Indolizine 1-sulfonates as potent inhibitors of 15-lipoxygenase from soybeans

Article abstract of DOI:10.1016/j.bmc.2005.02.056

A number of indolizine 1-sulfonates have been prepared by cyclization of cyclopropenones with pyridines followed by trapping of the intermediate 1-indolizinol with a sulfonyl halide, and examined as inhibitors of 15-lipoxygenase (15-LO). The compounds dis

Full text of DOI:10.1016/j.bmc.2005.02.056

Bioorganic & Medicinal Chemistry 13 (2005) 3127–3139
Indolizine 1-sulfonates as potent inhibitors of
15-lipoxygenase from soybeans
Solomon Teklu,a Lise-Lotte Gundersen,a,* Tove Larsen,b Karl E. Malterudb
and Frode Risea
aDepartment of Chemistry, University of Oslo, PO Box 1033, Blindern, N-0315 Oslo, Norway
bSchool of Pharmacy, University of Oslo, PO Box 1068, Blindern, N-0316 Oslo, Norway
Received 29 October 2004; accepted 25 February 2005
Abstract—A number of indolizine 1-sulfonates have been prepared by cyclization of cyclopropenones with pyridines followed by
trapping of the intermediate 1-indolizinol with a sulfonyl halide, and examined as inhibitors of 15-lipoxygenase (15-LO). The com-
pounds display IC50 values between 15 and 42 lM; all are more active than the well-known 15-LOinhibitor quercetin (IC 50 51 lM).
A wide variety of substituents are well tolerated. The enzyme inhibition was not affected by preincubation or the presence of a deter-
gent and no significant particle formation was observed. Hence, inhibition from aggregates of indolizines, promiscuous inhibition, is
highly unlikely.
ꢀ 2005 Elsevier Ltd. All rights reserved.
1. Introduction
a number of indolizine 1-sulfonates and examined their
ability to inhibit 15-LOfrom soybean.
For some time we have been studying antioxidant activ-
ity for indolizine derivatives1,2 and as part of this pro-
ject, we have previously found that certain indolizine
derivatives are profound inhibitors of 15-lipoxygenase
(15-LO) from soybeans as well as from rabbit reticulo-
cytes. Among the most active compounds were indoli-
zines carrying a –OTs group in the 1-position.2 There
were no correlations between enzyme inhibition and
ability to scavenge the DPPH radical or inhibit lipid pero-
xidation in vitro under conditions without active enz-
ymes present. We proposed that the indolizines are
so-called nonantioxidant inhibitors of 15-LOand that
they mediate their activity thru a direct interaction with
the enzyme. 15-LOhas been implicated in oxidation of
low-density lipoproteins (LDL). This process is believed
to be important for the development of atherosclerosis.3
In addition, 15-hydroperoxyeicosatetraenoic acid has
been shown to decrease prostacyclin synthesis4 and 15-
LOinhibitors may thus have a pro-thrombotic effect.
Even though it is not known whether these effects are
clinically important in humans, inhibitors of 15-LO
may have a drug potential, and we have now synthesized
2. Results and discussion
The target indolizine sulfonates were synthesized as
shown in Scheme 1. 2,3-Diaryl- or 2,3-dialkylcyclo-
propenones 1 were reacted with pyridine 2 to generate
the intermediate 1-indolizinol, which was trapped with
a sulfonyl chloride, as we have previously reported for
the synthesis of the tosylate 3a and triflate 3o1b (Scheme
1, Table 1). In order to elucidate the importance of
–OSO2R moiety in compounds 3 for biological activity,
we also synthesized the sulfone 6 as well as the com-
pounds 7, which are lacking a 1-substituent, via the
1-bromoindolizines 4. We have previously described
the preparation of the bromide 4a by halogenation of
the corresponding 1-indolizinol with Ph3PBr2.1b The
same methodology was used to synthesize bromides
4b–d. Minor amounts of the dibrominated products 5
were formed together with the 2,3-di(4-halophenyl)ind-
olizines 4b and 4c. Metal–halogen exchange on
1-bromoindolizines followed by trapping with an
electrophilic species is a convenient way to modify the
indolizine 1-position.1b When the 1-lithioindolizine
generated from 4a was reacted with tosyl fluoride,5 the
sulfone 6 was formed although in low yield.
*
Corresponding author. Tel.: +47 22857019; fax: +47 22855507;
e-mail: l.l.gundersen@kjemi.uio.no
0968-0896/$ - see front matter ꢀ 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmc.2005.02.056

3128
S. Teklu et al. / Bioorg. Med. Chem. 13 (2005) 3127–3139
R2
N
R2
R2
O
ClSO2R,
DMAP
DCE, 0 oC
+
OSO2R
OH
N
DCE
∆
R1
R1
N
R1
R1
2a: R2 = -H
2b: R2 = -CN
2c: R2 = -CHO
R1
1a: R1 = -Ph
R1
1b: R1 = C6H4-p-F
1c: R1 = -C6H4-p-Cl
1d: R1 = -C6H4-p-CH3
1e: R1 = -C6H4-p-OCH3
1f: R1 = -Et
3a-dd
2d: R2 = -COCH3
Ph3PBr2
CH3CN, 70 oC
2e: R2 = -But
1g: R1 = Bun
R2
N
R2
CN
Br
1) n-BuLi
THF, -78 oC
+
Br
Br
N
N
2) NH4Cl(aq)
R1
R1
R1
R1
R1
4a-d
R1
7a-d
5
R2
N
1) n-BuLi
2) TsF
THF, -78 oC
R3
CN
N
R1
R1
General struct. compounds
described in Table 1
O2
S
Ph
Ph
CH3
6
Scheme 1.
A few azaindolizine sulfonates were also examined
(Scheme 2). Cyclization of pyrimidine with cycloprope-
none 1a gives two regioisomeric azaindolizinols, which
previously have been isolated as acetates.6 We trapped
the azaindolizinols with tosyl chloride to get the isomers
9 and 10. It was crucial to perform the reaction in diox-
ane. When synthesis of compounds 9 and 10 in DCE
was attempted, we were only able to isolate compound
12. This product was probably formed by attack of
the intermediate azaindolizinol on the cyclopropenone
1a. The synthesis of compound 11 has been described
before.1c
Also in the indolizine 2- and 3-position a variety of sub-
stituents were tolerated. Generally, aryl substituents give
somewhat more active compounds than alkyl substitu-
ents (3f and 3g). When 2,3-diphenylinolizine 3a was
compared with analogs bearing para-substituted aryls
in the 2- and 3-position (compds 3b–e), no significant
differences could be found. Also among the different ind-
olizine 7-substituents (R2 in Table 1) examined (compds
3a, 3h–k), there were no significant differences in enzyme
inhibition. The sulfone 6, which is identical to the sulfo-
nate 3a except for the oxygen in the indolizine 1-position
in 3a, was only slightly less active, showing that the oxy-
gen is not required for enzyme inhibition to occur. Even
when the substituent in the 1-position was removed to-
tally (compds 7a–d) much of the activity was retained.
The indolizines 3, 6 and 7 and the azaindolizines 9–11
were examined as inhibitors of 15-lipoxygenase from
soybeans and the results are presented in Tables 1 and
2. All compounds were more active than the reference
compound quercetin and a variety of substituents on
the indolizine sulfonates were well tolerated. Sulfonates
3 with aryl and small alkyl groups attached to the sulfur
atom (R3, Table 1) were highly active. More bulky alkyl
groups (compd 3n and 3o) were somewhat weaker inhibi-
tors. If R3 is aryl, both electron donating and withdraw-
ing substituents may be present in active compounds
and the enzyme is apparently not very sensitive to steri-
cally demanding substituents. It seems to be a slight
preference for electron donating substituents on the aryl.
Also the azaindolizine sulfonates examined were power-
ful 15-lipoxygenase inhibitors (Table 2). When com-
pared to the corresponding sulfonate derived from
pyridine (compd 3h, IC50 25 lM), it appears that an ex-
tra nitrogen in the indolizine 5- or 8-position is beneficial
for activity.
As discussed above, a variety of indolizine sulfonates
were highly potent inhibitors of 15-lipoxygenase from
soybeans. However, we were somewhat surprised that
the activity was virtually independent of the substitution

S. Teklu et al. / Bioorg. Med. Chem. 13 (2005) 3127–3139
3129
Table 1. Inhibitory activity of indolizine derivatives 3, 6 and 7 against 15-LOfrom soybeans
Compd no.
R1
R2
R3
IC50 (lM)a,b 15-LOfrom soybeans
3a
3b
3c
3d
3e
3f
–Ph
–CN
–CN
–OTsc
–OTs
–OTs
–OTs
–OTs
–OTs
–OTs
–OTs
22
22
20
20
24
29
30
25
2
2
2
3
2
2
5
3
–C6H4–p-F
–C6H4–p-Cl
–C6H4–p-CH3
–C6H4–p-OCH3
–CH2CH3
–(CH2)3CH3
–Ph
–CN
–CN
–CN
–CN
3g
3h
3i
–CN
–H
–Ph
–Ph
Ts –CHO–O
–COCH3
–C(CH3)3
–CN
20
2
3j
–OTs
–OTs
–OSO2CH3
23
22
22
28
42
42
25
24
22
17
16
25
25
27
19
15
21
23
22
23
24
29
30
30
33
27
1
4
2
6
7
3
2
3
2
2
3
3
3
5
2
2
2
2
3
6
3
3
2
6
7
3
3k
3l
–Ph
–Ph
3m
3n
3o
3p
3q
3r
–Ph
–Ph
–CN
–CN
–OSO2(CH2)3CH3
–OSO2CH(CH3)2
–OSO2CF3
–Ph
–Ph
–CN
–CN
–OSO2N(CH3)2
–OSO2Ph
–Ph
–Ph
–CN
–CN
–OSO2–C6H4–o-CH3
–OSO2–C6H2–2,4,6-triCH3
–OSO2–C6H4–p-CH(CH3)2
–OSO2–C6H4–p-OCH3
–OSO2–C6H4–p-OCH3
–OSO2–C6H3–2,4-diOCH3
–OSO2–C6H3–3,4-diOCH3
–OSO2–C6H3–2,5-diOCH3
–OSO2–(2-thienyl)
–OSO2–(3-thienyl)
–OSO2–C6H4–p-Cl
–OSO2–C6H4–p-CF3
–OSO2–C6H4–p-SO2CH3
–SO2–C6H4–p-CH3
–H
3s
–Ph
–Ph
–CN
–CN
3t
3u
3v
3w
3x
3y
3z
3aa
3bb
3cc
3dd
6
–Ph
–CN
–CN
–C6H4–p-CH3
–Ph
–Ph
–CN
–CN
–Ph
–Ph
–CN
–CN
–Ph
–Ph
–CN
–CN
–Ph
–Ph
–CN
–CN
–Ph
–Ph
–CN
–CN
7a
7b
7c
7d
–C6H4–p-F
–C6H4–p-Cl
–C6H4–p-CH3
–CN
–CN
–H
–H
–CN
–H
a Data are shown SD.
b Quercetin was used as positive control, IC50 51 3 lM.
c OTs = OSO2–C6H4–p-CH3.
N
N
O
N
1) Dioxane, ∆
OTs
OTs
N
N
+
+
N
2) ClSO2R3, DMAP
0 oC
Ph
Ph
Ph
Ph
8
1a
Ph
9, 37%
Ph
10, 52%
N
Ph
N
OTs
O
N
N
Ph
O
Ph
Ph
Ph
Ph
12
11
Scheme 2.
pattern in most positions on the indolizines examined.
This led us to fear that the compounds were promiscu-
ous inhibitors that do not bind reversible to the enzyme
in a classical 1:1 ratio, but form larger aggregates, which
incorporate the enzyme or absorb to the enzyme surface.
To be judged promiscuous, an enzyme inhibitor must
inhibit in a time-dependent manner, be sensitive to
detergent and to enzyme concentration, and form parti-
cles detectable by light scattering.7 We chose to study
the potential promiscuity of indolizine sulfonates 3d
and 3m by observing the effect of preincubation and
detergents on the inhibition of 15-lipoxygenase. Samples

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S. Teklu et al. / Bioorg. Med. Chem. 13 (2005) 3127–3139
Table 2. Inhibitory activity of azaindolizine tosylates 9–11 against 15-
LOfrom soybeans
100
90
80
70
60
50
40
30
20
10
0
Compd no.
IC50 (lM)a,b
9
22
15
17
3
1
2
10
11
a Data are shown SD.
b Quercetin was used as positive control, IC50 51 3 lM.
for assays of promiscuity were chosen among the sub-
stances available to ensure variation both in enzyme
inhibition and solubility. It was also investigated if the
compounds form particles, which could be detected by
light scattering.
1.2
1.4
1.6
1.8
2
(a)
Log conc. inhibitor (µM)
Inhibitory activities of the indolizines 3d and 3m, as well
as quercetin, against 15-LOwere measured with and
without preincubation; the inhibitor, enzyme and buffer
were mixed and the linoleic acid substrate added after
5 min or immediately. % Inhibition versus log concn
inhibitor plots are shown in Figure 1. In all cases preincu-
bation appears to have only minor effects on inhibition.
100
90
80
70
60
50
40
30
20
10
0
In order to see if the presence of a detergent influence
the activity of the indolizines, inhibition with and with-
out the presence of 3-[(3-cholamidopropyl)dimethylam-
monio]-1-propanesulfonate (CHAPS) were determined
for compounds 3d, 3m and quercetin, and the results
are presented in Figure 2.
1.2
1.4
1.6
1.8
2
Log conc. inhibitor (µM)
(b)
Also the presence of CHAPS had minimal effect on
inhibitory activity, indicating that the compounds were
not promiscuous inhibitors.
100
90
80
70
60
50
40
30
20
10
0
Finally, we used dynamic light scattering (DLS) in order
to examine the tendency of the indolizines to form par-
ticles or aggregates. Buffered solutions (4.1 lM) of com-
pounds 3d, 3h and 3m containing 1.67% v/v DMSO, as
in the enzyme inhibition experiments, were used. The re-
sults are summarized in Table 3. No particles (3m) or
just few particles (3d and 3h) were observed. In case of
compound 3m, the experiment was repeated with 15-
LOpresent, and still no particles could be observed.
Since no significant aggregation was observed and the
inhibition was virtually unchanged by preincubation or
detergent addition, it is highly unlikely that the indoli-
zines are promiscuous enzyme inhibitors.
1.2
1.4
1.6
1.8
2
Log conc. inhibitor (µM)
(c)
Figure 1. Effect on preincubation on inhibitory activity: activity with
preincubation —j—, activity without preincubation Á Á ÁÇÁ Á Á for (a)
compound 3d; (b) compound 3m; (c) quercetin.
3. Conclusions
phy was available from Merck (Darmstadt, Germany)
(Merck No. 9385) or Fluka (Fluka No. 60752). Acetoni-
trile and DCE were distilled from CaH2, and THF and
1,4-dioxane from Na/benzophenone. Other reagents
Indolizine 1-sulfonates are profound inhibitors of 15-
lipoxygenase. A wide variety of substituents are well tol-
erated. It is believed that the indolizines are so-called
nonantioxidant inhibitors, which interact directly with
the enzyme. Inhibition from aggregates of indolizines,
promiscuous inhibition, is highly unlikely.
1
were used as received. The H NMR spectra were re-
corded at 300 MHz with a Bruker Avance DPX 300
instrument or at 200 MHz with a Bruker Avance DPX
200 instrument. The 13C NMR spectra were recorded
at 75 or 50 MHz, and the 19F NMR spectra at
188 MHz using instruments mentioned above. The spec-
tra are recorded at 20 ꢁC. Chemical shifts (d) are given in
ppm downfield from tetramethylsilane. MS spectra
under electron impact conditions were recorded with a
4. Experimental
15-Lipoxygenase (Type 1) was purchased from Sigma
(St. Louis, MO, USA). Silica gel for flash chromatogra-

S. Teklu et al. / Bioorg. Med. Chem. 13 (2005) 3127–3139
3131
tra were recorded with a Bruker Apex 47e FT-ICR mass
spectrometer. Melting points are uncorrected. All mea-
surements of 15-lipoxygenase activities were carried
out in a Shimadzu UV-160A spectrophotometer (Shima-
dzu, Kyoto, Japan) at 20–22 ꢁC. Compounds available
by the literature methods: 1b,8 1c,9 1d,9 1e,10 1f,11 1g,12
3a,1b 3o,1b 5a,1b 7a,1b 11.1c
100
90
80
70
60
50
40
30
20
10
0
4.1. 1-{[(4-Methylphenyl)sulfonyl]oxy}-2,3-bis(4-fluoro-
phenyl)-7-indolizinecarbonitrile (3b)
A mixture of 2,3-bis(4-fluorophenyl)-2-cyclopropen-1-
one 1b (121 mg, 0.50 mmol) and 4-cyanopyridine 2b
(52 mg, 0.50 mmol) in dry DCE (30 mL) was refluxed un-
der N2 for 24 h and cooled to 0 ꢁC, before N,N-4-dimeth-
ylaminopyridine (122 mg, 1.00 mmol) and toluene-4-
sulfonyl chloride (191 mg, 1.00 mmol) were added. The
resulting mixture was stirred under N2 at 0 ꢁC for
30 min and at ambient temperature for 24 h, washed with
water (25 mL) and brine (25 mL), dried (MgSO4) and
evaporated in vacuo. The product was purified by flash
chromatography on silica gel eluting with EtOAc–hex-
ane (1:4); yield 138 mg (55%), yellow crystals, mp
1.20
1.40
1.60
1.80
2.00
(a)
Log conc. inhibitor (µM)
100
90
80
70
60
50
40
30
20
10
0
1
192 ꢁC, Rf = 0.25 (SiO2, EtOAc–hexane, 1:4). H NMR
(200 MHz, CDCl3): d 2.39 (s, 3H, CH3), 6.60 (dd, 1H,
J = 7.6 and 1.6 Hz, H-6), 6.79–6.97 (m, 4H, Ph), 7.05–
7.28 (m, 6H, Ph), 7.44–7.48 (m, 2H, Ph), 7.87 (br s,
1H, H-8), 7.89 (m, 1H, H-5); 13C NMR (50 MHz,
CDCl3): d 22.0 (CH3), 101.3, 111.6, 115.3, 115.7, 116.9,
117.3, 118.8, 122.4, 122.6, 123.6, 125.0, 125.2 (d,
JCF = 3.55 Hz), 126.8 (d, JCF = 2.90 Hz), 128.8, 129.8,
131.8, 131.9, 132.1, 132.8, 133.1, 146.2, 162.9 (d,
JCF = 248.98 Hz); 19F NMR (188 MHz, CDCl3): d
111.1, 114.8; MS (EI) m/z (rel. %): 500 (1, M+), 345
(100), 214 (6), 131 (16), 103 (33), 91 (7); HRMS: Found
500.1006, calcd for C28H18F2N2O3S 500.1017.
1.20
1.40
1.60
1.80
2.00
(b)
Log conc. inhibitor (µM)
100
90
80
70
60
50
40
30
20
10
0
4.2. 1-{[(4-Methylphenyl)sulfonyl]oxy}-2,3-bis(4-chloro-
phenyl)-7-indolizinecarbonitrile (3c)
The title compound was prepared from cyclopropenone
1c, pyridine 2b and toluene-4-sulfonyl chloride as de-
scribed for 3b above. The product was purified by flash
chromatography on silica gel eluting with EtOAc–hex-
ane (1:4); yield 276 mg (52%), yellow crystals, mp 207–
209 ꢁC, Rf = 0.33 (SiO2, EtOAc–hexane, 1:4). 1H
NMR (300 MHz, CDCl3): d 2.29 (s, 3H, CH3), 6.55
(dd, 1H, J = 7.65 and 1.43 Hz, H-6), 6.79–6.81 (m, 2H,
Ar), 6.97–7.12 (m, 6H, Ar), 7.35–7.38 (m, 4H, Ar),
7.85 (br s, 1H, H-8), 7.87 (br s, 1H, H-5); 13C NMR
(75 MHz, CDCl3): d 23.1 (CH3), 101.6, 122.1, 122.3,
123.9, 125.1, 126.9, 127.4, 128.5, 128.7, 128.8, 129.2,
129.8, 130.2, 131.6, 131.5, 131.8, 132.1, 133.8, 135.7,
146.2; MS (EI) m/z (rel. %): 533 (26, M+), 381 (25),
345 (13), 157 (100), 139 (11); HRMS: Found 532.0493,
calcd for C28H18Cl2N2O3S 532.0510.
1.20
1.40
1.60
1.80
2.00
Log conc. inhibitor (µM)
(c)
Figure 2. Effect of detergent on inhibitory activity with CHAPS —j—,
without CHAPS Á Á ÁÇÁ Á Á for (a) compound 3d; (b) compound 3m; (c)
quercetin.
Table 3. Particle measurements from dynamic light scattering
experiments
Compd no.
KCPa
21.2
Particle sizeb
3d
Few particles
80 nm
3h
14.2
6.1
Few particles
63–77 nm
No particlesc
3m
a Kilocounts per second.
4.3. 1-{[(4-Methylphenyl)sulfonyl]oxy}-2,3-bis(4-methyl-
phenyl)-7-indolizinecarbonitrile (3d)
b Determined after 5–10 min.
c Few particles observed after 1 h.
The title compound was prepared from cyclopropenone
1d, pyridine 2b and toluene-4-sulfonyl chloride as de-
scribed for 3b above. The product was purified by flash
VG Prospec instrument at 70 eV ionizing voltage, and
are presented as m/z (% rel. int.). Electrospray MS spec-

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S. Teklu et al. / Bioorg. Med. Chem. 13 (2005) 3127–3139
chromatography on silica gel eluting with EtOAc–hex-
ane (1:9) followed by (1:4); yield 190 mg (77%), yellow
crystals, mp 205–208 ꢁC, Rf = 0.29 (SiO2, EtOAc–hex-
Found: C, 65.07; H, 5.39. C20H20N2O3S requires C,
65.20; H, 5.47.
1
ane, 1:4). H NMR (300 MHz, CDCl3): d 2.27 (s, 3H,
4.6. 1-{[(4-Methylphenyl)sulfonyl]oxy}-2,3-dibutyl-7-indo-
lizinecarbonitrile (3g)
CH3), 2.30 (s, 3H, CH3), 2.35 (s, 3H, CH3), 6.48 (dd,
1H, J = 7.5 and 1.8 Hz, H-6), 6.77–6.94 (m, 6H, Ar),
7.06–7.19 (m, 4H, Ar), 7.35–7.37 (m, 2H, Ar), 7.81 (br
s, 1H, H-8), 7.87 (dd, 1H, J = 7.5 and 0.89 Hz, H-5);
13C NMR (75 MHz, CDCl3): d 21.6 (CH3), 21.8
(CH3), 22.0 (CH3), 100.5, 111.0, 119.1, 122.4, 123.1,
123.3, 123.9, 124.8, 126.4, 126.9, 128.0, 128.8, 129.6,
130.2, 130.3, 130.7, 131.9, 137.0, 139.3, 145.7; MS (EI)
m/z (rel. %): 492 (1, M+), 337 (100), 205 (4), 131 (5),
103 (14); HRMS: Found 492.1507, calcd for
C30H24N2O3S 492.1491.
The title compound was prepared from cyclopropenone
1g (103 mg, 0.62 mmol), pyridine 2b (64 mg, 0.62 mmol)
and toluene-4-sulfonyl chloride (248 mg, 1.30 mmol) as
described for 3b above. The product was purified by
flash chromatography on silica gel, eluting with
EtOAc–hexane (1:29) followed by (1:19); yield 150 mg
(57%), yellow crystals, mp 121–123 ꢁC. 1H NMR
(200 MHz, CDCl3): d 0.86 (t, 3H, J = 7.1 Hz, CH3),
0.93 (t, 3H, J = 7.1 Hz, CH3), 1.15–1.28 (m, 4H,
2 · CH2), 1.31–1.51 (m, 4H, 2 · CH2), 2.32 (t,
2H, J = 7.7 Hz, CH2), 2.48 (s, 3H, CH3), 2.77 (t, 2H,
J = 7.6 Hz, CH2), 6.46 (dd, 1H, J = 7.3 and 1.7 Hz, H-
6) 7.01 (br s, 1H, H-8), 7.32 (d, 2H, J = 8.2 Hz, Ar),
7.59 (dd, 1H, J = 7.3 and 0.57 Hz, H-5), 7.75 (d, 2H,
J = 8.2 Hz, Ar); 13C NMR (50 MHz, CDCl3): d 14.2
(2 · CH3), 22.2 (CH2), 23.0 (CH2), 23.1 (CH2), 23.4
(CH2), 24.2 (CH2), 29.9 (CH2), 32.6 (CH3), 98.0,
110.1, 121.5, 121.7, 123.2, 123.6, 124.5, 127.6, 129.1,
130.4, 132.7, 146.6; MS (EI) m/z (rel. %): 424 (2, M+),
269 (100), 227 (16), 183 (7), 131 (5), 103 (15), 91 (7);
Anal. Found: C, 67.76; H, 6.70; N 6.45. C24H28N2O3S
requires C, 67.90; H, 6.65; N, 6.60.
4.4. 1-{[(4-Methylphenyl)sulfonyl]oxy}-2,3-bis(4-methoxy-
phenyl)-7-indolizinecarbonitrile (3e)
The title compound was prepared from cyclopropenone
1e (314 mg, 1.00 mmol), pyridine 2b (104 mg,
1.00 mmol) and toluene-4-sulfonyl chloride (382 mg,
2.00 mmol) as described for 3b above. The product
was purified by flash chromatography on silica gel elut-
ing with EtOAc–hexane (1:9) followed by (1:4); yield
220 mg (42%), yellow crystals, mp 204–205 ꢁC,
Rf = 0.50 (SiO2, EtOAc–hexane, 1:1). 1H NMR
(300 MHz, CDCl3): d 2.31 (s, 3H, CH3), 3.80 (s, 3H,
OCH3), 3.85 (s, 3H, OCH3), 6.47 (dd, 1H, J = 7.4 and
1.6 Hz, H-6), 6.57–6.61 (m, 2H, Ar), 6.80–6.94 (m, 6H,
Ar), 7.09–7.14 (m, 2H, Ar), 7.25–7.36 (m, 2H, Ar),
7.78 (dd, 1H, J = 1.6 and 0.90 Hz, H-8), 7.83 (dd, 1H,
J = 7.4 and 0.90 Hz, H-5); 13C NMR (75 MHz, CDCl3):
d 22.0 (CH3), 55.6 (OCH3), 55.7 (OCH3), 100.4, 111.0,
113.8, 114.7, 115.2, 119.2, 121.5, 122.4, 122.8, 123.2,
123.4, 123.5, 124.7, 126.8, 128.6, 128.9, 129.7, 131.4,
132.2, 132.7, 145.3, 159.1, 160.3; MS (CI) m/z (rel. %):
525 (2, M+1), 370 (91), 282 (6), 238 (2), 152 (3), 139
(22), 135 (28), 92 (100); HRMS: Found 524.1484, calcd
for C30H24N2O5S 524.1506.
4.7. 2,3-Diphenyl-1-indolizinol tosylate (3h)
The title compound was prepared from cyclopropenone
1a (309 mg, 1.50 mmol), pyridine 2a (121 lL,
1.50 mmol) and toluene-4-sulfonyl chloride (572 mg,
3.00 mmol) as described for 3b above. The product
was purified by flash chromatography on silica gel
eluting with EtOAc–hexane (1:29) followed by (1:19);
yield 383 mg (58%), yellow crystals, mp 156–159 ꢁC.
1H NMR (200 MHz, CDCl3): d 2.24 (s, 3H, CH3),
6.44 (m, 1H, H-6), 6.76 (m, 1H, H-7), 6.79–6.85 (m,
4H, Ph), 6.99–7.03 (m, 3H, Ph), 7.16–7.21 (m, 2H,
Ph), 7.21–7.32 (m, 5H, Ar), 7.54 (br d, 1H, J = 9.1 Hz,
H-8), 7.91 (br d, 1H, J = 7.2 Hz, H-5); 13C NMR
(50 MHz, CDCl3): d 22.0 (CH3), 111.7, 117.6, 118.8,
119.6, 120.8, 121.0, 123.5, 125.4, 126.5, 128.0, 128.3,
128.8, 129.3, 129.4, 130.5, 130.8, 131.2, 131.9, 132.2,
145.0; MS (EI) m/z (rel. %): 440 (14, M+), 285 (100),
256 (5), 178 (6), 157 (7), 139 (8), 106 (6), 92 (14), 78
(10); Anal. Found: C, 74.23; H, 4.92; N, 3.38.
C27H21NO3S requires C, 73.78; H, 4.82; N, 3.19.
4.5. 1-{[(4-Methylphenyl)sulfonyl]oxy}-2,3-diethyl-7-indo-
lizinecarbonitrile (3f)
The title compound was prepared from cyclopropenone
1f (163 mg, 1.48 mmol), pyridine 2b (154 mg, 1.48 mmol)
and toluene-4-sulfonyl chloride (573 mg, 3.00 mmol) as
described for 3b above. The product was purified by flash
chromatography on silica gel eluting with EtOAc–hex-
ane (1:29) followed by (1:19); yield 398 mg (73%), yellow
crystals, mp 110–114 ꢁC, Rf = 0.42 (SiO2, EtOAc–hex-
1
ane, 1:4). H NMR (200 MHz, CDCl3): d 1.09 (t, 3H,
4.8. 1-{[(4-Methylphenyl)sulfonyl]oxy}-2,3-diphenyl-7-
indolizinecarboxaldehyde (3i)
J = 7.6 Hz, CH3), 1.17 (t, 3H, J = 7.6 Hz, CH3), 2.51 (s,
3H, CH3), 2.53 (q, 2H, J = 7.6 Hz, CH2), 2.86 (q, 2H,
J = 7.6 Hz, CH2), 6.49 (dd, 1H, J = 7.4 and 1.8 Hz, H-
6), 6.94 (br s, 1H, H-8), 7.37 (d, 2H, J = 8.2 Hz, Ar),
7.63 (br d, 1H, J = 7.4 Hz, H-5), 7.77 (d, 2H,
J = 8.2 Hz, Ar); 13C NMR (50 MHz, CDCl3): d 12.4
(CH3), 15.3 (CH2), 16.8 (CH3), 17.7 (CH2), 22.1 (CH3),
98.0, 110.1, 119.4, 121.4, 123.5, 124.3, 125.5, 127.2,
129.1, 130.4, 132.7, 146.6; MS (EI) m/z (rel. %): 368 (2,
M+), 213 (100), 197 (4), 183 (4), 103 (20), 91 (5); HRMS:
Found 368.1194, calcd for C20H20N2O3S 368.1187; Anal.
The title compound was prepared from cyclopropenone
1a (309 mg, 1.50 mmol), pyridine 2c (142 lL,
1.50 mmol) and toluene-4-sulfonyl chloride (572 mg,
3.00 mmol) as described for 3b above. The product
was purified by flash chromatography on silica gel elut-
ing with EtOAc–hexane (1:29) followed by (1:19); yield
491 mg (70%), yellow crystals, mp 153–156 ꢁC. 1H
NMR (300 MHz, CDCl3): d 2.26 (s, 3H, CH3), 6.85
(br d, 1H, J = 7.4 Hz, H-6), 6.87–7.09 (m, 7H, Ph),

S. Teklu et al. / Bioorg. Med. Chem. 13 (2005) 3127–3139
3133
7.19–7.22 (m, 2H, Ar), 7.33–7.39 (m, 5H, Ar), 7.89 (br d,
1H, J = 7.4 Hz, H-5), 8.06 (dd, 1H, J = 1.6 and 0.83 Hz,
H-8), 9.89 (s, 1H, CHO); 13C NMR (75 MHz, CDCl3): d
22.0 (CH3), 107.5, 122.4, 122.9, 124.2, 124.4, 126.8,
127.2, 127.9, 128.2, 128.6, 128.8, 129.2, 129.5, 129.6,
130.4, 130.9, 131.6, 145.6, 189.9 (CO); MS (EI) m/z
(rel. %): 467 (1, M+), 312 (100), 282 (3), 106 (25), 92
(3); Anal. Found: C, 72.30; H, 4.90; N, 3.11.
C28H21NO4S requires C, 71.93; H, 4.53; N, 3.00.
CDCl3): d 2.60 (s, 3H, CH3), 6.51 (dd, 1H, J = 7.4 and
1.6 Hz, H-6), 7.22–7.45 (m, 7H, Ph), 7.46–7.55 (m, 3H,
Ph), 7.94 (dd, 1H, J = 7.4 and 1.0 Hz, H-5), 8.02 (dd,
1H, J = 1.6 and 1.0 Hz, H-8); 13C NMR (75 MHz,
CDCl3): d 37.6 (CH3), 101.4, 111.6, 118.9, 122.6,
123.6, 123.9, 124.8, 126.8, 128.3, 129.2, 129.2, 129.2,
129.5, 130.5, 130.9, 131.1; MS (EI) m/z (rel. %): 388
(5, M+), 309 (100), 178 (5), 131 (11), 103 (27); Anal.
Found: C, 67.85; H, 4.07; N, 7.03. C22H16N2O3S re-
quires C, 68.02; H, 4.15; N, 7.21.
4.9. 1-{[(4-Methylphenyl)sulfonyl]oxy}-2,3-diphenyl-7-
indolizinylethanone (3j)
4.12. 1-[(Butylsulfonyl)oxy]-2,3-diphenyl-7-indolizinecar-
bonitrile (3m)
The title compound was prepared from cyclopropenone
1a (309 mg, 1.50 mmol), pyridine 2d (165 lL, 1.50 mmol)
and toluene-4-sulfonyl chloride (572 mg, 3.00 mmol) as
described for 3b above. The product was purified by flash
chromatography on silica gel eluting with EtOAc–hex-
ane (1:29) followed by (1:19); yield 551 mg (76%), yellow
crystals, mp 149–152 ꢁC. 1H NMR (300 MHz, CDCl3): d
2.15 (s, 3H, CH3), 2.59 (s, 3H, CH3), 6.85 (br d, 1H,
J = 7.4 Hz, H-6), 6.87–6.89 (m, 3H, Ar), 7.01–7.08 (m,
4H, Ar), 7.18–7.23 (m, 2H, Ar), 7.32–7.35 (m, 5H, Ar),
7.86 (br d, 1H, J = 7.4 Hz, H-5), 8.17 (br s, 1H, H-8);
13C NMR (75 MHz, CDCl3): d 22.0 (CH3), 26.0 (CH3),
109.4, 121.4, 121.7, 122.6, 123.2, 123.8, 127.1, 127.7,
127.8, 128.2, 128.8, 129.0, 129.5, 129.6, 129.8, 130.2,
131.0, 131.3, 131.6, 145.5, 196.0 (CO); MS (EI) m/z
(rel. %): 481 (1, M+), 326 (100), 178 (5), 148 (5), 120
(23), 91 (8), 78 (4); Anal. Found: C, 72.11; H, 4.81; N,
2.92. C29H23NO4S requires C, 72.33; H, 4.81; N, 2.92.
The title compound was prepared from cyclopropenone
1a (206 mg, 1.00 mmol), pyridine 2b (104 mg, 1.00 mmol)
and n-butanesulfonyl chloride (258 lL, 2.00 mmol) as de-
scribed for 3b above. The product was purified by flash
chromatography on silica gel eluting with EtOAc–hexane
(1:19) followed by (1:9); yield 263 mg (61%), yellow crys-
tals, mp 172–174 ꢁC, Rf = 0.46 (SiO2, EtOAc–hexane,
1:4). 1H NMR (200 MHz, CDCl3): d 0.73 (t, 3H,
J = 7.23 Hz, CH3), 1.37 (m, 2H, CH2), 1.53 (m, 2H,
CH2), 2.75 (t, 2H, J = 5.1 Hz, CH2), 6.54 (dd, 1H,
J = 7.4 and 1.7 Hz, H-6), 7.23–7.31 (m, 7H, Ph), 7.35–
7.40 (m, 3H, Ph), 7.94 (dd, 1H, J = 7.4 and 0.98 Hz, H-
5), 8.05 (dd, 1H, J = 1.7 and 0.98 Hz, H-8); 13C NMR
(75 MHz, CDCl3): d 13.6 (CH3), 23.1 (CH2), 25.4
(CH2), 50.8 (CH2), 101.1, 111.5, 119.0, 122.6, 123.2,
123.6, 124.0, 125.1, 126.7, 128.2, 129.0, 129.2, 129.5,
129.7, 130.7, 130.8, 131.2; MS (EI) m/z (rel. %): 430 (2,
M+), 309 (100), 178 (5), 131 (8), 103 (19); HRMS: Found
430.1351, calcd for C25H22N2O3S 430.1351.
4.10. 7-(1,1-Dimethylethyl)-2,3-diphenyl-1-indolizinol
tosylate (3k)
4.13. 1-{[(2-Methyl)ethylsulfonyl]oxy}-2,3-diphenyl-7-indo-
lizinecarbonitrile (3n)
The title compound was prepared from cyclopropenone
1a (309 mg, 1.50 mmol), pyridine 2e (121 lL,
1.50 mmol) and toluene-4-sulfonyl chloride (572 mg,
3.00 mmol) as described for 3b above. The product
was purified by flash chromatography on silica gel elut-
ing with EtOAc–hexane (1:29) followed by (1:19); yield
The title compound was prepared from cyclopropenone
1a (309 mg, 1.50 mmol), pyridine 2b (156 mg,
1.50 mmol) and toluene-4-sulfonyl chloride (572 mg,
3.00 mmol) as described for 3b above. The product
was purified by flash chromatography on silica gel elut-
ing with EtOAc–hexane (1:29) followed by (1:19); yield
183 mg (44%), yellow crystals, mp 195–198 ꢁC,
Rf = 0.41 (SiO2, EtOAc–hexane, 1:4). 1H NMR
1
386 mg (52%), yellow crystals, mp 95–98 ꢁC. H NMR
(300 MHz, CDCl3): d 1.32 (s, 9H, 3 · CH3), 2.29 (s,
3H, CH3), 6.52 (dd, 1H, J = 7.6 and 1.2 Hz, H-6),
6.92–7.01 (m, 6H, Ar), 7.0–7.30 (m, 8H, Ar), 7.33
(br s, 1H, H-8), 7.92 (br d, 1H, J = 7.6 Hz, H-5); 13C
NMR (75 MHz, CDCl3): d 29.5 (3 · CH3), 30.8 (C),
32.1 (CH3), 111.3, 118.9, 121.0, 123.3, 125.4, 125.5,
126.8, 128.1, 128.1, 128.9, 129.3, 129.5, 130.5, 131.0,
131.2, 132.3, 132.6; MS (ESI) m/z (rel. %): 496 (100,
M+1); Anal. Found: C, 74.62; H, 5.55; N, 2.87.
C31H29NO3S requires C, 75.12; H, 5.90; N, 2.83.
(300 MHz, CDCl3):
d
1.22 (d, 6H, J = 6.9 Hz,
2 · CH3), 3.15 (m, 1H, CH), 6.53 (dd, 1H, J = 7.4 and
1.7 Hz, H-6), 7.16 (m, 7H, Ph), 7.35–7.42 (m, 3H, Ph),
7.94 (dd, 1H, J = 7.4 and 0.95 Hz, H-5), 8.07 (dd, 1H,
J = 1.7 and 0.95 Hz, H-8); 13C NMR (75 MHz, CDCl3):
d 17.0 (2 · CH3), 53.6 (CH), 100.9, 111.3, 119.1, 122.5,
123.4, 123.5, 124.2, 125.3, 126.2, 128.1, 128.6, 128.8,
129.3, 129.3, 129.6, 130.8, 130.9, 131.2; MS (EI) m/z
(rel. %): 416 (1, M+), 309 (100), 281 (7), 178 (8), 152
(2), 131 (10), 103 (25); HRMS: Found 416.1210, calcd
for C24H20N2O3S 416.1194.
4.11. 1-[(Methylsulfonyl)oxy]-2,3-diphenyl-7-indolizine-
carbonitrile (3l)
The title compound was prepared from cyclopropenone
1a (309 mg, 1.50 mmol), pyridine 2b (156 mg,
1.50 mmol) and methanesulfonyl chloride (344 mg,
3.00 mmol) as described for 3b above. The product
was purified by flash chromatography on silica gel elut-
ing with EtOAc–hexane (1:4); yield 411 mg (71%), yel-
low crystals, mp 210–212 ꢁC. 1H NMR (300 MHz,
4.14. 1-[(N,N-Dimethylaminosulfonyl)oxy]-2,3-diphenyl-
7-indolizinecarbonitrile (3p)
The title compound was prepared from cyclopropenone
1a (309 mg, 1.50 mmol), pyridine 2b (156 mg, 1.50 mmol)
and dimethylsulfamoyl chloride (323 lL, 3.00 mmol) as

3134
S. Teklu et al. / Bioorg. Med. Chem. 13 (2005) 3127–3139
described for 3b above. The product was purified by flash
chromatography on silica gel eluting with EtOAc–hexane
(1:19); yield 229 mg (55%), yellow crystals, mp 212–
213 ꢁC, Rf = 0.19 (SiO2, EtOAc–hexane, 1:4). H NMR
(300 MHz, CDCl3): d 2.61 (s, 6H, 2 · CH3), 6.54 (dd,
1H, J = 7.4 and 1.7 Hz, H-6), 7.26–7.33 (m, 7H, Ph),
7.39–7.43 (m, 3H, Ph), 7.97 (dd, 1H, J = 7.4 and
0.71 Hz, H-5), 8.14 (br s, 1H, H-8); 13C NMR
(75 MHz, CDCl3): d 38.6 (2 · CH3), 100.7, 111.3, 119.2,
122.4, 123.1, 123.3, 123.9, 125.4, 128.0, 128.8, 129.3,
129.4, 129.7, 130.8, 130.9, 131.4; MS (EI) m/z (rel. %):
417 (1, M+), 309 (100), 281 (7), 178 (7), 103 (23); HRMS:
Found 417.1165, calcd for C23H19N3O3S 417.1147.
1.50 mmol) and 2,4,6-trimethylbenzenesulfonyl chloride
(752 mg, 3.00 mmol) as described for 3b above. The
product was purified by flash chromatography on silica
gel eluting with EtOAc–hexane (1:19), yield 349 mg
(71%), yellow crystals, mp 196–199 ꢁC. 1H NMR
(200 MHz, CDCl3): d 2.28 (s, 3H, CH3), 2.35 (s, 6H,
2 · CH3), 6.56 (dd, 1H, J = 7.4 and 1.7 Hz), 6.71 (br s,
2H, Ar), 6.94–7.40 (m, 10H, Ph), 7.83 (br s, 1H, H-8),
7.95 (dd, 1H, J = 7.4 and 0.74 Hz, H-5); 13C NMR
(50 MHz, CDCl3): d 21.4 (CH3), 23.4 (2 · CH3), 100.8,
111.2, 119.1, 122.5, 123.6, 123.8, 124.1, 125.1, 127.0,
127.4, 128.2, 129.3, 129.6, 130.2, 130.6, 130.9, 132.2,
140.8, 144.4; MS (CI) m/z (rel. %): 493 (5, M+1), 310
(100), 281 (6), 185 (6), 178 (6), 167 (4), 151 (4), 120
(20), 105 (14), 91 (4); Anal. Found: C, 73.32; H, 5.11.
C30H24N2O3S requires C, 73.32; H, 5.11.
1
4.15. 1-[(Phenylsulfonyl)oxy]-2,3-diphenyl-7-indolizine-
carbonitrile (3q)
The title compound was prepared from cyclopropenone
1a (206 mg, 1.00 mmol), pyridine 2b (104 mg,
1.00 mmol) and benzenesulfonyl chloride (530 mg,
2.00 mmol) as described for 3b above. The product
was purified by flash chromatography on silica gel elut-
ing with EtOAc–hexane (1:19) followed by (1:9); yield
277 mg (41%), yellow crystals, mp 208–209 ꢁC,
Rf = 0.31 (SiO2, EtOAc–hexane, 1:4). 1H NMR
(200 MHz, CDCl3): d 6.58 (br d, 1H, J = 7.4 Hz, H-6),
6.94 (br d, 2H, J = 6.3 Hz, Ph), 7.11–7.30 (m, 7H, Ph),
7.41–7.47 (m, 4H, Ph), 7.54 (m, 2H, Ph), 7.94 (br d,
1H, J = 7.4 Hz, H-5), 7.98 (br s, 1H, H-8); 13C NMR
(50 MHz, CDCl3): d 101.1, 111.3, 122.5, 123.4, 125.0,
127.5, 128.5, 128.8, 129.1, 129.4, 129.7, 130.4, 130.9,
134.6, 134.6; MS (EI) m/z (rel. %): 450 (2, M+), 309
(100), 279 (4), 178 (6), 131 (10), 103 (24), 77 (6); HRMS:
Found 450.1038, calcd for C27H18N2O3S 450.1059.
4.18. 1-{{[4-(2-Methylethyl)phenyl]sulfonyl}oxy}-2,3-di-
phenyl-7-indolizinecarbonitrile (3t)
The title compound was prepared from cyclopropenone
1a (309 mg, 1.50 mmol), pyridine 2b (156 mg,
1.50 mmol) and p-isopropylbenzenesulfonyl chloride
(617 lL, 3.00 mmol) as described for 3b above. The
product was purified by flash chromatography on silica
gel eluting with EtOAc–hexane (1:19); yield 315 mg
(64%), yellow crystals, mp 138–142 ꢁC. 1H NMR
(200 MHz, CDCl3):
d
1.22 (d, 6H, J = 6.9 Hz,
2 · CH3), 2.89 (m, 1H, CH), 6.57 (dd, 1H, J = 7.6 and
1.5 Hz, H-6), 6.96–7.23 (m, 9H, Ar), 7.30–7.45 (m, 5H,
Ar), 7.93 (br s, 1H, H-8), 7.96 (m, 1H, H-5); 13C
NMR (50 MHz, CDCl3): d 23.9 (2 · CH3), 34.6 (CH),
101.0, 111.3, 122.5, 123.3, 123.5, 123.8, 125.0, 127.0,
127.2, 127.5, 128.5, 129.0, 129.4, 129.7, 130.3, 130.9,
132.1; MS (EI) m/z (rel. %): 492 (1, M+), 309 (100),
279 (2), 178 (4), 131 (8), 103 (20); Anal. Found: C,
73.08; H, 5.16; N, 5.34. C30H24N2O3S requires C,
73.15; H, 4.91; N, 5.69.
4.16. 1-{[(2-Methylphenyl)sulfonyl]oxy}-2,3-diphenyl-7-
indolizinecarbonitrile (3r)
The title compound was prepared from cyclopropenone
1a (309 mg, 1.50 mmol), pyridine 2b (156 mg,
1.50 mmol) and o-toluenesulfonyl chloride (572 mg,
3.00 mmol) as described for 3b above. The product
was purified by flash chromatography on silica gel elut-
ing with EtOAc–hexane (1:19); yield 357 mg (77%), yel-
low crystals, mp 162–165 ꢁC. 1H NMR (300 MHz,
CDCl3): d 2.48 (s, 3H, CH3), 6.56 (dd, 1H, J = 7.4 and
1.7 Hz, H-6), 6.90 (m, 2H, Ar), 7.08–7.17 (m, 7H, Ar),
7.30–7.42 (m, 4H, Ar), 7.43–7.64 (dd, 1H, J = 7.9 and
1.3 Hz, Ar), 7.89 (dd, 1H, J = 1.7 and 0.97 Hz, H-8),
7.96 (dd, 1H, J = 7.4 and 0.97 Hz, H-5); 13C NMR
(75 MHz, CDCl3): d 21.3 (CH3), 100.9, 111.3, 119.0,
122.5, 123.5, 123.7, 124.1, 125.0, 126.2, 127.0, 127.6,
128.5, 129.3, 129.3, 129.6, 130.3, 130.7, 130.8, 133.1,
133.9, 134.7; MS (EI) m/z (rel. %): 464 (1, M+), 309
(100), 281 (2), 178 (4), 131 (8), 103 (21), 91 (4); Anal.
Found: C, 72.04; H, 4.71; N, 5.80. C28H20N2O3S re-
quires C, 72.39; H, 4.34; N, 6.03.
4.19. 1-{[(4-Methoxyphenyl)sulfonyl]oxy}-2,3-diphenyl-7-
indolizinecarbonitrile (3u)
The title compound was prepared from cyclopropenone
1a (309 mg, 1.50 mmol), pyridine 2b (156 mg,
1.50 mmol) and p-methoxybenzenesulfonyl chloride
(309 mg, 3.00 mmol) as described for 3b above. The
product was purified by flash chromatography on silica
gel eluting with EtOAc–hexane (1:19) followed by (1:9)
and finally (1:4); yield 480 mg (67%), yellow crystals,
mp 212–214 ꢁC, Rf = 0.37 (SiO2, EtOAc–hexane, 1:4).
1H NMR (200 MHz, CDCl3): d 3.79 (s, 3H, OCH3),
6.54 (dd, 1H, J = 7.4 and 1.7 Hz, H-6), 6.60 (m, 2H,
Ar), 6.89–6.94 (m, 2H, Ph), 7.03–7.08 (m, 3H, Ph),
7.09–7.27 (m, 2H, Ph), 7.34–7.49 (m, 5H, Ar), 7.92
(dd, 1H, J = 7.4 and 0.96 Hz, H-5), 7.99 (dd, 1H,
J = 1.7 and 0.96 Hz, H-8); 13C NMR (50 MHz, CDCl3):
d 56.0 (OCH3), 100.9, 111.3, 114.2, 122.5, 123.1, 123.5,
123.8, 125.1, 125.6, 126.9, 127.4, 128.4, 129.6, 130.4,
130.9, 130.9, 131.0, 164.4; MS (EI) m/z (rel. %): 480
(1, M+), 309 (100), 178 (5), 131 (10), 103 (23); HRMS:
Found 480.1144, calcd for C28H20N2O4S 480.1157;
Anal. Found: C, 69.95; H, 4.48. C28H20N2O4S requires
C, 69.98; H, 4.20.
4.17. 1-{[(2,4,6-Trimethylphenyl)sulfonyl]oxy}-2,3-diphen-
yl-7-indolizinecarbonitrile (3s)
The title compound was prepared from cyclopropenone
1a (309 mg, 1.50 mmol), pyridine 2b (156 mg,

S. Teklu et al. / Bioorg. Med. Chem. 13 (2005) 3127–3139
3135
4.20. 1-{[(4-Methoxyphenyl)sulfonyl]oxy}-2,3-bis(4-methyl-
phenyl)-7-indolizinecarbonitrile (3v)
6), 6.83–6.90 (m, 3H, Ar), 7.05–7.10 (m, 4H, Ar),
7.12–7.22 (m, 2H, Ar), 7.39–7.47 (m, 3H, Ar), 7.95
(dd, 1H, J = 7.4 and 0.96 Hz, H-5), 8.01 (dd, 1H,
J = 1.7 and 0.96 Hz, H-8); 13C NMR (75 MHz, CDCl3):
d 56.3 (OCH3), 56.5 (OCH3), 101.1, 110.3, 110.6, 111.4,
119.0, 122.5, 123.2, 123.5, 123.7, 127.0, 127.3, 128.1,
129.3, 129.4, 129.7, 129.8, 130.3, 131.9, 149.0, 154.2;
MS (EI) m/z (rel. %): 510 (1, M+), 309 (100), 281 (2),
178 (3), 131 (7), 103 (18); Anal. Found: C, 67.76; H,
4.01; N, 5.52. C29H22N2O5S requires C, 68.20; H, 4.34;
N, 5.49.
The title compound was prepared from cyclopropenone
1d (117 mg, 0.50 mmol), pyridine 2b (52 mg, 0.50 mmol)
and p-methoxybenzenesulfonyl chloride (103 mg,
1.00 mmol) as described for 3b above. The product
was purified by flash chromatography on silica gel elut-
ing with EtOAc–hexane (1:19) followed by (1:9) and fi-
nally (1:4); yield 132 mg (52%), yellow crystals, mp
175–176 ꢁC, Rf = 0.21 (SiO2, EtOAc–hexane, 1:4). 1H
NMR (300 MHz, CDCl3): d 2.31 (s, 3H, CH3), 2.34 (s,
3H, CH3), 3.84 (s, 3H, OCH3), 6.53 (dd, 1H, J = 7.4
and 1.7 Hz, H-6), 6.59 (d, 2H, J = 9.0 Hz, Ar), 6.82 (d,
2H, J = 8.0 Hz, Ar), 6.90 (d, 2H, J = 8.0 Hz, Ar), 7.05
(m, 2H, Ar), 7.11 (d, 2H, J = 8.0 Hz, Ar), 7.41 (d, 2H,
J = 9.0 Hz, Ar), 7.91 (br d, 1H, J = 7.4 Hz, H-5), 7.94
(br s, 1H, H-8); 13C NMR (75 MHz, CDCl3): d 21.6
(CH3), 21.8 (CH3), 55.9 (OCH3), 100.6, 111.1, 114.1,
119.2, 122.4, 123.0, 123.4, 123.8, 124.9, 125.9, 126.4,
126.9, 128.1, 129.1, 130.2, 130.4, 130.8, 131.0, 136.9,
139.3, 164.5; MS (EI) m/z (rel. %): 508 (1, M+), 337
(100), 321 (5), 309 (4), 205 (5), 191 (2), 155 (4), 131
(6), 103 (16); Anal. Found: C, 70.70; H, 4.98; N, 5.17.
C30H24N2O4S requires C, 70.85; H, 4.76; N, 5.51.
4.23. 1-{[(2,5-Dimethoxyphenyl)sulfonyl]oxy}-2,3-diphen-
yl-7-indolizinecarbonitrile (3y)
The title compound was prepared from cyclopropenone
1a (309 mg, 1.50 mmol), pyridine 2b (156 mg,
1.50 mmol) and 2,5-dimethoxybenzenesulfonyl chloride
(710 mg, 3.00 mmol) as described for 3b above. The
product was purified by flash chromatography on silica
gel eluting with EtOAc–hexane (1:4) followed by (1:2)
and finally (1:1); yield 398 mg (78%), yellow crystals,
1
mp 193–195 ꢁC. H NMR (300 MHz, CDCl3): d 3.67
(s, 3H, OCH3), 3.73 (s, 3H, OCH3), 6.51 (d, 1H,
J = 7.4 and 1.6 Hz, H-6), 6.89–7.09 (m, 10H, Ph),
7.34–7.40 (m, 3H, Ar), 7.90 (dd, 1H, J = 7.4 and
0.85 Hz, H-5), 7.93 (dd, 1H, J = 1.6 and 0.85 Hz, H-8);
13C NMR (75 MHz, CDCl3): d 56.5 (OCH3), 56.8
(OCH3), 100.7, 111.2, 114.1, 115.8, 119.1, 122.4, 123.2,
123.3, 123.5, 123.7, 124.0, 125.1, 127.4, 128.3, 129.3,
129.6, 130.5, 130.8, 130.9, 152.5, 152.9; MS (EI) m/z
(rel. %): 510 (1, M+), 309 (100), 281 (2), 178 (3), 138
(2), 103 (19); Anal. Found: C, 68.03; H, 4.42; N, 5.26.
C29H22N2O5S requires C, 68.20; H, 4.34; N, 5.49.
4.21. 1-{[(2,4-Dimethoxyphenyl)sulfonyl]oxy}-2,3-diphen-
yl-7-indolizinecarbonitrile (3w)
The title compound was prepared from cyclopropenone
1a (309 mg, 1.50 mmol), pyridine 2b (156 mg,
1.50 mmol) and 2,4-dimethoxybenzenesulfonyl chloride
(710 mg, 3.00 mmol) as described for 3b above. The
product was purified by flash chromatography on silica
gel eluting with EtOAc–hexane (1:4) followed by (1:2)
and finally (1:1); yield 378 mg (74%), yellow crystals,
mp 101–104 ꢁC, Rf = 0.15 (SiO2, EtOAc–hexane, 1:4).
1H NMR (200 MHz, CDCl3): d 3.72 (s, 3H, OCH3),
3.79 (s, 3H, OCH3), 6.09 (s, 1H, Ar), 6.28 (dd, 1H,
J = 8.9 and 2.0 Hz, Ar), 6.52 (dd, 1H, J = 7.4 and
1.6 Hz, H-6), 6.96–7.61 (m, 11H, Ar), 7.91 (br d, 1H,
J = 7.4 Hz, H-5), 7.99 (br s, 1H, H-8); 13C NMR
(50 MHz, CDCl3): d 56.1 (OCH3), 56.2 (OCH3), 99.4,
100.6, 104.8, 111.6, 114.6, 119.1, 122.3, 123.8, 123.9,
125.3, 127.2, 128.2, 129.2, 129.4, 129.5, 130.5, 131.0,
133.9, 159.8, 166.5; MS (EI) m/z (rel. %): 510 (1, M+),
309 (100), 281 (10), 279 (4), 178 (8), 138 (13), 131 (8),
103 (22), 77 (2); HRMS: Found 510.1268, calcd for
C29H22N2O5S 510.1249.
4.24. 1-{[(2-Thienyl)sulfonyl]oxy}-2,3-diphenyl-7-indoli-
zinecarbonitrile (3z)
The title compound was prepared from cyclopropenone
1a (309 mg, 1.50 mmol), pyridine 2b (156 mg,
1.50 mmol) and 2-thiophenesulfonyl chloride (548 mg,
3.00 mmol) as described for 3b above. The product
was purified by flash chromatography on silica gel elut-
ing with EtOAc–hexane (1:4) followed by (1:2) and final-
ly (1:1); yield 169 mg (37%), yellow-green crystals, mp
222–225 ꢁC, Rf = 0.34 (SiO2, EtOAc–hexane, 1:4). 1H
NMR (300 MHz, CDCl3): d 6.57 (dd, 1H, J = 7.6 and
1.5 Hz, H-6), 6.79 (t, 1H, J = 4.4 Hz, H in thienyl),
6.93–7.02 (m, 2H, Ar), 7.11–7.16 (m, 3H, Ar), 7.23–
7.29 (m, 4H, Ar), 7.41–7.57 (m, 3H, Ar), 7.94 (m, 1H,
H-5), 7.96 (br s, 1H, H-8); 13C NMR (75 MHz, CDCl3):
d 101.3, 111.4, 118.9, 122.6, 123.3, 123.5, 123.9, 124.8,
126.8, 127.5, 127.9, 128.6, 129.3, 129.7, 130.4, 130.7,
130.9, 134.0, 135.5, 135.9; MS (EI) m/z (rel. %): 456
(2, M+), 309 (100), 279 (4), 178 (6), 131 (12), 103 (28),
84 (3); HRMS (ESI): Found 457.0670, calcd for
C25H16N2O3S2 457.0675.
4.22. 1-{[(3,4-Dimethoxyphenyl)sulfonyl]oxy}-2,3-diphen-
yl-7-indolizinecarbonitrile (3x)
The title compound was prepared from cyclopropenone
1a (309 mg, 1.50 mmol), pyridine 2b (156 mg,
1.50 mmol) and 3,4-dimethoxybenzenesulfonyl chloride
(710 mg, 3.00 mmol) as described for 3b above. The
product was purified by flash chromatography on silica
gel eluting with EtOAc–hexane (1:4) followed by (1:2)
and finally (1:1); yield 448 mg (88%), yellow crystals,
4.25. 1-{[(3-Thienyl)sulfonyl]oxy}-2,3-diphenyl-7-indoli-
zinecarbonitrile (3aa)
1
mp 208–210 ꢁC. H NMR (300 MHz, CDCl3): d 3.72
(s, 3H, OCH3), 3.87 (s, 3H, OCH3), 6.56 (d, 1H,
J = 8.6 Hz, Ar), 6.57 (dd, 1H, J = 7.4 and 1.7 Hz, H-
The title compound was prepared from cyclopropenone
1a (309 mg, 1.50 mmol), pyridine 2b (156 mg,

3136
S. Teklu et al. / Bioorg. Med. Chem. 13 (2005) 3127–3139
1.50 mmol) and 3-thiophenesulfonyl chloride (548 mg,
3.00 mmol) as described for 3b above. The product
was purified by flash chromatography on silica gel elut-
ing with EtOAc–hexane (1:19) followed by (1:9); yield
329 mg (72%), yellow crystals, mp 244–247 ꢁC,
Rf = 0.23 (SiO2, EtOAc–hexane, 1:4). 1H NMR
(300 MHz, CDCl3): d 6.57 (dd, 1H, J = 7.3 and 1.8 Hz,
H-6), 6.93 (m, 1H, thienyl), 7.00–7.05 (m, 3H, Ar),
7.13–7.17 (m, 3H, Ar), 7.23–7.40 (m, 2H, Ar), 7.41–
7.43 (m, 3H, Ar), 7.69–7.71 (m, 1H, thienyl), 7.93 (br
s, 1H, H-8), 7.96 (br s, 1H, H-5); 13C NMR (75 MHz,
CDCl3): d 101.2, 111.4, 122.5, 123.2, 123.4, 123.8,
124.9, 126.4, 127.6, 127.8, 128.6, 129.3, 129.4, 129.7,
130.3, 130.8, 130.9, 134.0, 134.2; MS (ESI) m/z (rel.
%): 457 (100, M+1); HRMS (ESI): Found 457.0657,
calcd for C25H16N2O3S2 457.0675.
4.28. 1-{[(4-Methylsulfonylphenyl)sulfonyl]oxy}-2,3-di-
phenyl-7-indolizinecarbonitrile (3dd)
The title compound was prepared from cyclopropenone
1a (206 mg, 1.00 mmol), pyridine 2b (104 mg,
1.00 mmol) and 4-methylsulfonylbenzenesulfonyl chlo-
ride (580 mg, 2.00 mmol) as described for 3b above.
The product was purified by flash chromatography on
silica gel eluting with EtOAc–hexane (1:9) followed by
(1:4) and finally (1:2); yield 433 mg (82%), yellow crys-
1
tals, mp 222–224 ꢁC. H NMR (300 MHz, CDCl3): d
2.97 (s, 3H, CH3), 6.58 (dd, 1H, J = 7.4 and 1.7 Hz,
H-6), 6.78 (d, 2H, J = 7.7 Hz, Ar), 7.01–7.15 (m, 5H,
Ar), 7.33–7.37 (m, 3H, Ar), 7.57–7.64 (m, 4H, Ar),
7.93 (dd, 1H, J = 7.4 and 0.74 Hz, H-5), 8.08 (br s,
1H, H-8); 13C NMR (75 MHz, CDCl3): d 44.6 (CH3),
101.7, 111.7, 118.8, 122.6, 122.7, 123.6, 123.9, 124.8,
126.3, 127.9, 128.8, 128.9, 129.6, 129.8, 130.1, 130.4,
130.8, 139.7, 145.6; MS (CI) m/z (rel. %): 529 (1,
M+1), 311 (100), 294 (5), 281 (7), 200 (24), 171 (7),
157 (49), 105 (6), 77 (10); Anal. Found: C, 63.60; H,
4.06; N, 5.05. C28H20N2O5S2 requires C, 63.62; H,
3.81; N, 5.30.
4.26. 1-{[(4-Chlorophenyl)sulfonyl]oxy}-2,3-diphenyl-7-
indolizinecarbonitrile (3bb)
The title compound was prepared from cyclopropenone
1a (206 mg, 1.00 mmol), pyridine 2b (104 mg,
1.00 mmol) and p-chlorobenzenesulfonyl chloride
(422 mg, 2.00 mmol) as described for 3b above. The
product was purified by flash chromatography on silica
gel eluting with EtOAc–hexane (1:19) followed by (1:9);
yield 310 mg (64%), yellow crystals, mp 193–195 ꢁC,
Rf = 0.38 (SiO2, EtOAc–hexane, 1:4). 1H NMR
(200 MHz, CDCl3): d 6.50 (dd, 1H, J = 7.4 and 1.3 Hz,
H-6), 6.74 (d, 2H, J = 6.7 Hz, Ar), 6.93–7.14 (m, 8H,
Ar), 7.19–7.31 (m, 4H, Ar), 7.87 (br d, 1H, J = 7.4 Hz,
H-5), 8.03 (br s, 1H, H-8); 13C NMR (50 MHz, CDCl3):
d 101.4, 111.5, 122.6, 122.9, 123.7, 125.0, 127.6, 128.5,
129.1, 129.2, 129.5, 129.7, 130.1, 130.3, 130.7, 130.9,
132.7, 141.4; MS (CI) m/z (rel. %): 310 (100), 144 (6),
112 (27), 77 (9); Anal. Found: C, 66.83; H, 3.70; N
5.51. C27H17ClN2O3S requires C, 66.87; H, 3.53; N,
5.78.
4.29. 1-Bromo-2,3-bis(4-fluorophenyl)-7-indolizinecarbo-
nitrile (4b) and 1,6-dibromo-2,3-bis(4-fluorophenyl)-7-
indolizinecarbonitrile (5b)
A mixture of 2,3-bis(4-fluorophenyl)-2-cyclopropen-1-
one 1b (121 mg, 0.50 mmol) and 4-cyanopyridine 2b
(52 mg, 0.50 mmol) in dry DCE (10 mL) was refluxed
under N2 for 20 h, cooled and the solvent was removed
under a stream of N2. The residue was dissolved in dry
acetonitrile (5 mL) and the mixture was stirred at ambi-
ent temperature under N2. A mixture of triphenylphos-
phine dibromide in acetonitrile [generated in a separate
flask from triphenylphosphine (393 mg, 1.50 mmol) and
bromine (240 mg, 1.50 mmol) in acetonitrile (3 mL) at
0 ꢁC] was added and the resulting mixture was stirred
at 70 ꢁC for 72 h, cooled and evaporated in vacuo.
The products were separated by flash chromatography
on silica gel eluting with EtOAc–hexane (1:29); yield
147 mg (72%) of 4b and 24 mg (10%) of 5b.
4.27. 1-{[(4-Trifluoromethylphenyl)sulfonyl]oxy}-2,3-di-
phenyl-7-indolizinecarbonitrile (3cc)
The title compound was prepared from cyclopropenone
1a (309 mg, 1.50 mmol), pyridine 2b (156 mg,
1.50 mmol) and 4-(trifluromethyl)benzenesulfonyl chlo-
ride (735 mg, 3.00 mmol) as described for 3b above.
The product was purified by flash chromatography on
silica gel eluting with EtOAc–hexane (1:19) followed
by (1:9); yield 384 mg (74%), yellow crystals, mp 180–
182 ꢁC, Rf = 0.50 (SiO2, EtOAc–hexane, 1:4). 1H
NMR (300 MHz, CDCl3): d 6.52 (dd, 1H, J = 7.4 and
1.3 Hz, H-6), 6.70 (m, 2H, Ar), 6.91–7.09 (m, 5H, Ph),
7.10–7.25 (m, 5H, Ph), 7.46 (m 2H, Ar), 7.68 (br d,
1H, J = 7.4 Hz, H-5), 8.05 (br s, 1H, H-8); 13C NMR
(75 MHz, CDCl3): d 101.6, 111.6, 118.9, 121.4, 122.6,
122.7, 123.6, 123.8, 124.9, 126.0 (q, JCF = 5.3 Hz),
127.6, 128.7, 128.9, 129.3, 129.5, 129.7, 130.2, 130.5,
130.8, 135.8 (q, JCF = 250 Hz, CF3), 137.9; 19F NMR
(188 MHz, CDCl3): d À63.9 (CF3); MS (EI) m/z (rel.
%): 518 (2, M+), 309 (100), 279 (3), 178 (4), 145 (3),
131 (9), 103 (22); HRMS: Found 518.0901, calcd for
C28H17F3N2O3S 518.0912.
4.30. 1-Bromo-2,3-bis(4-fluorophenyl)-7-indolizinecarbo-
nitrile (4b)
1
Yellow crystals, mp 180–182 ꢁC. H NMR (200 MHz,
CDCl3): d 6.65 (dd, 1H, J = 7.6 and 1.6 Hz, H-6),
6.99–7.24 (m, 8H, Ar), 7.90 (br s, 1H, H-8), 7.97 (br s,
1H, H-5); 13C NMR (50 MHz, CDCl3): d 93.8, 101.2,
111.0, 115.6, 116.0, 116.8, 119.0, 123.1, 125.5 (d,
JCF = 3.68 Hz), 125.7, 128.5, 128.6 (d, JCF = 3.33 Hz),
129.0, 129.3, 132.5, 132.7, 132.8, 163.0 (d,
JCF = 249 Hz); MS (EI) m/z (rel. %): 408/410 (100/99,
M+), 364 (25), 329 (71), 164 (17), 123 (2); HRMS:
Found 408.0058, calcd for C21H11BrF2N2 408.0074.
4.31. 1,6-Dibromo-2,3-bis(4-fluorophenyl)-7-indolizine-
carbonitrile (5b)
Yellow crystals, mp 206–210 ꢁC, Rf = 0.42 (SiO2,
EtOAc–hexane, 1:4). 1H NMR (200 MHz, CDCl3): d

S. Teklu et al. / Bioorg. Med. Chem. 13 (2005) 3127–3139
3137
7.02–7.30 (m, 8H, Ar), 7.98 (br s, 1H, H-8), 8.11 (br s,
1H, H-5); 13C NMR (75 MHz, CDCl3): d 95.0, 104.5,
105.2, 115.8, 116.1, 116.1, 117.1, 117.3, 117.4 123.3,
124.8 (d, JCF = 3.08 Hz), 126.5, 128.0, 129.9 (d,
JCF = 3.13 Hz), 132.4, 132.5, 132.6, 132.7, 163.0 (d,
JCF = 250 Hz); MS (EI) m/z (rel. %): 486/488/490 (50/
100/50, M+), 409 (30), 408 (10), 407 (31), 328 (9), 327
(8), 326 (10), 300 (6), 204 (5), 123 (11); HRMS: Found
485.9179, calcd for C21H10Br2F2N2 485.9198.
(14), 153 (13); HRMS: Found 400.0575, calcd for
C23H17BrN2 400.0584.
4.36. 1-[(4-Methylphenyl)sulfonyl]-2,3-diphenyl-7-indoli-
zinecarbonitrile (6)
n-Butyllithium (340 lL, 1.60 M solution in hexane,
0.49 mmol) was added dropwise to a stirred solution
of 1-bromo-2,3-diphenyl-7-indolizinecarbonitrile 4a
(183 mg, 0.49 mmol) in dry THF (10 mL) at À78 ꢁC
under N2 and the resulting mixture was stirred at
À78 ꢁC for 1 h, after which a solution of p-toluenesulfo-
nyl fluoride (860 mg, 4.90 mmol) in THF (5 mL) was
added. The resulting mixture was stirred for 2 h at
À78 ꢁC and for 8 h at ambient temperature. The product
was isolated by flash chromatography on silica gel
EtOAc–hexane (1:29) followed by (1:9) and finally
(1:4); yield 26 mg (12%), yellow crystals, mp 214–
4.32. 1-Bromo-2,3-bis(4-chlorophenyl)-7-indolizinecarbo-
nitrile (4c) and 1,6-dibromo-2,3-bis(4-chlorophenyl)-7-
indolizinecarbonitrile (5c)
The title compounds were prepared from 2,3-bis(4-
chlorophenyl)-2-cyclopropen-1-one 1c and 4-cyanopyri-
dine 2b as described for the synthesis of 4b and
5b above; yield 91 mg (41%) of 4c and 47 mg (18%) of
5c.
1
217 ꢁC, Rf = 0.33 (SiO2, EtOAc–hexane; 1:4). H NMR
(200 MHz, CDCl3): d 2.36 (s, 3H, CH3), 6.86 (dd, 1H,
J = 7.3 and 1.7 Hz, H-6), 7.07–7.11 (m, 2H, Ar), 7.23–
7.39 (m, 12H, Ar), 8.10 (br d, 1H, J = 7.3 Hz, H-5),
9.05 (br s, 1H, H-8); 13C NMR (50 MHz, CDCl3): d
21.9 (CH3), 105.6, 113.1, 115.9, 118.4, 124.1, 126.5,
127.4, 127.9, 128.3, 128.4, 128.7, 129.5, 129.6, 130.8,
131.2, 131.4, 131.8, 140.4, 143.9; MS (EI) m/z (rel. %):
448 (100, M+), 332 (1), 292 (7), 121 (13); HRMS: Found
448.1260, calcd for C28H20N2O2S 448.1248.
4.33. 1-Bromo-2,3-bis(4-chlorophenyl)-7-indolizinecarbo-
nitrile (4c)
1
Yellow crystals, mp 210–212 ꢁC. H NMR (300 MHz,
CDCl3): d 6.60 (dd, 1H, J = 7.4 and 1.5 Hz, H-6),
7.15–7.41 (m, 8H, Ar), 7.90 (br s, 1H, H-8), 7.94 (br d,
1H, J = 7.4 Hz, H-5); 13C NMR (50 MHz, CDCl3): d
93.8, 101.5, 111.8, 118.8, 122.8, 123.1, 125.7, 126.7,
127.7, 128.8, 129.2, 130.2, 132.0, 132.1, 132.3; MS (EI)
m/z (rel. %): 440/444 (60/45, M+), 442 (100), 396 (8),
361 (26), 291 (11), 185 (11), 145 (14); HRMS: Found
439.9507, calcd for C21H11BrCl2N2 439.9483.
4.37. 2,3-Bis(4-fluorophenyl)-7-indolizinecarbonitrile (7b)
n-Butyllithium (0.27 mL, 1.6 M solution in hexane,
0.49 mmol) was added drop wise to a stirred solution
of 1-bromo-2,3-bis(4-fluorophenyl)-7-indolizinecarbo-
nitrile 4b (200 mg, 0.49 mmol) in dry THF (20 mL) at
78 ꢁC under N2 and the resulting mixture was stirred
at À78 ꢁC for an additional 2 h before saturated aque-
ous ammonium chloride (1 mL) was added. The reac-
tion mixture was allowed to reach ambient
temperature, the phases were separated and the organic
layer was evaporated in vacuo. The product was purified
by flash chromatography on silica gel eluting with
EtOAc–hexane (1:49) followed by (1:29), (1:19) and fi-
nally (1:9); yield 105 mg (65%), yellow crystals,
mp 198–200 ꢁC, Rf = 0.48 (SiO2, EtOAc). 1H NMR
(200 MHz, CDCl3): d 6.60 (dd, 1H, J = 7.2 and 1.9 Hz,
H-6), 6.97 (br s, 1H, H-1), 6.99–7.39 (m, 8H, Ar), 7.88
(br s, 1H, H-8), 7.92 (br s, 1H, H-5); 13C NMR
(50 MHz, CDCl3): d 100.2, 104.9, 110.8, 115.7, 116.1,
117.0, 117.4, 122.8, 126.6, 130.1 (d, JCF = 3.48 Hz),
130.7, 130.8, 131.0 (d, JCF = 3.66 Hz), 132.9, 133.1,
163.3 (d, JCF = 250 Hz); MS (EI) m/z (rel. %):
330 (100, M+), 227 (6), 201 (3), 164 (6), 155 (5);
HRMS: Found 330.0980, calcd for C21H12F2N2
330.0969.
4.34. 1,6-Dibromo-2,3-bis(4-chlorophenyl)-7-indolizine-
carbonitrile (5c)
Yellow crystals, mp 212–215 ꢁC, Rf = 0.48 (SiO2,
1
EtOAc–hexane, 1:4). H NMR (300 MHz, CDCl3): d
7.09–7.41 (m, 8H, Ar), 7.92 (br s, 1H, H-8), 8.08 (br s,
1H, H-5); 13C NMR (75 MHz, CDCl3), d 95.1, 104.8,
105.4, 117.2, 123.3, 125.7, 126.5, 127.1, 128.3, 129.1,
130.4, 130.5, 131.9, 132.0, 134.6, 136.0; MS (EI) m/z
(rel. %): 518/520/522/524 (38/100/90/33, M+), 476 (3),
441 (27), 406 (11), 371 (5), 290 (11), 225 (16), 144 (8),
75 (2); HRMS: Found 517.8587, calcd for
C21H10Br2Cl2N2 517.8562.
4.35. 1-Bromo-2,3-bis(4-methylphenyl)-7-indolizinecarbo-
nitrile (4d)
The title compound was prepared from 2,3-bis(4-meth-
ylphenyl)-2-cyclopropen-1-one 1d and 4-cyanopyridine
2b as described for the synthesis of 4b and 5b above.
Yield 411 mg (41%), yellow crystals, mp 184–186 ꢁC,
Rf = 0.47 (SiO2, EtOAc–hexane, 1:4). 1H NMR
(300 MHz, CDCl3): d 2.12 (s, 3H, CH3), 2.16 (s, 3H,
CH3), 6.51 (dd, 1H, J = 7.4 and 1.8 Hz, H-6), 7.09–
7.22 (m, 8H, Ar), 7.88 (br s, 1H, H-8), 7.96 (dd, 1H,
J = 7.4 and 0.72 Hz, H-5); 13C NMR (75 MHz, CDCl3):
d 21.7 (CH3), 21.8 (CH3), 93.4, 100.5, 111.0, 119.3,
123.2, 125.5, 126.7, 126.8, 128.9, 129.3, 129.4, 129.8,
129.9, 130.3, 130.6, 130.8, 137.6, 139.3; MS (EI) m/z
(rel. %): 400/402 (100/100, M+), 356 (16), 321 (50), 306
4.38. 2,3-Bis(4-chlorophenyl)-7-indolizinecarbonitrile (7c)
The title compound was prepared from 1-bromo-2,3-
bis(4-chlorophenyl)-7-indolizinecarbonitrile 4c (111 mg,
0.250 mmol) as described for compound 7b above; yield
1
70 mg (77%), yellow crystals, mp 160–162 ꢁC. H NMR

3138
S. Teklu et al. / Bioorg. Med. Chem. 13 (2005) 3127–3139
(200 MHz, CDCl3): d 6.61 (dd, 1H, J = 7.4 and 1.8 Hz,
H-6), 6.97 (s, 1H, H-1), 7.19–7.29 (m, 6H, Ar), 7.44–
7.50 (m, 2H, Ar), 7.90 (br d, 1H, J = 7.4 Hz, H-5),
7.97 (br s, 1H, H-8); 13C NMR (50 MHz, CDCl3): d
100.5, 105.1, 111.0, 122.8, 124.4, 126.7, 128.8, 129.2,
130.0, 130.3, 130.4, 131.2, 132.3, 133.2, 133.6, 135.5;
MS (EI) m/z (rel. %): 362 (100, M+), 326 (16), 293
(13), 189 (5), 132 (3), 145 (13), 118 (2); HRMS: Found
362.0391, calcd for C21H12Cl2N2 362.0396.
4.42. 6,7-Diphenylpyrrolo[1,2-a]pyrimidin-8-ol tosylate
(10)
Yellow crystals, mp 197–200 ꢁC, Rf = 0.21 (SiO2,
EtOAc–hexane, 1:4). 1H NMR (200 MHz, CDCl3): d
2.40 (s, 3H, CH3), 6.55 (m, 1H, pyr), 6.98–7.13 (m,
7H, Ar), 7.24–7.38 (m, 7H, Ar), 8.22 (br s, 1H, pyr),
8.25 (m, 1H, pyr); 13C NMR (75 MHz, CDCl3): d 22.0
(CH3), 108.0, 120.4, 122.5, 123.0, 125.4, 127.0, 127.1,
128.3, 128.6, 128.8, 128.8, 129.5, 129.6, 130.6, 131.0,
131.0, 144.9, 145.0; MS (EI) m/z (rel. %): 440 (2, M+),
285 (100), 255 (3), 178 (6), 107 (15), 91 (7), 79 (21);
HRMS: Found 440.1195, calcd for C26H20N2O3S
440.1195.
4.39. 2,3-Bis(4-methylphenyl)-7-indolizinecarbonitrile
(7d)
The title compound was prepared from 1-bromo-2,3-
bis(4-methylphenyl)-7-indolizinecarbonitrile 4c (195
mg, 0.490 mmol) as described for compound 7b above;
yield 134 mg (83%), yellow crystals, mp 218–222 ꢁC,
Rf = 0.27 (SiO2, EtOAc–hexane, 1:4). 1H NMR
(200 MHz, CDCl3): d 2.37 (s, 3H, CH3), 2.48 (s, 3H,
CH3), 6.53 (dd, 1H, J = 7.4 and 1.8 Hz, H-6), 6.99 (br
s, 1H, H-1), 7.09–7.35 (m, 8H, Ar), 7.86 (br s, 1H, H-
8), 7.93 (br d, 1H, J = 7.4 Hz, H-5); 13C NMR
(50 MHz, CDCl3): d 21.6 (CH3), 21.9 (CH3), 99.4,
104.9, 110.3, 119.8, 122.9, 125.8, 126.7, 127.8, 129.0,
129.6, 130.5, 130.9, 130.9, 132.2, 137.0, 139.1; MS (EI)
m/z (rel. %): 322 (100, M+), 307 (4), 292 (4), 153
(6); HRMS: Found 322.1470, calcd for C23H18N2
322.1485.
4.43. 6,7-Diphenylpyrrolo[1,2-a]pyrimidin-8-ol 3-diphen-
yl-2-propenoate (12)
A
mixture of 2,3-diphenyl-2-cyclopropen-1-one 1a
(309 mg, 1.50 mmol), pyridine 8 (156 mg, 1.50 mmol)
and p-toluenesulfonyl chloride (572 mg, 3.00 mmol)
were reacted as described for the synthesis of 9 and 10
above except that in dry DCE (40 mL) was used as sol-
vent. The product was purified by flash chromatography
on silica gel eluting with EtOAc–hexane (1:29) followed
by (1:19), (1:9) and finally (1:4); yield 303 mg (41%), yel-
low crystals, mp 238–241 ꢁC, Rf = 0.33 (SiO2, EtOAc–
1
hexane, 1:4). H NMR (300 MHz, CDCl3): d 6.49 (dd,
1H, J = 7.2 and 3.8 Hz, pyr), 7.08–7.26 (m, 10H, Ph),
7.28–7.40 (m, 10H, Ph), 8.08 (s, 1H, @CH), 8.13 (dd,
1H, J = 3.8 and 1.5 Hz, pyr), 8.24 (dd, 1H, J = 7.2 and
1.5 Hz, H-5); 13C NMR (75 MHz, CDCl3): d 107.4,
116.9, 123.0, 123.5, 127.4, 128.2, 128.6, 128.6, 128.8,
129.0, 129.5, 129.6, 130.1, 130.4, 130.5, 130.6, 130.9,
131.2, 132.0, 135.0, 136.1, 142.8 (@CH), 143.6, 167.0
(CO); MS (EI) m/z (rel. %): 492 (22, M+), 286
(100), 207 (42), 179 (92), 152 (4), 107 (27), 79
(36); HRMS: Found 492.1831, calcd for C34H24N2O2
492.1838.
4.40. 6,7-Diphenylpyrrolo[1,2-c]pyrimidin-5-ol tosylate
(9) and 6,7-diphenylpyrrolo[1,2-a]pyrimidin-8-ol tosylate
(10)
A
mixture
of
2,3-diphenyl-2-cyclopropen-1-one
(309 mg, 1.50 mmol) and 4-cyanopyridine (156 mg,
1.50 mmol) in dry 1,4-dioxane (20 mL) was refluxed
under N2 for 24 h and cooled to 0 ꢁC, before N,N-4-di-
methylaminopyridine (366 mg, 3.00 mmol) and p-tolu-
enesulfonyl chloride (572 mg, 3.00 mmol) were added.
The resulting mixture was stirred under N2 at 0 ꢁC
for 30 min and at ambient temperature for 24 h,
washed with water (25 mL) and brine (25 mL), dried
(MgSO4) and evaporated in vacuo. The products
were separated by flash chromatography on silica gel
eluting with EtOAc–hexane (1:19) followed by (1:9)
and finally (1:4); yield 244 mg (37%) of 9 and 343 mg
(52%) of 10.
4.44. Inhibition of 15-lipoxygenase
Lipoxygenase activity was measured in borate buffer
solutions (0.2 M, pH 9.00) as previously described13,14
by the increase in absorbance at 234 nm from 30 to
90 s after addition of the enzyme, using linoleic acid
(134 lM) as substrate. The final enzyme concentration
was 167 U/mL. Test substances were added as DMSO
solutions (final DMSOconcn 1.6%); DMSOalone was
added in uninhibited control experiments. Six or more
parallels of controls and three or more parallels for each
test substance solution were measured. To ensure con-
stant enzyme activity throughout the experiment, the en-
zyme solution was kept on ice, and controls were
measured at regular intervals. Calculation of enzyme
activity was carried out as previously described14 and
IC50 values were determined by linear interpolation
between the measuring points closest to 50% activity.
Values are expressed as means SD. StudentÕs
t-test was employed for determination of statistical
significance.
4.41. 6,7-Diphenylpyrrolo[1,2-c]pyrimidin-5-ol tosylate
(9)
Yellow crystals, mp 178–180 ꢁC, Rf = 0.42 (SiO2,
1
EtOAc–hexane, 1:4). H NMR (200 MHz, CDCl3): d
2.32 (CH3), 6.77–6.95 (m, 4H, Ar), 7.14–7.25 (m, 3H,
Ar), 7.26–7.34 (m, 7H, Ar), 7.50 (br s, 1H, pyr),
7.52 (br s, 1H, pyr), 8.82 (s, 1H, pyr); 13C NMR
(50 MHz, CDCl3): d 14.6 (CH3), 111.7, 119.5, 124.0,
124.1, 127.3, 128.2, 128.8, 129.1, 129.2, 129.6, 130.4,
131.0, 131.1, 131.6, 132.9, 136.4, 145.4; MS (EI) m/z
(rel. %): 440 (3, M+), 285 (100), 178 (6), 107 (5), 91
(4), 79 (20); Anal. Found: C, 70.98; H, 4.60; N, 6.36.
C26H20N2O3S requires C, 70.89; H, 4.58; N, 6.36.

S. Teklu et al. / Bioorg. Med. Chem. 13 (2005) 3127–3139
3139
4.45. Inhibition of 15-lipoxygenase in preincubation
experiment
cil for the partial financing of the Bruker Avance NMR
instruments used in this study.
The inhibitor (50 lL), the enzyme solution dissolved in
DMSO(50 lL) and 0.2 M, pH 9.00 borate buffer were
mixed and incubated for 5 min. The reaction was initi-
ated with linoleic acid (final concn 134 lM) and the inhi-
bition was measured in the same way as described
above. For 15-lipoxygenase assays without incubation,
the inhibitor (50 lL), linoleic acid (134 lM) and borate
buffer were mixed. The reaction was initiated with
50 lL enzyme solution in DMSOand the inhibition
was measured in the same way as described above.
References and notes
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4.46. Inhibition of 15-lipoxygenase in the presence of
detergent
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Borate buffer containing CHAPS to its critical micellar
concentration, 0.2 mM, the inhibitor (50 lL), and lino-
leic acid (134 lM) were mixed. The reaction was initi-
ated with 50 lL enzyme solution in DMSOand the
inhibition was measured in the same way as described
above. For 15-lipoxygenase assays without CHAPS,
the inhibitor (50 lL), linoleic acid (134 lM) and borate
buffer (without CHAPS) were mixed. The reaction was
initiated with 50 lL enzyme solution in DMSOand
the inhibition was measured in the same way as de-
scribed above.
4.47. Dynamic light scattering (DLS)
Compounds were generally dissolved to 0.25 mM in
DMSOand diluted with filtered 200 mM borate buffer.
Compounds were analyzed with 10 mW He–Ne laser
at 633 nm with a Zetasizer 1000 HSa from Malvern
Instruments Limited. The measurements were done in
triplicate at 25 ꢁC, with a detector angle of 90ꢁ using
the Contin algorithm for size distribution.
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Acknowledgements
Quota Scholarship to S.T. is gratefully acknowledged.
The authors also thank The Norwegian Research Coun-
14. Malterud, K. E.; Farbrot, T. L.; Huse, A. E.; Sund, R. B.
Pharmacology 1993, 47(Suppl 1), 77–85.