Natural Products as Sources of New Fungicides (I): Synthesis and Antifungal Activity of Acetophenone Derivatives Against Phytopathogenic Fungi

Article abstract of DOI:10.1111/cbdd.12064

Several series of 45 acetophenone derivatives bearing various alkyl or benzyl substituents were conveniently synthesized and their structures characterized by ¹H and ¹³C NMR spectroscopy, HRMS and single-crystal X-ray analysis. Their in vitro antifungal activities against a panel of phytopathogenic fungi were evaluated by mycelial growth rate assay. Of them, 12 derivatives (e.g., 3a-c, 4c and 4e) exhibited more potent antifungal effects on some phytopathogens than a commercial fungicide hymexazol as positive control. In particular, compound 3b with IC₅₀ values of 10-19μg/mL was found to be the most active in this series and might be a potential lead structure for further optimization. The preliminary structure-activity relationship (SAR) studies of a series of acetophenones are also discussed. A series of acetophenone derivatives have been synthesized and tested for their antifungal activities. Of them 12 derivatives exhibited more potent antifungal effects on some phytopathogens than a positive control hymexazol. Especially, compound 3b (IC₅₀=10-19μg/mL) was found to be the most active and might be a potential lead structure. The SAR of these acetophenones is also discussed.

Full text of DOI:10.1111/cbdd.12064

Chem Biol Drug Des 2013; 81: 545–552
Research Letter
Natural Products as Sources of New Fungicides (I):
Synthesis and Antifungal Activity of Acetophenone
Derivatives Against Phytopathogenic Fungi
Recent studies have demonstrated the antifungal activities
of some naturally occurring acetophenone derivatives. For
example, xanthoxylin isolated from Melicope borbonica
leaves exhibited antifungal activity against Candida albicans
and Penicillium expansum (10); 4-hydroxy-3-(isopentent-2-
yl) acetophenone, from Helichrysum sp. showed antifungal
activity against Cladosporium herbarum and Phythophtora
capsicii (11); and 2,4-diacetylphloroglucinol (A), produced
by the bacteria Lysobacter gummosus on the salamander
Plethodon cinereus, inhibited pathogenic fungi (12,13); and
2,4-dihydroxy-5-methylacetophenone (B) (Figure 1) from
the cultures of the higher fungus Polyporus picipes was
claimed in our patent as a good antifungal agent against
several phytopathogens (14). The fungal metabolite 2,4-
dihydroxy-5-methylacetophenone (B) exhibited in vitro
significant growth inhibitory activity in particular toward
Fusarium oxysporium f. sp. vasinfectum (IC50 86.2 lg ⁄ mL),
Curvularia lunata (IC50 62.4 lg ⁄ mL), and Colletotrichum
gloeosporioides (IC50 63.4 lg ⁄ mL). These facts justify
further studies on this class of molecules to identify the
essential structural requirements for their antifungal activity.
Ya-Tuan Ma, Hua-Fang Fan, Yu-Qi Gao, He Li,
An-Ling Zhang* and Jin-Ming Gao*
Shaanxi Engineering Center of Bioresource Chemistry &
Sustainable Utilization, College of Sciences, Northwest
A&F University, Yangling, Shaanxi 712100, China
*Corresponding author: An-Ling Zhang,
anlingzh@nwsuaf.edu.cn and Jin-Ming Gao,
jinminggao@nwsuaf.edu.cn
Several series of 45 acetophenone derivatives bearing
various alkyl or benzyl substituents were conveniently
synthesized and their structures characterized by 1H
and 13C NMR spectroscopy, HRMS and single-crystal
X-ray analysis. Their in vitro antifungal activities
against a panel of phytopathogenic fungi were evalu-
ated by mycelial growth rate assay. Of them, 12 deriv-
atives (e.g., 3a–c, 4c and 4e) exhibited more potent
antifungal effects on some phytopathogens than a
commercial fungicide hymexazol as positive control. In
particular, compound 3b with IC50 values of 10–
19 lg ⁄ mL was found to be the most active in this ser-
ies and might be a potential lead structure for further
optimization. The preliminary structure–activity rela-
tionship (SAR) studies of a series of acetophenones
are also discussed.
In this study, we prepared a series of alkyl or benzyl ace-
tophenone ether derivatives 1a–o, 2a–o, 3a–e and 4a–j
and evaluated in vitro their antifungal activities against sev-
eral phytopathogens based on the precedent discovery of
the antifungal acetophenone 2,4-dihydroxy-5-methylace-
tophenone (B). Herein, we report the interesting results of
these acetophenone ether derivatives.
Key words: 2,4-dihydroxy-5-methylacetophenone, acetophe-
none derivatives, antifungal activity, natural products, struc-
ture–activity relationship
Received 30 April 2012, revised 8 August 2012 and accepted
for publication 13 September 2012
Methods and Materials
General
Crops are facing a tremendous damage from fungal dis-
eases which results in direct economic losses including
reduction in grain yield and quality (1,2). New fungicides
with novel chemical structures which have higher potency
and broader spectrum of activity against resistant fungal
strains have attracted great attentions recently. Acetophe-
none and its derivatives, as important intermediates for the
synthesis of some agrochemicals and pharmaceuticals,
have been shown to possess a wide range of biological
activities such as herbicides, phytoanticipin (3,4), as well
as antimicrobial (5,6), antipsychotic, antiasthmatic, cyto-
toxic, and antioxidant (7–9).
The melting points of the products were determined on an
XT-4 apparatus (Beijing Tech Instrument Co., Beijing, China)
and are uncorrected. The IR spectra were recorded on a
Bruker VECTOR22 spectrometer in film or KBr discs. 1H and
13C NMR spectra were taken on a Varian Mercury 400 MHz
(400 MHz for 1H and 100 MHz for 13C, respectively) or a
1
Bruker Avance 500 MHz (500 MHz for H and 125 MHz for
13C, respectively) spectrometer in CDCl3 and acetone-d6
solutions using TMS as an internal standard (d given in ppm,
J in Hz). MS spectra were taken on a Bruker Daltonics
esquire 6000 (ESI-ION TRAP) or on a Waters ESI-Q-TOF
ª 2012 John Wiley & Sons A/S. doi: 10.1111/cbdd.12064
545

Ma et al.
OH
O
rum f. sp. vasinfectum, F. oxysporum f. sp. niveum,
F. solani var. coeruleum, and F. graminearum, were pro-
vided by College of Sciences, Northwest A&F University.
Cultures of the test fungi were maintained on PDA slants at
4 ꢀC and were subcultured in Petri dishes prior to testing.
OH
O
O
HO
CH3
HO
OH
A
B
The in vitro antifungal activity of the test compounds was
evaluated by using mycelial growth inhibitory rate method
(16). Briefly, the media (100 mL) incorporating test samples
were inoculated at the center of agar discs of the test
fungi (4 mm diameter). Three replicate plates for each fun-
gus were incubated at 26 ( 2) ꢀC for all test fungi. Control
plates containing media mixed with acetone (1 mL) were
included. After incubation for 72–96 h, the mycelial growth
of fungi (mm) in both treated (T) and control (C) Petri
dishes was measured diametrically in three different direc-
tions (decussation method) till the fungal growth in the
control dishes was almost complete. The percentage of
growth inhibition (I) was calculated using the following for-
mula. I (%) = [(C)T) ⁄ C] · 100.
Figure 1: Structures of two antifungal natural products A and B.
Ultima Global mass spectrometer. Thin-layer chromatogra-
phy (TLC) was performed with silica gel plates using silica
gel 60 GF254 and column chromatography (CC) was carried
out on silica gel (200–300 mesh) (Qingdao Haiyang Chemi-
cal Co. Ltd. Qingdao,Shandong province, China).
Experimental
Synthetic procedures
All the solvents were of analytical grade, and alkyl or ben-
zyl halides and acetophenone products were commercial
reagents. Target compounds (1a–o, 2a–o, 3a–e, 4a–j)
were synthesized by the Williamson reactions of various
acetophenones with the corresponding benzyl chloride or
alkyl halide (15) (Scheme 1; Table 1).
Statistical analysis
The experimental data of the antifungal activities were ana-
lyzed using SPSS 13.0 for Windows (SPSS, Chicago, IL,
USA).
General Synthetic Procedure for Title Compounds. To a
mixture of monohydroxyacetophenones (1a–o and 2a–o),
dihydroxyacetophenones (2 mmol) (3a–e and 4a–j) and
anhydrous K2CO3 (2.5 mmol) in dry acetone (20 mL) was
added dropwise a solution of benzyl chloride or alkyl halide
(1a–o and 2a–o), aryl chloride or alkyl halide (3a–e and 4a–
j) (2.10 mmol, 4.00 mmol for 3e, that is, 1.05–2.00 equiv) in
dry acetone (3 mL). The reaction mixture was stirred under
reflux for 3–5 h (1a–o, 2a–o and 3e), at 10 ꢀC for 1–5 h
(3a–d and 4a–j). The mixture was cooled to r.t., filtered and
evaporated under vacuum. The residue was dissolved in
CH2Cl2, washed with saturated NaHCO3, brine and dried
over Na2SO4 and concentrated under vacuum. The con-
centrated mixture was subjected to silica gel CC and eluted
by the mixture of petroleum ether and ethyl acetate
(5:1ꢀ15:1, v ⁄ v) gradient elution to give title compounds.
Analytical data
1-(3-(3-methylbut-2-enyloxy)phenyl)ethanone (1n)
1
Light yellow oil. Yield 93.0%. H NMR (400 MHz, CDCl3) d
7.54–7.49 (m, 2H, Ph-H), 7.36 (t, J = 6.4 Hz,1H, Ph-
H),7.13–7.11 (m, 1H, Ph-H), 5.51–5.48 (m, 1H,
CH=C(CH3)2), 4.56 (d, J = 5.6 Hz, 2H, OCH2-), 2.59 (s,
3H, COCH3), 1.81 (s, 3H, CH=C(CH3)2), 1.76 (s, 3H,
CH=C(CH3)2); 13C NMR (100 MHz, CDCl3) d 198.2, 159.1,
138.7, 129.8, 129.5, 120.6, 119.2, 113.3, 64.9, 26.7,
25.8, 18.2. HR-MS (ESI) m ⁄ z [M + H]+ 205.1233 (calcd for
C
13H17O2, 205.1228).
1-(2-(4-fluorobenzyloxy)phenyl)ethanone (2c)
Antifungal bioassay
The tested phytopathogenic fungi, Colletotrichum gloeospo-
riodes, Botrytis cinerea, Alternaria solani, Fusarium oxyspo-
Light yellow semisolid. Yield 90.0%. IR (KBr) vmax (per cm):
1666, 1295 (C-F). H NMR (400 MHz, CDCl3) d 7.79–7.68
1
(m, 1H, Ph-H), 7.49–7.38 (m, 3H, Ph-H), 7.13–7.06 (m,
2H, Ph-H), 7.06–6.99 (m, 2H, Ph-H), 5.13 (s, 2H, OCH2-),
2.58 (s, 3H, COCH3); 13C NMR (100 MHz, CDCl3) d
199.8, 163.8, 161.3, 157.7, 133.5, 131.9, 130.4, 129.5,
129.4, 128.7, 120.9, 115.7, 112.7, 69.9, 32.0. HR-MS
(ESI) m ⁄ z [M + H]+ 245.0969 (calcd for C15H14FO2,
245.0978).
O
O
O
Acetone
K2CO3
+
R-X
R-X
HO
HO
R
O
1a-o, 2a-o
O
R'
R'
Acetone
K2CO3
+
R
O
4-((4-acetylphenoxy)methyl)benzonitrile (2d)
OH
OH
White solid. Yield 90.0%, m.p. 120–121 ꢀC. IR (KBr) vmax
3a-e
4a-j
,R'=Cl;
,R'=H
(per cm): 2227 (C”N), 1672 (C=O); 1H NMR (400 MHz,
Scheme 1: Synthetic route of the title compounds.
CDCl3)
d
7.93 (d, J = 8.8 Hz, 2H, Ph-H), 7.67 (d,
Chem Biol Drug Des 2013; 81: 545–552
546

Antifungal Acetophenone Derivatives
Table 1: Structures of 45 acetophenone derivatives
O
O
O
Cl
R3
R1
R2
1a-o
2a-o
R3
R3
R4
R4
4a-j
3a-e
Compound
R1
R2
R3
1a
1b
1c
1d
1e
1f
H
H
H
3-chloropropyloxy
H
H
Allyloxy
H
H
3-chloropropyloxy
H
H
Allyloxy
H
3-chloropropyloxy
H
H
Allyloxy
1g
1h
1i
H
H
H
Prop-2-ynyloxy
H
H
Prop-2-ynyloxy
H
Prop-2-ynyloxy
1j
H
H
Propoxy
1k
1l
H
Propoxy
H
H
H
propoxy
1m
1n
1o
2a
2b
2c
2d
2e
2f
H
H
H
3-methylbut-2-enyloxy
H
H
4-fluorobenzyloxy
H
H
4-cyanobenzyloxy
H
H
3-methylbut-2-enyloxy
H
H
4-fluorobenzyloxy
H
H
3-methylbut-2-enyloxy
H
H
4-fluorobenzyloxy
H
H
4-cyanobenzyloxy
H
4-cyanobenzyloxy
2g
2h
2i
H
H
H
3,5-difluorobenzyloxy
H
H
3,5-difluorobenzyloxy
H
3,5-difluorobenzyloxy
2j
2k
2l
H
H
H
3-(trifluoromethyl)benzyloxy
H
H
3-(trifluoromethyl)benzyloxy
H
3-(trifluoromethyl)benzyloxy
2m
2n
2o
H
H
H
Benzyloxy
H
H
Benzyloxy
H
Benzyloxy
Compound
R3
R4
3a
3b
3c
3d
3e
4a
4b
4c
4d
4e
4f
3-chloropropyloxy
Allyloxy
Prop-2-ynyloxy
Propoxy
Allyloxy
3-chloropropyloxy
Allyloxy
OH
OH
OH
OH
Allyloxy
H
H
H
H
H
Prop-2-ynyloxy
Propoxy
3-methylbut-2-enyloxy
3,5-difluorobenzyloxy
3-(trifluoromethyl)benzyloxy
4-cyanobenzyloxy
4-fluorobenzyloxy
Benzyloxy
H
H
H
H
4g
4h
4i
4j
H
J = 8.8 Hz, 2H, Ph-H), 7.54 (s, 2H, Ph-H), 6.97 (d,
J = 8.8 Hz, 2H, Ph-H), 5.17 (s, 2H, OCH2-), 2.54 (s, 3H,
COCH3); 13C NMR (100 MHz, CDCl3) d 196.6, 161.9,
141.6, 132.5, 130.9, 130.7, 127.5, 114.4, 111.9, 68.9,
26.4. HR-MS (ESI) m ⁄ z [M + H]+ 252.1028 (calcd for
C16H14NO2, 252.1024).
Chem Biol Drug Des 2013; 81: 545–552
547

Ma et al.
4-((3-acetylphenoxy)methyl)benzonitrile (2e)
Ph-H), 5.21 (s, 2H, OCH2-),2.60 (s, 3H, COCH3); 13C
NMR (100 MHz, CDCl3) d 199.7, 157.5, 137. 3, 133.6,
131.3, 130.6, 128.9, 125.1, 124.2, 122.9, 121.3, 112.7,
69.9, 31.9. HR-MS (ESI) m ⁄ z [M + H]+ 295.0954 (calcd for
Light yellow solid. Yield 91.0%, m.p. 79–81 ꢀC. IR (KBr)
vmax (per cm): 2231 (C”N), 1673(C=O); 1H NMR
(400 MHz, CDCl3) d 7.72 (d, J = 8.4 Hz, 2H, Ph-H),
7.65–7.55 (m, 4H, Ph-H), 7.43 (t, J = 8.4 Hz, 1H, Ph-H),
7.21–7.19 (m, 1H, Ph-H), 5.20 (s, 2H, OCH2-), 2.63 (s,
C
16H14F3O2, 295.0946).
3H, COCH3); 13C NMR (100 MHz, CDCl3)
d 197.7,
158.3, 141.9, 138.5, 132.4, 129.8, 127.6, 121.9,
120.3, 118.6, 113.0, 111.8, 68.8, 26.7. HR-MS (ESI)
m ⁄ z [M + H]+ 252.1030 (calcd for C16H14NO2,
252.1024).
1-(4-(3-chloropropoxy)-3-hydroxyphenyl)-2-
chloroethanone (3a)
Light yellow solid. Yield 72.5%, m.p. 105–107 ꢀC. IR (KBr)
1
vmax (per cm): 3488, 1696, 804 (C-Cl). H NMR (500 MHz,
CDCl3) d 7.56–7.48 (m, 2H, Ph-H), 6.95 (d, J = 9.0 Hz,
1H, Ph-H), 4.65 (s, 2H, COCH2Cl), 4.32 (t, J = 6.0 Hz,
2H, OCH2CH2CH2Cl), 3.75 (t, J = 6.0 Hz, 2H,
OCH2CH2CH2Cl), 2.39–2.29 (m, 2H, OCH2CH2CH2Cl);
13C NMR (125 MHz, CDCl3) d 189.8, 151.2, 150.3, 128.1,
124.2, 114.8, 111.4, 65.9, 45.8, 41.1, 29.7. HR-MS (ESI)
m ⁄ z [M + H]+ 263.0242 (calcd for C11H12Cl2O3,
263.0241).
1-(3-(3,5-difluorobenzyloxy)phenyl)ethanone (2h)
White solid. Yield 73.0%, m.p. 97–98 ꢀC; IR (KBr) vmax
(per cm): 1675, 1224 (C-F). 1H NMR (400 MHz, CDCl3) d
7.64–7.58 (m, 1H, Ph-H), 7.56–7.53 (m, 1H, Ph-H), 7.40
(t, J = 8.0 Hz, 1H, Ph-H), 7.20–7.14 (m, 1H, Ph-H), 7.04–
6.91 (m, 2H, Ph-H), 6.81–6.73 (m, 1H, Ph-H), 5.10 (s, 2H,
OCH2-), 2.61 (s, 3H, COCH3); 13C NMR (100 MHz, CDCl3)
d 197.7, 164.4, 161.9, 158.4, 138.6, 129.8, 121.8, 120.2,
113.2, 109.9, 109.8, 103.6, 103.4, 68.7, 26.7. HR-MS
(ESI) m ⁄ z [M + H]+ 263.0889 (calcd for C15H13F2O2,
263.0884).
1-(4-(allyloxy)-3-hydroxyphenyl)-2-chloroethanone
(3b)
Light yellow solid. Yield 72.5%, m.p. 78–80 ꢀC. IR (KBr)
1
vmax (per cm): 3426, 1676, 788 (C-Cl). H NMR (500 MHz,
CDCl3), d 7.64–7.46 (m, 2H, Ph-H), 6.91 (d, J = 8.5 Hz,
2H, Ph-H), 6.08–5.97 (m, 1H, OCH2CH=CH2), 5.43 (d,
J = 17.0 Hz, 1H, OCH2CH=CH2), 5.37 (d, J = 10.5 Hz,
1-(4-(3-(trifluoromethyl)benzyloxy)phenyl)ethanone
(2j)
White solid. Yield 95.0%, m.p. 87–88 ꢀC. 1H NMR
(400 MHz, CDCl3) d 7.97–7.94 (m, 2H, Ph-H), 7.71 (s, 1H,
Ph-H), 7.61–7.64 (m, 2H, Ph-H), 7.06–7.55 (m, 2H, Ph-H),
5.18 (s, 2H, OCH2-), 2.57 (s, 3H, COCH3); 13C NMR
(100 MHz, CDCl3) d 196.7, 162.1, 137.2, 131.2, 130.9,
129.8, 129.2, 129.0, 125.0, 124.1, 124.0, 122.6, 114.4,
114.2, 69.2, 26.4. HR-MS (ESI) m ⁄ z [M + H]+ 295.0947
(calcd for C16H14F3O2, 295.0946).
1H,
OCH2CH=CH2),
4.69
(d,
J = 5.5 Hz,
2H,OCH2CH=CH2), 4.65 (s, 2H, COCH2Cl); 13C NMR
(125 MHz, CDCl3), d 189.8, 150.3, 145.8, 132.0, 131.8,
127.9, 119.3, 114.7, 111.8, 70.8, 45.9. HR-MS (ESI)m ⁄ z
[M + H]+ 227.0474 (calcd for C11H11ClO3, 227.0475).
1-(3-hydroxy-4-(prop-2-ynyloxy)phenyl)-2-
chloroethanone (3c)
Light yellow solid. Yield 23%, m.p. 106–107 ꢀC. IR (KBr)
vmax (per cm): 3476, 2116 (C”C), 1689, 815 (C-Cl). 1H
NMR (500 MHz, CDCl3) d 7.62–7.51 (m, 2H, Ph-H), 7.05
(d, J = 9.0 Hz, 1H, Ph-H), 4.91–4.79 (m, 2H, OCH2-),
4.65 (s, 2H, COCH2Cl), 2.60 (d, J = 6.0 Hz, 1H, C”CH).
13C NMR(125 MHz, CDCl3), d 190.2, 154.8, 147.1, 130.5,
122.4, 115.9, 112.3, 78.7, 76.8, 57.2, 46.5. HR-MS (ESI)
m ⁄ z [M + H]+ 225.0308 (calcd for C11H9ClO3, 225.0318).
1-(3-(3-(trifluoromethyl)benzyloxy)phenyl)ethanone
(2k)
Semisolid. Yield 96.0%, m.p. 64–65 ꢀC. IR (KBr) vmax (per
cm): 1678, 1274 (C-F). 1H NMR (400 MHz, CDCl3) d 7.73
(s, 1H), 7.66–7.55 (m, 4H, Ph-H), 7.52 (t, J = 7.6 Hz, 1H,
Ph-H), 7.40 (t, J = 8.0 Hz, 1H, Ph-H), 7.21–7.16 (m, 1H,
Ph-H), 5.16 (s, 2H, OCH2-), 2.61 (s, 3H, COCH3); 13C
NMR (100 MHz, CDCl3) d 197.8, 158.6, 158.5, 137.5,
130.6, 129.8, 129.1, 124.9, 124.1, 121.7, 120.3, 113.2,
69.3, 26.7. HR-MS (ESI) m ⁄ z [M + H]+ 295.0933 (calcd for
1-(3-hydroxy-4-propoxyphenyl)-2-chloroethanone
(3d)
C
16H14F3O2, 295.0946).
Light yellow oil. Yield 45.0%, IR (neat) vmax (per cm): 3391,
1
1676, 788 (C-Cl). H NMR (500 MHz, CDCl3), d 7.59–7.50
1-(2-(3-(trifluoromethyl)benzyloxy)phenyl)ethanone
(2l)
(m, 2H, Ph-H), 6.90 (d, J = 9.0 Hz, 1H, Ph-H), 4.65 (s,
2H, COCH2Cl), 4.09 (t, J = 6.5 Hz, 2H, OCH2CH2CH3),
1.94–1.83 (m, 2H, OCH2CH2CH3), 1.07 (t, J = 7.5 Hz, 3H,
OCH2CH2CH3). 13C NMR (125 MHz, CDCl3), d 189.7,
150.8, 127.7, 114.9, 110.8, 110.7, 70.7, 45.8, 22.4, 10.4.
HR-MS (ESI) m ⁄ z [M + H]+ 229.0636 (calcd for
C11H9ClO3, 229.0631).
Light yellow oil. Yield 95.0%, IR (neat) vmax (per cm): 1667,
1234 (C-F). 1H NMR (400 MHz, CDCl3) d 7.76–7.74 (m,
1H, Ph-H), 7.72 (s, 1H, Ph-H), 7.62–7.66 (m, 2H, Ph-H),
7.54 (t, J = 6.4 Hz, 1H, Ph-H), 7.44–7.48 (m, 1H, Ph-H),
7.05 (t, J = 6.4 Hz, 1H, Ph-H), 7.01 (d, J = 6.4 Hz, 1H,
548
Chem Biol Drug Des 2013; 81: 545–552

Antifungal Acetophenone Derivatives
1-(3,4-bis(allyloxy)phenyl)-2-chloroethanone (3e)
In all cases, for the compounds 4a–j, besides the desired
para-O-alkylated isomers, we observed the formation of
the very small amount of ortho-O-alkylated isomers, as
analyzed by TLC. The presence of these compounds in
the reaction mixture made the purification of desired para-
O-alkylated products very difficult, and, in most cases, a
further purification by crystallization and column chroma-
tography using the mixture of petroleum ether and ethyl
acetate (5:1–15:1) was needed. For example, the best
results were obtained for 4a and 4f in yields of 93% and
96%, respectively.
White solid. Yield 52.0%, m.p. 74–75 ꢀC. IR (KBr) vmax (per
1
cm): 1676, 1590, 810 (C-Cl). H NMR (500 MHz, CDCl3) d
7.64–7.49 (m, 2H, Ph-H), 6.91 (d, J = 9.0 Hz, 1H, Ph-H),
6.10–6.05 (m, 2H, -OCH2CH=CH2), 5.47–5.38 (m, 2H, -
OCH2CH=CH2), 5.36–5.31 (m, 2H, -OCH2CH=CH2), 4.75–
4.60 (m, 6H, -OCH2CH=CH2 and -COCH2Cl); 13C NMR
(125 MHz, CDCl3) d 189.7, 153.5, 148.5, 132.7, 123.9,
118.4, 113.4, 113.1, 112.1, 69.6, 45.57. HR-MS (ESI) m ⁄ z
[M + H]+ 267.0788 (calcd for C14H15ClO3, 267.0788).
1-(4-(3-trifluoromethyl)benzyloxy-2-
hydroxyphenyl)ethanone (4g)
Among the synthetic compounds 3a–e and 4a–j, O-alkyl-
ation of the OH groups (ortho-, meta- and ⁄ or para-OH
groups) has been observed, but the O-alkylation of the
para-OH group gave the main products, which was attrib-
uted to the presence of intramolecular hydrogen bonds
between ortho-OH and carbonyl groups as well as to
highly weak acidity of the meta-OH group.
White sheet solid. Yield 78.0%, m.p. 98–100 ꢀC. IR (KBr)
vmax (per cm): 3454, 1629, 1259 (C-F). 1H NMR
(400 MHz, CDCl3) d 12.75 (s, 1H, OH), 7.72–7.57 (m, 4H,
Ph-H), 7.56–7.48 (m, 1H, Ph-H), 6.58–6.50 (m, 1H, Ph-H),
6.49 (d, J = 2.4 Hz, 1H, Ph-H), 5.13 (s, 2H, OCH2-), 2.57
(s, 3H, CH3); 13C NMR (100 MHz, CDCl3), d 202.9, 165.1,
164.6, 136.9, 132.4, 130.6, 129.2, 125.1, 124.1, 114.3,
107.9, 101.8, 69.2, 26.2. HR-MS (ESI) m ⁄ z [M + H]+
311.0889 (calcd for C16H14F3O3, 311.0895).
The structures of the title compounds obtained were fully
characterized by IR, 1H NMR, 13C NMR, and HR-MS, as
well as by X-ray crystal diffraction (for data of the known
compounds, see Appendix S1, Supporting Information).
The major O-alkylated isomers of dihydroxyacetophenon-
es, such as para-O-alkylated products 4a, 4f, and 4j,
were characterized by single-crystal X-ray diffraction (17–
19) and the literature comparison (see Appendix S1, Sup-
porting Information). On the other hand, the positional
selectivity was established by the high 1H NMR chemical
shift values; in a series of 4a–j except 4f, the presence of
intramolecular hydrogen bonds between the ortho-hydroxy
proton and the carbonyl O atom was clearly indicated by
the ortho-OH proton signals at ca. d 12.7 ppm in their 1H
NMR (CDCl3) spectra, suggesting the O-alkylation at the
para-position on the phenyl ring; in contrast, no high NMR
chemical shifts were observed for the meta-OH protons in
3a–e.
1-(4-(4-cyanobenzyloxy)-2-hydroxyphenyl)ethanone
(4h)
White sheet solid. Yield 70.0%, m.p. 147–148 ꢀC. IR (KBr)
vmax (per cm): 2924, 2229 (C”N), 1637 (C=O). 1H NMR
(400 MHz, CDCl3) d 12.73 (s, 1H, OH), 7.72–7.60 (m, 3H,
Ph-H), 7.53 (d, J = 8.8 Hz, 2H, Ph-H), 6.51–6.48 (m, 1H,
Ph-H), 6.46 (d, J = 2.4 Hz, 1H, Ph-H), 5.15 (s, 3H, OCH2-
), 2.57 (s, 3H, CH3); 13C NMR (100 MHz, CDCl3), d 202.7,
165.1, 164.3, 141.2, 132.2, 127.5, 118.5, 114.4, 112.0,
107.9, 101.8, 68.9, 26.3. HR-MS (ESI) m ⁄ z [M + H]+
268.0978 (calcd for C16H14NO3, 268.0973).
Results and Discussion
Chemistry
Evaluation of antifungal activity
As shown in Scheme 1, acetophenone ether derivatives
1a–o, 2a–o, 3a–e and 4a–j could be readily obtained in a
single step by the Williamson reaction of the appropriate
acetophenones with the corresponding alkyl halide or ben-
zyl halide in dried acetone in the presence of K2CO3 in
good or excellent yields. As shown in Table 1, among the
45 synthesized derivatives, 15 compounds 1n, 2c–e, 2h,
2j–l, 3a–e, 4g and 4h were new.
The in vitro antifungal activities of all synthetic acetophe-
none derivatives against seven phytopathogenic fungi, Col-
letotrichum gloeosporiodes, Botrytis cinerea, Alternaria
solani, Fusarium oxysporum f. sp. vasinfectum, F. oxyspo-
rum f. sp. niveum, F. solani var. coeruleum, and F. grami-
nearum, were evaluated by mycelial rate growth assay
(16), and the results are listed in Table 2.
Among acetophenone ethers 1a–c, with a 3-chloropropyl-
oxy group, 1a, and 1b showed moderate to strong anti-
fungal activities against the test phytopathogenic fungi
(except A. solani), with median inhibitory concentration
(IC50) values ranging from 35 to 86 lg ⁄ mL, while 1c, bear-
ing a 3-chloropropyloxy in the ortho-position, exerted very
weak activities with its IC50 being over 100 lg ⁄ mL. Anti-
fungal properties of 1a and 1b were very similar to
B. cinerea, as their IC50 values were 36.29 and
Specifically, as stated in experimental section, monoalky-
lated and dialkylated products of dihydroxyacetophenones,
such as 3b and 3e, were obtained by controlling reaction
temperature and time, respectively; the best results were
obtained for 3b at 10 ꢀC and 5 h in high yield (73%), and
for 3e at 58 ꢀC and 2 h, obtained in yield of 52%. The
progress of the reactions was monitored by TLC on silica
gel plates.
Chem Biol Drug Des 2013; 81: 545–552
549

Ma et al.
Table 2: Antifungal activities of acetophenone derivatives against phytopathogensa
b
IC50 (lg ⁄ mL)
Compound
C. g.
B. c.
A. s.
F. o.v.
F. o.n.
F. s.
F. g.
1a
1b
1c
1d
1e
1f
1g
1h
1i
1m
1n
1o
2a
72.51
54.01
>150
>150
>150
>150
35.03
36.29
>150
>100
>100
>150
>150
>150
>150
86.03
43.98
>100
>150
>150
>150
>100
>150
>150
51.58
>100
48.77
>100
>100
52.71
41.60
>100
>150
>150
>150
89.40
>150
>150
58.99
>100
53.00
>100
59.35
50.64
15.90
11.31
30.52
64.26
54.18
>100
>150
>150
>150
72.30
>150
>150
62.08
>100
51.96
>100
38.96
42.66
23.85
15.99
72.68
72.81
54.47
>100
>150
>150
>150
72.30
>150
>150
54.47
>100
67.34
>100
21.14
>150
28.53
>150
>150
>150
>150
>150
>150
>100
>100
81.82
>150
47.50
46.90
28.21
14.31
71.60
63.40
>150
>150
>100
>100
54.97
>150
59.65
35.52
28.42
14.57
53.42
>150
>150
>100
>100
36.54
>150
50.78
39.17
16.58
10.62
2b
2c
3a
3b
3c
64.08
22.35
13.23
39.79
19.33
92.78
>100
>100
3d
3e
4a
4b
4c
4e
>150
>150
>100
>100
>100
50.05
>100
23.78
>150
>100
>100
>100
87.87
>150
52.82
>150
>150
>150
>150
>100
>100
>100
37.14
35.37
95.09
>100
>100
>100
53.88
50.08
47.20
>100
>100
>100
46.99
51.10
31.13
>100
>100
>100
47.93
56.99
>150
>100
>100
>100
81.23
93.06
70.37
Hymexazol
aC. g., Colletotrichum gloeosporiodes; B. c., Botrytis cinerea; A. s., Alternaria solani; F. o.v., Fusarium oxysporum f. sp. vasinfectum; F.
o.n., Fusarium oxysporum f. sp. niveum; F. s., Fusarium solani var. coeruleum; F. g., Fusarium graminearum.
bThe IC50 values of compounds did not show in the table are all over 200 lg ⁄ mL.
35.03 lg ⁄ mL, respectively. This result revealed that the
introduction of a 3-chloropropyloxy substituent into the
ortho-position of the benzene ring could cause a decrease
in activity. The order of antifungal potency is meta-
> para- > ortho-3-chloropropyloxy acetophenone deriva-
tives.
21.14 lg ⁄ mL, in contrast to an IC50 value of 70.37 lg ⁄ mL
for a control reference, hymexazol. This suggests that the
introduction of a 4-fluorobenzyloxy group at the ortho- or
meta- position of an acetophenone largely enhanced activ-
ity against this pathogen. The order of antifungal activity is
ortho- > meta- > para- fluorobenzyloxy acetophenone
derivative, except both F. solani var. coeruleum and
F. graminearum, but 2b showed higher activity than 2c
against these two pathogens. Moreover, benzyloxy ace-
tophenone ethers 2d–o gave a little low activities. This
implied that the four benzyloxys (4-cyanobenzyloxy, 3,5-di-
fluorobenzyloxy, 3-(trifluoromethyl)benzyloxy and benzyloxy)
are detrimental to the activity.
Among the allyl acetophenone ethers 1d–1f and propynyl
acetophenone ethers 1g–i, compound 1g had higher
inhibitory activity on the test pathogens (except B. cinerea)
with its IC50 values of 63–100 lg ⁄ mL than the others with
their IC50 values larger than 150 lg ⁄ mL.
In case of the isopentenyl acetophenone ethers 1m–o,
antifungal activity of 1o, possessing a 3-methylbut-2-enyl-
oxy unit in the ortho-position of the benzene ring, against
the test pathogens except F. graminearum was quite
higher than 1n and 1m.
Among the a-chlorinated acetophenone ethers 3a–e, with
four different C3-alkyl lipophilic groups at the para-position
of the benzene ring, compared with hymexazol, com-
pounds 3a–c showed moderate to strong antifungal activ-
ity toward the test pathogens, except 3c being weakly
active against B. cinerea and A. solani, with their IC50 val-
ues in a range of 10–90 lg ⁄ mL. Compound 3a, with a 3-
chloropropyloxy group, gave much higher activity than 3d,
with a propoxy group, indicating that a chloro atom on an
alkyl chain could largely increase the activity. Compound
3b, having an allyloxy group, had more potent activity than
Benzyl acetophenone ethers 2a–c, with a 4-fluorobenzyl-
oxy group, showed moderate to strong antifungal activities
against the test pathogens (except F. graminearum,
F. oxysporum f. sp. vasinfectum), with IC50 values ranging
from 21 to 64 lg ⁄ mL. Among them, 2b was the most
active against F. graminearum with its lowest IC50 value of
550
Chem Biol Drug Des 2013; 81: 545–552

Antifungal Acetophenone Derivatives
Important carbonyl
Acknowledgments
O
X
Cl (X = Cl) much better
than H, crucial halogen
This manuscript was financially supported by grants from the National Nat-
ural Science Foundation of China (No. 30971882), the Program of Natural
Science Basis Research in Shaanxi (No. 2009JM3010), Shaanxi Province
Science and Technology (No. 2011k02-07), and Startup Foundation for
Docotors of Northwest A&F University (No. Z111020908).
Lipophilic alkyl substituents
are beneficial,
RO
OR better than OH
olefinic bond is better.
OH better than OR
Figure 2: Pharmacophore figure of acetophenones.
References
3c, bearing a prop-2-ynyloxy group (Figure 1, Table 2),
which also suggests that the presence of an olefinic bond
on a C3 alkyl chain could cause an increase in the activity.
Compounds 3a and 3b produced strong activities with 3b
higher than 3a. This suggests that the olefinic bond of the
alkyl chain is essential for activity. Compound 3b was the
most active with IC50 values ranging from 10 to 19 lg ⁄ mL,
in particular its IC50 values were 10.62 and 11.31 lg ⁄ mL
to A. solani and F. oxysporum f. sp. niveum, respectively.
In addition, disubstituted acetophenone ether 3e, bearing
two allyloxy groups, led sharply to low activity or a loss of
activity, indicating that a free hydroxy group on a meta-
position of the benzene ring may play an important role in
activity. Both 3a and 3b, with a broad-spectrum antifungal
activities, were found to exhibit much higher activities than
hymexazol with 3a slightly lower than the control to
B. cinerea only. Compound 3b gave the highest inhibiting
activity and might be a new lead compound for fungicides.
1. Cohen M.L. (2000) Changing patterns of infectious dis-
ease. Nature;406:762–767.
2. Janisiewicz W.J., Korsten L. (2002) Biological control of
postharvest diseases of fruits. Annu Rev Phytopa-
thol;40:411–441.
3. Mueller A.A., Reiter S.A., Heider K.G., Wagner H.
(1999) Plant-derived acetophenones with antiasthmatic
and anti-inflammatory properties: inhibitory effects on
chemotaxis, right angle light scatter and actin polymeri-
zation of polymorphonuclear granulocytes. Planta
Med;65:590–594.
4. VanEtten H.D., Sandrock R.W., Wasmann C.C., Soby
S.D., McCluskey K., Wang P. (1995) Detoxification of
phytoanticipins and phytoalexins by phytopathogenic
fungi. Can J Bot;73:518–525.
5. Lv J., Qian Y., Liu T., Wang Y. (2007) Synthesis and
evaluation of amphiphilic cationic quinine-derived for
antibacterial activity against methicillin-resistant Staphy-
lococcus aureus. Bioorg Med Chem Lett;17:4102–
4106.
Of the synthetic acetophenone ethers 4a–j, compound 4c,
bearing a prop-2-ynyloxy group at a para-position of the
benzene ring, had a higher inhibiting activity than 4e, with
an 3-methylbut-2-enyloxy group, except C. gloeosporiodes
and F. oxysporum f. sp. vasinfectum, while other benzyl
acetophenone ethers were relatively weak or inactive. This
implied that the benzyloxylation of acetophenones was
deleterious to the antifungal activity. These results revealed
that the coexistence of a meta-acidic phenolic hydroxyl
and a para-lipophilic alkyl residue of acetophenone deriva-
tives is an important chemical feature for activity.
6. Konstantinova L.S., Bol’shakov O.I., Obruchnikova N.V.,
Laborie H., Tanga A., Sopena V., Lanneluc I., Picot L.,
´
´
´
Sable S., Thiery V., Rakitin O.A. (2009) One-pot synthe-
sis of 5-phenylimino, 5-thieno or 5-oxo-1,2,3-dithiazoles
and evaluation of their antimicrobial and antitumor activ-
ity. Bioorg Med Chem Lett;19:136–141.
7. Gul H.I., Vepsalainen J., Gul M., Erciyas E., Hanninen
O. (2000) Cytotoxic activities of mono and bis Mannich
bases derived from acetophenone against Renca and
Jurkat cells. Pharm Acta Helv;74:393–398.
8. Sivakumar P.M., Sheshayan G., Doble M. (2008) Exper-
imental and QSAR of acetophenones as antibacterial
agents. Chem Biol Drug Des;72:303–313.
Taken together, a pharmacophore figure of this class of
substituted acetophenones using SAR data is given in Fig-
ure 2.
9. Zheng C.D., Li G., Li H.Q., Xu X.J., Gao J.M., Zhang
A.L. (2008) DPPH-scavenging activities and structure-
activity relationships of phenolic compounds. Nat Prod
Commun;5:1759–1765.
10. Simonsen H.T., Adsersen A., Bremner P., Heinrich M.,
Wagner Smitt U., Jaroszewski J.W. (2004) Antifungal
constituents of Melicope borbonica. Phytother
Res;18:542–545.
Conclusions
A series of acetophenone derivatives including 12 new
compounds were prepared and their in vitro antifungal
activities against phytopathogens evaluated for the first
time. Among the synthetic derivatives, some compounds
such as 3a and 3b were found to exert broad-spectrum
antifungal activities, which might be promising leads for
agricultural fungicides. In addition, structure–activity rela-
tionships showed that the co-occurrence of a meta-hydro-
xyl and a para-lipophilic alkyl substituents was beneficial to
their antifungal activity, and there are more works to be in
progress. The future work will be reported in due.
´
´
´
11. Tomas-Barberan F., Iniesta-Sanmartı´n E., Tomas-Lo-
rente F., Rumbero A. (1990) Antimicrobial phenolic
compounds from three Spanish Helichrysum species.
Phytochemistry;29:1093–1095.
12. Brucker R.M., Baylor C.M., Walters R.L., Lauer A., Har-
ris R.N., Minbiole K.P.C. (2008) The identification of
Chem Biol Drug Des 2013; 81: 545–552
551

Ma et al.
2,4-diacetylphloroglucinol as an antifungal metabolite
fungus associated with Melia azedarach, and their anti-
fungal, antifeedant, and toxic activities. J Agric Food
Chem;60:3424–3431.
produced by cutaneous bacteria of the salamander
Plethodon cinereus. J Chem Ecol;34:39–43.
13. Ligon J.M., Hill D.S., Hammer P.E., Torkewitz N.R.,
Hofmann D., Kempf H.J., van Pee K.H. (2000) Natural
products with antifungal activity from Pseudomonas
biocontrol bacteria. Pest Manag Sci;56:688–695.
14. Gao J.-M., Li Y., Xie S.-D., Zhang A.-L., Shi X.-W.,
Zhang W.-L. (2009) Isolation of antifungal agent 2,4-di-
hydroxy-5-methylacetophenone from Polyporus picipes
17. Ma Y.T., Wang J.J., Liu X.W., Yang S.X., Gao J.M.
(2010)
1-[4-(3-chloropropoxy)-2-hydroxyphenyl]etha-
none. Acta Cryst;66:o52.
18. Ma Y.T., Zhang A.L., Yuan M.S., Gao J.M. (2010) 1-[4-
(3,5-difluorobenzyloxy)-2-hydroxyphenyl]ethanone. Acta
Cryst;66:o2468.
19. Ma Y.T., Yang C.L., Li Z.S., Li Z.Q., Ding J.N. (2010)
cultures,
200910020963.7.
China
Patent
Application
Code,
1-(4-benzyloxy-2-hydroxyphenyl)ethanone.
Cryst;67:o3225.
Acta
15. Dai H.-L., Liu W.-Q., Xu H., Yang L.-M., Lv M.,
Zhang Y.-T. (2009) Anti human immunodeficiency
virus-1 (HIV-1) agents 1. Discovery of benzyl phenyl
ethers as new HIV-1 inhibitors in vitro. Chem Pharm
Bull;57:84–86.
Supporting Information
Additional Supporting Information may be found in the
online version of this article:
16. Li X.-J., Zhang Q., Zhang A.-L., Gao J.-M. (2012)
Metabolites from Aspergillus fumigatus, an endophytic
Appendix S1. Data for 30 known compounds.
552
Chem Biol Drug Des 2013; 81: 545–552