3-(Arylthiomethyl)isoxazole-4,5-dicarboxamides: Chemoselective Nucleophilic Chemistry and Insecticidal Activity

Article abstract of DOI:10.1021/jf901512t

A collection of 91 3-(arylthiomethyl)isoxazole-4,5-dicarboxamides was prepared starting from dimethyl 3-(chloromethyl)isoxazole-4,5-dicarboxylate. The thioether moieties in these compounds were subsequently oxidized to give the corresponding 3-(arylsulfonylmethyl)isoxazole-4,5-dicarboxamides. By carefully controlling stoichiometry and reaction conditions, the C4 and C5 carbomethoxy groups could be differentially derivatized to carboxamides. A total of 182 trisubstituted isoxazoles are reported and deposited in the National Institutes of Health Molecular Repository; an 80 compound subset was evaluated for insecticidal activity.

Full text of DOI:10.1021/jf901512t

7422 J. Agric. Food Chem. 2009, 57, 7422–7426
DOI:10.1021/jf901512t
3-(Arylthiomethyl)isoxazole-4,5-dicarboxamides:
Chemoselective Nucleophilic Chemistry and Insecticidal
Activity
†
,
G
T
UI J. Y
U
,† SATORI
I
WAMOTO,† LORI I. ROBINS,† JAMES C. FETTINGER
,†
HOMAS C. SPARKS,‡ BETH A. LORSBACH,*,‡ AND
MARK J. KURTH*
†Department of Chemistry, University of California, One Shields Avenue, Davis, California 95616, and
‡Dow AgroSciences LLC, Discovery R&D, 9330 Zionsville Road, Indianapolis, Indiana 46268
A collection of 91 3-(arylthiomethyl)isoxazole-4,5-dicarboxamides was prepared starting from
dimethyl 3-(chloromethyl)isoxazole-4,5-dicarboxylate. The thioether moieties in these compounds
were subsequently oxidized to give the corresponding 3-(arylsulfonylmethyl)isoxazole-4,5-dicarbox-
amides. By carefully controlling stoichiometry and reaction conditions, the C4 and C5 carbomethoxy
groups could be differentially derivatized to carboxamides. A total of 182 trisubstituted isoxazoles
are reported and deposited in the National Institutes of Health Molecular Repository; an 80
compound subset was evaluated for insecticidal activity.
KEYWORDS: Isoxazole; insecticidal activity; nucleophilic selectivity
INTRODUCTION
MATERIALS AND METHODS
General. All chemicals were purchased from commercial sup-
pliers and used without further purification. Analytical TLC was
carried out on precoated plates (silica gel 60, F254) and visualized
with UV light. Flash chromatography was performed with silica
gel 60 (230-400 mesh). NMR spectra (1H at 300, 400, and 600
MHz; 13C at 75, 100, and 150 MHz) were measured in acetone-d6
and CDCl3 as solvents indicated individually, and chemical shifts
are reported in parts per million (ppm) related to internal duter-
ated solvents or TMS. The LC-MS analyses were performed on a
Waters 2690 with electrospray (þ) ionization, mass range 100-
1500 Da, 23 V cone voltage, and Xterra MS C18 column (2.1 mm
ꢀ 50 mm ꢀ 3.5 μm).
The 5-membered isoxazole provides a valuable scaffold in
medicinal chemistry as well as a useful synthon in organic
synthesis (1). In addition, the aromatic isoxazole displays wide-
ranging biological activities, including pharmacological applica-
tions such as hypoglycemic, analgesic, antiinflammatory, anti-
bacterial, and HIV-inhibitory activities, as well as agrochemical
applications spanning herbicidal, fungicidal, and insecticidal
activities (2). As part of a collaboration with Dow AgroSciences,
lead generation libraries are designed and biologically evaluated
for new chemistry as well as product pipeline potential. Indeed,
there are several reports of combinatorial libraries as discovery
tools for agrochemicals, and these have provided numerous hits
and leads (3). These libraries serve to bothproduce molecules with
activity and, simultaneously, provide valuable information to
facilitate optimization. 3,4,5-Trisubstituted isoxazoles were re-
cently found to have novel PPARδ agonist’s properties with good
in vivo pharmacokinetics (4). The antiepileptic and antiobesity
drug zonisamide (5) (Figure 1) piqued our interest in sulfide/
sulfone substituents;functionalities that also have important
pharmaceutical applications (6);tethered to the isoxazole het-
erocycle. We previously reported that the three electrophilic
centers of dimethyl 3-chloromethylisoxazole-4,5-dicarboxylate
(1) are available for diversification and reported the elaboration
to a library of 5-alkylcarbamoyl-3-arylsulfanylmethylisoxazole-
4-carboxylic acids (e.g., 2) (7). Herein, we report the elaboration
of 1 to chemsets of 3-(arylthiomethyl)isoxazole-4,5-dicarbox-
amides (6 and 9) and 3-(arylsulfonylmethyl)isoxazole-4,5-dicar-
boxamides (7 and 10).
Preparation of Dimethyl 3-Chloromethylisoxazole-4,5-dicarb-
oxylate (1) (7). The procedure was adopted from the literature;
IR, 1H NMR, and 13C NMR matched literature data.
The intermediate oxime was not purified by distillation which
wasreported toleadtoa violent explosion. Inaddition, this oxime
was reported to irritate the eyes and the mucous membrane of the
nose as well as blister the skin. Following the literature routes as
well as the protocol outlined in Scheme 1, we had no exposure
problems.
General Procedure for the Preparation of Sulfide Ether: Dimeth-
yl 3-(Phenylthiomethyl)isoxazole-4,5-dicarboxylate (4{1}). To a
DMF (18 mL) solution of 1 (1.21 g, 5.19 mmol) under N2 gas were added
thiophenol (3{1}, 0.629 g, 5.71 mmol) and triethylamine (0.577 g, 5.71
mmol). The resulting solution was stirred at room temperature for 10 min,
at which time TLC analysis (hexane/ethyl acetate = 4:1) indicated that the
reaction had gone to completion. The reaction mixture was diluted with
water (200 mL) and extracted with ethyl acetate (2 ꢀ 50 mL). The
combined organic extracts were washed with 5% aqueous NaOH (2 ꢀ
50 mL) and brine (1 ꢀ 100 mL), dried over anhydrous Na2SO4, and
filtered; the solvent was removed in vacuo. The resulting yellow oil was
purified by flash column chromatography (SiO2/hexane/ethyl acetate =
4:1) to give 4{1} (1.54 g, 97%): 1H NMR (300 MHz, CDCl3) δ 7.35-7.23
(m, 5H, C6H5), 4.26 (s, 2H, CH2), 3.98 (s, 3H, CH3), 3.90 (s, 3H, CH3).
*Corresponding authors [(M.J.K.) telephone (530) 752-8192, fax
(530) 752-8995, e-mail mjkurth@ucdavis.edu; (B.A.L.) e-mail
balorsbach@dow.com].
pubs.acs.org/JAFC
Published on Web 07/22/2009
© 2009 American Chemical Society

Article
J. Agric. Food Chem., Vol. 57, No. 16, 2009 7423
Following this procedure also delivered 4{2-7} (90-95%).
δ 7.37-7.23 (m, 10H, phenyl C-H), 4.66 (d, J = 5.4 Hz, 2H, N-CH2),
4.26 (s, 2H, S-CH2), 3.90 (s, 3H, O-CH3); 13C NMR (150 MHz, CDCl3)
δ 166.0, 163.8, 161.8, 137.8, 134.2, 131.8, 128.7, 128.6, 128.2, 128.1, 128.0,
110.0, 53.8, 44.0, 30.2.
General Procedure for the Preparation of Homobisamides:
3-(Phenylthiomethyl)-N4,N5-dipropylisoxazole-4,5-dicarboxamide
6{1,1}. Propylamine (5{1}, 303 mg, 5.12 mmol) was added to a methanol
(1 mL) solution of crude 4{1} (157 mg, 0.512 mmol). The resulting solution
was stirred at room temperature overnight or 40 °C for 2 h, at which time
TLC analysis (hexane/ethyl acetate = 4:1) indicated that the reaction had
gone to completion. The reaction mixture was cooled with ice-water for
15 min, and the resulting white precipitate was collected by filtration and
washed with cold methanol. Alternatively, methanol can be evaporated
from the reaction mixture to give 6{1,1} (141 mg, 85%) as a white paste:
mp 102-103 °C; 1H NMR (400 MHz, (CD3)2CO) δ 10.04 (br s, 1H, N-
H), 8.62 (br s, 1H, N-H), 7.42-7.19 (m, 5H, phenyl), 4.59(s, 2H, S-CH2),
3.43 (apparent q, J = 8 Hz, 2H, N-CH2), 3.31 (apparent q, J = 8 Hz, 2H,
Without further purification, 8{1} (68 mg, 0.178 mmol) was suspended
in methanol (1 mL), and n-propylamine (5{1}, 105 mg, 1.78 mmol) was
added. The resulting suspension was stirred at room temperature, and the
reaction was monitored by TLC analysis (hexane/ethyl acetate = 4:1)
After 6 h, TCL analysis indicated that the reactionhad goneto completion.
The reaction mixture was concentrated (condensed air evaporation) to
give 9{1,1} (64.8 mg, 89%) as a white powder: mp 93-94 °C; 1H NMR
(400 MHz, (CD3)2CO) δ 9.96 (br s, 1H, N-H), 9.14 (br s, 1H, N-H),
7.42-7.18 (m, 10H, phenyl C-H), 4.67 (d, J = 4.4 Hz, N-CH2), 4.54 (s,
2H, S-CH2), 3.31 (apparent q, 2H, J = 8 Hz, N-CH2), 1.63-1.54 (m,
2H, C-CH2), 0.98-0.95 (t, 3H, J = 7.4 Hz, C-CH3); 13C NMR (100
MHz, (CD3)2CO) δ 163.6, 159.2, 157.7, 157.6, 138.1, 136.0, 130.1, 129.9,
129.2, 129.0, 128.8, 128.6, 128.1, 127.9, 127.5, 126.8, 115.8, 43.4, 43.3, 41.1,
22.7, 11.3, 11.2.
N-CH2), 1.72-1.55 (m, 4H, 2C-CH2), 1.00-0.94 (m, 6H, 2C-CH3); 13
NMR (100 MHz, (CD3)2CO) δ 163.6, 159.4, 159.2, 157.6, 136.0, 130.0,
129.1, 126.7, 115.5, 41.6, 41.0, 28.6, 22.6, 22.3, 11.2, 10.9.
C
Following this procedure, also delivered 6{1-7, 1-7}.
Following this procedure, also chemset 9{1-7,1-6} was delivered.
General Procedure for the Preparation of Homobisamides Sul-
fones: 3-(Pyridine-2-ylsulfonylmethyl)-N4,N5-dibenzylisoxazole-
4,5-dicarboxamide 7{5,7}. Hydrogen peroxide (30%; 39 μL, 0.382
General Procedure for the Preparation of Mixed Bisamides:
N5-Benzyl-3-(phenylthiomethyl)-N4-propylisoxazole-4,5-dicarbox-
amide (9{1,1}). Benzylamine (5{7}, 307 mg, 2.87 mmol) was added to a
methanol (10 mL) solution of crude 4{1} (881 mg, 2.87 mmol), and the
resulting solution was stirred at room temperature for 4 h, at which time a
white precipitate had formed. This precipitate was collected by filtra-
tion and washed with cold methanol to yield 8{1}, methyl 5-(benzyl-
carbamoyl)-3-(phenylthiomethyl)isoxazole-4-carboxylate (601 mg, 55%),
mmol) and catalysts (including Aliquat336, Na2WO4 2H2O, and
3
C6H5PO3H; 0.038 mmol each) were added to an acetic acid (2 mL) and
EtOAc (2 mL) solution of 6{5,7} (70 mg, 0.153 mmol). The resulting
mixture was stirred at room temperature and monitored by TLC analysis
(hexane/ethyl acetate = 1:1). After 12 h, TLC analysis indicated the
reaction was complete. The reaction mixture was diluted with 5% NaOH
(10 mL) and extracted with ethyl acetate (10 mL ꢀ 2). The organic layer
was collected and dried over anhydrous Na2SO4, filtered, and concen-
trated onto a small amount of silica gel for dry loading flash column. A
short column (hexane/ethyl acetate = 1:1) preceded to remove biphasic
catalyst to yield 7{5,7} (60 mg, 80%) as a white solid: mp 129-130 °C.
Following this procedure, 7{1-7, 1-7} as well as the mixed bisamides
10{1-7,1-6} were delivered.
as
a
white solid: mp 92-93 °C; 1H NMR (600 MHz, CDCl3)
Figure 1. Zonisamide;an antiepileptic and antiobesity drug; 3-chloro-
methylisoxazole-4,5-dicarboxylate as a discovery platform.
General Procedure for Bioassays. Insecticidal activity was evaluated as
described previously (8). Briefly, the primary screen used two 96-well-
Scheme 1. Reagents and Conditions: (a) NH2OH HCl, Water, RT, 30 min, Not Isolated; (b) DMAD, NaOCl, THF, 70%; (c) ArSH 3{1-7}, Et3N, DMF, 10
3
min, 95%; (d) RNH2 5{1-7}, 10 equiv, MeOH, 40 °C, 2-4 h, 85-90%; (e) C6H5CH2NH2, 5{7}, 1.1 equiv, MeOH, RT, 4-5 h; (f) RNH2 5{1-6}, 10 equiv,
MeOH, RT, 12 h, 75-80%; (g) H2O2, QþHSO4- (PTC Phase-Transfer-Catalyst), Na2WO4 2H2O, C6H5PO3H, EtOAc, HOAc, RT, 1 h
3

7424 J. Agric. Food Chem., Vol. 57, No. 16, 2009
Yu et al.
based high-throughput insect assays, one for beet armyworm (Spodoptera
exigua: Lepidoptera) larvae and another for yellow fever mosquito (Aedes
aegypti: Diptera). Artificial diet (100 μL/well, 96-well microtiter plate) that
had been pretreated with test compounds (12 μg dissolved in 30 μL of
DMSO/acetone/water (2:1:7) mixture, and then dried for several hours)
was seeded with eggs of S. exigua. Infested plates were then covered and
held in the dark (29 °C), and the mortality was recorded 6 days post-
treatment. The A. aegypti assay used 1-day-old larvae pipetted into each
well of pretreated (6 μg/well, dissolved in 15 μL of DMSO/acetone/water
(1:1:8) mixture, then allowed to dry) 96-well microtiter plate. The plates
were covered with a lid held at room temperature and then graded for
mortality 3 days post-treatment. There were six replicatesper treatment for
each assay. Compounds active in the primary screen (67%) were further
evaluated by means of a largerformat (3 mL, 128-well diet trays containing
1 mL of diet, and selected dosages of the test compound) diet-based
bioassay using second instar of S. exigua or Helicoverpa zea (corn
earworm: Lepidoptera) larvae. The wells (eight per treatment) were
covered with clear plastic, and percent mortality (average of the eight
wells) was recorded for each treatment 5 days after the assay was initiated.
Approximate LC50 values (lethal concentration for 50% of the
population) were estimated using probit analysis.
Figure 2. 3-(Arylthiomethyl)isoxazole- and 3-(arylsulfonylmethyl)-isoxa-
zole-4,5-dicarboxamides.
RESULTS AND DISCUSSION
In our earlier work, we established that the C5 carbomethoxy
of 1 was more reactive than the C4 carbomethoxy and, by
exploiting this reactivity difference, we were able to elaborate
isoxazole 1 to a 5-alkylcarbamoyl-3-arylsulfanylmethylisoxazole-
4-carboxylic acid (2) library (7). Two additional enabling dis-
coveries are reported here (Figure 2). The first is that thiolate
nucleophiles chemoselectively engage the C3 chloromethyl elec-
trophile. This observation suggested that isoxazole 1 might lead
to homobisamide 6 in two simple transformations: thiolate SN2
displacement of chloride followed by concomitant C4/C5 ester f
amide transformation. In addition, sulfone 7 could potentially be
derived from 6 by S-oxidation.
Dimethyl 3-chloromethylisoxazole-4,5-dicarboxylate (1), pre-
pared as previously described (7), reacts rapidly in the aprotic
solvent DMF with aryl thiols 3{1-7} in the presence of triethyl-
amine to give the corresponding thioethers in quantitative yield
4{1-7}; Scheme 1). No evidence for involvement of either ester is
detected, and the crude product of this reaction is obtained in
such high purity that it can be employed in subsequent reactions
without purification.
Treating a methanolic solution of crude bisester 4{1-7} with
an excess (10 equiv) of various primary amines 5{1-7} at 40 °C
for 30 min delivered novel homobisamides 6{1-7,1-7} in 85-
90% overall yield from the chlorodiester 1. Under these condi-
tions no mixed ester/amide products were detected upon workup,
but TLC monitoring of this reaction did reveal the appearance of
the presumed C5-amide/C4-ester intermediate, which, in the
presence of excess amine, then proceeds on to bisamide 6.
The presumed intermediacy of a C5-amide/C4-ester led us to
treat a methanol solution of crude bisesters 4{1-7} with primary
amine 5{7} at near stoichiometric levels and at room temperature
(instead of 40 °C). Under these conditions, the reaction required
4-12 h for completion, but cleanly delivered the C5-amide/C4-
ester. When TLC indicated complete consumption of bisester
4{1-7}, an excess (10 equiv) of primary amine 5{1-6} was
added, and stirring was continued for an additional 6-12 h.
This protocol delivered 42 mixed bisamides of general structure
9{1-7,1-6} in 75-80% overall yield from chlorodiester 1.
Interestingly, the mixed bisamide 9{2,5} has very low yield.
Two surprises accompanied this 8 f 9 transformation. First,
allowing a methanolic solution of monoamide-monoester 8 and
excess (10 equiv) amine to stir at room temperature for multiple
days led cleanly to the homobisamide product 6 instead of the
Figure 3. X-ray crystallography-determined structure of 9{1,1} [N5-ben-
zyl-3-(phenylthiomethyl)-N4-propylisoxazole-4,5-dicarboxamide].
mixed bisamide 9. That is, transamination of the C5 amide occurs
under extended reaction times, even at room temperature. This
transamination process can be expedited by warming the metha-
nolic reaction mixture to 40 °C (homobisamide obtained in 12 h).
Second, and related to the first, concentration of the crude
monoamide-monoester 8 plus excess amine reaction mixture
must be effected at room temperature; otherwise, a mixture
(sometimes only pure bisamide 6) of homobisamide 6 and mixed
bisamide 9 is obtained.
The regioselectivity of these mixed bisamide products 9 was, on
the basis of our previous results with 1 (7), presumed to derive
from the first amine reacting at the C5 ester and the second amine
reacting at the C4 ester. To verify this, crystalline mixed bisamide
9{1,1}, prepared by treatment first with benzyl amine (1.1 equiv)
and subsequently with propyl amine (10 equiv), was evaluated by
X-ray crystallographic analysis. As depicted in Figure 3, the first
amine reacted at the C5 ester, and the second amine reacted at the
C4 ester.
The thioether moieties in homobisamides 6{1-7,1-7} and
mixed bisamides 9{1-7,1-6} were oxidized to the corresponding
sulfones. Although a number of reagents are effective for this
transformation, green chemistry consideration led us to select a
recently reported tungsten-mediated procedure that employs
hydrogen peroxide as the stoichiometric oxidant. This procedure
also employs [CH3(n-C8H17)3N]HSO4 as a phase-transfer cata-
lyst and C6H5P(dO)(OH)2 as a phosphonic acid promoter (9).
Withthis protocol, we were able to use an ethyl acetate/acidicacid
solvent system instead of the more typical chlorohydrocarbon
solvent. With catalytic Na2WO4/ C6H5P(dO)(OH)2/[CH3(n-
C8H17)3N]HSO4 (physiologically harmless), these oxidation re-
actions generally went to completion in 12 h at room temperature.
TLC analysis indicated the presence of the sulfoxide intermediate
and, in cases when sulfone/sulfoxide mixtures were obtained
within 12 h, separation of the sulfoxide from the sulfone was
accomplished by silica gel chromatography. In those cases when

Article
J. Agric. Food Chem., Vol. 57, No. 16, 2009 7425
Table 1. Biological Activity against Spodoptera exigua (Beet Armyworm) for
Homobisamide Thioether Derivative (Chemset 6)
Table 2. Biological Activity against Spodoptera exigua (Beet Armyworm) for
Homobisamide Sulfone Derivative (Chemset 7)
% mortality % mortality
against S. exigua against S. exigua in
% mortality
against
S. exigua in HTS
% mortality
against S. exigua in
secondary assay
entry
Ar
R
in HTS
secondary assay
entry
Ar
C6H5
R
1
C6H5
4-Cl-C6H4
4-F-C6H4
CH3CH2CH2
CH3CH2CH2
CH3CH2CH2
50
50
33
50
50
50
33
33
17
67
17
17
67
17
83
83
67
NT
17
67
50
NT
33
50
NT
NT
NT
67
67
83
50
NT
50
0
NTa
NT
NT
NT
NT
NT
NT
NT
NT
0
1
2
CH3CH2CH2CH2
(CH3)2CH
100
100
100
100
100
100
100
83
75
0
2
C6H5
C6H5
C6H5
3
3
CH3CH2CH2
CH2dCHCH2
0
4
3,5-(Me)2C6H3 CH3CH2CH2
4
0
5
2-pyridine
3-OMeC6H4
4-pyridine
C6H5
CH3CH2CH2
CH3CH2CH2
CH3CH2CH2
CH2dCHCH2
CH2dCHCH2
CH2dCHCH2
5
4-Cl-C6H4 CH3CH2CH2CH2
4-Cl-C6H4 CH3OCH2CH2
4-Cl-C6H4 CH2dCHCH2
0
6
6
0
7
7
0
8
8
C6H5 CH3OCH2CH2
4-Cl-C6H4 CH3CH2CH2
4-Cl-C6H4 (CH3)2CH
75
0
9
4-Cl-C6H4
4-F-C6H4
9
83
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
10
97
0
3,5-(Me)2C6H3 CH2dCHCH2
NT
NT
0
2-pyridine
3-OMeC6H4
4-pyridine
C6H5
CH2dCHCH2
CH2dCHCH2
CH2dCHCH2
CH3OCH2CH2
CH3OCH2CH2
CH3OCH2CH2
Table 3. Biological Activity against Spodoptera exigua (Beet Armyworm) for
Mixed Bisamide Thioether Derivatives (Chemset 9)
NT
0
% mortality % mortality
against S. exigua against S. exigua in
4-Cl-C6H4
4-F-C6H4
0
0
entry
Ar
R
in HTS
secondary assay
3,5-(Me)2C6H3 CH3OCH2CH2
NT
NT
0
1
4-Cl-C6H4 (CH3)2CH
4-Cl-C6H4 CH3CH2CH2
100
100
100
83
83
83
83
67
67
17
17
0
0
0
2-pyridine
3-OMeC6H4
4-pyridine
C6H5
CH3OCH2CH2
CH3OCH2CH2
CH3OCH2CH2
CH3CH2CH2CH2
CH3CH2CH2CH2
CH3CH2CH2CH2
2
3
C6H5
CH3CH2CH2CH2
0
NT
NT
NT
NT
NT
NT
NT
0
4
4-Cl-C6H4 CH3CH2CH2CH2
4-Cl-C6H4 CH2dCHCH2
0
5
0
4-Cl-C6H4
4-F-C6H4
6
C6H5
C6H5
(CH3)2CH
CH3CH2CH2
0
7
38
0
3,5-(Me)2C6H3 CH3CH2CH2CH2
8
4-Cl-C6H4 (CH3)2CH2CH2
2-pyridine
3-OMeC6H4
4-pyridine
C6H5
CH3CH2CH2CH2
CH3CH2CH2CH2
CH3CH2CH2CH2
(CH3)2CH
9
C6H5
C6H5
(CH3)2CH2CH2
CH3OCH2CH2
0
10
11
12
NTa
NT
NT
4-Cl-C6H4 CH3OCH2CH2
C6H5 CH2dCHCH2
0
4-Cl-C6H4
4-F-C6H4
3,5-(Me)2C6H3 (CH3)2CH
(CH3)2CH
(CH3)2CH
0
NT
NT
NT
NT
NT
NT
0
a NT, not tested.
2-pyridine
3-OMeC6H4
4-pyridine
C6H5
(CH3)2CH
(CH3)2CH
(CH3)2CH
Eighty of the compounds synthesized as part of this study were
evaluated for insecticidal activity. The initial assays were high-
throughput screening (HTS) assays utilizing larvae of S. exigua
(beet armyworm) and A. aegypti (yellow fever mosquito). None
of the compounds prepared via Scheme 1 were active against A.
aegypti larvae. In contrast, more than half (68.8%) of the
compounds tested exhibited >67% mortality in the S. exigua
HTS assay (Tables 1-4), and nearly a fifth (18.8%) of the
compounds tested exhibited 100% mortality. Further evaluation
of the hits (>67% mortality) from the S. exigua HTS assay
involved testing in a larger format assay against two lepidopteran
species: S. exigua and H. zea (corn earworm). Although none of
the S. exigua HTS hits exhibited activity against H. zea larvae, 5
of the 44 hits (11.4%) exhibited some level of activity against S.
exigua larvae in the follow-up assay (Table 1, entry 38; Table 2,
entries 1 and 8; Table 3, entry 7; and Table 4, entry 5). Although
the activity for all five compounds never exceeded 75% mortality
at the 50 μg/cm2 dose, two of the compounds (Table 2, entries 1
and 8) exhibited LC50 values (lethal concentration for 50% of the
population) of approximately 30 and 19 μg/cm2, respectively.
Some structure-activity relationship trends can be gained from
these data. In general, it appears that the sulfones are more
efficacious than the corresponding thioethers (Table 1, chemset 6,
vs Table 2, chemset 7). One potential explanation for this
observation could be that the thioether moiety is not oxidized
tothe corresponding sulfone bythe insectlarvaeand/orthat other
parts of the molecules (i.e., amide linkages) are metabolized
before thio-oxidation occurs. An electron-withdrawing substitu-
ent on the S-aryl ring (in both the thioether and the sulfone series)
appears to be advantageous for delivering secondary assay
NT
33
100
100
NT
NT
NT
83
67
67
67
83
67
50
NT
(CH3)2CH2CH2
(CH3)2CH2CH2
(CH3)2CH2CH2
4-Cl-C6H4
4-F-C6H4
38
NT
NT
NT
0
3,5-(Me)2C6H3 (CH3)2CH2CH2
2-pyridine
3-OMeC6H4
4-pyridine
C6H5
(CH3)2CH2CH2
(CH3)2CH2CH2
(CH3)2CH2CH2
C6H5CH2
NT
0
4-Cl-C6H4
4-F-C6H4
3,5-(Me)2C6H3 C6H5CH2
C6H5CH2
C6H5CH2
0
0
2-pyridine
3-OMeC6H4
4-pyridine
C6H5CH2
C6H5CH2
C6H5CH2
0
NT
NT
a NT, not tested.
an allyl amide was present, 1H NMR analysis indicated that the
C,C-double bond remained unaffected.
Finally, we attempted a one-pot conversion of 3-(chloro-
methyl)isoxazole-4,5-dicarboxylate 1 to mixed bisamide 9 by
treating 1 sequentially with thiolate 3{1}, benzylamine 5{7} (1.1
equiv), and propan-2-amine 5{5} in methanol. Various procedur-
al modifications (equivalency, reaction temperature, reaction
time, microwave vs conventional heating, etc.) generally led to
a mixture of homobisamides and mixed bisamides which, due to
quite similar Rf values, proved difficult to separate. Conse-
quently, we found it to be more practical to effect 1 f 9 as a
three-pot/no intermediate purification procedure.

7426 J. Agric. Food Chem., Vol. 57, No. 16, 2009
Yu et al.
Table 4. Biological Activity against Spodoptera exigua (Beet Armyworm) for
Mixed Bisamide Sulfone Derivatives (Chemset 10)
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% mortality % mortality
against S. exigua against S. exigua in
entry
Ar
C6H5
R
in HTS
secondary assay
1
2
3
4
5
6
7
8
9
CH3OCH2CH2
CH2dCHCH2
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100
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83
NTa
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Supporting Information Available: 1H NMR, 13C NMR,
and LC-MS spectral data for representative library members
and crystallographic data of 9{1,1} and CIF file. This
material is available free of charge via the Internet at http://
pubs.acs.org.
Received for review May 6, 2009. Revised manuscript received July 8,
2009. Accepted July 10, 2009. We thank Dow AgroSciences, the
National Science Foundation (CHE-0614756), and the National
Institute for General Medical Sciences (GM076151) for their
financial support.