Green Synthesis of Potential Antifungal Agents: 2-Benzyl Substituted Thiobenzoazoles

Article abstract of DOI:10.1021/acs.jafc.7b04130

A series of benzyl-substituted thiobenzoazoles were synthesized by an environmentally friendly approach, to search for new antifungal agrochemicals. Compounds were prepared starting from 2-mercaptobenzoazoles, using KOH, benzyl halides, and water, resulting in a simple and ecological method. New antifungals were tested against a group of phytopathogenic fungi. Two compounds showed an interesting activity against Botrytis cinerea, Fusarium oxysporum, and Aspergillus spp.: 2-((4-(trifluoromethyl)benzyl)thio)benzo[d]thiazole, 3ac, and 2-((4-methylbenzyl)thio)benzo[d]thiazole, 3al. Thus, 3ac and 3al can be considered as broad spectrum antifungal agents. Furthermore, two new compounds, 2-((4-iodobenzyl)thio)benzo[d]thiazole, 3aj, and 2-(benzylthio)benzo[d]oxazole, 3ba, showed better inhibitory effect against Botrytis cinerea and Fusarium oxysporum when compared to the commercial fungicide Captan. Thus, 3aj and 3ba can be considered reduced-spectrum antifungals.

Full text of DOI:10.1021/acs.jafc.7b04130

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Article
Green Synthesis of Potential Antifungal
Agents: 2-Benzyl Substituted Thiobenzoazoles.
María Sol Ballari, Natividad Herrera Cano, Abel Gerardo Lopez,
Daniel A. Wunderlin, Gabriela Feresin, and Ana Noemi Santiago
J. Agric. Food Chem., Just Accepted Manuscript • DOI: 10.1021/acs.jafc.7b04130 • Publication Date (Web): 03 Nov 2017
Downloaded from http://pubs.acs.org on November 3, 2017
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Green Synthesis of Potential Antifungal Agents: 2-Benzyl Substituted Thiobenzoazoles.
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María Sol Ballari,† Natividad Herrera Cano,‡ Abel Gerardo Lopez,§ Daniel Alberto Wunderlin,#
Gabriela Egly Feresín,‡ and Ana Noemí Santiago*,†
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†INFIQC, Departamento de Química Orgánica, Facultad de Ciencias Químicas, CONICET,
Universidad Nacional de Córdoba, Ciudad Universitaria, 5000, Córdoba, Argentina. Phone: +54
351 5353867. Eꢀmail: santiago@fcq.unc.edu.ar
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‡Instituto de Biotecnología, Facultad de Ingeniería, Universidad Nacional de San Juan, CONICET.
Av. Libertador General San Martín 1109 (O), 5400, San Juan, Argentina.
§ICTA, Facultad de Ciencias Exactas, Físicas y Naturales, Universidad Nacional de Córdoba,
Ciudad Universitaria, 5000, Córdoba, Argentina.
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#ICYTAC, CONICET and Departamento de Química Orgánica, Facultad de Ciencias Químicas,
Universidad Nacional de Córdoba, Ciudad Universitaria, 5000, Córdoba, Argentina.
* Corresponding Author (Tel: +54 351 5353867; Eꢀmail: santiago@fcq.unc.edu.ar)
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ABSTRACT
A series of benzylꢀsubstituted thiobenzoazoles were synthesized by an environmentally friendly
approach, to search for new antifungal agrochemicals. Compounds were prepared starting from 2ꢀ
mercaptobenzoazoles, using KOH, benzyl halides and water, resulting in a simple and ecological
method. New antifungals were tested against a group of phytopathogenic fungi. Two compounds
showed an interesting activity against Botrytis cinerea, Fusarium oxysporum and Aspergillus spp.:
2ꢀ((4ꢀ(trifluoromethyl)benzyl)thio)benzo[d]thiazole, 3ac, and 2ꢀ((4ꢀ
methylbenzyl)thio)benzo[d]thiazole, 3al. Thus, 3ac and 3al can be considered as broad spectrum
antifungal agents. Furthermore, two new compounds, 2ꢀ((4ꢀiodobenzyl)thio)benzo[d]thiazole, 3aj,
and 2ꢀ(benzylthio)benzo[d]oxazole, 3ba, showed better inhibitory effect against Botrytis cinerea
and Fusarium oxysporum when compared to the commercial fungicide Captan. Thus, 3aj and 3ba
can be considered reducedꢀspectrum antifungals.
KEYWORDS: synthesis, antifungal activity, benzothiazole, benzoxazole.
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INTRODUCTION
Major crops are worldwide affected by several pests and diseases. In Argentina, as in other regions
of the world, fungi are important agricultural pests. Both wheat (Triticum spp.) and maize (Zea
mays L.) are among the most important crops in Argentina, either for local consumption or for
export. These crops may be contaminated by a variety of toxigenic mold species, mainly by
Aspergillus,1 Fusarium,2 Penicillium3 and Botrytis,4 causing health concerns and significant
economic losses. Botrytis cinerea is a necrotrophic fungal pathogen that attacks over 200 different
plant species, causing serious losses in the grape production and wine industry.5,6 Fusariosis is a
disease caused by several species of the genus Fusarium, which affects the major crops, such as
wheat,7 corn, soybean,8,9 barley and other small grains, causing great economic losses. Micotoxins
(aflatoxins,10 ochratoxins,11,12 among others) produced by Aspergillus spp. can cause economic and
health problems since they contaminate foods and feeds for both humans and animals. Chemical
protection against fungal disease is based on the use of protective fungicides. One of the most used
fungicides is Captan (Nꢀ(trichloromethylthio)ꢀ4ꢀcyclohexeneꢀ1,2ꢀdicarboximide) (Figure 1A). It has
been classified as carcinogenic by the International Agency for Research on Cancer,13 being also
considered as sensitizing and strong irritant of eyes, skin and respiratory tract.14–22 Such adverse
effects trigger the need for designing new antifungals, more effective and less toxic than the current
commercial compounds.
Some benzoazoles such as benzimidazole, benzothiazole and benzoxazole are often incorporated as
building blocks in medicinal chemistry studies.23 Benzothiazole derivatives find use in various
branches of chemical research, for instance, in polymer chemistry, dyes, drugs, among others
(Figure 1B).23 The benzoxazole scaffold is a constituent of several natural products (Figure 1C),24–26
and is often incorporated in drug design. Among the various biological applications reported for
these heterocycles, the fungicidal activity27–32 is recurrent. Thus, compounds derived from
benzimidazole, benzothiazole and benzoxazole have been extensively used in the clinic, for
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preventing and treating various types of diseases, showing low toxicity, high bioavailability, good
biocompatibility and curative effects.33
Different synthetic methodologies to obtain 2ꢀbenzylꢀsubstituted thiobenzoazoles have been
reported. Among these synthetic strategies, it is worth to mention reactions between 2ꢀ
mercaptobenzoazoles and benzyl halides. These reactions have different issues regarding green
approaches, such as heterogeneous catalysts,34 metalic sodium35 or refluxing acetone36 employment.
Other alternatives imply reactions between 2ꢀmercaptobenzoazoles and benzyl alcohols. For this
route, most conditions imply usage of environmentally problematic or hazardous solvents37 or
reactants, such as SOCl2,38 ClPPh2,39 dioxane,40 dichloromethane,38,39 acetonitrile,41 among others.
Other synthetic strategies involve use of different benzyl sources, such dibenzyl carbonate,42
oligomeric benzylsulfonium salts,43 or toluene derivatives.44 Also, there are alternatives for the
benzoazole insertion, such as the microwaveꢀassisted twoꢀstep reactions between oꢀhaloꢀanilines,
potassium Oꢀethyl dithiocarbonate (which form 2ꢀmercptobenzothiazole as intermediate) and
benzyl bromides,45 or reaction between 3Hꢀbenzoazoleꢀ2ꢀthione (easily interconvertible 2ꢀ
mercaptobenzoazole isomer) and Oꢀbenzylꢀisoureas.40 Summarizing, some of these methodologies
involve unsafe conditions or utilization of environmentally problematic or hazardous solvents.
There are also cases where atom economy is compromised by adding the benzyl source in excess. It
is as well remarkable that many of these methodologies require of previous preparation of substrates
and transition metal or organoꢀcatalysis employment. We have recently reported a new synthesis of
2ꢀaryl thiobenzothiazoles using two methodologies (photostimulation or microwave assistance).
These new antifungals were tested by the diffusion method against B. cinerea, showing an
interesting activity.28 Thus, the main goal of this work was to obtain 2ꢀbenzylꢀsubstituted
thiobenzothiazoles and thiobenzoxazoles by a simple and ecoꢀfriendly methodology, starting from
readily available materials and using water46 as solvent. Additionally, evaluation of the difference in
the antifungal activity when changing the substituted benzyl groups in the new synthesized
compounds was of interest. Thus, the activity of these new compounds against different
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phytopathogenic fungi, such as Botrytis cinerea, Fusarium oxysporum and Aspergillus spp. was
tested.
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MATERIALS AND METHODS
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Chemicals. 2ꢀmercaptobenzothiazole, 2ꢀmercaptobenzoxazole, benzyl halides, KOH, were
commercially available (Sigma, St. Louis, MO) and used as received. Ultrapure water (MilliQ) was
employed for all reactions.
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Microorganisms. New compounds were assayed against: a) Botrytis cinerea isolated from Vitis
vinifera cv. Chardonnay, cultivated in Province of San Juan, Argentina; b) Aspergillus ustus (PNꢀ
S4); c) Aspergillus terreus (M16C); d) Fusarium oxysporum (M15ꢀPa) (strains bꢀd were isolated
from soil samples from the Province of San Juan, Argentina); e) Aspergillus fumigatus (ATTC
26934); g) Aspergillus niger (ATCC 9029). The microorganisms were grown in Czapek medium
(Sigma, St. Louis, MO), enriched with a solution of mineral salts, at 30 °C for Aspergillus spp. and
Fusarium oxysporum, and at 22 °C for Botrytis cinerea, for a period of 5 ꢀ 10 days.
Reactions of benzyl halides with 2-mercaptobenzoazoles. 2ꢀmercaptobenzothiazole or 2ꢀ
mercaptobenzoxazole (0.6 mmol), KOH (0.5 mmol) and benzyl halide (0.5 mmol) were vigorously
mixed in 2 mL of ultrapure water in a sealed glass vessel, letting to react for 30 minutes at 50 °C.
Afterwards, the reaction mixture was extracted three times with ethyl acetate (2 mL each). The
combined organic layer was washed three times with ultrapure water (2 mL each), dried with
anhydrous Na2SO4, analyzed by gas chromatography (GC). The product was purified by circular
layer chromatography (CLC) using pentane/ethyl acetate (90:10) as mobile phase.
Antifungal susceptibility test. Antifungal activity was determined by applying the broth
microdilution method, in accordance to Clinical and Laboratory Standard Institute (CLSI) (M27ꢀA3
for yeasts and M38ꢀA2 for molds). Assays were performed in enriched Czapek broth. The inoculum
employed was 1 ꢀ 5 × 105 conidia/mL. Stock solutions of tested compounds were prepared in
DMSO to give serial twoꢀfold dilutions to final concentrations of 3.1 ꢀ 100 mg/L (final DMSO
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concentration ≤2%). Microtiter plates were incubated at 30 ºC for Aspergillus and Fusarium spp.,
and at 22 ºC for Botrytis cinerea in a moist and dark chamber. Inhibitory concentrations were
recorded after 48 h for Aspergillus and Fusarium spp. and after 72 h for B. cinerea, according to the
control fungal growth. A positive control of the commercial antifungal Captan and solvent control
using 2% aqueous DMSO were included. All tests were run in triplicate. The 50% Inhibitory
concentration (IC50) was defined as the minimum concentration of the compound that resulted in
50% inhibition of the fungal growth. IC50 values were calculated by linear regression plots of
%(inhibition) vs ln(concentration), considering 50% inhibition.
2-(benzylthio)benzo[d]thiazole, 3aa:35 Yellow solid, mp: 37.8 ꢀ 38.7 °C. 1HꢀNMR (400 MHz,
CDCl3), δ (ppm): 4.60 (s, 2H), 7.24 ꢀ 7.34 (m, 4H), 7.40ꢀ7.46 (m, 3H), 7.74 (d, J = 7.9 Hz, 1H),
7.90 (d, J = 8.1 Hz, 1H). 13CꢀNMR (100 MHz, CDCl3), δ (ppm): 37.73, 121.02, 121.59, 124.30,
126.08, 127.77, 128.73, 129.16, 135.36, 136.21, 153.19, 166.42. MS (EI+) m/z (%): 259.20 (9),
258.20 (14), 257.15 (79), 224.00 (72), 165.95 (8), 107.90 (13), 91.00 (100), 89.10 (5), 65.05 (33),
63.00 (9). HRMS (ESI): (M+Na): C14H11NS2Na, calculated: 280.0225, found: 280.0233.
2-((4-fluorobenzyl)thio)benzo[d]thiazole, 3ab: Yellow solid, mp: 66.3 ꢀ 67.0 °C. 1HꢀNMR (400
MHz, CDCl3), δ (ppm): 4.57 (s, 2H), 7.00 (tt, J = 8.7 Hz, J = 2.1 Hz, 2H), 7.30 (ddd, J = 8.1 Hz, J =
7.3 Hz, J = 1.2 Hz, 1H), 7.40 ꢀ 7.44 (m, 3H), 7.74 (ddd, J = 7.9 Hz, J = 1.1 Hz, J = 0.5 Hz, 1H),
7.89 (ddd, J = 8.1 Hz, J = 1.0 Hz, J = 0.5 Hz, 1H). 13CꢀNMR (100 MHz, CDCl3), δ (ppm): 36.88,
115.60 (d, J2FꢀC = 21.68 Hz), 121.04, 121.60, 124.39, 126.11, 130.81 (d, J3FꢀC = 8.2 Hz), 132.16 (d,
J4FꢀC = 3.2 Hz), 135.38, 153.12, 162.30 (d, J1FꢀC = 246.5 Hz), 165.99. 19FꢀNMR (376.5 MHz,
CDCl3), δ (ppm): ꢀ144.33 (tt, JoFꢀH = 8.7 Hz, JmFꢀH = 4.5 Hz). MS (EI+) m/z (%): 276.20 (5), 275.15
(32), 242.10 (22), 166.00 (3), 109.10 (100), 107.80 (8), 89.10 (1), 83.10 (13), 63.05 (4). HRMS
(ESI): (M+Na): C14H10NS2FNa, calculated: 298.0131, found: 298.0138.
2-((4-(trifluoromethyl)benzyl)thio)benzo[d]thiazole, 3ac: Yellow solid, mp: 87.8 ꢀ 88.3 °C. 1Hꢀ
NMR (400 MHz, CDCl3), δ (ppm): 4.64 (s, 2H), 7.31 (td, J = 7.6 Hz, J = 1.1 Hz, 1H), 7.43 (td, J =
7.7 Hz, J = 1.2 Hz, 1H), 7.58 (s, 4H), 7.75 (dd, J = 8.0 Hz, J = 0.5 Hz, 1H), 7.90 (dd, J = 8.1 Hz, J
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= 0.5 Hz, 1H). 13CꢀNMR (100 MHz, CDCl3), δ (ppm): 36.84, 121.08, 121.64, 124.03 (q, J1
=
FꢀC
272.2 Hz), 124.49, 125.62 (q, J3FꢀC = 3.7 Hz), 126.16, 129.46 (q, J4FꢀC = 0.5 Hz), 129.92 (q, J2
=
FꢀC
32.5 Hz), 135.44, 140.80 (q, J5FꢀC = 0.8 Hz), 153.04, 165.41. 19FꢀNMR (376.5 MHz, CDCl3), δ
(ppm): ꢀ62.58 (s). MS (EI+) m/z (%): 327.20 (9), 326.25 (14), 325.10 (95), 292.10 (66), 223.10 (17),
180.10 (10), 165.95 (21), 159.05 (100), 133.05 (3), 121.90 (14), 119.05 (11), 109.10 (47), 107.95
(29), 89.05 (7), 63.05 (10). HRMS (ESI): (M+Na): C15H10NS2F3Na, calculated: 348.0099, found:
348.0109.
4-((benzo[d]thiazol-2-ylthio)methyl)benzonitrile, 3ad:35 Yellow solid, mp: 64.0 ꢀ 65.0 °C. 1Hꢀ
NMR (400 MHz, CDCl3), δ (ppm): 4.62 (s, 2H), 7.31 (td, J = 7.6 Hz, J = 1.1 Hz, 1H), 7.43 (td, J =
7.7 Hz, 1.2 Hz, 1H), 7.56 ꢀ 7.61 (m, 4H), 7.75 (d, J = 8.0 Hz, 1H), 7.89 (d, J = 8.1, 1H). 13CꢀNMR
(100 MHz, CDCl3), δ (ppm): 36.83, 111.55, 118.58, 121.11, 121.66, 124.60, 126.21, 129.86,
132.41, 135.48, 142.44, 152.94, 164.94. MS (EI+) m/z (%): 284.20 (12), 283.25 (19), 282.15 (99),
250.25 (18), 249.05 (100), 179.95 (15), 166.00 (26), 122.00 (16), 116.10 (85), 108.00 (31), 90.10
(10), 89.00 (37), 76.05 (3), 63.05 (13). HRMS (ESI): (M+Na): C15H10N2S2Na, calculated:
305.0178, found: 305.0180.
2-((4-nitrobenzyl)thio)benzo[d]thiazole, 3ae:35 Yellow solid, mp: 89.7 ꢀ 91.4 °C. 1HꢀNMR (400
MHz, CDCl3), δ (ppm): 4.66 (s, 2H), 7.31 (td, J = 7.6 Hz, J = 0.8 Hz, 1H), 7.43 (td, J = 7.7 Hz, J =
0.9 Hz, 1H), 7.63 (d, J= 8.6 Hz, 2H), 7.74 (d, J = 8.0 Hz, 1H), 7.89 (d, J = 8.1 Hz, 1H), 8.16 (d, J =
8.7 Hz, 2H). 13CꢀNMR (100 MHz, CDCl3), δ (ppm): 36.47, 121.13, 121.67, 123.84, 124.63, 126.24,
130.00, 135.48, 144.54, 147.36, 152.91, 164.77. MS (EI+) m/z (%): 304.20 (12), 303.25 (16),
302.15 (100), 269.10 (21), 223.10 (50), 179.95 (13), 165.95 (22), 136.10 (9), 122.10 (13), 110.10
(2), 108.00 (28), 106.05 (18), 90.10 (29), 89.05 (29), 78.10 (36), 63.05 (14). HRMS (ESI): (M+Na):
C14H10N2S2O2Na, calculated: 325.0076, found: 325.0089.
2-((2-nitrobenzyl)thio)benzo[d]thiazole, 3af:35 Brown solid, mp: 67.1 ꢀ 68.5 °C. 1HꢀNMR (400
MHz, CDCl3), δ (ppm): 4.95 (s, 2H), 7.28 (td, J = 7.6 Hz, J = 1.0 Hz, 1H), 7.39 ꢀ 7.44 (m, 2H), 7.54
(td, J = 7.6 Hz, J = 1.2 Hz, 1H), 7.7 (d, J = 7.7 Hz, 1H), 7.81 (dd, J = 7.7 Hz, J = 1.0 Hz, 1H), 7.90
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(d, J = 8.1 Hz, 1H), 8.05 (dd, J = 8.2 Hz, J = 1.0 Hz, 1H). 13CꢀNMR (100 MHz, CDCl3), δ (ppm):
34.20, 121.05, 121.59, 124.39, 125.24, 126.07, 128.72, 132.75, 133.35, 133.52, 135.57, 148.37,
152.92, 165.67. MS (EI+) m/z (%): 303.25 (2), 302.20 (11), 223.10 (12), 168.10 (12), 167.00 (100),
165.95 (5), 136.15 (15), 122.10 (8), 110.10 (1), 108.10 (18), 106.15 (4), 89.10 (11), 78.10 (41),
77.10 (11), 65.10 (13), 63.05 (10). HRMS (ESI): (M+Na): C14H10N2S2O2Na, calculated: 325.0076,
found: 325.0084.
2-((2-chlorobenzyl)thio)benzo[d]thiazole, 3ag: Yellow oil. 1HꢀNMR (400 MHz, CDCl3), δ (ppm):
4.73 (s, 2H), 7.17 ꢀ 7.24 (m, 2H), 7.29 (td, J = 7.7 Hz, J = 1.1 Hz, 1H), 7.38 ꢀ 7.44 (m, 2H), 7.59
(dd, J = 6.9 Hz, J = 2.3 Hz, 1H), 7.74 (dd, J = 7.9 Hz, J = 0.5 Hz, 1H), 7.91 (dd, J = 8.1 Hz, J = 0.4
Hz, 1H). 13CꢀNMR (100 MHz, CDCl3), δ (ppm): 35.26, 121.03, 121.60, 124.33, 126.05, 127.01,
129.19, 129.74, 131.30, 134.40, 134.44, 135.50, 153.14, 166.08. MS (EI+) m/z (%): 292.80 (24),
291.00 (44), 257.75 (30), 255.95 (83), 223.05 (31), 165.85 (8), 126.85 (43), 124.95 (100), 122.05
(6), 107.85 (15), 98.95 (10), 90.05 (8), 89.00 (29), 62.95 (14). HRMS (ESI): (M+Na):
C14H10NS2ClNa, calculated: 313.9835, found: 313.9845.
2-((4-bromobenzyl)thio)benzo[d]thiazole, 3ah:36 Yellow solid, mp: 80.3 ꢀ 81.0 °C. 1HꢀNMR (400
MHz, CDCl3), δ (ppm): 4.54 (s, 2H), 7.28 ꢀ 7.34 (m, 3H), 7.40 ꢀ 7.45 (m, 3H), 7.74 (dd, J = 8.0 Hz,
J = 0.5 Hz, 1H), 7.89 (dd, J = 8.2 Hz, J = 0.4 Hz, 1H). 13CꢀNMR (100 MHz, CDCl3), δ (ppm):
36.92, 121.05, 121.61, 121.71, 124.42, 126.13, 130.82, 131.81, 135.40, 135.56, 153.08, 165.74. MS
(EI+) m/z (%): 337.05 (70), 335.10 (60), 304.00 (20), 302.10 (17), 223.15 (53), 171.00 (84), 169.05
(100), 166.00 (19), 143.00 (1), 122.10 (12), 108.00 (24), 90.10 (52), 89.05 (40), 63.05 (18). HRMS
(ESI): (M+Na): C14H10NS2BrNa, calculated: 357.9330, found: 357.9346.
2-((2-bromobenzyl)thio)benzo[d]thiazole, 3ai:36 Yellow oil. 1HꢀNMR (400 MHz, CDCl3), δ
(ppm): 4.74 (s, 2H), 7.13 (td, J = 7.7 Hz, J = 1.7 Hz, 1H), 7.24 (td, J = 7.6 Hz, J = 1.2 Hz, 1H), 7.29
(td, J = 7.1 Hz, J = 1.1 Hz, 1H), 7.43 (ddd, J = 8.3 Hz, J = 7.3 Hz, J = 1.2 Hz, 1H), 7.58 (dd, J = 8.0
Hz, J = 1.1 Hz, 1H), 7.61 (dd, J = 7.7 Hz, J = 1.6 Hz, 1H), 7.74 (dd, J = 8.0 Hz, J = 0.5 Hz, 1H),
7.91 (dd, J = 7.6 Hz, J = 0.4 Hz, 1H). 13CꢀNMR (100 MHz, CDCl3), δ (ppm): 37.91, 121.04,
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121.59, 124.32, 124.83, 126.05, 127.66, 129.38, 131.36, 133.05, 135.51, 136.12, 153.13, 166.03.
MS (EI+) m/z (%): 336.90 (27), 334.95 (28), 301.80 (2), 257.10 (18), 256.05 (100), 224.25 (15),
223.05 (79), 170.90 (61), 168.95 (81), 166.00 (27), 122.05 (21), 108.05 (36), 90.05 (75), 89.05 (57),
63.00 (31). HRMS (ESI): (M+Na): C14H10NS2BrNa, calculated: 357.9330, found: 357.9341.
2-((4-iodobenzyl)thio)benzo[d]thiazole, 3aj:36 Yellow solid, mp: 68.3 ꢀ 69.8 °C. 1HꢀNMR (400
MHz, CDCl3), δ (ppm): 4.52 (s, 2H), 7.20 (d, J = 8.3 Hz, 2H), 7.29 (td, J = 7.6 Hz, J = 1.1 Hz, 1H),
7.42 (td, J = 7.7 Hz, J = 1.1 Hz, 1H), 7.63 (d, J = 8.3 Hz, 2H), 7.74 (d, J = 7.9 Hz, 1H), 7.88 (d, J =
8.1 Hz, 1H). 13CꢀNMR (100 MHz, CDCl3), δ (ppm): 37.01, 93.25, 121.05, 121.61, 124.42, 126.12,
131.05, 135.40, 136.24, 137.78, 153.08, 165.74. MS (EI+) m/z (%): 384.15 (9), 383.05 (75), 350.05
(14), 223.05 (34), 217.00 (100), 165.95 (19), 122.05 (12), 108.00 (22), 90.05 (58), 89.05 (45), 63.00
(18). HRMS (ESI): (M+Na): C14H10NS2INa, calculated: 405.9192, found: 405.9202.
2-((2-iodobenzyl)thio)benzo[d]thiazole, 3ak: Yellow solid, mp: 48.2 ꢀ 49.4 °C. 1HꢀNMR (400
MHz, CDCl3), δ (ppm): 4.72 (s, 2H), 6.95 (td, J = 7.7 Hz, J = 1.5 Hz, 1H), 7.35 ꢀ 7.21 (m, 2H), 7.42
(td, J = 8.3 Hz, J = 1.1 Hz, 1H), 7.60 (dd, J = 7.6 Hz, J = 1.4 Hz, 1H), 7.73 (d, J = 8.0 Hz, 1H), 7.85
(dd, J = 7.9 Hz, J = 0.8 Hz, 1H), 7.91 (d, J = 8.2 Hz, 1H). 13CꢀNMR (100 MHz, CDCl3), δ (ppm):
42.78, 100.75, 121.04, 121.61, 124.33, 126.06, 128.55, 129.43, 130.68, 135.53, 139.30, 139.76,
153.14, 165.88. MS (EI+) m/z (%): 383.05 (35), 258.15 (11), 257.20 (18), 256.10 (100), 224.20
(19), 223.10 (92), 217.00 (84), 165.90 (10), 122.10 (11), 121.10 (16), 108.05 (18), 90.15 (98), 89.10
(48), 63.05 (20). HRMS (ESI): (M+Na): C14H10NS2INa, calculated: 405.9192, found: 405.9196.
2-((4-methylbenzyl)thio)benzo[d]thiazole, 3al:41 Yellow solid, mp: 49.5 ꢀ 50.7 °C. 1HꢀNMR (400
MHz, CDCl3), δ (ppm): 2.32 (s, 3H), 4.57 (s, 2H), 7.13 (d, J = 7.8 Hz, 2H), 7.28 (td, J = 7.6 Hz, J =
0.8 Hz, 1H), 7.33 (d, J = 7.9 Hz, 2H), 7.42 (td, J = 7.7 Hz, J = 4.6 Hz, 1H), 7.74 (d, J = 7.9 Hz, 1H),
7.89 (d, J = 8.1 Hz, 1H). 13CꢀNMR (100 MHz, CDCl3), δ (ppm): 21.16, 37.57, 121.00, 121.56,
124.25, 126.05, 129.06, 129.42, 133.03, 135.34, 137.57, 153.22, 166.62. MS (EI+) m/z (%): 272.20
(8), 271.10 (48), 238.20 (28), 223.05 (3), 165.95 (5), 122.10 (3), 107.95 (6), 106.15 (12), 105.05
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(100), 79.10 (15), 77.00 (17), 65.10 (2), 63.05 (3). HRMS (ESI): (M+Na): C15H13NS2Na,
calculated: 294.0382, found: 294.0380.
2-(benzylthio)benzo[d]oxazole, 3ba:35 White solid, mp: 48.8 ꢀ 50.2 °C. 1HꢀNMR (400 MHz,
CDCl3), δ (ppm): 4.57 (s, 2H), 7.22 ꢀ 7.36 (m, 5H), 7.42 ꢀ 7.46 (m, 3H), 7.62 (ddd, J = 7.7 Hz, J =
1.5 Hz, J = 0.8 Hz, 1H). 13CꢀNMR (100 MHz, CDCl3), δ (ppm): 36.60, 109.91, 118.50, 123.95,
124.32, 127.92, 128.78, 129.09, 135.87, 141.95, 151.91, 164.47. MS (EI+) m/z (%): 242.25 (18),
241.20 (74), 208.10 (34), 150.10 (6), 122.10 (20), 92.15 (28), 91.00 (100), 89.10 (8), 65.15 (40),
63.10 (16), 51.05 (11). HRMS (ESI): (M+Na): C14H11NOSNa, calculated: 264.0454, found:
264.0458.
2-((4-fluorobenzyl)thio)benzo[d]oxazole, 3bb: White solid, mp: 37.5 ꢀ 38.0 °C. 1HꢀNMR (400
MHz, CDCl3), δ (ppm): 4.57 (s, 2H), 7.01 (tt, J = 8,6 Hz, J = 2.4 Hz, 2H), 7.24 (td, J = 7.7 Hz, J =
1.4 Hz, 1H), 7.29 (td, J = 7.6 Hz, J = 1.3 Hz, 1H), 7.42 ꢀ 7.45 (m, 3H), 7.62 (dd, J = 7.4 Hz, J = 1.1
Hz, 1H). 13CꢀNMR (100 MHz, CDCl3), δ (ppm): 35.80, 109.93, 115.68 (d, J2FꢀC = 21.6 Hz), 118.52,
124.03, 124.36, 130.78 (d, J3FꢀC = 8.3 Hz), 131.83 (d, J4FꢀC = 3.1 Hz), 141.87, 151.92, 162.40 (d, J1
Fꢀ
C = 246.8 Hz), 164.25. 19FꢀNMR (376.5 MHz, CDCl3), δ (ppm): ꢀ114.07 (tt, JoFꢀH = 7.9 Hz, Jm
=
FꢀH
4.4 Hz). MS (EI+) m/z (%): 260.25 (13), 259.25 (65), 226.20 (23), 150.10 (6), 122.10 (19), 110.15
(26), 109.10 (100), 107.15 (10), 89.15 (4), 83.05 (35), 63.10 (14). HRMS (ESI): (M+Na):
C14H10NOSFNa, calculated: 282.0359, found: 282.0357.
2-((4-(trifluoromethyl)benzyl)thio)benzo[d]oxazole, 3bc: White solid, mp: 55.7 ꢀ 57.3 °C. 1Hꢀ
NMR (400 MHz, CDCl3), δ (ppm): 4.58 (s, 2H), 7.25 (td, J = 7.5 Hz, J = 1.5 Hz, 1H), 7.30 (td, J =
7.7 Hz, J = 1.4 Hz, 1H), 7.44 (dd, J = 7.5 Hz, J = 1.0 Hz, 1H), 7.59 (s, 4H), 7.62 (dd, J = 7.5 Hz, J
= 1.1 Hz, 1H). 13CꢀNMR (100 MHz, CDCl3), δ (ppm): 35.81, 109.98, 118.57, 123.99 (q, J1
=
FꢀC
272.1 Hz), 124.14, 124.43, 125.69 (q, J3FꢀC = 3.7 Hz), 129.41, 130.12 (q, J2FꢀC = 32.7 Hz), 140.37,
141.79, 152.00, 163.81. 19FꢀNMR (376.5 MHz, CDCl3), δ (ppm): ꢀ62.67 (s). MS (EI+) m/z (%):
310.30 (12), 309.20 (77), 276.20 (37), 160.15 (11), 159.05 (100), 150.05 (18), 133.15 (1), 132.10
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(5), 122.00 (33), 119.05 (8), 109.05 (31), 92.05 (1), 89.05 (5), 63.05 (10). HRMS (ESI): (M+Na):
C15H10NOSF3Na, calculated: 332.0327, found: 332.0330.
4-((benzo[d]oxazol-2-ylthio)methyl)benzonitrile, 3bd:35 Orange solid, mp: 104.9 ꢀ 106.4 °C. 1Hꢀ
NMR (400 MHz, CDCl3), δ (ppm): 4.56 (s, 2H), 7.24 ꢀ 7.32 (m, 2H), 7.44 (dd, J = 7.4 Hz, J = 1.1
Hz, 1H), 7.58 ꢀ 7.63 (m, 5H). 13CꢀNMR (100 MHz, CDCl3), δ (ppm): 35.83, 110.01, 111.77,
118.52, 118.60, 124.24, 124.49, 129.80, 132.49, 141.70, 141.96, 152.04, 163.48. MS (EI+) m/z (%):
267.30 (20), 266.15 (99), 234.25 (10), 233.15 (64), 164.10 (2), 150.05 (56), 122.00 (50), 117.15
(17), 116.10 (100), 92.05 (2), 90.05 (8), 89.00 (38), 76.00 (3), 63.05 (19). HRMS (ESI): (M+Na):
C15H10N2OSNa, calculated: 289.0406, found: 289.0405.
2-((4-nitrobenzyl)thio)benzo[d]oxazole, 3be:35 Yellow solid, mp: 105.3 ꢀ 106.6 °C. 1HꢀNMR (400
MHz, CDCl3), δ (ppm): 4.60 (s, 2H), 7.24 ꢀ 7.32 (m, 2H), 7.44 (dt, J = 7.7 Hz, J = 0.8 Hz, 1H), 7.61
(dt, J = 7.5 Hz, J = 0.9 Hz, 1H), 7.66 (d, J = 8.7 Hz, 2H), 8.18 (d, J = 8.7 Hz, 2H). 13CꢀNMR (100
MHz, CDCl3), δ (ppm): 35.49, 110.03, 118.62, 123.92, 124.28, 124.52, 129.96, 141.67, 144.02,
147.49, 152.05, 163.34. MS (EI+) m/z (%): 287.25 (15), 286.20 (100), 269.20 (2), 253.20 (24),
207.20 (17), 179.15 (1), 150.10 (64), 136.15 (31), 122.15 (77), 106.10 (29), 92.10 (2), 90.15 (28),
89.10 (38), 78.10 (53), 64.10 (13), 63.10 (25), 51.10 (11). HRMS (ESI): (M+Na): C14H10N2O3SNa,
calculated: 309.0304, found: 309.0305.
2-((2-nitrobenzyl)thio)benzo[d]oxazole, 3bf:35 Green solid, mp: 65.7 ꢀ 67.2 °C. 1HꢀNMR (400
MHz, CDCl3), δ (ppm): 4.88 (s, 2H), 7.21 ꢀ 7.30 (m, 2H), 7.41 ꢀ 7.47 (m, 2H), 7.56 ꢀ 7.62 (m, 2H),
7.86 (d, J = 7.6 Hz, 1H), 8.09 (d, J = 8.1 Hz, 1H). 13CꢀNMR (100 MHz, CDCl3), δ (ppm): 33.79,
109.98, 118.51, 124.01, 124.35, 125.42, 129.05, 132.75, 133.11, 133.77, 141.76, 148.04, 152.10,
164.39. MS (EI+) m/z (%): 287.15 (4), 286.20 (22), 240.20 (17), 223.30 (3), 221.20 (14), 167,15 (1),
152.15 (15), 151.10 (95), 150.10 (18), 136.15 (87), 122.10 (41), 106.15 (12), 92.10 (12), 91.10 (11),
89.10 (11), 78.10 (100), 77.05 (19), 65.10 (16), 64.05 (13), 63.05 (20), 51.05 (14). HRMS (ESI):
(M+Na): C14H10N2O3SNa, calculated: 309.0304, found: 309.0302.
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2-((2-chlorobenzyl)thio)benzo[d]oxazole, 3bg: White solid, mp: 62.9 ꢀ 64.2 °C. 1HꢀNMR (400
MHz, CDCl3), δ (ppm): 4.67 (s, 2H), 7.19 ꢀ 7.26 (m, 3H), 7.29 (td, J = 7.7 Hz, J = 1.3 Hz, 1H), 7.40
(dd, J = 7.4 Hz, J = 1.9 Hz, 1H), 7.43 (dq, J = 8.0 Hz, J = 0.7 Hz, 1H), 7.60 ꢀ 7.64 (m, 2H). 13Cꢀ
NMR (100 MHz, CDCl3), δ (ppm): 34.32, 109.93, 118.51, 123.96, 124.31, 127.06, 129.41, 129.78,
131.27, 134.07, 134.45, 141.93, 152.01, 164.43. MS (EI+) m/z (%): 277.10 (10), 275.05 (23),
242.15 (16), 241.20 (14), 240.05 (100), 207.10 (4), 150.00 (8), 127.05 (54), 126.10 (15), 125.00
(91), 121.95 (29), 99.00 (12), 92.05 (1), 90.05 (10), 89.05 (38), 63.00 (22). HRMS (ESI): (M+Na):
C14H10NOSClNa, calculated: 298.0064, found: 298.0059.
2-((4-bromobenzyl)thio)benzo[d]oxazole, 3bh: Yellow solid, mp: 67.4 ꢀ 67.9 °C. 1HꢀNMR (400
MHz, CDCl3), δ (ppm): 4.49 (s, 2H), 7.24 (td, J = 7.6 Hz, J = 3.2 Hz, 1H), 7.29 (td, J = 7.7 Hz, J =
1.4 Hz, 1H), 7.34 (d, J = 8.3 Hz, 2H), 7.42 ꢀ 7.46 (m, 3H), 7.61 (dt, J = 7.6 Hz, J = 0.8 Hz, 1H).
13CꢀNMR (100 MHz, CDCl3), δ (ppm): 35.84, 109.94, 118.54, 121.92, 124.06, 124.38, 130.75,
131.88, 135.20, 141.84, 151.95, 164.05. MS (EI+) m/z (%): 321.00 (62), 319.00 (55), 288.00 (15),
286.10 (14), 207.15 (12), 170.95 (99), 168.95 (100), 150.00 (9), 142.95 (1), 121.90 (34), 92.05 (2),
90.05 (53), 89.05 (45), 63.05 (24). HRMS (ESI): (M+Na): C14H10NOSBrNa, calculated: 341.9559,
found: 341.9565.
2-((2-bromobenzyl)thio)benzo[d]oxazole, 3bi: Yellow solid, mp: 68.2 ꢀ 69.3 °C. 1HꢀNMR (400
MHz, CDCl3), δ (ppm): 4.68 (s, 2H), 7.15 (td, J = 7.7 Hz, J = 1.6 Hz, 1H), 7.22 ꢀ 7.31 (m, 3H), 7.43
(dd, J = 7.5 Hz, J = 0.8 Hz, 1H), 7.59 (dd, J = 8.0 Hz, J = 0.9 Hz, 1H), 7.62 ꢀ 7.65 (m, 2H). 13Cꢀ
NMR (100 MHz, CDCl3), δ (ppm): 36.99, 109.94, 118.50, 123.96, 124.32, 124.81, 127.72, 129.60,
131.35, 133.10, 135.78, 141.92, 152.00, 164.39. MS (EI+) m/z (%): 320.95 (13), 319.05 (11),
241.20 (17), 240.10 (100), 207.15 (11), 170.95 (68), 168.95 (72), 150.00 (7), 122.05 (25), 92.05 (1),
90.10 (41), 89.05 (35), 63.00 (20). HRMS (ESI): (M+Na): C14H10NOSBrNa, calculated: 341.9559,
found: 341.9567.
2-((4-iodobenzyl)thio)benzo[d]oxazole, 3bj: Brown solid, mp: 83.6 ꢀ 85.3 °C. 1HꢀNMR (400
MHz, CDCl3), δ (ppm): 4.48 (s, 2H), 7.21 (d, J = 8.3 Hz, 2H), 7.25 (dd, J = 7.7 Hz, J = 1.4 Hz, 1H),
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7.29 (td, J = 7.4 Hz, J = 1.1 Hz, 1H), 7.43 (d, J = 8.1 Hz, 1H), 7.61 (d, J = 7.4 Hz, 1H), 7.65 (d, J =
8.3 Hz, 2H). 13CꢀNMR (100 MHz, CDCl3), δ (ppm): 35.95, 93.46, 109.94, 118.54, 124.06, 124.38,
130.97, 135.87, 137.86, 141.84, 151.95, 164.05. MS (EI+) m/z (%): 367.25 (79), 334.10 (16),
217.00 (100), 207.10 (8), 150.00 (4), 122.05 (14), 90.05 (52), 89.00 (39), 63.00 (16). HRMS (ESI):
(M+Na): C14H10NOSINa, calculated: 389.9420, found: 389.9424.
2-((2-iodobenzyl)thio)benzo[d]oxazole, 3bk: Brown solid, mp: 69.0 ꢀ 70.3 °C. 1HꢀNMR (400
MHz, CDCl3), δ (ppm): 4.67 (s, 2H), 6.97 (td, J = 7.7 Hz, J = 1.5 Hz, 1H), 7.36 ꢀ 7.17 (m, 3H), 7.43
(dd, J = 7.2 Hz, J = 0.7 Hz, 1H), 7.62 ꢀ 7.66 (m, 2H), 7.86 (dd, J = 7.9 Hz, J = 0.9 Hz, 1H). 13Cꢀ
NMR (100 MHz, CDCl3), δ (ppm): 41.83, 100.65, 109.94, 118.52, 123.96, 124.32, 128.60, 129.62,
130.68, 138.96, 139.80, 141.94, 152.01, 164.23. MS (EI+) m/z (%): 367.20 (8), 241.20 (16), 240.10
(100), 217.00 (91), 207.10 (8), 15.05 (3), 122.10 (11), 90.15 (58), 89.10 (32), 63.05 (13). HRMS
(ESI): (M+Na): C14H10NOSINa, calculated: 389.9420, found: 389.9435.
2-((4-methylbenzyl)thio)benzo[d]oxazole, 3bl: White solid, mp: 56.1 ꢀ 57.9 °C. 1HꢀNMR (400
MHz, CDCl3), δ (ppm): 2.33 (s, 3H), 4.53 (s, 2H), 7.14 (d, J = 7.8 Hz, 2H), 7.31 ꢀ 7.19 (m, 2H),
7.34 (d, J = 7.9 Hz, 2H), 7.43 (dd, J = 7.5 Hz, J = 0.9 Hz, 1H), 7.61 (d, J = 7.5 Hz, 1H). 13CꢀNMR
(100 MHz, CDCl3), δ (ppm): 21.13, 36.42, 109.88, 118.48, 123.90, 124.28, 129.00, 129.46, 132.73,
137.74, 141.99, 151.89, 164.67. MS (EI+) m/z (%): 256.20 (6), 254.95 (47), 221.90 (11), 150.05 (2),
122.00 (6), 106.15 (16), 105.00 (100), 103.05 (10), 89.00 (1), 79.10 (15), 77.00 (18), 65.05 (2),
63.05 (4). HRMS (ESI): (M+Na): C15H13NOSNa, calculated: 278.0610, found: 278.0608.
RESULTS AND DISCUSSION
In order to synthesize different compounds with antifungal activity, reaction conditions were
optimized for the nucleophilic substitution of benzyl halides, using 2ꢀmercaptobenzothiazole (1a)
and benzyl chloride (2a) as representative substrates. Water was chosen as solvent, as it is low cost,
abundant and safe, so reducing negative environmental effects.
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In a first instance, reaction between 1a and 2a was carried out using 2 equivalents of KOH to ensure
full deprotonation of the thiol group. Reaction conditions were 100 °C for 24 hours, ensuring 99%
substrate conversion with the concomitant product formation.
Afterwards, reaction time, temperature and base concentration were adjusted. Optimized reaction
conditions were 30 minutes, 50 °C and one equivalent of KOH, reaching a conversion of 97%. In
absence of base, only 51% conversion was reached, which is in accordance to a pKa of ca. 7.65
reported for 2ꢀmercaptobenzothiazole,47 indicating an increment in the reaction rate as the formed
anion fraction increases. Thus, to verify this behavior, one equivalent of different bases, such as
NaOH, K2CO3, NaHCO3 or sodium acetate were tested. Results of these last reactions did not show
significant differences in conversion percentages, demonstrating a general basic catalysis. The
method scope was further evaluated for 2ꢀmercaptobenzothiazole (1a) or 2ꢀmercaptobenzoxazole
(1b) and a series of benzyl halides (Table 1) using the previously optimized conditions (1
equivalent of KOH, 50 °C, 30 minutes). Substrates substituted with electron withdrawing (Table 1,
entries 2 to 11) and electron donating groups (Table 1, entry 12) were tested, without observing
differences in mesomeric or inductive effects on the reactivity. Moreover, no steric effects were
observed, as it can be seen from conversions from orthoꢀ (Table 1, entry 6) and paraꢀsubstituted
substrates (Table 1, entry 5). It is worth noting the versatility of this synthetic method for benzyl
thioethers, affording conversions from 91ꢀ 99%, without byꢀproducts formation.
Growth inhibition assay of phytopathogenic fungi.
Fungal growth was evaluated at six concentrations (3.1 ꢀ 100 mg/L), using enriched Czapek broth in
the presence of compounds 3aa ꢀ 3bl. Each treatment was carried out in triplicate. The 50%
Inhibitory Concentrations (IC50) are summarized in Table 2.
New antifungal compounds showed selectivity against some of the assayed microorganisms. The
best effect against B. cinerea was observed for the compounds 3ac, 3ad, 3ag, 3ah, 3aj, 3al, 3bb,
3bg, 3bi and 3bl, showing IC50 values significantly equal or lower than the commercial compound
(3ag, 1.1 µM; 3aj, 1.4 µM; 3bi, 1.4 µM; Captan, 17.8 µM). Comparing results obtained for 3aj and
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3ag with their aryl analogues 2ꢀ(4ꢀiodophenylthio)benzo[d]thiazole and 2ꢀ(2ꢀ
chlorophenylthio)benzo[d]thiazole, presented in our previous report,28 (IC50 2.63 µM and 2.5 µM,
respectively), it could be suggested that the bridge expansion between benzothiazole and aryl
groups, in these structures in particular, could positively influence the biological activity against B.
cinerea.
Several tested compounds (3aa, 3ab, 3ac, 3ad, 3ae, 3ag, 3ak, 3al, 3bc, 3bd, 3be, 3bf, 3bk and 3bl)
showed significant activity against different species of Aspergillus spp. The best activity against A.
fumigatus was confirmed for the compound 3bc, with an IC50 of 5 µM, higher than the positive
control (Captan, 15 µM). On the other hand, compounds 3ab and 3aa had the highest activity
against A. niger (6.5 x 10ꢀ39 µM and 5 µM, respectively), even higher than Captan (24 µM). In
addition, compound 3aa also showed an interesting activity against A. terreus, with an IC50 of 13.2
µM, in comparison with an IC50 of 55.8 µM for Captan. Moreover, a greater effect was observed
against A. ustus by the compound 3ac (0.0119 µM) compared to Captan (61 µM).
Most compounds (3aa, 3ab, 3ac, 3ad, 3ae, 3af, 3ag, 3ah, 3ak, 3al, 3ba, 3bb, 3bc, 3bf, 3bg, 3bh
and 3bi) had an activity similar or better than Captan (49 µM) against F. oxysporum. Furthermore,
compounds 3aa (0.23 µM), 3ab (0.0067 µM) and 3ba (3.0 µM) showed outstanding activity against
this mold. In general, most of the synthesized compounds showed an important antifungal activity
against the assayed fungi. No evident differences were observed when comparing benzothiazole and
benzoxazole heterocycles. Moreover, the influence of electron withdrawing or donating groups in
the benzyl moiety was also not evident.
Among the derivatives tested, compounds 3ag, 3aj, and 3bi had remarkable growth inhibition for
Botrytis cinerea. Compounds 3aa, 3ab and 3ba were outstanding inhibitors of Fusarium
oxysporum. In addition, compounds 3aa, 3ab, 3ac and 3bc showed an interesting activity against
Aspergillus spp. Compounds 3ac and 3al can be highlighted as potential highꢀspectrum antifungals.
Moreover, it could be suggested that having an extra carbon atom in the para position of the benzyl
substituent would be useful for a better interaction within the target active site. Additionally,
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compounds 3aj and 3ba could be considered as reducedꢀspectrum antifungals, since they showed
specificity against B. cinerea and F. oxysporum, respectively. These results suggest that these
compounds could be a valuable alternative to the antifungal agents currently used.
Summarizing, a practical and environmentally friendly method has been developed for a facile and
green synthesis of benzyl substituted thiobenzoazoles, starting from 2ꢀmercaptobenzoxazole or 2ꢀ
mercaptobenzothiazole and benzyl halides, affording excellent yields. Most reported derivatives
proved to be better inhibitors than the commercial antifungal Captan, which has undesirable effects
on both health and environment.
ACKNOWLEDGMENTS
This work was supported in part by CONICET, CICITCA UNSJ, SECYT and ANPCyT. M. S. B.
and N.H.C. gratefully acknowledge receipt of a fellowship from CONICET.
SUPPORTING INFORMATION DESCRIPTION
Reaction optimization, more details about antifungal susceptibility tests, spectroscopy data for all
compounds. This material is available free of charge via the Internet at http://pubs.acs.org.
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FIGURE CAPTIONS
Figure 1. (A) Captan, positive control. (B) Benzothiazole (red), a muntifunctional nucleus. (C)
Benzoxazole (blue) as part of diverse natural products.
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Table 1. Reactions of Benzyl Halides with 1a and 1ba.
Entry
1
R
H
X
Product (Y = S)
Conversionb
97%
Yieldsc
85%
Product (Y = O)
Conversionb Yieldsc
Cl
97%
91%d
93%d
94%
97%
98%
75%
74%
75%
89%
77%
75%
2
3
4
5
6
p-F
Cl
Cl
Br
Br
Br
99%d
98%d
96%
96%
97%
75%
86%
79%
82%
72%
p-CF3
p-CN
p-NO2
o-NO2
7
8
o-Cl
p-Br
o-Br
p-I
Cl
Br
Br
Br
Cl
Cl
95%d
99%
96%
97%
96%d
95%
86%
79%
78%
89%
93%
91%
98%d
98%d
91%d
98%d
99%d
98%d
74%
89%
71%
89%
91%
88%
9
10
11
12
o-I
p-CH3
b
a1a or 1b concentration was 0.30 M, 2a-l concentration were 0.25 M. Reactions performed with 1 equivalent of KOH. Conversions of 2a-l by GC
quantification. cIsolated yields. dNew compounds.
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Table 2. Antifungal Activity of Benzoazole Derivates 3
Inhibition rate IC50 (µM)a
Compound
Y
R
Botrytis
cinerea
ꢀ
Fusarium
oxysporum
0.23 ± 0.05b
0.0067 ± 0.0005e
57 ± 5
Aspergillus
fumigatus
267 ± 40
ꢀ
Aspergillus
Aspergillus
terreus
13.2 ± 1.1
56 ± 25
40 ± 6
22 ± 4
ꢀ
ꢀ
Aspergillus
ustus
93 ± 10
niger
3aa
3abd
3acd
3ad
3ae
S
S
S
S
S
S
S
S
S
H
p-F
5 ± 6c
ꢀ
(6.5 ± 1.4)x10ꢀ39 b
37 ± 6
p-CF3
p-CN
p-NO2
o-NO2
o-Cl
p-Br
o-Br
p-I
10.3 ± 1.7
ꢀ
34 ± 7
ꢀ
35 ± 11
0.0119 ± 0.0015c
4 ± 7f
7.2 ± 1.2g
29 ± 7
165 ± 12
92 ± 12
82 ± 13
149 ± 42
1.1 ± 0.3f
8.7 ± 2.1
40 ± 7
1.4 ± 0.9c
39 ± 9
20 ± 6
ꢀ
26 ± 7
36 ± 7
146 ± 30
97 ± 13
ꢀ
10.8 ± 1.9
41 ± 7
1.4 ± 0.6e
57 ± 7
33 ± 5
26 ± 7
ꢀ
ꢀ
ꢀ
3af
27 ± 5
27 ± 7
53 ± 8
189 ± 10
73 ± 3
46 ± 15
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
3agd
3ah
3ai
73 ± 18
127 ± 15
229 ± 40
ꢀ
ꢀ
ꢀ
ꢀ
161 ± 14
ꢀ
ꢀ
3aj
S
S
S
ꢀ
5.2 ± 2.3b
35 ± 11
60 ± 21
112 ± 19
ꢀ
61 ± 6
18 ± 12
23 ± 4
ꢀ
112 ± 12
3akd
3al
o-I
p-CH3
H
53 ± 11
79 ± 7
39 ± 12
29 ± 9
205 ± 16
104 ± 16
5 ± 5g
41 ± 11
45 ± 4
ꢀ
ꢀ
ꢀ
48 ± 8
62 ± 18
173 ± 13
211 ± 40
169 ± 27
38 ± 3
3ba
3bbd
3bcd
3bd
3be
O
O
O
O
O
O
O
O
O
O
O
O
3.0 ± 2.0f
53.6 ± 1.9
70 ± 7
93 ± 7
108 ± 7
44 ± 7
301 ± 30
p-F
p-CF3
p-CN
p-NO2
o-NO2
o-Cl
p-Br
o-Br
p-I
111 ± 9
141 ± 10
63 ± 9
46 ± 7
45 ± 3
29 ± 4
101 ± 11
91 ± 9
139 ± 30
49 ± 13
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
3bf
3bgd
3bhd
3bid
3bjd
3bkd
3bld
138 ± 20
ꢀ
102 ± 15
63 ± 9
196 ± 40
ꢀ
ꢀ
ꢀ
180 ± 29
46 ± 6
22 ± 4
162 ± 8
15 ± 4
ꢀ
ꢀ
ꢀ
ꢀ
o-I
p-CH3
9 ± 4
10 ± 3
46 ± 9
63 ± 16
61 ± 4
Captan
17.8 ± 1.9
24 ± 6
55.8 ± 1.5
a(ꢀ): No activity (˃ 100 mg/L). 100% inhibition at 3.1 mg/L. 80% inhibition at 3.1 mg/L. New compounds. 90% inhibition at
3.1 mg/L. f70% inhibition at 3.1 mg/L. g60% inhibition at 3.1 mg/L.
b
c
d
e
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FIGURE GRAPHICS
Figure 1.
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GRAPHIC FOR TABLE OF CONTENTS
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