Synthesis and antitumor activity of tetrahydrocarbazole hybridized with dithioate derivatives

Article abstract of DOI:10.3109/14756366.2014.922554

The present study reported the synthesis of tetrahydrocarbazoles hybridized with dithioate derivatives. Three series were synthesized namely alkyl dithiocarbonates (4a-d), heterocyclic dithiocarbamates (6a-g) and dialkyl dithiocarbamate (7). The synthesized compounds were tested in vitro on human breast adenocarcinoma cell line (MCF7) and the human colon tumor cell line (HCT116). Most of the synthesized compounds exploited potent antitumor activity, especially compound 6f [4-chlorophenylpiperazine derivative], which showed cytotoxic activity against MCF7 superior to doxorubicin with IC50 value of 7.24 nM/mL.

Full text of DOI:10.3109/14756366.2014.922554

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ISSN: 1475-6366 (print), 1475-6374 (electronic)
J Enzyme Inhib Med Chem, Early Online: 1–8
2014 Informa UK Ltd. DOI: 10.3109/14756366.2014.922554
!
Synthesis and antitumor activity of tetrahydrocarbazole hybridized with
dithioate derivatives
Hala Bakr El-Nassan
Pharmaceutical Organic Chemistry Department, Faculty of Pharmacy, Cairo University, Cairo, Egypt
Abstract
Keywords
The present study reported the synthesis of tetrahydrocarbazoles hybridized with dithioate
derivatives. Three series were synthesized namely alkyl dithiocarbonates (4a–d), heterocyclic
dithiocarbamates (6a–g) and dialkyl dithiocarbamate (7). The synthesized compounds were
tested in vitro on human breast adenocarcinoma cell line (MCF7) and the human colon tumor
cell line (HCT116). Most of the synthesized compounds exploited potent antitumor activity,
especially compound 6f [4-chlorophenylpiperazine derivative], which showed cytotoxic activity
against MCF7 superior to doxorubicin with IC50 value of 7.24 nM/mL.
Antitumor activity, dithiocarbamates, HCT116,
MCF7, tetrahydrocarbazole
History
Received 31 March 2014
Revised 30 April 2014
Accepted 5 May 2014
Published online 3 June 2014
Introduction
pH22. The resulting CS2 mediates protein cross-linking23.
Besides, the free thiol groups of dithiocarbamates can oxidize
During the past decade, dithiocarbamates have received consid-
erable attention owing to their diverse and excellent biological
activities. Thus, this class of compounds has been reported to
possess antibacterial1–3, antiviral4,5, anti-inflammatory6, anti-
histaminic7, antioxidant8 as well as antitumor activity2,8–17. The
story of dithiocarbamates started with the discovery of the natural
product brassinin (I, Figure 1). Brassinin is a phytoalexin first
isolated from cabbage and was reported as antifungal and antiviral
glutathione through a glutathione peroxidase-like activity24,25
.
Recently, the inhibitory activity of dithiocarbamates against
EGFR, ErbB-2 kinases9 and carbonic anhydrase10,26,27 was
reported and the combination of dithiocarbamates with EGFR9
or antifolates11) was reported to exert synergistic antitumor effect.
These after-mentioned trials utilized molecular hybridization
approach, in which two or more drug pharmacophores are
covalently combined into a single molecule. Molecular hybrid-
ization approach represents an effective tool to design novel and
highly active drugs since these hybridized molecules can act on
agent that displayed potential cancer preventive activity4,5,18
.
Structural modification of brassinin led to the identification of a
series of dithiocarbamate derivatives which proved to exhibit
various biological activities. For example, the heterocyclic
dithiocarbamate derivative [pyrrolidinedithiocarbamate, PDTC
(II)] is a well known antioxidant. PDTC was reported to strongly
inhibit the replication of human rhinoviruses and coxsackie virus
myocarditis. PDTC also showed inhibitory activity against murine
colon adenocarcinoma bearing mice through the inhibition of
multiple targets and thus can overcome drug resistance28,29
.
Many literature reported the molecular hybridization and
anticancer activity of dithiocarbamates with thalidomide8,
butenolide12, 1,2,3-triazoles14,15
,
quinazolines9,11,16,17
,
chro-
mones13, sulphonamides10 and saccharin derivatives2. However,
to the best of our knowledge, their molecular hybridization with
tetrahydrocarbazoles to afford anticancer agents have not been
reported before.
nuclear factor kB in the tumor tissue19,20
.
Dithiocarbamates were previously thought to exert their
antibacterial and antitumor activities through their reaction with
HS-groups of physiologically important enzymes in which the
alkyl group of the dithioester was transferred to the HS-function
of the enzyme21.
Later on, it was found that dialkyl dithiocarbamates and
heterocyclic dithiocarbamates are unstable at low pH and they
decompose rapidly to produce CS2 and a dialkylamine or cyclic
secondary amine. Whilst, heterocyclic dithiocarbamates, e.g.
pyrrolidinedithiocarbamate (PDTC), are more stable at serum
Recently, considerable interest has been focused on tetrahy-
drocarbazoles which were reported to display broad spectrum of
biological activities especially antitumor30–32 activity.
Tetrahydrocarbazole ring can be considered as an isostere to
b-carboline ring which is present in many naturally occurring
anticancer agents, such as the vinca alkaloids, vincamine (III) and
(–)-eburnamonine (IV) (Figure 1) isolated from the Madagascar
periwinkle (Catharanthus roseus)33–35. Although (–)-eburnamo-
nine (IV) was devoid of anticancer activity even at the high dose
of 100 M, its synthetic analogue 15-methylene-eburnamonine (V)
displayed in vitro micromolar activity against prostate and
myeloma cell lines36. Furthermore, the marine alkaloid
Eudistomin K (VI), isolated from the Caribbean ascidian
Eudistoma olivaceum, demonstrated potent antitumor activity
Address for correspondence: Hala Bakr El-Nassan, Pharmaceutical
Organic Chemistry Department, Faculty of Pharmacy, Cairo University,
33 Kasr El-Aini street, Cairo 11562, Egypt. Tel: 00202-23632245. Fax:
00202-23635140. E-mail: hala_bakr@hotmail.com
against L-1210, A-549, HCT-8 and P-388 cell lines37,38
.
In view of the above data, the present study reported the first
synthesis of tetrahydrocarbazoles hybridized with dithioate

2
H. B. El-Nassan
J Enzyme Inhib Med Chem, Early Online: 1–8
Figure 1. Structures of biologically active dithiocarbamates and carbazoles.
derivatives. Upon designing the dithioate derivatives, three series was a two-step method which involved the reaction of the
were chosen, namely alkyl dithiocarbonates (4a–d), heterocyclic appropriate primary alcohol or secondary amine with carbon
dithiocarbamates (6a–g) and dialkyl dithiocarbamate (7). By disulfide in the presence of potassium hydroxide to give O-alkyl
doing this, the effect of the alkyl group substituted on dithioates dithiocarbonates (3a–d) and N,N-disubstituted dithiocarbamates
on the antitumor activity could be determined. The synthesized (5a–h) following the previously reported procedures1,2,7,40–42. The
compounds were evaluated for their possible anticancer activity latter compounds 3 and 5 were reacted with equimolar amount of
against MCF7 and HCT116 cell lines.
the chloromethyl derivative 2 at room temperature to afford
carbodithioate derivatives (4a–d) and carbamodithioates (6a–g)
and (7) in poor to good yields (39–89%).
Results and discussion
The second method (method B) was a one-step procedure
comprised the reaction of the appropriate secondary amine,
Chemistry
The synthetic route towards the target tetrahydrocarbazole- carbon disulfide and chloromethyl derivative 2 in acetone in the
dithioate derivatives is shown in Scheme 1. presence of catalytic amount of sodium phosphate. This procedure
The starting compound, 2-chloro-1-(1,2,3,4-tetrahydro-9H- afforded the same compounds 6a–g and 7 in higher yields
carbazol-9-yl)ethanone (2) was prepared via acylation of and reduced time (4 h) and comprised more efficient use of the
1,2,3,4-tetrahydrocarbazole (1) with chloroacetyl chloride in chemical reagents.
refluxing toluene according to the procedure reported by Ettel
and Myska39.
The formation of compounds 4a–d, 6a–g and 7 was confirmed
by IR and NMR spectroscopy. The IR spectra revealed the
In the present work, two methods were adopted for the presence of C¼O band at 1678–1701 cmꢀ1. In addition, C¼S
synthesis of the target compounds. The first method (method A) band appeared at 1215–1267 cmꢀ1
.

DOI: 10.3109/14756366.2014.922554
Tetrahydrocarbazole hybridized with dithioates
3
Scheme 1. Synthesis of tetrahydrocarbazoles hybridized with dithioate derivatives.
The 1H-NMR spectra of all the compounds revealed the
On the other hand, 13C-NMR spectra of the synthesized
presence of the carbazole CH2 protons at position 2 and 3 as compounds revealed the presence of C¼O carbon at d 166–
multiplet signals at d 1.79–1.99 ppm. While the carbazole 167 ppm and C¼S carbon at d 195–213 ppm. Figure 2 shows the
CH2 protons at position 1 and 4 appeared as triplet signals at d 1H-NMR and 13C-NMR chemical shifts for compound 6b.
2.63–2.71 ppm and d 3.03–3.15 ppm, respectively (see Figure 2).
Besides, a singlet signal appeared at d 4.65–4.95 ppm corres-
ponding to CH2CO protons.
In vitro anticancer screening
Compounds 6a–g [containing cyclic secondary amine moieties All the synthesized derivatives were evaluated for their in vitro
(piperidine, morpholine and piperazine)] and compound 7 [con- cytotoxic activity against two cell lines; human breast cancer
taining diethylamine] revealed the appearance of N-(CH2)2 cell line, MCF7; and human colon tumor cell line, HCT116,
protons as two signals at d 3.85–4.22 ppm and d 4.05–4.46 ppm. using Sulforhodamine-B stain (SRB) assay44. Doxorubicin,
This magnetic non-equivalence might be attributed to the conju- which is one of the most effective anticancer agents was used
gation between the C¼S group and the nitrogen atom, which as the reference drug.
increased the double bond character of C–N bond sufficiently to
The relationship between surviving fraction of MCF7 or
restrict the rotation at room temperature (Figure 3). Consequently, HCT116 and drug concentration was plotted and the response
one of the CH2 groups is cis to the S atom and the other is trans to parameter IC50 was calculated. IC50 value corresponds to the
the S atom. The anisotropy of C¼S is sufficient to influence the concentration required for 50% inhibition of cell viability. The
chemical shift of the cis protons which appeared at lower chemical IC50 values of the test compounds and the reference drug on
shift than the trans protons. This phenomenon resembles that MCF7 and HCT116 are shown in Table 1 and the results are
reported for the protons of the two CH3 groups of DMF43.
represented graphically in Figure 4.

4
H. B. El-Nassan
J Enzyme Inhib Med Chem, Early Online: 1–8
23.8
123.4
2.67 (t)
8.15 (m)
124.3
119.1
21.2
-
1.83 1.96 (m)
-
7.23 7.30 (m)
115.8
7.23-7.30 (m)
130.4
1.83-1.96 (m)
21.8
135.0
135.9
26.8
117.8
3.10 (t)
7.40 (m)
N
N
166.6
45.0
S
195.6
S
S
S
O
O
4.92 (s)
N
N
O
51.2
66.2
51.2
66.2
4.06 (br s)
3.78 (t)
4.30 (br s)
3.78 (t)
O
1
Figure 2. The H-NMR and 13C-NMR chemical shifts for compound 6b. The data are expressed as d in ppm unit, br s: broad singlet; s: singlet; t:
triplet; m: multiplet.
7.24 nM/mL. Its cytotoxic activity against HCT116 was compar-
able to doxorubicin with IC50 value of 8.23 nM/mL.
cis
protons
protons
S
CH2R
CH2R
S
CH2R
CH2R
N+
N
Experimental
trans
General
Melting points were determined using a Griffin apparatus and
were uncorrected. IR spectra were recorded on Shimadzu IR 435
Figure 3. Effect of conjugation between C¼S and nitrogen atom.
spectrophotometer and values were represented in cmꢀ1 1H-
.
NMR and 13C-NMR spectra were carried out on Bruker 400 MHz
and 100 MHz spectrophotometer, respectively, Faculty of
The data presented in Table 1 revealed that most of the
synthesized compounds showed potent to moderate antitumor
activity. In general, MCF7 cell line was more sensitive to the
cytotoxic action of the test compounds than HCT116 cell line.
Structurally, the test compounds belonged to three series,
namely; alkyl dithiocarbonates (4a–d), heterocyclic dithiocarba-
mates (6a–g) and dialkyl dithiocarbamate (7).
Examining the data on MCF7 cell line pointed out that all the
test compounds showed moderate to potent cytotoxic activity
with IC50 values of 7.24–37.70 nM/mL. The alkyl dithiocarbo-
nates 4a–d displayed more potent antitumor activity than the
heterocyclic dithiocarbamates containing piperidine (6a) or
morpholine moieties (6b) but were less potent than the hetero-
cyclic dithiocarbamates containing piperazine (6c–g) or the
dialkyl dithiocarbamate (7). Regarding the substituted piperazine
derivatives 6c–g, it was found that substitution on the piperazine
ring enhanced the antitumor activity in the following order:
4-chlorophenyl4C2H544-methoxyphenyl4CH34phenyl. The
dialkyl dithiocarbamate (7) displayed cytotoxic activity compar-
able to the piperazine analogues.
Pharmacy, Cairo University, Cairo, Egypt, using TMS as an
internal standard and chemical shifts were recorded in ppm on d
scale. Elemental analyses were carried out at the regional center
for mycology and biotechnology, Al-Azhar University, Cairo,
Egypt. Analytical thin layer chromatography (TLC) on silica gel
plates containing UV indicator was employed routinely to follow
the course of reactions and to check the purity of products. All
reagents and solvents were purified and dried by standard
techniques. The starting compounds 1,2,3,4-tetrahydrocarbazole
(1) and 2-chloro-1-(1,2,3,4-tetrahydro-9H-carbazol-9-yl)ethanone
(2) were synthesized according to the reported procedures39,45
.
Potassium salts of O-alkyl dithiocarbonates (3a–d)2,41
A mixture of potassium hydroxide (2.25 g, 40 mmol) and the
appropriate alcohol (methanol, ethanol, n-butanol and cyclohex-
anol) (7.5 mL) was refluxed for 1h. The reaction was cooled in an
ice bath and carbon disulphide (3 mL, 40 mmol) was added to the
mixture drop-wise with stirring. The reaction mixture was stirred
at room temperature for 1 h. The solid formed was collected,
washed with diethyl ether (2 ꢁ 25 mL) and used without further
purification.
On the other hand, the data obtained on HCT116 cell line
revealed that the alkyl dithiocarbonates (4a–d) exhibited lower
cytotoxic activity (higher IC50 values) than the heterocyclic
dithiocarbamates (6a–g) and dialkyl dithiocarbamate (7).
Furthermore, the heterocyclic dithiocarbamates (6a–g) were
more potent than the dialkyl dithiocarbamate (7). Here also, the
heterocyclic dithiocarbamates containing piperazine (6c–g) dis-
Potassium salts of N,N-disubstitued dithiocarbamic acids
(5a–h)1,2,7,40,42
played more potent antitumor activity than the heterocyclic Potassium hydroxide (0.28 g, 5 mmol) was dissolved in ethanol
dithiocarbamates containing piperidine (6a) or morpholine (20 mL) then the appropriate secondary amine (5 mmol) was
moieties (6b). Besides, substitution on the piperazine ring added and the mixture was cooled in an ice bath. Carbon
enhanced the antitumor activity against HCT116 in the following disulphide (4 mL, 50 mmol) was added to the mixture drop-wise
order: 4-chlorophenyl 4 CH3 4 C2H5 4 4-methoxyphenyl 4 with stirring. The reaction mixture was stirred for 1 h at room
phenyl.
temperature and then left overnight. The solvent was removed
The most potent compound in this study was the under reduced pressure, and the solid formed was collected,
4-chlorophenylpiperazine derivative (6f) which showed cytotoxic washed with diethyl ether (2 ꢁ 25 mL) and used without further
activity against MCF7 superior to doxorubicin with IC50 value of purification.

DOI: 10.3109/14756366.2014.922554
Tetrahydrocarbazole hybridized with dithioates
5
Table 1. Results of in vitro cytotoxic activity of the synthesized
compounds on human breast adenocarcinoma cell line (MCF7) and
human colon tumor cell line (HCT116).
Method B
mixture of the appropriate amine (1 mmol) and
A
Na3PO4 ꢂ 12H2O (0.23 g, 0.6 mmol) in acetone (10 mL) was
stirred at room temperature for 30 min. Carbon disulfide
(0.3 mL, 5 mmol) was added drop-wise and the reaction mixture
was stirred at room temperature for 30 min. Then, compound 2
(0.25 g, 1 mmol) was added and the reaction mixture was stirred at
room temperature for 4 h. The reaction mixture was poured onto
water (100 mL) and the solid product was filtered, dried and
crystallized from ethyl acetate.
N
S
S
O
R
O-Methyl S-[2-oxo-2-(1,2,3,4-tetrahydro-9H-carbazol-9-
yl)ethyl] carbonodithioate (4a)
Yield: (method A: 74%); m.p.: 117–118 ꢃC; IR (cmꢀ1): 2939,
2839 (CH aliphatic), 1685 (C¼O), 1228 (C¼S); 1H-NMR
(CDCl3) d ppm 1.83–1.95 (m, 4H, carbazole CH2), 2.65 (m,
2H, carbazole CH2), 3.03 (m, 2H, carbazole CH2), 4.19 (s, 3H,
OCH3), 4.68 (s, 2H, CH2CO), 7.25–8.10 (m, 4H, Ar-H); Anal.
Calcd for C16H17NO2S2: C, 60.16; H, 5.36; N, 4.38. Found: C,
60.22; H, 5.34; N, 4.47.
IC50 in nM/mL*
Compound No.
R
MCF7
HCT116
Doxorubicin
–
–OCH3
–OCH2CH3
–OCH2CH2CH2CH3
8.43
14.10
10.51
26.87
12.14
6.86
4150
4150
66.20
4a
4b
4c
87.08
4d
6a
6b
O
O-Ethyl S-[2-oxo-2-(1,2,3,4-tetrahydro-9H-carbazol-9-
yl)ethyl] carbonodithioate (4b)
21.77
37.70
38.17
29.9
Yield: (method A: 75%); m.p.: 85–86 ꢃC; IR (cmꢀ1): 2926, 2839
(CH aliphatic), 1680 (C¼O), 1244 (C¼S); 1H-NMR (CDCl3)
d ppm 1.40 (t, 3H, CH3CH2, J ¼ 7.2 Hz), 1.83–1.96 (m, 4H,
carbazole CH2), 2.66 (t, 2H, carbazole CH2), 3.03 (t, 2H,
carbazole CH2), 4.62 (q, 2H, CH3CH2, J ¼ 7.2 Hz), 4.67 (s, 2H,
CH2CO), 7.24–8.11 (m, 4H, Ar-H); 13C-NMR (100 MHz, CDCl3)
d ppm 13.7 (CH3CH2), 21.1, 21.8, 23.8, 26.7 (carbazole C-3, C-2,
C-4, C-1), 43.8 (CH2CO), 70.8 (CH3CH2), 115.6, 117.9, 119.2,
123.5, 124.3, 130.4, 134.8, 135.8 (aromatic carbons), 166.0
(C¼O), 213.2 (C¼S); Anal. Calcd. for C17H19NO2S2: C, 61.23;
H, 5.74; N, 4.20. Found: C, 61.41; H, 5.78; N, 4.28.
N
N
O
11.63
9.22
19.20
19.28
6c
N
N
CH3
6d
CH2CH3
N
N
N
O-Butyl S-[2-oxo-2-(1,2,3,4-tetrahydro-9H-carbazol-9-
yl)ethyl] carbonodithioate (4c)
16.70
45.88
6e
Yield: (method A: 39%); m.p.: 86–87 ꢃC; IR (cmꢀ1): 2937, 2862
N
1
(CH aliphatic), 1685 (C¼O), 1215 (C¼S); H-NMR (CDCl3) d
7.24
9.39
8.23
26.10
44.72
ppm 0.95 (t, 3H, CH3CH2, J ¼ 7.4 Hz), 1.39 (sextet, 2H, CH3CH2,
J ¼ 7.4 Hz), 1.74 (quintet, 2H, CH3CH2CH2, J ¼ 7.4 Hz), 1.88–
1.99 (m, 4H, carbazole CH2), 2.70 (s, 2H, carbazole CH2), 3.06 (s,
2H, carbazole CH2), 4.61 (t, 2H, CH2CH2O, J ¼ 7.4 Hz), 4.67 (s,
2H, CH2CO), 7.26–8.13 (m, 4H, Ar-H); 13C-NMR (100 MHz,
CDCl3) d ppm 13.6 (CH3CH2), 19.1 (CH3CH2), 21.1, 21.8, 23.8,
26.7 (carbazole C-3, C-2, C-4, C-1), 30.3 (CH3CH2CH2), 43.7
(CH2CO), 74.7 (CH2O), 115.6, 117.9, 119.2, 123.5, 124.3, 130.4,
134.8, 135.8 (aromatic carbons), 166.0 (C¼O), 213.2 (C¼S);
Anal. Calcd. for C19H23NO2S2: C, 63.12; H, 6.41; N, 3.87. Found:
C, 63.21; H, 6.47; N, 3.98.
6f
6g
7
N
N
Cl
N
N
OCH
3
10.28
N
*The given values are means of three experiments.
O-Cyclohexyl S-[2-oxo-2-(1,2,3,4-tetrahydro-9H-carbazol-
9-yl)ethyl] carbonodithioate (4d)
General procedures for the synthesis of dithioate
derivatives 4a–d, 6a–g and 7
Yield: (method A: 46%); m.p.: 106–107 ꢃC; IR (cmꢀ1): 2935,
2856 (CH aliphatic), 1701 (C¼O), 1224 (C¼S); 1H-NMR
(CDCl3) d ppm 1.27–2.01 (m, 14H, carbazole CH2 and cyclohexyl
CH2), 2.71 (t, 2H, carbazole CH2, J ¼ 6 Hz), 3.06 (s, 2H,
carbazole CH2, J ¼ 6 Hz), 4.65 (s, 2H, CH2CO), 5.52 (quintet,
1H, cyclohexyl CH), 7.26–8.13 (m, 4H, Ar-H); 13C-NMR
(100 MHz, DMSO-d6) d ppm 21.1, 21.8, 23.8, 26.7 (carbazole
C-3, C-2, C-4, C-1), 23.5, 25.2, 30.8 (CH2CH2CH2 of cyclo-
hexyl), 43.4 (CH2CO), 83.4 (CHO), 115.6, 117.9, 119.2, 123.4,
124.3, 130.4, 134.8, 135.8 (aromatic carbons), 166.1 (C¼O),
Method A
A
mixture of 2-chloro-1-(1,2,3,4-tetrahydro-9H-carbazol-9-
yl)ethanone (2) (0.25 g, 1 mmol) and the appropriate potassium
salts of O-alkyl dithiocarbonates (3a–d) or N,N-disubstituted
dithiocarbamic acids (5a–h) (1 mmol) in absolute ethanol (10 mL)
was boiled till all the solid dissolved and then the reaction
mixture was left overnight at room temperature. The resulting
solid was filtered, washed with water (50 mL) and crystallized
from ethyl acetate.

6
H. B. El-Nassan
J Enzyme Inhib Med Chem, Early Online: 1–8
100
90
80
70
60
50
40
30
20
10
0
MCF7
HCT116
Dox 4a
4b
4c
4d
6a
6b
6c
6d
6e
6f
6g
7
Figure 4. IC50 in nM/mL of compounds 4–7 and doxorubicin against MCF7 and HCT116 cell lines.
212.1 (C¼S); Anal. Calcd. for C21H25NO2S2: C, 65.08; H, 6.50; 1H-NMR (CDCl3) d ppm 1.14 (t, 3H, CH3CH2, J ¼ 7.2 Hz), 1.87–
N, 3.61. Found: C, 65.19; H, 6.48; N, 3.78.
1.97 (m, 4H, carbazole CH2), 2.48 (q, 2H, CH3CH2, J ¼ 7.2 Hz),
2.59 (t, 4H, piperazine CH2), 2.70 (t, 2H, carbazole CH2,
J ¼ 6.0 Hz), 3.14 (t, 2H, carbazole CH2, J ¼ 6.0 Hz), 4.07 (br s,
2H, piperazine CH2), 4.37 (br s, 2H, piperazine CH2), 4.95 (s, 2H,
CH2CO), 7.26–8.20 (m, 4H, Ar-H); Anal. Calcd. for
C21H27N3OS2: C, 62.81; H, 6.78; N, 10.46. Found: C, 62.89; H,
6.82; N, 10.61.
2-Oxo-2-(1,2,3,4-tetrahydro-9H-carbazol-9-yl)ethyl
piperidine-1-carbodithioate (6a)
Yield: (method A: 76%; method B: 81%); m.p.: 166–167 ꢃC; IR
(cmꢀ1): 2931, 2848 (CH aliphatic), 1695 (C¼O), 1230 (C¼S);
1H-NMR (CDCl3) d ppm 1.59–1.65 (m, 6H, piperidine CH2),
1.79–1.87 (m, 4H, carbazole CH2), 2.63 (s, 2H, carbazole CH2),
3.06 (s, 2H, carbazole CH2), 3.97 (s, 2H, piperidine CH2), 4.14 (s,
2H, piperidine CH2), 4.93 (s, 2H, CH2CO), 7.22–8.14 (m, 4H, Ar-
H); Anal. Calcd. for C20H24N2OS2: C, 64.48; H, 6.49; N, 7.52.
Found: C, 64.56; H, 6.57; N, 7.68.
2-Oxo-2-(1,2,3,4-tetrahydro-9H-carbazol-9-yl)ethyl
4-phenylpiperazine-1-carbodithioate (6e)
Yield: (method A: 88%; method B: 88%); m.p.: 132–133 ꢃC; IR
(cmꢀ1): 2927, 2852 (CH aliphatic), 1678 (C¼O), 1226 (C¼S);
1H-NMR (CDCl3) d ppm 1.85–1.95 (m, 4H, carbazole CH2), 2.66
(t, 2H, carbazole CH2, J ¼ 6 Hz), 3.10 (t, 2H, carbazole CH2,
J ¼ 6 Hz), 3.32 (t, 4H, piperazine CH2), 4.18 (br s, 2H, piperazine
CH2), 4.46 (br s, 2H, piperazine CH2), 4.94 (s, 2H, CH2CO), 6.90-
8.16 (m, 9H, Ar-H); Anal. Calcd. for C25H27N3OS2: C, 66.78; H,
6.05; N, 9.35. Found: C, 66.93; H, 6.13; N, 9.52.
2-Oxo-2-(1,2,3,4-tetrahydro-9H-carbazol-9-yl)ethyl
morpholine-4-carbodithioate (6b)
Yield: (method A: 82%; method B: 86%); m.p.: 200–201 ꢃC; IR
(cmꢀ1): 2929, 2858 (CH aliphatic), 1681 (C¼O), 1224 (C¼S);
1H-NMR (CDCl3) d ppm 1.83–1.96 (m, 4H, carbazole CH2), 2.67
(t, 2H, carbazole CH2, J ¼ 6 Hz), 3.10 (t, 2H, carbazole CH2,
J ¼ 6 Hz), 3.78 (t, 4H, morpholine CH2O, J ¼ 4.8 Hz), 4.06 (br s,
2H, morpholine CH2N), 4.30 (br s, 2H, morpholine CH2N), 4.92
(s, 2H, CH2CO), 7.23-8.15 (m, 4H, Ar-H); 13C-NMR (100 MHz,
CDCl3) d ppm 21.2, 21.8, 23.8, 26.8 (carbazole C-3, C-2, C-4,
C-1), 45.0 (CH2CO), 51.2 (morpholine CH2N), 66.2 (morpholine
CH2O), 115.8, 117.8, 119.1, 123.4, 124.3, 130.4, 135.0, 135.9
(aromatic carbons), 166.6 (C¼O), 195.6 (C¼S); Anal. Calcd. for
C19H22N2O2S2: C, 60.93; H, 5.92; N, 7.48. Found: C, 61.08; H,
5.97; N, 7.62.
2-Oxo-2-(1,2,3,4-tetrahydro-9H-carbazol-9-yl)ethyl
4-(4-chlorophenyl)piperazine-1-carbodithioate (6f)
Yield: (method A: 74%; method B: 86%); m.p.: 164–165 ꢃC; IR
(cmꢀ1): 2924, 2835 (CH aliphatic), 1685 (C¼O), 1228 (C¼S);
1H-NMR (CDCl3) d ppm 1.83–1.97 (m, 4H, carbazole CH2), 2.68
(t, 2H, carbazole CH2, J ¼ 6 Hz), 3.11 (t, 2H, carbazole CH2,
J ¼ 6 Hz), 3.30 (t, 4H, piperazine), 4.22 (br s, 2H, piperazine),
4.45 (br s, 2H, piperazine), 4.94 (s, 2H, CH2CO), 6.82–8.18 (m,
8H, Ar-H); Anal. Calcd. for C25H26ClN3OS2: C, 62.03; H, 5.41;
N, 8.68. Found: C, 62.17; H, 5.46; N, 8.73.
2-Oxo-2-(1,2,3,4-tetrahydro-9H-carbazol-9-yl)ethyl
4-methylpiperazine-1-carbodithioate (6c)
Yield: (method A: 64%; method B: 80%); m.p.: 162–163 ꢃC; IR
(cmꢀ1): 2933, 2846 (CH aliphatic), 1681 (C¼O), 1232 (C¼S);
1H-NMR (CDCl3) d ppm 1.81–1.95 (m, 4H, carbazole CH2), 2.3
(s, 3H, CH3), 2.51 (t, 4H, piperazine CH2), 2.65 (t, 2H, carbazole
CH2, J ¼ 6 Hz), 3.08 (t, 2H, carbazole CH2, J ¼ 6 Hz), 4.02 (br s,
2H, piperazine CH2), 4.33 (br s, 2H, piperazine CH2), 4.89 (s, 2H,
CH2CO), 7.22–8.16 (m, 4H, Ar-H); Anal. Calcd. for
C20H25N3OS2: C, 61.98; H, 6.50; N, 10.84. Found: C, 62.12; H,
6.48; N, 10.92.
2-Oxo-2-(1,2,3,4-tetrahydro-9H-carbazol-9-yl)ethyl
4-(4-methoxyphenyl)piperazine-1-carbodithioate (6g)
Yield: (method A: 85%; method B: 86%); m.p.: 156–157 ꢃC; IR
(cmꢀ1): 2935, 2833 (CH aliphatic), 1697 (C¼O), 1224 (C¼S);
1H-NMR (CDCl3) d ppm 1.86–1.96 (m, 4H, carbazole CH2), 2.65
(t, 2H, carbazole CH2, J ¼ 6 Hz), 3.09 (t, 2H, carbazole CH2,
J ¼ 6 Hz), 3.16 (t, 4H, piperazine, J ¼ 5.2 Hz), 3.77 (s, 3H,
CH3O), 4.18 (br s, 2H, piperazine), 4.46 (br s, 2H, piperazine),
4.92 (s, 2H, CH2CO), 6.84–8.18 (m, 8H, Ar-H); 13C-NMR
(100 MHz, CDCl3) d ppm 21.2, 21.8, 23.8, 26.8 (carbazole C-3,
C-2, C-4, C-1), 45.2 (CH2CO), 50.4, 51.6 (piperazine carbons),
55.5 (CH3O), 114.6, 115.8, 117.8, 118.9, 119.1, 123.4, 124.3,
130.4, 135.0, 135.9, 144.5, 154.5 (aromatic carbons), 166.7
2-Oxo-2-(1,2,3,4-tetrahydro-9H-carbazol-9-yl)ethyl
4-ethylpiperazine-1-carbodithioate (6d)
Yield: (method A: 64%; method B: 82%); m.p.: 167–168 ꢃC; IR
(cmꢀ1): 2935, 2843 (CH aliphatic), 1681 (C¼O), 1234 (C¼S);

DOI: 10.3109/14756366.2014.922554
Tetrahydrocarbazole hybridized with dithioates
7
(C¼O), 195.1 (C¼S); Anal. Calcd. for C26H29N3O2S2: C, 65.10; dithiocarbamates (6c–g) [piperazine analogues] was comparable
H, 6.09; N, 8.76. Found: C, 65.23; H, 6.13; N, 8.92.
to dialkyl dithiocarbamate (7). Besides, the alkyl dithiocarbonates
(4a–d) displayed more potent antitumor activity than the hetero-
cyclic dithiocarbamates (6a,b) [piperidine and morpholine
analouges]. Whilst, SAR study of the test compounds on
HCT116 cell line indicated that heterocyclic dithiocarbamates
(6a–g) afforded more potent cytotoxic agents than alkyl
dithiocarbonate (4a–d) or dialkyl dithiocarbamate (7).
On both cell lines, heterocyclic dithiocarbamates bearing
piperazine moiety afforded more potent cytotoxic agents than
piperidine or morpholine analogues. Within the piperazine
derivatives, the antitumor activity was affected by the
N-substituent in the following order: 4-chlorophenyl 4 alkyl 4
4-methoxyphenyl 4 phenyl.
2-Oxo-2-(1,2,3,4-tetrahydro-9H-carbazol-9-yl)ethyl diethyl
carbamodithioate (7)
Yield: (method A: 54%; method B: 90%); m.p.: 97–98 ꢃC; IR
(cmꢀ1): 2929, 2850 (CH aliphatic), 1683 (C¼O), 1267 (C¼S);
1H-NMR (CDCl3) d ppm 1.25 (t, 3H, CH3CH2, J ¼ 7.2 Hz), 1.38
(t, 3H, CH3CH2, J ¼ 6.8 Hz), 1.85–1.99 (m, 4H, carbazole CH2),
2.70 (t, 2H, carbazole CH2, J ¼ 6.0 Hz), 3.15 (t, 2H, carbazole
CH2, J ¼ 6.0 Hz), 3.85 (q, 2H, CH3CH2, J ¼ 7.2 Hz), 4.05 (q, 2H,
CH3CH2, J ¼ 6.8 Hz), 4.95 (s, 2H, CH2CO), 7.26–8.22 (m, 4H,
Ar-H); 13C-NMR (100 MHz, DMSO-d6) d ppm 11.5, 12.6
(CH3CH2N), 21.2, 21.8, 23.8, 26.8 (carbazole C-3, C-2, C-4,
C-1), 45.5 (CH2CO), 47.2, 50.0 (CH3CH2N), 115.9, 117.8, 119.0,
123.3, 124.2, 130.4, 135.1, 135.9, (aromatic carbons), 167.0
(C¼O), 193.7 (C¼S); Anal. Calcd. for C19H24N2OS2: C, 63.30;
H, 6.71; N, 7.77. Found: C, 63.39; H, 6.77; N, 7.94.
Further work need to be done to determine the effect of the
linker between tetrahydrocarbazole and dithioate on the antic-
ancer activity and also to determine the mechanism inherited
behind the antitumor effect of these compounds.
Acknowledgements
Biological testing
The author is grateful to all members of the department of Cancer
Biology, National Cancer Institute, Cairo, Egypt, for carrying out the
cytotoxicity testing.
Materials and methods
The human breast adenocarcinoma cell line (MCF7) and the
human colon tumor cell line (HCT116) were obtained as a gift
from NCI, Bethesda, MD.
All chemicals and solvents were purchased from Sigma-
Aldrich (Munich, Germany).
Declaration of interest
The author reports no conflicts of interest. The author alone is responsible
for the content and writing of this article.
Measurement of potential cytotoxicity
The cytotoxic activity of the newly synthesized compounds was
measured in vitro on human breast adenocarcinoma cell line
(MCF7) and the human colon tumor cell line (HCT116) using
Sulforhodamine-B stain (SRB) assay applying the method
described by Skehan et al.44.
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