Iodophenyl tagged sphingosine derivatives: Synthesis and preliminary biological evaluation

Article abstract of DOI:10.1016/j.bmcl.2009.05.035

A facile synthesis of six 4-iodophenyl tagged sphingosine (SP) derivatives bearing alkyl chain lengths from 6 to 13 is described. The key steps for the assembly of these molecules, 5a-f, are Suzuki-Miyaura cross-coupling and cross-metathesis reactions. Th

Full text of DOI:10.1016/j.bmcl.2009.05.035

Bioorganic & Medicinal Chemistry Letters 19 (2009) 3382–3385
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Iodophenyl tagged sphingosine derivatives: Synthesis and preliminary
biological evaluation
a
a
a
a,b
Wenchao Qu a, , Karl Ploessl , Hong Truong , Mei-Ping Kung , Hank F. Kung
*
a Department of Radiology, University of Pennsylvania, 3700 Market Street, Room 305, Philadelphia, PA 19104, United States
b Department of Pharmacology, University of Pennsylvania, Philadelphia, PA 19104, United States
a r t i c l e i n f o
a b s t r a c t
Article history:
A facile synthesis of six 4-iodophenyl tagged sphingosine (SP) derivatives bearing alkyl chain lengths
from 6 to 13 is described. The key steps for the assembly of these molecules, 5a–f, are Suzuki–Miyaura
cross-coupling and cross-metathesis reactions. The feasibility of radiolabeling was demonstrated by syn-
thesizing two 125I labeled compounds, [125I]5c and [125I]5e. In vitro enzyme assays indicated that the
molecules, 5c–e, are potent inhibitors. Thus, they deserve further evaluation as potential radioactive
probes for tumor imaging.
Received 10 April 2009
Revised 8 May 2009
Accepted 12 May 2009
Available online 18 May 2009
Keywords:
Sphingosine
Ó 2009 Elsevier Ltd. All rights reserved.
Suzuki–Miyaura cross-coupling
Cross-metathesis
Radioiodination
Tumor imaging
Phospholipids play important roles in a diverse range of cellular
processes, including cell growth, apoptosis, migration, angiogene-
sis, and neurogenesis. Ceramide (Cer, 1), sphingosine (SP, 2), and
sphingosine-1-phosphate (S1P, 3) are key elements in this lipid
family (Fig. 1). They are responsible for regulating various signal
transductions in the sphingolipid signaling cascade. The dynamic
balance between ceramide and sphingosine levels versus S1P, of-
ten described as the ‘sphingolipid rheostat’, provides an important
factor in determining whether cells survive or die. One of the key
enzymes balancing these three elements is sphingosine kinase
(SphK), whose role is to catalyze the phosphorylation of SP to
S1P. It has been demonstrated that one isoform of SphK, SphK1,
is an oncogene and often overexpressed in many human solid tu-
mors.1–3 Therefore, SphK1 upregulation may be a useful biomarker
for tumor and a potential target for cancer therapeutics.4,5 Devel-
oping imaging tools that can non-invasively monitor changes of
SphK1 in cells may assist in localizing tumors and also provide
clues to the stages of tumor proliferation. Often, attaching a fluo-
rescent dye or radioactive nuclide moiety to a biologically active
molecule may provide a congener, which can serve as a surrogate
for easily detecting biological activity via imaging. Several papers
have been published on introducing different fluorescent dyes into
Cer, SP, or S1P molecules. The bioactivities of these SP analogs con-
taining a fluorescent dye at the tail-end of the alkyl chain (Fig. 2a)
have also been evaluated and the results demonstrated the feasi-
bility of using the substitution approach for developing SP analogs
for fluorescence imaging of SphK.6–10 So far, there are no reports of
radionuclide labeled probes suitable for single photon emission
computed tomography (SPECT) or positron emission tomography
(PET) imaging. We have chosen to use the same terminal substitu-
tion method for preparing radionuclide labeled SP. These SP ana-
logs, similar to the fluorescent dye-containing derivatives, are
neutral and relatively small. Therefore, we expect that they would
also fit into the SphK binding pocket. Particularly, we wish to test
and delineate the effects of carbon chain length on the binding
affinity toward SphK1 and SphK2. For this reason, SP analogs con-
taining alkyl chain lengths from 6 to 13 were prepared and tested.
It is important to note that these SP analogs may either serve as
substrates for the SphK, or as competing inhibitors blocking the
phosphorylation of the parent substrate, SP.
We report herein a facile synthesis of a series of 4-iodophenyl
tagged SP derivatives, 5a–f. Additionally, we also demonstrate
the feasibility of radiolabeling these SP analogs by synthesizing
two 125I labeled SP derivatives, [125I]5c and [125I]5e. Moreover,
we further evaluate the biological activity of this series of SP deriv-
atives by SphK enzyme assays. The inhibition constants (IC50) are
correlated with the structures and added carbon chain length of
these derivatives.
Various methods for the synthesis of sphingolipids were re-
cently reported based upon different carbon–carbon double bond
formation approaches as the key synthetic steps. These approaches
include the traditional Wittig or Horner–Wadsworth–Emmons
olefination,11,12 stereoselective Birch reduction of alkyne,9,10
* Corresponding author. Tel.: +1 215 349 8372; fax: +1 215 349 5035.
E-mail address: wenchao.qu@sunmac.spect.upenn.edu (W. Qu).
0960-894X/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2009.05.035

W. Qu et al. / Bioorg. Med. Chem. Lett. 19 (2009) 3382–3385
3383
O
C15H31
C13H27
NH2
NH2
NH
O
O
C13H27
OH
OH
C13H27
P
OH
OH
OH
OH
HO
3
2
1
Figure 1. Three key sphingolipids: ceramide (Cer, 1); sphingosine (SP, 2); sphingosine-1-phosphate (S1P, 3).
R1
(a)
NH
OR2
Dye
n
Linker
OH
R1 = H, C15H31CO
R2 = H, PO3H2
n = 3-13
Dye = Pyrene, Dansyl,
7-Nitro-4-benzofurazanamine (NBD),
Borondipyrromethene (BODIPY), etc.
4
6a, n = 6
6b, n = 8
6c, n = 9
6d, n = 10
6e, n = 11
6f, n = 13
(b)
I
n
NH2
OH
+
I
n
OH
NHBoc
OTBDMS
5a, n = 6
5b, n = 8
5c, n = 9
5d, n = 10
5e, n = 11
5f, n = 13
OH
7
Figure 2. (a) Reported fluorescent dye labeled SP derivatives, 4. (b) Designed 4-iodophenyl SP tagged derivatives, 5, and their retrosynthesis analysis.
de-hydrohalogenation,13 as well as palladium catalyzed thioester-
boronic acid cross-coupling method14 and Grubbs catalyst cata-
lyzed cross-metathesis olefination.6–8,15–23 We chose the cross-
metathesis approach (Fig. 2b) to assemble the E-double bond of
the SP skeleton. There are several advantages of using this method:
very mild reaction conditions, high functional group tolerance and
relative high stereoselectivity toward formation of trans olefins.24
Allyl alcohol, 7, was synthesized following a well-established
method reported by Yamamoto et al.15 The other intermediate 4-
iodophenyl tagged terminal alkenes, 6, were assembled through
through a Suzuki–Miyaura cross-coupling reaction.29–31 This palla-
dium catalyzed reaction that was carried out in an aqueous NaOH/
THF biphasic system afforded 1-(x-bromoalkyl)-4-trimethylsilyl-
benzenes, 10a–f, in 60–80% yields. After iodo-desilylation reac-
tions, these aryltrimethylsilanes, 10a–f, were converted to
corresponding aryliodides, 11a–f, in virtually quantitative yields.31
Finally, a de-hydrobromination reaction with an excess of t-BuOK
smoothly provided the desired alkenes, 6a–f.25,32
With both intermediate alkenes, 6a–f, and allyl alcohol, 7, in
hand, the olefin cross-metathesis reactions were conducted in
CH2Cl2 with 2 equiv of 6a–f to 1 equiv of 7 under the catalysis of
0.03 equiv of second generation Grubbs catalyst.15 The desired E-
alkenes, 12a–f, were isolated in 47–57% yields after 2 h at reflux.
Subsequent de-silylation with 1% HCl in 95% EtOH and THF and
de-Boc protection with trifluoroacetic acid afforded final products,
5a–f, with yields ranging from 65% to 90% (Scheme 2).33
a four-step synthetic pathway starting from 1-bromo-
x-alkenes,
8a–f (Scheme 1). Three 1-bromo- -alkene starting materials,
x
8d–f, which are not commercially available, were prepared using
either t-BuOK promoted de-hydrohalogenation method25 or Li2-
CuCl4 catalyzed Grignard reagent and alkyl halide coupling strat-
egy (see Supplementary data).26–28 After hydroboration with 9-
borabicyclo[3.3.1]nonane (9-BBN), the formed alkylboranes were
subsequently coupled with 1-bromo-4-trimethylsilylbenzene, 9,
Next, we chose two intermediates, 12c and 12e, for radiolabel-
ing test. Palladium catalyzed trans-stannylation in toluene at 75 °C
Br
c
a, b
d
I
Me3Si
I
Br
Br
n
n
n+2
n+2
10a: n=6; 10b: n=8
11a: n=6; 11b: n=8
11c: n=9; 11d: n=10
11e: n=11; 11f: n=13
8a: n=6; 8b: n=8
8c: n=9; 8d: n=10
8e: n=11; 8f: n=13
6a: n=6; 6b: n=8
6c: n=9; 6d: n=10
6e: n=11; 6f: n=13
10c: n=9; 10d: n=10
10e: n=11; 10f: n=13
Scheme 1. Reagents and conditions: (a) 9-BBN, THF, rt, 2 h, 60 °C, 2 h; (b) 1-bromo-4-trimethylsilylbenzene, 9, Pd(PPh3)4, 2.0 M NaOH, 75 °C, 18 h; (c) ICl, CH2Cl2, 0 °C,
25 min; (d) t-BuOK, THF, 0 °C to rt, 2 h.

3384
W. Qu et al. / Bioorg. Med. Chem. Lett. 19 (2009) 3382–3385
NHBoc
NH2
OTBDMS
OH
a
b, c
I
I
I
n
n
n
OH
OH
5a: n=6; 5b: n=8
5c: n=9; 5d: n=10
5e: n=11; 5f: n=13
6a: n=6; 6b: n=8
6c: n=9; 6d: n=10
6e: n=11; 6f: n=13
12a: n=6; 12b: n=8
12c: n=9; 12d: n=10
12e: n=11; 12f: n=13
Scheme 2. Reagents and conditions: (a) alkene 7, DCM, Grubbs 2nd generation catalyst, 40 °C, 2 h; (b) 1% HCl in 95% EtOH/THF, 0 °C to rt, 2 h; (c) TFA/CH2Cl2, 0 °C to rt,
50 min.
Table 1
provided tributyltin substituted radiolabeling precursors, 13a and
Inhibition constants (IC50) of SP and its analogs to SphK1 and SphK2
13b, with moderate yields (47% and 49%, respectively). Standard
iododestannylation reactions, using no-carrier-added sodium
[
Test compounds
Alkyl chain length (n)
IC50
(
l
M)
125I]iodide, H2O2, and HCl, were successfully conducted on both
SphK1
SphK2
precursors.34,35 Further deprotection with HCl and TFA to remove
TBDMS and Boc, two protecting groups, afforded two radioactive
products, [125I]5c and [125I]5e. Radiochemical yields were 40%
and 60%, respectively (Scheme 3). The radiochemical purities were
94% and 98%, respectively. The chemical identities of both 125I -la-
beled SP analogs were confirmed by co-injection of authentic stan-
dards (‘cold’ 5c and 5e) to show identical retention times on HPLC.
The structure–biological activity relationships of these newly
synthesized SP analogs were evaluated by using well-established
combined human SphK1 and SphK2 enzyme assays (see Supple-
mentary data for experimental details).5 Such preliminary tests
help to evaluate how the addition of a 4-iodophenyl group at the
end of alkyl chain and the change of alkyl chain length affect their
enzyme activity with respect to the natural substrate, SP. The com-
petition phosphorylation between the new ligands, 5a–f, SP and a
known SphK enzyme inhibitor, N,N-dimethylsphingosine (DMSP)
toward a radiolabeled ligand provided the inhibition constants,
IC50 values (Table 1). The IC50 values for sphingosine in inhibiting
Sphingosine (SP)
N,N-Dimethylsphingosine
13
13
6
8
9
10
11
13
3.86 0.001
2.17 0.001
3.96 0.001
0.50 0.001
2.78 0.001
2.19 0.001
2.25 0.001
3.98 0.001
1.56 0.001
>80
5a
5b
5c
5d
5e
5f
7.23 0.001
5.73 0.001
16.6 0.001
4.38 0.001
13.3 0.001
29.2 0.001
high affinities (low IC50 values) toward SphK1 (<10
l
M); while
the IC50 values toward SphK2 displayed more variability with
two of the derivatives, 5c and 5f, and showed IC50 >15 M. Appar-
ently, compound 5b (n = 8) displayed the highest binding affinity
to SphK1 with IC50 of 0.5 M.
l
l
In summary, we report a facile synthetic route to synthesize a
series of SP analogs, 4-iodophenyl tagged SP derivatives relying
on a cross-metathesis reaction as the stitching strategy. Mean-
while, we also report, to the best of our knowledge, the first syn-
thesis of radionuclide, 125I labeled sphingosine derivatives. In
principle, the flexibility of this synthetic route will allow further
exploration of labeling with various other radioisotopes, such as
18F, 76Br, or 11C, to the SP derivatives with minimum perturbation
of their biological functions. In addition, the preliminary biological
evaluation of 5a–f using a competition of phosphorylation enzyme
assay demonstrated that 5b–d bound to SphK1 with high affinity,
while the binding affinity to SphK2 in general was lower. On the
basis of these initial results, these newly synthesized 4-iodophenyl
tagged SP derivatives deserve further investigations as tools for
studying sphingosine biology in tumor proliferation and as poten-
tial in vivo tumor imaging agents.
SphK enzyme assays were 3.86 and 1.56
respectively. The enzyme assays also showed that the IC50 of DMSP
for SphK1 was 2.16 M; while the IC50 for SphK2 was >80 M. The
lM for SphK1 and SphK2,
l
l
data for sphingosine and its inhibitor, DMSP, demonstrated that
the enzyme assays provided inhibition values similarly to the pre-
viously reported results, except for the DMSP showed less activity
for SphK2.36 We speculate that this difference may be caused by
the attachment of 4-[125I]phenoxy group in that radiolabeled li-
gand we used for the competition phosphorylation. The IC50 values
of 5a–f to the SphK1 are in the same order of those determined for
SP and DMSP suggesting that they are close analogs. It is worthy to
mention that the addition of a 4-iodophenyl group does not affect
the binding affinity to this enzyme. Among these new derivatives,
5b–d, the carbon chain length ranged from 8 to 10 and displayed
NHBoc
NHBoc
OTBDMS
a
OTBDMS
Bu3Sn
n
I
n
OH
OH
13a: n=9
12c: n=9
13b: n=11
12e: n=11
b
NHBoc
NH2
OH
OTBDMS
c, d
125I
125I
n
n
OH
OH
125I]12c: n=9
[
[
125I]5c: n=9
125I]5e: n=11
[
[
125I]12e: n=11
Scheme 3. Reagents and conditions: (a) (Bu3Sn)2, Pd(PPh3)4, toluene, rt, 75 °C, 6 h; (b) H2O2, Na125I, HCl, EtOH, 0 °C to rt, 10 min; (c) 2 M HCl/EtOH, 0 °C to rt, 40 min; (d) TFA/
CH2Cl2, 0 °C to rt, 40 min.

W. Qu et al. / Bioorg. Med. Chem. Lett. 19 (2009) 3382–3385
3385
J = 8.3 Hz), 3.42 (t, 2H, J = 6.8 Hz), 2.55 (t, 2H, J = 7.6 Hz), 1.86 (p, 2H, J = 7.0 Hz),
1.58 (t, 2H, J = 6.8 Hz), 1.28 (br s, 14H). 1-Iodo-4-(undec-10-enyl)benzene (6c).
To an ice bath cooled stirred solution of 11c (0.437 g, 1.0 mmol) in 5 mL THF
under N2 was added a solution of t-BuOK in THF (1.0 M, 3.0 mL). The reaction
was stirred at room temperature for 4 h and then quenched with H2O. After
standard workup with CHCl3, FC on silica gel using hexanes as solvent gives 6c
as a colorless oil (0.356 g, 64.5%). 1H NMR (CDCl3) d 7.59 (dt, 2H, J1 = 8.2 Hz,
J2 = 2.0 Hz), 6.93 (d, 2H, J = 8.3 Hz), 5.93–5.72 (m, 1H), 5.06–4.91 (m, 2H), 2.55
(t, 2H, J = 7.6 Hz), 2.05 (quartet, 2H, J = 6.8 Hz), 1.58 (br s, 2H), 1.28 (br s, 12H).
33. Representative experimental procedures for synthesizing 5a–f: tert-Butyl
(2S,3R,E)-1-(tert-butyldimethylsilyloxy)-3-hydroxy-14-(4-iodophenyl)tetradec-4-
en-2-ylcarbamate (12c). To a solution of 6c (0.142 g, 0.4 mmol) in 3 mL CH2Cl2
Acknowledgment
The authors thank Ms. Catherine Hou for editorial assistance.
Supplementary data
General experimental procedures, details of the preparation,
biological evaluation, and analytical data for compounds 8d–f,
6a–f, 10a–f, 11a–f, 12a–f, 13c, and 13e. Supplementary data asso-
ciated with this article can be found, in the online version, at
doi:10.1016/j.bmcl.2009.05.035.
was added allylic alcohol
7 (0.066 g, 0.2 mmol) and Grubbs catalyst 2nd
generation (0.005 g, 0.006 mmol) at room temperature. After stirring at 40 °C
for 2 h, the solvent was evaporated under vacuum and the residue was purified
by FC on silica gel (EtOAc/hexanes, from 10/90 to 15/85) to provide a white
waxy solid (0.072 g, 54%). 1H NMR (CDCl3)
d 7.51 (dt, 2H, J1 = 8.3 Hz,
References and notes
J2 = 2.1 Hz), 6.85 (d, 2H, J = 8.3 Hz), 5.68 (dt, 1H, J1 = 15.4 Hz, J2 = 6.8 Hz), 5.43
(dd, 1H, J1 = 15.4 Hz, J2 = 5.8 Hz), 5.15 (d, 1H, J = 8.3 Hz), 4.12 (quartet, 1H,
J = 5.9 Hz), 3.86 (dd, 1H, J1 = 10.3 Hz, J2 = 3.0 Hz), 3.67 (dd, 1H, J1 = 10.3 Hz,
J2 = 3.1 Hz), 3.49 (br s, 1H), 3.22 (d, 1H, J = 7.4 Hz), 2.47 (t, 2H, J = 7.6 Hz), 1.98
(quartet, 2H, J = 6.6 Hz), 1.48 (br s, 2H), 1.38 (s, 9H), 1.20 (br s, 12H), 0.83 (s,
9H), 0.00 (s, 6H). 13C NMR (CDCl3) d 155.9, 142.6, 137.4, 133.2, 130.7, 129.7,
90.7, 79.6, 74.7, 63.6, 54.8, 35.6, 32.4, 31.4, 29.65, 29.62, 29.3, 28.6, 26.0, 18.3,
ꢀ5.42, ꢀ5.44. HRMS calcd for C31H54INaNO4Si (M+Na)+: 682.2765, found:
682.2755. (2S,3R,E)-2-Amino-14-(4-iodophenyl)tetradec-4-ene-1,3-diol (5c). To a
solution of 12c (0.032 g, 0.048 mmol) in 2 mL THF was added 2 mL HCl (1%
concd HCl in 95% EtOH) at 0 °C. The reaction mixture was then stirred at room
temperature for 3 h. The solvent was removed under vacuum and the residue
was re-dissolved in 2 mL CH2Cl2. After cooling down to 0 °C, 1 mL
trifluoroacetic acid (TFA) was added dropwise. The reaction mixture was
further stirred at room temperature for another 1 h. It was concentrated under
vacuum and the residue was submitted to FC on silica gel (CH2Cl2/MeOH/
NH4OH = 200/25/2.5) to give 5c as a white solid (0.019 g, 88%). 1H NMR
(CD3OD) d 7.58 (dt, 2H, J1 = 8.3 Hz, J2 = 2.0 Hz), 6.96 (d, 2H, J = 8.3 Hz), 5.74 (dt,
1H, J1 = 15.4 Hz, J2 = 6.6 Hz), 5.48 (dd, 1H, J1 = 15.4 Hz, J2 = 6.7 Hz), 4.00 (br s,
1H), 3.72 (br s, 1H), 3.52 (br s, 1H), 2.80 (br s, 1H), 2.55 (t, 2H, J = 7.5 Hz), 2.06
(quartet, 2H, J = 6.3 Hz), 1.58 (br s, 2H), 1.30 (br s, 12H). 13C NMR (CD3OD) d
144.0, 138.6, 135.5, 131.8, 130.7, 91.2, 75.0, 63.9, 57.9, 36.5, 33.5, 32.6, 30.74,
30.66, 30.46, 30.42, 30.35. HRMS calcd for C20H33INO2 (M+H)+: 446.1556;
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¼ ꢀ2:6 (c 0.83, CHCl3).
ꢁ
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35. Representative experimental procedures for synthesizing [125I]5c and 5e: tert-
Butyl (2S,3R,E)-1-(tert-butyldimethylsilyloxy)-3-hydroxy-14-(4-(tributylstannyl)-
phenyl) tetradec-4-en-2-ylcarbamate (13a).
A mixture of 12c (0.033 g,
0.05 mmol), bis(tributyltin) ((Bu3Sn)2, 0.145 g, 0.25 mmol), and palladium
tetrakistriphenylphosphine (Pd(PPh3)4, 0.006 g, 10 mol %) in toluene (3 mL)
was heated at 75 °C for 6 h. The reaction solution was cooled to room
temperature and concentrated under vacuum. The residue was submitted to
FC on silca gel (EtOAc/hexanes, 15/85) to provide 13a as a light yellow waxy solid
(0.019 g, 47%). 1H NMR (CDCl3) d 7.37 (d, 2H, J1 = 7.8 Hz), 7.15 (d, 2H, J = 7.7 Hz),
5.77 (dt, 1H, J1 = 15.4 Hz, J2 = 6.8 Hz), 5.51 (dd, 1H, J1 = 15.4 Hz, J2 = 5.7 Hz), 5.24
(d, 1H, J = 7.3 Hz), 4.19 (br s, 1H), 3.95 (dd, 1H, J1 = 10.3 Hz, J2 = 3.0 Hz), 3.76 (dd,
1H, J1 = 10.5 Hz, J2 = 2.9 Hz), 3.56 (br s, 1H), 3.31 (d, 1H, J = 7.9 Hz), 2.58 (t, 2H,
J = 7.7 Hz), 2.06 (quartet, 2H, J = 6.6 Hz), 1.72–1.20 (m, 35H), 1.08–0.86 (m, 24H),
0.08 (s, 6H). 13C NMR (CDCl3) d 156.0, 142.8, 138.4, 136.9, 136.6, 136.3, 133.3,
129.7, 128.8, 128.4, 128.0, 79.7, 74.8, 63.7, 54.8, 36.2, 32.5, 31.7, 29.8, 29.4, 29.3,
29.1, 28.6, 28.2, 27.6, 27.0, 26.0, 18.4, 13.9, 13.1, 13.0, 9.8, 6.5, 6.4, ꢀ5.4. HRMS
calcd for C43H82NO4SiSn (M+H)+: 824.5035, found: 824.5035. Radioiodination.
21. Rai, A. N.; Basu, A. Org. Lett. 2004, 6, 2861.
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24. Grubbs, R. H. Tetrahedron 2004, 60, 7117.
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26. Cahiez, G.; Chaboche, C.; Jezequel, M. Tetrahedron 2000, 56, 2733.
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28. Effenberger, F.; Heid, S. Synthesis 1995, 1126.
29. Beinhoff, M.; Weigel, W.; Rettig, W.; Bruedgam, I.; Hartl, H.; Schlueter, A. D. J.
Org. Chem. 2005, 70, 6583.
Tributyltin precursor, 13a, (200
with an ice bath. To the solution were added successively 100
125I]NaI (535
Ci, non-carrier-added, purchased from Perkin–Elmer) and 50
lg) was dissolved in 100 lL EtOH and cooled
l
L 1 M HCl, 10
l
l
L
L
[
l
H2O2 (3%). The ice bath was removed and the reaction was maintained at room
temperature for 10 min. Satd NaHSO3 (100 L) was added to terminate the
l
30. Sabat, M.; Johnson, C. R. Org. Lett. 2000, 2, 1089.
31. Bo, Z.; Schlueter, A. D. J. Org. Chem. 2002, 67, 5327.
reaction. The reaction mixture was neutralized with 1.5 mL satd NaHCO3. The
whole mixture was passed through an activated C-4 mini-column and washed
with 3 mL 20% EtOH. Labeled product was eluted with 1 mL EtOH (65%). Ethanol
32. Representative experimental procedures for synthesizing intermediates 6a–f:
(4-(11-Bromoundecyl)phenyl)trimethylsilane (10c). To an ice bath cooled stirred
solution of 8c (2.45 g, 10.5 mmol) was added a solution of 9-BBN in THF (0.5 M,
24 mL, 12 mmol) under N2. After the addition, the ice bath was removed, the
mixture was stirred for 2 h at room temperature and then was heated to 60 °C
for additional 2 h. The reaction solution was cooled to room temperature, 1-
bromo-4-trimethylsilylbenzene (2.29 g, 10 mmol), Pd(Ph3)4 (0.578 g,
0.5 mmol) and an aqueous solution of NaOH (2.0 M, 10 mL) were added. This
mixture was purged with N2 for 20 min and heated to 75 °C for 18 h. A
standard workup with CHCl3 followed flash chromatography (FC) with hexanes
afforded 10c as a clear oil (2.94 g, 77%). 1H NMR (CDCl3) d 7.45 (d, 2H,
J = 7.9 Hz), 7.18 (d, 2H, J = 7.8 Hz), 3.42 (t, 2H, J = 6.8 Hz), 2.60 (t, 2H, J = 7.7 Hz),
1.87 (p, 2H, J = 7.0 Hz), 1.63 (t, 2H, J = 7.2 Hz), 1.29 (br s, 14H), 0.28 (s, 9H). 1-
(11-Bromoundecyl)-4-iodobenzene (11c). To an ice bath cooled stirred solution
of 10c (0.383 g, 1.0 mmol) in 2 mL CH2Cl2 under N2 was added a solution of ICl
in CH2Cl2 (1.0 M, 1.2 mL). After stirring at 0 °C for 25 min, the reaction was
quenched by 10 mL 10% NaHSO3 solution. Standard workup with CH2Cl2
provided a quantitative amount of product and it was used without further
purification. 1H NMR (CDCl3) d 7.59 (dt, 2H, J1 = 8.3 Hz, J2 = 2.1 Hz), 6.93 (d, 2H,
was removed under a flow of Ar. The residue was dissolved in 200
200 L THF, cooled to 0 °C and treated with the addition of 200 L HCl (2.0 M).
After 10 min at 0 °C and 30 min at room temperature, the solvent was removed
under Ar flow. The residue was re-dissolved in 500 L CH2Cl2 and cooled in an ice
bath. To this solution was added 200 L trifluoroacetic acid (TFA). After 5 min at
0 °C and 50 min at room temperature, the reaction mixture was dried under Ar
flow. The residue was dissolved in 100 EtOH and purified by HPLC
lL EtOH and
l
l
l
l
l
L
(Phenomenex Si-column, CH2Cl2/MeOH/0.1% NH4OH 100/10/1 with a flow rate
of 0.7 mL/min). The collected solution was blown to dryness and the final
product was re-dissolved in EtOH for biological studies. Radiochemical purity
(RCP) of product was determined by HPLC (Phenomenex Si-column, CH2Cl2/
MeOH/0.1%NH4OH 100/10/1 with a flow rate of 1 mL/min) and its identity was
identified by co-injection with ‘cold’ 5c. The overall yield was 40% and RCP was
94%.
36. Paugh, S. W.; Paugh, B. S.; Rahmani, M.; Kapitonov, D.; Almenara, J. A.; Kordula,
T.; Milstien, S.; Adams, J. K.; Zipkin, R. E.; Grant, S.; Spiegel, S. Blood 2008, 112,
1382.