.04
0.14 ꢃ 0.05
0.03 ꢃ 0.02
0.16 ꢃ 0.03
2.74 ꢃ 1.58
0.19 ꢃ 0.07
0.23 ꢃ 0.05
2.79 ꢃ 0.65
0.09 ꢃ 0.08
0.19 ꢃ 0.13
0.11 ꢃ 0.01
0.11 ꢃ 0.01
0.01 ꢃ 0
0.09 ꢃ 1.23
0.01 ꢃ 0.08
0.08 ꢃ 0.97
2.08 ꢃ 0.23
0.16 ꢃ 0.06
0.11 ꢃ 0.01
2.5 ꢃ 0.93
0.08 ꢃ 0
2.49 ꢃ 0.27
0.14 ꢃ 0.01
0.12 ꢃ 0.02
3.09 ꢃ 0.24
0.08 ꢃ 0.02
0.08 ꢃ 0.02
0.09 ꢃ 0.02
0.05 ꢃ 0.02
0.12 ꢃ 0.06
0.08 ꢃ 0.03
0.14 ꢃ 0.02
0.16 ꢃ 0.02
Intestine

16
H. Zeng, H. Zhang / European Journal of Medicinal Chemistry 72 (2014) 10e17
The 99mTc-labeled fatty acid analogs reported here were incu-
thiophene branching at the b-position of 1b is beneficial to enhance
bated in rat serum for 3 h at 37 ꢀC and analyzed by radio-HPLC,
respectively. The results showed that over 94% of 1b, 98% of 2b,
99% of 3b, and 98% of 4b remained intact, indicating their high
in vitro stability to justify further investigation as molecular imag-
ing agents (Table 2).
The tissue compositions in rats can be considered as a special
type of solvent composed of lipophilic and hydrophilic molecules
(oil/water) [16]. The cardiomyocytes and the hepatocytes approx-
imatively represent the hydrophilic solvents and the lipophilic
solvents, respectively [17]. Hence the solubilities and bio-
distribution mechanism were studied by octanolewater partition
coefficients (P) of Tc-99m complexes. The log P values for 1b, 2b, 3b,
and 4b were 1.10 ꢃ 0.03, 1.21 ꢃ 0.03, 1.13 ꢃ 0.03, and 1.05 ꢃ 0.01,
respectively (Table 2). 1b shows a slightly lower log P than 2b and
3b shows a slightly higher log P than 4b, which indicate 1b and 4b
are more hydrophilic than that of 2b and 3b, respectively.
heart uptakes and decrease liver uptakes of Tc-99m-labeled fatty
acid analogs. For different animal species and experiment condi-
tions, it is probably inappropriate for direct comparisons in %ID/g of
radiotracers. However, a small-size Cyclopentadienyl Tricarbonyl
technetium-99m branched fatty acid may be superior to other
99mTc-labeled fatty acid analogs in terms of its facile conjugation of
[
99mTc(CO)3]þ to a fatty acid analog, some significant myocardial
accumulation, retention and low liver uptake [11].
Fatty acids can be metabolized in both heart and liver, thus it is
not sufficient that analysis of radioactive metabolites reported by
the previous researches was carried out in urine samples [5,6].
Recently, the radioactive metabolite of 99mTc-CpTT-pentadecanoic
acid [7] and 99mTc-CpTT-16-oxo-HDA [8] were analyzed using an
isolated Langendorff-perfused rat heart model and a simple
extraction from myocardial tissues method, respectively. In this
study, heart samples with 1b uptake were homogenized in a
mixture of CHCl3eMeOH-0.03 M NaOH and then the aqueous
fractions, organic and residual tissue pellets were counted with
results of 91.6:2.2:6.1 at 30 min (aqueous fraction:organic frac-
tion:tissue pellet), respectively (Table 4). When the aqueous frac-
tions and 1b were analyzed by HPLC under the same conditions,
respectively, a 99:1 ratio of the radioactive aqueous fractions at the
retentions times of 3.95 and 7.57 min was detected and a signal
peak of 1b at the retentions times of 7.56 min was observed, which
suggested that the retentions times of 3.95 and 7.57 min represent
the radioactive metabolite and 1b, respectively (Fig. 2). In order to
obtain the structure of the radioactive metabolite at 3.95 min, 1a as
a surrogate for 1b was injected into the rats via tail vein and the
metabolites from heart samples were characterized with the mass
spectrometric data (m/z (%) ¼ 700.2, Mþ; 701.1, [M þ H]þ). The mass
of the metabolite is derived from the mass difference between 1a
To evaluate the pharmacokinetics of 99mTc-CpTT-oxo-fatty acid
analogs in the heart, biodistribution experiments were performed
in normal Kunming mice, which were fasted for 12 h before ex-
periments because fatty acids are predominantly metabolized in
the fasting state. The results of the biodistribution experiments
showed that 1b and 2b are superior to 3b and 4b because they have
higher heart uptakes and heart-to-blood uptake ratios (Table 3). 1b
and 2b showed the maximum myocardial accumulation of 9.39 %
ID/g and 7.85 %ID/g at 1 min postinjection, respectively, followed by
a gradual washout from the heart. Low radioactivity levels of 3b
and 4b accumulated in blood, heart, spleen, lung and muscle except
liver and kidney at 1 min postinjection, followed by rapid clearance
from tissues. 3b demonstrated maximum myocardial uptake of 1.48
%ID/g at 15 min postinjection and the highest heart-to-blood up-
take ratio of 7.14 among the four tracers. The myocardial uptakes
and heart-to-blood uptake ratios of 3b increased at first and sub-
sequently lowered. As while 4b showed the maximum myocardial
accumulation of 0.35 %ID/g at 1 min postinjection, followed by
gradual clearance from the heart (Table 3). This branched agent, 3b,
exhibited the expected prolonged retention in the myocardium by
comparison with the unbranched analog 4b, which suggests that
the methyl branching at the beta-position may be an effective
means of inhibiting myocardial metabolism of Tc-99m-labeled fatty
acids. However, the medium chain fatty acids have faster oxidation
process and shorter retention time than the long chain fatty acids.
High radioactivity levels of 1b and 2b accumulated in liver,
heart, kidneys, lung and blood at 1 min postinjection, and cleared
rapidly with time from blood. While a low background of 1b and 2b
accumulated in blood, brain, muscle, intestine and bone from 5 min
postinjection. 1b (9.39 %ID/g at 1 min, 4.47 %ID/g at 5 min, 3.19 %ID/
g at 15 min, 1.48 %ID/g at 30 min and 0.93 %ID/g at 60 min post-
injection) was superior to that of 2b (7.85 %ID/g at 1 min, 3.74 %ID/g
at 5 min, 2.32 %ID/g at 15 min, 1.20 %ID/g at 30 min and 0.64 %ID/g
at 60 min postinjection) because 1b had higher heart uptakes and
heart-to-blood uptake ratios (%ID/g ratio of 1b vs 2b: 2.1 vs 1.7 at
1 min, 5.39 vs 3.34 at 5 min, 5.70 vs 3.52 at 15 min, 3.52 vs 3.53 at
30 min and 3.00 vs 2.29 at 60 min postinjection). The maximum
heart-to-liver uptake ratio of 1b (0.91 at 1 min postinjection) was
higher than that of 2b (0.29 at 1 min postinjection) and other
similar tracers from literature (Table 3), which suggested that the
Table 4
Distribution of radioactivity in mouse heart homogenates at 30 min postinjection of
1b.a
Fig. 2. Metabolite analysis of heart tissue samples from mice injected via a tail vein
with 1b. Upper chart: radiochromatogram in aqueous fractions of heart samples at
30 min postinjection of 1b; lower chart: radiochromatogram of 1b. HPLC analysis was
% Aqueous fraction
% Organic fraction
2.2
% Tissue pellet
6.1
91.6
conducted using an analytical column (Alltima C-18, 5
NaI(Tl) radioactivity detector.
m, 4.6 mm ꢁ 250 mm) and a
a
Values are given as means ꢃ SD of 3 experiments.

H. Zeng, H. Zhang / European Journal of Medicinal Chemistry 72 (2014) 10e17
17
and eCH2e, which indicates that the metabolite is not produced by
pentadecanoyl Thiopheneacetic
Acid
1 cycle of 1a b-oxidation. Thus, the metabolism of 1b is different
from that of 99mTc-MAMA-HDA, 99mTc-CpTT-pentadecanoic acid
and 99mTc-CpTT-16-oxo-HDA, which are metabolized to 99mTc-
MAMA-butyric acid, 99mTc-CpTT-propionic acid and 99mTc-CpTT-4-
[
99mTc]CpTR-15-oxo-PA (2b) 15-Cyclopentadienyl Tricarbonyl
technetium-99m 15-oxo-
pentadecanoic Acid
oxo-butyric acid via
b
-oxidation in myocardium, respectively.
[
99mTc]CpTR-5-oxo-MVA (3b) 5-Cyclopentadienyl Tricarbonyl
technetium-99m 3-methyl 5-oxo-
Metabolite analysis has not been carried out for other [99mTc]CpTT-
fatty acid analogs in Table 3. Anyway, the introduction of the
Cyclopentadienyl Tricarbonyl technetium-99m and the thiophene
valeric Acid
[
99mTc]CpTR-6-oxo-HA (4b) 6-Cyclopentadienyl Tricarbonyl
group at the
b
-position of 1b don’t significantly affect the biological
technetium-99m 6-oxo-hexanoic Acid
properties of [99mTc]CpTT-fatty acid analogs.
IPPA
123I-iodophenylpentadecanoic acid
BMIPP 15-(p-[123I]iodophenyl)-3-methylpentadecanoic acid
99mTc-MAMA-HDA [99mTc]-MAMA-hexadecanoic acid
99mTc-CpTT-16-oxo-HDA 16-Cyclopentadienyl Tricarbonyl 99mTc
16-Oxo-hexadecanoic Acid
4. Conclusions
The novel tricarbonyl rhenium/technetium-99m-labeled fatty
acid analogs were prepared in yield of 11.7e30.3% (no decay cor-
rected) by a double ligands transfer reaction. The in vivo evaluation
of 1b, 2b, 3b and 4b demonstrated that high heart-to-blood uptake
ratios and moderate retention time in heart were beneficial to
ischemia myocardial evaluation, but 3b and 4b cannot be used as
myocardical imaging agent for poor myocardial uptake and lower
heart-to-liver ratios.1b have high initial myocardial uptake and low
liver uptakes, and radioactive metabolite analysis suggested that 1b
99mTc-CpTT-PA [99mTc]Tricarbonyl(15-cyclopentadieyl
pentadecanoic acid)-technetium
9-THDA 9-[123mTe]-telluraheptadecanoic acid
DTPA
EDTA
Diethylene triamine pentacetate acid
Ethylene diamine tetraacetic acid
References
was not metabolized via
b-oxidation in myocardium. Further
[1] K. Yoshinaga, N. Tamaki, Curr. Opin. Biotechnol. 18 (2007) 52e59.
[2] N. Tamaki, K. Morita, Y. Kuge, E. Tsukamoto, J. Nucl. Med. 41 (2000) 1525e
1534.
[3] M. Eisenhut, W.D. Lehmann, A. Sutterle, Nucl. Med. Biol. 20 (1993) 747e754.
[4] F.F. Knapp Jr., P. Franken, J. Kropp, J. Nucl. Med. 36 (1995) 1022e1030.
[5] Y. Magata, T. Kawaguchi, M. Ukon, N. Yamamura, T. Uehara, K. Ogawa,
Y. Arano, T. Temma, T. Mukai, E. Tadamura, H. Saji, Bioconjugate Chem. 15
(2004) 389e393.
investigation with metabolites is now under way. These results
suggest that 1b can be used as a substrate for evaluation of
myocardial viability.
Acknowledgments
The authors are gratefully acknowledged financial support from
the Natural Science Foundation of China (No. 21071021) and the
Research Fund for the Doctoral Program of Higher Education (No.
20120101120039).
[6] B.C. Lee, D.H. Kim, J.H. Lee, H.J. Sung, Y.S. Choe, D.Y. Chi, K.H. Lee, Y. Choi,
B.T. Kim, Bioconjugate Chem. 18 (2007) 1332e1337.
[7] T. Uehara, T. Uemura, S. Hirabayashi, S. Adachi, K. Odaka, H. Akizawa,
Y. Magata, T. Irie, Y. Arano, J. Med. Chem. 50 (2007) 543e549.
[8] B.C. Lee, D.H. Kim, I. Lee, Y.S. Choe, D.Y. Chi, K.H. Lee, Y. Choi, B.T. Kim, J. Med.
Chem. 51 (2008) 3630e3634.
[9] W.C. Eckelman, S.M. Karesh, R.C. Reba, J. Pharm. Sci. 64 (1975) 704e706.
[10] S.M. Karesh, W.C. Eckelman, R.C. Reba, J. Pharm. Sci. 66 (1977) 225e228.
[11] H. Zeng, L. Zhao, S. Hu, Y. Liu, H. Yu, N. Chen, H. Zhang, Dalton Trans. 42 (2013)
2894e2901.
[12] J. Bernard, K. Ortner, B. Spingler, H.J. Pietzsch, R. Alberto, Inorg. Chem. 42
(2003) 1014e1022.
[13] F.F. Knapp Jr., K.P. Ambrose, A.P. Callahan, J. Nucl. Med. 21 (1980) 258e263.
[14] M. Eisenhut, E.H. William, W.J. Wilhelm, H. Johannes, Z. Jorg, R. Zimmermann,
J. Nucl. Med. 38 (1997) 1864e1869.
[15] T.W. Spradau, J.A. Katzenellenbogen, Organometallics 17 (1998) 2009e2017.
[16] M. Orozco, F.J. Luque, Chem. Rev. 100 (2000) 4187e4226.
[17] H. Zhang, Y. Zhang, J. Med. Chem. 49 (2006) 5815e5829.
Abbreviations used
SPECT
PET
Single-photon emission computed tomography
Positron emission tomography
HPLC
SD
High-performance liquid chromatography
Sprague Dawley
[
[
99mTc]CpTT [99mTc]cyclopentadienyltricarbonyltechnetium
99mTc]CpTT-15-oxo-PTA (1b) 15-Cyclopentadienyl Tricarbonyl
technetium-99m 15-oxo-