Synthesis and in vitro cytotoxic evaluation of N-alkylbromo and N-alkylphthalimido-isatins

Article abstract of DOI:10.1016/j.bmcl.2011.03.043

The manuscript pertains to the synthesis and in vitro cytotoxic evaluation of a series of N-alkylbromo and N-alkylphthalimido-isatins against four different human cancer cell lines namely Colon: HCT-15; Liver: Hep-2; Lung: A-549 and Leukemia: THP-1 at 10 and 100 μM concentrations. The active compounds based on preliminary studies were evaluated for their IC₅₀ value against six cell lines viz. Colo-205, HCT-15 (Colon), THP-1 (Leukemia), A-549 (Lung), PC-3 (Prostate) and HeLa (Cervix). The active analogue IS-4 exhibited IC₅₀ values of 4.57, 10.90, 11.75, 12.40 and 54.20 μM against HeLa, PC-3, HCT-15, THP-1 and Colo-205, respectively.

Full text of DOI:10.1016/j.bmcl.2011.03.043

Bioorganic & Medicinal Chemistry Letters 21 (2011) 3017–3020
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Synthesis and in vitro cytotoxic evaluation of N-alkylbromo
and N-alkylphthalimido-isatins
a
b
a
b
a,
⇑
Pardeep Singh , Sharanjeet Kaur , Vipan Kumar , P. M. S. Bedi , M. P. Mahajan ,
c
c
c
Irum Sehar , Harish Chandra Pal , Ajit Kumar Saxena
Department of Chemistry, Guru Nanak Dev University, Amritsar 143005, India
Department of Pharmaceutical Sciences, Guru Nanak Dev University, Amritsar 143005, India
Cancer Pharmacology Division, Indian Institute of Integrative Medicine, Jammu 180001, J & K, India
a
b
c
a r t i c l e i n f o
a b s t r a c t
Article history:
The manuscript pertains to the synthesis and in vitro cytotoxic evaluation of a series of N-alkylbromo and
N-alkylphthalimido-isatins against four different human cancer cell lines namely Colon: HCT-15; Liver:
Received 6 January 2011
Revised 5 February 2011
Accepted 11 March 2011
Available online 21 March 2011
Hep-2; Lung: A-549 and Leukemia: THP-1 at 10 and 100
on preliminary studies were evaluated for their IC50 value against six cell lines viz. Colo-205, HCT-15
Colon), THP-1 (Leukemia), A-549 (Lung), PC-3 (Prostate) and HeLa (Cervix). The active analogue IS-4
lM concentrations. The active compounds based
(
exhibited IC50 values of 4.57, 10.90, 11.75, 12.40 and 54.20
Colo-205, respectively.
l
M against HeLa, PC-3, HCT-15, THP-1 and
Keywords:
N-Alkylbromo-isatins
N-Alkylphthalimido-isatins
Cytotoxic evaluation
THP-1 (Leukemia)
HeLa (Cervix)
Ó 2011 Elsevier Ltd. All rights reserved.
4
Cancer is known to be one of the major causes of mortality and
the development of newer and potent anticancer agents is consid-
ered to be of great significance because of the problems like severe
toxicity as well as resistance with the existing drugs. Anticancer
agents exert their biological effect usually by targeting various
intracellular targets; therefore, the current research in the area
mainly focuses on therapeutic targets involved in cell proliferation.
Inhibition of the cancer cell proliferation is one of the most effec-
tive principles in the treatment of cancer using chemotherapy.
Many compounds presently used in cancer treatment affect prolif-
eration and/or lead to cancer cell death via apoptosis, necrosis, or
alike. Indole derivatives have been found to exhibit anticancer
activity by interacting with different intracellular targets. Naturally
occurring and synthetic indolocarbazoles indicated inhibitory
activity against cyclindependent kinases (CDKs) and antiprolifera-
tive activities in a variety of cell lines.1
moieties. N-Alkylated indoles are well known to exhibit antican-
5
cer activity. However, until recently, little has been reported on
the antineoplastic activity of N-alkyl- and N-aryl-isatins. Recent
revelations by Nguyen and Wells showed the apoptosis behaviour
of N-alkyl isatins in a panel of human cancer cell lines.6 The
approach has been further extended by Vine et al. through intro-
duction of various hydrophobic substituents like N-phenethyl,
N-benzyl and N-2-naphthylmethyl on the parent nucleus that
significantly increased their cytotoxicity towards lymphoma cells
and against a wide range of human cancer cell lines, including
MDA-MB-231 metastatic breast adenocarcinoma cells and U937
7
human monocyte-like histiocytic lymphoma cells.
Thus in continuation of our interest towards the synthesis of
novel heterocyclic compounds with diverse medicinal potential8
and the lack of extensive literary reports on the cytotoxicity stud-
ies of N-alkylisatins, we report herein the synthesis and cytotoxic
evaluation of novel N-alkylbromo and N-alkylphthalimido-isatins
against four different human cancer cell lines namely Colon:
HCT-15; Liver: Hep-2; Lung: A-549 and Leukemia: THP-1 at 10
,2
Isatin (1H-indole-2,3-dione) and its derivatives demonstrate a
diverse array of biological and pharmacological activities including
anticonvulsant, antibacterial, antifungal, antiviral and anticancer
3
properties. This broad spectrum of biochemical targets has been
and 100 lM concentrations. The alkyl chain length has been varied
facilitated by the synthetic versatility of isatin, which has allowed
the generation of a large number of structurally diverse derivatives
including analogues derived from substitution of the aryl ring,
and/or derivatisation of the isatin nitrogen and C2/C3 carbonyl
to ascertain the quantitative structure–activity relationship of the
resulting scaffolds against a panel of human cancer cell lines. The
replacement of bromo with phthalimido substituent has been done
7
on the basis of literature rationale as the anticancer potential in-
creases with introduction of aryl substituent on N-alkylated isatins.
The procedure for the synthesis of the N-bromoalkyl derivatives
⇑
Corresponding author.
E-mail address: mahajanmohinderp@yahoo.co.in (M.P. Mahajan).
was based on a
combination of the literature methods.9
0
960-894X/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2011.03.043

3
018
P. Singh et al. / Bioorg. Med. Chem. Lett. 21 (2011) 3017–3020
N-bromoalkyl isatin derivatives IS were synthesised by treating a
solution of isatin in DMF with sodium hydride (NaH) resulting in
the formation of intense purple coloured anion that was subse-
quently reacted with appropriate dibromoalkane (Scheme 1). The
reaction mixture was then heated to 60 °C until the completion
of reaction as evidenced by tlc. This upon quenching with water,
extraction with ethyl acetate and subsequent concentration under
reduced pressure resulted in the isolation of N-alkylbromo isatins
in PBS (pH 7.4) containing 0.02% EDTA]. Cells with viability of more
than 98% as determined by trypan blue exclusion, were used for
5
determination of cytotoxicity. The cell suspension of 1 Â 10
cells/ml was prepared in complete growth medium. Stock solu-
À2
tions (2 Â 10 M) of compounds were prepared in DMSO. The
stock solutions were serially diluted with complete growth med-
ium containing 50 lg/ml of gentamycin to obtain working test
solutions of required concentrations. The final DMSO concentra-
(IS 1-6).
tion was 0.5% and 0.05% when the test material was used at 100
The anionic intermediate A, being an ambident anion could un-
and 10
lM, respectively.
1
dergo N- or O-alkylation, however spectral evidences viz. IR, H and
In vitro cytotoxicity against human cancer cell lines of different
1
3
12
10,11
C spectroscopic studies exhibited exclusive N-alkylation. The
compound IS-4, for example, analyzed for C12 12BrNO showed a
tissues was determined
The 100 L of cell suspension was added to each well of the 96-
well tissue culture plate. The cells were allowed to grow in carbon
dioxide incubator (37 °C, 5% CO , 90% RH) for 24 h. Test materials
in complete growth medium (100 L) were added after 24 h of
using 96-well tissue culture plates.
H
2
l
molecular ion peak at 283. Its IR spectrum showed a sharp absorp-
À1
tions at 1607 and 1738 cm corresponding to the two carbonyls of
2
1
the isatin ring. Its H NMR showed a four proton multiplet at d 1.95
l
corresponding to two –CH
CH Br and another multiplet at d 4.12 (J = 7.6 Hz) for –NCH
from the aromatic protons. The presence of requisite number of
carbons in C NMR further corroborates the assigned structure.
Further, the compound IS upon stirring with potassium phthali-
mide in DMF at 60 °C resulted in the isolation of N-alkylphthlami-
do FIS in good yields (Scheme 1). The structures of FIS were
established on the basis of analytical evidences and spectral data,
the details of which are provided in the experimental section while
salient features are mentioned here.13 The compound FIS-6, for
2
, a multiplet at d 3.45 corresponding to
incubation to the wells containing cell suspension. The plates were
further incubated for 48 h in a carbon dioxide incubator. The cell
growth was stopped by gently layering trichloroacetic acid (50%,
2
2
apart
1
3
50 lL) on top of the medium in all the wells. The plates were incu-
bated at 4 °C for 1 h to fix the cells attached to the bottom of the
wells. The liquid of all the wells was gently pipetted out and dis-
carded. The plates were washed five times with distilled water to
remove trichloroacetic acid, growth medium low molecular weight
metabolites, serum proteins, etc., and air-dried. The plates were
stained with sulforhodamine B dye (0.4% in 1% acetic acid,
example, analyzed for C22
H
20
N
2
O
4
showed a molecular ion peak
100
tic acid and then air-dried. The adsorbed dye was dissolved in
Tris–HCl Buffer (100 L, 0.01 M, pH 10.4) and plates were gently
lL) for 30 min. The plates were washed five times with 1% ace-
1
1
at 378. Its IR spectrum showed sharp absorptions at 1637, 1709,
À1
1
743 and 1768 cm corresponding to the carbonyls. Its 1H NMR
l
spectrum showed a multiplet at d 1.55 corresponding to –CH
2
–
stirred for 10 min on a mechanical stirrer. The optical density
(OD) was recorded on ELISA reader at 540 nm. The cell growth
was determined by subtracting mean OD value of respective blank
from the mean OD value of experimental set. Percent growth in
presence of test material was calculated considering the growth
in absence of any test material as 100% and in turn percent growth
inhibition in presence of test material was calculated.
The newly synthesized N-alkylbromo and N-alkylphthalimido
derivatives were initially tested for their cytotoxicity against a pa-
nel of four human cancer cell lines including HCT-15, Hep-2, A-549
and THP-1 using Sulforhodamine B assay. The concentration
dependent cytotoxicity of these compounds against human cancer
cell lines is shown in Table 1. Adriamycin has been used as
standard in case of A-549 and THP-1 while 5-fluorouracil and
CH –CH –CH , a triplet at d 3.65 (J = 7.2 Hz) and another triplet
2
2
2
13
at d 4.06 (J = 7.5 Hz) apart from the aromatic protons. C NMR fur-
ther showed the presence of isatin amide carbonyl at 157.9, phtha-
limido carbonyls at 168.3 and an isatin keto-carbonyl at 181.7
along with the required carbons confirming the assigned structure.
The human cancer cell lines were procured from National
Cancer Institute, Frederick, PO Box B, Frederick, MD 21702-1201,
U.S.A. Cells were grown in tissue culture flasks in complete growth
medium (RPMI-1640 medium with 2 mM glutamine, pH 7.4, sup-
plemented with 10% fetal calf serum, 100
and 100 units/ml penicillin) in a carbon dioxide incubator (37 °C,
% CO , 90% relative humidity). The cells at subconfluent stage
were harvested from the flask by treatment with trypsin [0.05%
lg/ml streptomycin
5
2
O
O
O
NaH, DMF
Br Br
n
O
O
O
o
N
60 C
N
N
H
n
Br
1
IS
A
O
DMF
60°C
NK
Entry
n
% yield
Entry
n
% yield
O
IS-1
IS-2
IS-4
IS-5
IS-6
2
3
4
5
6
84%
82%
83%
84%
85%
FIS-1
FIS-2
FIS-4
FIS-5
FIS-6
2
3
4
5
6
70%
72%
71%
74%
73%
O
O
O
N
n
N
O
FIS
Scheme 1.

P. Singh et al. / Bioorg. Med. Chem. Lett. 21 (2011) 3017–3020
3019
Table 1
In vitro cytotoxicity against human cancer cell lines
Serial No.
Compound
Concd (
l
M)
Tissue
Colon
Liver
Lung
Leukemia
Cell lines
HCT-15
Hep-2
A-549
THP-1
%
Growth inhibition
1
2
3
4
5
6
7
8
9
IS-1 (n = 2)
IS-2 (n = 3)
IS-4 (n = 4)
IS-5 (n = 5)
IS-6 (n = 6)
FIS-1 (n = 2)
FIS-2 (n = 3)
FIS-4 (n = 4)
FIS-5 (n = 5)
FIS-6 (n = 6)
Adriamycin
10
4
89
59
93
62
88
62
91
67
95
3
86
1
58
4
89
9
97
49
91
—
14
71
36
93
33
68
40
81
48
86
10
68
11
30
15
73
10
85
39
90
—
38
44
0
37
30
49
0
40
0
53
18
43
0
1
0
36
4
36
0
14
96
80
95
90
90
85
91
94
93
9
100
10
100
10
100
10
100
10
100
10
100
10
100
10
100
10
100
10
100
1
96
8
96
44
92
60
93
96
95
96
—
1
0
37
55
—
5
-Fluorouracil
1
1
31
—
—
31
Mitomycin-c
—
—
Table 2
IC50 determination of cytotoxicity of compounds against human cancer cell lines
S. No.
Compound
Tissue
Colon
Leukemia
Lung
Prostate
PC-3
Cervix
Cell lines
Colo-205
HCT-15
THP-1
A-549
HeLa
IC50 (lM)
1
2
3
4
5
IS-2
IS-4
IS-5
IS-6
FIS-6
>100
54.20
>100
>100
>100
13.84
11.75
8.46
12.38
9.73
>100
12.40
42.30
26.50
>100
>100
>100
>100
>100
>100
15.26
10.90
11.45
11.72
12.77
7.77
4.57
5.49
11.97
8.82
mitomycin-C have been used as standards in case of HCT-15 and
Hep-2 cancer cell lines, respectively, for evaluating the cytotoxic
profiles of the newly synthesized scaffolds. Although, the test com-
pounds showed comparatively poor cytotoxic profiles compared to
the standard agents, however, they exhibited an interesting
structure–activity relationship and substituent effect with consid-
N-alkylphthalimido-isatins also increased with the increase in
alkyl chain length as evidenced by the comparable cytotoxic pro-
files of the compound FIS-6 with that of N-alkylbromo derivatives
viz. IS-2, IS-4, IS-5 and IS-6. Compound FIS-1, FIS-2, FIS-4 and FIS-
5 showed poor cytotoxicity against HCT-15, Hep-2, A-549 cancer
cell lines while the compound FIS-6 showed moderate cytotoxicity
erable% growth inhibition at 10
lM. The results clearly revealed
against liver and lung cancer cell lines. At 100 lM compound, FIS-
that the N-alkylbromo compounds showed concentration depen-
dent cytotoxicity in case of HCT-15, Hep-2 and THP-1 with sub-
stantial increase in growth inhibition as the concentration
1, FIS-2, FIS-4, FIS-5 showed moderate to good cytotoxicity against
HCT-15, Hep-2, THP-1 but poor cytotoxicity against A-549 cancer
cell lines.
increases from 10 to 100
l
M. Further, the cytotoxicity increases
Among the ten compounds evaluated for their cytotoxicity, IS-2,
IS-4, IS-5, IS-6 and FIS-6 showed maximum cell growth inhibition
at 10 lM concentration against the THP-1 cell line and were fur-
ther evaluated for their IC50 values, which is the concentration
required to inhibit 50% of cell viability by the test compounds after
exposure to cells, as summarized in Table 2. The cytotoxic effect of
these compounds was evaluated against six cell lines, Colo-205,
HCT-15, THP-1, A-549, PC-3 and HeLa. The effect was more pro-
nounced against HeLa followed by PC-3 cell line. The most active
analogue in the N-bromoalkyl series was IS-4 which exhibited
by increasing carbon linkers between nitrogen and bromo group
as evidenced by compounds IS-2, IS-4, IS-5 and IS-6 which showed
maximum growth inhibition in case of HCT-15, Hep-2 and THP-1
while the compound IS-1 showed poor growth inhibition. The
compound IS-1 and IS-4 showed moderate growth inhibition
against A-549 while the other N-alkyl bromo derivatives showed
practically no cytotoxicity against the same cell line. The
N-alkylphthalimido-isatins have shown considerably poor cytotox-
icity at 10
however considerable cytotoxicity was noticed as the concentra-
tion is increased from 10 to 100 M. Further, the cytotoxicity of
lM when compared with N-alkyl bromo derivatives;
IC50 values of 4.57, 10.90, 11.75, 12.40 and 54.20
lM against HeLa,
l
PC-3, HCT-15, THP-1 and Colo-205, respectively, as compared to

3
020
P. Singh et al. / Bioorg. Med. Chem. Lett. 21 (2011) 3017–3020
other compounds of the series. However, all the compounds were
devoid of any cytotoxic activity against A-549.
9. (a) Garden, S. J.; Torres, J. C.; da Silva, J. F. M.; Pinto, A. C. Synth. Commun. 1998,
8, 1679; (b) Bouhfid, R.; Joly, N.; Massoui, M.; Cecchelli, R.; Lequart, V.; Martin,
2
P.; Essassi, E.-M. Heterocycles 2005, 65, 2949.
The present communication describes the synthesis and cyto-
toxic evaluation of a number of N-alkylbromo and N-alkylphthaim-
ido-Isatins against a range of human cancer cell lines. During initial
studies, all compounds of N-alkylbromo series viz. IS-1, IS-2, IS-4,
IS-5, IS-6 and one of the N-alkylphthalimido derivatives FIS-6,
showed good cytotoxicity against HCT-15, Hep-2, THP-1 cancer cell
lines with effects more pronounced in case of THP-1. These preli-
minary results indicate a marked dependence of cytotoxicity on
the alkyl chain length as well as a preference for bromo substitu-
tion. The potent compounds were further evaluated for their IC50
values against six human cancer cell lines and all the compounds
have shown good cytotoxic profiles in case of HeLa. IS-4 and IS-5
were the two most active compounds against all the cell lines
tested except A-549 and Colo-205 and have IC50 values of 4.57
1
1
1
0. Monks, A.; Scudiero, D.; Skehan, P.; Shoemaker, R.; Paull, K.; Vistica, D.; Hose,
C.; Langley, J.; Cronise, P.; Vaigro-Wolff, A.; Gray-Goodrich, M.; Campbell, H.;
Mayo, J.; Boyd, M. J. Natl. Cancer Inst. 1991, 83, 757.
1. Skehan, P.; Storeng, R.; Scudiero, D.; Monks, A.; Mc Mohan, J.; Vistica, D.;
Warren, J. T.; Bokesch, H.; Kenney, S.; Boyd, M. R. J. Natl. Cancer Inst. 1990, 82,
1107.
2. General procedure and analytical data for N-alkyl bromo isatin IS: To a stirred
suspension of Sodium hydride (1.5 mmol) in dry DMF (10 ml) was added isatin
(
1 mmol) and the resulting solution was stirred at room temperature for
20 min before the addition of dibromoalkane (1 mmol). The reaction mixture
was heated to 60 °C with constant stirring for about 2 h. After the completion
of reaction, as evidenced by tlc, it was quenched by drop wise addition of water
(
20 ml) and extracted with ethyl acetate (3 Â 30 ml). The combined organic
layers were washed with brine solution, dried over anhydrous Na SO and
2
4
concentrated in vacuo. Purification of the reaction mixture by column
chromatography using hexane: ethyl acetate (8:2) furnished the desired N-
alkylbromo derivatives in good yields. 1-(4-Bromo-butyl)-1H-indole-2,3-dione
(IS-4): yellow solid, mp 100–102 °C.
1
and 5.49
lM against HeLa cells, respectively. The results described
H NMR (300 MHz, CDCl
13a,13b), d 4.12(m, 2H, H10a,10b), d 7.54 (m,4H, Ar-H). C NMR: d 28.09, 29.52,
6.60, 41.04, 117.75, 120.77, 124.21, 129.95, 139.31, 144.62, 157.96, 181.46.
3
) d 1.95 (m, 4H, H11a,11b, H12a,12b), d 3.45 (m, 2H,
13
H
3
m
in the present manuscript indicate that these compounds could
serve as the basis for the development of a new group of cancer
chemotherapeutics.
À1
+
2
max (KBr)/cm 1607, 1738 MS (EI) m/z 283 (M ). Calcd for C12H12BrNO : C,
51.09; H, 4.29; N, 4.96. Found: C, 51.32, H, 4.62, N, 4.70.
O
Acknowledgments
4
8
3
5
6
2
O
Financial assistance from CSIR New Delhi under Emeritus Scien-
tist Scheme (M.P.M.) and DST New Delhi under Fast Track Young
Scientist Scheme (V.K.) is gratefully acknowledged.
9
N
1
H
11a
H
11b
7
H
10a
H
13a
13b
H
10b
H
H
12a
H
12b
Br
References and notes
1
3. Procedure and analytical data for N-alkylphthalimido FIS: To a stirred solution of
N-bromoisatin (IS) (1 mmol) in anhydrous DMF was added potassium
phthalimide (2 mmol) and the reaction mixture was heated to 60 °C for 2 h.
On completion as monitored by tlc, water (20 ml) was added to the reaction
mixture and extracted with ethyl acetate (3 Â 30 ml). Combined organic layers
1
.
Schultz, R. M.; Merriman, R. L.; Toth, J. E.; Zimmermann, J. E.; Hertel, L. W.;
Andis, S. L.; Dudley, D. E.; Rutherford, P. G.; Tanzer, L. R.; Grindey, G. B. Oncol.
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2
.
Zhu, G.; Conner, S. E.; Zhou, X.; Shih, C.; Li, T.; Anderson, B. D.; Brooks, H. B.;
Campbell, R. M.; Considine, E.; Dempsey, J. A.; Faul, M. M.; Ogg, C.; Patel, B.;
Schultz, R. M.; Spencer, C. D.; Teicher, B.; Watkins, S. A. J. Med. Chem. 2003, 46,
2 4
were washed with brine solution, dried over anhydrous Na SO and
concentrated under reduced pressure to yield crude yellow solid which was
then recrystallized by using hexane:ethyl acetate (5:5).
2
027.
(a) Pandeya, S. N.; Smitha, S.; Jyoti, M.; Sridhar, S. K. Acta Pharm. 2005, 55, 27;
b) Cerchiaro, G.; Ferreira, A. M. D. C. J. Braz. Chem. Soc. 2006, 17, 1473; (c) Cane,
1
-[6-(1,3-Dioxo-1,3-dihydro-isoindol-2-yl)-hexyl]-1H-indole-2,3-dione (FIS-6):
3
.
yellow solid, mp 80–83 °C.
(
1
3
H NMR (300 MHz, CDCl ) d 1.55 (m, 8H, H11a,11b, H12a,12b,H13a,13b,H14a,14b), d
A.; Tournaire, M. C.; Barritault, D.; Crumeyrolle-Arias, M. Biochem. Biophys. Res.
Commun. 2000, 276, 379.
3
.65 (t, 7.2 Hz, 2H, H15a,15b), d 4.06 (t, 7.5 Hz, 2H, H10a,10b), d 7.75(m, 8H, ArH).
C NMR: d 25.94, 26.32, 28.28, 29.20, 37.65, 41.80, 117.73, 120.75, 123.20,
23.48, 124.06, 129.67, 132.03, 133.84, 134.20, 139.21, 140.38, 144.83, 157.90,
13
4
.
.
Vine, K. L.; Matesic, L.; Locke, J. M.; Ranson, M.; Skropeta, D. Anti-Cancer Agents
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(a) Liu, Y.; Lashuel, H. A.; Choi, S.; Xing, X.; Case, A.; Ni, J.; Yeh, L. A.; Cuny, G. D.;
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Emig, P.; Vanhoefer, U.; Seeber, S.; Shandra, A.; Klenner, T.; Beckers, T. Cancer
Res. 2001, 61, 392.
1
1
À1
+
68.35, 181.71. mmax (KBr)/cm 1637, 1709, 1743, 1768 MS (EI) m/z 378 (M ).
5
Calcd for C22
.21.
H
20
2
N O
4
: C, 70.20; H, 5.36; N, 7.44. Found: C, 70.56, H, 5.72, N,
7
O
4
6
7
.
.
Nguyen, J. T.; Wells, J. A. Proc. Natl. Acad. Sci. U.S.A. 2003, 100, 7533.
(a) Vine, K. L.; Locke, J. M.; Ranson, M.; Benkendorff, K.; Pyne, S. G.; Bremner, J.
B. Bioorg. Med. Chem. 2007, 15, 931; (b) Vine, K. L.; Locke, J. M.; Ranson, M.;
Pyne, S. G.; Bremner, J. B. J. Med. Chem. 2007, 50, 5109; (c) Matesic, L.; Locke, J.
M.; Bremner, J. B.; Pyne, S. G.; Skropeta, D.; Ranson, M.; Vine, K. L. Bioorg. Med.
Chem. 2008, 16, 3118.
8
3
5
6
2
O
9
N
1
H
11a
7
H
10a
H
11b
H
13a
H
10b
H
12a
H
13b
8
.
(a) Anand, A.; Bhargava, G.; Kumar, V.; Mahajan, M. P. Tetrahedron Lett. 2010,
H
12b
H
15a
51, 2312; (b) Singh, P.; Bhargava, G.; Kumar, V.; Mahajan, M. P. Tetrahedron Lett.
H
15b
H
14a
2
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