A series of 5-aminosubstituted 4-fluorobenzyl-8-hydroxy-[1,6]naphthyridine-7-carboxamide HIV-1 integrase inhibitors

Article abstract of DOI:10.1016/j.bmcl.2006.03.003

A series of 5-amino derivatives of 8-hydroxy[1,6]-naphthyridine-7-carboxamide exhibiting sub-micromolar potency against replication of HIV-1 in cell culture was identified. One of these analogs, compound 12, displayed excellent pharmacokinetic properties

Full text of DOI:10.1016/j.bmcl.2006.03.003

Bioorganic & Medicinal Chemistry Letters 16 (2006) 2900–2904
A series of 5-aminosubstituted
4-fluorobenzyl-8-hydroxy-[1,6]naphthyridine-7-carboxamide
HIV-1 integrase inhibitors
James P. Guare,a,* John S. Wai,a Robert P. Gomez,a Neville J. Anthony,a
Samson M. Jolly,a Amanda R. Cortes,a Joseph P. Vacca,a Peter J. Felock,b
Kara A. Stillmock,b William A. Schleif,c Gregory Moyer,c Lori J. Gabryelski,c
Lixia Jin,d I-Wu Chen,d Daria J. Hazudab and Steven D. Younga
aDepartment of Medicinal Chemistry, Merck Research Laboratories, West Point, PA 19486, USA
bDepartment of Biological Chemistry, Merck Research Laboratories, West Point, PA 19486, USA
cDepartment of Vaccine and Biologics Research, Merck Research Laboratories, West Point, PA 19486, USA
dDepartment of Drug Metabolism and Pharmacology, Merck Research Laboratories, West Point, PA 19486, USA
Received 7 February 2006; revised 28 February 2006; accepted 1 March 2006
Available online 22 March 2006
Abstract—A series of 5-amino derivatives of 8-hydroxy[1,6]-naphthyridine-7-carboxamide exhibiting sub-micromolar potency
against replication of HIV-1 in cell culture was identified. One of these analogs, compound 12, displayed excellent pharmacokinetic
properties when dosed orally in rats and in monkeys. This compound was demonstrated to be efficacious against replication of
simian-human immunodeficiency virus (SHIV) 89.6P in infected rhesus macaques.
Ó 2006 Elsevier Ltd. All rights reserved.
Resistance to the current chemotherapeutic agents for
the treatment of HIV-1 infections continues to drive re-
search toward developing new and better antiretroviral
treatments. Principal therapies currently in use target re-
verse transcriptase and protease, two of the three virally
encoded enzymes that play critical roles in the reproduc-
tive cycle of HIV. The third enzyme, integrase, is respon-
sible for inserting the pro-viral DNA into the cellular
genome via endonucleolytic processing and strand trans-
fer processes.1
strand transfer process of integration with an IC50
of 33 nM3,4 and also inhibits the replication of
HIV-1 in cell culture with a CIC95 of 1250 nM.5 In
the presence of 50% normal human serum (NHS),
a 4-fold drop in potency (CIC95 = 6000 nM) is ob-
served due to the binding of drug to serum protein
(99.2%).6
O
N
OH
N
The 8-hydroxy-[1,6]naphthyridine scaffold was discov-
ered to be a potent replacement for the diketoacid
pharmacophore of HIV-1 integrase inhibitors in our
laboratories.2,3 Further exploration led to the identifi-
cation of the N-(4-fluorobenzyl)-8-hydroxy-[1,6]naph-
thyridine-7-carboxamide 1 as a potent platform for
extensive studies (Fig. 1). Compound 1 inhibits the
O
OH
O
OH
CH3
N
O
O
N
N
F
H3C
N
H
F
N
N
N
H
N
O
OH
Keywords: HIV-1; Integrase; Inhibitor; Monkey; Rhesus; Macaque;
Naphthyridine.
O
OH
1
2
*
Corresponding author. Tel.: +215 652 6980; fax: +215 652
6345; e-mail: jim_guare@merck.com
Figure 1. Evolution of naphthyridine integrase inhibitors.
0960-894X/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2006.03.003

J. P. Guare et al. / Bioorg. Med. Chem. Lett. 16 (2006) 2900–2904
2901
We explored the incorporation of polar heterocycles
into compound 1 to improve both intrinsic potency
and physical properties. Recently, a series of 5-dihydro-
zyme.10 These two functional groups were incorporated
into the naphthyridine inhibitor scaffold to provide com-
pounds 9 and 10 (Table 1). Compound 10 displayed sig-
nificantly less affinity toward human serum proteins
(83.3% compared to 98–99% for compounds 7 and 8).
This reduction in protein binding with compound 10
translated to a less than 2-fold shift in potency against
HIV-1 replication in the presence of 50% NHS (Table
1). Little decrease in affinity for serum protein was ob-
served with inhibitor 9.
uracil 8-hydroxy[1,6]naphthyridine-7-carboxamides
2
was reported to potently inhibit HIV-1 replication in
cell culture and to give good pharmacokinetic profiles
in rats and dogs.7 In this communication, we describe
a series of 5-amino derivatives of 8-hydroxy[1,6]naph-
thyridine-7-carboxamide as potent inhibitors of HIV-1
integrase and viral replication in cell culture. One of
these analogs, compound 12, was shown to be effica-
cious against replication of simian-human immunodefi-
ciency virus (SHIV) 89.6P in infected rhesus
macaques.8
Intravenous dosing of DMSO solutions of analogs 7, 8,
and 10 in rats at 2 mg/kg resulted in rapid clearance of
the compounds from plasma (Table 1; clearance
42–150 mL/min/kg). Further studies indicated that these
analogs were primarily cleared via glucuronidation. It
has been reported that acetylation of the methylamino
group para to the hydroxyl group of 4-N-methylamin-
ophenol reduces its rate of glucuronidation by 5-fold rel-
ative to the parent compound.11 This feature was
incorporated into the 5-amino-8-hydroxy[1,6]naphthyri-
dine-7-carboxamide template to afford the acetyl amin-
onaphthyridine 11 (Table 1). Compound 11 exhibited
very low clearance (1.8 mL/min/kg) following intrave-
nous dosing in rats. It also had antiviral activity compa-
rable to those of inhibitors 7–10 when assayed in the
presence of 10% FBS. However, there was a 5-fold shift
in its antiviral activity in the presence of 50% NHS.
Compound 11 was found to have higher affinity for
human serum protein than 10 (95.6% vs. 83.3%),
although its affinity was lower than those observed for
compounds 7–9.
The chemistry used to prepare these analogs is illustrated
in Scheme 1. Reaction of the accessible bromonaphthyri-
dine 39 with primary or secondary amines provided a ser-
ies of substituted aminonaphthyridines 4. The products
derived from reactions with primary amines were further
functionalized to compounds 5 and 6 for optimization of
biological and physical properties.
Substitution at the 5 position of 8-hydroxy[1,6]naph-
thyridine-7-carboxamide with secondary amino groups,
such as N-acetylpiperazine and N-methylpiperazine,
provided inhibitors 7 and 8, respectively (Table 1). Com-
pounds 7 and 8 exhibited comparable potency to com-
pound 1 against HIV-1 integrase in the enzyme assay.
Both analogs were significantly more active against rep-
lication of HIV-1 in cell culture in the presence of 10%
fetal bovine serum (FBS). Presumably the polar hetero-
cyclic substitution improved cell penetration of these
analogs. However, when the antiviral replication assay
was repeated with these compounds in the presence of
50% normal human serum (NHS), there was a 10-fold
decrease in potency with compound 7 and a nearly 3-
fold decrease with compound 8. These shifts in potency
appear to correlate with the high affinities of the com-
pounds for human serum proteins as determined in vitro
(Table 1; 98–99% for compounds 1, 7, and 8). Two
amino functionalities, MeNCH2CH2NMe)Ac and
MeNCH2CONMe2, were recently reported to exhibit
low affinity for the serum proteins fibrinogen and lyso-
Combination of the unique structural features of com-
pounds 10 and 11 led to the preparation of naphthyri-
dine oxalylamide 12 (Table 1). Compound 12 exhibited
balanced biological and physical properties, with an
antiviral CIC95 of 103 nM and a moderate affinity for
human serum protein (93.2%) that led to a modest 2.5-
fold shift of the CIC95 to 250 nM in the presence of
50% NHS. Furthermore, analog 12 exhibited low clear-
ance of 5.6 mL/min/kg in rats when dosed intravenously
at 2 mg/kg as a solution in DMSO. Compound 12 was
found to be well absorbed with an oral bioavailability
of 71% and excellent exposure (AUC of 52 lM h) when
dosed at 10 mg/kg as a suspension in 0.5% methylcellu-
lose (Fig. 2). Mean plasma concentration of compound
12 at the 24th hour was determined to be ꢀ600 nM,
which was significantly higher than the 250 nM required
for inhibition of 95% of viral growth in the presence of
50% human serum.
R1
N
R2
Br
N
a or b
F
F
N
H
H
N
N
N
N
O
OH
O
OH
4
3
O
R1 = CH3,
R2 = H
c
R4
Replacement of the dimethylamino moiety of the oxa-
lylamide 12 with methylamino and amino groups led
to the preparation of compounds 13 and 14. Improve-
ments in their intrinsic activities against integrase were
observed (Table 2); however, both compounds were less
active against replication of HIV-1 in cell assays. Pre-
sumably, the introduction of additional amido hydro-
gen(s) adversely affects cell penetration and increases
binding to human serum proteins10 (Table 2). Substitu-
tion with piperidine and pyrrolidine led to the prepara-
tion of compounds 15 and 16. The pyrrolidine analog 16
Cl
R3
O
N
R5
O
H3C
H3C
N
R3
N
O
d
R3 = CO CH2CH3
F
F
N
N
H
H
N
N
N
N
2
O
OH
O
OH
6
5
Scheme 1. Reagents and conditions: (a) R1R2NH, DIEA, DMSO,
THF, 140 °C, 72 h; (b) R1R2NH, i-Pr2NEt, DMSO, THF, microwave
at 170 °C, 1 h; (c) i-Pr2NEt, THF, 0–25 °C; (d) R4R5NH, MeOH, 0 °C.

2902
J. P. Guare et al. / Bioorg. Med. Chem. Lett. 16 (2006) 2900–2904
Table 1. SAR of 5-substituted amino 1,6-naphthyridines
R
F
N
H
N
N
O
OH
CIC95 (nM) (10% FBS)b
1250
CIC95 (nM) (50% NHS)c
6000
PB (%)d
99.2
Cle
na
a
IC50 (nM)
Compound
R =
H
1
33
O
7
8
25
40
128
234
1344
677
99.0
97.9
77.3
N
N
N
CH3
42.3
N CH3
CH3
H3C
N
9
O
30
58
156
156
625
234
98.3
83.3
na
N
CH3
H3C
CH3
N
10
150.0
N
CH3
O
O
N
CH3
11
12
25
40
125
103
612
250
95.6
93.2
1.8
5.6
CH3
CH3
N
O
CH3
N
CH3
O
a Assays were performed with recombinant HIV-integrase (0.1 lM) preassembled on immobilized oligonucleotides.4
b Cell culture inhibitory concentrations (CIC95) are defined as those which inhibited by >95% the spread of HIV-1 infection in MT-4 human
T-lymphoid cells maintained in RPMI 1640 medium containing 10% heat-inactivated fetal bovine serum.5a Cytotoxicity was not observed in cell
culture at concentrations up to 20 lM.5b
c Cell culture assayed in the presence of 50% normal human serum.5a
d Percentage of compound bound to human serum proteins.6
e Rat clearance values; i.v. dosing as a solution in DMSO (2 mg/kg).
than compound 12 in the presence of human serum.
Compound 17, which contains a 2,3-piperazine dione
substituent as a cyclic version of the oxalylamide in
12, maintained potency against integrase, but was 10-
fold less active against replication of the virus.
Compound 12, possessing balanced biological and phys-
ical properties, was chosen for further characterization.
It was found to exhibit an excellent pharmacokinetic
profile in rhesus monkey with 60% bioavailability and
a half life of 5 h when dosed orally at 10 mg/kg as a sus-
pension in 0.5% methylcellulose. Compound 12 is active
against both HIV-1 and the simian lentivirus, SIV, with
CIC95 values of 250 and 350 nM, respectively, in the
presence of 50% human and rhesus serum. These favor-
able features made it an excellent tool for evaluation of
the antiviral efficacy of an integrase inhibitor against
SHIV in an animal model. More than 400 g of
compound 12 was prepared for biological studies.12
Figure 2. Pharmacokinetic profile of compound 12 in rats dosed orally
at 10 mg/kg as a suspension in 0.5% aqueous methylcellulose.
was the most potent compound in this series of naph-
thyridine oxalylamides in the antiviral assay and was
nearly 2-fold more active than compound 12 when as-
sayed in the presence of fetal bovine serum. However,
binding to human serum protein also crept up to
96.7%, which rendered compound 16 2-fold less active
In the early intervention cohort of the study, 10 days
after rhesus monkeys were infected intravenously with
50 monkey infectious doses of cell-free SHIV 89.6P,

J. P. Guare et al. / Bioorg. Med. Chem. Lett. 16 (2006) 2900–2904
Table 2. SAR of 1,6-naphthyridine oxalylamides
2903
R
F
N
H
N
N
O
OH
CIC95 (nM) (10% FBS)a
CIC95 (nM) (50% NHS)a
PB (%)a
a
IC50 (nM)
Compound
R =
H3C
CH3
CH3
O
N
12
40
15
20
7
103
250
93.2
98.3
98.2
97.8
96.7
N
O
CH3
O
HN
13
14
15
16
500
563
125
63
>1000
750
N
CH3
O
O
NH2
O
N
CH3
N
O
500
N
O
CH3
N
O
O
40
500
N
CH3
O
O
17
10
1000
>1000
98.8
N
N
CH3
a See footnotes under Table 1.
dosing of the animals with integrase inhibitor 12 as a
suspension in 0.5% aqueous methylcellulose was initiat-
ed at 10 mg/kg, twice daily. This resulted in a plasma
concentration of ꢀ700 nM of 12 at 12 h, well above
the CIC95 of 350 nM.8 Sustained suppression of viral
replication in vivo was achieved in less than 4 weeks.
Continued inhibition of viral growth was maintained
subsequently with a once-daily dose of 20 mg/kg of 12
through 87 days post-infection.
References and notes
1. For a recent review on the structure and function of HIV-1
integrase see: Davies, D. R.; Chiu, T. K. Curr. Top. Med.
Chem. 2004, 4, 965; For recent reviews on HIV-1 integrase
inhibitors, see: (a) Anthony, N. J. Curr. Top. Med. Chem.
2004, 4, 979; (b) Pommier, Y.; Johnson, A. A.; Marchard,
C. Nat. Rev. Drug Disc. 2005, 4, 236.
2. (a) Goldgur, Y.; Craigie, R.; Cohen, G. H.; Fujiwara, T.;
Yoshinaga, T.; Fugishita, T.; Sugimoto, H.; Endo, T.;
Murai, H.; Davies, D. R. Proc. Natl. Acad. Sci. U.S.A.
1999, 96, 13040; (b) Wai, J. S.; Egbertson, M. S.; Payne, L.
S.; Fisher, T. E.; Embrey, M. W.; Tran, L. O.; Melamed, J.
Y.; Langford, H. M.; Guare, J. P., Jr.; Zhuang, L.; Grey,
V. E.; Vacca, J. P.; Holloway, M. K.; Naylor-Olsen, A.
M.; Hazuda, D. J.; Felock, P. J.; Wolfe, A. L.; Stillmock,
K. A.; Schleif, W. A.; Gabryelski, L. J.; Young, S. D.
J. Med. Chem. 2000, 43, 4923.
3. (a) Zhuang, L.; Wai, J. S.; Embrey, M. W.; Fisher, T. E.;
Egbertson, M. S.; Payne, L. S.; Guare, J. P., Jr.; Vacca, J.
P.; Hazuda, D. J.; Felock, P. J.; Wolfe, A. L.; Stillmock,
K. A.; Witmer, M. V.; Moyer, G.; Schleif, W. A.;
Gabryelski, L. J.; Leonard, Y. M.; Lynch, J. J., Jr.;
Michelson, S. R. J. Med. Chem. 2003, 46, 453; (b) Hazuda,
D. J.; Anthony, N. J.; Gomez, R. P.; Jolly, S. M.; Wai, J.
S.; Zhuang, L.; Fisher, T. E.; Embrey, M. W.; Guare, J. P.,
Jr.; Egbertson, M. S.; Vacca, J. P.; Huff, J. R.; Felock, P.
J.; Witmer, M. V.; Stillmock, K. A.; Danovich, R.;
Grobler, J.; Miller, M. D.; Espeseth, A. S.; Jin, L.; Chen,
I.-W.; Lin, J.; Kassahun, K.; Ellis, J. D.; Wong, B. K.; Xu,
W.; Pearson, P. G.; Schleif, W. A.; Cortese, R.; Emini, E.;
In summary, a potent series of 5-amino derivatives of
8-hydroxy[1,6]naphthyridine-7-carboxamide exhibiting
sub-micromolar potency against replication of HIV-1
in cell-based assay was identified. The most potent
inhibitor, analog 16, inhibited viral growth with a
CIC95 of 63 nM in the presence of 10% FBS. Compound
12 displayed balanced biological and physical proper-
ties, and excellent pharmacokinetic profiles in rats and
monkey. Oxalylamide 12 was demonstrated to be
efficacious against replication of simian-human immu-
nodeficiency virus (SHIV) 89.6P in infected rhesus
macaques.
Acknowledgments
The authors are grateful to Drs. Terry A. Lyle and
Donnette D. Staas for helpful discussions.

2904
J. P. Guare et al. / Bioorg. Med. Chem. Lett. 16 (2006) 2900–2904
Summa, V.; Holloway, M. K.; Young, S. D. Proc. Natl.
Acad. Sci. U.S.A. 2004, 101, 11233.
4. Hazuda, D. J.; Felock, P.; Hastings, J. C.; Pramanik, B.;
Wolfe, A. J. Virol. 1997, 71, 7005.
J = 8.4, 4.3 Hz, 1H), 7.37 (m, 2H), 7.06 (t, J = 8.6 Hz, 2H),
5.00 (m, 1H), 4.67 (d, J = 6.3 Hz, 2H), 3.06 (d, J = 4.8 Hz,
3H). HRMS m/z calcd for C17H15FN4O2 (M+1) 327.1252,
found 327.1264. N-(7-{[(4-fluorobenzyl)amino]carbonyl}-
8-hydroxy-1,6-naphthyridin-5-yl)-N,N0,N0-trimethylethane-
diamide (12): To a cold (0 °C) solution of compound 4
(415 g, 1.27 mol; R1 = H, R2 = CH3) and diisopropylethyl-
amine (1.3 kg, 10.2 mol) in THF (20 L), ethyl chlorooxoac-
etate (690 g, 5.1 mol) was added dropwise over a period of
20 min. The resultant mixture was stirred at the same
temperature for 2 h, allowed to warm to 25 °C, and stirred
for an additional 18 h. The product mixture was filtered and
the filtrate was concentrated under vacuum. The residual oil
was dissolved in ethyl acetate and filtered again. The ethyl
acetate solution was washed successively with 1 M aqueous
HCl, water, and brine, dried over anhydrous Na2SO4,
filtered, and concentrated under vacuum to provide the bis-
oxalation product as a brown oil (670 g). This material was
used in the following step without further purification. To a
cold (0 °C) solution of the above crude bis-oxalate (670 g) in
methanol (8 L), anhydrous dimethylamine gas (400 g,
8.8 mol) was bubbled into the mixture with its temperature
maintained below 5 °C. After the reaction mixture was
stirred at 0 °C for 18 h, another 400 g of methylamine was
added. The resultant mixture was stirred at 0 °C for 4 h,
warmed to 25 °C, and stirred for 18 h. The mixture was then
purged with nitrogen gas for 15 min. The product mixture
was concentrated under vacuum and the residue was
dissolved in ethyl acetate (8 L). The organic solution was
washed successively with 0.5 M aqueous HCl, water, and
brine, dried over anhydrous Na2SO4, filtered, and concen-
trated under vacuum. The residual oil was dissolved in
boiling ethyl acetate (4 L), decolorized with activated
charcoal, and filtered. The precipitate that formed upon
cooling was filtered to provide compound 12 as a white
crystalline solid (400 g, 74% yield from 4). 1H NMR
(400 MHz, CDCl3) d 9.21 (m, 1H), 8.35 (dd, J = 8.5,
1.6 Hz, 0.84H, rotamer A), 8.26 (dd, J = 8.5, 1.6 Hz,
0.16H, rotamer B), 8.09 (m, 0.16H), 7.92 (m, 0.84H), 7.72
(dd, J = 8.5, 4.2 Hz, 0.84H), 7.67 (dd, J = 8.5, 4.2 Hz,
0.16H), 7.36 (m, 2H), 7.08 (m, 2H), 4.69 (d, J = 6.1 Hz,
0.16H), 4.66 (d, J = 6.3 Hz, 0.84H), 3.47 (s, 0.16H), 3.41 (s,
0.84H), 3.16 (s, 0.16H), 3.11 (s, 0.16H), 2.88 (s, 0.84H), 2.54
(s, 0.84H). In experiments run at elevated temperatures,
peaks coalesced and sharpened, indicating that the rate
of equilibration of the two rotamers is temperature-
dependent: 1H NMR (600 MHz, DMSO-d6, 135 °C): d
9.16 (dd, J = 4.3, 0.9 Hz, 1H), 8.85 (br s, 1H), 8.36 (br s,
1H), 7.81 (dd, J = 4.3, 8.7 Hz, 1H), 7.43 (t, J = 5.9 Hz,
2H), 7.11 (t, J = 8.7 Hz, 2H), 4.61 (d, J = 6.7 Hz, 2H),
3.39 (s, 3H), 2.97 (br s, 3H), 2.51 (br s, 3H). HRMS m/z
calcd for C21H20FN5O4 (M+1) 426.1572, found
426.1590. Anal. Calcd for C21H20FN5O4: C, 59.29; H,
4.74; N, 16.46. Found: C, 59.40; H, 4.65; N, 16.34. Mp:
195–196 °C.
5. (a) Vacca, J. P.; Dorsey, B. D.; Schleif, W. A.; Levin, R.
B.; McDaniel, S. L.; Darke, P. L.; Zugay, J.; Quintero, J.
C.; Blahy, O. M.; Roth, E.; Sardana, V. V.; Schlabac, A.
J.; Graham, P. I.; Condra, J. H.; Gotlib, L.; Holloway, M.
K.; Lin, J.; Chen, I.-W.; Vastag, K.; Ostovic, D.; Ander-
son, P. S.; Emini, E. E.; Huff, J. R. Proc. Natl. Acad. Sci.
U.S.A. 1994, 91, 4096; (b) Cytotoxicity is evaluated by
visual inspection of the culture for cytopathic effects
distinguished as gross morphological changes, growth
pattern change and metabolic change as indicated by lack
of change in the medium pH indicator.
6. Analytical HPLC/UV detection based assay that measures
the ability of a compound to bind with human plasma
(primarily albumin) in pH 7.4 buffer at rt.
7. Embrey, M. W.; Wai, J. S.; Funk, T. W.; Homnick, C. F.;
Perlow, D. S.; Young, S. D.; Vacca, J. P.; Hazuda, D. J.;
Felock, P. J.; Stillmock, K. A.; Witmer, M. V.; Moyer, G.;
Schleif, W. A.; Gabryelski, L. J.; Jin, L.; Chen, I.; Ellis, J.
D.; Wong, B. K.; Lin, J. H.; Leonard, Y. M.; Tsou, N. N.;
Zhuang, L. Biol. Med. Chem. Lett. 2005, 15, 4550.
8. Hazuda, D. J.; Young, S. D.; Guare, J. P.; Anthony, N. J.;
Gomez, R. P.; Wai, J. S.; Vacca, J. P.; Handt, L.; Motzel,
S. L.; Klein, H. J.; Dornadula, G.; Danovich, R. M.;
Witmer, M. V.; Wilson, K. A. A.; Tussey, L.; Schleif, W.
A.; Gabryelski, L. S.; Jin, L.; Miller, M. D.; Casimiro, D.
R.; Emini, E. A.; Shiver, J. W. Science 2004, 305, 528.
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M.; Wai, J. S.; Zhuang, L.; Embrey, M.; Tran, L.;
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12. Preparation of compound 12. N-(4-Fluorobenzyl)-8-hy-
droxy-5-(methylamino)-1,6-naphthyridine-7-carboxamide
(4, R1 = H, R2 = CH3): A mixture of bromonaphthyridine 3
(35 g, 93 mmol)9, methylamine (107 mL, 214 mmol, 2 M in
THF), diisopropylethylamine (12 g, 93 mmol), and 50 mL
DMSO in a 400 mL reaction vessel was heated in a
microwave reactor at 170 °C for 1 h. The product mixture
was cooled to room temperature and poured into ice/water
(3 L). The yellow solid which precipitated was collected by
filtration and air-dried to yield 20 g (66%) of 4 (R1 = H,
R2 = CH3). This procedure was repeated 21 times to
accumulate 415 g of 4. 1H NMR (400 MHz, CDCl3) d
9.11 (m, 1H), 8.30 (m, 1H), 8.10 (d, 8.5 Hz), 7.53 (dd,