Synthesis of novel coumarin-7,8-cyclophosphoramide analogs

Article abstract of DOI:10.1080/00397910903219369

Coumarin-7,8-cyclophosphoramide derivatives were conveniently prepared by a facile method. 7-Hydroxycoumarin was aminomethylated regioselectively at the 8-C position using the Mannich reaction. The newly formed 8-(N-alkylaminomethyl) coumarins were then coupled with bis-chloroethyl dichlorophosphamide to form coumarin-7,8-cyclophosphoramide analogs. An efficient, highly regioselective method to synthesize coumarin-7,8-cyclophosphoramide derivatives is provided, and the approach has the merits of mild reaction conditions. Copyright

Full text of DOI:10.1080/00397910903219369

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Synthesis of Novel Coumarin-7,8-
cyclophosphoramide Analogs
Xiaolan Chen a , Yadong Zhou a , Lingbo Qu a b , Xiangqian Liu a ,
Jinwei Yuan b & Yufen Zhao a c
a Department of Chemistry , Zhengzhou University , Zhengzhou,
China
b Henan University of Technology , Zhengzhou, China
c Key Laboratory for Bioorganic Phosphorus Chemistry, Department
of Chemistry , School of Life Sciences and Engineering, Tsinghua
University , Beijing, China
Published online: 08 Jun 2010.
To cite this article: Xiaolan Chen , Yadong Zhou , Lingbo Qu , Xiangqian Liu , Jinwei Yuan &
Yufen Zhao (2010) Synthesis of Novel Coumarin-7,8-cyclophosphoramide Analogs, Synthetic
Communications: An International Journal for Rapid Communication of Synthetic Organic Chemistry,
40:13, 1992-1997, DOI: 10.1080/00397910903219369
To link to this article: http://dx.doi.org/10.1080/00397910903219369
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Synthetic Communications1, 40: 1992–1997, 2010
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397910903219369
SYNTHESIS OF NOVEL COUMARIN-
7,8-CYCLOPHOSPHORAMIDE ANALOGS
Xiaolan Chen,1 Yadong Zhou,1 Lingbo Qu,1,2 Xiangqian Liu,1
Jinwei Yuan,2 and Yufen Zhao1,3
1Department of Chemistry, Zhengzhou University, Zhengzhou, China
2Henan University of Technology, Zhengzhou, China
3Key Laboratory for Bioorganic Phosphorus Chemistry, Department of
Chemistry, School of Life Sciences and Engineering, Tsinghua University,
Beijing, China
Coumarin-7,8-cyclophosphoramide derivatives were conveniently prepared by a facile
method. 7-Hydroxycoumarin was aminomethylated regioselectively at the 8-C position
using the Mannich reaction. The newly formed 8-(N-alkylaminomethyl) coumarins were
then coupled with bis-b-chloroethyl dichlorophosphamide to form coumarin-7,8-
cyclophosphoramide analogs. An efficient, highly regioselective method to synthesize
coumarin-7,8-cyclophosphoramide derivatives is provided, and the approach has the merits
of mild reaction conditions.
Keywords: Coumarin-7,8-cyclophosphoramide; cyclophosphoramide; 7-hydroxycoumarin; Mannich
reaction
INTRODUCTION
Coumarin (1,2-benzopyrone) is a widely distributed natural product with low
human toxicity.[1] Coumarin and its derivatives exhibit different biological and
pharmacological activities including anticoagulant, estrogenic, dermal photosensitiz-
ing, vasodilator, molluscacidal, anthelmintic, sedative, hypnotic, analgesic,
hypothermic,[2] antimicrobial,[3] anti-inflammatory,[4] antifungal,[5] and antiulcer[6]
activities. In vitro, coumarin and its derivatives inhibit the proliferation of several
human tumor cell lines; namely, coumarin retards the development of renal[7] and
prostate carcinoma[8,9] and prevents the recurrence of melanoma.[10] Coumarin
may be a prodrug, and its major biotransformed product is 7-hydroxycoumarin
(Fig. 1a).[11] 7-Hydroxycoumarin also exhibits cytotoxic effects against the lung
adenocarcinoma cell lines KB,[9] A549,[12] SK-LU-1,1.3.15, 3A5A, and A-427.[13]
Cyclophosphamide (Fig. 1b), one of the most successful anticancer agents
developed over the past few decades,[14] was used to treat various types of cancer
Received September 11, 2008.
Address correspondence to Xiaolan Chen, Department of Chemistry, Zhengzhou University,
Zhengzhou 450052, China. E-mail: chenxl@zzu.edu.cn
1992

COUMARIN-7,8-CYCLOPHOSPHORAMIDE ANALOGS
1993
Figure 1. (a) Structure of 7-hydroxycoumarin and (b) structure of cyclophosphamide.
Scheme 1. Synthesis of title coumarin–cyclophosphamide analogs. Reagents and reaction conditions: (a)
HCHO (1 equiv.), RNH2 (1 equiv.), reflux 8–12 h; (b) bis-b-chloroethyl dichlorophosphamide (1 equiv.),
Et3N (2 equiv.), reflux 3–4 h.
and some autoimmune disorders as a prodrug. Given the biological importance of
coumarin and cyclophosphamide, two pharmic groups were coupled to form new
cyclophosphoramide analogs of coumarin, which would be favorable in achieving
some specificity of pharmacological action in view of the development of effective
clinical anticancer drugs.
The Mannich reaction is an important organic reaction, with important appli-
cations in the design and synthesis of medicine. The Mannich reaction is one method
for chemical modification that introduces a basic function into a molecule. It devel-
ops a new field for the modification of natural products, which attracts increasing
numbers of researchers. To search for new compounds with higher antitumor activi-
ties and lower toxicity, in this article a convenient procedure is introduced to synthe-
size new cyclophosphamide analogs of coumarin via the Mannich reaction and
cyclized reaction (Scheme 1). The structures of these compounds were confirmed
by electrospray ionization–mass spectrometry (ESI-MS), high-resolution mass spec-
trometry (HR-MS), NMR (including two-dimensional NMR), and infrared (IR).
RESULTS AND DISCUSSION
In the present study, five Mannich bases were successfully synthesized starting
from 7-hydroxycoumarin (1) with formaldehyde and suitable amine in tetrahydro-
furan (THF). It is generally known that the reaction pathway of the Mannich reaction
depends on the nucleophilicity of substrate. The Mannich reaction, under present
experimental conditions, was found to proceed regioselectively, favoring attack at
8-C of 7-hydroxycoumarin. Considering the Mannich reaction begins from electro-
philic attack, we calculated the comparison of density of charges of 8-C and 6-C. It
is well known that the region with heavy density of charges is prone to electrophilic

1994
X. CHEN ET AL.
Table 1. Series of coumarin-7,8-analogs (3)
Entry
R
Yield (%)
3a
3b
3c
3d
CH2CH2CH3
CH(CH3)2
89
88
90
87
CH2CH2CH2CH3
C(CH3)3
3e
85
reaction. The calculated result shows that the net charge of 8-C is more than that of
6-C. Therefore, 8-C is supposed to be the main reaction site. This conclusion was also
confirmed by two-dimensional NMR of compound 3d. For example, the heteronuc-
lear multiple bond correlation (HMBC) spectrum of compound 3d showed that 7-C at
d 153.8, 8-C at d 115.3, and 9-C at d 149.9 are related, through three bonds, to 14-H at
d 4.36–4.29 and 4.68–4.60. If the Mannich reaction occurred at 6-C, there would be
any correlation among 8-C, 9-C, and 14-H. HMBC spectrum also showed that 7-C
at d 153.8 is related, through two bonds, to 5-H at d 7.44 and 6-H at 7.02; 9-C at d
149.9 showed no correlation to 6-H. The resulting 8-(N-alkylaminomethyl)coumarins
(2) were then coupled with bis-b-chloroethyl dichlorophosphamide to form a series of
coumarin-7,8-cyclophosphoramide analogs (3) (Table 1).
In conclusion, a convenient procedure for preparation of novel coumarin-7,8-
cyclophosphoramide analogs were reported using commercially available materials.
These compounds were synthesized by two steps: Mannich reaction and cyclized
reaction. Mannich reaction, under the present experimental conditions, was found
to proceed regioselectively, favoring attack at 8-C of 7-hydroxycoumarin. The syn-
thetic procedure of coumarin-7,8-cyclophosphoramide analogs might be valuable for
development of new cyclophosphamide coumarin prodrugs.
EXPERIMENTAL
All starting materials were obtained from commercial sources and used with-
out further purification. Melting points were recorded on a microscopical determina-
tor XT4 (the thermometer was not adjusted). IR spectra were recorded on a
1
Shimadazuir-408 spectrophotomer. H NMR, 13C NMR, and 31P NMR spectra
were obtained on a Bruker Avance DPX-400 spectrophotomer; chemical shifts were
expressed in parts per million with positive values downfield from internal tetra-
methylsilane (TMS) and external 85% H3PO4 (31P). Coupling constants were
expressed in Hertz. ESI-MS was recorded on a Bruker Esquire-3000 instrument.
7-Hydroxycoumarin (1) (5 mmol) was dissolved in THF (20 ml), and the appro-
priate amine (5 mmol) and 37% formaldehyde (5 mmol) were added. The resulting
mixture was refluxed for 8–12 h, and the reaction was monitored by thin-layer chro-
matography (TLC). After cooling at À5 to 10 ꢀC, it was left overnight, and the resi-
due was filtered. The crude Mannich base (2) was obtained as a yellow solid, which
was used for the following reaction without further purification.
A solution of bis-b-chloroethyl dichlorophosphamide (2 mmol)[15] in dry THF
(10 mL) was added dropwise into a stirred solution of crude Mannich base (2)

COUMARIN-7,8-CYCLOPHOSPHORAMIDE ANALOGS
1995
(2 mmol) and triethylamine (4 mmol) in dry THF (20 ml) at room temperature over
30 min. The resulting mixture was further stirred for 2 h. The temperature was slowly
raised to 50–55 ꢀC and maintained at this temperature for 3–4 h. After the triethyl-
amine hydrochloride was filtered off, the solution was evaporated under reduced
pressure to afford a white solid residue. It was further purified by silica-gel column
chromatography, eluting with methanol and ethyl acetate (1:5, v=v).
Compound 3a. Yellow powder, mp 117–118 ꢀC; 1H NMR (CDCl3 400 MHz)
d: 0.97 (m, 3H, ꢁCH2CH2CH3), 1.80–1.70 (m, 2H, ꢁCH2CH2CH3), 3.18–3.09 (m,
2H, ꢁCH2CH2CH3), 3.71–3.36 (m, 8H, 15-H & 16-H), 4.54–4.50 (m, 2H, 14-H),
6.37 (d, J ¼ 9.56, 1H, 3-H), 6.96 (d, J ¼ 8.52, 1H, 6-H), 7.42 (d, J ¼ 8.52, 1H,
5-H), 7.71 (d, J ¼ 9.60, 1H, 4-H). 13C NMR (CDCl3 100 MHz) d: 11.3
(ꢁCH2CH2CH3), 21.1 (d, ꢁCH2CH2CH3, J ¼ 3.18), 42.2 (14-C), 43.5 (16-C), 49.3
(d, ꢁCH2CH2CH3, J ¼ 4.36), 50.0 (d, 15-C, J ¼ 2.8), 111.6 (d, 6-C, J ¼ 7.21), 114.6
(3-C), 114.7 (10-C), 115.0 (d, 8-C, J ¼ 7.34), 128.0 (5-C), 143.5 (4-C), 150.6 (9-C),
153.3 (d, 7-C, J ¼ 8.42), 159.9 (2-C); 31P NMR (CDCl3þ 162 MHz) d: 7.99; IR
(KBr): 1236 cmꢁ1 (P O); ESI-MS, m=z: 441 [M þ Na] ; HR-MS (ESI): m=z
=
[M þ Na]þ calcd. for C17H21Cl2N2O4P: 441.0514; found: 441.00519.
Compound 3b. Yellow powder, mp 137–138 ꢀC; 1H NMR (CDCl3 400 MHz)
d: 1.31 [m, 6H, ꢁCH(CH3)2], 3.71–3.36 (m, 8H, 15-H & 16-H), 4.00–3.95 [m, 1H,
ꢁCH(CH3)2], 4.46–4.42 (m, 2H, 14-H), 6.37 (d, J ¼ 9.60, 1H, 3-H), 6.96 (d,
J ¼ 8.52, 1H, 6-H), 7.43 (d, J ¼ 8.52, 1H, 5-H), 7.73 (d, J ¼ 9.56, 1H, 4-H). 13C
NMR (CDCl3 100 MHz) d: 20.3 [ꢁCH(CH3)2], 35.9 (14-C), 42.1 (16-C), 46.9 [d,
J ¼ 2.86, ꢁCH(CH3)2], 49.2 (d, J ¼ 4.06, 15-C), 112.2 (d, 6-C, J ¼ 7.16), 114.7
(3-C), 114.8 (10-C), 114.9 (d, 8-C, J ¼ 7.16), 128.0 (5-C), 143.5 (4-C), 150.6 (9-C),
153.5 (d, 7-C, J ¼ 8.55), 160.0 (2-C); 31P NMR (CDCl3þ 162 MHz) d: 8.69; IR
(KBr): 1248 cmꢁ1 (P O); ESI-MS, m=z: 441 [M þ Na] ; HR-MS (ESI): m=z
=
[M þ Na]þ calcd. for C17H21Cl2N2O4P: 441.0514; found: 441.0518.
Compound 3c. Yellow powder, mp 143–144 ꢀC; 1H NMR (CDCl3 400 MHz)
d: 0.98 (m, 3H, ꢁCH2CH2CH2CH3), 1.41–1.35 (m, 2H, ꢁCH2CH2CH2CH3),
1.76–1.67 (m, 2H, ꢁCH2CH2CH2 CH3), 3.20–3.12 (m, 2H, ꢁCH2CH2CH2CH3),
3.71–3.37 (m, 8H, 15-H & 16-H), 4.53–4.49 (m, 2H, 14-H), 6.36 (d, J ¼ 9.56, 1H,
3-H), 6.95 (d, J ¼ 8.52, 1H, 6-H), 7.43 (d, J ¼ 8.52, 1H, 5-H), 7.73 (d, J ¼ 9.60,
1H, 4-H); 13C NMR (CDCl3 100 MHz) d: 13.8 (ꢁCH2CH2CH2CH3), 20.1
(ꢁCH2CH2CH2CH3), 29.8 (ꢁCH2CH2CH2CH3), 42.1 (14-C), 43.4 (16-C), 48.1
(–CH2CH2CH2CH3), 49.2 (d, 15-C, J ¼ 4.00), 111.4 (6-C), 111.5 (3-C), 114.7
(10-C), 114.9 (d, 8-C, J ¼ 7.21), 128.0 (5-C), 143.5 (4-C), 150.6 (9-C), 153.3 (d,
7-C, J ¼ 8.40), 159.9 (2-C); 31P NMR (CDCl3 162 MHz): d: 8.60; IR (KBr):
þ
þ
1244 cmꢁ1 (P O); ESI-MS, m=z: 455 [M þ Na] ; HR-MS (ESI): m=z [M þ Na]
=
calcd. for C18H23Cl2N2O4P: 455.0677; found: 455.0670.
Compound 3d. Yellow powder, mp 132–133 ꢀC; 1H NMR (CDCl3 400 MHz)
d: 1.47 [s, 9H, ꢁC(CH3)3], 3.53–3.39 (m, 4H, 15-H), 3.73–3.59 (m, 4H, 16-H),
4.68–4.29 (m, 2H, 14-H), 6.38 (d, J ¼ 9.56, 1H, 3-H), 7.02 (d, J ¼ 8.40, 1H, 6-H),
7.44 (d, J ¼ 8.44, 1H, 5-H), 7.72 (d, J ¼ 9.60, 1H, 4-H); 13C NMR (CDCl3
100 MHz) d: 28.7 [ꢁC(CH3)3], 39.1 (d, 14-C, J ¼ 1.90), 42.0 (16-C), 50.2 (d, 15-C,

1996
X. CHEN ET AL.
J ¼ 4.17), 56.9 [d, ꢁC(CH3)3, J ¼ 3.83], 114.9 (3-C), 114.9 (d, 6-C, J ¼ 5.6), 115.2
(10-C), 115.3 (d, 8-C, J ¼ 7.20), 128.3 (5-C), 143.6 (4-C), 149.9 (9-C), 153.8 (d,
7-C, J ¼ 8.44), 159.9 (2-C); 31P NMR (CDCl3 162 MHz); d: 8.62; IR (KBr):
þ
þ
1259 cmꢁ1 (P O); ESI-MS, m=z: 455 [M þ Na] ; HR-MS (ESI): m=z [M þ Na]
=
calcd. for C18H23Cl2N2O4P: 455.0677; found: 455.0672.
Compound 3e. Yellow powder, mp 179–181 ꢀC; 1H NMR (CDCl3 400 MHz)
d: 1.98–1.13 & 3.45–3.36 (m, 11H, cyclohexyl-H), 3.72–3.50 (m, 8H, 15-H & 16-H),
4.47 (m, 2H, 14-H), 6.37 (d, J ¼ 9.56, 1H, 3-H), 6.95 (d, J ¼ 8.52, 1H, 6-H), 7.41 (d,
J ¼ 8.48, 1H, 5-H), 7.71 (d, J ¼ 9.56, 1H, 4-H); 13C NMR (CDCl3 100 MHz) d: 25.2,
25.8, 30.6, 55.3 (cyclohexane), 37.2 (14-C), 42.2 (16-C), 49.2 (d, 15-C, J ¼ 4.36),
112.5 (d, 6-C, J ¼ 7.00), 114.7 (3-C), 114.7 (10-C), 115.0 (d, 8-C, J ¼ 7.19), 128.0
(5-C), 143.5 (4-C), 150.6 (9-C), 153.6 (d, 7-C, J ¼ 8.44), 160.1 (2-C); 31P NMR (CDCl3
þ
162 MHz) d: 8.87; IR (KBr): 1247 cmꢁ1 (P O); ESI-MS, m=z: 481 [M þ Na] ; HR-MS
=
(ESI): m=z [M þ Na]þ calcd. for C20H25Cl2N2O4P: 481.0827; found: 481.0821.
ACKNOWLEDGMENTS
We are grateful to the National Science Foundation of China (No. 20472076)
and the Henan Science Foundation for Excellent Youth (No. 0512001400) for
financial support.
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