Synthesis of alkenyldiarylmethanes (ADAMs) containing benzo[d]isoxazole and oxazolidin-2-one rings, a new series of potent non-nucleoside HIV-1 reverse transcriptase inhibitors

Article abstract of DOI:10.1016/j.ejmech.2008.09.013

As a continuation of efforts to replace the metabolically labile methyl esters of lead alkenyldiarylmethanes (ADAMs) with stable bioisosteres, compounds bearing benzo[d]isoxazole and oxazolidine-2-one rings were designed and evaluated as a new series of p

Full text of DOI:10.1016/j.ejmech.2008.09.013

European Journal of Medicinal Chemistry 44 (2009) 1210–1214
Contents lists available at ScienceDirect
European Journal of Medicinal Chemistry
journal homepage: http://www.elsevier.com/locate/ejmech
Original article
Synthesis of alkenyldiarylmethanes (ADAMs) containing benzo[d]isoxazole
and oxazolidin-2-one rings, a new series of potent non-nucleoside HIV-1
reverse transcriptase inhibitors
Bo-Liang Deng a, Yujie Zhao a, Tracy L. Hartman b, Karen Watson b, Robert W. Buckheit, Jr. b,
,
Christophe Pannecouque c, Erik De Clercq c, Mark Cushman a
*
a Department of Medicinal Chemistry and Molecular Pharmacology, School of Pharmacy and Pharmaceutical Sciences, and the Purdue Cancer Center, Purdue University,
West Lafayette, IN 47907, USA
b ImQuest BioSciences, 7340 Executive Way, Suite R, Frederick, MD 21704, USA
c Rega Institute for Medical Research, Katholieke Universiteit Leuven, B-3000 Leuven, Belgium
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 10 March 2008
Received in revised form 3 September 2008
Accepted 4 September 2008
Available online 19 September 2008
As a continuation of efforts to replace the metabolically labile methyl esters of lead alkenyldiaryl-
methanes (ADAMs) with stable bioisosteres, compounds bearing benzo[d]isoxazole and oxazolidine-2-
one rings were designed and evaluated as a new series of potent HIV-1 non-nucleoside reverse
transcriptase inhibitors with anti-HIV activity. All of the resulting ADAMs were found to inhibit HIV-1 RT
with poly(rC)$oligo(dG) as the template primer. The most promising compound in this series was ADAM
3, with EC50 values of 40 nM (vs HIV-1RF) and 20 nM (vs HIV-1IIIB). Compound 3 also inhibited HIV-1
Keywords:
Alkenyldiarylmethanes (ADAMs)
Anti-HIV
Non-nucleoside reverse transcriptase
inhibitors (NNRTIs)
reverse transcriptase with an IC50 of 0.91
a plasma half-life of 51.4 min.
m
M. ADAM 4 has an antiviral EC50 of 0.6
mM in CEM-SS cells and
Ó 2008 Elsevier Masson SAS. All rights reserved.
1. Introduction
The alkenyldiarylmethanes (ADAMs) are a unique class of potent
and highly specific HIV NNRTIs [4–15]. Certain ADAMs have been
found to inhibit the cytopathic effect of HIV-1 in cell culture at low
nanomolar concentrations. In addition, some of the ADAMs have
displayed synergistic activity with AZT and have shown enhanced
activity when tested against AZT-resistant strains of HIV-1 [5].
Unfortunately, most of the ADAMs are too unstable toward
hydrolysis in blood plasma to be interesting as possible therapeutic
candidates [12]. Therefore, one of the current research objectives is
to optimize the ADAMs by replacing the metabolically unstable
methyl ester moieties with stable isosteres while maintaining the
antiviral potency.
Human immunodeficiency virus type 1 (HIV-1) is the etiological
agent of acquired immunodeficiency syndrome (AIDS), one of the
world’s most serious health problems with about 33 million people
infected worldwide in 2007. The reverse transcriptase (RT) of HIV-1
is an essential enzyme in HIV replication and has been a key target
in anti-AIDS drug discovery. The non-nucleoside reverse tran-
scriptase inhibitors (NNRTIs) nevirapine, delavirdine, and efavirenz
have been approved by the Food and Drug Administration (FDA) for
the treatment of AIDS [1]. They are very useful drugs in combina-
tion therapy with nucleoside analogues (NRTIs) and protease
inhibitors (PIs) [2,3] for the treatment of AIDS. However, a number
of problems still remain with these agents. In particular, significant
resistance has developed against these drugs. Therefore, consider-
able effort has been expended to develop new NNRTIs that would
overcome the current drug resistance. More than 30 structurally
different classes of molecules have been reported as NNRTIs [1–3].
Recently, the NNRTI etravirine was approved by the FDA for treat-
ment of antiretroviral drug-resistant HIV infections.
Recently, we synthesized ADAM
1 bearing a 3-fluoro-5-
trifluoromethylphenyl group and a benzo[d]isoxazole ring, which
was inactive as an inhibitor of the cytopathic effect of HIV-1RF in
CEM-SS cells and HIV-1IIIB in MT-4 cells [13]. However, replacement
of the 3-fluoro-5-trifluoromethylphenyl group in compound 1 with
an N-methyl benzoxazolone ring resulted in ADAM 2, which dis-
played significant antiviral activity but was unstable in rat blood
plasma [14]. Compound 2 inhibited the cytopathic effects of two
strains of HIV-1 (RF and IIIB) in cell cultures with values EC50 of
260 nM (vs HIV-1RF in CEM-SS cells) and 330 nM (vs HIV-1IIIB in MT-
4 cells), and it also inhibited HIV-1 reverse transcriptase with an IC50
of 250 nM. Encouraged by the strong anti-HIV activity of compound
* Corresponding author. Tel.: þ1 765 494 1465; fax: þ1 765 494 6790.
E-mail address: cushman@pharmacy.purdue.edu (M. Cushman).
0223-5234/$ – see front matter Ó 2008 Elsevier Masson SAS. All rights reserved.
doi:10.1016/j.ejmech.2008.09.013

B.-L. Deng et al. / European Journal of Medicinal Chemistry 44 (2009) 1210–1214
1211
2, a new series of ADAMs bearing a benzo[d]isoxazole ring were
designed and synthesized to investigate the structure–activity
relationships of ADAMs. First of all, it was hypothesized that
compound 3, having a methyl ester on the aryl ring, would possess
anti-HIV activity. Compound 4, in which the methyl ester moiety in
the side chain of the ADAM 3 is replaced with an oxazolidin-2-one
group, might have greater stability to plasma esterases. It is estab-
lished that the stereochemistry of the alkene in the ADAM system
has a strong influence on the anti-HIV activity [15]. Therefore,
compound 5, an isomeric analogue of compound 4, was also
considered. Incorporation of halogens in the inhibitors has been
shown in various examples to result in biologically active RT inhib-
itors [13,15,16]. Accordingly, the replacement of the methyl group in
compound 5 with a chlorine atom, as shown in compound 6, was
also planned. It would also be very interesting to synthesize ADAM
analogue 7, having two identical benzo[d]isoxazole rings. A number
of ADAM analogues incorporating an N-methyl benzoxazolone ring
inhibit HIV-1 RT with submicromolar IC50 values and exhibit anti-
HIV-1 activity in low micromolar to submicromolar concentration
ranges in cellular assays [14]. Therefore, replacement of the methyl
ester moiety of compound 5 with an N-methyl benzoxazolone ring,
as shown in compound 8, was also considered. ADAMs having
a cyanophenyl trans to the side chain generally retain or increase the
inhibitory activity [13]. ADAM 9, having a cyanophenyl trans to the
side chain, was therefore synthesized (Fig. 1).
2. Chemistry
The syntheses of these compounds were accomplished via the
Stille cross-coupling of an arylstannane with an aryl iodide or
bromide in the presence of Pd(PBut3)2 and CsF in toluene at reflux
temperature (Scheme 1). This method is a general and practical one
to synthesize alkenyldiarylmethanes having non-identical aromatic
substituents and has been used to synthesize number of ADAM
analogues [13–15]. The key intermediate, 5-iodo-3-methoxy-7-
methylbenzo[d]isoxazole (12), was prepared in a multi-step fashion
from 3-methyl salicyclic acid (10) via methyl 2-hydroxy-5-iodo-3-
methylbenzoate (11) as described previously [13]. The syntheses of
CH3
CH3
CH3
R1
R2
R3
O
O
O
N
N
N
O
CH3
CH3
CH3
OH
OH
O
OCH3
OCH3
CH3
N
I
I
COOCH3
COOH
OCH3
10
12
11
H3CO
O
H3CO
O
1: R1 = F; R2 = H; R3 = CF3
3: R1 = CH3; R2 = OCH3;
R3 = COOCH3
2
CH3
CH3
H3CO
H3COOC
H3CO
H3COOC
SnBu3
CH3
CH3
SnBu3
H3CO
O
N
O
H3COOC
N
OCH3
CH3
13
O
14
H3CO
O
O
O
O
N
N
3
4
a
a
I
4
OCH3
12
R1
CH3
b, c
R2
R3
O
5: R1 = CH3; R2 = OCH3;
N
CH3
CN
R3 = COOCH3
H3CO
H3COOC
5
6: R1 = C1; R2 = OCH3;
CH3
OCH3
R
3 = COOCH3
O
I
9: R1 = CN; R2 = R3 = H
Br
N
N
Bu3Sn
16
19
9
O
OCH3
a
a
O
CH3
CH3
CH3
CH3
CH3
Cl
N
O
O
N
H3CO
O
O
N
O
O
O
N
O
OCH3
N
O
N
15
I
H3COOC
I
H3C
OCH3
CH3
17
OCH3
18
a
12
a
a
N
N
8
6
7
O
O
O
O
Scheme 1. Reagents and conditions: (a) Pd(PBut3)2, CsF, toluene, reflux; (b) 3-but-3-
ynyl-1,3-oxazolidin-2-one, PdCl2(PPh3)2, Cu(I)I, Et3N, THF; (c) Bu3SnH, Pd(PPh3)4, THF,
room temperature.
8
7
Fig. 1. Structures of ADAMs non-nucleoside reverse transcriptase inhibitors.

1212
B.-L. Deng et al. / European Journal of Medicinal Chemistry 44 (2009) 1210–1214
aryl stannanes 13–15 and aryl iodides 16–18 have also been
reported previously [13,15]. Compounds 3 and 4 were synthesized
from the same iodide 12 with different vinylstannanes 13 and 14 by
the Stille cross-coupling reaction in the presence of Pd(PBut3)2 and
CsF in toluene at reflux temperature. The same reaction conditions
were employed to synthesize ADAMs 5–9.
4. Conclusion
A series of alkenyldiarylmethanes (ADAMs) with a benzo[d]i-
soxazole ring in place of a metabolically unstable methyl ester
moiety and an adjacent methoxyl group were synthesized using
the Stille cross-coupling of a vinylstannane with an aryl halide. The
anti-HIV activities and metabolic stabilities of these compounds
were investigated. All of the resulting ADAMs were found to inhibit
HIV-1 RT with poly(rC)$oligo(dG) as the template primer. Among
these, ADAM 3 also exhibited anti-HIV-1 activity with EC50 values
in the 20–40 nanomolar range. These initial results indicate that the
benzo[d]isoxazole ring is an effective bioisosteric replacement of
the metabolically labile methyl ester moiety in ADAMs. The
replacement of methyl esters with fused benzo[d]isoxazole and
oxazolidine-2-one rings could prove to be generally useful in
situations that require alternatives to hydrolytically unstable
methyl esters.
3. Biological results and discussion
The cytotoxicities of the newly synthesized ADAMs were
determined along with their abilities to inhibit the cytopathic
effect of HIV-1 in cell culture. The inhibition of HIV-1 RT by the
ADAMs, and their metabolic stabilities in rat plasma were also
investigated. The data are shown in Table 1. Five of the nine
ADAMs (compounds 1–4 and 7) were found to inhibit HIV-1 RT
with poly(rC)$oligo(dG) as the template primer with IC50 values
ranging from 0.25 to 0.93
values from 3.60 to 39.2
m
M. The others had intermediate IC50
m
M. Only compounds 2–4 inhibited the
cytopathic effect of the virus at concentrations that were not
cytotoxic. ADAM 3 was the most promising compound, and
exhibited very potent inhibitory activity against the cytopathic
effect of HIV-1 with EC50 values of 40 nM (vs HIV-1RF in CEM-SS
cells) and 20 nM (vs HIV-1IIIB in MT-4 cells) [17]. The EC50 of
5. Experimental
Melting points were obtained in capillary tubes and are uncor-
rected. NMR spectra were obtained at 300 MHz (1H) and 75 MHz
(
13C) in CDCl3 using CHCl3 as the internal standard. IR spectra were
compound
3 was lower than the IC50. In this case, the
recorded using a Perkin–Elmer 1600 series FT-IR. Electrospray mass
spectra were obtained using a FinniganMATT LCQ (Thermoquest
Corp., San Jose, CA) instrument at the Purdue Campus-Wide Mass
Spectrometry Center. Microanalyses were performed at the Purdue
University Microanalysis Laboratory. All yields given refer to iso-
lated yields. Flash chromatography was performed with 230–400
mesh silica gel. TLC was carried out using Baker-flex silica gel IB2-F
plates of a 2.5 mm thickness. Unless otherwise stated, chemicals
and solvents were of reagent grade and used as obtained from
commercial sources without further purification. Lyophilized rat
plasma (lot 052K7609) was obtained from Sigma Chemical Co., St.
Louis, MO.
discrepancy may simply reflect the differences between the in
vitro enzymatic assay, which uses a synthetic template/primer,
and the cellular system, in which natural template/primers are
utilized by RT [17]. Although the replacement of the metaboli-
cally unstable methyl ester moieties in the ADAM system with
metabolically stable bioisoteres led to several very stable
compounds, such as ADAMs 7–9, they turned out to be inactive
as antiviral agents. However, active compound 4 (EC50 ¼ 0.6
mM)
had improved stability relative to ADAMs 1–3 in rat plasma with
a half-life value of 51.4 min. Replacement of the side chain in
compound
3
(EC50 ¼ 40 nM) with an oxazolidinonyl group
afforded compound 4 (EC50 ¼ 600 nM) with a significant drop in
antiviral potency. These results suggest further modification of
the side chain of the ADAMs with other methyl esters bio-
isosteres [18–20].
5.1. General procedure for the synthesis of alkenyldiarylmethanes
by the Stille cross-coupling reaction of vinylstannanes with aromatic
iodides or bromides
The ADAMs 1–4, having the alkenyl side chain trans to the
benzo[d]isoxazole ring, were submicromolar inhibitors of HIV-1 RT,
while those with a cis relationship (ADAMs 5, 6, 8 and 9) were much
less active. This structure–activity trend carried over to their anti-
viral activities as well. ADAM 7, having benzy[d]isoxazole rings both
cis and trans to the alkenyl side chain, was active as an RT inhibitor
but was inactive as an antiviral agent.
A mixture of vinylstannane (1 equiv), aryl halide (1.2–1.5 equiv),
cesium fluoride (3.0–4.5 equiv), and Pd(PBut3)2 (w10 mol%) in
toluene (1 mL) was stirred under argon at different temperatures
for various periods of time. The reaction mixture was cooled to
room temperature, filtered through a short column of silica gel
Table 1
Anti-HIV activities, cytotoxicities, and metabolic stabilities of ADAM analogues
TId
Rat plasma, t1/2 (min ꢀ SD)
a
b
c
Compound
IC50
(m
M)
EC50
(m
M)
CC50
(m
M)
HIV-1RF
HIV-1IIIB
HIV-2ROD
CEM-SS
MT-4
CEM-SS
MT-4
1
2
3
4
5
6
7
8
0.90
0.25
0.91
0.63
>2.1
0.26
0.04
0.6
>1.88
>8.25
>1.85
>2.99
>0.91
>5.76
0.33
0.02
>5.76
>7.26
>1.09
>1.1d
>3.79
>4.73
>1.86
>9.54
NTe
2.1
2.08
0.5
5.76
7.26
1.09
>1.1
3.79
4.73
1.86
9.54
NTe
<1
8
12.5
2
<1
<1
<1
<1
<1
<1
22
54.5
<1
<1
4.26 ꢀ 0.13
1.58 ꢀ 0.13
3.46 ꢀ 0.31
51.4 ꢀ 1.52
2.96 ꢀ 0.01
NTe
>1.1
1.2
18.2
>3.79
>4.73
>1.86
>9.54
NTe
1.88
8.25
1.85
2.99
0.91
5.88
0.93
3.6
<1
<1
>1440
>1440
<1
9
39.2
NTe
>800
>1440
Nevirapine [21]
0.25
NTe
>200
NTe
a
Inhibitory activity vs HIV-1 reverse transcriptase with poly(rC)$oligo(dG) as the template primer.
b
c
EC50 is the 50% inhibitory concentration for inhibition of cytopathicity of HIV-1RF in CEM-SS cells, and HIV-1IIIB or HIV-2ROD in MT-4 cells.
The CC50 is the 50% cytotoxic concentration for mock-infected CEM-SS cells or MT-4 cells.
TI: therapeutic index, ratio CC50/EC50.
d
e
Not tested. All data represent mean values for at least two separate experiments.

B.-L. Deng et al. / European Journal of Medicinal Chemistry 44 (2009) 1210–1214
1213
(5 g), and the column was washed with ethyl acetate. The organic
solution was concentrated.
764 cmꢂ1
;
1H NMR
d
7.37 (d, J ¼ 2.4 Hz, 1H), 7.22 (s, 1H), 7.13
(d, J ¼ 2.4 Hz, 1H), 7.04 (s, 1H), 5.99 (t, J ¼ 7.5 Hz, 1H), 4.23
(t, J ¼ 7.5 Hz, 2H), 4.15 (s, 3H), 3.85 (s, 3H), 3.78 (s, 3H), 3.35
(t, J ¼ 6.9 Hz, 2H), 3.31 (t, J ¼ 7.5 Hz, 2H), 2.48 (s, 3H), 2.34 (dt,
5.1.1. (Z)-2-Methoxy-5-[5-methoxycarbonyl-1-(3-methoxy-7-
methylbenzo[d]isoxazol-5-yl)-pent-1-enyl]-3-methylbenzoic
acid methyl ester (3)
J ¼ 6.9 Hz and 7.5 Hz, 2H), 2.24 (s, 3H); 13C NMR
d 167.14, 166.76,
162.47, 158.29, 157.47, 142.07, 137.51, 134.55, 133.69, 132.44,
130.50, 127.62, 125.97, 124.20, 121.03, 118.71, 113.65, 61.47, 61.37,
57.27, 52.09, 44.24, 43.82, 27.81, 16.02, 14.58; ESIMS m/z (rel
intensity) 480.75 (MHþ, 100). Anal. Calcd for C26H28N2O7: C,
64.99; H, 5.87; N, 25.83. Found: C, 65.24; H, 5.92; N, 5.59.
The general procedure was followed using methyl 6-(tributyl-
stannyl)-6-[4-methoxy-5-methoxycarbonyl-3-methylphenyl]-hex-
5-enoate (13) (349 mg, 0.59 mmol), 5-iodo-3-methoxy-7-methyl-
benzo[d]isoxazole (12) (253 mg, 0.88 mmol), cesium fluoride
(320 mg, 2.09 mmol), and Pd(PBut3)2 (39 mg, 0.08 mmol). The
mixture was stirred at room temperature for 5 h, at 60 ꢁC for 16 h,
at 80 ꢁC for 8 h, and at 110 ꢁC for 16.5 h. The residue was purified by
column chromatography on silica gel (15 g), eluting with EtOAc–
hexanes (0–10%), to afford the product 3 (91 mg) as an oil in 33%
yield. IR (KBr) 2950, 1732, 1548, 1496, 1436, 1395, 1318, 1255, 1203,
5.1.4. (E)-3-Chloro-2-methoxy-5-[1-(3-methoxy-7-methyl-
benzo[d]isoxazol-5-yl)-4-(2-ox-oxazolidin-3-yl)-but-1-enyl]-
benzoic acid methyl ester (6)
The general procedure was followed using the vinylstannane 15
(385 mg, 0.65 mmol), 3-chloro-5-iodo-2-methoxybenzoic acid
methyl ester (17) (266 mg, 0.82 mmol), cesium fluoride (410 mg,
2.67 mmol), and Pd(PBut3)2 (33 mg, 0.06 mmol). The mixture was
stirred under argon at room temperature for 25 h, at 65 ꢁC for 24 h,
and at 100 ꢁC for 6 h. The residue was purified by column chroma-
tography on silica gel (20 g), eluting with EtOAc–hexanes (0–50%), to
afford the product 6 (225 mg) as a white foam in 69% yield: mp 59–
60 ꢁC. IR (KBr) 2946, 1749, 1616, 1548, 1498, 1476, 1425, 1316, 1263,
1141, 1009, 910, 765 cmꢂ1
;
1H NMR
d
7.41 (d, J ¼ 2.1 Hz, 1H), 7.18
(broad singlet, 1H), 7.16 (broad singlet, 1H), 7.10 (broad singlet, 1H),
5.97 (t, J ¼ 7.4 Hz, 1H), 4.13 (s, 3H), 3.89 (s, 3H), 3.86 (s, 3H), 3.61 (s,
3H), 2.45 (s, 3H), 2.31 (s, 3H), 2.34–2.29 (m, 2H), 2.18–2.11 (dt,
J ¼ 7.4 Hz, 2H), 1.83–1.73 (pentet, J ¼ 7.4 Hz, 2H); 13C NMR
d 173.83,
167.32, 166.73, 162.64, 157.40, 140.64, 138.41, 136.28, 135.11, 132.76,
130.46, 130.25, 129.54, 124.31, 120.38, 116.56, 113.54, 61.49, 57.26,
52.16, 51.46, 33.43, 29.12, 24.99, 16.13, 14.65; ESIMS m/z (rel
intensity) 467.99 (MHþ, 100). Anal. Calcd for C26H29NO7: C, 66.80;
H, 6.25; N, 3.00. Found: C, 66.52; H, 6.32; N, 3.05.
1206, 1096, 1043, 998, 911, 765, 733, 663 cmꢂ1 1H NMR
; d 7.46 (d,
J ¼ 2.4 Hz, 1H), 7.30 (t, J ¼ 2.4 Hz, 1H), 7.21 (s, 1H), 7.03 (s, 1H), 6.03 (t,
J ¼ 7.5 Hz,1H), 4.22 (t, J ¼ 7.8 Hz, 2H), 4.13 (s, 3H), 3.90 (s, 3H), 3.86 (s,
3H), 3.35 (t, J ¼ 6.9 Hz, 2H), 3.31 (t, J ¼ 7.8 Hz, 2H), 2.49 (s, 3H), 2.35
(dt, J ¼ 6.9 Hz and 7.5 Hz, 2H); ESIMS m/z (rel intensity) 522.82/
524.78 (MNaþ, 100/32). Anal. Calcd for C25H25ClN2O7: C, 59.84; H,
5.03; N, 5.59, Cl, 7.08. Found: C, 59.86; H, 5.23; N, 5.70, Cl, 7.01.
5.1.2. (Z)-2-Methoxy-5-[1-(3-methoxy-7-methylbenzo[d]isoxazol-
5-yl)-4-(2-oxo-oxazolidin-3-yl)-but-1-enyl]-3-methyl-benzoic acid
methyl ester (4)
The general procedure was followed using 1-(tributylstannanyl)-
2-methoxy-3-methyl-5-[4-(2-oxo-oxazolidin-3-yl)-but-1-enyl] ben-
zoic acid methyl ester (14) (329 mg, 0.54 mmol), 5-iodo-3-methoxy-
7-methylbenzo[d]isoxazole (12) (232 mg, 0.80 mmol), cesium
fluoride (320 mg, 2.09 mmol), and Pd(PBut3)2 (28 mg, 0.05 mmol).
The mixture was stirred at room temperature for 22.5 h, at 60 ꢁC for
29 h, and at 110 ꢁC for 19.5 h. The residue was purified by column
chromatography on silica gel (30 g), eluting with EtOAc–hexanes (0–
50%) to afford the product 4 (161 mg) as a foam in 62% yield: mp 53–
54 ꢁC. IR (KBr) 2947, 1755, 1729, 1614, 1548, 1495, 1435, 1396, 1318,
5.1.5. 3-[4,4-Bis-(3-methoxy-7-methyl-benzo[d]isoxazol-5-yl)-but-
3-enyl]-oxazolidin-2-one (7)
The general procedure was followed using the vinylstannane 15
(392 mg, 0.66 mmol), 5-iodo-3-methoxy-7-methylbenzo[d]isox-
azole (12) (243 mg, 0.84 mmol), cesium fluoride (350 mg,
2.28 mmol), and Pd(PBut3)2 (38 mg, 0.07 mmol) in toluene (1 mL).
The mixture was stirred under argon at room temperature for 23 h,
at 65 ꢁC for 24 h, and at 110 ꢁC for 23 h. The residue was purified by
column chromatography on silica gel (20 g), eluting with EtOAc–
hexanes (0–50%), to afford the product 7 (51 mg) as an oil in 17%
yield. IR (KBr) 2942, 1750, 1614, 1548, 1497, 1425, 1387, 1354, 1315,
1267, 1225, 1105, 1043, 954, 911, 764, 732, 695, 642 cmꢂ1; 1H NMR
1263,1229,1204,1146,1121,1044,1009, 911, 800, 763, 732, 686 cmꢂ1
1H NMR
;
d
7.36 (d, J ¼ 1.2 Hz, 1H), 7.15 (broad singlet, 1H), 7.10 (broad
singlet, 1H), 7.07 (d, J ¼ 1.2 Hz, 1H), 5.92 (t, J ¼ 7.5 Hz, 1H), 4.19 (t,
J ¼ 7.8 Hz, 2H), 4.05 (s, 3H), 3.83 (s, 3H), 3.82 (s, 3H), 3.33 (t, J ¼ 6.6 Hz,
2H), 3.30 (t, J ¼ 7.8 Hz, 2H), 2.38 (s, 3H), 2.34 (dt, J ¼ 7.5 Hz and 6.6 Hz,
d
7.24 (s, 1H), 7.18 (s, 1H), 7.12 (s, 1H), 7.05 (s, 1H), 6.01 (t, J ¼ 7.2 Hz,
1H), 4.22 (t, J ¼ 7.8 Hz, 2H), 4.12 (s, 3 H), 4.07 (s, 3H), 3.37 (t,
J ¼ 6.9 Hz, 2H), 3.29 (t, J ¼ 7.8 Hz, 2H), 2.47 (s, 3H), 2.42 (s, 3H), 2.36
2H), 2.26 (s, 3H); 13C NMR
d 167.17, 166.50, 162.50, 158.32, 157.40,
142.08, 137.92, 136.03, 134.77, 132.90, 130.45, 129.89, 126.06, 124.34,
120.35, 116.72, 113.41, 61.43, 57.10, 52.09, 44.16, 43.75, 27.79, 16.00,
14.51;ESIMSm/z (rel intensity)481.01 (MHþ,100), 503.12 (MNaþ, 55).
Anal. Calcd for C26H28N2O7: C, 64.99; H, 5.87; N, 5.83. Found: C, 64.91;
H, 5.97; N, 5.60.
(dt, J ¼ 6.9 Hz and 7.2 Hz, 2H); 13C NMR
d 167.27, 167.16, 162.68,
162.50, 158.35, 142.58, 138.20, 135.03, 132.48, 130.45, 126.00, 121.11,
120.48, 118.77, 116.79, 113.70, 113.52, 61.49, 57.32, 57.18, 44.20,
43.84, 27.84, 14.61; ESIMS m/z (rel intensity) 486.18 (MNaþ, 31),
464.16 (MHþ, 29). Anal. Calcd for C25H25N3O6: C, 67.79; H, 5.44; N,
9.07. Found: C, 64.40; H, 5.52; N, 8.80.
5.1.3. (E)-2-Methoxy-5-[1-(3-methoxy-7-methylbenzo[d]isoxazol-
5-yl)-4-(2-ox-oxazolidin-3-yl)-but-1-enyl]-3-methylbenzoic acid
methyl ester (5)
5.1.6. (E)-5-[1-(3-Methoxy-7-methylbenzo[d]isoxazol-5-yl)-4-(2-
ox-oxazolidin-3-yl)-but-1-enyl]-3,7-dimethyl-3H-
The general procedure was followed using 3-[4-(tributyl-
stannanyl)-4-(3-methoxy-7-methylbenzo[d]isoxazol-5-yl)-but-3-
enyl]-oxazolidin-2-one (15) (404 mg, 0.68 mmol), 5-iodo-2-
methoxy-3-methylbenzoic acid methyl ester (16) (265 mg,
0.87 mmol), cesium fluoride (324 mg, 2.11 mmol), and Pd(PBut3)2
(42 mg, 0.05 mmol). The mixture was stirred at room tempera-
ture for 23 h, at 60 ꢁC for 24 h, and at 110 ꢁC for 23 h. The residue
was purified by column chromatography on silica gel (20 g),
eluting with EtOAc–hexanes (0–50%), to afford the product 5
(81 mg) as an oil in 25% yield. IR (KBr) 2946, 1752, 1727, 1615,
1548, 1498, 1425, 1317, 1266, 1208, 1142, 1043, 1007, 910,
benzoxazol-2-one (8)
The general procedure was followed using the vinylstannane 15
(390 mg, 0.66 mmol), 5-iodo-3,7-dimethyl-3H-benzoxazol-2-one
(18) (229 mg, 0.79 mmol), cesium fluoride (355 mg, 2.31 mmol),
and Pd(PBut3)2 (35 mg, 0.07 mmol) in toluene (1 mL). The mixture
was stirred under argon at room temperature for 21 h, at 60 ꢁC for
24 h, and at 110 ꢁC for 25 h. The residue was purified by column
chromatography on silica gel (20 g), eluting with EtOAc–hexanes
(0–50%), to afford the product 8 (140 mg) as a solid in 46% yield; mp
187–188 ꢁC. IR (KBr) 2925, 1775, 1618, 1548, 1496, 1448, 1426, 1359,
1333, 1305, 1267, 1226, 1153, 1104, 1065, 1043, 973, 955, 912,

1214
B.-L. Deng et al. / European Journal of Medicinal Chemistry 44 (2009) 1210–1214
881 cmꢂ1
;
1H NMR
d
7.23 (s, 1H), 7.05 (s, 1H), 6.67 (s, 1H), 6.64 (s,
described [11]. 1,1-Diphenylethylene was used as an internal
standard.
1H), 5.97 (t, J ¼ 7.5 Hz, 1H), 4.21 (t, J ¼ 8.1 Hz, 2H), 4.14 (s, 3H), 3.37
(t, J ¼ 6.6 Hz, 2H), 3.32 (s, 3H), 3.25 (t, J ¼ 8.1 Hz, 2H), 2.48 (s, 3H),
2.39 (dt, J ¼ 6.6 Hz and 7.5 Hz, 2H), 2.28 (s, 3H); 13C NMR
d 167.19,
Acknowledgment
162.52, 158.49, 154.99, 142.91, 140.63, 138.68, 134.99, 132.50, 131.31,
126.14, 123.80, 121.09, 119.87, 118.79, 113.68, 104.88, 61.52, 57.37,
44.10, 43.79, 28.15, 27.74, 14.64, 14.40; ESIMS m/z (rel intensity)
486.00 (MNaþ, 100). Anal. Calcd for C25H25N3O6: C, 64.79; H, 5.44;
N, 9.07. Found: C, 65.01; H, 5.41; N, 9.00.
This investigation was made possible by Grant RO1-AI-43637,
awarded by the National Institutes of Health, DHHS. This research
was conducted in a facility constructed with support from Research
Facilities Improvement Program Grant Number C06-14499 from
the National Center for Research Resources of the National Insti-
tutes of Health. We are grateful to Kristien Erven for her excellent
technical assistance.
5.1.7. (Z)-3-[1-(3-Methoxy-7-methylbenzo[d]isoxazol-5-yl)-4-(2-
ox-oxazolidin-3-yl)-but-1-enyl]-benzonitrile (9)
The general procedure was followed using the vinylstannane 15
(396 mg, 0.669 mmol), 3-bromobenzonitrile (19) (117 mg,
0.91 mmol), cesium fluoride (350 mg, 2.28 mmol), and Pd(PBut3)2
(37 mg, 0.07 mmol) in toluene (1 mL). The mixture was stirred
under argon at room temperature for 4 h, at 55 ꢁC for 41.5 h, and at
95 ꢁC for 5 h. The residue was purified by column chromatography
on silica gel (15 g), eluting with EtOAc–hexanes (0–20%), to afford
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