The Synthesis and Biological Evaluation of Anithiactin A/Thiasporine C and Analogues

Article abstract of DOI:10.1071/CH15461

The synthesis of anithiactin A has been achieved in four steps. Several closely related analogues were synthesised and their biological activity against colon and breast cancer cell lines evaluated. Anithiactin A was found not to be cytotoxic even at a hi

Full text of DOI:10.1071/CH15461

RESEARCH FRONT
CSIRO PUBLISHING
Aust. J. Chem. 2015, 68, 1829–1833
Full Paper
http://dx.doi.org/10.1071/CH15461
The Synthesis and Biological Evaluation of
Anithiactin A/Thiasporine C and Analogues
A C
,
A C
,
A
Richard A. Lamb,
Michael P. Badart,
Brooke E. Swaney,
A
B
A D
,
Sinan Gai, Sarah K. Baird, and Bill C. Hawkins
A
Department of Chemistry, University of Otago, PO Box 56, Dunedin 9054,
New Zealand.
B
Department of Pharmacology and Toxiciology, University of Otago, PO Box 56,
Dunedin 9054, New Zealand.
C
These authors contributed equally to this work.
D
Corresponding author. Email: bhawkins@chemistry.otago.ac.nz
The synthesis of anithiactin A has been achieved in four steps. Several closely related analogues were synthesised and their
biological activity against colon and breast cancer cell lines evaluated. Anithiactin A was found not to be cytotoxic even
at a high concentration (100 mM); however, two 4-substituted phenyl thiazoles were found to be moderately cytotoxic
at 10 mM. Based on these results, 4-substitution on the phenyl group appears to be critical for cytotoxicity. However, the
exact electronic and structural requirements are unclear.
Manuscript received: 31 July 2015.
Manuscript accepted: 7 September 2015.
Published online: 5 October 2015.
Introduction
NHMe
S
The structural diversity and vast biological activity of natural
products is especially evident when examining clinically used
drugs. Approximately 50 % of all clinically used drugs are
either natural products, analogues thereof, or directly inspired
by natural products.[1] Marine actinomycetes account for ,7000
of the natural compounds listed in the Dictionary of Natural
Products. These actinomycetes are a rich source of bioactive
secondary metabolites with a wide range of properties including
antibiotic, antitumour, and immunosuppressive.[2]
OMe
OMe
OMe
S
N
N
O
OMe
O
1
2
Fig. 1. Anithiactin A (1) and the potent cytotoxic thiazole 2.
Recently, anithiactin A (1) was isolated from streptomyces
sp., which was found in a sample of intertidal mudflat sediment
collected on the southern coast of the Korean peninsula.[3] At
approximately the same time, the same molecule was isolated
from the marine derived actinomycetospora chlora SNC-032
and named thiasporine C.[4] Anithiactin A (thiasporine C)
contains a 2-phenylthiazole core which has previously been
shown to be a useful scaffold in the design of compounds with
anti-cancer properties.[5] In particular, methoxybenzoyl phe-
nylthiazoles have been shown to possess low nanomolar activity
with selectivity for both melanoma and prostate cancer cell lines
(2, Fig. 1)[6] and preliminary investigations on their mode of
action suggests they operate via inhibition of tubulin polymeri-
sation.[6] While anithiactin A was found to possess moderate
activity against acetylcholinesterase,[3,7] no significant biologi-
cal activity was found against four non-small-cell lung cancer
cell lines.[4] Notably, no data has been provided for their activity
against other cancer types.
synthesis of anithiactin A which could also allow ready access to
analogues. While the previous synthesis provided rapid access
to anithiactin A, a potential limitation lies in the limited number
of commercially available primary aryl amides. We believe
greater pre-existing structural diversity could be found using
commercially available aromatic carboxylic acids.
Our general approach to the key 2-phenyl thiazole motif
is outlined in Fig. 2. Disconnection through the thiazole ring
unveiled the amide 4 which could be further disconnected
to cystine methyl ester (6) and benzoic acid (5) (Fig. 2). The
advantage of using cystine is that the disulfide functional group
provides protection of the reactive thiol functional group while
maintaining complete atom economy. An additional benefit to
this approach is the plethora of commercially available aromatic
carboxylic acids which could provide rapid access to analogues
for a medicinal chemistry program.
Results and Discussion
In light of previous work establishing the cytotoxicity of the
2-phenylthiazoles motif against cancer cells,[6] and with only
one reported synthesis of anithiactin A,[3] we sought to develop a
In a forward sense, the synthesis began with treatment of
N-Boc anthranilic acid with sodium hydride followed by methyl
Journal compilation Ó CSIRO 2015
www.publish.csiro.au/journals/ajc

1830
R. A. Lamb et al.
O
H2N
R
R
OMe
R
S
S
O
S
ꢀ
OH
SPG
HN
N
OMe
O
CO2Me
CO2R
H2N
O
3
4
5
6
Fig. 2. General strategy to access 2-phenyl thiazoles.
R
O
OMe
S
R
N
O
6
, PyBOP
N
H
N
COOH
DCM, NEt3
S
N
H
O
N
N
35 %
R
O
Boc
MeO
8a,b
7a R ꢁ Boc
R ꢁ H
b
K2CO3, 4 Å
molecular sieves
S
OMe
HN
1. PBu3, MeOH
2. TiCl4, DCM
OMe
HN
S
DMF
N
O
O
34 %
66 %
9
1
Scheme 1.
iodide to provide the commercially available compound 7a
(Scheme 1). Treatment of the carboxylic acid with standard
breast cancer cell line MDA-MB-231, and the non-transformed
mesenchymal stem cell line RCB2157. However, 4-substituted
phenyl thiazoles 12c and 13c did have cytotoxic effects in all cell
types and at all-time points tested in a concentration- and time-
dependent manner. The levels of cytotoxicity at 10 mM in the
MCF7 breast cancer cells and the HT29 colon cancer cells are
shown in Table 1.
From this small set of analogues it appears that substitution
in the 2-position of the phenyl ring is detrimental to activity,
probably due to excessive twisting of the thiazole out of the
plane of the phenyl group. Substitution of the phenyl ring in the
4-position is clearly optimal for activity, but the electronic and
precise structural requirements are unclear at this stage. The
synthesis of more analogues will be required to unravel the
structure–activity relationship.
1-ethyl-3-(30-(dimethylamino)propyl)carbodiimide
(EDCI)/
1-hydroxybenzotriazole (HOBt) coupling protocols failed to
deliver the amide 8a; however, benzotriazol-1-yl-oxytripyrro-
lidinophosphonium hexafluorophosphate (PyBOP) was found
to afford the bis-amide 8a in 35 % yield. Protection of the amine
with the Boc group was found to be unnecessary with a similar
yield obtained for the coupling of the free amine 7b with cystine.
Reduction of the disulfide bond by treatment with tributylpho-
sphine in methanol,[8] provided the corresponding thiol, which
was used in the subsequent reaction without further purification.
Titanium(IV) mediated cyclodehydration of the thiol forged the
thiazoline ring and concomitantly removed the Boc group to
deliver 9 in 66 % yield.[9]† Subsequent oxidation under literature
conditions provided anithiactin A (1) in 34 % yield, which was
spectroscopically identical to that reported for the material
isolated from the natural sources.[3,4]
With a synthetic procedure in place to access the 2-phenyl
thiazole core, a small series of electronically diverse aromatic
carboxylic acids (5a–d) were subjected to the reaction condi-
tions outlined above with the following exception. The forma-
tion of amides 10a–d was conducted using standard EDCI/
HOBt coupling conditions as this cleanly provided the corre-
sponding compounds without the need for chromatographic
purification. Following this sequence the unsubstituted phenyl
2-thiazole 12a, the electron poor ortho and para-nitrophenyl
2-thiazoles 12b and 12c and the electron rich 3,5-dimethoxy-
phenyl 2-thiazole 12d were all obtained in moderate yield
(Scheme 2). Iron mediated reduction of 12b and 12c provided
the anilines 13b and 13c, respectively, in good yield (Scheme 3).[10]
Compounds 1, 12a, b, d, and 13b were found to be non-toxic
up to concentrations of 100 mM in the colon cancer cell line
HT29, the breast cancer cell line MCF7, the triple negative
Conclusions
A robust synthesis of anithiactin A has been achieved in four
steps, this synthetic procedure was then applied to the synthesis
of five analogues. The work suggests that substituents at the
4-position of the phenyl ring is important for cytotoxicity. Work
on creating a series of structurally diverse analogues at this
position is underway and will be reported in due course.
Experimental
General
Thin-layer chromatography (TLC) was performed on ALUGRAM
aluminium-backed UV254 silica gel 60 (0.20 mm) plates.
Compounds were visualised with either p-anisaldehyde or 20 %
w/w phosphomolybdic acid in ethanol. Column chromatogra-
phy was performed using silica gel 60. Infrared spectra were
recorded on a Bruker Optics Alpha ATR FT-IR spectrometer.
High-resolution mass-spectra (HRMS) were recorded on a
†As previously noted,[8] under these reaction conditions racemisation can be minimised through conducting the reaction at lower temperatures. Since this
stereocentre is destroyed in the subsequent oxidation we did not monitor for racemisation.

Synthesis of 2-Phenyl Thiazoles and Anithiactin A
1831
O
OMe
S
O
6, EDCI, HOBt
H
N
COOH
R
DCM
R
N
H
R
S
51–83 %
O
O
5a R ꢁ Ph
MeO
b R ꢁ 2-NO2Ph
c R ꢁ 4-NO2Ph
d R ꢁ 3,5-diOMePh
10a–d
OMe
1. PBu3, MeOH
2. TiCl4, DCM
S
OMe
S
K2CO3, 4 Å molecular sieves
DMF
N
R
N
O
R
O
38–76 %
34–65 %
11a–d
12a–d
Scheme 2.
O
O
OMe
Amide 8a
S
N
S
H2N
Fe powder, AcOH,
)))))))
O2N
A solution of 7a (177 mg, 1.17 mmol), pyBOP (582 mg,
1.17 mmol), and Et3N (179 mL, 1.28 mmol) in DCM (5 mL) was
stirred for 15 min to which was added L-cystine dimethyl ester
dihydrochloride (200 mg, 0.586 mmol). The mixture was stirred
overnight under an inert atmosphere. The mixture was con-
centrated under vacuum, and taken up in EtOAc (10 mL). The
organic layer was washed with H2O (10 mL), NaHCO3 (10 mL),
brine (10 mL), dried over MgSO4, filtered, and concentrated
under vacuum. The product was purified using column chro-
matography with EtOAc–petroleum eluent, which afforded the
title compound as a white amorphous solid (300 mg, 35 % yield).
dH (400 MHz, CDCl3) 7.70 (d, J 7.6, 1H), 7.45 (td, J 7.7, 1.6,
1H), 7.40 – 7.07 (m, 4H), 5.02 (s, 1H), 3.76 (s, 3H), 3.29 (m, 2H),
3.19 (s, 3H), 1.33 (s, 9H). dC (100 MHz, CDCl3) 170.5, 141.4,
131.7, 129.5, 128.1, 127.3, 80.8, 52.8, 51.9, 40.5, 29.7, 28.2.
HRMS (ESI) m/z 757.2507; calcd for C34H46N4O10S2Na [M þ
Naþ] 757.2548. nmax/cmꢀ1 3337, 2960, 1743, 1664, 1152, 730.
OMe
N
13b (ortho), 86 %
13c (para), 80 %
12b,c
Scheme 3.
Table 1. Compounds 12c and 13c are cytotoxic towards HT29 colon
cancer cells and MCF7 breast cancer cells. The cells were treated with
the compounds at 10 lM for 24–72 h and an MTT assay conducted to
assess the quantity of remaining viable cells. Cell viability is expressed as
a percentage of vehicle-only treated control cells and the standard
deviation is shown
Cell type
HT29
Treatment time
Cell viability ꢁ s.d.
12c
13c
24 h
48 h
72 h
24 h
48 h
72 h
76.7 ꢁ 1.5
52.5 ꢁ 3.8
52.5 ꢁ 3.0
40.2 ꢁ 1.9
37.8 ꢁ 1.4
35.5 ꢁ 2.2
82.3 ꢁ 1.6
73.1 ꢁ 3.2
54.7 ꢁ 4.8
74.3 ꢁ 2.1
57.3 ꢁ 2.0
50.9 ꢁ 3.9
General Procedure for EDCI/HOBt Amide Coupling
A suspension of the benzoic acid (1.17 mmol) and L-cystine
dimethyl ester dihydrochloride (341 mg, 0.586 mmol) in anhy-
drous DCM (5 mL) was cooled to 08C to which was added Et3N
(179 mL, 1.28 mmol), HOBt (17 mg, 0.117 mmol), and EDCI
(181 mg, 1.17 mmol). The resulting suspension was warmed to
room temperature and stirred overnight, eventually turning into
a clear solution. The mixture was diluted with EtOAc (10 mL)
and washed successively with HCl (1 M, 10 mL), saturated
NaHCO3 (10 mL), and brine (10 mL). The organic phases were
dried over MgSO4, filtered, and concentrated under vacuum to
afford the corresponding amide.
Compound 10a was obtained as a white amorphous solid
(60 % yield). dH (400 MHz, CDCl3) 7.82 (d, J 7.1, 2H), 7.51
(ddd, J 8.5, 8.5, 2.3), 7.42 (t, J 7.5, 2H), 7.10 (d, J 7.2, 1H), 5.08
(m, 1H), 3.78 (s, 3H), 3.35 (d, J 5.1, 2H). dC (100 MHz, CDCl3)
170.9, 167.1, 133.4, 132.0, 128.6, 127.2, 52.9, 52.3, 40.9. HRMS
(ESI) m/z 499.0926; calcd for C22H24N2O6S2Na [M þ Naþ]
499.0968. nmax/cmꢀ1 3320, 3067, 2919, 1740, 1579, 1266, 1016,
702, 418.
MCF7
Bruker microTOFQ mass spectrometer using an electrospray
ionisation (ESI) source in either the positive or negative modes.
1H NMR spectra were recorded at either 400 MHz on a Varian
400-MR NMR system or at 500 MHz on a Varian 500 MHz
AR premium shielded spectrometer. All spectra were recorded
from samples in CDCl3 at 258C in 5 mm NMR tubes. Chemical
shifts are reported relative to the residual chloroform singlet at
7.26 ppm. Resonances were assigned as follows: chemical shift
(multiplicity, coupling constant(s), number of protons, assigned
proton(s)). Multiplicity abbreviations are reported by the con-
ventions: s (singlet), d (doublet), dd (doublet of doublets), ddd
(doublet of doublet of doublets), t (triplet), td (triplet of doub-
lets), q (quartet), qd (quartet of doublets), and m (multiplet).
Proton decoupled 13C NMR spectra were recorded at either
100 MHz on a Varian 400-MR NMR system or at 125 MHz on a
Varian 500 MHz AR premium shielded spectrometer under the
same conditions as the 1H NMR spectra. Chemical shifts have
been reported relative to the CDCl3 triplet at 77.16 ppm.
Dichloromethane (DCM) was dried using a PURE SOLV MD-6
solvent purification system. All other solvents and reagents were
used as received
Compound 10b was obtained as a white amorphous solid
(51 % yield). dH (400 MHz, CDCl3) 8.02 (m, 1H), 7.71–7.61 (m,
1H), 7.62–7.54 (m, 2H), 6.90 (d, J 7.3, 1H), 5.07 (m, 1H), 3.82 (s,
3H), 3.40 (d, J 4.9, 2H).dC (100 MHz, CDCl3) 170.4, 166.1,
146.4, 133.8, 132.0, 130.7, 128.8, 124.5, 53.0, 52.3, 40.4. HRMS
(ESI) m/z 589.0658; calcd for C22H22N4O10S2Na [M þ Naþ]
589.0670. nmax/cmꢀ1 3263, 2925, 1740, 1528, 1347, 732.

1832
R. A. Lamb et al.
Compound 10c was obtained as a white amorphous solid
5.27 (t, J 9.1, 1H), 3.82 (s, 3H), 3.81 (s, 6H), 3.73–3.58 (m, 2H).
dC (100 MHz, CDCl3) 171.1, 160.7, 134.2, 106.5, 104.5, 78.0,
55.6, 52.8, 35.4. HRMS (ESI) m/z 304.0592; calcd for
C15H15NOSNa [M þ Naþ] 304.0614. nmax/cmꢀ1 2950, 1737,
1583, 1424, 1153, 1061, 684.
(56 % yield). dH (400 MHz, CDCl3) 8.27 (d, J 8.9, 2H), 7.98
(d, J 8.9, 2H), 7.18 (d, J 7.1, 1H), 5.15–4.97 (m, 1H), 3.82
(s, 3H), 3.37 (dd, J 5.0, 2.3, 2H).dC (100 MHz, CDCl3) 170.5,
165.2, 149.9, 138.9, 128.4, 123.9, 53.1, 52.5, 40.5. HRMS (ESI)
m/z 589.0620; calcd for C22H22N4O10S2Na [M þ Naþ] 589.067.
n
max/cmꢀ1 3284, 2924, 1739, 1520, 1342, 719.
General Procedure for Thiazoline Oxidation
Compound 10d was obtained as a white amorphous solid
To a solution of thiazoline (0.139 mmol) dissolved in DMF
˚
(3 mL) was added 4 A molecular sieves (200 wt-%) and anhy-
(83 % yield). dH (400 MHz, CDCl3) 7.03 (d, J 7.3, 1H), 6.95
(d, J 2.3, 2H), 6.59 (t, J 2.3, 1H), 5.04 (m, 1H) 3.81 (s, 6H), 3.79
(s, 3H), 3.34 (d, J 5.1, 2H). dC (100 MHz, CDCl3) 170.8, 166.9,
160.9, 135.6, 105.1, 104.1, 55.6, 52.9, 52.3. HRMS (ESI) m/z
619.1373; calcd for C26H32N2O10S2Na [M þ Naþ] 619.1391.
drous K2CO3 (0.419 mmol) and the suspension stirred at 808C
for 4 h. The mixture was cooled to room temperature and par-
titioned between H2O (5 mL) and EtOAc (5 mL) and the aque-
ous layer was extracted with EtOAc (3 ꢂ 5 mL). The combined
organic layers were washed with brine, dried over MgSO4,
filtered, and concentrated under vacuum. Purification by col-
umn chromatography yielded the corresponding thiazole.
Compound 1 was obtained was a white amorphous solid
(34 % yield). dH (400 MHz, CDCl3) 8.4 (s, 2H), 8.0 (s, 1H), 7.6
(dd, J 7.8, 1.5, 1H), 7.3 (ddd, J 8.6, 7.1, 1.5, 1H), 6.8 (dd, J 8.4,
1.0, 1H), 6.7 (td, J 7.6, 1.1, 1H), 4.0 (s, 4H), 3.0 (s, 5H).
Compound 12a was obtained as a white amorphous solid
(56 % yield). dH (400 MHz, CDCl3) 8.17 (s, 1H), 8.00 (dd, J 6.6,
3.1, 2H), 7.53–7.38 (m, 3H), 3.98 (s, 3H). dC (100 MHz, CDCl3)
169.0, 161.9, 147.7, 132.7, 130.7, 129.0, 127.3, 126.9, 78.8,
52.5.
Compound 12b was obtained a yellow amorphous solid
(65 % yield). dH (400 MHz, CDCl3) 8.18 (s, 1H), 8.00 (dd, J
6.7, 2.9, 2H), 7.49–7.42 (m, 3H), 3.98 (s, 3H). dC (100 MHz,
CDCl3) 163.1, 161.6, 147.5, 132.7, 132.1, 131.1, 129.3, 127.7,
124.7, 77.2, 52.6. HRMS (ESI) m/z 287.0087; calcd for
C11H8N2O4SNa [M þ Naþ] 287.0097. nmax/cmꢀ1 3071, 2921,
2851, 1718, 1680, 1528, 1289, 1211, 704, 545.
n
max/cmꢀ1 3291, 2953, 1744, 1593, 1206, 1158, 421.
General Procedure for Disulfide Reduction and
Cyclodehydration
To a solution of the disulfide (0.811 mmol) in MeOH (5 mL) was
added n-tributylphosphine (0.444 mmol) and the reaction was
monitored by TLC. Upon consumption of the starting material
the mixture was concentrated under vacuum and filtered through
a plug of silica to remove any tributylphosphine oxide. The
filtrate was concentrated under vacuum and subsequently taken
up in DCM (5 mL), to which was added TiCl4 (2.43 mmol, 1 M
in DCM) dropwise over 5 min at 08C. The mixture was stirred
at room temperature for 4 h and then quenched with saturated
NH4Cl(aq). The aqueous phase was extracted with EtOAc
(3 ꢂ 5 mL) and the combined organic layers were washed with
brine (10 mL), dried over MgSO4, filtered, and concentrated
under vacuum. Purification by column chromatography eluting
with EtOAc/petroleum ether afforded the corresponding
thiazoline.
Compound 12c was obtained as a yellow amorphous solid
(60 % yield). dH (400 MHz, CDCl3) 8.32 (dd, J 8.9, 2.1, 2.1, 2H),
8.30 (s, 1H), 8.18 (dd, J 8.9, 2.1, 2.1, 2H), 4.00 (s, 3H). dC
(100 MHz, CDCl3) 165.9, 161.5, 148.9, 148.5, 138.1, 128.8,
127.7, 124.4, 52.7. HRMS (ESI) m/z 287.0075; calcd for
C11H8N2O4SNa [M þ Naþ] 287.0097. nmax/cmꢀ1 3090, 2923,
2851, 1718, 1522, 1343, 1209, 851, 752, 638.
Compound 9 was obtained as a white amorphous solid (66 %
yield). dH (400 MHz, CDCl3) 7.49 (dd, J 7.9, 1.6, 1H), 7.33 (ddd,
J 8.6, 7.1, 1.6, 1H), 6.73 (d, J 8.4, 1H), 6.70–6.59 (m, 1H), 5.33
(t, J 8.8, 1H), 3.83 (s, 3H), 3.52 (m, 2H), 2.93 (s, 3H). HRMS
(ESI) m/z 273.0653; calcd for C12H14N2O2SNa [M þ Naþ]
273.0668. dC (100 MHz, CDCl3) 172.0, 171.5, 148.9, 132.9,
132.8, 114.9, 110.7, 78.3, 52.7, 33.6, 29.8.
Compound 12d was obtained as a white amorphous solid
(64 % yield). dH (400 MHz, CDCl3) 8.17 (s, 1H), 7.14 (d, J 2.3,
2H), 6.56 (s, 1H), 3.98 (s, 4H), 3.87 (s, 8H). dC (100 MHz,
CDCl3) 168.9, 161.9, 161.1, 147.5, 134.5, 127.5, 104.9, 103.1,
55.6, 52.5. HRMS (ESI) m/z 302.0429; calcd for
C13H13NO4SNa [M þ Naþ] 302.0457. nmax/cmꢀ1 3112, 2952,
2836, 1734, 1708, 1594, 1444, 1222, 747, 672.
Compound 11a was obtained as a white amorphous solid
(76 % yield). dH (400 MHz, CDCl3) 7.87 (m, 1H), 7.48 (ddd,
J 7.3, 7.3, 1.7, 1H), 7.41 (m, 1H), 5.29 (t, J 9.1, 1H), 3.83 (s, 3H),
3.76–3.59 m, 1H). dC (100 MHz, CDCl3) 163.1, 161.5, 148.5,
147.4, 132.8, 132.1, 131.1, 129.3, 127.7, 124.7, 52.6. HRMS
(ESI) m/z 244.0394; calcd for C11H11NO2SNa [M þ Naþ]
244.0403. nmax/cmꢀ1 2950, 1737, 1446, 1227, 1199, 931, 688.
Compound 11b was obtained as a white amorphous solid
(41 % yield). dH (400 MHz, CDCl3) 7.96 (d, J 7.8, 1H), 7.67–
7.62 (m, 2H), 7.62–7.56 (m, 1H), 5.28 (t, J 9.2, 1H), 3.84 (s, 3H),
3.90–3.71 (m, 2H). dC (100 MHz, CDCl3) 170.4, 168.0, 132.9,
131.2, 130.5, 128.4, 124.5, 78.4, 52.9, 36.9. HRMS (ESI) m/z
General Procedure for Nitro Reduction
To a solution of the nitro aromatic compound (0.174 mmol) in a
mixture of glacial acetic acid (0.60 mL), ethanol (0.6 mL), and
water (0.3 mL) was added reduced iron powder (0.870 mmol).
The resulting suspension was exposed to ultrasonic irradiation
for 1 h at 308C and monitored by TLC. The reaction mixture was
filtered and the iron residue was washed with EtOAc (2 ꢂ 5 mL).
The reaction mixture was partitioned between 2 M KOH (5 mL)
and the basic layer further extracted with EtOAc (3 ꢂ 5 mL).
The combined organic extracts were washed with brine (10 mL),
dried over MgSO4, and concentrated under reduced pressure.
Purification by column chromatography using EtOAC/petro-
leum ether as eluent yielded the title compound.
289.0239; calcd for C11H10N2O4SNa [M þ Naþ] 289.0253. nmax
/
cmꢀ1 2952, 1736, 1527, 1347, 1201, 945, 709.
Compound 11c was obtained as a white amorphous solid
(43 % yield). dH (400 MHz, CDCl3) 8.27 (d, J 8.9, 2H), 8.04
(d, J 8.9, 2H), 5.35 (t, J 9.3, 1H), 3.86 (s, 3H), 3.95–3.61 (m, 1H).
dC (100 MHz, CDCl3) 170.6, 169.4, 149.6, 137.9, 129.6, 123.7,
78.4, 53.0, 35.9. HRMS (ESI) m/z 289.0233; calcd for
C11H10N2O4SNa [M þ Naþ] 289.0253. nmax/cmꢀ1 2956,
1738, 1521, 1347, 1203, 850, 690.
Compound 11d was obtained as a white amorphous solid
(38 % yield). dH (400 MHz, CDCl3) 7.01 (s, 1H), 6.56 (s, 1H),
Compound 13b was obtained as a brown amorphous solid
(86 % yield). dH (400 MHz, CDCl3) 8.07 (s, 1H), 7.61 (dd, J 7.9,

Synthesis of 2-Phenyl Thiazoles and Anithiactin A
1833
1.4, 1H), 7.22 (ddd, J 8.3, 7.2, 1.5, 1H), 6.84 (dd, J 8.2, 0.8, 1H),
6.77–6.73 (m, 1H), 3.95 (s, 2H). dC (100 MHz, CDCl3) 169.6,
161.7, 146.4, 145.1, 131.4, 129.2, 125.3, 117.5, 52.3. HRMS
(ESI) m/z 257.0354; calcd for C11H10N2O2SNa [M þ Naþ]
257.0355. nmax/cmꢀ1 3433, 3316, 2954, 2921, 1719, 1614, 1486,
1219, 754.
Compound 13c was obtained as a brown amorphous solid
(80 % yield). dH (500 MHz, CDCl3) 8.06 (s, 1H), 7.81 (d, J 8.5,
2H), 6.70 (d, J 8.4, 2H), 3.97 (s, 3H). dC (125 MHz, CDCl3)
172.2, 164.8, 151.6, 149.8, 131.2, 128.5, 126.0, 117.4, 55.0.
HRMS (ESI) m/z 257.0341; calcd for C11H10N2O2SNa [M þ
Naþ] 257.0355. nmax/cmꢀ1 3479, 3323, 2952, 2923, 1717, 1618,
1467, 1211, 775.
concentration of each compound. No significant toxicity
was found.
Statistical Analysis
The results are presented as mean ꢁ standard deviation (s.d.)
of three independent experiments. Absorbance values were
normalized to the vehicle only control (DMSO) for each
experiment.
Supplementary Material
1H NMR and 13C NMR spectra of all compounds are available
on the Journal’s website.
Acknowledgements
Cell Lines and Cell Culture
R.A.L. and S.G. thank the University of Otago for Ph.D. scholarships. The
authors thank Ian Stewart and Jenny Pentelow for NMR and mass spec-
trometry technical support.
MDA-MB-231 and MCF7 breast cancer cells were obtained
from Prof. R. Rosengren. HT29 colon cancer cells were pur-
chased from CellBank Australia and the immortalised bone
marrow-derived mesenchymal stem cell line RCB2157 (MSC)
was from the Riken BioResource Center through the National
Bio-Resource Project of the MEXT, Japan. Cell lines were cul-
tured in Dulbecco’s Modified Eagle Medium (DMEM) with 5 or
10 % (for the MSCs) heat inactivated fetal bovine serum (FBS),
100 units mLꢀ1 penicillin, and 100 mg mLꢀ1 streptomycin. Cells
were incubated at 378C in humidified conditions with 5 % CO2.
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DMSO at 10 % was used as a positive control and resulted
in ,70–75 % cell death in each assay. DMSO was also used as a
vehicle control, added at the volume used for the highest