Design, synthesis, and SAR of a novel pyrazinone series with non-nucleoside HIV-1 reverse transcriptase inhibitory activity

Article abstract of DOI:10.1021/jm040829e

A series of novel pyrazinones designed as non-nucleoside reverse transcriptase inhibitors (NNRTIs) was synthesized and their anti-HIV structure-activity relationship (SAR) was studied.

Full text of DOI:10.1021/jm040829e

1910
J. Med. Chem. 2005, 48, 1910-1918
Design, Synthesis, and SAR of a Novel Pyrazinone Series with Non-Nucleoside
HIV-1 Reverse Transcriptase Inhibitory Activity
Jan Heeres,*,‡ Marc R. de Jonge,‡ Lucien M. H. Koymans,‡ Frits F. D. Daeyaert,‡ Maarten Vinkers,‡
Koen J. A. Van Aken,‡ Eddy Arnold,§ Kalyan Das,§ Amuri Kilonda,| Georges J. Hoornaert,| Frans Compernolle,|
Marek Cegla, Rasha A. Azzam,# Koen Andries,$ Marie-Pierre de Be´thune,∞ Hilde Azijn,∞ Rudi Pauwels,∞
Paul J. Lewi,‡ and Paul A. J. Janssen‡,†
Center for Molecular Design, Janssen Pharmaceutica, Antwerpsesteenweg 37, B-2350 Vosselaar, Belgium, Center for Advanced
Biotechnology and Medicine, and Chemistry Department, Rutgers University, 679 Hoes Lane, Piscataway, New Jersey 08854,
Laboratorium voor Organische Synthese, Department of Chemistry, K.U. Leuven, Celestijnenlaan 200F,
B-3001 Leuven, Belgium, Department of Organic Chemistry, Faculty of Pharmacy, Jagiellonian University,
Medyczna 9, 30-688 Cracow, Poland, Department of Chemistry, Helwan University, Ain-Helwan, Cairo 11795, Egypt;
J&JPRD, Department of Virology, Janssen Pharmaceutica, Turnhoutseweg 30, B-2340 Beerse, Belgium, and
Tibotec, Generaal De Wittelaan L 11 B3, B-2800 Mechelen, Belgium
Received May 10, 2004
A series of novel pyrazinones designed as non-nucleoside reverse transcriptase inhibitors
(NNRTIs) was synthesized and their anti-HIV structure-activity relationship (SAR) was
studied.
Introduction
Reverse transcriptase (RT), being essential in the
replication process of human immunodeficiency virus
(HIV), can still be considered as one of the most
attractive targets for the development of new antiret-
roviral drugs. Currently three non-nucleoside reverse
transcriptase inhibitors (NNRTIs) have been approved
Figure 1. Structural formula of dapivirine (R147681, TMC120).
by the FDA for clinical use, namely, nevirapine, delavir-
dine, and efavirenz.
Protein-ligand interaction studies have shown that
NNRTIs bind in an induced allosteric pocket located
at a distance of approximately 10 Å from the DNA
polymerase active site.1,2
Different chemical classes have been reported to
inhibit RT, such as the TIBOs,3 HEPTs,4 R-APAs,5
pyridones,6 ITUs,7 and finally the DATA and DAPY
series,8,9 of which dapivirine (R 147681, TMC120, Figure
Figure 2. Structural formula of etravirine (R165335, TMC125).
1) and etravirine (R 165335 or TMC 125, Figure 2) are
representatives.
compounds. The intermediate pyrazinone building blocks
Dapivirine and etravirine both display high activity
were synthesized as follows. Treatment of the ap-
against HIV-1 LAI virus (IIIB) and a large panel of
propriately substituted hydrobromide salt of amino-
derived single and double mutants.9
acetonitrile 3 and 2-aminopropanenitriles 4 and 5 with
In this paper we report the synthesis and HIV-1-
oxalyl bromide gave the 3,5-dibromopyrazinones 6-8
inhibiting properties of a novel series of 3,5-disubsti-
(Scheme 1). The condensation of the hydrochloride salt
tuted pyrazinone derivatives.
of 5 with oxalyl chloride to form the corresponding 3,5-
dichloropyrazinone 9 was effected according to a pro-
Chemistry
cedure described previously.10,11
We developed a general and useful synthesis of
3-anilino-5-halopyrazinone scaffolds, which were uti-
lized for coupling reactions with phenols and thiophe-
nols leading to the desired 3,5-disubstituted target
Substitution of the reactive imidoyl halide moiety in
the C3-position of the 2(1H)-pyrazinones 6-9 with
4-aminobenzonitrile in the presence of camphorsulfonic
acid as a catalyst gave the key precursors 10-14
(Scheme 1). The 3-anilino analogues 15-20 were ob-
tained by conversion of 6 and 7 with different anilines
under the same reaction conditions (Scheme 2).
Subsequent coupling of the 5-bromopyrazinones with
the appropriately substituted phenols and benzenethiols
was accomplished by heating with Cs2CO3 and CuCl in
refluxing toluene to afford target compounds 21-42
(Scheme 3). The yields of these reactions were generally
* To whom correspondence should be addressed. Tel: +32/14
442286. Fax: +32/14 410503. E-mail: jheeres@prdbe.jnj.com.
‡ Center for Molecular Design, Janssen Pharmaceutica.
§ Rutgers University.
| K.U. Leuven.
Jagiellonian University.
# Helwan University.
$ J&JPRD, Department of Virology, Janssen Pharmaceutica.
∞ Tibotec.
† Deceased.
10.1021/jm040829e CCC: $30.25 © 2005 American Chemical Society
Published on Web 11/09/2004

Novel Pyrazinones with NNRTI Activity
Journal of Medicinal Chemistry, 2005, Vol. 48, No. 6 1911
Scheme 1a
a Reagents and conditions:(a) BrCOCOBr, DMF, CH2Cl2, reflux, 24 h; (b) ClCOCOCl, Et4NCl, Ph-Cl, 20 °C, 48 h; (c) 4-aminobenzonitrile,
camphorsulfonic acid, i-PrOH, reflux, 48 h.
Scheme 2a
Scheme 3a
low due to the formation of side products, which resulted
either from the replacement of the 5-Br atom with
hydrogen or, for 6-unsubstituted 2(1H)-pyrazinones,
from the substitution of H-6 with a second phenoxy or
phenylsulfanyl group. To reduce or prevent the replace-
ment of the halogen in 5-position by hydrogen, we
coupled 5-chloropyrazinone 14 instead of the corre-
sponding 5-bromopyrazinone 12 with 2-methylben-
zenethiol in the presence of Cs2CO3 in N-methylpyrroli-
dinone at 130 °C to the 5-phenylsulfanyl-2(1H)-pyrazi-
none analogue 43, which was isolated in acceptable
yield. Subsequent N-debenzylation to yield target com-

1912 Journal of Medicinal Chemistry, 2005, Vol. 48, No. 6
Heeres et al.
Scheme 4a
a Reagents and conditions: (a) 2-methylbenzenethiol, Cs2CO3, NMP, 130 °C, 3 h; (b) AlCl3, 1,2-dichlorobenzene, 160 °C, 6 h.
Scheme 5a
a Reagents and conditions: (a) m-CPBA, CH2Cl2, rt, 24 h.
pound 44 was effected by heating 43 with AlCl3 in 1,2-
dichlorobenzene at 160 °C (Scheme 4).
3-position; and the left aryloxy(sulfanyl) wing in the
5-position of the pyrazinone ring, respectively.
Compounds 31 and 34 were converted into the cor-
responding sulfonyl analogues 45 and 46 via oxidation
with m-CPBA (Scheme 5).
First of all we evaluated the effect on activity of
different substituents in the 4-position of the aniline
ring (see Table 1). The parent compound 21 (R ) H)
displayed activity against LAI HIV-1 virus (IC50, 0.251
µmol) and was not further tested against mutants.
Introduction of a methyl group in 4-position (23) re-
sulted in a reduction of activity. Decreased activity was
also observed when the 4-position was substituted with
a fluorine atom (22) or a CF3 group (26). Modeling
studies revealed that the hydrogen in position 4 (21)
can undergo a favorable electrostatic interaction with
the backbone carbonyl of H235 of the RT enzyme,
whereas the corresponding fluorine compound (22)
undergoes an unfavorable electrostatic interaction with
the same carbonyl, explaining the lower activity of
compound 22. A similar difference occurs for the hy-
drogens in the methyl moiety of compound 23, in
contrast with the fluorines in the CF3 of 26; with the
backbone hydrogen of H235, this partially explains the
differences in activity. A second interaction especially
relevant at this position is the dipole-dipole interaction
with the backbone carbonyl of H235 and one of the CF
bonds present in compound 26, where there is no such
interaction with one of the CH bonds in compound 23.
Moreover, in both compounds 23 and 26 steric factors
diminish the interaction between the central ring
system and a number of key residues of RT, yielding
an overall negative effect on the activity. Increased
activity was obtained for the 4-chloro compound 24,
which further showed a weak activity against the
mutants L100I, K103N, and Y181C (IC50, 5.012 µmol).
A dramatic increase in activity could be observed in this
small series for the cyano compound 29 (IC50, <0.001
µmol against HIV-1 LAI virus. Moreover this compound
Results and Discussion
Evaluation of the antiviral activity of the pyrazinone
compounds was based on the potency of inhibiting
replication of wild-type HIV-1 (LAI strain, IIIB) virus
and a panel of important monomutants derived from
it, like L100I, K103N, Y181C, and Y188L. Mutated
variants of HIV-1 LAI strain are characterized in the
tables by their amino acid position and the one letter
residue codes. For instance, K103N refers to replace-
ment of lysine at position 103 by asparagine. Concen-
trations required to achieve 50% protection from HIV-1
cytopathicity in MT-4 cells (IC50, µmol) were determined
by the MTT method.12 All the determinations are the
median results of multiple tests. Optimization of activity
was guided by molecular modeling, which in turn was
based on the X-ray crystal structure of HIV-1 RT bound
with dapivirine.13
The modeling approach used to predict activity for
these compounds is based on evaluating the interaction
energy between a designed compound and the various
amino acids surrounding it in its predicted bound
conformation inside the HIV NNRTI binding site.14 This
method also allows for the identification of potentially
relevant mutations, by the separate contributions to-
ward the binding energy for each of the amino acids. A
more extensive study of mutant sensitivity was not
performed on the NNRTIs described in this paper,
because the energy contributions of the side chains
provided sufficient information to aid the synthesis. A
full statistical treatment of complex mutation interac-
tion that can also be computed with this method is
illustrated in the resistance study for the HIV protease
inhibitor Amprenavir.15
displayed a clear activity against the mutants (IC50
0.400 µmol).
<
From modeling studies we learned that a small
halogen substituent like fluorine that has no or low π-π
interaction with the CdO backbone of H235 had a
negative effect on interaction energy, whereas a larger
The target molecules can be considered to be built up
from three parts, namely, the central pyrazinone ring;
the right wing, consisting of the aniline moiety in the

Novel Pyrazinones with NNRTI Activity
Journal of Medicinal Chemistry, 2005, Vol. 48, No. 6 1913
Table 1. Antiviral Activity against Wild-type HIV-1 LAI Virus and a Panel of Single Mutant Strains of Pyrazinones with
Substituent Variations of R on the Right Wing
Figure 3. Compounds 24 and 29 docked into the HIV-1 NNRTI binding site.
chlorine atom which is closer to the backbone hydrogen
of H235 and which has a more favorable π-π interaction
with the CdO backbone of H235 results in higher
activity relative to a hydrogen substituent. A cyano
group is an even better choice (Figure 3). In this case
the cyano moiety is located in a subpocket of the RT
enzyme in such a way that it experiences a strong
dipole-dipole interaction with the backbone carbonyl
of H235 in the RT enzyme, while its relatively small
volume allows for an excellent orientation of the inhibi-
tor inside the protein.
We concluded that in this series the cyano substituent
in the 4-position of the aniline moiety is the optimal
choice, similar to that observed in the DATA/DAPY
compounds.8,9
Considering the 6-position in the pyrazinone ring, we
compared compounds 27 (R3 ) H, Table 2) and 36 (R3
) CH3, Table 1). From this comparison it appears that
on the level of wild-type HIV-1 LAI virus the presence
of a 6-methyl group instead of hydrogen in the pyrazi-
none ring generally did not give much difference in
activity, but there was a favorable effect on activity
against the majority of the mutants.
induced superior activity against all four single mu-
tants. Molecular modeling revealed that the 2-carbonyl
moiety of the pyrazinone ring made a strong acceptor
hydrogen bond with the backbone NH group of K101,
whereas the aniline NH made a strong hydrogen donor
bond with the backbone CdO group of K101.
In analogy with the DATA/DAPY compounds, we
introduced substituents in 2-, 2,4-, and 2,4,6-positions
on the benzene ring of the left wing (5-position of
pyrazinone ring; see Tables 1 and 2). An additional
methyl substituent in the para-position (see compound
29 compared to 27) not only induces an increase in
activity against LAI virus but also against the different
single mutants. In both compounds the phenyl ring of
the left wing can undergo a perfect stacking interaction
with the phenyl of Y181, which is responsible for a high
interaction energy with nonmutated RT and can be
associated with a high activity against LAI strain.14 The
additional methyl in the four position in compound 29
is responsible for an additional interaction with W229
in HIV-1 RT, resulting in a higher potency. In the case
of the Y181C mutation, we lose the strong π-π interac-
tion energy, resulting in a serious decrease in activity
against this mutant for both compounds. In the case of
the L100I and Y188L mutations, steric hindrance fac-
tors play a major role in the decrease of activity. Against
Modification in the 1-position of the pyrazinone ring
from R ) CH3 (37) to R ) H (44) (Table 2) led to an
equivalent activity against HIV-1 LAI virus but clearly

1914 Journal of Medicinal Chemistry, 2005, Vol. 48, No. 6
Heeres et al.
Table 2. Antiviral Activity against Wild-type HIV-1 LAI Virus and a Panel of Single Mutant Strains of Pyrazinones with
Substituent Variations of R1 and R2 on the Left Wing
Table 3. Antiviral Activity against Wild-type HIV-1 LAI Virus and a Panel of Single Mutant Strains of Compounds with
Modifications of X
Table 4. Antiviral Activity against Wild-type HIV-1 LAI Virus and a Panel of Single and Double Mutant Strains of Some
Pyrazinones and Reference Compound Efavirenz
the K103N mutant we lose interaction energy, but in
the case of an additional interaction of the p-methyl in
compound 29 with amino acid W229 in HIV-1 RT, there
is a compensating mechanism, delivering a compound
with acceptable activity against this mutant. The 2,4,6-
trimethyl analogue (40) was less potent than the cor-
responding 2,4-dimethyl analogue (41) against LAI virus
and the various mono mutants. Introduction of the
6-methyl moiety (40) limits the free rotation of the
phenoxy group in the 5-position compared to compound
41, reduces the stacking interaction with Y181, and
subsequently reduces the activity on LAI virus. Substi-
tuting a cyano moiety (42) for the 4-methyl in compound
40 resulted in an equivalent activity against LAI virus,
but this modification strongly enhanced the activity
against the four single mutants. Modeling the substitu-
tion of the 4-methyl (40) with a cyano moiety indicated
a strongly improved interaction with amino acid W229
of HIV-1 RT. This may explain the observed improve-
ment of HIV activity to the mutants. Comparison of the
antiviral activity of compound 42 with that of efavirenz
shows that both compounds displayed an activity on the
same order of magnitude against wild-type LAI virus.
Against the single Y181C mutant efavirenz was more
potent, but against mutants such as L100I, K103N, and
Y188L, compound 42 was superior (see Table 4). The
activity of both compounds against the K103N + Y181C
double mutant was of the same order of magnitude.
However, the picture dramatically changed against the
double L100I + K103N viral mutant, where efavirenz
demonstrated no activity even at concentrations up to
10 µmol, which was in contrast with compound 42
showing activity below 0.16 µmol. The nature of the
connecting group (ether, thioether, or sulfonyl) between
the left wing phenyl group and the 5-position of the
pyrazinone ring had clear consequences for antiviral
activity (31, 40, 45, and 46; see Table 3). The compounds
31 (X ) S) and 45 (X ) SO2) were virtually equipotent
against LAI virus with a small difference in favor of the
sulfonyl linker, which was only confirmed for the 181C

Novel Pyrazinones with NNRTI Activity
Journal of Medicinal Chemistry, 2005, Vol. 48, No. 6 1915
d6) δ 151.5, 144.5, 141.1, 133.3, 127.7, 112.2, 119.7, 119.2,
103.9, 32.9, 18.4; HR-MS calcd for C13H11BrN4O 318.0116
[M+•], found 318.0127.
mutant. A methyl group in the 6-position (46) of the
pyrazinone ring not only improved activity against LAI
virus but activity against the 181C mutant also was
significantly increased (IC50, 0.032 µmol). Substituting
the ether linkage (40) for SO2 (46) had no effect on
activity against LAI virus. On the other hand, activity
against 100I, 103N, and 188L mutants increased by this
modification but decreased against 181C mutant.
4-(4-Benzyl-6-bromo-5-methyl-3-oxo-3,4-dihydropyrazin-
2-ylamino)benzonitrile (12): column chromatography (elu-
ent CH2Cl2); yield 91%; mp 262 °C; 1H NMR (300 MHz, CDCl3)
δ 8.44 (s, 1H), 7.86 (d, J 8.8 Hz, 2H), 7.61 (d, J 8.8 Hz, 2H),
7.36-7.31 (m, 3H), 7.16 (d, J 6.6 Hz, 2H), 5.37 (s, 2H), 2.40 (s,
3H); 13C NMR (75 MHz, CDCl3) δ 152.3, 144.4, 142.8, 134.9,
133.7, 129.5, 126.8, 126.8, 126.3, 119.6, 118.9, 115.1, 105.9,
49.7, 18.6; HR-MS calcd for C19H15BrN4O 394.0429 [M+•], found
394.0419.
Experimental Section
Melting points were taken using an Electro-thermal IA 9000
digital melting apparatus and were uncorrected. Mass spectra
were run using a Hewlett-Packard MS-Engine 5989A ap-
paratus for EI and CI spectra and a Kratos MS50TC instru-
ment for exact mass measurements performed in the EI mode
at a resolution of 10 000. 1H NMR and 13C NMR spectra were
recorded on a Bruker WM-250, a Bruker Avance 300, or a
Bruker AMX 400 operating respectively at 250, 300, and 400
MHz for 1H and 62.9, 75, and 100 MHz for 13C. CDCl3 and
4-(4-Benzyl-6-bromo-3-oxo-3,4-dihydropyrazin-2-ylami-
no)benzonitrile (13): column chromatography (eluent CH2-
1
Cl2); yield 70%; mp 261 °C; H NMR (300 MHz, DMSO-d6) δ
10.03 (s, 1H), 8.13 (d, J 8.7 Hz, 2H), 7.62 (s, 1H), 7.42-7.32
(m, 5H), 5.10 (s, 2H); 13C NMR (75 MHz, DMSO-d6) δ 150.4,
147.2, 143.6, 136.2, 133.3, 129.0, 128.4, 128.3, 120.6, 119.8,
119.6, 111.6, 104.6, 52.0; HR-MS calcd for C18H13BrN4O
380.0153 [M+•], found 380.0160.
4-(4-Benzyl-6-chloro-5-methyl-3-oxo-3,4-dihydropyrazin-
2-ylamino)benzonitrile (14): column chromatography (elu-
ent CH2Cl2/EtOAc 95/5); yield 80%; mp 254 °C; 1H NMR (400
MHz, DMSO-d6) δ 9.88 (s, 1H), 8.15 (d, J 8.8 Hz, 2H), 7.37-
7.22 (m, 5H), 5.36 (s, 2H), 2.28 (s, 3H); 13C NMR (100 MHz,
DMSO-d6) δ 151.3, 144.3, 143.5, 135.5, 132.8, 127.3, 126.3,
124.5, 122.3, 119.2, 119.1, 103.8, 48.0, 15.5; HR-MS calcd for
C19H15ClN4O 350.0934 [M+•], found 350.0931.
1
DMSO were taken as a solvent, and the H and 13C chemical
shifts are reported in ppm relative to TMS. Analytical and
preparative thin-layer chromatography was carried out using
Merck silica gel 60 PF-224. For column chromatography, 70-
230 mesh silica gel 60 (E. M. Merck) was used as the stationary
phase. Preparative HPLC was carried out on a Pre-packed RT
250-25 Lichrosorb si 60.7 µm column. All the isolated
compounds have a purity of +98%.
3,5-Dibromo-1-methylpyrazin-2(1H)-one (6). Oxalyl bro-
mide (8.82 g, 40 mmol) and DMF (0.5 mL) were successively
added to a suspension of methylaminoacetonitrile hydrobro-
mide 3 (3.02 g, 20 mmol) in CH2Cl2 (250 mL). The mixture
was refluxed (oil bath 55 °C) for 24 h and then evaporated.
Column chromatography of the residue over silica gel (eluent
EtOAc/CH2Cl2 10/90) yielded compound 6 (4.7 g, 87%) as a
solid: mp 98 °C (lit.10 mp 98 °C).
5-Bromo-3-phenylamino-1-methylpyrazin-2(1H)-one
(15): column chromatography (eluent CH2Cl2/EtOAc 95/5);
1
yield 71%; mp 180 °C; H NMR (300 MHz, CDCl3) δ 8.30 (s,
1H), 7.75 (d, J 7.68 Hz, 2H), 7.36 (dd, J 7.68, 7.32 Hz, 2H),
7.09 (t, J 7.32, 1H), 6.74 (s, 1H), 3.51 (s, 3H); 13C NMR (75
MHz, CDCl3) δ 151.4, 147.1, 138.6, 129.4, 124.0, 119.5, 118.6,
114.4, 37.2; HR-MS calcd for C11H10BrN3O 279.0007 [M+•],
found 279.0003.
5-Bromo-3-(4-fluorophenylamino)-1-methylpyrazin-
2(1H)-one (16): column chromatography (eluent CH2Cl2/
EtOAc 90/10); yield 53%; mp 201-202 °C; 1H NMR (300 MHz,
DMSO-d6) δ 9.56 (s, 1H), 7.93 (2, 2H), 7.30 (s, 1H), 7.16 (s,
2H), 3.43 (s, 3H); 13C NMR (75 MHz, DMSO-d6) δ 158.2, 150.8,
147.1, 135.9, 121.8, 120.0, 115.4, 111.8, 36.6; CI-MS 298 [M +
H]+.
3,5-Dibromo-1,6-Dimethylpyrazin-2(1H)-one (7). This
was prepared from 2-(methylamino)propionitrile hydrobromide
4 (3.30 g, 20 mmol) and oxalyl bromide (8.82 g, 40.8 mmol)
according to the procedure described for the synthesis of
compound 6 to yield 3.9 g (69%) of compound 7 after column
chromatography over silica gel (eluent, EtOAc/CHCl3 5/95):
1
mp 120 °C; H NMR (300 MHz,CDCl3) δ 3.66 (s, 3H), 2.52 (s,
3H); 13C NMR (75 MHz, CDCl3) δ 153.2, 138.2, 136.0, 113.0,
34.3, 19.1; HR-MS calcd for C6H6Br2N2O 279.8846 [M+•], found
279.8864.
5-Bromo-3-(4-methylphenylamino)-1-methylpyrazin-
2(1H)-one (17): yield 74%; mp 204 °C; 1H NMR (300 MHz,
CDCl3) δ 8.24 (s, 1H), 7.63 (d, J 8.4 Hz, 2H), 7.16 (d, J 8.4 Hz,
2H), 6.72 (s, 1H), 3.51 (s, 3H); 13C NMR (75 MHz, CDCl3) δ
151.5, 147.1, 136.0, 133.7, 129.9, 119.5, 118.2, 114.4, 37.1, 21.3;
HR-MS calcd for C12H12BrN3O 293.0163 [M+•], found 293.0197.
5-Bromo-3-(4-chlorophenylamino)-1-methylpyrazin-
2(1H)-one (18): yield 53%; mp 259 °C; 1H NMR (300 MHz,
CDCl3) δ 8.28 (s, 1H), 7.71 (d, J 8.8 Hz, 2H), 7.32 (d, J 8.8 Hz,
2H), 6.77 (s, 1H), 3.53 (s, 3H); 13C NMR (75 MHz, CDCl3) δ
151.3, 146.9, 137.1, 129.4, 128.9, 120.7, 119.0, 114.0, 37.2; HR-
MS calcd for C11H9BrClN3O 312.9617 [M+•], found 312.9670.
5-Bromo-1-methyl-3-[4-(trifluoromethyl)phenylamino]-
pyrazin-2(1H)-one (19): column chromatography (eluent
CH2Cl2/EtOAc 90/10); yield 59%; mp 198-199 °C; 1H NMR
(300 MHz, DMSO-d6) δ 9.85 (s, 1H), 8.15 (d, J 8.15 Hz, 2H),
7.69 (d, J 8.78 Hz, 1H), 7.69 (s, 2H), 3.47 (s, 3H); 13C NMR (75
MHz, DMSO-d6) δ 150.9, 146.9, 143.1, 126.1, 124.7, 123.1,
121.4, 119.8, 112.2, 36.7; CI-MS 348 [M + H]+.
5-Bromo-3-(4-chlorophenylamino)-1,6-dimethylpyrazin-
2-(1H)-one. (20): column chromatography (eluent CH2Cl2/
EtOAc 95/5). Yield 70%; mp 216 °C; 1H NMR (300 MHz, CDCl3)
δ 8.12 (s, 1H), 7.69 (d, J 8.8 Hz, 2H), 7.30 (d, J 8.8 Hz, 2H),
3.60 (s, 3H), 2.44 (s, 3H); 13C NMR (75 MHz, CDCl3) δ 152.2
144.4, 137.6, 129.4, 128.2, 124.6, 120.2, 114.9, 33.1, 18.7; HR-
MS calcd for C12H11BrClN3O 326.9774 [M+•], found 326.9779.
General Procedure for the Preparation of Compounds
21-41. A mixture of pyrazinone 10-20 (0.75 mmol), substi-
tuted phenol or benzenethiol Ar-XH (1.5 mmol), cesium
carbonate (1.5 mmol), copper(I) chloride (30-50 mg), and 3-5
drops of ethyl acetate in toluene (50 mL) was heated at 120
1-Benzyl-3,5-dibromo-6-methylpyrazin-2(1H)-one (8).
The same reaction procedure was used for the conversion of 5
(4.82 g, 20 mmol) with oxalyl bromide (8.64 g, 40 mmol). The
yield of compound 8 after crystallization from EtOH was 4.30
1
g, 60%: mp 126 °C; H NMR (300 MHz, CDCl3) δ 7.38-7.17
(m, 5H), 5.38 (s, 2H), 2.43 (s, 3H); 13C NMR (75 MHz, CDCl3)
δ 153.9, 138.5, 137.4, 134.2, 129.6, 128.7, 127.3, 114.1, 51.0,
19.3; HR-MS calcd for C12H10Br2N2O 355.9159 [M+•], found:
355.9202.
General Procedure for the Preparation of 3-Phen-
ylaminopyrazin-2(1H)-ones (10-20). A mixture of 3,5-
dihalopyrazin-2-one (5 mmol), aniline (7.5 mmol), and 10-
camphorsulfonic acid (5 mmol) in i-PrOH was refluxed for 48
h. After cooling the reaction mixture the precipitate was
collected by filtration and successively washed with i-PrOH,
aqueous potassium carbonate, water, and diethyl ether. The
products were purified by column chromatography over silica
gel.
4-(6-Bromo-4-methyl-3-oxo-3,4-dihydropyrazin-2-ylami-
1
no)benzonitrile (10): yield 73%; mp 293-294 °C; H NMR
(300 MHz, DMSO-d6) δ 9.94 (1H), 8.14 (d, J 8.8 Hz, 2H) 7.78
(d, J 8 Hz, 2H), 7.47 (s, 1H), 3.46 (3H); 13C NMR (75 MHz,
DMSO-d6) δ 150.9, 146.8, 143.8, 133.3 121.9, 119.8, 119.7,
110.9, 104.4, 36.8; CI-MS 305 [M + H]+.
4-(6-Bromo-4,5-dimethyl-3-oxo-3,4-dihydropyrazin-2-
1
ylamino)benzonitrile (11): yield 84%; mp 254 °C. H NMR
(300 MHz, DMSO-d6) δ 9.80 (s, 1H), 8.13 (d, J 8.76 Hz, 2H),
7.76 (d, J 8.76 Hz, 2H), 3.55 (s, 3H); 13C NMR (75 MHz, DMSO-

1916 Journal of Medicinal Chemistry, 2005, Vol. 48, No. 6
Heeres et al.
°C for 3-48 h. After evaporation of the solution, the residue
was purified by column chromatography and when necessary
further recrystallization or HPLC to give pure compounds 21-
41.
5-(2,4-Dimethylphenoxy)-1-methyl-3-(phenylamino)-
pyrazin-2-(1H)-one (21): column chromatography (eluent
CH2Cl2/AcOAc 9/1), followed by HPLC (hexanes/EtOAc: 2/3);
yield 28%, solid; mp 166-166.5 °C; 1H NMR (250 MHz, CDCl3)
δ 8.34 (s, 1H), 7.63 (d, J 8.06 Hz, 2H), 7.25 (m, 2H), 6.99 (m,
4H), 6.15 (s, 1H), 3.51 (s, 3H), 2.34 (s, 3H), 2.25 (s, 3H); CI-
MS m/z 322 [M + H]+. Anal. (C19H19N3O2) C, H, N.
5-(2,4-Dimethylphenoxy)-3-(4-fluorophenylamino)-1-
methylpyrazin-2(1H)-one (22): column chromatography
(eluent CH2Cl2/AcOAc 9/1), followed by HPLC (hexanes/EtOAc
2/3); yield 20%, solid; mp 151-152 °C; 1H NMR (250 MHz,
CDCl3) δ 8.37 (s, 1H), 7.59 (m, 2H), 7.06 (s, 1H), 6.94 (m, 4H),
6.15 (s, 1H), 3.49 (s, 3H), 2.33 (s, 3H), 2.23 (s, 3H); CI-MS m/z
340 [M + H]+. Anal. (C19H18FN3O2) C, H, N.
5-(2,4-Dimethylphenoxy)-3-(p-toluidino)-1-methyl-
pyrazin-2(1H)-one (23). Column chromatography (eluent
CH2Cl2/AcOAc 9/1), followed by HPLC (hexanes/EtOAc: 2/3);
yield 25%, solid; mp 153.5-155 °C; 1H NMR (250 MHz, CDCl3)
δ 8.28 (s, 1H), 7.51 (d, J 8.5 Hz, 2H), 6.99 (m, 5H), 6.12 (s,
1H), 3.49 (s, 3H), 2.34 (s, 3H), 2.29 (s, 3H); 13C NMR (62.9
MHz, CDCl3) δ 151.4, 150.5, 145.9, 136.6, 136.1, 133.8, 1131.9,
129.7, 129.4, 127.4, 120.1, 118.9, 102.4, 37.1, 20.8, 20.7, 16.2;
CI-MS m/z 336 [M + H]+. Anal. (C20H21N3O2) C, H, N.
5-(2,4-Dimethylphenoxy)-3-(4-chlorophenylamino)-1-
methylpyrazin-2(1H)-one (24): column chromatography
(eluent CH2Cl2/AcOAc 9/1), followed by HPLC (hexanes/EtOAc
2/3); yield 28%, solid; mp 180-181 °C; 1H NMR (250 MHz,
CDCl3) δ 8.32 (s, 1H), 7.56 (m, J 8.85 Hz, 2H), 7.18 (d, J 8.85,
2H), 7.08 (s, 1H), 7.00 (d, J 7.5 Hz 1H), 6.90 (d, J 7.5 Hz 1H),
6.19 (s, 1H), 3.51 (s, 3H), 2.35 (s, 3H), 2.24 (s, 3H); CI-MS m/z
356 [M + H]+. Anal. (C19H18ClN3O2) C, H, N.
118.6, 105.4, 37.1, 20.7; CI-MS m/z 349 [M + H]+. Anal.
(C19H16N4OS) C, H, N.
4-[6-(2,4-Dimethylphenoxy)-4-methyl-3-oxo-3,4-dihy-
dropyrazin-2-ylamino]benzonitrile (29): column chroma-
tography (eluent CH2Cl2/EtOAc 9/1), followed by HPLC (hexane/
EtOAc 2/3); yield 22%, solid; mp 200.5-202 °C; 1H NMR (250
MHz, CDCl3) δ 8.54 (s, 1H), 7.70 (d, J 8.8 Hz, 2H), 7.46 (d, J
8.8 Hz, 2H), 7.09 (s, 1H), 7.01 (d, J 7.3 Hz, 1H), 6.90 (d, J 7.3
Hz, 1H), 6.31 (s, 1H), 3.54 (s,3H), 2.36 (s, 3H) 2.24 (s, 3H); 13
C
NMR (62.9 MHz, CDCl3) δ 151.0, 150.2, 145.2, 145.1, 140.2,
142.4, 134.3, 133.1, 131.9, 129.8, 127.5, 120.1, 119.1, 118.7,
105.5, 104.4, 37.4, 20.7; CI-MS m/z 347 [M + H]+. Anal.
(C20H18N4O2) C, H, N.
4-[6-(2,4-Dimethylphenylthio)-4-methyl-3-oxo-3,4-dihy-
dropyrazin-2-ylamino]benzonitrile (30): column chroma-
tography (eluent CH2Cl2/AcOAc 95/5), followed by HPLC
(hexanes/EtOAc: 2/3); yield 40%, solid; mp 231-232 °C; 1H
NMR (250 MHz, CDCl3) δ 8.38 (s, 1H), 7.63 (d, J 8.7 Hz, 2H),
7.47 (d, J 8.7 Hz, 2H), 7.40 (d, J 7.89 Hz 1H), 7.12 (s, 1H),
7.03 (d, J 7.89 Hz, 1H), 6.74 (s, 1H), 3.52 (s,3H), 2.43 (s, 3H)
2.36 (s, 3H); CI-MS m/z 363 [M + H]+. Anal. (C20H18N4OS) C,
H, N.
4-[6-(Mesithylthio)-4-methyl-3-oxo-3,4-dihydropyrazin-
2-ylamino]benzonitrile (31): column chromatography (elu-
ent hexane/EtOAc 2/3); yield (33%); solid; mp 273-275 °C; 1H
NMR (250 MHz, CDCl3) δ 8.35 (s, 1H), 7.54 (d, J 8.8 Hz, 2H),
7.45 (d, J 8.8 Hz, 2H), 7.04 (s, 2H), 6.50 (s, 1H), 3.50 (s, 3H),
2.48 (s, 6H), 2.35 (s, 3H); CI-MS m/z 377 [M + H]+. Anal.
(C21H20N4OS) C, H, N.
4-[4-Benzyl-3-oxo-6-(o-tolyloxy)-3,4-dihydropyrazin-2-
ylamino]benzonitrile (32): yield 25%; mp 199 °C; reaction
1
time 48 h; H NMR (300 MHz, CDCl3) δ 8.52 (s, 1H), 7.60 (d,
J 8.82 Hz, 2H), 7.45 (d, J 8.82 Hz, 2H), 7.38-7.33 (m, 5H),
7.28-7.22 (m, 1H), 7.20-7.07 (m, 2H), 6.93 (d, J 8.0, 1H), 6.46
(s, 1H), 5.10 (s, 2H), 2.25 (s, 3H); HR-MS calcd for C25H20N4O2
408.1586 [M+•], found 408.1580. Anal. (C25H20N4O2) C, H, N.
4-[4-Benzyl-3-oxo-6-(2,4-dimethylphenoxy)-3,4-dihy-
dropyrazin-2-ylamino]benzonitrile (33): yield 12.5%; mp
175 °C; reaction time 48 h; 1H NMR (300 MHz, CDCl3) δ 8.51
(s, 1H), 7.63 (d, J 8.8 Hz, 2H), 7.36 (d, J 8.8 Hz, 2H), 7.38-
7.32 (m, 5H), 7.07 (s, 1H), 7.02 (d, J 8.0, 1H), 6.86 (d, J 8.0,
1H), 6.39 (s, 1H), 5.10 (s, 2H), 2.35 (s, 3H), 2.25 (s, 3H); HR-
MS calcd for C26H22N4O2 422.1743 [M+•], found 422.1737. Anal.
(C26H22N4O2) C, H, N.
5-Mesitylthio-3-(4-chlorophenylamino)-1-methyl-
pyrazin-2-(1H)-one (25): column chromatography (eluent
CH2Cl2/AcOAc 95/5); yield 58%, solid; mp 224-225 °C; 1H
NMR (250 MHz, CDCl3) δ 8.17 (s, 1H), 7.42 (d, J 8.9 Hz, 2H),
7.13 (d, J 8.9 2H), 7.02 (s, 2H), 6.39 (s, 1H), 3.46 (s, 3H), 2.46
(s, 6H), 2.34 (s, 3H); 13C NMR (62.9 MHz, CDCl3) δ 150.7,
150.5, 145.8, 143.8, 139.3, 137.4, 130.9, 129.2, 129.1, 128.6,
126.7, 119.9, 115.3, 37.0, 21.9, 21.1; CI-MS m/z 386 [M + H]+.
Anal. (C20H20ClN3OS) C, H, N.
4-[6-(Mesitylthio)-4,5-dimethyl-3-oxo-3,4-dihydropy-
5-(2,4-Dimethylphenoxy)-1-methyl-3-[4-(trifluorometh-
yl)phenylamino]pyrazin-2(1H)-one (26): column chroma-
tography (eluent CH2Cl2/AcOAc 9/1), followed by HPLC (hex-
razin-2-ylamino]benzonitrile (34): yield 33%; mp 226-227
1
°C; H NMR (300 MHz, CDCl3) δ 8.20 (s, 1H), 7.28 (d, J 8.8
1
Hz, 2H), 7.20 (d, J 8.8, 2H), 7.04 (s, 2H), 3.60 (s, 3H), 2.53 (s,
3H), 2.40 (s, 3H), 2.38 (s, 3H); 13C NMR (75 MHz, CDCl3) δ
151.1, 144.2, 143.8, 142.9, 139.0, 132.8, 128.9, 128.1, 127.4,
123.4,119.5, 118.0, 104.2, 32.0, 22.0, 21.1, 15.6; CI-MS m/z 391
[M + H]+. Anal. (C22H22N4OS) C, H, N.
anes/EtOAc 2/3); yield 10%, solid; mp 147-148 °C; H NMR
(250 MHz, CDCl3) 8.54 (s, 1H), 7.71 (d, J 8.5 Hz, 2H), 7.45 (d,
J 8.5 Hz, 2H), 7.09 (d, J 1.86 Hz, 1H), 7.01 (dd, J 8.10, 1.86
Hz, 1H), 6.90 (d, J 8.10, 1H), 6.26 (s, 1H), 3.52 (s,3H), 2.44 (s,
3H), 2.24 (s, 3H); 13C NMR (62.9 MHz, CDCl3) δ 151.2, 150.3,
145.5, 145.4, 141.6, 134.1, 131.9, 129.7, 127.4, 126.0, 124.5,
124.2, 120.0, 118.4, 103.8, 37.3, 20.7, 26.1, 16.1; CI-MS m/z
390 [M + H]+. Anal. (C20H18F3N3O2) C, H, N.
4-[4-Methyl-3-oxo-6-(o-tolyloxy)-3,4-dihyropyrazin-2-
ylamino]benzonitrile (27): column chromatography (eluent
CH2Cl2/AcOAc 9/1), followed by HPLC (hexanes/EtOAc 2/3);
yield 25%, solid; mp 202-204 °C; 1H NMR (400 MHz, CDCl3)
δ 8.52 (s, 1H), 7.65 (d, J 8.8 Hz, 2H), 7.46 (d, J 8.8 Hz, 2H),
7.28 (d, J 7.4 Hz, 1H), 7.20 (dd, J 7.8, 7.4 Hz, 1H), 7.15 (t, J
7.4, 1H), 6.99 (d, J 7.8, 1H), 6.40 (s, 1H), 3.56 (s,3H), 2.28 (s,
3H), 2.24 (s, 3H); 13C NMR (100 MHz, CDCl3) δ 153.4, 150.3,
145.2, 144.9, 142.4, 133.1, 131.4, 130.17, 127.0, 124.6, 120.1,
119.1, 118.7, 105.5, 104.9, 37.4, 16.2; CI-MS m/z 333 [M + H]+.
Anal. (C19H16N4O2) C, H, N.
4-[4-Methyl-3-oxo-6-(o-tolylthio)-3,4-dihydropyrazin-2-
ylamino]benzonitrile (28): column chromatography (eluent
CH2Cl2/AcOAc 95/5), followed by HPLC (hexanes/EtOAc 2/3);
yield 30%, solid; mp 242.7-243.5 °C; 1H NMR (300 MHz,
CDCl3) δ 8.32 (s, 1H), 7.53 (d, J 8.78 Hz, 2H), 7.39 (d, J 8.42
Hz, 3H), 7.21-7.09 (m, 3H), 6.77 (s, 1H), 3.47 (s,3H), 2.38 (s,
3H); 13C NMR (75 MHz, CDCl3) δ 150.8, 147.7, 142.5, 140.2,
133.3, 131.1, 132.6 130.6, 128.5, 128.3, 126.6, 120.5, 119.2,
3-(4-Chlorophenylamino)-1,6-dimethyl-5-(2-methyl-
phenoxy)pyrazin-2(1H)-one (35): yield 35%; mp 222 °C; 1H
NMR (300 MHz, CDCl3) δ 8.12 (s, 1H), 7.40 (d, J 9.15 Hz, 2H),
7.25 (d, J 7.32 Hz, 1H), 7.18-7.03 (m, 4H), 6.85 (dd, J 8.07,
1.1 Hz, 1H), 3.62 (s,3H), 2.35 (s, 3H), 2.30 (s, 3H); 13C NMR
(75 MHz, CDCl3) δ 154.9, 151.6, 143.6, 141.4, 137.9, 131.4,
129.6, 129.1, 127.5, 127.1, 123.7, 119.8, 118.8, 112.9, 32.3, 16.7,
12.7; HR-MS calcd for C19H18ClN3O2 355.1087 [M+•], found
355.1080. Anal. (C19H18ClN3O2) C, H, N.
4-[4,5-Dimethyl-3-oxo-6-(o-tolyloxy)-3,4-dihyropyrazin-
2-ylamino]benzonitrile (36): yield 40%; mp 236 °C; 1H NMR
(300 MHz, CDCl3) δ 8.31 (s, 1H), 7.50 (d, J 8.8 Hz, 2H), 7.39
(d, J 8.8 Hz, 2H), 7.27 (d, J 9.1 Hz, 1H), 7.20-7.07 (m, 2H),
6.85 (d, J 8.0 Hz, 1H), 3.64 (s, 3H), 2.39 (s, 3H), 2.29 (s, 3H);
13C NMR (75 MHz, CDCl3) δ 154.6, 151.4, 143.1, 143.0, 141.3,-
133.4, 131.5, 129.8, 127.1, 124.1, 119.6, 119.1, 118.5, 114.5,
105.1, 32.4, 16.7, 12.8; HR-MS calcd for C20H18N4O2 346.1430
[M+•], found 346.1436. Anal. (C20H18N4O2) C, H, N.
4-[4,5-Dimethyl-3-oxo-6-(o-tolylthio)-3,4-dihyropyrazin-
2-ylamino]benzonitrile (37): yield 47%; mp 240 °C; 1H NMR
(250 MHz, CDCl3) δ 8.23 (s, 1H), 7.42-7.20 (m, 8H), 3.62 (s,
3H), 2.54 (s, 3H), 2.39 (s, 3H); 13C NMR (62.9 MHz, CDCl3) δ

Novel Pyrazinones with NNRTI Activity
Journal of Medicinal Chemistry, 2005, Vol. 48, No. 6 1917
151.7, 144.8, 143.2, 140.9,134.0, 133.4, 133.2, 130.9, 128.5,
127.3, 126.9, 126.8, 119.1, 118.5, 104.9, 32.7, 21.2, 17.0; HR-
MS calcd for C20H18N4OS: 362.1201 [M+•], found 362.1202.
Anal. (C20H18N4OS) C, H, N.
3-(4-Chlorophenylamino)-5-(2,4-dimethylphenoxy)-1,6-
dimethylpyrazin-2(1H)-one (38): yield 25%; mp 214 °C; 1H
NMR (300 MHz, CDCl3) δ 8.12 (s, 1H), 7.41 (d, J 9.15 Hz, 2H),
7.06-7.01 (m, 1H), 6.94 (d, J 8.07 Hz, 1H), 6.74 (d, J 8.07 Hz,
1H), 3.61 (s, 3H), 2.34 (s, 3H), 2.33 (s, 3H), 2.25 (s, 3H); 13C
NMR (75 MHz, CDCl3) δ 152.7, 151.5, 143.5, 141.6, 138.0,
133.1, 132.0, 129.3, 129.0, 127.4, 119.8, 118.8, 112.8 104.9,
32.2, 21.1, 16.7, 12.7; HR-MS calcd for C20H20ClN3O2 369.1244
[M+•], found 369.1242. Anal. (C20H20ClN3O2) C, H, N.
3-(4-Chlorophenylamino)-5-(2,4-dimethylphenylthio)-
1,6-dimethylpyrazin-2(1H)-one (39). yield 40%; mp 213 °C;
1H NMR (250 MHz, CDCl3) δ 8.02 (s, 1H), 7.35-7.25 (m, 3H),
7.10-7.01 (m, 4H), 3.59 (s, 3H), 2.51 (s, 3H), 2.37 (s, 3H), 2.35
(s, 3H); 13C NMR (62.9 MHz, CDCl3) δ 151.8, 145.1, 141.0,
138.5, 138.0, 134.6, 131.7, 129.8, 128.9, 127.6, 127.2, 125.4,
119.8, 32.5, 21.5, 21.2, 16.8; HR-MS calcd for C20H20ClN3OS:
385.1016 [M+•], found 385.1016. Anal. (C20H20ClN3OS) C, H,
N.
(75 MHz, CDCl3) δ 151.5, 144.8, 142.7, 140.8, 134.9, 134.0,
133.0, 32.7, 130.6, 129.1, 128.3, 128.0, 127.1, 126.5, 126.4,
119.6, 118.1, 104.7, 49.0, 20.8, 16.3; HR-MS calcd for C26H22N4-
OS 438.1514 [M+•], found 438.1518. Anal. (C26H22N4OS) C, H,
N.
4-[5-Methyl-3-oxo-6-(o-tolylthio)-3,4-dihydropyrazin-2-
ylamino]benzonitrile (44). To a solution of 43 (0.438 g, 1
mmol) in dry o-dichlorobenzene was added AlCl3 (0.134 g, 1
mmol) with stirring under nitrogen. After the addition was
complete, the reaction mixture was heated (oil bath) at 160
°C for 6 h. After cooling the reaction mixture was treated with
water very carefully to decompose residual AlCl3, followed by
extraction with CH2Cl2, drying over MgSO4, filtration, and
evaporation in a vacuum. Crystallization from ethyl acetate
yielded 0.104 g (30%) of 44: mp 290-291°C; 1H NMR (300
MHz, DMSO-d6) δ 12.4 (s, 1H), 9.62 (s, 1H), 7.89 (d, J 8.7 Hz,
2H), 7.54 (d, J 8.7 Hz, 2H), 7.29-7.09 (m, 4H), 2.33 (s, 3H),
2.26 (s, 3H); 13C NMR (75 MHz, DMSO-d6) δ 151.6, 146.3,
144.4, 137.7, 134.7, 132.9, 130.6, 130.4, 127.1, 127.0, 118.9,
130.1, 120.9, 119.8, 103.2, 20.3, 16.6; HRMS calcd for C19H16N4-
OS 348.1045 [M+•], found 348.1044. Anal. (C19H16N4OS) C, H,
N.
4-[6-(2,4,6-Trimethylphenoxy)-4,5-dimethyl-3-oxo-3,4-
dihydropyrazin-2-ylamino]benzonitrile (40): The synthe-
sis of compound 40 was accomplished following the general
procedure described using a large excess of 2,4,6-trimethylphe-
nol (5 equiv) and cesium carbonate (5 equiv). Purification after
column chromatography (eluent heptane/EtOAc 2/3) gave a
solid: mp 220 °C, yield 27%; 1H NMR (300 MHz, CDCl3) δ
8.22 (s, 1H), 7.28 (m, 4H), 6.94 (s, 2H), 3.65 (s, 3H), 2.49 (s,
3H), 2.49 (s, 3H), 2.37 (s, 3H), 2.09 (s, 6H); 13C NMR (75 MHz,
CDCl3) δ 150.5, 149.3, 142.9, 142.9, 142.1, 142.0, 134.3, 132.8,
131.3, 129.0, 119.4, 117.9, 110.4, 104.4, 32.0, 20.8, 16.5, 12.1;
CI-MS m/z 375 [M + H]+. Anal. (C22H22N4O2) C, H, N.
4-[6-(Mesitylsulfonyl)-4-methyl-3-oxo-3,4-dihydropy-
razin-2-ylamino]benzonitrile (45). A solution of 31 (0.097
g, 0.26 mmol) in CH2Cl2 was stirred with 3-chloroperbenzoic
acid (0.103 g, 0.52 mmol) during 24 h at room temperature.
The reaction mixture was washed with an aqueous potassium
carbonate solution, followed by drying over MgSO4, filtration,
and evaporation in a vacuum. The residue was purified by
column chromatography (silica gel, eluent 10% ethyl acetate
90% CH2Cl2) to give 0.06 g of 45 (57% yield): mp 313-314 °C;
1H NMR (250 MHz, CDCl3) δ 8.37 (s, 1H), 7.76 (s, 1H), 7.61
(d, J 9.0 Hz, 2H), 7.53 (d, J 9.0 Hz, 2H), 7.02 (s, 2H), 3.66
(s,3H), 2.71 (s, 6H) 2.33 (s, 3H); CI-MS m/z 409 [M + H]+. Anal.
(C21H20N4O3S) C, H, N.
4-[6-(2,4-Dimethylphenoxy)-4,5-dimethyl-3-oxo-3,4-di-
hydropyrazin-2-ylamino]benzonitrile (41): yield 35%; mp
4-[6-(Mesitylsulfonyl)-4,5-dimethyl-3-oxo-3,4-dihydro-
pyrazin-2-ylamino]benzonitrile (46). Compound 46 was
prepared from compound 34 according to the reaction proce-
1
208 °C; H NMR (300 MHz, CDCl3) δ 8.28 (s, 1H), 7.52 (d, J
8.76 Hz, 2H), 7.39 (d, J 8.76, 2H), 7.08 (s, 1H), 6.97 (d, J 8 Hz,
1H), 6.74 (d, J 8 Hz, 1H), 3.64 (s, 3H), 2.39 (s, 3H), 2.35 (s,
3H), 2.25 (s, 3H); 13C NMR (75 MHz, CDCl3) δ 152.4, 151.4,
143.2, 142.9, 141.5, 133.5, 133.4, 132.1, 129.5, 127.5, 119.7,
119.1, 118.5, 114.2, 105.1, 32.4, 21.1, 16.7, 12.9; HR-MS calcd
forC21H20N4O2360.1586[M+•],found360.1591.Anal.(C21H20N4O2)
C, H, N.
1
dure described for 45: yield 31%; mp 282-284 °C; H NMR
(300 MHz, CDCl3) δ 8.22 (s, 1H), 7.30 (d, J 8.8 Hz, 2H), 7.14
(d, J 8.8 Hz, 2H), 7.06 (s, 2H), 3.64 (s,3H), 2.85 (s, 3H) 2.59 (s,
3H); CI-MS m/z 423 [M + H]+. Anal. (C22H22N4O3S) C, H, N.
Acknowledgment. We thank Walter Van den Bro-
eck and Hilde De Man for their help with the prepara-
tion of the manuscript.
4-[3,4-Dimethyl-5-oxo-6-(4-cyanophenylamino)-4,5-di-
hydropyrazin-2-yloxy]-3,5-dimethylbenzonitrile (42). A
mixture consisting of 11 (0.240 g, 0.75 mmol), 4-hydroxy-3,5-
dimethylbenzonitrile (0.220 g, 1.50 mmol), cesium carbonate
(0.344 g, 1.05 mmol), copper(I) chloride (0.040 g, 2 mmol),
1-naphthoic acid (0.180 g, 1.05 mmol), and molecular sieves 4
Å (0.20 g) was refluxed for 6 days. After evaporation under
diminished pressure, the residue was first purified by column
chromatography (silica gel, 15% ethyl acetate, 85% CH2Cl2)
and then by HPLC (40% hexane, 60% ethyl acetate) to give
0.028 g (10%) of 42: mp 287-290 °C; 1H NMR (300 MHz,
CDCl3) δ 8.26 (s, 1H), 7.47 (s, 2H), 7.33 (d, J 8.79, 2H), 7.22
(d, J 8.79 Hz, 2H), 3.66 (s, 3H), 2.49 (s, 3H), 2.19 (s, 6H); CI-
MS m/z 386 [M + H]+. Anal. (C22H19N5O2) C, H, N.
Supporting Information Available: Analysis data for
compounds 21-46. This material is available free of charge
via the Internet at http://pubs.acs.org.
Note Added after ASAP Publication. This manu-
script was released ASAP on 11/9/2004 with labels in
Tables 1-4 that should not be present and with an
incomplete author listing for ref 14. The correct version
was posted on 12/1/2004.
4-[4-Benzyl-5-methyl-3-oxo-6-(o-tolylthio)-3,4-dihydro-
pyrazin-2-ylamino]benzonitrile (43). To a solution of in-
termediate 14 (0.7 g, 2 mmol) in dry NMP (10 mL) was added
freshly distilled 2-methylbenzenethiol (0.523 g, 4 mmol) in a
two-necked round-bottomed flask under a slow flow of nitro-
gen. Subsequently solid cesium carbonate (1.638 g, 5 m mol)
was added with stirring and the reaction mixture was heated
in an oil bath at 130 °C for 3 h. After cooling to room
temperature the solution was evaporated under reduced
pressure. The residue was treated with water and was
extracted three times with CH2Cl2. The organic phase was
washed with brine and dried over MgSO4, filtered, and
evaporated in a vacuum. Purification by column chromatog-
raphy (eluent, CH2Cl2/EtOAc 90/10) gave 0.525 g (60%) of 43:
References
(1) Smerdon, S. J.; Ja¨ger, J.; Wang, J.; Kohlstaedt, L. A.; Chirino,
A. J.; Friedman, J. M.; Rice, P. A.; Steitz, T. A. Structure of the
binding site for non nucleoside inhibitors of the reverse tran-
scriptase of human immunodeficiency virus type 1. Proc. Natl.
Acad. Sci. U.S.A. 1994, 91, 3911-3915.
(2) Arnold, E.; Das, K.; Ding, J.; Yadav, P. N. S.; Hsiou, Y.; Boyer,
P. L.; Hughes, S. H. Targeting HIV reverse transcriptase for
anti-AIDS drug design: Structural and biological considerations
for chemotherapeutic strategies. Drug des. Discovery 1996, 13,
29-47.
(3) Pauwels, R.; Andries, K.; Desmijter, J.; Schols, D.; Kukla, M.
J.; Breslin, H. J.; Raeymaeckers, A.; Van Gelder, J.; Woesten-
borghs, R.; Heykants, J.; Schellekens, K.; Janssen, M. A. C.; De
Clercq, E.; Janssen, P. A. J. Potent and selective inhibition of
HIV-1 replication in vitro by a novel series of TIBO derivatives.
Nature 1990, 343, 470-474.
1
mp 195 °C; H NMR (300 MHz, CDCl3) δ 8.29 (s, 1H), 7.45-
7.15 (m, 13H), 5.32 (s, 2H), 2.47 (s, 3H), 2.39 (s, 3H); 13C NMR

1918 Journal of Medicinal Chemistry, 2005, Vol. 48, No. 6
Heeres et al.
(4) Tanaka, H.; Takashima, H.; Ubasawa, M.; Sekiya, K.; Nitta, I.;
Baba, M.; Shigeta, S.; Walker, R. T.; De Clercq, E.; Miyasaka,
T. Synthesis and antiviral activity of 1-[(2-hydroxyethoxy)-
methyl]-6-(phenylthio)thymine (HEPT) as potent and selective
anti-HIV-1 agents. J. Med. Chem. 1992, 35, 4713-4719.
(5) Pauwels, R.; Andries, K.; Debryser, Z.; Van Daele, P.; Schols,
D.; Stoffels, P.; De Vreese, K.; Woestenborghs, R.; Vandamme,
A.; Janssen, C. G. M.; Anne, J.; Cauwenbergh, G.; Desmyter,
J.; Heykants, J.; Janssen, M. A. C.; De Clercq, E.; Janssen, P.
A. J. Potent and highly selective human immunodeficiency virus
type 1 (HIV-1) inhibition by a series of R-anilinophenylacetamide
derivatives targeted at HIV-1 reverse transcriptase. Proc. Natl.
Acad. Sci. U.S.A. 1993, 90, 1711-1715.
(6) Goldman, M. E.; Nunberg, J. H.; O’Brien, J. A.; Quintero, J. C.;
Schleif, W. A.; Freund, K. F.; Lee Gaul, S.; Saari, W. S.; Wai, J.
S.; Hoffman, J. M.; Anderson, P. S.; Hupe, D. J.; Emini, E. A.;
Stern, A. M. Pyridone derivatives: Specific human immunode-
ficiency virus type 1 reverse transcriptase inhibitors with
antiviral activity. Proc. Natl. Acad. Sci. U.S.A. 1991, 88, 6863-
6867.
(7) Ludovici, D. W.; Kukla, M. J.; Grous, P. G.; Krishnan, S.;
Andries, K.; De Be´thune, M.-P.; Azijn, H.; Pauwels, R.; De
Clercq, E.; Arnold, E.; Janssen, P. A. J.; Evolution of anti-HIV
drug candidates. Part 1: From R-Anilinophenylacetamide (R-
APA) to imidoyl thiourea (ITU). Bioorg. Med. Chem. Lett. 2001,
11, 2225-2228.
(8) Ludovici, D. W.; Kavash, R. W.; Kukla, M. J.; Ho, C. Y.; Ye, H.;
De Corte, B. L.; Andries, K.; De Be´thune, M.-P.; Azijn, H.;
Pauwels, R.; Moereels, H. E. L.; Heeres, J.; Koymans, L. M. H.;
De Jonge, M. R.; Van Aken, K. J. A.; Daeyaert, F. F. D.; Lewi,
P. J.; Das, K.; Arnold, E.; Janssen, P. A. J. Evolution of anti-
HIV drug candidates. Part 3: Diaryltriazine (DATA) analogues.
Bioorg. Med. Chem. Lett. 2001, 11, 2229-2234.
(9) Ludovici, D. W.; De Corte, B. L.; Kukla, M. J.; Ye, H.; Ho, C. Y.;
Lichtenstein, M. A.; Kavash, R. W.; Andries, K.; De Be´thune,
M.-P.; Azijn, H.; Pauwels, R.; Lewi, P. J.; Heeres, J.; Koymans,
L. M. H.; De Jonge, M. R.; Van Aken, K. J. A.; Daeyaert, F. F.
D.; Das, K.; Arnold, E.; Janssen, P. A. J. Evolution of anti-HIV
drug candidates. Part 3: Diarylpyrimidine (DAPY) analogues.
Bioorg. Med. Chem. Lett. 2001, 11, 2235-2239.
(10) Vekemans, J.; Pollers-Wiee¨rs, C.; Hoornaert, G. A new synthesis
of substituted 2(1H)-pyrazinones. J. Heterocycl. Chem. 1983, 20,
919-923.
(11) Loozen, P. K.; Tutonda, M. G.; Khorasani, M. F.; Compernolle,
F.; Hoornaert, G. J. Cycloadducts of ethene with 2(1H)-pyrazi-
nones and their conversion into 2,5-diazabicyclo[2.2.2]octane-
3,6-diones. Tetrahedron 1991, 47, 9259-9268.
(12) Pauwels, R.; Balzarini, J.; Baba, M.; Snoek, R.; Schols, D.;
Herdewijn, P.; Desmyter, J.; De Clercq, E. Rapid and automated
tetrazolium-based colorimetric assay for the detection of anti-
HIV compounds. J. Virol. Methods 1988, 20, 309-321.
(13) Das, K.; Clarc, A. D., Jr.; Lewi, P. J.; Heeres, J.; De Jonge, M.
R.; Koymans, L. M. H.; Vinkers, H. M.; Daeyaert, F. F. D.;
Ludovici, D. W.; Kukla, M. J.; De Corte, B. L.; Kavash, R. W.;
Ho, C. Y.; Ye, H.; Lichtenstein, M. A.; Andries, K.; Pauwels, R.;
De Be´thune, M.-P.; Boyer, P. L.; Clark, P.; Hughes, S. H.;
Janssen, P. A. J.; Arnold, E. Roles of conformational and
positional adaptability in structure based design of TMC125-
R165335 (Etravirine) and related nonnucleoside reverse tran-
scriptase inhibitors that are highly potent and effective against
wild-type and drug-resistant HIV-1 variants. J. Med. Chem.
2004, 47, 2550-2560.
(14) De Jonge, M. R.; Koymans, L. M. H.; Vinkers, H. M.; Daeyaert,
F. F. D.; Heeres, J.; Lewi, P. J.; Janssen, P. A. J. Structure based
activity prediction of HIV-1 reverse transcriptase inhibitors. J.
Med. Chem. Submitted (manuscript jm049534r).
(15) Boutton, C, De Bondt, H.; De Jonge, M. R. Genotype dependent
QSAR for HIV-1 protease inhibition. J. Med. Chem. Submitted
(manuscript jm049596h).
JM040829E