Discovery of ectoparasiticidal hydrazonotrifluoromethanesulfonanilides

Article abstract of DOI:10.1016/j.bmcl.2009.11.054

A series of hydrazonotrifluorosulfonanilide derivatives were synthesized and evaluated for in vitro activity against the ectoparasites Ctenocephalides felis and Rhipicephalus sanguineus. Some compounds with excellent activity against tick were identified.

Full text of DOI:10.1016/j.bmcl.2009.11.054

Bioorganic & Medicinal Chemistry Letters 20 (2010) 649–652
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Discovery of ectoparasiticidal hydrazonotrifluoromethanesulfonanilides
Abdelselam Ali a, Petr Fisara b, Jamie A. Freemont a, Stella Kyi a, Adam G. Meyer a, Andrew G. Riches a,
,
*
Roger M. Sargent b, David G. Sawutz c, Kathleen A. Turner a, Kevin N. Winzenberg a, Qi Yang a
a CSIRO Molecular and Health Technologies, Bag 10, Clayton South, Vic 3169, Australia
b Intervet Schering-Plough Animal Health, 26 Artisan Rd, Seven Hills, NSW 2147, Australia
c Schering-Plough Research Institute, 2015 Galloping Hill Road, Kenilworth, NJ 07033-1300, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of hydrazonotrifluorosulfonanilide derivatives were synthesized and evaluated for in vitro activ-
ity against the ectoparasites Ctenocephalides felis and Rhipicephalus sanguineus. Some compounds with
excellent activity against tick were identified.
Received 9 October 2009
Revised 12 November 2009
Accepted 16 November 2009
Available online 2 December 2009
Ó 2009 Elsevier Ltd. All rights reserved.
Keywords:
Trifluoromethanesulfonanilide
Ectoparasiticide
Ctenocephalides felis (cat flea)
Rhipicephalus sanguineus (brown dog tick)
Trifluoromethanesulfonanilide (TFMS) derivatives display insec-
ticidal and acaricidal properties1 which are exerted through uncou-
pling of oxidative phosphorylation in mitochondria.2 As part of a
program to discover new drugs to control commercially significant
ectoparasites on companion animals,3 we recently reported the dis-
covery of alkoxy and aryloxy iminoalkyl (oxime ether) TFMS deriva-
tives (e.g., 1–3, Fig. 1) with significant in vitro insecticidal and
acaricidal activity.4 As an extension to that study, compound 4 was
prepared as a prototype hydrazone analog of the oxime ethers and
logs of 4 (compounds 46 and 47) were prepared by condensation of
phenylhydrazine with nitroaryl enone 48,12 using a modification of
the method of Mannich and Lammering,13 followed by nitro reduc-
tion14 and amine triflation to give pyrazoline 46. Dehydrogenation
of 46 with DDQ gave pyrazole 47.
Taking active compound 4 as the lead compound for an SAR study
of hydrazone TFMS derivatives, we first varied R1, while maintaining
R2 = Me and R3 = Ph. Phenyl and cyclohexyl groups (compounds 7
and 8, respectively) both gave inferior flea activity to methyl.
By fixing R1 as methyl or ethyl and R3 as phenyl, the effect of
varying R2 was next examined. While R2 = H (compounds 9 and
10) gave poor flea activity, various small alkyl groups (compounds
11–13) gave good flea activity. Compounds 11 and 12 were also
effective in the rapid tick assay, with the latter demonstrating an
excellent LD50. In contrast, allyl and propargyl substituents (com-
pounds 14 and 15, respectively) gave poor flea activity, while ben-
zyl (compound 16) gave good flea activity but poor tick activity.
gave 100% mortality in a single-dose (1.26
cat flea (Ctenocephalides felis) activity and 98% mortality in a rapid
screen (10 g/tick) against brown dog tick (Rhipicephalus sanguin-
l
g/cm2) rapid screen for
l
eus).5 By virtue of their additional site of substitution, hydrazones
enable exploration of considerably greater chemical space than the
corresponding oxime ethers. The 4-chloro-TFMS pharmacophore
present in the most active oxime ether TFMS derivatives was main-
tained in the current study. The substituents on the hydrazone moi-
ety were systematically varied in an effort to optimize parasiticidal
activity. Compounds were initially screened against cat flea, then se-
lected active compounds were subjected to a rapid dog tick screen
and, where appropriate, LC50 (flea) and LD50 (tick) determination.5
Hydrazone TFMS derivatives 4 and 7–45 were synthesized by
condensation of ketones 56,7 with hydrazines 68 as indicated in
Scheme 1 and Table 1.9,10 The hydrazones were obtained either
as single isomers or mixtures of geometrical isomers.11 Cyclic ana-
CF3SO2
CF3SO2
NH R1
NH Me Me
N
O
R2
N
N
Cl
Cl
1 R1 = Me, R2 = (CH2)2OMe
2 R1 = Et, R2 = 4-Chlorobenzyl
3 R1 = Et, R2 = 3,4-diCl-Ph
4
* Corresponding author. Tel.: +61 3 9545 2540; fax: +61 3 9545 2446.
E-mail address: andrew.riches@csiro.au (A.G. Riches).
Figure 1. Oxime ether trifluoromethanesulfonanilides and prototype hydrazone
analog.
0960-894X/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2009.11.054

650
A. Ali et al. / Bioorg. Med. Chem. Lett. 20 (2010) 649–652
Table 1
Activity of hydrazonotrifluoromethanesulfonanilides 4, 7–47 against C. felis (C.f.) and R. sanguineus (R.s.)
CF3SO2
NH R1 R2
N
N
R3
Cl
4, 7-47
C.f. % mortality 24 h C.f. LC50b (ng/cm2) R.s. % mortality 24 hb R.s. LD50
(lg/tick)
Compound Method of preparationa R1
R2
R3
b
4
7
8
9
10
A
A
A
A
B
Me
Ph
Me
Me
Ph
Ph
Ph
Ph
2,4-DiCl–
Ph
100
59
98
Cyclohexyl Me
Me
Et
14
H
H
20c
5c
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
C, A
C, A
A, D
C, A
C, A
C, A
A
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Et
Ph
Ph
Ph
Ph
100
100
100
59
38
100
66
100
75
n-Pr
i-Pr
Allyl
1.2
Propargyl Ph
Bn
Me
Me
Me
Me
Et
Et
Me
Et
Me
Me
Me
Me
Et
Me
Me
Et
Ph
Me
33
E, F
E, F
Cyclopentyl 85
98
73
95
97
100
100
95
100
100
100
100
98
95
90
83
100
78
1.01
1.29
1.4
Cyclohexyl
4-Cl–Ph
4-Cl–Ph
4-F–Ph
4-Br–Ph
4-Br–Ph
4-CF3–Ph
4-Me–Ph
3-Cl–Ph
3-F–Ph
3-F–Ph
3-CF3–Ph
2-Cl–Ph
2-Cl–Ph
2-F–Ph
3,4-DiCl–
Ph
100
A, D
A, D
A, D
A, D
A, D
A, D
A, D
A, D
A, D
A, D
G, H
C, A
A, D
A, D
A, D
100
100
100
100
100
100
100
100
100
100
98
52.3
42.7
27.3
5.6
24.8
14.6
13.4
7.46
2.6
2.0
2.1
0.68
100
89
100
99
Me
Me
8.66
35.3
1.6
3.0
35
36
37
38
39
A, D
A, D
A, D
A, D
A, D
Me
Me
Me
Me
Me
Me
Me
Et
3,5-DiCl–
Ph
2,3-DiCl–
Ph
2,4-DiCl–
Ph
2,6-DiCl–
Ph
100
100
100
100
75
33.0
30.8
95
70
90
40
3.1
4.0
8.5
n-Pr
Me
Me
2,5-DiCl–
Ph
2-Pyridyl
40
41
42
43
44
45
46
47
I, A
A
A
A
J
A
K
L
Me
Me
Me
Me
Me
Me
30
CH2CH2OCH2CH2
–(CH2)5–
100
100
23
100
48
95
78
0.75
0.64
–(CH2)6–
–(CH2)4–
93
0.74
CH2CH2N(Me)CH2CH2
CH2CH2
CH@CH
Ph
Ph
37
43
Fipronil
Permethrin
0.6–1.0
0.13–0.35
a
b
c
See Scheme 1 for reaction conditions.
No entry indicates that the compound was not assayed.
Measured at 8 h.
With R1 fixed as methyl and R2 as methyl or ethyl, the effect of
potency (as measured by LD50) was decreased relative to the
monohaloaryl compounds. Replacement of the phenyl ring with
the 2-pyridyl group (compound 40) gave poor activity in the ra-
pid flea screen.
varying R3 was examined. Poor activity was observed when
R3 = methyl (compound 17), while cycloalkyl groups in this posi-
tion (compounds 18 and 19) showed good flea and excellent tick
activity. Several 2, 3 or 4-monosubstituted aryl rings gave good
flea and tick activity (compounds 20–33) with 29 and 33 being
representative of compounds which exhibited good potency
across both dose response assays, and 30 giving the best tick
activity. Various dichloro substituted aryl groups (compounds
34–39) were generally effective in both rapid screens, but tick
Compounds 41, 42 and 44, in which R2 and R3 formed morpho-
line, piperidine and pyrrolidine rings, respectively, were effective
in the rapid flea screen and (together with 30) showed the best tick
activity of all the alkylhydrazones in Table 1. In contrast to com-
pound 4, conformationally-restricted, cyclic analogs 46 and 47
gave poor activity in the rapid flea assay.

A. Ali et al. / Bioorg. Med. Chem. Lett. 20 (2010) 649–652
651
R2
NH
Boc
E
NH2
H
N
N
H
CF3SO2
NH R1 R2
Me
NH
P, S
H2N
R2
N
H2N
X
N
X
H2N
N
X
5
H2N
I
O
M, N, O,
Q, T
O
C, D, G
R2
CF3SO2
CF3SO2
H
49
NH R1
Cl
NH R1 R2
N
X
50-72
R
N
N
R3
N
H2N
O
R3
N
O
6
Scheme 2. Reagents and conditions:15 (M) EtOH, 100 °C, sealed tube, 16 h; (N)
EtOH, rt, 16 h; (O) EtOH, 45 °C, 16 h; (P) (i) HCO2H/H2O (1:1), rt; (ii) Ac2O, 100 °C;18
(iii) HCl, rt, 5 h;19 (Q) toluene, reflux (Dean–Stark); (R) (i) DMF, R2X, rt to 60 °C; (ii)
EtOH/H2O (3:2), reflux 6 h; (iii) EtOH, rt, 16 h; (S) (i) (R2 = H) acrylonitrile; (ii) acid
chloride, THF, NEt3, À70 °C to rt; (T) 1-aminohydantoinÁHCl, K2CO3, EtOH, 80 °C,
10 h.
A, B, D, F, H, J
Cl
Cl
5
4, 7-45
CF3SO2
CF3SO2
NH
NH
Cl
NO2
O
N
N
N
Ph
Ph
L
N
K
Substituted phenacylhydrazones 51–54 showed good activity
against flea and excellent activity against ticks. Replacement of the
R2 alkyl group with hydrogen was not as detrimental to the flea
activity of the phenacylhydrazones 55 and 56 as it was to the
alkylhydrazones in Table 1. When R2 was a phenyl group (compound
57) poor flea activity was obtained, while R2 = cyanoethyl gave good
tick control over a range of substituents X (compounds 58–62).
Semicarbazones 63 and 64 (R2 = H) showed poor activity in the rapid
flea assay. Alkoxycarbonyl hydrazones 65–69 retained high flea
activity whilst delivering outstanding tick activity, with compounds
Cl
Cl
47
46
48
Scheme 1. Reagents and conditions:15 (A) EtOH, rt; (B) arylhydrazineÁHCl, KOAc,
EtOH, rt; (C) NaOH (aq), n-Bu4NCl, R2I, rt;16 (D) (i) NaH, DMF; (ii) R2I, rt, 16 h; (E) (i)
cycloalkyl ketone, MeOH, rt; (ii) Na(CN)BH3 HOAc, H2O;17 (iii) R2I, K2CO3, CH3CN,
microwave, 120 °C; (iv) 6 N HCl, rt; (F) 6ÁHCl, NaHCO3, toluene, reflux (Dean–Stark);
(G) (i) arylhydrazineÁHCl, PhCHO, K2CO3, EtOH; (ii) NaH, DMF, R2X; (iii) 12% HCl,
reflux (Dean–Stark); (iv) NaOMe, MeOH; (H) toluene, reflux (Dean–Stark); (I) 2-
chloropyridine, K2CO3, i-PrOH, microwave, 180 °C, 18 h; (J) 6ÁHCl, K2CO3, EtOH, rt;
(K) (i) phenylhydrazine, EtOH, rt; (ii) SnCl2, EtOH or H2, Pd–C, HOAc, HCl (aq); (iii)
Tf2O, C5H5N; (L) DDQ, CH2Cl2.
65 (LD50 = 0.39 lg/tick) and 66 (LD50 = 0.28 lg/tick) showing
in vitro efficacy comparable to that of Permethrin. Oxazolidinones
70 and 71 and hydantoin 72 were active against both parasites.
The excellent cat flea and dog tick dose response results shown
by several compounds in this study provide encouragement that a
single compound may be developed to possess potent insecticidal
and acaricidal activity. In particular, the potent acaricides 65 and
66 are candidates for subsequent in vivo evaluation as ectoparasi-
In an effort to further optimize the insecticidal and/or acaricidal
activity of hydrazone TFMS derivatives, the scope of the study was
extended by condensing ketone TFMS 5 with a selection of acy-
lhydrazines, semicarbazides, carbazates and N-amino heterocycles
49 to give compounds 50–72 (Scheme 2 and Table 2).
Table 2
Activity of acyl hydrazonotrifluoromethanesulfonanilides 50–72 against C. felis (C.f.) and R. sanguineus (R.s.)
CF3SO2
NH R1 R2
N
X
N
O
Cl
50-72
Method of preparationa R1
R2
X
C.f. % mortality 24 h
C.f. LC50 (ng/cm2) R.s. % mortality 24hb R.s. LD50
(lg/tick)
b
b
Compound
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
M
N
O
N
O
N
O
P, Q
S, N
S, N
S, N
S, N
S, N
N
Me Me
Me Me
Ph
66
4-Cl-Ph
4-Cl-Ph
2,4-DiCl–Ph
2,4-DiCl–Ph
4-Cl-Ph
2-Cl-Ph
Me
100
100
100
88
100
86
22
100
73
51.3
39.3
71.8
42.3
54.8
100
100
100
100
75
1.8
1.49
1.6
2.0
7.1
Et
Me
Me Me
Et
Et
Et
Me
H
H
Me Ph
Me CH2CH2CN Me
Me CH2CH2CN Et
Me CH2CH2CN i-Pr
Me CH2CH2CN n-Pentyl
Me CH2CH2CN Ph
90
0.53
100
100
89
100
100
88
0.71
0.56
Me
Me
H
H
NHPh
NH(4-CF3–Ph) 18
17
N
65
66
67
68
69
70
71
72
R
R
R
N
R, N
N
Q
Me Et
Et Et
Me Et
OMe
OMe
OEt
OEt
OEt
100
100
100
95
100
100
95
0.39
0.28
0.64
0.69
0.54
0.99
100
100
97
100
100
100
100
Me Me
Et
Et
Me
Et
Me
–CH2CH2O–
–CH2CH2O–
–CH2CONH–
100
100
T
43.8
1.7
Fipronil
Permethrin
0.6–1.0
0.13–0.35
a
See Scheme 2 for reaction conditions.
No entry indicates that the compound was not assayed.
b

652
A. Ali et al. / Bioorg. Med. Chem. Lett. 20 (2010) 649–652
7. Meyer, A. G.; Winzenberg, K. N.; Sawutz, D. G.; Liepa, A. J. PCT Int. Appl. WO06/
034333, 2006; Chem. Abstr. 2006, 144, 331134.
8. Hydrazine starting materials were commercially available or were prepared
according to Scheme 1/Table 1.
ticides. In view of the mechanism of action of the compounds re-
ported herein, it is difficult to discern clear trends in the SAR data.
It is likely that subtle structural differences which affect the phys-
icochemical and pharmacokinetic properties of the hydrazone
TFMS derivatives give rise to the observed differences in activity.20
9. Winzenberg, K. N.; Meyer, A. G.; Yang, Q.; Riches, A. G. U.S. Pat. Appl. Publ. US
2007/238,700; Chem. Abstr. 2007, 147, 421326.
10. All synthetic intermediates and final products were characterized by 1H NMR
and MS.
11. Upon attempted separation of isomers, individual isomers were observed to re-
equilibrate to isomeric mixtures.
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may generate toxic metabolites, several hydrazones were tested on dogs for up
to 28 days with no adverse effect.