Synthesis, structure and cytotoxicity of trimethylsilyl oligothienylcarbaldehydes and their derivatives

Article abstract of DOI:10.1016/S0022-328X(01)00835-X

Trimethylsilyl end-capped bi- and terthiophene carbaldehydes were prepared by reaction of bi- and terthienyl lithium with DMF. Condensation of 5-trimethylsilyl-2,2′-bithiophene-5′-carbaldehyde with dinitrile of malonic acid gave silylbithienyl methylidenedinitrile in good yield, while reaction with hydroxylamine was accompanied by desilylation. The reaction of hydroxylamine with silylbithienyldinitrile leads to the formation of 2-[5-(5′-trimethylsilyl-2,2′-bithienyl)methylidene]malonic acid bisamidoxime. The cytotoxic effect of bi- and terthiophene derivatives was investigated in vitro on two monolayer tumor cell lines: MG-22A (mouse hepatoma) and HT-1080 (human fibrosarcoma). The molecular structure of 5-trimethylsilyl-2,2′-bithiophene-5′-carbaldehyde was studied by X-ray diffraction.

Full text of DOI:10.1016/S0022-328X(01)00835-X

Journal of Organometallic Chemistry 636 (2001) 26–30
www.elsevier.com/locate/jorganchem
Synthesis, structure and cytotoxicity of trimethylsilyl
oligothienylcarbaldehydes and their derivatives
Edmunds Lukevics a,*, Giovanna Barbarella b, Pavel Arsenyan a, Irina Shestakova a,
Sergey Belyakov a, Juris Popelis a, Olga Pudova a
a Lat6ian Institute of Organic Synthesis, 21 Aizkraukles St., LV-1006 Riga, Lat6ia
b CNR, I.Co.C.E.A., Via Gobetti 101, I-40129 Bologna, Italy
Received 15 February 2001; accepted 16 March 2001
Dedicated to Professor O.M. Nefedov on the occasion of his 70th birthday
Abstract
Trimethylsilyl end-capped bi- and terthiophene carbaldehydes were prepared by reaction of bi- and terthienyl lithium with
DMF. Condensation of 5-trimethylsilyl-2,2%-bithiophene-5%-carbaldehyde with dinitrile of malonic acid gave silylbithienyl methyli-
denedinitrile in good yield, while reaction with hydroxylamine was accompanied by desilylation. The reaction of hydroxylamine
with silylbithienyldinitrile leads to the formation of 2-[5-(5%-trimethylsilyl-2,2%-bithienyl)methylidene]malonic acid bisamidoxime.
The cytotoxic effect of bi- and terthiophene derivatives was investigated in vitro on two monolayer tumor cell lines: MG-22A
(mouse hepatoma) and HT-1080 (human fibrosarcoma). The molecular structure of 5-trimethylsilyl-2,2%-bithiophene-5%-carbalde-
hyde was studied by X-ray diffraction. © 2001 Elsevier Science B.V. All rights reserved.
Keywords: Terthiophene carbaldehydes; Trimethylsilyl; Cytotoxicity
Taking into account the cytotoxic and antitumor
activity of 5-silylsubstituted furfurals and thiophene
1. Introduction
carbaldehydes [14,15], the influence of the a-oligothio-
The increasing interest in p-conjugated thiophene-
phene chain elongation on the cytotoxic effect was
based materials for exploring their electronic and opti-
investigated in vitro on two monolayer tumor cell lines:
cal properties has resulted in an extended research in
MG-22A (mouse hepatoma) and HT-1080 (human
the field of oligothiophenes chemistry [1–5]. However,
fibrosarcoma).
2,2%-bithiophenes and 2,2%:5%,2¦-terthiophenes are also
very important from the biological point of view. These
compounds were extracted from various plants, such as
Blumea obliqua [6], Tagetes minuta [7] and Tagetes sp.
2. Results and discussion
[8] and showed high antibacterial (Staphylococcus au-
2.1. Synthesis of silylsubstituted bi- and terthiophene
reus, Escherichia coli ) [9], antifungal (Epidermophyton
carbaldehydes and their deri6ati6es
floccosum, Pleurotus ostreatus) [6], anti-HIV [10] and
insecticidal [7,11] activity. For a series of terthiophene
Scheme 1 outlines the synthetic methods for the
derivatives the protein kinase C inhibitory activity was
preparation of trimethylsilyl end-capped bi- and
evaluated. Terthiophenes containing aldehyde or hy-
terthiophene carbaldehydes 3 and 4. Bithiophene and
terthiophene were converted to monosilylsubstituted
oligothiophenes (1 and 2) by lithiation following silyla-
tion. Subsequent metalation of compounds 1 and 2 in
ether by n-BuLi and treatment with dry DMF afforded
aldehydes 3 and 4 in 75 and 61% yields, respectively.
droxymethyl groups in position 5 were most potent
inhibitors (IC50B1 mM) [12,13].
* Corresponding author. Tel.: +371-7551822; fax: +371-7550338.
E-mail address: sinta@osi.lv (E. Lukevics).
0022-328X/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved.
PII: S0022-328X(01)00835-X

E. Luke6ics et al. / Journal of Organometallic Chemistry 636 (2001) 26–30
27
tion of aldehyde 3 with hydroxylamine in CH2Cl2 pro-
ceeded with desilylation to afford 2,2%-bithiophene-
5-carbaldoxime (6) in 67% yield. Amidoximization of
dinitrile 5 was carried out in ethanol with two equiva-
lents of hydroxylamine to yield 2-[5-(5%-trimethylsilyl-
2,2%-bithienyl)methylidene]malonic acid bisamidoxime
(7) containing the silyl group in position 5% of bithio-
phene (Scheme 2).
Scheme 1.
2.2. Molecular structure of
5-trimethylsilyl-(2,2%-bithienyl)-5%-carbaldehyde (3)
The molecular structure of 5-trimethylsilyl-(2,2%-
bithienyl)-5%-carbaldehyde (3) is presented in Fig. 1.
Table 1 gives the values of bond lengths and angles in
molecule 3. As in 5,5%-bis(trimethylsilyl)-2,2%-bithio-
phene [16] two thiophene heterocycles of aldehyde 3 are
almost coplanar (twisting angle 2.6(2)°) and their sulfur
atoms lie anti to each other. On the other hand, the title
structure differs from that of bithiophene carbaldehyde
[17] in which the disordered sulfur atoms have a pre-
dominantly (80%) cisoid structure about the ring junc-
tion. The push–pull character of trimethylsilyl and
aldehyde substituents leads to increased conjugation
Scheme 2.
Condensation of 5-trimethylsilyl-2,2%-bithiophene-5%-
carbaldehyde (3) with dinitrile of malonic acid in etha-
nol at room temperature in the presence of catalytic
amount of piperidine gave 1-[5-(5%-trimethylsilyl-2,2%-
bithienyl)]-2,2-dicyanoethylene (5). The cleavage of the
SiꢀCthiophene bond did not occur. On the contrary, reac-
,
and as a result bond lengths C(2)ꢀC(2%) (1.420 A),
,
,
C(3)ꢀC(4) (1.399 A) and C(3%)ꢀC(4%) (1.388 A) are
,
shortened and C(4)ꢀC(5) (1.376 A) is elongated [18].
However, the push–pull effect of these groups is weak
and only slightly increases the role of the mesomeric
structure of semiquinoid type [19].
The presence of trimethylsilyl and aldehyde sub-
stituents at the terminal positions of bithiophene 3
plays an important role in the molecular packing of this
compound (Figs. 2 and 3). The crystal unit cell contains
four molecules of aldehyde 3 (Z=4). In the crystal
structure the molecules form rouleaus along crystallo-
graphic axis y and lie on a screw axis (21). p-Stacking
interaction occurs between these molecules (see Fig. 3).
The mean distance between p-stacked bithiophene
Fig. 1. Molecular structure of 5-trimethylsilyl-2,2%-bithienylcarb-5%-
aldehyde (3).
Table 1
,
Bond lengths (A) and bond angles (°) for molecule 3
S(1)ꢀC(5)
S(1)ꢀC(2)
C(2)ꢀC(3)
C(2)ꢀC(2%)
C(3)ꢀC(4)
C(4)ꢀC(5)
C(5)ꢀSi(1)
Si(1)ꢀC(6)
Si(1)ꢀC(7)
Si(1)ꢀC(8)
S(1%)ꢀC(5%)
S(1%)ꢀC(2%)
C(2%)ꢀC(3%)
C(3%)ꢀC(4%)
C(4%)ꢀC(5%)
C(5%)ꢀC(6%)
C(6%)ꢀO(1)
1.686(8)
1.726(7)
1.352(9)
1.420(9)
1.399(10)
1.376(10)
1.876(8)
1.832(11)
1.860(9)
1.868(10)
1.708(7)
1.737(6)
1.354(9)
1.388(10)
1.361(9)
1.456(10)
1.232(9)
C(5)ꢀS(1)ꢀC(2)
C(3)ꢀC(2)ꢀC(2%)
C(3)ꢀC(2)ꢀS(1)
C(2%)ꢀC(2)ꢀS(1)
C(2)ꢀC(3)ꢀC(4)
C(5)ꢀC(4)ꢀC(3)
C(4)ꢀC(5)ꢀS(1)
C(4)ꢀC(5)ꢀSi(1)
S(1)ꢀC(5)ꢀSi(1)
C(5%)ꢀS(1%)ꢀC(2%)
C(3%)ꢀC(2%)ꢀC(2)
C(3%)ꢀC(2%)ꢀS(1%)
C(2)ꢀC(2%)ꢀS(1%)
C(2%)ꢀC(3%)ꢀC(4%)
C(5%)ꢀC(4%)ꢀC(3%)
C(4%)ꢀC(5%)ꢀC(6%)
C(4%)ꢀC(5%)ꢀS(1%)
C(6%)ꢀC(5%)ꢀS(1%)
O(1)ꢀC(6%)ꢀC(5%)
94.2(4)
129.6(6)
109.4(6)
120.9(5)
113.1(7)
114.5(7)
108.9(6)
127.6(6)
123.5(4)
91.9(4)
129.9(6)
109.1(6)
121.0(5)
115.4(7)
111.9(7)
126.6(7)
111.7(6)
121.7(6)
123.9(7)
Fig. 2. Molecular packing of bithiophene 3.

28
E. Luke6ics et al. / Journal of Organometallic Chemistry 636 (2001) 26–30
Fig. 3. Stereoview of bithiophene 3.
Table 2
In vitro cell cytotoxicity and the ability of intracellular NO generation caused
by oligothiophenesabc

E. Luke6ics et al. / Journal of Organometallic Chemistry 636 (2001) 26–30
29
,
3.1.1. 5-Trimethylsilyl-(2,2%-bithienyl)-5%-carbaldehyde
(3)
planes is equal to half of period b (3.629(3) A). As
terminal substituents of bithiophene 3 have different
electronic effects the p-stacked layers are orientated in
such a manner that the aldehyde group of one molecule
lies over the trimethylsilyl group of the neighboring
molecule. Probably, the mentioned packing type of
bithiophene 3 is determined by the dipole–dipole
interaction.
To a solution of 5-trimethylsilyl-2,2%-bithiophene
(0.05 mol) in 30 ml of Et2O was added 20 ml of 2.5 N
n-BuLi in hexanes (0.05 mol) at room temperature
(r.t.). After 1 h, excess (0.08 mol) of DMF was added
dropwise. The reaction mixture was refluxed for 2 h,
hydrolyzed with a saturated solution of NH4Cl, ex-
tracted with Et2O, dried over Na2SO4 and evaporated.
The residue was purified on silica gel using CH2Cl2 as
2.3. Cytotoxicity of oligothiophenes
eluent. M.p. 85–86°C. Yield 75%. IR (cm−1) w(CꢁO)
=
1
1660. MS–GC: 266. H-NMR (CDCl3): l 0.33 (s, 9H),
7.16 (d, 1H, J=3.4 Hz), 7.24 (d, 1H, J=3.4 Hz), 7.38
(d, 1H, J=3.4 Hz), 7.65 (d, 1H, J=3.4 Hz), 9.85 (s,
1H). 13C-NMR (CDCl3): l −0.2, 124.3, 127.3, 135.0,
137.4, 140.5, 141.6, 143.4, 147.1, 182.6. 29Si-NMR
(CDCl3): l −5.86. Anal. Found: C, 54.12; H, 5.31; S,
24.11. Calc. for C12H14OS2Si: C, 54.10; H, 5.30; S,
24.07%.
Cytotoxic activity of silylsubstituted bi- and terthio-
phene carbaldehydes and their derivatives was tested in
vitro on two monolayer tumor cell lines: MG-22A
(mouse hepatoma) and HT-1080 (human fibrosar-
coma). The cytotoxic effect of silicon-containing com-
pounds was compared with silicon-free analogs (Table
2), prepared by the Pd0 catalyzed coupling of thienyl-
stannanes with bromothiophene carbaldehydes [20,21].
5-Trimethylsilyl-(2,2%-bithienyl)-5%-carbaldehyde (3) ex-
hibits higher cytotoxicity than the product of its con-
densation with dinitrile of malonic acid 5 and analog
with terthiophene chain 4. The effect of bisamidoxime 7
is comparable with aldehyde 3 in MG-22A and more
pronounced in the HT-1080 cell line. As compared with
3.1.2. 5-Trimethylsilyl-(2,2%:5%,2¦-terthienyl)-5¦-
carbaldehyde (4)
1
M.p. 144–145°C. Yield 61%. H-NMR (CDCl3): l
0.34 (s, 9H), 7.12–7.16 (m, 2H), 7.22 (d, 1H, J=4.2
Hz), 7.26 (d, 2H, J=3.6 Hz), 7.66 (d, 1H, J=4 Hz),
9.85 (s, 1H). 13C-NMR (CDCl3): l 0.8, 124.9, 125.6,
126.7, 127.9, 135.4, 135.9, 138.3, 140.2, 142.2, 142.5,
147.9, 183.3. 29Si-NMR (CDCl3): l −6.2. Anal.
Found: C, 55.10; H, 4.60; S, 27.53. Calc. for
C16H16OS3Si: C, 55.13; H, 4.63; S, 27.60%.
desilylated
oligothiophene
carbaldehydes
8–10
organosilicon compounds are less cytotoxic. Monosub-
stituted ter- and quaterthiophene carbaldehydes 9 and
10 show significant cytotoxic effect (IC50=1–7
mg ml−1).
3.1.3. 1-[5-(5%-Trimethylsilyl-2,2%-bithienyl)]-2,2-
dicyanoethylene (5)
M.p. 173–174°C. Yield 95%. MS–GC: 314. 1H-
NMR (CDCl3): l 0.34 (s, 9H), 7.20 (d, 1H, J=3.6 Hz),
7.27 (d, 1H, J=3.6 Hz), 7.46 (d, 1H, J=3.4Hz), 7.62
(d, 1H, J=4.2 Hz), 7.75 (s, 1H). 13C-NMR (CDCl3): l
0.7, 76.9, 114.4, 115.2, 125.6, 129.3, 134.4, 136.3, 140.8,
141.1, 146.3, 150.4, 151.3. 29Si-NMR (CDCl3): l −
5.53. Anal. Found: C, 57.30; H, 4.52; N, 8.86; S, 20.35.
Calc. for C15H14N2S2Si: C, 57.29; H, 4.49; N, 8.91; S,
20.39%.
3. Experimental
3.1. General considerations and materials
All solvents used in the reactions were dried by
standard procedures. The following reagents were ob-
tained from commercial sources and used without fur-
ther purification: 2-bromothiophene, n-BuLi (2.5 M
hexane solution), trimethylchlorosilane. 2,2%-Bithio-
phene and a-terthiophene were prepared by catalytic
coupling of 2-thienylmagnesium bromide with 2-bro-
mothiophene and 2,5-dibromothiophene, respectively.
Column chromatography was carried out using 60–200
mesh silica gel from Acros.
3.1.4. 2-[5-(5%-Trimethylsilyl-2,2%-bithienyl)methylidene]-
malonic acid bisamidoxime (7)
To a solution of 1-[5-(5%-trimethylsilyl-2,2%-bithienyl)]-
2,2-dicyanoethylene (8) (0.01 mol) in 10 ml of EtOH
was added hydroxylamine (0.02 mol). The reaction
mixture was refluxed for 2 h. After cooling the solvent
was removed and residue purified on silica gel using
EtOAc as eluent, m.p. 128–130°C. Yield 98%. 1H-
NMR (CDCl3): l 0.04 (s, 9H), 5.73 (s, 4H, NH2), 5.93
(s, 2H, OH), 7.03 (d, 1H, J=3.4 Hz), 7.13 (d, 1H,
J=3.4 Hz), 7.33 (d, 1H, J=4.2 Hz), 7.37 (d, 1H,
J=4.2 Hz), 7.93 (s, 1H). 13C-NMR (CDCl3): l −0.2,
122.8, 123.6, 125.7, 125.9, 129.3, 130.6, 132.7, 134.8,
134.9, 141.2, 144.8, 163.2. Anal. Found: C, 47.38; H,
1
The H-, 13C- and 29Si-NMR spectra were recorded
on a Varian Mercury 200 spectrometer at 200.06, 50.31
and 39.74 MHz, respectively, at 303 K. The chemical
shifts are given relative to Me4Si from the solvent
(CDCl3) signal (lH=7.25 ppm). Mass spectra were
recorded on a Hewlett Packard apparatus (70 eV). The
melting points were determined on a ‘Digital Melting
Point Analyzer’ (Fisher) and the results are given with-
out correction.

30
E. Luke6ics et al. / Journal of Organometallic Chemistry 636 (2001) 26–30
Table 3
crystal violet (CV) or 3-(4,5-dimethylthiazol-2-yl)-2,5-
diphenyltetrazolinium bromide (MTT) coloration, which
was assayed by a multiscan spectrophotometer. The
quantity of cells alive on the control plate was taken in
calculations for 100% [24,25]. The concentration of NO
was determined according to Ref. [24].
Crystal data and structure refinement for 3
Formula weight Mr
Temperature (K)
Wavelength (A)
Crystal system
Space group
266.44
293(2)
0.71073
Monoclinic
P21/c
,
Unit cell dimensions
4. Supplementary material
,
a (A)
16.652(8)
7.258(3)
11.499(6)
90
95.05
90
1384.4(11)
4
,
b (A)
,
c (A)
Crystallographic data for the structural analysis have
been deposited with the Cambridge Crystallographic
Data Centre, CCDC no. 157444 for compound 3. Copies
of this information may be obtained free of charge from
The Director, CCDC, 12 Union Road, Cambridge CB2
1EZ, UK (Fax: +44-1223-336033; e-mail: deposit@
ccdc.cam.ac.uk or www: http://www.ccdc.cam.ac.uk).
h (°)
i (°)
k (°)
3
,
V (A )
Z
Dcalc (mg m−3
)
1.278
0.449
560
Absorption coefficient (mm−1
F(000)
)
Crystal size (mm)
Two-theta (max) (°)
Index ranges
0.75×0.25×0.10
45.0
−175h517, −75k50,
References
05l512
1939
[1] R. Azumi, G. Go¨tz, P. Ba¨uerle, Chem. Eur. J. 6 (2000) 735.
[2] J.M. Tour, Acc. Chem. Res. 33 (2000) 791.
[3] M.C. Suh, B. Jiang, T.D. Tilley, Angew. Chem. Int. Ed. Engl. 39
(2000) 2870.
[4] G. Barbarella, P. Ostoja, P. Maccagnani, O. Pudova, L. Antolini,
D. Casarini, A. Bongini, Chem. Mater. 10 (1998) 6383.
[5] G. Barbarella, M. Zambianchi, L. Antolini, P. Ostoja, P. Maccag-
nani, E.A. Marseglia, E. Tedesko, G. Gigli, R. Cingolani, J. Am.
Chem. Soc. 121 (1999) 8920.
Reflections collected
Independent reflections
Refinement method
Data/restraints/parameters
Goodness-of-fit on F2
Final R factor [I\2|(I)]
1824
Full-matrix least-squares on F2
1824/0/145
1.018
0.0725
[6] V.U. Ahmad, N. Alam, J. Nat. Prod. 58 (1995) 1426.
[7] M.J. Perich, C. Wells, W. Bertsch, K.E. Tredway, J. Am. Mosq.
Control Assoc. 11 (1995) 307.
5.33; N, 14.71; S, 16.80. Calc. for C15H20N4O2S2Si: C,
47.35; H, 5.30; N, 14.73; S, 16.85%.
[8] B.M. Housen, B. Helmke, Contact Dermatitis 33 (1995) 33.
[9] M. Ciofalo, S. Petruso, D. Schillaci, Planta Med. 62 (1996) 374.
[10] J.B. Hudson, R.J. Marles, C. Soucy-Breau, L. Harris, J.T.
Arnason, Photochem. Photobiol. 60 (1994) 591.
[11] G. Guillet, J. Harmatha, T.G. Waddell, B.J. Philogene, J.T.
Arnason, Photochem. Photobiol. 71 (2000) 111.
[12] D.S.H.L. Kim, C.L. Ashendel, Q. Zhou, C.-t. Chang, E.-S. Lee,
C.-j. Chang, Bioorg. Med. Chem. Lett. 8 (1998) 2695.
[13] W.-C. Xu, Q. Zhou, C.L. Ashendel, C.-t. Chang, C.-j. Chang,
Bioorg. Med. Chem. Lett. 9 (1999) 2279.
[14] E. Lukevics, N.P. Erchak, L.E. Demicheva, V.N. Verovskii, I.
Augustane, Khim.-Farm. Zh. 26 (1992) 45.
[15] E. Lukevics, N.P. Erchak, I. Castro, A.A. Zidermane, A.Zh.
Dauvarte, Izv. Akad. Nauk LatvSSR Ser. Khim. (1983) 735.
[16] C. Alema´n, E. Brillas, A.G. Davies, L. Fajar´ı, D. Giro´, L. Julia´,
J.J. Pe´rez, J. Rius, J. Org. Chem. 58 (1993) 3091.
[17] S.P. Armes, P.A. Chaloner, P.B. Hitchcock, M.R. Simmons, Acta
Crystallogr. C 50 (1994) 1945.
3.2. Crystal structure determination
For X-ray crystal structure analysis a four-circle sin-
gle-crystal Sintex P21 diffractometer with graphite-
monochromated Mo–Ka (u=0.71069 A) radiation was
used for intensity data collection. Reflection intensities
were collected at r.t. using the q/2q scan technique.
Multisolution direct method package SHELX-86 [22] was
used for the solution of the structure. SHELXL-93 pro-
grams [23] were used for the refinement calculations.
Other crystallographic, measurement and refinement
data for bithiophene 3 are listed in Table 3.
,
3.3. In 6itro cytotoxicity assay
[18] E. Lukevics, G. Barbarella, P. Arsenyan, S. Belyakov, O. Pudova,
Chem. Heterocycl. Comp. 36 (2000) 630.
[19] E. Lukevics, V. Ryabova, P. Arsenyan, S. Belyakov, J. Popelis,
O. Pudova, J. Oganomet. Chem. 610 (2000) 8.
[20] J. Nakayama, Y. Nakamura, T. Tajiri, M. Hoshino, Heterocycles
24 (1986) 637.
[21] J. Nakayama, T. Konishi, M. Hoshino, Heterocycles 27 (1988)
1731.
[22] G.M. Sheldrick, Acta Crystallogr. A 46 (1990) 467.
[23] G.M. Sheldrick, Crystallogr. Computing 6 (1993) 110.
[24] D.J. Fast, R.C. Lynch, R.W. Leu, J. Leuckocyt. Biol. 52 (1992)
255.
[25] P.J. Freshney, Culture of Animal Cells (A Manual of Basic
Technique), Wiley–Liss, New York, 1994 (pp. 296–297).
Monolayer cell lines were cultivated for 72 h in
DMEM standard medium without an indicator and
antibiotics. The control cells and cells with tested sub-
stances in the range of 2–5×104 cell ml−1 concentration
(depending on line nature) were placed on separate 96
wells plates. Solutions containing the test compounds
were diluted and added in wells to give the final concen-
trations of 50, 25, 12.5, and 6.25 mg ml−1. Control cells
were treated in the same manner but only in the absence
of test compounds. Plates were cultivated for 72 h. The
quantity of cells that survived was determined using