Hetero-Diels-Alder reaction of 1,3-bis(trimethylsilyloxy)-1,3-butadienes with arylsulfonylcyanides. Synthesis and antimicrobial activity of 4-hydroxy-2-(arylsulfonyl)pyridines

Article abstract of DOI:10.1016/j.bmc.2008.10.033

Hetero-Diels-Alder reactions of 1,3-bis(silyloxy)-1,3-butadienes with arylsulfonylcyanides afforded a variety of 4-hydroxy-2-(arylsulfonyl)pyridines. Several derivatives show antimicrobial activity against Gram-positive bacteria.

Full text of DOI:10.1016/j.bmc.2008.10.033

Bioorganic & Medicinal Chemistry 16 (2008) 9898–9903
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry
journal homepage: www.elsevier.com/locate/bmc
Hetero-Diels–Alder reaction of 1,3-bis(trimethylsilyloxy)-1,3-butadienes
with arylsulfonylcyanides. Synthesis and antimicrobial activity
of 4-hydroxy-2-(arylsulfonyl)pyridines
Ibrar Hussain a, Mirza Arfan Yawer a, Michael Lalk b, Ulrike Lindequist b, Alexander Villinger a,
Christine Fischer c, Peter Langer a,c,
*
a Institut für Chemie, Universität Rostock, Albert-Einstein-Str. 3a, 18059 Rostock, Germany
b Institut für Pharmazie, Ernst-Moritz-Arndt-Universität Greifswald, F.-L.-Jahn-Str. 17, 17487 Greifswald, Germany
c Leibniz-Institut für Katalyse e. V. an der Universität Rostock, Albert-Einstein-Str. 29a, 18059 Rostock, Germany
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 4 July 2008
Revised 10 October 2008
Accepted 14 October 2008
Available online 17 October 2008
Hetero-Diels–Alder reactions of 1,3-bis(silyloxy)-1,3-butadienes with arylsulfonylcyanides afforded a
variety of 4-hydroxy-2-(arylsulfonyl)pyridines. Several derivatives show antimicrobial activity against
Gram-positive bacteria.
Ó 2008 Elsevier Ltd. All rights reserved.
Keywords:
Antimicrobial activity
Cyclizations
Pyridines
Silyl enol ethers
1. Introduction
which often undergo elimination or oxidation reactions to the cor-
responding pyridine derivatives. Noteworthy, intermolecular reac-
Nitriles represent versatile electrophilic building blocks in base-
mediated cyclization reactions with nucleophiles.1,2 In contrast,
cycloaddition reactions of nitriles are more rare.1 Known examples
include, for example, transition metal-catalyzed [2 + 2 + 2] cyclo-
addition of nitriles with two molecules of alkynes.3 The photo-
chemical [2 + 2] cycloaddition of aryl nitriles with electron rich
alkenes has been reported to give azetines.4a–c A 1,3-azetin-2-one
has been prepared by [2 + 2] cycloaddition of trichloroacetylisocy-
anate with trichloroacetonitrile.4d The [3 + 2] cycloaddition of ni-
triles with azides has been reported to give 1H-tetrazoles.5 The
best yields were generally obtained for nitriles containing an elec-
tron deficient substituent. Sharpless et al. studied the synthesis of
tetrazoles by Cu-catalyzed ‘click reaction’ of nitriles with azides.6
For example, 1-substituted-5-tosyltetrazoles were prepared from
tosyl cyanide (TsCN); the tosyl group was subsequently elaborated
by nucleophilic substitution reactions. The 1,3-dipolar cycloaddi-
tion of diazomethane with TsCN has been reported to give 1,2,3-
triazines.7
tions of this type are relatively rare and highly activated nitriles,
such as arylsulfonylnitriles and cyanoformates, have to be em-
ployed.8 Breitmaier and Rüffer reported8f an efficient synthesis of
functionalized pyridines by cyclization of 1,3-butadienes, includ-
ing 2-silyloxy-1,3-butadienes, with tosylcyanide9 (TsCN). Pyridines
have been prepared also by cyclization of pyran-2-ones with TsCN
with extrusion of carbon dioxide.10 Recently, the synthesis of 1-
azabicyclo[2.2.2]oct-1-enes by cyclization of 2-silyloxycyclohexa-
1,3-diene with TsCN has been reported.11 Recently, we reported,12
based on the work of Breitmaier, the hetero-Diels–Alder reaction of
1,3-bis(trimethylsilyloxy)-1,3-butadienes13 with TsCN. Herein, we
report full details of these studies and a considerable extension
of the scope. The reactions reported herein allow a convenient syn-
thesis of a variety of functionalized 4-hydroxy-2-(arylsulfonyl)pyr-
idines which are not readily available by other methods.
In recent years, it has been shown that 2-(arylsulfonyl)pyridines
and related molecules are of considerable pharmacological rele-
vance. 10-Oxa-9-thia-1-aza-anthracene-9,9-dioxide possesses
in vitro (rat brain homogenate) inhibitory activity against mono-
amine oxidase (MAO).14 6-(Benzenesulfonyl)-pyrido[3,2-d]pyrimi-
dine-2,4-diamine shows parenteral antimalarial effects against
Plasmodium Berghi in mice.15 1-(10,10-Dioxo-5k9-dihydro-10,6-
thiochromeno[2,3-b]pyridin-5-yl)-1,3-dimethyl-urea shows gas-
The [4 + 2] cycloaddition of nitriles with 1,3-dienes (hetero-
Diels–Alder reaction) has been reported to give dihydropyridines
* Corresponding author. Tel.: +49 381 4986410; fax: +49 381 4986412.
E-mail address: peter.langer@uni-rostock.de (P. Langer).
0968-0896/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmc.2008.10.033

I. Hussain et al. / Bioorg. Med. Chem. 16 (2008) 9898–9903
9899
activity.16
2-Benzenesulfonyl-4-methyl-
Table 1
Synthesis of 3a–v
tric
benzo[h]quinolines show antibiotic activity against various patho-
gens.17
6-(Benzenesulfonyl)-pyrido[3,2-d]pyrimidine-2,4-dia-
antisecretory
1
2
3
R1
R2
R3
% (3)a
mines have been reported to inhibit Pneumocystis carinii
dihydrofolate reductase and Toxoplasma gondii dihydrofolate
reductase.18 3-[5-(Phenylcarbamoyl)-pyridine-2-sulfonyl]-benzoic
acids show binding activity to Sf9 cell membranes.19 2,4-Diami-
no-10,10-dioxo-5,10-dihydro-10k6-thiochromeno[2,3-b]pyridine-
3-carbonitrile and related derivatives inhibit recombinant MAP ki-
nase-activated protein kinase 2.20 2-(Benzenesulfonyl)-5-nitro-
pyridines and related compounds show inhibitory activity of re-
combinant SARS coronavirus main protease 2.21 2-(4-Fluoro-ben-
zenesulfonyl)-5-[(E)-2-(4-fluoro-phenyl)-vinyl]-pyridine binds to
the human 5-HT2A receptor.22 Other derivatives have been shown
to bind to the human cannabinoid CB2 receptor.23 Other effects
have also been reported.24 Herein, we report the antimicrobial
activity of several 2-(arylsulfonyl)-4-hydroxypyridines prepared
by our new synthetic methodology.
a
b
c
d
e
a
b
f
g
h
i
j
k
l
g
h
m
n
o
i
a
a
a
a
a
a
b
b
b
b
b
b
b
b
a
a
b
a
a
a
a
a
a
b
c
d
e
f
g
h
i
j
k
l
m
n
o
p
q
r
H
H
H
H
H
H
H
H
OMe
OEt
CH2OMe
Me
O(CH2)2OMe
OMe
OEt
OiPr
OEt
OEt
OEt
Me
OMe
Me
OEt
OEt
OMe
Me
Me
OEt
Me
Me
Me
Me
Me
Me
Me
H
H
H
H
H
H
H
H
H
Me
Me
H
Me
Me
Me
Me
Me
43
30
30
33
12
10
38
31
56
59
61
53
56
79
48
54
60
58
57
62
64
51
Cl
F
O(3,5-Me2C6H3)
SPh
SPh
S(3-MeC6H4)
Cl
F
Et
O(3-MeC6H4)
O(4-MeC6H4)
O(3,5-Me2C6H3)
SPh
s
t
u
v
2. Results and discussion
j
p
S(4-MeC6H4)
The reaction of 1-methoxy-1,3-bis(trimethylsilyloxy)-1,3-buta-
diene (1a), readily available from methyl acetoacetate,25 with p-
toluenesulfonyl cyanide (TsCN, 2a) afforded the 4-hydroxy-2-
tosylpyridine 3a in 43% yield (Scheme 1, Table 1). The best yields
were obtained when a neat mixture of the starting materials was
allowed to slowly warm from –78 °C to ambient temperature. A
complex mixture was obtained when the reaction was carried
out at elevated temperatures or when a solvent was added. An
aqueous work-up using NH4Cl or HCl was necessary. The formation
of 3a can be explained by [4 + 2] cycloaddition to give intermediate
A and subsequent acid-mediated cleavage of the silyloxy group and
aromatization.
The cyclization of 1,3-bis(silyloxy)-1,3-butadienes 1a–p with
arylsulfonyl cyanides 2a,b afforded the 4-hydroxy-2-sulfonylpyri-
dines 3a–v (Table 1). The reaction conditions were optimized.
The reactions of dienes 1a,b,e,f, prepared from unsubstituted b-
ketoesters, were carried out at 20 °C (the starting materials were
added at –78 °C and the mixture was subsequently warmed to
20 °C during 30 min. The reaction time was in the range of 24–
28 h. A considerable extension of the reaction time was necessary
for the less reactive dienes 1c and 1d derived from pentane-2,4-
dione and 1-methoxy-pentane-2,4-dione, respectively. In these
cases, the starting materials were added at 0 rather than –78 °C.
The reactions were carried out at 20 °C. An increase of the temper-
a
Yields of isolated products.
ature resulted in partial decomposition. The reactions of dienes
1g–i and 1m–o were carried out at 45 °C (48 h). The arylthio-
substituted dienes 1j–l,p solidify at 20 °C. Since all reactions re-
ported herein had to be carried out without solvent (neat) it proved
to be advantageous to carry out the reactions of 1j–l,p at 60 °C
(96 h).
Noteworthy, the yields of pyridines 3i–v were considerably
higher than those of 3a–h. This can be explained by the cisoid con-
formation of 1,3-bis(silyloxy)-1,3-butadienes 1g–s, due to the
presence of the substituent located at the central carbon atom.
The reaction of 2a with 1,3-bis(silyloxy)-1,3-butadienes containing
a substituent located at the terminal carbon atom proved to be
unsuccessful, presumably due to steric reasons. The reaction of
1a with ethoxycarbonyl cyanide was also unsuccessful, due to
the low reactivity of the latter compared to 2a. No conversion
was observed when the reaction was carried out at 20 and 60 °C.
Forcing conditions (neat, 120 °C) resulted in decomposition and
1,5 O ? C TMS shift of the 1,3-bis(silyl enol ether) to give a 3-silyl-
oxy-4-silylcrotonate.26
The structures of the products were elucidated by spectroscopic
methods (2D NMR). The structures of 3l and 3r were indepen-
dently confirmed by X-ray crystal structure analyses (Figs. 1 and
2).27
Me3SiO
OSiMe3
R2
All arylsulfonyl-pyridines were tested towards their antimicro-
bial activity. The agar diffusion test method was used to evaluate
the influence on the growth of the Gram-positive bacteria Staphy-
lococcus aureus and Bacillus subtilis as well as the Gram-negative
Escherichia coli and the yeast Candida maltosa. The results of that
screening are summarized in Table 2. Some of the compounds
showed considerable activities against S. aureus and B. subtilis. In
this screening no activity against the Gram-negative E. coli was ob-
served. Only 3o showed a weak activity against the yeast C. malto-
sa. Compound 3o is also among the most active derivatives in this
study. To evaluate the antimicrobial potential of the most active
compounds minimal inhibitory concentrations were determined.
The results of these investigations are summarized in Table 3.
Derivatives 3i,j,o, containing a halogen atom located at the pyri-
dine moiety, show the best activities. A good activity was also ob-
served for derivative 3n containing a tolylthio moiety.
1) 78 20 ºC
neat
2) H+, H2O
OH
N
R3
R1
R2
R1
1a-p
S
R3
+
O
O
C N
3a-v
NH4Cl, H2O
S
O
O
2a,b
OSiMe3
R3
R1
OH
S
N
R2
O
O
A
The chloro derivatives 3i and 3o show a good antibiotic activity
against the tested Gram-positive pathogenes. Interestingly, the
Scheme 1. Synthesis of 3a–v.

9900
I. Hussain et al. / Bioorg. Med. Chem. 16 (2008) 9898–9903
Table 2
Results of the antimicrobial screeninga
3
S. aureus ATCC
6538
B. subtilis ATCC
6051
E. coli ATCC
11229
C. maltosa
SBUG 700
a
b
c
d
e
f
g
h
i
j
k
l
m
n
o
p
q
r
10
r
r
r
r
r
r
r
12
12
r
9
r
13
13
r
r
r
8
8
r
r
r
r
r
r
r
r
r
11
11
r
10
10
10
10
8
r
r
7
r
r
r
r
r
r
r
r
r
r
r
r
r
r
r
r
r
r
r
r
r
r
r
r
r
r
r
r
r
r
r
r
r
r
r
r
r
9
r
r
r
r
r
r
r
s
t
u
v
10
10
8
Ampicillin 27
25
n.t.
19
n.t.
n.t.
28
Nystatin
n.t.
a
Inhibition zones are stated in diameter (mm) without the diameter of the paper
disc (6 mm); r, resistant; n.t., not tested.
Figure 1. Crystal structure of 3l.
Table 3
Minimal inhibitory concentrations of selected compounds 3 (values give in mM)a
3
S. aureus ATCC 6538
B. subtilis ATCC 6051
i
j
n
o
u
v
1.59
3.36
0.67
1.53
0.67
0.32
1.59
1.68
0.33
1.52
0.34
0.16
Ampicillin
0.003
0.011
a
Minimal inhibitory concentrations were determined by a dilution assay (results
are averages of three independent experiments).
be a better bioavailability in case of the non-chlorinated deriva-
tives in the dilution assay. All compounds show much lower activ-
ity compared to Ampicillin in this study. In future studies, the
influence of a halogenation at position R2 or R3 in the thioaryl
derivatives could be of interest to get better insight into the struc-
ture-activity relationships.
3. Conclusions
In conclusion, the hetero-Diels–Alder reaction of 1,3-bis(silyl-
oxy)-1,3-butadienes with arylsulfonylcyanides afforded a variety
of 4-hydroxy-2-(arylsulfonyl)pyridines. The products, which are
not readily available by other methods, show a considerable anti-
microbial activity against Gram-positive bacteria.
Figure 2. Crystal structure of 3r.
4. Experimental section
4.1. General comments
thio-substituted sulfonyl-pyridines 3l–n and 3u–v are also active,
but at a lower level in the agar diffusion assay. In contrast to this
observation, the MIC of 3n, 3u and 3v are lower compared to the
chlorinated compounds 3i and 3o. A possible explanation would
All solvents were dried by standard methods and all reactions
were carried out under an inert atmosphere. For 1H and 13C NMR
spectra the deuterated solvents indicated were used. Mass spectro-

I. Hussain et al. / Bioorg. Med. Chem. 16 (2008) 9898–9903
9901
metric data (MS) were obtained by electron ionization (EI, 70 eV),
chemical ionization (CI, H2O) or electrospray ionization (ESI). For
preparative scale chromatography, silica gel (60–200 mesh) was
used. Melting points are uncorrected.
CHPh). 13C NMR (75 MHz, CDCl3): d = 12.1 (OCH2CH3), 19.3
(2CH3Xyl), 61.2 (OCH2CH3), 104.8 (CHHeter), 111.1 (2CHPh), 122.9
(CHXyl), 125.9 (CHeter), 126.9 (2CHPh), 127.1 (2CHXyl), 131.7 (CHPh),
136.7 (CXyl), 137.5 (CPh), 148.8 (2CXyl), 154.5 (COHHeter), 155.1,
~
155.6 (CHeter). IR (neat, cmÀ1):
m = 3324 (w), 1592 (s), 1468 (m),
4.2. General procedure for the synthesis of 2-(arylsulfonyl)-4-
hydroxypyridines 3a–v
1429 (m), 1305 (m), 1132 (s), 1095 (m), 997 (m), 831 (m), 724
(s), 679 (s), 594 (s). HRMS (ESI, Positive): Calcd for C21H21NO5S
([M+H]+): 400.12132; found: 400.12108, ([M+Na]+): 422.10299;
found: 422.10326.
To the arylsulfonyl cyanide 2 (1.0 equiv) was added dropwise
the 1,3-bis(silyl enol ether) 1 (2.0–2.5 equiv) at À78 °C. The neat
reaction mixture was allowed to warm 45À60 °C during 48À96 h
with stirring. To the mixture was added a saturated aqueous solu-
tion of NH4Cl (20 mL) and the organic and the aqueous layer were
separated. The latter was extracted with CH2Cl2 (3 Â 20 mL). The
combined organic layers were dried (Na2SO4), filtered and the fil-
trate was concentrated in vacuo. The residue was purified by chro-
matography (silica gel, n-heptane/EtOAc) to give 3a–v. The
synthesis of 3a–h has been previously reported in our preliminary
communication.13
4.6. 2-Methyl-6-(phenylsulfonyl)-3-(phenylthio)pyridin-4-ol
(3l)
Starting with 2b (0.167 g, 1.0 mmol) and 1j (0.704 g,
2.0 mmol), 3l was isolated as a yellow viscous oil (0.189 g,
53%). Reaction conditions: 96 h, 60 °C. 1H NMR (250 MHz,
CDCl3): d = 2.46 (s,
3
H, CH3Heter), 6.89 (dd, 3J = 8.2 Hz,
4J = 1.9 Hz, 2 H, CHTol), 7.10 (m, 3 H, CHTol), 7.38 (s(br), 1 H, OHH-
eter), 7.47 (m, 3 H, CHTol), 7.59 (s, 1 H, CHHeter), 7.95 (dd,
3J = 8.4 Hz, 4J = 1.5 Hz, 2 H, CHTol). 13C NMR (62 MHz, CDCl3):
d = 20.4 (CH3Heter), 108.17 (CHHeter), 117.7 (CPh), 126.1 (CHeter),
127.1 (2CHPh), 129.1 (2CHPh), 129.6 (2CHPh), 129.9 (2CHPh),
133.9 (2CHPh), 138.5 (CPh), 159.1, 165.5 (CHeter), 165.6 (COHHeter).
~
m = 3249 (w), 1562 (m), 1446 (m), 1397 (m),
4.3. 3-Chloro-2-ethoxy-6-(phenylsulfonyl)pyridin-4-ol (3i)
Starting with 2a (0.167 g, 1.0 mmol) and 1 g (0.617 g,
2.0 mmol), 3i was isolated as a yellow viscous oil (0.175 g, 56%).
Reaction conditions: 48 h, 45 °C. 1H NMR (250 MHz, CDCl3):
d = 1.22 (t, 3J = 7.1 Hz, 3 H, OCH2CH3), 4.27 (q, 3J = 7.1 Hz, 2 H,
OCH2CH3), 7.19 (s(br), 1 H, OHHeter), 7.44À7.49 (m, 2 H, CHPh),
7.52 (m, 1 H, CHPh), 7.55 (s, 1 H, CHHeter), 7.96 (dd, 3J = 8.4 Hz,
IR (neat, cmÀ1):
1307 (m), 1156 (s), 1082 (m), 905 (s), 721 (s), 684 (m), 601
(s). GC–MS (EI, 70 eV): m/z (%) = 357 ([M]+, 4), 292 (100), 252
(4), 216 (6), 147 (6), 109 (24), 77 (19), 65 (7), 51 (10). HRMS
(EI): Calcd for C18H15NO3S2: 357.04879; found: 357.04863.
4J = 1.5 Hz,
2
H, CHPh). 13C NMR (75 MHz, CDCl3): d = 14.2
(OCH2CH3Heter), 64.1 (OCH2CH3), 105.6 (CHHeter), 106.9 (CHeter),
4.7. 2-Methoxy-6-(phenylsulfonyl)-3-(phenylthio)pyridin-4-ol
(3m)
128.9 (2CHPh), 129.0 (2CHPh), 133.8 (CHPh), 138.4 (CPh), 153.6
(COHHeter), 159.9, 160.4 (CHeter). IR (neat, cmÀ1):
= 3312 (w),
~
m
1731 ((br), w), 1608 (m), 1417 (m), 1385 (m), 1347 (m), 1304
(m), 1251 (m), 1159 (m), 1093 (s), 1076 (s), 840 (s), 725 (s), 592
(s). HRMS (ESI, Positive): Calcd for C13H12ClNO4S ([M+H]+, 35Cl):
314.02483; found: 314.02486, ([M+Na]+, 35Cl): 336.006433; found:
336.00678.
Starting with 2b (0.167 g, 1.0 mmol) and 1 k (0.746 g,
2.0 mmol), 3m was isolated as a yellow solid (0.210 g, 56%). Reac-
tion conditions: 96 h, 60 °C. 1H NMR (250 MHz, CDCl3): d = 3.73 (s,
3 H, OCH3Heter), 7.02 (m, 1 H, CHPh), 7.05 (m, 1 H, CHPh), 7.15 (m, 2
H, CHPh), 7.18 (m, 2 H, CHPh), 7.45 (s, 1 H, CHHeter), 7.47 (m, 1 H,
CHHeter), 7.50 (s(br), 1 H, OHHeter), 7.54À7.57 (m, 1 H, CHPh), 8.01
(d, 3J = 6.9 Hz, 2 H, CHPh).. 13C NMR (75 MHz, CDCl3): d = 55.1
(OCH3Heter), 104.7 (CHHeter), 125.2 (CHeter), 127.1 (CHPh), 128.1
(2CHPh), 125.9 (2CHPh), 129.2 (2CHPh), 129.3 (2CHPh), 132.6, 137.3
(CPh), 133.8 (CHPh), 138.3 (CPh), 157.4 (COHHeter), 164.9, 166.5
~
4.4. 2-Ethoxy-3-fluoro-6-(phenylsulfonyl)pyridin-4-ol (3j)
Starting with 2b (0.167 g, 1.0 mmol) and 1 h (0.589 g,
2.0 mmol), 3j was isolated as a red solid (0.179 g, 59%). Reaction
conditions: 48 h, 45 °C 1H NMR (250 MHz, CDCl3): d = 1.22 (t,
3J = 7.1 Hz, 3 H, OCH2CH3), 4.26 (q, 3J = 7.0 Hz, 2 H, OCH2CH3),
7.19 (s(br), 1 H, OHHeter), 7.43 (m, 1 H, CHHeter), 7.46À7.50 (m, 2
(CHeter). IR (neat, cmÀ1):
m = 3246 (w), 1625 (m), 1559 (w), 1503
(m), 1445 (m), 1385 (m), 1301 (s), 1142 (s), 1076 (s), 906 (m),
724 (s), 600 (s). HRMS (ESI, Positive): Calcd for C18H15NO4S2
([M+H]+): 374.05153; found: 374.05163, ([M+Na]+): 396.03360;
found: 396.03347.
H, CHPh), 7.53À7.56 (m,
1
H, CHPh), 7.95 (dd, 3J = 8.4 Hz,
4J = 1.5 Hz,
2
H, CHPh). 13C NMR (75 MHz, CDCl3): d = 14.1
(OCH2CH3), 63.6 (OCH2CH3), 107.8 (CHHeter), 128.9 (2CHPh), 129.0
(2CHPh), 133.8 (CHPh), 136.8 (d, 1J = 252.4 Hz, CFHeter), 138.4 (CPh),
149.4 (d, 4J = 6.7 Hz, CHeter), 151.3 (d, 2J = 10.2 Hz, COHHeter), 153.8
(d, 2J = 9.9 Hz, CHeter). 19F NMR (235 MHz, CDCl3): À162.05 (CFHeter).
~
4.8. 2-Methyl-6-(phenylsulfonyl)-3-(m-tolylthio)pyridin-4-ol
(3n)
IR (neat, cmÀ1):
m
= 3354 (w), 1576 (m), 1440 (m), 1353 (m), 1317
Starting with 2b (0.167 g, 1.0 mmol) and 1l (0.733 g, 2.0 mmol),
3n was isolated as a yellow viscous oil (0.296 g, 79%). Reaction con-
ditions: 96 h, 60 °C. 1H NMR (250 MHz, CDCl3): d = 2.20 (s, 3 H,
CH3Tol), 2.48 (s, 3 H, CH3, CH3Heter), 6.82 (d, 3J = 8.2 Hz, 2 H, CHTol),
6.98 (d, 3J = 8.1 Hz, 1 H, CHPh), 7.45 (m, 1 H, CHTol), 7.48 (m, 1 H,
CHPh), 7.55 (s(br), 1 H, OHHeter), 7.63 (m, 1 H, CHHeter), 7.52 (m, 1
H, CHTol), 8.00 (dd, 3J = 8.1 Hz, 4J = 1.5 Hz, 1 H, CHPh). 13C NMR
(75 MHz, CDCl3): d = 18.9 (CH3Tol), 21.9 (CH3Heter), 105.9 (CHHeter),
113.2, 116.3 (CHeter), 126.0 (2CHPh), 126.7 (CHTol), 127.1 (2CHTol),
127.2 (CHTol), 127.9 (CPh), 128.4 (2CHPh), 131.8 (CHPh), 135.5 (CTol),
136.6 (CTol), 157.0 (COHHeter), 163.4 (CHeter). IR (neat, cmÀ1):
~
(m), 1149 (s), 1076 (m), 1022 (m), 740 (s), 724 (s), 682 (s), 585 (s).
HRMS (ESI, Positive): Calcd for C13H12FNO4S ([M+H]+): 298.05438;
found: 298.05413, ([M+Na): 320.03652; found: 320.03633.
4.5. 3-(3,5-Dimethylphenoxy)-2-ethoxy-6-
(phenylsulfonyl)pyridin-4-ol (3k)
Starting with 2b (0.167 g, 1.0 mmol) and 1i (0.756 g, 2.0 mmol),
3 k was isolated as yellow viscous oil (0.243 g, 61%). Reaction con-
ditions: 48 h, 45 °C. 1H NMR (250 MHz, CDCl3): d = 0.99 (t,
3J = 7.0 Hz,
3
H, OCH2CH3), 2.14 (s,
6
H, CH3Xyl), 4.16 (q,
m = 3377 (w), 2921 (w), 1561 (m), 1491 (m), 1446 (m), 1396 (m),
3J = 7.0 Hz, 2 H, OCH2CH3), 6.37 (s, 2 H, CHXyl), 6.59 (s, 1 H, CHXyl),
6.77 (s(br), 1 H, OHHeterl), 7.45À7.48 (m, 2 H, CHPh), 7.48 (s, 1 H,
CHHeter), 7.51 (m, 1 H, CHPh), 7.98 (dd, 3J = 8.5 Hz, 4J = 1.5 Hz, 2 H,
1306 (m), 1155 (s), 1081 (m), 1015 (w), 905 (s), 803 (m), 722 (s),
684 (m), 600 (s). GC–MS (CI, Positive, 70 eV): m/z (%) = 371 ([M]+,
14), 306 (100), 292 (5), 274 (4), 216 (5), 186 (3), 135 (6), 123

9902
I. Hussain et al. / Bioorg. Med. Chem. 16 (2008) 9898–9903
(27), 91 (8), 77 (24), 65 (4), 45 (7). HRMS (EI): Calcd for
C19H17NO3S2 ([M]+): 371.06444; found: 371.06407.
(m, 1 H, CHTol), 6.53 (s, 1 H, CHHeter), 6.75 (d, 3J = 7.3 Hz, 1 H, CHTol),
7.00À7.06 (m, 2 H, CHTol), 7.21 (d, 3J = 8.2 Hz, 2 H, CHTol), 7.62
(s(br), 1 H, OHHeter), 7.82 (d, 3J = 8.2 Hz, 2 H, CHTol). 13C NMR
(75 MHz, CDCl3): d = 17.1 (CH3Heter), 19.4, 19.7 (CH3Tol), 108.9
(CHHeter), 109.9, 113.6, 121.9 (CHTol), 126.9 (2CHTol), 127.5 (CHTol),
127.8 (2CHTol), 133.9, 137.8 (CTol), 138.2 (CHeter), 142.9 (CTol), 152.2
(CHeter), 152.6 (CTol), 154.3 (COHHeter), 179.3 (CHeter). GC–MS (CI, Po-
sitive, 70 eV): m/z (%) = 370 ([M+1]+, 100), 305 (58), 291 (4), 232
(8), 69 (24). HRMS (ESI, Positive): Calcd for C20H19NO4S ([M+H]+):
370.11076; found: 370.11067, ([M+Na]+): 392.09270; found:
392.09270.
4.9. 3-Chloro-2-ethoxy-6-tosylpyridin-4-ol (3o)
Starting with 2a (0.094 g, 1.0 mmol) and 1 g (0.617 g,
2.0 mmol), 3o was isolated as a red viscous oil (0.156 g, 48%). Reac-
tion conditions: 48 h, 45 °C. 1H NMR (250 MHz, CDCl3): d = 1.25 (t,
3J = 7.8 Hz, 3 H, OCH2CH3), 2.35 (s, 3 H, CH3Tol), 4.28 (q, 3J = 6.8 Hz, 2
H, OCH2CH3), 7.19 (s, 1 H, CHHeter), 7.24 (d, 3J = 8.1 Hz, 2 H, CHTol),
7.42 (s(br), 1 H, OHHeterl), 7.84 (d, 3J = 8.2 Hz, 2 H, CHTol). 13C NMR
(75 MHz, CDCl3): d = 14.2 (OCH2CH3Heter), 21.6 (CH3Tol), 64.0
(OCH2CH3), 105.4 (CHHeter), 106.7 (CHeter), 129.1 (2CHTol), 129.6
(2CHTol), 135.5, 144.8 (CTol), 153.9 (COHHeter), 159.8, 160.3 (CHeter).
~
4.13. 2-Methyl-3-(p-tolyloxy)-6-tosylpyridin-4-ol (3s)
IR (neat, cmÀ1):
m
= 2952 (w), 1594 (m), 1415 (m), 1338 (m), 1252
Starting with 2a (0.141 g, 0.75 mmol) and 1o (0.525 g,
1.75 mmol), 3s was isolated as a yellow solid (0.210 g, 57%).
Reaction conditions: 48 h, 45 °C. 1H NMR (250 MHz, CDCl3):
d = 2.17 (s, 3 H, CH3Tol), 2.21 (s, 3 H, CH3Tol), 2.34 (s, 3 H,
CH3Heter), 6.61 (d, 3J = 8.5 Hz, 2 H, CHTol), 6.98 (d, 3J = 8.3 Hz, 2
H, CHTol), 7.19 (s, 1 H, CHHeter), 7.24 (d, 3J = 8.1 Hz, 2 H, CHTol),
7.64 (s(br), 1 H, OHHeter), 7.86 (d, 3J = 8.2 Hz, 2 H, CHTol). 13C
NMR (75 MHz, CDCl3): d = 19.1, 21.6 (CH3Tol), 30.9 (CH3Heter),
110.3 (CHHeter), 113.8 (CTol), 114.7 (2CHTol), 128.9 (2CHTol),
129.7 (2CHTol), 129.9 (CTol), 130.4 (2CHTol), 130.7 (CTol), 132.7,
136.0, 139.6 (CHeter), 144.7 (CTol), 154.7 (COHHeter). MS (EI,
70 eV): m/z (%) = 369 ([M]+, 1), 320 (1), 305 (100), 288 (10),
214 (13), 186 (9), 139 (8), 107 (9), 91 (45), 65 (16). HRMS
(ESI): Calcd for C20H19NO4S ([M+1]+): 370.11076; found:
370.11067, ([M+Na]+): 392.09270; found: 392.09732.
(m), 1115 (s), 1078 (s), 840 (s), 676 (s), 589 (s). MS (CI, Positive,
70 eV): m/z (%) = 330 ([M+1]+, 37Cl, 35), 328 ([M+1]+, 35Cl, 100),
299 (4), 279 (2), 257 (5), 233 (3), 219 (3), 193 (3), 177 (4), 141
(5), 125 (5), 81 (37Cl, 11), 79 (35Cl, 97), 71 (17). HRMS (ESI, Posi-
tive): Calcd for C14H14ClNO4S ([M+H]+, 35Cl): 328.04048; found:
328.04058, ([M+Na]+, 35Cl): 350.02243; found: 350.0039.
4.10. 2-Ethoxy-3-fluoro-6-tosylpyridin-4-ol (3p)
Starting with 2a (0.188 g, 1.0 mmol) and 1 h (0.589 g,
2.0 mmol), 3p was isolated as a red viscous oil (0.178 g, 54%). Reac-
tion conditions: 48 h, 45 °C. 1H NMR (250 MHz, CDCl3): d = 1.24 (t,
3J = 6.8 Hz, 3 H, OCH2CH3), 2.35 (s, 3 H, CH3Tol), 4.27 (q, 3J = 6.8 Hz, 2
3
H, OCH2CH3), 7.23 (s(br), 1 H, OHHeter), 7.27 (d, J = 8.1 Hz, 2 H,
CHTol), 7.46 (dH,
,
4J = 5.0 Hz, 1 H, CHHeter), 7.82 (d, 3J = 8.5 Hz, 2
F
H, CHTol). 13C NMR (75 MHz, CDCl3): d = 14.2 (OCH2CH3), 21.6
(CH3Tol), 63.5 (OCH2CH3), 107.6 (CHHeter), 128.9 (2CHTol), 129.6
(2CHTol), 135.5 (CTol), 137.8 (d, 1J = 251.9 Hz, CFHeter), 144.8 (CTol),
149.7 (d, 4J = 6.2 Hz, CHeter), 151.3 (d, 2J = 9.9 Hz, COHHeter), 153.7
(d, 2J = 9.9 Hz, CHeter). 19F NMR (235 MHz, CDCl3): À162.63 (CFHet-
~
4.14. 3-(3,5-Dimethylphenoxy)-2-ethoxy-6-tosylpyridin-4-ol
(3t)
Starting with 2a (0.188 g, 1.0 mmol) and 1i (0.757 g, 2.0 mmol),
3t was isolated as a red viscous oil (0.253 g, 62%). Reaction condi-
tions: 48 h, 45 °C. 1H NMR (250 MHz, CD3OD): d = 0.97 (t,
3J = 7.3 Hz, 3 H, OCH2CH3), 2.29 (s, 6 H, CH3Xyl), 2.52 (s, 3 H, CH3Tol),
4.28 (q, 3J = 7.4 Hz, 2 H, OCH2CH3), 6.54 (s, 2 H, CHXyl), 6.72 (s, 1 H,
CHXyl), 7.26 (s, 1 H, CHHeterl), 7.51 (d, 3J = 8.0 Hz, 2 H, CHTol), 8.01 (d,
er). IR (neat, cmÀ1):
m = 3255 (w), 1624 (m), 1505 (m), 1425 (m),
1383 (m), 1261 (s), 1140 (m), 1084 (m), 811 (m), 686 (m), 600
(m). MS (CI, Positive, 70 eV): m/z (%) = 312 ([M+1]+, 100), 247 (8),
219 (6), 177 (3), 119 (11), 69 (7). HRMS (ESI, Positive): Calcd for
C14H14FNO4S ([M+H]+): 312.07003; found: 312.06950, ([M+Na]+):
334.05198; found: 334.05194.
3J = 8.3 Hz,
2
H, CHTol). 13C NMR (75 MHz, CD3OD): d = 14.2
(OCH2CH3Heter), 21.3 (2CH3Xyl), 21.4 (CH3Tol), 62.7 (OCH2CH3Heter),
106.7 (CHHeter), 113.8 (2CHXyl), 124.9 (CHXyl), 129.6 (2CHTol),
131.0 (2CHTol), 140.3 (CTol), 143.3 (2CXyl), 149.6 (CTol), 158.4
(CHeter), 159.7 (CXyl), 159.9, 160.4 (CHeter), 170.8 (COHHeter). IR (neat,
~
4.11. 3-Ethyl-2-methoxy-6-(phenylsulfonyl)pyridin-4-ol (3q)
Starting with 2b (0.188 g, 1.0 mmol) and 1 m (0.576 g,
2.0 mmol), 3q was isolated as a yellow viscous oil (0.176 g, 60%).
Reaction conditions: 48 h, 45 °C. 1H NMR (250 MHz, CD3OD):
d = 0.97 (t, 3J = 7.9 Hz, 3 H, CH2CH3), 2.46 (q, 3J = 7.7 Hz, 2 H,
CH2CH3), 3.24 (s, 3 H, OCH3Heter), 6.97 (s, 1 H, CHHeter), 7.32À7.35
(m, 3 H, CHPh), 7.78 (d, 3J = 9.8 Hz, 2 H, CHPh). 13C NMR (75 MHz,
CD3OD): d = 12.7 (CH2CH3), 17.3 (CH2CH3), 50.0 (OCH3Heter), 104.9
(CHHeter), 118.1 (CHeter), 129.5 (2CHPh), 130.9 (2CHPh), 137.7 (CHPh),
146.5 (CPh), 151.5 (COHHeter), 164.7, 165.3 (CHeter). IR (neat, cmÀ1):
~
cmÀ1):
m = 3248 (w), 2952 (w), 1632 (s), 1436 (m), 1309 (m), 1178
(s), 1092 (m), 1035 (m), 952 (w), 805 (s), 696 (s). HRMS (ESI): Calcd
for C20H19NO4S ([M+1]+): 414.13784; found: 414.13769,
([M+Na]+): 436.47982; found: 436.47842.
4.15. 2-Methyl-3-(phenylthio)-6-tosylpyridin-4-ol (3u)
Starting with 2a (0.188 g, 1.0 mmol) and 1j (0.705 g, 2.0 mmol),
3u was isolated as colorless oil (0.240 g, 64%). Reaction conditions:
96 h, 60 °C. 1H NMR (250 MHz, CDCl3): d = 2.27 (s, 3 H, CH3Tol), 2.41
(s, 3 H, CH3Heter), 6.80 (d, 3J = 8.2 Hz, 2 H, CHTol), 7.02À7.06 (m, 3 H,
CHPh), 7.09 (s(br), 1 H, OHHeter), 7.18 (d, 3J = 8.0 Hz, 2 H, CHPh), 7.55
m
= 3417 (w), 2933 (w), 1726 (m), 1613 (m), 1413 (m), 1319 (s),
1267 (s), 1146 (s), 1083 (s), 904 (w), 812 (m), 674 (s), 592 (s).
MS (EI, 70 eV): m/z (%) = 293 ([M]+, 100), 229 (96), 186 (8), 160
(14), 139 (64), 91 (37), 69 (26). HRMS (ESI, Positive): Calcd for
C14H15NO4S ([M+H]+): 294.07946; found: 294.07964, ([M+Na]+):
316.06140; found: 316.06148.
(s, 1 H, CHHeter), 7.82 (d, 3J = 8.3 Hz, 2 H, CHTol . 13C NMR (62 MHz,
)
CDCl3): d = 21.6 (CH3Tol), 23.7 (CH3Heter), 108.1 (CHHeter), 117.7
(CPh), 126.9 (CHPh), 127.3 (2CHTol), 129.1 (2CHPh), 129.5 (2CHPh),
129.8 (2CHTol), 132.7 (CTol), 135.5 (CHeter), 145.1 (CTol), 159.2
(COHHeter), 165.3, 165.8 (CHeter). IR (neat, cmÀ1):
m = 3057 (w),
~
4.12. 2-Methyl-3-(m-tolyloxy)-6-tosylpyridin-4-ol (3r)
1552 (w), 1396 (m), 1316 (m), 1152 (s), 1081 (s), 905 (m), 728
(s), 678 (s), 590 (s). GC–MS (EI, 70 eV): m/z (%) = 371 ([M]+, 1),
306 (100), 292 (3), 266 (6), 230 (4), 214 (3), 190 (4), 147 (5), 109
(22), 91 (17), 77 (6), 65 (14). HRMS (EI): Calcd for C19H17NO3S2:
371.06444; found: 371.06400.
Starting with 2a (0.141 g, 0.750 mmol) and 1n (0.525 g,
1.5 mmol), 3r was isolated as colorless solid (0.240 g, 58%). Reac-
tion conditions: 48 h, 45 °C. 1H NMR (250 MHz, CDCl3): d = 2.16
(s, 3 H, CH3Tol), 2.18 (s, 3 H, CH3Tol), 2.32 (s, 3 H, CH3Heter), 6.47

I. Hussain et al. / Bioorg. Med. Chem. 16 (2008) 9898–9903
9903
Urabe, H.; Sato, F. J. Am. Chem. Soc. 2002, 124, 3518; (m) Takahashi, T.; Tsai, F.-
Y.; Kotora, M. J. Am. Chem. Soc. 2000, 122, 4994; (n) Takahashi, T.; Tsai, F.-Y.; Li,
Y.; Wang, H.; Kondo, Y.; Yamanaka, M.; Nakajima, K.; Kotora, M. J. Am. Chem.
Soc. 2002, 124, 5059.
4.16. 2-Methyl-3-(p-tolylthio)-6-tosylpyridin-4-ol (3v)
Starting with 2a (0.188 g, 1.0 mmol) and 1p (0.733 g, 2.0 mmol),
3v was isolated as colorless oil (0.200 g, 51%). Reaction conditions:
96 h, 60 °C. 1H NMR (250 MHz, CDCl3): d = 2.17 (s, 3 H, CH3Tol), 2.31
(s, 3 H, CH3Tol), 2.45 (s, 3 H, CH3Heter), 6.85 (d, 3J = 8.2 Hz, 2 H, CHTol),
6.94 (d, 3J = 8.1 Hz, 2 H, CHTol), 7.22 (d, 3J = 8.0 Hz, 2 H, CHTol), 7.60
(s, 1 H, CHHeter), 7.76 (s(br), 1 H, OHHeter), 7.85 (d, 3J = 8.2 Hz, 2 H,
4. (a) Yang, N.-C. C.; Kim, B.; Chiang, W.; Hamada, T. J. Chem. Soc., Chem. Commun.
1976, 729; (b) Cantrell, T. S. J. Am. Chem. Soc. 1972, 94, 5929; (c) Cantrell, T. S. J.
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5. (a) Dunica, J. V.; Pierce, M. E.; Santella, J. B., III J. Org. Chem. 1991, 56, 2395; (b)
Wittenberger, S. J.; Donner, B. G. J. Org. Chem. 1993, 58, 4139; (c) Curran, D. P.;
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Finnegan, W. G.; Henry, R. A.; Lofquist, R. J. Am. Chem. Soc. 1958, 80, 3908; (i)
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Geterotsikl. Soedin. 1992, 1214; (j) Koguro, K.; Oga, T.; Mitsui, S.; Orita, R.
Synthesis 1998, 910.
CHTol).
13C NMR (62 MHz, CDCl3): d = 20.9, 21.6 (CH3Tol), 23.9
(CH3Heter), 107.7 (CHHeter), 118.0 (CTol), 127.9 (2CHTol), 128.8
(2CHTol), 129.1 (2CHTol), 129.7 (2CHTol), 135.6, 137.3 (CTol), 130.7
(CTol), 144.8, 159.5, 165.1 (CHeter), 165.4 (COHHeter). IR (neat,
~
cmÀ1):
m = 3279 (w), 1583 (m), 1546 (m), 1490 (m), 1393 (m),
1306 (m), 1154 (s), 1124 (s), 1076 (s), 964 (w), 799 (s), 680 (s).
MS (EI, 70 eV): m/z (%) = 385 ([M]+, 13), 320 (100), 306 (7), 280
(11), 228 (11), 160 (6), 135 (10), 123 (45), 91 (38), 79 (12), 65
(9), 45 (13). HRMS (EI): Calcd for C20H19NO3S2: 385.08009; found:
385.07955.
6. (a) Demko, Z. P.; Sharpless, K. B. J. Org. Chem. 2001, 66, 7945; (b) Kolb, H. C.;
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4.17. Antimicrobial screening
The bacterial cultures were obtained from the ATCC. Assay for
antimicrobial activity: a modified disc diffusion method was used
to determine the antimicrobial activity. A sterile filter disc of
6 mm diameter (B & D research) was impregnated with the test
compounds. The amount of the compounds tested in these exper-
iments was 1 lmol per paper disc. The paper disc was placed on
the agar plate seeded with respective microorganisms. The plates
were kept in the refrigerator at 4 °C for 4 h. The plates were then
turned over to incubate overnight at 37 °C (at 25 °C in case of C.
maltosa) in an inverted position. At the end of the incubation per-
iod the clear zones of inhibition around the paper disc were mea-
sured. Negative control experiments were performed by using
paper discs loaded with an equivalent volume of solvent, and posi-
tive control experiments were performed by the use of an equiva-
lent amount of Ampicillin (in the case of S. aureus, B. subtilis and
E. coli) and Nystatin (C. maltosa). All experiments were done in
triplicate.
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12. For
a review of 1,3-bis(trimethylsilyloxy)-1,3-butadienes, see Langer, P.
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13. Preliminary communication: Emmrich, T.; Reinke, H.; Langer, P. Synthesis 2006,
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Acknowledgments
Financial support by the state of Pakistan (HEC scholarships for
I.H. and for M.A.Y.) is gratefully acknowledged.
References and notes
21. Lu, I.-L.; Mahindroo, N.; Liang, P.-H.; Peng, Y.-H.; Kuo, C.-J.; Tsai, K.-C.; Hsieh,
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1. For a review of applications of nitriles as reagents for organic synthesis with
loss of the nitrile functionality (including cycloaddition reactions), see Collier,
S.; Langer, P. Science of Synthesis. In Shinkai, I., Murahashi, S., Eds.; Thieme:
Stuttgart, 2004. Chapter 19.5.15.
2. For examples from our laboratory, see (a) Langer, P.; Appel, B. Tetrahedron Lett.
2003, 5133; (b) Blank, J.; Kandt, M.; Pfeiffer, W.-D.; Hetzheim, A.; Langer, P. Eur.
J. Org. Chem. 2003, 182; (c) Langer, P.; Bodtke, A. Tetrahedron Lett. 2003, 5965;
(d) Langer, P.; Bodtke, A. Synlett 2003, 1743; (e) Langer, P.; Albrecht, U. Synlett
2003, 1503; (f) Langer, P.; Döring, M.; Schreiner, P. R.; Görls, H. Chem. Eur. J.
2001, 7, 2617; (g) Langer, P.; Döring, M.; Seyferth, D. Chem. Commun. 1998,
1927; (h) Langer, P.; Döring, M.; Seyferth, D.; Görls, H. Eur. J. Org. Chem. 2003,
1948.
3. (a) Bönnemann, H. Angew. Chem. Int. Ed. Engl. 1978, 17, 505; (b) Bönnemann, H.;
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27. Crystallographic data (excluding structure factors) for the structures in this
paper have been deposited with the Cambridge Crystallographic Data Centre as
supplementary publication no. CCDC-686724 (3l) and CCDC-686725 (3r).
Copies of this data can be obtained, free of charge, on application to CCDC, 12
Union Road, Cambridge CB2 1EZ, UK; fax: +44(1223)336033 or e-mail:
deposit@ccdc.cam.ac.uk) or via www.ccdc.cam.ac.uk/conts/retrieving.html.