Cancer chemopreventive activity of sulforamate derivatives

Article abstract of DOI:10.1016/j.ejmech.2005.10.002

Chemoprevention can be defined as an intervention in the carcinogenic process by use of natural or synthetic substances. Induction of Phase II enzyme is an important mechanism of chemoprevention. In the present studies we have synthesized several derivati

Full text of DOI:10.1016/j.ejmech.2005.10.002

European Journal of Medicinal Chemistry 41 (2006) 121–124
http://france.elsevier.com/direct/ejmech
Short communication
Cancer chemopreventive activity of sulforamate derivatives
Robert M. Moriarty, Rajesh Naithani *, Jerome Kosmeder, Om Prakash
4500, Department of Chemistry, SES Building, 845, W. Taylor Street, University of Illinois at Chicago, Chicago 60607, IL, USA
Received 9 May 2005; received in revised form 30 September 2005; accepted 6 October 2005
Available online 21 November 2005
Abstract
Chemoprevention can be defined as an intervention in the carcinogenic process by use of natural or synthetic substances. Induction of Phase II
enzyme is an important mechanism of chemoprevention. In the present studies we have synthesized several derivatives of (+)(–) 4-methylsulfi-
nyl-1-(S-methyldithiocarbamyl)-butane (sulforamate) and evaluated their effectiveness as monofunctional inducer of the NAD(P)H Quinone oxi-
doreductase [quinone reductase (QR)] a phase II enzyme in cultured Hepa1c1c7 murine hepatoma cells. The cytotoxicity of some of the deriva-
tives was strongly reduced in comparison to [(–)-1-isothiocyanato-4(R)-(methylsulfinyl)butane] (sulforaphane). However, the induction potential
of these compounds was comparable to sulforaphane. On the basis of these results sulforamate derivatives can be regarded as simple, inexpensive
and readily available chemopreventive agents.
© 2005 Elsevier SAS. All rights reserved.
Keywords: Chemoprevention; Phase II enzymes; Sulforamate; Quinone oxidoreductase (QR); Monofunctional inducer
The term “cancer chemoprevention” coined by Sporn [1,2]
and coworkers in 1976 has been defined as a strategy for redu-
cing cancer mortality by the prevention, delay or reversal of
cancer by ingestion of dietary or pharmaceutical agents capable
of mediating the process of carcinogenesis [3]. In recent years
cancer prevention by natural products has received consider-
able attention. Much emphasis has been placed on dietary in-
take of certain fruits and vegetables that have shown to reduce
the risk of developing cancer. Numerous epidemiological stu-
dies have shown an association between reduced cancer risk
and increased intake of green yellow fresh vegetables [4–6].
Particularly noteworthy is the group of food plant generally
falls in the family Cruciferae and genus brassica, i.e. cauli-
flower, cabbage, brussel sprouts and broccoli [7].
animal models [8–10]. Feeding of vegetables induces enzymes
of xenobiotic metabolism and thereby accelerates the metabolic
disposal of the xenobiotics. The human body’s first lines of
defense against cancer are the Phase I and Phase II enzymes.
The metabolic activation and deactivation of carcinogens is
catalyzed by xenobiotic Phase I and II enzymes. By measure-
ment of induction of Phase II detoxifying enzymes, such as
quinone reductase (QR), glutathione S-transferase, UDP-glu-
coronosyl transferase and epoxide hydrolase, compounds may
be screened for anticarcinogenic activity10a. These enzymes
can convert electrophiles (ultimate carcinogens) to less reactive
compounds, which can in turn conjugate to sugars, glutathione
and sulfates resulting in less toxic and more excretable com-
pounds. Phase I enzymes are promoted by cytochromes P-450
that are mediated by the cytosolic Ah receptor (Aryl hydrocar-
bon). When ligands bind to the Ah receptors the complex is
transported to the nucleus and binds to the xenobiotic respon-
sive elements (XRE) upstream for P-450 genes10b. Phase I en-
zymes typically carry out oxidation and reduction reactions
that make carcinogens more water soluble, however they are
capable of activating compounds to electrophilic species,
which can damage DNA. These two families of enzyme help
It has already been established that three dietary compo-
nents brassinin (1, indole based dithiocarbamate), cyclobrassi-
nin (2) spirobrassinin (3) sulforaphane (4, aliphatic isothiocya-
nate) and 1.2-dithiol-3-thione (5) found in the Cruciferous
plants are capable of mediating chemopreventive activity in
* Corresponding author. Tel.: +1 312 996 9585; fax: +1 312 996 0431.
E-mail address: naithani@uic.edu (R. Naithani).
0223-5234/$ - see front matter © 2005 Elsevier SAS. All rights reserved.
doi:10.1016/j.ejmech.2005.10.002

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R.M. Moriarty et al. / European Journal of Medicinal Chemistry 41 (2006) 121–124
body protect itself from all types of carcinogens that routinely
enter the human body through the diet and the environment.
A key component in the understanding the initial events of
carcinogenesis is the reorganization of the fact that many of the
carcinogens are not chemically reactive per se but undergo me-
tabolic activation to form electrophilic reactants [10c].
Amount of carcinogens available represents a balance be-
tween activating and detoxifying reactions of Phase I and
Phase II enzymes, respectively [11–13]. This balance under
normal circumstances is genetically controlled but gets modu-
lated by variety of factors like age, hormone, and exposure to
drugs.
Scheme 1.
dithiocarbamate has been replaced by different groups (alipha-
tic chain, substituted benzyl) Scheme 1.
On the basis of structural similarities of brassinin to com-
pounds like indole-3-carbinol and indole-3-acetonitrile, it was
found to induce drug-metabolizing enzymes in cell culture. It
was found that Brassinin also induced the activity of P-450
isoenzymes. This particular induction is a risk factor in the ac-
tivation of carcinogens. Infact indole-3-carbinol was found to
induce liver carcinogenesis in rainbow trout when applied to
the post initiation stage [14]. Although indole-3-carbinol and
related compound demonstrate significant chemopreventive ac-
tivity, induction of Phase I metabolizing enzymes, is consid-
ered as a risk factor in the activation of carcinogens. On the
basis of this potential cancer risk of the indole based com-
pounds and relative toxicity of the isothiocyanates a hybrid
molecule was conceptualized. Isothiocyanate was replaced by
the dithiocarbamate moiety of brassinin thus exchanging the
indole ring with methyl sulfinyl butane side chain.
We anticipated that during metabolism the ability of these
moieties to act as a good leaving group would have effect on
the induction potential. Compound 10f (having para-fluoro
benzyl group instead of methyl in sulforamate) 10b and 10c
(having propyl and butyl group, respectively, in place of
methyl in sulforamate) have shown excellent activity. The
CD (concentration required to double QR induction) and CQ
(concentration required to quadruple QR induction) of these
compounds are comparable to sulforaphane. In addition to this
the reduced toxicity of these compounds make it far better che-
mopreventive agent than sulforaphane. The chemopreventive
index (CI) of these compounds is three to four times that of
Sulforaphane (Table 1).
Synthesis of 10 (Scheme 1) was carried out by addition of
sodium thiomethoxide to N-(4-bromobutyl)pthalimide that in
turn was obtained by treating phtalimide with 1,4, dibromobu-
tane. Subsequent oxidation with hydrogen peroxide resulted in
the formation of sulfoxide 8, which upon addition of hydra-
zines afforded the amines (9).
In a program directed towards discovery of the novel chemo
preventive agents and to evaluate the potential of test agents to
enhance the activity of the QR we currently report the synth-
esis and activity of six novel sulforamate derivatives. These
compounds are aliphatic analogs of Brassinin and show struc-
tural similarity to sulforaphane. The methyl group of the
The amine (9) was later treated with triethylamine, carbon
disulfide and then iodomethane to yield 10 in good yields.
Table 1
Compound number
Concentration required to double Concentration for 50% inhibition CQ concentration required to
CI
QR induction (CD) (μg/M)
of cell viability (IC50) (μg/M)
quadruple QR induction (μg/M)
Sulforaphane
0.06
0.08
0.07
0.2
0.07
0.1
1.7
9.9
7.9
17.9
1.5
2.5
6.1
0.8
0.55
0.94
0.24
1.5
0.6
1.4
28
10a
10b
10c
10d
10e
10f
123
112
90
21
25
0.05
0.06
0.5
0.4
122
13
10g

R.M. Moriarty et al. / European Journal of Medicinal Chemistry 41 (2006) 121–124
123
1. QR assay
0.95–1.01 (m, 3H, CH3), 1.62–1.69(m,2H,CH2) 1.85(m,4H,
CH2CH2), 2.57(s,3H,CH3), 2.70–2.76 (m,2H,CH2), 3.17–3.26
(m,2H,CH2), 3.74–3.76 (m,2H,CH2), 8.46(brs,1H,NH). Anal.
Calc. for C9H19NOS3 (253): C, 42.6; H, 7.50; N, 5.53, Found
C, 42.56; H, 7.51; N, 5.44.
10(c) Butyl-4-(methylsulfinyl)butylcarbamodithioate, yield:
54%(0.57 g), m.p. 68–70 °C 1H NMR (CDCl3): 1H NMR
(CDCl3): δ 0.86–0.92 (m,3H,CH3), 1.35–1.40 (m, 2H, CH2)
1.56–1.65 (m, 2H, CH2) 1.82 (m, 4H, CH2CH2), 2.57(s,3H,
CH3), 2.70–2.76 (m, 2H, CH2), 3.17–3.26 (m, 2H, CH2),
3.74–3.76 (m,2H,CH2), 8.46(brs,1H). Anal. Calc. for
C10H21NOS3 (267) C, 44.9; H, 7.80; N, 5.24, Found C,
44.76; H, 7.65; N, 5.97.
10(d) p-Nitro-benzyl-4-(methylsulfinyl)butylcarbamodithio-
ate, yield: 58% (0.802 g), m.p. 132–135 °C 1H NMR (CDCl3):
δ 1.86–1.91 (m, 4H,CH2CH2), 2.59 (s, 3H, CH3) 2.72–2.78 (m,
2H, CH2), 3.78–3.81(d,2H, CH2) 4.63 (s, 2H, benzylic CH2),
7.53 (d, 2H, Ar–H), 8.15 (d, 2 h, Ar–H) 8.06 (brs, 1H). Anal.
Calc. for C13H18N2O3S3 (346) C, 44.82; H, 5.2; N, 8.0, Found
C, 44.49; H, 5.14; N, 7.98.
10(e) p-Chloro-benzyl-4-(methylsulfinyl)butylcarbamodi-
thioate, yield: 54% (0.72 g), m.p. 92–94 °C 1H NMR
(CDCl3): δ 1.84 (m, 4H), 2.56 (s, 3H, CH3) 2.71–2.77 (m,
2H), 3.75–3.77 (d, 2H, CH2), 4.66–4.72 (s, 2H, benzylic
CH2), 7.56–7.9 (m, 4H, –ArH), 8.07 (brs, 1H, NH). Anal. Calc.
for C13H18ClNOS3 (335) C, 46.5; H, 5.37; N, 4.17, Found C,
46.45; H, 5.41; N, 4.22.
To evaluate the potency of the compounds (10a–10g) as
inducers of QR, murine Hepa1c1c7 cells were used as de-
scribed previously. In brief Hepa1c1c7 were plated at a density
of 1 × 104 cells per ml in 96 well plates. After preincubation of
for 24 hours the medium was changed Samples were added in
final concentration of 0.15–20 μg/ml. The cells were incubated
for 48 h. QR was determined by measuring NAD(P)H depen-
dent menadiol mediated reduction of the MTT [3(4,5-di-
methylthiazo-2-yl)-2,5-diphenyltetrazolium bromide]. Induc-
tion of the QR activity was calculated by comparing the QR
specific activity of compound treated cells with that of solvent
treated cells Enzyme activity was expressed as CD, concentra-
tion required to double QR induction. CI is obtained by divid-
ing IC values (Concentration for 50% inhibition of cell viabi-
lity) with CD values. The results have been tabulated in
Table 1.
On the basis of these encouraging results and in particular
reduced cytotoxicity of the sulforamate derivatives these can be
regarded as novel chemopreventive agents that require a de-
tailed further investigation.
2. Experimental
Cell cultures and supplements were purchased from Life
Technologies (Grand Island, New York). 1H NMR spectra
were taken on 400-MHz Bruker NMR spectrometer. All the
melting points have been taken in open capillaries and are un-
corrected.
10(f)
p-Fluoro-benzyl-4-(methylsulfinyl)butylcarbamodi-
thioate, yield: 50% (0.638 g), m.p. 72–73 °C 1H NMR
(CDCl3): δ 1.87 (m, 4H, CH2), 2.57(s, 3H, CH3) 2.72–2.75
(m, 2H), 3.76–3.79 (d, 2H, CH2), 4.52 (s, 2H, CH2), 7.53(d,
2H, Ar–H), 8.10 (d, 2H, Ar–H) 8.07 (brs, 1H). Anal. Calc. for
C13H18FNOS3 (319) C, 48.90; H, 5.66; N, 4.40, Found C,
48.40; H, 5.57; N, 5.03.
3. General procedure
The sulforamate derivatives were synthesized as outlined in
Scheme 1. Using modification of the literature procedure [15]
(+)(–)1-amino-4-(methylsulfinyl)butane (9) was synthesized
from N-(4-bromobutyl)phthalimide (6). Carbon disulfide
(0.3 g, 4 mmol,) was added dropwise to the dichloromethane
(40 ml) solution of 9 (0.5 g, 4 mmol) and imidiazole (0.8 g,
12 mmol) under Argon (0 °C). The mixture was stirred for
1 hour followed by dropwise addition of iodomethane. It may
be noted that alkyl iodide was used in preparation compounds
10a–10c while arylnenzyl bromides were used for the synthesis
of compounds 10d–10g. The resulting mixture was stirred for
2 hours. The bulk of the solution was removed in vacuo and
the residue taken in diethylether. The resulting mixture was
washed with 1.2 N HCl extracted with diethyl ether and dried
with MgSO4. The excess of solvent was removed and the re-
sidue was purified on silica flash gel. The fractions were con-
centrated and recrystallized from ether/petrol ether to yield 10a
as white solid. Other compounds 10b–10g were synthesized in
similar manner.
10(g)
Benzyl-4-(methylsulfinyl)butylcarbamodithioate,
1
yield: 53% (0.612 g), m.p. 88–89 °C, H NMR (CDCl3): δ
1.83–1.85 (m, 4H), 2.56 (s, 3H) 2.72–2.73 (m, 2H), 3.76–
3.79 (d, 2H, CH2), 4.52 (s, 2H, CH2), 7.23–7.37 (m, 5H, Ar–
H) 8.46 (brs, 1H, NH). Anal. Calc. for C13H19NOS3 (289) C,
51.8; H, 6.3; N, 4.65, Found C, 49.21, H 5.97; N, 4.72.
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