Synthesis and cytotoxic activity of new 2-[(3-aminopropyl)dimethylsilyl]-5- triethylsilylfurans

Article abstract of DOI:10.1002/aoc.1538

Highly cytotoxic 3-aminopropyl derivatives of 5-triethylsilyl-2- dimethylsilylfuran (LC₅₀ 1-3 μg ml^-1) have been prepared by hydrosilylation of heterocyclic N-allylamineswith corresponding hydrosilane in the presence of Speier's cata

Full text of DOI:10.1002/aoc.1538

Full Paper
Received: 26 May 2009
Revised: 30 June 2009
Accepted: 2 July 2009
Published online in Wiley Interscience: 16 September 2009
(www.interscience.com) DOI 10.1002/aoc.1538
Synthesis and cytotoxic activity of new
2-[(3-aminopropyl)dimethylsilyl]-5-
triethylsilylfurans
Luba Ignatovich∗, Velta Muravenko, Irina Shestakova, Ilona Domrachova,
Juris Popelis and Edmunds Lukevics
Highly cytotoxic 3-aminopropyl derivatives of 5-triethylsilyl-2-dimethylsilylfuran (LC50 1–3 µg ml−1) have been prepared by
hydrosilylation of heterocyclic N-allylamines with corresponding hydrosilane in the presence of Speier’s catalyst. The influence
c
of the amine structure on the cytotoxicity has been investigated. Copyright ꢀ 2009 John Wiley & Sons, Ltd.
1
Keywords: 2-[(3-aminopropyl)dimethylsilyl]-5-triethylsilylfurans; 5-triethylsilyl-2-dimethylsilylfuran; hydrosilylation; synthesis; H; 13C;
29Si NMR; cytotoxic activity
Introduction
Technologies 7890 GC system with 5975C EI/CI MSD (70 eV)
on capilary column HP-5. IR spectra (KBr) were registered on
a Shimadzu Prestige-21 spectrometer. All solvents were dried
on CaH2, and distilled prior to use. Thin-layer chromatography
(TLC) was performed on a Merck silica gel 60 F254 with various
eluents. Column chromatography was performed on Silica gel
(0.060–0.200 mm,porediameter6 nm,‘Acros’).2-Triethylsilylfuran
was prepared by the known method.[33]
Heterocycles are important building blocks for the construction
of anticancer drugs.[1] The fragment analysis[2] of clinically used
antineoplastic agents shows that in many cases a heterocyclic
amino group has been introduced to increase the solubility
and bioavailability of the active substance, e.g. piperidine in
Arzoxifene[3–6], Flavopiridol[7] and Perifosine,[8–10] morpholine in
Canertinib,[11,12] Gefinitib[13–15] andMofarotene,[16] thiomorpholine
inPrinomastat,[17] piperazineinDasatinib[18] andImatinib,[19,20] and
pyrrolidine in Idoxifene[21,22]. These heterocyclic amines are also
used for formation of libraries of cytotoxic agents[23]. In some
cases the benzene ring has been substituted for thiophene or
furan to enhance the activity and increase the therapeutic index.
Examples are thiophene-containing folate analogue Raltitrexed[24]
and antimetastatic agent Batimastat[25,26] and furan-containing
anticancer agent Lapatinib.[27]
Our previous investigations have demonstrated that
heterylaminoalkyl(siloxy)-silanes, which contain an alkyl(or siloxy)
group attached to the silicon atom, have anticancer, neurotropic
and bacteriostatic activity.[28,29]
Taking into consideration the information gained from the
fragment analysis of known anticancer drugs and the fact that
silylation increases the lypophilicity of the compounds and can
change their metabolism,[30–32] we decided to combine in one
molecule the fragments of silylated furan and heterocyclic amine
and to test their cytotoxicity.
Chemistry
5-Triethylsilyl-2-dimethylsilylfuran (1)
A solution of 3.8 g (20 mmol) of 2-triethylsilylfuran in 40 ml of
dry ether was placed in a three-necked flask fitted with a reflux
condenser, athermometer, amagneticstirrerandarubberstopper
in a stream of argon. The flask with the solution was cooled to
ꢁ30 ŽC, and 8.3 ml (20 mmol) of a 2.5N solution of n-BuLi in hexane
was added dropwise so slowly to maintain the temperature below
ꢁ25 ŽC. When all the n-BuLi had been added the mixture was
stirred for 1 h at ꢁ10 ŽC, and for 2 h at 10 ŽC. Then 1.98 g (20 mmol)
of dimethylchlorosilane was added dropwise at ꢁ25 ŽC. After the
addition of chlorosilane the mixture was stirred for 10 min at
ꢁ25 ŽC, the temperature was slowly raised to room temperature,
and the mixture was stirred for 12 h. The precipitate was filtered off
through Al2O3, solvents evaporated and the residue was distilled
under reduced pressure at 66–67 ŽC (4.5 mmHg), to give 3.4 g
(70.8%) of the compound 1. 1H NMR: δ ppm 0.37 (s, 6H, Si–CH3),
0.77–1.05 (m, 15H, Si–C2H5), 4.45 (m, 1H, SiH), 6.67 (m, 1H, H3
furan), 6.72 (d, J D 3.6 Hz, 1H, H4 furan), 29Si NMR: δ ppm ꢁ3.62
Experimental
(SiEt3), ꢁ28.40 (Si–H), GC-MS (m/z, %): 240 (MC, 9), 211 (MC
ꢁ
Materials and Methods
C2H5, 61), 183 (12), 161 (46), 133 (100), 117 (9), 105 (63), 83 (21), 71
(17), 59 (84). IR spectrum ν, mꢁ1 (Si–H) 2129.5.
The 1H, 13C and 29Si NMR spectra were recorded on a Varian
200 Mercury instrument at 200, 50 and 40 MHz, respectively, in
CDCl3 as a solvent, (Me3Si)2O as a standard for 1H, TMS (external)
as the standard for 29Si, and the signal on the residual proton
of the solvent (δ 77.05 ppm) for 13C. The mass spectra under
electron impact conditions were recordered on a GC-MS Agilent
Ł
Correspondence to: Luba Ignatovich, Latvian Institute of Organic Synthesis,
Aizkraukles 21, Riga, LV-1006, Latvia. E-mail: ign@osi.lv
Latvian Institute of Organic Synthesis, Aizkraukles 21, Riga, LV-1006, Latvia
c
Appl. Organometal. Chem. 2010, 24, 158–161
Copyright ꢀ 2009 John Wiley & Sons, Ltd.

New 2-[(3-aminopropyl)-dimethylsilyl]-5-triethylsilylfurans
Table 1. The spectral characteristics of 2-[(3-aminopropyl)dimethylsilyl]-5-triethylsilylfurans (2–11)
δ
13C δ (ppm)
(C2H5)3Si–, Si(CH3)2CH2CH2CH2 R
Compound
C(4)
C(3)
C(5)
C(2)
δ
29Si (ppm)
2
120.06
120.05
120.04
120.02
120.09
120.04
120.06
120.05
120.02
120.09
119.37
119.33
119.36
119.35
119.40
119.36
119.44
119.43
119.38
119.47
163.77
163.88
163.71
163.72
163.70
163.74
163.53
163.56
163.58
163.65
162.70
162.70
162.68
162.71
162.45
162.71
162.75
162.77
162.71
162.79
56.48, 47.89, 21.27, 13.11, 7.34, ꢁ3.34
ꢁ3.80, ꢁ9.67
ꢁ3.84, ꢁ9.63
ꢁ3.81, ꢁ9.63
ꢁ3.85, ꢁ9.56
ꢁ3.87, ꢁ9.71
ꢁ3.85, ꢁ9.67
ꢁ3.83, ꢁ9.62
ꢁ3.80, ꢁ9.63
ꢁ3.83, ꢁ9.68
ꢁ3.77, ꢁ9.57
3
57.74, 53.95, 41.69, 29.34, 21.30, 20.81, 14.12, 13.04, 7.36, 3.45, ꢁ3.31
59.91, 54.14, 23.32, 13.32, 7.34, 3.42, ꢁ3.45
4
5
62.95, 54.58, 25.97, 24.49, 21.11, 13.16, 7.33, 3.40, ꢁ3.37
57.72, 55.80, 52.32, 34.79, 26.31, 24.19, 19.54, 13,24, 7.39, 3.46, ꢁ3.34
61.67, 55.45, 27.71, 27.01, 21.45, 13.01, 7.34, 3.41, ꢁ3.41
66.97, 62.32, 53.70, 20.81, 12.96, 7.33, 3.40, ꢁ3.40
6
7
8
9
62.67, 54.97, 27.99, 20.74, 12.98, 7.34, 3.40, ꢁ3.35
10
11
61.98, 55.14, 53.18, 21.16, 13.03, 7.32, 3.38, ꢁ3.43
151.39, 129.8, 119.61, 62.00, 53.14, 49.14, 21.17, 13.08, 7.38, 3.44, ꢁ3.37
2-[(3-Diethylaminopropyl)dimethylsilyl]-5-triethylsilylfuran (2)
Si–CH3), 0.60–1.03 (m, 20H, Si–CH2, Si–C2H5, C–CH3), 1.24–1.28
(m, 3H, CH2, CH), 1.44–1.70 (m, 6H, CH2), 2.08–2.46 (m, 2H, CH2),
2.58–2.84 (m, 2H, CH2), 6.60 (s, 2H, H3H4). GC-MS, m/z (%): 379
(MC, 13), 364 (MC ꢁ Me, 33), 350 (11), 239 (5), 207 (6), 182 (20), 169
(13), 153 (40), 133 (25), 141 (25), 113 (100), 98 (25), 87(27), 69 (18),
55 (55).
A solution of 0.25 g (1.1 mmol) of silane 1, and 0.12 g (1.1 mmol)
N,N-diethylallylamine and one drop of H2PtCl6. 6H2O (0.1%
in i-PrOH) were placed in a flask with a reflux condenser, a
thermometer and a magnetic stirrer. The mixture was heated at
90 ŽCfor1 h,cooledandanalyzedbyGC-MS.Separationbycolumn
chromatography (CH2Cl2:CH3OH D 20 : 1) gave 0.25 g (66.7%) of
compound 2. 1H NMR δ ppm: 0.23 (s, 6H, Si–CH3), 0.66–0.77 (m,
8H, Si–CH2, CH3), 0.95–1.00 (m, 15H, SiC2H5), 1.45–1.53 (m, 2H,
CH2), 2.36–2.40 (m, 2H, CH2N), 2.46–2.51 (m, 4H, CH2N), 6.59 (s,
2H, H3H4). GC-MS, m/z (%): 353 (MC, 4), 181 (18), 153 (32), 140 (24),
125(15), 86 (100), 59 (40).
2-[(3-Hexamethyleneiminopropyl)dimethylsilyl]-5-triethylsilylfuran
(7)
Compound
7
was
prepared
from
1
and
N-
allylhexamethyleneimine. Yield: 57.1%. 1H NMR δ(ppm):
0.23 (s, 6H, Si–CH3), 0.74–1.00 (m, 17H, Si–C2H5, Si–CH2),
1.51–1.62 (m, 10H, CH2), 2.40–2.50 (m, 2H, CH2), 2.62 (bs, 4H,
CH2N), 6.60 (s, 2H, H3H4). GC-MS, m/z (%): 379 (MC, 5), 207 (5), 153
(9), 112 (100), 59 (5).
The compounds 3–11 were prepared and isolated in the same
manner as described for compound 2. The 13C and 29Si NMR data
for compounds 2–11 are given in Table 1.
2-[(3-Di-n-butylaminopropyl)dimethylsilyl]-5-triethylsilylfuran (3)
2-[(3-Morpholinopropyl)dimethylsilyl]-5-triethylsilylfuran (8)
Compound 3 was prepared from 1 and N,N-di-n-butylallylamine.
Yield 75.8%. 1H NMR δ (ppm): 0.24 (s, 6H, Si–CH3), 0.66–1.00 (m,
25H, Si–CH2, Si–C2H5, CH3), 1.20–1.51 (m, 14H, CH2), 2.34–2.38
(m, 6H, CH2N), 6.60 (s, 2H, H3H4). GC-MS, m/z (%): 409 (MC, 7), 394
(MC ꢁ Me, 3), 195 (34), 170 (9), 142 (100), 125(5), 100 (14), 59 (10).
Compound 8 was prepared from 1 and N-allylmorpholine. Yield:
1
60%. H NMR δ (ppm): 0.24 (s, 6H, Si–CH3), 0.73–1.00 (m, 17H,
Si–C2H5, Si–CH2), 1.53–1.60 (m, 2H, CH2), 2.27–2.50 (m, 6H, CH2),
3.68–3.78 (m, 4H, CH2N), 6.60 (s, 2H, H3H4). GC-MS, m/z (%): 367
(MC, 14), 352 (MC ꢁ Me, 27), 280 (5), 252 (15), 208(5), 181 (30), 153
(85), 142(67), 127 (54), 100 (100), 87(55), 70 (30), 59 (100).
2-[(3-Pyrrolidinopropyl)dimethylsilyl]-5-triethylsilylfuran (4)
Compound 4 was prepared from 1 and N-allylpyrrolidine. Yield
62.2%. 1H NMR δ (ppm): 0.24 (s, 6H, Si–CH3), 0.70–1.00 (m, 17H,
Si–CH2,Si–C2H5),1.55–1.68(m,2H,CH2),1.78–1.86(m,4H,CH2N),
2.42–2.55 (m, 6H, CH2N, CH2), 6.59 (s, 2H, H3H4). GC-MS, m/z (%):
353 (MC, 4), 181 (18), 153 (32), 140 (24), 125(15), 86 (100), 59 (40).
2-[(3-Thiomorpholinopropyl)dimethylsilyl]-5-triethylsilylfuran (9)
Compound 9 was prepared from 1 and N-allylthiomorpholine.
Yield: 49.7%. 1H NMR δ (ppm): 0.24 (s, 6H, Si–CH3), 0.66–1.00 (m,
17H, Si–CH2, Si–C2H5), 1.49–1.60 (m, 2H, CH2), 2.30–2.34 (m, 2H,
CH2N), 2.66 (s, 8H, CH2), 6.60 (s, 2H, H3H4). GC-MS, m/z (%): 368
(MC ꢁ Me, 5), 200 (8), 181 (12), 173 (24), 158 (42), 142 (16), 128 (43),
116 (100), 105 (25), 88 (49), 73 (10), 59 (69).
2-[(3-Piperidinopropyl)dimethylsilyl]-5-triethylsilylfuran (5)
Compound 5 was prepared from 1 and N-allylpiperidine. Yield
70.8%. 1H NMR δ (ppm): 0.23 (s, 6H, Si–CH3), 0.66–0.99 (m, 17H,
Si–CH2, Si–C2H5), 1.40–1.42 (m, 2H, CH2), 1.50–1.60 (m, 6H, CH2),
2.24–2.40 (m, 6H, CH2N), 6.59 (s, 2H, H3H4). GC-MS, m/z (%): 365
(MC, 5), 336 (MC ꢁ Me, 5), 182 (12), 153 (18), 124 (11), 96 (100), 82
(10), 59 (18).
2-f[3-(4-Methylpiperazino)propyl]dimethylsilylg-5-triethylsilylfuran
(10)
Compound 10 was prepared from
1
and N-allyl-4-
methylpiperazine. Yield: 59.8%. 1H NMR δ(ppm): 0.22 (s, 6H,
Si–CH3), 0.67–0.99 (m, 17H, Si–C2H5, Si–CH2), 1.49–1.57 (m,
2H, CH2), 2.26–2.52 (m, 13H, CH2, CH2N, CH3), 6.60 (s, 2H, H3H4).
GC-MS, m/z (%): 380 (MC, 26), 200 (8), 181 (5), 153 (17), 140 (11),
133 (14), 128(12), 113 (100), 91 (11), 83 (11), 70 (81), 59 (23).
2-f[3-(2-Methylpiperidino)propyl]dimethylsilylg-5-triethylsilylfuran
(6)
Compound
6
was prepared from
1
and N-allyl–2-
methylpiperidine. Yield: 60.4%. 1H NMR δ (ppm): 0.23 (s, 6H,
c
Appl. Organometal. Chem. 2010, 24, 158–161
Copyright ꢀ 2009 John Wiley & Sons, Ltd.
www.interscience.wiley.com/journal/aoc

L. Ignatovich et al.
CH2=CHCH2R
H2PtCl6.6H2O
1) n-BuLi
Et3Si
Et3Si
SiMe2
(CH2)3R
Et3Si
SiHMe2
2) Me2SiHCl
O
O
O
1
2-11
Me
R = -NEt2 (2), -N(n-Bu)2 (3), -N
(4), -N
(5), -N
(6), -N
(7),
-N
O
(8), -N
S (9), -N
N
Me (10), -N
N
Ph (11)
Scheme 1. Hydrosilylation reaction of heterocyclic allylamines.
2-f[3-(4-Phenylpiperazino)propyl]dimethylsilylg-5-triethylsilylfuran
(11)
or moderate yield. The 13C and 29Si NMR spectra are given in
Table 1.
The cytotoxicity of silylamines 2–11 in vitro has been inves-
tigated on tumor cells HT-1080 (human fibrosarcoma), MG-22A
(mouse hepatoma) and normal mouse fibroblasts 3T3 to de-
termine the effect of the amine on the antitumor activity. The
experimental evaluation of cytotoxic properties is presented
in Table 2. Most of the studied compounds (2,4–6,10) exhib-
ited high cytotoxic activity (LC50 1–3 µg mlꢁ1). The amines 4,
6 and 7 showed high cytotoxic activity in cancer cells accom-
panied by the highest cytotoxic activity on normal cells 3T3
(LC50 0.3–0.8 µg mlꢁ1). It means that the therapeutic index for
these compounds is low. In the case of piperidino (5) and mor-
pholino (8) derivatives some selectivity has been found: amine 5 is
cytotoxic against human fibrosarcoma but morpholino derivative
8 is cytotoxic against mouse hepatoma. Morpholino derivative
8 was more active than thiomorpholino derivative 9 for both
cancer cells lines and less cytotoxic for normal fibroblasts. The
N-methylpiperazino derivative 10 showed high cytotoxic activ-
ity in both cancer cell lines but substitution of N-methyl group
for the N-phenyl (compound 11) led to the loss of activity. The
toxicity of studied compounds decreases in the series: hexam-
ethyleneimino (7) > pyrrolidino (4) > piperidino (5). Introduction
of the sulfur and oxygen atoms leads to a further decrease
in toxicity: piperidino (5) > thiomorpholino (9) > morpholino
( 8).
Compound 11 was prepared from
1
and N-allyl-4-
phenylpiperazine. Yield: 68.3%. 1H NMR δ(ppm): 0.25 (s, 6H,
Si–CH3), 0.71–1.00 (m, 17H, SiCH2, Si–C2H5), 1.54–1.62 (m, 2H,
CH2), 2.34–2.38 (m, 2H, CH2N), 2.54–2.57 (m, 4H, CH2), 3.16–3.19
(m, 4H, CH2), 6.61 (s, 2H, H3H4), 6.81–6.92 (m, 3H, C6H4), 7.22–7.24
(m, 2H, C6H4). GC-MS, m/z (%): 442 (MC, 12), 207(5), 175(100), 132
(10), 105(8), 70 (12).
Cytotoxicity in Vitro
Monolayer tumor cell lines MG-22A (mouse hepatoma), HT-1080
(human fibrosarcoma) and NIH 3T3 (normal mouse fibroblasts)
were cultivated for 72 h in standard Dulbecco’s modified Eagle’s
medium (Sigma) without indicator and antibiotics.[34] After the
ampoule was thawed not more than four passages were per-
formed. The control cells and cells with tested substances in the
range of 2–5 ð 104 cell mlꢁ1 concentration (depending on line
nature) were placed on separate 96-well plates. Solutions con-
taining test compounds were diluted and added into wells to
give the final concentrations of 50, 25, 12.5 and 6.25 µg mlꢁ1
.
The control cells were treated in the same manner only in the
absence of test compounds. Plates were cultivated for 72 h. A
quantity of survived cells was determined using Crystal Violet
(CV), Neutral Red (NR) or 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-
2H-tetrazolium bromide (MTT) coloration, which was assayed by
multiscan spectrophotometer Tetretek Multiscan MCC/340. The
quantity of living cells on control plate was taken in calculations
for 100%.[34,35] Concentration of NO was determined according
to Fast et al.[35] Mean lethal dose (LD50) has been determined on
3T3 cells (alternative to LD50 in vivo test) according to the pro-
tocols of Interagency Coordinating Committee on the Validation
of Alternative Methods and National Toxicology Program of In-
teragency Center for the Evaluation of Alternative Toxicological
Methods.[36]
The diethylamino derivative 2 is the most promising compound
in this series of compounds: low toxicity (LD50, 646 mg kgꢁ1), high
cytotoxicity on both cancer cell lines (LC50 2–3 µg mlꢁ1) and lower
cytotoxicity on normal fibroblasts (LC50 11 µg mlꢁ1). Its precursor -
2-[(3-diethylaminopropyl)dimethylsilyl]furan containing only one
silicon atom at the furan ring is less active (LC50 6–27 µg mlꢁ1
)
and more toxic (LD50 407 mg kgꢁ1). Thus, introduction of
the second silyl group at the furan ring improves both the
cytotoxicity against cancer cells and the cytoselectivity of the
furylsilylamines.
Conclusion
Results and Discussion
In summary, we propose an entirely new approach to construction
of biologically active compounds – double silylation. It consists of
a direct silylation of the furan ring to increase the lipophilicity
followed by hydrosilylation for binding with amines. Using this
approach we have synthesized a new class of highly active
cytotoxic agents (LC50 1–3 µg mlꢁ1 for cancer cell lines HT-1080
and MG-22A) – silylfurylsilylamines containing two silicon atoms
in the heterocyclic substituent bound to the heterocyclic amine.
The starting 5-triethylsilyl-2-dimethylsilylfuran (1) has been pre-
pared from the furan by two consecutive organolithium syn-
theses. It has been used for the hydrosilylation of heterocyclic
allylamines in the presence of Speier’s catalyst (Scheme 1). Hy-
drosilylation of all studied allyamines by hydrosilane 1 occurred
smoothly during 1 h heating of the mixture of compounds
with a drop of catalyst. The reaction afforded a series of sily-
lamines 2–11 containing two different heterocycles in good
c
www.interscience.wiley.com/journal/aoc
Copyright ꢀ 2009 John Wiley & Sons, Ltd.
Appl. Organometal. Chem. 2010, 24, 158–161

New 2-[(3-aminopropyl)-dimethylsilyl]-5-triethylsilylfurans
Table 2. Cytotoxicity (LC50 µg mlꢁ1) of
Et3Si
SiMe2
O
(CH2)3R
Compounds
Cell line
HT-1080
Method
2
3
4
5
6
7
8
9
10
11
CV
2
3
35
34
71
2
2
3
3
3
3
3
3
10
7
17
25
3
35
32
MTT
3
ž
NO
150
250
150
133
100
75
150
250
200
MG-22A
CV
2
2
19
20
1
1
9.3
6.5
450
5.7
251
2
2
2
2
3
3
10
19
2
3
23
22
MTT
ž
NO
200
100
250
150
100
133
100
150
100
NIH 3T3
NIH 3T3
NR
11
2
0.8
106
0.4
76
0.3
76
14
11
5
30
LD50 (mg kgꢁ1
)
646
168
368
345
228
576
LC50 (µg mlꢁ1) providing 50% cell killing effect [CV, crystal violet coloration, action on cell membranes; MTT, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-
ž
2H-tetrazolium bromide coloration, influence on the activity of mitochondrial enzymes]; NR, neutral red; NO concentration.[34]
Acknowledgments
[16] A. R. Lera, W. Bourguet, L. Altucci, H. Gronemeyer, Nat.Rev.Drug
Discov. 2006, 5, 717.
The work was carried out with financial support from the Latvian
Council of Science (grant 1329).
[17] S. L. Martin, A. McDowell, J. F. Lynas, J. Nelson, B. Walker,
J. Pharm.Pharmac. 2001, 53, 333.
[18] H. Kantarjian, E. Jabbour, J. Grimley, P. Kirkpatrick, Nature Rev.Drug
Discov. 2007, 6, 811.
[19] I. R. Radford, Curr.Opin.Invest.Drugs 2002, 3, 492.
[20] A. Bilir, M. Erguven, G. Oktem, A. Ozdemir, A. Uslu, E. Aktas,
B. Bonavinda, Int. J. Oncol. 2008, 32, 829.
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