6606 Journal of Medicinal Chemistry, 2010, Vol. 53, No. 18
Jarkas et al.
The very high tumor to brain ratios and in vivo stability to
defluorination suggest that 2-FACPC is an excellent candi-
date for further evaluation for imaging tumors in humans.
Because [18F]4b was evaluated as a racemic mixture, it is possi-
ble that the single enantiomers would exhibit different bio-
distribution profiles. Studies are underway to determine the
transport properties of the isolated enantiomers of [18F]4b in a
variety of human cancer cell lines.
2-Benzyloxycyclopentanone (6). A mixture of benzyl alcohol
(0.33 g, 3.06 mmol) and HCl-diethyl ether (1.0 M solution)
(1.04 mL) was cooled to 0 °C, and 5 (0.65 g, 2.66 mmol) was
added dropwise with stirring. After completion of the addition,
the mixture was refluxed for 4 h and concentrated under reduced
pressure. Purification by silica gel flash column chromatogra-
phy using DCM/EtOAc (80/20) afforded 6 as a light yellow oil
(0.45 g, 88%). 1H NMR (CDCl3, δ): 1.79 (m, 2H), 2.04 (m, 1H),
2.25 (m, 2H), 2.43 (m, 1H), 3.80 (t, 1H), 4.69 (d, 1H, J = 12.0
Hz), 4.83 (d, 1H, J = 12.0 Hz), 7.35 (m, 5H). HRMS, m/z, calcd
for C12H13O2 [M - H]þ, 190.10; found, 189.09081.
syn-3-(N-(tert-Butoxycarbonyl)amino)-4-cyclopentane-1,2,3-
oxathiazolidine-4-carboxylic Acid tert-Butyl Ester 2,2-Dioxide
(12). A solution of 11 (58 mg, 0.17 mmol) in acetonitrile (7 mL)
was cooled in an ice bath and treated successively with sodium
periodate (NaIO4) (41 mg, 0.19 mmol), a catalytic amount of
Experimental Section
Materials and Instrumentation. Reagents were purchased
from Aldrich Chemical Co. (Milwaukee, WI) with purities of
>99% andusedwithoutfurtherpurification. Thin-layerchromato-
graphy (TLC) analyses were performed using 250 μm UV254
silica gel backing on aluminum plates purchased from Whatman
Ltd. (Maidstone, Kent, U.K.). Flash column chromatography
was carried out using Merck Kieselgel silica gel 60 (230-400 mesh).
Proton nuclear magnetic resonance (1H NMR) spectra were run
on a Mercury Unit 300 at 300 MHz in CDCl3 with tetramethyl-
silane (TMS) as internal standard at Emory University CSI.
Elemental analyses were performed by Atlantic Microlabs, Inc.
(Norcross, GA), and the purities of the tested compounds were
>95% unless otherwise indicated. Mass spectra were run on a
JEOL JMS-SX102/SX102A/E or VG 70-S double focusing
mass spectrometer using high-resolution electrospray ionization
(ESI). The animal experiments were carried out in compliance
with the Emory Institutional University Animal Care Committee
(IUCAC) and Radiation Safety regulations. The [18F]fluoride
was produced at Emory University CSI with an 11 MeV Siemens
RDS 111 negative-ion cyclotron (Knoxville, TN) by the 18O(p, n)18F
reaction using [18O]H2O (95%). Alumina N SepPaks and HLB
Oasis cartridges were purchased from Waters, Inc. (Milford,
MA). The ion retardation (IR) chromatography columns and
the IR resin AG 11A8 (50-100 mesh) were purchased from Bio-
Rad Laboratories (Hercules, CA). Trap/release cartridges model
DW-TRC were purchased from D&W, Inc. (Oakdale, TN).
Radiometric TLC was performed with the same type of silica
plates from Whatman and analyzed using a Raytest system
(model Rita Star, Germany). Compound 1 was prepared as pre-
viously reported.10a The target compound 4b was prepared as a
racemic mixture in both its fluorine-18 and fluorine-19 forms.
Chemistry. anti-1-Amino-2-fluorocyclopentyl-1-carboxylic Acid
(4b). To a solution of 3b (17 mg, 0.069 mmol) in methanol (1 mL)
was added 4 N HCl (1 mL). The reaction vessel was sealed and
heated at 100 °C for 20 min. After cooling, the clear pale yellow
solution was loaded on an ion retardation resin (AG 11A8) column
in series with an alumina N SepPak and a C18 SepPak and eluted
with water. The aqueous solution was washed with 3 ꢀ 5 mL of
CH2Cl2 and then concentrated under reduced pressure to dryness
to provide the amino acid (4b) (6.2 mg, 61%). 1H NMR (D2O, δ):
1.78 (m, 4H), 2.19 (m, 2H), 4.26 (s, 1H). HRMS, m/z, calcd for
C6H9FNO2 [M - H]þ, 146.07; found, 146.06878. Anal. (C8H18-
Cl2FNO4) Calcd: C, 34.06; H, 6.43; N, 4.96. Found: C, 34.40; H,
5.76; N, 4.79. The combustion analysis showed that the target
compound (4b) is solvated; it contains traces amounts of CH3OH,
H2O, and CH2Cl2. The quantity of solvents was included in the
compound formula (C8H18Cl2FNO4).
ruthenium(IV) oxide hydrate (RuO2 H2O) (0.4 mg), and H2O
3
(4 mL). After 30 min of stirring, the ice bath was removed and
the reaction was continued for 30 min at room temperature. The
reaction mixture was partitioned between EtOAc and water.
The aqueous layer was further extracted with EtOAc. Organic
layers were combined, washed with saturated NaHCO3 solution
and water, dried over Na2SO4, filtered, and concentrated under
reduced pressure. Purification by silica gel flash column chromato-
graphy using hexane/EtOAc (90/10) afforded 12 as a clear oil
(54.10 mg, 87%). 1H NMR (CDCl3, δ): 1.49 (s, 9H), 1.56 (s, 9H),
1.98 (m, 3H), 2.20 (m, 2H), 2.58 (m, 1H), 4.88 (s, 1H). HRMS, m/z,
calcd for C15H29N2O7S [M þ NH4]þ, 381.14; found, 381.16917.
Anal. (C15H25NO7S) C, H, N.
Radiolabeling. anti-1-Amino-2-[18F]fluorocyclopentyl-1-carboxylic
Acid ([18F]4b). The preparation of [18F]4b was based on the
previously reported automated synthesis of anti-[18F]FACBC.6
To a glass vessel containing a solution of K222/CH3CN (2.0 mg/
mL) (1.0 mL) was added 1700 mCi (n = 4) of no-carrier-added
[18F]HF (50 μA, 60 min bombardment) through a trap/release
(T/R) cartridge by using a solution of K2CO3/H2O (1.5 mg/mL)
(0.6 mL). The solvent was removed at 110 °C with a nitrogen
flow, and an additional CH3CN (4.0 mL) was added followed by
evaporation of the solvent with a nitrogen flow to remove
residual H2O. Cyclic sulfamidate precursor 12 (1.0 mg) in dry
CH3CN (0.5 mL) was added to the vial, and the reaction mixture
was heated at 110 °C for 10 min. The intermediate product was
treated with 6 N HCl (0.5 mL) at 110 °C for 10 min and purified
by passing through an IR column assembly consisting of a 7 mmꢀ
120 mm bed of AG 11A8 IR resin column, a neutral alumina
SepPak (preconditioned with water (20.0 mL)), and an HLB Oasis
reverse phase cartridge (preconditioned with ethanol (10.0 mL)
and water (10.0 mL)). [18F]4b, eluted in series through the assem-
bly with three successive portions of sterile saline (∼3.0 mL),
passed through a 0.22 μm sterile filter into a dose vial and was
ready for the in vitro and in vivo studies. Further evidence of the
identity of [18F]4b was achieved by comparing the Rf of the
radioactive product visualized with radiometric TLC with the
Rf of the authentic 19F compound visualized with ninhydrin
stain, using the solvent CH3CN/H2O/CH3OH = 10:5:5 (Rf =
0.64 ( 0.01, Whatman silica gel plates). The only peak present
on radiometric TLC analysis corresponded to 4b, and the radio-
chemical purity of the product exceeded 99%. The isolated radio-
chemical yields were determined using a dose calibrator.
In Vitro Amino Acid Uptake and Inhibition Assays. These assays
were performed with cultured rat 9L gliosarcoma cells as
described previously.10e Briefly, approximately 0.5ꢀ106 cells
were exposed to 100 μCi of [18F]4b in amino acid free Hanks’
balanced salt solution (HBSS) (0.1 mL) with or without
transport inhibitors (10 mM final concentration of BCH,
MeAIB, or ACS) for 30 min under incubator conditions in
1.5 mL conical tubes. Each assay condition was performed in
triplicate. The data from these studies were presented as per-
cent ligand uptake of the initial dose per 0.5 ꢀ 106 cells and
analyzed using one-tailed paired t-test.
1,2-Bis(trimethylsiloxy)cyclopentene (5). In a modification to
the method previously reported, sodium (0.63 g, 0.027 g atom)
3
in toluene (10 mL) was reacted with trimethylchlorosilane (3.16 g,
29.08 mmol) and dimethyl glutarate (1.00 g, 6.24 mmol) under
reflux conditions and strong stirring for 5 h. The reaction
mixture was filtered through silica and rinsed with DCM/Et2O
(80/20). The solvent was evaporated under reduced pressure and
at 40 °C to dryness to yield a pale yellow oil (1.30 g, 85%) used
without further purification. 1H NMR (CDCl3, δ): 0.18 (s,
18H,), 1.76 (q, 2H), 2.24 (t, 4H). HRMS, m/z, calcd for C11H23-
O2Si2 [M - H]þ, 243.13; found, 243.122 68.
Jarkas, Nachwa
