One-pot mild and efficient synthesis of [1,3]thiazino[3,2-: A] indol-4-ones and their anti-proliferative activity

Article abstract of DOI:10.1039/c9ob00500e

A base mediated environmentally benign one-pot efficient methodology has been developed for the synthesis of [1,3]thiazino[3,2-a]indol-4-ones using indoline-2-thiones and propiolate esters in aqueous medium. The conjugate addition of thiones first results in ethyl (3-(indol-2-yl)thio)acrylates in situ, which subsequently undergoes intramolecular cyclization to produce indole-fused thiazin-4-ones in good to excellent yields. The cytotoxic screening of the synthesized compounds using MTT assay revealed the anti-proliferative nature of these frameworks against triple negative breast cancer cell lines with the highest activity emanating from 4H-[1,3]thiazino[3,2-a]indol-4-one and 8-methyl-2-propyl-4H-[1,3]thiazino[3,2-a]indol-4-one compounds.

Full text of DOI:10.1039/c9ob00500e

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One-pot mild and efficient synthesis of [1,3]thiazino[3,2-a]indol-
4-ones and their anti-proliferative activity
Steven Rhodes,a Spencer Short,a Sidhika Sharma,b Ramneet Kaur,b and Mukund Jhaa*
Received 00th January 20xx,
Accepted 00th January 20xx
A base mediated environmentally benign one-pot efficient methodology has been developed for the synthesis of
[1,3]thiazino[3,2-a]indol-4-ones using indoline-2-thiones and propiolate esters in aqueous medium. The conjugate addition
of the thione first results in ethyl (3-(indol-2-yl)thio)acrylates in situ, which subsequently undergoes intramolecular
cyclization to produce indole-fused thiazin-4-ones in good to excellent yields. The cytotoxic screening of the synthesized
compounds using MTT assay revealed the anti-proliferative nature of this framework against triple negative breast cancer
cell lines with the highest activity emanating from 4H-[1,3]thiazino[3,2-a]indol-4-one and 8-methyl-2-propyl-4H-
[1,3]thiazino[3,2-a]indol-4-one compounds.
DOI: 10.1039/x0xx00000x
www.rsc.org/
[1,3]thiazino ring systems are known in the literature. For instance,
our group reported a Cu-mediated two-step synthesis of indole fused
thiazins starting from indoline-2-thiones.11 Lv and co-workers
published a Cu-catalyzed domino intramolecular C-S coupling
strategy for the assembly of 12H-benzo[5,6][1,3]thiazino[3,2-
Introduction
Synthesis of fused heterocyclic frameworks is an important area of
research because of their great potential for being biologically
active.1,2 In particular, indole-fused naturally occurring tricyclic
compounds, functionalized at C-2 and C-3 positions of indole, have
been found to display numerous interesting properties. Some
representative examples include carbazole (1),3 carbolines 2,4
cruciferous phytoalexins (e.g. brassilexin (3) and sinalexin (4)),5 etc.
(Figure 1). Indoles functionalized at positions N-1 and C-2, such as
indo[2,1-b][1,3]benzoxazines 5, have been used for the treatment of
atrial arrhythmia and CNS disorders,6 tryptanthrins 6 and their
derivatives display antibacterial,7 antifungal,8 and anticancer9
activities. Similarly, S-containing analogs, such as [1,3]thiazino[3,2-
a]indoles 7, have been identified as CRTH2 and 5HT4 receptor
antagonists (Figure 1).10
a]indol-12-one
involving
2-mercapto-N-
(2-(2,2-
dibromovinyl)phenyl)-benzamide.12 Kobayashi et al. developed the
synthesis of S-containing indole-fused tricyclic compounds from 2-
(sulfinyl(or sulfonyl)methyl)phenyl isothiocyanates.13 More
specifically, very little work has been done on the synthesis of
[1,3]thiazino[3,2-a]indol-4-one ring systems (Scheme 1). For
example, Sakamoto demonstrated a reaction of indoline-2-thione (8)
with diketene 9 to produce 2-methyl-4H-[1,3]thiazino[3,2-a]indol-4-
one (10) in 44% yield.14 Similarly, methyl 4-oxo-4H-indolo[2,l-
b][l,3]thiazine-2-carboxylate (12) was synthesized using the thione 8
and dimethyl acetylenedicarboxylate (DMAD, 11) by Acheson and
Wallis in 16.5% yield.15 The related compound, N-acylated indole was
transformed into 12H-benzo[5,6][1,3]thiazino[3,2-a]indol-12-one
upon heating at reflux in p-xylene by Bates and Habib.16 However,
these represent only isolated literature examples for the synthesis of
this class of heterocyclic framework, and are reported in poor yields
(Scheme 1). To the best of our knowledge no systematic study on the
synthesis of [1,3]thiazino[3,2-a]indol-4-one core is reported in the
literature.
Figure 1. Representative examples of biologically active indole-fused tricyclic
heterocycles.
In recent years, our lab has demonstrated the use of indoline-2-
thiones as a useful precursor for the synthesis of a variety of indole-
based S-containing heterocycles.11,17-20 In continuation of these
studies, herein, we report a base-mediated one-pot mild and
efficient synthesis of [1,3]thiazino[3,2-a]indol-4-ones, e.g. 10, in
aqueous medium starting from indoline-2-thiones 8 (Scheme 1).
Remarkably, the synthesized series of compounds were found to be
However, only
a handful examples of indole-annulated
a. Department of Biology and Chemistry, Nipissing University, North Bay, ON P1B
8L7, Canada, E-mail: mukundj@nipissingu.ca
b. Department of Biology, University of North Georgia, Oakwood, GA, 30566, USA
Electronic Supplementary Information (ESI) available: [Copies of NMR (1H & 13C)
spectra for synthesized compounds 10, 17, and 19-34]. See
DOI: 10.1039/x0xx00000x
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Scheme 3. Synthesis of 4H-[1,3]thiazino[3,2-a]indol-4-one (17)
cytotoxic towards two triple negative breast cancer cell lines MDA
231 and MDA 468 revealing the anti-proliferative nature of this type
of indole-fused heterocyclic ring system.
View Article Online
DOI: 10.1039/C9OB00500E
When 13a was replaced with its derivative having an internal
alkyne, 13b, the yield of the corresponding product 10 increased
slightly to 17%. In order to further improve the reaction yields we
proceeded to optimize the reaction conditions by varying the solvent
and the reaction temperature using acid 13b in subsequent
reactions. The results are summarized in Table 1. Unfortunately,
despite screening several solvents the yield of 10 could not be
improved significantly. The best results were obtained in anhydrous
THF at room temperature (Table 1, entry 6), in which 10 was
obtained in 35%. In a couple of cases, the reactions were performed
at lower temperatures (Table 1, entries 8 and 9) to facilitate the
detection of any reaction intermediate(s) formed prior to the
formation of cyclic product 10, however, none were found.
Scheme 1. (A) Literature exaples of the synthesis of 2-methyl-4H-[1,3]thiazino[3,2-
a]indol-4-one (10, Ref 14) and 4-oxo-4H-indolo[2,l-b][l,3]thiazine-2-carboxylate (12, Ref
15), (B) Synthesis of 2-methyl-4H-[1,3]thiazino[3,2-a]indol-4-one heterocyclic core
(current work).
Table 1. DCC-mediated synthesis of 2-methyl-4H-[1,3]thiazino[3,2-a]indol-4-one (10)a
Results and discussion
Propiolic acid 13 and its derivatives have been conveniently used
for the synthesis of coumarins upon condensation with various
phenols.21 The thio-enolic form 8a of indoline-2-thione (8) is
analogous to phenols, and appears to be an ideal candidate to
undergo condensation reactions with propiolic acid, similar to
phenols. However, our literature survey revealed no such reactions
have been reported. We envisaged a reaction of indoline-2-thione 8
with propiolic acid 13a to produce a corresponding thioester 14,
which could potentially undergo intramolecular cyclization to form
an indole-fused thiocoumarin skeleton 15 via C-C coupling or
[1,3]thiazino[3,2-a]indol-2-one core 16 involving a hydroamination
step. Hence, we set out to explore the reactions of propiolic acids 13
with indoline-2-thiones 8.
Reaction
Temperature (°C)
10
Yield (%)b
17
Entry
Solvent
Time (h)
1
2
3
4
5
6
7
8
9
DCM
toluene
acetonitrile
DMF
chloroform
THF
methanol
THF
THF
rt
rt
rt
rt
rt
rt
rt
0
-20
24
24
24
24
24
4
24
0.5
0.5
10
ndc
trace
10
35
trace
25
28
aReaction conditions: 1 (0.34 mmol), 13 (0.37 mmol), DCC (0.40 mmol) and DMAP
(20 mol%), solvent (10 mL). bIsolated yield. cNot detected.
Although we were gratified with the success of the reaction in
producing 10 and 17, we were not content with the reaction yields.
Examples in the literature exist where thiophenols have been
regioselectively alkylated using propiolate esters to form vinyl
sulfides.23 This prompted us to modify our synthetic strategy slightly
to access the heterocyclic skeleton 17. We postulated that, once we
succeeded in obtaining the vinyl sulfide 19 from 8 it could potentially
undergo a nucleophilic acyl substitution reaction to form the desired
Scheme 2. Expected tri-cyclic products 15 and 16 from thione 8 and propiolic acid
13a.
Indoline-2-thione 8 and its derivatives were synthesized from
corresponding indolin-2-ones using
a
previously reported
procedure.17 Propiolic acid 13 and its analogs were obtained from
commercial sources. At first, the unsubstituted thione 8 and propiolic
acid (13a) were chosen as model reactants for exploring the desired
reactions. Preliminary attempts for the conversion of thione 8 to its
thioester 14 were made in the presence DCC as condensing agent in
solvent DCM, as per the reaction conditions reported for phenols.22
The initial trials lead to a yellow coloured product, in less than 10%
yield, which was characterized as 4H-[1,3]thiazino[3,2-a]indol-4-one
(17) using spectroscopic methods (Scheme 3). It was quite interesting
to note that, contrary to our hypothesis, the condensation of thione
8 with the acid 13a appeared to have occured at the N-1 position of
the indole nucleus to form its amide in situ. Following which, the
nucleophilic attack of S at the terminal alkyne C resulted in 17.
4H-[1,3]thiazino[3,2-a]indol-4-one ring system 17.
We were
delighted to find out the thione 8 reacted smoothly with propiolate
18 to produce the vinyl sulfide 19 exclusively in near quantitative
yields, under very mild aqueous basic conditions using K2CO3 in just
15 minutes. The product 19 was isolated and characterized before
subjecting it to the next step. The subsequent intramolecular
cyclization of 19 was first attempted by treating it with aqueous
K2CO3 solution. Unfortunately, no reaction occurred under these
conditions even after refluxing the reaction mixture for 24 h (Table
2, entry 1). Whereas, when a stronger base KOH was used, in place
of K2CO3, the reaction resulted in the formation of 10. A complete
conversion of 19 to 10 was achieved in 6 h at 60 °C in 68% yield. These
results led us to attempt a one-pot conversion of 8 to 10 with the
2 | J. Name., 2012, 00, 1-3
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intent of improving the overall reaction efficiency, without having
the need to isolate the intermediate vinyl sulfide 19. In the next trial,
8 was mixed with 18 in aqueous KOH solution and left to stir at room
temperature. The conversion of 8 to 19 completed in 15 minutes, as
evidenced by TLC, after which the reaction temperature was
incrementally raised to 60 °C, which produced 10 in 45% yield (Table
2, entry 2). Encouraged by these outcomes, the stoichiometric ratios
of KOH and the propiolate ester 18 with respect to 8 were adjusted
slightly to arrive at the conditions optimal for the one-pot conversion
of 8 to 10 (Table 2, entry 4, 75% yield). Furthermore, in the presence
of bases other than KOH, such as NaOH and LiOH, the condensation
reaction seemed to proceed faster, however, the isolated yields of
10 were slightly inferior in these cases (Table 2, entries 5 and 6).
Increasing the reaction temperature had a detrimental effect on the
reaction outcome. The reaction mixture underwent rapid
decomposition when heated to a 100 °C (Table 2, entry 7) within 0.5
hour. It is likely the hydrolysis of the ester functionality in 19 might
have taken place at the elevated temperature under these
conditions.
View Article Online
DOI: 10.1039/C9OB00500E
aReaction conditions: 1 (1.0 mmol), 18 (0.51 mmol), KOH (0.84 mmol), water (5
mL). bIsolated yield
The mechanism for the formation of 4H-[1,3]thiazino[3,2-
a]indol-4-ones appears to be quite straightforward. Based on
literature report23 and our own experience of working with indoline-
Table 2. Optimization of base-mediated synthesis of 2-methyl-4H-[1,3]thiazino[3,2-
11,17-20,24,25
a]indol-4-one (10)a
2-thione (8)
we propose the conjugate addition of soft
nucleophile S present on 8 with propiolate 18 occurs in the first step,
leading to 19. Thereafter, a base promoted intramolecular
nucleophilic acyl substitution reaction between the N of 19 and the
ester functionality could yield compound 10, as depicted in Scheme
4.
Base
(equiv.)
10
Yield (%)b
ndc
Entry
18 (equiv.)
Time (h)
1
2
3
4
4
5
6
7
K2CO3 (1.5)
KOH (1.5)
KOH (2.5)
KOH (2.5)
KOH (2.5)
NaOH (2.5)
LiOH (2.5)
KOH (2.5)
1.1
1.1
1.1
1.5
1.5
1.5
1.5
1.5
24
6
6
6
6
45
60
75
75
Scheme 4.
A plausible mechanism for the synthesis of 2-methyl-4H-
[1,3]thiazino[3,2-a]indol-4-one (10).
3
48
2
61
The chemical structure of 4H-[1,3]thiazino[3,2-a]indol-4-ones
ring system could be quite appealing to synthetic and medicinal
chemists as the most reactive position, i.e. C-10, lies vacant. Being a
nucleophilic center it could potentially be exploited for further
chemical manipulations with electrophiles. To test this, we
0.5d
ndc
aReaction conditions: 1 (0.34 mmol), 18, base, water (5 mL). bIsolated yield. cNot
detected. dReaction carried out at 100 °C
Next, after having optimized the reaction conditions for the
synthesis of heterocyclic core 4H-[1,3]thiazino[3,2-a]indol-4-one 10
we proceeded to examine the scope of our developed reaction
methodology. As shown in Table 3, combining a variety of indoline-
2-thiones 8 and propiolates 18 resulted in diversely substituted
indole-fused 4H-[1,3]thiazino[3,2-a]indol-4-ones 17 and 20-32 in
good to excellent yields. Substituents such as methyl, fluoro, and
chloro on the indole nucleus were tolerated well in the reaction
under investigation. The propiolates having internal and terminal
alkynes also reacted smoothly to form the corresponding tricyclic
products.
attempted a Vilsmeier-Haack formylation reaction on 22 and 27. As
predicted, compounds 22 and 27 underwent formylations with
relative ease to produce 33 and 34 respectively in excellent yields
(Scheme 5).
Scheme 5. Vilsmeier-Haack formylation of compounds 22 and 27.
Biological Activity
Table 3. Base-mediated synthesis of 2-methyl-4H-[1,3]thiazino[3,2-a]indol-4-one (10)
and analogs in aqueous medium.a,b
Triple negative breast cancers (TNBCs) are among the most
aggressive forms of breast cancer.26,27 These types of cancer cells lack
the protein markers ER, PR and Her-2, which are typically targeted
for developing anti cancer drugs. Hence, the development of anti-
cancer agents for the treatment of TNBCs remain very challenging.
Prilimnary effects of the synthesized compounds (new chemical
entities) on the cell viability (MTT assay28) of TNBC cells were
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conducted using MDA 231 and MDA 468 cell lines. Both cell lines
were treated with different concentrations of the synthesized
compounds for 48 h and their IC50 values were determined (Table 4).
Among the tested compounds 10 and 29 were found to be most
effective against these cell lines (Table 4, entries 1 and 11). These
compounds were more effective against MDA 468 compared to MDA
231 cells.
mass spectra (HRMS) were carried out using a quadrupole time-of-
flight (qTOF) mass spectrometer. Chemicals obtained from the
commercial suppliers were used without further purification.
View Article Online
DOI: 10.1039/C9OB00500E
Procedure for the synthesis of 2-methyl-4H-[1,3]thiazino[3,2-
a]indol-4-one (10) using propiolic acid (13b): In a clean oven-dried
50 mL RB flask a mixture of indoline-2-thione (8, 0.34 mmol), DCC
(0.40 mmol), and DMAP (20 mol%) in 10 mL dry THF was added
propiolic acid (13b, 0.37 mmol). The reaction was then stirred at
room temperature under nitrogen for 30 minutes. On completion of
the reaction (as indicated by TLC), the mixture was diluted with water
(5 mL) and extracted with DCM (2 x 10 mL), the organic layer was
then washed with brine (5 ml) and dried over Na2SO4. The dried
organic layer was concentrated in vacuo and the resulting residue
was purified using column chromatography (15% ethyl acetate in
hexanes) to obtain 10.
Table 4. MTT cytotoxicity assay for [1,3]thiazino[3,2-a]indol-4-ones.
IC50 (μM) (n=2)
Entry
New Chemical Entity
MDA-231
MDA-468
1
2
3
4
5
6
7
8
9
10
11
12
13
14
10
20
21
22
23
24
25
26
27
28
29
30
31
32
302
827
1075
825
3183
996
1361
>2000
690
790
330
116
793
423
380
3040
202
206
>2000
736
785
General procedure for the synthesis of 4H-[1,3]thiazino[3,2-
a]indol-4-ones 10, 17, 20-32 using propiolate esters: In a clean 50
mL RB flask appropriate indoline-2-thione (0.34mmol) was mixed
with water (5 mL) followed by the addition of the propiolate ester
(0.51 mmol) and KOH (0.84 mmol). The reaction mixture was stirred
at room temperature until the thione was consumed completely (as
indicated by TLC). The reaction temperature was then increased to
60 °C and mixture was allowed to stir until the intermediate
compound transformed to a new product (as evidenced by TLC). The
reaction mixture was then diluted with water (5 mL) and extracted
with DCM (2 x 10 mL), the organic layer was then washed with brine
(5 ml), dried over Na2SO4 and concentrated in vacuo. The residue
obtained was purified using column chromatography (15% ethyl
acetate in hexanes) to produce 4H-[1,3]thiazino[3,2-a]indol-4-ones
10, 17, and 20-32.
97
475
>2000
>2000
>2000
>2000
>2000
Conclusions
In conclusion, we have developed
a
one-pot
straightforward, versatile, and efficient synthesis of tricyclic
heterocycle 4H-[1,3]thiazino[3,2-a]indol-4-ones starting from
indoline-2-thiones
8
and propiolate esters 18 in
environmentally benign aqueous medium. Our studies revealed
the propiolate esters 18 are better substrates for the
condensation with thiones 8 compared to propiolic acids 13 to
produce the framework of 10 and its analogs. Furthermore, we
have demonstrated the heterocyclic ring system of 10 could be
regioselectively exploited for further chemical manipulations
under appropriate conditions. Most importantly, two of the
synthesized compounds, 4H-[1,3]thiazino[3,2-a]indol-4-one
(10) and 8-methyl-2-propyl-4H-[1,3]thiazino[3,2-a]indol-4-one
(29), showed decent anti-proliferative activity against TNBC
MDA 231 and MDA 468 cell lines. This establishes the scope of
developing tricyclic heterocycle 4H-[1,3]thiazino[3,2-a]indol-4-
one moiety as potential chemotherapeutic agents for fighting
TNBCs, which are currently perceived as highly challenging
targets. Having the C-10 position of the ring system 10 open for
further chemical operations could be crucial for developing
more potent anti-cancer compounds based on this heterocycle.
2-Methyl-4H-[1,3]thiazino[3,2-a]indol-4-one (10): Yellow solid,
yield 75%; mp 133-139 C; 1H NMR (300 MHz, CDCl3) δ 8.80-8.78 (m
1H, Ar), 7.58-7.57 (m, 1H, Ar), 7.38- 7.35 (m, 2H, Ar), 6.70 (s, 1H, Ar),
6.30 (s, 1H, CH), 2.33 (s, 3H, CH3); 13C NMR (75 MHz, CDCl3) δ 160.2,
147.8, 134.5, 128.6, 127.1, 124.3, 123.2, 119.0, 117.0, 114.5, 103.4,
22.4,; IR (neat): ν 3120, 2925, 2852, 1666, 1430, 1337, 824, 779 cm-
1; HRMS (ESI) calcd for C12H9NOS 216.0405 [M + H]+, found 216.0482.
4H-[1,3]thiazino[3,2-a]indol-4-one (17): Yellow solid, yield 68%;
mp 112-114 C; 1H NMR (300 MHz, CDCl3) δ 8.83-8.80 (m, 1H, Ar),
7.60-7.57 (m, 1H, Ar), 7.45-7.37 (m, 3H, Ar, CH), 6.77(s, 1H, Ar), 6.49
(d, J = 10.2Hz, 1H, CH); 13C NMR (75 MHz, CDCl3) δ 159.8, 134.5,
134.2, 128.2, 126. 6, 124.4, 123.4, 119.0, 117.2, 115.7 104.4; IR
(neat): ν 3114, 3045, 1661, 1435, 1344, 801, 769 cm-1; HRMS (ESI)
calcd for C11H7NOS 202.0248 [M + H]+, found 202.0329.
8-fluoro-2-methyl-4H-[1,3]thiazino[3,2-a]indol-4-one
(20):
Yellow solid, yield 64%; mp 125-126 C; 1H NMR (300 MHz, CDCl3) δ
8.73-8.70 (m, 1H, Ar), 7.22-7.19(m, 1H, Ar), 7.11-7.03 (m, 1H, Ar),
6.67(d, J = 2.1 Hz, 1H, Ar) 6.34 (s, 1H, CH), 2.40 (s, 3H, CH3); 13C NMR
(75 MHz, CDCl3) δ 160.0 (1JC-F = 241.2Hz). 159.8, 147.8, 130.9,
Experimental Section
129.6(3JC-F = 10.5Hz), 128.9, 118.2(3JC-F = 9.2Hz), 114.5, 111.1(2JC-F
=
Melting points were determined in open capillary tubes on an
automated melting point apparatus and are uncorrected. Reactions
were monitored using thin layer chromatography (TLC) on 0.2 mm
silica gel F254 plates. The chemical structures of final products were
determined by their NMR spectra (1H and 13C NMR) using 300 MHz
spectrometer. 13C NMR spectra are fully decoupled. High-resolution
25.2Hz), 104.4(2JC-F = 24.1Hz) 103.1 (4JC-F = 4.2Hz), 22.5; IR (neat): ν
3180, 3064, 2952, 1670, 880, 775 cm-1; HRMS (ESI) calcd for
C12H8FNOS 234.0311 [M + H]+, found 234.0386.
2,8-dimethyl-4H-[1,3]thiazino[3,2-a]indol-4-one (21): Yellow oil,
yield 72%;1H NMR (300 MHz, CDCl3) δ 8.65 (d, J = 8.5Hz, 1H, Ar), 7.36
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(s, 1H, Ar), 7.18 (d, J = 8.5 Hz, 1H, Ar), 6.64 (s, 1H, Ar), 6.32 (s, 1H, CH),
8-fluoro-2-propyl-4H-[1,3]thiazino[3,2-a]indol-4-one (28): Yellow
View Article Online
2.49 (s, 3H, CH3), 2.36 (s, 3H, CH3); 13C NMR (75 MHz, CDCl3) δ 160.0, solid, yield 65%; mp 90-95 C; 1H NMR (300DMOHI:z1,0C.1D0C39l3/)Cδ9O8B.7040-580.700E
147.5, 133.9, 132.7, 128.9, 127.0, 124.7, 118.8, 116.6, 114.5, 103.1, (m, 1H, Ar), 7.21-7.17 (m, 1H, Ar), 7.09-7.02 (m, 1H, Ar), 6.66 (s, 1H,
22.4, 21.6; IR(neat); ν 2924, 2851, 1667, 1442, 1355, 805 cm-1; Ar), 6.34 (s, 1H, CH), 2.57 (t, J = 7.5 Hz, 2H, CH2), 1.80-1.68 (m, 2H,
HRMS (ESI) calcd for C13H11NOS 230.0561 [M + H]+, found 230.0639.
CH2), 1.02 (t, J = 7.3 Hz, 3H, CH3); 13C NMR (75 MHz, CDCl3) δ 160.0
(1JC-F = 240.8 Hz), 159.9, 152.7, 130.8, 129.6 (3JC-F = 10.5Hz), 129.0,
118.1 (3JC-F = 9.2Hz), 113.5, 111.0 (2JC-F = 25.1Hz), 104.3 (2JC-F = 24.2Hz),
103.2 (4JC-F =4.3Hz), 38.4, 22.4, 13.4; IR (neat): ν 3123, 3065, 2962,
2930, 1669, 829, 775 cm-1; HRMS (ESI) calcd for C14H12FNOS
262.0624 [M + H]+, found 262.0702.
7-chloro-2-methyl-4H-[1,3]thiazino[3,2-a]indol-4-one (22):
Yellow solid, yield 70%; mp 145-147 C; 1H NMR (300 MHz, CDCl3) δ
8.79 (s, 1H, Ar), 7.45 (d, J = 8.4 Hz, 1H, Ar), 7.33-7.28 (m, 1H, Ar), 6.65
(s, 1H, Ar), 6.30 (s, 1H, CH), 2.38 (s, 3H, CH3); 13C NMR (75 MHz, CDCl3)
δ 159.8, 148.2, 134.5, 129.0, 127.8, 127.0, 124.8, 119.6, 117.0, 114.3,
103.1, 22.5; IR (neat): ν 3120, 2924, 2852, 1669, 1358, 1202, 814,
8-methyl-2-propyl-4H-[1,3]thiazino[3,2-a]indol-4-one
(29):
716 cm-1; HRMS (ESI) calcd for C12H8ClNOS 250.0015 [M + H]+, found Yellow solid, yield 68%; mp 132-134 C; 1H NMR (300 MHz, CDCl3) δ
250.0087.
8.67 (d, J = 8.5 Hz, 1H, Ar), 7.35 (s, 1H, Ar), 7.19 (d, J = 8.5 Hz, 1H, Ar),
6.68 (s, 1H, Ar), 6.36 (s, 1H, CH), 2.60 (t, J = 7.4 Hz, 2H, CH2), 2.49 (s,
3H, CH3), 1.80-1.71 (m, 2H, CH2), 1.04 (t, J = 7.3 Hz, 3H, CH3); 13C NMR
(75 MHz, CDCl3) δ 160.2, 152.4, 133.9, 132.7, 128.9, 127.1, 124.6
118.8, 116.6, 113.7, 103.3, 38.4, 22.4, 21.6, 13.4; IR (neat): ν 3125,
2960, 2871, 1660, 1351, 820 cm-1; HRMS (ESI) calcd for C15H15NOS
258.0874 [M + H]+, found 258.0959.
2-ethyl-4H-[1,3]thiazino[3,2-a]indol-4-one (23): Yellow solid,
yield 80%; mp 70-74 C;1H NMR (300 MHz, CDCl3) δ 8.82-8.79 (m, 1H,
Ar), 7.58 (m, 1H, Ar) , 7.39-7.35 (m, 2H, Ar), 6.73 (s, 1H, Ar), 6.36 (s,
1H, CH), 2.63 (q, J = 7.5 Hz, 2H, CH2), 1.36-1.31 (t, J = 7.5 Hz, 3H, CH3);
13C NMR (75 MHz, CDCl3) δ 160.4, 154.2, 134.4, 128.6, 127.1, 124.2,
123.2, 119.0, 117.0, 112.9, 103.6, 29.8, 13.5; IR (neat): ν 3150,
2974, 2926, 1668, 1511, 1331, 753 cm-1; HRMS (ESI) calcd for
C13H11NOS 230.0561 [M + H]+, found 230.0638.
7-chloro-2-propyl-4H-[1,3]thiazino[3,2-a]indol-4-one
(30):
Yellow solid, yield 71%; mp 90-91C;1H NMR (300 MHz, CDCl3) δ 8.81
(s, 1H, Ar), 7.46 (d, J = 8.4 Hz, 1H, Ar), 7.34-7.28 (m, 1H, Ar), 6.66 (s,
1H, Ar), 6.34 (s, 1H, CH), 2.59 (t, J = 7.6 Hz, 2H, CH2), 1.82-1.68 (m,
2H, CH2), 1.04 (t, J = 7.3Hz, 3H, CH3); 13C NMR (75 MHz, CDCl3) δ
160.0, 153.1, 134.5, 129.0, 127.9, 127.0, 124.9, 119.6, 117.1, 113.5,
103.2, 38.5, 22.4, 13.4; IR (neat): ν 3119, 2960, 2926, 1660, 1361,
820 cm-1; HRMS (ESI) calcd for C14H12ClNOS 278.0328 [M + H]+,found
278.0406.
2-ethyl-8-fluoro-4H-[1,3]thiazino[3,2-a]indol-4-one (24): Yellow
solid, yield 65%; mp 111-114C;1H NMR (300 MHz, CDCl3) δ 8.73-8.69
(m, 1H, Ar), 7.19-7.16 (m, 1H, Ar), 7.08-7.01 (m, 1H, Ar), 6.65 (s, 1H,
Ar), 6.35 (s, 1H, CH), 2.63 (q, J = 7.4Hz, 2H, CH2), 1.33 (t, J = 7.5Hz, 3H,
CH3); 13C NMR (75 MHz, CDCl3) δ 160.0 (1JC-F = 210.9Hz), 160.0, 154.2,
130.8, 129.6 (3JC-F = 10.6Hz), 129.0, 118.1 (3JC-F = 9.3Hz), 112.8, 111.0
(2JC-F = 25.1Hz), 104.3 (2JC-F = 24.1Hz), 103.2 (4JC-F = 4.2Hz), 29.8, 13.4;
IR (neat): ν 3122, 3064, 2973, 2926, 1670, 1203, 889, 779 cm-1;
2-phenyl-4H-[1,3]thiazino[3,2-a]indol-4-one (31): Yellow solid,
HRMS (ESI) calcd for C13H10FNOS 248.0467 [M + H]+, found 248.0544. yield 66%; mp 164-166 C; 1H NMR (300 MHz, CDCl3) δ 8.86-8.83 (m,
1H, Ar), 7.71 (d, J = 7.4 Hz, 2H, Ar), 7.64-7.62 (m, 1H, Ar), 7.55-7.52
(m, 3H, Ar), 7.43-7.40 (m, 2H, Ar), 6.88 (s, 1H, Ar), 6.78 (s, 1H, CH);
2-ethyl-8-methyl-4H-[1,3]thiazino[3,2-a]indol-4-one (25): Yellow
solid, yield 68%; mp 102-105C; 1H NMR (300 MHz, CDCl3) δ 8.65 (d,
13C NMR (75 MHz, CDCl3) δ 160.6, 149.6, 135.1, 134.4, 131.3, 129.4,
J = 8.6Hz, 1H, Ar), 7.38 (s, 1H, Ar), 7.19 (d, J = 8.4Hz, 1H, Ar), 6.69 (s,
128.7, 127.0, 126.8, 124.4, 123.4, 119.1, 117.1, 112.8, 104.2; IR
1H, Ar), 6.38 (s, 1H, CH), 2.67 (q, J = 7.5Hz 2H, CH2), 2.50 (s, 3H, CH3),
(neat): ν 3124, 3052, 2926, 1660,1344, 896, 735 cm-1; HRMS (ESI)
1.35 (t, J = 7.5Hz, 3H, CH3); 13C NMR (75 MHz, CDCl3) δ 160.3, 153.9,
calcd for C17H11NOS 278.0561 [M + H]+, found 278.0639.
133.9, 132.7, 128.9, 127.0, 124.6, 118.8, 116.6, 112.9, 103.3, 29.8,
21.6, 13.5; IR (neat): ν 3122, 2912, 1668, 1443, 1375, 806, 776 cm-
8-methyl-2-phenyl-4H-[1,3]thiazino[3,2-a]indol-4-one
(32):
1; HRMS (ESI) calcd for C14H13NOS 244.0718 [M + H]+,found 244.0795. Yellow solid, yield 70%; mp 164-170 C; 1H NMR (300 MHz, CDCl3) δ
8.70 (d, J = 8.5 Hz, 1H, Ar), 7.70-7.67 (m, 2H, Ar), 7.53-7.51 (m, 4H,
7-chloro-2-ethyl-4H-[1,3]thiazino[3,2-a]indol-4-one (26): Yellow
Ar), 7.41 (s, 1H, Ar), 7.22 (d, J = 8.5 Hz, 1H, Ar), 6.78 (s, 1H, Ar), 6.75
solid yield 66%; mp 85-88C; 1H NMR (300 MHz, CDCl3) δ 8.82 (s, 1H,
(s, 1H, CH), 2.51 (s, 3H, CH3); 13C NMR (75 MHz, CDCl3) δ 160.4, 149.4,
Ar), 7.47 (d, J = 8.4Hz, 1H, Ar) 7.35-7.28 (m, 1H, Ar), 6.69 (s, 1H, Ar),
6.37 (s, 1H, CH), 2.66 (q, J = 7.5Hz, 2H, CH2), 1.35 (t, J = 7.5Hz, 3H,
135.2, 134.1, 132.7, 132.6, 131.2, 129.3, 129.0, 126.8, 124.9, 118.9,
116.7, 112.8, 103.9, 21.6; IR (neat): ν 3065, 2923, 1656, 1364, 803,
CH3); 13C NMR (75 MHz, CDCl3) δ 160.1, 154.6, 134.5 ,129.0, 127.8,
760 cm-1; HRMS (ESI) calcd for C18H13NOS 292.0718 [M + H]+, found
127.1, 124.9, 119.6, 117.1, 112.7, 103.3, 29.8, 13.5; IR (neat): ν
292.0791.
3119, 3070, 2973, 2926, 1671, 1366, 822 cm-1; HRMS (ESI) calcd
for C13H10ClNOS 263.0172 [M + H]+, found 264.0247.
Procedure for the synthesis of ethyl 3-((1H-indol-2-yl)thio)but-2-
enoate (19): In a clean 50 mL RB flask appropriate indoline-2-thione
(0.34mmol) was mixed with water (5 mL) followed by propiolate
ester (0.50 mmol) and powdered KOH (0.84 mmol). The reaction
mixture was stirred at room temperature until the thione was
completely consumed (as indicated by TLC). The reaction mixture
was then diluted with water (5 mL) and extracted with DCM (2 x 10
mL) the organic layer was then washed with brine (5 ml), dried over
Na2SO4 and concentrated in vacuo. The residue obtained was
purified using column chromatography (15% ethyl acetate in
2-propyl-4H-[1,3]thiazino[3,2-a]indol-4-one (27): Yellow solid,
yield 72%; mp 87-89 C;1H NMR (300 MHz, CDCl3) δ 8.81-8.79 (m, 1H,
Ar), 7.59 (d, J = 5.1 Hz, 1H, Ar), 7.37-7.35 (m, 2H, Ar), 6.74 (s, 1H, Ar),
6.36 (s, 1H, CH), 2.58 (t, J = 7.4 Hz, 2H, CH2), 1.79-1.72 (m, 2H, CH2),
1.04 (t, J = 7.3 Hz, 3H, CH3); 13C NMR (75 MHz, CDCl3) δ 160.4, 152.6,
134.4, 128.6, 127.2, 124.3, 123.2, 119.0, 117.0, 113.6, 103.6, 38.4,
22.4, 13.4; IR (neat); ν 3123, 3065, 2960, 2926, 2868, 1662, 831,
752 cm-1; HRMS (ESI) calcd for C14H13NOS 244.0718 [M + H]+, found
244.0795.
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J. Name., 2013, 00, 1-3 | 5
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Organic & Biomolecular Chemistry
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hexanes) to produce ethyl 3-((1H-indol-2-yl)thio)but-2-enoate (19). incubator overnight and the plate was read at 550nm using
View Article Online
White solid, yield 90%; mp 104-109C; 1H NMR (300 MHz, CDCl3) δ microplate reader the next day.
DOI: 10.1039/C9OB00500E
8.43 (bs, 1H, NH), 7.64 (d, J = 7.9 Hz, 1H, Ar), 7.42 (d, J = 8.2 Hz, 1H,
Ar), 7.27 (dd, J = 7.7 and 7.7 Hz, 1H, Ar), 7.16 (dd, J = 7.5 and 7.5 Hz,
1H, Ar), 6.84 (s, 1H, Ar) 5.93 (s, 1H, CH), 4.25 (q, J = 7.1 Hz, 2H, CH2),
Conflicts of Interest
1.91 (s, 3H, CH3), 1.33 (t, J = 7.1 Hz, 3H, CH3); 13C NMR (75 MHz, CDCl3)
δ 166.4, 158.3, 137.6, 128.2, 123.6, 123.4, 120.9, 120.4, 113.3, 112.9,
111.1, 60.2, 24.1, 14.4; ν 3314.30, 2979.56, 2897.97, 1667.33,
1586.29, 1187, 754 cm-1; HRMS (ESI) calcd for C14H12ClNOS
262.0823 [M + H]+, found 262.0899.
There are no conflicts of interest to declare.
Acknowledgements
The authors gratefully acknowledge the financial support
provided by Natural Sciences and Engineering Research Council
of Canada (NSERC), Nipissing University, the Canada Foundation
for Innovation (CFI) and the Northern Ontario Heritage Fund
Corporation (NOHFC) to conduct this research.
General procedure for the synthesis of 2-methyl-4-oxo-4H-
[1,3]thiazino[3,2-a]indole-10-carbaldehydes 33 and 34: To a
solution of POCl3 (0.15 mmol) in DMF (2 mL) appropriate 4H-
[1,3]thiazino[3,2-a]indol-4-one (0.10 mmol) was added. The reaction
mixture was left to stir at 50 °C for 2h. Upon completion, the mixture
was cooled to room temperature and quenched with 2% aqueous
NaOH solution, until it turned basic. The mixture was then extracted
with ethyl acetate (2 x 10 mL). The combined organic layers were
washed with brine (5 mL) and dried over Na2SO4. The dried organic
layer was concentrated in vacuo and the resulting residue was
purified using column chromatography (30% ethyl acetate in
hexanes) to obtain 2-methyl-4-oxo-4H-[1,3]thiazino[3,2-a]indole-10-
carbaldehydes 33 and 34.
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7-chloro-2-methyl-4-oxo-4H-[1,3]thiazino[3,2-a]indole-10-
1
carbaldehyde (33): Pink Solid, yield 88%; mp 205-206 C; H NMR
(300 MHz, CDCl3) δ 10.36 (s, 1H, CHO), 8.86 (s, 1H, Ar), 7.94 (d, J = 7.7
Hz, 1H, Ar), 7.49 (d, J = 6.6 Hz, 1H, Ar), 6.58 (s, 1H, CH), 2.51 (s, 3H,
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130.6, 126.5, 124.6, 117.9, 117.6, 116.4, 114.8, 22.7; IR (neat): ν
3113, 3060, 2957, 2921, 2832, 2791, 1702, 1650, 1490, 1408, 817
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carbaldehyde (34): Off-white solid, yield 90%; mp 159-161 C; H
1
NMR (300 MHz, CDCl3) δ 10.32 (s, 1H, CHO), 8.80 (s, 1H, Ar), 7.89 (d,
J = 8.5 Hz, 1H, Ar), 7.45 (d, J = 8.4 Hz, 1H, Ar), 6.56 (s, 1H, CH), 2.69 (t,
J = 7.5 Hz, 2H, CH2), 1.85-1.78 (m, 2H, CH2), 1.06 (t, J = 7.3 Hz, 3H,
CH3); 13C NMR (75 MHz, CDCl3) δ 183.1, 159.0, 154.9, 138.3, 135.6,
130.5, 126.4, 124.7, 117.8, 117.6, 115.5, 114.9, 38.6, 22.6, 13.4; IR
(neat): ν 3110, 3079, 2969, 2925, 2879, 2790, 1698, 1648, 1408,
883, 735 cm-1; HRMS (ESI) calcd for C15H12ClNO2S 306.0277 [M + H]+,
306.0354.
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Cell line Culture: Two human adenocarcinoma triple negative
breast cancer cells lines MDA 231 and MDA 468 were purchased
from ATCC, USA. The cell lines were checked for mycoplasma
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