Synthesis, analytical behaviour and biological evaluation of new 4-substituted pyrrolo[1,2-a]quinoxalines as antileishmanial agents

Article abstract of DOI:10.1016/j.bmc.2006.09.068

An original series of 4-substituted pyrrolo[1,2-a]quinoxaline derivatives, new structural analogues of Galipea species quinoline alkaloids, was synthesized from various substituted 2-nitroanilines via multistep heterocyclizations and tested for in vitro antiparasitic activity upon Leishmania amazonensis and Leishmania infantum strains. Structure-activity relationships enlighten the importance of the 4-substituted alkenyl side chain on the pyrrolo[1,2-a]quinoxaline moiety to modulate the antileishmanial activity.

Full text of DOI:10.1016/j.bmc.2006.09.068

Bioorganic & Medicinal Chemistry 15 (2007) 194–210
Synthesis, analytical behaviour and biological evaluation of new
4-substituted pyrrolo[1,2-a]quinoxalines as antileishmanial agents
Jean Guillon,a,* Isabelle Forfar,a Maria Mamani-Matsuda,b Vanessa Desplat,b
a
b
a
a
a
`
´
´
Marion Saliege, Denis Thiolat, Stephane Massip, Anais Tabourier, Jean-Michel Leger,
Benoit Dufaure,a Gilbert Haumont,b Christian Jarrya and Djavad Mossalayib
aEA 2962—Pharmacochimie, UFR des Sciences Pharmaceutiques, Universite´ Victor Segalen Bordeaux 2,
146 rue Le´o Saignat, 33076 Bordeaux Cedex, France
bEA 3677—Bases The´rapeutiques des Inflammations et Infections, UFR des Sciences Pharmaceutiques,
Universite´ Victor Segalen Bordeaux 2, 146 rue Le´o Saignat, 33076 Bordeaux Cedex, France
Received 10 July 2006; revised 19 September 2006; accepted 29 September 2006
Available online 1 October 2006
Abstract—An original series of 4-substituted pyrrolo[1,2-a]quinoxaline derivatives, new structural analogues of Galipea species quin-
oline alkaloids, was synthesized from various substituted 2-nitroanilines via multistep heterocyclizations and tested for in vitro anti-
parasitic activity upon Leishmania amazonensis and Leishmania infantum strains. Structure–activity relationships enlighten the
importance of the 4-substituted alkenyl side chain on the pyrrolo[1,2-a]quinoxaline moiety to modulate the antileishmanial activity.
ꢀ 2006 Elsevier Ltd. All rights reserved.
1. Introduction
zonensis and Leishmania mexicana cause CL.6 Therapy
of patients with leishmaniasis is still a serious problem.
Historically, leishmaniasis chemotherapy has been based
on the use of toxic heavy metals, particularly antimony
compounds. In fact, the drugs for leishmaniasis’s
treatment of all their clinical forms are meglumine
antimonite (Glucantimeꢁ) and sodium stibogluconate
(Pentostamꢁ), despite the fact that they exhibit renal
and cardiac toxicity (Fig. 1).7,8 When this kind of treat-
ment is not effective, alternative drugs include pentami-
dine (Pentostamꢁ) and amphotericin B (Fungizoneꢁ,
Ambisomeꢁ), also very toxic with serious side effects.9
Protozoan parasites affect 3 billion people, with malaria
and trypanosomatid parasites causing the greatest mor-
bidity.1,2 Leishmaniasis is a widespread parasitic disease
that is caused by protozoan parasites of the genus Leish-
mania in tropical and subtropical areas in both the old
and new worlds. According to recent World Health
Organization reports, 88 countries are affected, compre-
hending 12 million infected people worldwide, with
approximately 350 million people at risk. The incidence
is increasing worldwide, with 1–2 million new cases reg-
istered annually, despite all efforts being made to fight
the disease.1–5 It occurs in two major forms; cutane-
ous/muco-cutaneous (CL) and visceral leishmaniasis
(VL, or Kala-azar), depending upon parasite species.
Leishmania donovani and Leishmania infantum are major
causative agents of VL, while Leishmania major, Leish-
mania tropica and Leishmania aethiopica, Leishmania
braziliensis, Leishmania panamensis, Leishmania ama-
Miltefosine,
a phosphocholine analogue originally
developed as an anticancer agent, has been found to
be highly effective against leishmaniasis in vitro and
in vivo. Now, this compound is the only oral agent
against cutanous10 and visceral11 leishmaniasis,
although presenting severe gastrointestinal problems.12
As the leishmaniasis chemotherapy is still inefficient,
there is an urgent need for the development of new, effi-
cient and safe drugs.6,13,14 Traditional and ethnic medi-
cine is often a good source for researchers looking for
bioactive substances. Leishmaniasis is not an exception,
and plants have been used for the treatment of people
living far from modern medicine.15–17 Such compounds
belong to the following groups: alkaloids, terpenes,
Keywords: Pyrrolo[1,2-a]quinoxaline derivatives; Antileishmanial
activity; Synthesis; Lipohilicity.
*
Corresponding author. Fax: +33 0 5 57 57 13 52; e-mail: Jean.
Guillon@chimphys.u-bordeaux2.fr
0968-0896/$ - see front matter ꢀ 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmc.2006.09.068

J. Guillon et al. / Bioorg. Med. Chem. 15 (2007) 194–210
195
OH
CH2NHCH3
HO
CH2OH
HCO
HCO
OCH
OH
Sb+
-O
O
O
O
HO
OCH
O
O
O
O Sb
HCOH
HCOH
HOCH
HOCH
+
3 Na
Sb
O-
OH
-O
CH2OH
CH2NHCH3
O
O
Meglumine antimoniate
Sodium stibugluconate
NH
NH
H2N
NH2
O
O
Pentamidine
OH
OH
O
CH3
HO
O
OH
OH
O
OH
OH
OH
OH
O
CH3
H
CH3
O
O
CH3
OH
Amphotericin B
O
NH2
OH
CH2CH2N+(CH3)3
CH3(CH2)14CH2
O
P
O
O-
Miltefosine
Figure 1. Structures of meglumine antimoniate (Glucantimeꢁ), sodium stibogluconate (Pentostamꢁ), amphotericin B (Fungizoneꢁ, Ambisomeꢁ),
pentamidine (Pentacarinatꢁ) and miltefosine.
quinines, lactones, coumarins, acetogenins of annona-
ceae, chalcones, tetralones, lignans and saponins.18–22
For example, some 2-substituted quinoline derivatives
active against leishmaniasis were isolated from Galipea
longiflora, through a bioactivity-guided fractionation
process from an ethnopharmacological investigation in
Bolivia.17,23 The 2-substituted quinoline alkaloids 2-n-
propylquinolines, chimanines A/B/C/D, 2-n-pentylquin-
olines, 2-phenylquinolines, 2-phenylethylquinolines and
4-methoxy-2-pentenylquinoline were extracted from
the bark, root and leaves of Galipea longiflora Krause
(Rutaceae) (Fig. 2).23–27 Galipea officinalis and Galipea
bracteata are also known to contain quinoline alkaloids
such as cusparine, galipine, 2-phenylquinolines, 2-n-pen-
tylquinolines and 2-pentenylquinolines (Fig. 2).28–30
Hence, chimanine B isolated from Galipea species was
claimed as the lead molecule useful for further
pharmacomodulations.31,32
series of 4-substituted pyrrolo[1,2-a]quinoxalines 1 upon
L. amazonensis and L. infantum (Fig. 3).
As it was already noticed,37 an often limiting factor for
in vivo activity of new designed antiparasitic compounds
is their lack of distribution to the intracellular target. As
this property is often related to their molecular lipophil-
icity, we attempted a physico-chemical study of new pyr-
rolo[1,2-a]quinoxalines 1 achieved in order to define
their analytical profile. logD, the distribution coefficient
between the aqueous and the lipid phase, was chosen as
the parameter describing the accumulation of an ioniz-
able drug in cells. Thus, we explored the behaviour of
the 4-substituted pyrrolo[1,2-a]quinoxaline derivatives
through logD HPLC determination achieved at physio-
logical pH. On the other hand, pKa values of the
4-substituted pyrrolo[1,2-a]quinoxaline derivatives were
calculated through an in silico methodology.
We previously described a novel synthetic approach to
pyrrolo[1,2-a]quinoxaline derivatives designed as inter-
esting bioactive analogues of quinoline derivatives.33–36
They could be developed as new isosteres of Galipea spe-
cies quinoline alkaloids. Hence, we reported here the
synthesis and in vitro antiparasitic activity study of a
Finally, all compounds were tested against L. amazone-
nesis and L. infantum protozoa with chimanine B as the
reference drug. The 4-(E/Z)-propenyl and 4-(E)-pente-
nyl pyrrolo[1,2-a]quinoxalines were found as active as
the reference providing an interesting alternative to dif-
ficult extraction procedure of quinoline alkaloids from

196
J. Guillon et al. / Bioorg. Med. Chem. 15 (2007) 194–210
R
R
N
N
CH3
R = H : 2-n-propylquinoline
O
R = OCH : chimanine A
3
O
R
R = H : 2-(3,4-methylenedioxy)phenylethylquinoline
R = OCH : cusparine
3
R
N
CH3
R = H : chimanine B
R = OCH : chimanine C
3
N
O
O
O
N
chimanine D
R
CH3
R = OCH : 2-(3,4-methylenedioxy)styrylquinoline
3
R
N
CH3
N
R = H : 2-n-pentylquinoline
OCH3
OCH3
R = OCH : 4-methoxy-2-n-pentylquinoline
3
R = H : 2-(3,4-dimethoxy)phenylethylquinoline
R
R = OCH : galipine
3
R
N
CH3
R = H : 2-n-pentenylquinoline
N
R = OCH : 4-methoxy-2-n-pentenylquinoline
3
R = H : 2-phenylquinoline
R = OCH : 4-methoxy-2-phenylquinoline
3
Figure 2. Structure of extracted 2-substituted quinoline alkaloids isolated from Galipea species.
Galipea species. These results were exploited for SAR
studies that enlightened the influence of the nature of
the 4-substituted alkenyl side chain on the pyrrolo[1,2-
a]quinoxaline moiety for the modulation of antiparasitic
activity. These preliminary results suggest that 4-alke-
nylpyrrolo[1,2-a]quinoxalines could be further devel-
oped as potential antileishmanial drugs.
1-(2-nitrophenyl)pyrroles intermediates 3a–c were sub-
sequently reduced into the attempted 1-(2-aminophe-
nyl)pyrroles 2a–c using a BiCl3–NaBH4 treatment
(Scheme 1). Not commercially available 5-methoxy-2-
nitroaniline was prepared according to the litera-
ture.38,39 The reaction of various alkyl-, alkenyl-, or
aryl-acid chlorides with 2a–d led to the acetamides
4a–n. The 4-substituted pyrrolo[1,2-a]quinoxalines
1a–n were prepared by cyclisation of these amides 4a–n
in refluxing phosphorus oxychloride according to the
Bischler-Napieralski reaction.40 All the synthesized com-
pounds were characterized by nuclear magnetic reso-
nance (1H and 13C NMR). The 4-propenyl derivatives
2. Results and discussion
2.1. Chemistry
1
All of the reported 4-substituted pyrrolo[1,2-a]quinoxa-
line derivatives 1a–n were obtained from 1-(2-aminophe-
nyl)pyrroles 2a–c. Preparation of the latter was
performed in acetic acid according to the Clauson–Kaas
reaction starting from 2-nitroanilines and 2,5-di-
methoxytetrahydrofuran (DMTHF). The resulting
1c–e were afforded as single E isomers. Thus, their H
NMR spectra showed the characteristic chemical shifts
of a trans-propenyl chain at 7.25–7.08 ppm (1H, qd,
J = 16.50–15.35 and 6.80–6.70 Hz), 6.88–6.82 ppm (1H,
dd, J = 16.50–15.35 and 1.70–1.25 Hz), and 2.08–
2.01 ppm (3H, dd, J = 6.80–6.70 and 1.70–1.25 Hz). A

J. Guillon et al. / Bioorg. Med. Chem. 15 (2007) 194–210
197
CH3
CH3
O
2
1
CH3
CH2
9
3
R2
R1
N
8
4
CH3
R =
7
N5
R
6
O
CH3
1a-v
O
CH3
H, OCH
3
R , R =
1
2
OCH3
CH3O
CH3
Figure 3. General structure of synthesized 4-substituted pyrrolo[1,2-a]quinoxaline derivatives 1a–v.
coupling constant value of 16.50–15.35 Hz was in favor
of a trans configuration in the double bond. Analysis
8a,b with various aryl- or alkenylboronic acids in the
presence of Pd(PPh3)4 as a catalyst and a 2 M aqueous
solution of sodium carbonate (Scheme 4).47–49 The cis
1
of the H NMR of compounds 1h–j showed two signals
1
in the olefinic region [d 7.21–7.15 (ddd) and d 6.83–6.77
(ddd)] and also revealed the presence of a trans substitut-
ed double bond.
configuration of 1s was established by H NMR study,
that is, a typical pattern of the cis olefinic protons was
observed at 6.77 and 6.30 ppm (J = 11.25 Hz). Deriva-
tive 1t was synthesized via the palladium-catalyzed
cross-coupling reaction of a vinylboronate with 8a in
the presence of potassium hydroxide used as the base.50
The heteroaryl chlorides 8a,b were previously prepared
by reacting 2a,b with triphosgene in toluene to give the
lactams 7a,b, which were subsequently chlorodehydr-
oxylated with phosphorous oxychloride.36 Moreover,
the Sonogashira coupling reaction of 4-chloroquinoxa-
lines 8a,b with 1-hexyne in the presence of
[PdCl2(PPh3)2]/CuI, in refluxing triethylamine gave
1u,v (Scheme 4).51,52
The 4-(E)-styrylpyrrolo[1,2-a]quinoxalines 1o,p were
easily synthesized by the Perkin reaction of 4-methylpyr-
rolo[1,2-a]quinoxalines 6a,b, previously obtained via the
amides 5a,b, with benzaldehyde in refluxing Ac2O under
conditions inspired by those of Kaslow and Stayner
(Scheme 2).41,42
To prepare the 4-epoxypropylpyrrolo[1,2-a]quinoxaline
1q, structural analogue of chimanine D, we first synthe-
sized the pyrrolo[1,2-a]quinoxaline-4-carboxaldehyde 7
by oxidation of 6a with SeO2 in dioxane.43 The Corey–
Chaykovsky reaction of the sulfur ylide generated from
triethylsulfonium tetrafluoroborate on aldehyde 7 gave
the epoxides 1q,r (Scheme 3), as a separable mixture of
Z and E isomers (ratio: 1/4).43–45 The stereochemistry
Compounds 1a–p and 1t–v were then converted into
their hydrochlorides in 32–80% yields by treatment with
hydrochloric acid gas in diethyl ether (Table 1). Howev-
er, acidic treatment of the oily 4-(Z)-propenylpyrrolo-
quinoxaline 1s always led to the hydrochloride salt of
1c through a cis to trans isomerization. A X-ray single
crystal analysis was performed on pyrroloquinoxaline
1c as base in order to study the lateral chain configura-
tion (Fig. 4). The 4-propenylpyrroloquinoxaline system
was found quite planar. The C(14)–C(15) propenyl dou-
1
of these epoxides was determined by studying their H
0
0
NMR spectra: measure of JH2 -H3 (4.35 and 1.95 Hz
for Z and E isomers, respectively) and comparison
with the H NMR spectrum of the E antileishmanial
1
natural epoxide.
˚
We also synthesized the 4-propenylpyrrolo[1,2-a]qui-
noxaline 1c by Wittig olefination between the aldehyde
7 and ethyltriphenylphosphonium bromide to afford 1c
as single E isomer in 40% yield (Scheme 3).43,46
ble bond was noticed at 1.344(7) A, as typically ob-
served for the C@C double bonds. The crystalline
cohesion could be ensured by a rigidification of the se-
quence N(7)–C(8)–C(4)–C(15) through a van der Waals
˚
contact between N(7) and H(15) observed at 2.605 A.
This contact could be necessary for the solid form cohe-
sion and subsequent molecular stability.
Due to the moderate yields obtained in the synthesis of
the 4-alkenylpyrrolo[1,2-a]quinoxalines by the Bischler-
Napieralski or Wittig reactions, we investigated new
general methods for their preparation. Thus, 4-alkenyl-
pyrrolo[1,2-a]quinoxalines 1c,d, 1h,i, 1n–p and 1s were
easily prepared in quite good yield (51–86%) by a direct
Suzuki cross-coupling reaction of 4-chloroquinoxalines
2.2. Antileishmanial activity
Compounds 1a–v were tested for their in vitro antileish-
manial activity upon the L. amazonensis and L. infantum

198
J. Guillon et al. / Bioorg. Med. Chem. 15 (2007) 194–210
R1 R1
R1
R2
R2
R2
i
ii
NO2
NH2
NO2
N
N
NH2
2a-c
3a-c
R1
R-
R -
1
R -
2
R2
O
H-
4a, 1a
4b, 1b
H-
CH3
iii
CH O-
H-
3
NH
R
CH3
CH3
N
4c, 1c
4d, 1d
4e, 1e
H-
H-
H-
4a-n
CH O-
3
CH3
CH3
H-
H-
CH O-
3
R2
R1
N
H-
4f, 1f
CH3
iv
4g, 1g
4h, 1h
CH O-
H-
H-
H-
3
CH3
CH3
CH
N
R
H-
1a-n
4i, 1i
4j, 1j
CH O-
3
H-
H-
CH O-
R -
R -
2
3
1
CH3
H-
H-
H-
2a, 3a
2b, 3b
2c, 3c
H-
4k, 1k
CH O-
3
H-
CH O-
3
O
O
4l, 1l
H-
H-
OCH3
CH3O
4m, 1m
4n, 1n
H-
H-
H-
H-
Scheme 1. Synthesis of 4-substituted pyrrolo[1,2-a]quinoxaline derivatives 1a–n. Reagents and conditions: (i) DMTHF, AcOH, D; (ii) BiCl3, NaBH4,
EtOH; (iii) RCOCl, pyridine, dioxane, D; (iv) 1—POCl3, toluene, D; 2—NaHCO3, H2O, rt.
strains with chimanine B as the reference (Table 2).
Amphotericin B was also used in these tests as the refer-
ence standard drug. The pyrroloquinoxalines 1c–e, 1h–
k, 1s,t and 1v were found the most active compounds
against the promastigote forms of L. amazonensis
with IC50 from 0.5 to 7 lM. In particular, 1c, designed
as a chimanine B structural analogue, was found to
be 10 times more active than the reference alka-
loid (IC50 = 0.5 lM vs IC50 = 5 lM). The 7-methoxy
and 8-methoxy-4-(E)-propenylpyrroloquinoxalines 1d,e
showed an IC50 of 7 and 1 lM, respectively. The intro-
duction of a (Z)-propenyl or vinyl substituent on posi-
tion C-4 of the pyrroloquinoxaline moiety (compounds
1s,t) seems to slightly decrease the activity in compari-
son with compound 1c with IC50 = 4 and 3 lM,
respectively.
With respect to 1c, the alkenyl chain replacement by a
styryl one in compounds 1o,p induced anactivity loss, that
is, IC50 = 35 and 36 lM for 1o,p, respectively, whereas the
increase of the carbon alkenyl chain length in 1h–j gave
slightly less potent compounds (IC50 =4–6 lM). If the
alkenyl function is found in a restricted configuration as
observed in the cyclohexenyl ring (1m), this compound
was found inactive until 50 lM. On the other hand, the
replacement of a pentenyl chain by an hexynyl one in com-
pounds 1u,v did not increase the antileishmanial activity
for 1u (IC50 = 18 lM), but is less detrimental for 1v

J. Guillon et al. / Bioorg. Med. Chem. 15 (2007) 194–210
199
R1
O
N
i
ii
2a-b
NH
CH3
R1
N
CH3
N
6a-b
5a-b
R -
1
H-
5a, 6a, 1o
5b, 6b, 1p
N
iii
CH O-
3
R
N
1o-p
Scheme 2. Synthesis of 4-substituted pyrrolo[1,2-a]quinoxaline derivatives 1o,p. Reagents and conditions: (i) CH3COCl, pyridine, dioxane, D;
(ii) 1—POCl3, toluene, D; 2—NaHCO3, H2O, rt; (iii) C6H5–CHO, Ac2O, D.
N
N
N
N
iii
i
6a
CH3
CHO
7
1c
ii
N
N
+
O
O
H
CH3
N
N
1r
1q
H
CH3
H
H
Scheme 3. Synthesis of 4-substituted pyrrolo[1,2-a]quinoxaline derivatives 1c and 1q,r. Reagents and conditions: (i) SeO2, dioxane, D; (ii) Et3SBF4,
KOH, MeCN/H2O; (iii) Et(C6H5)3PBr, t-BuOK, toluene, 0 ꢂC then D.
N
N
N
N
N
i
iii / iv
ii
2a-b
R1
N
H
O
R1
R
R1
Cl
7a-b
8a-b
1c-d, 1h-i, 1n-p, 1s-t
v
R -
1
R-
R -
1
CH3
CH2
H-
7a, 8a
7b, 8b
1s
1t
H-
H-
N
CH O-
3
R1
N
CH3
CH3
H-
1u
1v
R
1u-v
CH O-
3
Scheme 4. Synthesis of 4-substituted pyrrolo[1,2-a]quinoxaline derivatives 1c,d, 1h,i, 1n–p, 1s,t and 1u,v. Reagents and conditions: (i) CO(OCCl3)2,
toluene, D; (ii) POCl3, D; (iii) R–B(OH)2, Pd[P(C6H5)3]4, Na2CO3, C6H6, D.; (iv) H2C@CH–B(O-n-Bu)2, KOH; Pd[P(C6H5)3]4, C6H6, D; (v)
PdCl2[P(C6H5)3]2, HC„C–R, CuI, TEA, D.

200
J. Guillon et al. / Bioorg. Med. Chem. 15 (2007) 194–210
Table 1. Physical properties of the final amines 1
Compound
pKa
logD7.4
Salta
Mp (ꢂC) of the
salts or bases
% yield
1a
1b
9.19
3.35
3.40
3.44
3.47
3.48
4.04
4.38
4.44
4.52
4.30
3.84
2.97
4.12
3.60
4.84
5.34
2.61
2.55
3.30
3.08
4.36
4.35
2.23
HCl
HCl
HCl
HCl
HCl
HCl
HCl
HCl
HCl
HCl
HCl
HCl
HCl
HCl
HCl
HCl
132
139
170
90
91
82
89
63
77
94
68
52
56
84
92
90
85
75
70
90
40
13
51
65
80
60
89
9.45
9.59
9.84
9.72
9.12
9.37
9.63
9.88
9.49
9.25
9.17
9.08
9.86
9.51
9.76
10.98
10.98
9.47
9.52
9.28
9.53
4.67
1c
1d
1e
156
124
101
121
155
71
1f
1g
1h
1i
1j
1k
157
124
88
1l
1m
1n
1o
123
157
119
62
1p
1q
b
—
b
1r
—
b
—
—
1s
—
1t
1u
HCl
HCl
HCl
HCl
>300
91
1v
Chimanine B
100
129
a The 4-substituted pyrrolo[1,2-a]quinoxalines 1 were dissolved in 25 mL of Et2O and treated with hydrochloric acid gas. The hydrochloride salts
which precipitated were collected by filtration and were washed with Et2O.
b Compound tested as a free base.
Figure 4. The ORTEP drawing of 4-[(E)-prop-1-enyl]pyrrolo[1,2-a]quinoxaline 1c with thermal ellipsoids at 30% level.

J. Guillon et al. / Bioorg. Med. Chem. 15 (2007) 194–210
201
Table 2. In vitro sensitivity of Leishmania amazonensis and L infantum strains, and cytotoxicity on human peripheral blood mononuclear cells
PNMC + PHA
Compound
IC50 values (lM)a
Leishmania strains
Index of selectivityb
Cytotoxicity on human
peripheral blood
mononuclear cells
(PMNC)
L. amazonensis L. infantum
L. amazonensis promastigotes L. infantum promastigotes PMNC
PMNC + PHA
Amphotericin B
Chimanine B
1
0.2
1
0.9 0.1
7
>100
43
96 10
96
8.4
106.6
6
5
2
3
42
100
4
1a
1b
1c
1d
1e
1f
>50
>50
>50
>50
>100
>100
6
90 10
0.5 0.1
7
0.7 0.1
0.3
6
5
7
0.3
1
5
0.4
0.5
0.3
3
10
7.1
2.5
10
1
0.1
2
5
0.7
5
1
0.5 0.1
>50
>50
0.8
5
>50
>50
5
>100
66
30
45
<1
<1
10.4
6.7
7.5
9.3
>3.3
<1
<1
7.4
40
1g
1h
1i
4
5
0.2
1
7
1
0.6
0.1
70 12 52
3
6
60
55
5
5
40
30
65
4
1j
4
0.2
0.8
6
2.5 0.4
>50
>50
4
12
1k
1l
7
>100
>100
>100
>100
>100
>100
>100
>100
5
30
>50
>50
>100
>100
>100
>100
>100
>100
>100
1m
1n
1o
1p
1q
1r
1s
1t
>50
>50
35 10
>50
5
>2.9
>2.8
36
>50
>50
4
9
0.6
>20
>50
>50
0.3
0.3
6
0.8 0.1
0.5 0.1
8
0.9
0.2
6
6
0.9
1.5
0.3
1.4
1.7
7.5
2
3
3
1
0.2
3
1u
1v
18
3
25
7
6
50
6
25
5
1
0.7
0.1
1
0.3
0.3
a IC50 values were measured on the promastigotes of the Leishmania amazonensis (MHOM/BR/1987/BA) and L. infantum (clone MCAN/GR/82/
LEM497) strains. The IC50 (lM) values correspond to means SD from three independent experiments.
b Index of selectivity (I.S.) was defined as the ratio between the IC50 value on the PMNC + PHA cells and the IC50 value against the L. amazonensis
and L. infantum strain.
(3 lM). A total loss of activity was observed for com-
pounds 1a,b and 1f,g possessing a three- or five-carbon
saturated side chain (IC50 > 50 lM).
pounds 1a, 1c, 1f and 1h). Only the 7-methoxysubstitut-
ed 4-alkynyl derivative 1v was more potent than its
unsubstituted analogue 1u (IC50 = 3 compared with
18 lM for 1u).
With the galipine as a model we designed then com-
pounds 1k,l with a phenethyl-substituted C-4 chain.
Whereas the substituted 4-(3,4-dimethoxyphenylethyl)
compound 1l was found with a moderate activity
(IC50 = 30 lM), surprisingly the 4-(3,4-methylenedioxy-
phenylethyl)pyrrolo[1,2-a]quinoxaline 1k exhibited a
potent antiL. amazonensis activity with a 7 lM IC50 val-
ue. Moreover, the trans epoxide 1q, a structural ana-
logue of chimanine D, was found inactive until 50 lM
against L. amazonensis, as its cis epoxide homologue
1r. Finally, compound 1n, with a phenyl group in posi-
tion 4, did not show any antileishmanial activity.
A second evaluation was achieved against the promasti-
gote forms of L. infantum in an experimental visceral
leishmaniasis model, with chimanine B as the reference
(Table 2). Compounds 1d, 1h–j, 1p and 1v showed almost
the same level of activity with IC50 ranging from 1 to
7 lM. It must be noticed that four compounds 1c, 1e, 1s
and 1t showed an IC50 < 1 lM, more potent than the ref-
erence (IC50 = 7 lM). Hence, the introduction of a meth-
oxy substituent in position C-7 or C-8 of the 4-alkenyl or
4-alkynylpyrrolo[1,2-a]quinoxaline moiety resulted in the
increase of the antileishmanial activity in comparison
with their respective unsubstituted 4-alkenyl or 4-alkynyl-
pyrrolo[1,2-a]quinoxaline homologues (i.e., 1e compared
to 1c, 1i,j to 1h, 1p to 1o and 1v to 1u).
From a SAR point of view, these pharmacological re-
sults enlighten the importance of the nature of the 4-lat-
eral chain on the pyrrolo[1,2-a]quinoxaline moiety, in
our series. Hence, an a-unsaturated (trans- or cis-alkenyl
or alkynyl) lateral chain induces a notable increase in
the activity. On the other hand, the substitution at posi-
tion 7 or 8 of the pyrrolo[1,2-a]quinoxaline heterocycle
by one methoxy group is not crucial as illustrated by re-
sults for compounds 1b, 1d,e, 1g and 1i,j in comparison
with those of their unsubstituted homologues (com-
In summary, except for 1p and 1k, all compounds
showed almost the same level of activity on L. amazon-
ensis and on L. infantum promastigotes. The mechanism
by which these new 4-substituted pyrrolo[1,2-a]quinoxa-
lines are active against Leishmania parasites is unknown.
Further pharmacological studies should now be investi-
gated to determine the target of action.

202
J. Guillon et al. / Bioorg. Med. Chem. 15 (2007) 194–210
2.3. Cytotoxicity
2.4. Lipophilicity
All compounds 1a–v were tested on activated
(PBMC + PHA) and not activated (PBMC) human
peripheral blood mononuclear cells (Table 2). Not acti-
vated cells were considered as control measurements. As
expected, most of the already inactive pyrrolo[1,2-
a]quinoxalines showed a low cytotoxicity against mono-
cytes (IC50 > 100 lM), whereas cytotoxicity was noticed
for most active ones. However, among these last com-
pounds, the most active (E)-propenylpyrroloquinoxaline
1c on L. amazonensis strain exhibited a higher level of
cytotoxicity against host cells (IC50 = 5 lM). Such
an observation was also noticed for the active (Z)-
propenyl and vinyl compounds 1s,t (IC50 of 6 and
1 lM, respectively). Moreover, the (E)-propenylpyr-
rolo[1,2-a]quinoxalines 1d,e, both substituted by a
methoxy function in position 7 or 8, also showed
high cytotoxicity (IC50 = 5 lM, both), while their
(E)-pentenyl analogues 1i,j displayed IC50 values of
40 and 30 lM, respectively. Otherwise, the unsubsti-
tuted pentenylpyrroloquinoxaline 1h was also found
less toxic than its methoxy substituted analogues 1i,j
(IC50 = 52 lM). Data also indicated that the introduc-
tion of hexynyl group in 1u,v increased the toxicity
(IC50 = 25 and 5 lM, respectively). The other different
substitutions on the pyrrolo[1,2-a]quinoxaline moiety
seem to have less influence on the PBMC + PHA
IC50 values than those observed for the antileishma-
nial activity.
The activity of an ionizable drug is determined by two
major parameters: the partition coefficient logP between
the aqueous and the lipid phases and its modification by
the ionization constant pKa of the drug. For partially
ionized compounds, the partition coefficient between
two phases at any fixed pH is called the distribution
coefficient D, usually expressed as logD.53 Here, for all
new synthesized compounds, logD was determined by
an HPLC method at pH 7.4, considered as the biological
medium pH54 and the acidity constant pKa calculated
using Pallasꢁ program (Table 1).55 This allowed us to
calculate the partial ionization percentage according to
the Henderson–Hasselbach equation56 at pH 7.4, always
found inferior than 2% except for chimanine B (>99%).
logD values were found between 2.23 for the reference
chimanine B and 5.34 for 1p. As expected the highest
lipophilic pyrroloquinoxalines 1 (logD > 4.0) present a
substituent in position 4 of the heterocyclic moiety that
is either a 5- or 6-carbon atom chain (1f–j and 1u,v) or a
bulky group (1l–p).
A plot of antileishmanial IC50 versus logD values is pre-
sented in Figure 5, permitting to classify compounds in
various subsets. The two more lipophilic (1o,p) and the
three less lipophilic (1r, 1q and 1l) are almost inactive
while the following 1t and 1s are active. logD values
of compounds 1a,b substituted by a three carbon satu-
rated linear chain and of their homologues 1c–e substi-
tuted by a three-carbon unsaturated chain are in the
same range (3.35–3.48), but not their activity. The four
compounds (1n, 1k, 1f and 1m) with logD between
3.60 and 4.12 are inactive. An heterogeneous behaviour
was found for compounds with logD between 4.30 and
4.52 as 1j, 1v, 1u, 1h and 1i are active while 1g is devoid
of appreciable potency.
Index of selectivity (IS) was defined as the ratio of
the IC50 value on the human mononuclear cells to
the IC50 value on the L. amazonensis or L. infantum
strains (promastigotes). This led to the identification
of compound 1p with IS > 20 on L. infantum. On
the other hand, the (E)-pentenylpyrrolo[1,2-a]quinoxa-
lines 1h–j are remarkable with IS = between 7 and
40, on both strains. These four molecules would
constitute suitable pharmacophores for the design
of new candidates in forthcoming pharmacological
investigations.
These results clearly indicated that the choice and the
introduction of an a-unsaturation in position 4 of the
pyrrolo[1,2-a]quinoxaline moiety correlated with a
particular lipophilic behaviour seem to be fundamental
50
6
logD
IC
50
μM
5
4
3
2
1
0
40
30
20
10
0
L.amazonensis
L. infantum
logD
Figure 5. logD/activity relationship for pyrrolo[1,2-a]quinoxalines 1a–v.

J. Guillon et al. / Bioorg. Med. Chem. 15 (2007) 194–210
203
for the antileishmanial activity observed for this
new series.
plates (POLYGRAM SIL G/UV254) with visualisation
by irradiation with a UV lamp. Silica gel 60 (70–
230 mesh) was used for column chromatography. Ele-
mental analyses (C, H, N) for new compounds were per-
formed by CNRS (Vernaison-France) and agreed with
the proposed structures within 0.3% of the theoretical
values. Chimanine B was synthesized in analogy to de-
scribed procedure.45
3. Conclusion
In conclusion, new 4-substituted pyrrolo[1,2-a]quinoxa-
line derivatives were designed as new structural ana-
logues of Galipea species quinoline alkaloids. They
were synthesized via Bischler-Napieralski, Perkin, Corey-
Chaykovsky, Wittig, Suzuki or Sonogashira reactions,
and tested for their in vitro antiparasitic activity on
two strains: L. amazonensis and L. infantum. The use
of the palladium-catalyzed Suzuki cross-coupling reac-
tions enabled one to access easily to new substituted
4-alkenylpyrrolo[1,2-a]quinoxaline derivatives, more
difficultly obtained through a classical 4-substituted
pyrrolo[1,2-a]quinoxaline synthetic pathway.
4.1.1. General procedure for 1-(2-alkanoyl- or 2-alkenoyl-
or 2-benzoylaminophenyl)pyrrole (4a–n). To a solution of
1-(2-aminophenyl)pyrrole 2a–c (0.02 mol) in dioxane
(80 mL) were added pyridine (0.022 mol) then propano-
yl chloride (0.02 mol). The reaction mixture was refluxed
for 4 h and the solvent then removed under reduced
pressure. The residue was triturated with water and
extracted with diethyl ether (2 · 80 mL). The organic
layers were collected, washed with an aqueous sodium
hydrogen carbonate solution (100 mL) then with water
(100 mL), dried over Na2SO4 and evaporated to dry-
ness. The precipitate was crystallized from petroleum
ether to afford 4a–n.
The biological results obtained with chimanine B as the
reference highlighted the crucial role of C-4 substitution
introduced on the pyrrolo[1,2-a]quinoxaline nucleus, on
the antileishmanial activity modulation. Hence, an a-un-
saturated (trans- or cis-alkenyl or alkynyl) lateral chain
induces a notable increase in the antiparasitic activity on
both strains. On the other hand, the advantage of the
substitution at position 7 or 8 of the pyrrolo[1,2-a]qui-
noxaline heterocycle by one methoxy group depends
on the studied strain, that is, it is only beneficial for
the visceral L. infantum strain.
4.1.1.1. 1-(2-Propanoylaminophenyl)pyrrole (4a).
White crystals (60%); mp 48 ꢂC; IR (KBr) 3200 (NH),
1650 (C@O); 1H NMR (CDCl3) d: 8.38 (d, 1H,
J = 7.75 Hz, H-3), 7.40 (t, 1H, J = 7.75 Hz, H-4), 7.32
(d, 1H, J = 7.75 Hz, H-6), 7.16 (t, 1H, J = 7.75 Hz, H-
5), 6.94 (br s, 1H, NH), 6.76 (dd, 2H, J = 1.95 and
1.95 Hz, H-a), 6.39 (dd, 2H, J = 1.95 and 1.95 Hz, H-
b), 2.17 (t, 2 H, J = 7.35 Hz, CH2), 1.59 (sex, 2H,
J = 7.35 Hz, CH2), 0.92 (t, 3H, J = 7.35 Hz, CH3); 13C
NMR (CDCl3) d: 171.2 (C@O), 133.9 (C-1), 130.5 (C-
2), 128.7 (C-6), 126.7 (C-3), 123.9 (C-5), 121.9 (C-a),
121.4 (C-4), 110.4 (C-b), 39.7 (CH2), 18.7 (CH2), 13.6
(CH3). Anal. Calcd for C14H16N2O: C, 73.65; H, 7.06;
N, 12.27. Found: C, 73.69; H, 6.91; N, 12.36.
The physico-chemical profile of new 4-substituted pyr-
rolo[1,2-a]quinoxaline derivatives was studied through
logD HPLC determination achieved at physiological
pH and pKa calculation through an in silico methodolo-
gy. These results have been discussed in terms of lipo-
philic behaviour for
a preliminary SAR study.
Although antiparasitic activity is generally related to
the distribution of studied compounds to the intracellu-
lar target it was not possible to establish pertinent and
definitive correlation. Nevertheless, it appeared that pyr-
rolo[1,2-a]quinoxalines endowed with lipophilic unsatu-
rated carbon chain could open the way to new valuable
antileishmanial chemistry scaffolding. This will be the
target of further investigations.
4.1.1.2. 1-(4-Methoxy-2-propanoylaminophenyl)pyr-
role (4b). Pale-yellow crystals (78%); mp 51 ꢂC; IR
1
(KBr) 3240 (NH), 1655 (C@O); H NMR (CDCl3) d:
8.10 (d, 1H, J = 2.75 Hz, H-3), 7.16 (d, 1H,
J = 8.70 Hz, H-6), 6.89 (br s, 1H, NH), 6.71 (dd, 2H,
J = 2.05 and 2.05 Hz, H-a), 6.65 (dd, 1H, J = 8.70 and
2.75 Hz, H-5), 6.36 (dd, 2H, J = 2.05 and 2.05 Hz, H-
b), 3.84 (s, 3H, CH3O), 2.16 (t, 2H, J = 7.35 Hz, CH2),
1.60 (sex, 2H, J = 7.35 Hz, CH2), 0.91 (t, 3H,
J = 7.35 Hz, CH3). Anal. Calcd for C15H18N2O2: C,
69.74; H, 7.02; N, 10.85. Found: C, 69.65; H, 6.85; N,
10.98.
4. Experimental
4.1. Chemistry
Commercial reagents were used as received without
additional purification. Melting points were determined
with an SM-LUX-POL Leitz hot-stage microscope and
are uncorrected. IR spectra were recorded on a BRU-
KER IFS-25 spectrophotometer. NMR spectra were
recorded with tetramethylsilane as an internal standard
using a BRUKER AVANCE 300 spectrometer (1H,
13C, 2D-COSY). Splitting patterns have been designated
as follows: s, singlet; br s, broad singlet; d, doublet; dd,
double doublet; qd, quadruple doublet; t, triplet; q,
quartet; qt, quintuplet; sex, sextuplet; m, multiplet. Ana-
lytical TLC was carried out on 0.25 precoated silica gel
4.1.1.3. 1-(2-trans-Crotonylaminophenyl)pyrrole (4c).
White crystals (59%); mp 58 ꢂC; IR (KBr) 3240 (NH),
1655 (C@O); 1H NMR (CDCl3) d: 8.47 (d, 1H,
J = 8.25 Hz, H-3), 7.36 (t, 1H, J = 8.25 Hz, H-4), 7.25
(d, 1H, J = 8.25 Hz, H-6), 7.12 (t, 1H, J = 8.25 Hz, H-
5), 6.99 (br s, 1H, NH), 6.89 (qd, 1H, J = 15.15 and
6.90 Hz, =CH), 6.81 (dd, 2H, J = 2.10 and 2.10 Hz, H-
a), 6.39 (dd, 2H, J = 2.10 and 2.10 Hz, H-b), 5.70 (dd,
1H, J = 15.15 and 1.65 Hz, HC@), 1.84 (dd, 3H,
J = 6.90 and 1.65 Hz, CH3); 13C NMR (CDCl3) d:
163.9 (CO), 141.8 (@CH), 134.1 (C-1), 130.7 (C-2),
128.8 (HC@), 126.9 (C-6), 125.6 (C-3), 124.1 (C-5),

204
J. Guillon et al. / Bioorg. Med. Chem. 15 (2007) 194–210
122.1 (C-a), 121.6 (C-4), 110.6 (C-b), 17.9 (CH3). Anal.
Calcd for C14H14N2O: C, 74.31; H, 6.23; N, 12.38.
Found: C, 74.41; H, 6.28; N, 12.47.
2H, J = 2.15 and 2.15 Hz, H-a), 6.40 (dd, 2H, J = 2.15
and 2.15 Hz, H-b), 5.66 (dd, 1H, J = 15.45 and
1.15 Hz, HC@), 2.14 (m, 2H, CH2), 1.45 (sex, 2H,
J = 7.35 Hz, CH2), 0.91 (t, 3 H, J = 7.35 Hz, CH3); 13C
NMR (CDCl3) d: 163.9 (CO), 146.6 (@CH), 133.9
(C-1), 130.4 (C-2), 128.7 (C-6), 126.7 (HC@), 123.9 (C-
3), 123.8 (C-5), 122.0 (C-a), 121.3 (C-4), 110.4 (C-b),
34.0 (CH2), 21.4 (CH2), 13.6 (CH3). Anal. Calcd for
C16H18N2O: C, 75.56; H, 7.13; N, 11.01. Found: C,
75.52; H, 7.21; N, 10.93.
4.1.1.4.
1-[2-(trans-Crotonylamino)-4-methoxyphe-
nyl]pyrrole (4d). White crystals (71%); mp 71 ꢂC; IR
1
(KBr) 3240 (NH), 1665 (C@O); H NMR (CDCl3) d:
8.18 (d, 1H, J = 2.75 Hz, H-3), 7.16 (d, 1H,
J = 8.70 Hz, H-6), 6.92 (br s, 1H, NH), 6.84 (qd, 1H,
J = 15.15 and 6.85 Hz, @CH), 6.72 (dd, 2H, J = 1.95
and 1.95 Hz, H-a), 6.65 (dd, 1H, J = 8.70 and 2.75 Hz,
H-5), 6.38 (dd, 2H, J = 1.95 and 1.95 Hz, H-b), 5.65
(dd, 1H, J = 15.15 and 1.50 Hz, HC@), 3.84 (s, 3H,
CH3O), 1.83 (dd, 3H, J = 6.85 and 1.50 Hz, CH3). Anal.
Calcd for C15H16N2O2: C, 70.29; H, 6.29; N, 10.93.
Found: C, 70.23; H, 6.20; N, 10.99.
4.1.1.9.
1-[2-(trans-Hexenoylamino)-4-methoxyphe-
nyl]pyrrole (4i). Pale-yellow crystals (61%); mp 51 ꢂC;
1
IR (KBr) 3215 (NH), 1640 (C@O); H NMR (CDCl3)
d: 8.19 (d, 1H, J = 2.80 Hz, H-3), 7.16 (d, 1H,
J = 8.65 Hz, H-6), 6.94 (br s, 1H, NH), 6.81 (m, 1H,
@CH), 6.73 (dd, 2H, J = 1.90 and 1.90 Hz, H-a),
6.68 (dd, 1H, J = 8.65 and 2.80 Hz, H-5), 6.37 (dd,
2H, J = 1.90 and 1.90 Hz, H-b), 5.63 (d, 1H,
J = 15.25 Hz, HC@), 3.84 (s, 3H, CH3O), 2.15 (m,
2H, CH2), 1.44 (sex, 2H, J = 7.40 Hz, CH2), 0.90 (t,
3H, J = 7.40 Hz, CH3). Anal. Calcd for C17H20N2O2:
C, 71.80; H, 7.09; N, 9.85. Found: C, 71.84; H, 7.18;
N, 9.77.
4.1.1.5.
1-[2-(trans-Crotonylamino)-5-methoxyphe-
nyl]pyrrole (4e). Pale-yellow crystals (60%); mp 127 ꢂC;
1
IR (KBr) 3230 (NH), 1650 (C@O); H NMR (CDCl3)
d: 8.38 (d, 1H, J = 8.15 Hz, H-3), 6.94–6.76 (m, 6H,
H-4, H-6, NH, @CH and H-a), 6.37 (dd, 2H, J = 1.90
and 1.90 Hz, H-b), 5.71 (dd, 1H, J = 15.15 and
1.35 Hz, HC@), 3.79 (s, 3H, CH3O), 1.84 (dd, 3H,
J = 6.85 and 1.35 Hz, CH3). Anal. Calcd for
C15H16N2O2: C, 70.29; H, 6.29; N, 10.93. Found: C,
70.36; H, 6.45; N, 11.14.
4.1.1.10. 1-[2-(trans-Hexenoylamino)-5-methoxyphe-
nyl]pyrrole (4j). White crystals (60%); mp 82 ꢂC; IR
1
(KBr) 3200 (NH), 1645 (C@O); H NMR (CDCl3) d:
4.1.1.6.
1-(2-Hexanoylaminophenyl)pyrrole
(4f).
8.28 (d, 1H, J = 8.75 Hz, H-3), 6.95 (m, 2H, H-4 and
H-6), 6.87 (m, 2H, @CH and NH), 6.83 (dd, 2H,
J = 1.95 and 1.95 Hz, H-a), 6.40 (dd, 2H, J = 1.95 and
1.95 Hz, H-b), 5.71 (d, 1H, J = 15.25 Hz, HC@), 3.82
(s, 3H, CH3O), 2.16 (m, 2H, CH2), 1.47 (sex, 2H,
J = 7.35 Hz, CH2), 0.93 (t, 3H, J = 7.35 Hz, CH3). Anal.
Calcd for C17H20N2O2: C, 71.80; H, 7.09; N, 9.85.
Found: C, 71.95; H, 7.02; N, 9.97.
White crystals (71%); mp 40 ꢂC; IR (KBr) 3220 (NH),
1645 (C@O); 1H NMR (CDCl3) d: 8.37 (d, 1H,
J = 7.70 Hz, H-3), 7.36 (t, 1H, J = 7.70 Hz, H-4), 7.25
(d, 1H, J = 7.70 Hz, H-6), 7.13 (t, 1H, J = 7.70 Hz, H-
5), 7.00 (br s, 1H, NH), 6.77 (dd, 2H, J = 1.80 and
1.80 Hz, H-a), 6.38 (dd, 2H, J = 1.80 and 1.80 Hz, H-
b), 2.19 (t, 2H, J = 7.00 Hz, CH2), 1.57 (m, 4H, CH2),
1.27 (m, 4H, CH2), 0.87 (t, 3H, J = 7.00 Hz, CH3); 13C
NMR (CDCl3) d: 172.1 (CO), 134.4 (C-1), 131.1 (C-2),
129.3 (C-6), 127.3 (C-3), 124.6 (C-5), 122.6 (C-a),
122.0 (C-4), 110.9 (C-b), 38.4 (CH2), 31.8 (CH2), 25.6
(CH2), 22.9 (CH2), 14.5 (CH3). Anal. Calcd for
C16H20N2O: C, 74.96; H, 7.86; N, 10.93. Found: C,
75.06; H, 7.95; N, 11.12.
4.1.1.11. 1-[2-(3,4-Methylenedioxy)phenylethanoylam-
inophenyl]pyrrole (4k). White crystals (74%); mp 85 ꢂC;
1
IR (KBr) 3220 (NH), 1640 (C@O); H NMR (CDCl3)
d: 8.34 (d, 1H, J = 7.90 Hz, H-3), 7.38 (t, 1H,
J = 7.90 Hz, H-4), 7.22 (d, 1H, J = 7.90 Hz, H-6),
7.13 (t, 1H, J = 7.90 Hz, H-5), 6.90 (br s, 1H, NH),
6.64 (m, 5H, H-20, H-50, H-60 and H-a), 6.35 (dd,
2H, J = 2.00 and 2.00 Hz, H-b), 5.89 (s, 2H, OCH2O),
2.86 (t, 2H, J = 7.45 Hz, CH2), 2.45 (t, 2H,
J = 7.45 Hz, CH2). Anal. Calcd for C20H18N2O3: C,
71.84; H, 5.42; N, 8.38. Found: C, 72.02; H, 5.56; N,
8.52.
4.1.1.7. 1-(2-Hexanoylamino-4-methoxyphenyl)pyrrole
(4g). Pale-yellow crystals (74%); mp 44 ꢂC; IR (KBr)
3220 (NH), 1645 (C@O); 1H NMR (CDCl3) d: 8.09
(d, 1H, J = 2.70 Hz, H-3), 7.16 (d, 1H, J = 8.65 Hz,
H-6), 6.90 (s, 1H, NH), 6.71 (dd, 2H, J = 1.85 and
1.85 Hz, H-a), 6.64 (dd, 1H, J = 8.65 and 2.70 Hz, H-
5), 6.36 (dd, 2H, J = 1.85 and 1.85 Hz, H-b), 3.83 (s,
3H, CH3O), 2.15 (t, 2H, J = 6.80 Hz, CH2), 1.55 (m,
2H, CH2), 1.26 (m, 4H, CH2), 0.86 (t, 3H, J =
6.80 Hz, CH3). Anal. Calcd for C17H22N2O2: C,
71.30; H, 7.74; N, 9.78. Found: C, 71.42; H, 7.96; N,
10.03.
4.1.1.12. 1-[2-(3,4-Dimethoxy)phenylethanoylamino-
phenyl]pyrrole (4l). White crystals (63%); mp 91 ꢂC; IR
1
(KBr) 3210 (NH), 1645 (C@O); H NMR (CDCl3) d:
8.35 (d, 1H, J = 7.85 Hz, H-3), 7.38 (t, 1H,
J = 7.85 Hz, H-4), 7.24 (d, 1H, J = 7.85 Hz, H-6), 7.14
(t, 1H, J = 7.85 Hz, H-5), 6.89 (br s, 1H, NH), 6.75
(m, 2H, H-50 and H-60), 6.67 (d, 1H, J = 1.15 Hz, H-
20), 6.61 (dd, 2H, J = 1.90 and 1.90 Hz, H-a), 6.32 (dd,
2H, J = 1.90 and 1.90 Hz, H-b), 3.85 (s, 3H, CH3O),
3.78 (s, 3H, CH3O), 2.88 (t, 2H, J = 7.45 Hz, CH2),
2.47 (t, 2H, J = 7.45 Hz, CH2). Anal. Calcd for
C21H22N2O3: C, 71.98; H, 6.33; N, 7.99. Found: C,
72.11; H, 6.27; N, 8.21.
4.1.1.8. 1-(2-trans-Hexenoylaminophenyl)pyrrole (4h).
White crystals (72%); mp 46 ꢂC; IR (KBr) 3210 (NH),
1640 (C@O); 1H NMR (CDCl3) d: 8.48 (d, 1H,
J = 7.75 Hz, H-3), 7.37 (t, 1H, J = 7.75 Hz, H-4), 7.26
(d, 1H, J = 7.75 Hz, H-6), 7.13 (t, 1H, J = 7.75 Hz, H-
5), 7.01 (br s, 1H, NH), 6.83 (m, 1H, @CH), 6.78 (dd,

J. Guillon et al. / Bioorg. Med. Chem. 15 (2007) 194–210
205
4.1.1.13.
1-[2-(Cyclohex-1-enecarbonyl)aminophe-
and 1.15 Hz, H-3), 6.89 (dd, 1H, J = 3.95 and 2.70 Hz,
H-2), 6.88 (dd, 1H, J = 15.40 and 1.70 Hz, HC@), 2.08
(dd, 3H, J = 6.80 and 1.70 Hz, CH3). Anal. Calcd for
C14H12N2: C, 80.74; H, 5.81; N, 13.45. Found: C,
80.80; H, 5.97; N, 13.54.
nyl]pyrrole (4m). White crystals (79%); mp 119 ꢂC; IR
(KBr) 3210 (NH), 1645 (C@O); H NMR (CDCl3) d:
1
8.55 (d, 1H, J = 7.85 Hz, H-3), 7.42 (t, 1H,
J = 7.85 Hz, H-4), 7.33 (br s, 1H, NH), 7.31 (d, 1H,
J = 7.85 Hz, H-6), 7.16 (t, 1H, J = 7.85 Hz, H-5), 6.81
(dd, 2H, J = 2.10 and 2.10 Hz, H-a), 6.60 (m, 1H,
@CH), 6.43 (dd, 2H, J = 2.10 and 2.10 Hz, H-b), 2.17
(m, 2H, CH2), 2.09 (m, 2H, CH2), 1.69–1.56 (m, 4 H,
CH2). Anal. Calcd for C17H18N2O: C, 76.66; H, 6.81;
N, 10.52. Found: C, 76.81; H, 6.82; N, 10.49.
4.1.2.4. 7-Methoxy-4-[(E)-prop-1-enyl]pyrrolo[1,2-
a]quinoxaline (1d). Method A: yellow crystals (16%);
1
mp 80 ꢂC; IR (KBr) 1610 (C@N); H NMR (CDCl3)
d: 7.83 (dd, 1H, J = 2.55 and 1.15 Hz, H-1), 7.69 (d,
1H, J = 8.95 Hz, H-9), 7.38 (d, 1H, J = 2.75 Hz, H-6),
7.20 (qd, 1H, J = 15.35 and 6.75 Hz, @CH), 7.07 (dd,
1H, J = 8.95 and 2.75 Hz, H-8), 6.94 (dd, 1H, J = 3.90
and 1.15 Hz, H-3), 6.87 (dd, 1H, J = 15.35 and
1.55 Hz, HC@), 6.82 (dd, 1H, J = 3.90 and 2.55 Hz,
H-2), 3.89 (s, 3H, CH3O), 2.03 (dd, 3H, J = 6.75 and
1.55 Hz, CH3). Anal. Calcd for C15H14N2O: C, 75.61;
H, 5.92; N, 11.76. Found: C, 75.55; H, 6.08; N, 11.64.
4.1.1.14. 1-(2-Benzamidophenyl)pyrrole (4n). White
crystals (71%).32
4.1.2. General procedure for 4-alkyl- or 4-alkenyl- or 4-
arylpyrrolo[1,2-a]quinoxaline (1a–n). A solution of acet-
amide 4a–n (0.02 mol) and phosphorous oxychloride
(0.1 mol) in toluene (100 mL) was heated under reflux
for 4 h. After cooling, the precipitate was filtered and
dissolved in water (80 mL). The solution was then made
alkaline with sodium hydrogen carbonate and extracted
with methylene chloride (150 mL). The organic layer
was dried over Na2SO4 and evaporated to dryness under
reduced pressure. The residue was purified by column
4.1.2.5.
8-Methoxy-4-[(E)-prop-1-enyl]pyrrolo[1,2-
a]quinoxaline (1e). Yellow crystals (22%); mp 45 ꢂC; IR
1
(KBr) 1610 (C@N); H NMR (CDCl3) d: 7.82 (d, 1H,
J = 8.95 Hz, H-6), 7.78 (m, 1H, H-1), 7.19 (d, 1H,
J = 2.40 Hz, H-9), 7.08 (qd, 1H, J = 16.50 and
6.70 Hz, @CH), 6.97 (dd, 1H, J = 8.95 and 2.40 Hz,
H-7), 6.93 (m, 1H, H-3), 6.85 (m, 1H, H-2), 6.82 (dd,
1H, J = 16.50 and 1.25 Hz, HC@), 3.96 (s, 3H, CH3O),
2.01 (dd, 3H, J = 6.70 and 1.25 Hz, CH3). Anal. Calcd
for C15H14N2O: C, 75.61; H, 5.92; N, 11.76. Found:
C, 75.72; H, 6.03; N, 11.89.
chromatography (SiO2,
ether = 20:80) to give 1a–n.
ethyl
acetate/petroleum
4.1.2.1. 4-Propylpyrrolo[1,2-a]quinoxaline (1a). White
crystals (78%); mp 33 ꢂC ; IR (KBr) 1620 (C@N); H
1
NMR (CDCl3) d: 7.89 (d, 1H, J = 7.95 Hz, H-9), 7.85
(dd, 1H, J = 2.60 and 1.25 Hz, H-1), 7.77 (d, 1H,
J = 7.95 Hz, H-6), 7.41 (m, 2H, H-7 and H-8), 6.88
(dd, 1H, J = 3.90 and 1.25 Hz, H-3), 6.81 (dd, 1H,
J = 3.90 and 2.60 Hz, H-2), 2.98 (t, 2H, J = 7.45 Hz,
CH2), 1.91 (sex, 2H, J = 7.45 Hz, CH2), 1.07 (t, 3H,
J = 7.45 Hz, CH3); 13C NMR (CDCl3) d: 157.9 (C-4),
136.6 (C-9a), 129.9 (C-5a), 127.8 (C-3a), 127.3 (C-8),
126.6 (C-7), 125.5 (C-6), 114.5 (C-9), 114.0 (C-1),
113.8 (C-3), 106.7 (C-2), 38.3 (CH2), 22.4 (CH2), 14.8
(CH3). Anal. Calcd for C14H14N2: C, 79.96; H, 6.71;
N, 13.32. Found: C, 80.08; H, 6.73; N, 13.43.
4.1.2.6. 4-Pentylpyrrolo[1,2-a]quinoxaline (1f). Color-
less oil (61%); IR (KBr) 1615 (C@N); 1H NMR (CDCl3)
d: 7.90 (dd, 1H, J = 7.90 Hz, H-9), 7.81 (dd, 1H, J = 2.65
and 1.10 Hz, H-1), 7.72 (d, 1H, J = 7.90 Hz, H-6), 7.38
(m, 2H, H-7 and H-8), 6.86 (dd, 1H, J = 3.90 and
1.10 Hz, H-3), 6.78 (dd, 1H, J = 3.90 and 2.65 Hz, H-
2), 2.98 (t, 2H, J = 7.00 Hz, CH2), 1.89 (m, 2H, CH2),
1.44 (m, 4H, CH2), 0.90 (t, 3H, J = 7.00 Hz, CH3); 13C
NMR (CDCl3) d: 158.1 (C-4), 136.5 (C-9a), 129.9 (C-
5a), 127.8 (C-3a), 127.3 (C-8), 126.5 (C-7), 125.5 (C-6),
114.6 (C-9), 114.1 (C-1), 113.9 (C-3), 106.7 (C-2), 36.5
(CH2), 32.6 (CH2), 28.9 (CH2), 23.1 (CH2), 14.6
(CH3). Anal. Calcd for C16H18N2: C, 80.63; H, 7.61;
N, 11.75. Found: C, 80.57; H, 7.72; N, 11.82.
4.1.2.2. 7-[(Methoxy-4-propylpyrrolo[1,2-a]quinoxa-
line (1b). Beige crystals (50%); mp 45 ꢂC; IR (KBr)
1615 (C@N); 1H NMR (CDCl3) d: 7.82 (dd, 1H,
J = 2.55 and 1.15 Hz, H-1), 7.71 (d, 1H, J = 8.95 Hz,
H-9), 7.38 (d, 1H, J = 2.75 Hz, H-6), 7.06 (dd, 1H,
J = 8.95 and 2.75 Hz, H-8), 6.86 (dd, 1H, J = 3.95 and
1.15 Hz, H-3), 6791 (dd, 1H, J = 3.95 and 2.55 Hz, H-
2), 3.89 (s, 3H, CH3O), 2.96 (t, 2 H, J = 7.40 Hz,
CH2), 1.89 (sex, 2H, J = 7.40 Hz, CH2), 1.06 (t, 3H,
J = 7.40 Hz, CH3). Anal. Calcd for C15H16N2O: C,
74.97; H, 6.71; N, 11.66. Found: C, 75.06; H, 6.54; N,
11.78.
4.1.2.7. 7-Methoxy-4-pentylpyrrolo[1,2-a]quinoxaline
(1g). Yellow oil (93%); IR (KBr) 1610 (C@N); 1H
NMR (CDCl3) d: 7.75 (m, 1H, H-1), 7.64 (d, 1H,
J = 8.90 Hz, H-9), 7.36 (d, 1H, J = 1.70 Hz, H-6), 7.01
(dd, 1H, J = 8.90 and 1.70 Hz, H-8), 6.83 (m, 1H,
H-3), 6.76 (m, 1H, H-2), 3.86 (s, 3H, CH3O), 2.96
(t, 2H, J = 7.15 Hz, CH2), 1.87 (m, 2H, CH2), 1.40 (m,
4H, CH2), 0.89 (t, 3H, J = 7.15 Hz, CH3). Anal. Calcd
for C17H20N2O: C, 76.08; H, 7.51; N, 10.44. Found:
C, 75.89; H, 7.42; N, 10.38.
4.1.2.3. 4-[(E)-prop-1-enyl]pyrrolo[1,2-a]quinoxaline
(1c). Pale-yellow crystals (23%); mp 89 ꢂC; IR (KBr)
1615 (C@N); 1H NMR (CDCl3) d: 7.98 (dd, 1H,
J = 7.60 and 2.00 Hz, H-9), 7.94 (dd, 1 H, J = 2.70 and
1.15 Hz, H-1), 7.85 (dd, 1H, J = 7.60 and 2.00 Hz, H-
6), 7.51–7.41 (m, 2H, H-7 and H-8), 7.25 (qd, 1H,
J = 15.40 and 6.80 Hz, @CH), 7.01 (dd, 1H, J = 3.95
4.1.2.8. 4-[(E)-Pent-1-enyl]pyrrolo[1,2-a]quinoxaline
(1h). Yellow oil (54%); IR (KBr) 1615 (C@N); 1H
NMR (CDCl3) d: 7.92 (dd, 1H, J = 7.85 and 2.05 Hz,
H-9), 7.84 (dd, 1H, J = 2.85 and 1.20 Hz, H-1), 7.73
(dd, 1H, J = 7.85 and 2.05 Hz, H-6), 7.37 (m, 2H, H-7
and H-8), 7.21 (m, 1H, @CH), 6.97 (dd, 1H, J = 4.00

206
J. Guillon et al. / Bioorg. Med. Chem. 15 (2007) 194–210
and 1.20 Hz, H-3), 6.85 (dd, 1H, J = 4.00 and 2.85 Hz,
H-2), 6.83 (dd, 1H, J = 15.40 and 1.25 Hz, HC@), 2.37
(m, 2H, CH2), 1.63 (sex, 2H, J = 7.30 Hz, CH2), 1.01
(t, 3H, J = 7.30 Hz, CH3). Anal. Calcd for C16H16N2:
C, 81.32; H, 6.82; N, 11.86. Found: C, 81.29; H, 6.98;
N, 11.85.
(CH3O), 37.7 (CH2), 33.7 (CH2). Anal. Calcd for
C21H20N2O2: C, 75.88; H, 6.06; N, 8.43. Found: C,
76.07; H, 6.30; N, 8.57.
4.1.2.13. 4-(Cyclohex-1-enyl)pyrrolo[1,2-a]quinoxaline
(1m). Yellow oil (48%); IR (KBr) 1615 (C@N); 1H NMR
(CDCl3) d: 7.96 (d, 1H, J = 8.00 Hz, H-9), 7.93 (dd, 1H,
J = 2.75 and 1.30 Hz, H-1), 7.82 (d, 1H, J = 8.00 Hz,
H-6), 7.47 (t, 1H, J = 8.00 Hz, H-8), 7.42 (t, 1H,
J = 8.00 Hz, H-7), 6.98 (dd, 1H, J = 4.00 and 1.30 Hz,
H-3), 6.85 (dd, 1H, J = 4.00 and 2.75 Hz, H-2), 6.59
(m, 1H, @CH), 2.69 (m, 2H, CH2), 2.33 (m, 2H, CH2),
1.93–1.77 (m, 4H, CH2). Anal. Calcd for C17H16N2: C,
82.22; H, 6.49; N, 11.28. Found: C, 82.10; H, 6.45; N,
11.13.
4.1.2.9.
7-Methoxy-4-[(E)-pent-1-enyl]pyrrolo[1,2-
a]quinoxaline (1i). Yellow oil (37%); IR (KBr) 1610
(C@N); 1H NMR (CDCl3) d: 7.84 (dd, 1H, J = 2.90
and 1.25 Hz, H-1), 7.71 (d, 1H, J = 8.95 Hz, H-9), 7.40
(d, 1H, J = 2.80 Hz, H-6), 7.15 (m, 1H, @CH), 7.06
(dd, 1H, J = 8.95 and 2.80 Hz, H-8), 6.97 (dd, 1H,
J = 3.90 and 1.25 Hz, H-3), 6.83 (dd, 1H, J = 3.90 and
2.90 Hz, H-2), 6.77 (dd, 1H, J = 15.30 and 1.15 Hz,
HC@), 3.90 (s, 3H, CH3O), 2.36 (m, 2H, CH2), 1.62
(sex, 2H, J = 7.35 Hz, CH2), 0.97 (t, 3H, J = 7.35 Hz,
CH3). Anal. Calcd for C17H18N2O: C, 76.66; H, 6.81;
N, 10.52. Found: C, 76.51; H, 6.75; N, 10.56.
4.1.2.14.
4-Phenylpyrrolo[1,2-a]quinoxaline
(1n).
White crystals (53%).34
4.1.3. General procedure for 1-(2-acetylaminophenyl)pyr-
role (5a,b). To a solution of 1-(2-aminophenyl)pyrrole
2a,b (0.02 mol) in dioxane (80 mL) were added pyridine
(0.022 mol) then acetyl chloride (0.02 mol). The reaction
mixture was refluxed for 4 h and the solvent then re-
moved under reduced pressure. The residue was triturat-
ed with water and extracted with diethyl ether (2·
80 mL) The organic layers were collected, washed with
an aqueous sodium hydrogen carbonate solution
(100 mL) then with water (100 mL), dried over Na2SO4
and evaporated to dryness. The precipitate was crystal-
lized from petroleum ether to afford 5a,b.
4.1.2.10. 8-Methoxy-4-[(E)-pent-1-enyl]pyrrolo[1,2-
a]quinoxaline (1j). Yellow oil (26%); IR (KBr) 1610
(C@N); H NMR (CDCl3) d: 7.88 (d, 1H, J = 8.95 Hz,
1
H-6), 7.82 (dd, 1H, J = 2.75 and 1.30 Hz, H-1), 7.24
(d, 1H, J = 2.65 Hz, H-9), 7.15 (ddd, 1H, J = 15.60
and 6.95 Hz, =CH), 7.03 (dd, 1H, J = 8.95 and
2.65 Hz, H-7), 6.98 (dd, 1H, J = 4.00 and 1.30 Hz, H-
3), 6.87 (dd, 1H, J = 4.00 and 2.75 Hz, H-2), 6.82
(ddd, 1H, J = 15.60 and 1.50 Hz, HC@), 3.95 (s, 3H,
CH3O), 2.38 (m, 2H, CH2), 1.63 (sex, 2H, J = 7.40 Hz,
CH2), 1.04 (t, 3H, J = 7.40 Hz, CH3). Anal. Calcd for
C17H18N2O: C, 76.66; H, 6.81; N, 10.52. Found: C,
76.44; H, 6.73; N, 10.68.
4.1.3.1. 1-(2-Acetylaminophenyl)pyrrole (5a). White
crystals (67%).34
4.1.2.11. 4-(3,4-Methylenedioxyphenethyl)pyrrolo[1,2-
a]quinoxaline (1k). White crystals (77%); mp 69 ꢂC; IR
(KBr) 1615 (C@N); 1H NMR (CDCl3) d: 7.94 (d,
1H, J = 8.00 Hz, H-9), 7.88 (m, 1H, H-1), 7.82 (d,
1H, J = 8.00 Hz, H-6), 7.43 (m, 2H, H-7 and H-8),
6.87–6.74 (m, 5H, H-2, H-3, H-20, H-50 and H-60),
5.90 (s, 2H, OCH2O), 3.28 (m, 2H, CH2), 3.15 (m,
2H, CH2); 13C NMR (CDCl3) d: 156.2 (C-4), 147.8
(C-30), 145.9 (C-40), 135.7 (C-10), 129.7 (C-9a), 127.4
(C-5a), 127.1 (C-3a), 126.1 (C-8), 125.2 (C-7), 121.4
(C-60), 114.3 (C-9), 113.8 (C-6), 113.6 (C-3), 109.1 (C-
1), 108.4 (C-50), 106.2 (C-2 and C-20), 100.9 (OCH2O),
37.8 (CH2), 33.9 (CH2). Anal. Calcd for C20H16N2O2:
C, 75.93; H, 5.10; N, 8.85. Found: C, 76.11; H, 5.13;
N, 8.74.
4.1.3.2.
1-(2-Acetylamino-4-methoxyphenyl)pyrrole
(5b). Pale-yellow crystals (62%); mp 73 ꢂC; IR (KBr)
3200 (NH), 1650 (C@O); H NMR (CDCl3) d: 8.04 (d,
1
1H, J = 2.50 Hz, H-3), 7.15 (d, 1H, J = 8.55 Hz, H-6),
6.90 (s, 1H, NH), 6.72 (dd, 2H, J = 1.95 and 1.95 Hz,
H-a), 6.64 (dd, 1H, J = 8.55 and 2.50 Hz, H-5), 6.35
(dd, 2H, J = 1.95 and 1.95 Hz, H-b), 3.83 (s, 3H,
CH3O), 2.00 (s, 3H, CH3). Anal. Calcd for
C13H14N2O2: C, 67.81; H, 6.13; N, 12.17. Found: C,
67.75; H, 6.03; N, 12.22.
4.1.4. General procedure for 4-methylpyrrolo[1,2-a]qui-
noxaline (6a,b). A solution of 1-(2-propanoylaminophe-
nyl)pyrrole 5a,b (0.02 mol) and phosphorous
oxychloride (0.1 mol) in toluene (100 mL) was heated
under reflux for 4 h. After cooling, the precipitate was
filtered and dissolved in water (80 mL). The solution
was then made alkaline with sodium hydrogen carbon-
ate and extracted with methylene chloride (150 mL).
The organic layer was dried over Na2SO4 and evaporat-
ed to dryness under reduced pressure to give 6a,b.
4.1.2.12. 4-(3,4-Dimethoxyphenethyl)pyrrolo[1,2-a]-
quinoxaline (1l). White crystals (70%); mp 174 ꢂC; IR
(KBr) 1615 (C@N); 1H NMR (CDCl3) d: 7.89 (d,
1H, J = 7.90 Hz, H-9), 7.83 (dd, 1H, J = 2.65 and
1.15 Hz, H-1), 7.78 (d, 1H, J = 7.90 Hz, H-6), 7.43
(m, 2H, H-7 and H-8), 6.88–6.81 (m, 5H, H-2, H-3,
H-20, H-50 and H-60), 3.84 (s, 3H, CH3O), 3.82 (s,
3H, CH3O), 3.30 (m, 2H, CH2), 3.17 (m, 2H, CH2);
13C NMR (CDCl3) d: 156.2 (C-4), 148.9 (C-30), 147.4
(C-40), 135.9 (C-10), 134.4 (C-9a), 129.4 (C-5a), 127.2
(C-3a), 126.9 (C-8), 125.7 (C-7), 125.1 (C-60), 120.2
(C-6), 114.2 (C-9), 113.6 (C-3), 113.5 (C-1), 112.0 (C-
20), 111.4 (C-50), 106.1 (C-2), 55.9 (CH3O), 55.8
4.1.4.1. 4-Methylpyrrolo[1,2-a]quinoxaline (6a). White
crystals (67%).34
4.1.4.2. 7-Methoxy-4-methylpyrrolo[1,2-a]quinoxaline
(6b). Pale-orange crystals (58%); mp 50 ꢂC; IR (KBr)
1620 (C@N); 1H NMR (CDCl3) d: 7.82 (dd, 1H,

J. Guillon et al. / Bioorg. Med. Chem. 15 (2007) 194–210
207
J = 2.75 and 1.15 Hz, H-1), 7.71 (d, 1H, J = 8.95 Hz, H-
9), 7.37 (d, 1H, J = 2.75 Hz, H-6), 7.07 (dd, 1H, J = 8.95
and 2.75 Hz, H-8), 6.85 (dd, 1H, J = 3.90 and 1.15 Hz,
H-3), 6.80 (dd, 1H, J = 3.90 and 2.75 Hz, H-2), 3.89 (s,
3H, CH3O), 2.70 (s, 3H, CH3). Anal. Calcd for
C13H12N2O: C, 73.56; H, 5.70; N, 13.20. Found: C,
73.65; H, 5.78; N, 13.15.
with an aqueous saturated sodium hydrogen carbonate,
then with a brine solution, dried over Na2SO4 and
evaporated to dryness. The residue was chromato-
graphed on silica gel with dichloromethane/hexane
(4:1) as eluent to give 1c as yellow crystals (29%). IR
1
and H NMR data were in accordance with those of
Method A.
4.1.5. General procedure for 4-styrylpyrrolo[1,2-a]quinox-
aline (1o,p). 4-Methylpyrrolo[1,2-a]quinoxaline 6a,b
(3.3 mmol), benzaldehyde (3.3 mmol) and Ac2O (5 mL)
were refluxed for 5 h. The solvent was then evaporated
under reduced pressure. The residue was triturated in
water and extracted with dichloromethane. The organic
layer was washed with an aqueous saturated sodium
hydrogen carbonate solution, dried over Na2SO4 and
evaporated and then chromatographed over Si gel. Elu-
tion with hexane/AcOEt (8:2) afforded the pure com-
pound 1o,p.
4.1.8. General procedure for trans-4-(2-methyloxira-
ne)pyrrolo[1,2-a]quinoxaline (1q) and cis-4-(2-methyloxi-
rane)pyrrolo[1,2-a]quinoxaline (1r).
A
mixture of
triethylsulfonium tetrafluoroborate (2.24 mmol), potas-
sium hydroxide pellets (15.7 mmol), 8 mL of acetonitrile
and 0.1 mL of water was warmed at 60 ꢂC for 15 min in
the absence of light. A solution of pyrrolo[1,2-a]quinox-
aline-4-carboxaldehyde 7 (2.24 mmol) in 8 mL of aceto-
nitrile was then added dropwise and the mixture was
stirred at 60 ꢂC for 2 h. The mixture was filtered and
the solid was extracted with acetonitrile then with
dichloromethane. The organic layers were dried over
Na2SO4 and evaporated to dryness. The residue was
chromatographed on silica gel with hexane/AcOEt
(8:2) as eluent. The first eluted product (Rf = 0.38) was
the trans epoxide 1q, followed by the cis epoxide 1r
(Rf = 0.20).
4.1.5.1. 4-Styrylpyrrolo[1,2-a]quinoxaline (1o). Yellow
crystals (41%).34
4.1.5.2. 7-Methoxy-4-styrylpyrrolo[1,2-a]quinoxaline
(1p). Pale-yellow crystals (30%); mp 156 ꢂC; IR (KBr)
1615 (C@N); 1H NMR (CDCl3) d: 8.04 (d, 1H,
J = 15.95 Hz, HC@), 7.86 (dd, 1H, J = 2.65 and
1.25 Hz, H-1), 7.73 (d, 1H, J = 9.15 Hz, H-9), 7.66 (m,
2H, Ar0-H), 7.49 (d, 1H, J = 15.95 Hz, @CH), 7.44 (d,
1H, J = 2.65 Hz, H-6), 7.39 (m, 3H, Ar0-H), 7.07 (m,
2H, H-8 and H-3), 6.87 (dd, 1H, J = 3.90 and 2.65 Hz,
H-2), 3.92 (s, 3H, CH3O). Anal. Calcd for
C20H16N2O: C, 79.97; H, 5.37; N, 9.33. Found: C,
80.13; H, 5.27; N, 9.36.
4.1.8.1. Trans-4-(2-methyloxirane)pyrrolo[1,2-a]qui-
noxaline (1q). Yellow crystals (40%); mp 62 ꢂC; IR
1
(KBr) 1610 (C@N); H NMR (CDCl3) d: 7.93 (d, 1H,
J = 7.85 Hz, H-9), 7.89 (dd, 1H, J = 2.55 and 1.30 Hz,
H-1), 7.78 (d, 1H, J = 7.85 Hz, H-6), 7.47 (t, 1H,
J = 7.85 Hz, H-8), 7.39 (t, 1H, J = 7.85 Hz, H-7), 7.12
(dd, 1H, J = 3.90 and 1.30 Hz, H-3), 6.83 (dd, 1H,
J = 3.90 and 2.55 Hz, H-2), 3.99 (d, 1H, J = 2.00 Hz,
H-10), 3.59 (qd, 1H, J = 5.15 and 2.00 Hz, H-20), 1.54
(d, 3H, J = 5.15 Hz, CH3). Anal. Calcd for
C14H12N2O: C, 74.98; H, 5.39; N, 12.49. Found: C,
75.15; H, 5.56; N, 12.50.
4.1.6. [Pyrrolo [1,2-a]quinoxaline-4-carboxaldehyde (7).
4-Methylpyrrolo[1,2-a]quinoxaline 6a (2.3 mmol) and
SeO2 (3.45 mmol) were stirred in dioxane (10 mL) un-
der reflux for 4 h. After cooling and filtration, the
solution was concentrated and the residue was puri-
fied on silica gel. Elution with CH2Cl2 gave 7 as or-
ange crystals (59%); mp 162 ꢂC; IR (KBr) 1680
(C@O); 1H NMR (CDCl3) d: 10.12 (s, 1H, CHO),
8.13 (d, 1H, J = 8.05 Hz, H-9), 8.02 (dd, 1H,
J = 2.75 and 1.20 Hz, H-1), 7.92 (d, 1H,
J = 8.05 Hz, H-6), 7.69 (dd, 1H, J = 4.05 and
1.20 Hz, H-3), 7.67 (t, 1H, J = 8.05 Hz, H-8), 7.54
(t, 1H, J = 8.05 Hz, H-7), 7.03 (dd, 1H, J = 4.05
and 2.75 Hz, H-2). Anal. Calcd for C12H8N2O: C,
73.46; H, 4.11; N, 14.28. Found: C, 73.54; H, 4.31;
N, 14.39.
4.1.8.2. Cis-4-(2-methyloxirane)pyrrolo[1,2-a]quinoxa-
1
line (1r). Yellow oil (13%); IR (KBr) 1610 (C@N); H
NMR (CDCl3) d: 8.01 (d, 1H, J = 7.80 Hz, H-9), 7.94
(dd, 1H, J = 2.65 and 1.10 Hz, H-1), 7.83 (d, 1H,
J = 7.80 Hz, H-6), 7.50 (t, 1H, J = 7.80 Hz, H-8), 7.41
(t, 1H, J = 7.80 Hz, H-7), 7.15 (dd, 1H, J = 4.00 and
1.10 Hz, H-3), 6.86 (dd, 1H, J = 4.00 and 2.65 Hz, H-
2), 4.33 (d, 1H, J = 4.35 Hz, H-10), 3.54 (qd, 1H,
J = 5.30 and 4.35 Hz, H-20), 1.25 (d, 3H, J = 5.30 Hz,
CH3). Anal. Calcd for C14H12N2O: C, 74.98; H, 5.39;
N, 12.49. Found: C, 75.06; H, 5.21; N, 12.38.
4.1.9. General procedure for 4-alkenyl- or 4-arylpyrrolo
[1,2-a]quinoxaline (1c,d), (1h,i), (1n–p), and (1s). Method
C: A mixture of the 4-chloropyrrolo[1,2-a]quinoxaline
8a34 or 8b36 (5 mmol), the alkenylboronic acid
(5.5 mmol) and Pd(PPh3)4 (0.15 mmol) in benzene
(21 mL), ethanol (1.6 mL) and 2 M aqueous sodium car-
bonate solution (5.4 mL) was stirred and heated under
reflux under nitrogen for 24 h. It was then cooled, trans-
ferred to a separating funnel, and the reaction flask
washed out with water (3· 50 mL) and dichloromethane
(3· 90 mL), the washings being added to the separating
funnel. The organic layer was separated and the aqueous
4.1.7. 4-[(E)-Prop-1-enyl]pyrrolo[1,2-a] quinoxaline (1c).
Method B: To a suspension of ethyltriphenylphospho-
nium bromide (2.44 mmol) in 6 mL of anhydrous tolu-
ene at 0 ꢂC was added potassium tert-butoxide
(2.94 mmol). After 20 min of stirring at 0 ꢂC, a solution
of aldehyde 7 (1.22 mmol) in 8 mL of anhydrous tetra-
hydrofuran was added to the reaction mixture. The
mixture reaction was then heated at 70 ꢂC for 1.5 h.
After cooling, the mixture was hydrolysed by adding
7 mL of water. The aqueous layer was then extracted
with AcOEt, the resultant organic extracts were washed

208
J. Guillon et al. / Bioorg. Med. Chem. 15 (2007) 194–210
phase extracted with dichloromethane (2· 100 mL). The
combined organic extracts were then washed with water
(3· 130 mL), dried over Na2SO4, filtered and the filtrate
evaporated under reduced pressure. Column chroma-
tography of the residue on silica gel using diethyl
ether/petroleum ether (1:3) as eluent gave the pure prod-
uct 1c,d, 1h,i, 1n–p, or 1s.
chromatography of the residue on silica gel using diethyl
ether/petroleum ether (1:3) as eluent gave the pure prod-
uct 1t as yellow crystals (30%); mp 76 ꢂC; IR (KBr) 1610
1
(C@N); H NMR (CDCl3) d: 7.99 (d, 1H, J = 8.05 Hz,
H-9), 7.96 (dd, 1H, J = 2.75 and 1.20 Hz, H-1), 7.86
(d, 1H, J = 8.05 Hz, H-6), 7.51 (t, 1H, J = 8.05 Hz, H-
8), 7.45 (t, 1H, J = 8.05 Hz, H-7), 7.18 (dd, 1H,
J = 17.30 and 10.85 Hz, HC@), 7.04 (dd, 1H, J = 4.05
and 1.20 Hz, H-3), 6.91 (dd, 1H, J = 4.05 and 2.75 Hz,
H-2), 6.65 (dd, 1H, J = 17.30 and 1.65 Hz, @CH2),
5.79 (dd, 1H, J = 10.85 and 1.65 Hz, @CH2). Anal.
Calcd for C13H10N2: C, 80.39; H, 5.19; N, 14.42. Found:
C, 80.31; H, 5.34; N, 14.49.
4.1.9.1. 4-[(E)-Prop-1-enyl]pyrrolo[1,2-a]quinoxaline
(1c). Pale-yellow crystals (77%); IR and H NMR data
were in accordance with those of Methods A and B.
1
4.1.9.2.
a]quinoxaline (1d). Yellow crystals (65%); IR and 1H
NMR data were in accordance with those of Method A.
7-Methoxy-4-[(E)-prop-1-enyl]pyrrolo[1,2-
4.1.11. General procedure for 4-(hex-1-ynyl)pyrrolo[1,2-
a]quinoxaline (1u,v). A mixture of CuI (0.05 mmol),
Pd(PPh3)2Cl2 (0.05 mmol), anhydrous triethylamine
4.1.9.3. 4-[(E)-Pent-1-enyl]pyrrolo[1,2-a]quinoxaline
(1h). Yellow crystals (61%); IR and 1H NMR data were
in accordance with those of Method A.
(10 mL),
4-chloropyrrolo[1,2-a]quinoxaline
8a,b
(2.5 mmol) and 1-hexyne (3.75 mmol) was stirred and
heated at 80 ꢂC for 24 h. The reaction mixture was
cooled to rt and filtered. The solid residue was washed
thoroughly with hexane, combined filtrates were evapo-
rated under reduced pressure, and the residue was puri-
fied over a column of silica gel with hexane/AcOEt
(10:1) as eluent to give 1u,v.
4.1.9.4.
7-Methoxy-4-[(E)-pent-1-enyl]pyrrolo[1,2-
a]quinoxaline (1i). Yellow crystals (56%); IR and 1H
NMR data were in accordance with those of Method A.
4.1.9.5. 4-Phenylpyrrolo[1,2-a]quinoxaline (1n). White
crystals (85%); IR and H NMR data were in accor-
1
dance with those of Method A.34
4.1.11.1. 4-(Hex-1-ynyl)pyrrolo[1,2-a]quinoxaline (1u).
Yellow oil (29%); IR (KBr) 2210 (C„C); 1H NMR
(CDCl3) d: 7.93 (d, 1H, J = 8.00 Hz, H-9), 7.89 (dd,
1H, J = 2.70 and 1.20 Hz, H-1), 7.80 (d, 1H,
J = 8.00 Hz, H-6), 7.48 (t, 1H, J = 8.00 Hz, H-8), 7.41
(t, 1H, J = 8.00 Hz, H-7), 7.00 (dd, 1H, J = 3.95 and
1.20 Hz, H-3), 6.86 (dd, 1H, J = 3.95 and 2.70 Hz, H-
2), 2.55 (t, 2H, J = 7.10 Hz, CH2), 1.69 (qt, 2H,
J = 7.10 Hz, CH2), 1.52 (sex, 2H, J = 7.10 Hz, CH2),
0.96 (t, 2H, J = 7.10 Hz, CH3). Anal. Calcd for
C17H16N2: C, 82.22; H, 6.49; N, 11.28. Found: C,
82.36; H, 6.34; N, 11.35.
4.1.9.6. 4-Styrylpyrrolo[1,2-a]quinoxaline (1o). Yellow
crystals (86%); IR and H NMR data were in accor-
dance with those described above.
1
4.1.9.7. 7-Methoxy-4-styrylpyrrolo[1,2-a]quinoxaline
(1p). Yellow crystals (75%); IR and 1H NMR data were
in accordance with those described above.
4.1.9.8. 4-[(Z)-Prop-1-enyl]pyrrolo[1,2-a]quinoxaline
(1s). Yellow oil (51%); IR (KBr) 1610 (C@N); 1H
NMR (CDCl3) d: 7.99 (dd, 1H, J = 7.90 and 1.65 Hz,
H-9), 7.92 (dd, 1H, J = 2.65 and 1.35 Hz, H-1), 7.84
(dd, 1H, J = 7.90 and 1.65 Hz, H-6), 7.49 (ddd, 1H,
J = 7.90, 7.25 and 1.65 Hz, H-8), 7.43 (ddd, 1H,
J = 7.90, 7.25 and 1.65 Hz, H-7), 6.89 (dd, 1H,
J = 3.95 and 1.35 Hz, H-3), 6.86 (dd, 1H, J = 3.95 and
2.65 Hz, H-2), 6.77 (qd, 1H, J = 11.65 and 1.80 Hz,
HC@), 6.30 (qd, 1H, J = 11.65 and 7.20 Hz, @CH),
2.26 (dd, 3H, J = 7.20 and 1.80 Hz, CH3). Anal. Calcd
for C14H12N2: C, 80.74; H, 5.81; N, 13.45. Found: C,
80.60; H, 5.94; N, 13.59.
4.1.11.2. 4-(Hex-1-ynyl)-7-methoxypyrrolo[1,2-a]qui-
noxaline (1v). Yellow oil (42%) ; IR (KBr) 2210
1
(C„C); H NMR (CDCl3) d: 7.85 (dd, 1H, J = 2.65
and 1.35 Hz, H-1), 7.76 (d, 1H, J = 9.00 Hz, H-9), 7.45
(d, 1H, J = 2.80 Hz, H-6), 7.13 (dd, 1H, J = 9.00 and
2.80 Hz, H-8), 7.02 (dd, 1H, J = 4.00 and 1.35 Hz, H-
3), 6.87 (dd, 1H, J = 4.00 and 2.65 Hz, H-2), 3.91 (s,
3H, CH3O), 2.59 (t, 2H, J = 7.15 Hz, CH2), 1.73 (qt,
2H, J = 7.15 Hz, CH2), 1.59 (sex, 2H, J = 7.15 Hz,
CH2), 1.00 (t, 3H, J = 7.15 Hz, CH3). Anal. Calcd for
C18H18N2O: C, 77.67; H, 6.52; N, 10.06. Found: C,
77.75; H, 6.44; N, 9.86.
4.1.10. 4-(Eth-1-enyl)pyrrolo[1,2-a]quinoxaline (1t). A
mixture of the 4-chloropyrrolo[1,2-a]quinoxaline 8a
(3.4 mmol), the vinylboronic acid di-n-butyl ester
(3.8 mmol) and Pd(PPh3)4 (0.10 mmol) in benzene
(15 mL), and 4 M aqueous potassium hydroxide solu-
tion (2.4 mL) was stirred and heated under reflux under
nitrogen for 5 h. It was then cooled, transferred to a sep-
arating funnel, and the reaction flask washed out with
water (3· 50 mL) and benzene (2· 40 mL), the washings
being added to the separating funnel. The organic layer
was separated, washed with an aqueous saturated sodi-
um hydrogen carbonate, then with a brine solution,
dried over Na2SO4, and evaporated to dryness. Column
4.2. X-ray data
Pale-yellow single crystal (0.15 · 0.01 · 0.01 mm3) of 1c
was obtained by slow evaporation from methanol/chlo-
roform (20:80) solution: orthorhombic, space group P n
˚
˚
˚
a 21, a = 13.079(6) A, b = 19.592(9) A, c = 4.289(4) A,
3
˚
a = 90ꢂ, b = 90ꢂ, c = 90ꢂ, V = 1099.08(12) A , Z = 4,
d(calcd) = 1.259 Mg mꢀ3, FW = 208.26 for C14H12N2,
F(000) = 440. The unit cell dimensions were determined
using the least-squares fit from 25 reflections
(25ꢂ < h < 35ꢂ). Intensities were collected with an En-

J. Guillon et al. / Bioorg. Med. Chem. 15 (2007) 194–210
209
raf-Nonius CAD-4 diffactometer using the CuKa radia-
tion and a graphite monochromator up to h = 55ꢂ. No
intensity variation of two standard reflections monitored
every 90 min was observed. Full crystallographic results
have been deposited at the Cambridge Crystallographic
Data Centre (CCDC-297422), UK, as Supplementary
material.57 The data were corrected for Lorentz and
polarization effects and for empirical absorption correc-
tion.58 The structure was solved by direct methods Shelx
ric assay system, which measures the reduction of a tet-
razolium component (MTT) into an insoluble formazan
product by the mitochondria of viable cells. After incu-
bation of the cells with the MTT reagent, a detergent
solution was added to lyse the cells and solubilize the
coloured crystals. The samples were read using an ELI-
SA plate reader at a wavelength of 570 nm. The amount
of colour produced was directly proportional to the
number of viable cells. In some experiments, parasites
were diluted in culture medium and directly counted un-
der microscope. Each concentration was screened in
triplicate. The results are expressed as the concentra-
tions inhibiting parasite growth by 50% (IC50) after a
1–2 day incubation period.
59
86 and refined using Shelx 9360 suite of programs.
4.3. Partition coefficients logD (pH 7.4)
The relative logD (pH 7.4) in this study was assessed by
the micro-HPLC method.61 These determinations were
performed with a chromatographic apparatus (Spectra
4.4.2. Cytotoxicity test upon cells.64 The toxicity of
various molecules was evaluated on non-activated,
freshly isolated normal human peripheral blood mono-
nuclear cells (PBMC), as well as phytohaemagglutinin
(PHA)-induced cells. PBMC from healthy volunteers
were obtained following centrifugation on Ficoll gradi-
ent. Cells were then incubated in medium alone or in-
duced to enter cell cycle by the addition of PHA (5 lg/
ml, Murex Biotech Limited, Dartford, UK). Various
molecules were added as described under results.
Following cell cultures during 3–4 days, cells were
harvested, washed and counted with trypan blue exclu-
sion. In some experiments, the proliferation of PBMC
was checked using the MTT colorimetric method as
described previously. The 50% inhibitory concentrations
(IC50) were determined by linear regression analysis,
expressed in lM SD and the maximum tolerated
concentration expressed in lM was evaluated for each
compound.
Series, San Jose, USA) equipped with
a model
P1000XR pump and a model SCM 1000 vacuum mem-
brane degasser, a model UV 150 ultraviolet detector
(203 nm 6 kmax 6 253 nm) and a ChromJet data mod-
ule integrator (ThermoFinnigan, San Jose, USA). A re-
versed phase column was used: a Waters SunFireTM C18
(3.0 · 150 mm; 5 lm particle size) with a mobile phase
consisting of acetonitrile – phosphate buffer (pH 4.5)
(65:35, v/v (1g, 1i–m, 1o,p and 1u,v); 60:40, v/v (1f, 1h,
1n, 1s, and chimanine B); 55:45, v/v (1e); 50:50, v/v
(1a–d); 40:60, v/v (1q,r). The compounds were parti-
tioned between 1-octanol (HPLC grade) and phosphate
buffer (pH 7.4). Octanol was presaturated with the ade-
quate phosphate buffer (2%), and conversely. An
amount of 1 mg of each compound was dissolved in
an adequate volume of methanol in order to achieve
1 mg/mL stock solutions. Then an appropriate aliquot
of these methanolic solutions was dissolved in buffer
to obtain final concentration of 100 lg/mL. Under the
above-described chromatographic conditions, 100 lL
of this aqueous phase was injected into the chromato-
graph, leading to the determination of a peak area be-
fore partitioning (W0). In screw-capped tubes, 2000 lL
of the aqueous phase (Vaq) was then added to 10 lL
of n-octanol (Voct). The mixture was shaken by mechan-
ical rotation during 30 min. Then the centrifugation was
achieved at 3000 rpm in 15 min. An amount of 100 lL
of the lower phase was injected into the chromatograph
column. This led to the determination of a peak area
after partitioning (W1). The logD value was determined
by the formula: logD = log [(W0 ꢀ W1)Vaq/W1Voct].
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