Synthesis and preliminary evaluation of (R,R)(S,S) 5-(2-(2-[4-(2-[18F]fluoroethoxy)phenyl]-1-methylethylamino)- 1-hydroxyethyl)-benzene-1,3-diol ([18F]FEFE) for the in vivo visualisation and quantification of the β2-adrenergic receptor status in lung

Article abstract of DOI:10.1016/S0960-894X(03)00538-9

The ¹⁸F-labeled β2-adrenergic receptor ligand (R,R)(S,S) 5-(2-(2-[4-(2-[¹⁸F]fluoroethoxy)phenyl]-1-methylethylamino)- 1-hydroxyethyl)-benzene-1,3-diol, a derivative of the original highly selective racemic fenoterol, was synthesized in an overall radiochemical yield of 20% after 65 min with a radiochemical purity higher than 98%. The specific activity was in the range of 50-60 GBq/μmol. In vitro testing of the non-radioactive fluorinated fenoterol derivative with isolated guinea pig trachea was conducted to obtain an IC₅₀ value of 60 nM. Preliminary ex vivo organ distribution and in vivo experiments with positron emission tomography (PET) on guinea pigs were performed to study the biodistribution as well as the displacement of the radiotracer to prove specific binding to the β2-receptor.

Full text of DOI:10.1016/S0960-894X(03)00538-9

Bioorganic & Medicinal Chemistry Letters 13 (2003) 2687–2692
Synthesis and Preliminary Evaluation of (R,R)(S,S) 5-(2-(2-[4-(2-
[18F]fluoroethoxy)phenyl]-1-methylethylamino)-1-hydroxyethyl)-
benzene-1,3-diol ([18F]FEFE) for the In Vivo Visualisation and
Quantification of the ꢀ2-Adrenergic Receptor Status in Lung
Esther Schirrmacher,a,* Ralf Schirrmacher,a Oliver Thews,b Wolfgang Dillenburg,b
d
Andreas Helisch,c IgnatzWessler, Roland Buhl,e Sabine Hohnemann,a
Hans-Georg Buchholz,c Peter Bartenstein,c Hans-Jurgen Machullaf and Frank Roscha
aInstitute of Nuclear Chemistry, University of Mainz, Fritz Strassmann-Weg 2, D-55128 Mainz, Germany
bInstitute of Physiological Chemistry, University of Mainz, Mainz, Germany
cDepartment of Nuclear Medicine, University of Mainz, Mainz, Germany
dInstitute of Pharmacology, University of Mainz, Mainz, Germany
eIII. Medical Clinic, University of Mainz, Mainz, Germany
fSection Radiopharmaceutical Chemistry, University of Tuebingen, Tuebingen, Germany
Received 12 February 2003; revised 2 May 2003; accepted 26 May 2003
Abstract—The 18F-labeled b2-adrenergic receptor ligand (R,R)(S,S) 5-(2-(2-[4-(2-[18F]fluoroethoxy)phenyl]-1-methylethylamino)-1-
hydroxyethyl)-benzene-1,3-diol, a derivative of the original highly selective racemic fenoterol, was synthesized in an overall radio-
chemical yield of 20% after 65 min with a radiochemical purity higher than 98%. The specific activity was in the range of 50–60
GBq/mmol. In vitro testing of the non-radioactive fluorinated fenoterol derivative with isolated guinea pig trachea was conducted to
obtain an IC50 value of 60 nM. Preliminary ex vivo organ distribution and in vivo experiments with positron emission tomography
(PET) on guinea pigs were performed to study the biodistribution as well as the displacement of the radiotracer to prove specific
binding to the b2-receptor.
# 2003 Elsevier Ltd. All rights reserved.
The obvious advance of positron emission tomography
(PET) has led to the development of syntheses of biologi-
cally important tracer molecules labeled with the most
common positron emitters carbon-11 and fluorine-18.
The advantage of obtaining a high specific radioactivity
of these radionuclides has opened up the possibility of
visualising and quantifying the amount of specific bio-
logical receptors in vivo by utilizing labeled receptor
ligands and PET. In particular, the investigation of the
distribution and density of the dopaminergic receptors
in the brain is an example of the potential of this tech-
nique in the determination of normal and diseased
states in humans.1
The knowledge on the interaction of radiolabeled neuro-
transmitter ligands with distinct subtypes of neuro-
receptors in terms of chemistry, biochemistry,
pharmacology, in vivo quantification and modeling can
be transferred to peripheral ligand–receptor systems
such as the human peripheral adrenoceptors of the
heart, which have already been investigated.2
In humans, peripheral beta-adrenoceptors are widely
distributed throughout the lung, with more than 70% of
them being of the b2-subtype. The b2 receptors occur in
bronchial epithelium, submucosal glands, immune cells
and airway smooth muscle fibres.3
The b2 receptor system is important for the neuronal
and humoral regulation of the epithelial, glandular and
muscular lung function. The b2 agonists mediate a
relaxation of the bronchial smooth muscle via the second
*Corresponding author. Tel.: +49-6131-392-5302; fax: +49-6131-
392-4692; e-mail: frank.roesch@uni-mainz.de
0960-894X/03/$ - see front matter # 2003 Elsevier Ltd. All rights reserved.
doi:10.1016/S0960-894X(03)00538-9

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E. Schirrmacher et al. / Bioorg. Med. Chem. Lett. 13 (2003) 2687–2692
messenger cAMP.4 The role of b2 adrenoceptor density
for obstructive respiratory diseases (such as asthma or
chronic obstructive bronchitis) is still not clarified,5
although changes in beta-receptor function in the lung
have been correlated to chronic obstructive lung disease
and cystic fibrosis,5 and although beta-agonist drugs
have been widely applied to treat asthma.
synthesized in a convergent multistep synthesis starting
from commercially available 4-hydroxyphenylacetone
(1) which was reacted with 1-bromo-2-fluoroethane in
acetone using K2CO3 as a base to yield 2. Subsequent
reductive amination with benzylamine under 5 bar
hydrogen in an autoclave gave racemic benzyl-(2-[4-(2-
fluoroethoxy)phenyl]-1-methylethyl)-amine (3) in an
overall yield of 64%.14
For understanding the pathogenesis, therapy and prog-
nosis of such diseases, a non-invasive, quantifiable imag-
ing of b2 adrenoceptor density would be valuable.
Consequently, a variety of radiolabeled ligands has been
synthesized. However, only a few candidates have been
introduced for direct quantification of the b2 adreno-
ceptor density in lung in vivo via PET. Most of them
were 11C-labeled antagonists such as (S) [11C]CGP
121777 (4-(3-tert-butylamino-2-hydroxy-propoxy)-1,3-
dihydro-benzoimidazol-2-[11C]one), which are not use-
ful for the quantification of the high-affinity state of the
b2 adrenoceptor. Nevertheless, a similar compound, (S)
[11C]CGP 12388,8 was proposed to become the tracer of
choice due to its facile synthesis and in vivo data.
2-(3,5-Bisbenzyloxyphenyl)oxirane (5) was synthesized
starting from 3,5-bisbenzyloxybenzaldehyde (4), which
was reacted with trimethylsulfoniumiodide in DMF
using sodium hydride as a base in a yield of 74%.15
Following analogous literature procedures, we attemp-
ted to couple 3 and 5 in DMSO at high reaction tem-
peratures of 100–150 ꢀC, but only small yields of the
desired product (20%) could be obtained.16 A sig-
nificant cleavage of the fluoroethyl-benzylether moiety
was observed. To circumvent these difficulties, we
applied ytterbium trifluoromethanesulfonate as a highly
effective catalyst for the opening of the oxirane moiety
at room temperature with amines.17 Using this method,
the yield could be increased to 80%. Final cleavage of
the benzyl protecting groups was achieved quantita-
tively with hydrogen on Pd/C-catalyst at 1 bar to give
the two diastereomeric pairs (R,R)(S,S)-6 and
(R,S)(S,R)-6 (Fig. 1).18
Attempts to use 18F-labeled antagonists such as
[18F]CGP12388 have so far resulted in a reduced affinity
to the receptor.8 [18F]Carazolol was found to be of little
subtype specifity.9 [18F]Fluoropropanolol has been
evaluated and showed a rapid off-rate which could
impair quantification.10
The two diastereomeric pairs (R,R)(S,S)-6 and
(R,S)(S,R)-6 could be easily separated via column
chromatography.19 To assign each separated compound
There have been attempts to characterize b2 adrecocep-
tors with carbon-11 labeled agonists such as [11C]for-
moterol11 and [11C]procaterol12 but, to our knowledge,
no fluorine-18 labeled agonists have been used so far.
1
its corresponding configuration, their H NMR spectra
were compared to the original (R,R)(S,S)-fenoterol1
(Boehringer Ingelheim, Germany) and as a result
(R,R)(S,S)-6 could be clearly identified.20 First labeling
experiments starting from original (R,R)(S,S) feno-
terol1 as a labeling precursor indicated that an addi-
tional by-product was formed in nearly the same
radiochemical yields as the product which was assumed
to be the 18F-fluoroethyl-resorcinol ether (R,R)(S,S)-
[18F]8 or the tertiary 2-fluoroethylamino compound
(R,R)(S,S)-[18F]14. To identify the by-product, the two
Fenoterol represents a full b2 receptor agonist, widely
used as a short-acting escape medication in treatment of
bronchoconstruction. In binding studies, fenoterol dis-
criminates between b1 and b2 subtype with a ratio of
>10 and binds with a rapid onset time directly to the
receptor protein. In contrast, the more lipophilic com-
pound salmeterol shows a slow dissociation and a
binding to a specific exo-site domain of the b2 receptor
protein.
The aim of this study was to label a hydrophilic, highly
selective subtype-specific agonist to image membrane-
bound high-affinity state b2-receptors only.
Fenoterol is a highly subtype-specific high-affinity
ligand with little lipophilicity.13 Thus, we intented to
label fenoterol with fluorine-18, whose half-life of 109.6
min would allow longer measuring times with PET and
improved scientific and clinical protocols compared to
carbon-11 labeled analogues.
Figure 1. Synthesis of the non-radioactive standard compound
(R,R)(S,S)-(6); Reagents and conditions: (a) 1-bromo-2-fluoroethane
(1.2 equiv), K2CO3 (2 equiv), acetone, reflux, 12 h (80%); (b) benzyl-
amine (1.2 equiv), H2 (5 bar), 5% Pt/C, ethanol, rt, 24 h (80%); (c)
trimethylsulfonium iodide (1 equiv), NaH (1 equiv), DMF, rt, 1 h
(74%); (d) ytterbium trifluoromethanesulfonate (0.1 equiv), dichloro-
methane, 1 h (78%); (e) 10% Pd/C, methanol, H2 (1 bar), rt, 3 h (80%).
Chemistry
The non-radioactive standard compound (R,R)(S,S) 5-
(2-(2-[4-(2-fluoroethoxy)phenyl]-1-methylethylamino)-1-
hydroxy-ethyl)-benzene-1,3-diol [(R,R)(S,S)-6], required
for in vitro evaluation and analytically purposes, was

E. Schirrmacher et al. / Bioorg. Med. Chem. Lett. 13 (2003) 2687–2692
2689
non-radioactive standard compounds (R,R)(S,S)-8 and
(R,R)(S,S)-14 were synthesized according to Figure 2.
In the case of (R,R)(S,S)-8, (R,R)(S,S)-fenoterol hydro-
bromide1 was used for the synthesis. Unfortunately,
the synthesis of (R,R)(S,S)-6 could not be achieved via
an analogous route because the obtained compound
contained too many impurities for the in vitro
evaluation which were not removable via column chro-
matography.
first deprotonating step using 1 N NaOH, the phenolic
hydroxy-function should become more acidic than the
remaining HO-moiety of the resorcinolate anion. How-
ever, extensive labeling experiments using varying
equivalents of base (NaOH 1 N) for the deprotonation
of the different aromatic HO-functions revealed that an
amount of 0.9 equivalents of base led to the highest
radiochemical yields of (R,R)(S,S)-[18F]16. This experi-
mental outcome suggests that the phenolic hydroxy-
function is more acidic than the resorcinol. Further-
more, after the use of more equivalents of base the for-
mation of the 2-[18F]fluoroethyl-resorcinol ether
(R,R)(S,S)-[18F]8 also became a side-reaction.
As in the case of (R,R)(S,S)-6, the diastereomeric pairs
of 14 could be isolated via column chromatography21
and were identified by adding each of the isolated dia-
stereomeric pairs to the crude labeling reaction mixture
and comparing the UV-HPLC-chromatogram to the
radioactive chromatogram. The HPLC analyses of both
compounds (R,R)(S,S)-8 and (R,R)(S,S)-14 identified
the by-product to be the tertiary 2-fluoroethyl amino
compound (R,R)(S,S)-[18F]14 and not the 2-fluoroethyl
resorcinol ether (R,R)(S,S)-[18F]8.
The isolation of the radiotracer was achieved by high-
performance liquid chromatography (HPLC).25 The
HPLC-chromatogram showed two peaks from which
the first peak at 12 min could be related to (R,R)(S,S)-
[18F]6 whereas the second one at 16 min could be
assigned to the tertiary 2-[18F]fluoroethylamino com-
pound (R,R)(S,S)-[18F]14 (Fig. 4).
The radioactive labeling was achieved using (R,R)(S,S)
fenoterol1 (15) liberated from fenoterol hydro-
bromide122 and the secondary labeling precursor 2-
[18F]fluoroethyltosylate23 (Fig. 3). The radiochemical
yield of (R,R)(S,S)-[18F]6 was 60% referring to the
starting activity of 2-[18F]fluoroethyltosylate. The
remaining 40% of detected radioactivity belonged to the
2-[18F]fluoroethylamino compound (R,R)(S,S)- [18F]14.
The overall radiochemical yield was 20% referring to
the end of bombardment (EOB). Incremental calcula-
tions suggested that the most acid H-atom is the HO-
moiety of the resorcinol structure element.24 After the
After successful collection of the radiotracer, the liquid
phase was diluted with water and passed through a solid
phase column (C-181, Waters) which led to the fixation
of the radiotracer. After drying with nitrogen the tracer
was eluted from the solid phase with 1 mL of ethanol
which was subsequently removed in vacuo. The radio-
tracer was dissolved in an appropriate amount of iso-
tonic NaCl solution for further use.26 Figure 5 shows
the quality control chromatogram obtained by HPLC
(radioactivity channel and UV-channel).
Figure 3. Radioactive labeling of (R,R)(S,S)-fenoterol1 (15),
Reagents and conditions: (a) NaOH 1 N (0.9 equiv), 2-[18F]fluoro-
ethyltosylate, DMF, 130 ꢀC, 8 min (60%).
Figure 2. Synthesis of the non-radioactive by-products (R,R)(S,S)-(8)
and (R,S)(S,S)-(14); Reagents and conditions: (a) (R,R)(S,S)-fenoterol
hydrobromide1 (15) (Boehringer Ingelheim, Germany), potassium
methanolate (2 equiv), methanol, 5 min, removal of methanol, DMF,
1-bromo-2-fluoroethane, 60 ꢀC, 24 h (10%); (b) benzylamine, 5% Pt/
C, H2 (5 bar), ethanol, rt, 12 h (80%); (c) 10% Pd/C, H2 (3 bar), eth-
anol, HCOOH (trace amount), rt, 6 h (60%); (d) benzylchloride (1
equiv), KOH (1 equiv), NaI (trace amount), ethanol/water, reflux, 48 h
(60%); (e) 1-bromo-2-fluoroethane (1,2 equiv), Ki (trace amount),
K2CO3 (2 equiv), acetone, reflux, 24 h (75%); (f) ytterbium tri-
fluoromethanesulfonate (0.1 equiv), dichloromethane, rt, 2 h (25%);
(g) 10% Pd/C, H2 (1 bar), methanol, rt, 3 h (50%).
Figure 4. Radio- and UV-HPLC chromatogram of the crude reaction
mixture (upper curve refers to the detected radioactivity; lower curve
refers to the UV-absorbtion).

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fluoroethylated derivative (R,R)(S,S)-6 were added and
the relaxation measured analogously. The results
showed that the IC50 value of (R,R)(S,S) fenoterol and
its fluoroethylated derivative 6 were both in the range of
60 nM. Thus the affinity of the ligand to the b2 adreno-
ceptor did not change by the derivatisation within the
accuracy of the measurement.
ExVivo Organ Distribution and In Vivo Evaluation of
(R,R)(S,S)-[18F]6 on Guinea Pigs Using PET
The receptor binding of the compound and its organ
distribution was assessed in Hartley guinea pigs
(Charles River Wiga, Sulzfeld, Germany; body weight
400 g). All experimentation had previously been
approved by the regional animal ethics committee and
was conducted according to German federal law. Ani-
mals were anaesthetized with ketamine (10 mg/kg,
Ketanest, Parke–Davis, Berlin, Germany) and xylazine
(0.6 mg/kg, Rompun, Bayer, Leverkusen, Germany). A
catheter was placed in the carotic artery and the jugular
vein, respectively. Animals breathed spontaneously
through a tracheal tube during the entire experiment.
(R,R)(S,S)-[18F]6 was dissolved in isotonic saline and
injected iv with an activity of 12–18 MBq. For the PET
images the camera ECAT EXACT with axial resolution
of 4.5 mm in the central field of view in 2D-mode was
used. Dynamic PET studies over 60 min with
[18F]FEFE were performed either as a baseline study
(study group 1, n=3) or as a displacement study [study
group 2, n=3; 2 mg/kg (R,R)(S,S)-fenoterol 10 min
post injection of [18F]FEFE]. Partial volume correction
was applied on iterative reconstructed images.28 Figure
6 shows a coronal PET image (slice thickness: 6.7 mm)
of the baseline study at 60 min pi. For the modeling of
the b2-receptor binding potentials a region-of-interest
(ROI) based reference tissue model was used.29 Figure 7
shows a time–activity curve for one animal from study
group 1. The unspecific activity correlates to a ROI in
the neck area, where no b2 adrenoceptors are located.
Figure 5. Radio- and UV-HPLC chromatogram of the isolated
radiotracer (R,R)(S,S)-[18F]6 (upper curve refers to the detected
radioactivity; lower curve refers to the UV-absorption).
Determination of the Partition Coefficient of
(R,R)(S,S)-[18F]6
The lipid/water partition coefficient of compound
(R,R)(S,S)-[18F]6 was measured by adding 5 mL of the
radioactive compound in saline solution to a 2-mL vial
containing 0.5 mL each of 1-octanol and pH 7.4 phos-
phate buffer. The vial was capped and vortexed vigor-
ously for 10 min at room temperature. After reaching
equilibrium, the organic phase was pipetted out and
each phase was analyzed via radio-TLC on an Instant
Imager (Packard Canberra). A partition coefficient of
0.5Æ0.05 was calculated as Àlog [counts per min (cpm)
in octanol/cpm in pH 7.4 phosphate buffer].
In Vitro Evaluation of the Non-radioactive Standard Com-
pound (R,R)(S,S)-6 Using Isolated Guinea Pig Trachea
Dunkin–Hartley guinea pigs of both genders were used.
After execution, the trachea were removed and kept in a
physiological saline solution through which a constant
flow of carbogen, a mixture of 5% carbon dioxide in
oxygen, was maintained at all times. The trachea was
split in half and fixated in a special apparatus as descri-
bed previously.27 The pre-contraction of the trachea was
achieved by treatment with oxotremorin, a muscarinic
acetylcholine receptor ligand. Increasing concentrations
of 1–1000 nM of either (R,R)(S,S)-fenoterol1 or the
Figure 7. Time–activity curve for comparison of radioactivity uptake
in lung versus neck area as a site of unspecific binding (one animal
from study group 1).
Figure 6. 18F-FEFE PET of pulmonary b2-receptors of the lung
(arrows) in guinea pigs (baseline study, 60 min p.i.).

E. Schirrmacher et al. / Bioorg. Med. Chem. Lett. 13 (2003) 2687–2692
2691
At the end of the PET measurements, animals were
sacrificed at 65 min pi and multiple organ samples were
taken. The tissues were dissolved in KOH (4 N) at 75 ꢀC
for 30 min and the 18F-organ activity was measured in a
g-counter. In the baseline study, group 1, 18F organ
uptake in % of injected activity/gram (%ID/g) of the
lung, heart, liver, spleen, kidneys, brain, intestine and
blood was 1.16Æ0.05, 0.49Æ0.06, 0.95Æ0.1, 0.84Æ0.2,
0.70Æ0.1, 0.02Æ0.005, 0.77Æ0.08 and 0.22Æ0.09,
respectively. [18F]FEFE showed specific binding to pul-
monary b2 receptors (Fig. 6), which was displaceable by
fenoterol by 50% of the baseline uptake (study group 2)
as measured in vivo by means of PET. These results
correlated well with the ex vivo measurements of the
explanted lungs: 1.16Æ0.05%ID/g baseline versus
0.42Æ0.07%ID/g displacement.
9. Elsinga, P. H.; Vos, M. G.; van Waarde, A.; Braker, A. H.;
de Groot, T. J.; Anthonio, R. L.; Weemaes, A. A.; Brodde,
O. E.; Visser, G. M.; Vaalburg, W. Nucl. Med. Biol. 1996, 159.
10. Tewson, T. J.; Stekhova, S.; Kinsey, B.; Chen, L.; Wiens,
L.; Barber, R. Nucl. Med. Biol. 1999, 26, 891.
11. Visser, T. J.; van Waarde, A.; Doze, P.; Elsinga, P. H.; van
der Mark, T. W.; Kraan, J.; Ensing, K.; Vaalburg, W. Eur. J.
Pharmacol. 1998, 361, 35.
12. Visser, T. J.; van der Wouden, E. A.; van Waarde, A.;
Doze, P.; Elsinga, P. H.; Vaalburg, W. Appl. Radiat. Isot.
2000, 52, 857.
13. Kontoyianni, M.; DeWeese, C.; Penzotti, J. E.; Lybrand,
T. J. Med. Chem. 1996, 35.
14. General method: Freifelder, M.; Ng, Y. H.; Helgren, P. F.
J. Med. Chem. 1964, 381.
15. Albrecht, R.; Loge, O. Eur. J. Med. Chem. 1985, 51.
16. Hett, R.; Fang, Q. K.; Gao, Y.; Hong, Y.; Butler, H. I.;
Nie, X.; Wald, S. A. Tetrahedron Lett. 1997, 38, 1125.
17. Auge, J.; Leroy, F. Tetrahedron Lett. 1996, 37, 7715.
18. Willson, T. M.; Kocienski, P.; Jarowicki, K.; Isaac, K.;
Hitchcock, P. M.; Faller, A.; Campbell, S. F. Tetrahedron
1990, 46, 1767.
Conclusion
The fluorine-18 labeled analogue of the b2 subtype spe-
cific b-adrenoceptor ligand fenoterol was synthesized as
racemic compound (R,R)(S,S) 5-(2-(2-[4-(2-[18F]fluoro-
ethoxy)phenyl]-1-methylethylamino)-1-hydroxyethyl)-
benzene-1,3-diol ([18F]FEFE) in an overall radio-
chemical yield of 20% after 65 min with a radiochemical
purity higher than 98%. First in vitro, ex vivo and in
vivo PET evaluation studies indicate that this com-
pound binds specifically to the b2 adrenoceptors of the
lung of guinea pigs.
19. Column chromatography (Si-60): solvent=ethylacetate/
methanol 9/1; [(R,S)(S,R)-6, Rf=0.15]; [(R,R)(S,S)-6, Rf=0.1]
1
20. (R,R)(S,S) fenoterol1: H NMR (400 MHz, DMSO-d6) d
9.0 (s, 3H), 6.9 (d, 2H), 6.7 (d, 2H), 6.2 (s, 2H), 6.0 (s, 1H), 5.0
(s, 1H), 4.4 (t, 1H), 3.4 (d, 2H), 2.7 (m, 1H), 2.6 (m, 2H), 2.2
(m, 1H), 0.8 (d, 3H); 13C NMR (400 MHz, DMSO-d6) d
159.8, 156.3, 147.9, 130.1, 129.7, 116.5, 104.8, 102.3, 71.4, 56.1,
55.8, 48.5, 19.8; MS (FD): m/z (% rel. int.) 304.7 (100%,
[M+1]+), additionally, elemental analysis (C, H, N), 1H-1H
1
and H–13C 2D-NMR were performed for classification. Ele-
mental analysis: calcd C 67.31, H 6.98, N 4.62; found C 67.28,
H 7.00, N 4.61. (R,R)(S,S)-6: 1H NMR (400 MHz, DMSO-d6)
d 9,2 (s, 2H), 6.9 (d, 2H), 6.7 (d, 2H), 6.3 (s, 2H), 6.0 (s, 1H),
4.6 (t, 1H), 4.5 (t, 1H), 4.4 (t, 1H), 4.2 (t, 1H), 4.1 (t, 1H), 3.3
Thus, further evaluations with enantiomerically pure
[18F]FEFE are planned to elucidate its use in scientific
and clinical studies using quantitative PET.
(m, 1H), 3.0 (m, 2H), 2.7 (m, 1H), 2.5 (d, 2H), 0.8 (d, 3H); 13
C
NMR (400 MHz, DMSO-d6) d 159.5, 158.1, 131.7, 130.2,
129.8, 115.4, 104.9, 102.7, 81.6, 72.3, 67.8, 55.3, 55.1, 41.0,
20.4; 19F NMR (400 MHz, DMSO-d6) d À224.2 (m, F); MS
(FD): m/z (% rel. Int.) 350.7 (100%, [M+1]+); additionally,
elemental analysis (C, H, N), 1H–1H and 1H–13C 2D-NMR
were performed for classification. Elemental analysis: calcd C
65.33, H 6.92, N 4.01; found C 65.31, H 6.96, N 4.11.
(R,S)(S,R)-6: 1H NMR (400 MHz, DMSO-d6) d 9,1 (s, 2H),
6.7 (d, 2H), 6.6 (d, 2H), 6.3 (s, 2H), 6.0 (s, 1H), 4.6 (t, 1H), 4.5
(t, 1H), 4.6 (t, 1H), 4.3 (t, 1H), 4.2 (t, 1H), 3.3 (m, 1H), 3.0
(m, 2H), 2.9 (m, 1H), 2.5 (d, 2H), 0.95 (d, 3H); 13C NMR
(400 MHz, DMSO-d6) d 159.4, 158.4, 131.4, 130.2, 129.4,
115.3, 104.5, 102.7, 81.6, 72.3, 67.6, 55.3, 55.1, 41.3, 20.2; 19F
NMR (400 MHz, DMSO-d6) d À224.2 (m, F); MS (FD): m/z
(% rel. int.) 350.7 (100%, [M+1]+; Elemental analysis: calcd
C 65.33, H 6.92, N 4.01; found C 65.28, H 6.98, N 4.07 (che-
mical shifts which are underlined were used for assigning the
diastereomers).
Acknowledgements
The authors thank Boehringer Ingelheim, Germany, for
providing (R,R)(S,S)-fenoterol hydrobromide1. Support
by DFG grant FOR 471 is gratefully acknowledged.
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5. Szentivanyi, A. J. Allergy 1986, 133, 362.
21. (R,R)(S,S)-8: 1H NMR (400 MHz, DMSO-d6) d 9.2 (s,
1H), 9.1 (s, 1H), 6.9 (d, 2H), 6.7 (d, 2H), 6.3 (s, 2H), 4.6 (t,
1H), 4.5 (t, 1H), 4.4 (m, 1H), 4.2 (t, 1H), 4.1 (t, 1H), 3.0 (m,
2H), 2.7 (m, 1H), 2.5 (d, 2H), 0.85 (d, 3H); 13C NMR
6. Davis, P. B. Autonomous Function in Patients with Airway
Obstruction. In The Airways. Neural Control in Health and
Disease; Kaliner, M. A., Barns, P. J. Eds.: New York, Marcel
Dekker; 1988. p 87.
7. Ueki, J.; Rhodes, C. G.; Hughes, J. M.; De Silva, R.;
Lefroy, D. C.; Ind, P. W.; Qing, F.; Brady, F.; Luthra, S. K.;
Steel, C. J.; Waters, S. L.; Lammertsma, A. A.; Camici, P. G.;
Jones, T. J. Appl. Physiol. 1993, 75, 559.
(400 MHz, DMSO-d6)
d
159.5, 158.1, 131.7, 130.2,
129.8,115.4, 104.9, 102.7, 81.6, 72.3, 67.8, 55.3, 55.1, 41.0,
20.4; 19F NMR (400 MHz, DMSO-d6) d À224.2 (m, F); MS
(FD): m/z (% rel. int.) 350.5 (100%, [M+1]+; (R,R)(S,S)-14:
1H NMR (400 MHz, DMSO-d6) d 9.0 (s, 3H), 6.9 (d, 2H), 6.7
(d. 2H), 6.2 (s, 2H), 6.0 (s, 1H), 5.0 (s, 1H), 4.3 (m, 2H), 4.3 (t,
1H), 2.8 (m, 2H), 2.7 (m, 1H), 2.6 (m, 2H), 2.5 (dd, 1H), 2.4
(dd, 1H), 0.8 (d, 3H); 13C NMR (400 MHz, DMSO-d6) d
159.8, 156.3, 147.9, 130.1, 129.7, 116.5, 104.8, 102.3, 84.2, 71.4,
56.1, 55.8, 52.6, 48.5, 19.8; 19F NMR (400 MHz, DMSO-d6) d
8. Elsinga, P. H.; van Waarde, A.; Jaeggi, K. A.; Schreiber, G.;
Heldoorn, M.; Vaalburg, W. J. Med. Chem. 1997, 40, 3829.

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E. Schirrmacher et al. / Bioorg. Med. Chem. Lett. 13 (2003) 2687–2692
À198.2 (m, F); MS (FD): m/z (% rel. int.) 350.2 (100%,
[M+1]+
mm), flow: 1 mL/min, solvent: methanol/water (30/70+1%
sodium dihydrogen phospate-buffer), Rf (R,R)(S,S)-[18F]6=12
min.
22. 5 g (3.5 mmol) Fenoterol hydrobromide1 was dissolved
in methanol (5 mL), NaOH (1.75 mL, 2 N) was added and
26. In a typical experiment, 500 MBq of (R,R)(S,S)-[18F]6
could be obtained from 2.2–2.5 GBq [18F]fluoride starting
activity.
the mixture was stirred for
5 min. The solution was
extracted with ether (3Â25 mL) and the organic phase was
dried over Na2SO4. After removing the solvent in vacuum
the product could be obtained as a white powder (0.97 g,
90%).
27. Wessler, I.; Holz, C.; Maclagan, J.; Pohan, D.; Reinhei-
mer, T.; Racke, K. Naunyn-Schmiedeberger’s Arch. Pharmacol.
1993, 348, 14.
23. Block, D.; Coenen, H. H.; Stocklin, G. J. Label. Compd.
Radiopharm. 1986, 23, 1042.
24. Perrin, D. D.; Dempsey, B.; Serjeant, E. P. pKa Prediction for
Organic Acids and Bases; Chapman and Hall: New York, 1981.
25. HPLC-column: Waters Symmetry1 5 mm C-18 (4.6Â150
28. Helisch, A.; Thews, O.; Buchholz, H. G.; Karg, A.;
Schreiber, W.; Vaupel, P.; Bartenstein, P. Eur. J. Nucl. Med.
2002, 29, 138.
29. Gunn, R. N.; Gunn, S. R.; Cunningham, V. J. J. Cereb.
Blood Flow Metab. 2001, 21, 635.