Exploration of the structure-activity relationship of the diaryl anilide class of ligands for translocator protein - Potential novel positron emitting tomography imaging agents

Article abstract of DOI:10.1016/j.bmcl.2012.07.093

A series of novel ligands based on the diaryl anilide (DAA) class of translocator protein (TSPO) ligands was synthesised and evaluated as potential positron emitting tomography (PET) ligands for imaging TPSO in vivo. Fluorine-18 labelling of the molecules was achieved using direct radiolabelling or synthon based labelling approaches. Several of the ligands prepared have promising profiles as potential TSPO PET imaging ligands and will be evaluated further as potential clinical imaging agents.

Full text of DOI:10.1016/j.bmcl.2012.07.093

Bioorganic & Medicinal Chemistry Letters 22 (2012) 5795–5800
Contents lists available at SciVerse ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Exploration of the structure–activity relationship of the diaryl anilide class
of ligands for translocator protein—potential novel positron emitting
tomography imaging agents
Harry Wadsworth, Paul A. Jones, Wai-Fung Chau, Clare Durrant, Véronique Morisson-Iveson,
Joanna Passmore, Dennis O’Shea, Duncan Wynn, Imtiaz Khan, Andrew Black, Michelle Avory,
⇑
William Trigg
GE Healthcare, The Grove Centre, White Lion Road, Amersham, Bucks HP7 9LL, UK
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of novel ligands based on the diaryl anilide (DAA) class of translocator protein (TSPO) ligands was
synthesised and evaluated as potential positron emitting tomography (PET) ligands for imaging TPSO in
vivo. Fluorine-18 labelling of the molecules was achieved using direct radiolabelling or synthon based
labelling approaches. Several of the ligands prepared have promising profiles as potential TSPO PET imag-
ing ligands and will be evaluated further as potential clinical imaging agents.
Received 25 June 2012
Revised 24 July 2012
Accepted 25 July 2012
Available online 3 August 2012
Ó 2012 Elsevier Ltd. All rights reserved.
Keywords:
TSPO
PBR
PET
Neuroinflammation
Synthesis
Translocator protein (TSPO—formerly known as the peripheral
benzodiazepine receptor) has been established as a target for the
imaging of inflammation using both positron emitting tomography
(PET) and single photon emission computed tomography (SPECT).
radiolabelling which are high yielding and amenable to automa-
tion. As such, we have not investigated alternative radiolabelling
approaches and have focused on exploring the structure–activity
relationships (SAR) in this class of molecules.
In the initial phase of our studies we prepared the published
compounds from the DAA class shown in Table 1, measuring Ki
and lipophilicity to enable direct comparison with the novel ana-
logues prepared in our programme.
DAA1106 2 has very high affinity for TSPO but has a poor imag-
ing profile due to its high lipophilicity. Our studies were aimed at
designing and evaluating novel fluorine-18 labelled analogues of
DAA1106 which retained high affinity but were less lipophilic
and have a more suitable biodistribution profile for a brain imaging
agent. We probed the SAR in this series by varying each of the aro-
matic rings (nature and substitution patterns) whilst utilizing the 2
established radiolabelling strategies. Scheme 1 highlights the gen-
eral synthetic route employed to synthesise the unlabelled com-
pounds for affinity testing.
[
11C]PK11195 has been used clinically for more than 20 years1,2
and has provided valuable insight into the manifestation of inflam-
mation in a wide variety of diseases. [11C]PK11195 is not an ideal
PET tracer due to poor pharmacokinetics and the carbon-11 radio-
label limits its use to PET centres with an on-site cyclotron. There
remains a need to discover improved PET tracers for TSPO imaging
and this has led to the development of many new PET tracer can-
didates.1–8 A major class of TSPO ligands is the diaryl anilide
(DAA) which includes the carbon-11 labelled DAA1106 and
PBR28 as well as the fluorine-18 labelled FE-DAA1106, PBR06
and FE-PPA (Fig. 1).
The DAA pharmacophore (Fig. 2) represents an excellent
starting point for a medicinal chemistry programme with a facile
synthetic route and multiple opportunities to vary the substitution
around the core molecule. In addition to offering
opportunity for structural modification this class of molecule has
two well established radiolabelling approaches to enable efficient
a
wide
Starting from commercially available fluoro nitro aryl com-
pounds the second aryl ring can be introduced using a nucleophilic
aromatic substitution reaction (SnAr) reaction. Reduction of the
nitro group followed by reduction to the corresponding aniline af-
fords the starting material for a reductive amination. The final step
of acetylation or fluoro acetylation yielded the desired compound
for affinity screening.
⇑
Corresponding author.
E-mail address: william.trigg@ge.com (W. Trigg).
0960-894X/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.bmcl.2012.07.093

5796
H. Wadsworth et al. / Bioorg. Med. Chem. Lett. 22 (2012) 5795–5800
O
O
O
O
O
N
F
N
O
N
O
N
N
O
Cl
1. PK11195
F
2. DAA1106
3. PBR28
F
O
F
O
O
O
O
O
N
O
N
O
N
F
N
O
O
O
6. FE-PPA
4. FE-DAA1106
5. PBR06
Figure 1. Examples of the DAA class of PET ligands for TSPO.
Table 2 details the compounds we prepared using the strategy
outlined in Scheme 1 in which the bottom ring and the connecting
atom to the middle ring were modified.
From these results it is clear that whilst the bottom phenyl ring
can be replaced by an aliphatic group giving a less lipohilic mole-
cule and still retain moderate potency, the aromatic ring gives
compounds with considerably higher affinity. Replacement of the
linking oxygen atom is also possible using a thiophenolic link with
moderate affinity retained but replacement with carbon or sulfone
linkage led to a dramatic reduction of potency.
Ar3
W
Ar2
N
Y
W
W
O
X
W
Ar1
Figure 2. DAA phamacophore.
Table 3 details the compounds we prepared using the strategy
outlined in Scheme 1 the middle ring was modified.
Table 1
From these data it is clear that modification of the middle ring
by replacing the phenyl group with a pyridyl or pyrimidine group
leads to some loss of potency when compared to DAA1106 or
PBR28 but that the 2-pyridyl compound (when the fluorine is
introduced in to the top ring) retain good potency. Somewhat sur-
prisingly, with the 4-pyridyl middle ring and the fluoroacetamide
labelling approach (compound 18—effectively a PBR28/PBR06 hy-
brid) affinity for TSPO was not retained.
Measured Ki data for TSPO in rat heart and LogD 7.4 for known DAA compounds and
PK1195
Compound
Ki nM9
LogD 7.4
1 PK11195
2 DAA1106
3 PBR28
4 FE-DAA1106
5 PBR06
1.24
0.43
1.14
0.19
0.28
0.05
3.73
4.47a
2.10
3.28
2.36
2.88
6 FEPPA
Table 4 details the compounds we prepared using the strategy
outlined in Scheme 1 the top ring was modified.
a
Calculated logP rather than logD 7.4.
Our modifications of the top-ring substitution show that a 6-
membered aromatic group is preferred with attempts at replace-
ment with a 5-membered ring led to a significant reduction in
affinity. Substituted phenyl and fused oxygen containing heterocy-
les are reasonably well tolerated as were pyridyl compounds.
Interestingly the pyridone derivative, which was isolated during
the synthesis of the corresponding pyridine as a byproduct, did
not retain affinity suggesting that a fully planar group is required
in the position.
For the radiolabelling precursors where the labelling approach
was via the fluoroacateamide strategy, the precursors were pre-
pared in a directly analogous fashion to the unlabelled compounds
with bromoacetyl chloride used to afford the bromide direct label-
ling precursors (Scheme 2).
NO2
(i)
NH2
NO2
(ii)
F
X
X
R1
R1
R2
R2
O
NH
N
(iv)
(iii)
Y
X
X
R1
R1
For compounds where the radiolabel was introduced in the flu-
oroethyl group (radiolabelling with the fluorethyl tosylate syn-
thon) the phenolic precursors were prepared. For future studies
direct labelling precursor could be envisioned but at this stage a
Scheme 1. General route for synthesis of DAA1106 analogues. Reagents and
conditions: (i) R1XH, K2CO3, DMF; (ii) H2, Pd-C, MeOH, (iii) R2CHO, NaBH4, MeOH;
(iv) Acetic anhydride, or fluoroacetyl chloride, triethylamine, DCM.

H. Wadsworth et al. / Bioorg. Med. Chem. Lett. 22 (2012) 5795–5800
5797
Table 2
Structures of bottom ring modified compounds and measured Ki data for TSPO in rat heart and LogD 7.410
O
X
N
Y
F
O
z
R1
Compound
X
Y
Z
R1
Ki nM
0.46
LogD 7.4
7
8
9
10
11
12
13
OCH3
H
H
H
H
F
H
H
H
O
O
O
O
CH2-
S
SO2
Cyclopentanyl
Cyclopentanyl
Isopropyl
Isopropyl
Phenyl
3.80
2.35
2.62
6.65
3.80
9.84
OCH3
OCH3
OCH3
OCH3
OCH3
3.89a
4.95a
5.09a
4.08a
219
4.48
3430
Phenyl
Phenyl
Bottom and middle ring fused:
14
OCH3
6.38
2.59
O
a
Calculated logP rather than logD 7.4.
Table 3
Table 4
Structures of middle ring modified compound and measured Ki data for TSPO in rat
Structures of top ring modified compound and measured Ki data for TSPO in rat heart
heart and LogD 7.411
and LogD 7.413
X
Ar
O
N
O
Y
X
z
O
N
Y
A
O
O
B
Compound
X
F
Y
Ar
Ki nM
3.77
LogD 7.4
O
N
Compound
A
B
X
Y
Z
Ki nM
LogD 7.4
21
H
2.38
15
16
17
18
19
20
CH
CH
CH
N
CF
N
N
N
N
CH
CH
N
–CH2CH2F
–CH2CH2F
–CH3
–CH3
–CH3
H
H
F
F
F
H
OCH3
H
H
OCH3
OCH3
4.24
7.28
125.00
2.18
0.05
63.00
1.69
1.58
1.51
2.72a
2.06
2.79a
22
F
H
72.10
2.19
O
–CH3
F
23
24
F
F
H
H
163.00
497.00
1.98
1.79
S
a
eLogP derived using HPLC method12
.
O
F
generic synthon approach was utilised. The required phenols were
prepared using the general process outlined in Scheme 3.
Radiolabelling of the compounds was achieved using either of
the approaches shown in Scheme 4.
Non-decay corrected end of synthesis yields for both radiolabel-
ling strategies were typically 10–35%.16 The radiolabelled mole-
cules were purified by HPLC prior to the biological evaluations.
In the uninjured human CNS the expression of TSPO is very
low17 and the same true for the rat with the exception of the olfac-
tory bulbs which have a high expression of TSPO compared to
other brain areas.18 As previously described,19 we used this differ-
ence in tracer retention between the olfactory bulbs (OB) and the
25
26
H
H
H
H
1.02
2.60
2.20
O
O
N
F
105.00
N
(continued on next page)

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H. Wadsworth et al. / Bioorg. Med. Chem. Lett. 22 (2012) 5795–5800
18F (in target
water)
Table 4 (continued)
Compound
X
F
Y
Ar
Ki nM
0.31
LogD 7.4
N
O
O
O
[K(K2.2.2)]HCO3
N
O
O
27
28
H
2.68
18F
Br
O
N
O
F
F
F
3.52
1.14
2.30
1.96
Acetonitrile
100oC, 10 mins
18F
O
O
29
30
H
HO
O
O
OTs
18F
F
F
H
H
2.03
2.66
2.80
2.60
N
O
O
N
O
O
Cs2CO3, Acetonitrile
100oC, 60-120 mins
O
31
Scheme 4. Direct and indirect labelling radiosynthesis methods employed.16
R2
R2
NH
(i)
N
Table 5
Br
Regional brain data from the biodistribution data of 18F-compounds naïve Wistar rats
(n = 3)
O
X
R
X
R
Compound
number
Whole brain
2 min pi (% id/g
(SD))
OB 30 min pi OB:Str
Str
2:30 min
pi ratio
(% id/g (SD))
30 min pi
Scheme 2. Reagents: (i) bromoacetyl chloride, triethylamine, DCM.14
ratio
7
8
0.53 (0.08)
0.77 (0.09)
0.61 (0.05)
0.68 (0.06)
0.45 (0.02)
0.25 (0.05)
0.55 (0.11)
0.73 (0.09)
0.66 (0.13)
0.81 (0.07)
0.84 (0.05)
0.72 (0.11)
0.65 (0.02)
0.58 (0.07)
0.74 (0.09)
0.23 (0.04)
0.42 (0.03)
0.17 (0.04)
0.35 (0.06)
0.40 (0.08)
0.26 (0.04)
0.15 (0.05)
0.70 (0.17)
0.33 (0.14)
0.68 (0.07)
0.50 (0.13)
0.40 (0.13)
0.37 (0.06)
0.23 (0.02)
0.49 (0.07)
0.21 (0.02)
0.63 (0.05)
2.56
3.23
1.88
3.50
3.08
5.20
1.36
2.06
2.54
2.52
2.78
2.50
2.85
1.53
3.50
2.10
2.17
5.56
5.46
6.22
6.30
2.85
4.40
4.82
1.71
3.92
2.52
4.39
3.88
4.77
3.80
4.64
3.20
1.79
12
14
15
16
17
19
21
27
28
29
30
31
low TSPO expressing striata (Str) as the basis for screening and pri-
oritisation of our novel compounds.
The biodistribution of the 18F-labelled compounds was evalu-
ated in naïve Wistar rats. The key brain data for the compounds
in our screening programme (those which relate to ability to image
neuroinflammation in the brain) are detailed in Table 5. The corre-
sponding data for [11C]PK11195 and [18F]PBR06 and [18F]FEPPA are
included for comparison.
From these data it is clear that, in common with the previously
reported DAA class molecules such as PBR06 and FE-PPA, this com-
pound class has significantly higher whole brain uptake than
PK11195 and that many of our novel compounds show good differ-
entiation of the high expressing regions over the lower expressing
brain regions.
[
[
[
18F]PBR06
11C]PK11195 0.28-0.43
18F]FE-PPA
0.63 (0.07)
In vivo metabolic stability was also assessed in brain and plas-
ma using HPLC. For an imaging agent targeted at the CNS it is
important that the signal in the brain is attributable to the parent
molecule and not a radiolabelled metabolite. In our programme we
were targeting >90% parent at 60 min post injection (pi). Table 6
shows the data from the compounds which showed promise in
the naïve rat biodistribution and the key comparator compounds.
These data show that for this class of molecules there is a signif-
icant chance that radiolabelled metabolites which can cross the
HO
HO
R1
(ii)
R1
NH2
(i)
NH
N
X
R
O
X
X
R
R
Scheme 3. General synthetic route to radiolabelling precursors. Reagents and conditions: (i) substituted benzaldehyde, NaBH4, MeOH, (ii) Acetic anhydride, then aq. NaOH.15

H. Wadsworth et al. / Bioorg. Med. Chem. Lett. 22 (2012) 5795–5800
5799
Table 6
Brain data from in vivo metabolism study of 18F-compounds naïve Wistar rats (n = 1 unless stated)
Compound number
Brain 60 min pi (% parent)
Compound number
Brain 60 min pi (% parent)
7
8
14
18
24
27 (n = 3)
45
62
80
52
28
29
30
72
82
92
91
100
87
[
[
[
18F]PBR06
44
11C]PK11195
18F]FE-PPA
91 (SD = 2)
which are suitable for further investigation in studies to demon-
strate utility as TSPO PET imaging agents.
Table 7
High affinity to low affinity binding ratios
Compound number
Ratio of affinity HAB to LAB
Supplementary data
14
27
104
78
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.bmcl.2012.07.
093.
30
56
66
878
1.2
51
PBR28
PBR06
PK11195
FE-PPA
References and notes
1. Chauveau, F.; Boutin, H.; Van Camp, N.; Dollé, F.; Tavitian, B. Eur. J. Nucl. Med.
Mol. Imaging 2008, 35, 2304.
2. Katsifis, A.; Mattner, F.; Zhang, Z.; Dikic, B.; Papazian, V. J. Labelled Compd.
Radiopharm. 2000, 43, 385.
3. Zhang, M.-R.; Kida, T.; Noguchi, J.; Furutsuka, K.; Maeda, J.; Suhara, T.; Suzuki,
K. Nucl. Med. Biol. 2003, 30, 513.
4. James, M. L.; Fulton, R. R.; Henderson, D. J.; Eberl, S.; Meikle, S. R.; Thomson, S.;
Allan, R. D.; Dollé, F.; Fulham, M. J.; Kassiou, M. Bioorg. Med. Chem. 2005, 13,
6188.
5. Imaizumi, M.; Kim, H.-J.; Zoghbi, S. S.; Briard, E.; Hong, J.; Musachio, J. L.;
Ruetzler, C.; Chuang, D.-M.; Pike, V. W.; Innis, R. B.; Fujita, M. Neurosci. Lett.
2007, 411, 200.
blood brain barrier are formed and only compounds 27 and 30
reach the desired target specification.
Recent publications20,21 have identified a genetic polymorphism
in the binding domain of TSPO, resulting in two phenotypes
(classed as ‘high’ and ‘low’ affinity based on binding assays with
[3H]PBR2820). We undertook a study to evaluate whether the dif-
ference in binding affinities was observed with our novel ligands
using the platelet binding assay described by Owen et al.22,23 Table
7 shows the ratio of the affinities between the high and low affinity
binding sites.
6. Zhang, M.-R.; Maeda, J.; Furutsuka, K.; Yoshida, Y.; Ogawa, M.; Suhara, T.;
Suzuki, K. Bioorg. Med. Chem. Lett. 2003, 13, 201.
7. James, M. L.; Fulton, R. R.; Vercoullie, J.; Henderson, D. J.; Garreau, L.; Chalon, S.;
Dollé, F.; Selleri, S.; Guilloteau, D.; Kassiou, M. J. Nucl. Med. 2008, 49, 814.
8. Imaizumi, M.; Briard, E.; Zoghbi, S. S.; Gourley, J. P.; Hong, J.; Musachio, J. L.;
Gladding, R.; Pike, V. W.; Innis, R. B.; Fujita, M. Synapse 2007, 61, 595.
9. TSPO Affinity Assay carried out using homogenated rat heart tissue with
Figure 3 shows examples of the data obtained from the platelet
based assay. Platelets from 2 high affinity binder subjects and 2
low affinity binder subjects were used in these assays.
From these data, whilst it is clear that the newly identified com-
pounds we have described do not address the issue of 2 binding
sites for TSPO ligands, we have discovered several novel ligands
[3H]PK11195 as the radioligand. Ki measurements are averaged from
experiments across 6 concentrations (see Supplementary data).
2
10. Example analytical data (compound 7): 1H NMR (300 MHz, CDCl3) dH 1.52–
1.96(8H, m, CH2), 3.46(3H, s, OCH3), 3.71(3H, s, OCH3), 4.45(2H, dd, J = 12 and
Figure 3. Selected data from the platelet binding assays.

5800
H. Wadsworth et al. / Bioorg. Med. Chem. Lett. 22 (2012) 5795–5800
20 Hz, CH2F), 4.55 (1H, d, J = 12 Hz CHN), 4.68–4.71 (1H m, CHO), 5.15 (1H, d,
J = 12 Hz CHN), 6.60–6.90 (6H, m, ArH), 7.20 (1H, dd, J = 4 and 12 Hz, ArH); 13
preparative HPLC. The purified [18F](CH2)2OTs intermediate was trapped onto a
conditioned light t-C18 sep pak and dried on a high flow N2 line for 15–20 min.
A Wheaton vial (1 ml) containing a stirrer, corresponding hyroxy precursor (2–
C
NMR (75 MHz, CDCl3) dC 21.3, 29.9, 30.3, 43.3, 43,4, 53.0, 77.5, 77.2, 108.6,
110.6, 110.7, 113.9, 117.4, 123.3, 125,5, 127.1, 127.4, 149.2, 150.7, 151.0, 164.5.
11. Example analytical data (compound 15): 1H NMR (300 MHz, CDCl3) dH 1.98(3H,
s, CH3), 3.84–4.12 (2H, m CH2O), 4.46–4,62 (2H, m, CH2F), 4.90 (1H. d, J = 12 Hz,
CHN), 5.25 (1H. d, J = 12 Hz, CHN), 6.70 (1H, d, J = 8 Hz, ArH), 6.85 (2H, m, ArH),
7.0 (2H, d, J = 8 Hz, ArH), 7.2(2H, t, J = 8 Hz, ArH), 7.3–7.4 (4H, m, ArH); 8.0 (1H.
d, J = 4 Hz, ArH); 13C NMR (75 MHz, CDCl3) dC 22.2,45.6, 67.9 (d, J = 20 Hz,
CH2O), 81.5(d, J = 170 Hz CH2F), 111.0, 118.4, 121.0, 121.2, 124.8, 125.3, 126.4,
128.7, 129.4, 131.3, 139.0, 146.4, 153.1, 156.3, 159.4, 170.3.
4 mg, 6–12 lmol), Cs2CO3 (8–10 mg, 24–30 lmol) in acetonitrile(100 lL) was
stirred at room temperature for 1–2 h. The trapped intermediate on the dried
lite t-C18 sep pak was eluted with acetonitrile (0.5 mL) into the Wheaton vial
and heated at 120–130 °C/15 min. The crude product was purified by HPLC and
formulated in ethanol/PBS for biological studies (tR [18F]compound 15 ca.
16 min. Radiochemical yield of [18F]compound 15 ca. 16% non-decay corrected
yield). The total process time was ca. 120–150 min.
17. Scarf, A. M.; Kassiou, M. J. Nucl. Med. 2011, 52, 677.
12. Donovan, S. F.; Pescatore, M. C. J. Chromatogr. A 2002, 952, 47.
18. Casellas, P.; Galiegue, S.; Basile, A. S. Neurochem. Int. 2002, 40, 475.
19. Wadsworth, H.; Jones, P.A.; Chau, W.; Durrant, C.; Fouladi, N.; Passmore, J.;
O’Shea, D.; Wynn, D.; Morisson-Iveson, V.; Ewan, A.; Thaning, M.; Mantzilas,
D.; Gausemel, I.; Khan, I.; Black, A.; Avory, M.; Trigg, W. Bioorg. Med. Chem. Lett.
13. Example analytical data (compound 27): 1H NMR (300 MHz, CDCl3) dH 2.9–
3.15(2H, m, CH2-Ar), 4.30 (2H, q, J = 8 Hz, CH2O), 4.80 (2H, d, J = 8 Hz, J = 8 Hz,
CH2F), 4.78 (1H, d, J = 12 Hz, CHN), 5.10 (1H, d, J = 12 Hz, CHN), 6.67(1H t,
J = 8 Hz, ArH), 6.75–7.50 (11H, m, ArH); 13C NMR (75 MHz, CDCl3) dC 26.7, 43.3,
68.0. 75.8(J = 175 Hz), 114.0, 115.0, 116.4, 117.3, 120.3, 121.3, 126.4, 126.9,
127.4, 150.8, 152.6, 155.7, 164.3(J = 20 Hz).
2012, 22, 1308.Male Wistar rats (200–300 g,
3 per time-point) were
intravenously injected test compound (approximately 1–3 MBq at 10 MBq/
mL—volume less than 5 mL/Kg, formulated <10% Ethanol in phosphate
buffered saline) under anaesthesia (4% isoflurane). At 2, 10, 30 or 60 min
post-injection animals were sacrificed by cervical dislocation under
anaesthesia. Animals for either humanely restrained or kept in short term
metabolism cages to allow for collection of faeces and urine. Blood, bone
(whole femur, tibia and fibula from both hind legs), muscle (from both hind
legs), skin sample, fat sample, faeces, whole organs/tissues (kidneys, bladder
(including urine and voided urine), lung, liver, spleen, stomach (including
contents), small and large intestine (including contents), heart, adrenals),
injection site (whole tail) and remaining carcass were assessed for radioactivity
by a gamma counter. The brain was dissected into striatum, cerebellum,
hippocampus, pre-frontal cortex, remaining cortex, pons and medulla,
thalamus, olfactory bulbs, hypothalamus and remaining brain and activity
14. Example analytical data (27 precursor): 1H NMR (300 MHz, CDCl3) dH 2.93–
3.15(2H, m, CH2Ar), 3.77 (1H, d, J = 12 Hz, CH2Br), 3.85 (1H, d, J = 12 Hz, CH2Br),
4.15–4.47 (2H, m, CH2Ar), 4.70 (1H, d, J = 12 Hz, CH2N), 5.13 (1H, d, J = 12 Hz,
CH2N), 6.70 (1H, t, J = 8 Hz, ArH), 6.80–7.40 (11H, m, ArH)); 13C NMR (75 MHz,
CDCl3) dC 27.8, 29.7, 46.8, 70.9, 118.0, 119.4, 120.3, 123.1, 124.1, 124.2, 126.0,
129.4, 129.7, 129.8, 130.3, 131.0 153.5, 155.6, 1158.6, 166.6.
15. Example analytical data (18 precursor): 1H NMR (300 MHz, CDCl3) dH 3.50 (3H, s,
OCH3), 3.68 (3H, s, OCH3,), 3.97 (2H, d, J = 2 Hz, ClCH2), 4.84 (1H, d, J = 14 Hz,
NCH), 5.18 (1H, d, J = 14 Hz, NCH), 6.55–6.98 (6H, m, ArH), 7.24–7.46 (3H, m,
ArH), 8.21 (1H, s, ArH), and 8.30 (1H, d, J = 6 Hz, ArH.
16. Direct labelling: KrytofixÒ2.2.2 (4 mg, 10.6
(0.1 mol dmÀ3, 100
L, 10 mg, 10
to [18F]Fluoride/H2O (ca.100–200
nitrogen for 20–25 min. The labelling mixture containing the corresponding
bromide precursor for compound 27 (2–3 mg, 4–6 mol) in acetonitrile (1 mL)
l
moL), potassium bicarbonate
moL) and acetonitrile (0.5 mL) was added
L) and heated at 100 °C under a stream of
l
l
l
determined by a gamma counter. Whole body and regional brain
biodistribution was generated. All animal studies were performed in
accordance with the Animals (Scientific Procedures) Act 1986 act.
20. Owen, D. R.; Howell, O. W.; Tang, S.; Wells, L. A.; Bennacef, I.; Bergstrom, M.;
Gunn, R. N.; Rabiner, E. A.; Wilkins, M. R.; Reynolds, R.; Matthews, P. M.; Parker,
C. A. J. Cereb. Blood Flow Metab. 2010, 1.
21. Fujita, M.; Imaizumi, M.; Zoghbhi, S. S.; Fujimura, Y.; Farris, A. G.; Suhara, T.;
Hong, J.; Pike, V. W.; Innis, R. B. Neuroimage 2008, 43.
22. Owen, D. R.; Gunn, R. N.; Rabiner, E. A.; Bennacef, I.; Fujita, M.; Kreis, W. C.;
Innis, R. B.; Pike, V. W.; Reynolds, R.; Matthews, P. M.; Parker, C. A. J. Nucl. Med.
2011, 52, 24.
l
was added and heated at 100 °C/10 min. After 10 min, the reaction was cooled
and then purified by semi-preparative HPLC then formulated in ethanol/PBS for
biological studies (tR ca. 19 min. Radiochemical yield of [18F]compound 27, ca.
30% non-decay corrected yield). The total process time was ca. 90 min. (B)
Indirect labelling (radiosynthesis of compound 15): KrytofixÒ2.2.2 (4 mg,
10.6
and acetonitrile (0.5 mL) was added to [18F]Fluoride/H2O (ca.100–200
heated at 100 °C under a stream of nitrogen for 20–25 min. Ethylene glycol-
ditosylate (3–5 mg, 8–13.5 moL) in acetonitrile (1 mL) was added and heated
at 100 °C/10min. The crude intermediate,
18F](CH2)2OTs, was purified by
l
mol), potassium bicarbonate (0.1 mol dmÀ3, 100
l
L, 10 mg, 10
lmoL)
l
L) and
l
23. All human tissue was used in accordance to UK Human Tissue Act 2004.
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