Technetium-99m-labeled long chain fatty acid analogues metabolized by β-oxidation in the heart

Article abstract of DOI:10.1021/jm061017g

The development of ^99mTc-labeled fatty acid analogues metabolized by β-oxidation in the myocardium constitutes an unsolved challenge. On the basis of our recent findings that [¹⁸⁸Re] tricarbonyl(cyclopentadienylcarbonate)rhenium ([¹⁸⁸Re]CpTR-COOH) was recognized as an aromatic compound and was metabolized as such in the body, [^99mTc]cyclopentadienyltricarbonyltechnetium ([^99mTc]CpTT) was conjugated at the ω-position of pentadecanoic acid to prepare [ ^99mTc]CpTT-PA. When injected into rats, [^99mTc]CpTT-PA exhibited the maximum myocardial accumulation and heart-to-blood ratio of 3.85 %ID/g at 1 min and 4.60 at 10 min postinjection, respectively. The metabolic study using isolated Langendorff perfused rat hearts demonstrated that approximately 67% of perfused [^99mTc]CpTT-PA was incorporated and [^99mTc]-CpTT-propionic acid, the metabolite after six cycles of β-oxidation of [^99mTc]CpTT-PA, was detected as the major radiometabolite in the perfusate and myocardium. These findings indicate that [^99mTc]CpTT-PA was recognized, transported, and metabolized as a long chain fatty acid analogue for energy production in the myocardium.

Full text of DOI:10.1021/jm061017g

J. Med. Chem. 2007, 50, 543-549
543
Technetium-99m-Labeled Long Chain Fatty Acid Analogues Metabolized by â-Oxidation in the
Heart
†
†
†
†
‡
†
Tomoya Uehara, Tomoe Uemura, Seiji Hirabayashi, Sayaka Adachi, Kenichi Odaka, Hiromichi Akizawa,
§
‡
†,
Yasuhiro Magata, Toshiaki Irie, and Yasushi Arano *
Graduate School of Pharmaceutical Sciences, Chiba UniVersity, 1-8-1 Inohana, Chuo-ku, Chiba 260-8675, Japan, Molecular Imaging Center,
National Institute of Radiological Sciences, Anagawa, Inage-ku, Chiba 260-8888, Japan, and Photon Medical Research Center, Hamamatsu
UniVersity School of Medicine, 1-20-1 Handayama, Hamamatsu 431-3192, Japan
ReceiVed August 23, 2006
The development of 99mTc-labeled fatty acid analogues metabolized by â-oxidation in the myocardium
1
88
constitutes an unsolved challenge. On the basis of our recent findings that [ Re]tricarbonyl(cyclopenta-
188
dienylcarbonate)rhenium ([ Re]CpTR-COOH) was recognized as an aromatic compound and was
metabolized as such in the body, [9 Tc]cyclopentadienyltricarbonyltechnetium ([ Tc]CpTT) was conjugated
9m
99m
9
9m
99m
at the ω-position of pentadecanoic acid to prepare [ Tc]CpTT-PA. When injected into rats, [ Tc]CpTT-
PA exhibited the maximum myocardial accumulation and heart-to-blood ratio of 3.85 %ID/g at 1 min and
4
.60 at 10 min postinjection, respectively. The metabolic study using isolated Langendorff perfused rat
9
9m
99m
hearts demonstrated that approximately 67% of perfused [ Tc]CpTT-PA was incorporated and [ Tc]-
CpTT-propionic acid, the metabolite after six cycles of â-oxidation of [ Tc]CpTT-PA, was detected as
the major radiometabolite in the perfusate and myocardium. These findings indicate that [ Tc]CpTT-PA
was recognized, transported, and metabolized as a long chain fatty acid analogue for energy production in
the myocardium.
9
9m
9
9m
Introduction
Long chain fatty acids constitute a major source of energy
in normal myocardium.1,2 Since regional alternations in the
myocardial fatty acid metabolism usually occur in ischemic heart
disease and cardiomyophathies, radiolabeled long chain fatty
acid analogues play an important role in the diagnosis of heart
3
disease and have been proven useful in the differential diagnosis
4
11
of unstable angina or severe heart ischemia. Carbon-11 ( C)
123
123
labeled palmitic acid, iodine-123 ( I) labeled 15-(p-[ I]-
123
a
iodophenyl)pentadecanoic acid ([ I]IPPA, Figure 1A), and
5-(p-[123I]iodophenyl)-3-(R,S)-methylpentadecanoic acid ([123I]-
BMIPP) are the representative fatty acid analogues used in
Figure 1. Chemical strucures of IPPA (A) and CpTT-PA (B).
1
We have previously observed that 99mTc-labeled N-[[[(2-
mercaptoethyl)amino]carbonyl]methyl]-N-(2-mercaptoethyl)-6-
5
,6
clinical studies. However, an on-site cyclotron is required to
99m
1
1
aminohexanoic acid ([ Tc]MAMA-HA), a medium chain fatty
produce C-labeled palmitic acid, and radioiodinated com-
pounds must be obtained from radiopharmaceutical companies.
Since heart disease generally requires an urgent examination,
it would be useful if an on-site radiopharmaceutical could be
used for clinical diagnosis. Thus, efforts have been made to
1
5
acid analogue, was metabolized by â-oxidation in the liver
9
9m
and that [ Tc]MAMA-conjugated hexadecanoic acid (HDA),
a long chain fatty acid analogue of [ Tc]MAMA-HA, showed
heart-to-blood ratios of 3.6 at 2 min postinjection. The
metabolic study also indicated that [ Tc]MAMA-HDA was
99m
16
9
9m
99m
7-14
develop Tc-labeled fatty acid analogues.
However, these
99m
metabolized by â-oxidation in the body. These findings suggest
Tc-labeled fatty acid analogues suffered from poor myocar-
9
9m
that an incorporation of an appropriate
chain fatty acid would provide
Tc chelate to a long
Tc-labeled fatty acid ana-
logues recognized and metabolized by the heart.
dial uptake. In addition, it remains uncertain whether they were
metabolized by â-oxidation in the heart.
9
9m
188
We have also observed that [ Re]tricarbonyl(cyclopentadi-
enylcarbonate)rhenium ([ Re]CpTR-COOH) was recognized
as an aromatic compound and was metabolized as such in the
body. The organometallic rhenium compounds have chemical
properties similar to technetium counterparts.
*
To whom correspondence should be addressed. Tel: +81-43-226-2896.
1
88
Fax: +81-43-226-2897. E-mail: arano@p.chiba-u.ac.jp.
†
Chiba University.
National Institute of Radiological Sciences.
Hamamatsu University School of Medicine.
Abbreviations: CpTR-COOH, tricarbonyl(cyclopentadienylcarbonate)-
‡
17
§
18-20
a
These results
rhenium; CpTT, cyclopentadienyltricarbonyltechnetium; IPPA, 15-(p-io-
dophenyl)pentadecanoic acid; BMIPP, 15-(p-iodophenyl)-3-(R,S)-methyl-
pentadecanoic acid; CpTT-PA, tricarbonyl(15-cyclopentadienyl pentadecanoic
acid)technetium; CpTR-PA, tricarbonyl(15-cyclopentadienyl pentadecanoic
acid)rhenium; CpTT-propionic acid, tricarbonyl(3-cyclopentadienyl propi-
onic acid)technetium; CpTR-propionic acid, tricarbonyl(3-cyclopentadienyl
propionic acid)rhenium; MAMA-HA, N-[[[(2-mercaptoethyl)amino]carbo-
nyl]methyl]-N-(2-mercaptoethyl)-6-aminohexanoic acid; MAMA-HDA,
N-[[[(2-mercaptoethyl)amino]carbonyl]methyl]-N-(2-mercaptoethyl)-con-
jugated hexadecanoic acid.
suggest that cyclopentadienyltricarbonyltechnetium (CpTT) may
constitute an appropriate molecule to prepare a
99m
Tc-labeled
long chain fatty acid that reflects fatty acid metabolism in the
heart.
In this study, [99mTc]CpTT was introduced at the ω-position
99m
of a pentadecanoic acid to prepare [ Tc]CpTT-PA (Figure 1B).
The biodistribution of radioactivity after injection of [ Tc]-
CpTT-PA was compared with [ I]IPPA in rats. The myocar-
99m
1
25
1
0.1021/jm061017g CCC: $37.00 © 2007 American Chemical Society
Published on Web 01/05/2007

5
44 Journal of Medicinal Chemistry, 2007, Vol. 50, No. 3
Uehara et al.
Scheme 1. Synthetic Procedure for [185/187Re]CpTR-PA and [99mTc]CpTT-PAa
a
Reagents and conditions: (a) SOCl2, MeOH; (b) Ba(OH)2; (c) SOCl2; (d) AlCl3, ferrocene; (e) CrCl3, Cr(CO)6, 99mTcO4- or 185/187ReO4 ; (f) TiCl4,
-
Et3SiH; (g) 2 N NaOH.
Table 1. RP-HPLC Retention Times of [99mTc]CpTT-PA,
observed with [125I]IPPA from 2 to 30 min postinjection. As a
185/187
[
Re]CpTR-PA, and Their Synthetic Precursors
125
result, while [ I]IPPA exhibited the highest heart-to-blood ratio
99m
retention
of the radioactivity of 12.46 at 2 min postinjection, [ Tc]-
CpTT-PA reached the highest ratio of 4.60 at 10 min postin-
jection. In contrast, the radioactivity levels in the liver remained
compd
time (min)
4
4
5
5
a
b
a
b
14
15.5
23
24
15.5
17.5
125
99m
unchanged after injection of [ I]IPPA, whereas [ Tc]CpTT-
PA showed a gradual increase with times. The radioactivity
levels in the stomach were low for the two radiolabeled fatty
acid analogues.
1
85/187
[
[
Re]CpTR-PA
Tc]CpTT-PA
9
9m
Metabolic Analysis. Metabolite analysis was carried out in
an isolated perfused rat heart model. After completion of the
perfusion, the rat heart contained 34.5 ( 3.83% of perfused
dium metabolism of [99mTc]CpTT-PA was also compared with
125
[
I[IPPA using the Langendorff rat heart model. The molecular
99m
design of [ Tc]CpTT-PA for measuring fatty acid metabolism
in the heart was estimated.
99m
125
radioactivity for [ Tc]CpTT-PA and 90.5 ( 4.59% for [ I]-
99m
125
IPPA. More than 93% of Tc and I radioactivity in the heart
homogenates was extracted into the organic phase. Figure 2
depicts TLC radiochromatograms of the rat heart extract. The
highest radioactivity counts were detected in fractions of higher
Results
Synthesis of [185/187Re]CpTR-PA, [ Tc]CpTT-PA, and
99m
1
85/187
Their Derivatives. Both nonradioactive [
[
Re]CpTR-PA and
9
9m
125
Rf values than intact [ Tc]CpTT-PA or [ I]IPPA (55% for
99m
Tc]CpTT-PA were synthesized under similar procedures as
9
9m
125
[
Tc]CpTT-PA and 76% for [ I]IPPA). The minor compo-
nents were observed as [ Tc]CpTT-PA (15%) and more
hydrophilic compounds (30%) for [ Tc]CpTT-PA, [ I]IPPA
(14%) and more hydrophilic compounds (10%) for [ I]IPPA.
outlined in Scheme 1. Compound 3 was prepared by acylation
9
9m
of ferrocene with acid chloride of compound 2 in the presence
99m
125
of AlCl3.21 The double ligand transfer reaction of the ferrocene
125
1
85/187
-
precursor, compound 3, with nonradioactive
ReO4 or
9
9m
-
20
TcO4 produced compound 4a or 4b. The carbonyl group
After hydrolysis of the rat heart extract, more than 92% of
Tc and I radioactivity was recovered in the organic phase.
Figure 3a shows RP-HPLC radiochromatograms of the hydro-
9
9m
125
in compounds 4a and 4b was then reduced according to the
procedure of Bhattacharyya22 using titanium(IV) chloride and
9
9m
125
triethylsilane. Afterward, the methyl ester of compounds 5a and
lyzed rat heart extract of Tc radioactivity trace (left) and
I
99m
99m
5
b was saponified to produce [185/187Re]CpTR-PA and [ Tc]-
radioactivity trace (right). Besides [ Tc]CpTT-PA, multiple
radioactivity peaks were observed at retention times shorter than
Tc]CpTT-PA. A polar component (5.5 min) showed a
retention time similar to that of [ Tc]CpTT-propionic acid,
CpTT-PA. After purification by RP-HPLC, [ 9mTc]CpTT-PA
9
9
9m
was obtained with a radiochemical yield and purity of 10.1%
[
9
9m
(
not decay corrected) and over 93%. The comparative RP-HPLC
99m
185/187
retention times of CpTM (M )
are summarized in Table 1.
Tc or
Re) derivatives
125
as determined by co-chromatography. Similarly, the I radio-
activity trace of the hydrolyzed heart extract exhibited some
radioactivity peaks with the major radioactivity peak being
observed at a retention time of 26 min, similar to that of 13-
Nonradioactive tricarbonyl(3-cyclopentadienyl propionic acid)-
1
85/187
99m
rhenium ([
Re]CpTR-propionic acid) and its
Tc coun-
9
9m
terpart ([ Tc]CpTT-propionic acid) were synthesized accord-
(
p-iodophenyl)tridecanoic acid, as determined by co-chroma-
tography.
The rat heart perfusate was extracted by organic solvents with
ing to the procedure as described above. [1
85/187
Re]CpTR-
propionic acid showed a retention time of 5.0 min on RP-HPLC
9
9m
(
system 2), while [ Tc]CpTT-propionic acid had a retention
9
9m
125
more than 92% efficiency for both Tc and I radioactivity.
Figure 3b shows the radiochromatograms of the perfusate.
time of 5.5 min under similar conditions.
Biodistribution Study. The biodistribution of radioactivity
9
9m
after simultaneous injection of [9 Tc]CpTT-PA and [ I]IPPA
9m
125
[
Tc]CpTT-PA accounted for approximately 50% of the
9
9m
to rats is summarized in Table 2. [99mTc]CpTT-PA showed the
radioactivity in the perfusate. Besides [ Tc]CpTT-PA, the
9
9m
Tc radioactivity trace showed two major radioactivity peaks
at retention times of 2.5 min and 5.5 min. The radioactive peak
maximum myocardial accumulation of 3.85 %ID/g at 1 min
postinjection, followed by a gradual washout from the heart.
9
9m
1
25
at a retention time of 5.5 min was coeluted with [ Tc]CpTT-
[
I]IPPA registered the time-course of radioactivity in the heart
1
25
125
99m
125
propionic acid. The I radioactivity trace showed [ I]IPPA
along with a radioactivity peak at a retention time of 5 min,
which was coeluted with p-iodobenzoic acid. Approximately
40% of the radioactivity in the perfusate was detected at [1 I]-
IPPA fraction.
similar to [ Tc]CpTT-PA except that [ I]IPPA reached the
maximum radioactivity level of 7.59 %ID/g at 1 min post-
injection. [9 Tc]CpTT-PA showed a slow elimination rate of
radioactivity from the blood at earlier postinjection time,
whereas a gradual increase in radioactivity in the blood was
9m
25

99mTc-Labeled Fatty Acid Analogue
Journal of Medicinal Chemistry, 2007, Vol. 50, No. 3 545
Table 2. Biodistribtuion of Radioactivity in Rats after Co-Injection of [99mTc]CpTT-PA and [125I]IPPAa
time after injection
1
min
2 min
5 min
10 min
30 min
[99m
Tc]CpTT-PA
blood
heart
liver
kidney
stomach
heart/blood
4.59 (0.20)
3.85 (0.58)
3.04 (0.30)
1.07 (0.11)
0.34 (0.04)
0.84 (0.15)
2.70 (0.15)
3.64 (0.48)
5.01 (0.33)
1.15 (0.11)
0.43 (0.02)
1.35 (0.15)
0.93 (0.12)
2.71 (0.44)
6.44 (0.30)
1.30 (0.20)
0.42 (0.05)
2.93 (0.36)
0.41 (0.04)
1.87 (0.14)
7.56 (0.43)
1.76 (0.23)
0.40 (0.05)
4.60 (0.46)
0.38 (0.10)
1.27 (0.28)
7.86 (1.84)
1.79 (0.40)
0.39 (0.10)
3.44 (0.55)
b
[125I]IPPAc
blood
heart
liver
kidney
stomach
1.28 (0.10)*
7.59 (1.00)*
2.60 (0.38)
1.45 (0.08)
0.64 (0.11)
5.98 (1.12)*
0.57 (0.09)*
6.90 (1.02)*
3.56 (0.30)*
1.55 (0.12)
0.64 (0.05)
12.46 (3.29)*
0.78 (0.15)*
5.67 (1.03)*
3.56 (0.38)*
1.41 (0.29)
0.52 (0.05)
7.59 (2.33)*
0.78 (0.18)*
5.22 (0.57)*
3.71 (0.39)*
1.30 (0.12)
0.51 (0.05)
7.11 (2.57)*
0.92 (0.13)*
4.19 (1.66)*
2.65 (0.61)*
1.16 (0.26)
0.48 (0.14)
4.52 (1.88)
b
heart/blood
a
Tissue radioactivity is expressed as % ID/g for each group (n ) 5); results are expressed as mean (SD). Expressed as %ID. c Significances determined
b
9
9m
by unpaired student’s t-test; (*) p < 0.05 compared to [ Tc]CpTT-PA.
PA, and [99mTc]CpTT-PA are summarized in Table 1. 99mTc-
1
85/187
labeled compounds and their [
Re]CpTR counterparts
exhibited similar changes in their retention times after each
reaction. Slight differences in RP-HPLC retention times between
9
9m
185/187
[
Tc]CpTT derivatives and their [
Re]CpTR counterparts
9
9m
were observed, and [ Tc]CpTT derivatives showed slightly
longer retention times than did their [
1
85/187
Re]CpTR counter-
parts, as shown in Table 1. Similar differences in RP-HPLC
99m
retention times were observed between [ Tc]CpTT derivatives
1
85/187
Re]CpTR counterparts.23,24 From these
and their
[
99m
Figure 2. TLC radioactivity profiles of rat heart extracts after 2 h
results, we concluded that the chemical structure of [ Tc]-
9
9m
125
perfusion of [ Tc]CpTT-PA (a) and [ I]IPPA (b). Under these
CpTT-PA would be identical to its rhenium counterpart,
9
9m
125
185/187
conditions, [ Tc]CpTT-PA and [ I]IPPA had R
.35, respectively.
f
values of 0.30 and
[
Re]CpTR-PA.
0
The Langendorff perfusion study was performed according
2
5
26
to the procedure of Yamamichi et al. and Mori et al. with
1
25
slight modifications. The majority of perfused [ I]IPPA was
incorporated in the myocardium and detected in lipid fractions
as 13-(p-[ I]iodophenyl)tridecanoic acid (Figures 2 and 3). On
the other hand, p-[ I]iodobenzoic acid was observed as the
major radiometabolite in the perfusate (Figure 3). Previous
studies of radiolabeled and non-radioactive IPPA in perfused
heart showed the presence of a variety of metabolites including
p-iodobenzoic acid and 11-(p-iodophenyl)undecanoic acid along
125
1
25
27,28
with a small amount of IPPA.
A variety of radiometabolites
were also observed in the hydrolyzed heart extracts of perfused
123
25,29,30
heart following injection of [ I]BMIPP.
There were some
differences in the components of perfusate between present and
previous studies, which would have affected the metabolism of
1
25
[
I]IPPA in the heart. These results indicated that the present
Langendorff perfusion model would be appropriate for estimat-
ing fatty acid metabolism of the heart.
[99m
Tc]CpTT-PA exhibited the highest myocardial accumula-
Figure 3. RP-HPLC radioactivity profiles of hydrolyzed rat heart lipids
9
9m
tion of 3.85 %ID/g at 1 min postinjection with a maximum heart-
to-blood ratio of 4.60 at 10 min postinjection (Table 2). In the
(
a) and rat heart perfusate (b) after 2 h perfusion of [ Tc]CpTT-PA
125
and [ I]IPPA. RP-HPLC profiles of authentic samples are also shown
in (c). Under these conditions, [ Tc]CpTT-PA, [ Tc]CpTT-propionic
acid, [ I]IPPA, 13-(p-[ I]iodophenyl)tridecanoic acid, and p-[ I]-
iodobenzoic acid had retention times of 26, 5.5, 28.5, 26.5, and 5 min,
respectively.
99m
99m
Langendorff perfusion study, approximately 34% of perfused
1
25
125
125
99m
[
3
Tc]CpTT-PA was retained in the heart, and approximately
3% in the perfusates was present as metabolites (Figures 2
9
9m
and 3). Since high in vivo stability of CpTM (M )
Tc or
the
1
86/188
17,20,23,24,31
Re) structure has been well documented,
Discussion
99m
multiple radioactivity peaks on RP-HPLC between [ Tc]-
CpTT-PA and [ Tc]CpTT-propionic acid suggested the pres-
[99m
Tc]CpTT-PA and its precursors were synthesized accord-
99m
ing to the procedures similar to those of nonradioactive rhenium
compounds, as outlined in Scheme 1, and were characterized
by RP-HPLC using their well-characterized nonradioactive
ence of multiple radiometabolites, as also observed in the
25,27-30
metabolic studies of radioiodinated fatty acid analogues.
9
9m
The gathered findings demonstrated that [ Tc]CpTT-PA was
incorporated into myocardium, recognized as a fatty acid and
metabolized as such.
1
85/187
[
Re]rhenium counterparts as references. The RP-HPLC
185/187
retention times of compounds 4a, 4b, 5a, 5b, [
Re]CpTR-

5
46 Journal of Medicinal Chemistry, 2007, Vol. 50, No. 3
Uehara et al.
of the heart. Thus, the present study may pave the way for
9
9m
developing
Tc-labeled fatty acid analogues that provide
myocardial fatty acid metabolism by external imaging in clinical
studies.
Experimental Section
General Information. [99mTc]Pertechnetate (99mTcO -) was
4
eluted in saline solution on a daily basis from Daiichi Radioisotopes
Labs generator (Chiba, Japan). Reversed phase HPLC (RP-HPLC)
was performed with a Cosmosil 5C18-AR-300 column (4.6 × 150
mm, Nacalai Tesque, Kyoto, Japan) at a flow rate of 1 mL/min
with a gradient mobile phase starting from 30% A (0.1% aqueous
trifluoroacetic acid (TFA)) and 70% B (acetonitrile with 0.1% TFA)
to 0% A and 100% B at 30 min (system 1) or from 50% A and
Figure 4. Fate of [99mTc]CpTT-PA and [125I]IPPA in perfused rat hearts
after 2 h recirculation of perfusate.
5
0% B to 0% A and 100% B at 30 min (system 2). Each eluent
Figure 4 summarizes the fate of [99mTc]CpTT-PA and [125I]-
IPPA in perfused rat heart after 2 h recirculation of perfusate.
The proportion of [9 Tc]CpTT-PA incorporated into myocar-
was collected with a fraction collector (RediFlac, GE Healthcare
Bioscience, Tokyo, Japan) at 30 s intervals, and the radioactivity
counts in each fraction (500 µL) were determined with an auto
well γ counter (ARC-380M, Aloka, Tokyo). The radioactivity of
9m
1
25
dium during perfusion was lower than that of [ I]IPPA
99m
approximately 67% for [99mTc]CpTT-PA and 96% for [ I]-
125
the eluent was measured immediately for Tc radioactivity (120
(
125
-
150 keV) and 5 days later for I radioactivity (20 - 40 keV) to
IPPA). Similar results were observed in a biodistribution study
99m 125
99m
reduce the crossover of the Tc radioactivity to the I channel.
where myocardial uptake of [ Tc]CpTT-PA was significantly
lower than that of [1 I]IPPA (Table 2). Besides passive
diffusion, long chain fatty acids are incorporated into myocar-
dium via protein-mediated system such as translocase/CD36 and
The crossover of 1 I activity to the 99mTc channel was negligible.
25
25
TLC analyses were performed with silica plates (Silica gel 60 F254
,
Merck, Tokyo) developed with chloroform. SepPak Plus (C18 short
body, 360 mg/cartridge, Waters, Tokyo) was activated with 6 mL
each of ethanol and water prior to use. Proton nuclear magnetic
resonance ( H-NMR) spectra were recorded on a JEOL JNM-
ALPHA 400 spectrometer (JEOL Ltd., Tokyo) with tetramethyl-
silane as an internal standard. Fast-atom bombardment mass spectra
fatty acid transport protein.1
,32-34
[
99m
Tc]CpTT-PA is a lipophilic
125
1
compound with a retention time slightly shorter than [ I]IPPA
on RP-HPLC. Thus, the lower myocardial uptake of [ Tc]-
CpTT-PA would be attributable to the low affinity of [ Tc]-
CpTT-PA for the fatty acid transporter(s). This may also account
9
9m
9
9m
(FAB-MS) were taken on a JEOL JMS-HX-110A mass spectrom-
eter (JEOL Ltd.). Two masses were reported for rhenium-containing
fragments to indicate the significant isotopic abundances of both
for the slower elimination rate of radioactivity from the blood
at earlier postinjection time of [99mTc]CpTT-PA.
185
187
Re and Re. Each peak was observed to have the proper relative
abundances. Elemental analyses were performed by PE-2400
Once taken up in the myocardium, more than 92% of [99mTc]-
CpTT-PA was metabolized to [9 Tc]CpTT-propionic acid or
converted to lipids. Similarly, approximately 88% of perfused
9m
125
(Perkin-Elmer Japan, Tokyo). 15-(p-[ I]Iodophenyl)pentadecanoic
125
acid ([ I]IPPA) and 13-(p-iodophenyl)tridecanoic acid were
prepared according to the procedure described previously.
reagents were of reagent grade and used as received.
1
25
16,40
[
I]IPPA was metabolized or converted to lipids. The majority
Other
125
of [ I]IPPA was stored in lipids after one cycle of â-oxidation.
In contrast, the majority of [ Tc]CpTT-PA was metabolized
to [ Tc]CpTT-propionic acid, a metabolite after six cycles of
99m
Pentadecanedioic Acid Monomethyl Ester (2). Thionyl chlo-
ride (4 mL, 55 mmol) was added dropwise to methanol (40 mL) at
-10 °C. After the solution stood for 10 min at the same temperature,
pentadecanedioic acid (1) (6.0 g, 22 mmol) was added. The
temperature of the solution was gradually increased to the boiling
point, and the solution was refluxed for 5 h. After the solution was
cooled to room temperature, the solvent was evaporated in vacuo,
and the residue was dissolved in ether (40 mL). The organic layer
was washed with saturated aqueous NaCl (40 mL × 3) and then
9
9m
9
9m
â-oxidation of [ Tc]CpTT-PA, and excreted from the myo-
cardium although [99mTc]CpTT-COOH was expected as the final
radiometabolite. These results suggest that an introduction of
9
9m
[
Tc]CpTT moiety at the ω-position of pentadecanoic acid
99m
may have hindered further recognition of [ Tc]CpTT-propi-
onic acid by the enzymes involved in â-oxidation and may have
affected metabolic pathway during â-oxidation. Similar results
4
dried over anhydrous CaSO . After the solvent was removed,
99m
were observed in the metabolic studies of [ Tc]MAMA-HA
dimethyl ester of compound 1 was obtained as a white solid (6.3
g, 95.0%). This compound was used without further purification.
A solution of barium hydroxide (1.48 g, 8.5 mmol) in dry
methanol (100 mL) was added dropwise to a solution of the
dimethyl ester of compound 1 (5.25 g, 17 mmol) in dry methanol
(120 mL). After the mixture stood for 17 h at room temperature,
the precipitate was collected by suction filtration and washed with
methanol (20 mL). The barium salt was shaken for a few minutes
in a separatory funnel with a mixture of 4 N HCl (100 mL) and
ether (100 mL). The aqueous layer, together with any precipitated
barium chloride was removed and extracted again with ether (100
mL). The combined ether extracts were washed with water and
in the liver and [9 Tc]MAMA-HDA in the body, where [ Tc]-
9m
99m
MAMA-butyric acid was observed as the final radiometabolite
1
5,16 99m
of the two compounds.
[
Tc]CpTT-8-oxooctanoic acid also
generated [9 Tc]CpTT-4-oxobutyric acid in the body. This
suggests that an introduction of [ Tc]CpTT group at the
9m
23
99m
ω-position of a fatty acid would impair enzyme recognition less
9
9m
99m
than that of [ Tc]MAMA or [ Tc]CpTT-oxo group.
Conclusion
At the initial stage of 99mTc radiopharmaceutical development,
4
dried over anhydrous CaSO . After the solvent was removed, the
residue was purified by open column chromatography using silica
it was thought that Tc is a foreign substance and should be
recognized as such by the body. However, the development of
gel and subsequent elution with a mixture of ethyl acetate-hexane
9
9m
Tc-labeled compounds that cross the intact blood-brain
1
(1:2) to produce compound 2 (3.80 g, 78.2%). H-NMR (CDCl
3
)
-
3
5-37
barrier
stimulated the development of currently available
δ: 3.84 [s, 3H, CH
CH -CO-], 1.49 [s, 18H, -CH
Found: 287.
3
], 2.84 [m, 4H, -CH
2
-CO-], 1.79 [m, 4H, -CH
-]. FAB-MS: m/z 287 (M + H) .
2
+
9
9m
38,39
Tc-labeled perfusion agents of the brain.
The findings
2
2
in this study demonstrated for the first time that a long chain
99m
Tc-labeled fatty acid analogue, [99mTc]CpTT-PA, was trans-
15-Ferrocenoyl-15-oxopentadecanoic Acid Methyl Ester (3).
ported and metabolized as a substrate for the energy production
This compound was synthesized according to the procedure of

99mTc-Labeled Fatty Acid Analogue
Journal of Medicinal Chemistry, 2007, Vol. 50, No. 3 547
Vogel et al. with slight modification as follows.21 Compound 2
subsequent reduction of the carbonyl group, according to the
procedure described above in 5% yield. This compound showed a
(
2.0 g, 6.9 mmol) was dissolved in thionyl chloride (5 mL, 69
mmol) and refluxed for 3 h. After residual thionyl chloride was
removed in vacuo, the crude 1-methyl pentadecanedioic acid
chloride was dissolved in dichloromethane (10 mL) containing
anhydrous aluminum chloride (1.3 g, 9.8 mmol), and then it was
added dropwise to a solution of ferrocene (1.3 g, 6.9 mmol) in dry
dichloromethane (10 mL). The mixed solution was kept stirring
overnight and then poured into ice-cold water (30 mL). Ethyl acetate
single peak at a retention time of 5.0 min on RP-HPLC (system
1
2). H-NMR (CDCl
3
) δ: 5.23 [s, 4H, Cp], 2.35 [t, 2H, -CH
-CO-], 1.43-1.50 [m, 2H, -CH -]. FAB-MS: m/z
Re) C, H, N.
Tc]Tricarbonyl(15-cyclopentadienyl-15-oxopentadecano-
ic acid methyl ester)technetium (4b). This compound was
2
-Cp-],
2.30 [t, 2H, -CH
407/408 (M + H) . Found: 406/408. Anal. (C11
2
2
+
9 5
H O
99m
[
20
synthesized according to the procedure of Spradau et al. with slight
modification as follows. A solution of [9 Tc]NaTcO4 in dry
methanol (500 µL) was added to the mixture of compound 3 (10
mg, 22 µmol), chromium hexacarbonyl (14 mg, 64 µmol), and
chromium(III) chloride (11 mg, 58 µmol) in the pressure tube (0.8
× 8.5 cm, Taiatsu glass kogyo). The tube was inserted in silicon
oil at 180 °C for 45 min. After being cooled to room temperature,
the solvent was evaporated in vacuo. The residue was dissolved in
chloroform and purified by open column chromatography using
silica gel and subsequent elution with chloroform as an eluent to
produce the compound 4b in radiochemical yield of 80%.
9m
(
30 mL) was added to the solution, and the organic phase was
extracted and washed with brine (30 mL × 3) and then dried over
anhydrous CaSO . After the solution was removed, the residue was
4
purified by open column chromatography using silica gel and
subsequent elution with a mixture of chloroform-hexane (5:2) to
1
produce compound 3 (1.5 g, 49%). H-NMR (CDCl
2
3
) δ: 4.75 [s,
H, ferrocene], 4.47 [s, 2H, ferrocene], 4.18 [s, 5H, ferrocene],
.65 [s, 3H, COO-CH ], 2.68 [t, 2H, -CH -CO-], 2.29 [t, 3H, -CH
-CH -CO-], 1.24 [s, 18H, -CH -].
FAB-MS: m/z 455 (M + H) . Found: 455.
3
3
2
2
-
COO-], 1.59-1.70 [m, 4H -CH
2
2
2
+
99m
Tricarbonyl(15-cyclopentadienyl-15-oxopentadecanoic acid
methyl ester)rhenium (4a). This compound was synthesized
according to the procedure of Spradau et al.20 with slight modifica-
tion as follows. To a mixture of compound 3 (472 mg, 1.0 mmol),
ammonium perrhenate (89 mg, 0.33 mmol), chromium hexacarbonyl
[
Tc]Tricarbonyl(15-cyclopentadieyl pentadecanoic acid
methyl ester)technetium (5b). Titanium(IV) chloride (8 µL)
dissolved in dichloromethane (0.5 mL) was added to compound
4b. Triethylsilane (50.5 µL) dissolved in dichloromethane (0.5 mL)
was added to the mixture with stirring. After the mixture was stirred
for 1 h at room temperature, ether (2 mL) and water (2 mL) were
added to the mixture. The organic solvent was extracted from the
mixture and evaporated in vacuo to produce the compound 5b in
radiochemical yield of 55%.
(410 mg, 1.9 mmol), and chromium(III) chloride anhydrous (110
mg, 0.67 mmol) in a pressure tube (0.8 × 8.5 cm, Taiatsu glass
kogyo, Tokyo) was added dry methanol. After the tube was inserted
in silicon oil at 180 °C for 45 min, the reaction mixture was cooled
at room temperature. After the filtration through Celite, the filtrate
was removed in vacuo, and the residue was purified with open
column chromatography using silica gel and subsequent elution
using a mixture of ethyl acetate and hexane (1:4) to produce
99m
[
Tc]Tricarbonyl(15-cyclopentadieyl pentadecanoic acid)-
99m
technetium ([ Tc]CpTT-PA). Compound 5b was dissolved in
ethanol (600 µL) and mixed with 2 N aqueous sodium hydroxide
(200 µL) at 95 °C for 10 min. After being cooled to room
temperature, the mixture was neutralized with 2 N HCl and loaded
onto a SepPak plus cartridge. The cartridge was successively washed
with water (5 mL) and eluted with ethanol (3 mL). The first eluted
ethanol fraction (100 µL) was discarded, and the combined eluents
were evaporated in vacuo. The residue was purified by RP-HPLC
(system 1) to produce [9 Tc]CpTT-PA in radiochemical yield
1
compound 4a (54.5 mg, 27.3%) as a white powder. H-NMR
(
2
4
CDCl
3
) δ: 5.96 [s, 2H, Cp], 5.37 [s, 2H, Cp], 3.64 [s, 3H, CH
.55 [t, 2H, -CH -CO-], 2.28 [t, 3H, -CH -COO-], 1.55-1.68 [m,
H -CH -CH -CO-], 1.23 [s, 18H, -CH -]. FAB-MS: m/z 603/605
3
],
2
2
2
2
2
+
(M + H) . Found: 603/605.
9m
Tricarbonyl(15-cyclopentadienyl pentadecanoic acid methyl
ester)rhenium (5a). This compound was synthesized according to
the procedure of Bhattacharyya22 as follows. Compound 4a (47
mg, 78 µmol) was dissolved in dichloromethane (1 mL), and
titanium(IV) chloride (14.7 mg, 78 µmol) dissolved in dichloro-
methane (1 mL) was added to the solution. A solution of
triethylsilane (36.3 mg, 312 µmol) in dichloromethane (1 mL) was
then added to the mixture with stirring. After the mixture was stirred
for 14 h at room temperature, the organic layer was washed with
of 49%.
99m
[
Tc]Tricarbonyl(3-cyclopentadieyl propionic acid)techne-
tium ([9 Tc]CpTT-Propionic Acid). This compound was syn-
thesized by the reaction of ferrocene and malonic acid monomethyl
ester according to the procedure described above in radiochemical
yield of 21%. [9 Tc]CpTT-propionic acid showed a single
radioactivity peak at a retention time of 5.0 min on RP-HPLC
(system 2).
9m
9m
5
% sodium carbonate (5 mL) and dried over anhydrous CaSO
4
.
Biodistribution Study. Animal studies were conducted in
accordance with our institutional guidelines and were approved by
After the solvent was removed in vacuo, the residue was purified
by open column chromatography using silica gel and subsequent
elution using a mixture of chloroform-hexane (5:2) to produce the
99m
the Chiba University Animal Care Committee. [ Tc]CpTT-PA
(1.85 MBq) and [1 I]IPPA (1.85 MBq) were dissolved in ethanol
(750 µL) and added dropwise to a stirred solution of 1% bovine
serum albumin (BSA, 14.25 mL) in saline. The solution was then
filtered through a 0.22 µm polycarbonate filter. The solution (37
25
1
compound 5a as a white powder (23 mg, 50%). H-NMR (CDCl
3
)
δ: 5.20 [s, 4H, Cp], 3.62 [s, 3H, CH
.29 [t, 2H, -CH -CO-], 1.43-1.71 [m, 4H, -CH
CH -CO-], 1.23 [s, 20H, -CH -]. FAB-MS: m/z 589/591 (M +
3
], 2.37 [t, 2H, -CH
2
-Cp-],
2
2
2
-CH -Cp, -CH -
2
2
kBq each of [9 Tc]CpTT-PA and [ I]IPPA) was administered
to Wistar rats (male, 200 g) from tail vein. At appropriate time
points after the injection, rats were sacrificed by decapitation.
Tissues of interest were removed and weighed, and the radioactivity
counts were determined using an auto well γ counter.
9m
125
2
2
+
H) . Found: 589/591.
Tricarbonyl(15-cyclopentadienyl pentadecanoic acid)rhenium
[1
85/187
Re]CpTR-PA). Compound 5a (11 mg, 19 µmol) was
(
dissolved in ethanol (600 µL) and mixed with aqueous sodium
hydroxide (2 N, 200 µL) for 8 h at room temperature. After being
acidified with concentrated HCl (ca. 120 µL), ethyl acetate (5 mL)
was added to the solution and it was washed with 1% HCl solution
Isolated Rat Heart Studies. This study was performed according
to the procedure of Yamamichi et al.25 and Mori et al. with slight
modifications. The hearts were rapidly removed from the male
Wistar rats (200-300 g) anesthetized with pentobarbital (50 mg/
kg) and mounted on a Langendorff perfusion system. The perfusate
used was 5 mM HEPES buffer (pH 7.4) containing 123 mM NaCl,
5 mM KCl, 1 mM MgSO , 5 mM AcONa, 5 mM CaCl , and 6
26
(
5 mL × 3). After the solution was dried over anhydrous CaSO
4
,
185/187
the solution was evaporated in vacuo to obtain [
Re]CpTR-
) δ: 5.21
-CO-], 1.42-1.69 [m,
-CO-], 1.21 [s, 20H, -CH -]. FAB-
1
PA as a white solid (8.3 mg, 77.4%). H-NMR (CDCl
3
[s, 4H, Cp], 2.35 [m, 4H, -CH
2 2
-Cp-, -CH
4
2
4
H, -CH -CH -Cp, -CH -CH
2
2
2
2
2
mM glucose. The hearts were perfused at a steady rate of 8-10
mL/min by a peristaltic pump (Pump P-1, GE Healthcare Bio-
sciences), and oxygenation of the perfusate was achieved with a
+
MS: m/z 575/577 (M + H) . Found: 575/577. Anal. (C23
33 5
H O -
Re) C, H, N.
Tricarbonyl(3-cyclopentadienylpropionicacid)rhenium([185/187Re]-
CpTR-Propionic Acid). This compound was synthesized by the
reaction of ferrocene and malonic acid monomethylester and
mixture of 95% O
2 2
and 5% CO . The hearts had a steady rate of
contraction (180-200 times/min). After stabilizing the hearts for
10 min, a mixture of [9 Tc]CpTT-PA (74 kBq) and [ I]IPPA
9m
125

5
48 Journal of Medicinal Chemistry, 2007, Vol. 50, No. 3
Uehara et al.
(
74 kBq) in 0.3 mL of saline containing 1% BSA were loaded into
(13) Mach, R. H.; Kung, H. F.; Jungwiwattanaporn, P.; Guo, Y. Z.
Synthesis and biodistribution of a new class of 9 Tc-labeled fatty
acid analogs for myocardial imaging. Int. J. Radiat. Appl. Instrum.,
Part B 1991, 18, 215-226.
14) Maresca, K. P.; Shoup, T. M.; Femia, F. J.; Burker, M. A.; Fischman,
A.; Babich, J. W.; Zubieta, J. Synthesis, characterization, and
biodistribution of a Technetium-99m ‘3+1 fatty acid derivative. The
crystal and molecular structures of a series of oxorhenium model
complexes. Inorg. Chim. Acta. 2002, 338, 149-156.
9m
the perfusate (30 mL). After the perfusate was recirculated for 2 h,
the perfusate (5 mL) was acidified with 1 N HCl to pH 1.0 and the
radioactive fractions were extracted by passage through a SepPak
cartridge that was then eluted with methanol (5 mL, extract
efficiency of 92.6%). These methanol solutions were analyzed using
RP-HPLC (system 2). After the completion of the experiments, the
hearts were dismounted, minced, and homogenized. The lipids were
(
extracted using a modified Folch technique2
myocardial homogenates were mixed with 5 mL of 2:1 chloroform-
methanol and acidified with 50% H SO (pH 1) (extraction
efficiency of 93.2%). After the precipitate was removed, the filtrates
were analyzed by TLC. The filtrates were then hydrolyzed with
1
5
chloroform (3 mL, extraction efficiency: 92.7%). The extracts were
evaporated in vacuo and analyzed by RP-HPLC (system 2).
9,41
(15) Yamamura, N.; Magata, Y.; Arano, Y.; Kawaguchi, T.; Ogawa, K.;
Konishi, J.; Saji, H. Technetium-99m-labeled medium-chain fatty
acid analogues metabolized by beta-oxidation: radiopharmaceutical
for assessing liver function. Bioconjugate Chem. 1999, 10, 489-
in which the
2
4
495.
(
16) Magata, Y.; Kawaguchi, T.; Ukon, M.; Yamamura, N.; Uehara, T.;
Ogawa, K.; Arano, Y.; Temma, T.; Mukai, T.; Tadamura, E.; Saji,
H. A Tc-99m-labeled long chain fatty acid derivative for myocardial
imaging. Bioconjugate Chem. 2004, 15, 389-393.
0 M KOH (1 mL) at 60 °C for 1 h. After bringing acidified with
0% H SO (pH 1), the final products were extracted with
2
4
(
17) Uehara, T.; Koike, M.; Nakata, H.; Miyamoto, S.; Motoishi, S.;
Hashimoto, K.; Oku, N.; Nakayama, M.; Arano, Y. In vivo
recognition of cyclopentadienyltricarbonylrhenium (CpTR) deriva-
tives. Nucl. Med. Biol. 2003, 30, 327-334.
Acknowledgment. The authors appreciate Mr. Takashi
Kikawa at the Department of Radiology, Chiba University
Hospital, for supporting the experiments. The authors are
grateful to Dr. Yoshihiro Yamamichi at Nihon Medi-Phisics
Co. Ltd., Sodegaura, Japan, and Dr. Haruaki Nakaya at the
Department of Pharmacology, Graduate School of Medicine,
Chiba University, for technical advice about the isolated rat heart
study. The authors thank Mr. Takio Kobayashi for financial
support.
(
18) Schibli, R.; Schubiger, P. A. Current use and future potential of
organometallic radiopharmaceuticals. Eur. J. Nucl. Med. Mol. Imag-
ing 2002, 29, 1529-1542.
(
19) Mull, E. S.; Sattigeri, V. J.; Rodriguez, A. L.; Katzenellenbogen,
J. A. Aryl cyclopentadienyl tricarbonyl rhenium complexes:
novel ligands for the estrogen receptor with potential use as
estrogen radiopharmaceuticals. Bioorg. Med. Chem. 2002, 10, 1381-
1398.
(
20) Spradau, T. W.; Katzenellenbogen, J. A. Protein and peptide labeling
with (cyclopentadienyl)tricarbonyl rhenium and technetium. Biocon-
jugate Chem. 1998, 9, 765-772.
Supporting Information Available: Elemental analyses data
(21) Vogel, M.; Rausch, M.; Rosenberg, H. Derivatives of ferrocene. III.
Preparation of acyl- and alkylferrocenes. J. Org. Chem. 1957, 22,
1016-1018.
for tricarbonyl(15-cyclopentadienyl pentadecanoic acid)rhenium
185/187
([
Re]CpTR-PA) and tricarbonyl(3-cyclopentadienoyl propionic
185/187
(22) Bhattacharyya, S. Titanium(IV) Chloride-Triethylsilane: An Efficient,
Mild System for the Reduction of Acylferrocenes to Alkylferrocenes.
J. Org. Chem. 1998, 63, 7101-7102.
acid)rhenium ([
available free of charge via the Internet at http://pubs.acs.org.
Re]CpTR-propionic acid). This material is
(
23) Lee, B. C.; Choe, Y. S.; Chi, D. Y.; Paik, J. Y.; Lee, K. H.; Choi,
References
99m
Y.; Kim, B. T. 8-cyclopentadienyltricarbonyl
Tc 8-oxooctanoic
acid: a novel radiotracer for evaluation of medium chain fatty
(
1) Koonen, D. P.; Glatz, J. F.; Bonen, A.; Luiken, J. J. Long-chain fatty
acid uptake and FAT/CD36 translocation in heart and skeletal muscle.
Biochim. Biophys. Acta. 2005, 1736, 163-180.
acid metabolism in the liver. Bioconjugate Chem. 2004, 15, 121-
127.
(
24) Skaddan, M. B.; Wust, F. R.; Jonson, S.; Syhre, R.; Welch, M. J.;
Spies, H.; Katzenellenbogen, J. A. Radiochemical synthesis and tissue
distribution of Tc-99m-labeled 7alpha-substituted estradiol complexes.
Nucl. Med. Biol. 2000, 27, 269-278.
(25) Yamamichi, Y.; Kusuoka, H.; Morishita, K.; Shirakami, Y.;
Kurami, M.; Okano, K.; Itoh, O.; Nishimura, T. Metabolism of iodine-
123-BMIPP in perfused rat hearts. J. Nucl. Med. 1995, 36, 1043-
1050.
(26) Mori, K.; Hara, Y.; Saito, T.; Masuda, Y.; Nakaya, H. Anticholinergic
effects of class III antiarrhythmic drugs in guinea-pig atrial
cells: different molecular mechanisms. Circulation 1995, 91, 2834-
2843.
(2) van der Vusse, G. J.; Glatz, J. F.; Stam, H. C.; Reneman, R. S. Fatty
acid homeostasis in the normoxic and ischemic heart. Physiol. ReV.
1992, 72, 881-940.
(
(
(
3) Corbett, J. R. Fatty acids for myocardial imaging. Semin. Nucl. Med.
1999, 29, 237-258.
4) Nishimura, S.; Ohta, Y. BMIPP in angina pectoris. Int. J. Card.
Imaging 1999, 15, 35-39.
5) Shikama, N.; Nakagawa, T.; Takiguchi, Y.; Aotsuka, N.; Kuwabara,
Y.; Komiyama, N.; Terano, T.; Hirai, A. Assessment of myocardial
perfusion and fatty acid metabolism in a patient with Churg-Strauss
syndrome associated with eosinophilic heart disease. Circ. J. 2004,
68, 595-598.
(6) Schelbert, H. R. PET contributions to understanding normal and
(
27) Eisenhut, M.; Lehmann, W. D.; Sutterle, A. Metabolism of 15-(4′-
abnormal cardiac perfusion and metabolism. Ann. Biomed. Eng. 2000,
123
123
[
I]iodophenyl)pentadecanoic acid ([ I]IPPA) in the rat heart;
28, 922-929.
identification of new metabolites by high pressure liquid chroma-
tography and fast atom bombardment-mass spectrometry. Nucl. Med.
Biol. 1993, 20, 747-754.
(7) Astheimer, L.; Linse, K. H.; Ramamoorthy, N.; Schwochau, K.
99
99m
Synthesis, characterization and evaluation of Tc/ Tc DIARS and
DMPE complexes containing pentadecanoic acid. Int. J. Radiat. Appl.
Instrum, Part B 1987, 14, 545-553.
(
(
(
(
28) Schmitz, B.; Reske, S. N.; Machulla, H. J.; Egge, H.; Winkler, C.
Cardiac metabolism of omega-(p-iodo-phenyl)-pentadecanoic acid:
a gas-liquid chromatographic-mass spectrometric analysis. J. Lipid
Res. 1984, 25, 1102-1108.
(
8) Chu, T.; Zhang, Y.; Liu, X.; Wang, Y.; Hu, S.; Wang, X. Synthesis
9
9m
and biodistribution of Tc-carbonyltechnetium-labeled fatty acids.
Appl. Radiat. Isot. 2004, 60, 845-850.
29) Kropp, J.; Ambrose, K. R.; Knapp, F. F., Jr.; Nissen, H. P.; Biersack,
H. J. Incorporation of radioiodinated IPPA and BMIPP fatty acid
analogues into complex lipids from isolated rat hearts. Int. J. Radiat.
Appl. Instrum., Part B 1992, 19, 283-288.
(
9) Jones, G. S. J.; Elmaleh, D. R.; Strauss, H. W.; Fischman, A., J. 7,
1
0-Bis(2-mercapto-2-methyl)propyl-7,10-diazapalmitic acid: A novel,
N2S2 ligand for technetium-99m. Bioorg. Med. Chem. Lett. 1996,
, 2399-2404.
6
30) Mokler, F. T.; Lin, Q.; Luo, H.; McPherson, D. W.; Beets, A. L.;
Bockisch, A.; Kropp, J.; Knapp, F. F., Jr. Dual-label studies with
(
10) Jung, C. M.; Kraus, W.; Leibnitz, P.; Pietzsch, H.-J.; Kropp, J.; Spies,
H. Syntheses and first crystal structures of rhenium complexes derived
from ω-functionalized fatty acids as model compounds of technetium
tracers for myocardial metabolism imaging. Eur. J. Inorg. Chem.
125
131
[
I]-3(R)/[ I]-3(S)-BMIPP show similar metabolism in rat tissues.
J. Nucl. Med. 1999, 40, 1918-1927.
31) Uehara, T.; Jin, Z. L.; Ogawa, K.; Akizawa, H.; Hashimoto, K.;
Nakayama, M.; Arano, Y. Assessment of 1 Re chelate-conjugated
bisphosphonate for the development of new radiopharmaceuticals for
bones. Nucl. Med. Biol. In press.
2002, 5, 1219-1225.
86
(
11) Karesh, S. M.; Eckelman, W. C.; Reba, R. C. Biological distribution
of chemical analogs of fatty acids and long chain hydrocarbons
containing a strong chelating agent. J. Pharm. Sci. 1977, 66, 225-
228.
(32) Bonen, A.; Campbell, S. E.; Benton, C. R.; Chabowski, A.; Coort,
S. L.; Han, X. X.; Koonen, D. P.; Glatz, J. F.; Luiken, J. J. Regulation
of fatty acid transport by fatty acid translocase/CD36. Proc. Nutr.
Soc. 2004, 63, 245-249.
(
12) Liang, F. H.; Virzi, F.; Hnatowich, D. J. The use of diaminodithiol
for labeling small molecules with technetium-99m. Int. J. Radiat.
Appl. Instrum., Part B 1987, 14, 63-67.

99mTc-Labeled Fatty Acid Analogue
Journal of Medicinal Chemistry, 2007, Vol. 50, No. 3 549
(
33) Brinkmann, J. F.; Abumrad, N. A.; Ibrahimi, A.; van der Vusse, G.
J.; Glatz, J. F. New insights into long-chain fatty acid uptake by
heart muscle: a crucial role for fatty acid translocase/CD36. Biochem.
J. 2002, 367, 561-570.
(38) Leveille, J.; Demonceau, G.; Roo, M. D.; Rigo, P.; Taillefer, R.;
Morgan, R. A.; Kupranick, D.; Walovitch, R. C. Characterization of
Technetium-99m-L,L-ECD for Brain Perfusion Imaging, Part 2:
Biodistribution and Brain Imaging in Humans. J. Nucl. Med. 1989,
(
34) Ehehalt, R.; Fullekrug, J.; Pohl, J.; Ring, A.; Herrmann, T.; Stremmel,
W. Translocation of long chain fatty acids across the plasma
membrane-lipid rafts and fatty acid transport proteins. Mol. Cell.
Biochem. 2006, 284, 135-140.
30, 1902-1910.
(
39) Neirinckx, R. D.; Canning, L. R.; Piper, I. M.; Nowotink, D. P.;
Pickett, R. D.; Holmes, R. A.; Volkert, W. A.; Forster, A. M.;
Weisner, P. S.; Marriott, J. A.; Chaplin, S. B. Technetium-99m d.l-
HMPAO: A new radiopharmaceutical for SPECT imaging of
regional cerebral blood flow. J. Nucl. Med. 1987, 28, 191-202.
(
35) Kung, H. F.; Molnar, M.; Billings, J.; Wicks, R.; Blau, M. Synthesis
and Biodistribution of Neutral Lipid-Soluble Tc-99m Complexes that
Cross the Blood-Brain Barrier. J. Nucl. Med. 1984, 25, 326-332.
36) Volkert, W. A.; Hoffman, T. J.; Seger, R. M.; Troutner, D. E.;
(
(40) Machulla, H. J.; Dutschka, K.; Van Beuningen, D.; Chen, T.
Development of 15-(p-iodine-123-phenyl)pentadecanoic acid for in
vivo diagnosis of the myocardium. J. Radioanal. Chem. 1981, 65,
9
9m
99m
Holmes, R. A.
potential brain radiopharmaceutical. Eur. J. Nucl. Med. 1984, 9, 511-
16.
Tc-propylene amine oxime ( Tc-PnAO); a
5
279-286.
(
37) Yokoyama, A.; Yamada, A.; Arano, Y.; Horiuchi, K.; Yamamoto,
K.; Torizuka, K. Tc-99m Bifunctional Radiopharmaceutical from a
Glucose Derivatives: A Potential Agent for Brain Study. In Tech-
netium in Chemistry and Nuclear Medicine; Deutsch, E., Nicolini,
M., Wagner, H., Jr., Eds; Raven Press: New York, 1983; pp 1051-
(41) Folch, J.; Lees, M.; Sloane, S. A simple method for the isolation
and purification of total lipids from animal tissues. J. Biol. Chem.
1957, 226, 497-509.
1053.
JM061017G