Synthesis and antifungal activity of new N-isoxazolyl-2-iodobenzamides

Article abstract of DOI:10.1016/S0014-827X(98)00108-6

N-Isoxazolyl-2-iodobenzamides 3 and 9, with a benodanil-like structure, were synthesized by refluxing in acetic acid the corresponding benzotriazinones 2 and 8 with potassium iodide for 1 h with the aim to ascertain if they were active as fungicides again

Full text of DOI:10.1016/S0014-827X(98)00108-6

Il Farmaco 54 (1999) 90–94
Synthesis and antifungal activity of new
N-isoxazolyl-2-iodobenzamides
Demetrio Raffa a,*, Giuseppe Daidone a, Benedetta Maggio a, Domenico Schillaci a,
Fabiana Plescia a, Livio Torta b
a Dipartimento di Chimica e Tecnologie Farmaceutiche, Uni6ersita` degli Studi di Palermo, 6ia Archirafi 32, I-90123 Palermo, Italy
b Istituto di Patologia Vegetale, Uni6ersita` degli Studi di Palermo, Viale delle Scienze 2, I-90128 Palermo, Italy
Accepted 5 May 1998
Abstract
N-Isoxazolyl-2-iodobenzamides 3 and 9, with a benodanil-like structure, were synthesized by refluxing in acetic acid the
corresponding benzotriazinones 2 and 8 with potassium iodide for 1 h with the aim to ascertain if they were active as fungicides
against Phytophthora citricola Saw., Botrytis cinerea Pers., Rhizoctonia sp. and Alternaria sp. Among the tested iodo derivatives,
compounds 3b and 9a possess interesting activities against the aforesaid fungal strains in several cases similar to that of benodanil
I taken as reference drug. © 1999 Elsevier Science S.A. All rights reserved.
Keywords: N-Isoxazolyl-2-iodobenzamides; Antifungal activity
(BASF), exhibited a spectrum of activities including
primarly smuts (Ustilaginales), ruts (Uredinales), and
1. Introduction
rots caused by Rhizoctonia solani [1,5,6]. It is also
known that 2-iodobenzamides bearing a heterocycle
nucleus, i.e. II (Fig. 1) are useful compounds to control
the attack of mildew [7].
Owing to facile availability in our hands of the
starting material, we synthesized the N-isoxazolyl-2-
iodobenzamides III and IV (Fig. 1), with a benodanil-
like structure, with the aim to ascertain if they were
active as agricultural fungicides.
Since the discovery of systemic antifungal properties
of carboxamides [1], several compounds, such as car-
boxin (Vitavax®) [1,2], oxycarboxin (Plantavax®) [1,3],
fenfuram (Panoram®) [1,4], and benodanil (Carilus®)
[1,5], were synthesized and introduced as agricultural
fungicides [1].
Among these, benodanil, namely N-phenyl-2-iodo-
benzamide I (Fig. 1), active principle of Carilus®
Compounds III and IV were therefore tested at 100
mg/ml against four representative genera of phytopatho-
genic fungi: Phytophthora citricola Saw. (Mastigomy-
cotina), Botrytis cinerea Pers. ex Fr. (Deuteromycotina,
Hyphomycetes), anamorph of Botryotinia fuckeliana
(De Bary) Whetzel (Ascomycotina), Rhizoctonia sp.
(Deuteromycotina, Micelia sterilia), anamorph of many
Basidiomycotina (Ceratobasidium, Thanatephorus, etc.),
and Alternaria sp. (Deuteromycotina, Hyphomycetes)
anamorph of many Ascomycotina.
Alternaria sp., besides being very common phytotoxic
fungi, can also play a considerable role in human
pathology, especially in patients with immunological
deficiency. Its pathogenic role in human pathology is
mainly expressed by asthma [8], even if cases of der-
Fig. 1. Structure of the agricultural fungicides I–IV.
* Corresponding author. Fax: +39-091-6161475.
0014-827X/99/$ - see front matter © 1999 Elsevier Science S.A. All rights reserved.
PII: S0014-827X(98)00108-6

D. Raffa et al. / Il Farmaco 54 (1999) 90–94
91
Scheme 1.
maly alternariosis, occurring during an immunosuppres-
sive therapy, are reported too [9].
at 50, 25, 12.5 mg/ml, respectively. At 6.2 mg/ml only
benodanil I showed a poor inhibition.
Against B. cinerea compound 3b exhibited good activ-
ity only at 100 mg/ml and moderate or poor activity at
50 and 25 mg/ml, respectively; compound 9a showed a
moderate activity at 100 mg/ml and a very poor inhibition
at 50 mg/ml; percentages of growth inhibition of the
reference drug were much better than those of the tested
compounds at all tested concentrations except 6.2 mg/ml.
For that concerning Rhizoctonia sp., compounds 3b
showed a good activity at 100 mg/ml and a weak activity
at 50 mg/ml, while compound 9a exhibited a poor activity
only at 100 mg/ml. Benodanil showed good activities at
100 and 50 mg/ml but not a significant percentage of
growth inhibition at lower concentrations.
2. Chemistry
N-(Isoxazol-5-yl)-2-iodo-4-R-5-R1-benzamides 3a–c
and N-(isoxazol-3-yl)-2-iodo-4-R-5-R1-benzamides 9a–c
were synthesized, as shown in Schemes 1 and 2. The
starting N-(isoxazol-3-yl)-2-nitro-4-R-5-R1-benzamides
6a–c, were prepared by condensing the proper 2-ni-
troaroyl chloride 4a–c with 5-methyl-3-aminoisoxazole
5, in chloroform solution. When compounds 6 were
treated with stannous chloride in concentrated hy-
drochloric acid the N-(isoxazol-3-yl)-2-amino-4-R-5-R1-
benzamides 7a–c were obtained. Treatment of
compounds 1 [10] and 7 with potassium nitrite in acetic
acid afforded the corresponding benzotriazinones 2a [12],
b,c and 8a–c. Finally, the 2-iodo-N-isoxazolylbenza-
mides 3 and 9 were obtained by refluxing compounds 2
and 8 in acetic acid with potassium iodide for 1 h.
Proof of structure of all new products was achieved on
the basis of microanalyses and spectroscopic evidences
(see Section 4).
Compound 3b was more active than the reference
drug against Alternaria sp. at all tested concentrations
3. Biological results and discussion
Compounds 3a–c and 9a–c were screened for antifun-
gal activity at 100 mg/ml against the following isolates of
phytopathogenic fungi: P. citricola, B. cinerea, Rhizocto-
nia sp. and Alternaria sp. Results are reported in Tables
1 and 2.
Compounds 3b and 9a which resulted the most active
compounds in the above preliminary screening (Table 1)
were tested again at lower concentrations (50, 25, 12.5,
6.2 mg/ml). The reference drug benodanil was included
in all tests as positive control (Tables 1 and 2).
Compounds 3b and 9a showed percentages of growth
inhibition against P. citricola comparable to the control
Scheme 2.

92
D. Raffa et al. / Il Farmaco 54 (1999) 90–94
Table 1
Inhibitory effects of compounds 3a–c, 9a–c and benodanil at 100 mg/ml on radial growth of some phytopathogenic fungal strains
Compound
% Inhibition
Phytophthora citricola
Botrytis cinerea
Rhizoctonia sp.
Alternaria sp.
3a
3b
3c
9a
9b
9c
16.6
38.0
ns
36.3
ns
nsa
ns
52.0
ns
27.8
ns
ns
ns
43.0
ns
17.7
ns
ns
58.5
11.1
44.3
11.1
12.5
67.1
ns
36.0
Benodanil
63.7
31.5
a ns, not significant i.e. below 10% of inhibition; values are the mean of at least three determinations.
Table 2
Inhibitory effects of compounds 3b, 9a and benodanil on radial growth of selected fungal strains
Compound
Concentration
% Inhibition
(mg/ml)
Phytophthora citricola
Botrytis cinerea
Rhizoctonia sp.
Alternaria sp.
3b
50
25
12.5
6.2
50
30.5
25.2
24.7
nsa
23.1
20.6
18.9
ns
34.1
22.3
18.0
18.0
39.5
16.9
ns
ns
11.8
ns
ns
ns
55.2
45.7
24.8
ns
19.2
ns
ns
ns
ns
ns
ns
ns
53.8
ns
31.2
29.4
11.2
ns
ns
ns
ns
ns
ns
ns
9a
25
12.5
6.2
50
25
12.5
6.2
Benodanil
ns
ns
ns
ns
a ns, not significant i.e. below 10% of inhibition; values are the mean of at least three determinations.
except 6.2 mg/ml, while compound 9a showed a weak
activity only at 100 mg/ml.
Iodo derivatives 3a–c and 9a–c were also evaluated
for their in vitro growth inhibiting activity against the
yeasts C. albicans ATCC 10231 and C. tropicalis ATCC
13803, but no compound showed activity at the highest
tested concentration (200 mg/ml).
To summarize, compounds 3b and 9a possess interest-
ing activities against some fungal strains of agricultural
interest, in several cases similar to the reference drug.
Further investigations, like in vivo research and toxicity,
are in progress.
obtained in CDCl3 or DMSO-d6 using a Bru¨ker AC-E
250 MHz spectrometer (using TMS as the internal
standard). Elemental analyses (C, H, N) performed by
the Dipartimento di Scienze Farmaceutiche, Universita`
di Catania, were within 90.4% of the theoretical values.
4.1.1. 2-Nitrobenzoylchloride 4a–c
Compound 4a is commercially available. Substituted
2-nitrobenzoylchlorides 4b,c were obtained by refluxing
the proper 2-nitrobenzoic acid derivative (0.04 mol) with
thionyl chloride (28.9 ml) for 5 h [11].
4.1.2. 3-(3-Methylisoxazol-5-yl)-1,2,3-benzotriazin-
4(3H)-ones 2b,c
Compounds 2b,c were prepared by general methods
previously described [12]. The physical and spectroscopic
data are reported in Table 3.
4. Experimental
4.1. Chemistry
4.1.3. N-(3-Methylisoxazol-5-yl)-2-iodobenzamides
3a–c
A solution of 0.01 mol of the proper benzotriazinones
2a [12], b,c in glacial acetic acid (200 ml) was refluxed for
1 h with 0.02 mol of potassium iodide.
Melting points were determined on a Bu¨chi tottoli
apparatus and are uncorrected; IR spectra were recorded
with a Jasco IR-810 spectrophotometer as a Nujol mull
supported on a NaCl disk; 1H NMR spectra were

D. Raffa et al. / Il Farmaco 54 (1999) 90–94
93
Table 3
Physical and spectroscopic data for compounds 2b,c, 3a–c, 6a–c, 7a–c, 8a–c and 9a–c
Com-
M.p. (°)a
Formula
Yield (%)
IR (Nujol) (cm−1
)
1H NMR (l)b
pound
2b
2c
3a
187–188
225–226
146-149
C11H7N4O2Cl 85
C11H7N4O2Cl 88
1710 (CO)
1700 (CO)
2.44 (s, 3H, CH3); 6.67 (s, 1H, isoxazole H-4); 7.78–8.41 (a set
of signals, 3H, aromatic protons).
2.42 (s, 3H, CH3); 6.65 (s, 1H, isoxazole H-4); 7.95–8.38 (a set
of signals, 3H, aromatic protons).
2.14 (s, 3H, CH3); 6.37 (s, 1H, isoxazole H-4); 7.16–7.91 (a set
of signals, 4H, aromatic protons); 9.51 (s, 1H, exchangeable
NH).
C11H9N2O2I
33
3320–3040 (NH);
1680 (CO)
3b
3c
6a
6b
6c
7a
7b
7c
157–159
181–183
177–179
214–216
162–163
188–189
202–203
198–200
C11H8N2O2ClI 20
C11H8N2O2ClI 39
3310–3100 (NH);
1680 (CO)
2.19 (s, 3H, CH3); 6.37 (s, 1H, isoxazole H-4); 7.38–7.88 (a set
of signals, 4H, aromatic protons); 9.54 (s, 1H, exchangeable
NH).
2.21 (s, 3H, CH3); 6.38 (s, 1H, isoxazole H-4); 7.12–7.83 (a set
of signals, 3H, aromatic protons); 9.38 (s, 1H, exchangeable
NH).
2.42 (s, 3H, CH3); 6.74 (s, 1H, isoxazole H-4); 7.77–8.18 (a set
of signals, 4H, aromatic protons); 11.66 (s, 1H, exchangeable
NH).
2.42 (s, 3H, CH3); 6.74 (s, 1H, isoxazole H-4); 7.80–8.26 (a set
of signals, 3H, aromatic protons); 11.73 (s, 1H, exchangeable
NH).
3320–3100 (NH);
1680 (CO)
C11H9N3O4
43
3300–3020 (NH);
1695 (CO)
C11H8N3O4Cl 53
C11H8N3O4Cl 70
3400–3010 (NH);
1680–1670 (CO)
3300–3000 (NH);
1695 (CO)
2.43 (s, 3H, CH3); 6.74 (s, 1H, isoxazole H-4); 7.82–8.22 (a set
of signals, 3H, aromatic protons); 11.73 (s, 1H, exchangeable
NH).
C11H11N3O2
90
3480–3040 (NH and 2.40 (s, 3H, CH3); 6.55–7.77 (a set of signal, 7H, aromatic
NH2); 1665 (CO)
protons, isoxazole H-4, exchangeable NH2); 10.92 (s, 1H, ex-
changeable NH).
C11H10N3O2Cl 90
C11H10N3O2Cl 60
3500–3020 (NH and 2.40 (s, 3H, CH3); 6.53–7.75 (a set of signal, 6H, aromatic
NH2); 1680 (CO)
protons, isoxazole H-4, exchangeable NH2); 10.99 (s, 1H, ex-
changeable NH).
3500–3020 (NH and 2.40 (s, 3H, CH3); 6.68–7.82 (a set of signal, 6H, aromatic
NH2); 1680 (CO)
1720–1700 (CO)
1710 (CO)
protons, isoxazole H-4, exchangeable NH2); 11.07 (s, 1H, ex-
changeable NH).
2.56 (s, 3H, CH3); 6.63 (s, 1H, isoxazole H-4); 7.86–8.45 (a set
of signals, 4H, aromatic protons).
2.56 (s, 3H, CH3); 6.60 (s, 1H, isoxazole H-4); 7.81–8.40 (a set
of signals, 3H, aromatic protons).
2.56 (s, 3H, CH3); 6.08 (s, 1H, isoxazole H-4); 7.96–8.65 (a set
of signals, 3H, aromatic protons).
8a
8b
8c
9a
173–174
202–203
208–209
147–148
C11H8N4O2
70
C11H7N4O2Cl 65
C11H7N4O2Cl 44
1700 (CO)
C
11H9N2O2I
43
3220–3100 (NH);
1685–1675 (CO)
2.35 (s, 3H, CH3); 6.88 (s, 1H, isoxazole H-4); 7.16–7.93 (a set
of signals, 4H, aromatic protons); 10.17 (s, 1H, exchangeable
NH).
9b
9c
170–172
178–179
C11H7N4O2ClI 50
C11H7N4O2ClI 61
3300–3100 (NH);
1705 (CO)
2.37 (s, 3H, CH3); 6.86 (s, 1H, isoxazole H-4); 7.43–7.93 (a set
of signals, 3H, aromatic protons); 10.33 (s, 1H, exchangeable
NH).
2.38 (s, 3H, CH3); 6.89 (s, 1H, isoxazole H-4); 7.15–7.86 (a set
of signals, 3H, aromatic protons); 10.90 (s, 1H, exchangeable
NH).
3300–3100 (NH);
1705 (CO)
a Crystallization solvent: ethanol.
b CDCl3 for compounds 2b,c, 3a–c, 8a–c, and 9a–c. DMSO-d6 for compounds 6a–c and 7 a–c.
4.1.5. 3-(5-Methylisoxazol-3-yl)-1,2,3-benzotriazin-
4(3H)-ones 8a–c and N-(5-methylisoxazol-3-yl)-2-
iodobenzamides 9a–c
All these compounds were synthesized by the same
procedure previously employed for 2b,c and 3a–c, re-
spectively (see Table 3).
After this time, 500 ml of water were added and the
precipitate which separated out was collected, air
driedand crystallized from ethanol to give 3. Com-
pounds 3a–c are listed in Table 3.
4.1.4. N-(5-Methylisoxazol-3-yl)-2-nitrobenzamides
6a–c and N-(5-methylisoxazol-3-yl)-2-aminobenza-
mides 7a–c
4.2. Biology
Compounds 6 and 7 were obtained by preparative
methods previously reported [13] (see Table 3).
The in vitro antifungal activity against isolates of
plant pathogenic fungi was evaluated by an agar dilu-

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D. Raffa et al. / Il Farmaco 54 (1999) 90–94
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suitable volume of each substance (in a solution of
DMSO) was added to 20 ml of molten agar (at 50°C)
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