Synthetic transformations of sesquiterpene lactones. V.* synthesis and cytotoxicity of 13-Aryl-substituted tourneforin derivatives

Article abstract of DOI:10.1007/s10600-012-0214-4

13-Aryl-substituted tourneforin derivatives were synthesized via the Heck reaction with aryliodides. The structure of (E)-13-(3,4-dimethoxybenzyl)- eudesma-4(5),11(13)-dien-6α,12-olide was confirmed by an XSA. A study of the cytotoxicity of the synthesized derivatives for CEM-13, MT-4, and U-937 tumor models showed promise for the modification.

Full text of DOI:10.1007/s10600-012-0214-4

Chemistry of Natural Compounds, Vol. 48, No. 2, May, 2012 [Russian original No. 2, March-April, 2012]
SYNTHETIC TRANSFORMATIONS OF SESQUITERPENE LACTONES.
ꢀ
V. SYNTHESIS AND CYTOTOXICITY OF 13-ARYL-SUBSTITUTED
TOURNEFORIN DERIVATIVES
1*
1,2
1
E. E. Shulꢁts, S. S. Patrushev, A. V. Belovodskii,
UDC 547.913.5:548.737:544.478
1
1
2
M. M. Shakirov, T. V. Rybalova, A. G. Pokrovskii,
M. A. Pokrovskii, G. A. Tolstikov, and S. M. Adekenov
2
1
3
13-Aryl-substituted tourneforin derivatives were synthesized via the Heck reaction with aryliodides. The
structure of (E)-13-(3,4-dimethoxybenzyl)-eudesma-4(5),11(13)-dien-6ꢂ,12-olide was confirmed by an XSA.
A study of the cytotoxicity of the synthesized derivatives for CEM-13, MT-4, and U-937 tumor models showed
promise for the modification.
Keywords: tourneforin, Heck reaction, 13-aryleudesmanolides, tumor cells, XSA.
Compounds containing an ꢂ-methylene-ꢃ-lactone, in particular sesquiterpene lactones, are interesting because of a
variety of physiological activity, including antitumor properties [2]. It was found during a study of the structure–activity
relationship of a series of sesquiterpene lactones that high cytotoxicity correlated with the presence of an exocyclic double
bond in the lactone ring [3]. It was proposed that the antitumor activity of these compounds was due to induction of apoptosis
of tumor cells by activating caspase-3 [4]. The antitumor drug Arglabin was developed based on a sesquiterpene
methylenelactone [5]. We showed earlier that the structure of eudesmane-type methylenelactones can be modified using the
13
Heck reaction [6]. Herein C arylation of tourneforin (1), an available sesquiterpene lactone of Artemisia tournefortiana
Rchb. [7], is reported.
14
H C
3
O
O
R
3
H C
3
1
R
R
2
a
9
R
R
3
10
H
+
H
O
7
5
3
13
11
1
H
H
2
12
O
O
CH
CH
3
3
I
R
1
15
O
1
2a - c
2a, 3a: R = H, R = R = OCH
3
3a - c
1
2
3
2b, 3b: R = R = OCH , R = H
1
3
3
2
2c, 3c: R = R = H, R = F
1
2
3
a. Pd(OAc) , P(o-Tol) , Et N, DMF, 120ꢅC, 16 h
2
3
3
The reaction of 1 with 4-iodoveratrol (2a), 2,4-dimethoxyiodobenzene (2b), and 4-iodo-1-fluorobenzene (2c) was
carried out in the catalytic system Pd(OAc) –(o-Tol) P (4/16 mol%) in DMF solution in the presence of Et N. Heating the
2
3
3
mixture of components for 16 h resulted in complete conversion of the starting compound. Column and analytical
chromatography over silica gel isolated the corresponding (E)-13-aryleudesma-4(5),11(13)-dien-6ꢂ,12-olides (3a–c) (27–
45% yields).
ꢄꢄꢄꢄꢄꢄ
ꢀ
For No. IV, see Ref. [1].
1) N. N. Vorozhtsov Novosibirsk Institute of Organic Chemistry, Siberian Branch, Russian Academy of Sciences,
630090, Novosibirsk, fax: (383) 330 97 52, e-mail: schultz@nioch.nsc.ru; 2) Novosibirsk State University, Novosibirsk,
Russia; 3) International Scientific-Production Holding Fitokhimiya, 100009, Karaganda, Republic of Kazakhstan,
fax: (87212) 43 37 73, e-mail: arglabin@phyto.kz. Translated from Khimiya Prirodnykh Soedinenii, No. 2, March–April,
2012, pp. 221–224. Original article submitted August 10, 2011.
©
0009-3130/12/4802-0245 2012 Springer Science+Business Media, Inc.
245

TABLE 1. Cytotoxicity of Tourneforin (1) and 13-Aryl-Substituted Derivatives 3a–c
Compound
CEM-13 tumor cells, CCID50, ꢈM
U-937 tumor cells, CCID50, ꢈM
MT-4 tumor cells, CCID50, ꢈM
> 200
25.7
18.6
11.8
> 200
54.5
56.1
41.2
> 200
5.5
12.3
8.9
1
3a
3b
3c
______
CCID is the dose inhibiting tumor cell viability by 50%.
50
C1
C2
C14
O5
C9
C10
C3
C17
O1
C8
C7
C5
ꢁ
C4
ꢁ
C4
C15
C6
ꢁ
C5
C6
C13
C3
ꢁ
C12
O2
C1
ꢁ
C2
C16
ꢁ
C11
O3
O4
Fig. 1. Molecular structure of 3a from an XSA.
The structures of the synthesized compounds were established based on elemental analyses and spectral characteristics.
The structure of 3a was confirmed by an x-ray crystal structure analysis (XSA) (Fig. 1). The bond lengths of the tricyclic
moiety were similar to analogous ones in starting 1 [7]. The lactone ring had the half-chair conformation with a folding angle
°
of 15.8(6)° [atoms C7, C11, C12, O3 were planar within 0.009(8) A]. The angle between the benzene ring (C1ꢁꢆC6ꢁ) and the
plane of C7C11C12O3 was 16.4(6)°.
The methoxyls O2C16H and O1C17H were practically coplanar with the benzene ring. The torsion angles
3
3
C3ꢁ-C4ꢁ-O1-C17 and C4ꢁ-C3ꢁ-O2-C16 were 178.3(2) and 179.3(2)°, respectively. The six-membered ring (C5ꢆC10) adopted
°
a distorted twist conformation. The cyclohexene moiety had a conformation similar to a boat with C1 deviating by 0.664(5) A
°
from the plane of C2C3C4C5C10 [planar within 0.040(3) A]. The crystal structure had molecular sheets extended along the
b axis that were formed by H-bonds C6ꢁ–H…O4 and C7–H7…O4 (with parameters C–H 0.93 and 0.98, H…O 2.50 and 2.41,
°
C…O 3.383(2) and 3.175(2) A, C–H…O 158 and 135°, respectively) and H-bond C5ꢁ–H…O3 [parameters C–H 0.93, H…O
°
2.58, C…O 3.330(2) A, C–H…O 138°].
PMR spectra of 3a–c contained resonances for H-13 in the range 7.42–7.50 ppm. The (E)-configuration of the
11 13
13
3
C –C double bond of 3a–c was inferred from the presence in the C NMR spectra (single-resonance mode) of C–H J-cis
3
coupling constants between the olefinic proton and the lactone carbonyl C atom ( J = 7.2 Hz). A characteristic feature of the
7
PMR spectra of 3a–c was a weak-field shift of H ( 3.98–4.03 ppm) compared with the position of the corresponding proton
in the spectrum of 1 ( 3.65 ppm). According to PMR spectra and GC–MS of the reaction mixture, 3a–c were the only reaction
products of cross-conjugation of 1 with aryliodides 2a–c.
The course of the Heck reaction of the methylenelactones depended significantly on the structure of the lactone.
Thus, the reaction of ꢂ-methylene-ꢃ-butyrolactone with the aryliodides occurred with formation of products with the
(Z)-configuration [8]. The reaction of isoalantolactone with arylhalides produced (E)-13-aryleudesma-4(15),11(13)-dien-
8ꢂ,12-olides and products of isomerization of the double bond and configuration inversion at C(8), i.e., 13-aryleudesma-
4(15),7(11)-dien-8ꢇ,12-olides [6]. The reaction of 11,13-dehydrosantonin with the aryliodides gave exclusively the
corresponding 13-arylidenelactones with the (E)-configuration of the double bond. Products of a double-bond shift were not
observed [9]. We obtained an analogous result for the Heck reaction of 1.
Table 1 presents the cytotoxicity of 1 and its arylidene-substituted derivatives 3a–c. It can be seen that introducing
the aromatic substituent into the C(13) position of 1 increased the cytotoxicity against lymphoid tumor cells.
Thus, a method for preparing 13-aryl-derivatives using the Heck reaction was proposed based on the available
A. tournefortiana metabolite tourneforin. Significant cytotoxicity was found for the new derivatives of eudesmane-type
methylenelactones against MT-4 and CEM-13 tumor cell lines.
246

EXPERIMENTAL
NMR spectra were recorded in CDCl or CD OD solutions on Bruker AV-400 (operating frequency 400.13 for
3
3
1
13
1
13
H and 100.78 MHz for C) and AV-600 (operating frequency 600.30 for H and 150.96 MHz for C) spectrometers.
Resonances in NMR spectra were assigned using various types of H–H and C–H shift correlation spectroscopy (COSY,
13
COXH, COLOC, NOESY). Multiplicities of resonances in C NMR spectra were determined by recording spectra in
J-mode. A DFS Thermo Scientific high-resolution mass spectrometer (ionizing electron energy 70 eV, vaporizer temperature
230–280°C) was used to record mass spectra and to determine molecular weights and elemental compositions. Melting points
were determined on a Stuart SMF-38 heating stage.
IR spectra were recorded in KBr pellets on a Vector-22 instrument. UV absorption spectra were recorded in EtOH on
20
an HP 8453 UV–Vis spectrometer. Specific rotations [ꢂ] were measured on a PolAAr3005 polarimeter. X-ray diffraction
D
experiments for 3a were performed at room temperature on a Bruker KappaAPEX II diffractometer (Mo Kꢂ-radiation, graphite
monochromator, CCD-detector, maximum angle 2ꢉ = 54.2°).
Reaction products were separated by column chromatography over silica gel (Acros, 0.035–0.070 mm) and additionally
by preparative TLC on a loose layer of silica gel containing K-35 luminophore (1%) on plates (20 ꢊ 20 cm) with a thin layer
of sorbent (1 mm) using benzene:EtOAc and CHCl :EtOH as eluents. Pd(OAc) was synthesized by the literature
3
2
method [10]; 2,4-dimethoxyiodobenzene (2b), as before [11].
(3aS,5aS,9bR,E)-3-(3,4-Dimethoxybenzylidene)-5a,9-dimethyl-3a,4,5a,6,7,8-hexahydronaphtho[1,2-b]furan-
2,5(3H,9bH)-dione (3a). Atwo-necked glass ampul was filled withAr, in a stream of which the ampul was charged successively
with 1 (247 mg, 1 mmol), 4-iodoveratrol (2a, 290 mg, 1.1 mmol), Pd(OAc) (9 mg, 0.04 mmol), tris-(o-tolyl)phosphine
2
°
(49 mg, 0.16 mmol), DMF (5 mL), and Et N (142 mg, 1.4 mmol). Molecular sieves (3 A) were added. The ampul was sealed
3
(slight excess of Ar pressure). The mixture was heated for 16 h at 120°C and cooled. The ampul was opened. The contents
were poured into a Petri dish. The solid precipitate was dissolved in the minimal amount of CHCl and chromatographed over
3
silica gel (CHCl :EtOH eluent, 100:0ꢋ10:1). tris-(o-Tolyl)phosphine, starting lactone, and a mixture of lactone and reaction
3
products (CHCl :EtOH eluent) were eluted sequentially. Repeated chromatography on a plate with a loose layer of silica gel
3
and recrystallization from EtOH afforded 3a (164 mg, 45%), mp 196–198°C (EtOH), [ꢂ] –78.5° (c, CHCl ). IR spectrum
589
3
–1
(ꢌ, cm ): 825, 849, 926, 964, 1021, 1105, 1140, 1160, 1193, 1218, 1250, 1266, 1319, 1334, 1423, 1443, 1463, 1518, 1597,
1644, 1713, 1734, 2836, 2937, 2970. UV spectrum (EtOH, ꢍ , nm, log ꢎ): 203 (4.37), 242 (4.12), 330 (4.35).
max
PMR spectrum (CDCl , , ppm, J/Hz): 1.33 (3H, s, H-14), 1.53 (1H, ddd, J = 12.8, 5.8, 3.6, H-1), 1.59 (1H, ddd,
3
J = 13.0, 12.8, 3.4, H-1), 1.63–1.79 (2H, m, H-2), 1.85 (3H, s, H-15), 2.14 (1H, m, H-3), 2.49 (1H, dd, J = 13.2, 3.1, H-8), 2.82
(1H, dd, J = 13.2, 8.7, H-8), 3.88 (3H, s, OCH ), 3.91 (3H, s, OCH ), 3.98 (1H, dddd, J = 8.7, 7.3, 3.1, 1.5, H-7), 5.65 (1H, d,
3
3
J = 7.3, H-6), 6.88 (1H, d, J = 8.3, H-5ꢁ), 6.95 (1H, d, J = 1.5, H-2ꢁ), 7.09 (1H, dd, J = 8.3, 1.5, H-6ꢁ), 7.49 (1H, d, J = 1.5,
H-13).
13
C NMR spectrum (CDCl , , ppm): 17.69 (C-2), 19.39 (C-14), 24.42 (C-15), 32.13 (C-3), 33.83 (C-1), 37.60 (C-8),
3
38.83 (C-7), 47.83 (C-10), 55.87 (2ꢊOCH ), 75.05 (C-6), 111.17 (C-2ꢁ), 112.99 (C-5ꢁ), 123.99 (C-6ꢁ), 125.35 (C-5), 126.25
3
(C-1ꢁ), 128.76 (C-11), 137.98 (C-4), 138.03 (C-13), 149.01 (C-4ꢁ), 150.86 (C-3ꢁ), 171.32 (C-12), 213.35 (C-9).
Mass spectrum (m/z, I , %): 382 (100), 245 (15), 217 (24), 151 (11), 91 (6). Found: MW 382.1773. C H O .
rel
23 26 5
Calcd: 382.1775.
(3aS,5aS,9bR,E)-3-(2,4-Dimethoxybenzylidene)-5a,9-dimethyl-3a,4,5a,6,7,8-hexahydronaphtho[1,2-b]furan-
2,5(3H,9bH)-dione (3b). The method described above was used with 1 (247 mg, 1 mmol) and 2,4-dimethoxyiodobenzene
(2b, 290 mg, 1.1 mmol) to afford 3b (172 mg, 45%), mp 221–222°C (EtOH), [ꢂ] –48° (c 1.23, CHCl ). IR spectrum (ꢌ,
589
3
–1
cm ): 837, 928, 970, 1032, 1120, 1159, 1180, 1225, 1275, 1302, 1335, 1423, 1464, 1500, 1603, 1637, 1736, 2931, 2976.
UV spectrum (EtOH, ꢍ , nm, log ꢎ): 201 (3.79), 213 (3.80), 221 (3.93), 245 (3.97), 300 (4.09), 341 (4.36).
max
PMR spectrum (CDCl , , ppm, J/Hz): 1.31 (3H, s, H-14), 1.51 (1H, ddd, J = 12.8, 3.8, 3.6, H-1), 1.57 (1H, ddd,
3
J = 13.0, 12.8, 3.4, H-1), 1.71 (1H, m, H-2), 1.80 (1H, m, H-2), 1.83 (3H, s, H-15), 2.11 (2H, m, H-3), 2.43 (1H, dd, J = 13.5,
3.5, H-8), 2.73 (1H, dd, J = 13.5, 8.5, H-8), 3.82 (3H, s, OCH ), 3.83 (3H, s, OCH ), 3.98 (1H, dddd, J = 8.6, 8.5, 7.5, 2.0,
3
3
H-7), 5.61 (1H, d, J = 7.5, H-6), 6.44 (1H, d, J = 2.4, H-3ꢁ), 6.47 (1H, dd, J = 8.5, 2.4, H-5ꢁ), 7.31 (1H, d, J = 8.5, H-6ꢁ), 7.42
(1H, d, J = 2.0, H-13).
13
C NMR spectrum (CDCl , , ppm): 17.76 (C-2), 19.39 (C-14), 24.60 (C-15), 32.21 (C-3), 33.76 (C-1), 37.65 (C-8),
3
38.78 (C-7), 47.63 (C-10), 55.37 (OCH ), 55.49 (OCH ), 74.86 (C-6), 98.28 (C-32), 105.25 (C-52), 115.50 (C-1ꢁ), 124.61
3
3
(C-5), 128.92 (C-11), 130.12 (C-6ꢁ), 132.60 (C-13), 137.97 (C-4), 160.21 (C-2ꢁ), 162.81 (C-4ꢁ), 171.68 (C-12), 213.51 (C-9).
247

Mass spectrum (m/z, I , %): 382 (100), 367 (6), 351 (7), 339 (6), 323 (9), 309 (11), 245 (28), 217 (35), 151 (27), 91
rel
(10). Found: MW 382.1769. C H O . Calcd: 382.1775.
23 26
5
(3aS,5aS,9bR,E)-3-(4-Fluorobenzylidene)-5a,9-dimethyl-3a,4,5a,6,7,8-hexahydronaphtho[1,2-b]furan-
2,5(3H,9bH)-dione (3c). The method described above was used with 1 (247 mg, 1 mmol) and 4-iodo-1-fluorobenzene (2c,
245 mg, 1.1 mmol) to afford 3c. The compound was purified by column chromatography over silica gel and Al O and by
2
3
–1
TLC. Yield 92 mg (27%) of an oil. IR spectrum (ꢌ, cm ): 2979, 1746, 1713, 1650, 1600, 1510, 1372, 1326, 1313, 1294,
1192, 1176, 1153, 1132, 1104, 970, 927, 837, 756. UV spectrum (EtOH, ꢍ , nm, log ꢎ): 194 (3.52), 206 (3.96), 220 (3.84),
max
286 (4.02), 294 (4.01), 302 (3.93).
PMR spectrum (CDCl , , ppm, J/Hz): 1.31 (3H, s, H-14), 1.50 (1H, ddd, J = 12.6, 3.7, 3.5, H-1 ), 1.57 (1H, ddd,
3
a
J = 12.9, 12.8, 3.4, H-1 ), 1.73 (1H, m, H-2 ), 1.81 (1H, m, H-2 ), 1.83 (3H, s, H-15), 2.13 (2H, m, H-3), 2.38 (1H, dd, J = 13.3,
b
a
b
3.2, H-8 ), 2.82 (1H, dd, J = 13.3, 8.7, H-8 ), 4.03 (1H, dddd, J = 8.7, 7.2, 3.2, 1.7, H-7), 5.65 (1H, d, J = 7.2, H-6), 7.09 (2H,
a
b
dd, J = 8.6, 8.5, H-3ꢁ, H-5ꢁ), 7.44 (2H, dd, J = 8.5, 5.4, H-2ꢁ, H-6ꢁ), 7.50 (1H, d, J = 1.7, H-13).
13
C NMR spectrum (CDCl , , ppm): 17.67 (C-2), 19.32 (C-14), 24.37 (C-15), 32.12 (C-3), 33.78 (C-1), 37.56 (C-8),
3
38.56 (C-7), 47.72 (C-10), 75.18 (C-6), 116.18 (C-3ꢁ, C-5ꢁ), 127.76 (C-5), 128.58 (C-11), 129.65 (C-1ꢁ), 132.02 (C-2ꢁ, C-6ꢁ),
136.64 (C-13), 138.22 (C-4), 163.42 (C-4ꢁ), 170.86 (C-12), 213.06 (C-9). C H FO .
21 21
3
X-ray Crystal Structure Analysis of 3a. Crystals of 3a were orthorhombic, a = 9.3112(4), b = 13.1142(6),
°
° 3
3
–1
c = 17.233(1) A, V = 2104.4(2) A , space group P2 2 2 , Z = 4, C H O , d = 1.207 g/cm , ꢈ = 0.084 mm , crystal size
1 1 1
23 26
5
calcd
0.43 ꢊ 0.25 ꢊ 0.15 mm. Intensities of 4462 independent reflections were measured. Absorption corrections were applied
using the SADABS program (transmission 0.9647–0.9875). The structure was solved by direct methods using the
SHELXS-97 program and refined by anisotropic and isotropic (for H) methods using the SHELXL-97 program. Positions of
H atoms were calculated geometrically. Parameters of H atoms were refined isotropically using a rider model. The final
refinement parameters were wR = 0.1106, S = 1.046. A total of 258 parameters were refined (R = 0.0382 for 3709 F > 4ꢏ).
2
Atomic coordinates and bond lengths and angles were deposited in the Cambridge Crystallographic Data Centre
(CCDC-825956).
Cell Culture. We used human tumor cell lines MT-4, CEM (human T-cell leucosis cells), and U-937 (human
monocytes). Cells were cultured in RPMI-1640 medium containing fetal calf serum (10%), L-glutamine (2 mmol/L), gentamicin
(80 ꢈg/mL), and lincomycin (30 mg/mL) at 37°C in a CO incubator. Test compounds were dissolved in DMSO and added to
2
cell culture at the required concentrations. We used three wells for each concentration. Cells incubated without added test
compounds were used as the control.
MTT Test. The standard MTT test was used to determine CCID (dose inhibiting cell viability by 50%) values
50
[12, 13].
ACKNOWLEDGMENT
The work was supported financially by an Integrated Project of the SB, RAS, with organizations of CIS countries
(No. 79).
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