3-Benzamido, ureido and thioureidoimidazo[1,2-a]pyridine derivatives as potential antiviral agents

Article abstract of DOI:10.1248/cpb.49.1631

This work reports the synthesis and the antiviral activities of 3-benzamido, 3-phenylureido and 3-phenylthioureido derivatives in the imidazo[1,2-a]pyridine series. The structure was proven by NMR spectroscopy. The synthesized compounds were evaluated against a large number of viruses. The 3-phenylthioureido derivative 7 showed moderate activity against human cytomegalovirus (HCMV) in vitro. The crystallographic data for 8 are also reported and explain the absence of activity against human immunodeficiency virus (HIV).

Full text of DOI:10.1248/cpb.49.1631

December 2001
Notes
Chem. Pharm. Bull. 49(12) 1631—1635 (2001)
1631
3-Benzamido, Ureido and Thioureidoimidazo[1,2-a]pyridine Derivatives
as Potential Antiviral Agents
Aziz CHAOUNI-BENABDALLAH,a,b Christophe GALTIER,a Hassan ALLOUCHI,c Abdelak KHERBECHE,b
Olivier CHAVIGNON,d Jean-Claude TEULADE,d Myriam WITVROUW,e Christophe PANNECOUQUE,e
Robert SNOECK,e Graciela ANDREI,e Jan BALZARINI,e Erik DE CLERCQ,e Florence FAUVELLE,f
Cécile ENGUEHARD,a and Alain GUEIFFIER*,a
E.A. Groupe de Recherche en Chimie Hétérocyclique et Thérapeutique, Laboratoire de Chimie Thérapeutique, Faculté de
Pharmacie,a 31 Avenue Monge, 37200 Tours, France, Laboratoire de Catalyse et Environnement, Université Sidi Mohamed
Ben Abdellah, Ecole Supérieure de Technologie de Fès,b B.P. 2427, Route d’Imouzzer, Fès, Maroc, Laboratoire de Chimie
Physique, Faculté de Pharmacie,c 31 Avenue Monge, 37200 Tours, France, Laboratoire de Chimie Organique, Faculté de
Pharmacie,d 28 place H. Dunant, 63001 Clermont-Ferrand, France, Rega Institute for Medical Research, Katholieke
Universiteit Leuven,e Minderbroedersstraat 10, B-3000 Leuven, Belgium, and Centre de Recherche du Service de Santé des
Armées/BCM,f 24 Avenue des Maquis du Grésivaudan, BP 87, 38702 La Tronche Cedex, France.
Received May 9, 2001; accepted August 10, 2001
This work reports the synthesis and the antiviral activities of 3-benzamido, 3-phenylureido and 3-phenyl-
thioureido derivatives in the imidazo[1,2-a]pyridine series. The structure was proven by NMR spectroscopy. The
synthesized compounds were evaluated against a large number of viruses. The 3-phenylthioureido derivative 7
showed moderate activity against human cytomegalovirus (HCMV) in vitro. The crystallographic data for 8 are
also reported and explain the absence of activity against human immunodeficiency virus (HIV).
Key words imidazo[1,2-a]pyridine; cytomegalovirus; phenylthioureido; crystallographic data
The first antiretroviral agents approved for the treatment of concentrated sulfuric acid was treated with nitric acid, the
AIDS were nucleosidic inhibitors of reverse transcriptase temperature not rising above 5 °C. Then the reaction mixture
such as Zidovudine. Later, the human immunodeficiency was allowed to stand at 20 °C to give the 3-nitro compounds
virus (HIV) protease inhibitors (e.g. saquinavir) were intro- 3a, b in good yields. Reduction of the nitro compounds using
duced as therapeutics. Recently, a third class of antiretroviral tin in hydrochloric acid at room temperature gave the amino
agents, the non-nucleosidic reverse transcriptase inhibitors
(NNRTIs) (i.e. nevirapine, delavirdine, efavirenz) have been
marketed. Since the discovery of the anti-HIV activi-
ty of 1-[(2-hydroxyethoxy)methyl]-6-(phenylthio)thymidine
(HEPT)1) and tetrahydroimidazo[4,5,1-jk][1,4]benzodiazepin-
2(1H)-one and thione (TIBO)2) as the first NNRTIs, numer-
ous additional compounds have been reported as NNRTIs.3)
From all the active compounds, some common characteris-
tics have emerged. First, NNRTIs interact with a non-sub-
strate binding site that is located in the close vicinity of the
substrate binding site of HIV-1. As a consequence, all these
compounds are deprived of activity against HIV-2.
Furthermore, structural studies have shown that these de-
rivatives contain a central hydrophilic part and two hy-
drophobic moieties, generally an aromatic cycle forming a
butterfly-like conformation.4) Finally, most of these com-
pounds contain an amide, thioamide, urea or thiourea func-
tion in their structure.5) In continuation of our studies on the
antiviral activities of bridgehead nitrogen heterocycles,6) we
were interested in the synthesis of amide, urea and thiourea
derivatives within the imidazo[1,2-a]pyridine series. In a first
approach, we studied the introduction of these functions in
the 3-position.
Chemistry
The 2-aminopyridine 1a was reacted with bromoacetone
or bromopinacolone in refluxing ethanol to give the imi-
dazo[1,2-a]pyridines 2a, b (Chart 1). It is now well estab-
lished that in this series, electrophilic substitution occurs in
the 3-position.7) Thus a cooled solution (Ϫ5 °C) of 2a, b in
Chart 1
To whom correspondence should be addressed. e-mail: gueiffier@univ-tours.fr
© 2001 Pharmaceutical Society of Japan

1632
Vol. 49, No. 12
derivatives 4a, b. First, the amide 5 was obtained by reaction
of the amine 4a with benzoyl chloride using usual methods.
Then the ureas and thioureas 6—9 were obtained by nucle-
ophilic addition of 4a, b on phenylisocyanate or isothio-
cyanate at room temperature in acetonitrile following the
conditions reported by Cantrell et al.8) The ureas and
thioureas were obtained in 65 to 75% yields. Proof of the
structures was obtained from 1H- and 13C-NMR spectra. Sur-
prisingly, in the case of the thiourea derivative 9, the spec-
trum in deuteriodimethylsulfoxide (DMSO-d6) showed the
presence of two species at a ratio of 34—66%. This result
was interpreted as indicating the existence under the experi-
mental conditions of two configurations of the thiourea due
to the restricted rotation around the C–N bond as reported by
Tompa et al.9) From the dissymmetry of the thiourea, the (Z)
and (E)-conformations could concern either the NH linked to
the phenyl ring or the imidazo[1,2-a]pyridinic moiety. Using
1H–1H correlation spectroscopy (COSY) and X–H correla-
tion spectroscopy (XHCOR) all the resonances could be as-
signed. In order to determine the two species present in the
solution, nuclear Overhauser effect (NOE) studies were
made. Unfortunately, neither differential nuclear Overhauser
enhancement (NOEDIFF) nor two-dimensional (2D) nuclear
Overhauser enhancement spectroscopy (NOESY) with mix-
ing times of 250 and 400 ms led to spatial interaction fulfill-
ing our goal.
Fig. 1. Ellipsoïd Representation of the Non-hydrogen Atoms (Probability
20%) of One Molecule and Atomic Labelling of 8 (X-Ray Numbering)
With a view to studying the interaction of these com-
pounds with reverse transcriptase, we were then interested in
the crystallographic data for one of the synthesized com-
pounds, and a crystal structure was obtained for compound 8.
Crystal Structure The thermal ellipsoid representation
and the labelling of non-hydrogen atoms10) for both confor-
mations are presented in Fig. 1.
The imidazo[1,2-a]pyridine ring л1 (atoms N1 to C8A),
urea л2 (atoms N9, C10, O1 and N11), and phenyl ring л3
(atoms C1Љ to C6Љ) are planar.
There are numerous weak van der Waals interactions so
the crystal cohesion is assumed through several hydrogen
bonds (Fig. 2). The molecule I is involved in hydrogen bond-
ing between the NH groups of I and O atom of a neighbour-
ing molecule II.
Antiviral Activities The activities of the synthesized
compounds were evaluated against a large number of viruses.
None of the synthesized compounds showed any activity
against HIV [HIV-1 (IIIB) or HIV-2 (strain ROD)] in MT-4
cells. A partial explanation for the inactivity could be found
in the crystal data that showed no butterfly-like conformation
for the described compounds. The compounds were also de-
void of activity against herpes simplex virus [HSV-1 (strain
KOS), thymidine kinase deficient (TKϪ) HSV-1 resistant to
aciclovir (ACVR), HSV-2 (G)], vaccinia virus (VV), vesicular
stomatitis virus (VSV) in embryonic skin-muscle (E6SM)
cell cultures, VSV, Coxsackie virus B4, respiratory syncytial
virus in Hela cell cultures, and parainfluenza-3 virus, Sindbis
virus, Coxsackie virus B4 and Punta Toro virus in Vero cell
cultures. However, some of the compounds showed moderate
activity against human cytomegalovirus (HCMV) (Table 1).
Structure Activity Relationship From the activity data
against HCMV it appeared that amide is less active than urea
and thiourea. A bulky group in position 2 decreased the an-
tiviral activity. Finally, thioureas were more potent than
Fig. 2. Packing Representation of 8
Table 1. Anti-HCMV Activities and Cytotoxic Properties in Human Em-
bryonic Lung (HEL) Cells
Antiviral activity
Cytotoxicity
(mg/ml)
IC50 (mg/ml)a)
Compound
Cell morphology Cell growth
AD 169 strain Davis strain
(MCC)b)
(CC50)c)
5 (U3)
6 (U1)
7 (U2)
8 (U5)
9 (U6)
Ͼ50
50
13
Ͼ50
Ͼ50
Ͼ50
33
10
32
27
Ͼ50
Ͼ50
Ͼ50
Ͼ50
Ͼ50
Ͼ50
Ͼ50
Ͼ50
Ͼ50
Ͼ50
a) Inhibitory concentration required to reduce virus-induced cytopathicity by 50%.
Virus input was 100 plaque forming units2 (PFU). b) Minimum cytotoxic concentra-
tion causing a microscopically detectable alteration of normal cell morphology. c)
Cytotoxic concentration required to reduce cell growth by 50%.

December 2001
1633
Table 2. Bond Lengths (Å) and Standard Deviations in Brackets
ureas. These findings appeared compatible with our previ-
ously reported results, which indicated that the 3-aralkylth-
iomethyl derivatives are more potent than the corresponding
ethers.11) Interestingly, the compounds described herein ex-
hibited very weak if any, cytotoxicity, as exemplified by a se-
lectivity index higher than 5 for compound 7. Further devel-
opments in these series of compounds are under progress in
order to enhance their potency against HCMV.
Molecule I
Molecule II
O1–C10
N1–C8A
N1–C2
C2–C3
C2–C1Ј
C3–N4
C3–N9
N4–C5
N4–C8A
C5–C6
C6–C7
1.246 (8)
1.323 (9)
1.370 (9)
1.341 (10)
1.523 (10)
1.402 (9)
1.419 (9)
1.373 (9)
1.367 (8)
1.345 (10)
1.411 (11)
1.356 (10)
1.421 (10)
1.366 (9)
1.344 (8)
1.433 (9)
1.510 (12)
1.517 (12)
1.527 (10)
1.364 (11)
1.362 (11)
1.371 (11)
1.341 (13)
1.368 (14)
1.368 (12)
1.234 (8)
1.344 (9)
1.357 (9)
1.365 (10)
1.510 (10)
1.390 (8)
1.410 (9)
1.365 (9)
1.389 (9)
1.363 (10)
1.404 (12)
1.346 (10)
1.423 (11)
1.368 (8)
1.334 (9)
1.409 (9)
1.476 (12)
1.518 (11)
1.541 (12)
1.368 (10)
1.384 (11)
1.381 (12)
1.361 (14)
1.346 (14)
1.365 (12)
Experimental
Melting points were determined on a Köfler hotstage apparatus and are
uncorrected. NMR spectra were recorded on a Bruker DPX 200 or a Bruker
C7–C8
Table 1a. Atomic Coordinates and Equivalent Ueq Factors for Molecule I
C8–C8A
N9–C10
C10–N11
N11–C1Љ
C1Ј–C4Ј
C1Ј–C3Ј
C1Ј–C2Ј
C1Љ–C2Љ
C1Љ–C6Љ
C2Љ–C3Љ
C3Љ–C4Љ
C4Љ–C5Љ
C5Љ–C6Љ
x/a
y/b
z/c
Ueq
O1
N1
C2
C3
N4
C5
C6
C7
0.4833 (6)
0.4458 (7)
0.5380 (8)
0.5930 (8)
0.5318 (7)
0.5515 (9)
0.4773 (10)
0.3822 (10)
0.3638 (10)
0.4442 (8)
0.6884 (6)
0.6243 (8)
0.7230 (7)
0.5694 (8)
0.4135 (10)
0.6650 (15)
0.6501 (12)
0.6809 (8)
0.7521 (11)
0.7144 (13)
0.6080 (12)
0.5369 (11)
0.5705 (11)
0.3212 (2)
0.1089 (3)
0.1676 (4)
0.1898 (4)
0.1441 (3)
0.1409 (4)
0.0895 (5)
0.0396 (4)
0.0427 (4)
0.0961 (4)
0.2473 (3)
0.3134 (4)
0.3684 (3)
0.1942 (4)
0.2086 (6)
0.2619 (6)
0.1354 (5)
0.4417 (4)
0.4795 (5)
0.5498 (5)
0.5825 (5)
0.5441 (5)
0.4736 (5)
0.7154 (5)
0.8853 (6)
0.9032 (7)
0.7904 (8)
0.6949 (6)
0.5641 (8)
0.4967 (8)
0.5583 (9)
0.6877 (9)
0.7598 (7)
0.7533 (5)
0.7376 (6)
0.7493 (6)
1.0401 (7)
1.1001 (9)
1.0450 (9)
1.1150 (9)
0.7643 (7)
0.8612 (8)
0.8784 (10)
0.8031 (11)
0.7063 (11)
0.6881 (9)
0.0510 (14)
0.0486 (16)
0.0400 (18)
0.044 (2)
0.0408 (16)
0.055 (2)
0.066 (3)
0.066 (3)
0.061 (2)
0.0414 (19)
0.0421 (16)
0.0378 (19)
0.0511 (18)
0.048 (2)
0.098 (4)
0.109 (4)
0.095 (4)
0.0433 (19)
0.066 (2)
C8
C8A
N9
C10
N11
C1Ј
C2Ј
C3Ј
C4Ј
C1Љ
C2Љ
C3Љ
C4Љ
C5Љ
C6Љ
Table 3. Bond Angles (°) and Standard Deviations in Brackets
Molecule I
Molecule II
C8A–N1–C2
N1–C2–C3
C3–C2–C1Ј
N1–C2–C1Ј
C2–C3–N4
C2–C3–N9
N4–C3–N9
C5–N4–C8A
C5–N4–C3
C8A–N4–C3
C6–C5–N4
105.6 (6)
110.6 (6)
130.7 (7)
118.6 (6)
106.8 (6)
134.1 (7)
119.0 (6)
122.8 (7)
132.1 (6)
105.1 (6)
118.4 (8)
121.1 (8)
120.3 (8)
118.8 (8)
111.9 (6)
129.6 (7)
118.5 (7)
119.0 (6)
123.0 (7)
121.5 (6)
115.5 (6)
125.7 (6)
110.5 (8)
108.0 (7)
112.9 (6)
108.8 (8)
109.1 (8)
107.5 (6)
119.6 (7)
117.9 (7)
122.4 (7)
119.5 (9)
121.7 (9)
118.4 (9)
121.1 (10)
119.6 (9)
105.2 (6)
111.3 (6)
128.7 (7)
120.0 (7)
106.8 (6)
134.8 (7)
118.2 (7)
122.9 (6)
132.0 (7)
105.1 (6)
117.7 (8)
121.2 (8)
121.2 (8)
118.5 (8)
111.5 (6)
130.0 (8)
118.3 (7)
120.5 (6)
122.9 (7)
120.6 (6)
116.5 (6)
125.5 (6)
108.7 (7)
111.0 (8)
114.0 (7)
108.1 (9)
106.0 (9)
108.9 (7)
118.9 (7)
118.8 (7)
122.3 (7)
119.3 (9)
121.0 (9)
118.5 (9)
121.8 (10)
120.0 (9)
0.081 (3)
0.075 (3)
0.080 (3)
0.070 (3)
Table 1b. Atomic Coordinates and Equivalent Ueq Factors for Molecule II
x/a
y/b
z/c
Ueq
C5–C6–C7
C8–C7–C6
O1
N1
C2
C3
N4
C5
C6
C7
0.9879 (6)
0.9411 (7)
1.0350 (8)
1.0968 (8)
1.0394 (7)
1.0650 (9)
0.9905 (10)
0.8890 (11)
0.8657 (9)
0.9411 (9)
1.1901 (7)
1.1259 (9)
1.2206 (7)
1.0581 (10)
1.0666 (16)
1.2071 (12)
0.9232 (15)
1.1791 (8)
1.2371 (10)
1.1968 (12)
1.0952 (13)
1.0472 (12)
1.0827 (10)
0.2901 (3)
0.1253 (3)
0.1831 (4)
0.1910 (4)
0.1355 (3)
0.1165 (5)
0.0577 (5)
0.0187 (5)
0.0364 (4)
0.0980 (4)
0.2427 (3)
0.2929 (4)
0.3434 (3)
0.2292 (4)
0.1809 (5)
0.2717 (6)
0.2765 (7)
0.3985 (4)
0.4662 (4)
0.5206 (5)
0.5095 (6)
0.4425 (6)
0.3874 (5)
0.8454 (5)
0.5499 (6)
0.5580 (7)
0.6796 (7)
0.7532 (6)
0.8790 (7)
0.9230 (9)
0.8424 (10)
0.7176 (9)
0.6698 (7)
0.7420 (5)
0.8197 (7)
0.8662 (6)
0.4407 (8)
0.3208 (9)
0.4453 (10)
0.4233 (12)
0.9508 (7)
0.9310 (8)
1.0131 (11)
1.1089 (11)
1.1312 (10)
1.0513 (8)
0.0529 (15)
0.0476 (17)
0.044 (2)
0.0413 (19)
0.0422 (16)
0.054 (2)
0.065 (3)
0.070 (3)
0.060 (2)
0.046 (2)
0.0435 (16)
0.0346 (18)
0.0490 (17)
0.053 (2)
0.113 (4)
0.100 (4)
0.145 (6)
0.046 (2)
0.062 (2)
0.079 (3)
0.086 (3)
0.084 (3)
0.061 (2)
C7–C8–C8A
N1–C8A–N4
N1–C8A–C8
N4–C8A–C8
C10–N9–C3
O1–C10–N11
O1–C10–N9
N11–C10–N9
C10–N11–C1Љ
C4Ј–C1Ј–C3Ј
C4Ј–C1Ј–C2
C3Ј–C1Ј–C2
C4Ј–C1Ј–C2Ј
C3Ј–C1Ј–C2Ј
C2–C1Ј–C2Ј
C2Љ–C1Љ–C6Љ
C2Љ–C1Љ–N11
C6Љ–C1Љ–N11
C1Љ–C2Љ–C3Љ
C4Љ–C3Љ–C2Љ
C3Љ–C4Љ–C5Љ
C6Љ–C5Љ–C4Љ
C5Љ–C6Љ–C1Љ
C8
C8A
N9
C10
N11
C1Ј
C2Ј
C3Ј
C4Ј
C1Љ
C2Љ
C3Љ
C4Љ
C5Љ
C6Љ

1634
Vol. 49, No. 12
Table 4. Significative Torsion Angles (°) with Standard Deviations in tracted with dichloromethane. After the usual workup, the dried residue was
Brackets
chromatographed on neutral alumina eluted with dichloromethane/methanol
(98/2 v/v).
Molecule I
Molecule II
3-Amino-2-methylimidazo[1,2-a]pyridine (4a): 85% yield; mp 134 °C
1
[lit.14) mp 134 °C]; H-NMR (CDCl3, 200 MHz) d: 2.38 (3H, s, CH3), 3.04
N1–C2–C1Ј–C2Ј
Ϫ56.2 (10)°
Ϫ61.0 (9)°
96.8 (8)°
156.7 (6)
Ϫ166.0 (6)
130.6 (8)
Ϫ37.7 (10)
78.8 (10)
Ϫ74.3 (8)
Ϫ174.5 (6)
Ϫ177.9 (6)
Ϫ139.3 (7)
(2H, br s, NH2), 6.76 (1H, td, J5,6ϭJ6,7ϭ6.8, J6,8ϭ1.2, H-6), 7.01 (1H, ddd,
N1–C2–C1Ј–C4Љ
N4–C3–N9–C10
C3–N9–C10–N11
N9–C10–N11–C1Љ
C10–N11–C1Љ–C2Љ
J
7,8ϭ9, J5,7ϭ1.4, H-7), 7.38 (1H, dd, J7,8ϭ9, H-8), 7.92 (1H, dd, H-5).
3-Amino-2-tert-butylimidazo[1,2-a]pyridine (4b): Oil (66%); 1H-NMR
(CDCl3, 200 MHz) d: 1.46 (9H, s, 3CH3) 3.10 (2H, br s, NH2), 6.69 (1H, td,
5,6ϭJ6,7ϭ6.8, J6,8ϭ1.2, H-6), 6.99 (1H, ddd, J7,8ϭ9, J5,7ϭ1.2, H-7), 7.43
(1H, dt, J5,8ϭ1.2, H-8), 7.94 (1H, dt, H-5). Anal. Calcd for C11H15N3: C,
69.84; H, 7.94; N, 22.22. Found: C, 69.72; H, 7.83; N, 22.13.
J
N-(2-Methylimidazo[1,2-a]pyridin-3-yl)benzamide (5) To a solution
of 4a (200 mg, 1.36 mmol) in dichloromethane (113 ml) was added benzoyl
chloride (0.158 ml, 191 mg, 1.36 mmol). The mixture was stirred for 30 min
at room temperature, then evaporated to dryness. The residue was dissolv-
ed in water, basified with sodium carbonate, then extracted with di-
chloromethane. The organic layers were dried over calcium chloride and
evaporated in vacuo. The residue was chromatographed on neutral alumina
eluted with dichloromethane to give the amide 5 (302 mg, 89%); mp 211—
214 °C; 1H-NMR (CDCl3, 200 MHz) d: 2.19 (3H, s, CH3), 6.77 (1H, td,
Table 5. Table of Dihedral Angles (°) with Standard Deviations in Brack-
ets
Molecule I
Molecule II
л2/л1
л3/л1
л3/л2
70.9 (2)°
87.6 (2)°
42.1 (3)°
55.9 (2)°
74.0 (2)°
41.5 (3)°
J5,6ϭJ6,7ϭ6.8, J6,8ϭ0.8, H-6), 7.14 (1H, ddd, J7,8ϭ9, J5,7ϭ1.2, H-7), 7.42
(1H, br d, H-8), 7.60 (3H, m, H-3Ј, 4Ј, 5Ј), 7.78 (1H, br d, H-5), 8.15 (2H, d,
Jϭ7.1, H-2Ј, 6Ј), 9.16 (1H, br s, NH); 13C-NMR (CDCl3, 50 MHz) d: 12.3
(CH3), 111.8 (C-6), 115.5 (C-3), 116.2 (C-8), 122.8 (C-5), 124.3 (C-7),
128.0 (C-3Ј, 5Ј), 128.7 (C-2Ј, 6Ј), 132.4 (C-1Ј), 132.8 (C-4Ј), 137.4 (C-2),
142.3 (C-8a), 167.2 (CϭO). Anal. Calcd for C15H13N3O: C, 71.71; H, 5.18;
N, 16.73. Found: C, 71.82; H, 5.23; N, 16.63.
Table 6. Table of Hydrogen Bond
...
...
D–H
A
d (D A) (Å)
D–H–A (°)
3-(2-Methylimidazo[1,2-a]pyridin-3-yl)-1-phenylurea (6) A solution
of amine 4a (250 mg, 1.7 mmol) in acetonitrile (3.5 ml) was treated with
phenylisocyanate (0.185 ml, 1.7 mmol) and the mixture was stirred for 2 h.
The precipitate which was formed was filtered off and washed with ether to
give 6 (331 mg, 73%); mp 217—219 °C; 1H-NMR (DMSO-d6, 200 MHz) d:
2.28 (3H, s, CH3), 6.90 (1H, ps.t, J5,6ϭJ6,7ϭ6.7, H-6), 7.00 (1H, m, H-7),
7.26 (3H, m, H-3Ј, 4Ј, 5Ј), 7.49 (3H, m, H-2Ј, 6Ј, 8), 8.05 (1H, br d, H-5),
8.21 (1H, br s, NH), 9.11 (1H, br s, NH); 13C-NMR (DMSO-d6, 50 MHz) d:
13.2 (CH3), 111.8 (C-6), 116.6 (C-8), 116.7 (C-3), 118.9 (C-2Ј, 6Ј), 122.4
(C-5), 123.6 (C-7), 124.1 (C-4Ј), 129.1 (C-3Ј, 5Ј), 137.7 (C-1Ј), 140.1 (C-2),
141.7 (C-8a), 154.1 (CϭO). Anal. Calcd for C15H14N4O: C, 67.67; H, 5.26;
N, 21.05. Found: C, 67.58; H, 5.30; N, 21.13.
...
N9–H9-I O1-II
2.856
2.880
2.957
2.827
128.45
139.26
139.10
153.58
...
N11–H11-I O1-II
...
N9–H9-II O1-I*
...
N11–H11-II O1-I*
AM 400 WB spectrometer. The J values are expressed in hertz. Elemental
microanalyses were performed by the microanalytical center, Ecole Normale
Supérieure de Montpellier (ENSCM), Montpellier. 2-Methylimidazo[1,2-
a]pyridine 2a was obtained according to a described procedure.12)
3-(2-Methylimidazo[1,2-a]pyridin-3-yl)-1-phenylthiourea
compound was obtained according to the above procedure using phenyl
isothiocyanate (0.2 ml, 1.7 mmol) in 67% yield; mp 240—243 °C; H-NMR
(DMSO-d6, 200 MHz) d: 2.29 (3H, s, CH3), 6.93 (1H, ps.t., J5,6ϭJ6,7ϭ6.6,
H-6), 7.22 (2H, m, H-7, 4Ј), 7.38 (2H, t, Jϭ7.4, H-3Ј, 5Ј), 7.38 (1H, br d,
(7) This
2-tert-Butylimidazo[1,2-a]pyridine (2b) A solution of 2-aminopyridine
(2.6 g, 2.8 mmol) and bromopinacolone (5 g, 2.6 mmol) was refluxed in
ethanol (50 ml) for 5 h. After cooling, the solution was concentrated in
vacuo, poured into water and made alkaline with sodium carbonate. The
aqueous layer was extracted with dichloromethane. The combined and dried
organic phases were evaporated to dryness and the residue chromatographed
on neutral alumina eluting with dichloromethane to give colorless crystals
(77%); mp 80 °C; 1H-NMR (CDCl3) d: 1.43 (9H, s, 3CH3), 6.72 (1H, td,
1
J
7,8ϭ9, H-8), 7.54 (2H, m, H-2Ј, 6Ј), 8.03 (1H, br d, H-5), 9.46 (1H, br s,
NH), 10.23 (1H, br s, NH); 13C-NMR (DMSO-d6, 50 MHz) d: 13.4 (CH3),
111.8 (C-6), 116.6 (C-8, 2Ј, 6Ј, 3), 123.6 (C-5), 124.3 (C-7), 125.4 (C-4Ј),
128.9 (C-3Ј, 5Ј), 138.3 (C-1Ј), 139.5 (C-2), 141.9 (C-8a), 182.1 (CϭS).
Anal. Calcd for C15H14N4S: C, 63.83; H, 4.96; N, 19.86. Found: C, 63.72; H,
5.04; N, 19.77.
J6,7ϭJ5,6ϭ6.8, J6,8ϭ1.2, H-6), 7.12 (1H, ddd, J7,8ϭ9.1, J5,7ϭ1.2, H-7), 7.36
(1H, s, H-3), 7.59 (1H, dd, H-8), 8.06 (1H, dt, J5,8ϭ1.2, H-5).
General Procedure for Nitration The imidazo[1,2-a]pyridine (0.04
mol) was slowly added to concentrated sulfuric acid (60 ml) cooled to Ϫ5 °C
without the temperature rising above 5 °C. To the solution was added nitric
acid (6 ml, dϭ1.41), also without allowing the temperature to rise above
5 °C. At the end of the addition the mixture was allowed to stand until it
reached room temperature and then stirred for a further 2 h. The mixture was
poured onto ice (400 g) and the formed precipitate was collected and dis-
solved in dichloromethane. The organic solution was dried on calcium chlo-
ride and chromatographed on neutral alumina eluted with dichloromethane.
2-Methyl-3-nitroimidazo[1,2-a]pyridine (3a): 60% yield; mp 142 °C
1-Phenyl-3-(2-tert-butylimidazo[1,2-a]pyridin-3-yl)urea (8) The urea
8 was obtained from 4b according to the procedure of 6 in 75% yield; mp
1
Ͼ260 °C; H-NMR (DMSO-d6, 200 MHz) d: 1.41 (9H, s, 3CH3), 6.90 (1H,
ps.t, J5,6ϭJ6,7ϭ6.7, H-6), 6.99 (1H, t, Jϭ7.4, H-4Ј), 7.24 (1H, ddd, J7,8ϭ9.1,
J
5,7ϭ1.2, H-7), 7.30 (2H, dd, Jϭ7.7, H-3Ј, 5Ј), 7.51 (2H, d, Jϭ7.7, H-2Ј, 6Ј),
7.52 (1H, d, H-8), 8.04 (1H, d, H-5), 8.08 (1H, br s, NH), 9.06 (1H, br s,
NH); 13C-NMR (DMSO-d6, 50 MHz) d: 30.8 (CH3), 33.5 (C), 112.3 (C-6),
114.9 (C-3), 117.3 (C-8), 119.2 (C-2Ј, 6Ј), 122.8 (C-4Ј), 123.8 (C-5), 124.8
(C-7), 129.6 (C-3Ј, 5Ј), 140.6 (C-1Ј), 141.3 (C-8a), 149.3 (C-2), 154.7
(CϭO). Anal. Calcd for C18H20N4O: C, 70.13; H, 6.49; N, 18.18. Found: C,
70.22; H, 6.56; N, 18.03.
1
[lit.13) mp 142—144 °C]; H-NMR (CDCl3, 200 MHz) d: 2.82 (3H, s, CH3),
7.23 (1H, td, J6,7ϭJ5,6ϭ6.9, J6,8ϭ1.4, H-6), 7.61 (1H, ddd, J7,8ϭ9.0, J5,7ϭ
1.4, H-7), 7.73 (1H, dt, J5,8ϭ1.4, H-8), 9.40 (1H, dt, H-5).
1-Phenyl-3-(2-tert-butylimidazo[1,2-a]pyridin-3-yl)thiourea (9) Com-
pound 9 was obtained from 4b according to the procedure of 6 in 69% yield;
2-tert-Butyl-3-nitroimidazo[1,2-a]pyridine (3b): 70% yield; mp 173 °C;
1
1H-NMR (CDCl3, 200 MHz) d: 1.56 (9H, s, 3CH3), 7.27 (1H, t, J6,7ϭ
mp Ͼ260 °C; H-NMR (DMSO-d6, 200 MHz) d: 1.39 (s, 3CH3 maj), 1.41
(s, 3CH3 min), 6.89 (t, J5,6ϭJ6,7ϭ6.7, H-6 maj), 6.96 (t, J5,6ϭJ6,7ϭ6.6, H-6
min), 7.17 (t, Jϭ7.5, H-4Ј maj), 7.19—7.31 (m, H-2Ј, 6Ј min, H-3Ј, 5Ј min,
H-4Ј min, H-7 minϩmaj), 7.38 (dd, Jϭ7.8, H-3Ј, 5Ј maj), 7.50 (d, J7,8ϭ9, H-
8 maj), 7.54 (d, J7,8ϭ9, H-8 min), 7.64 (d, H-2Ј, 6Ј maj), 7.95 (d, H-5 maj),
7.96 (d, H-5 min), 9.24 (br s, NH maj), 9.34 (br s, NH min), 9.73 (br s, NH
min), 10.39 (br s, NH maj); 13C-NMR (DMSO-d6, 50 MHz) d: 30.6 (3CH3
minϩmaj), 33.6 (C minϩmaj), 112.1 (C-6 maj), 113.1 (C-6 min), 113.4 (C-
3 min), 116.6 (C-3 maj), 117.1 (C-8 maj), 117.6 (C-8 min), 123.3 (C-5 min),
124.2 (C-5 maj), 124.4 (C-2Ј, 6Ј maj), 125.1 (C-7 maj), 125.6 (C-7 min),
J5,6ϭ6.9, H-6), 7.65 (1H, dd, J7,8ϭ8.8, H-7), 7.86 (1H, br d, H-8), 9.51 (1H,
br d, H-5). Anal. Calcd for C11H13N3O2: C, 60.27; H, 5.94; N, 19.18. Found:
C, 60.12; H, 6.07; N, 19.13.
General Procedure for Reduction To concentrated hydrochloric acid
(60 ml) cooled to Ϫ15 °C was added tin (4 g, 33.6 mmol), then the nitro de-
rivative 3a, b (22.5 mmol) was added portionwise without the temperature
rising above 0 °C. The reaction mixture was allowed to stand at room tem-
perature and stirred for a further 2 h. The suspension was diluted with ice
cooled water (20 ml), made alkaline with concentrated ammonia and ex-

December 2001
1635
cultures that had not been treated with the test compounds.
125.8 (C-4Ј maj), 126.2 (C-4Ј min), 127.3 (C-2Ј, 6Ј min), 128.7 (C-3Ј, 5Ј
min), 129.6 (C-3Ј, 5Ј maj), 139.9 (C-1Ј maj), 140.4 (C-1Ј min), 141.3 (C-8a
maj), 142.2 (C-8a min), 149.0 (C-2 maj), 150.1 (C-2 min), 182.7 (CϭS
maj), 183.1 (CϭS min). Anal. Calcd for C18H20N4S: C, 66.67; H, 6.17; N,
17.28. Found: C, 66.52; H, 6.12; N, 17.34.
X-Ray Diffraction of Compound 8 Colourless crystals of 8 were
grown by slow evaporation of ethanol–chloroform solution at 293 °K. The
crystal used for X-ray measurement was lamellar, with dimensions:
0.05ϫ0.28ϫ0.38 mm. The studied compound, C18H20N4O, Mxϭ308.4
g·molϪ1 crystallized in the monoclinic system, space group Pc (Zϭ4) two
independent molecules per asymmetric unit. The unit cell parameters were
obtained by a least-squares fit of the setting angles of 25 reflections with q
between 16 and 33° and were as follows: aϭ8.665(5), bϭ18.765(12),
cϭ10.370(6) Å and bϭ91.55(5)° with a cell volume of 1686 Å3. The calcu-
lated density was 1.215 g·cmϪ3. The linear absorption coefficient was
mϭ0.623 mmϪ1 for the CuKa radiation (lϭ1.54178 Å).
The diffracted intensities were collected with a CAD-4 Enraf–Nonius
diffractometer equipped with a graphite monochromator for qmaxϭ50°:
0ՅhՅ8, 0ՅkՅ18, Ϫ10ՅlՅ10 and an wϪ2q scan. Three standard reflec-
tions were used to monitor the data collected and to detect any decrease of
intensity (Ϫ3 7 1, 3 3 Ϫ3, 3 7 Ϫ1); the transmission factor T(hkl) lay between
0.884 and 1.0; nevertheless, the crystal absorption correction was performed
using the Y scan technique.15) There were 1697 independent reflections,
1359 of which were considered as observed [IϾ2s(I), Rintϭ0.023].
References
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The crystal structure was solved by application of direct methods and re-
fined by full-matrix least squares on F2 using the SHELX97 program.16)
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allowed to ride with the atoms to which they are attached. The final reliabil-
ity factors were: Rϭ0.046, wRϭ0.105 and the goodness of fit was equal to
sϭ1.05. The weight was equal to: wϭ1/[s2(Fo2)ϩ(0.0752P)2], where
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Diagrams,” Univ. of Ultrecht, Netherlands, 1999.
2
Pϭ(Fo ϩ2Fc2)/3. The minimum and maximun residual densities were equal
to Ϫ0.157 and 0.160 e·ÅϪ3, respectively.
11) Elhakmaoui A., Gueiffier A., Milhavet J.-C., Blache Y., Chapat J.-P.,
Chavignon O., Teulade J.-C., Snoeck R., Andrei G., De Clercq E.,
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Inhibition of HIV-1-Induced Cytopathicity in MT-4 and CEM Cells
The methodology of the anti-HIV assays has been described previously.18)
Briefly, human MT-4 (ca. 4ϫ105 cell mlϪ1) cells were infected with 100
CCID50 (the amount of virus that is infective to 50% of a series of identical
cell cultures) of HIV-1 (IIIB)/ml or HIV-2(ROD)/ml and seeded in 200-ml
wells of a microtiter plate containing appropriate dilutions of the test com-
pounds. After 5 d of incubation at 37 °C, the number of viable (MT-4) cells
was determined by an automated MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-
diphenyltetrazolium bromide] dye staining of living cells.
Antiviral Assays The antiviral assays, other than HIV-1, were based on
inhibition of virus-induced cytopathicity in either E6SM cells (HSV-1, HSV-
2, VV, VSV), Human Embryonic Lung (HEL) cells [Varicella Zoster Virus
(VZV), HCMV], Hela cells (respiratory syncytial virus) or Vero cells (Cox-
sackie B4 virus, parainfluenza-3 virus, Sindbis virus, Punta Toro virus, re-
ovirus-1), following previously established procedures.19) Briefly, confluent
cell cultures in microtiter 96-well plates were inoculated with 100 CCID50 of
virus, 1 CCID50 being the virus dose required to infect 50% of the cell cul-
tures. After a 1-h virus adsorption period, residual virus was removed, and
the cell cultures were incubated in the presence of varying concentrations
(400, 200, 100, … mg/ml) of the test compounds. Viral cytopathicity was
recorded as soon as it reached completion in the control virus-infected cell