Preparation of acyclo nucleoside phosphonate analogues based on cross-metathesis

Article abstract of DOI:10.1016/j.tet.2008.01.140

In our on-going program targeting anti-pox activity, we report here the synthesis of hitherto unknown acyclic nucleoside phosphonates using olefin cross-metathesis (CM) as a key assembly step. Modification at the C-5 position of the uracil moiety was performed under optimized Pd(0)-catalyzed Stille cross-coupling conditions. None of the obtained compounds were active against poxviruses, nor do they exhibit any toxicity.

Full text of DOI:10.1016/j.tet.2008.01.140

Available online at www.sciencedirect.com
Tetrahedron 64 (2008) 3517e3526
www.elsevier.com/locate/tet
Preparation of acyclo nucleoside phosphonate analogues based
on cross-metathesis
a
b
a
a
a
`
Hiroki Kumamoto , Dimitri Topalis , Julie Broggi , Ugo Pradere , Vincent Roy ,
Sabine Berteina-Raboin a, Steven P. Nolan c, Dominique Deville-Bonne b, Graciela Andrei d,
Robert Snoeck d, Daniel Garin e, Jean-Marc Crance e, Luigi A. Agrofoglio a,
*
a Institut de Chimie Organique et Analytique, CNRS UMR-6005, Universite´ d’Orle´ans, BP 6759, 45067 Orle´ans, France
b Laboratoire d’Enzymologie Moleculaire et Fonctionnelle, FRE CNRS 2852, Universite´ Pierre et Marie Curie, Paris, France
c Institute of Chemical Research of Catalonia (ICIQ), Av. Pa€ısos Catalans 16, 43007 Tarragona, Spain
d Rega Institute, B-3000 Leuven, Belgium
e Centre de Recherches du Service Sante´ des Arme´es, La Tronche, France
Received 28 November 2007; received in revised form 23 January 2008; accepted 31 January 2008
Available online 6 February 2008
Abstract
In our on-going program targeting anti-pox activity, we report here the synthesis of hitherto unknown acyclic nucleoside phosphonates using
olefin cross-metathesis (CM) as a key assembly step. Modification at the C-5 position of the uracil moiety was performed under optimized Pd(0)-
catalyzed Stille cross-coupling conditions. None of the obtained compounds were active against poxviruses, nor do they exhibit any toxicity.
Ó 2008 Elsevier Ltd. All rights reserved.
1. Introduction
Thus, two series of vinyl ANP (3, 15aef) and their allyl
analogues (7, 16aef) have been obtained from the same N1-
crotyl-5-phenylthiouracil (Fig. 1).
The cidofovir (CDV, HPMPC, 1-(S)-[3-hydroxy-2-(phos-
phonomethoxy)propyl]cytosine)1 is an acyclo nucleoside
phosphonate (ANP), which possesses a biologically stable car-
bonephosphorus bond. It is a potent and selective anti-DNA
virus agent, licensed against the treatment of human cytomeg-
alovirus. It also exhibits in vitro and in vivo potent anti-pox ac-
tivity (against smallpox virus and monkeypox virusdpotential
bioterrorism weapons). Because of therapeutic potential, sev-
eral developments in the modification of cidofovir either on
the pyrimidinone (5-aza analogue) or on the side chain (2-pen-
tenyl) have been reported.2
As part of an on-going program on orthopox virus, we de-
scribe herein an efficient synthesis of several hitherto unknown
acyclic nucleoside phosphonates. The key synthetic steps lead-
ing to these involve the olefin cross-metathesis reaction and
the palladium-mediated C5-alkylation of the uracil moiety.
2. Results and discussion
Unsaturated phosphonates are primarily formed under the
MichaeliseArbuzov reaction,3 or phosphonylation of unsatu-
rated aldehydes,4 palladium5,6 catalyzed cross-coupling of hy-
drogen phosphonates to conjugated dienes, allenes or alkynes.
Nevertheless, often those methods suffer from elimination
and/or loss of olefin stereochemical integrity, due to high reac-
tion temperatures and provide low regioselectivity in the case
of highly substituted phosphonate products. Over the past de-
cade, the olefin metathesis7 reaction has become a most pow-
erful tool for advanced organic synthesis, mainly due to the
introduction of various ruthenium catalysts such as those
developed by Grubbs,8 Hoveyda,9 Nolan.10 The ring-closing
metathesis reactions have been already utilized in the
construction of a variety of phosphorus containing organic
molecules.11
* Corresponding author. Tel.: þ33 2 3849 4582; fax: þ33 2 3841 7281.
E-mail address: luigi.agrofoglio@univ-orleans.fr (L.A. Agrofoglio).
0040-4020/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2008.01.140

3518
H. Kumamoto et al. / Tetrahedron 64 (2008) 3517e3526
NH2
N
E-isomer (6a, 72%) with the minor Z-isomer present in small
amounts (6b, 15%) (Scheme 2). Both isomers can be separated
by liquid chromatography on silica gel.
NH2
N
O
P
N
O
O
P
OH
N
O
O
HO
HO
HO
O
N
O
N
O
N
O
HO
HPMPC,
NH
NBz
O
NBz
O
NBz
O
a
b
c
Cidofovir analogues
O
(Cidofovir)
N
H
(99%)
(87%)
5
4
O
R
O
R
HO
NH
Me
MeO
NH
P
P
HO
MeO
O
O
N
O
O
O
P
OH
N
O
7a (98%, E)
and 7b (66%, Z)
isomers separable by chromatography
6a (E) and 6b (Z)
P
HO
HO
E/Z : 8/2
OH
3, 15a-f
vinyl ANP
7, 16a-f
allyl ANP
Scheme 2. Reagent and conditions: (a) crotyl bromide, K2CO3, DMF; (b)
dimethyl allyl phosphonate (4 equiv), [Ru]¼catalyst (5 mol %), CH2Cl2,
reflux; (c) TMSBr (4.0 equiv), CH2Cl2.
Figure 1. Some bioactive acyclic nucleoside phosphonates and our target
compounds.
These results indicated that the allyl phosphonate would be
more active metathesis partner than the vinyl analogue.
Based on those results, we next extended this approach to
several 5-substituted uracil derivatives, which were obtained
using the 5-phenylthiouracil derivative (8) as a synthetic com-
mon intermediate for the construction of either the C5-halo-
geno- (11aec) or the C5-carbon-substituted (11def) uracil
analogues as well as their N3-protected analogues (12aef)
(Scheme 3).
Recently, Grubbs et al.12 reported on a general model for
selectivity in cross-metathesis (CM), by ranking the olefin re-
activity in CM by categorizing the olefins in their abilities to
undergo homodimerization via CM and by the stability of
those homodimers. Based on this model, we began to explore
the cross-metathesis reaction of the reactive crotylated uracil
(1) with vinyl diethylphosphonate, (Scheme 1). A mixture of
the heterodimer (2) with the homodimer (20) was obtained.
The desired cross-coupling heterodimer (2) was obtained in
67% yield as the E isomer. It is important to note that the re-
action proceeded without the protection at the N3-position of
the heterocycle. Compound 2 was deprotected with TMSBr
to afford the desired ANP.
O
N
O
N
O
PhS
Bu3Sn
Me
NR
NH
NBz
O
a
b
O
O
Me
N
H
(65%)
(86%)
8 R=H
10
1
e
80%
O
N
O
N
d
O
N
9 R=Bz
c
(78-92%)
NH
(56-66%)
NH
NH
a
b
O
O
O
(67%)
O
O
N
(98%)
a R = Ph
X
R
NR1
O
1
NR1
b R = 4-F-Ph
c R = 4-MeO-Ph
e X = Cl
OH
OH
OEt
OEt
P
N
O
P
Me
N
Me
Me
O
O
f
X = Br
11a-c R1=H
(59-87%)
12a-c R1=Bz
3
11e-f R1=H
(63-93%)
12e,f R1=Bz
2
Mes N
Mes
Ph
e
e
Cl
Cl
Ru
PCy3
Scheme 3. Reagent and conditions: (a) (i) PhSH, NCS, pyridine, MeCN, re-
flux, (ii) crotyl bromide, K2CO3, DMF, (iii) K2CO3, MeOH; (b) Bu3SnH,
AIBN, toluene, reflux; (c) RI, PdCl2(PPh3)2 (10 mol %), CuI, DMF, rt; (d)
NXS (for 11e and 11f); (e) BzCl, DMAP, i-Pr2Net, MeCN.
cross-metathesis catalyst
Scheme 1. Reagent and conditions: (a) diethylvinylphosphonate,
[Ru]¼catalyst (5 mol %), CH2Cl2, reflux.
The same procedure was successfully applied to the cross-
metathesis involving dimethyllallyl phosphonate. Our prelim-
inary results indicated that the expected heterodimers were
isolated in only low yields (20e30%). We thus hypothesized
that the active N3-proton of the pyrimidine would avoid for
a metathesis reaction. Thus starting with the N3-benzoylated
crotylated uracil (5) prepared from N3-benzoyluracil (4),13
the CM reaction gave the desired allyl phosphonate (6), iso-
lated as a mixture of major and thermodynamically stable
Thus, the 5-phenylthio derivative (8) was prepared from 4
by (i) introduction of phenylthio group at the C5-position,
(ii) crotylation of the N1-position, and (iii) debenzoylation of
N3-position in 65% over three steps. By treating 8 with tribu-
tyltin radical, a sulfur-extrusive stannylation14 occurred and
the desired tin derivative 10 was obtained in high yields. On
the one hand, the Pd(0)-mediated Stille-coupling reaction15 in-
volving 10 allowed for the isolation of the desired C5-carbon
substituted derivatives (11aec). On the other hand, compound

H. Kumamoto et al. / Tetrahedron 64 (2008) 3517e3526
3519
O
N
O
R
R
NH
NH
O
P
HO
O
P
EtO
a
c
O
N
O
HO
EtO
O
N
(37-71%)
(71-98%)
R
NR1
O
13a-f
15a-f
O
N
O
N
Me
R
R
NBz
O
NH
R1=H 8, 11a-f
=Bz 9, 12a-f
b
O
c
O
O
(74-94%)
P
P
(54-92%)
MeO
HO
a R = Ph-
OMe
OH
b R = 4-F-Ph-
c R = 4-MeO-Ph-
d R = Ph-S-
e R = Cl
14a-f
16a-f
5:1 E/Z mixture of chromatographically
separable isomers
f
R = Br
Scheme 4. Reagent and conditions: (a) diethyl vinyl phosphonate (4 equiv), [Ru]¼catalyst 4 (5 mol %), CH2Cl2, reflux; (b) dimethyl allyl phosphonate (4.0 equiv),
[Ru]¼catalyst (5 mol %), CH2Cl2, reflux; (c) TMSBr (4.0 equiv), CH2Cl2.
10 was easily converted into the 5-chloro (11e), 5-bromo (11f)
derivatives by simple treatment with NCS or NBS, respec-
tively. A final benzoylation of 11aef afforded the desired pro-
tected analogues 12aef. The 5-phenylthiouracil analogue (8)
was benzoylated into 9.
toxicity at concentration up to 100 mM in HEL and Vero cells.
The nucleotide binding of all those new acyclic phosphonate
analogs to human UMPeCMP kinase or to TMK kinase was
performed and results are reported elsewhere.16
The C5-substituted N3-unprotected uracil derivatives (8,
11aef) were engaged in a cross-metathesis reaction with di-
ethyl vinyl phosphonate. The desired cross-metathesis products
(13aef) were isolated in moderate to good yield. The stereo-
chemistry of the olefin was confirmed 1H NMR and 31P NMR
spectroscopy. The coupling constants of the olefinic protons
(average of 17.0 Hz) and the coupling constants of phosphine
oxide [average of JHeP¼25.0 Hz and JHtranseP¼22.5 Hz
gave a triplet (3JHciseP¼41.5 Hz)] are in agreement with the
exclusive formation of the thermodynamically stable (E)-
isomer. A final deprotection by treatment with TMSBr in
CH2Cl2 afforded the free phosphonates 15aef in good yields
(Scheme 4).
4. Experimental section
4.1. General
Commercially available chemicals were reagent of grade
and used as received. THF was distilled from sodium/benzo-
phenone ketyl; CH2Cl2 from CaH2 immediately prior use
and benzene over Na. The reactions were monitored by thin
layer chromatography (TLC), analysis using silica gel plates
(Kieselgel 60 F254, E. Merck). Compounds were visualized
by UV irradiation, followed by charring at 150 ꢀC. Column
chromatography was performed on Silica Gel 60M (0.040e
2
3
0.063 mm, E. Merck). The H and 13C NMR spectra were re-
1
The cross-metathesis of N3-protected uracil analogues (9,
12aef) with allyl diethylphosphonate was also performed
and the cross products 14aef were isolated as a mixture of
E and Z isomers (average E/Z ratio 8:2) separable by chroma-
tography. The final deprotection of N3-benzoyl and diethyl-
phosphonate was similarly performed by treatment with
TMSBr in CH2Cl2, and the free phosphonates (16aef) were
obtained in good yields, respectively.
corded on a Bruker Avance DPX 250 and Varian Inova Unity
400 spectrometer (1H: 399.81 MHz, 13C: 100.54 MHz) in
CDCl3 or DMSO-d6shift values in parts per million relative
to SiMe4 as internal reference, and the 31P spectra were re-
ported using aq phosphoric acid as external reference (31P:
161.97 MHz) in CD3OD, unless otherwise stated; J in hertz.
UVevisible spectra were recorded on PerkineElmer
Lambda25. High Resolution Mass spectra (HRMS) were per-
formed by the Centre Regional de Mesures Physiques de l’Ou-
est (University of Rennes, France), using FAB (Fast Atom
Bombardment) or ESI (Electron Spray Ionization).
3. Conclusion
In summary, the syntheses of various acyclic nucleoside
phosphonates based on alkene cross-metathesis have been
achieved. The reactivity and stereochemistry of the cross-cou-
pling metathesis of various C5-substituted crotylated uracil
with vinyl(and allyl) phosphonate have been established.
The anti-vaccinia virus activity of all synthesized compounds
were tested systematically in E6SM or HEL cell cultures in-
fected with vaccinia virus (Lederle strain ATCC VR-118),
on Vero cells infected by vaccinia virus (Lister strain) or by
cowpox virus (Brighton strain). No significant activities were
observed; these compounds did not exhibit any significant
4.2. N1-Crotyluracil (1)17
Registry number: 852998-43-7.
4.3. N1-[(E)-3-Diethoxyphosphinyl-2-propenyl]uracil (2)
To a CH2Cl2 (10 mL) solution of N1-crotyluracil (1)
(300 mg, 1.80 mmol) and diethyl vinyl phosphonate
(1.119 mL, 7.22 mmol), [Ru]¼catalyst 4 (76 mg, 0.05 mmol)
was added. This solution was refluxed for 22 h under positive

3520
H. Kumamoto et al. / Tetrahedron 64 (2008) 3517e3526
pressure of dry Ar. After evaporation of all volatiles, the resi-
due was purified by chromatography on silica gel (AcOEt/
MeOH: 15:1). Yield: 67% (347 mg) as a foam. 1H NMR
(CD3OD) d: 1.27 (t, 6H, J¼6.9 Hz, eOCH2CH3), 3.99 (q,
2H, J¼6.9 Hz, OCH2CH3), 4.02 (q, 2H, J¼6.9 Hz, OCH2CH3),
4.58 (m, 2H, UeCH2e), 5.73 (d, 1H, J¼8.0 Hz, H5), 5.85 (t,
1H, J¼16.8 Hz, CH]CH), 6.80 (ddt, 1H, J¼4.4, 16.8,
21.9 Hz, CH]CH), 7.57 (d, 1H, J¼8.0 Hz, H6), 9.55 (br s,
1H, NH). 13C NMR (DMSO-d6) d: 16.9, 17.0, 62.0, 62.1,
102.3, 117.3, 120.2, 146.1, 147.3, 151.5, and 164.2.
of dry Ar. After evaporation of all volatiles, the residue was pu-
rified by chromatography on silica gel (EtOAc/MeOH¼15:1 for
6b, EtOAc/MeOH¼10:1 for 6a). This gave the major 6a
(504 mg, 72%) and the minor 6b (107 mg, 15%) as oils, respec-
1
tively. NMR data for 6a: H NMR (CDCl3) d: 2.65 (dd, 2H,
J¼21.4, 5.7 Hz, P(O)CH2e), 3.75 (d, 6H, J¼10.7 Hz,
P(OMe)2), 4.35e4.38 (2H, m, UeCH2e), 5.75e5.79 (m, 2H,
CH]CH), 5.83 (1H, d, J¼8.2 Hz, H5), (d, 1H, J¼8.2 Hz,
H6), 7.47e7.53 (m, 2H, Harom), 7.63e7.65 (m, 1H, Harom),
7.92e7.95 (m, 2H, Harom). 13C NMR (CDCl3) d: 26.7, 28.9,
48.2, 51.4, 51.5, 101.0, 124.5, 124.7, 126.6, 126.9, 127.7,
129.0, 130.0, 133.7, 141.8, 148.2, 160.8, and 167.3. HRMS:
C17H19N2O6P calcd for m/z 378.3206, found m/z 378.3207.
4.4. N1-[(E)-3-Dihydroxyphosphinyl-2-propenyl]uracil (3)
1
Compound (2) (74 mg, 0.26 mmol), was solubilized in
CH2Cl2 (15 mL), and TMSBr (138 mL, 1.04 mmol) was added
and stirred for 60 h at room temperature under positive pres-
sure of dry Ar. MeOH (5 mL) was added and evaporated
with heating (ca. 60 ꢀC). MeOH (5 mL) was added again,
and this procedure was repeated three times more. The residue
was extracted with H2O and CH2Cl2, and the inorganic phase
was evaporated to dryness. The desired compound 3 (59 mg,
NMR data for 6b: H NMR (CDCl3) d: 2.75 (dd, 2H, J¼22.9
and 7.3 Hz, P(O)CH2e), 3.76 (d, 6H, J¼11.0 Hz, P(OMe)2),
4.46e4.50 (m, 2H, UeCH2e), 5.70e5.81 (m, 2H, CH]CH),
5.83 (d, 1H, J¼7.8 Hz, H5), 7.47e7.53 (m, 2H, Harom), 7.60
(d, 1H, J¼7.8 Hz, H6), 7.62e7.69 (m, 1H, Harom), 7.92e7.95
(m, 2H, Harom). 13C NMR (CDCl3) d: 22.4, 24.6, 43.4, 51.4,
51.5, 101.0, 122.2, 122.4, 126.0, 126.2, 127.7, 129.0, 130.0,
133.6, 142.6, 148.5, 161.0, and 167.4.
1
98%) was isolated as a foam. H NMR (DMSO-d6) d: 4.40e
4.41 (2H, m, UeCH2e), 5.62 (d, 1H, J¼6.6 Hz, H5), 5.69
(t, 1H, J¼17.0 Hz, CH]CH), 6.60 (ddt, 1H, J¼4.7, 17.0,
21.2 Hz, CH]CH), 7.60 (d, 1H, J¼6.6 Hz, H6), 11.35 (br s,
1H, NH). 13C NMR (DMSO-d6) d: 47.9, 100.7, 121.7,
124.6, 140.1, 140.2, 144.8, 150.0, and 163.0. HRMS:
C7H9N2O5P calcd for m/z 232.1322, found m/z 232.1325.
4.7. N1-[(E)-4-Dihydroxyphosphinyl-2-butenyl]uracil (7a)
To a CH2Cl2 (30 mL) solution of 6a (254 mg, 0.67 mmol),
TMSBr (360 mL, 2.69 mmol) was added and stirred for 60 h at
room temperature under positive pressure of dry Ar. MeOH
(5 mL) was added and evaporated with heating (ca. 60 ꢀC).
MeOH (5 mL) was added again, and this procedure was re-
peated three more times. The residue was extracted with
H2O and CH2Cl2 and the inorganic phase was evaporated.
4.5. N3-Benzoyl-N1-crotyluracil (5)
A DMF (30 mL) solution of N3-Benzoyluracil (4)3 (2.19 g,
10.1 mmol) was stirred at room temperature where K2CO3
(2.1 g, 15.1 mmol) and crotyl bromide (1.55 mL, 15.15 mmol)
were added. This mixture was stirred for 1 h at room tempera-
ture under positive pressure of dry Ar. The mixture was treated
with EtOAc and aq saturated NH4Cl, and the organic phase w
extracted and dried over MgSO4. After filtration and evapora-
tion of the solution, the residue was purified by column chroma-
tography (petroleum ether/EtOAc¼1:2). This procedure
Compound 7a was isolated as a foam (165 mg, >98%). H
1
NMR (DMSO-d6) d: 2.35e2.46 (m, 2H, PeCH2e), 4.24e
4.26 (m, 2H, UeCH2e), 5.56 (d, 1H, J¼8.2 Hz, H5), 5.61e
5.69 (m, 2H, CH]CH), 7.57 (d, 1H, J¼8.2 Hz, H6), 11.26
(br s, 1H, NH). 13C NMR (DMSO-d6) d: 31.7, 33.8, 49.1,
101.8, 127.0, 127.1, 128.2, 128.4, 145.9, 151.5, and 164.4.
HRMS: C8H11N2O5P calcd for m/z 246.1590, found m/z
246.1592.
1
provided 5 (2.7 g, 99%) as an oil. H NMR (CDCl3) d: 1.75
4.8. N1-[(Z)-4-Dihydroxyphosphinyl-2-butenyl]uracil (7b)
(dd, 3H, J¼6.6, 1.3 Hz, Me), 4.26e4.30 (m, 2H, UeCH2 major),
2 minor
4.39e4.42 (m, 2H, UeCH
), 5.46e5.58 (m, 1H, CH]CH),
Compound 7b was prepared from 6b (100 mg, 0.26 mmol)
using the same procedure as mentioned above. Compound 7b
was isolated as a foam (43 mg, 66%). 1H NMR (DMSO-d6) d:
2.52e2.65 (m, 2H, PeCH2e), 4.25e4.36 (m, 2H, UeCH2e),
5.48e5.70 (m, 3H, H5 and CH]CH), 7.69 (d, 1H, J¼7.8 Hz,
H6), 11.26 (br s, 1H, NH). 13C NMR (DMSO-d6) d: 31.7, 33.8,
46.2, 103.3, 127.7, 127.9, 129.0, 147.6, 153.3, and 166.0.
HRMS: C8H11N2O5P calcd for m/z 246.1590, found m/z
246.1591.
5.74e5.92 (m, 1H, CH]CH), 5.75 (1H, d, J¼7.9 Hz, H5), 7.27
(1H, d, J¼7.9 Hz, H6), 7.40e7.52 (m, 2H, Harom), 7.61e7.68
(m, 1H, Harom), 7.91e7.94 (m, 2H, Harom). 13C NMR (CDCl3)
d: 11.3, 16.0, 42.6, 48.3, 100.3, 100.4, 121.0, 122.1, 127.3,
127.4, 128.7, 128.9, 129.7, 131.0, 133.3, 141.7, 148.0, 148.1,
160.7, and 167.2. HRMS: C15H14N2O3 calcd for m/z
270.2872, found m/z 270.2881.
4.6. N3-Benzoyl-N1-[(3-methoxyphosphinyl-2-butenyl]-
uracil (6)
4.9. N1-Crotyl-5-phenylthiouracil (8)
A mixture of 5 (500 mg, 1.85 mmol), dimethyl allyl phos-
phonate (1.11 g, 7.4 mmol), and 5 (74 mg, 0.09 mmol) in
CH2Cl2 (19 mL) was refluxed for 16 h under positive pressure
A mixture of NCS (3.7 g, 27.8 mmol) in MeCN (60 mL)
was cooled to 0 ꢀC. PhSH (2.9 mL, 27.8 mmol) was added
dropwise to the mixture and stirred. After 0.5 h, 1 (2.0 g,

H. Kumamoto et al. / Tetrahedron 64 (2008) 3517e3526
3521
9.25 mmol) was added at 0 ꢀC and stirred for 0.5 h. Pyridine
(2.28 mL, 27.8 mmol) was then added and the mixture was re-
fluxed for 16 h under positive pressure of dry Argon. After
evaporation of all volatiles, the residue was purified by chro-
matography on silica gel (petroleum ether/EtOAc¼1:2). This
gave crude 5-phenylthiouracil derivative (this included some
of succinimide). This was used for the next reaction without
further purification. A DMF (40 mL) solution of the crude 5-
phenylthiouracil (4.03 g), K2CO3 (3.84 g, 27.8 mmol), and
crotyl bromide (1.9 ml, 18.5 mmol) was stirred for 40 min at
room temperature under positive pressure of dry Argon. After
extraction of this reaction mixture with EtOAc and aq satu-
rated NH4Cl, the organic phase was separated and dried over
MgSO4, filtered, and evaporated to dryness. This was purified
by chromatography on silica gel (petroleum ether/
EtOAc¼1:1). This gave crotylated product (2.61 g) as an oil.
This product was used in the next step. A mixture of the above
crotylated product (2.61 g) and NH3/MeOH (0 ꢀC, saturated,
50 mL) was kept below 0 ꢀC for 22 h. After evaporation of
all volatiles, the residue was purified by chromatography on
silica gel (petroleum ether/EtOAc¼1:2). This gave 8 (2.27 g,
65% over 3 steps) as a solid (1:3 of stereoisomeric mixture).
1H NMR (CDCl3) d: 1.69e1.77 (m, 3H, CH3), 4.30 (d, 2H, J¼
6.6 Hz, UeCH2 major), 4.41 (d, 2H, J¼7.2 Hz, UeCH2 minor),
5.45e5.57 (m, 2H, CH]CHmajor), 5.73e5.91 (m, 2H,
CH]CHminor), 7.17e7.32 (m, 5H, Harom), 7.59 (s, 1H, H6),
9.16 (br s, 1H, NH). 13C NMR (CDCl3) d: 18.2, 50.3, 107.5,
123.0, 124.2, 127.3, 129.2, 132.1, 133.4, 135.4, 148.4,
148.8, 150.8, and 161.8. HRMS: C14H14N2O2S calcd for m/z
274.3428, found m/z 274.3431.
2.73 mmol), and Et3N (2.54 mL, 18.2 mmol) were refluxed
for 2 h under positive pressure of dry Argon. After evaporation
of all volatiles, this was purified by chromatography on silica
gel (petroleum ether/EtOAc¼2:1). The product 10 (3.56 g,
86%) was obtained as an oil (1:3 of stereoisomeric mixture).
1H NMR (CDCl3) d: 0.82e1.55 (m, 27H, SnBu3), 1.73e1.78
(m, 3H, CH3), 4.27 (d, 2H, J¼6.0 Hz, UeCH2 major), 4.39
(d, 2H, J¼6.0 Hz, UeCH2 minor), 4.39 (d, 2H, J¼7.2 Hz,
UeCH2), 5.46e5.55 (m, 2H, CH]CH), 5.68e5.82 (m, 2H,
CH]CH), 6.91 (t, 1H, JH,Sn¼15.7 Hz, H6), 8.23 (br, 1H,
NH). 13C NMR (CDCl3) d: 8.7, 12.6, 16.7, 26.2, 27.9, 48.1,
111.1, 123.7, 130.1, 146.6, 150.2, and 165.5.
4.12. General procedure for the Stille reaction
A mixture of 9 (500 mg, 1.1 mmol), aryliodide (370 mL,
3.3 mmol), PdCl2(PPh3)2 (77 mg, 0.11 mmol), and CuI
(42 mg, 0.22 mmol) in DMF (2 mL) was stirred for 15 h at
room temperature under positive pressure of dry Ar. This mix-
ture was extracted with brine and EtOAc. The organic phase
was dried over MgSO4, filtered, and evaporated. The residue
was purified by chromatography on silica gel (petroleum
ether/EtOAc¼1:1) and the desired compound was isolated.
4.12.1. N1-Crotyl-5-phenyluracil (11a)
Yield: 66% (175 mg) as a solid (1:3 stereoisomeric mix-
1
ture). H NMR (CDCl3) d: 1.26e1.81 (m, 3H, CH3), 4.36
(d, 2H, J¼6.6 Hz, UeCH2 major), 4.48 (d, 2H, J¼6.9 Hz, Ue
CH2 minor), 5.50e5.61 (m, 2H, CH]CH), 5.74e5.88 (m,
2H, CH]CH), 7.26e7.53 (m, 6H, Harom and H6), 9.12 (br,
1H, NH). 13C NMR (CDCl3) d: 18.1, 50.3, 115.7, 124.6,
128.3, 128.4, 128.8, 132.5, 141.4, 150.2, and 162.7. HRMS:
C14H14N2O2 calcd for m/z 242.2768, found m/z 242.2773.
4.10. N3-Benzoyl-N1-crotyl-5-phenylthiouracil (9)
To a stirred MeCN (15 mL) solution of crotyluracil ana-
logue (8) (400 mg, 1.46 mmol), N,N-dimethylaminopyridine
(320 mg, 2.62 mmol) and i-Pr2NEt (608 mL, 3.50 mmol), ben-
zoyl chloride (302 mL, 2.62 mmol) was added and stirred for
1 h at room temperature under positive pressure of dry Ar.
This mixture was then extracted with CH2Cl2 and aq saturated
NaHCO3. The organic layer was dried over MgSO4, filtered,
and evaporated. The residue was purified by chromatography
on silica gel (petroleum ether/EtOAc¼1:2) to yield the desired
compound 9. Yield: 80% (440 mg) as an oil (1:3 of stereoiso-
4.12.2. N1-Crotyl-5-(4-fluorophenyl)-uracil (11b)
Yield: 66% (376 mg) as a solid (1:3 of stereoisomeric mix-
1
ture). H NMR (CDCl3) d: 1.73e1.80 (m, 3H, CH3), 4.35 (d,
2H, J¼6.3 Hz, UeCH2 major), 4.46 (d, 2H, J¼7.2 Hz, Ue
CH2 minor), 5.49e5.61 (m, 2H, CH]CH), 5.75e5.86 (m, 2H,
CH]CH), 7.02e7.11 (m, 2H, 4-FePh), 7.31 (s, 1H, H6),
7.45e7.53 (m, 2H, 4-FePh), 10.49 (br s, 1H, NH). 13C NMR
(CDCl3) d: 16.5, 48.5, 113.2, 113.1, 113.5, 123.0, 126.9,
128.6, 128.7, 131.0, 139.6, 148.9, 160.9, and 163.3. HRMS:
C14H13FN2O2 calcd for m/z 260.2673, found m/z 260.2675.
1
meric mixture). H NMR (CDCl3) d: 1.77 (dd, 3H, J¼0.6,
6.2 Hz, CH3), 4.32 (d, 2H, J¼6.6 Hz, UeCH2 major), 4.43 (d,
2H, J¼7.2 Hz, UeCH2 minor), 5.46e5.57 (m, 1H, CH]CH),
5.79e5.88 (m, 1H, CH]CH), 7.09e7.26 (m, 5H, Harom),
7.31e7.37 (m, 2H, Harom), 7.56e7.66 (m, 1H, Harom), 7.67
(s, 1H, H6), 7.87e7.90 (m, 2H, Harom). 13C NMR (CDCl3)
d: 13.4, 18.1, 45.0, 50.6, 107.9, 108.2, 122.7, 123.8, 127.5,
128.4, 129.5, 129.9, 130.5, 130.7, 131.5, 132.4, 133.9,
134.0, 135.4, 142.4, 147.7, 149.8, 161.0, and 168.6.
4.12.3. N1-Crotyl-5-(4-methoxyphenyl)-uracil (11c)
Yield: 56% (336 mg) as a solid (1:3 of stereoisomeric mix-
1
ture). H NMR (CDCl3) d: 1.73e1.80 (m, 3H, CH3), 3.82 (s,
3H, CH3eOePh), 4.35 (d, 2H, J¼6.3 Hz, UeCH2 major),
4.47 (d, 2H, J¼7.2 Hz, UeCH2 minor), 5.52e5.58 (m, 2H,
CH]CH), 5.76e5.85 (m, 2H, CH]CH), 6.94 (d, 2H,
J¼9.0 Hz, Harom), 7.24 (s, 1H, H6), 7.44 (d, 2H, J¼9.0 Hz,
4.11. N1-Crotyl-5-(tributyl)stannyluracil (10)
H
arom), 8.93 (br s, 1H, NH). 13C NMR (CDCl3) d: 17.0,
48.9, 54.6, 113.3, 114.4, 123.8, 128.6, 131.2, 139.4, 149.6,
158.8, and 163.8. HRMS: C15H16N2O3 calcd for m/z
272.3030, found m/z 272.3033.
A toluene (50 mL) solution of 8 (2.5 g, 9.11 mmol), tri-n-
butyltin hydride (3.68 mL, 13.67 mmol), AIBN (448 mg,

3522
H. Kumamoto et al. / Tetrahedron 64 (2008) 3517e3526
4.12.4. 5-Chloro-N1-crotyluracil (11e)
4.13.2. N3-Benzoyl-N1-crotyl-5-(4-fluorophenyl)-uracil (12b)
Yield: 87% (282 mg) as an oil (1:3 stereoisomeric mixture).
1H NMR (CDCl3) d: 1.77 (dd, 3H, J¼1.2, 6.2 Hz, CH3), 4.38
(d, 2H, J¼6.6 Hz, UeCH2 major), 4.51 (d, 2H, J¼7.2 Hz, Ue
CH2 minor), 5.49e5.64 (m, 1H, CH]CH), 5.79e5.94 (m,
1H, CH]CH), 7.03e7.11 (m, 2H, Harom), 7.39 (s, 1H, H6),
7.45e7.52 (m, 2H, Harom), 7.64 (m, 1H, Harom), 7.94e7.98
(m, 2H, Harom), 8.10e8.13 (m, 2H, Harom). 13C NMR
(CDCl3) d: 18.2, 50.5, 114.7, 115.7, 116.1, 123.2, 124.3,
128.1, 128.2, 128.9, 129.5, 130.2, 130.3, 130.6, 130.8,
131.9, 132.0, 133.3, 134.1, 135.5, 140.7, 140.8, 149.7,
161.1, 161.9, 165.0, 169.2, and 172.2.
A THF (10 ml) solution of 9 (1.0 g, 2.2 mmol) and NCS
(588 mg, 4.4 mmol) was refluxed for 24 h under positive
pressure of dry Ar. After evaporation of all of volatiles, this
was purified by chromatography on silica gel (petroleum
ether/AcOEt¼1:1). This gave 10e (360 mg, 81%) as a solid
1
(1:3 of stereoisomeric mixture). H NMR (CDCl3) d: 1.74e
1.79 (m, 3H, CH3), 4.28 (d, 2H, J¼7.5 Hz, UeCH2 major),
4.40 (d, 2H, J¼7.5 Hz, UeCH2 minor), 5.28e5.56 (m, 2H,
CH]CH), 5.73e5.93 (m, 2H, CH]CH), 7.39 (s, 1H,
H6minor), 7.49 (s, 1H, H6major), 11.43 (br s, 1H, NH). 13C
NMR (CDCl3) d: 16.0, 50.6, 106.4, 121.4, 130.4, 138.8,
148.6 and 158.2. HRMS: C8H9ClN2O2 calcd for m/z
200.6240, found m/z 200.6242.
4.13.3. N3-Benzoyl-N1-crotyl-5-(4-methoxyphenyl)-uracil (12c)
Yield: 74% (314 mg) as an oil (1:3 stereoisomeric mixture).
1H NMR (CDCl3) d: 1.76 (dd, 3H, J¼0.9, 6.2 Hz, CH3), 3.80
(s, 3H, OMe), 4.37 (d, 2H, J¼6.6 Hz, UeCH2 major), 4.49 (d,
2H, J¼6.9 Hz, UeCH2 minor), 5.52e5.63 (m, 1H, CH]CH),
5.78e5.87 (m, 1H, CH]CH), 6.88e6.94 (m, 2H, Harom), 7.36
(s, 1H, H6), 7.44e7.52 (m, 4H, Harom), 7.61e7.67 (m, 1H,
4.12.5. 5-Bromo-N1-crotyluracil (11f)
A THF (10 mL) solution of 9 (1.0 g, 2.2 mmol) and NBS
(508 mg, 2.86 mmol) was stirred for 1.5 h at room tempera-
ture under positive pressure of dry Ar. After extraction of
that between CH2Cl2 and H2O, the organic phase was dried
with MgSO4, filtrated, and evaporated. This was purified by
chromatography on silica gel (petroleum ether/EtOAc¼1:2).
This gave 10f (496 mg, 92%) as an oil (1:3 stereoisomeric
mixture). 1H NMR (CDCl3) d: 1.75e1.78 (m, 3H, CH3),
4.30 (d, 2H, J¼6.6 Hz, UeCH2 major), 4.42 (d, 1H,
J¼7.2 Hz, UeCH2 minor), 5.43e5.56 (m, 2H, CH]CH),
5.75e5.90 (m, 21H, CH]CH), 7.48 (s, 1H H6minor), 7.51
(s, 1H H6major), 8.96 (br s, 1H, NH). 13C NMR (CDCl3) d:
19.4, 51.5, 98.0, 124.1, 125.3, 134.7, 144.6, 151.6, and
160.8. HRMS: C8H9BrN2O2 calcd for m/z 245.0753, found
m/z 245.0757.
H
arom), 7.95e7.98 (m, 2H, Harom). 13C NMR (CDCl3) d: 20.3,
52.5, 57.8, 116.5, 117.4, 125.4, 126.5, 131.6, 132.9, 133.9,
134.1, 135.1, 137.4, 142.0, 142.2, 151.8, 162.1, 164.2, and171.5.
4.13.4. N3-Benzoyl-5-chloro-N1-crotyluracil (12e)
Yield: 93% (706 mg) as an oil (1:3 stereoisomeric mixture).
1H NMR (CDCl3) d: 1.77 (dd, 3H, J¼1.0, 6.6 Hz, CH3), 4.31
(d, 2H, J¼6.6 Hz, UeCH2 major), 4.44 (d, 2H, J¼7.5 Hz, Ue
CH2 minor), 5.37e5.58 (m, 1H, CH]CH), 5.79e5.96 (m,
1H, CH]CH), 7.45e7.53 (m, 2H, Harom), 7.50 (s, 1H, H6),
7.63e7.69 (m, 1H, Harom), 7.89e7.93 (m, 2H, Harom). 13C
NMR (CDCl3) d: 17.8, 50.3, 108.5, 119.5, 122.1, 123.4,
129.2, 130.5, 131.0, 132.3, 133.8, 135.3, 140.1, 140.2,
148.8, 158.3, and 167.6.
4.13. General procedure for N3-benzoylation of uracil
analogues
4.13.5. N3-Benzoyl-5-bromo-N1-crotyluracil (12f)
To a stirred MeCN (15 mL) solution of crotyluracil ana-
logue (428 mg, 1.75 mmol), N,N-dimethylaminopyridine
(320 mg, 2.62 mmol) and i-Pr2NEt (608 mL, 3.50 mmol), ben-
zoyl chloride (302 mL, 2.62 mmol) was added, and stirred for
1 h at room temperature under positive pressure of dry Ar.
This was extracted with CH2Cl2 and aq saturated NaHCO3.
The organic layer was dried with MgSO4, filtered, and evapo-
rated. The residue was purified by chromatography on silica
gel (petroleum ether/EtOAc¼1:2) to yield the desired
compound.
Yield: 63% (387 mg) as a solid (1:3 stereoisomeric mix-
ture). 1H NMR (CDCl3) d: 1.77 (dd, 3H, J¼1.2, 6.5 Hz,
CH3), 4.30 (d, 2H, J¼6.9 Hz, UeCH2 major), 4.44 (d, 2H,
J¼7.5 Hz, UeCH2 minor), 5.42e5.59 (m, 1H, CH]CH),
5.74e5.96 (m, 1H, CH]CH), 7.44e7.50 (m, 2H, Harom),
7.52e7.63 (m, 1H, Harom), 7.62 (s, 1H, H6), 7.75e7.78 (m,
2H, Harom). 13C NMR (CDCl3) d: 17.4, 17.5, 49.5, 49.9,
95.8, 95.9, 121.8, 122.2, 123.0, 123.3, 128.8, 130.1, 130.6,
131.4, 131.9, 132.6, 133.4, 134.9, 142.4, 142.5, 148.7,
149.6, 157.9, 158.8, and 167.3.
4.13.1. N3-Benzoyl -N1-crotyl-5-phenyluracil (12a)
4.14. General procedure for cross-metathesis with diethyl
vinyl phosphonate
Yield: 59% (279 mg) as an oil (1:3 stereoisomeric mixture).
1H NMR (CDCl3) d: 1.77 (dd, 3H, J¼1.2, 6.5 Hz, CH3), 4.37
(d, 2H, J¼6.4 Hz, UeCH2 major), 4.50 (d, 2H, J¼6.9 Hz, Ue
CH2 minor), 5.49e5.63 (m, 1H, CH]CH), 5.78e5.80 (m,
1H, CH]CH), 7.29e7.41 (m, 4H, Harom and H6), 7.49e
7.54 (m, 4H, Harom), 7.61e7.66 (m, 1H, Harom), 7.95e7.99
(m, 2H, Harom). 13C NMR (CDCl3) d: 20.4, 52.6, 117.7,
125.4, 126.5, 130.7, 131.1, 131.7, 133.0, 134.2, 134.3,
135.4, 137.5, 143.1, 143.2, 151.9, 164.1, and 171.6.
To a CH2Cl2 (10 mL) solution of N1-crotyl-5-substituted
uracil (300 mg, 1.03 mmol) and diethyl vinyl phosphonate
(635 mL, 4.1 mmol), (4) (42 mg, 0.05 mmol) was added.
This solution was refluxed for 22 h under positive pressure
of dry Ar. After evaporation of all volatiles, the residue was
purified by chromatography on silica gel (EtOAc/
MeOH¼15:1).

H. Kumamoto et al. / Tetrahedron 64 (2008) 3517e3526
3523
4.14.1. N1-[(E)-3-Diethoxyphosphinyl-2-propenyl]-5-phenyl-
uracil (13a)
(ddt, 1H, J¼4.7, 17.1, 21.6 Hz, CH]CH), 7.35 (s, 1H, H6),
9.44 (br s, 1H, NH). 13C NMR (CDCl3) d: 17.9, 18.0, 51.7,
63.9, 64.1, 111.2, 121.4, 124.4, 141.9, 145.3, 151.1, and
160.5. HRMS: C11H16ClN2O5P calcd for m/z 322.6842, found
m/z 322.6839.
Yield: 67% (222 mg) as a solid. 1H NMR (CDCl3) d: 1.31 (t,
6H, J¼7.3 Hz, eOCH2CH3), 4.07 (q, 2H, J¼7.3 Hz,
OCH2CH3), 4.12 (q, 2H, J¼7.3 Hz, OCH2CH3), 4.55e4.59
(m, 2H, UeCH2e), 5.85 (t, 1H, J¼16.9 Hz, CH]CH), 6.78
(ddt, 1H, J¼5.0, 16.9, 21.9 Hz, CH]CH), 7.23e7.50 (m, 6H,
H6 and Harom), 8.68 (br s, 1H, NH). 13C NMR (CDCl3) d:
15.2, 15.3, 48.9, 61.2, 61.4, 115.2, 118.4, 121.4, 127.1, 127.3,
127.6, 130.6, 139.7, 143.1, 143.2, 148.8, and 160.8. HRMS:
C17H21N2O5P calcd for m/z 364.3370, found m/z 364.3372.
4.14.6. 5-Bromo-N1-[(E)-3-diethoxyphosphinyl-
2-propenyl]uracil (13f)
Yield: 37% (302 mg) as a foam. 1H NMR (CDCl3) d: 1.33 (t,
6H, J¼7.2 Hz, eOCH2CH3), 4.09 (q, 2H, J¼7.2 Hz,
OCH2CH3), 4.12 (q, 2H, J¼7.2 Hz, OCH2CH3), 4.49e4.53 (m,
2H, UeCH2e), 5.84 (t, 1H, J¼17.0 Hz, CH]CH), 6.77 (ddt,
1H, J¼4.7, 17.0, 21.9 Hz, CH]CH), 7.46 (s, 1H, H6), 9.44 (br
s, 1H, NH). 13C NMR (CDCl3) d: 18.6, 18.7, 52.0, 52.4, 64.4,
64.6, 99.6, 122.0, 125.0, 145.2, 152.0, and 161.4. HRMS:
C11H16BrN2O5P calcd for m/z 367.1355, found m/z 367.1357.
4.14.2. N1-[(E)-3-Diethoxyphosphinyl-2-propenyl]-5-
(4-fluorophenyl)uracil (13b)
1
Yield: 71% (198 mg) as a foam. H NMR (CDCl3) d: 1.25
(t, 6H, J¼6.9 Hz, eOCH2CH3), 4.13 (m, 4H, eOCH2CH3),
4.54e4.58 (m, 2H, UeCH2e), 5.85 (t, 1H, J¼17.2 Hz,
CH]CH), 6.78 (ddt, 1H, J¼5.0, 17.2, 21.3 Hz,
CH]CH),7.03e7.12 (m, 2H, 4-FePh), 7.23 (s, 1H, H6),
7.43e7.49 (m, 2H, 4-FePh), 9.55 (br s, 1H, NH). 13C NMR
(CDCl3) d: 15.4, 15.5, 48.7, 61.3, 61.4, 114.9, 118.5, 121.5,
126.8, 126.9, 129.0, 139.8, 143.4, 143.5, 149.2, 159.8,
161.4, and 163.8. HRMS: C17H20FN2O5P calcd for m/z
382.3275, found m/z 382.3276.
4.15. General procedure for cross-metathesis with dimethyl
allyl phosphonate
A mixture of protected N1-crotyl-5-substituted uracil
(332 mg, 0.95 mmol), dimethyl allyl phosphonate (572 mg,
3.8 mmol), and (4) (41 mg, 0.05 mmol) in CH2Cl2 (10 mL)
was refluxed for 16 h under positive pressure of dry Ar. After
evaporation of all volatiles, the residue was purified by chro-
matography on silica gel (EtOAc/MeOH¼20:1) to yield the
desired compound.
4.14.3. N1-[(E)-3-Diethoxyphosphinyl-2-propenyl]-5-(4-
methoxyphenyl)uracil (13c)
1
Yield: 52% (135 mg) as a foam. H NMR (CDCl3) d: 1.32
(t, 6H, J¼7.2 Hz, eOCH2CH3), 3.83 (s, 3H, MeO), 4.08 (q,
2H, J¼7.2 Hz, OCH2CH3), 4.11 (q, 2H, J¼7.2 Hz,
OCH2CH3), 4.55 (m, 2H, UeCH2e), 5.84 (t, 1H,
J¼17.3 Hz, CH]CH), 6.77 (ddt, 1H, J¼5.0, 17.3, 22.0 Hz,
CH]CH), 6.92 (d, 2H, J¼8.8 Hz, Harom), 7.17 (1H, s, H6),
7.42 (d, 2H, J¼8.8 Hz, Harom), 8.80 (br s, 1H, NH). 13C
NMR (CDCl3) d: 17.9, 18.0, 57.0, 63.8, 63.9, 115.7, 117.6,
120.9, 123.9, 125.5, 127.5, 131.0, 141.5, 145.9, 146.0,
151.5, 161.3, and 163.8. HRMS: C18H23N2O6P calcd for m/z
394.3632, found m/z 394.3634.
4.15.1. N3-Benzoyl-N1-(4-dimethoxyphosphinyl-2-butenyl)-
5-phenyluracil (14a)
Yield: 94% (270 mg), as an oil. 1H NMR (CDCl3) d: 2.57e
2.83 (m, 2H, PeCH2e), 3.66e3.78 (m, 6H, P(OMe)2),
4.42e4.46 (m, 2H, UeCH2), 5.72e5.85 (m, 2H, CH]CH),
7.27e7.69 (m, 8H, Harom), 7.43 (s, 1H, H6), 7.95e7.99 (m,
2H, Harom). 13C NMR (CDCl3) d: 28.6, 30.8, 50.0, 53.1,
53.2, 115.8, 120.5, 126.5, 126.7, 128.5, 128.7, 128.8, 128.9,
129.0, 129.6, 131.9, 132.0, 135.5, 140.9, 141.5, 149.7,
161.9, and 169.3. HRMS: C23H23N2O6P calcd for m/z
454.4182, found m/z 454.4179.
4.14.4. N1-[(E)-3-Diethoxyphosphinyl-2-propenyl]-5-phenyl-
thiouracil (13d)
4.15.2. N3-Benzoyl-N1-(4-dimethoxyphosphinyl-2-butenyl)-
5-(4-fluorophenyl)uracil (14b)
1
Yield: 42% (111 mg) as a solid. H NMR (CDCl3) d: 1.33
(t, 6H, J¼7.2 Hz, eOCH2CH3), 4.06 (q, 2H, J¼7.2 Hz,
OCH2CH3), 4.09 (q, 2H, J¼7.2 Hz, OCH2CH3), 4.51e4.55
(m, 2H, UeCH2e), 5.80 (t, 1H, J¼17.3 Hz, CH]CH), 6.73
(ddt, 1H, J¼4.7, 17.3, 22.2 Hz, CH]CH), 7.15e7.28 (m,
5H, Harom), 7.63 (s, 1H, H6), 11.20 (br s, 1H, NH). 13C
NMR (CDCl3) d: 17.2, 17.3, 41.0, 62.9, 63.0, 108.3, 120.0,
127.6, 129.2, 130.0, 145.4, 149.5, 151.4, and 163.0. HRMS:
C17H21N2O5PS calcd for m/z 396.403, found m/z 396.4032.
Yield: 81% (199 mg) as an oil. 1H NMR (CDCl3) d: 2.61e
2.85 (m, 2H, PeCH2e), 3.67e3.77 (m, 6H, P(OMe)2),
4.43e4.47 (m, 2H, UeCH2), 5.70e5.81 (m, 2H, CH]CH),
7.03e7.11 (m, 2H, Harom), 7.41 (s, 1H, H6), 7.47e7.68 (m,
4H, Harom), 7.68e7.76 (m, 1H, Harom), 7.94e7.96 (2H, m,
Ph). 13C NMR (CDCl3) d: 29.3, 31.6, 50.9, 53.9, 54.0,
115.7, 116.5, 127.0, 127.4, 127.6, 128.8, 129.3, 129.5,
129.7, 130.4, 131.0, 131.2, 131.6, 132.6, 141.4, 150.4,
161.9, 162.6, and 169.9. HRMS: C23H22FN2O6P calcd for
m/z 472.4086, found m/z 472.4088.
4.14.5. 5-Chloro-N1-[(E)-3-diethoxyphosphinyl-2-propenyl]
uracil (13e)
1
Yield: 63% (260 mg) as a solid. H NMR (CDCl3) d: 1.34
4.15.3. N3-Benzoyl-N1-(4-dimethoxyphosphinyl-2-butenyl)-
5-(4-methoxyphenyl)uracil (14c)
Yield: 92% (320 mg) as an oil. 1H NMR (CDCl3) d: 2.58e
2.76 (m, 2H, PeCH2e), 3.67e3.74 (m, 6H, P(OMe)2), 3.80 (s,
(t, 6H, J¼7.1 Hz, eOCH2CH3), 4.08 (q, 2H, J¼7.1 Hz,
OCH2CH3), 4.12 (q, 2H, J¼7.1 Hz, OCH2CH3), 4.50e4.52
(m, 2H, UeCH2e), 5.83 (t, 1H, J¼17.1 Hz, CH]CH), 6.73

3524
H. Kumamoto et al. / Tetrahedron 64 (2008) 3517e3526
3H, MeO), 4.42e4.45 (m, 2H, UeCH2), 5.70e5.88 (m, 2H,
CH]CH), 6.89e6.92 (m, 2H, Harom), 7.37 (s, 1H, H6),
7.44e7.68 (m, 6H, Harom), 7.61e7.68 (m, 1H, Harom), 7.95e
7.98 (m, 2H, Harom). 13C NMR (CDCl3) d: 29.5, 31.7, 50.9,
54.0, 54.1, 56.7, 115.3, 116.5, 121.5, 125.2, 127.3, 127.5,
128.3, 129.6, 129.8, 130.5, 130.7, 131.8, 132.9, 136.3,
140.8, 150.6, 161.0, 163.0, and 170.3. HRMS: C24H25N2O7P
calcd for m/z 484.4444, found m/z 484.4449.
4.16.1. N1-[(E)-3-Dihydroxyphosphinyl-2-propenyl]5-
phenyluracil (15a)
Yield: 97% (162 mg) as a foam. 31P NMR (CD3OD) d:
15.60 (t, J¼19.8 Hz). 1H NMR (DMSO-d6) d: 4.50e4.52
(m, 2H, UeCH2e), 5.86 (t, 1H, J¼17.4 Hz, CH]CH), 6.53
(ddt, 1H, J¼4.4, 17.4, 22.9 Hz, CH]CH), 7.27e7.58 (m,
5H, Harom), 7.94 (s, 1H, H6), 11.56 (br s, 1H, NH). 13C
NMR (DMSO-d6) d: 47.9, 115.3, 124.7, 127.6, 129.4, 130.1,
130.2, 135.1, 145.2, 152.4 and 164.7. HRMS: C13H13N2O5P
calcd for m/z 308.2298, found m/z 308.2296.
4.15.4. N3-Benzoyl-N1-(4-dimethoxyphosphinyl-2-butenyl)-
5-phenylthiouracil (14d)
Yield: 74% (357 mg, oil) 1H NMR (CDCl3) d: 2.58e2.80 (m,
2H, PeCH2e), 3.73e3.79 (m, 6H, P(OMe)2), 4.37e4.41
(m, 2H, UeCH2), 5.66e5.88 (m, 2H, CH]CH), 7.19e7.32
(m, 5H, Harom), 7.45e7.51 (m, 2H, Harom), 7.61e7.64 (m, 1H,
4.16.2. N1-[(E)-3-Dihydroxyphosphinyl-2-propenyl]5-(4-
fluorophenyl)uracil (15b)
Yield: 97% (113 mg) as a foam. 31P NMR (CD3OD) d:
13.89 (t, J¼19.4 Hz). 1H NMR (DMSO-d6) d: 4.49e4.50
(m, 2H, UeCH2e), 5.79 (t, 1H, J¼17.2 Hz, CH]CH), 6.45
(ddt, 1H, J¼5.9, 17.2, 22.9 Hz, CH]CH), 7.19e7.26 (m,
2H, Harom), 7.58e7.64 (m, 2H, Harom), 7.95 (s, 1H, H6),
11.59 (br s, 1H, NH). 13C NMR (DMSO-d6) d: 47.3, 110.8,
113.5, 113.8, 121.3, 124.1, 128.0, 128.6, 128.7, 139.5,
141.8, 148.9, and 161.3. HRMS: C13H12FN2O5P calcd for
m/z 326.2203, found m/z 326.2205.
H
arom), 7.70 (s, 1H, H6), 7.87e7.94 (m, 2H, Harom). 13C NMR
(CDCl3) d: 26.6, 28.9, 48.3, 51.2, 51.3, 106.5, 125.3, 125.5,
125.8, 126.1, 126.3, 127.6, 127.7, 127.9, 128.0, 128.9, 129.6,
132.7, 133.6, 145.7, 147.9, 159.0, and 166.5. HRMS:
C23H23N2O6PS calcd for m/z 486.4842, found m/z 486.4843.
4.15.5. N3-Benzoyl-5-chloro-N1-(4-dimethoxyphosphinyl-2-
butenyl)uracil (14e)
Yield: 87% (668 mg) as an oil. 1H NMR (CDCl3) d: 2.58e
2.80 (m, 2H, PeCH2e), 3.69e3.81 (m, 6H, P(OMe)2),
4.35e4.39 (m, 2H, UeCH2), 5.65e5.92 (m, 2H, CH]CH),
7.48e7.54 (m, 2H, Harom), 7.55 (s, 1H, H6), 7.64e7.70 (m,
1H, Harom), 7.90e7.94 (m, 2H, Harom). 13C NMR (CDCl3) d:
28.7, 31.0, 50.4, 53.4, 53.6, 109.3, 125.1, 127.4, 127.9,
128.3, 129.8, 131.1, 131.5, 135.9, 140.7, 149.4, 158.7, and
168.1. HRMS: C17H18ClN2O6P calcd for m/z 412.7654, found
m/z 412.7657.
4.16.3. N1-[(E)-3-Dihydroxyphosphinyl-2-propenyl]5-
(4-methoxyphenyl)uracil (15c)
Yield: 95% (101 mg) as a foam. 31P NMR (CD3OD) d:
1
13.95 (t, J¼19.2 Hz). H NMR (DMSO-d6) d: 3.77 (s, 3H,
MeO), 4.48e4.49 (m, 2H, UeCH2e), 5.78 (t, 1H,
J¼17.0 Hz, CH]CH), 6.47 (ddt, 1H, J¼4.7, 17.0, 21.6 Hz,
CH]CH), 6.96 (d, 2H, J¼8.8 Hz, Harom), 7.50 (d, 2H,
J¼8.8 Hz, Harom), 7.84 (s, 1H, H6), 11.51 (br s, 1H, NH).
13C NMR (DMSO-d6) d: 47.9, 53.9, 111.7, 112.4, 121.4,
124.3, 127.9, 139.6, 139.7, 140.8, 149.0, 157.4, and 161.5.
HRMS: C14H15N2O6P calcd for m/z 338.2560, found m/z
338.2561.
4.15.6. N3-Benzoyl-5-bromo-N1-(4-dimethoxyphosphinyl-2-
butenyl)uracil (14f)
Yield: 74% (323 mg) as an oil. 1H NMR (CDCl3) d: 2.62e
2.80 (m, 2H, PeCH2e), 37.6e38.1 (m, 6H, P(OMe)2),
4.37e4.41 (m, 2H, UeCH2), 5.66e5.93 (m, 2H, CH]CH),
7.48e7.54 (m, 2H, Harom), 7.64 (s, 1H, H6), 7.64e7.70 (m,
1H, Harom), 7.90e8.00 (m, 2H, Harom). 13C NMR (CDCl3) d:
26.4, 28.6, 48.1, 51.0, 51.1, 94.7, 125.4, 125.6, 125.7, 125.9,
127.4, 128.8, 129.1, 133.5, 140.7, 147.2, 156.4, and 165.7.
HRMS: C17H18BrN2O6P calcd for m/z 452.2167, found m/z
452.2169.
4.16.4. N1-[(E)-3-Dihydroxyphosphinyl-2-propenyl]5-
phenylthiouracil (15d)
Yield: 88% (75 mg) as a foam. 31P NMR (CD3OD) d: 13.92
1
(t, J¼19.6 Hz). H NMR (DMSO-d6) d: 4.34e4.35 (m, 2H,
UeCH2e), 5.66 (t, 1H, J¼17.2 Hz, CH]CH), 6.29 (ddt,
1H, J¼4.7, 17.2, 21.6 Hz, CH]CH), 7.00e7.19 (m, 5H,
H
arom), 8.11 (s, 1H, H6), 11.58 (br s, 1H, NH). 13C NMR
(DMSO-d6) d: 47.9, 103.2, 123.1, 126.0, 126.6, 129.4,
136.8, 140.8, 140.9, 151.0, 152.4, and 162.3. HRMS:
C13H13N2O5PS calcd for m/z 340.2958, found m/z 340.2963.
4.16. General procedure for the deprotection of phosphonate
diesters
To a CH2Cl2 (15 mL) solution of phosphonate diester
(153 mg, 0.42 mmol), TMSBr (222 mL, 1.67 mmol) was added
and stirred for 60 h at room temperature under positive pres-
sure of dry Ar. MeOH (5 mL) was added and evaporated
with heating (ca. 60 ꢀC). MeOH (5 mL) was added again,
and this procedure was repeated three times. The residue
was extracted with deionized H2O (ELGAÒ Water) and
CH2Cl2, then the aqueous phase was evaporated to yield the
expected compound.
4.16.5. 5-Chloro-N1-[(E)-3-dihydroxyphosphinyl-2-
propenyl]uracil (15e)
Yield: 71% (275 mg) as a foam. 31P NMR (CD3OD) d:
13.83 (t, J¼18.6 Hz). 1H NMR (DMSO-d6) d: 4.40e4.41
(m, 2H, UeCH2e), 5.77 (t, 1H, J¼17.2 Hz, CH]CH), 6.39
(ddt, 1H, J¼4.7, 17.2, 21.9 Hz, CH]CH), 8.14 (s, 1H, H6),
11.87 (br s, 1H, NH). 13C NMR (DMSO-d6) d: 47.9, 109.6,
128.6, 140.0, 145.7, 152.9, and 162.5. HRMS: C7H8ClN2O5P
calcd for m/z 266.5770, found m/z 266.5771.

H. Kumamoto et al. / Tetrahedron 64 (2008) 3517e3526
3525
4.16.6. 5-Bromo-N1-[(E)-3-dihydroxyphosphinyl-2-
propenyl]uracil (15f)
4.16.11. 5-Chloro-N1-(4-dihydroxyphosphinyl-2-butenyl)-
uracil (16e)
Yield: >95% (130 mg) as a foam. 31P NMR (CD3OD) d:
13.77 (t, J¼18.6 Hz). 1H NMR (DMSO-d6) d: 4.40e4.41
(m, 2H, UeCH2e), 5.83 (t, 1H, J¼17.0 Hz, CH]CH), 6.40
(ddt, 1H, J¼4.4, 17.0, 21.0 Hz, CH]CH), 8.19 (s, 1H, H6),
11.80 (br s, 1H, NH). 13C NMR (DMSO-d6) d: 49.7, 96.0,
126.2, 141.4, 146.3, 151.5, and 160.5. HRMS: C7H8BrN2O5P
calcd for m/z 231.1243, found m/z 231.1246.
Yield: 96% (351 mg) as a foam. 31P NMR (CD3OD) d: 23.93.
1H NMR (CD3OD) d: 2.56e5.84 (m, 2H, PeCH2), 4.35e4.44
(m, 2H, UeCH2), 5.68e5.84 (m, 2H, CH]CH), 7.87 (s, 1H,
H6). 13C NMR (CD3OD) d: 27.9, 30.1, 32.2, 34.4, 51.5, 52.0,
109.5, 109.7, 128.1, 128.3, 128.6, 128.8, 129.5, 129.7, 130.0,
130.2, 144.5, 144.6, 152.7, and 162.7. HRMS: C8H10ClN2O5P
calcd for m/z 280.6038, found m/z 280.6032.
4.16.12. 5-Bromo-N1-(4-dihydroxyphosphinyl-2-butenyl)-
uracil (16f)
4.16.7. N1-(4-Dihydroxyphosphinyl-2-butenyl)-5-
phenyluracil (16a)
Yield: 92% (161 mg) as a foam. 31P NMR (CD3OD) d:
Yield: 81% (68 mg) as an oil. 31P NMR (CD3OD) d: 24.12.
1H NMR (DMSO-d6) d: 2.36e2.41 (m, 2H, PeCH2e), 4.35
(br s, 2H, UeCH2e), 5.65e5.76 (m, 2H, CH]CH), 7.29
(m, 1H, Harom),7.38 (m, 2H, Harom), 7.57 (m, 2H, Harom),
7.88 (s, 1H, H6), 11.48 (br s, 1H, NH). 13C NMR (DMSO-
d6) d: 30.9, 49.7, 114.8, 126.64, 128.0, 128.9, 129.3, 129.5,
134.1, and 143.0. HRMS: C14H15N2O5P calcd for m/z
340.2471, found m/z 340.2473.
1
24.31 (t, J¼21.0 Hz). H NMR (CD3OD) d: 2.59e2.66 (m,
2H, PeCH2), 4.37 (m, 2H, UeCH2), 5.69e5.83 (m, 2H,
CH]CH), 7.98 (s, 1H, H6), 11.65 (br s, 1H, NH). 13C
NMR (CD3OD) d: 33.0, 50.6, 96.6, 127.1, 129.4, 146.1,
152.1, 162.0. HRMS: C8H10BrN2O5P calcd for m/z
280.6038, found m/z 280.6032.
Acknowledgements
4.16.8. N1-(4-Dihydroxyphosphinyl-2-butenyl)-5-(4-
fluorophenyl)uracil (16b)
These studies were supported in part by a grant from Sa-
nofi-Aventis France (Sanofi-Aventis Group) and Bayer Pharma
as part of a multi-organism call for proposals, and in part by an
‘ANR-05-BLAN-0368-03’. S.P.N. acknowledges the ICIQ
Foundation and ICREA (Research Professorship) as well as
Yield: 63% (79 mg) as an oil. 31P NMR (CD3OD) d: 24.26.
1H NMR (DMSO-d6) d: 2.51e2.82 (m, 2H, PeCH2e), 4.47e
4.48 (m, 2H, UeCH2e), 4.56e4.57 (m, 2H, UeCH2e),
5.78e5.84 (m, 2H, CH]CH), 7.30e7.38 (m, 2H, Harom),
7.71e7.79 (m, 2H, Harom), 8.15 (s, 1H, H6), 11.65 (br s, 1H,
NH). 13C NMR (DMSO-d6) d: 31.0, 33.2, 50.8, 114.1,
116.9, 117.3, 128.7, 128.9, 129.6, 130.8, 132.0, 132.2,
145.0, 152.4, and 164.7. HRMS: C14H14FN2O5P calcd for
m/z 340.2471, found m/z 340.2473.
´
the Ministerio de Educacion y Ciencia for support.
References and notes
´
1. (a) Holy, A.; Votruba, I.; De Clercq, E. Collect. Czech. Chem. Commun.
1982, 47, 1392; (b) Holy, A.; Votruba, I.; Masojıdkova, A. G.; Snoeck,
´
´
´
R.; Neasens, L.; De Clercq, E.; Balzarini, J. J. Med. Chem. 2002, 45,
´
1918; (c) Holy, A. Nucleosides Nucleotides 1987, 6, 147; (d) Naesens,
L.; Snoeck, R.; Andrei, G.; Balzarini, J.; Neyts, J.; De Clercq, E. Antivir.
4.16.9. N1-(4-Dihydroxyphosphinyl-2-butenyl)-5-(4-
methoxyphenyl)uracil (16c)
´
Chem. Chemother. 1997, 8, 1; (e) Hockova, D.; Holy, A.; Holy, M.;
´
´
Andrei, G.; Snoeck, R.; De Clercq, E.; Balzarini, J. Bioorg. Med. Chem.
´
Yield: 70% (144 mg) as a foam. 31P NMR (CD3OD) d:
23.82. 1H NMR (CD3OD) d: 2.55e2.64 (m, 2H, PeCH2),
3.79 (s, 3H, OMe), 4.40e4.51 (m, 2H, UeCH2), 5.77e5.78
(m, 2H, CH]CH), 6.89e6.93 (m, 2H, Harom), 7.43e7.46
(m, 2H, Harom), 7.62 (s, 1H, H6). 13C NMR (CD3OD) d:
25.1, 48.9, 56.6, 115.6, 116.8, 127.0, 130.4, 130.5, 131.5,
143.9, 153.2, and 166.0. HRMS: C15H17N2O6P calcd for m/z
352.2828, found m/z 352.2830.
´
´
2004, 12, 3197; (f) Hockova, D.; Holy, A.; Holy, M.; Andrei, G.; Snoeck,
R.; De Clercq, E.; Balzarini, J. J. Med. Chem. 2003, 46, 5064; (g) Ying,
´
´
C.; Holy, A.; Hockova, D.; Havlas, Z.; De Clercq, E.; Neyts, J. Antimi-
crob. Agents Chemother. 2005, 49, 1177.
ꢀ
´
´
´
´
2. (a) Krecmerova, M.; Holy, A.; Pıskala, A.; Masojıdkova, M.; Andrei, G.;
Naesens, L.; Neyts, J.; Balzarini, J.; De Clercq, E.; Snoeck, R. J. Med.
´
Chem. 2007, 50, 1069; (b) Holy, A. Curr. Pharm. Des. 2003, 9, 2567;
´
(c) De Clercq, E. Antiviral Res. 2007, 75, 1; (d) Holy, A. Antiviral Res.
2006, 71, 248; (e) Ruiz, J. C.; Beadle, J. R.; Aldern, K. A.; Keith,
K. A.; Hartline, C. B.; Kern, E. R.; Hostetler, K. Y. Antiviral Res. 2007,
75, 87; (f) Ciesla, S. L.; Trahan, J.; Wan, W. B.; Beadle, J. R.; Aldern,
K. A.; Painter, G. R.; Hostetler, K. Y. Antiviral Res. 2003, 59, 163; (g)
4.16.10. N1-(4-Dihydroxyphosphinyl-2-butenyl)-5-
phenylthiouracil (16d)
´
Keith, K. A.; Hitchcock, M. J.; Lee, W. A.; Holy, A.; Kern, E. R. Antimi-
Yield: 54% (135 mg) as a foam. 31P NMR (CD3OD) d:
23.98 (t, J¼22.9 Hz). 1H NMR (DMSO-d6) d: 2.34e2.51
(m, 2H, PeCH2e), 4.32e4.33 (m, 2H, UeCH2e), 4.41e
4.42 (m, 2H, UeCH2e), 5.58e5.75 (m, 2H, CH]CH),
7.13e7.37 (m, 5H, Harom), 8.21 (s, 1H, H6), 11.65 (br s, 1H,
NH). 13C NMR (DMSO-d6) d: 33.3, 33.6, 51.2, 105.1,
128.0, 128.2, 129.2, 129.4, 129.9, 130.1, 131.6, 139.1,
153.2, 154.4, and 164.4. HRMS: C14H15N2O5PS calcd for
m/z 354.3226, found m/z 354.3229.
crob. Agents Chemother. 2003, 47, 2193; (h) Bindanset, D. J.; Beadle,
J. R.; Wan, W. B.; Hostetler, K. Y.; Kern, E. R. J. Virol. 2004, 190, 499.
3. (a) Arbuzov, B. A. Pure Appl. Chem. 1964, 9, 307; (b) Bhattacharya,
A. K.; Thyagarajan, G. Chem. Rev. 1981, 81, 415.
4. (a) Rowe, B. J.; Spilling, C. D. Tetrahedron: Asymmetry 2001, 12, 1701;
(b) Groaning, M. D.; Rowe, J.; Spilling, C. D. Tetrahedron Lett. 1998, 39,
5485.
5. (a) Hirao, T.; Masunaga, T.; Oshiro, Y.; Agawa, T. Tetrahedron Lett. 1980,
2, 3595; (b) Imamoto, T.; Oshiki, T.; Onazawa, T.; Kusumoto, T.; Sato, K.
J. Am. Chem. Soc. 1990, 112, 5244; (c) Zhao, C.-Q.; Han, L. B.; Tanaka,
M. Organometallics 2000, 19, 4196.

3526
H. Kumamoto et al. / Tetrahedron 64 (2008) 3517e3526
´ ˆ
´
6. (a) Jerome, F.; Monnier, F.; Lawicka, H.; Derien, S.; Dixneuf, P. H. Chem.
Commun. 2003, 696; (b) Zhao, C.-Q.; Han, L. B.; Goto, M.; Tanaka, M.
Angew. Chem., Int. Ed. 2001, 40, 1929; (c) Han, L.-B.; Zhao, C.-Q.;
Tanaka, M. J. Org. Chem. 2001, 66, 5929.
10. Hang, J.; Stevens, E. D.; Nolan, S. P.; Peterson, J. L. J. Am. Chem. Soc.
1999, 121, 8168.
11. (a) Hanson, P. R.; Stoianova, D. S. Tetrahedron Lett. 1998, 39, 3939; (b)
Hanson, P. R.; Stoianova, D. S. Tetrahedron Lett. 1999, 40, 3297; (d)
Bujard, M.; Gouverneur, V.; Mioskowski, C. J. Org. Chem. 1999, 64,
2119; (e) Schuman, M.; Trevitt, M.; Redd, A.; Gouverneur, V. Angew.
Chem., Int. Ed. 2000, 39, 2491.
7. (a) Amblard, F.; Nolan, S. P.; Agrofoglio, L. A. Tetrahedron 2005, 61,
7067; (b) Agrofoglio, L. A.; Nolan, S. P. Curr. Top. Med. Chem. 2005,
5, 1541; (c) Furstner, A. Angew. Chem., Int. Ed. 2000, 39, 3012; (d)
¨
Grubbs, R. H.; Miller, S. J.; Fu, G. C. Acc. Chem. Res. 1995, 28, 446;
(e) Dieters, A.; Martin, S. F. Chem. Rev. 2004, 104, 2199.
8. (a) Fu, G. C.; Grubbs, R. H. J. Am. Chem. Soc. 1992, 114, 5426; (b) Fu,
G. C.; Nguyen, S. T.; Grubbs, R. H. J. Am. Chem. Soc. 1993, 115, 9856;
(c) Scholl, M.; Trnka, T. M.; Morgan, J. P.; Grubbs, R. H. Tetrahedron
Lett. 1999, 40, 2247.
12. Chatterjee, A. K.; Choi, T.-L.; Sanders, D. P.; Grubbs, R. H. J. Am. Chem.
Soc. 2003, 125, 11360.
13. Cruickshank, K. A.; Jiricny, J.; Reese, C. B. Tetrahedron Lett. 1984, 25, 681.
14. Tanaka, H.; Hayakawa, H.; Obi, K.; Miyasaka, T. Tetrahedron 1986, 42,
4187.
15. Agrofoglio, L. A.; Gillaizeau, I.; Saito, Y. Chem. Rev. 2003, 103, 1875
(and references herein cited).
9. (a) Kingsbury, J. S.; Harrity, J. P. A.; Bonitatebus, P. J.; Hoveyda, A. H.
J. Am. Chem. Soc. 1999, 121, 791; (b) Harrity, J. P. A.; Visser, M. S.;
Gleason, J. D.; Hoveyda, A. H. J. Am. Chem. Soc. 1997, 119, 1488; (c)
Garber, S. B.; Kingsbury, J. S.; Gray, B. L.; Hoveyda, A. H. J. Am.
Chem. Soc. 2000, 122, 8168.
16. Topalis, D.; Kumamoto, H.; Amaya Velasco, M.-F.; Dugue, L.; Haouz, A.;
Alexandre, J. A. C.; Gallois-Montbrun, S.; Alzari, P. M.; Pochet, S.;
Agrofoglio, L. A.; Deville-Bonne, D. FEBS J. 2007, 274, 3704.
17. Malik, V.; Singh, P.; Kumar, S. Tetrahedron 2005, 61, 4009.