Synthesis of (+)-thiersindole C

Article abstract of DOI:10.1055/s-2007-984893

The indole diterpene alkaloid (+)-thiersindole C has been synthesised from ent-halimic acid. Firstly was elaborated the bicyclic system, secondly a Fischer indolization was used to obtain the north side chain and finally elongation of the south side chain

Full text of DOI:10.1055/s-2007-984893

LETTER
2017
Synthesis of (+)-Thiersindole C
S
ynthesi
s
s of (+)-T
i
hiersind
d
ole
C
ro S. Marcos,*a Miguel A. Escola,a Rosalina F. Moro,a Pilar Basabe,a David Diez,a Faustino Mollinedo,b,c
Julio G. Uronesa
a
Departamento de Química Orgánica, Facultad de Ciencias Químicas, Universidad de Salamanca, Plaza de los Caídos 1–5,
37008 Salamanca, Spain
Fax +34(923)294574; E-mail: ismarcos@usal.es
b
Centro de Investigación del Cáncer, Instituto de Biología Molecular y Celular del Cáncer, Consejo Superior de Investigaciones
Científicas, Universidad de Salamanca, Campus Miguel de Unamuno, 37007 Salamanca, Spain
c
APOINTECH, Campus Miguel de Unamuno, 37007 Salamanca, Spain
Received 26 February 2007
This paper is dedicated to Prof. V. Gotor on the occasion of his 60th birthday.
Thiersindoles A–C structures and their relative stereo-
chemistries were determined by analysis of NMR data
(1H and 13C, HMQC, HMBC and NOESY). The absolute
stereochemistry of thiersindole B was assigned by appli-
Abstract: The indole diterpene alkaloid (+)-thiersindole C has been
synthesised from ent-halimic acid. Firstly was elaborated the bi-
cyclic system, secondly a Fischer indolization was used to obtain
the north side chain and finally elongation of the south side chain
was achieved with an isoprene unit. The synthesis of (+)-thiersin- cation of the modified Mosher NMR method. The other
dole C has corroborated the absolute configuration for the natural
two thiersindoles were assumed to posses the same
absolute stereochemistry.3
product (–)-thiersindole C. The synthesized (+)-thiersindole C
showed antitumor activity against a number of human tumor cell
lines with an IC50 in the range of 10–5 M.
In this paper we show the synthesis of thiersindole C, con-
firming the proposed structure and absolute configura-
tion,3 from the natural product ent-halimic acid (1)5
(Figure 2). This compound, whose structure and absolute
configuration are known, and which has been previously
used by us for the synthesis of bioactives products such as
ent-halimanolides,6 ent-agelasine C,7 chettaphanins I8 and
II9 and sesterterpenolides,10 was chosen as starting mate-
rial for the synthesis of thiersindole C.
Key words: indole diterpene alkaloids, thiersindole C, ent-halimic
acid
The indole diterpene alkaloids isolated from fungi show
structural diversity1 and bioactivities such as insecticidal,
tremorgenic or pollen growth inhibitory activity among
others.2
Penicillium thiersii is a new Penicillium species that
colonize sclerotia or stromata of wood decay fungi.3
Extracts of P. thiersii cultures show potent insecticidal
activity, and chemical studies of this species led to the dis-
covery of indole diterpenoids such as thiersinines A and
B4 with a new ring system, and more recently three new
indole diterpenoids thiersindoles A–C3 with quite dif-
ferent structures from those isolated previously in this
species (Figure 1).
15
CH2OH
H
N
16
20
1
B
10
17
A
8
5
3
HO
H
19
COOH
18
ent-halimic acid (1)
thiersindole C
H
N
H
H
N
N
C
Figure 2 Structures for ent-halimic acid and thiersindole C.
H
H
The main transformations for the synthesis of thiersindole
C from ent-halimic acid are (Figure 2):
HO
HO
HO
(a) Functionalization at C-3 and isomerization of the
anular double bond to the tetrasubstituted position.
thiersindole C
thiersindole A
thiersindole B
(b) Elaboration of the indole unit on the north side chain.
Figure 1 Thiersindoles A–C structures.
(c) Addition of an isoprenic unit at C-18 in order to form
the south side chain.
The retrosynthetic patway is shown in Scheme 1. Elabo-
ration of the south side chain of thiersindole C can be
achieved from the intermediate 4 (Scheme 1), via elonga-
tion by a one-carbon unit and then by a four-carbons
SYNLETT 2007, No. 13, pp 2017–2022
Advanced online publication: 12.07.2007
DOI: 10.1055/s-2007-984893; Art ID: D05207ST
© Georg Thieme Verlag Stuttgart · New York
1
3
.0
8
.2
0
0
7

2018
I. S. Marcos et al.
LETTER
15
CH2OH
16
CHO
CH2OAc
20
1
10
17
2
8
2
3
5
3
H
H
AcO
19
COOMe
CH2OAc
COOH
18
2
3
ent-halimic acid (1)
H
1
H
H
N
N
2
N
9
3
7
10
5
27
12
20
28
11
15
17
26
16
29
HO
TBSO
AcO
21
CH2OAc
CHO
thiersindole C
4
5
23
24
25
Scheme 1
fragment, by displacement of a good leaving group such Synthesis of Intermediate 3 Functionalized at C-3 and
as iodide or tosylate group to give 5. The north side chain Tetrasubstituted Double Bond
can be elaborated by Fischer’s methodology with an alde-
This stage included the degradation of the side chain of
hyde derivative from the intermediate 3. The functional-
ent-halimic acid (1) by three carbon atoms to elaborate the
ization of the bicyclic system can be achieved with the
derivative 2, and then functionalization on C-3, followed
trinorderivative 2, previously obtained from ent-halimic
by isomerization of the double bond.
acid (1)5 by allylic oxidation at C-2 position, subsequent
Methylketone 6 was obtained from ent-halimic acid (1;
Scheme 2), following our protocol.10 Trapping the kinetic
enolate of 6 by treatment with LDA and TMSCl gave the
silylenolether 7 which by oxidation with OsO4–NMO9,11
produced the a-hydroxyketone 8. Reduction of the last
compound with NaBH4 followed by cleavage of the diol
unit of 9 with Pb(OAc)4 gave the required aldehyde 2.
oxygenation at C-3, and removal of the carbonyl group at
C-2. Ulterior migration of the double bond to C5–C10 will
give the intermediate 3, after changing to the adequate
functional groups.
The synthesis of thiersindole C was carried out in three
parts:
1) Synthesis of the intermediate 3 functionalized at C-3
Functionalization at C-3 (Scheme 3) was achieved by
oxidation of C-2. Subsequent removal of the carbonyl
group obtained gave the intermediate 21 (Scheme 3).
and tetrasubstituted double bond.
2) Synthesis of the indole intermediate 4.
3) Synthesis of thiersindole C, and final transformations.
OH
15CH2OH
O
R
TMSO
16
CHO
20
1
10
c
a
b
e
17
8
5
3
H
H
H
H
H
19
COOMe
COOMe
COOMe
COOH
COOMe
18
R
=O
OH
6
2
7
ent-halimic acid (1)
8
9
d
Scheme 2 Reagents and conditions: (a) Ref. 10; (b) LDA, TMSCl, THF, –78 ºC, 30 min (96%); (c) OsO4, NMO, t-BuOH, THF, H2O, r.t.,
overnight (97%); (d) NaBH4, EtOH, r.t., 30 min (93%); (e) Pb(OAc)4, C6H6, r.t., 20 min (98%).
Synlett 2007, No. 13, 2017–2022 © Thieme Stuttgart · New York

LETTER
Synthesis of (+)-Thiersindole C
2019
OAc
OAc
OR
CHO
TMSO
O
a
d
c
2
3
H
H
H
H
COOMe
COOMe
COOMe
COOMe
R
H
Ac
13
2
12
10
11
b
e
g
R2
OAc
OR
OAc
S
O
O
l or m
i or j
f
S
3
3
R1
AcO
RO
HO
H
H
H
H
COOMe
COOMe
COOMe
COOMe
R1 R2
14 3R
15 3S
16 3R
17 3S
R
h
22 OAc
21 OH
19
18
20
OAc OAc
OAc
OH OH
H
k
Scheme 3 Reagents and conditions: (a) NaBH4, EtOH, r.t., 30 min (95%); (b) Ac2O, pyridine, r.t., overnight (98%); (c) Na2CrO4, Ac2O,
AcOH, NaOAc, C6H6, 55 °C, overnight (71%); (d) LDA, TMSCl, THF, –78 °C, 30 min (95%); (e) OsO4, NMO, t-BuOH, THF, H2O, r.t., over-
night; (f) Ac2O, pyridine, r.t., overnight (12: 14%; 16: 38%; 17: 38%, from 13, two steps); (g) Mn(OAc)3·2H2O, C6H6, 130 °C, overnight (16:
48%; 17: 49%); (h) NaH, THF, 70 °C, 1 h (88%, based on recovered starting material); (i) ethane-1,3-dithiol, CH2Cl2, BF3·Et2O, r.t., overnight
(18: 11%; 19: 83%); (j) 1,2-ethanedithiobis(trimethylsilane), ZnI2, Et2O, –20 °C → r.t. (19, 92%); (k) K2CO3–MeOH (3%), r.t., overnight
(96%); (l) 19 to 22: Ni (Raney), EtOH, 50 °C, 2 h (22: 65%; 11: 31%); (m) 20 to 21: Ni (Raney), EtOH, 50 °C, 2 h (96%).
Reduction of 2 with NaBH4 followed by acetylation of the Once we had introduced the hydroxy group at C-3, we
hydroxyderivative 10 led to the acetoxyderivative 11 that proceeded to reduce the carbonyl group at C-2. Treatment
was treated with Na2CrO4 to afford 12 in good yield.
of 17 with ethanedithiol in the presence of BF3·Et2O led to
compounds 18 (11%) and 19 (83%). However, best results
were obtained when the reaction of 17 took place with
1,2-ethanedithiobis(trimethylsylane) and ZnI2,13 afford-
ing 19 in a 92% yield. If dithiane 19 was made to react
with Ni Raney14 a mixture of 22 and 11 was obtained,
however if diol 20, (obtained by alkaline hydrolysis of 19
with K2CO3), reacted with Ni Raney,14 it afforded only the
diol 21 in an excellent yield (77% from 17).
Oxidation at C-3 in 12 was carried out in two different
ways:
a) Trapping the enolate derived from the kinetic deproto-
nation of enone with chlorotrimethylsilane provided the
O-trimethylsilyldienol ether 13. Oxidation of the later
compound with OsO4 (or MCPBA) led to the mixture of
dihydroxy derivatives 14 and 15, which without further
isolation were characterized as the acetyl derivatives 16
and 17.
b) Better results were obtained by reaction of 12 with
Mn(OAc)312 that gave 16 and 17 in an excellent yield. The
undesirable isomer 16 could be recycled into 17, by treat-
ment with NaH that gave a mixture of 16 and 17, with 17
being the major component.
Once the C-3 goup had been oxygenated, the only task
that remained was to isomerize the annular double bond
(Scheme 4). This isomerization in acidic media has been
achieved before for other derivatives of ent-halimic
acid,15 but it must not be done in the absence of the meth-
oxycarbonyl at C-18, because if the reaction takes place
OR
OR
OAc
OAc
c
e
b
O
RO
RO
AcO
H
H
AcO
O
H
COOMe
CH2OR
CH2OAc
23
R
R
3
21 OH
22 OAc
24 OH
25 OAc
a
d
Scheme 4 Reagents and conditions: (a) Ac2O, pyridine, r.t., overnight (98%); (b) HI, C6H6, 85 °C, 8 h (75%); (c) LiAlH4, Et2O, r.t., 1 h (96%);
(d) Ac2O, pyridine, r.t., overnight (98%); (e) HI, C6H6, 85 °C, 8 h (92%).
Synlett 2007, No. 13, 2017–2022 © Thieme Stuttgart · New York

2020
I. S. Marcos et al.
LETTER
H
1
N
OAc
9
2
R
7
3
10
20
27
19
16
5
a
c
18
17
28
11
12
AcO
AcO
AcO
CH2OAc
29 CH2OAc
21
CH2OAc
R
4
3
26 CH2OH
27 CHO
b
Scheme 5 (a) K2CO3–MeOH (0.7%), 0 °C, 5 h (94%); (b) CrO3, pyridine, CH2Cl2, r.t., 1 h (99%); (c) PhNHNH2, AcOH, r.t., 2 h, and 130 °C,
2 h (93%).
with this functionality, g-lactones 10,18-olides are gener- and protect C-3. Due to neopentyl character of the primary
ated, as showed by reaction of the acetyl derivative 22 hydroxy group it was necessary to introduce the remain-
with HI that gave lactone 23 (Scheme 4). That is the ing five carbons in two steps, first elongation by one
reason we decided to obtain the acetyl derivative 25, orig- carbon and then by four carbons (Scheme 6).
inated by LiAlH4 reduction of 21 and subsequent acetyla-
tion of triol 24 that led to the desired triacetate 3 by acidic
treatment of 25.
Hydrolysis of 4 led to diol 28 that by acetylation with one
equivalent of Ac2O in pyridine afforded the monoacetyl
derivative 29. Protection of the hydroxy group at C-3,
with TBDMSOTf gave 30, that by hydrolysis generated
the hydroxy derivative 31, which was oxidized with tetra-
propylammonium perruthenate (TPAP)–NMO to give the
Synthesis of Indole Intermediate 4
aldehyde 32. Reaction of 32 with methoxymethylene-
To introduce the indole system in the side chain of the tri-
triphenylphosphonium chloride in the presence of
acetate 3, it was necessary to obtain the aldehyde 27 and
NaHMDS18 gave 33 that by careful hydrolysis with p-
make use of the Fischer reaction.16 (Scheme 5).
TsOH led to the aldehyde 5.
Chemoselective hydrolysis of 3 with K2CO3 afforded the
Reduction of 5 with NaBH4 produced the hydroxy deriv-
diacetyl derivative 26, which by oxidation with CrO3 in
ative 34 that by treatment with TsCl in pyridine gave the
pyridine gave the aldehyde 27 in nearly quantitative yield.
tosylate 35. Reaction of the latter with the appropriate
Reaction of 27 with phenylhydrazine in AcOH gave the cuprate19 afforded 36. Final deprotection of 36 with
indole derivative 417a in a very good yield. The X-ray TBAF gave 3720 ([a]D +54) whose physical data are
22
experiments confirmed the absolute configuration of 417b exactly the same as those describe by Gloer et al. for
22
(Figure 3).
(–)-thiersindole C ([a]D –42)3 (Figure 1) except for the
sign of the optical rotation which it is exactly the opposite.
In this manner the structure for thiersindole C was
confirmed and the absolute configuration for the natural
product was corroborated. Further studies on the synthesis
of thiersindoles A and B are currently under progress.
The in vitro antitumor activity of (+)-thiersindole C was
determined by the XTT assay in different human tumor
cell lines,21 including HeLa (human epitheloid cervix car-
cinoma), A549 (human lung carcinoma), HT-29 (human
colon adenocarcinoma), and HL-60 (human acute
myeloid leukemia). The synthesized (+)-thiersindole C
inhibited proliferation of HeLa (IC50 = 25.8 3.1 mM),
A549 (IC50 = 28.0 3.2 mM), HT-29 (IC50 = 30.5 2.2
mM) and HL-60 (IC50 = 26.2 2.8 mM) cells. These data
show that compound 37 inhibits proliferation of various
human tumor cells, including leukemic and solid tumor
cells, with an IC50 in the range of 25 mM. These results
indicate that this compound has approximately the same
antitumor potency as several diterpenes such as tubin-
gensins A and B.22
Figure 3 ORTEP view of compound 4.
Synthesis of Thiersindole C and Final Trans-
formations
Finally, the transformation of 4 into thiersindole C re-
quired elongation of the south chain with an isoprenic
unit. It was necessary to distinguish both acetoxy groups
Synlett 2007, No. 13, 2017–2022 © Thieme Stuttgart · New York

LETTER
Synthesis of (+)-Thiersindole C
2021
H
N
H
N
H
N
f
a
AcO
TBSO
R1
b
21
CH2OAc
R2
29
R1
R2
22
MeO
4
28 OH
29 OH
30 OTBS CH2OAc
31 OTBS CH2OH
32 OTBS CHO
CH2OH
CH2OAc
33
c
d
e
g
H
H
N
H
N
1
N
9
2
3
5
10
20
7
27
12
j
k
28
11
17
16
15
21
TBSO
HO
TBSO
29
R
R
5
CHO
37
36
23
h
i
34 CH2OH
35 CH2OTs
26
24
25
Scheme 6 Reagents and conditions: (a) K2CO3–MeOH (1%), 0 ºC, 8 h (97%); (b) Ac2O (1 equiv), pyridine, r.t., overnight (4: 7%; 29: 89%);
(c) TBDMSOTf, 2,6-lutidine, CH2Cl2, 0 ºC to r.t., 45 min (98%); (d) LiAlH4, Et2O, r.t., 1 h (97%); (e) TPAP–NMO, CH2Cl2, r.t., 2 h (96%);
(f) MeOCH2PPh3Cl, NaHMDS, THF, –78 ºC, 20 min (94%); (g) p-TsOH, Me2CO, H2O (0.03 M), r.t., overnight (95%); (h) NaBH4, EtOH, r.t.,
1 h (96%); (i) TsCl, pyridine, r.t., 2 h (97%); (j) 2-methylpropenylmagnesium bromide, ClCuSMe2, THF, –45 ºC to r.t., 4 h (86%); (k) TBAF,
THF, 70 ºC, 3 h (77%).
Simmonds, M. S. J.; Urones, J. G. Tetrahedron Lett. 2000,
41, 2553. (c) Marcos, I. S.; Pedrero, A. B.; Sexmero, M. J.;
Díez, D.; García, N.; Escola, M. A.; Basabe, P.; Conde, A.;
Moro, R. F.; Urones, J. G. Synthesis 2005, 3301.
Acknowledgment
The authors are grateful to Dr. A. M. Lithgow, Dr. C. Raposo and
Dr. F. Sanz, for the NMR, mass spectra and X-ray analysis, respec-
tively. The authors also thank Mr. Janis de la Iglesia-Vicente and
Ms. Beatriz García-Sierra (Centro de Investigación del Cáncer and
(7) Marcos, I. S.; García, N.; Sexmero, M. J.; Basabe, P.; Díez,
D.; Urones, J. G. Tetrahedron 2005, 61, 11672.
APOINTECH, Salamanca, Spain) for the biological tests, the
(8) Marcos, I. S.; Hernández, F. A.; Sexmero, M. J.; Díez, D.;
CICYT (CTQ2005-04406) for financial support and Junta de
Basabe, P.; Pedrero, A. B.; García, N.; Urones, J. G.
Castilla y Leon for a doctoral fellowship to M.A.E.
Tetrahedron 2003, 60, 685.
(9) Marcos, I. S.; Hernández, F. A.; Sexmero, M. J.; Díez, D.;
Basabe, P.; García, N.; Pedrero, A. B.; Sanz, F.; Urones, J.
G. Tetrahedron Lett. 2002, 43, 1245.
References and Notes
(10) Marcos, I. S.; Pedrero, A. B.; Sexmero, M. J.; Diez, D.;
Basabe, P.; García, N.; Moro, R. F.; Broughton, H. B.;
Mollinedo, F.; Urones, J. G. J. Org. Chem. 2003, 68, 7496.
(11) Oliver, S. F.; Högenauer, K.; Simic, O.; Antonello, A.;
Smith, M. D.; Ley, S. V. Angew. Chem. Int. Ed. 2003, 42,
5996.
(1) (a) Smith, A. B. III; Davulku, A. H.; Kürti, L. Org. Lett.
2006, 8, 1672. (b) Smith, A. B. III; Davulku, A. H.; Kürti, L.
Org. Lett. 2006, 8, 1668. (c) Smith, A. B. III; Cui, H. Helv.
Chim. Acta 2003, 86, 3908.
(2) Fueki, S.; Tokiwano, T.; Toshima, H.; Oikawa, H. Org. Lett.
2004, 6, 2697.
(12) (a) Demir, A. S.; Jeganathan, A. Synthesis 1992, 235.
(b) Sing, T. K. M.; Zhu, X. Y.; Yeung, Y. Y. Chem. Eur. J.
2003, 9, 5489. (c) Sing, T. K. M.; Yeung, Y. Y. Chem. Eur.
J. 2006, 12, 8367. (d) Sing, T. K. M.; Yeung, Y. Y. Angew.
Chem. Int. Ed. 2005, 44, 7981.
(3) Li, C.; Gloer, J. B.; Wicklow, D. T. J. Nat. Prod. 2003, 66,
1232.
(4) Li, C.; Gloer, J. B.; Wicklow, D. T.; Dowd, P. F. Org. Lett.
2002, 4, 3095.
(5) Urones, J. G.; Pascual Teresa, J. de; Marcos, I. S.; Diez, D.;
Garrido, N. M.; Alfayate, R. Phytochemistry 1987, 26, 1077.
(6) (a) Marcos, I. S.; Pedrero, A. B.; Sexmero, M. J.; Díez, D.;
Basabe, P.; Hernández, F. A.; Urones, J. G. Tetrahedron
Lett. 2003, 44, 369. (b) Marcos, I. S.; González, J. L.;
Sexmero, M. J.; Díez, D.; Basabe, P.; Williams, D. J.;
(13) Tsuda, M.; Hatakeyama, A.; Kobayashi, J. J. Chem. Soc.,
Perkin Trans. 1 1998, 149.
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2022
I. S. Marcos et al.
LETTER
(14) (a) Bull, J. R.; Sickle, E. S. J. Chem. Soc., Perkin Trans. 1
2000, 4476. (b) Paquette, L. A. Reagents for Organic
Synthesis, Vol. 6; John Wiley & Sons: New York, 1995,
4401. (c) Kawabata, T.; Grieco, P. A.; Sham, H.-L.; Kim, H.;
Jaw, J.; Tu, S. J. Org. Chem. 1987, 52, 3346.
(20) (+)-Thiersindole C(37): [a]D22 +54.0 (c = 0.20, CH2Cl2). IR
(film): 3411, 3056, 2927, 1457, 1375, 1261, 1094, 1046,
1012, 995, 740 cm–1. 1H NMR (400 MHz, CDCl3): d = 7.89
(br s, 1 H, H-1), 7.60 (d, J = 7.9 Hz, 1 H, H-5), 7.32 (d, J =
8.1 Hz, 1 H, H-8), 7.16 (ddd, J = 1.1, 7.2, 8.1 Hz, 1 H, H-7),
7.10 (ddd, J = 1.1, 7.2, 7.9 Hz, 1 H, H-6), 7.05 (s, 1 H, H-2),
5.10 (br t, J = 6.0 Hz, 1 H, H-23), 3.82 (dd, J = 3.7, 11.1 Hz,
1 H, H-17), 2.92 (d, J = 15.8 Hz, 1 H, HA-10), 2.84 (d, J =
15.8 Hz, 1 H, HB-10), 2.37 (m, 1 H, HA-14), 2.25 (m, 1 H,
HB-14), 2.02 (m, 1 H, HA-19), 2.00 (m, 1 H, HA-22), 1.73 (m,
2 H, HB-19, HB-22), 1.71 (m, 1 H, H-12), 1.70 (m, 1 H, HA-
18), 1.68 (s, 3 H, Me-26), 1.60 (m, 1 H, HA-21), 1.55 (s, 3 H,
Me-25), 1.49 (m, 1 H, HA-13), 1.39 (m, 1 H, HB-13), 1.36 (m,
1 H, HB-21), 1.03 (s, 3 H, Me-27), 0.98 (s, 3 H, Me-29), 0.86
(d, J = 6.8 Hz, 3 H, Me-28). 13C NMR (100 MHz, CDCl3):
d = 121.4 (C-2), 113.1 (C-3), 128.9 (C-4), 118.7 (C-5), 119.1
(C-6), 121.6 (C-7), 110.8 (C-8), 135.4 (C-9), 31.2 (C-10),
42.1 (C-11), 33.3 (C-12), 27.2 (C-13), 24.8 (C-14), 134.7
(C-15), 43.1 (C-16), 80.0 (C-17), 27.5 (C-18), 24.9 (C-19),
135.0 (C-20), 35.6 (C-21), 23.1 (C-22), 124.8 (C-23), 131.1
(C-24), 25.6 (C-25), 17.7 (C-26), 21.7 (C-27), 16.7 (C-28),
20.4 (C-29). HRMS (ESI): m/z [M+ + Na] calcd for
C28H39NONa: 428.2924; found: 428.2928.
(21) The in vitro antitumor activity for compound 37, (+)-
thiersindole C, was determined by measurement of its
cytostatic and cytotoxic properties in human tumor cell lines
by the XTT assay, in which the metabolic activity of viable
cells was assessed. Cells were incubated in RPMI-1640 (HL-
60) or DMEM (HeLa, A549, HT-29) culture medium
containing 10% fetal calf serum, in the absence and in the
presence of the indicated compound at a concentration range
of 10–4 to 10–8 M in 96-well plates, and following a 72-h
incubation at 37 °C in a humidified atmosphere of air–CO2
(19:1) the XTT assay was performed. Measurements were
done in triplicate, and the IC50 value, defined as the drug
concentration required to cause 50% inhibition in the
cellular proliferation with respect to the untreated controls,
were determined. Values shown are means SE of four
independent determinations.22
(15) Marcos, I. S.; Martínez, B.; Sexmero, M. J.; Díez, D.;
Basabe, P.; Urones, J. G. Synthesis 2006, 3865.
(16) (a) Rogers, C. U.; Corson, B. B. Org. Synth., Coll. Vol. 4;
Wiley: New York, 1967, 884. (b) Trudell, M. L.; Fukada,
N.; Cook, J. M. J. Org. Chem. 1987, 52, 4293. (c)Robinson
B.; The Fischer Indole Synthesis; Wiley-Interscience: New
York, 1982.
(17) (a) Numbering for compound 4 agrees with that for the
thiersindole C skeleton. (b) Crystal data for 4: C27H35NO4,
monoclinic, space group P21 (no 4), a = 7.4100 (15) Å, b =
10.169 (2) Å, c = 16.045 (3) Å, a = g = 90°, b = 97.11 (3)°,
V = 1199.7 (4) Å3, Z = 2, Dc = 1.211 Mg/m3, m(Cu – Ka) =
0.640 mm–1, F(000) = 472. The number of reflections
collected was 1963, of which 937 were considered to be
observed with I > 2sI. The structure was determined by
direct methods using the SHELXTLTM suite of programs.
Hydrogen atoms were placed in calculated positions. Full-
matrix least squares refinement based on F2 with anisotropic
thermal parameters for the non-hydrogen atoms led to
agreement factors, R1 = 0.0721 and wR2 = 0.1823.
Crystallographic data (excluding structure factors) for the
structure reported in this paper has been deposited at the
Cambridge Crystallographic Data Centre as supplementary
material no. CCDC-628164.
(18) (a) Liu, H. J.; Shia, K.-S. Tetrahedron 1998, 54, 13449.
(b) Levine, S. J. J. Am. Chem. Soc. 1958, 80, 6150.
(c) Wittig, G.; Schlosser, M. Chem. Ber. 1961, 94, 1383.
(d) Wittig, G.; Böll, W.; Krück, K.-H. Chem. Ber. 1962, 95,
2514. (e) Wittig, G. Angew. Chem. 1956, 68, 505.
(f) Marcos, I. S.; Pedrero, A. B.; Sexmero, M. J.; Díez, D.;
Basabe, P.; Hernández, F. A.; Broughton, H. B.; Urones, J.
G. Synlett 2002, 105.
(19) Makita, N.; Hoshino, Y.; Yamamoto, H. Angew. Chem. Int.
Ed. 2003, 42, 941.
(22) (a) TePaske, M. R.; Gloer, J. B.; Wicklow, D. T.; Dowd, P.
F. Tetrahedron Lett. 1989, 30, 5965. (b) TePaske, M. R.;
Gloer, J. B.; Wicklow, D. T.; Dowd, P. F. J. Org. Chem.
1989, 54, 4743.
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