Synthesis of a [18F]-labeled ceritinib analogue for positron emission tomography of anaplastic lymphoma kinase, a receptor tyrosine kinase, in lung cancer

Article abstract of DOI:10.1002/jlcr.3373

Anaplastic lymphoma kinase (ALK), an oncogenic receptor tyrosine kinase, has emerged as a therapeutic target in solid and hematologic tumors. Although several ALK inhibitors have gained recent approval for therapy, non-invasive indicators of target engagement or for use as predictive biomarkers in vivo are lacking. Therefore, we designed and synthesized a radiolabeled analogue of the ALK inhibitor ceritinib, [¹⁸F]fluoroethyl-ceritinib ([¹⁸F]-FEC), for use with positron emission tomography. We used two methods to synthesize [¹⁸F]-FEC. First, [¹⁸F]fluoroethyl-tosylate was prepared, coupled with ceritinib, and the product purified to yield [¹⁸F]-FEC. Alternatively, a precursor compound was synthesized, directly fluorinated with ¹⁸F-fluoride, and purified to yield [¹⁸F]-FEC. The first method produced [¹⁸F]-FEC with an average decay-corrected yield of 24% (n = 4), specific activity of 1200 mCi/μmol, and >99% purity; synthesis time was 115 min from the end of bombardment. The second method produced [¹⁸F]-FEC with an average yield of 7% (n = 4), specific activity of 1500 mCi/μmol, and >99% purity; synthesis time was 65 min from the end of bombardment. The synthesis of a novel ¹⁸F-labeled analogue of ceritinib has been achieved in acceptable yields, at high purity, and with high specific activity. The compound is a potential positron emission tomography imaging agent for the detection of ALK-overexpressing solid tumors such as lung cancer. Synthesis of [¹⁸F]-fluoroethyl-ceritinib for positron emission tomography is reported. Reaction of [¹⁸F]-fluoroethyl-tosylate with ceritinib produced the product in good yield, with high purity and specific activity. The compound is a potential positron emission tomography imaging agent for the detection of anaplastic lymphoma kinase-overexpressing solid tumors such as lung cancer.

Full text of DOI:10.1002/jlcr.3373

Research article
Received 19 November 2015,
Revised 30 December 2015,
Accepted 30 December 2015
Published online 8 February 2016 in Wiley Online Library
(wileyonlinelibrary.com) DOI: 10.1002/jlcr.3373
18
Synthesis of a [ F]-labeled ceritinib analogue
for positron emission tomography of
anaplastic lymphoma kinase, a receptor
tyrosine kinase, in lung cancer
*
Sandun Perera, David Piwnica-Worms, and Mian M. Alauddin
Anaplastic lymphoma kinase (ALK), an oncogenic receptor tyrosine kinase, has emerged as a therapeutic target in solid and
hematologic tumors. Although several ALK inhibitors have gained recent approval for therapy, non-invasive indicators of
target engagement or for use as predictive biomarkers in vivo are lacking. Therefore, we designed and synthesized a
radiolabeled analogue of the ALK inhibitor ceritinib, [18F]fluoroethyl-ceritinib ([18F]-FEC), for use with positron emission
tomography. We used two methods to synthesize [18F]-FEC. First, [18F]fluoroethyl-tosylate was prepared, coupled with
ceritinib, and the product purified to yield [18F]-FEC. Alternatively, a precursor compound was synthesized, directly
fluorinated with 18F-fluoride, and purified to yield [18F]-FEC. The first method produced [18F]-FEC with an average decay-
corrected yield of 24% (n = 4), specific activity of 1200 mCi/μmol, and >99% purity; synthesis time was 115 min from the
end of bombardment. The second method produced [18F]-FEC with an average yield of 7% (n = 4), specific activity of
1500 mCi/μmol, and >99% purity; synthesis time was 65 min from the end of bombardment. The synthesis of a novel
18F-labeled analogue of ceritinib has been achieved in acceptable yields, at high purity, and with high specific activity.
The compound is a potential positron emission tomography imaging agent for the detection of ALK-overexpressing solid
tumors such as lung cancer.
Keywords: lung cancer; tyrosine kinase; ceritinib; 18F; PET
echinoderm microtubule-associated protein-like 4-ALK fusion
Introduction
gene.7,8 Although crizotinib is very effective against ALK-positive
The discovery of a variety of molecular and genetic alterations
NSCLC overall, some patients with the disease have ALK
point mutations that cause resistance to the drug.9,10 In
in different malignancies leading to oncogenesis has provided
insight into the complexity of tumorigenesis and the
an effort to circumvent drug resistance caused by ALK
opportunity to target specific markers with the objective of
mutations, investigations have advanced significantly into
improving patient outcomes.1 In this context, tyrosine kinase
assessing second-generation ALK inhibitors in crizotinib-
(TK) inhibitors have become a mainstream molecular-targeted
resistant ALK-positive NSCLC. For example, ceritinib and
therapy for many solid tumors, including several subtypes of
alectinib have been approved by the FDA for the treatment of
lung cancer.2,3 Many TKs, especially receptor TKs, are found
patients with ALK-positive metastatic NSCLC whose disease
upstream or downstream of clinically relevant oncogenes.4
One TK receptor, anaplastic lymphoma kinase (ALK), was first
identified in 1994 as a part of the nucleophosmin-ALK fusion
gene, which occurs in 60% of anaplastic large-cell lymphomas.
ALK is also part of the echinoderm microtubule-associated
protein-like 4-ALK fusion gene, which occurs in 3–7% of non-
progressed during treatment with crizotinib or who were
intolerant to crizotinib.11,12 Other potent ALK inhibitors,
including X-396, ASP3026, AP26113, PF-06463922, CEP-37440
and TSR-011, some with enhanced specificity, are also in Phase
1 and 2 clinical trials.13–20 Most recently, the FDA approved
ceritinib for the treatment of patients with certain lung cancers
small cell lung cancers (NSCLCs).5,6 ALK, which is grouped with
leukocyte TK in a subfamily of the insulin receptor superfamily,
is an attractive therapeutic target in cancers expressing
activating mutations or fusions of the gene; as a result, a
variety of ALK inhibitors, including crizotinib, ceritinib, and
alectinib, have been developed and examined in clinical trials
(Figure 1).
Among these inhibitors, crizotinib, in 2011, was the first small
molecule inhibitor the US Food and Drug Administration (FDA)
approved for the treatment of NSCLC containing the
that relapsed after first-line therapy.21,22
Department of Cancer Systems Imaging, The University of Texas MD Anderson
Cancer Center, Houston, TX 77030, USA
*Correspondence to: Mian M. Alauddin, Department of Cancer Systems Imaging,
The University of Texas MD Anderson Cancer Center, 1881 East Road,
3SCRB4.3626, Unit 1907, Houston, TX 77054, USA.
E-mail: alauddin@mdanderson.org
J. Label Compd. Radiopharm 2016, 59 103–108
Copyright © 2016 John Wiley & Sons, Ltd.

S. Perera et al.
Figure 1. Structures of anaplastic lymphoma kinase inhibitors.
Although extensive work on the development of therapeutic and radiochemistry for the synthesis of this potential PET
drugs for ALK inhibition has been reported, no diagnostic imaging agent.
compound for assessing molecular-specific pharmacodynamics
and target sensitivity to ALK inhibition in vivo, such as an
imaging agent, has been yet reported. The current lack of
Experimental
Reagents and instrumentation
diagnostic assays and markers predictive of disease sensitivity
to ALK inhibition in vivo can limit the ability to properly select
patients for clinical trials of drugs targeting the ALK kinase. The
lack of effective markers and methods for non-invasive
monitoring of the early efficacy of therapy also presents a major
clinical challenge to selecting the optimal setting(s) in which to
test and monitor the biological and therapeutic efficacy of these
novel drugs. Positron emission tomography (PET) with ALK-
specific radiolabeled agents could provide enhanced assessment
of the relative levels and heterogeneity of ALK protein in tumors
in individual patients, and thus hone the selection criteria for the
inclusion of patients in redesigned clinical trials.
Reagents and solvents were purchased from Sigma-Aldrich Co., LLC
(St. Louis, MO) and used without further purification. Ceritinib was
purchased from Pure Chemistry Scientific, Inc. (Sugar Land, TX). Silica
gel solid-phase extraction cartridges (Sep-Pak, 900 mg) were purchased
from Alltech Associates (Deerfield, IL, USA). K18F/kryptofix 2.2.2. was
purchased from Cyclotope, Inc. (Houston, TX) as an aqueous solution.
Thin layer chromatography was performed on pre-coated Kieselgel
60 F254 glass plates (Merck, Darmstadt, Germany). Proton, 13C, and 19F
nuclear magnetic resonance (NMR) spectrometry was performed at The
University of Texas MD Anderson Cancer Center using a Bruker 300-
MHz or 600-MHz spectrometer with tetramethylsilane as an internal
reference or hexafluorobenzene as an external reference. High-resolution
mass spectrometry (HRMS) was performed on a Bruker BioTOF II mass
spectrometer at the University of Minnesota using electrospray
ionization.
High-performance liquid chromatography (HPLC) was performed on
1100 series pumps (Agilent Technologies, Stuttgart, Germany) with a
built-in ultraviolet (UV) detector and a radioactivity detector with a
single-channel analyser (Bioscan, Washington, DC). Purifications and
quality control analyses were performed on an Econosil semi-preparative
C18 reverse-phase column (Alltech, 10 × 250 mm) and an analytical C18
column (Alltech, 4.6 × 250 mm), respectively. Quality control analyses
were performed in a 60% MeCN/40% H2O/0.5% trifluoracetic acid solvent
system.
Previously, [18F]-labeled imatinib and dasatinib analogues for
PET imaging of Bcr-Abl, c-KIT, and Src protein kinases were
reported, and furthermore, K562 leukemic cell tumor xenografts
in mice have been visualized with both [18F]-labeled imatinib
and dasatinib.23,24 Structure–activity relationship and molecular
modeling analyses of ceritinib suggest that the compound’s
central pyrimidine ring, which can participate in hydrogen bonds
to the hinge area via the pyrimidine and amino nitrogen atoms,
is critical for its ALK inhibition activity.4 Therefore, substitutions
on the piperidine nitrogen are fairly well tolerated; however,
the properties of the substituents substantially influence the
ALK inhibition activity of ceritinib.4 To further study ALK
inhibition activity, investigators have prepared ceritinib
derivatives in which the piperidine nitrogen was substituted
with various phosphoramides and carbamates; with this
modification, at least one analogue showed enhanced efficacy
over ceritinib.4 We hypothesized that ceritinib, minimally
modified with the attachment of a radioisotope, would retain
its efficacy and may be a potential imaging agent for
monitoring lung cancers expressing ALK protein. We have
Preparation of fluoroethyl-tosylate: 1
Ethylene glycol di-tosylate (50 mg, 1 equiv.) was dissolved in dry MeCN
(3 mL); then a solution of Bu4NF in tetrahydrofuran (150 μL, 1 M,
1.1 equiv.) was added, and the reaction mixture was heated at 95 °C for
1 h. The crude reaction mixture was concentrated, purified by column
chromatography, and eluted with 20% ethyl acetate in hexane. After
evaporation of the solvent, 150 mg of the compound was obtained as
a liquid in 60% yield. 1H NMR (CDCl3, 600 MHz) δ: 7.81 (d, J = 8.3 Hz,
2 H), 7.36 (d, J = 8.3 Hz, 2 H), 4.57 (dt, J = 47.1 Hz and 4.1 Hz, 2 H), 4.26
(dt, J = 27.1 Hz and 4.1 Hz, 2 H), 2.46 (s, 3 H). 19F NMR (CDCl3, 300 MHz)
δ: À224.65 (s, decoupled).
designed and synthesized an
[
18F]-labeled analogue of
ceritinib, [18F]fluoroethyl-ceritinib ([18F-FEC), for PET imaging
of ALK protein in lung cancer. Herein, we report the chemistry
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Copyright © 2016 John Wiley & Sons, Ltd.
J. Label Compd. Radiopharm 2016, 59 103–108

S. Perera et al.
Preparation of fluoroethyl-ceritinib: 2
Preparation of [18F]fluoroethyl-ceritinib: [18F]-2
Ceritinib (23 mg, 0.041 mmol) was dissolved in dry acetonitrile (2.0 mL),
Method 1: The aqueous solution of K18F/kryptofix [2.2.2] (110 mCi in
and then triethylamine (300 μL) was added. To this mixture, 0.5 mL) was transferred into a V-vial. Water was removed by azeotropic
fluoroethyl-tosylate 1 (10 mg, 0.045 mmol, 1.1 equiv.) was added and evaporation with acetonitrile (1.0 mL) at 100 °C under a stream of argon.
the reaction mixture was refluxed for 4 h. The mixture was
concentrated under vacuum, then the crude product purified by flash
A solution of ethylene glycol ditosylate (5–7 mg) in anhydrous
acetonitrile (0.5 mL) was added to the dry K18F/kryptofix [2.2.2]. The
chromatography on
a
silica gel column, and eluted with 5%
reaction mixture was heated at 110 °C for 15 min, an aliquot was assessed
MeOH/CH2Cl2 to obtain FEC 2 as a pale yellow solid (16 mg, 64% yield). by analytical HPLC, which showed a high conversion to the desired
1H NMR (CDCl3, 600 MHz) δ: 9.49 (s, 1 H, NH), 8.58 (d, J = 8.4 Hz, 1 H),
8.15 (s, 1 H), 8.00 (s, 1 H), 7.93 (dd, J = 7.9 Hz and 1.5 Hz, 1 H), 7.62 (td,
product [18F]-1. The crude reaction mixture was passed through a silica
Sep-Pak cartridge followed by elution with two portions of ethyl acetate
J = 7.8 Hz and 1.6 Hz, 1 H), 7.54 (s, 1 H, NH), 7.26 (td, J = 7.6 Hz and (2.5 mL, total), and the solvent was evaporated at 80 °C under a stream of
1.0 Hz, 1 H), 6.81 (s, 1 H), 4.62 (dt, J = 47.8 Hz and 4.8 Hz, 2 H), 4.52
(septet, J = 6.1 Hz, 1 H), 3.26 (septet, J = 6.7 Hz, 1 H), 3.12 (d,
J = 11.8 Hz, 2 H), 2.77 (dt, J = 28.4 Hz and 4.8 Hz, 2 H), 2.68 (m, 1 H),
2.20 (td, J = 11.2 Hz and 3.6 Hz, 2 H), 2.16 (s, 3 H), 1.79 (m, 4 H), 1.36
(d, J = 6.1 Hz, 6 H), 1.32 (d, J = 6.8 Hz, 6 H). 13C NMR decoupled (CDCl3,
125 MHz) δ: 157.49, 155.36, 155.30, 144.69, 138.48, 137.68 9, 134.66,
131.23, 127.37, 126.80, 124.86, 123.69, 123.08, 120.60, 110.73, 105.68,
81.86 (d, 1JF, C = 167.3 Hz), 71.34, 58.68 (d, 2JF, C = 19.6 Hz), 55.42,
54.90, 37.84, 32.82, 22.26, 18.93, 15.36. 19F NMR, decoupled (CDCl3,
300 MHz) δ: À217.9 (s). HRMS: m/z [M + H]+ calculated for
C30H40ClFN5O3S, 604.1788; found, 604.2540.
argon. The residue was dissolved in 60% acetonitrile/water (1.0 mL) and
injected onto the HPLC connected to a semipreperative C18 column.
The product [18F]-1 was eluted with 55% acetonitrile/water at a flow of
4 mL/min. The appropriate fraction (radioactive) was collected, and an
aliquot of the product [18F]-1 was analyzed on an analytical HPLC column
to verify its identity and purity by co-injection with the nonradioactive
authentic sample 1. The solvent from the rest of the product was partially
evaporated under reduced pressure and then water (10 mL) was added.
The solution was passed through a C18 reverse-phase cartridge; the
cartridge was dried by vacuum for 5 min followed by flashing with argon
for 5 min. The product was eluted with 1.5 mL of dry acetonitrile and
collected into a V-vial containing ceritinib (10 mg).
The reaction mixture in the V-vial was heated at 100 °C for 20 min, and
an aliquot was injected onto the analytical HPLC system, which showed
that no radioactive starting material ([18F]-1) remained. The solvent was
evaporated by a stream of argon, and the product was purified by
normal-phase flash chromatography and eluted with 5% MeOH in
CH2Cl2. One milliliter fractions were collected, the appropriate fractions
(radioactive) were combined, and radioactivity was counted in a dose
calibrator (Capintech). The solvent was evaporated under a stream of
argon, the product was dissolved in MeCN/H2O, and an aliquot analyzed
in analytical HPLC by co-injection with standard compound 2 to verify its
identity and purity.
Method 2: Chloroethyl-ceritinib 4 (5–7 mg) was placed in a V-vial, and
a solution of dry K18F/kryptofix [2.2.2] in anhydrous acetonitrile (0.5 mL)
was added. The reaction mixture was heated at 110 °C for 20 min, an
aliquot was analyzed by HPLC, which showed presence of the product.
The solvent from the reaction mixture was evaporated to dryness; the
product was dissolved in CH2Cl2 and loaded onto a silica Sep-Pak
cartridge. The product was eluted with 30% acetone in hexane and
1 mL fractions were collected. The radioactive fractions were combined,
and the solvent was evaporated at 40 °C under a stream of argon. The
product [18F]-2 was dissolved in MeCN, and an aliquot was analyzed on
an analytical HPLC column to verify its identity and purity by co-injection
with the nonradioactive authentic sample 2.
Preparation of hydoxyethyl-ceritinib: 3
Ceritinib (200 mg, 0.36 mmol) was dissolved in acetonitrile (4.0 mL), and
then triethylamine (2.0 mL) was added. To this mixture, hydroxyethyl-
tosylate (196 mg, 0.91 mmol, 2.5 equiv.) was added and the reaction
mixture refluxed at 85 °C for 4 h. The mixture was concentrated under
vacuum, then the crude product purified by flash chromatography on a
silica gel column, and eluted with 4% MeOH/CH2Cl2. After solvent
evaporation, hydoxyethyl-ceritinib was obtained as an off-white solid
(190 mg, 88% yield). 1HNMR (CDCl3, 600 MHz), δ: 9.49 (s, 1 H, NH), 8.58
(d, J = 8.4 Hz, 1 H), 8.15 (s, 1 H), 8.01 (s, 1 H), 7.93 (d, J = 7.9 Hz, 1 H), 7.62
(t, J = 7.7 Hz, 1 H), 7.54 (s, 1 H, NH), 7.26 (t, J = 7.9 Hz, 1 H), 6.79 (s, 1 H),
4.57 (septet, J = 6.0 Hz, 1 H), 3.67 (t, J = 5.1 Hz, 2 H), 3.26 (septet,
J = 6.9 Hz, 1 H), 3.08 (d, J = 10.2 Hz, 2 H), 2.69 (m, 1 H), 2.61 (t, J = 5.1,
2 H), 2.23 (m, 2 H), 2.16 (s, 3 H), 1.77 (m, 4 H), 1.38 (d, J = 6.1 Hz, 6 H),
1.32 (d, J = 6.8 Hz, 6 H).
Preparation of chloroethyl-ceritinib: 4
Hydroxyethyl-ceritinib 3 (41 mg, 0.068 mmol) was dissolved in dry
pyridine (3.0 mL), cooled to 0 °C under argon, followed by the drop-
wise addition of
a solution of tosyl chloride (55 mg, 0.29 mmol,
4.2 equiv.) in dry dichloromethane (1.0 mL). This mixture was allowed
to slowly warm to room temperature over 3 h followed by continued
stirring for another 15 h. The crude reaction mixture was concentrated
under vacuum, re-dissolved in dichloromethane (5 mL), and
subsequently washed with 0.1 M NaHCO3 solution (aq., 3 × 3 mL). The
organic layer was isolated, dried under MgSO4, concentrated,
Results and discussion
Method 1: Fluoroethyl-tosylate 1 was obtained in-house by the
reaction of ethylene glycol ditosylate with Bu4NF in 60% yield.
The compound was characterized by 1H and 19F NMR
spectroscopy, which showed peaks consistent with those
associated with the compound. Non-radioactive FEC 2 was
chromatographed over
MeOH/CH2Cl2. After solvent evaporation, chloroethyl-ceritinib was
obtained as
a silica gel column, and eluted with 3%
a
white solid (20 mg, 48% yield). 1H NMR (CDCl3, prepared according to Scheme 1. The chemical yield of 2 was
600 MHz), δ: 9.49 (s, 1 H, NH), 8.58 (d, J = 8.3 Hz, 1 H), 8.15 (s, 1 H),
8.00 (s, 1 H), 7.92 (dd, J = 7.9 Hz and 1.3 Hz, 1 H), 7.62 (td, J = 7.9 Hz
and 1.5 Hz, 1 H), 7.53 (s, 1 H, NH), 7.26 (t, J = 7.9 Hz, 1 H), 6.80 (s, 1 H),
4.52 (septet, J = 6.1 Hz, 1 H), 3.64 (t, J = 7.0 Hz, 2 H), 3.26 (septet,
J = 6.9 Hz, 1 H), 3.07 (d, J = 11.3 Hz, 2 H), 2.79 (t, J = 7.0, 2 H), 2.66 (m,
1 H), 2.22 (m, 2 H), 2.15 (s, 3 H), 1.77 (m, 4 H), 1.36 (d, J = 6.0 Hz, 6 H),
1.32 (d, J = 6.8 Hz 6 H). 13C NMR decoupled (CDCl3, 125 MHz) δ:
157.61, 155.50, 155.45, 144.83, 138.63, 134.78, 131.39, 127.63, 126.96,
125.02, 123.82, 123.22, 120.73, 110.90, 105.87, 71.56, 68.29, 60.40,
55.57, 54.79, 38.00, 32.83, 22.40, 19.08, 15.51. HRMS: m/z [M + H]+
calculated for C30H39Cl2N5O3S, 620.2229; found, 620.2207.
64% after chromatographic purification in this single-step
experiment. The product was fully characterized using
spectroscopic methods, including 1H, 13C, and 19F NMR
spectrometry and HRMS.
Scheme 2 shows the radiosynthesis of FEC 2 ([18F]-2). All
radiosyntheses were performed using 100–110 mCi of K18F/
kryptofix [2.2.2]. This synthesis was achieved by a two-step
process: (i) radiosynthesis of [18F]-fluoroethyl-tosylate ([18F]-1)
followed by (ii) coupling of [18F]-1 with ceritinib. The mean
decay-corrected radiochemical yield of [18F]fluoroethyl-tosylate
J. Label Compd. Radiopharm 2016, 59 103–108
Copyright © 2016 John Wiley & Sons, Ltd.
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S. Perera et al.
Scheme 1. Reagents and conditions: FCH2CH2OTs (1.1 equiv.), Et3N (50 equiv.), CH3CN, 85 °C, 4 h, 64% yield.
automate for routine production. Therefore, we explored the
synthesis of the compound using a simple alternative one-step
method, fluorination followed by purification (Method 2).
Method 2: We initially sought to prepare tosylethyl-ceritinib,
which could be fluorinated to afford FEC 2. We attempted the
reaction of ceritinib with ethylene glycol ditosylate to obtain
tosylethyl-ceritinib, but this reaction produced ethylene di-
ceritinib, implicating that both tosylates of ethylene reacted with
certinib. The compound was isolated in low yield and tentatively
confirmed by 1H NMR spectrometry (data not shown). The
mono-substituted product, tosylethyl-ceritinib could not be
obtained from this reaction. Alternatively, we attempted to
prepare tosylethyl-ceritinib via hydroxyethyl-ceritinib (Scheme 3).
Compound 3 was prepared by the reaction of ceritinib with
hydroxyethyl-tosylate in 88% yield (purified). The product was fully
characterized by 1H NMR spectroscopy, and the spectrum was
consistent with that reported in the literature.13
Scheme 2. Radiosynthesis of [18F]fluoroethyl ceritinib. Reagents and conditions:
(a) [18F]-KF/Kryptofix CH3CN, 110 °C, 15 min, 48% yield. (b) CH3CN, 110 °C, 20 min,
74% yield.
The reaction of compound 3 with either tosyl-chloride or
mesyl-chloride did not produce the desired sulfonylethyl-
ceritinib, but instead produced compound 4 in a moderate yield
(48%). The reaction of hydroxyethyl-ceritinib with mesyl chloride
showed two spots on thin layer chromatography, and the lower
spot was gradually converted to the higher one with time at
room temperature, which suggested that the mesylethyl-
ceritinib was formed. However, it was difficult to isolate a pure
product from the reaction mixture. Therefore, we allowed the
reaction to run to completion at the higher spot, which resulted
in chloroethyl-ceritinib (compound 4). Compound 4 was fully
was 48% (range 45–53%) after HPLC purification (n = 5). The
mean radiochemical yield in the coupling step was 74% (range,
65–85%) (n = 4). The mean decay-corrected yield of [18F]-2 in
two-steps was 24% (range, 20–28%) in four runs after
purification in both steps. The product was >99% pure and
had an average specific activity of 1200 mCi/μmol. The synthesis
time was 115 min from the end of bombardment.
This method requires two purifications: (i) HPLC purification of
[18F]fluoroethyl-tosylate and (ii) a second purification after
coupling ceritinib with [18F]-1 by either HPLC or flash
chromatography. After the first purification with HPLC, [18F]
fluoroethyl-tosylate required the removal of water from the
HPLC solvent, which could be achieved using a reverse-phase
C18 cartridge. After a brief evaporation of MeCN from the HPLC
solvent under vacuum, further dilution with additional water
(10 mL) rendered the product retainable in the C18 cartridge.
After drying the cartridge, the product could be eluted with a
small volume of dry MeCN directly to the V-vial containing
certinib. There was no loss of activity in the C18 cartridge during
the concentration step.
1
characterized by H and 13C NMR spectroscopy and HRMS. All
Purification of the final product [18F]-2 by HPLC was not
suitable because of the slow wash-out of ceritinib from the
column. As a result, a small quantity of ceritinib remained in
the final product, representing a major contaminant, which
would compete with [18F]-2 during biological studies. Therefore,
flash chromatography was used to provide the desired product
[18F]-2, which was both chemically and radiochemically pure.
An HPLC chromatogram of the radioactive product [18F]-2 co-
injected with non-radioactive standard compound is presented
in Figure 2.
Although this method produced reasonably good yields and a
clean product, the handling of radioactive material in multiple
steps was not convenient, and the method was difficult to
Figure 2. High-performance liquid chromatography of [18F]fluoroethyl-ceritinib,
co-injected with the non-radioactive standard. Analytical column; 60% MeCN/
H2O/0.5% trifluoracetic acid, flow 1 mL/min.
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S. Perera et al.
Scheme 3. Reagents and conditions: (a) HOCH2CH2OTs (2.5 equiv.), Et3N (40 equiv.), CH3CN, 85 °C, 3 h, 88% yield. (b) TsCl (4 equiv.), Pyridine/DCM (3/1 mL), 0 °C 3 h, rt
15 h, 50% conversion, 40% yield, (c) Bu4NF (3 equiv.), CH3CN, 110 °C, 2 h, 55% yield.
Scheme 4. Reagents and conditions: K18F/kryptofix CH3CN, 110 °C, 7% yield.
data were consistent with the identity of the product. compound in PET imaging of specific types of solid tumors,
Fluorination of compound 4 produced the desired compound including lung cancer.
2 in 55% yield. The spectral data of the product 2 by this method
was identical to those obtained by Method 1.
Conclusion
Scheme 4 shows the radiosynthesis of [18F]-FEC following a
direct fluorination of the precursor compound 4. The mean
decay-corrected radiochemical yield of [18F]-2 using this method
was 7% (range, 6–10%) in four runs. The product was >99%
radiochemically pure and had an average specific activity of
1500 mCi/μmol. The synthesis time was 65–70 min from the
end of bombardment.
We synthesized a novel [18F]-labeled analogue of ceritinib,
[18F]-fluoroethyl-ceritinib, in good yields with high purity and
specific activity. The compound is a potential PET imaging agent
for the detection of ALK-overexpressing lung cancer and should
be tested in vitro in cell culture and in vivo in tumor-bearing mice.
Although the fluorination of compound 4 with Bu4NF
produced the nonradioactive product 2 in a 55% yield, the
radiofluorination of 4 produced lower yields. This may be due
to the limited availability of 18F-fluoride in the reaction mixture.
The main drawback of Method 2 was the purification of the
product [18F]-2. Analytical HPLC revealed that the crude product
had a couple of unknown UV peaks, which eluted very close to
the desired product; as a result, it was difficult to isolate a
chemically pure product by HPLC. Alternatively, we used flash
chromatography and separated the radioactive product, and
HPLC of this radiochemically pure product also showed the
unknown UV-active material. Although the second method
seemed to be simple and straightforward, it produced lower
yields, and the product contained chemical impurities that could
potentially compete with the desired radioactive compound in
biological studies. Nonetheless, further optimization of the
procedure may improve the method. Of these two methods,
we judged Method 1 to be the better choice for producing a
pure compound for biological applications in vitro and in vivo.
Further studies will be required to test the efficacy of the
Acknowledgements
This work was supported by the National Institutes of Health
through the Washington University-MD Anderson Cancer Center
Inter-Institutional Molecular Imaging Center grant (NCI P50
CA94056) (DP-W) and by an MD Anderson Cancer Center
Institutional Research Grant (MMA).
Conflict of interest
The authors did not report any conflict interest.
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