Synthesis of a highly potent leukocyte function-associated antigen-1 antagonist and its metabolite labeled with stable isotopes and carbon-14, part 2

Article abstract of DOI:10.1002/jlcr.1934

(S)-2-[(R)-7-(3,5-Dichlorophenyl)-5-methyl-6-oxo-5-(4- trifluoromethoxybenzyl)-6,7-dihydro-5H-imidazo[1,2-a]imidazole-3-sulfonylamino] -proprionamide (1), a potent lymphocyte function-associated antigen-1 antagonist and its sulfonamide metabolite (2) labe

Full text of DOI:10.1002/jlcr.1934

Research Article
Received 26 July 2011,
Revised 21 August 2011,
Accepted 26 August 2011
Published online 10 October 2011 in Wiley Online Library
(wileyonlinelibrary.com) DOI: 10.1002/jlcr.1934
Synthesis of a highly potent leukocyte function-
associated antigen-1 antagonist and its
metabolite labeled with stable isotopes and
carbon-14, part 2
*
Bachir Latli, Matt Hrapchak, Yibo Xu, Fenghe Qiu,
Dhileepkumar Krishnamurthy, and Chris H. Senanayake
(S)-2-[(R)-7-(3,5-Dichlorophenyl)-5-methyl-6-oxo-5-(4-trifluoromethoxybenzyl)-6,7-dihydro-5H-imidazo[1,2-a]imidazole-3-
sulfonylamino]-proprionamide (1), a potent lymphocyte function-associated antigen-1 antagonist and its sulfonamide
metabolite (2) labeled with stable isotopes and carbon-14 were prepared for Drug Metabolism and PharmacoKinetics
and other studies. A long linear route was used to prepare [13C2, 2H3]-(1) using [3,3,3-2H]-D-alanine and [13C2]-glycine
in 15 steps and 2.5% overall yield. With the availability of [13C6]-3,5-dichloroaniline, the sulfonamide [13C6]-(2) was pre-
pared in 12 steps and in 5.6% overall yield. For the carbon-14 synthesis, a six-step synthesis gave both compounds
[
14C]-(1) and [14C]-(2) from the common sulfonyl chloride intermediate [14C]-(15) in 18% and 4% radiochemical yields
and specific activities of 44 and 40.5 mCi/mmol, respectively.
Keywords: leukocyte function-associated antigen-1 antagonist; carbon-14; carbon-13; deuterium; metabolites; radiosynthesis
gave the 5,5-disubstituted imidazolidinone [2H3]-(7) in 79% yield.
Introduction
Hydrolysis of this material using benzyltrimethyl- ammonium
The lymphocyte function-associated antigen-1 (LFA-1) is an essen-
hydroxide and 50% aqueous sodium hydroxide in dioxane at
50ꢀC, followed by treatment with 6N aqueous HCl gave the amino
derivative [2H3]-(8) in 97% yield. The stereospecific formation of the
trans-imidazolidinone (5) and subsequent alkylation, then hydroly-
sis to (8) have been described in detail before.3,5–7 Glycine (13C2, 99
atom % 13C) was first protected using di-tert-butyl dicarbonate and
10% triethylamine in methanol under reflux as seen before4 and
was isolated by crystallization from hexanes in 92%. The protected
amino acid was then activated as the mixed anhydride by reaction
with pivaloyl chloride and triethylamine and coupled to [2H3]-(8) in
96% yield after flash chromatography purification. Removal of the
protecting group at 55 ꢀC using PTSA in methanol gave the free
amine [13C2,2H3]-(10) in 75% yield after silica gel flash chromatogra-
phy purification. Reaction with 1,1′-thiocarbonyldiimidazole in THF
gave the thiohydantoin derivative [13C2,2H3]-(11), which was used
without further purification in the next step. Cuprous chloride and
Hunig’s base were used to form the bicyclic lactam [13C2,2H3]-(12).5
The lithium enolate produced from treatment of [13C2,2H3]-(12) with
a solution of LiHMDS in THF at À40 ꢀC was trapped as the diethyl
phosphate [13C2,2H3]-(13).5,8 Without purification, this phosphate
was reacted with iodotrimethylsilane, produced in situ from NaI
tial component in normal immune system function and is a target
for drug discovery for its broad therapeutic potential in treating
inflammatory diseases. In a previous paper, we described the
synthesis of some potent antagonists of LFA-1.1 The search for bet-
ter compounds with high potency and good pharmacokinetics led
to the discovery of compound (1).2 Here, we report the synthesis of
this potent antagonist and its sulfonamide metabolite (2) labeled
with stable isotopes and carbon-14 to support drug metabolism
and pharmacokinetics studies.
Results and discussion
The synthesis of (1) labeled with stable isotopes was accomplished
in a long linear synthetic route and with an overall yield of 2.5%
from D-alanine-3, 3, 3-2H3, Scheme 1. Following a route developed
by our process chemists to prepare the first generation LFA-1
antagonists.3 D-Alanine-3,3,3-2H3 was first protected at the amino
group and activated as the mixed anhydride with isobutyl
chloroformate before it was coupled to 3,5-dichloroaniline to give
[2H3]-(3) in 99% yield.4 Deprotection of the amino group using con-
centrated aqueous HCl gave 3,5-dichlorophenylpropionamide
[2H3]-(4) in 77% yield. This amine was reacted with pivaldehyde
in toluene at 55 ꢀC to give the imidazolidinone [2H3]-(5) as a white
solid in 98% yield. Protection using trifluoroacetic anhydride and
triethylamine gave [2H3]-(6) in 72% yield after crystallization from
warm hexane. Deprotonation with lithium hexamethyldisilazane
at À20 ꢀC and alkylating with 4-trifluormethoxybenzyl bromide
Chemical Development, Boehringer Ingelheim Pharmaceuticals, Inc., 900 Ridgebury
Road, Ridgefield, Connecticut 06877, USA
*Correspondence to: Chemical Development, Boehringer Ingelheim Pharmaceuticals,
Inc., 900 Ridgebury Road, Ridgefield, Connecticut 06877 USA.
E-mail: bachir.latli@boehringer-ingelheim.com
J. Label Compd. Radiopharm 2011, 54 799–808
Copyright © 2011 John Wiley & Sons, Ltd.

B. Latli et al.
CD3
HN
O
CD3
CD3
CD3
H
a, b
H
N
Cl
N
Cl
e
72%
OH
c
77%
d
98%
N
Cl
Boc-NH
H2N
H2N
99%
O
O
O
[2H3]-(3)
[2H3]-(5)
Cl
Cl
[2H3]-(4)
Cl
Cl
Cl
Cl
Cl
OCF3
13C
OH
13C
CD3
O
Boc-NH
O
NH
g
CD3
O
O
NH
O
O
N
N
Cl
f
79%
O
CF3
H
13C
CD3
97%
N
N
Cl
N
h
13C
CD3
Boc-NH
H2N
CF3
96%
Cl
O
[2H3]-(6)
13C2, 2H3]-(9)
[2H3]-(7)
Cl
Cl
[
OCF3
[2H3]-(8)
Cl
OCF3
Cl
Cl
Cl
Cl
Cl
Cl
NH
O
N
O
S
NH
H
i
O
N
O
N
j
N
H
13C
k
52.5%
CD3
13C
CD3
N
l
N
N
13C
75%
13C
N
H2N
CD3
13C
13C
O
13C
100%
N
CD3
85%
13C
O
O
O
O
P
OCF3
13C2, 2H3]-(13)
13C2, 2H3]-(10)
Cl
OCF3
O
[
OCF3
[
13C2, 2H3]-(11)
OCF3
Cl
O
[
[
13C2, 2H3]-(12)
Cl
Cl
Cl
Cl
O
O
O
N
N
N
m
50%
n
o
38%
N
13C
N
N
N
13C
CD3
CD3
N
13C
CD3
13C
N
13C
13C
H
O
N
O
I
S
SO2Cl
O
OCF3
H2N
OCF3
13C2, 2H3]-(14)
OCF3
[
[
13C2, 2H3]-(1)
[
13C2, 2H3]-(15)
Scheme 1. (a) Boc2O, triethylamine, MeOH; (b) t-BuCOCl, 4-methyl morpholine, 3,5-dichloroaniline; (c) 12 N aq. HCl, MeOH; (d) t-BuCHO, toluene, 55 ꢀC; (e) (CF3CO)2O,
triethylamine, CH2Cl2; (f) [(CH3)3Si]2NLi, THF, 4-trifluoromethoxybenzyl bromide; (g) BnMe3NOH, 50% aq. NaOH, 1,4-dioxane, 6 N HCl; (h) triethylamine, t-BuCOCl; (i)
TsOH.H2O, MeOH, 55 ꢀC; (j) TCDI, THF; (k) CeliteW, i-Pr2NEt, CuCl, toluene/MeCN; (l) [(CH3)3Si]2NLi, ClP(O)(OEt)2, THF; (m) TMSCl, NaI, CH2Cl2; (n) (1) i-PrMgCl, THF; (2) SO2,
(3) N-chlorosuccinimide, THF; (o) L-alaninamide, triethylamine, dimethylformamide.
and trimethylsilyl chloride. The reaction gave besides the desired The resulting urea derivative [13C6]-(16) was subjected to a
iodide [13C2,2H3]-(14), the des-iodo product [13C2,2H3]-(18) (Scheme 2) dehydration cyclization according to Appel to give [13C6]-(17).11
in 50% and 23% yields, respectively. Compound [13C2,2H3]-(14) was Treatment with p-toluenesulfonic acid (PTSA) in hot ethyl acetate
easily separated by flash chromatography and the des-iodo was gave the bicyclic imidazole [13C6]-(18) in 71% yield.2 Regeoseletive
subjected to iodination again using N-iodosuccinimide (NIS), iodination gave the iodo-derivative [13C6]-(14) in 71% yield which
Scheme 2. The iodo-intermediate [13C2,2H3]-(14) was first treated was easily separated from the diodo-derivative by-product [13C6]-
with isopropyl magnesium chloride and then reacted with sulfur (19), Figure 3, by silica gel chromatography using toluene as eluent.
dioxide to give the sulfur Grignard complex.9 This complex was The sulfonyl chloride derivative [13C6]-(15) was then prepared as
finally treated with N-chlorosuccinimide in THF in one pot to described earlier on Scheme 1. Reaction with ammonium hydroxide
give the sulfonyl chloride [13C2,2H3]-(15). The sulfonyl chloride in DMF in the presence of cesium carbonate gave [13C6]-(2) in 58%
2
[13C2, H3]-(15) was then treated with L-alaninamide in dimethyl- yield over two steps, Scheme 2.
formamide (DMF) to give [13C2,2H3]-(1) labeled with both deute-
rium and carbon13 and in 2.5% overall yield.
In the synthesis of [14C]-(1) and [14C]-(2), the isocyanate prepared
under Schotten–Baumann conditions from [14C]-phosgene and
The collision-induced dissociation-Tandem Mass Spectrometry aminoacetaldehyde dimethyl acetal was reacted with chiral amine
(CID-MS/MS) spectra of unlabeled reference sample (1) and (8) to give [14C]-(16) in 71% yield, Scheme 3. The following dehy-
[13C2,2H3]-(1) are compared in Figure 1. The major fragmentation dration/cyclization of the urea derivative to compound [14C]-(17)
pathways are consistent with the structure; see the fragmenta- was accomplished as seen before in 100% radiochemical yield.
tion pattern in Figure 2.
Heating in ethyl acetate in the presence of PTSA gave the bicyclic
With the availability of [13C6]-3,5-dichloroaniline,10 the metabolite [14C]-(18) in 96% yield. Iodination or bromination of this compound
[13C6]-(2) was prepared according to Scheme 2. The amine deriva- gave [14C]-(14) and [14C]-(20) in 66% and 69%, respectively.2 The
tive [13C6]-(8) was prepared as shown on Scheme 1 in 24% overall sulfonyl chloride [14C]-(15) prepared as reported before, was either
yield. Then, it was reacted with the dimethoxyethyl isocyanate pro- treated with L-alaninamide to give [14C]-(1) or with ammonium
duced in situ from the action of phosgene on aminoacetaldehyde hydroxide to give metabolite [14C]-(2) in 40% and 8%, respectively.
dimethyl acetal under Schotten–Baumann conditions in 71% yield. The low yields are due possibly to the presence of moisture during
www.jlcr.org
Copyright © 2011 John Wiley & Sons, Ltd.
J. Label Compd. Radiopharm 2011, 54 799–808

B. Latli et al.
CH3
CH3
CH3
c
N
Cl
b
77%
a
N
Cl
H2N
BocHN
OH
BocHN
13C
99%
O
90%
13C
O
6
O
6
Cl
Cl
13C6]-(4)
[
13C6]-(3)
[
13C
6
Cl
Cl
OCF3
H3C
HN
O
H3C
O
O
HN
d
f
O
H3C
O
O
N
Cl
e
88%
N
Cl
N
H2N
CF3
84%
48%
N
N
Cl
13C
13C
CF3
6
6
13C
Cl
Cl
6
Cl
[
13C6]-(5)
OCF3
[
13C6]-(7)
[
13C6]-(6)
[
13C6]-(8)
13C
HN
Cl 13C6
6
Cl
Cl
Cl
N
N
j
O
i
O
g
O
H
h
71%
H
O
O
HN
O
O
N
O
N
N
O
80%
O
H2N
99%
O
O
[
13C6]-(17)
[
13C6]-(16)
OCF3
OCF3
Cl
13C
Cl
Cl 13C
13C
6
13C
Cl
6
6
6
Cl
Cl
Cl
Cl
N
N
N
N
N
N
N
N
O
l
k
O
m
58%
N
O
O
N
N
O
N
S
O
S
Cl
O
NH2
71%
I
O
OCF3
13C6]-(2)
OCF3
13C6]-(15)
OCF3
13C6]-(18)
OCF3
13C6]-(14)
[
[
[
[
Scheme 2. (a) t-BuCOCl, 4-methyl morpholine, [13C6]-3,5-dichloroaniline; (b) 12 N aq. HCl, MeOH; (c) t-BuCHO, toluene, 55 ꢀC; (d) (CF3CO)2O, triethylamine, CH2Cl2; (e)
[(CH3)3Si]2NLi, THF, 4-trifluoromethoxybenzyl bromide; (f) BnMe3NOH, 50% aq. NaOH, 1,4-dioxane, conc. HCl; (g) phosgene, toluene; (h) [13C6]-(8), Sat’d NaHCO3,
CH2Cl2; (i) Ph3P, CCl4, triethylamine, CH2Cl2; (j) p-toluenesulfonic acid, EtOAc; (k) N-iodosuccinimide, pyridinium p-toluenesulfonate, CH2Cl2; (l) (1) i-PrMgCl, THF; (2)
SO2; (3) N-chlorosuccinimide, THF; (m) NH4OH, Cs2CO3, dimethylformamide.
Figure 1. CID-MS/MS spectra of (1) top and [13C2,2H3]-(1).
J. Label Compd. Radiopharm 2011, 54 799–808
Copyright © 2011 John Wiley & Sons, Ltd.
www.jlcr.org

B. Latli et al.
USA) and from PerkinElmer (Boston, MA, USA). The rest of the re-
agents were purchased from Aldrich Chemicals Company.
Synthesis of [13C2,2H3]-(1)
t-Butyloxycarbonyl [3,3,3-2H]-D-alanine: To a suspension of
[3,3,3-2H]-D-alanine (2.0 g, 21.505 mmol) in a solution of triethylamine
(3.26 mL, 23.28 mmol) in methanol (30 mL), was added di-tert-butyl
dicarbonate (9.5 g, 43.1 mmol), and the mixture was refluxed for
30 minutes to give a clear solution. After cooling to room tempera-
ture, the solution was concentrated in vacuo. The residue was treated
with an aqueous solution of 1.0 N HCl at 0 ꢀC and then extracted with
ethyl acetate (2 Â 100 mL), dried over MgSO4, filtered, and concen-
trated in vacuo. Ether was added, and the precipitate was filtered.
The filtrate was concentrated then crystallized from hexanes in
Figure 2. Fragmentation pathways of [13C2,2H3]-(1), molecular ion m/z 611.
1
99.4% yield or a total of 4.11 g of a white solid. H NMR (DMSO-d6)
the transformation from the derivatives [14C]-(14) and [14C]-(20) to
the sulfonyl chloride [14C]-(15). Sulfonic acid [14C]-(21) was the
major product after the treatment with ammonium hydroxide.
d: 12.39(s, 1H), 7.06(d, J= 7.60 Hz, 1H, NH), 3.88(d, J=7.60Hz, 1H,
CH), 1.35(br s, 9H). 1H NMR (CDCl3) d: 10.20(br s, 1H), 5.0(s, 1H), 4.26
(d, J= 4.33 Hz, 1H), 1.45(br s, 9H), liquid chromatography mass
spectrometry (LCMS): m/z: 193.74 (100%).
[(R)-1-(3,5-Dichloro-phenylcarbamoyl)-[2H3]ethyl]-carbamic
acid tert-butyl ester )-[2H3]-(3): To a solution of the aforemen-
tioned t-boc-D-alanine-2H3 (3.8 g, 19.772 mmol) in anhydrous THF
(60.0 mL), was added 4-methyl morpholine (4.56 mL, 41.31 mmol)
dropwise at 0 ꢀC. The clear solution was stirred for 10 minutes before
isobutyl chloroformate (2.6 mL, 19.48 mmol) was added dropwise to
give a white mixture. This mixture was stirred for 1 hour at 0 ꢀC, then
3,5-dichloroaniline (3.3 g, 19.96 mmol) in THF (40.0 mL) was added
dropwise in a 60-minute period. After stirring at this temperature
for 2 hours, the ice-bath was removed, and the mixture was warmed
to room temperature and stirred overnight. The mixture was then
concentrated in vacuo to remove THF and then diluted with methy-
lene chloride and washed with saturated aq. NaHCO3 (50 mL), dried
over MgSO4, filtered and concentrated in vacuo to give 8.91 g of a
yellowish oil, which was used in the next step without further purifi-
cation. 1H NMR (CDCl3) d: 8.89(br s, 1H), 7.44(d, J= 1.63 Hz, 2H), 7.03
(t, J= 1.63 Hz, 1H), 5.03(d, J= 7.12 Hz, 1H), 4.28(d, J=7.12Hz, 1H),
1.43(br s, 9H), LCMS: e/z: 335 (100%).
Experimental
Materials and methods
Liquid scintillation counting was accomplished using a Beckman
LS5000TA and ready safe™ cocktail (Beckman, Fullerton, CA, USA).
Radio-thin layer chromatography (TLC) was carried out on a BIOSCAN
System 200 imaging scanner using an auto-changer 1000 and
WinScan software version 2.1a (Bioscan Inc., Washington, DC, USA).
The quantification of the HPLC chromatograms was carried out using
an HPLC system comprised of a radiomatic A515 Flo-one\Beta radio-
activity flow detector (Packard Instrument Company, Meriden, CT,
USA), two pumps (HITACHI L-6200A intelligent pump), a linear UVIS
200, Ultima Flo™ AP cocktail (Packard, Meriden CT, USA), and radio-
matic 500TR V 3.60 for data evaluation. Mass spectra for nonradioac-
tive compounds were acquired by a Hewlett–Packard auto sampler
Series 1100, connected to a Micromass Platform LCZ in the electron
spray (ES) mode. Nuclear magnetic resonance (NMR) spectra were
recorded with a Bruker 400MHz DPX spectrometer (Billerica, MA,
USA) using deuterated chloroform or methanol as a solvent and
tetramethyl silane as the internal standard unless stated otherwise.
Precoated TLC sheets (silica gel 60 F254) and silica gel 60-200 Mesh
(Nominal, I.D., grade 62) for flash chromatography were obtained from
EM Science (Gibbstown, NJ, USA). Phosgene, 20% solution in toluene
was obtained from Fluka (Milwaukee, WI, USA). D-Alanine3,3,3-2H3
(R)-2-Amino-N-(3,5-dichloro-phenyl)-[3,3,3-2H]propionamide
[2H3]-(4): To a solution of the aforementioned material (8.91 g,
19.88 mmol) in methanol (100 mL), was added conc. HCl (10 mL of
12 N and 5.0 mL of water) at 0 ꢀC. The resulting solution was stirred
at this temperature for 2 hours then warmed to room temperature
and stirred overnight. TLC indicated that the reaction was over. The
solution was then concentrated in vacuo to about 5–10 mL, and
toluene was added. The mixture was cooled down in an ice-bath
and treated with 20 mL of 50% w/w NaOH in water. The toluene
layer was removed, and the aqueous was extracted with methylene
chloride. The combined organic extracts were dried over MgSO4,
filtered, and concentrated in vacuo to give 4.91 of yellow oil. Purifi-
cation by flash chromatography using chloroform, then 10%–20%
methanol in chloroform gave 3.55 g of pale yellow oil in 77% yield.
1H NMR (CDCl3) d: 9.65(br s, 1H), 7.56(d, J = 1.23 Hz, 2H), 7.06(t,
J = 1.23 Hz, 1H), 3.62(s, 1H), 1.62(br s, 2H). LCMS: e/z: 237 (100%).
(2S,5R)-2-tert-Butyl-3-(3,5-dichlorophenyl)-5-[2H3]methyl-
imidazolidin-4-one [2H3]- (5): A solution of the aforemen-
tioned amine (3.55 g, 15.02 mmol) in toluene (30 mL) was
treated at room temperature with trimethyl acetaldehyde
(2.5 mL, 22.33 mmol), dropwise. The resulting cloudy solution
was heated to 55 ꢀC and stirred overnight. TLC (10% MeOH/
CHCl3) showed the presence of starting material. The solution
was then concentrated in vacuo, and hexane was added to
the residue to give a white solid. Hexane was decanted off,
2
(99.9 H %) atom was purchased from CDN, (Pointe Claire Quebec,
Canada). [14C]-Phosgene was obtained from Vitrax (Placentia, CA,
Cl
Cl
Cl
Cl
N
N
I
N
N
O
O
N
N
O
S
I
O
HO
OCF3
(19)
OCF3
(21)
Figure 3. Structures of the diiodo and sulfonic acid derivatives.
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Copyright © 2011 John Wiley & Sons, Ltd.
J. Label Compd. Radiopharm 2011, 54 799–808

B. Latli et al.
Cl
Cl
*
Cl
Cl
N
*
HN
N
O
H
N
O
O
H
N
d
O
c
O
b
HN
O
O
a
N
14C
O
H2N
O
96%
O
O
O
100%
71.5%
[
14C]-(16)
Cl
[
14C]-(17)
OCF3
OCF3
Cl
Cl
Cl
Cl
Cl
Cl
Cl
*
N
N
*
N
*
*
N
N
g
N
N
N
N
O
e
f
N
O
O
O
N
O
S
N
O
O
O
40%
S
X
NH
O
Cl
H2N
OCF3
14C]-(1)
OCF3
14C]-(18)
OCF3
[
OCF3
[
14C]-(15)
[
[
14C]-(14)
X = I, 66%
[
14C]-(20)
X = Br, 69%
h
8%
Cl
Cl
*
N
N
O
N
O
S
O
NH2
OCF3
[
14C]-(2)
Scheme 3. (a) [14C]-phosgene, toluene; (b) (8), Sat’d NaHCO3, CH2Cl2; (c) Ph3P, CCl4, triethylamine, CH2Cl2; (d) p-toluenesulfonic acid, EtOAc; (e) N-iodosuccinimide, pyridinium
p-toluenesulfonate, CH2Cl2, or N-bromosuccinimide, triethylamine, CH2Cl2; (f) (1) i-PrMgCl, THF; (2) SO; (3) N-chlorosuccinimide, THF; (g) L-alaninamide, triethylamine, dimethyl-
formamide; (h) NH4OH, Cs2CO3, dimethylformamide. Asterisks indicate position of 14C atom.
and the white solid was further dried in vacuo to give 2.0 g of lithium hexamethyldisilazane (LiHMDS) (12.87 mL, 1.0 M in THF)
product. The mother liquor was concentrated to give 2.48 g of at À20 ꢀC (CCl4-dry-ice-bath) dropwise under Argon atmosphere.
a yellowish solid. Total yield 4.48 g or 98% yield. 1H NMR (CDCl3) After stirring for about 2 hours (temperature up to À15 ꢀC), a solu-
d: 7.32(d, J = 1.72 Hz, 2H), 7.20(t, J = 1.72 Hz, 1H), 4.86(s, 1H), 3.76 tion of 4-trifluomethoxy benzyl bromide (2.12 mL, 12.85 mmol) in
(s, 1H), 2.03(s, 1H), 0.83(br s, 9H). LCMS: e/z: 304.55 (100%).
THF (5.0 mL) was added dropwise. The reaction was left to warm
(2S,5R)-2-tert-Butyl-3-(3,5-dichlorophenyl)-5-[2H3]methyl- to room temperature overnight. A saturated solution of ammo-
1-(2,2,2-trifluoroacetyl)-imidazolidin-4-one [2H3]-(6): To a nium chloride (100 mL) was added, and the mixture was extracted
solution of the aforementioned material (2.0 g, 6.57 mmol) in methy- with ethyl acetate (3Â 100 mL), dried over MgSO4, filtered, and
lene chloride (15 mL), was added triethyl amine (1.23 mL, 8.78 mmol) concentrated in vacuo to give 7.92 g of a yellowish solid. Crystalli-
at À5ꢀC. After stirring for 10 minutes, trifluoroacetic anhydride zation from hexane gave 4.71 g of a white solid. The mother liquor
(1.08 mL, 7.55 mmol) was added dropwise to give a pale yellow solu- was concentrated to give 2.24 g of a solid which was crystallized
tion. The ice-bath was removed, and the reaction was warmed to from ethanol to give an extra 0.58 g of a white solid, which was
room temperature and stirred overnight. The solution was cooled combined with the first batch. A total of 5.29 g was obtained in
again to 0 ꢀC, and water (15 mL) was added. The aqueous layer 79% yield. 1HNMR (CDCl3) d: 7.28(m, 2H), 7.02(m, 4H), 6.28(t,
was extracted with methylene chloride, and the combined extracts J = 1.42 Hz, 1H), 5.39(s, 1H), 3.74(d, J = 14.1 Hz, 1H), 3.25(d,
were dried over MgSO4, filtered, and concentrated in vacuo to give J = 14.1 Hz, 1H). LCMS: e/z : 574.49, nitrile adduct 603.42.
3.8 g of a yellow solid. Crystallization from warm hexanes gave
(2R)-2-Amino-N-(3,5-dichlorophenyl)-2-[2H3]methyl-3-\[4-
1.9 g of a solid in 72% yield. The mother liquor was kept for further trifluoromethoxy)phenyl]propanamide [2H3]-(8): To a sus-
purification. 1H NMR (CDCl3) d: 7.47(d, J= 1.48 Hz, 2H), 7.27(t, pension of the aforementioned material (4.92 g, 8.57 mmol) in
J= 1.48 Hz, 1H), 6.27(s, 1H), 4.51(s, 1H), 0.86(br s, 9H). LCMS: e/z: dioxane (20 mL), was added a solution of benzyltrimethylammo-
441.51 (100%).
nium hydroxide (7.1 mL, 40% solution in water) followed by 50%
(2R,5R)-2-tert-Butyl-3-(3,5-dichlorophenyl)-5-[2H3]methyl-1- aqueous NaOH (1.37 mL), and the biphasic yellow mixture was stir-
(2,2,2-trifluoroacetyl)-5-[[4-(trifluoromethoxy)phenyl]methyl]
red at 50 ꢀC overnight. The mixture was cooled down to room tem-
imidazolidin-4-one [2H3]-(7): To a solution of the aforemen- perature and then cooled in an ice-bath, and 14 mL of 6 N aqueous
tioned material (4.68 g, 11.70 mmol) in THF (10 mL), was added HCl was added. The mixture was heated again at 50 ꢀC for 3 hours.
J. Label Compd. Radiopharm 2011, 54 799–808
Copyright © 2011 John Wiley & Sons, Ltd.
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B. Latli et al.
Dioxane was then removed in vacuo, and the residue was diluted (d, J= 13.82 Hz, 1H), 3.56(dd, J= 5.25, 1.38 Hz, 1H), 3.22(dd, J= 5.25,
with toluene (20 mL), and 50% aqueous NaOH was added until pH = 1.38 Hz, 1H), 3.12(d, J=13.82Hz, 1H), 1.57(s, 3H). LCMS: e/z: 469.52
12. The aqueous was extracted with toluene then with ethyl acetate, (100%).
and the combined organic extracts were dried over MgSO4, filtered,
and concentrated in vacuo to give 5.68 g of viscous oil. TLC (50%
(2R)-N-(3,5-Dichlorophenyl)-2-[2H3]methyl-2-(5-oxo-2-thioxo-
[
13C2]imidazolidin-1-yl)-3-[4-(trifluoromethoxy)phenyl]propa-
2
EtOAc: Hexane): starting material Rf =0.82, product Rf =0.33. Purifica- namide [13C2, H3]-(11): To solution of 1,1′-thiocarbonyldiimida-
tion by silica gel chromatography using chloroform then 10%–50% zole (TCDI, 178.22 mg, 0.95 mmol) in THF (4.0mL), was added the
EtOAc: CHCl3 gave 3.41 g of yellow oil in 97% yield. 1H NMR (CDCl3) amine [13C2, 2H3]-(10) (470 mg, 1.0 mmol) in THF (4.0mL), the flask
d:9.73(s, 1H), 7.52(d, J= 1.17 Hz, 2H), 7.19(d, J= 8.66 Hz, 2H), 7.12(d, was washed with another 4.0mL of THF and added to the reaction
J= 8.66 Hz, 2H), 7.08(t, J= 1.17 Hz, 1H), 3.48(d, J= 13.51 Hz, 1H), 2.67 vessel. The resulting solution was stirred for 1 hour at room tem-
(d, J=13.51Hz, 1H), 1.46(s, 2H). LCMS: e/z : 410.58 (100%).
perature, TLC, showed no starting material. Water was added fol-
tert-Butyloxycarbonyl-[13C2]glycine: To a suspension of gly- lowed by ethyl acetate. The organic layer was washed with 10%
cine (1.0 g, 13 mmol, 99 atom % 13C) in a solution of 10% triethylamine K2CO3 (10 mL), water (10 mL), brine (10 mL), then dried over
in methanol (20 mL), was added di-tert-butyl dicarbonate (5.67 g, MgSO4, filtered, and concentrated in vacuo to give 609 mg of a
25.72 mmol), and the mixture was refluxed for 30 minutes to give a solid. TLC (10% MeOH/CHCl3): Rf = 0.31. This crude was used in
1
clear solution. After cooling to room temperature, the mixture was the next step without further purification. HNMR (CDCl3) d: 7.42
concentrated, and the residue was treated with a 1.0 N solution of (s, 1H), 7.40(d, J = 1.73 Hz, 2H), 7.21(d, J = 8.59 Hz, 2H), 7.13(d,
aqueous HCl (16.0 mL) at 0 ꢀC. The solution was then extracted with J = 8.59 Hz, 2H), 7.13(t, J = 1.73 Hz, 1H), 4.30(d, J = 13.47 Hz, 1H),
ethyl acetate (2 Â 100 mL), dried over MgSO4, filtered, and concen- 3.50–4.10(m, 3H), 3.24(d, J = 13.47 Hz, 1H). LCMS: e/z: 511.75
trated in vacuo. Ether was added to the oily residue to give a solid (100%).
(triethylamine-HCl salt) which was filtered. The filtrate was concen-
(5R)-7-(3,5-Dichlorophenyl)-5-[2H3]methyl-5-[[4-(trifluoro-
trated under reduced pressure to give 3.4 g of viscous oil. Crystalliza- methoxy)phenyl]methyl]-2H-imidazo[1,2-a][13C2]imidazole-
tion from hexane gave 2.14 g of a white solid in 91% yield. 1H NMR 3,6-dione [13C2, 2H3]-(12): To a solution of the aforementioned
(CDCl3) d: 10.35(s, 1H), 4.14(m, 1H), 3.75(m, 1H), 1.45(br s, 9H), LCMS: material (512 mg, 1.0 mmol) in toluene (10 mL) and acetonitrile
m/z: 177.60 (100%).
(1.0 mL), were added CeliteW (0.5 g) and Hunig’s base
tert-Butyl N-[2-[[(1R)-2-(3,5-dichloroanilino)-1-[2H3]methyl-2- (0.418 mL, 2.376 mmol). CuCl (227.7 mg, 2.231 mmol) was then
oxo-1-[[4-(trifluoromethoxy)phenyl]methyl]ethyl]amino]-2-oxo- added in one portion with stirring to give a dark mixture, which
[13C2]ethyl]carbamate [13C2, 2H3]-(9): To a solution of N-t-boc-[13C2] was heated to 80 ꢀC in 10 minutes. After 15 minutes at this tem-
glycine (1.68 g, 9.5 mmol) in dry THF (20 mL), was added triethylamine perature, the reaction was checked by TLC, no starting material.
(1.37 mL, 9.86 mmol) at À20 ꢀC. Trimethylacetyl chloride (1.17 mL, The dark mixture was filtered through CeliteW and the filter cake
9.40 mmol) was then added dropwise, and the resulting white suspen- was washed with toluene. Evaporation of two-thirds of the
sion was stirred at this temperature for 1 hour. The amine (8) (3.0 g, volume under reduced pressure, then treating the dark solution
7.31 mmol) in THF (20 mL) and added dropwise with triethylamine with 1.0 N HCl, followed with 7% NH4OH, water, and brine. The
(1.07 mL, 7.68 mmol). The flask was washed with THF (10 mL) and solution was treated with charcoal and heated to 80 ꢀC for
added to the reaction vessel. The resulting mixture was warmed 10 minutes, filtered over a short pad of silica gel, and washed
slowly to room temperature and stirred for 48 hours. A saturated solu- with ethyl acetate to give 420 mg of a dark solid after concen-
tion of ammonium chloride (20 mL) was added, and the biphasic solu- tration. Purification by flash chromatography silica gel using
tion was extracted with ethyl acetate. The combined ethyl acetate chloroform and 5–10% EtOAc:CHCl3 gave 253 mg of pure mate-
extracts were dried over MgSO4, filtered, and concentrated in vacuo rial as foam in 52.5% yield. TLC: 10% MeOH/CHCl3: Rf of starting
to give 4.9 g of an off-white solid. TLC (50% EtOAc: Hex) Rf of the material = 0.31, Rf of product = 0.66. 1HNMR (CDCl3) d: 7.33(t,
product = 0.46. The crude was purified by flash chromatography using J = 1.80 Hz, 1H), 7.28(d, J = 1.80 Hz, 2H), 7.12(m, 4H), 4.40(ddd,
10%–50% EtOAc in hexanes to give 4.0 g of a white solid in 96% yield. J = 3.8, 25.69, 47.3 Hz, 1H), 4.06(ddd, J = 3.8, 35.69, 47.3 Hz, 1H),
1H NMR (CDCl3) d:9.08(s, 1H), 7.73(m, 2H), 7.14(m, 5H), 7.07(t, 3.48(d, J = 13.88 Hz, 1H), 3.28(d, J = 13.88 Hz, 1H). LCMS: e/z:
J= 1.62 Hz, 1H), 3.75–3.95(m, 1H), 3.67(d, J= 13.89 Hz, 1H), 3.42–3.58 477.47 (100%).
(m, 1H), 3.14(d, J= 13.89 Hz, 1H), 1.42(br s, 9H), 1.24(m, 2H). LCMS:
e/z: 569.69 (100%).
[(5R)-7-(3,5-Dichlorophenyl)-5-[2H3]methyl-6-oxo-5-[[4-
(trifluoromethoxy)phenyl]-methyl]-2,3-dihydroimidazo[1,2-
(2R)-2-[(2-Aminoacetyl)amino]-N-(3,5-dichlorophenyl)-2-[2H3] a][13C2]imidazol-3-yl] diethyl phosphate [13C2, 2H3]-(13): To a
methyl-3-[4-(trifluoromethoxy)phenyl][13C2]propanamide [13C2, solution of the aforementioned lactone (587 mg, 1.23 mmol) in
2H3]-(10): To a solution of the aforementioned material (4.0 g, THF (10 mL), was added LiHMDS (1.6 mL, 1.0 M in THF) dropwise
7.02 mmol) in methanol (25 mL), was added TsOH.H2O (1.76 g, at À30 ꢀC in a three-neck flask equipped with a magnetic stirrer
9.13 mmol) in methanol (10 mL) at 55 ꢀC, and the resulting was stir- and a thermometer, under nitrogen atmosphere. Keeping the
red overnight. The solution was cooled down to room temperature, temperature below À20 ꢀC, the resulting dark solution was stir-
and a 1.0N NaOH (10mL) was added dropwise. The mixture was red for 30 minutes before diethylchlorophosphate (0.214 mL,
concentrated in vacuo to remove most of the methanol, and the resi- 1.44 mmol) was added dropwise. The reaction was stirred for
due was dissolved in ethyl acetate and treated with water. The 45 minutes at À30 ꢀC, then 10 mL of 20% aqueous NH4Cl was
organic phase was washed with water, dried over MgSO4, filtered, added, and the mixture was warmed to room temperature.
and concentrated in vacuo to give 3.89 g of yellow oil. Purification The aqueous was extracted with ethyl acetate, and the com-
by flash chromatography using 10%–50% EtOAc/chloroform to bined extracts were washed with 5% NaCl solution, dried over
remove nonpolar impurities, then product was eluted with 50% MgSO4, filtered, and concentrated in vacuo to give 0.8 g of dark
MeOH/CHCl3 to give 2.47 g of white foam in 75% yield. 1HNMR oil in 85% yield. This material was used in the next step without
(CDCl3) d: 10.43(s, 1H), 7.87(s, 1H), 7.53(d, J= 1.81 Hz, 2H), 7.22(d, further purification. LCMS: e/z: 613.27 (100%), Rf = 0.21 in 50%
J= 8.71 Hz, 2H), 7.15(d, J= 8.71 Hz, 2H), 7.07(t, J= 1.81 Hz, 1H), 3.63 EtOAc:Hexanes.
www.jlcr.org
Copyright © 2011 John Wiley & Sons, Ltd.
J. Label Compd. Radiopharm 2011, 54 799–808

B. Latli et al.
(5R)-7-(3,5-Dichlorophenyl)-3-iodo-5-[2H3]methyl-5-[[4- 1H), 3.85(d, J = 13.88 Hz, 1H), 3.26(d, J = 13.88 Hz, 1H), 1.36(d,
(trifluoromethoxy)phenyl]-methyl]imidazo[1,2-a][13C2]imidazol- J = 7.05 Hz, 3H). LCMS: e/z: [M + H]+ = 611.1 (100%), [M + H +
6-one
[ a
13C2, 2H3]-(14): To suspension of NaI (0.74 g, CH3CN]+ = 652.1 (25%), see Figures 1 and 2.
4.887 mmol) in methylene chloride (5.0 mL), was added TMSCl
(0.625 mL, 4.9 mmol), and the mixture was stirred for 20 minutes
Synthesis of [13C6]-(2)
at room temperature (pink-colored mixture of iodine). To this, [(R)-1-(3,5-Dichloro-phenyl[13C6]carbamoyl)-ethyl]-carbamic
[13C2, 2H3]-(13) (0.75 g, 1.23 mmol) in CH2Cl2 (5.0 mL) was added, acid tert-butyl ester [13C6]-(3): To a solution of t-boc-D-alanine
the flask was rinsed twice with methylene chloride (5.0 mL) fol- (2.48 g, 13.14 mmol) in anhydrous THF (30 mL), was added 4-
lowed by 58 mL of water. The reaction was stirred for 2 hours at methyl morpholine (3.0 mL, 26.52 mmol) at 0 ꢀC under nitrogen
room temperature before 30 mL of Na2CO3 solution was added atmosphere. After stirring for 10 minutes, isobutyl chlorofor-
to the dark reaction. Ethyl acetate (20 mL) and water (20 mL) mate (1.74 mL, 13.35 mmol) was added dropwise. The resulting
were added. The organic phase was washed with Na2S2O3 mixture was stirred for 1 hour at 0 ꢀC, before [13C6]-3,5-dichloroani-
(20 mL) to give a yellowish solution. The organic solution was line (1.79 g, 10.65 mmol) in THF (15 mL) was added dropwise. The
dried over MgSO4, filtered, and concentrated in vacuo to give resulting solution was left to stir for 14 hours as the ice melted. TLC
0.75 g of viscous oil. Purification by flash chromatography using showed all the aniline was consumed. The reaction was concentrated
chloroform then 2% EtOAc:CHCl3 gave the desired product in vacuo to remove most of the THF and then treated with a satu-
(360 mg in 50% yield), Rf = 0.67 in 50% EtOAc: Hexanes, and rated solution of aqueous NaHCO3 (200 mL). The organic was
130 mg of the des-iodo-product in 23% yield, Rf = 0.46 in 50% extracted with methylene chloride (2x 100 mL), and the combine
1
EtOAc: Hexanes. HNMR (CDCl3) d: 7.51(d, J = 1.80 Hz, 2H), 7.25 extracts were dried over MgSO4, filtered, and concentrated in vacuo
(t, J = 1.80 Hz, 1H), 7.01(d, J = 8.27 Hz, 2H), 6.97(dd, J = 14.84, to give 6.6 g of viscous oil. Purification by combiFlash using a 120 g
198.4 Hz, 1H), 6.92(d, J = 8.27 Hz, 2H), 3.58(d, J = 14.1 Hz, 1H), disposable silica gel column and up to 15% EtOAc in CH2Cl2
1
3.27(d, J = 14.1 Hz, 1H). LCMS: e/z: 587.15 (100%). Des-iodo gave 4.3 g of foam in 90% yield. HNMR (CDCl3) d: 9.31(s, 1H), 7.40
[13C2, 2H3]-(18):. 1HNMR (CDCl3) d: 7.69(d, J = 1.85 Hz, 2H), 7.24 (d, J= 173 Hz, 2H), 7.05(d, J=173Hz, 1H), 5.50(d, J= 7.06, 1H), 4.33
(t, = 1.85 Hz, 1H), 7.01(d, J = 8.26 Hz, 2H), 6.96(ddd, J = 1.53, (m, 1H), 1.47(br s, 9H), 1.43(d, J=7.06Hz, 3H). 13CNMR (CDCl3) d:
16.23, 33.33 Hz, 2H), 6.90(d, J = 8.26 Hz, 2H). LCMS: e/z: 461.24 171.91, 171.25, 156.51, 135.75(m), 139.77(dt, J= 3.97, 64.05 Hz),
(100%).
134.89(t, J= 68.4 Hz), 123.78 (dt, J= 4.0, 65.84 Hz), 117.65(dt, J=4.01,
65.78 Hz), 80.91, 60.40, 53.44, 50.99, 28.35, 17.8. LCMS: e/z: 239.23
(100 %).
(R)-7-(3,5-Dichloro-phenyl)-5-[2H3]methyl-6-oxo-5-(4-
trifluoromethoxybenzyl)-6,7-dihydro-5H-imidazo[1,2-a][13C2]
imidazole-3-sulfonyl chloride [13C2, H3]-(15): To a solution of
(R)-2-Amino-N-(3,5-dichloro-phenyl[13C6])-propionamide
2
the iodo-derivative [13C2, 2H3]-(14) (0.33 g, 0.56 mmol) in THF
[
13C6]-(4): To a solution of the aforementioned material (4.19 g,
(5mL), was added a solution of isopropyl magnesium chloride 12.36 mmol) in methanol (50 mL), was added a solution of 9 N
(0.32 mL, 2.0M in THF) dropwise at À40 ꢀC (dry-ice-acetonitrile aqueous HCl (10 mL) dropwise at 0 ꢀC. The reaction was stirred
bath). The resulting solution was stirred at this temperature for for 12 hours and warmed gradually to room temperature. Most
1 hour before SO2 gas was introduced for 3 minutes via a needle of the solvents was evaporated, and the residue was treated at
just above the solution surface. The resulting bright yellow solu- 0 ꢀC with a solution of 6 N aqueous NaOH until pH = 12 then
tion was warmed gradually to room temperature overnight. The extracted with methylene chloride (2 Â 10 mL). The combined
solution was then concentrated in vacuo to give yellowish foam, extracts were dried over MgSO4, filtered, and concentrated
which was dissolved in THF (5.0mL) and cooled to À25ꢀC. N- in vacuo to give 2.27 g in 77% yield. 1HNMR (CDCl3) d: 9.66
Chlorosuccinimide (NCS) (93 mg, 0.683 mmol) in THF (3.0mL) (s, 1H), 7.57(dm, J = 171.84 Hz, 2H), 7.08(dm, J = 171.84 Hz, 1H),
was added dropwise at this temperature, and the resulting solu- 3.61(q, J = 7.1 Hz, 1H), 1.60(s, 2H), 1.42(d, J = 7.1 Hz, 3H). 13CNMR
tion was stirred for 1.0hour. The reaction was warmed to room (CDCl3) d: 173.96, 139.58 (dt, J = 4.4, 64 Hz), 135.21(dt, J = 4.4,
temperature and used in the next step without further purifica- 64 Hz), 123.85(dt, J = 4.4, 64 Hz), 117.62(dt, J = 4.4, 64 Hz), 51.80,
tion. LCMS: e/z: 559.76 (100%).
21.49. LCMS: e/z: 239.26 (100%).
(2S)-2-[[(5R)-7-(3,5-Dichlorophenyl)-5-[2H3]methyl-6-oxo-
(2S,5R)-2-tert-Butyl-3-(3,5-dichlorophenyl[13C6])-5-methyl-
5-(4-trifluoromethoxybenzyl)-imidazo[1,2-a][13C2]imidazol- imidazolidin-4-one [13C6]-(5): Trimethylacetaldehyde (1.27 mL,
3-yl]sulfonylamino]propanamide [13C2, 2H3]-(1): To a mix- 11.54 mmol) was added dropwise to a solution of the above
ture of L-alaninamide-hydrochloride (102 mg, 0.82 mmol) in amine (2.21 g, 9.36 mmol) in toluene (20 mL), and the mixture
DMF (10 mL), was added triethylamine (0.18 mL, 1.28 mmol) at was heated to 55 ꢀC for 12 hours. The reaction was concentrated
room temperature under nitrogen atmosphere. The cloudy in vacuo, and the residue was triturated with hexanes filtered
solution was stirred for 15 minutes before the chloride [13C2, and dried to give 2.8 g of a solid in 98.6% yield, which was used
2H3]-(15) (229 mg, 0.41 mmol) in THF (5 mL) was added using as it is in the next step. LCMS: e/z: 307.18 (100%).
a double ended needle. The resulting yellow solution was stir-
(2S,5R)-2-tert-Butyl-3-(3,5-dichlorophenyl[13C6])-5-methyl-
red for 48 hours. Ethyl acetate and water were added, and the 1-(2,2,2-trifluoroacetyl)-imidazolidin-4-one [13C6]-(6): To a
organic phase was washed with water, brine, dried over solution of the aforementioned material (2.73 g, 8.87 mmol) in
MgSO4, filtered, and concentrated in vacuo. The residue was CH2Cl2 (20 mL), was added triethylamine (1.61 mL, 11.56 mmol)
dissolved in chloroform and purified by silica gel chromatogra- at À2 ꢀC under nitrogen. The resulting was further cooled to
phy using up to 50% EtOAc/CHCl3 as eluent to remove a non- À10 ꢀC. and trifluroacetic anhydride (1.32 mL, 9.33 mmol) was
polar by-product. The product was eluted with 10–20 MeOH/ added dropwise in a 20-minute period. After stirring below
CHCl3, Rf = 0.1 in 10% MeOH/CHCl3 to give 95 mg of a fluffy À5 ꢀC for 1 hour, the reaction was warmed to room temperature
white solid in 38% yield. 1HNMR (CDCl3) d: 7.42(dd, J = 14.01, and stirred for 6 hours. The reaction was then cooled in an ice-
198.75 Hz, 1H), 7.38(d, J = 1.81 Hz, 2H), 7.30(t, J = 1.81 Hz, 1H), bath and treated with water (20 mL) and extracted with CH2Cl2
6.98(br s, 4H), 6.06(br s, 1H), 5.89(s, 1H), 4.02(q, J = 7.05 Hz, (2 Â 50 mL). The combined extracts were dried over MgSO4,
J. Label Compd. Radiopharm 2011, 54 799–808
Copyright © 2011 John Wiley & Sons, Ltd.
www.jlcr.org

B. Latli et al.
filtered, and concentrated in vacuo to give 4.28 g of foam. Purifi- room temperature. The colorless solution turned slowly to yellow.
cation by chromatography using silica gel treated with triethyla- The reaction was stirred overnight. It was diluted with ethyl acetate
mine and up to 30% EtOAcHexanes gave 3.0g of a solid in 84% (50 mL) and washed twice with 1.0 N HCl solution (2x 25 mL). The
yield. LCMS: e/z: 403.27 (100%). The product was used in the next organic phase was dried over Na2SO4, filtered, and concentrated in
step without further characterization.
vacuo to give 1.22 g of a semisolid residue in 99% yield. TLC (50%
(2R,5R)-2-tert-Butyl-3-(3,5-dichlorophenyl[13C6])-5-methyl-1- EtOAc: Hexanes) showed no starting material and a more polar pro-
(2,2,2-trifluoroacetyl)-5-[[4-(trifluoromethoxy)phenyl]methyl] duct. This crude material was used in the next step without further
imidazolidin-4-one [13C6]-(7): To a solution of the aforemen- purification. HNMR (CDCl3) d:7.90(s, 1H), 7.72(d, J= 8.4 Hz, 2H), 7.51
1
tioned material (3.0 g, 7.44 mmol) in anhydrous THF (20 mL), (d, J= 8.4 Hz, 2H), 7.44(dm, J= 172 Hz, 2H), 6.80(dm, J= 172 Hz, 1H),
was added a solution of 1.0 M LiHMDS in THF (8.2 mL, 8.2 mmol) 4.51(d, J= 6.25 Hz, 2H), 3.85(t, J= 6.25 Hz, 1H), 3.65(s, 6H), 3.42(q,
dropwise at –40 ꢀC under nitrogen atmosphere. After stirring for J= 7.22 Hz, 2H), 1.25(s, 3H). 13CNMR (CDCl3) d: 192.1, 167.5, 162.4,
2 hours from À40 to À25 ꢀC, 4-trifuromethoxybenzyl bromide 161.1, 140.2, 132.6(dt, J= 4.4, 64 Hz), 132.5, 130.2, 129.2, 127.5 (dt,
(1.35 mL, 8.43 mmol) in THF (10 mL) was added slowly. The reac- J= 4.4, 64 Hz), 122.8(m), 122.3 (dt, J= 4.4, 64 Hz), 120.1 (dt, J=4.4,
tion was warmed gradually to room temperature overnight. After 64 Hz), 117, 113.6, 65.5, 61.4, 14.7. LCMS: e/z: 526.34 (100%).
the usual work-up, 3.8g of product was isolated in 88% yield and
used as it is in the next step. LCMS: e/z: 577.35 (100%).
(R)-1-(3,5-Dichlorophenyl[13C6])-3-methyl-3-(4-trifluoro-
methoxybenzyl)-1H-imidazo[1,2-a]imidazol-2-one
13C6]-
[
(R)-2-Amino-N-(3,5-dichloro-phenyl[13C6])-2-methyl-3-(4- (18): A solution of the aforementioned material (242 mg,
trifluoromethoxyphenyl)-propionamide [13C6]-(8): A suspen- 0.46 mmol) and PTSA.H2O (87.5 mg, 0.46 mmol) in EtOAc
sion of the aforementioned material (3.6 g, 6.23 mmol) in dioxane (10 mL) was heated to 70 ꢀC for 10 hours. After cooling to room
(20 mL) was treated with a 40% solution of benzyltrimethylammo- temperature, the solution was washed with a saturated solution
nium hydroxide in water (10 mL) and aqueous 50% NaOH (1.5mL) of NaHCO3 (20 mL), dried over MgSO4, filtered, and concentrated
and heated at 50 ꢀC for 12 hours. After cooling to room tempera- to give 0.64 g of a solid. Purification by combiFlash using a 40 g
ture, the mixture was treated with concentrated aqueous HCl until disposable silica gel column and up to 5% MeOH/ CH2Cl2 gave
pH= 3 and heated again at 50 ꢀC for 12 hours. The mixture was 170 mg of product in 80% yield. 1HNMR (CDCl3) d:, 7.72(d,
then cooled to room temperature and concentrated in vacuo then J = 2 Hz, 2H), 7.03(ABq, J = 8.1 Hz, 2H), 6.98(dm, J = 172 Hz, 2H),
treated with 50% aqueous NaOH until pH= 12. The aqueous layer 6.92(dm, J = 172 Hz, 1H), 6.91(ABq, J = 8.1 Hz, 2H), 3.32(d,
was extracted with EtOAc (3Â 100mL), and the combined extracts J = 14.2 Hz, 1H), 3.22(d, J = 14.2 Hz, 1H), 1.82(s, 3H). 13C NMR
were dried over MgSO4, filtered, and concentrated to give 3.6g of (CDCl3) d: 175.2, 149.1, 145.6, 135.5 (dt, J = 4.4, 64 Hz), 134.7,
viscous oil. The crude product was purified by CombiFlash using 131.7 (dt, J = 4.4, 64 Hz), 131.2, 129.3, 127.2 (dt, J = 4.4, 64 Hz),
up to 10% EtOAc:CH2Cl2 to give 1.24 g of the desired product in 121.0, 120.1 (dt, J = 4.4, 64 Hz), 120.0(m), 119.8, 111.3, 66.4, 43.8,
1
48% yield. HNMR (CDCl3) d: 9.74(s, 1H), 7.51(dm, J = 180 Hz, 2H), 32.4. LCMS: e/z: 462.25 (100%).
7.25(d, J = 8.25 Hz, 2H), 7.15(d, J = 8.25 Hz, 2H), 7.05(dm, J = 180Hz,
(R)-5-Iodo-1-(3,5-dichlorophenyl[13C6])-3-methyl-3-(4-tri-
1H), 2.70(d, J = 13.51 Hz, 1H), 2.10(d, J = 13.51 Hz, 1H), 1.45(s, 3H). fluoromethoxybenzyl)-1H-imidazo[1,2-a]imidazol-2-one, [13C6]-
LCMS: e/z: 412.77 (100%).
(14): To a solution of the aforementioned material (168 mg,
(R)-N-(3,5-Dichloro-phenyl[13C6])-2-[3-(2,2-dimethoxyethyl)- 0.36 mmol) in CH2Cl2 (5 mL), was added pyridinium p-toluenesulfo-
ureido]-2-methyl-3-(4-trifluoromethoxyphenyl)-propionamide nate (PPTS) (14 mg, 0.055 mmol). The resulting solution was cooled
[
13C6]-(16): To a solution of aminoacetadehyde dimethyl acetal in an ice-bath, and NIS (87.3 mg, 0.387 mmol) was added in one por-
(0.18 g, 1.7 mmol) in CH2Cl2 (7mL), was added a solution of satu- tion and stirred for 14 hours. After diluting the solution with EtOAc
rated aqueous NaHCO3 (7mL), and the mixture was stirred in an (25 mL), it was quenched with a saturated aqueous Na2S2O3
ice-bath. A solution of 20% per weight of phosgene in toluene (12 mL). The organic phase was removed, dried over MgSO4, filtered,
(1.4mL, 2.55 mmol) was added to the organic phase after the stir- and concentrated to give 0.31 g of a yellow solid. Purification by
ring was stopped. Stirring was resumed and continued for silica gel chromatography using toluene as eluent gave 70 mg of
1.5hours before the above amine (0.42 g, 1.0mmol) was added the diiodo-derivative [13C6]-(19) (LCMS:e/z: 716.02) and 150 mg of
1
in CH2Cl2, and the mixture was stirred for 6 hours. The clear bipha- the desired mono-iodo derivative in 71% yield. H NMR (CDCl3) d:
sic solution was extracted with CH2Cl2 (2Â 20 mL), and the com- 7.51(dm, J= 173 Hz, 2H), 7.27(dm, J= 173 Hz, 1H), 7.01(ABq,
bined extracts were dried over MgSO4, filtered, and concentrated. J= 8.3 Hz, 2H), 6.97(ABq, J= 8.3 Hz, 2H), 6.86(s, 1H), 3.55(d,
The residue was purified by combiFlash on a 40 g disposable silica J= 14.1 Hz, 1H), 3.35(d, J= 14.1 Hz, 1H), 1.95(s, 3H). LCMS: e/z:
gel column using up to 10% MeOH/CH2Cl2 to give 0.27 g of pro- 587.15 (100%), Rf = 0.67 in 50% EtOAc:hexanes. 13C NMR (CDCl3) d:
duct in 71% yield and 0.13g of unreacted starting material. 1HNMR 173.8, 150.1, 145.7, 136.1, 134.8 (dt, J= 4.4, 64 Hz), 134.2, 132.1,
(CDCl3) d: 7.68(dm, J =171 Hz, 2H), 7.10(dm, J= 171 Hz, 1H), 7.02 131.0 (dt, J= 4.4, 64 Hz), 128.8, 127.5 (dt, J= 4.4, 64 Hz), 121.1, 120.5
(ABq, J = 7.95 Hz, 2H), 6.92(ABq, J = 7.95Hz, 2H), 6.13(t, J= 6.3Hz, (dt, J= 4.4, 64 Hz), 120.1(m), 95.5, 68.4, 42.3, 22.5.
1H), 3.42(d, J = 13.89 Hz, 1H), 3.30(s, 6H), 3.12(d, J= 13.89 Hz, 1H),
(R)-7-(3,5-Dichlorophenyl[13C6])-5-methyl-6-oxo-5-(4-
1.78(br s, 3H). 13CNMR (CDCl3) d: 174.98, 149.03, 146.01, 135.58(dt, trifluoromethoxybenzyl)-6,7-dihydro-5H-imidazo[1,2-a]-
J = 3.84, 66.81 Hz), 134.9(m), 131.99, 131.15, 129.14, 127.57(dt, imidazole-3-sulfonic acid amide [13C6]-(2): To a solution of
J = 3.89, 65.2 Hz), 125.40, 122.47, 121.8(q, J= 254 Hz), 120.36(dt, the aforementioned iodide ( 149 mg, 0.253 mmol) in anhydrous
J = 4.70, 66.28), 53.63, 44.17, 23.93. LCMS: e/z: 544.35 (100%).
THF (5 mL) was added a solution of 2 M i-PrMgCl in THF
(R)-3-(3,5-Dichlorophenyl[13C6])-2-[(Z)-2,2-dimethoxy- (0.2 mL, 0.4 mmol) at –40 ꢀC under nitrogen. After stirring for
ethylimino]-5-methyl-5-(4-trifluoromethoxybenzyl)-imidazolidin- 90 minutes from À40 to À30 ꢀC, sulfur dioxide was bubbled
4-one [13C6]-(17): A mixture of the aforementioned dimethyl acetal slowly for few minutes, and the resulting bright yellow solution
(1.26 g, 2.33 mmol), triphenyl phosphine (1.29 g, 4.86 mmol), carbon was stirred overnight at it warmed to room temperature. The
tetrachloride (0.48 mL, 4.87 mmol), and triethylamine (0.68 mL, solution was concentrated and then dissolved again in anhy-
4.89 mmol) in anhydrous methylene chloride (15 mL) was stirred at drous THF (5 mL) and cooled to –20 ꢀC. NCS (48 mg, 0.36 mmol)
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Copyright © 2011 John Wiley & Sons, Ltd.
J. Label Compd. Radiopharm 2011, 54 799–808

B. Latli et al.
in THF (2 mL) was added, and the resulting solution was warmed more polar product. This crude material (127 mCi) was used in
slowly to ambient temperature and stirred for 1 hour. The solu- the next step without further purification.
tion was cooled again to 0 ꢀC, and Cs2CO3 (124 mg, 0.38 mmol)
(5R)-7-(3,5-dichlorophenyl)-5-methyl-5-[[4-(trifluoromethoxy)
was added in one portion followed by ammonium hydroxide phenyl]methyl]-[14C]imidazo[1,2-a]imidazol-6-one [14C]-(18): A
solution (28-30% NH3, 0.5 mL) and DMF (1.0 mL). The reaction solution of the aforementioned material (1.22 g, 2.33 mmol) and
was warmed to room temperature and stirred for 2 hours. Water PTSA monohydrate (0.46 g, 2.38 mmol0 in ethyl acetate (30 mL)
(10 mL) and EtOAc (20 mL) were added. The aqueous was was heated to 70 ꢀC and stirred overnight. The yellow solution was
removed, and the organic layer was washed 10% solution of cooled to room temperature and diluted with ethyl acetate then
Na2CO3, brine, dried over MgSO4, filtered, and concentrated to washed with 1.0 N aqueous NaOH solution (2 Â 30 mL). The organic
give 130 mg of a solid. Purification by silica gel chromatography phase was concentrated and purified by flash chromatography
using up to 5% MeOH/CH2Cl2 gave 80 mg of the desired product using RediSep disposable column (40 g) and methylene chloride as
1
in 58% yield. H NMR (CDCl3) d: 7.43(s, 1H), 7.36(dm, J = 173 Hz, eluent to give 1.03 g (122.25 mCi) of pale yellow oil in 96% chemical
2H), 7.30(dm, J = 173 Hz, 1H), 6.98(br s, 4H), 3.85(d, J = 14.31 Hz, yield. The product has the same Rf as the unlabeled reference mate-
1H), 3.25(d, J = 14.31 Hz, 1H), 2.01(br s, 3H). 13C NMR (CDCl3) d: rial in 50% EtOAc: Hexanes. The product was used in the next step
175.5, 149.2, 135.92 (dt, J = 6, 66 Hz), 132.72 (dt, J = 6, 66 Hz), without further characterization.
130.73, 130.06, 127.81 (dt, J = 6, 66 Hz), 124.85, 121.05(dt, J = 6,
66 Hz), 70.16, 53.44, 42.50, 29.71, 22.24. HPLC: Zorbax XDB-C18, methoxy)phenyl-methyl][14C]imidazo[1,2-a]imidazol-6-one
20%–100% acetonitrile, water both solvents 10 mM TFA, tR =
14C]-(14): A solution of the aforementioned material (1.0 g,
(5R)-7-(3,5-Dichlorophenyl)-3-iodo-5-methyl-5-[[4-(trifluoro-
[
22.08 minutes. LCMS ES+, M+ = 541.56 (100%), 99% isotopic 2.18 mmol, 122 mCi) in methylene chloride (12 mL) was stirred
enrichment.
at 0 ꢀC in an ice-bath. PPTS (55 mg, 0.22 mmol) were then added
followed by NIS (0.49 g, 2.07 mmol), and the resulting orange
solution was stirred overnight in the dark. Ethyl acetate
Synthesis of [14C]-(1)
(2R)-N-(3,5-Dichlorophenyl)-2-(2,2-dimethoxyethyl[14C]- (100 mL) was added, and the organic phase was washed with a
carbamoylamino)-2-methyl-3-[4-(trifluoromethoxy)phenyl] saturated solution of Na2S2O3 (100 mL), water (100 mL), and
propanamide [14C]-(16): To a biphasic solution of aminoacetal- brine (100 mL). The organic phase was concentrated, and the
dehyde dimethyl acetal (0.44 mL, 4.0 mmol) in methylene chlor- residue was purified by flash chromatography using RediSep col-
ide (5 mL) and a saturated solution of NaHCO3 (5 mL), was added umn (40 g). The column was first wetted with hexane. The crude
[14C]-phosgene (200 mCi, at 57 mCi/mmol) in anhydrous toluene material was dissolved in toluene and applied to the column. The
(2 mL) followed by 0.6 mL of cold phosgene (20% in toluene, to bis-iodo by-product was eluted first to give 48 mg of a cream
wash the radioactive container) to the organic phase via a long colored solid (3.0 mCi). The vials containing the product were
needle at 0 ꢀC. Stirring was resumed and continued for 1 hour. combined and concentrated to give 842 mg in 66% yield of a
The amine (8) (1.63 g, 4.0 mmol) was then added in 5 mL of cream colored solid, 81 mCi.
methylene chloride, and the vial containing the amine was
(5R)-7-(3,5-dichlorophenyl)-5-methyl-6-oxo-5-[[4-(trifluoro-
washed with another 5 mL of methylene chloride, and the reac- methoxy)phenyl]-methyl][14C]imidazo[1,2-a]imidazole-3-sul-
tion was warmed slowly to room temperature. To the resulting fonyl chloride [14C]-(15): To a solution of the aforementioned
colorless mixture (biphasic), water was added, and the aqueous iodide (0.842 g, 1.44 mmol, 81 mCi) in dry THF (10 mL), was
phase was extracted with methylene chloride (3 Â 20 mL). The added a solution of isopropyl magnesium chloride (0.87 mL,
combined extracts were dried over MgSO4, filtered, and concen- 2.0 M in THF) dropwise at À40 ꢀC. The resulting yellow solution
trated. Purification by flash chromatography using a 40 g was stirred at this temperature for 1 hour before sulfur dioxide
RediSep disposable column (Isco, Inc., Lincoln, NE, USA) and was bubbled slowly into the reaction for about 5 minutes. The
methylene chloride, then 10%–20% EtOAc: CH2Cl2 gave 1.42 g resulting bright yellow solution was stirred at À40 ꢀC for 1 hour
of pure product as a white solid. The product co-eluted with and then warmed to room temperature in another hour. The
unlabeled reference compound on TLC (10% MeOH/CHCl3). Total reaction was then concentrated and further dried under reduced
activity 143 mCi in 71.5% radiochemical yields with a specific pressure overnight. The resulting bright yellow foam was dis-
activity of 54.36 mCi/mmol. HPLC: Column: Zorbax Eclipse XDB- solved in 10 mL of dry THF under nitrogen atmosphere and
C8 (4.6 Â 150 mm, 5 mm) fitted with opti-guard (1.0 mm, C8). cooled to À20 ꢀC. N-Chlorosuccinimide (236 mg, 1.73 mmol) in
Column heater at 35 ꢀC, Gradient: 20%–100% B in 30 minutes; dry THF (5 mL) was added dropwise at À20 ꢀC, and the resulting
A = water, B = acetonitrile both contain 10 mM TFA. Flow: yellow-orange solution was stirred at this temperature for 1 hour.
1.0 mL/minute, UV 254 nm. tR = 19.17 minutes, 99.93% . tR = 19.33 This product was used in the next step as a THF solution.
minutes, 99.99% radio-detection of 1.0 mM solution in EtOH.
(2S)-2-[[(5R)-7-(3,5-dichlorophenyl)-5-methyl-6-oxo-5-[[4-
(5R)-3-(3,5-Dichlorophenyl)-2-(2,2-dimethoxyethylimino)-5- (trifluoromethoxy)phenyl]methyl][14C]imidazo[1,2-a]imidazol-
methyl-5-[[4-(trifluoromethoxy)phenyl]methyl][14C]imidazolidin- 3-yl]sulfonylamino]propanamide [14C]-(1): To a cloudy solution
4-one [14C]-(17): A mixture of the dimethyl acetal (16) (1.26 g, of L-alaninamide, HCl (0.36 g, 2.89 mmol), and triethylamine
2.33 mmol, 127 mCi), triphenyl phosphine (1.29 g, 4.86 mmol), (0.61 mL, 4.33 mmol) in DMF (10 mL), was added via cannula
carbon tetrachloride (0.47 mL, 4.86 mmol), and triethylamine the sulfonyl chloride solution at room temperature. The flask
(0.68 mL, 4.89 mmol) in anhydrous methylene chloride (15 mL) was further rinsed with dry DMF (5 mL), and the resulting
was stirred at room temperature. The colorless solution turned orange-yellow mixture was stirred for 12 hours. The yellow mix-
slowly to yellow. The reaction was stirred overnight. It was ture was concentrated to remove most of the DMF, and the resi-
diluted with ethyl acetate (50 mL) and washed with 1.0 N HCl due was diluted in ethyl acetate (100 mL). Water (40 mL) was
solution (2 Â 25 mL). The organic phase was dried over Na2SO4, added, and the solution was stirred vigorously. The aqueous
filtered, and concentrated to give 1.22 g of a semisolid residue. layer was pipetted out, and the organic layer was washed with
TLC (50% EtOAc: Hexanes) showed no starting material and a another 20 mL of water. The organic phase was then
J. Label Compd. Radiopharm 2011, 54 799–808
Copyright © 2011 John Wiley & Sons, Ltd.
www.jlcr.org

B. Latli et al.
concentrated, and the residue was purified by flash chromato- column Zorbax SXB C8 (4.5 Â 150 mm, 5 mm), tR: 28.04 minutes,
graphy using a 40 g RediSep disposable column. The column 96%, co-eluted with unlabeled reference compound.
was wetted with methylene chloride, and the crude material
(R)-1-(3,5-Dichlorophenyl)-3-methyl-2-oxo-3-(4-(trifluor-
was eluted with 100% methylene chloride to remove nonpolar omethoxy)benzyl)-2,3-dihydro-1H-[14C]-imidazo[1,2-a]imi-
impurities and then with 20%–50% EtOAc:CH2Cl2 to elute the dazole-5-sulfonamide ([14C]-(2). NH4OH (2 mL) was added to a
pure material to give 350 mg of a foam, TLC co-elutes with unla- mixture of [14C]-(15) (120 mg, 0.186 mmol), Cs2CO3 (80 mg,
beled (1) in 10% MeOH/CHCl3 or in 50% EtOAc:Hexanes. Crystal- 0.25 mmol) in DMF (2mL) and THF (2mL) at 0 ºC. The mixture
lization from chloroform gave 305 mg of a fluffy white solid. A was stirred at 0 ºC for 0.5 hour. The reaction was quenched by
total of 22.15 mCi was obtained with a specific activity 44 mCi/ the addition of 10 % K2CO3, extracted with EtOAc. The EtOAc
mmol and in 40% radiochemical yield. HPLC conditions: Column: extract was washed sequentially with water (Â2), brine, dried over
Zorbax Eclipse XDB-C8 (4.6 Â 150 mm, 5 mm), fitted with an opti- Na2SO4, and concentrated. The crude solid was purified by
guard (1.0 mm, C8). UV detection was at 220 and 254 nm. Mobile CombiFlash Companion (12 g RediSep column, EtOAc/Hexane) to
phase: A: water, B: MeCN, both contain 10 mM TFA. Injections give a white solid (19 mg). The solid was further purified by
volumes: 10 mL, tR = 19.20 minutes (UV) and tR = 19.50 (rad). For CombiFlash Companion (4g RediSep column, EtOAc/Hexane) to
radio-TLC, about 2.0 mL of cold and radioactive (1) (1.0 mM) solu- give as a white solid, which was finally purified by preparative HPLC
tions were applied to a 20 cm  10 cm TLC plate (solvent front using Chiracel OD (4.6 mm  25 cm) 20% IPA/Hexane to give [14C]-
17 cm and base line of 2 cm) and developed in 10% MeOH/ (2) (8 mg, 605 mCi with a specific activity of 40.5 mCi/mmol) as a
1
CHCl3. The plate was dried then a coat of Crystal Clear Acrylic white solid in 8% yield. H NMR (500 MHz, CDCl3) d: 7.38 (s, 1H),
Coating (KRYLON, Solon, OH) was applied. After drying and 7.33 (m, 2H), 7.23 (m, 1H), 6.92 (m, 4H), 5.08 (m, 2H), 3.97 (d,
removing loose silica gel under a stream of nitrogen, the plate J= 14 Hz, 1H), 3.21 (d, J= 14 Hz, 1H), 1.96 (s, 3H). HPLC: mobile phase
was scanned using BIOSCAN System 200 Imaging Scanner. Rf = gradient 30%–90% (MeCN/H2O both 10mM TFA) over 30minutes;
0.4, 99.8%. NMR was taken using double encapsulation. Both column Zorbax SXB C8 (4.5 Â 150 mm, 5 mm), tR: 20.16 minutes, 99%.
unlabeled standard (8 mg) and [14C]-(1) in 300 mL of deuterated
Conclusion
methanol (methanol-d4, D, 99.8% contains 0.05% v/v TMS). The
1
spectra were identical. H NMR (MeOH-d4) d: 7.48(m, 3H), 7.05
A long linear route was used to prepare [13C2, 2H3]-(1), (2S)-2-[[(5R)-
(br s, 4H), 4.02(q, J = 7.2 Hz, 1H), 3.98(d, J = 13.51 Hz, 1H), 3.21(d,
7-(3,5-dichlorophenyl)-5-methyl-6-oxo-5-[[4-(trifluoromethoxy)-phe-
J = 13.51 Hz, 1H), 2.05(br s, 3H), 1.45(d, J = 7.2 Hz, 3H). 13C NMR
nyl]methyl]-imidazo[1,2-a]imidazol-3-yl]sulfonylamino]propanamide
(MeOH-d4) d: 177.05, 175.41, 150.4, 150.10, 136.48, 135.84,
using D-alanine (3,3,3-2H3) and [13C2]glycine in 15 steps and 2.5%
135.26, 134.37, 132.29, 128.68, 128.35, 122.61, 121.98, 121.7(m),
overall yield. [13C6]-3,5-Dichloroaniline was used to prepare the
71.58, 53.53, 43.41, 22.17, 19.59.
metabolite (R)-1-(3,5-Dichlorophenyl)-3-methyl-2-oxo-3-(4-(trifluoro-
methoxy)benzyl)-2,3-dihydro-1H-imidazo[1,2-a]imidazole-5-sulfona-
Synthesis of [14C]-(2)
mide [13C6]-(2) in 12 steps and in 5.6% overall yield. For the
carbon-14 synthesis, a six-step synthesis gave both compounds
[14C]-(1) and [14C]-(2) from the common sulfonyl chloride intermedi-
ate [14C]-(15) in 18% and 4% radiochemical yields and specific activ-
ities of 44 and 40.5 mCi/mmol, respectively.
(R)-5-Bromo-1-(3,5-dichlorophenyl)-3-methyl-3-(4-(trifluoro-
methoxy)benzyl)-1H-[14C]-imidazo[1,2-a]imidazol-2(3H)-one
[
14C]-(20). N-bromosuccinimide (NBS) (47 mg, 0.26 mmol) was
added in four portions at room temperature to [14C]-(18)
(125 mg, 0.27 mmol) and Et3N (8 mg, 0.06 mmol) in CH2Cl2
(5 mL) at 0 ºC. The mixture was warmed to room temperature
and stirred for 14 hours (an HPLC aliquot revealed a starting
material: product ratio of 66:33). The reaction was cooled to
0 ºC, NBS (20 mg) was added, and the mixture was stirred for
0.5 hour. The reaction was quenched by addition of water,
extracted with EtOAc. The EtOAc extract was washed with brine,
dried over Na2SO4, and concentrated to give a yellow solid. The
crude solid was purified by CombiFlash Companion (12 g
RediSep column, EtOAc/Hexanes) to give 90 mg of product in
69% yield as a white solid. HPLC: mobile phase gradient
30%–90% (MeCN/H2O both 10 mM TFA) over 30 minutes; col-
umn Zorbax SXB C8 (4.5 Â 150 mm, 5 mm), tR: 27.00 minutes, 98%.
(R)-1-(3,5-Dichlorophenyl)-3-methyl-2-oxo-3-(4-(trifluoro-
methoxy)benzyl)-2,3-dihydro-1H-[14C]-imidazo[1,2-a]imidazole-
5-sulfonyl chloride. [14C]-(15): i-PrMgCl (0.3 mL, 2.0 M solution
THF) was added dropwise to a solution of [14C]-(20) (100 mg,
0.186 mmol) in THF at À10 ºC. After stirring for 0.5 hour, SO2/
THF (0.25 mL, 22% by weight) was added; after 15 minutes, NCS
(100 mg, 0.75 mmol) was added and stirred for 15 minutes. The
reaction was quenched by the addition of H2O, extract with
EtOAc. The EtOAc extract was washed with brine, dried over
Na2SO4, and concentrated to give the title compound, which
was used as it is in the next step. HPLC: mobile phase gradient
Acknowledgment
We thank our colleague Scott Leonard for analytical support.
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www.jlcr.org
Copyright © 2011 John Wiley & Sons, Ltd.
J. Label Compd. Radiopharm 2011, 54 799–808