Synthesis of linear geranylphenols and their effect on mycelial growth of plant pathogen Botrytis cinerea

Article abstract of DOI:10.3390/molecules19021512

Natural geranyl compounds are known to exhibit important biological activities. In this work a series of geranylphenols were synthesized to evaluate their effect on the mycelial growth of Botrytis cinerea. Geranyl derivatives were synthesized by direct ge

Full text of DOI:10.3390/molecules19021512

Molecules 2014, 19, 1512-1526; doi:10.3390/molecules19021512
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molecules
ISSN 1420-3049
www.mdpi.com/journal/molecules
Article
Synthesis of Linear Geranylphenols and Their Effect on
Mycelial Growth of Plant Pathogen Botrytis cinerea
Luis Espinoza 1,*, Lautaro Taborga 1, Katy Díaz 1, Andrés F. Olea 2 and Hugo Peña-Cortés 3
1
Departamento de Química, Universidad Técnica Federico Santa María, Av. España No. 1680,
Valparaíso 2340000, Chile; E-Mails: lautaro.taborga@usm.cl (L.T.); katy.diaz@usm.cl (K.D.)
2
Departamento de Ciencias Químicas, Facultad de Ciencias Exactas, Universidad Andrés Bello,
Quillota 980, Viña del Mar 2520000, Chile; E-Mail: aolea@unab.cl
3
Dirección de Investigación, Universidad de Valparaíso, Blanco 951, Valparaíso 2340000, Chile;
E-Mail: hugo.pena@uv.cl
* Author to whom correspondence should be addressed; E-Mail: luis.espinozac@usm.cl;
Tel.: +56-032-265-4225; Fax: +56-032-265-4782.
Received: 9 December 2013; in revised form: 4 January 2014 / Accepted: 15 January 2014 /
Published: 27 January 2014
Abstract: Natural geranyl compounds are known to exhibit important biological activities.
In this work a series of geranylphenols were synthesized to evaluate their effect on the
mycelial growth of Botrytis cinerea. Geranyl derivatives were synthesized by direct
geranylation reactions between the corresponding phenol derivatives and geraniol, using
.
BF3 OEt2 as catalyst and AgNO3 as secondary catalyst. Previously reported molecules
[geranylhydroquinone (2), geranylhydroquinone diacetate (6) and geranylphloroglucinol (9)],
and new substances [(E)-4-(3,7-dimethylocta-2,6-dienyl)benzene-1,2,3-triol (geranyl-
pyrogallol, 7), (E)-4-(3,7-dimethylocta-2,6-dienyl)benzene-1,2,3-triyl triacetate (8), (E)-2-(3,7-
dimethylocta-2,6-dienyl)benzene-1,3,5-triyl triacetate geranylphloroglucinol triacetate (10),
2,4-bis((E)-3,7-dimethylocta-2,6-dienyl)benzene-1,3,5-triyl triacetate (11), 2,6-bis((E)-3,7-
dimethylocta-2,6-dienyl)-3,5-dihydroxyphenyl acetate (12)], were obtained. All compounds
were characterized by IR, HRMS and NMR spectroscopic data. The inhibitory effect of the
synthesized compounds on the mycelial growth of Botrytis cinerea was tested in vitro.
Excepting compound 11, all substances constrained the mycelial growth of Botrytis
cinerea. The antifungal activity depends on the chemical structure of geranylphenol
derivatives. Compounds 2 and 9 were the more effective substances showing inhibition
degrees higher than those obtained with the commercial fungicide Captan, even at lower
concentrations. Monosubstitution on the aromatic nucleus by a geranyl chain seems to be

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more effective for the inhibition of mycelial growth than a double substitution. These
1513
results suggest that the new derivatives of geranylphenols have the ability to block the
mycelial development of the plant pathogen B. cinerea and that this capacity depends
strongly on the structural features and lipophilicity of the compounds.
Keywords: synthesis; linear geranylphenols; antifungal activity; Botrytis cinerea
1. Introduction
Several factors highlight the urgent need for the development of new control strategies for the
phytopathogenic fungus Botrytis cinerea and other plagues affecting important agricultural crops.
They include the emergence of highly resistant strains of B. cinerea to fungicides, contamination of
soil and water, high cost of chemical control and the limited availability of fungicides [1]. In addition,
the strong worldwide trend towards sustainable development and environmentally friendly substances
should be considered [2]. It has been extensively documented that multiple metabolites, obtained from
species belonging to the plant kingdom, have special biological properties suitable for controlling
several types of animal and plant pathogens. For instance, linear geranylquinones or geranylhydroquinones,
present in higher plants and in marine urochordates [3], exhibit cytotoxic activity and inhibit larval growth
and development. Some particular compounds such as 2-geranylbenzoquinone (1), isolated from Ascindian
Synoicum castellatum [4], 2-geranylhydroquinone (2) isolated from the Cordia alliodora tree [2],
Phacelia crenulata [5–7], Aplidium antillense [8] and the tunicate Amaroucium multiplicatum [9],
have been related to biological activities including toxicity, cytotoxicity, antimicrobial, anti-cancer
protective and antioxidant effects, among others [6,9–13]. Additionally, linear geranylmethoxyphenol/
acetates (compounds 3–5, see Figure 1), isolated from Phaceliaixodes [8], are cytotoxic, allergenic and
insecticidal, and topical application of 100 µg of geranylbenzoquinone on pupae of Tenebrio caused
severe abnormalities and death [14].
Several marine sesquiterpenoid quinones and hydroquinones are of considerable scientific interest
because of their versatile biological activities where a particular (hydro)quinone may display multiple
activities [15].
In previous studies we have reported the synthesis and cytotoxic activity of compounds 1–2 and
some geranylmethoxyphenol/acetate analogs [16,17]. Considering the activity against phytophagous
insects and pathohens of compounds 3 and 4 [14] and assuming the presence of this property in other
geranylphenol analogs, we have recently reported the synthesis and structure determination of
14 linear geranylphenols molecules [16].
Thus, our interest is to get a broader insight into the relationship between the molecular structure
and the biological activity against plant pathogens of geranylquinone and geranylhydroquinone
derivatives and geranylphenols. We believe that this knowledge might be useful to provide new
substances to control such kinds of pathogens. Therefore, in this research we report the synthesis, structure
determination, and in-vitro antifungal effect against phytopathogenic fungus Botrytis cinerea of a series of
geranylphenols derivatives 2, 6–12, (see Figure 2). These compounds were obtained by a modification of a

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previously reported synthetic method [12,14,16], which consisted in the use of acetonitrile as a solvent
instead of dioxane. Also we have evaluated the use of AgNO3 as secondary catalyst.
Figure 1. Structure of some active linear geranylphenols.
Figure 2. Structure of linear geranylphenols 2, 6–12 synthesized in this work.
2. Results and Discussion
2.1. Chemistry
Compound 2 was prepared by using the previously described coupling between geraniol and
hydroquinone [16–18], but using acetonitrile instead of dioxane as solvent and assessing the use of
AgNO3 as secondary catalyst. In this case, the compound 2 was obtained with a 32% yield, which is
slightly higher than that previously reported by us [16], but similar to that reported by other
authors [19]. Compound 6 was obtained in 92.8% yield from compound 2 by a standard acetylation
reaction using Ac2O and DMAP in CH2Cl2. The spectroscopic data of compounds 2 and 6 were
consistent with those previously reported [5,6,8,20].
Compound 7 (for which the name geranylpyrogallol is proposed in analogy with the name of
geranylphloroglucinol [18,21]) was prepared in 18.1% yield following the same experimental

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procedure described for the synthesis of compound 2. The structure of 7 was mainly established by
NMR, where aromatic signals at δH = 6.53 (d, J = 8.3 Hz, 1H) and δH = 6.44 (d, J = 8.3 Hz, 1H) were
observed as two doublets for hydrogens H-5 and H-6, confirming the aromatic monosubstitution
position. Additionally, in the HMBC spectrum, the signal at δH = 3.30 ppm assigned to H-1' (d, J = 7.1 Hz,
2H, H-1') shows 3JH-C coupling with C-3 (δC = 142.5), C-3' (δC = 138.4 ppm) and C-5 (δC = 120.2 ppm)
2
and JH-C coupling with C-2' and C-4 (δC = 122.2 ppm and 119.5 respectively). These HMBC
correlations are shown in Figure 3. In order to establish the E geometry of the C-2'-C-3' double bond of
the geranyl chain, selective 1D NOESY NMR experiments were recorded for compound 7.
These correlations are shown in Figure 3, where the most important of those correspond to the
correlations observed between the H-1' and the hydrogen H-5 and methyl group in the C-3' position.
1
Figure 3. Top: mayor 2D H-13C HMBC and sel. 1D NOESY correlations for compound 7.
1
Bottom: standard H-NMR spectrum; (a) selective irradiation NOESY at 5.31ppm (H-2').
(b) selective irradiation NOESY at 3.30 ppm (H-1').
Compound 8 was obtained from compound 7 in 93% yield by standard acetylation, using Ac2O and
1
DMAP in CH2Cl2. In the H-NMR spectrum of the triacetylated derivative 8, three singlets at
δH = 2.29, 2.27 and 2.26 ppm (each 3H, CH3CO) were observed. Additionally, in the 13C-NMR
spectrum the signals appearing at δC = 168.0, 167.7 and 167.1 ppm (C=O), confirmed the presence of
the triacetylated derivative.
The synthesis of compound 9 from phloroglucinol and geraniol was performed following the
experimental procedure described in Scheme 1. However, after completion of reaction two main spots
were observed in the TLC analysis. Subsequent column chromatography (C.C.) separation and
purification allowed the isolation of the two fractions, a less polar one corresponding to a complex

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mixture (Fraction I), and a more polar fraction (Fraction II) corresponding to compound 9, obtained in
32% yield. The spectroscopic data of compound 9 was consistent with that previously reported [18,21].
Scheme 1. Synthesis of compounds 9–12.
Subsequently, compound 10 was obtained (in 86.8% yield) from 9 by standard acetylation with
1
Ac2O and DMAP in CH2Cl2. The H-NMR spectrum of the triacetylated derivative 10 shows two
singlet signals at δH = 2.26 ppm (2 × CH3CO) and 2.24 ppm (CH3CO). Additionally, in the 13C-NMR
spectrum the signals at δC = 168.6 (2 × C=O) and 168.5 ppm (C=O), confirm the presence of the
triacetylated derivative.
Compound 11 was obtained in 70.3% yield by standard acetylation of the complex mixture
(Fraction I). Spectroscopic evidence of double substitution on the aromatic nucleus by geranyl chains
1
was established from the H-NMR spectrum by the following observations: a unique Ar-H signal
appears at 6.83 ppm (s, 1H, H-6); and the intensity of this signal was 1:4 relative to the signal at 3.12 ppm
1
(bs, 4H, H-1'). The presence of three acetate groups was evidenced in the H-NMR spectrum by the
observed signals at δH = 2.26 ppm (s, 3H, COCH3) and 2.24 ppm (s, 6H, COCH3), and corroborated by
13
the presence in the C-NMR spectrum of signals at δC = 168.6 (2 × COCH3) and 168.4 (COCH3).
Finally, the complete determination of symmetrical structure was established by 2D HMBC and
selective 1D NOESY experiments. The major 2D HMBC correlations, which were considered to
3
confirm the structure of compound 11 were a JH-C coupling observed between H-1' with C-3
(δC = 148.6 ppm), with C-1 and C-5 (δC = 147.2 ppm) and C-3' (δC = 135.6 ppm), while 2JH-C coupling
was observed with C-2 and C-4 (δC = 124.6 ppm) and C-2' (δC = 121.0 ppm). From selective 1D
NOESY experiments, the E geometry in the C-2'-C-3' double bond position of the geranyl chain was
established. Here the most important correlations were observed between the H-1' and methyl group in
C-3' position and those detected with the acetate groups (Figure 4). The 2D HMBC and 1D NOESY
correlations are shown in Figure 4. Additionally, the possible incorporation of two geranyl chains in
the aromatic ring was previously described for geranylmethoxyphenol analogues by other authors [22].

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Figure 4. Top: mayor 2D 1H-13C HMBC and sel. 1D NOESY correlations for compound 11.
1
Bottom: standard H-NMR spectrum; (a) selective irradiation NOESY at 5.02 ppm (H-2').
(b) selective irradiation NOESY at 3.12 ppm (H-1').
Finally, compound 12 was obtained in 96% yield by saponification of 11 under mild conditions
(Et3N/MeOH) at room temperature. The structure of compound 12 was established mainly by
1
comparison of the NMR spectra of compounds 11 and 12. In the H-NMR of compound 12, only one
acetate group signal was observed at δH = 2.30 ppm (s, 3H, CH3CO), while in the 13C-NMR spectrum,
only the signal at δC = 169.3 ppm (CO2) was observed. The position of the acetyl group in the structure
was proposed from the observation of long-range interactions in the 1D NOESY experiments between
CH3CO and the hydrogens of C-1' (see Figure 5).
On the other hand, the use of AgNO3 as secondary catalyst has significant effects on the
Friedel-Crafts direct geranylation reaction used to obtain compound 9, namely, the reaction yield was
increased from 4.2% to 32% [20], the formation of compounds disubstituted in the aromatic ring is
enhanced, and the degradation of geraniol products is reduced (as evidenced by TLC analysis) and a
lower difficulty in the C.C. separation process is observed in all of the cases. This suggests that AgNO3
stabilizes geraniol during the reaction process in CH3CN solution.

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Figure 5. Main selective 1D NOESY correlations for compound 12.
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2.2. Anti-phytopathogenic Activity against Botrytis cinerea
To evaluate the biological activity of the geranylphenol derivatives 2, 6–12 (Figure 2), their effect
on the growth of mycelia of B. cinerea was determined in vitro after 48 h of incubation by using the
agar-diffusion assay technique with PDA as medium. Figure 6 shows a representative example of three
independent assays for evaluating the biological activity of the studied compounds. Details of
experimental conditions are given in the Experimental section. The results are expressed as percentage
of inhibition, which is calculated as the ratio of the area of B. cinerea in the presence and absence of
geranylphenols, are summarized in Table 1. For comparison, in this table the percentage of inhibition
values of captan, a molecule that is widely used to control the growth of B. cinerea are included
(measured at the same concentration used to determine the activity of geranylphenols).
Figure 6. Effect of linear geranylphenols on in vitro mycelial growth of B. cinerea. (a)
Negative control, represents a medium containing only PDA; (b) positive control,
measured in the presence of 250 mg/L of Captan; (c) the medium includes compound 2 at
250 mg/L; (d) medium contains compound 9 at 250 mg/L.
The data in Table 1 shows that all compounds, with the exception of compound 11, affect the
development of the mycelia of B. cinerea, reducing its growth between 56%–86%, compared to the
negative control, at concentrations of 150–250 mg/L after 48 h of incubation. Compounds 2 and 9
were the more active ones, showing an inhibitory effect on the mycelial growth that depends on the
applied concentration. At 150 mg/L compounds 9 and 2 exhibited inhibitory effects of 66% and 81%,
respectively, which increased up to 81% and 86% at higher concentration (250 mg/L). The observed
inhibitory capacity exceeds even the value of inhibition obtained with the commercial fungicide captan
used as positive control (Table 1). On the other hand, compound 11 seems to be inactive against
B. cinerea. A grade of the mycelial growth inhibition lower than 50% is observed, independently of the
applied concentration.

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Table 1. Effect of linear geranylphenols and new derivatives on mycelial growth of B. cinerea.
Percentage of inhibition on in vitro mycelial growth of Botrytis cinerea (%) a
Compounds
50 mg/L
58 ± 2.15
40 ± 7.20
45 ± 1.36
28 ± 2.44
38 ± 0.21
33 ± 5.48
0 ± 0.00
150 mg/L
82 ± 3.04
67 ± 1.67
63 ± 0.65
56 ± 5.70
66 ± 7.95
56 ± 1.80
16 ± 4.10
30.4 ± 2.30
0 ± 0.00
250 mg/L
86 ± 1.35
76 ± 1.54
72 ± 1.78
64 ± 1.76
81 ± 2.57
72 ± 0.87
26 ± 0.00
66 ± 3.90
0 ± 0.00
2
6
7
8
9
10
11
12
0 ± 0.00
C–
Captan
0 ± 0.00
39 ± 7.33
60 ± 8.45
80 ± 2.92
a
The percentage of inhibition of mycelial growth was based on colony diameter measurements after 48 h
of incubation. Each point represents the mean of at least three independent experiments ± standard deviation.
Analysis of the results indicates that the antifungal activity depends on the chemical structure of the
geranylphenol derivatives. Thus, compounds having hydroxyl groups attached to the aromatic nucleus
(compounds 2, 7, and 9) exhibit a 86%, 72% and 81% of inhibitory activity against the growth of the
mycelia of B. cinerea compared to those acetylated compounds having acetate groups in the same
positions which have 76, 64 and 72% mycelial growth inhibition (compounds 6, 8 and 10).
These results suggest that the activity is mainly determined by the presence of the geranyl chain.
However, by comparing the activities of compounds 11 and 10 it can be concluded that the inhibitory
effect almost disappears with a double geranyl chain substitution on the triacetylated aromatic nucleus.
The activity is partly recovered when two acetyl groups of compound 11 are replaced by two hydroxyl
groups in compound 12. Thus, for double geranyl substituted compounds the activity depends strongly
on the presence of hydroxyl groups.
Our results are consistent with previous investigations [23–26] reporting that molecules with
similar structure present high potential antifungal activity (in the range 1.0 to 10.0 µg) against
Cladosporium cladosporioides and C. sphaerospermum [25]. Taken together with our results it could
be concluded that addition of a geranyl chain and hydroxyl groups to the aromatic nucleus increases
the biological activity of the molecule by at least a factor of two.
3. Experimental
3.1. General
Unless otherwise stated, all chemical reagents purchased (Merck, Darmstadt, Germany or Aldrich,
St. Louis, MO, USA) were of the highest commercially available purity and were used without
previous purification. IR spectra were recorded as thin films in a FT-IR Nicolet 6700 spectrometer
(Thermo Scientific, San Jose, CA, USA) and frequencies are reported in cm−1. Low resolution mass
spectra were recorded on an Agilent 5973 spectrometer (Agilent Technologies, Santa Clara, CA, USA)
at 70eV ionising voltage in a DB-5 m, 30 m × 0.25 mm × 0.25 µm column, and data are given as m/z
(% rel. int.). High resolution mass spectra were recorded on an LTQ Orbitrap XL spectrometer

Molecules 2014, 19
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(Thermo Scientific, San Jose, CA, USA) by applying a voltage of 1.8 kV in the positive and 1.9 kV in
the negative, ionization mode. The spectra were recorded using full scan mode, covering a mass range
from m/z 100–1,300. The resolution was set to 50,000 and maximum loading time for the ICR cell was
13
13
1
set to 250 ms.1H, C, C DEPT-135, sel. gs1D H NOESY, gs2D HSQC and gs2D HMBC spectra
were recorded in CDCl3 solutions and are referenced to the residual peaks of CHCl3 at δ = 7.26 ppm
1
13
and δ = 77.0 ppm for H and C, respectively, on a Bruker Avance 400 Digital NMR spectrometer
(Bruker, Rheinstetten, Germany), operating at 400.1 MHz for 1H and 100.6 MHz for 13C.
Chemical shifts are reported in δ ppm and coupling constants (J) are given in Hz. Silica gel (Merck
200–300 mesh) was used for C.C. and silica gel plates HF254 for TLC. TLC spots were detected by
heating after spraying with 25% H2SO4 in H2O.
3.2. Synthesis of Geranylphenol Derivatives
(E)-2-(3,7-Dimethylocta-2,6-dienyl)benzene-1,4-diol (1,4-geranylhydroquinone) (2). To a solution of
1,4-hydroquinone (1.12 g, 10.2 mmol) and geraniol (1.57 g, 10.2 mmol) in acetonitrile (30 mL),
.
saturated with AgNO3, was slowly added BF3 OEt2 (0.45 g, 3.2 mmol) dropwise with stirring at room
temperature and under a N2 atmosphere. After the addition was completed, the stirring was continued
for 48 h. The end of the reaction was verified by TLC, and then the mixture was poured onto crushed ice
(30 g) and extracted with EtOAc (3 × 20 mL). The organic layer was washed with 5% NaHCO3 (30 mL)
and water (2 × 15 mL), dried over Na2SO4, and filtered. The solvent was evaporated under reduced
pressure. The crude was re-dissolved in CH2Cl2 (5 mL) and chromatographed on silica gel with
petroleum ether/EtOAc mixtures of increasing polarity (19.8:0.2→14.0:6.0). Compound 2 was
obtained as a brownish oil (0.736 g, 32% yield). Spectroscopic data of compound 2 was consistent
with those in the literature [12,16,17].
(E)-2-(3,7-Dimethylocta-2,6-dienyl)-1,4-phenylene diacetate (6). To a solution of compound 2
(0.05 g, 0.45 mmol), DMAP (5.0 mg) in dichloromethane (20 mL) and pyridine (2.0 mL) was added
Ac2O (0.54 g, 5.3 mmol). The end of the reaction was verified by TLC (0.5 h), and the mixture was
extracted with EtOAc (2 × 20 mL). Then the organic layer was washed with 5% KHSO4 (2 × 10 mL)
and water (2 × 10 mL), dried over Na2SO4, filtered and the solvent was evaporated under reduced
pressure. The crude was re-dissolved in CH2Cl2 (5 mL) and chromatographed on silica gel with
petroleum ether/EtOAc mixtures of increasing polarity (19.8:0.2→16.8:3.2). Compound 6 was
obtained as a viscous yellow oil (0.0818 g, 92.8% yield). IR (cm−1): 2967; 2917; 1763; 1490; 1368;
1169; 1012; 914. 1H-NMR: 7.02 (d, J = 9.5 Hz, 1H, H-6); 6.94 (m, 2H, H-3 and H-5); 5.22 (t, J = 7.2 Hz,
1H, H-2'); 5.09 (t, J = 6.1 Hz, 1H, H-6'); 3.23 (d, J = 7.2 Hz, 2H, H-1'); 2.30 (s, 3H, COCH3); 2.28
(s, 3H, COCH3); 2.09–2.08 (m, 2H, H-5'); 2.06–2.05 (m, 2H, H-4'); 1.68 (s, 3H, H-8'); 1.66 (s, 3H,
CH3-C3'); 1.60 (s, 3H, CH3-C7'). 13C-NMR: 169.4 (2 × COCH3); 148.3 (C-4); 146.3 (C-1); 137.6 (C-3');
134.9 (C-2); 131.6 (C-7'); 124.1 (C-6'); 122.9 (C-6); 122.6 (C-3); 120.7 (C-2'); 119.9 (C-5); 39.6 (C-4');
28.5 (C-1'); 26.5 (C-5'); 25.7 (C-8'); 21.1 (COCH3); 20.8 (COCH3); 17.7 (CH3-C7'); 16.1 (CH3-C3').
(E)-4-(3,7-Dimethylocta-2,6-dienyl)benzene-1,2,3-triol (7). To a solution of pyrogallol (1.25 g, 9.9 mmol)
and geraniol (1.8 g, 11.9 mmol) in acetonitrile (30 mL), saturated with AgNO3, was slowly added
.
BF3 OEt2 (0.7 g, 4.8 mmol) dropwise with stirring at room temperature and under a N2 atmosphere.

Molecules 2014, 19
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After the addition was completed, the stirring was continued for 24 h. The end of the reaction was
verified by TLC, and then the mixture was poured onto crushed ice (30 g) and it was extracted with
EtOAc (3 × 20 mL). The organic layer was washed with 5% NaHCO3 (30 mL) and water (2 × 15 mL),
dried over Na2SO4, and filtered. The solvent was evaporated under reduced pressure. The crude
product was redissolved in CH2Cl2 (5 mL) and chromatographed on silica gel with petroleum ether/EtOAc
in isocratic mixtures (20:80). Compound 7 was obtained as a reddish oil (0.47 g, 18.1% yield). IR (cm−1):
1
3396; 2966; 2917; 1627; 1472; 1375; 1285; 1027; 794. H-NMR: 6.53 (d, J = 8.3 Hz, 1H, H-5); 6.44
(d, J = 8.3 Hz, 1H, H-6); 5.45 (bs, 3H, OH); 5.31 (t, J = 7.1 Hz, 1H, H-2'); 5.06 (t, J = 5.9 Hz, 1H, H-6');
3.30 (d, J = 7.1 Hz, 2H, H-1'); 2.13–2.11 (m, 2H, H-5'); 2.09–2.06 (m, 2H, H-4'); 1.76 (s, 3H, CH3-C3');
1.68 (s, 3H, H-8'); 1.60 (s, 3H, CH3-C7'). 13C-NMR: 142.5 (C-3); 142.3 (C-1); 138.4 (C-3'); 132.1 (C-7');
132.0 (C-2); 123.8 (C-6'); 122.2 (C-2'); 120.2 (C-5); 119.5 (C-4); 107.4 (C-6); 39.6 (C-4'); 29.4 (C-1');
26.3 (C-5'); 25.7 (C-8'); 17.7 (CH3-C7'); 16.1 (CH3-C3'). HRMS: (M + 1) calcd. for C16H22O3:
263.1569, found: 263.1547.
(E)-4-(3,7-Dimethylocta-2,6-dienyl)benzene-1,2,3-triyl triacetate (8). To a solution of compound 7
(0.05 g, 0.129 mmol) and DMAP (3.0 mg) in dichloromethane (20 mL) and pyridine (1.0 mL) was
added Ac2O (0.54 g, 5.3 mmol). The end of the reaction was verified by TLC (0.5 h), and the mixture
was extracted with EtOAc (2 × 20 mL). The organic layer was washed with 5% NaHCO3 (30 mL) and
water (2 × 15 mL), dried over Na2SO4, and filtered. The solvent was evaporated under reduced
pressure. Then the organic layer was washed with 5% KHSO4 (2 × 10 mL) and water (2 × 10 mL),
dried over Na2SO4, filtered and the solvent was evaporated under reduced pressure. The crude was
re-dissolved in CH2Cl2 (5 mL) and chromatographed on silica gel with petroleum ether/EtOAc
mixtures of increasing polarity (19.8:0.2→15.4:4.6). Compound 8 was obtained as a viscous yellow oil
(0.0686 g, 93% yield). IR (cm−1): 2925; 1781; 1491; 1370; 1188; 1045; 871. 1H-NMR: 7.12 (d, J = 8.6 Hz,
1H, H-5); 7.05 (d, J = 8.6 Hz, 1H, H-6); 5.21 (t, J = 7.2 Hz, 1H, H-2'); 5.09 (t, J = 6.4 Hz, 1H, H-6');
3.23 (d, J = 7.2 Hz, 2H, H-1'); 2.29 (s, 3H, COCH3); 2.27 (s, 3H, COCH3); 2.26 (s, 3H, COCH3);
2.11–2.09 (m, 2H, H-5'); 2.08–2.05 (m, 2H, H-4'); 1.69 (s, 3H, H-8'); 1.66 (s, 3H, CH3-C3'); 1.60 (s,
3H, CH3-C7'). 13C-NMR: 168.0 (COCH3); 167.7 (COCH3); 167.1 (COCH3); 141.7 (C-3); 141.3 (C-2);
137.6 (C-3'); 134.7 (C-1); 132.7 (C-4); 131.6 (C-7'); 126.3 (C-5); 124.1 (C-6'); 120.6 (C-2'); 120.4 (C-6);
39.6 (C-4'); 28.2 (C-1'); 26.4 (C-5'); 25.7 (C-8'); 20.6 (COCH3); 20.2 (COCH3); 20.1 (COCH3);
17.7 (CH3-C7'); 16.0 (CH3-C3'). HRMS: (M + 1) calcd. for C22H28O6: 389.1886, found: 389.1867.
(E)-2-(3,7-Dimethylocta-2,6-dienyl)benzene-1,3,5-triol (9). To a solution of phloroglucinol (5.0 g,
39.6 mmol) and geraniol (6.12 g, 39.6 mmol) in acetonitrile (60 mL), saturated with AgNO3, was
.
slowly added BF3 OEt2 (1.84 g, 12.8 mmol) dropwise with stirring at room temperature and under a N2
atmosphere. After the addition was completed, the stirring was continued for 48 h. The end of the
reaction was verified by TLC. The mixture was poured onto crushed ice (30 g) and 20 mL of NaCl
(10%) and extracted with EtOAc (3 × 30 mL). Then the organic layer was washed with 5% NaHCO3
(30 mL) and water (2 × 20 mL), dried over Na2SO4, filtered and the solvent was evaporated under
reduced pressure. The crude was re-dissolved in CH2Cl2 (5 mL) and chromatographed on silicagel with
petroleum ether/EtOAc mixtures of increasing polarity (19.8:0.2→6.0:14.0). Two fractions were
obtained. Fraction I: a complex mixture (630 mg), and Fraction II: Compound 9 (3.30 g, 32% yield)

Molecules 2014, 19
1522
obtained as yellow viscous oil. MS (m/z, %): M+ 262 (0.2); 191 (100); 175 (52.7); 137 (49.8); 123
(47.8); 69 (22.1). IR (cm−1): 3397; 2967; 2925; 1706; 1620; 1515; 1463; 1377. 1H-NMR: 5.99 (bs, 2H,
OH); 5.93 (s, 2H, H-4 and H-6); 5.22 (t, J = 6.8 Hz, 1H, H-2'); 5.03 (t, J = 5.9 Hz, 1H, H-6'); 3.30 (d,
J = 6.8 Hz, 2H, H-1'); 2.08–2.05 (m, 2H, H-5'); 2.03–2.02 (m, 2H, H-4'); 1.76 (s, 3H, CH3-C3'); 1.66
13
(s, 3H, H-8'); 1.57 (s, 3H, CH3-C7'). C-NMR: 155.7 (C-1 and C-3); 154.7 (C-5); 138.7 (C-3'); 131.9
(C-7'); 123.7 (C-6'); 122.0 (C-2'); 106.3 (C-2); 96.07 (C-4 and C-6); 39.6 (C-4'); 26.3 (C-5'); 25.6 (C-8');
21.9 (C-1'); 17.6 (CH3-C3'); 16.0 (CH3-C7').
(E)-2-(3,7-Dimethylocta-2,6-dienyl) benzene-1,3,5-triyl triacetate (10). To a solution of compound 9
(0.109 g, 0.41 mmol) and DMAP (5.0 mg) in dichloromethane (20 mL) and pyridine (2.0 mL) was
added Ac2O (1.08 g, 10.6 mmol). The end of the reaction was verified by TLC (~1 h), and the mixture
was extracted with EtOAc (2 × 25 mL). The organic layer was washed with 5% NaHCO3 (30 mL) and
water (2 × 15 mL), dried over Na2SO4, and filtered. The solvent was evaporated under reduced
pressure. Then the organic layer was washed with 5% KHSO4 (2 × 15 mL) and water (2 × 10 mL),
dried over Na2SO4, filtered and the solvent was evaporated under reduced pressure. The crude was
redissolved in CH2Cl2 (5 mL) and chromatographed on silica gel with petroleum ether/EtOAc mixtures
of increasing polarity (19.8:0.2→13.6:6.4). Compound 10 was obtained as a viscous yellow oil (0.138 g,
86.8% yield). MS (m/z, %): 240 (27.5); 180 (18.8); 121 (39.8); 120 (64.0); 109 (54.7); 97 (82.3); 82
(49.4); 69 (56.2); 68 (100). IR (cm−1): 2969; 2924; 2851; 1775; 1620; 1432. 1H-NMR: 6.82 (s, 2H, H-4
and H-6); 5.06 (t, J = 6.8 Hz, 1H, H-2'); 5,02 (t, J = 5.8 Hz, 1H, H-6'); 3.17 (d, J = 6.6 Hz, 2H, H-1');
2.26 (s, 6H, COCH3); 2.24 (s, 3H, COCH3); 2.04–2.03 (m, 2H, H-5'); 1.97–1.95 (m, 2H, H-4'); 1.71 (s,
13
3H, H-8'); 1.66 (s, 3H, CH3-C3'); 1.58 (s, 3H, CH3-C7'). C-NMR: 168.6 (COCH3); 168.5 (COCH3);
149.6 (C-1 and C-3); 148.5 (C-5); 135.9 (C-3'); 131.5 (C-7'); 124.0 (C-2); 124.0 (C-2'); 120.8 (C-6');
113.8 (C-4 and C-6); 39.5 (C-4'); 26.5 (C-5'); 25.6 (C-8'); 23.6 (C-1'); 21.0 (COCH3); 20.8 (COCH3);
17.6 (CH3-C3'); 16.2 (CH3-C7'). HRMS: (M + 1) calcd. for C22H28O6: 389.1886, found: 389.1855.
2,4-bis((E)-3,7-Dimethylocta-2,6-dienyl)benzene-1,3,5-triyl triacetate (11). To a solution containing
Fraction I (630 mg), DMAP (6.0 mg) in dichloromethane (20 mL) and pyridine (2.0 mL) was added
Ac2O (1.08 g, 10.6 mmol). The end of the reaction was verified by TLC (~1 h), and the mixture was
extracted with EtOAc (2 × 25 mL). Then the organic layer was washed with 5% KHSO4 (2 × 20 mL)
and water (2 × 20 mL), dried over Na2SO4, filtered and the solvent was evaporated under reduced
pressure. The crude was redissolved in CH2Cl2 (5 mL) and chromatographed on silica gel with
petroleum ether/EtOAc in isocratic mixtures (90:10). Compound 11 was obtained as viscous yellow oil
1
(443 mg, 70.3% yield from mixture). IR (cm−1): 2968; 2923; 2867; 1772; 1615; 1434. H-NMR:
6.83 (s, 1H, H-6); 5.06 (t, J = 6.8 Hz, 2H, H-6'); 5.02 (t, J = 6.5 Hz, 2H, H-2'); 3.12 (bs, 4H, H-1'); 2.26
(s, 3H, COCH3); 2.24 (s, 6H, COCH3); 2.07–2.02 (m, 4H, H-5'); 1.97–1.94 (m, 4H, H-4'); 1.70 (s, 6H,
CH3-C3'); 1.66 (s, 6H, H-8'); 1.58 (s, 6H, CH3-C7'); 13C-NMR: 168.6 (COCH3); 168.4 (COCH3); 148.6
(C-3); 147.2 (C-1 and C-5); 135.6 (C-3'); 131.3 (C-7'); 124.6 (C-2 and C-4); 124.0 (C-6'); 121.0 (C-2');
114.9 (C-6); 39.4 (C-4'); 26.4 (C-5'); 25.5 (C-8'); 24.1 (C-1'); 20.7 (COCH3); 20.4 (COCH3); 17.6
(CH3-C7'); 16.1 (CH3-C3'). HRMS: (M + 1) calcd. for C32H44O6: 525. 3138, found: 525.3114.

Molecules 2014, 19
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2,6-bis((E)-3,7-Dimethylocta-2,6-dienyl)-3,5-dihydroxyphenyl acetate (12). To a solution of compound 11
(0.109 g, 0.41 mmol) in methanol (30 mL) was added Et3N (0.218 g, 2.15 mmol). Then the reaction
mixture was stirred at room temperature for two hours. The end of the reaction was verified by TLC.
The solvent was evaporated and the residue resuspended in EtOAc (25 mL). The organic layer was
washed with 5% HCl (2 × 10 mL) and water (2 × 20 mL), dried over Na2SO4, filtered, and the solvent
was evaporated under reduced pressure. The crude was redissolved in CH2Cl2 (5 mL) and
chromatographed on silica gel with petroleum ether/EtOAc mixtures of increasing polarity
(19.8:0.2→10.6:9.4). Compound 12 was obtained as a viscous yellow oil (0.098 g, 96% yield).
IR (cm−1): 3446; 2967; 2922; 2856; 1738; 1622; 1446. 1H-NMR: 6.16 (s, 1H, H-4); 5.16 (t, J = 6.7 Hz,
2H, H2'); 5.05 (t, J = 6.5 Hz, 2H, H-6'); 3.14 (bs, 4H, H-1'); 2.30 (s, 3H, COCH3); 2.10–2.05(m, 4H,
H-5'); 2.02–2.01 (m, 4H, H-4'); 1.75 (s, 6H, CH3-C3'); 1.66 (s, 6H, H-8'); 1.58 (s, 6H, CH3-C7');
13C-NMR: 169.6 (COCH3); 153.8 (C-3 and C-5); 147.8 (C-1); 137.5 (C-3'); 131.8 (C-7'); 123.9 (C-6');
121.8 (C-2'); 112.2 (C-2 and C-6); 102.4 (C-4); 39.6 (C-4'); 26.4 (C-5'); 25.6 (C-8'); 23.5 (C-1');
20.6 (COCH3); 17.6 (CH3-C7'); 16.1 (CH3-C3'). HRMS: (M + 1) calcd. for C28H40O4: 441.2927,
found: 441.2909.
3.3. Fungal Isolate and Culture Condition
In this study, the strain UK of Botrytis cinerea was used in all experiments. This strain was isolated
from a naturally infected grape (Vitis vinifera) and was maintained on potato dextrose agar medium
(PDA; Difco, Detroit, MI, USA) at 4 °C. The inoculum of the pathogen was grown on PDA
inphotoperiod of 16 h light/8 h dark at 23 °C for 5 days.
3.4. Effect of the Compounds on the Mycelial Growth of Botrytis Cinerea In Vitro
The anti-phytophatogenic activities of compounds, the negative control (C−) and the positive
control (commercial fungicide captan (C+) were assessed using the agar-diffusion assay technique on
PDA medium [27]. The compounds were dissolved in ethanol (1%) and water; added at different
amounts to obtain a final concentrations of 50, 150 and 250 mg/L in the PDA medium. Negative and
positive control experimental conditions for the growth of mycelia of B. cinerea were included.
Negative control conditions means PDA medium containing 1% ethanol, whereas positive control
indicates PDA medium including the commercial fungicide captan at the same concentration specified
for the compounds of interest.
A plug (4 mm) of PDA medium with 5-day-old mycelium colonies of the pathogen was placed at
the center of a Petri dish with PDA medium with or without compounds of interest. Subsequently, they
were incubated under controlled conditions of temperature to 23 °C and photoperiod 16 h light/8 h
for 48 h.
The percentage of inhibition was determined for each compounds by expressing the area of
B. cinerea as a percentage of the negative control. The evaluation was conducted through measuring
diameters of mycelial growth after 48 h of incubation. The inhibition percentages of mycelial growth
were calculated according to Hou et al. [23] for each compound and compared with the negative
control. All treatments were performed independently three times in triplicate.

Molecules 2014, 19
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4. Conclusions
Linear geranylphenols 2, 7, 9 were obtained in yields ranging from 18% to 32% by a previously
reported direct Friedel-Craft geranylation reaction. In this work acetonitrile was used as solvent instead
of dioxane, and AgNO3 was used as secondary catalyst. Under these conditions the yield of 9 was
increased from 4% to 32% and a disubstituted coupling product is formed. It seems that AgNO3 is able
to stabilize the geraniol in CH3CN solution. The acetylated derivatives 6, 8, 10, 11 were obtained with
yields over 70% by standard acetylation reactions with Ac2O and DMAP in CH2Cl2.
The evaluation of biological activity of geranylphenol derivatives on the growth of mycelia of
B. cinerea was determined in vitro after 48 h of incubation by using an agar-diffusion assay technique
with PDA medium. The results show that all compounds, excepting 11, inhibit its growth between
56%–86% compared to the negative control, at concentrations between 150 to 250 mg/L.
The antifungal activity depends on the chemical structure of the geranylphenol derivatives and is
mainly determined by the presence of the geranyl chain. Interestingly, the activity is strongly reduced
when the aromatic nucleus is substituted with two geranyl chains. Finally, the activity of these
compounds is also enhanced by the presence of hydroxyl groups, which is in line with results reported
by other authors for similar systems.
Acknowledgments
The authors thank to FONDECYT (grant No. 1120996) and the Dirección General de Investigación
y Postgrado (DGIP-USM grant No. 131305) of Universidad Técnica Federico Santa María.
Conflicts of Interest
The authors declare no conflict of interest.
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Sample Availability: Samples of the compounds 2, 6–12 are available from the authors.
© 2014 by the authors; licensee MDPI, Basel, Switzerland. This article is an open access article
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