Synthesis and biological evaluation of new quinoxaline derivatives of ICF01012 as melanoma-targeting probes

Article abstract of DOI:10.1021/ml400468x

The aim of this study was the synthesis and pharmacokinetic selection of a best melanin-targeting ligand for addressing anticancer agents to pigmented melanoma. Seven quinoxaline carboxamide derivatives were synthesized and radiolabeled with iodine-125. Biodistribution studies of compounds [ ¹²⁵I]1a-g performed in melanoma-bearing mice tumor showed significant tumor uptake (range 2.43-5.68%ID/g) within 1 h after i.v. injection. Fast clearance of the radioactivity from the nontarget organs mainly via the urinary system gave high tumor-to-blood and tumor-to-muscle ratios. Given its favorable clearance and high tumor-melanoma uptake at 72 h, amide 1d was the most promising melanoma-targeting ligand in this series. Compound 1d will be used as building block for the design of new melanoma-selective drug delivery systems.

Full text of DOI:10.1021/ml400468x

Letter
pubs.acs.org/acsmedchemlett
Synthesis and Biological Evaluation of New Quinoxaline Derivatives
of ICF01012 as Melanoma-Targeting Probes
Radhia El Aissi,†,‡ Jianrong Liu,†,‡ Sophie Besse,†,‡ Damien Canitrot,†,‡ Olivier Chavignon,†,‡
Jean-Michel Chezal,†,‡ Elisabeth Miot-Noirault,†,‡ and Emmanuel Moreau*,†,‡
†INSERM−Universite
́
d’Auvergne, UMR 990, IMTV, BP 184, F-63005 Clermont-Ferrand Cedex, France
Universite d’Auvergne, Imagerie Moleculaire et Therapie Vectorisee, BP 10448, F-63005 Clermont-Ferrand
‡Clermont Universite,
́
́
́
́
́
Cedex, France
S
* Supporting Information
ABSTRACT: The aim of this study was the synthesis and
pharmacokinetic selection of a best melanin-targeting ligand
for addressing anticancer agents to pigmented melanoma.
Seven quinoxaline carboxamide derivatives were synthesized
and radiolabeled with iodine-125. Biodistribution studies of
compounds [125I]1a−g performed in melanoma-bearing mice tumor showed significant tumor uptake (range 2.43−5.68%ID/g)
within 1 h after i.v. injection. Fast clearance of the radioactivity from the nontarget organs mainly via the urinary system gave high
tumor-to-blood and tumor-to-muscle ratios. Given its favorable clearance and high tumor-melanoma uptake at 72 h, amide 1d
was the most promising melanoma-targeting ligand in this series. Compound 1d will be used as building block for the design of
new melanoma-selective drug delivery systems.
KEYWORDS: Melanoma, melanin-targeting ligand, radiolabeling, iodine-125
Since the 1990s our research group has focused on the
development of radiotracers able to specifically bind to
melanins for the diagnosis of disseminated melanoma. Several
structure−activity relationship studies have demonstrated that
the chemical scaffold of these compounds should contain an
aromatic moiety together with a tertiary amino group to allow
sufficient binding to melanins via ionic and π stacking
interactions (Figure 1A).8 Recently (2008−2013) a phase 3
clinical trial (compound I, called [123I]BZA2) was initiated to
evaluate the sensitivity and specificity of [123I]BZA2 versus
[18F]FDG for the imaging of patients with melanoma.10
With the aim of increasing uptake and tumor retention for
targeted radionuclide therapy application with iodine-131,
isseminated melanoma is an incurable disease. Its
Dprognosis has remained unchanged over the past 20
years. To date no treatment strategy has proved better than
dacarbazine monochemotherapy, which remains the first line of
treatment for this lethal form of skin cancer. Newly developed
multidrug chemotherapy, biochemotherapy, and targeted
therapy have all yielded disappointing results, with poorer
quality of life and no real survival benefit for the patient.1
However, the concept of targeted cancer therapy, which has
emerged during the past decade, opens a wider therapeutic
window than traditional cytotoxic drugs. An emblematic
example is imatinib (STI571, Gleevec, Glivec), the first drug
approved by the FDA that revolutionized the small molecular
kinase inhibitor concept.2 These targeted therapies improve
anticancer treatment efficacy through interference with specific
cellular pathways involved in tumor growth and progression.
To increase antitumor efficacy while reducing systemic side
effects, nanoparticles were used to permit an accumulation in
certain solid tumors by EPR effect. For example, an albumin
bound paclitaxel nanoparticle Abraxane was recently approved
by the FDA for the treatment of breast cancer (2005) and for
nonsmall cell lung cancer (2012).3
The key step in the development of an effective cancer
treatment is based on the identification of the biological
characteristics and/or pathways of individual tumors.4 Regard-
ing melanoma cancer, several mutations have been used to
develop specific treatments (CDKN2A, CDK9, NSRAS, and
BRAF).5 Other targets have also been identified and
investigated, such as sigma-1 and melanocortin-1 receptors
and melanin pigments.6−9
Figure 1. From clinical molecular imaging to preclinical targeted
therapy of melanoma.
Received: November 15, 2013
Accepted: February 20, 2014
Published: February 20, 2014
© 2014 American Chemical Society
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ACS Medicinal Chemistry Letters
Letter
optimization of the (hetero)aromatic moiety of BZA2 was
designed.11 The synthesized compounds were then tested in
vivo to evaluate their biodistribution in the melanoma-bearing
mouse model. Among all these new derivatives, quinoxaline
radiotracer II (called [125I]ICF01012) (Figure 1A) demon-
strated a very favorable tumor uptake and dosimetry
parameters.11,12 Given its favorable pharmacological properties,
it will be evaluated for clinical application in radionuclide
therapy for disseminated melanoma ([131I]ICF01012 (II)).13
On the basis of our lead melanin-targeting ligand ICF01012,
bimodal agents were developed and showed specific affinity for
melanoma, allowing both early SPECT (123I) or PET (18F)
imaging and efficient targeted radionuclide therapy (131I) of
melanoma.14−16,18 These original radiotracers were synthesized
by substituting one of the ethyl residues by an N-
ethoxyfluoropyrinyl moiety (Figure 1B, blue part). The
ICF01012 scaffold has also been conjugated to Gd-based
nanoparticles for radiosensitizing purposes via the functional-
ization of the aromatic part (Figure 1C, red part). Biacore
studies have shown that such modified particles bind efficiently
to melanin pigments.19
and pharmacokinetic profile to help build a promising melanin-
targeting pro-drug.
Results and Discussion. Access to compounds 1a−g was
achieved from the aminoquinoxaline derivative 1018 (for 1d−g)
and its corresponding carbamate 1118 (for 1a−c) as starting
materials with 2-(iodoaryl)amino derivatives 3a−c or ω-(2-
iodophenoxy)alkoxy acid derivative 3d−g, respectively. Briefly,
compounds 3a−c were synthesized from 1-(bromomethyl)-2-
iodobenzene 2: a direct reaction with 2-mercaptoethamine
yielded 3a. Compound 3b was obtained by nucleophilic
substitution of 2 in the presence of N-Boc ethanolamine,
followed by a deprotection under trifluoroacetic acid
conditions. Compound 3c was prepared in three steps. After
monobenzylation of tetraethyleneglycol with 2-iodobenzyl
bromide 2, the terminal hydroxyl group of compound 5 was
converted into iodo derivative 6, which gave 3c after a Gabriel
reaction (Scheme 2).
a
Scheme 2
Various strategies to treat melanoma based on melanin-
targeted chemotherapy have also been studied in our
laboratory. Despite very promising biodistribution profiles of
acridine analogues of BZA or ICF01012 with DNA-
intercalating properties,20−22 only moderately good results
have been obtained in melanoma mouse models. These
disappointing results may be explained by the scavenger effect
suggested by Chen et al., involving melanosomal sequestration
of melanin-targeted chemotherapy.23 On the basis of these
findings, we decided to change our approach to a two-step
prodrug targeted delivery strategy. First, the prodrug was to be
addressed to the tumoral melanosomes using a melanin-
targeting ligand. The anticancer agent would then be released
by tumor selective cleavage.
a
Reactants and conditions: (i) 2-aminothioethanol hydrochloride,
LiOH monohydrale, H2O/EtOH (1/3, v/v), 35 °C; (ii) tert-butyl (2-
hydroxyelhyl)coarbamate, KOH, dry dichloromelhane, rt; (iii) TFA,
dry dichloromethane, rt; (iv) NaH, dry THF, rt; (v) imidazole, PPh3,
l2, dry dichlorom ethane, rt; (vi) (a) potassium phtalimide, dry DMF,
30 °C; (b) hydrazine monohydrate, ethanol, 30 °C.
To investigate this concept of melanoma-directed prodrug
therapy, we examined a novel family of melanin-targeting
ligands combining an alkyl spacer and an aromatic platform
based on ICF01012 (Figure 1D, blue and red parts). We first
designed and synthesized two subfamilies of ICF01012
analogues substituted by a 2-(iodoaryl)urea (or amide) alkyl
chain at the C-6 position of the quinoxaline core. For
compounds 1a−c, we included a thioalkyl chain (Scheme 1a:
X = S, m = 1) or an alkoxy chain in the chemical scaffold
(Scheme 1b,c: X = O, m = 1, 4, respectively).
When the quinoxaline moiety was substituted by an amido
group, with the length of alkyl chain ranging from one to five
carbons (Figure 1, compounds 1d−g with n = 1, 3, 4, or 5).
Compounds 1a−g were then radiolabeled with iodine-125 and
evaluated in a melanoma-bearing mouse model to identify the
best candidate presenting optimal melanin targeting properties
For compounds 3d−g, after a first esterification of
commercially available ω-halogenated acids (7d−g, n = 1, 3−
5), an O-alkylation in anhydrous DMF in the presence of
anhydrous potassium carbonate and 2-iodophenol was
performed to give ethyl ω-(2-iodophenoxy)carboxylate com-
pounds. Then, compounds 9d−g were saponified with lithium
hydroxide monohydrate and converted into acid 3d−g after
acidification (Scheme 3).
a
Scheme 3
a
Reactants and conditions: (i) acetyl chloride, dry ethanol, rt; (ii) 2-
iodophenol, dry DMF, 80 °C; (iii) (a) LiOH monohydrate, THF/
H2O/MeOH (3/1/1, v/v/v), rt; (b) HCI (1 N).
Scheme 1
Finally, compounds 1a−g were synthesized as outlined in
Scheme 4. Urea derivatives 1a−c were obtained from 11 and
DMAP with the appropriate amino derivatives 3a−c in
moderate yields (44−66%). Access to amido derivatives 1d−
g was achieved from derivatives 3d−g: after treatment of these
acids with thionyl chloride, adding amine 10 afforded 1d−g
with yields in the range 29−98%.
For a whole-body distribution study, seven quinoxaline
derivatives (1a−g) were radioiodinated at low specific activity
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ACS Medicinal Chemistry Letters
Letter
a
Scheme 4
Table 1. In Vitro Binding to Melanin and log P of [125I]1a−g
% bound to synthetic melanin
a
compd
H2O
PBS
log P
[
[
[
[
[
[
[
[
125I]1a
92.8 0.6
96.2 0.7
94.0 0.1
93.9 0.4
96.0 0.7
96.0 0.2
95.0 2.7
96.8 0.5
87.7 0.6
74.0 1.2
81.0 0.4
73.3 3.1
86.4 2.5
86.5 0.2
68.4 4.2
72.1 1.0
2.06 0.03
1.76 0.04
1.89 0.07
1.25 0.03
2.07 0.04
1.30 0.05
1.33 0.04
1.12
125I]1b
125I]1c
125I]1d
125I]1e
125I]1f
125I]1g
b
125I]ICF01012
a
Partition coefficient between n-octanol and phosphate buffer solution
b
(PBS, pH 7.4). For ICF01012, binding melanin and log P values were
obtained from previous work.3
affinity increased with log P values for urea series (compounds
[
125I]1a−c). For amide series, an interpretation of the data was
complex: indeed, the affinity was similar (86%) for [125I]1f and
[
125I]1e, but log P values were very different (log P ([125I]1f) =
a
1.30 vs log P ([125I]1e) = 2.07). Moreover, log P values were
Reagents and conditions: (i)4-nitrophenylchloroformate, pyridine,
similar for [125I]1f and [125I]1g, but the melanin affinity of
dry DCM, rt; (ii) 3a−c, DMAP, dryTHF, TA; (iii) (a) 3d−g, thionyl
chloride, dry DCM, 45 °C; b) 10, DMAP, dry DCM, 45 °C; (iv) 2 N
HCl diethyl ether, rt; (v) (a) Na125I, acetic acid, 130 °C; (b) 2 N HCl
diethyl ether, rt.
[
125I]1g decreased dramatically. We concluded no correlation
between lipophilicity and melanin binding in water and in PBS
Whole body distribution was assessed by scintigraphic
imaging performed at 1, 3, 24, and 72 h post-i.v. injection
(3.7 MBq/0.2 mL of NaCl 0.9%) (Figures S1 and S2,
Supporting Information). Biodistribution in tumor and organs
was evaluated by ex vivo counting at the same time-points.
Intravenous administration of 125I- radiolabeled compounds
was well tolerated, with no evidence over 72 h of side effects
such as lethargy, rough coat, and closed eyes. For [125I]1a−g,
high B16F0 melanoma uptakes were observed as early as 1 h
postinjection (p.i.), ranging from 1.05 to 2.22 and 2.43 to
5.68%ID/g for urea and amido compounds, respectively (Table
2). We noted a similar radioactivity uptake profile in the
pigmented structures of eyes. These results were consistent
with a melanin binding uptake mechanism as previously
described and observed by us24 with different N,N-diethyle-
thylenamino aryl compounds.14−16 Considering the highly
pigmented eyes of the C57BL6J model, these observations have
to be interpreted carefully on the basis of the melanin content
differences between humans and animal eyes, as recently
published by Durairaj et al.17
using a nucleophilic aromatic isotopic exchange reaction with
no-carrier-added [125I]NaI in the presence of CuSO4 at 130
°C.8 For each radiotracer, the following radiolabeling reaction
parameters were optimized: reaction time (15−45 min) and
acid conditions (method A, acetic acid; method B, citrate
buffer) (Table S1, Supporting Information).
After purification by semipreparative radio-reversed phase-
high pressure liquid chromatography analyses, compounds
[
125I]1a−g were converted to hydrochloride salts (more
soluble in aqueous medium) with good radiochemical yields
(RCY, 43−56%), high radiochemical purities (RCP > 98%),
and with a specific activity (SA) in the range 18.5−37.3 MBq/
μmol. Reaction conditions and radiochemical data are reported
in the Supporting Information (Tables S1−S3). All the
radiotracers studied showed a very high chemical stability
when incubated in physiological serum (NaCl 0.9%) at 37 °C
for 24 h (RCP > 97%).
In ongoing work to design quinoxaline derivatives for tumor-
targeted melanoma chemotherapy, the first challenge was to
maintain a high affinity for melanin. Compared with the
standard ICF01012, all the newly synthesized quinoxaline
derivatives [125I]1a−g displayed a strong affinity for synthetic
melanin in water (Table 1).
For all the compounds evaluated, tumor retention was
observed over 72 h (range 0.30−2.72%ID/g).
For the urea series, tumor accumulation of [125I]1a−c was
observed to be as early as 1 h after i.v. administration, with for
[
125I]1c a high value of 2.22% ID/g peaking at 3 h p.i. (3.18%
Similarly to the previous results obtained with [125I]-
ICF01012, the binding of [125I]1 to synthetic melanin in
PBS significantly decreased except for urea [125I]1a. However,
molecular binding to synthetic melanin was better than that
observed with BZA or similar to ICF01012 data.11 The
lipophilicity values (log P (n-octanol/PBS), Table 1) of the
compounds studied were all higher than those obtained for
ICF01012 (range 1.25−2.07 for log P (1a−g) vs. 1.12 for log P
(ICF01012)). The lipophilic character of the compounds
studied seemed to some extent be related to melanin binding
affinity in PBS except for [125I]1f. Nevertheless, for compounds
ID/g) and then decreasing rapidly to 0.71% ID/g at 24 h and
0.61% ID/g at 72 h. A similar profile was observed for [125I]1a
b (Table 2). For the three urea compounds, similar
biodistribution profiles were also observed in eyes between 3
and 72 h. We noted a rapid release from nontarget tissues
leading to rapidly unquantifiable ratios when organ concen-
tration was within the range of the background value (Table S2,
Supporting Information) for compound [125I]1a,c. Only
compound [125I]1b showed sustained liver and kidney uptakes
of 0.22 and 0.33%ID/g at 24 h p.i., respectively.
For the amide series, compounds [125I]1d−g exhibited a
tumor affinity three times higher than [125I]1a-c, ranging from
2.43 to 5.68% ID/g at 1 h p.i. Similarly, from 24 h p.i., %ID/g
values of [125I]1d−g were higher than the maximum values
[
125I]1a−g, it was difficult to establish a correlation between
melanin binding affinity and log P values. Analysis of the data
obtained in these experiments showed that melanin binding
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ACS Medicinal Chemistry Letters
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Table 2. Biodistribution of [125I]1a-g Compared with
ICF01012 at Various Times after i.v. Administration in
B16F0 Melanoma-Bearing Mice
Table 3. Melanoma/Organ Ratios of [125I]1a−g and
ICF01012 Uptake in B16 Melanoma-Bearing Mice at
Different Times after Injection
a
a
a
a
a
time
(h)
thyroid and
ab
compd
125I]1a
time (h)
T/L
T/M
T/B
T/E
T/TSG
a
a
,
compd
125I]1a
melanoma
eyes
SG
[
[
[
[
[
[
[
1
0.12
0.66
1.72
3.59
2.14
6.05
0.66
0.71
0.49
0.27
0.87
0.63
0.51
0.30
1.12
1.33
0.54
0.43
1.00
0.87
0.67
0.34
0.91
0.98
0.81
0.33
1.16
1.03
0.81
0.38
0.93
1.05
0.64
0.36
0.50
1.11
0.66
0.27
0.36
0.54
0.37
0.49
1.01
1.72
0.51
1.12
2.36
1.08
0.45
1.38
4.83
10.00
5.58
1.11
3.79
2.32
1.03
0.98
1.25
5.54
3.89
0.60
1.55
3.36
2.32
[
[
[
[
[
[
[
1
1.05 0.15
1.15 0.32
0.83 0.26
0.37 0.14
1.92 1.02
2.03 0.09
1.27 0.70
0.87 0.50
2.22 0.05
3.18 0.72
0.71 0.01
0.61 0.26
5.68 1.16
5.60 1.56
3.30 0.75
2.40 0.30
2.43 0.39
1.86 0.50
1.67 0.10
0.75 0.29
1.58 0.07
1.62 0.18
1.67 0.38
1.36 0.56
2.21 0.11
3.22 0.11
2.50 1.16
2.91 0.57
1.97 0.41
2.39 0.59
1.32 0.09
1.41 0.28
5.67 0.30
6.46 0.18
4.88 1.98
7.04 2.35
2.66 0.83
1.89 0.64
2.05 0.15
2.28 0.61
3.87 0.17
3.18 0.61
1.54 0.67
0.99 0.34
3.93 1.24
2.01 0.01
0.74 0.21
1.69 1.19
1.99 0.13
1.35 0.83
0.66 0.03
1.37 0.49
4.12 0.86
1.16 0.20
0.33 0.04
0.43 0.12
2.19 0.33
0.49 0.03
0.72 0.31
0.73 0.51
3
3
24
72
1
24
72
1
125I]1b
125I]1c
125I]1d
125I]1e
125I]1f
125I]1g
0.30
1.26
5.77
6.21
1.09
2.81
2.66
5.97
3.31
125I]1b
125I]1c
125I]1d
125I]1e
125I]1f
125I]1g
3
10.15
3
24
72
1
24
72
1
8.53
3.26
6.49
3
24.46
3
24
72
1
24
72
1
0.91
3.36
6.60
3.40
4.91
3
20.74
3
24
72
1
24
72
1
0.47
2.24
3.42
15.5
4.11
9.3
3
3
24
72
1
24
72
1
0.36
0.60
3.73
4.73
4.99
4.21
d
d
d
5.74
4.96
5.87
3
3
4.55 1.15
5.60 2.10
2.72 1.76
3.62 0.09
5.82 1.26
2.99 0.57
2.64 0.37
17.0 11.1
27.7 7.0
4.40 0.19
6.93 2.88
7.15 1.76
3.90 0.16
5.54 0.27
4.64 0.91
7.30 0.42
33.82 3.47
24.79 6.78
32.30 6.52
25.26 8.38
3.63 0.05
1.01 0.07
0.70 0.20
6.08 0.41
3.75 0.12
0.89 0.01
1.14 0.32
c
24
72
1
24
72
1
0.2
1.76
6.33
2.41
8.82
3
0.84
3
24
72
1
21.35
24
72
1
ICF01012
1.29
3.12
14.54
8.33
4.92
9.51
7.02
e
ICF01012
3
32.20
24.94
0.69
0.22
3
39.76 23.47
94.22 27.48
c
24
72
24
72
21.7 10.8
12.45 1.6
a
L, liver; M, muscle; B, blood; E, eye; TSG, thyroid and submaxillary
a
Radioactive concentration values are expressed as means of %ID/g to
SD (two mice, n determinations for each compound at each time
point). SG: submaxillary glands. No value: no radioactive signal
detected in the tissue. No standard deviation when only one
glands.
b
c
d
e
determination was made per organ. ICF01012 values were obtained
from previous work.11
observed from [125I]1a−c over a period of 72 h (3.18−5.60%
ID/g for [125I]1d−g vs 1.15−3.18%ID/g for [125I]1a−c). For
[
125I]1d−g, we observed a melanoma uptake twice higher at 72
h than compounds [125I]1a−c except for [125I]1e. For amido
quinoxaline derivatives, no measurable activity in liver, kidney,
blood, muscle, thyroid, or SG tissues was detected after 24 h
(Table S4, Supporting Information). Such profiles offer high
tumor/nontarget ratios (Table 3) and a rapid clearance of the
radioactivity from the nontarget organs (Table S3, Supporting
Information). Considering melanoma uptake and tumor/
muscle ratio, compound [125I]1d appears to be the most
promising ICF01012 derivatives among the seven new
synthesized derivatives. Compared with [125I]ICF01012,
compound [125I]1d exhibited a lower tumoral uptake, but a
higher clearance over the 24−72 h period.
Figure 2. Radioactivity uptake in selected tissues after i.v. injection of
[
125I]1d in B16F0 melanoma-bearing C57Bl/6J mice. Mean
SD
(two mice, n determinations at each time point).
early as 1 h post-i.v. injection, together with a rapid clearance
from nontarget organs, mostly via the urinary excretion,
allowing a well-defined contrast tumor from 6 h.
In this work we report the synthesis, radiolabeling with
iodine-125, and biodistribution in B16F10 melanoma-bearing
mice using scintigraphic imaging and organ counting of seven
new quinoxaline derivatives. We demonstrate that the
adjunction of a urea or amido phenyl group at the C-6 position
of the ICF01012 scaffold did not modify the affinity for
melanoma in vivo. On the basis of these results, we consider
As illustrated in Figure 2, a high tumor to nontarget ratio
could be evidenced from 3 h post injection. The scintigraphic
imaging performed after i.v. injection of [125I]1d is reported in
Figure 3. The images illustrate the accumulation in the tumor as
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ACS Medicinal Chemistry Letters
Letter
biodistribution studies. Tables S1, S2, S3, and S4, Figures S1
and S2, and procedures for radiolabeling and biodistribution
ratios. This material is available free of charge via the Internet at
http://pubs.acs.org.
Figure 3. In vivo kinetics of compound [125I]1d in a B16F0
melanoma-bearing C57Bl/6J mouse illustrated by serial planar
scintigraphic images using a dedicated γ imager for small animals, at
1 h (A), 3 h (B), 6 h (C), 24 h (D), and 72 h (E) after a 37 MBq i.v.
injection dose (acquisition time = 10 min). T, tumor; A, abdomen; B,
bladder.
AUTHOR INFORMATION
■
Corresponding Author
*(E.M.) Phone: (33) 4 73 15 08 06. Fax: (33) 4 73 15 08 01. E-
mail: emmanuel.moreau@udamail.fr.
Author Contributions
All the authors contributed to the drafting of the manuscript.
All authors have given their approval to the final version of the
manuscript.
that compound 1d presents the most favorable in vivo behavior
for the future design of melanoma directed pro-drug delivery
systems (Figure 1, third family). Consequently, chemical
ligation of compound 1d with a spacer that incorporates a
predetermined breaking point allowing the drug to be released
at the melanoma tumor site,25,26 as previously evaluated by
us,27 is being investigated.
Experimental Section. General Method for Synthesis of
Quinoxaline Derivatives 1a−c. To a solution of 4-nitrophenyl
(2-((2-(diethylamino)ethyl)carbomoyl)quinoxalin-6-yl)-
carbamate (11) (1.1 equiv) dissolved in dry THF (20 mL), was
added 1.65 equiv of DMAP, and the resulting mixture was
stirred at room temperature for 30 min. The appropriate amine
derivative (3a−c) (1 equiv) dissolved in dry THF (20 mL) was
then added dropwise. The reaction mixture was stirred at room
temperature until disappearance of the starting material as
monitored by TLC. The reaction mixture was evaporated under
reduced pressure. The crude product was dissolved with a
saturated solution of NaHCO3 (20 mL) and extracted with
dichloromethane (3 × 40 mL). The pooled organic layers were
washed with a saturated solution of NaHCO3 (15 mL), water
(15 mL), and brine (15 mL), dried over magnesium sulfate,
filtered, and evaporated under reduce pressure.
Notes
The authors declare no competing financial interest.
ABBREVIATIONS
■
i.v., intravenous; p.i., postinjection; BZA, arylcarboxamide;
[18F]FDG, 2-deoxy-2-(18F)fluoro-D-glucose; SPECT, single-
photon emission computer tomography; PET, positron
emission tomography
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ASSOCIATED CONTENT
■
S
* Supporting Information
General methods for the synthesis of 1a−g, 3a−g, 4−6, 8d−g,
9d−g, and 11, radiolabeling of [125I]1a−g. Full experimental
1
details, H and 13C NMR, IR, and SM data for synthesized
compounds 1a−g, 3a−g, 4−6, 8d−g, 9d−g, and 11. General
methods for partition coefficient measurements, in vitro
binding to melanin, cell culture, biodistribution in B16F0
melanoma bearing mice, scintigraphic imaging, and ex vivo
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