Chemistry of phosphorus ylides 32: Synthesis of phosphoranylidene-pyrano- and -cyclobutyl-xanthenones with potential antitumor activity

Article abstract of DOI:10.1007/s00706-011-0683-3

The reaction of active phosphacumulenes with xanthenones and anthrone yields xanthene(anthracene)-and/or phosphoranylidene xanthene(anthracene)- depending upon the nature of reactants and reaction conditions. Pertinent reaction mechanisms were considered

Full text of DOI:10.1007/s00706-011-0683-3

Monatsh Chem (2012) 143:965–973
DOI 10.1007/s00706-011-0683-3
ORIGINAL PAPER
Chemistry of phosphorus ylides 32: synthesis
of phosphoranylidene-pyrano- and -cyclobutyl-xanthenones
with potential antitumor activity
•
Fouad M. Soliman Medhat M. Said
•
•
Mahmoud Youns Shaban A. Darwish
Received: 9 January 2011 / Accepted: 2 November 2011 / Published online: 21 December 2011
Ó Springer-Verlag 2011
Abstract The reaction of active phosphacumulenes with
xanthenones and anthrone yields xanthene(anthracene)-
and/or phosphoranylidene xanthene(anthracene)- depend-
ing upon the nature of reactants and reaction conditions.
Pertinent reaction mechanisms were considered and com-
patible spectroscopic measurements were recorded for all
new compounds. The cytotoxic activity of some new
products was evaluated against human cervical and breast
carcinoma cell lines. Certain tested compounds showed
promising results.
as antimicrobial [13], antidepressive [14], and vasorelaxant
[15] agents. On the other hand, xanthenone derivatives are
capable of inhibiting the enzyme a-glycosidase which
plays an important role in digestion of carbohydrates,
glycoproteins, and glycolipids [16]. Therefore, the syn-
thesis of novel bioactive xanthenones is important. Of
particular interest are antitumor products with high effi-
ciency and low side effects.
Results and discussion
Keywords Active phosphacumulenes ꢀ Xanthenones ꢀ
Cyclobutanes ꢀ Pyranoxanthenones ꢀ Antitumor activity
On the basis on these considerations and in continuation of
our work on active phosphacumulenes [17–20], we have
synthesized a series of new cyclic xanthenone derivatives
with anticipated antitumor activity. Therefore, we studied
the reaction of an active nucleophilic phosphacumulene
(N-phenyliminovinylidene)triphenylphosphorane (2a), with
9H-xanthen-9-one (1). The corresponding N,N0-[2-(triphe-
nylphosphoranylidene)-4-(9H-xanthen-9-ylidene)cyclobu-
tane-1,3-diylidene]dianiline (6) was obtained together with
triphenylphosphine oxide. On the basis of analytical and
spectroscopic data the structure of 6 was deduced. The
distinguishing feature in the IR of 6 is the absence of a
carbonyl signal which was recorded at 1,657 cm-1 in the
starting xanthenone 1. Moreover, a signal at d = 15.23
ppm was recorded in the 31P NMR of 6 which fits with
phosphorane with a four-membered ring [21]. Formation of
the phosphoranylidene cyclobutane 6 by the reaction of
phosphacumulene 2a with xanthenone 1 occurs by a [2?2]
cycloaddition of the carbonyl group in 1 to the ylidic C–P
bond of the phosphacumulene 2a to give the oxaphosphe-
tane 4, through the dipolar intermediate 3 [22–24].
Expulsion of triphenylphosphine oxide from 4 affords the
unstable ketene 5 [25], which is followed immediately by
Introduction
Natural and synthetic xanthenones are an important class of
compounds [1, 2]. They have demonstrated multiple
pharmacological properties such as antioxidant [3, 4], anti-
inflammatory [5], and antimalarial activities [6] as well as
inhibition of a variety of tumor cell lines [7–10] and
modulation of protein kinase C (PKC) isoforms [11, 12].
Moreover, they have found broad applications in medicine
Electronic supplementary material The online version of this
article (doi:10.1007/s00706-011-0683-3) contains supplementary
material, which is available to authorized users.
F. M. Soliman (&) ꢀ M. M. Said ꢀ S. A. Darwish
Department of Organometallic and Organometalloid Chemistry,
National Research Centre, Dokki, Cairo, Egypt
e-mail: solimanfma2@yahoo.com
M. Youns
Faculty of Pharmacy, Biochemistry and Molecular Biology
Department, Helwan University, Cairo, Egypt
123

966
F. M. Soliman et al.
[2?2] cycloaddition to a second molecule of 2a, giving the
four-membered ring phosphoranylidene cyclobutane 6
(Scheme 1).
reaction, leading to the pyrano compound 9 and triphenyl-
phosphine oxide (Scheme 2).
The reaction of 2-acetyl-1-hydroxy-9H-xanthen-9-one
(10a) with (N-phenyliminovinylidene)triphenylphospho-
rane (2a) is of particular interest. Compound 10a reacted
with 2a in boiling toluene for 10 h to afford 4-methyl-2-
(phenylimino)-2H,12H-pyrano[2,3-a]xanthen-12-one (12a)
along with triphenylphosphine oxide. Addition of the hy-
droxyxanthenone 10a to the phosphonium ylide 2a afforded
the intermediate phosphorane 11a, which cyclized by Wittig
reaction with the active side chain carbonyl rather than the
xanthenone carbonyl, leading to the pyranoxanthenone 12a.
The IR spectrum of 12a shows the xanthenone carbonyl
group at 1,667 cm-1 and in the 13C NMR it appeared at
d = 174.20 ppm. 2-Acetyl-1-hydroxy-9-xanthen-9H-one
(10a) reacted with (oxovinylidene)triphenylphosphorane
When 1-hydroxy-9H-xanthen-9-one (7) was treated with
equimolar amounts of (N-phenyliminovinylidene)triphenyl-
phosphorane (2a) in toluene at reflux temperature, N-(2H-
pyrano[2,3,4-kl]xanthen-2-ylidene)aniline (9) was obtained
in fairly good yield, together with triphenylphosphine
oxide. The most important feature in the mass spectrum of 9
is that the M? was found at m/z = 311. Moreover, no car-
bonyl group was observed in the IR and 13C NMR spectra of
compound 9. Formation of the pyranoxantheneylidene
aniline 9 from the reaction of 2a and 7 can be explained by
the addition of the hydroxyxanthenone to the phosphacu-
mulene to give first the complicated phosphonium ylide 8,
which undergoes cyclization by an intramolecular Wittig
Scheme 1
123

Chemistry of phosphorus ylides 32
967
Scheme 2
(2b) to afford the new 4-methyl-2H,12H-pyrano[2,3-
a]xanthene-2,12-dione (12b). On the other hand, 2-benzoyl-
1-hydroxy-9H-xanthen-9-one (10b) reacted with the
phosphacumulenes 2a and 2b under the same experi-
mental conditions to give 4-phenyl-2-(phenylimino)-
2H,12H-pyrano[2,3-a]xanthen-12-one (12c) and 4-phenyl-
2H,12H-pyrano[2,3-a]xanthene-2,12-dione (12d) and tri-
phenylphosphine oxide, respectively (Scheme 3).
When 2-allyl-1-hydroxy-9H-xanthen-9-one (16) was trea-
ted with (oxovinylidene)triphenylphosphorane (2b), the 1:1
aduct 1-hydroxy-2-[(2-oxo-3-(triphenylphosphoranylidene)-
cyclobutyl)methyl]-9H-xanthen-9-one (17) was isolated.
Formation of 17 is enhanced by preferential nucleophilic
[2?2?4] attack by the carbanionic center in 2b on the
electron-deficient center of the exocyclic ethylenic bond in
16. Compound 17 was equally obtained whether 1 or 2 molar
equivalents of the phosphorane 2b were used with respect to
1 molar equivalent of 16. The most important reason for
assigning structure 17 is the sharp band at 3,417 cm-1 (OH)
and broad band at 1,625 cm-1 (2 C=O, xanthenone and
cyclobutane) in its IR spectrum. In the 31P NMR spectrum
of 17 a signal at d = 22.31 ppm was observed, which
supported the ylidene-phosphorane structure [26, 27]
(Scheme 5).
We have found that the reaction of 2-cinnamoyl-1-
hydroxy-9H-xanthen-9-one (13) with (N-phenylimino-
vinylidene)triphenylphosphorane (2a) and (oxovinylidene)
triphenylphosphorane (2b) proceeds in boiling toluene for
10 h in the case of 2a or 15 h in the case of 2b by addition
with subsequent cyclization to give 1-hydroxy-2-[4-phenyl-
2-(phenylimino)-2H-pyran-6-yl]-9H-xanthen-9-one (15) and
2-[3,4-dihydro-2-oxo-4-phenyl-3-(triphenylphosphoranylidene)-
2H-pyran-6-yl]-1-hydroxy-9H-xanthen-9-one (14b), respec-
tively. The intermediate 14a was not isolated, it changed
directly via Hofmann degradation to compound 15 and
triphenylphosphine. Compounds 14b and 15 were obtained
in the same yields irrespective of whether 1 or 2 molar
equivalents of the phosphacumulenes 2a, 2b were used. The
IR spectrum of 15 showed strong absorption bands at
3,430 cm-1 (OH) and 1,647 cm-1 (xanthenone C=O). Its 1H
NMR spectrum showed the OH absorption band at
d = 14.14 ppm (D2O), and in the mass spectra the M? was
found at m/z = 457. Moreover, a signal at d = 13.88 ppm
was observed in the 31P NMR spectrum of 14b (Scheme 4).
In addition, the reaction of anthracen-9(10H)-one (18)
with the active phosphacumulenes 2a, 2b was investigated.
When the anthrone 18 was treated with (N-phenylimino-
vinylidene)triphenylphosphorane (2a), N,N0-[2,4-di(anthra-
cen-9(10H)ylidene)cyclobutane-1,3-diylidene]dianiline
(21), N,N0-[2-(anthracen-9(10H)-ylidene)-4-(triphenylphos-
phoranylidene)cyclobutane-1,3-diylidene]dianiline
(22a),
and triphenylphosphine oxide were isolated. On the other
hand, the reaction of (oxovinylidene)triphenylphosphorane
(2b) with 18 afforded only 2-(anthracen-9(10H)-ylidene)-
4-(triphenylphosphoranylidene)cyclobutane-1,3-dione (22b)
and triphenylphosphine oxide. This reaction proceeds via
123

968
F. M. Soliman et al.
Scheme 3
Scheme 4
123

Chemistry of phosphorus ylides 32
969
Scheme 5
[2?2] cycloaddition of the carbonyl group to the ylidic C–P
bond of 2a, 2b to furnish the oxaphosphetane 19. Elimina-
tion of triphenylphosphine oxide from 19 forms the unstable
ketene 20 which dimerizes in the case of using 2a to give 21
and/or adds another molecule of 2a to 20 to give the cyclo-
butane 22a. But in the case of using the phosphacumulene
2b, only the cyclobutane 22b was isolated (Scheme 6).
difference in the nucleophilic character and reactivity of
the phosphacumulenes (2a [ 2b) [29] is also demonstrated
in this study. Therefore, the reaction course between the
active phosphacumulenes and xanthenone derivatives is
rather dependent on a number of parameters, including the
nature of the reactants and the reaction conditions. Our
tested compounds have shown promising anticancer
activities against the human breast cancer cell line (MCF7)
and the human cervical cancer cell line (HeLa cells) at very
low concentrations.
Cytotoxicity assay
Cancerous diseases are a serious threat to the health and
development of mankind and the research for effective
anticancer agents continues. Considerable progress has
been made in recent years in the field of drug development
against different types of cancer. Moreover, chemotherapy
is a major approach for both localized and metastasized
cancers [28], and for many years xanthenone-related
compounds have proved to have significant therapeutic
potential [7–10]. On the basis of these considerations,
certain of the newly synthesized compounds were screened
for their in vitro cytotoxic and growth inhibitory activities
against human breast carcinoma cell line (MCF7) and
human carcinoma cervical cells (HeLa). In order to deter-
mine the possible anticancer activity of our compounds,
MCF7 and HeLa cells were cultured in a monolayer and
treated with our compounds for 72 h. The sulforhodamine
B (SRB) assay was performed to assess the rate of prolif-
eration, and the resulting growth curves showed that our
molecules exhibited cytotoxicity against the aforemen-
tioned cell lines with very low IC50 values. From the data
presented in Table 1, it can be seen that compounds 6 and
12a exhibited high activity against MCF7 and HeLa with
IC50 = 0.07 lg/cm3, 5.55 lg/cm3 (HELA) and 0.10 lg/
cm3, 5.99 lg/cm3 (MCF7), respectively. Moreover, com-
pounds 9, 12b, 12d, 15, and 17 displayed certain activity
against MCF7 and HeLa cells.
Experimental
Melting points were determined with an electrothermal
digital melting point apparatus. The IR spectra were
recorded in KBr disks on a Jasco FT-IR spectrophotometer
model FT/IR-3000E. H, 13C, and 31P NMR spectra were
1
obtained from a Jeol EcA 500 MHz NMR spectrometer
using CDCl3 as a solvent and TMS as an internal reference
at 500.1, 125.8, and 202.4 MHz, respectively. Mass spectra
(EI-MS) were obtained at 70 eV with a Finnigan MAT
SSQ 7000 spectrometer. Elemental analysis results agreed
satisfactorily with the calculated values. The reported
yields are based upon pure materials isolated by column
chromatography on silica gel 60 (Merck) and thin-layer
chromatography (TLC) which was performed on Merck
Kieselgel F254 precoated plates (Merck). Solvents were
dried/purified according to literature procedures.
N,N0-[2-(Triphenylphosphoranylidene)-4-(9H-xanthen-9-
ylidene)cyclobutane-1,3-diylidene]dianiline (6, C47H33N2OP)
A mixture of 9H-xanthen-9-one (1, 196 mg, 1 mmol)
and (N-phenyliminovinylidene)triphenylphosphorane (2a,
754 mg, 2 mmol) [30] in 50 cm3 dry toluene was refluxed
for 20 h. The solvent was evaporated under reduced
pressure to give a brown precipitate of compound 6, which
was chromatographed on silica gel using petroleum ether
(60–80)/chloroform (7:3, v/v) as an eluent to afford
Conclusion
ꢀ
450 mg (67%) of 6. M.p.: 312 °C; IR (KBr): m = 1,612
1
(C=N), 1,431 (P–Ar) cm-1; H NMR (CDCl3): d = 6.93-
The reactions of the active phosphacumulenes 2a, 2b
represent an interesting approach to the synthesis of new
cyclic bioactive xanthenone derivatives. Moreover, the
7.50 (m, 33H, ArH) ppm; 13C NMR (CDCl3): d = 105.52
(C–C=N), 115.52, 119.66, 123.20, 125.79, 128.08, 129.32,
123

970
F. M. Soliman et al.
Scheme 6
132.97, 133.52, 135.73, 139.08, 143.31, 147.04 (Ar C),
152.67 (C=P), 164.67 (2C=N) ppm; 31P NMR (CDCl3):
d = 15.23 ppm.
Triphenylphosphine oxide was isolated, m.p. and mixed
m.p.: 151 °C. When the reaction was performed using
(oxovinylidene)triphenylphosphorane (2b) instead of 2a,
no reaction was observed.
phosphorane (2a, 377 mg, 1 mmol) was refluxed for 20 h
in 50 cm3 dry toluene. The solvent was evaporated under
reduced pressure to afford a brown precipitate which was
purified by preparative TLC using petroleum ether (60–80)/
chloroform (1:1, v/v) as an eluent to afford 160 mg (52%)
ꢀ
1
of 9. M.p.: 235 °C; IR (KBr): m = 1,660 (C=N) cm-1; H
NMR (CDCl3): d = 6.90 (s, 1H, CH), 7.25–7.70 (m, 12H,
ArH) ppm; 13C NMR (CDCl3): d = 106.66 (CH–C=N),
116.52, 117.94, 124.25, 128.85, 129.00, 130.42, 131.50,
132.65, 137.87, 141.63, 143.08, 143.98, 148.67, 150.00,
152.08 (Ar C), 162.97 (C=N) ppm; MS (EI): m/z =
311.20 (M?).
N-(2H-Pyrano[2,3,4-kl]xanthen-2-ylidene)aniline
(9, C21H13NO2)
A mixture of 1-hydroxy-9H-xanthen-9-one (7, 212 mg,
1 mmol) [31] and (N-phenyliminovinylidene)triphenyl-
123

Chemistry of phosphorus ylides 32
971
4-Phenyl-2-(phenylimino)-2H,12H-pyrano[2,3-a]xanthen-
12-one (12c, C28H17NO3)
mixture of 2-benzoyl-1-hydroxy-9H-xanthen-9-one
Table 1 Cytotoxic activity of the synthesized xanthenone derivatives
against MCF7 and HELA
IC50/lg cm-3
A
Compound
(10b, 316 mg, 1 mmol) [32] and (N-phenyliminovinyli-
dene)triphenylphosphorane (2a, 377 mg, 1 mmol) in
20 cm3 dry toluene was refluxed for 8 h. The solvent was
evaporated under reduced pressure to give a pale yellow
precipitate which was crystallized from ether to afford
HeLa
MCF7
6
0.07
17.12
5.55
0.10
13.60
5.99
9
12a
12b
12d
15
17
ꢀ
250 mg (64%) of 12c. M.p.: 222 °C; IR (KBr): m = 1,667
18.27
7.95
10.30
18.3
1
(C=O), 1,644 (C=N) cm-1; H NMR (CDCl3): d = 6.23
(s, 1H, CH), 6.92–8.30 (m, 16H, ArH) ppm; 13C NMR
(CDCl3): d = 110.18 (CH–C=N), 120.64, 121.33, 122.63,
124.16, 127.33, 127.60, 128.19, 128.57, 129.00, 129.25,
131.10, 134.48, 134.71, 135.59, 144.32, 145.71, 146.50,
147.81 (Ar C), 157.71 (C=N), 174.46 (C=O) ppm.
15.47
7.81
31.20
15.40
IC50 value was defined as the concentration at which 50% survival of
cells was observed. Dimethyl sulfoxide (DMSO) was used as negative
control
No reaction was observed with (oxovinylidene)triphenyl-
phosphorane (2b) instead of 2a, even when the reaction was
carried out in boiling xylene and using triethylamine as a base.
4-Phenyl-2H,12H-pyrano[2,3-a]xanthene-2,12-dione
(12d, C22H12O4)
A
mixture of 2-benzoyl-1-hydroxy-9H-xanthen-9-one
(10b, 316 mg, 1 mmol) and (oxovinylidene)triphenylphos-
phorane (2b, 302 mg, 1 mmol) in 20 cm3 dry toluene was
refluxed for 10 h. The solvent was evaporated under
reduced pressure to a give brown precipitate which was
chromatographed on silica gel using petroleum ether
(60–80)/chloroform (9:1, v/v) as an eluent, affording
4-Methyl-2-(phenylimino)-2H,12H-pyrano[2,3-a]xanthen-
12-one (12a, C23H15NO3)
A mixture of 2-acetyl-1-hydroxy-9H-xanthen-9-one (10a,
254 mg, 1 mmol) [32] and (N-phenyliminovinylidene)tri-
phenylphosphorane (2a, 377 mg, 1 mmol) in 20 cm3 dry
toluene was refluxed for 10 h. The solvent was evaporated
under reduced pressure to give 12a as a brown precipitate
which was chromatographed on silica gel using petroleum
ether (60–80)/ethyl acetate (8:2, v/v) as an eluent to afford
ꢀ
240 mg (70%) of 12d. M.p.: 240 °C; IR (KBr): m = 1731
(pyranone C=O), 1,666 (xanthenone C=O) cm-1; 1H NMR
(CDCl3): d = 6.24 (s, 1H, CH), 7.52–8.38 (m, 11H, ArH)
ppm; 13C NMR (CDCl3): d = 114.23 (CH–C=O), 117.59,
123.31, 124.94, 128.53, 129.94, 132.22, 134.92, 135.16,
135.96, 139.08, 146.34, 147.84, 154.95, 155.16 (Ar C),
159.65 (pyranone C=O), 174.60 (xanthenone C=O) ppm.
ꢀ
240 mg (68%) of 12a. M.p.: 285 °C; IR (KBr): m = 1,667
(C=O), 1,604 (C=N) cm-1; 1H NMR (CDCl3): d = 2.49 (s,
3H, CH3), 6.67 (s, 1H, CH), 7.18–7.93 (m, 11H, ArH) ppm;
13C NMR (CDCl3): d = 19.00 (CH3), 113.69 (CH–C=N),
117.88, 119.52, 121.33, 123.11, 123.45, 125.69, 126.28,
128.21, 128.47, 128.97, 129.76, 130.64, 133.33, 141.93,
147.07, 154.00 (Ar C), 163.20 (C=N), 174.20 (C=O) ppm;
MS (EI): m/z = 352.35 ([M-H]?).
2-[3,4-Dihydro-2-oxo-4-phenyl-3-(triphenylphosphor-
anylidene)-2H-pyran-6-yl]-1-hydroxy-9H-
xanthen-9-one (14b, C42H29O5P)
A mixture of 2-cinnamoyl-1-hydroxy-9H-xanthen-9-one
(13, 342 mg, 1 mmol) [32] and (oxovinylidene)triphenyl-
phosphorane (2b, 302 mg, 1 mmol) in 50 cm3 dry toluene
was refluxed for 15 h. The solvent was evaporated under
reduced pressure to give a yellow precipitate which was
purified by preparative TLC using petroleum ether
(60–80)/acetone (10:2, v/v) as an eluent to afford
4-Methyl-2H,12H-pyrano[2,3-a]xanthene-2,12-dione
(12b, C17H10O4)
A mixture of 2-acetyl-1-hydroxy-9H-xanthen-9-one (10a,
254 mg, 1 mmol) and (oxovinylidene)triphenylphospho-
rane (2b, 302 mg, 1 mmol) [33] in 20 cm3 dry toluene was
refluxed for 15 h. The solvent was evaporated under reduced
pressure to give a yellow precipitate which was crystallized
from petroleum ether to afford 180 mg (65%) of 12b. M.p.:
114 °C; IR (KBr) showed the xanthenone and pyranone
ꢀ
350 mg (55%) of 14b. M.p.: 312 °C; IR (KBr): m =
3,403 (OH), 1,636 (xanthenone, pyranone broad band
C=O), 1,431 (P–Ar) cm-1
;
1H NMR (CDCl3): d =
carbonyls as a broad band centered at m = 1,581 cm-1; 1H
ꢀ
7.52–8.37 (m, 28H, ArH), 14.58 (s, 1H, OH, D2O-
exchangeable) ppm; 13C NMR (CDCl3): d = 29.77
(CH–Ph), 96.47 (CH), 117.64, 123.11, 124.90, 126.94,
129.09, 131.06, 132.90, 133.85, 133.97, 136.11, 138.03,
142.85, 148.66, 150.32, 153.92 (Ar C), 155.03 (C=P),
157.36 (pyranone C=O), 180.00 (xanthenone C=O) ppm;
31P NMR (CDCl3): d = 13.88 ppm.
NMR (CDCl3): d = 2.20 (s, 3H, CH3), 6.90 (s, 1H, CH),
7.25–8.92 (m, 6H, ArH) ppm; 13C NMR (CDCl3):
d = 23.05 (CH3), 106.50 (CH–C=O), 116.20, 117.90,
120.61, 124.13, 125.09, 126.14, 132.22, 135.62, 136.70,
141.70 (Ar C), 159.14 (pyranone C=O), 182.81 (xanthenone
C=O) ppm; MS (EI): m/z = 279.09 ([M?H]?).
123

972
F. M. Soliman et al.
1-Hydroxy-2-[4-phenyl-2-(phenylimino)-2H-pyran-6-yl]-
9H-xanthen-9-one (15, C30H19NO4)
754 mg, 2 mmol) in 30 cm3 dry toluene was refluxed for
40 h. The solvent was evaporated under reduced pressure
to give a red precipitate which was crystallized from ether
A mixture of 2-cinnamoyl-1-hydroxy-9H-xanthen-9-one
(13, 342 mg, 1 mmol) and (N-phenyliminovinylidene)tri-
phenylphosphorane (2a, 377 mg, 1 mmol) in 50 cm3 dry
toluene was refluxed for 10 h. The solvent was evaporated
under reduced pressure to give an orange precipitate which
was crystallized from acetone to afford 330 mg (72%) of 15.
to afford 450 mg (67%) of 22a. M.p.: 215 °C; IR (KBr):
1
m = 1,639 (C=N), 1,439 (P–Ar) cm-1; H NMR (CDCl3):
ꢀ
d = 3.38, 3.40 (2H, CH2), 7.08–7.66 (m, 33H, ArH) ppm;
13C NMR (CDCl3): d = 31.27 (CH2), 104.73 (C=C–C=N),
115.57, 119.18, 127.03, 127.25, 128.61, 128.76, 129.04,
129.58, 130.13, 130.20, 136.60, 137.11, 141.35, 142.90,
148.12, 153.20 (Ar C), 154.30 (C=P), 156.56 (2C=N) ppm;
31P NMR (CDCl3): d = 15.74 ppm.
ꢀ
M.p.: 258 °C; IR (KBr): m = 3,430 (OH), 1,647 (C=O),
1,612 (C=N) cm-1; 1H NMR (CDCl3): d = 6.50 (s, 1H, CH),
6.80 (s, 1H, CH), 7.25–8.30 (m, 16H, ArH), 14.40 (s, 1H,
OH, D2O) ppm; 13C NMR (CDCl3): d = 112.69 (CH–C=N),
118.37, 124.99, 127.12, 127.26, 128.54, 128.94, 129.04,
129.16, 129.30, 129.39, 135.98, 138.67, 141.21, 145.65,
147.44, 147.30, 149.79, 150.14, 153.55 (Ar C), 166.85
(C=N), 185.20 (C=O) ppm; MS (EI): m/z = 457.09 (M?).
2-(Anthracen-9(10H)-ylidene)-4-(triphenylphosphoranylidene)-
cyclobutane-1,3-dione (22b, C36H25O2P)
A mixture of anthracen-9(10H)-one (18, 194 mg, 1 mmol)
and (oxovinylidene)triphenylphosphorane (2b, 604 mg,
2 mmol) in 50 cm3 dry toluene was refluxed for 50 h.
The solvent was evaporated under reduced pressure to give
a brown precipitate which was crystallized from petroleum
1-Hydroxy-2-[[2-oxo-3-(triphenylphosphoranylidene)-
cyclobutyl]methyl]-9H-xanthen-9-one (17, C36H27O4P)
A mixture of 2-allyl-1-hydroxy-9H-xanthen-9-one (16,
252 mg, 1 mmol) [34] and (oxovinylidene)triphenylphos-
phorane (2b, 302 mg, 1 mmol) in 50 cm3 dry toluene was
refluxed for 20 h. The solvent was evaporated under reduced
pressure to give a brown precipitate which was crystallized
from ether to afford 360 mg (65%) of 17. M.p.: 105 °C; IR
ether (60–80) to afford 300 mg (58%) of 22b. M.p.:
-1
ꢀ
200 °C; IR (KBr): m = 1,661 (C=O), 1,435 (P–Ar) cm
;
1H NMR (CDCl3): d = 3.49, 3.53 (2H, CH2), 7.22–8.45
(m, 23H, ArH) ppm; 13C NMR (CDCl3): d = 37.20 (CH2),
119.02, 123.53, 127.30, 128.63, 130.50, 132.20, 134.21,
135.05, 138.13, 140.27, 144.39, 146.85, 150.05 (Ar C),
153.78 (C=P), 192.10 (2C=O) ppm; 31P NMR (CDCl3):
d = 19.70 ppm; MS (EI): m/z = 522.20 ([M ? 2H]?).
ꢀ
(KBr): m = 3,417 (OH), 1,625 (xanthenone, cyclobutanone
1
broad band C=O), 1,434 (P–Ar) cm-1; H NMR (CDCl3):
d = 2.02(m, 3H, CH2, CH),3.26(m, 2H, CH2),7.42–7.70(m,
21H, ArH) ppm; 13C NMR (CDCl3): d = 18.54 (cyclobuta-
none CH2), 29.32 (CH2), 48.83 (cyclobutanone CH), 118.95,
119.73, 122.59, 123.52, 126.44, 127.65, 130.45, 130.56,
133.34, 135.09, 135.12, 137.04, 139.12, 143.91, 147.02,
147.86, 149.55 (Ar C), 154.03 (C=P), 175.00 (xanthenone
C=O), 201.00 (cyclobutanone C=O) ppm; 31P NMR (CDCl3):
d = 22.31 ppm; MS (EI): m/z = 554.20 (M?).
Cytotoxicity screening
Cell lines and treatments
The human breast cancer cell line (MCF7) and the human
cervical carcinoma cells (HeLa) cells were obtained from
the American Type Culture Collection and grown in
DMEM medium with 10% foetal bovine serum, 100 units/
cm3 penicillin, and 100 lg/cm3 streptomycin (Invitrogen).
Cells were maintained at 37 °C in a humidified atmosphere
of 5% CO2. Stock solutions of our compounds were pre-
pared in DMSO and stored at -20 °C. All controls were
exposed to DMSO alone; DMSO concentration was always
\0.1%.
N,N0-[2,4-Di(anthracen-9(10H)-ylidene)cyclobutane-1,3-
diylidene]dianiline (21, C44H30N2)
A mixture of anthracen-9(10H)-one (18, 194 mg, 1 mmol)
and (N-phenyliminovinylidene)triphenylphosphorane (2a,
377 mg, 1 mmol) in 50 cm3 dry toluene was refluxed for
40 h. The solvent was evaporated under reduced pressure to
give a brown precipitate which was crystallized from
methylene chloride/ether (4:1), affording 320 mg (55%) of
ꢀ
Cell viability assay (SRB assay)
1
21. M.p.: 285 °C; IR (KBr): m = 1,649 (C=N) cm-1; H
Cells were plated in 96-well plates and incubated for 48 h.
After treatment, cell medium was aspirated, and 100 mm3/
well of 10% trichloroacetic acid was added. After fixation
at 4 °C and washing, 50 mm3 of 0.4% (w/v) sulforhoda-
mine B (SRB; Sigma-Aldrich) was added. Plates were
incubated at room temperature for 30 min. Unbound SRB
was removed with 1% acetic acid. Bound SRB was solu-
bilized with 100 mm3 of 10 mM Tris-base solution.
Absorbance was determined in a plate reader (TECAN
Infinite) at 570 and 650 nm (background). Cell viability
NMR (CDCl3): d = 3.50 (4H, 2 CH2), 6.95–7.90 (m, 26H,
ArH) ppm; 13C NMR (CDCl3): d = 38.88 (2CH2), 103.20
(cyclobutane 2C), 124.66, 128.53, 128.63, 132.14, 132.23,
137.09, 145.80, 146.09, 148.02 (Ar C), 163.20 (2C=N) ppm.
N,N0-[2-(Anthracen-9(10H)-ylidene)-4-(triphenyl-
phosphoranylidene)cyclobutane-1,3-diylidene]dianiline
(22a, C48H35N2P)
A mixture of anthracen-9(10H)-one (18, 194 mg, 1 mmol)
and (N-phenyliminovinylidine)triphenylphosphorane (2a,
123

Chemistry of phosphorus ylides 32
973
8. Pedro M, Cerqueira F, Sousa ME, Nascimento MS, Pinto M
(2002) Bioorg Med Chem 10:3725
9. Valenti P, Bisi A, Rampa A, Belluti F, Gobbi S, Zampiron A,
Carrara M (2002) Bioorg Med Chem 8:239
was expressed as the percentage of cell survival relative to
untreated cells.
Data analysis
10. Yoshimi N, Matsunaga K, Katayama M, Yamada Y, Kuno T,
Qiao Z, Hara A, Yamahara J, Mori H (2001) Cancer Lett 163:163
11. Saraiva L, Fresco P, Pinto E, Sousa E, Pinto M, Goncalves J
(2002) Bioorg Med Chem 10:3219
.12. Saraiva L, Fresco P, Pinto E, Sousa E, Pinto M, Goncalves J
(2003) Bioorg Med Chem 11:1215
13. Nguemeving JR, Azebaze AGB, Kuete V, Carly NNE, Beng VP,
Meyer M, Bland A, Bodo B, Nkengfack AE (2006) Phyto-
chemistry 67:1341
14. Demirkiran O (2007) Top Heterocycl Chem 9:139
15. Wang Y, Shi JG, Wang MZ, Che CT, Yeung JH (2007) Life Sci
81:2016
16. Liu Y, Ma L, Chen WH, Wang B, Xu ZL (2007) Bioorg Med
Chem 15:2810
17. Soliman FM, Said MM, Maigali SS (2005) Heteroatom Chem
16:476
18. Maigali SS, Said MM, Abd El-Maksoud MA, Soliman FM (2008)
Monatsh Chem 139:495
19. Said MM, Maigali SS, Abd El-Maksoud MA, Soliman FM (2008)
Monatsh Chem 139:1299
The dose–response curve of compounds was analyzed
using the Emax model.
ꢀ
ꢁ
m
½Dꢃ
Cell viabilityð%Þ ¼ ð100 ꢁ RÞ ꢂ 1 ꢁ
þ R
m
Kdm þ ½Dꢃ
where R is the residual unaffected fraction (the resistance
fraction), [D] is the drug concentration used, Kd is the drug
concentration that produces a 50% reduction of the maxi-
mum inhibition rate and m is a Hill-type coefficient. IC50
was defined as the drug concentration required to reduce
fluorescence to 50% of that of the control (i.e., Kd = IC50
when R = 0 and Emax = 100 - R). Results are repre-
sented as mean standard error of the mean (SEM) of
three independent experiments. Data analysis was done
using SigmaPlot 11 software.
20. Soliman FM, Abd-Ellah I, Maigali SS, Abd-El-Naim G (2009) J
Chem Res 277
21. Bestmann HJ, Schmid G, Sandmeier D, Kisielowski L (1977)
Angew Chem 89:275
References
22. Matthews CN, Birum GH (1969) Acc Chem Res 2:373
23. Vedejs E, Snoble KA (1973) J Am Chem Soc 95:5778
24. Schlosser M, Piskala A, Tarchini C, Tuong HB (1975) Chimia
29:341
25. Bestmann HJ, Schmid G (1974) Angew Chem Int Ed 13:273
26. Johnson AW (1993) Ylides and imines of phosphorus. Wiley,
New York
1. Hay AE, Aumond MC, Mallet S, Dumontet V, Litaudon M,
Rondeau D, Richomme P (2004) J Nat Prod 67:707
2. Mondal M, Puranik VG, Argade NP (2006) J Org Chem 71:4992
3. Jung HA, Su BN, Keller WJ, Mehta RG, Kinghorn AD (2006) J
Agric Food Chem 54:2077
4. Lee BW, Lee JH, Lee ST, Lee HS, Lee WS, Jeong TS, Park KH
(2005) Bioorg Med Chem Lett 15:5548
5. Lin CN, Chung MI, Liou SJ, Lee TH, Wang TH (1996) J Pharm
Pharmacol 48:532
6. Dua VK, Ojha VP, Roy R, Joshi BC, Velacha N, Devi CU,
Bhatnagar MC, Sharma VP, Subbarao SJ (2004) Ethnopharma-
cology 95:274
7. Giri R, Goodell JR, Xing C, Benoit A, Kaur H, Hiasa H, Ferguson
DM (2010) Bioorg Med Chem 18:1456
27. Grim SO, McFarlane W, Marks T (1967) Chem Commun 1191
28. Surth YJ (2003) Nat Rev Cancer 3:750
29. Bestmann HJ (1977) Angew Chem Int Ed 16:349
30. Bestmann HJ, Schmid G (1975) Tetrahedron Lett 4025
31. Desai BM, Desai PR, Desai RD (1960) J Indian Chem Soc 37:53
32. Mustafa A, Hishmat OH (1975) J Am Chem Soc 79:2225
33. Bestmann HJ, Sandmeier D (1975) Angew Chem Int Ed 14:634
34. Scheinmann F, Suschitzky H (1959) Tetrahedron 7:31
123