Novel synthetic route to α-aminophosphonates containing benzothiazole moiety

Article abstract of DOI:10.1002/cjoc.201200831

A novel and ef?cient synthetic route to α-aminophosphonates containing benzothiazole moiety via a cascade three-component reaction from conveniently available starting materials has been developed. The target compounds 3a-3g, 7 and 8a, 8b were evaluated for their anticancer activities against the cancer cell line HL-60 in vitro by the MTT method. Compound 3g showed good cancer inhibitory activity against the tested cell line. Further study is necessary to find out the potential antitumor activities. A novel and ef?cient synthetic route to α-aminophosphonates containing benzothiazole moiety via a cascade three-component reaction from conveniently available starting materials has been developed. Copyright

Full text of DOI:10.1002/cjoc.201200831

FULL PAPER
DOI: 10.1002/cjoc.201200831
Novel Synthetic Route to α-Aminophosphonates Containing
Benzothiazole Moiety
Gu, Liju*,a(谷利军)
Wang, Ruia(王锐)
Huang, Xiangzhonga(黄相中)
Jin, Chengb(金诚)
a Key Laboratory of Chemistry in Ethnic Medicinal Resources, State Ethnic Affairs Commission & Ministry of
Education, Yunnan University of Nationalities, Kunming, Yunnan 650500, China
b Changzhou Tianma Group Limited Company, Changzhou, Jiangsu 213127, China
A novel and efficient synthetic route to α-aminophosphonates containing benzothiazole moiety via a cascade
three-component reaction from conveniently available starting materials has been developed. The target compounds
3a—3g, 7 and 8a, 8b were evaluated for their anticancer activities against the cancer cell line HL-60 in vitro by the
MTT method. Compound 3g showed good cancer inhibitory activity against the tested cell line. Further study is
necessary to find out the potential antitumor activities.
Keywords cascade three-component reaction, α-aminophosphonates, antitumor activity
Introduction
Experimental
In past decades, the synthesis of heterocycles has
continued to attract the interest of synthetic chemists.[1]
Among these heterocycles, benzothiazoles with a nitro-
gen substituent in the 2-position in natural products play
pharmacologically important roles because of the broad
spectrum of their biological activities.[2]
On the other hand, α-aminophosphonic acids and
their corresponding α-aminophosphonates have received
much interest in organic and medicinal chemistry be-
cause they are analogues to both natural and unnatural
amino acids.[3] Some of them have been used as potent
enzyme inhibitors, antimicrobial, antitumor and antiviral
agents.[4-6] Among these compounds, studies are mainly
concentrated on heterocycle moieties such as thiophene,
furan, benzothiazole. α-Aminophosphonates containing
benzothiazole moiety have been suggested as antitumor
agent.[7]
Synthesis
Materials and equipment Reagents were obtained
commercially and used as received. Solvents were puri-
fied and dried by standard methods. Primary 1-amino-
phosphonates were synthesized according the literature
methods.[10] The melting points were determined on an
XT-4 micro melting point apparatus and uncorrected. IR
spectra were recorded on an EQUINOX-55 spectrome-
ter on a KBr matrix. NMR spectra were recorded on an
INOVA-400 NMR instrument at room temperature us-
ing TMS as internal standard. Coupling constants (J)
were measured in Hz. Elemental analyses were per-
formed on a Vario EL III CHNS analyzer. Electrospray
mass spectra were obtained with an MALDI-TOF mass
spectrometer. 200—300 mesh silica gel was used for
column chromatography.
Typical procedure for the synthesis of target com-
pounds A reaction mixture of 1-bromo-2-nitrobenzene
4 (1 mmol), CS2 (1.5 mmol), primary 1-aminophospho-
nate 5 (1.4 mmol), K2CO3 (3 mmol), CuCl2•2H2O (1
mmol) and SnCl2•2H2O (4 mmol) in DMF (3.5 mL) was
stirred at 110 ℃ for 7 h. The reaction mixture was par-
titioned between ethyl acetate and water. The organic
layer was washed with water and brine, and dried over
anhydrous MgSO4 and concentrated under vacuum to
yield the crude product. The crude product was purified
by flash chromatography (ethyl acetate ∶petroleum
ether, 1∶2, volum ratio).
In view of this research and our desire to develop
new anticancer agents of high potency, we fused bio-
logical benzothiazole and aminophosphonate structures
to obtain compounds possessing better biological activi-
ties. Among numerous synthetic methodologies of
α-aminophosphonate, the most noteworthy and remark-
able one is Kabachnik-Fields reaction, generally using
amines, dialkyl phosphites and carbonyl compounds as
the reactants.[8] In connection with our ongoing project
on the Cu-catalyzed reaction,[9] we herein describe a
new strategy to construct α-aminophosphonates con-
taining benzothiazole moiety.
*
E-mail: gulijun2005@126.com
Received August 18, 2012; accepted September 21, 2012.
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/cjoc.201200831 or from the author.
Chin. J. Chem. 2012, 30, 2483—2487 © 2012 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
2483

Gu et al.
FULL PAPER
O,O'-Diethyl-α-(benzothiazole-2-yl) amino-
(phenylmethyl) phosphonate (3a) White powder,
6.25, N 10.02, S 7.64; found C 57.31, H 6.19, N 10.11,
S 7.66.
1
yield 84%, m.p. 112—114 ℃ (lit.[11] m.p. 112 ℃); H
O,O'-Diethyl-α-(benzothiazole-2-yl) amino-(4-
methoxyphenylmethyl) phosphonate (3e) Pale yel-
NMR (CDCl3, 400 MHz) δ: 7.54 (dd, J＝7.2, 7.2 Hz,
1
4H), 7.06—7.39 (m, 5H), 5.54 (d, JH P＝22.4 Hz, 1H),
low solid, yield 84%, m.p. 175—177 ℃; H NMR
—
4.84 (bs, 1H), 3.98—4.22 (m, 4H), 1.30 (t, J＝7.2 Hz,
3H), 1.15 (t, J＝7.2 Hz, 3H); 13C NMR (CDCl3, 75
MHz) δ: 151.9, 135.0, 131.0, 128.5, 128.2, 128.1, 125.8,
(CDCl3, 400 MHz) δ: 7.08—7.56 (m, 6H), 6.88 (d, J＝
8.4 Hz, 2H), 5.49 (d, JH P＝22.0 Hz, 1H), 4.81 (bs, 1H),
—
3.74—4.24 (m, 7H), 1.32 (t, J＝7.2 Hz, 3H), 1.22 (t,
J＝7.2 Hz, 3H); 13C NMR (CDCl3, 75 MHz) δ: 165.9 (d,
J＝9.3 Hz), 152.0, 131.1, 129.4, 127.0, 125.7, 121.8,
121.8, 120.7, 119.3, 63.6 (d, JC P＝10.7 Hz), 56.7, 55.1,
—
16.4, 16.2; 31P NMR (CDCl3, 200 MHz) δ: 22.7; IR
－
1
(KBr) v: 3210, 2907, 1256 and 1031 cm ; MALDI-
TOF MS m/z: 399 [M ＋Na] ＋ . Anal. calcd for
C18H21N2O3PS: C 57.44, H 5.62, N 7.44, S 8.52; found
C 57.56, H 5.69, N 7.41, S 8.49.
120.6, 119.3, 114.0, 63.4 (d, JC P＝5.3 Hz), 56.0, 55.2,
—
54.5, 16.4 (d, JC P＝4.2 Hz), 16.2 (d, JC P＝4.2 Hz); 31P
—
—
NMR (CDCl3, 200 MHz) δ: 20.6; IR (KBr) v: 3228,
－
1
3011, 2989, 1232, 1025 cm ; MALDI-TOF MS m/z:
429 [M＋Na]＋. Anal. calcd for C19H23N2O4PS: C 56.15,
H 5.70, N 6.89, S 7.89; found C 56.20, H 5.66, N 6.71,
S 7.81.
O,O'-Diethyl-α-(benzothiazole-2-yl) amino-(4-
fluoro-phenylmethyl) phosphonate (3b)
White
powder, yield 83%, m.p. 167—169 ℃; 1H NMR
(CDCl3, 400 MHz) δ: 7.06—7.61 (m, 8 H), 5.57 (d, JH
O,O'-Dimethyl-α-(benzothiazole-2-yl) amino-(4-
methoxyphenylmethyl) phosphonate (3f) Brownish
yellow solid, yield 81%, m.p. 169—171 ℃ (lit.[12] m.p.
170 ℃); 1H NMR (CDCl3, 400 MHz) δ: 7.04—7.54 (m,
—
P
＝22.0 Hz, 1H), 4.81 (bs, 1H), 3.81—4.24 (m, 4H), 1.32
(t, J＝7.0 Hz, 3H), 1.15 (t, J＝7.0 Hz, 3H); 13C NMR
(CDCl3, 75 MHz) δ: 165.3 (d, J＝9.3 Hz), 150.9, 131.0,
129.9 (t, JC F＝6.0 Hz), 129.8, 125.8, 122.0, 120.7,
6H), 6.89 (d, J＝8.8 Hz, 2H), 5.56 (d, JH P＝21.6 Hz,
—
—
119.4, 115.6, 115.4, 63.5 (d, JC P＝4.8 Hz), 55.8, 54.3,
1H), 4.50 (bs, 1H), 3.82 (d, J＝10.8 Hz, 3H), 3.76 (s,
3H), 3.54 (d, J＝10.8 Hz, 3H); 13C NMR (CDCl3, 75
MHz) δ: 165.7 (d, J＝9.1 Hz), 151.9, 131.1, 129.4,
129.3, 126.7, 125.7, 121.8, 120.7, 119.3, 114.1, 55.5,
55.2, 54.0 (d, JC P＝5.3 Hz), 53.9 (d, JC P＝2.7 Hz); 31P
—
16.4 (d, JC P＝4.2 Hz), 16.2 (d, JC P＝4.2 Hz); 31P
—
—
NMR (CDCl3, 200 MHz) δ: 21.3; IR (KBr) v: 3216,
－
1
2903, 2828, 1233, 1021 cm ; MALDI-TOF MS m/z:
417 [M＋Na]＋. Anal. calcd for C18H20FN2O3PS: C
54.82, H 5.11, N 7.10, S 8.13; found C 54.91, H 5.20, N
7.11, S 8.09.
—
—
NMR (CDCl3, 200 MHz) δ: 21.3; IR (KBr) v: 3221,
－
1
3031, 2941, 1239, 1018 cm ; MALDI-TOF MS m/z:
401 [M＋Na]＋. Anal. calcd for C17H19N2O4PS: C 53.96,
H 5.06, N 7.40, S 8.47; found C 54.01, H 5.17, N 7.47,
S 8.56.
O,O'-Diethyl-α-(benzothiazole-2-yl) amino-(4-
chlorophenylmethyl) phosphonate (3c) Pale yellow
solid, yield 85%, m.p. 194—195 ℃ (lit.[11] m.p. 195
℃); 1H NMR (CDCl3, 400 MHz) δ: 7.07—7.56 (m, 8 H),
O,O'-Diethyl-α-(benzothiazole-2-yl) amino-(4-
nitrophenylmethyl) phosphonate (3g) Yellow solid,
5.59 (d, JH P＝22.8 Hz, 1 H), 4.81 (bs, 1H), 3.85—4.25
—
1
(m, 4H), 1.29 (t, J＝7.2 Hz, 3H), 1.20 (t, J＝7.2 Hz, 3H);
13C NMR (CDCl3, 75 MHz) δ: 165.6 (d, J＝9.1 Hz),
151.8, 134.1, 133.8, 131.0, 129.5, 128.7, 125.8, 122.0,
yield 86%, m.p. 162—164 ℃; H NMR (CDCl3, 400
MHz) δ: 8.49 (d, J＝2.0 Hz, 1H), 8.15 (d, J＝7.6 Hz,
1H), 7.96 (d, J＝7.2 Hz, 1H), 7.10—7.56 (m, 5H), 5.83
120.7, 119.4, 63.7 (d, JC P＝3.6 Hz), 55.9, 54.3, 16.4 (d,
(d, JH P＝22.8 Hz, 1H), 4.69 (bs, 1H), 3.96—4.34 (m,
—
JC P＝4.2 Hz), 16.2 (d, JC P＝4.2 Hz); 31P NMR
—
4H), 1.36 (t, J＝7.2 Hz, 3H), 1.26 (t, J＝7.2 Hz, 3H);
13C NMR (CDCl3, 75 MHz) δ: 165.2 (d, J＝9.1 Hz),
151.7, 137.9, 134.2, 134.1, 131.1, 129.4, 125.8, 123.1,
—
—
(CDCl3, 200 MHz) δ: 19.7; IR (KBr) v: 3239, 3021,
－
1
2831, 1225, 1024 cm ; MALDI-TOF MS m/z: 433 [M
＋Na]＋. Anal. calcd for C18H20ClN2O3PS: C 52.62, H
4.91, N 6.82, S 7.80; found C 52.71, H 4.83, N 6.88, S
7.86.
123.0, 122.1, 120.7, 119.5, 64.0 (d, JC P＝10.4 Hz),
—
55.7, 54.1, 16.5 (d, JC P＝4.2 Hz), 16.2 (d, JC P＝4.2
—
—
Hz); 31P NMR (CDCl3, 200 MHz) δ: 19.6; IR (KBr) v:
3229, 3011, 2972, 1502, 1334, 1225, 1022 cm－
;
1
O,O'-Diethyl-α-(benzothiazole-2-yl) amino-(4-
dimethylaminophenylmethyl) phosphonate (3d)
MALDI-TOF MS m/z: 444 [M＋Na]＋. Anal. calcd for
C18H20N3O5PS: C 51.30, H 4.78, N 9.97, S 7.61; found
C 51.39, H 4.85, N 9.90, S 7.72.
1
White solid, yield 85%, m.p. 181—182 ℃; H NMR
(CDCl3, 400 MHz) δ: 7.07—7.56 (m, 7 H), 6.70 (d, J＝
8.8 Hz, 1H), 5.23 (d, JH P＝22.0 Hz, 1H), 4.48 (bs, 1H),
O,O'-Diethyl-α-(benzothiazole-2-yl) amino-(ferro-
cenylmethyl) phosphonate (7) Yellow solid, yield
76%, m.p. 153—155 ℃; 1H NMR (CDCl3, 400 MHz) δ:
—
3.75—4.20 (m, 4H), 2.95 (d, J＝19.6 Hz, 6H), 1.28 (t,
J＝7.2 Hz, 3H), 1.15 (t, J＝7.2 Hz, 3H); 13C NMR
(CDCl3, 75 MHz) δ: 166.2 (d, J＝9.9 Hz), 152.0, 131.3,
131.0, 129.0, 128.9, 125.7, 121.7, 120.7, 119.3, 112.3,
7.11—7.64 (m, 5H), 5.44 (d, JH P＝19.2 Hz, 1H), 4.68
—
(bs, 1H), 3.92—4.42 (m, 13H), 1.24 (t, J＝4.4 Hz, 3H),
1.20 (t, J＝4.4 Hz, 3H); 13C NMR (CDCl3, 75 MHz) δ:
165.7 (d, J＝4.2 Hz), 152.1, 130.9, 125.9, 121.8, 120.8,
63.3 (d, JC P＝5.4 Hz), 56.5, 54.9, 40.5, 40.4, 16.4 (d,
—
JC P＝4.2 Hz), 16.3 (d, JC P＝4.2 Hz); 31P NMR
—
—
(CDCl3, 200 MHz) δ: 21.3; IR (KBr) v: 3223, 3029,
119.2, 84.0, 83.9, 68.9, 68.2, 67.9, 66.2, 63.3 (d, JC ＝
—
P
－
1
2891, 1236, 1018 cm ; MALDI-TOF MS m/z: 442
5.2 Hz), 52.3, 50.8, 16.4, 16.3; 31P NMR (CDCl3, 200
[M＋Na]＋. Anal. calcd for C20H26N3O3PS: C 57.27, H
MHz) δ: 21.1; IR (KBr) v: 3233, 3089, 2931, 1443,
2484
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© 2012 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Chin. J. Chem. 2012, 30, 2483—2487

Novel Synthetic Route to α-Aminophosphonates Containing Benzothiazole Moiety
－
1
1272, 1220, 1039, 751 cm ; MALDI-TOF MS m/z: 507
[M＋Na]＋. Anal. calcd for C22H25FeN2O3PS: C 54.56,
H 5.20, N 5.78, S 6.62; found C 54.67, H 5.23, N 5.80,
S 6.69.
1% penicillin-streptomycin solution (10000 units of
penicillin and 10 mg of streptomycin in 1 mL 0.9%
NaCl). The cancer cell line was cultured in minimum
essential medium (MEM). Four-thousand cells (per well)
suspended in MEM, were plated onto each well of a
96-well plate and incubated for 24 h. The tested com-
pounds at the indicated final concentrations were added
to the culture medium and the cell cultures were contin-
ued for 72 h. Fresh MTT was added to each well at the
terminal concentration of 5 μg/mL and incubated with
cells at 37 ℃ for 4 h. The formazan crystals were dis-
solved in 100 μL DMSO each well, and the absorbency
at 492 nm (for absorbance of MTT formazan) and 630
nm (for the reference wavelength) was measured using
the ELISA reader. All of the compounds were tested in
triplicate in the cell line. The results expressed as IC50
(inhibitory concentration 50%) were the averages of
three measurements and calculated by using the Bacus
Laboratories Incorporated Slide Scanner (Bliss) soft-
ware.
O,O'-Diethyl-α-(5-methylbenzothiazole-2-yl) ami-
no-(phenylmethyl) phosphorrnate (8a) White pow-
1
der, yield 85%, m.p. 133—134 ℃; H NMR (CDCl3,
400 MHz) δ: 7.18—7.89 (m, 8H), 5.58 (d, JH P＝22.4
—
Hz, 1H), 4.54 (bs, 1H), 3.76—4.24 (m, 4H), 2.22 (s, 3H),
1.32 (t, J＝6.0 Hz, 3H), 1.15 (t, J＝6.0 Hz, 3H); 13C
NMR (CDCl3, 75 MHz) δ: 164.2 (d, J＝8.9 Hz), 150.7,
136.9, 133.2, 133.1, 131.2, 129.3, 125.8, 123.0, 122.1,
120.1, 118.5, 63.8 (d, JC P＝22.5 Hz), 55.7, 54.2, 22.4,
—
16.4 (d, JC P＝4.2 Hz), 16.2 (d, JC P＝4.2 Hz); 31P
—
—
NMR (CDCl3, 200 MHz) δ: 19.9; IR (KBr) v: 3194,
－
1
3030, 2903, 1233, 1027 cm ; MALDI-TOF MS m/z:
413 [M＋Na]＋. Anal. calcd for C19H23N2O3PS: C 58.45,
H 5.94, N 7.17, S 8.21; found C 58.51, H 5.88, N 7.23,
S 8.29.
O,O'-Diethyl-α-(5-methoxybenzothiazole-2-yl)
amino-(phenylmethyl) phosphonate (8b) Pale yel-
1
low solid, yield 81%, m.p. 142—144 ℃; H NMR
Results and Discussion
(CDCl3, 400 MHz) δ: 7.08—7.55 (m, 7 H), 6.78 (d, J＝
Ma and his group have developed a copper-catalyzed
three-component synthesis of 2-N-substituted benzothia-
zoles in 2011.[2] According to the structure of O,O'-di-
9.2 Hz, 1H), 5.53 (d, JH P＝22.0 Hz, 1H), 4.53 (bs, 1H),
—
3.79—4.28 (m, 7H), 1.30 (t, J＝7.2 Hz, 3H), 1.19 (t,
J＝7.2 Hz, 3H); 13C NMR (CDCl3, 75 MHz) δ: 165.4 (d,
J＝9.1 Hz), 151.2, 134.2, 131.4, 128.0, 126.7, 122.8,
ethyl-α-(benzothiazole-2-yl)
amino-(phenylmethyl)
phosphonate, we envisioned that 2-bromoaniline 1 may
be used to react with primary 1-aminophosphonate 2
under the catalysis of CuCl2•2H2O in presence of carbon
disulfide, K2CO3 and N,N-dimethylformamide (DMF) to
synthesize such products. Performing the reaction using
the conditions similar to those reported by Ma and co-
workers, the desired product was obtained in 84% yield
(Scheme 1).
121.2, 118.4, 116.3, 64.1 (d, JC P＝5.1 Hz), 55.1, 54.2,
—
53.7, 16.5, 16.3; 31P NMR (CDCl3, 200 MHz) δ: 20.2;
IR (KBr) v: 3239, 3023, 2991, 1241, 1015 cm－
;
1
MALDI-TOF MS m/z: 429 [M＋Na]＋. Anal. calcd for
C19H23N2O4PS: C 56.15, H 5.70, N 6.89, S 7.89; found
C 56.08, H 5.75, N 6.80, S 7.92.
O,O'-Diethyl-α-(5-chlorobenzothiazole-2-yl) ami-
no-(phenylmethyl) phosphonate (8c) Pale yellow
1
solid, yield 80%, m.p. 117—119 ℃; H NMR (CDCl3,
Scheme 1 Synthesis of α-aminophosphonate derivative 3a
400 MHz) δ: 7.61 (d, J＝6.0 Hz, 1H), 7.26—7.44 (m,
Ph
6H), 7.10 (t, J＝7.6 Hz, 1H), 5.64 (d, JH P＝22.4 Hz,
—
NH2
Br
catalysis
OEt
1H), 4.72 (bs, 1H), 3.86—4.23 (m, 4H), 1.32 (t, J＝7.2
Hz, 3H), 1.11 (t, J＝7.2 Hz, 3H); 13C NMR (CDCl3, 75
MHz) δ: 163.8 (d, J＝9.1 Hz), 149.1, 135.0, 132.4,
+
CS2
H2N
P
+
DMF, K2CO3
OEt
O
1
2
131.3, 128.5, 128.1, 121.2, 120.7, 119.7, 62.7 (d, JC
＝
—
P
10.4 Hz), 55.1, 54.2, 16.5 (d, JC P＝4.1 Hz), 16.3 (d,
—
—
JC P＝4.1 Hz); 31P NMR (CDCl3, 200 MHz) δ: 22.8; IR
N
S
Ph
OEt
N
P
－
1
OEt
H
(KBr) v: 3293, 3017, 2911, 1226, 1021 cm ; MALDI-
TOF MS m/z: 433 [M ＋Na] ＋ . Anal. calcd for
C18H20ClN2O3PS: C 52.62, H 4.91, N 6.82, S 7.80;
found C 52.71, H 4.85, N 6.92, S 7.88.
O
3a
Encouraged by the result, we replaced 2-bromo-
aniline 1 with 1-bromo-2-nitrobenzene 4 and carried out
the reaction using the following reaction conditions:
1-bromo-2-nitrobenzene (1 equiv.), CS2 (1.5 equiv.),
primary 1-aminophosphonate (1.4 equiv.), K2CO3 (4
equiv.), CuCl2•2H2O (1 equiv.) and SnCl2•2H2O (3
equiv.) in DMF. To our delight, the desired product was
isolated in 76% yield after reacting for 7 h at 110 ℃.
Then, we briefly examined the effect of different tem-
peratures and ratio of 4/SnCl2•2H2O. The results showed
that at 110 ℃, the reaction preceded smoothly in high
Antitumor activities assay in vitro
The antitumor activities of the target compounds
(3a—3g, 7 and 8a, 8b) were evaluated with HL-60
(human acute promyelocytic leukemia). HL-60 was ob-
tained from the American Type Culture Collection (Ma-
nassas, VA). Cells were cultured in RPMI 1640 and
maintained in a Thermo incubator (Waltham, MA) with
a humidified air containing 5% CO2, 95% air. All cul-
ture media contained 10% fetal bovine serum (FBS) and
Chin. J. Chem. 2012, 30, 2483—2487
© 2012 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.cjc.wiley-vch.de
2485

Gu et al.
Scheme 2 Synthesis of α-aminophosphonate derivative 7
FULL PAPER
yield. To further evaluate the influence of the ratio of
4/SnCl2•2H2O, the reaction was carried out in DMF at
110 ℃ using a 1∶1 to 1∶5 ratio of 4/SnCl2•2H2O,
leading to 3a in 29%, 43%, 74%, 84%, and 79% yields,
respectively. We concluded the best ratio of 4/SnCl2•
2H2O was 1∶4.
Fc
NO2
Br
OEt
catalysis
+
CS2
H2N
P
+
DMF, K2CO3
OEt
O
6
4
With optimized conditions in hand, a series of sub-
stituted primary 1-aminophosphonates 5 were investi-
gated, as shown in Table 1. Both electron-donating and
-withdrawing primary 1-aminophosphonates could be
successfully converted to the corresponding α-amino-
phosphonates in high yields. In addition, a high level of
functional group tolerance was observed, and the effi-
ciency of the reaction was not affected in the presence
of halides, ether, and nitro group.
N
Fc
OEt
S
N
P
OEt
H
O
7
Scheme 3 Synthesis of α-aminophosphonate derivatives 8
Ph
R1
NO2
Br
catalysis
OEt
+
CS2
H2N
Ph
P
+
DMF, K2CO3
OEt
Table 1 Substrate scope of primary 1-aminophosphonates 5
O
Ar
OR
NO2
Br
R1
catalysis
N
H2N
P
+
CS2
+
OEt
OR
DMF, K2CO3
O
S
N
P
OEt
H
4
5
O
8a: R1 = Me, 8b: R1 = OMe,
8c: R1 = Cl
N
S
Ar
OR
N
P
OR
H
O
3
sphonate 2 with carbon disulfide in the presence of
K2CO3. Next, the reaction of dithiocarbamate salts A
with 2-bromoaniline 1 afforded dithiocarbamates B. The
amine group of B could attack the C-S double bond to
generate intermediate C, which would deliver the de-
sired products 3 via elimination of hydrogen sulfide
with the aid of CuCl2•2H2O.
Entry Ar
R
Product
3a
Yielda/%
1
2
3
4
5
6
7b
Ph
Et
Et
Et
Et
Et
Me
Et
84
83
85
85
84
81
86
p-F-Ph
3b
p-Cl-Ph
3c
p-N(Me)2-Ph
p-MeO-Ph
p-MeO-Ph
m-NO2-Ph
3d
3e
Scheme 4 Proposed reaction mechanism
3f
tin (II)
1
4
3g
OR
RO
O
OR
a Isolated yields. b Reaction conditions: 2-bromoaniline (1 equiv.),
CS2 (1.5 equiv.), primary 1-aminophosphonate (1.4 equiv.),
K2CO3 (4 equiv.), CuCl2•2H2O (1 equiv.) in DMF.
RO
O
CS2
P
NH
SK
P
NH2
K2CO3
Ar
S
Ar
A
5
Cu (II)
OR
H
NH2
S
To highlight the utility of this transformation, pri-
mary 1-aminophosphonate 6 containing ferrocenyl
group is subjected to the standard reaction conditions
under a nitrogen atmosphere (Scheme 2). The desired
product was isolated in good yield (76%). In the case,
the purification of the final product has been achieved
by column chromatography on cellulose powder.
To further explore the potential of our methodology,
4-substituted 1-bromo-2-nitrobenzenes 9 were investi-
gated as shown in Scheme 3. The substrates 9 also pro-
vided the expected α-aminophosphonates 8a—8c in
high yields under the standard reaction condition
(Scheme 3).
Ar
N
SH
S
Ar
OR
N
P
O
S
N
P
H
OR
H
OR
O
C
B
-H2S
3
The structure of α-aminophosphonate derivatives 3a
—3g, 7 and 8a—8c was thoroughly characterized with
spectral and elemental analysis. The infrared spectrum
of compound 7 displayed bands at 3233, 1220 and 1039
cm－1 due to N—H, P＝O, and P—O stretching frequen-
cies, respectively. The characteristic bands of the ferro-
cenyl group in the infrared spectrum of the compound
－
1 [13]
A possible mechanism for the formation of the target
compounds was proposed and shown in Scheme 4.
1-Bromo-2-nitrobenzene 4 was reduced by tin(II) chlo-
ride to 2-bromoaniline 1, and the dithiocarbamate salt A
was generated via the reaction of primary 1-aminopho-
appear at 3089, 1443 and 751 cm .
1
The H NMR spectrum of compound 7 exhibited a
multiplet at δ 7.11—7.64, which accounts for the aro-
matic protons of the benzothiazole ring; a doublet ap-
peared at δ 5.44, which accounts for CH proton; a mul-
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© 2012 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Chin. J. Chem. 2012, 30, 2483—2487

Novel Synthetic Route to α-Aminophosphonates Containing Benzothiazole Moiety
tiplet appeared at δ 3.92—4.42, which accounts for the
CH2 and ferrocenyl protons. The two ethoxys of the
phosphonates are magnetically nonequivalent, which is
caused by the different shielding effects of α-ferrocenyl
on the two ethoxy groups. The mass spectrum displayed
the molecular ion [M＋Na]＋ peak at m/z 507. All of the
nonequivalent carbon atoms were identified in 13C NMR
and the total number of protons calculated from the in-
tegration curve accorded (in 1H NMR) with the assigned
structures.
Table 2 The antitumor activities of the target compounds
－
IC50/(μmol•L )
1
Entry
1
Compound
3a
＞100
2
3b
3c
3d
3e
3f
22.4±2.0
35.7±2.5
＞100
＞100
＞100
3
4
5
6
7
8
9
10
3g
7
8a
8b
8.2±0.3
13.1±1.1
＞100
Biological activities
＞100
The antitumor activities were determined by the
standard MTT assay against the cancer cell line
HL-60.[14] The screening results expressed as IC50 are
summarized in Table 2. The IC50 values were the aver-
age of three independent experiments. The antitumor
screening results revealed that some target compounds
exhibited moderate to good antitumor activity against
HL-60. Compound 3b bearing a fluorine atom at
4-position of phenyl ring showed moderate cancer in-
hibitory activities against HL-60 with IC50 of 22.4
μmol/L, removal of the fluorine atom of 3b to give 3a
resulted in loss of potency, and replacement of the fluo-
rine with chlorine atom in the 4-position of phenyl ring
rendered lower activity (3b vs. 3c, Table 2). Compounds
3d and 3e, which have 4-dimethylamino and 4-methoxyl
substituted phenyl rings, respectively, were inactive
against HL-60. The antitumor activity of 3f to HL-60
that was substituted by Me of phosphonate was inactive.
Compound 7 bearing a ferrocenyl moiety showed mod-
erate cancer inhibitory activity against HL-60 with IC50
of 13.1 μmol/L. Interestingly, compound 3g bearing a
nitro group at 3-position of phenyl ring showed good
cancer inhibitory activity against the tested cell line.
From the above results, some interesting struc-
ture-activity relationships can be disclosed: the substitu-
tion of electron-donating groups at 4-position of phenyl
ring is not important for potent activity, and incorpora-
tion of an electrowithdrawing group in the phenyl ring
leads to significant improvement of potency.
fication and steric parameters on structure activity rela-
tionships for identifying lead bioactive compound would
be taken up in our future course of investigation.
Acknowledgement
We are grateful for the financial support from the
State Ethnic Affairs Commission; Opening Fund of Key
Laboratory of Ethnic Medicine Resource Chemistry (No.
MZY 1117).
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Chin. J. Chem. 2012, 30, 2483—2487
© 2012 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.cjc.wiley-vch.de
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