Pd-catalyzed Suzuki-Miyaura coupling reactions in the synthesis of 5-aryl-1-[2-(phosphonomethoxy)ethyl]uracils as potential multisubstrate inhibitors of thymidine phosphorylase

Article abstract of DOI:10.1016/j.tetlet.2007.02.107

-5-Aryl-1-[2-(phosphonomethoxy)ethyl]uracils were prepared via Pd-catalyzed Suzuki-Miyaura coupling reaction of the appropriate 5-bromouracil derivative with a series of arylboronic acids followed by deprotection. These compounds were designed as potentia

Full text of DOI:10.1016/j.tetlet.2007.02.107

Tetrahedron Letters 48 (2007) 3065–3067
Pd-catalyzed Suzuki–Miyaura coupling reactions in the synthesis
of 5-aryl-1-[2-(phosphonomethoxy)ethyl]uracils as potential
multisubstrate inhibitors of thymidine phosphorylase
*
´
´
Karel Pomeisl, Antonın Holy and Radek Pohl
Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, 166 10 Prague, Czech Republic
Received 22 January 2007; revised 8 February 2007; accepted 23 February 2007
Available online 28 February 2007
Abstract—-5-Aryl-1-[2-(phosphonomethoxy)ethyl]uracils were prepared via Pd-catalyzed Suzuki–Miyaura coupling reaction of the
appropriate 5-bromouracil derivative with a series of arylboronic acids followed by deprotection. These compounds were designed
as potential multisubstrate inhibitors of thymidine phosphorylase based on an assumption that the potential hydrophobic effect of
the aryl groups might modify the inhibitory effect towards this enzyme and they may also demonstrate cytostatic activity.
ꢀ 2007 Elsevier Ltd. All rights reserved.
O
Pyrimidine acyclic nucleoside phosphonates (ANPs)
possess a broad spectrum of biological activity1 and
Me
HN
have been investigated as multisubstrate and cataboli-
O
N
cally stable inhibitors2 of thymidine phosphorylase
(TP). This enzyme is crucial for phosphorolysis of
thymidine to thymine and 2-deoxy-D-ribose-1-phos-
phate.3a The latter compound is then dephosphorylated
to 2-deoxy-D-ribose which was recently identified as an
endothelial-cell chemoattractant (PD-ECGF)3 and an
angiogenesis-inducing factor.4 Therefore, development
of multisubstrate TP inhibitors which block thymine
(dThd) and phosphate-binding sites2,5 may be useful as
tumor growth4c suppressors.
R
O
P(O)(OH)2
PMET, R = H, Ki/dThdKm
)-PMPT, R = Me, Ki/dThdKm
)-HPMPT, R = CH2OH, Ki/dThdKm
)-FPMPT, R = F, Ki/dThdKm
0.0026
=
0.0175
0.0082
0.0044
(
S
=
(R
=
(R
=
Figure 1. Structure of 1-[2-(phosphonomethoxy)alkyl]thymines which
inhibit thymidine phosphorylase from SD-lymphoma.
In this study, we prepared 5-aryl substituted uracil
ANPs in order to modify the bioactivity of 1-[2-(phos-
phonomethoxy)ethyl]pyrimidine derivatives (PME com-
pounds) which display only a marginal inhibitory effect
on human TP.6–8 On the other hand, 1-[2-(phosphono-
methoxy)ethyl]thymine demonstrates inhibitory activ-
ity towards TP from SD-lymphoma.6 Therefore, we
assumed that the active sites of both enzymes could be
significantly different. In addition, the inhibitory effect
towards TP from SD-lymphoma also decreased in the
presence of other bioactive pyrimidine ANPs (e.g.,
FPMPT, HPMPT, PMPT, see Fig. 1). This is probably
caused by the absence of alkyl substitutents on the side
chain of the 2-(phosphonomethoxy)alkyl group as
documented in a previous paper.6 Therefore, our efforts
were directed in particular to increasing the inhibitory
effect by modification of the possible hydrophobic inter-
action of PME derivatives with TP near the C-5-position
of the uracil moiety.
It is known, that some 5-aryl-6-chloro-substituted ura-
cils demonstrate a significant impact on the inhibitory
activity towards human TP in which the favoured
hydrophobic interaction of the aryl substituents is prob-
ably directed by the halogen electron-withdrawing
effect.9 Based on this hypothesis we expected that
the hydrophobic effect could also be influenced by the
Keywords: Acyclic nucleoside phosphonates; Thymidine phosphoryl-
ase; Suzuki coupling; Pyrimidine.
*
Corresponding author. Tel.: +420 220 183 475; fax: +420 220 183
560; e-mail: pomeislk@uochb.cas.cz
0040-4039/$ - see front matter ꢀ 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2007.02.107

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K. Pomeisl et al. / Tetrahedron Letters 48 (2007) 3065–3067
Table 1. Reaction of 5-bromo derivative 4 with boronic acids 5a–i
followed by hydrolysis
introduction of different aryl substituents bearing
electron-withdrawing groups, heteroatoms or other
conjugated moieties such as naphthyl, 2-phenylvinyl,
4-fluorophenyl, 3-nitrophenyl, 3-furyl, 3-thienyl, pyr-
idin-3- and 4-yl. Efficient arylation methods are usually
based on Pd-catalyzed Stille coupling reactions using
toxic aryl(trialkyl)stannanes.10 However, the conve-
nience of this method is limited for biochemical or
medicinal purposes owing to the difficulty in removing
undesirable stannane by-products. In contrast, aryl-
boronic acids used as arylating agents in Suzuki–
Miyaura coupling reactions10,11 have wide application
due to their low toxicity. Arylation of the C-5 position
of the uracil moiety has not been so far studied in detail
via this process.11 Therefore, we decided to introduce
various aryl and heteroaryl groups to pyrimidine ANP
derivatives using the Suzuki–Miyaura coupling reaction
for the first time.
Entry
R
Yielda,b of 6 (%)
Yieldb of 7 (%)
a
24
75
S
b
44
59
O
c
34
30
48
80
d
F
O2N
e
f
30
58
24
38
63
34
72
78
Firstly, we prepared the 5-bromouracil derivative 4 as a
suitable building block by a simple three-step synthesis
from 4-methoxypyrimidin-2(1H)-one12 (1) (Scheme 1).
Alkylation of the protected base with PME synthon 2
and further hydrolysis was carried out using our
improved method7 and afforded 3 in a good preparative
yield. Likewise, bromination of the uracil moiety using
N-bromosuccinimide in THF catalyzed with azobis-
isobutyronitrile gave 4 in quantitative yield. For cou-
pling reactions we applied a number of commercial
aryl and heteroaryl boronic acids 5a–i. Simple transfor-
mation of 5-bromo derivative 4 to pyrimidinones 6a–i
took place in DMF–H2O solution catalyzed by
Pd(PPh3)4. Sodium carbonate was used for the activa-
tion of the boronic acids. Full conversion of 4 to the
g
h
N
N
i
35
58
a Conditions: 1.0 equiv 4, 2 equiv 5, 0.1 equiv Pd catalyst, base
(3.3 equiv of Na2CO3), 6–9 h, 130 ꢁC; 8:1 DMF/H2O.
b All products were isolated and characterized by NMR and MS
spectroscopy; yields are unoptimized.
products took place in all cases at a temperature of
ꢀ130 ꢁC (analysis by TLC). However, the products of
arylation13 were isolated in only 24–58% yields (see
Table 1) probably due to losses caused by difficulties
in purification. From this point of view, the presented
cross-coupling reactions report only unoptimized yields.
O
O
Br
OCH3
HN
HN
N
a,b
c
O
N
On the other hand, this method can be considered as a
significant tool with regard to its simplicity to prepare
sufficient quantities of final products by further treat-
ment with bromotrimethylsilane followed by hydroly-
sis14 and the corresponding compounds 7a–i were thus
obtained in good preparative yields. Therefore, this
method should be amenable for the introduction of var-
ious functionalized aryl substituents.
O
N
O
N
H
O
P(O)(OiPr)2
O
P(O)(OiPr)2
1
4
3
R-B(OH)2
5a-5i
d
In conclusion, we have developed a simple alternative
method for the rapid preparation of 5-aryl substituted
pyrimidine ANPs as potential multisubstrate inhibitors
of TP. The inhibitory potency of all the synthesized
compounds together with their potential modified
hydrophobic effects will be investigated in further
research.
O
N
O
N
R
R
HN
HN
e
O
O
O
P(O)(OH)2
O
P(O)(OiPr)2
7a-7i
6a-6i
R = a-i see Table 1
Acknowledgements
Scheme 1. Reagents and conditions: (a) NaH, CH2ClCH2OCH2-
P(O)(OiPr)2 (2), DMF, 80 ꢁC, 49%; (b) Dowex 50 (H+), 90% aq
MeOH, 91%; (c) NBS, AIBN, THF, 60 ꢁC, 99%; (d) Pd(PPh3)4,
Na2CO3, DMF, H2O, 130 ꢁC; (e) (CH3)3SiBr, CH3CN, rt.
The study was supported by the Centre of New Antivi-
rals and Antineoplastics 1M0508 supported by the Min-
istry of Education of the Czech Republic within the

K. Pomeisl et al. / Tetrahedron Letters 48 (2007) 3065–3067
3067
(379 mg, 3.39 mmol), Pd(PPh3)4 (200 mg, 0.17 mmol) and
sodium carbonate (593 mg, 5.59 mmol) in DMF (40 mL)
and degassed H2O (5 mL) was heated (ꢀ130 ꢁC, oil bath)
under argon for 6 h. The mixture was then concentrated
and codistilled with toluene (2 · 20 mL). The residue was
diluted with EtOAc (20 mL) and washed with aqueous
EDTA saturated with NH4Cl (5 mL). The organic layer
was dried over anhydrous MgSO4, filtered and concen-
trated. The residue was purified by preparative TLC on
silica gel (chloroform/methanol 20:1) to give 300 mg (44%
yield) of 6b as a yellow amorphous solid. IR: mmax (CHCl3)
3404, 3164, 2985, 1721, 1712, 1701, 1643, 1432, 1575, 1466,
1387, 1376, 1237, 1159, 1104, 1078, 1023, 1016, 999,
886 cmÀ1. For C17H25N2O7P (400.4) calcd: C, 51.00; H,
6.29; N, 7.00. Found: C, 50.82; H, 6.28; N, 6.97.
FABHRMS: For C17H26N2O7P: Found: 401.1477. Calcd:
401.1481. FABMS, m/z: 401 [MH]+ (61). 1H NMR
(400 MHz, CDCl3): 1.23 and 1.26 (2 · d, 2 · 6H,
Jvic = 6.2, (CH3)2CH); 3.75 (d, 2H, JH,P = 8.4, CH2P);
3.86 (t, 2H, Jvic = 4.8, CH2O); 4.04 (m, 2H, CH2N); 4.69
(dh, 2H, JH,P = 7.6, Jvic = 6.2, CH(CH3)2); 6.45 (dd, 1H,
J4,3 = 3.4, J4,5 = 1.8, H-4-fur); 7.03 (dd, 1H, J3,4 = 3.4,
J3,5 = 0.8, H-3-fur); 7.35 (dd, 1H, J5,4 = 1.8, J5,3 = 0.8, H-
5-fur); 7.80 (s, 1H, H-6); 8.78 (br s, 1H, NH). 13C NMR
(100.6 MHz, CDCl3): 23.84 and 23.92 (d, JC,P = 4,
(CH3)2CH); 49.04 (CH2N); 66.24 (d, JC,P = 168, CH2P);
70.78 (d, JC,P = 11, CH2O); 71.21 (d, JC,P = 7,
CH(CH3)2); 106.41 (C-5); 109.23 (CH-3-fur); 111.84
(CH-4-fur); 139.64 (CH-6); 141.01(CH-5-fur); 145.64 (C-
2-fur); 149.67 (C-2); 160.21 (C-4).
program of Gilead Sciences Research Centre. The finan-
cial support of the Descartes Prize HPAW-CT-2002-
9001 of the European Union and of Gilead Sciences
(Foster City, CA, USA) is gratefully acknowledged.
The authors also thank Dr. Michal Hocek for helpful
discussions.
References and notes
1. (a) Holy´, A. Curr. Pharm. Des. 2003, 9, 2567–2592; (b)
Holy´, A. In Recent Advances in Nucleosides: Chemistry and
Chemotherapy; Chu, C. K., Ed.; Elsevier: Amsterdam,
2002; p 167.
2. Esteban-Gamboa, A.; Balzarini, J.; Esnouf, R.; De Clercq,
´
´
E.; Camarasa, M.-J.; Perez-Perez, M.-J. J. Med. Chem.
2000, 43, 971–983.
3. (a) Friedkin, M.; Roberts, D. W. J. Biol. Chem. 1954, 207,
245–256; (b) Miyazono, K.; Okabe, T.; Urabe, A.;
Takaku, F.; Heldin, Ch. J. Biol. Chem. 1987, 262, 4098–
4103; (c) Usuki, K.; Sarasi, J.; Waltenberger, J.; Miya-
zono, K.; Pierce, G.; Thomason, A.; Heldin, Ch. Biochem.
Biophys. Res. Commun. 1992, 184, 1311–1316.
4. (a) Furakawa, T.; Yoshimura, A.; Sumizawa, T.; Harag-
uchi, M.; Akiyama, S.; Fukui, K.; Ishizawa, M.; Yamada,
Y. Nature 1992, 356, 668; (b) Haraguchi, M.; Miyadera,
K.; Uemura, K.; Sumizawa, T.; Furukawa, T.; Yamada,
K.; Akiyama, S.; Yamada, Y. Nature 1994, 368, 198; (c)
Matsushita, S.; Nitanda, T.; Furukawa, T.; Sumizawa, T.;
Tani, A.; Nishimoto, K.; Akiba, S.; Miyadera, K.;
Fukushima, M.; Yamada, Y.; Yoshida, H.; Kanzaki, T.;
Akiyama, S. Cancer Res. 1999, 59, 1911–1916.
14. A typical procedure for the deprotection of 5-aryluracil-
substituted ANPs: A mixture of 6b (269 mg, 0.67 mmol)
and bromotrimethylsilane (1.03 g, 6.70 mmol) in aceto-
nitrile (15 mL) was stirred overnight at room temperature.
The mixture was concentrated and then codistilled with
water (2 · 2 mL). The residue was heated with Dowex
50 · 8 (H+form) (2 mL) in water (15 mL) at 70 ꢁC for 1 h.
The mixture was then cooled to room temperature and
filtered. The filtrate was concentrated and the residue was
purified on DEAE-Sephadex (ClÀ, 0–0.4 M TEAB) with
subsequent deionization of the product on activated
charcoal with water. The product was eluted with 12%
aqueous ammonia/methanol (1:1). The residue was lyo-
philized to give 125 mg (59% yield) of 7b as a white
amorphous solid. IR: mmax (CHCl3) 3235, 1705, 1686,
´
5. Balzarini, J.; Degreve, B.; Esteban-Gamboa, A.; Esnouf,
R.; De Clercq, E.; Engelborghs, Y.; Camarasa, M.-J.;
´
´
Perez-Perez, M.-J. FEBS Lett. 2000, 483, 181–185.
´
´
´
6. Votruba, I.; Pomeisl, K.; Tlousˇt’ova, E.; Holy, A.; Otova,
B. Biochem. Pharmacol. 2005, 69, 1517–1521.
7. Pomeisl, K.; Pohl, R.; Holy´, A.; Votruba, I. Collect.
Czech. Chem. Commun. 2006, 71, 595–624.
8. Pomeisl, K.; Pohl, R.; Holy´, A.; Votruba, I. Collect.
Czech. Chem. Commun. 2005, 70, 1465–1481.
´
9. Nencka, R.; Votruba, I.; Hrˇebabecky´, H.; Tlousˇt’ova, E.;
´
´
Masojidkova, M.; Holy A. Abstracts of Papers, XVII
International Rountable on Nucleosides, Nucleotides and
Nucleic Acids, Bern, Switzerland, September 3–7, 2006;
PO167.
1638, 1516, 1431, 3161, 1572, 1160, 1083, 1108 cmÀ1
.
FABHRMS: For C11H14N2O7P: Found: 317.0544. Calcd:
317.0539. FABMS, m/z: 317 [MH]+ (28). 1H NMR
(400 MHz, D2O, refdioxane = 3.75 ppm): 3.66 (d, 2H,
JH,P = 8.5, CH2P); 3.87 (t, 2H, Jvic = 5.2, CH2O); 4.05
(m, 2H, CH2N); 6.54 (dd, 1H, J4,3 = 3.4, J4,5 = 1.9, H-4-
fur); 6.83 (dd, 1H, J3,4 = 3.4, J3,5 = 0.8, H-3-fur); 7.53 (dd,
1H, J5,4 = 1.9, J5,3 = 0.8, H-5-fur); 8.05 (s, 1H, H-6). 13C
NMR (100.6 MHz, D2O, refdioxane = 69.3 ppm): 51.12
(CH2N); 69.73 (d, JC,P = 156, CH2P); 72.72 (d, JC,P = 11,
CH2O); 109.07 (C-5); 111.24 (CH-3-fur); 114.29 (CH-4-
fur); 144.60 (CH-6); 144.95 (CH-5-fur); 148.33 (C-2-fur);
154.10 (C-2); 165.65 (C-4). 31P NMR (100.6 MHz, D2O):
16.36.
10. (a) Sgrofoglio, L. A.; Gillaizeau, I.; Saito, Y. Chem. Rev.
2003, 103, 1875–1916; (b) Wigerinck, C.; Pannecouque,
C.; Snoeck, R.; Claes, P.; De Clercq, E.; Herdewinjn, P. J.
Med. Chem. 1991, 34, 2383–2389.
11. Guo, Z.; Chen, Y.; Huang, Ch. Q.; Gross, T. D.; Pontillo,
J.; Rowbotton, M. W.; Saunders, J.; Struthers, S.; Tucci,
F. C.; Xie, Q.; Wade, W.; Zhu, Y.-F.; Wu, D.; Chen, Ch.
Bioorg. Med. Chem. Lett. 2005, 2519–2522.
12. Holy´, A.; Ivanova, G. S. Nucleic Acids Res. 1974, 1, 19–34.
13. A typical procedure for Suzuki–Miyaura coupling of 2-
bromouracil derivative 4 with arylboronic acids: A mixture
of compound 4 (700 mg, 1.69 mmol), aryl boronic acid 5b