Bleaching activity of 4-phenyl-3-(substituted benzylthio)-4H-1,2,4-triazoles.

Article abstract of DOI:10.1271/bbb.66.1671

A variety of 4-aryl- and 4-alkyl-3-(substituted benzylthio)-4H-1,2,4-triazoles were prepared and evaluated for their bleaching activity by the lettuce seedling test. Among the series of tested compounds, 4-(3-fluorophenyl)-3-(4-trifluoromethylbenzylthio)-

Full text of DOI:10.1271/bbb.66.1671

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Bleaching Activity of 4-Phenyl-3-(substituted
benzylthio)-4H-1,2,4-triazoles
Naotaka YAMADAa, Daisuke KUSANOa & Eiich KUWANOa
a Department of Applied Genetics and Pest Management, Faculty of Agriculture, Kyushu
University Higashi-ku, Fukuoka 812-8581, Japan
Published online: 22 May 2014.
To cite this article: Naotaka YAMADA, Daisuke KUSANO & Eiich KUWANO (2002) Bleaching Activity of 4-Phenyl-3-
(substituted benzylthio)-4H-1,2,4-triazoles, Bioscience, Biotechnology, and Biochemistry, 66:8, 1671-1676, DOI: 10.1271/
bbb.66.1671
To link to this article: http://dx.doi.org/10.1271/bbb.66.1671
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Biosci. Biotechnol. Biochem., 66 (8), 1671–1676, 2002
Bleaching Activity of 4-Phenyl-3-(substituted benzylthio)-4H-1,2,4-triazoles
Naotaka YAMADA,† Daisuke KUSANO, and Eiich KUWANO
Department of Applied Genetics and Pest Management, Faculty of Agriculture, Kyushu University,
Higashi-ku, Fukuoka 812-8581, Japan
Received January 30, 2002; Accepted March 23, 2002
A variety of 4-aryl- and 4-alkyl-3-(substituted ben-
zylthio)-4H-1,2,4-triazoles were prepared and evaluated
for their bleaching activity by the lettuce seedling test.
Among the series of tested compounds, 4-(3-‰uoro-
derivatives inhibit
the accumulation of
There have been few reports on the
z
-carotene desaturase, resulting in
-carotene in treated plants.
-carotene
z
z
desaturase inhibition of 1,2,4-triazole derivatives,
except for amitorole which aŠects the lipid environ-
ment of desaturase in the thylakoid membrane result-
phenyl)-3-(4-tri‰uoromethylbenzylthio)-4
zole (39) exhibited the highest bleaching activity, caus-
ing complete bleaching symptoms at 10 . In the dark
condition, compound 39 inhibited the formation of
such carotenoids as -carotene, violaxanthin, neoxan-
thin and lutein, resulting in the formation of -carotene,
phytoene, phyto‰uene and -zeacarotene, which were
not detected in the untreated control. Treatment by
compound 39 at 50 resulted in the amount of ac-
cumulated -carotene being seven-fold higher than that
of phytoene, phyto‰uene and -zeacarotene. These
results suggest that compound 39 might have interfered
with desaturation, especially -carotene desaturation,
during carotenoid biosynthesis.
H-1,2,4-tria-
m
M
ing in the accumulation of phytoene and
z-caro-
tene.7–9) In the present paper, we describe details of
the structure-bleaching activity relationship of 4-aryl-
b
z
and 4-alkyl-3-(substituted benzylthio)-4H-1,2,4-tria-
zoles, and the eŠect of these compounds on the
colored carotenoid content of lettuce seedlings.
b
mM
z
Materials and Methods
b
Chemicals. All the 4-aryl- and 4-alkyl-3-(substitut-
ed benzylthio)-4H-1,2,4-triazoles used in this study
z
were synthesized according to the same method
reported previously.4) The general procedure in-
volved cyclization of 4-aryl- or 4-alkyl-1-formyl-3-
thiosemicarbazides that has been prepared by
treating formylhydrazine with aryl- or alkyl isothioc-
yanates. The resulting 4-aryl- and 4-alkyl-3-mercap-
Key words: bleaching; z-carotene; b-carotene; triazole
Bleaching herbicides interfere with the formation
of colored carotenoids that play an essential role by
photoprotecting chlorophyll against photooxidative
destruction by singlet oxygen. A target of the many
bleaching herbicides is phytoene desaturase on the
carotenoid biosynthetic pathway (Fig. 1).1) The inhi-
bitors of phytoene desaturase, such as ‰uridone and
‰urtamone, cause an accumulation of phytoene.2,3)
We have previously reported that 4-(4-
to-4
benzyl halide to aŠord to 4-aryl- or 4-alkyl-3-ben-
zylthio-4 -1,2,4-triazole. The following procedure
for the preparation of 4-(3-‰uorophenyl)-3-(4-
tri‰uoromethylbenzylthio)-4 -1,2,4-triazole (39) is
H-1,2,4-triazole was alkylated by an appropriate
H
H
typical. To a solution of 2.35 g of formylhydrazine in
20 ml of dry tetrahydrofuran was added 5.0 g of
3-tri‰uorophenyl isothiocyanate. After re‰uxing for
6 h, the insoluble product [4-(3-‰uorophenyl)-1-for-
myl-3-thiosemicarbazide] was collected by ˆltration.
A solution of the product and 2.58 g of potassium
hydroxide in 50 ml of water was stirred for 2 h at
chlorophenyl)-3-propargylthio-4
showed bleaching activity against lettuce seedlings,
and that 3-benzylthio-4-phenyl-4 -1,2,4-triazole (2)
caused some bleaching symptoms. It was clear that a
treatment by compound 1 at 50 resulted in a
greatly reduced
H-1,2,4-triazole (1)
H
m
M
b
-carotene content in radish seedlings
9
70 C. After cooling, the solution was acidiˆed with a
with the accumulation of a large amount of
2 N HCl solution. The resulting precipitate was col-
lected by ˆltration, washed with water and recrystal-
lized from hexane and ethyl acetate to aŠord 3.80 g
phytoene.4) We have recently found that compound 2
decreased the
tion of both phytoene and
dlings. In light-grown seedlings treated with 250
of compound 2, the accumulation of -carotene was
b
-carotene content with the accumula-
z
-carotene in lettuce see-
(60
triazole. To a mixture of 0.5 g of this 4-(3-‰uoro-
phenyl)-3-mercapto-4 -1,2,4-triazole and 2.0 g of
z
) of 4-(3-‰uorophenyl)-3-mercapto-4H-1,2,4-
m
M
z
H
2-fold higher than that of phytoene. It is known that
potassium carbonate in 20 ml of acetone was added
0.67 g of 4-tri‰uoromethylbenzylbromide. After stir-
some dihydropyrone5) and 6-methylpyrimidine6)
†
To whom correspondence should be addressed. Fax: +81-92-642-2858; E-mail: n-yamada
＠
agr.kyushu-u.ac.jp

1672
N. YAMADA et al.
Fig. 1. Pathway for Carotenoid Biosynthesis.
ring night over at room temperature, the solution was
concentrated in vacuo. The residue was extracted
with diethylether, successively washed with a 1 N
NaOH solution, water and brine, and dried over
Na2SO4. After evaporating the solution, the residue
was recrystallized from hexane and ethyl acetate to
yield 0.84 g of 4-(3-‰uorophenyl)-3-(4-tri‰uoro-
cotyledons was carried out by a modiˆcation of the
method described previously.4) On a ˆlter paper in a
Petri dish (15 cm in diameter) was poured 3 ml of an
acetone solution of the test compound. After
evaporating the solvent, 100 seeds were placed on the
ˆlter paper and cultivated in 15 ml of deionized water
at 25
9
C under a 12-h photoperiod. After 4 days, the
methylbenzylthio)-4
H
-1,2,4-triazole (93
C. H-NMR (400 MHz, CDCl3, TMS)
: 4.52 (2H, s), 6.95–7.03 (2H, m), 7.18–7.23 (5H,
m), 7.44–7.55 (4H, m), 8.28 (1H, s). Anal. Found: C,
z
). Melting
cotyledons were cut and stored at „40
9
C. A known
1
point: 94–95
d
9
amount of the cotyledons was ground with quartz in
2 ml of iced methanol in the dark. The extract was
ˆltered, and the ˆltrate topped up to 10 ml with
methanol. Two milliliter of the solution was taken
out, and chlorophyll content was determined by its
absobance at 665 and 650 nm, according to the
method described by MacKinney. To extract the
colored carotenoids, to the remaining methanol solu-
tion (8.0 ml), 3 ml of a methanol solution containing
54.61; H, 3.11; N, 12.01
z
. Calcd. for C16H11F4N3S:
C, 54.39; H, 3.14; N, 11.89.
Bioassay.
Lettuce seedling test. Lettuce (Lactuca sativa L
.
cv. Sacramento) seeding test was conducted by the
method described previously.10) After 4 days of culti-
vation, the bleaching activity was estimated on a
scale of 0–4 according to the following ordinal cate-
gories: 0, no visual change compared with the con-
trol; 1, faint bleaching at the edges of the leaves; 2,
intermediate between categories 1 and 3; 3, small
green area remaining on the leaves; 4, complete
bleaching. The bleaching activity from each treat-
ment is indicated by the average result from 60 tested
seedings.
22
was added, and the mixture was incubated at 60
for 20 min. The colored carotenoids were partitioned
into 10 diethyl ether (v v) in petroleum ether, and
z z
KOH (the ˆnal KOH concentration was 6 )
9C
z
W
the ether solution was successively washed with water
and brine, and dried (Na2SO4). After concentrating
the ether solution, the residue was dissolved in 200
of methanol, and 20 of the solution was
chlomatographed by HPLC on a 4.6 250 mm 5-
ml
m
l
×
m
m
Spherisorb ODS-II column. The pigments were sepa-
rated by gradient elution chromatography according
to a modiˆcation of Yi Li's method.11) The elution
program consisted of a linear gradient of water and a
Determination of pigments. Extraction of the chlo-
rophyll and colored carotenoids from lettuce

Bleaching Activity of 3,4-Disubstituted 4
H
-1,2,4-triazoles
1673
Table 1. Bleaching Activity of 4-Phenyl-3-substituted 4
triazoles against Lettuce Seedlings
H
-1,2,4-
Table 2. Bleaching Activity of 3-Benzylthio-4-substituted 4H-
1,2,4-triazoles against Lettuce Seedlings
Bleaching activity
Bleaching activity
Concentration (m )
M
Concentration (mM)
No.
250
50
No.
250
50
11
12
13
14
15
16
17
allyl
0
0
0
1
0
1
0
0
0
0
0
0
n
-butyl
2
3
1
tert-butyl
cyclohexyl
a
-naphthyl
benzyl
3
4
2
3
0
0
0
0
0
0
0
1
0
0
0
0
0
0
b
-
phenylethyl
1
0
Bleaching was visually evaluated (Activity rating; 0, no bleaching; 1, faint
bleaching; 2, intermediate between categories 1 and 3; 3, deˆnite bleaching;
4, complete bleaching).
5
structure activity relationship between 3-alkylthio-
4-(substituted phenyl)-4H-1,2,4-triazoles and the
6
bleaching activity on 4-day-old lettuce seedlings. In
the 4-phenyl-4 -1,2,4-triazole series, 3-propar-
gylthio and 3-propylthio analogs showed the com-
H
7
pleted bleaching activity at 250
m , and the activities
M
8
were higher than that of other 3-alkylthio analogs.
Since compound 2 caused some bleaching symptoms,
several related 4-phenyl-4H-1,2,4-triazole analogs
9
which have aryl group at 3-position were prepared
and tested for their bleaching activity against lettuce
10
seedlings (Table 1). 3-
showed bleaching activity comparable to that of
compound 2 at 250 , while 3- -phenylethylthio
analog 3 had low activity. No activity was apparent
with 3- -ethylbenzylthio (5), 3-phenyl-thio ester (6),
3-phenacylthio (7) and 3-phenyl-thiocarbamate (8)
analogs, even at 250 . Oxidation of the sulˆde
a-Methylbenzylthio analog 4
Bleaching was visually evaluated (Activity rating: 0, no bleaching; 1, faint
bleaching; 2, intermediate between categories 1 and 3; 3, deˆnite bleaching;
4, complete bleaching).
m
M
b
a
mixture of acetonitrile methanol 2-propanol (7:2:1
m
M
W
W
(v v v)) from 88
z
to 100
z
of the organic mixture
group of compound 2 to a sulfone group (compound
9) and conversion of the sulfur atom to an oxygen
atom (compound 10) completely eliminated the activ-
m , indicating that the benzylthio group at
the 3-position on the triazole ring was necessary for
activity.
WW
over 18 min at 1.5 ml min. This system could
W
separate very well the various xanthophylls and caro-
tenes at the same time. The carotenoids were simul-
taneously detected by a diode array (Shimadzu CO.,
Japan) at ˆve diŠerent wavelengths, and identiˆed by
their retention times and electron absorption spectra.
Quantitative analyses of the carotenoids were con-
ducted on the areas under selected peaks by integrat-
ing at each wavelength with the appropriate extinc-
tion coe‹cients, as described previously.11–13) The
determined extinction coe‹cients were as follows:
phytoene, 863 at 290 nm; phyto‰uene, 1466 at
ity at 250
M
We also examined whether the phenyl group at the
4-position on the triazole ring in compound 2 could
be replaced by other substituents (Table 2). The 4-
allyl (11), 4-
naphthyl (15) analogs were completely inactive. The
4-cyclohexyl (14), 4-benzyl (16) and 4- -phenylethyl
(17) analogs had faint bleaching activity at 250
n-butyl (12), 4-tert-butyl (13) and 4-a-
b
mM.
350 nm;
1940 at 427 nm;
z
-carotene, 2331 at 425 nm;
b
-zeacarotene,
This result indicates that the presence of the 4-phenyl
group was signiˆcant for higher bleaching activity.
Thus, among this series of 4-aryl- and 4-alkyl-3-
substituted-4H-1,2,4-triazoles, 3-benzylthio-4-phenyl
analog 2 exhibited the highest activity.
b
-carotene, 2600, violaxanthin,
2500, neoxanthin, 2500 and luteine, 2600, at all
445 nm. Each determination is the mean of ˆve
independent measurements.
Further modiˆcation was made by introducing
various substituents on the two benzene rings of com-
pound 2 (Table 3). The introduction of some sub-
stituents on the benzene ring of the benzylthio moiety
tended to increase the activity. Substitution at the
Results and Discussion
Bleaching activity
We have previously described the studies on the

1674
N. YAMADA et al.
Table 3. Bleaching Activity of the 4-Phenyl-3-benzylthiol-4H-
1,2,4-triazole Derivatives against Lettuce Seedlings
Bleaching activity
Concentration (mM)
No.
R1
R2
250
50
10
5
1
2
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
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
2-Cl
2-Me
2-MeO
3-Cl
3-Me
3-MeO
4-Cl
4-Me
4-Et
4-MeO
4-CF3O
4-EtO
4-F
4-CF3
3,4-diCl
4-CF3
4-CF3
4-CF3
4-CF3
4-CF3
4-CF3
4-CF3
4-CF3
4-CF3
4-CF3
4-CF3
4-CF3
3
3
4
4
4
3
4
4
4
4
4
4
4
4
4
4
0
0
3
4
4
4
4
4
4
3
4
2
1
1
3
2
3
3
3
4
4
4
4
4
4
2
4
3
0
0
0
0
0
0
0
2
2
1
2
4
1
0
4
2
Scheme
1
0
0
0
2
0
0
showed slightly higher activity than that of com-
pound 31, whereas the other 3-substituted phenyl
analogs, such as the 3-methylphenyl (37), 3-methox-
yphenyl (38) and 3-trifuluoromethylphenyl (40) ana-
logs, had lower activity and showed no bleaching
0
1
symptoms at 5
m . 3-Chlorophenyl analog 36 had
M
3
0
slightly lower activity than that of compound 31, and
the additional introduction of a chlorine atom
(compound 44) led to greatly reduced activity. In
conclusion, the 4-tri‰uoromethylbenzyl moiety and
3-‰uorophenyl group on the triazole ring appeared to
be essential for high bleaching activity.
2-Cl
2-Me
2-MeO
3-Cl
3-Me
3-MeO
3-F
3-CF3
4-Cl
4-Me
4-MeO
3,4-diCl
3
4
4
4
4
3
4
2
1
1
0
3
3
3
4
2
2
0
0
0
2
0
0
3
0
0
1
2
It is noteworthy that the introduction of a methyl
group into the 5-position of the triazole ring (com-
pound 45) in compound 24 induced a reduction in the
potency, and 2-(4-chlorobenzylthio)-1-phenylimida-
zole (46) caused no visible bleaching symptoms at
250
m
M
(data are not shown). These results suggest
Bleaching was visually evaluated (Activity rating: 0, no bleaching; 1, faint
bleaching; 2, intermediate between categories 1 and 3; 3, deˆnite bleaching;
4, complete bleaching).
that the 1,2,4-triazole ring of 4-phenyl-3-(substituted
benzylthio)-4H-1,2,4-triazole played an important
role in exhibiting the bleaching activity.
para position on the benzene ring exhibited relatively
high activity. The 4-chloro (24), 4-methyl (25), 4-
methoxy (27), and 4-ethoxy (29) analogs showed
almost the same activity, causing complete bleaching
EŠect on carotenoids content
Table 4 shows the in‰uence of representative com-
pounds 1 and 39 on the chlorophyll and carotenoid
contents of lettuce seedlings cultivated under light or
dark conditions. Under light conditions, both com-
pounds 1 and 39 markedly reduced chlorophyll and
symptoms at 50
mM. The additional introduction of a
chlorine atom at the 3-position on the benzene ring of
compound 24 slightly decreased the activity (com-
pound 32). The most favorable substituents were 4-
tri‰uoromethoxy and 4-tri‰uoromethyl (compounds
28 and 31, respectively), both compounds showing
such carotenoids as b-carotene, violaxanthin, neox-
anthin and luteine. The amount of violaxanthin,
neoxanthin and luteine diminished approximately in
proportion to the decrease of
b-carotene in the
complete bleaching injury at 10
m
M
.
presence of compounds 1 and 39. Compound 1
caused a large accumulation of phytone in lettuce
seedlings, as has been observed for radish seedlings.4)
On the other hand, in lettuce seedlings treated with
Based on the foregoing results, the 3-(4-tri‰uoro-
methyl)benzyl moiety of compound 31 was selected
as the partial structure necessary for high activity,
and some substituents were introduced to the phenyl
group at the 4-position. The introduction of a chloro
(compounds 33 and 41), methyl (compounds 34 and
42) or methoxy (compounds 35 and 43) substituent to
the phenyl group at the ortho or para position on the
benzene ring of compound 31 caused a decrease in
the bleaching activity, in particulars, the 2-chlo-
rophenyl (18) and 2-methylphenyl (19) analogs were
1
m
M
of compound 39 under light conditions, a rela-
tively large amount of -carotene was accumulated
z
which was not detected in the untreated control.
However, at higher concentrations, the accumulation
z-carotene decreased. The accumulation of
phytoene caused by compound 39 was much less than
that found with compound 1.
In contrast to the results found under light condi-
tions, treatment of compound 39 in darkness resulted
of
inactive at 250
mM. Only 3-‰uorophenyl analog 39

Bleaching Activity of 3,4-Disubstituted 4
H
-1,2,4-triazoles
1675
Fig. 2. Chemical Structures of
z-Carotene Desaturase Inhibitors.
in a signiˆcant increase in the
z-carotene content,
particularly at higher concentrations. This result sug-
gests that z-carotene was very sensitive to photodes-
truction in the light. Compound 39 caused the ac-
cumulation of phytoene as well, but its amount was
much lower compared to
z
-carotene, suggesting that
-carotene
desaturation step rather than phytoene desaturation.
compound 39 predominantly inhibited
z
Neurosporene formed by the desaturation of z-
carotene was not detected in the lettuce seedlings not
treated and treated with compound 39, while the
accumulation of
b-zeacarotene, which is a mono-
cyclized product of neurosporene, was observed to
some extent by treating with compound 39. At lower
concentrations revealing some bleaching injury, the
b
-zeacarotene content was higher than that of
phytoene.
Although a number of bleaching herbicides have
been found to inhibit the desaturation of phytoene,
only a few compounds are known to interfere with
the z
-carotene desaturation reaction.7) It has been
reported that 4-(2-chlorobenzyloxy)-6-methyl-2-
propylpyrimidine (J-334) caused an accumulation of
14)
z
-carotene in Dunaliella bardawil
.
However, low
J-334 concentrations induced a large amount of
b-
zeacarotene, while at higher concentrations, it block-
ed the desaturation of phytoene as well as z-carotene.
The herbicidal compound, ethyl-cis-5-methyl-6-
ethyl-2-phenyl-5,6-dihydropyran-4-one-3-carboxy-
late (LS 80707) has been shown to interfere with z-
carotene desaturase in the blue-green alga.15) In this
case, a large accumulation of phytoene was observed
at the same time. We found that compound 39, with
increasing concentration, accumulated
a much larger amount than those of phytoene,
phyto‰uene and -zeacarotene, indicating that the
desaturation of -carotene was preferentially inhibit-
ed. 4-Phenyl-3-(substituted benzylthio)-4 -1,2,4-
z-carotene in
b
z
H
triazoles in this article might be a reasonable lead for
generating of a new bleaching herbicide as well as an
eŠective tool to elucidate the structural and function-
al features of z-carotene desaturase.
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