Bioorganic & Medicinal Chemistry Letters
Antifungal activity of alkyl gallates against plant pathogenic fungi
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Shinsaku Ito , Yasutaka Nakagawa , Satoru Yazawa , Yasuyuki Sasaki, Shunsuke Yajima
Department of Bioscience, Faculty of Applied Bioscience, Tokyo University of Agriculture, 1-1-1 Sakuragaoka, Setagaya, Tokyo 156-8502, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
The antifungal activity of alkyl gallates against plant pathogenic fungi was evaluated. All of the fungi
tested in this study were susceptible to some alkyl gallates, and the effect of linear alkyl gallates against
plant pathogenic fungi was similar to the previously reported effects against Gram-negative and
Gram-positive bacteria. We found that branched alkyl gallates showed stronger activity than did linear
alkyl gallates with similar logP values. In addition, the antifungal activity of alkyl gallates was correlated
with gallate-induced inhibition of the activity of mitochondrial complex II. The antifungal activity of alkyl
gallates likely originates, at least in part, from their ability to inhibit the membrane respiratory chain.
Ó 2014 Elsevier Ltd. All rights reserved.
Received 22 October 2013
Revised 28 January 2014
Accepted 7 February 2014
Available online 20 February 2014
Keywords:
Drug design
Gallic acid
Structure–activity relationship study
Gallic acid and its alkyl esters such as propyl, octyl, and dodecyl
gallates are used as food preservatives owing to their antioxidant
activity. To date, it has been reported that these chemicals exhibit
various biological activities, including cardiovascular protection,
tyrosinase inhibition, as well as antibacterial, antifungal, antican-
cer, anti-inflammatory, and antioxidant activities. With respect to
antifungal activity, Kubo et al. reported that octyl gallate was effec-
tive against Saccharomyces cerevisiae, Zygosaccharomyces bailii,
Candida albicans, and Aspergillus niger; the length of the alkyl group
played an important role in determining the antifungal activity.1 In
a subsequent study by Kubo et al., nonyl gallate showed the
highest activity against S. cerevisiae among linear gallates.2 Leal
et al. performed a similar study, which demonstrated that gallates
with linear alkyl chains of 7–9 carbons showed the highest
antifungal activity against yeasts, hialohyphomycetes, and derma-
tophytes.3 These studies showed the antifungal activity of linear
alkyl gallate against human opportunistic pathogenic fungi likely
depend on the hydrophobic alkyl chain. However, structure–
activity relationship studies of alkyl gallates against plant patho-
genic fungi have not yet been performed. Furthermore, the target
site(s) of gallates is unknown.
The chemicals were prepared as described previously.2
Gallic acid and alkanols dissolved in tetrahydrofuran and dichloro-
methane (CH2Cl2) were stirred at room temperature in the pres-
ence of N,N’-dicyclohexylcarbodiimide. The reaction mixture was
quenched with distilled water. The aqueous layer was extracted
with ethyl acetate. The organic layer was dried and concentrated
under reduced pressure. The resulting oil was purified by column
chromatography. Figure 1 shows the structures and logP values
of the alkyl gallates used in this Letter. LogP values were calculated
by ChemBioDraw Ultra software. Plant pathogenic fungi were gifts
from Professor Natsuaki (Tokyo Univ. of Agric.).
First, we estimated the effect of alkyl gallates against four plant
pathogenic fungi (Table 1A). Strains were grown on potato dex-
trose agar (PDA) plates. The antifungal assay was performed as de-
scribed below. Small agar blocks containing hyphal tips were cut
out from the colony margins and placed onto glycerol peptone
medium (0.12% KH2PO4, 3% glycerol, 0.2% polypeptone, 0.02%
MgSO4, 0.00012% CuSO4, 0.00021% FeCl3, 0.000102% NaMoO4,
0.000021% FeSO4, 0.000006% CoCl2 and 0.000006% CaCl2) supple-
mented with each gallate dissolved by dimethyl sulfoxide and cul-
tured at 30 °C for one day. Antifungal activities were determined
by measuring the minimum inhibitory concentration (MIC). Gallic
acid was not effective against these four fungi. Previously, it was
reported that gallic acid purified from Terminalia nigrovenulosa
bark possessed high antifungal activity against F. solani.4 However,
the F. solani strain used in this study was different from that used
by Nguyen et al, which may be why gallic acid did not inhibit the
growth of F. solani in this study. Some of the linear alkyl gallates
tested here (7–12) showed antifungal activity against all fungi
strains (Table 1A). Alkyl gallates possessing alkyl chains of 8–12
carbon atoms were particularly strong activity. While the length
of the alkyl group was generally associated with antifungal activ-
In this study, we synthesized 14 alkyl gallates and investigated
the antifungal activity of these gallates against the following four
plant pathogenic fungi: Fusarium solani, Colletotrichum acutatum,
Colletotrichum dematium, and Alternaria brassicicola, which cause
serious damage to economically important crops and fruits world-
wide. Here, we investigated structure–activity relationships and
the mode of action of gallates against these four fungi.
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Corresponding author. Tel.: +81 3 5477 2768.
These authors contributed equally to this work.
0960-894X/Ó 2014 Elsevier Ltd. All rights reserved.