Synthesis and biological properties of benzothiazole, benzoxazole, and chromen-4-one analogues of the potent antitumor agent 2-(3,4-dimethoxyphenyl)-5- fluorobenzothiazole (PMX 610, NSC 721648)

Article abstract of DOI:10.1021/jm800418z

New fluorinated 2-aryl-benzothiazoles, -benzoxazoles, and -chromen-4-ones have been synthesized and their activity against MCF-7 and MDA 468 breast cancer cell lines compared with the potent antitumor benzothiazole 5. Analogues such as 9a,b and 12a,d yielded submicromolar GI₅₀ values in both cell lines; however, none of the new compounds approached 5 in terms of antitumor potency. For 5, binding to the aryl hydrocarbon receptor appeared to be necessary but not sufficient for growth inhibition.

Full text of DOI:10.1021/jm800418z

J. Med. Chem. 2008, 51, 5135–5139
5135
Synthesis and Biological Properties of Benzothiazole, Benzoxazole, and Chromen-4-one
Analogues of the Potent Antitumor Agent 2-(3,4-Dimethoxyphenyl)-5-fluorobenzothiazole (PMX
610, NSC 721648)1
Stefania Aiello,†,¶ Geoffrey Wells,§,∆ Erica L. Stone,‡ Hachemi Kadri,† Rana Bazzi,# David R. Bell,# Malcolm F. G. Stevens,‡,§
Charles S. Matthews,‡ Tracey D. Bradshaw,*,‡ and Andrew D. Westwell*,†
Welsh School of Pharmacy, Cardiff UniVersity, Redwood Building, King Edward VII AVenue, Cardiff, CF10 3NB, U.K., Dipartimento
Farmacochimico Tossicologico e Biologico, Facolta` di Farmacia, UniVersita` degli Studi di Palermo, 90123 Palermo, Italy, Pharminox Ltd.,
BioCity, Pennyfoot Street, Nottingham NG1 1GF, U.K., Centre for Biomolecular Sciences, School of Pharmacy, UniVersity of Nottingham,
UniVersity Park, Nottingham NG7 2RD, U.K., and School of Biology, UniVersity of Nottingham, UniVersity Park, Nottingham NG7 2RD, U.K.
ReceiVed April 11, 2008
New fluorinated 2-aryl-benzothiazoles, -benzoxazoles, and -chromen-4-ones have been synthesized and their
activity against MCF-7 and MDA 468 breast cancer cell lines compared with the potent antitumor
benzothiazole 5. Analogues such as 9a,b and 12a,d yielded submicromolar GI50 values in both cell lines;
however, none of the new compounds approached 5 in terms of antitumor potency. For 5, binding to the
aryl hydrocarbon receptor appeared to be necessary but not sufficient for growth inhibition.
Introduction
(phase II metabolism) may limit the clinical application of 3,
and the potential use of metabolically stabilized (fluorinated)
benzothiazoles such as 4 in the Alzheimer’s diagnosis setting
has been reported.16
The versatile and synthetically accessible 2-arylbenzothiazole
scaffold has provided the inspiration for the discovery of a
number of new antitumor agents with unusual mechanisms of
action in recent years.2 The 2-(4-aminophenyl)benzothiazoles
(Figure 1) provide a case in point and illustrate the wider benefits
of a “chemistry-led” approach to drug discovery.3 The original
(non-fluorinated) lead compound in this class4 (1, DF 203) was
found to activate the arylhydrocarbon receptor (AhRa),5,6
inducing selective expression of the cytochrome P450 CYP1A1
in sensitive cancer cell lines (e.g., breast and ovarian) following
translocation to the nucleus.7,8 The major exportable 6-hydroxy-
lated metabolite of 1 from drug-CYP1A1 interaction was found
to be inactive and antagonistic to the antitumor activation
process,9 leading to the development of fluorinated benzothia-
zoles to thwart the deactivation process.10,11 Among the
fluorinated analogues, 2-(4-amino-3-methylphenyl)-5-fluoroben-
zothiazole (2, 5F 203) emerged as the lead compound and, based
on a favorable comparison with doxorubicin against a panel of
breast cancer xenografts,12 is now in phase 1 clinical trial in
the U.K. in the form of its water soluble L-lysyl amide prodrug
(Phortress).13 It is noteworthy that the 11C-methylated derivative
of one of the inactive hydroxylated metabolites has recently
re-emerged as an amyloid-affinic agent (3, [11C]PIB) in clinical
trials for early diagnosis of Alzheimer’s disease using positron
emission tomography (PET).14,15 Once again, metabolic stability
More pertinent to the present work, a related simple ben-
zothiazole 2-(3,4-dimethoxyphenyl)-5-fluorobenzothiazole (5,
PMX 610, formerly GW 610; NSC 721648) has been shown to
exhibit exquisitely potent (GI50 < 0.1 nM) and selective in vitro
antitumor properties in human cancer cell lines (e.g., colon, non-
small-cell lung and breast subpanels) of the National Cancer
Institute (NCI) 60 human cancer cell line screen.17 Lead
compound 5 was developed from the related antitumor 2-(4-
hydroxyphenyl)benzothiazole.18 Surprisingly, SAR studies in-
dicated that minor modifications of the dimethoxyphenyl group,
removal of the fluoro group, or its replacement with other
halogens had a profoundly dyschemotherapeutic effect with
respect to in vitro growth-inhibitory activity. Despite a selectivity
profile reminiscent of the fluorinated aminophenylbenzothiazoles
1 and 2, preliminary pharmacological investigations revealed
that 5 showed distinctive features in cell line selectivity and
mechanism of action.17 The synthesis of an 11C-labeled version
of 5 as a potential PET probe has been reported.19
In our earlier work we were intrigued by the fact that
benzothiazole (5) appeared to represent a “pinnacle” of antitu-
mor activity surrounded by a desert of inactive benzothiazole
analogues.17 Structurally related 2-phenylbenzimidazole deriva-
tives such as 6a,b have also been shown to be devoid of the
potent antitumor effects of 5.20 We have now reinvestigated
this idiosyncratic effect and report the synthesis of further
phenolic 2-arylbenzothiazoles not reported in our earlier work,
plus isosteric related 2-arylbenzoxazole and 4H-chromen-4-one
heterocycles, all bearing additional substituents in the hetero-
cycle moiety (generally fluoro) and one or more oxygen
substituents in the 2-aryl fragment. Thus, we anticipated that
the present work would reveal novel agents at least equiactive
to 5 in in vitro screens but also with reduced lipophilicity
consequent on replacing the benzothiazole bicycle with its
benzoxazole and 4H-chromen-4-one counterparts and related
* To whom correspondence should be addressed. For T.D.B. (biology):
phone, +44 1159 513419; fax, +44 1159 513412; e-mail, tracey.bradshaw@
nottingham.ac.uk. For A.D.W. (chemistry): phone, +44 2920 875800; fax,
+44 2920 874537; e-mail, WestwellA@cf.ac.uk.
†
Cardiff University.
Universita` degli Studi di Palermo.
Pharminox Ltd.
¶
§
∆
Present address: School of Pharmacy, University of London, 29-39
Brunswick Square, London, WC1N 1AX, U.K.
‡
School of Pharmacy, University of Nottingham.
School of Biology, University of Nottingham.
#
a Abbreviations: AhR, arylhydrocarbon receptor; CYP, cytochrome P450;
PET, positron emission tomography; NCI, National Cancer Institute; SAR,
structure-activity relationship; DMAP, 4-dimethylaminopyridine; MTT,
1-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide; R-NF,
R-naphthoflavone.
10.1021/jm800418z CCC: $40.75
2008 American Chemical Society
Published on Web 07/31/2008

5136 Journal of Medicinal Chemistry, 2008, Vol. 51, No. 16
Brief Articles
Figure 1. Potential therapeutic/diagnostic 2-arylbenzazoles.
Scheme 1a
a Reagents: (i) KOH(aq), reflux; (ii) substituted benzaldehyde, PPh3, p-TsOH, toluene, reflux.
structures (5 is highly lipophilic with a calculated log P of 4.2
[ChemDraw Ultra, version 9.0]).
2; see Supporting Information for details). Analytical and
spectroscopic data of intermediate benzanilides 11a-r and
benzoxazoles 12a-r are recorded in Supporting Information.
Synthesis of 2-Phenyl-4H-chromen-4-ones (18a,b). Related
syntheses from 4-fluoro- (16a) and 5-fluoro-2-acetylphenol (16b)
with 3,4-dimethoxybenzoyl chloride in dry pyridine afforded
intermediate esters (17a,b), which were used without further
purification and cyclized under basic conditions to 2-arylben-
zopyranones (18a,b) in 42% and 34% yield, respectively
(Scheme 2, experimental details in Supporting Information).
Chemistry
Synthesis of 2-Arylbenzothiazoles (9a-j). Substituted 2-ami-
nobenzothiazoles 7a-i were oxidatively ring-opened to the
corresponding bis(2-aminophenyl) disulfides 8a-i in aqueous
KOH according to our previous work.10 Cyclization to ben-
zothiazoles 9a-j was achieved by condensation with hydroxy-
benzaldehydes in refluxing toluene containing triphenylphos-
phine and catalytic p-toluenesulfonic acid (general method A,
Scheme 1; see Experimental Section). 1H NMR data for
intermediate disulfides 8a-i and spectroscopic data of 9a-j
are recorded in Supporting Information.
Synthesis of 2-Phenylbenzoxazoles (12a-r). 2-Phenylben-
zoxazoles were obtained in good overall yields via a simple
two-step procedure based on the methodology reported by
Evindar and Batey (general methods B and C, Scheme 2; see
Experimental Section).21 DMAP-promoted Schotten-Baumann
reaction of commercially available 5- or 4-fluoro-2-bromoaniline
(10a,b) with benzoyl chlorides bearing oxygen substituents
under basic conditions gave the intermediate o-bromobenzanil-
ides 11a-r, which were cyclized without further purification
by treatment with a catalyst system comprising copper (I) iodide
and 1,10-phenanthroline ligand, plus cesium carbonate as base,
to give the desired substituted 2-phenylbenzoxazole products
12a-r. The regiochemistry of cyclization was governed by the
position of the bromide leaving group, using a strategy similar
to that employed for the regiospecific synthesis of antitumor
fluorinated benzothiazoles.22
Biological Results and Discussion
In Vitro Growth-Inhibitory Assays. In earlier work we
showed that the human breast cancer cell lines MDA 468
(estrogen receptor negative, ER-) and MCF-7 (estrogen receptor
positive, ER+) employed in MTT assays following 3-day drug
exposure were suitable for study of SAR in the 2-arylbenzothia-
zole class of compound.17 Table 1 shows the antiproliferative
data for newly synthesized benzothiazoles 9a-j, benzoxazoles
12a-r, and chromenones 18a,b. The previously reported
potently active 2-(3,4-dimethoxyphenyl)-5-fluorobenzothiazole
5
17 and inactive 2-(3,4-dimethoxyphenyl)-5-fluorobenzimidazole
6a20 were used here as reference compounds.
It was previously noted that demethylation of one or other of
the methoxyl groups of lead 5 resulted in less active compounds;
however, we were intrigued to explore the activity of monohy-
droxylated 2-phenylbenzothiazoles bearing fluorine or related
substituents on the benzothiazole ring. Since demethylation could
potentially be an initial antitumor mechanistic step, it was desirable
to synthesize and evaluate biologically representative 2-hydroxy-
phenyl derivatives in the benzothiazole series. Accordingly com-
pounds 9a-j were tested for growth inhibitory activity in both
MCF-7 and MDA 468 human cancer cell lines (see Table 1). In
general the new benzothiazoles were more active against the ER
-ve breast cancer cell line MDA 468, giving GI50 values in the
submicromolar range for compounds bearing halogen (F, Cl, Br)
or trifluoromethyl substituents on the benzothiazole ring (9a-f).
An alternative synthesis of benzoxazole (12d) was achieved
starting from 4-fluoro-2-nitrophenol (13), which was reacted
with 3,4-dimethoxybenzoyl chloride in pyridine to yield the ester
(14), which was reduced by catalytic hydrogenation over 5%
Pd/C to yield amine (15). Cyclization of 15 was achieved in
boiling toluene containing catalytic p-toluenesulphonic acid to
give 2-(3,4-dimethoxyphenyl)-5-fluorobenzoxazole 12d (Scheme

Brief Articles
Journal of Medicinal Chemistry, 2008, Vol. 51, No. 16 5137
Scheme 2a
a Reagents: (i) NEt3, DMAP, CH2Cl2; (ii) CuI, 1,10-phenanthroline, Cs2CO3, DME, reflux; (iii) 3,4-dimethoxybenzoyl chloride, pyridine, room temp; (iv)
H2 (40 psi), 5% Pd/C, EtOH; (v) p-TsOH, toluene, reflux; (vi) 3,4-dimethoxybenzoyl chloride, pyridine, room temp; (vii) KOH, pyridine, 50 °C, then AcOH,
H2SO4, reflux.
In the MCF-7 (ER +ve) cell line the most active compounds were
found to be the fluorinated (3-hydroxyphenyl)- and (4-hydrox-
yphenyl)benzothiazoles derivatives 9a and 9b (GI50 of 0.57 and
0.40 µM, respectively). Compounds bearing ethyl, alkoxy, or
methylsulfonyl substitutents on the benzothiazole ring (9g-j) were
found to be much less active.
benzimidazole 6. We conclude, and remarkably so, that none
of the new compounds remotely approach benzothiazole (5) in
potency against these two breast cancer cell lines. This new
finding, that replacement of the (fluorinated) bicyclic benzothia-
zole moiety of 5 with benzoxazole and chromen-4-one conge-
ners impairs activity, builds on our earlier work that confirmed
similar dyschemotherapeutic effects consequent on modifying
the oxygen substituents on the 2-aryl group of 5.17
2-(3,4-Dimethoxyphenyl)-5-fluorobenzoxazole (12d), the di-
rect benzoxazole analogue of 5, exhibited submicromolar
potency against both cell lines (Table 1). Overall, compounds
in the benzoxazole series (12) were more active against the
MDA 468 cell line with IC50 varying over a >5000-fold range
(0.017-98.6 µM). Against the generally less sensitive MCF-7
cell line, benzoxazoles displayed a >250-fold range of activities.
It was difficult to discern what influence the position of the
fluoro group, or position and multiplicity of the methoxyl
groups, was having on growth-inhibitory activity; thus, 5-fluoro-
2-(2-methoxyphenyl)benzoxazole (12a) and its 6-fluoro analogue
(12j) had submicromolar potency against MCF-7, whereas
benzoxazole (12p) with a 6-fluoro group and 2,6-dimethoxy
substitution in the 2-aryl moiety was the least potent agent in
this class. 6-Fluorobenzoxazole compounds 12m and 12q
(bearing 3,4-dimethoxy and 3,4,5-trimethoxy substituents on the
phenyl ring) were found to be potently active on the MDA 468
cell lines, giving GI50 values of 17 and 37 nM, respectively.
The two 4H-chromen-4-one derivatives 18a,b gave rather
modest growth inhibitory activity in these two cell lines.
For the 5-fluoro heterocycles (6-fluoro in the benzopyranones)
with a 3,4-dimethoxy disposition in the 2-aryl group, activity
across the heterocyclic series was in the order benzothiazole >
benzoxazole . benzimidazole20 and chromen-4-one, with a 106-
fold difference between the most potent agent (5) and the inert
Cell Cycle Perturbations. Flow cytometric analysis of
cellular DNA content was used to determine cell cycle phase
perturbations during treatment of MDA 468 cells with 2-(3,4-
dimethoxyphenyl)-5-fluorobenzothiazole, benzoxazole, and ben-
zimidazole congeners 5, 12d, and 6a. Figure 2 charts the
percentage of cells in the different stages of cell cycle (pre-G1,
G1, S, and G2/M), data taken directly from the flow cytometric
DNA histograms (not shown). Consistent with growth inhibitory
potency, profound G2/M cell cycle arrest followed treatment of
MDA 468 cells with 5 (0.1 µM) over 24 h (Figure 2b, p <
0.03), compared with control (nontreated) MDA 468 cells
(Figure 2a). The G2/M block observed after 24 h in MDA 468
cells was typically maintained for 48 and 72 h (Figure 2b),
although treatment with higher concentrations of 5 (1 µM)
revealed decreasing numbers of cells arrested within G2/M as
events accrue in a pre-G1 apoptotic peak, consistent with DNA
damage induction (data not shown). At 0.1 µM, the less potent
analogues 12d and 6a failed to perturb MDA 468 cell cycle
profiles (24 h). However, following treatment of cells with 1
µM 12d (24 h), G2/M events were enhanced in MDA 468 cell
populations (Figure 2c). Noticeably in MDA 468 cells treated
with 1 µM 12d (24 h), events accumulated in S phase and an
apoptotic pre-G1 population emerged (Figure 2c). In line with

5138 Journal of Medicinal Chemistry, 2008, Vol. 51, No. 16
Brief Articles
Table 1. Activity of New Substituted 2-Phenyl-benzazoles and
Binding to the Aryl Hydrocarbon Receptor. (AhR). As part
of wider efforts to uncover mechanistic targets underpinning
the antitumor activity of the O-substituted 2-phenylbenzazole
series, we have examined the potential role of the aryl
hydrocarbon receptor (AhR) in mediating the potent antitumor
activity of lead benzothiazole 5. By use of a previously described
CRL:WI rat liver cytosol [3H]tetrachlorodibenzo-p-dioxin (TCDD)
displacement AhR assay23 (see Supporting Information for
details), an IC50 of 25 nM was obtained for benzothiazole 5 (Ki
) 6.8 nM). Lead compound 2-(3,4-dimethoxyphenyl)-5-fluo-
robenzothiazole 5 is therefore a high affinity ligand for the aryl
hydrocarbon receptor (AhR).
Depletion of 5 from Nutrient Media. Depletion of ben-
zothiazole 5 from nutrient media was monitored by HPLC across
a range of sensitive and insensitive cell lines (see Supporting
Information for details). Rapid depletion of 5 from nutrient
media supporting sensitive MCF-7 cells was observed; 50%
depletion occurred within 6 h. Insensitive breast cancer cell lines,
MDA 231 and MDA 435, were significantly less able to
sequester 5, and only 30% was depleted from the nutrient media
after 72 h. Sensitive colon cell lines KM12 and HCC 2998
consumed 5 from nutrient media less avidly than MCF-7 cells,
with approximately 50% depletion after 24 h (Supporting
Information).
-Chromen-4-ones against Human Breast Cancer Cell Linesa
GI50 (µM)b in cell linesc
compd
MCF-7
MDA 468
5
6a
9a
9b
9c
9d
9e
9f
9g
9h
9i
9j
12a
12b
12c
12d
12e
12f
12g
12h
12i
12j
12k
12l
12m
12n
12o
12p
12q
12r
18a
18b
<0.0001d
85.7e
0.57
0.40
13.8
54.0
26.5
4.16
>100
45.8
>100
62.3
0.36
39.5
22.7
0.83
2.16
45.4
58.1
16.0
61.4
0.82
35.1
41.0
3.53
69.9
3.72
90.7
1.09
19.2
83.4
27.9
<0.0001d
94.4e
0.20
0.21
0.10
0.50
0.28
0.28
>100
9.67
>100
42.2
0.27
0.87
0.76
0.33
0.54
0.79
22.0
2.58
14.5
1.19
2.02
9.55
0.017
3.29
0.46
98.6
0.037
6.77
20.6
0.45
Intriguingly, the AhR antagonist R-naphthoflavone (R-NF)24
drastically reduced sequestration of benzothiazole 5 by sensitive
MCF-7 cells, with <45% depletion of 5 from medium after
72 h. Correspondingly, R-NF (10 µM) diminished the activity
of 5 in MCF-7 and MDA 468 breast cancer cell lines, whereas
alone, 5 inhibited the growth of MCF-7 and MDA 468 cell lines
with GI50 < 1 nM (Table 1). In the presence of 10 µM R-NF,
5 elicited significantly weakened (>2000-fold) growth inhibitory
activity against MCF-7 and MDA 468 cells, where GI50 values
of 0.514 and 0.27 µM were achieved, respectively (Supporting
Information).
a Determined by MTT assay (72 h drug exposure); see biological
experimental section for details. b Compounds tested in triplicate, data
expressed as mean values of three independent experiments. c Cancer cell
line origin: MCF-7 (breast, ER +ve), MDA 468 (breast, ER -ve). d Data
previously obtained; see ref 17. e Data previously obtained; see ref 20.
Conclusions
The synthesis of a range of 2-phenyl-benzothiazoles, -ben-
zoxazoles, and -chromen-4-ones related to the potent antitumor
lead compound 2-(3,4-dimethoxyphenyl)-5-fluorobenzothiazole
5 has been accomplished. Evaluation against the MCF-7 and
MDA 468 breast cancer cell lines revealed compounds within
the new series with potent (submicromolar GI50) activity in both
cell lines (e.g., 9a,b and 12a,d). Although none of the new series
was able to recapitulate the potent antitumor properties of 5,
the new compounds were significantly more active than the
structurally related benzimidazoles.20 Antitumor potency ap-
peared to correlate with the emergence of a G2/M cell cycle
block. For lead compound 5, binding to the aryl hydrocarbon
receptor appeared to play an important role in growth inhibition.
Work continues to identify further potent antitumor compounds
from this intriguing class and to further delineate the antitumor
mode of action.
Experimental Section
Chemistry. Melting points were measured on a Griffin apparatus
and are uncorrected. Mass spectra were recorded on a Bruker
MicroTOF LC instrument. NMR spectra were recorded on a Bruker
AVANCE 500 MHz instrument; coupling constants (J) are in Hz.
Merck silica gel 60 (40-60 µM) was used for column chroma-
tography. All commercially available starting materials were used
without further purification.
General Method A for the Synthesis of 2-Arylbenzothiaz-
oles (9a-j). Substituted disulfides (8a-i, 0.71 mmol), prepared in
35-75% yields by hydrolysis of 2-aminobenzothiazoles (7a-i) in
Figure 2. Cell cycle analyses following exposure of mammary
carcinoma cells to 5, 12d or 6a. Representative bar charts illustrate
perturbations in cell cycle phases following treatment of MDA 468
cells with 100 nM 5 for 24-72 h (b), compared to nontreated control
(a), and 1 µM 12d or 6a for 24 h (c). Independent analyses were
performed g3 times, and 10 000 events per sample were analyzed.
inactivity against MDA 468 cells, benzimidazole 6a (1 µM,
24 h) effected neither perturbation of MDA 468 cell cycle nor
an apoptotic population.

Brief Articles
Journal of Medicinal Chemistry, 2008, Vol. 51, No. 16 5139
hydrocarbon receptor deficient MCF-7 cells. Br. J. Cancer 2003, 88,
refluxing aqueous KOH followed by air oxidation as previously
described,10 were heated under reflux in toluene (20 mL) containing
PPh3 (0.185 g, 0.71 mmol) and p-TsOH (2 mg) for 3 days. After the
mixture was cooled, solvent was removed in vacuo and the benzothia-
zoles were purified by column chromatography (EtOAc/hexane, 1:4).
1H NMR data for disulfides (8a-i) are given in Supporting Informa-
tion. Microanalytical data and spectroscopic properties for benzothia-
zoles 9a-j in given in Supporting Information.
General Method B for the Synthesis of o-Bromobenzanil-
ides (11a-r). Substituted benzoyl chloride (10 mmol) was added
to a mixture of 4- or 5-fluoro-2-bromoaniline (10a,b, 10 mmol),
triethylamine (11 mmol), and 4-dimethylaminopyridine (2 mmol)
in CH2Cl2 (20 mL), and the mixture was stirred at room temperature
for 18 h. The mixture was diluted with further dichloromethane
(30 mL), then washed with 1 M HCl (50 mL), and the aqueous
fraction was extracted with dichloromethane (50 mL). The com-
bined organic layers were dried (MgSO4), filtered, and concentrated
in vacuo. The crude product benzanilides were checked for purity
(1H NMR) and then used directly in the next step.
599–605.
(7) Chua, M.-S.; Kashiyama, E.; Bradshaw, T. D.; Stinson, S. F.; Brantley,
E.; Sausville, E. A.; Stevens, M. F. G. Role of CYP1A1 in modulation
of antitumor properties of the novel agent 2-(4-amino-3-methylphe-
nyl)benzothiazole (DF 203, NSC 674495) in human breast cancer cells.
Cancer Res. 2000, 60, 5196–5203.
(8) Brantley, E.; Trapani, V.; Alley, M. C.; Hose, C. D.; Bradshaw, T. D.;
Stevens, M. F. G.; Sausville, E. A.; Stinson, S. F. Fluorinated 2-(4-
amino-3-methylphenyl)benzothiazoles induce CYP1A1 expression,
become metabolized, and bind to macromolecules in sensitive human
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L. R.; Kaur, G.; Sausville, E. A.; Bradshaw, T. D.; Westwell, A. D.;
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General Method C for the Synthesis of 2-Phenylbenzox-
azoles 12a-r. To a mixture of o-bromobenzanilide 11a-r (5 mmol),
copper(I) iodide (47.5 mg, 0.25 mmol), 1,10-phenanthroline (94 mg,
0.5 mmol), and cesium carbonate (2.45 g, 7.5 mmol) was added DME
(50 mL) at room temperature, under a nitrogen atmosphere. The
mixture was heated under reflux for 18 h and then allowed to cool to
room temperature. The mixture was diluted with water (100 mL) and
then CH2Cl2 (200 mL). The organic layer was extracted, then dried
(MgSO4), filtered, and concentrated in vacuo. The crude product was
purified by column chromatography (diethyl ether/petroleum ether) to
give the required substituted 2-arylbenzoxazole in 61-91% yields.
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Acknowledgment. We thank the European Association for
Cancer Research (EACR) for the award of the Travel Fellowship
(to S.A.), and the Algerian Government for the award of a Ph.D.
studentship (to H.K.). Part of this work was supported by a
Program Grant to the Cancer Research U.K. Experimental
Cancer Chemotherapy Research Group (University of Notting-
ham),andadditionalsupportfromPharminoxLtd.isacknowledged.
Supporting Information Available: Spectroscopic and analyti-
cal data for new compounds and intermediate structures; microana-
lytical data (CHN) for new compounds; details on cell culture,
growth inhibitory assay, cell cycle analyses, aryl hydrocarbon
receptor binding assay, uptake/stability studies; two figures showing
depletion of 5 from nutrient media and effect of R-naphthoflavone
on growth and viability of MCF-7 and MDA 468 cells. This material
is available free of charge via the Internet at http://pubs.acs.org.
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