Synthesis and biological evaluation of benzyl styrylsulfonyl derivatives as potent anticancer mitotic inhibitors

Article abstract of DOI:10.1016/j.bmcl.2011.03.041

We herein report the synthesis, biological activity and structure activity relationship of derivatives of benzylstyrylsulfone, benzylstyrylsulfine and benzylsulfonyl-N-phenylacetamide. A lead compound 7 represents a new class of mitotic inhibitors that demonstrates potent anti-proliferative activity and selectively induces cancer cell apoptosis while sparing non-transformed lung fibroblast.

Full text of DOI:10.1016/j.bmcl.2011.03.041

Bioorganic & Medicinal Chemistry Letters 21 (2011) 3066–3069
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Synthesis and biological evaluation of benzyl styrylsulfonyl derivatives
as potent anticancer mitotic inhibitors
Osama Chahrour a, Ashraf Abdalla a, Frankie Lam a, Carol Midgley b, Shudong Wang a,
⇑
a School of Pharmacy and Centre for Biomolecular Sciences, University of Nottingham, Nottingham NG7 2RD, UK
b Department of Life Sciences, The Open University, Milton Keynes MK7 6AA, UK
a r t i c l e i n f o
a b s t r a c t
Article history:
We herein report the synthesis, biological activity and structure activity relationship of derivatives of
benzylstyrylsulfone, benzylstyrylsulfine and benzylsulfonyl-N-phenylacetamide. A lead compound 7 rep-
resents a new class of mitotic inhibitors that demonstrates potent anti-proliferative activity and selec-
tively induces cancer cell apoptosis while sparing non-transformed lung fibroblast.
Received 27 January 2011
Revised 9 March 2011
Accepted 9 March 2011
Available online 17 March 2011
Crown Copyright Ó 2011 Published by Elsevier Ltd. All rights reserved.
Keywords:
Mitotic inhibitor
Polo-like kinase
Serine/threonine kinase
Anticancer therapy
Sodium (E)-{N-[2-methyloxy-5-(2,4,6-trimethoxy-styryl sulfo-
nyl)methylenephenyl]amino}acetate (ON 01910.Na, Onconova
Therapeutics Inc., Fig. 1) is a novel anticancer agent currently in
phase I clinical trials in patients. ON 01910 is a cell-cycle inhibitor
and selectively causes mitotic arrest by creating spindle abnormal-
ities and abnormal centrosome localization and fragmentation
leading to apoptosis in cancer cells. It has been shown to inhibit
PLK1 pathway activity at a nanomolar range in a substrate-depen-
dent and ATP-independent manner, although targeting other
kinases has also been reported.1,2 This compound inhibits a broad
spectrum of human tumour cell growth with GI50 values in the
nanomolar range and is active in a number of human xenografts
in mice.3,4 Currently, the drug is in several phase I and II clinical tri-
als in adult patients with a variety of solid tumours as well as
hematological malignancies.5–8 Anti-tumour activity was observed
in all phase I trials. Recent phase I studies in human B-cell chronic
lymphocytic leukaemia (CLL) demonstrated that ON 01910.Na
selectively induced apoptosis in all CLL samples tested and reduced
PLK1 activity in the leukeamic cells3 ON 01910.Na is currently also
being tested in phase I combination therapy in patients with solid
tumors.
O
R
O
H
N
O
O
NaO
S
O
O
O
O
ON 01910.Na
Ph
S
H
N
R
Ph
S
O
Ph
S
R
O
O
O
O
II
I
III
Figure 1. Structures of ON 01910.Na and the designated derivatives.
activity relationship established has provided guidance for us to
rapidly progress our drug discovery programme. Here, we report
the synthesis and biological evaluation of analogue benzylstyryl-
sulfones, benzylstyrylsulfines and benzylsulfonyl-N-phenylaceta-
mides (Class-I, -II and -III, Fig. 1). This study suggests that the
benzylstyrylsulfinyl chemotype offers great potential for develop-
ment of anti-cancer agents.
The synthetic chemistry employed to prepare Class I–III
compounds is outlined in Scheme 1. The synthesis started from 2-
(4-methoxy-3-nitrobenzylthio)acetic acid 1, which can be obtained
by halogenation of 1-methoxy-4-methyl-2-nitrobenzene followed
by treatment with 2-mercaptoacetic acid.14,15 2-(4-Methoxy-3-nitro-
benzylsulfonyl)acetic acid 2 or 2-(4-methoxy-3-nitrobenzylsulfi-
nyl)acetic acid 5 were obtained by chemoselective oxidation of 1.
Doebner modification of Knoevenagel condensation16 between 2 or
5 with substituted aromatic aldehyde in pyridine and catalytic
amounts of piperidine yielded the corresponding (E)-1-methoxy-2-
Our efforts to develop small molecule cell-cycle inhibitors for
cancer therapy has resulted in the development of several classes
of CDK and Aurora kinase inhibitors.9–13 In the process of designing
novel class PLK1 inhibitors we prepared and evaluated the biolog-
ical activity of ON 01910 and several derivatives. The structure
⇑
Corresponding author. Tel.: +44 1158466863; fax: +44 01159513412.
E-mail address: shudong.wang@nottingham.ac.uk (S. Wang).
0960-894X/$ - see front matter Crown Copyright Ó 2011 Published by Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2011.03.041

O. Chahrour et al. / Bioorg. Med. Chem. Lett. 21 (2011) 3066–3069
3067
H
R'
N
S
R
b
O
O
O
O
4
c
R
R'
O
O2N
CO2H
O2N
O
S
CO2H
S
a
S
O
O
O
O
3
1
O
2
d
R
e
H2N
O2N
S
O
R
O2N
b
CO2H
S
S
O
O
O
O
O
7
5
6
Scheme 1. Reagents and conditions: (a) H2O2, AcOH, 50 °C, 6 h, 98%; (b) aromatic aldehyde, cat. piperidine, pyridine, rt, 36 h, 19–50%; (c) (i) Sulfurous dichloride, EtOAc,
reflux, 40 min, 100%; (ii) aniline, anhydrous THF, reflux, 3 h, 80–91%; (d) H2O2, AcOH, 0 °C, 6 h, 95%; (e) Fe0, AcOH/MeOH (1:2), reflux, 3 h, 95–96%.
Table 1
Structure and growth inhibitory activity of selected compounds against human tumour cancer cells
Compd
Structure
Cytotoxicity, 72 h MTT (GI50
HCT-116
, l
M)a
R
R0
T47D
MDA-468
MCF-7
MRC-5
3a
3b
3c
3d
3e
3f
3g
3h
3i
2,4,6-(OMe)3
2,3,4-(OMe)3
2,6-(OMe)2
3,5-(OMe)2
2,4,6-(OMe)3
2,3,4-(OMe)3
2,6-(OMe)2
3,5-(OMe)2
2,4,6-(OMe)3
2,4,6-(OMe)3
H
NO2
NO2
NO2
NO2
NH2
NH2
NH2
NH2
NHCOMe
NHCH2CO2H
NO2
NO2
NO2
NO2
NO2
NH2
NH2
NT
NT
0.66
27.85
10.22
>30
<0.01
5.31
0.02
0.54
0.15
0.05
>30
7.91
18.80
>30
>30
>30
0.88
>30
13.71
>30
<0.01
5.95
0.04
0.49
0.35
0.05
>30
>30
>30
>30
>30
>30
>30
<0.01
2.91
>0
>30
>30
>30
NT
5.90
0.05
0.53
NT
<0.01
>30
>30
>30
>30
>30
>30
>30
0.06
21.89
5.46
16.46
0.03
3.48
0.06
0.52
NT
0.02
>30
>30
>30
>30
>30
>30
0.08
>30
17.09
>30
0.81
0.71
>30
27.96
>30
>30
>30
>30
>30
>30
3j
4a
4b
4c
4d
4e
4f
2,4,6-(Me)3
2,4,6-(OMe)3
2,5-(OMe)2
NO2
>30
>30
> 30
<0.01
H
4g
7
2,4,6-(Me)3
2,4,6-(OMe)3
>30
<0.01
—
a
Values are means of at least three independent determinations. NT: not tested.
nitro-4-(styrylsulfonylmethyl)benzene 3a, 3b, 3c and 3d (R0 = NO2,
Scheme 1 and Table 1) or (E)-1-methoxy-2-nitro-4-(styrylsulfinylm-
ethyl)benzene 6 (R = 2,4,6-trimethoxyl). Reduction of 3a, 3b, 3c or 3d,
as well as 6 resulted in their respective anilino derivatives 3e, 3f, 3g,
3h and 7. Acylation of 3e (R0 = NH2, R = 2,4,6-(OMe)3) with acylchlo-
ride afforded 3i (R0 = NHCOMe, R = 2,4,6-(OMe)3, Table 1). Treatment
of 3e with ethyl 2-bromoacetate in the presence of sodium acetate
followed by hydrolysis in aqueous sodium carbonate yielded 3j
(R0 = NHCH2COOH, R = 2,4,6-(OMe)3, e.g. ON 01910).
To prepare chemotype-III sulfonyl-N-phenyl acetamides (Fig. 1)
2-(4-methoxy-3-nitrobenzylsulfonyl)acetic acid 2 was converted
to 2-(4-methoxy-3-nitrobenzylsulfonyl)acetyl chloride. The later,
treated with various substituted anilines, resulted in 4a, 4b, 4c,
4d and 4e. Reduction of 4a and 4b in the presence of tin chloride
generated 4f and 4g, respectively.
3e and 3j (ON 01910) were the most potent anti-proliferative
agents with GI50 below 0.1 M; the 2,4,6-trimethoxy substituted
l
styryl moiety seems important for the optimum potency observed.
Interestingly, MRC-5 non-transformed cells appeared insensitive
towards 3g and 3h, being <280- and <80-fold less cytotoxic com-
pared with the cancer cells tested. Replacement of the amino group
on benzyl moiety in 3f, 3g and 3h with nitro group resulting in cor-
responding analogue 3b, 3c and 3d abolished the activity. Com-
pound 3a which contained the favourable 2,4,6-trimethoxylstyryl
moiety gained some degree of activity compared to its analogues
3b–3d. Replacement of the sulfonyl in 3e with sulfinyl afforded
(E)-2-methoxy-5-((2,4,6-trimethoxystyrylsulfinyl)methyl)aniline
7, which showed the excellent anti-tumour activity, being compa-
Anti-proliferative activity was assessed against colorectal
carcinoma HCT-116, breast carcinoma MCF-7, MDA-468, MDA-
231 and T74D using a standard 72-h MTT cytotoxicity assay.17
The compounds were also tested against non-transformed lung
fibroblast MRC-5. The results are summarized in Table 1.
Table 2
Time course MTT assay in MDA-468 cells
Time (h)
Cytotoxicy, MTT (GI50, l
M)a
3j
7
24
48
72
0.601 0.065
0.302 0.021
0.014 0.003
0.559 0.095
0.137 0.023
<0.01
Most (E)-2-methoxy-5-(styrylsulfonylmethyl)anilines, particu-
larly 3e, 3g, 3h, 3i and 3j, exhibited potent anti-proliferative
activity with GI50 <1
lM in cancer cells, except compound 3f
a
Represent as the mean of three independent assay SD.
(R = 2,3,4-(OMe)3) which has only modest activity (GI50 <5
lM).

3068
O. Chahrour et al. / Bioorg. Med. Chem. Lett. 21 (2011) 3066–3069
Figure 2. Cell cycle analysis of MDA-468 cells following treatment with compound 3j or 7 for a period of 20 h at the concentrations shown. Vertical bars represent the
mean SD of three independent experiments. Values significantly (p <0.05) different from DMSO vehicle control are marked with an asterisk (⁄).
rable to 3e. Significantly, compound 7 selectively killed cancer cells
while sparing non-transformed MRC-5 cells. Replacement of sty-
rylsulfonyl with sulfonyl-N-phenylacetamide was poorly tolerated
and compounds 4a–4g were completely inactive in the assay.
The structure activity relationship analysis suggests that the
styrylbenzylsulfonyl or styrylbenzylsulfinyl moiety is essential
for potency, replacement with sulfonyl-N-phenylacetamide show-
ing a dramatic loss in activity. Substitutions on the styryl ring
system were generally found to be tolerated, although 2,4,6-tri-
methoxyl was the most favourable function. Substitutions with
electron donating group on the benzyl ring system may be amena-
ble to optimization.
The primary cellular mode of action of 7 was investigated when
compared with 3j. The time-dependent growth inhibitory activity
was examined in MDA468 cells. As shown in Table 2, both com-
Figure 4. Analysis of stability under MCF-7 and MRC-5 cell culture conditions using
HPLC and HR-MS methods. Vertical bars represent the mean SD of two indepen-
dent experiments.
pounds exhibited comparable cytotoxicity and increased potency
with extended time. We next examined the cell-cycle effects.18
Analyses by flow cytometry exposed severe perturbation of cell-cy-
ble staining18 in MDA-468 cells following treatment with either 3j
cle progression following treatment of cells with P0.5
7 (Fig. 2). 20 h post treatment of MDA-468 cells with 3j at 0.5
(GI50) and 1
events—58% and 84%, respectively. This was consistent with ON
01910 mechanism of action described previously.15,3 Compound
7 demonstrated a similar cell-cycle profile; treatment of the cells
lM of 3j or
or 7 at 0.5
induced significant numbers of apoptotic cells, effectively starting
from 0.5 M in a dose-dependent manner (Fig. 3).
To investigate cellular metabolic stability compound 7 (1
lM, 1 lM and 10 lM for a period of 20 h. Both 3j and 7
lM
l
M (2 ꢀ GI50) resulted in accumulation of G2/M
l
lM)
was incubated in cell culture medium in the presence or absence
of MCF-7 and MRC-5 cells respectively. Aliquots were taken at
the time points and stabilised. After centrifugation, the samples
were analysed by HPLC and HR-MS. As shown in Fig. 4. Compound
7 was stable under MCF-5 and MRC5 cell culture conditions and no
conversion to 3j was detected.
with 7 at 0.5
l
M (GI50) and 1.0
l
M (2 ꢀ GI50) causing 77% and
85% cells with G2/M DNA content, respectively. Induction of apop-
tosis by the compounds was further analyzed by annexinV/PI dou-
In conclusion, a series of benzylstyrylsulfonyl derivatives and
benzylsulfonyl-N-phenylacetamides were prepared19 and the struc-
ture activity relationships were established. (E)-2-Methoxy-5-
((2,4,6-trimethoxystyrylsulfinyl)methyl)aniline 7 possessed potent
anti-proliferative activityagainst cancercelllines, being comparable
to 3j. Compound 7 showed similar cell-cycle effects to 3j and was
capable of inducing cancer cells to apoptosis.
Acknowledgments
O. Chahrour and A. Abdalla thank University of Damascus and
Islamic Development Bank (IDB) for their respective studentships.
References and notes
1. Gumireddy, K.; Reddy, M. V.; Cosenza, S. C.; Boominathan, R.; Baker, S. J.;
Papathi, N.; Jiang, J.; Holland, J.; Reddy, E. P. Cancer Cell 2005, 7, 275–286.
2. Strebhardt, K. Nat. Rev. Drug Discov. 2010, 9, 643–660.
3. Schoffski, P. Oncologist 2009, 14, 559–570.
4. Chun, A. W.; Cosenza, S. C.; Taft, D. R.; Maniar, M. Cancer Chemother. Pharmacol.
2009, 65, 177–186.
Figure 3. Apoptosis of MDA-468 cells following treatment with 3j or 7 for 20 h at
concentrations indicated. The percentage of cells undergoing apoptosis was defined
as the sum of early apoptosis (annexin V-positive cells) and late apoptosis (annexin
V-positive and PI-positive cells). Vertical bars represent the mean SD of three
independent experiments. Values significantly (p <0.05) different from DMSO
vehicle control are marked with an asterisk (⁄).
5. Reagan-Shaw, S.; Ahmad, N. IUBMB Life 2005, 57, 677–682.

O. Chahrour et al. / Bioorg. Med. Chem. Lett. 21 (2011) 3066–3069
3069
6. Jimeno, A.; Li, J.; Messersmith, W. A.; Laheru, D.; Rudek, M. A.; Maniar, M.;
Hidalgo, M.; Baker, S. D.; Donehower, R. C. J. Clin. Oncol. 2008, 26, 5504–5510.
7. Jimeno, A.; Chan, A.; Cusatis, G.; Zhang, X.; Wheelhouse, J.; Solomon, A.; Chan,
F.; Zhao, M.; Cosenza, S. C.; Ramana Reddy, M. V.; Rudek, M. A.; Kulesza, P.;
Donehower, R. C.; Reddy, E. P.; Hidalgo, M. Oncogene 2009, 28, 610–618.
8. Prasad, A.; Park, I. W.; Allen, H.; Zhang, X.; Reddy, M. V.; Boominathan, R.;
Reddy, E. P.; Groopman, J. E. Oncogene 2009, 28, 1518–1528.
9. Wang, S.; McClue, S. J.; Ferguson, J. R.; Hull, J. D.; Stokes, S.; Parsons, S.;
Westwood, R.; Fischer, P. M. Tetrahedron: Asymmetry 2001, 12, 2891–2894.
10. Wang, S.; Wood, G.; Meades, C.; Griffiths, G.; Midgley, C.; McNae, I.; McInnes,
C.; Anderson, S.; Jackson, W.; Mezna, M.; Yuill, R.; Walkinshaw, M.; Fischer, P.
M. Bioorg. Med. Chem. Lett. 2004, 14, 4237–4240.
11. Wang, S.; Meades, C.; Wood, G.; Osnowski, A.; Anderson, S.; Yuill, R.; Thomas,
M.; Mezna, M.; Jackson, W.; Midgley, C.; Griffiths, G.; Fleming, I.; Green, S.;
McNae, I.; Wu, S. Y.; McInnes, C.; Zheleva, D.; Walkinshaw, M. D.; Fischer, P. M.
J. Med. Chem. 2004, 47, 1662–1675.
12. Wang, S.; Griffiths, G.; Midgley, C. A.; Barnett, A. L.; Cooper, M.; Grabarek, J.;
Ingram, L.; Jackson, W.; Kontopidis, G.; McClue, S. J.; McInnes, C.; McLachlan, J.;
Meades, C.; Mezna, M.; Stuart, I.; Thomas, M. P.; Zheleva, D. I.; Lane, D. P.;
Jackson, R. C.; Glover, D. M.; Blake, D. G.; Fischer, P. M. Chem. Biol. 2010, 17,
1111–1121.
13. Wang, S.; Midgley, C. A.; Scaerou, F.; Grabarek, J. B.; Griffiths, G.; Jackson, W.;
Kontopidis, G.; McClue, S. J.; McInnes, C.; Meades, C.; Mezna, M.;
Plater, A.; Stuart, I.; Thomas, M. P.; Wood, G.; Clarke, R. G.; Blake, D. G.;
Zheleva, D. I.; Lane, D. P.; Jackson, R. C.; Glover, D. M.; Fischer, P. M. J. Med.
Chem. 2010.
14. Reddy, P. E.; Reddy, R. M. V.; Bell, S. C.; Onconova Therapeutics, Inc. Temple
University, USA, WO2003072062.
15. Reddy, M. V.; Mallireddigari, M. R.; Cosenza, S. C.; Pallela, V. R.; Iqbal, N. M.;
Robell, K. A.; Kang, A. D.; Reddy, E. P. J. Med. Chem. 2008, 51, 86–100.
16. Inokuchi, T.; Kawafuchi, H. J. Org. Chem. 2006, 71, 947–953.
methanol, sodium carbonate (0.40 g) and 4-(bromomethyl)-1-methoxy-2-
nitrobenzene (0.62 g, 2.5 mmol) was added, and the mixture was refluxed for
1 h, cooled, and spilled over ice (300 g). The pH was adjusted to 3 by addition of
2 N HCl aq to give a yellow precipitate. Recrystallisation from Pet/EtOAc
afforded 5 as pale yellow crystals (0.56 g, 88% yield). mp 128–131 °C; 1H NMR
(DMSO-d6) d 3.14 (s, 2H, CH2), 3.83 (s, 2H, CH2), 3.91 (s, 3H, OCH3) 7.33 (d,
J = 8.4 Hz, 1H, Ph-H), 7.61 (dd, J = 8.4, 2.0 Hz, 1H, Ph-H), 7.83 (d, J = 2.0 Hz, 1H,
Ph-H), 12.62 (s, 1H, CO2H). 13C NMR (DMSO-d6) d 33.04, 34.39, 57.15, 114.86,
125.58, 130.97, 135.45, 139.29, 151.54, 171.65. HRMS (ESI-) m/z 256.0065
[Mꢁ1]ꢁ, C10H11NO5S requires 257.0358.
2-(4-Methoxy-3-nitrobenzylsulfinyl) acetic acid (6): solution of 2-(4-methoxy-3-
nitrobenzylthio) acetic acid (0.26 g, 1 mmol) in 20 mL of acetic acid was cooled
to 0 °C on an ice bath. Hydrogen peroxide 35% w/v (0.15 mL, 1.5 mmol) was
added and the mixture was stirred at 0 °C for 6 h. After concentration the
reaction mixture was purified by flash chromatography using EtOAc to yield 6
as a pale yellow solid (0.26 g, 95% yield); mp 67–68 °C; 1H NMR (DMSO-d6) d
3.52 (d, J = 14.4 Hz, 1H, CH2), 3.88 (d, J = 14.4 Hz, 1H, CH2), 3.94 (s, 3H, OCH3),
4.11 (d, J = 12.8 Hz, 1H, CH2), 4.28 (d, J = 12.8 Hz, 1H, CH2), 7.40 (d, J = 8.8 Hz,
1H, Ph-H), 7.61 (dd, J = 8.8, 2.17 Hz, 1H, Ph-H), 7.85 (d, J = 2.17 Hz, 1H, Ph-H).
13C NMR (DMSO-d6) d 55.12, 55.82, 57.24, 115.02, 123.69, 127.08, 136.97,
139.33, 152.35, 167.91. HRMS (ESI-) m/z 272.0130 [Mꢁ1]ꢁ, C10H11NO6S
requires 273.0307.
(E)-2-Methoxy-5-((2,4,6-trimethoxystyrylsulfinyl)methyl)aniline
(7):
2-(4-
methoxy-3-nitrobenzylsulfinyl)acetic acid (0.55 g, 2 mmol) and 2,4,6-
trimethoxybenzaldehyde (0.49 g, 2.5 mmol) were dissolved in mixture of
anhydrous pyridine (10 mL) and anhydrous piperidine (few drops). After
stirring at rt for 36 h the mixture was evaporated to give gummy brown
residue which was dissolved in ethyl acetate (20 mL) and washed with 2 N
NaOH aq (10 mL), 2 N HCl aq (10 mL), and distilled water (10 mL). After being
dried over anhydrous MgSO4, the organic solution was evaporated to afford a
mixture
of
(E)-1,3,5-trimethoxy-2-(2-(4-methoxy-3nitrobenzylsulfinyl)-
17. Mosmann, T. J. Immunol. Methods 1983, 65, 55–63.
vinyl)benzene. Without further purification the compound was dissolved in
hot methanol (10 mL) and treated with Iron powder (10 mmol) in acetic acid
(5 mL). After refluxing for 3 h, the mixture was treated with ammonia solution
(2 N aq) and extracted with EtOAc (20 mL). The organic layer was concentrated
and purified by flash chromatography (EtOAc) to give 7 as a pale brown solid
(0.30 g, 40% yield); mp 117–119 °C; 1H NMR (Acetone-d6) d 3.16 (s, 3H, OCH3),
3.85 (s, 2H, CH2), 3.87 (s, 3H, OCH3), 3.90 (s, 6H, OCH3 ꢀ 2), 6.29 (s, 2H, Ph-H),
6.61(dd, J = 8.0, 2.0 Hz, 1H, Ph-H), 6.73 (d, J = 2.0 Hz, 1H, Ph-H), 6.80 (d, J
18. Cell cycle analysis: Exponentially growing cells were seeded at a density of
4 ꢀ 105 and incubated at 37 °C in a humidified, 5% CO2 atmosphere overnight.
Following 20 h incubation with compound at appropriate concentrations, the
cells were collected. Cell pellets were washed once with cold PBS and re-
suspended in 0.4 ml hypotonic fluorochrome solution. Cell cycle status was
analysed using a Beckman Coulter EPICS-XL MCL™ flow cytometer and data
analyzed using EXPO32™ software.
AnnexinV/propidium iodide (PI) staining: was used to quantitatively determine
the percentage of apoptotic cells. Cells (4 ꢀ 105) per well were treated with
compounds after overnight culture. Sample preparation, staining, and analysis
were performed following the protocol provided by BD (BD Bioscience).
19. Synthesis of lead compound 7: 2-(4-Methoxy-3-nitrobenzylthio) acetic acid (5):
8.0 Hz, 1H, Ph-H), 7.26 (d, J = 15.6 Hz, 1H, CH), 7.45 (d, J = 15.6 Hz, 1H, CH). 13
C
NMR (Acetone-d6) d 54.90, 54.99, 55.31, 61.28, 90.61, 105.50, 110.17, 115.84,
118.91, 123.50, 125.30, 131.25, 137.80, 147.50, 160.34, 162.50. HRMS (ESI+) m/
z 377.9233 [M+1]+, C19H23NO5S requires 377.1297. Anal. RP-HPLC (Kromasil
C18 column, 250 ꢀ 4.6 mm, H2O/CH3CN containing 0.3% CF3COOH):
tR = 2.4 min, purity >99%.
To
a solution of 2-mercaptoacetic acid (0.35 mL, 5 mmol) in 100 mL of