Synthesis and antibacterial activity of new symmetric polyoxygenated dibenzofurans

Article abstract of DOI:10.1016/j.ejmech.2017.09.062

A series of symmetric polyoxygenated dibenzofurans with 2-methylbutyril moieties at C-4 and C-6 were obtained from commercial phloroglucinol through a sequence of reactions that include monoacylation, iodination, Suzuki-Miyaura coupling, oxidative dimeriz

Full text of DOI:10.1016/j.ejmech.2017.09.062

Accepted Manuscript
Synthesis and antibacterial activity of new symmetric polyoxygenated dibenzofurans
Sandra Oramas-Royo, Kriss Dayana Pantoja, Ángel Amesty, Carmen Romero, Isabel
Lorenzo-Castrillejo, Félix Machín, Ana Estévez-Braun
PII:
S0223-5234(17)30777-8
10.1016/j.ejmech.2017.09.062
EJMECH 9777
DOI:
Reference:
To appear in: European Journal of Medicinal Chemistry
Received Date: 24 May 2017
Revised Date: 8 September 2017
Accepted Date: 27 September 2017
Please cite this article as: S. Oramas-Royo, K.D. Pantoja, Á. Amesty, C. Romero, I. Lorenzo-Castrillejo,
Fé. Machín, A. Estévez-Braun, Synthesis and antibacterial activity of new symmetric polyoxygenated
dibenzofurans, European Journal of Medicinal Chemistry (2017), doi: 10.1016/j.ejmech.2017.09.062.
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ACCEPTED MANUSCRIPT
OH
OH HO
O
O
OBn
O
OBn
R
R
I
R
HO
OH
HO
OH
BnO
OBn
BnO
OBn
phloroglucinol
O
O
Staphylococcus aureus

ACCEPTED MANUSCRIPT
Synthesis and Antibacterial Activity of New Symmetric Polyoxygenated
Dibenzofurans
a
a,b
a
a
Sandra Oramas-Royo, Kriss Dayana Pantoja, Ángel Amesty, Carmen Romero, Isabel
c
c
a,*
Lorenzo-Castrillejo, Félix Machín, Ana Estévez-Braun
a
Instituto Universitario de Bio-Orgánica Antonio González (CIBICAN)
Departamento de Química Orgánica, Universidad de La Laguna.
Avda. Astrofísico Fco. Sánchez 2. 38206. La Laguna, Tenerife, Spain.
E-mail: aestebra@ull.es
b
c
Universidad del Valle, Colombia
Unidad de Investigación, Hospital Universitario Nuestra Señora de Candelaria, Carretera del
Rosario, 145, 38010, Santa Cruz de Tenerife, Spain.
1

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Abstract
A series of symmetric polyoxygenated dibenzofurans with 2-methylbutyril moieties at C-4
and C-6 were obtained from commercial phloroglucinol through a sequence of reactions
that include monoacylation, iodination, Suzuki-Miyaura coupling, oxidative dimerization
and cyclization. Some of the compounds obtained were active against Gram-positive
bacteria, including multiresistant Staphylococcus aureus clinical isolates. The dibenzofuran
2
8 with propyl chains at C-2 and C-8 exhibited the best antibacterial activity with values
comparable to those of the natural dibenzofuran achyrofuran. From the obtained results
some structure-activity relationships were outlined.
2

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Introduction
The bacterial resistance to drugs is a pressing issue worldwide as it might have
devastating consequences on public health. Additionally, the current lack of sufficient and
effective antimicrobial drugs and the scarce interest of pharmaceutical companies on
developing novel antimicrobial drugs, point out that common bacterial infections might
cause serious complications in a near future, even death, as it has been stated by the World
Health Organization (WHO) [1]. The discovery of new and improved antimicrobial agents
is, therefore, one of the most urgent needs along with preventive measures to avoid the
advance of the so-called AMR (Antimicrobial Resistance) crisis. One of the most studied
pathogens with great ability to acquire drug resistance is Staphylococcus aureus, a Gram-
positive bacterium responsible for health care-associated and community-associated skin
and soft tissue infections [2]. Natural occurring antimicrobials currently used (i.e.
penicillins, cephalosporins, glycopeptides and β-lactams) with a precedent therapeutic
potential have been proved to be increasingly ineffective in eradicating the most virulent
strains MRSA (methicillin resistant Staphylococcus aureus) and VISA (vancomycin
intermediate Staphylococcus aureus) [3-7]. Natural products are well-known essential
sources of pharmacologically active scaffolds in drug discovery [8-11], providing a wide
variety of novel lead structures and making possible the obtention of semi-synthetic
derivatives with different mechanisms of action. Few antibiotics [12-14] isolated from
natural sources have been approved by the FDA since 1990’s. Hereof, our research group
found that dichloromethane extracts from the southamerican species Achyroclyne
satureoides (Asteraceae) showed a remarkable antibacterial activity. The compound
responsible for such activity was identified as achyrofuran (1) [15-16], a prenylated
3

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polyoxygenated dibenzofuran, which showed extraordinary antibacterial activity against a
set of clinically relevant Gram-positive bacteria, including MRSA and VISA. Other natural
dibenzofurans, such as compound (2) isolated from the branches of A. Satureoides [17],
compounds 3 and 4 from the leaves of Pilidiostigma glabrum [18], and rhodomyrtoxins B
(5) and C (6) from Rhodomyrtus macrocarpa [19-20] (Fig.1) have also showed
antibacterial activity.
Fig. 1. Structures of antibacterial natural dibenzofurans.
Hence, substitution patterns, symmetry and electronic and steric effects seem to play
an important role for the antimicrobial activity. Since a limited number of substituted
dibenzofurans with antibacterial properties has been reported, there are not conclusive
structure-activity relationships. For this reason, the obtention of more dibenzofurans from
natural sources as well as synthetic approaches is necessary to determine the structural
requirements for obtaining high antimicrobial activity and also for a rational design of
4

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antimicrobial entities. Taking this into account, we planned the synthesis of symmetric
dibenzofurans maintaining the positions of α-methylbutyril moieties at C-4 and C-6 and
varying the alkyl substituents at C-2 and C-8. In these sense, we wanted to analyze the
influence in the activity of lipophilic chains such as isopentyl and propyl chains and also
evaluate the no presence of alkyl chains at these positions (Fig. 2).
Fig. 2. Symmetric dibenzofurans.
Results and discussion
There are not many synthetic approaches of fully substituted polyoxygenated
dibenzofurans. In this respect, the synthesis of rhodomyrtoxins C (6) by Sargent and
coworkers [21] and, the synthesis of a compound dubbed “pre-achyrofuran” [22] as an
application of a protocol for aryl-benzyl ketone synthesis based on catalytic carbon
insertion of nonstabilized diazoalkanes, are the only examples in the literature. In the last
case, only 3.8 mg of “pre-achyrofuran” were obtained and not enough spectroscopic data
were given in order to confirm the proposed regiosubstitution.
There are not reports regarding the preparation of symmetric polyoxygenated
5

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dibenzofurans with acyl groups located at C-4 and C-6. The access to this type of
compounds was planned following the retrosynthetic analysis shown in Scheme 1. As we
can see the benzofuran nucleus (7) was envisioned to originate from an oxidative
dimerization of a disubstituted phloroglucinol (8) with regioselective ring closure.
Compound (8) should be derivable from deprotection of the corresponding compound (9)
whose alkyl substituent could be introduced from an appropriated Suzuki-Miyaura coupling
between commercially available boronic acids and the iodinated compound (10). This
compound (10) should be achieved by a sequence of reactions from the commercial
phloroglucinol such as protection of the hydroxyl groups (12), followed by acylation (11)
and subsequent iodination.
Scheme 1. Retrosynthetic analysis of symmetric dibenzofurans.
As depicted in Scheme 2, the synthesis of the iodinated compound (16) began with
the preparation of the tribenzylated phloroglucinol 14, which was obtained from the
triacetyl derivative 13 employing previously reported reaction conditions [23-24]. Initially
the hydroxyl groups were protected as methyl ethers but we found many problems in the
6

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final deprotection step of the trimethoxylated derivative 9, so we decided alternatively to
use the benzyl ether as protecting group. The monoacylation of 14 was carried out with an
excess of the mixed anhydride pre-formed from trifluoroacetic anhydride and (±)-2-
methylbutyric acid [25], since the standard conditions (AlCl , CH Cl , rt) only led to the
3
2
2
formation of the triacylated derivative. Acyl compound 15 was obtained in this way in a
9% yield and its subsequent iodination using N-iodosuccinimide as iodinating agent [26],
6
in the presence of trifluoroacetic acid led to compound 16 in 97% yield.
Scheme 2. Synthesis of the iodinated derivative 16.
Next, the corresponding Suzuki-Miyaura couplings with the boronic acids 3-methyl-
2
-butenylboronic acid pinacol ester (17) and cis-1-propen-1-ylboronic acid (18) were
carried out. Acceptable yields only were achieved when a large excess of boronic acid was
used. Optimal reaction conditions under conventional heating and microwave irradiation
were investigated by initially performing the reaction with compound (16) and
prenylboronic ester (17) using 1,4-dioxane or THF as organic solvents and Pd(PPh ) (20
3
4
7

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mol%) as catalyst (Table 1).
Table 1. Optimization of the coupling reaction conditions between 16 and 17.
a
Entry
Ratio 16:17
1:4
Reaction Conditions
1,4-dioxane, ∆, 16 h
Yield (%)
1
2
3
4
5
6
7
8
9
60
77
44
73
20
51
30
45
44
55
91
1:4
1,4-dioxane, ∆, 24 h
1:6
1,4-dioxane, ∆, 24 h
1:6
THF, ∆, 84 h
1:6
1,4-dioxane, MW, 150ºC, 5 min
1,4-dioxane, MW, 170ºC, 15 min
1,4-dioxane, MW, 180ºC, 35 min
THF, MW, 170ºC, 30 min
THF, MW, 170ºC, 15 min
THF, MW, 170ºC, 15 min
THF, MW, 170ºC, 20 min
1:6
1:6
1:4
1:6
1
1
0
1
1:7
1:7
a
Isolated yield
Moderated yields were obtained under conventional heating using large reaction
times (entries 1-4). So, in order to improve the yields and shorten the reaction times, MW
irradiation was used (entries 5-11). The best yield for the Suzuki-Miyaura coupling was
achieved when the reaction was irradiated at 170º C for 20 minutes in THF and using 7.0
8

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equiv of the prenylboronic ester 17 (entry 11). Using these reaction conditions, derivative
2
0 was obtained in 88 % yield employing cis-1-propen-1-ylboronic acid (18).
The next step was the cleavage of the benzyl ethers 15, 19 and 20 to obtain the
corresponding substituted phloroglucinols (21-23). We tried different hydrogenolysis
2
conditions, and the best results were obtained with Pd(OH) /C (25 mol %) under 5 bar of
hydrogen pressure (Scheme 3).
Scheme 3. Preparation of the debenzylated derivatives (21-23).
The last step was the oxidative cyclization of the substituted triphenols (21-23). We
used different catalysts and promoters, such as Pd(OAc)
2
or Pd(OAc)
O [29], but only the use of FeCl
30] led to the desired dibenzofurans in low yield together with the corresponding biphenyl
2
/O
2
in acetic acid
[
27], PIFA-BF
3
Et
2
O [28], and FeCl
3
-PIFA-BF
3
Et
2
3
/SiO
2
[
precursors (Scheme 4).
9

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Scheme 4. Preparation of the dibenzofurans (24, 26, 28) and the biphenyls (25, 27, 29).
1
13
The H NMR and C NMR spectra of the obtained dibenzofurans showed only half
of the full set of signals, indicating a symmetrical structure for these compounds. The
regiosubstitution was established by the correlations observed in the HMBC spectra. Thus
for example for compound 28 (Fig. 3), the correlations detected for the benzylic CH and
2
the chelated hydroxyl group corroborated the position of the acyl moieties at C-4 and C-6,
and the propyl chains at C-2 and C-8.
Fig. 3. Key HMBC correlations for compound 28.
The formation of only one regioisomer could be explained considering the
minimum energy conformation of the precursor biphenyl (Fig. 4) [31], which shows two
hydrogen bonds between the carbonyl groups and the hydroxyl groups at C-2 and C-2´.
1
0

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Furthermore other two hydrogen bonds between the hydroxyls OH-C-2 /OH-C-6´ and OH-
C-2´ /OH-C-6 are also found. All these hydrogen-bond interactions reveal a great stability
for the biphenyls formed and, probably under the cyclization conditions the break of the
weaker hydrogen bonds (OH-C-2 /OH-C-6´ and OH-C-2´ /OH-C-6) favours the formation
of the furan ring involving the hydroxyls at C-6 and C-6´.
Fig. 4. Minimum energy conformation of the biphenyl 29.
The obtained tetrahydroxybenzofurans 24, 26 and 28 together with the 2,2’-
biphenyl derivatives 27 and 29 were evaluated for antibacterial activity against two
reference and clinically relevant S. aureus strains, namely, vancomycin- and methicillin-
sensitive Staphylococcus aureus ATCC25923 and vancomycin-intermediate and
methicillin-resistant S. aureus NRS402. They were also evaluated against another Gram-
1
1

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positive bacteria Enterococcus faecalis (ATCC29212). E. faecalis also causes life-
threatening nosocomial infections and is rapidly acquiring multiresistance [3]. Furthermore,
we used the reference Saccharomyces cerevisiae BY4741 strain and derivatives thereof to
check for any possible cytotoxic activity on eukaryotic cell related to DNA damage,
cytoskeleton damage or oxidative stress [32]. We also decided to include in this evaluation
the substituted precursor triphenols (21-23) and the 1,3,7,9-tetrahydroxybenzofuran (30)
[33] in order to outline reliable structure-activity relationships. The results are shown in
Table 2.
Table 2. MIC (µM) of phenols (21-23), benzofurans (24, 26, 28, 30) and, biphenyls (27,
2
9).
Compound NRS402 S. aureus ATCC25923 S. aureus
VISA) (MSSA)
ATCC29212
(E.faecalis)
Several strains2
(
(S.cereviciae)
µM
µg/ml
µM
µg/ml
µM
µg/ml
µM
µg/ml
2
2
2
2
2
2
2
1
2
3
4
6
7
8
32
32
64
8
6.72
8.96
16.13
3.2
64
32
64
8
13.44
8.96
16.13
3.2
64
32
64
32
2
13.44
8.96
16.13
12.8
1.08
2.23
0.24
> 128
> 128
> 128
> 128
> 128
> 128
> 128
> 30
> 30
> 30
> 30
> 30
> 30
> 30
4
2.16
0.56
0.24
4
2.16
4.64
0.24
1
8
4
0.5
0.5
0.5
1
2

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2
3
9
0
0.5
> 128
0.25
150
0.25
> 30
0.14
64
4
2
2
> 128
0.5
1
> 30
0.28
4
> 128
> 128
> 128
ND
> 30
> 30
> 30
ND
> 128
0.5
> 30
0.28
0.125
1
achyrofuran
1
Oxa
≤
0.3
≤
9.5
1
Van
5.5
8
0.7
1.4
2
ND
ND
1
These antibiotics were used in a range from 0.125 to 128 µg/ml, and the represented MIC in µM was then calculated
from the molecular weight of their commercial formulations (sodium oxacillin and vancomycin hydrochloride). Oxacillin
is an improved version of methicillin which has replaced the latter in clinical use. ND, not determined.
2
This column summarizes the results for four strains of S. cerevisiae: BY4741 (reference wild type), rad52ꢀ rad9ꢀ
(hypersensitive to DNA damage), mad2ꢀ (hypersensitive to microtubule depolymerisation) and yap1ꢀ (hypersensitive to
oxidative stress). For most compounds there was no growth inhibition whatsoever: growth at 128 µM was similar to the
control (DMSO 1% v/v) in the four strains. Only triphenols 22 and 23 gave a slight growth delay in yap1ꢀ: After 24h
incubation, 20-40% growth at 128 µM relative to DMSO (neither observed at 64 µM x 24h nor at 128 µM x 48h). This
indicates that these two phenols might be weak oxidative stressors.
As we can see, the phenols 21, 22 and 23, were slightly active against gram positive
bacteria. In the dibenzofuran series (24, 26, 28, 30), the tetrahydroxy-dibenzofuran (30)
resulted to be inactive, the introduction of acyl moieties at C-4 and C-6 led to a derivative
(24) more active, and clearly the activity is improved with the introduction of alkyl chains
at C-2 and C-8 (compounds 26 and 28). Compound 28 exhibited the best antibacterial
activity with values comparable to those of the natural achyrofuran. Regarding the biphenyl
compounds (27 and 29), they showed good activity, and resulted to be more selective
towards VISA.
Some bacteria develop resistance to methicillin by expressing the alternate form of
penicillin-binding protein 2 named PBP2a (also called PBP2′), which is the major cell wall
transpeptidase. This protein expressed in MRSA strains is the main cause of clinical
resistance because of low affinity for most of β-lactam antibiotics. Recently it has been
1
3

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demonstrated that PBP2a has two binding sites, an allosteric site and an active site
separated by 60 Å. Binding of an allosteric effector can influence protein function, and
predisposes PBP2a to inactivation, and thus, allosteric binding sites can be targets for new
drugs [34, 35]. The quinazolinone (E)-3-(3-carboxyphenyl)-2-(4-cyanostyryl)quinazolin-
4
(3H)-one, a non-β-lactam antibiotic, which exhibits in vitro and in vivo activity against S.
aureus, represents an example of an antibiotic which exerts it action by binding to the
allosteric site of PBP2a [36]. In order to propose a mode of action of the antibacterial
activity of synthesized polyoxygenated dibenzofurans, we have carried out a preliminary
molecular docking study using the Glide software [37] on reported crystal structure of
PBP2a (PDB 4CJN). Hence, we have docked the compounds 24, 26, 27, 28, 29 and
achyrofuran into the allosteric site of PBP2a to see if these compounds could interact with
this target and, consequently to understand the possible binding mode and key active site
interactions. An analysis of the docking results shows that the compounds fit well into the
allosteric site. However the analysis of the docking poses showed that in some cases polar
groups were within hydrogen bond distances but not properly oriented to interact favorably.
Therefore, to further account for the allosteric binding site flexibility, binding modes of
active compounds were regenerated through Glide/Induced Fit Docking (IFD)[38]. In
general, IFD binding modes were found to show an optimized network of protein ligand
interactions as compared to previous docking results. These docking results strongly
suggested that the compounds 27, 28 and 29 share a common binding mode into PBP2a.
These compounds showed a good steric and electronic complementarity with the PBP2a
allosteric binding site. According to the predicted binding modes, the most active
compounds showed a π−π stacking interaction and hydrogen-bonds between the functional
1
4

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groups present in these compounds and some amino acid residues. After the IFD analysis
-1
the highest docking scores were ranged from -8.57 to -6.96 kcal mol (See Table S1 in
Supplementary Data). In the predicted pose of the most active compound (28), the
aromatic ring of the dibenzofuran nucleus showed a key π-π interaction with Tyr 297 and,
five hydrogen bonds were detected between the residues Asn 104, Lys 316, Lys 273, Asp
2
95, Asn 146 and the hydroxyl groups present in 28. Moreover α-methylbutyril moieties
at C-4 and C-6 and the lipophilic chains at C-2 and C-8 make hydrophobic contacts with
Tyr 105, Ile 144, Asp 275 and Glu 294. The presence of polar contacts with a considerable
number of residues seems to play a fundamental role in the binding of compounds.
1
5

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Fig. 5. Predicted binding mode of 28 into the allosteric site of PBP2a (PDB 4CJN).
Hydrogen bonds are represented as yellow dotted lines. (Image created using Maestro
1
1.1).
In conclusion a new set of symmetric polyoxygenated dibenzofurans was
synthesized from phloroglucinol in order to establish some structure-antibacterial activity
relationships. The key steps of the synthetic approach were the Suzuki-Miyaura coupling
for introducing the alkyl chains at C-2 and C-8 and the oxidative dimerization followed of
regioselective cyclization for forming the dibenzofuran nucleus. The desired dibenzofurans
with 2-methylbutyryl moieties at C-4 and C-6 were obtained together the corresponding
1
6

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biphenyl precursors. The dibenzofurans (24, 26, 28, 30), the biphenyls (27, 29) and the
disubstituted phloroglucinol derivatives (21-23) were evaluated for antibacterial activity.
From the obtained results some structure-activity relationships were outlined. Thus, the
inactivity of 1,3,7,9-tetrahydroxydibenzofuran (30) shows the importance of the acyl and
alky substituents in the polyoxygenated dibenzofuran nucleus. The introduction of 2-
methylbutyryl moieties at C-4 and C-6 (24) increases the activity against VISA and MSSA,
and the best activities were achieved with the introduction of lipophilic chains at C-2 and
C-8 (26, 28). The fully substituted biphenyls (27, 29) also showed good activities but less
than the corresponding dibenzofurans. Induced Fit Docking studies revealed that the most
active compounds had appreciable binding free energies and affinities with the allosteric
site of PBP2a of Staphylococcus aureus (PDB 4CJN) suggesting a starting point for
designing more effective compounds against MRSA strains.
Experimental Section
General Experimental Procedures. IR spectra were recorded on a Bruker IFS 28/55
1
13
spectrophotometer. H and C NMR spectra were acquired in CDCl
3
1
or CD
3
OD at room
temperature using Bruker Avance instruments (500 or 600 MHz for H NMR and 125 or
1
3
1
50 MHz for C NMR). Chemical shifts are reported in (δ) parts per million and coupling
1
13
constants (J) in hertz (Hz). H and C NMR spectra were referenced using the solvent
signal as internal standard. Melting points were measured on a Büchi (B-540) apparatus and
are uncorrected. The microwave reactions irradiation were performed in a Biotage Initiator
1
7

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2
.5 using sealed microwave glass vessels (capacity 2 or 5 mL) and a normal absorption
level. MS and HRMS data were recorded in a VG Micromass ZAB-2F spectrometer and a
ESI instrument LCT Premier XE Micromass (ESI-TOF). All reactions, except
hydrogenations, were carried out under argon atmosphere. Catalytic hydrogenation
reactions were carried out in an Anton-Parr shaker hydrogenation apparatus. All solvents
and reagents were purified by standard techniques reported [39]. Pd(PPh ) was prepared
3
4
following the procedure described in reference [40]. Analytical thin-layer chromatography
was performed on Polygram SIL G/UV254 silica gel plates and chromatograms were
visualized under UV light (254 and 360 nm). Purification on column chromatography was
carried out on Merck silica gel 60 (0.063-0.2 mm) with the indicated solvent mixtures. Pre-
coated TLC plates SIL G-100 UV254 (Macherey-Nagel) and SILICA GEL GF plates (1000
µm, Analtech) were used for preparative TLC purification. Size-exclusion chromatography
using SEPHADEX LH-20 (Biosigma) was performed on mixtures of
hexanes/CH Cl /MeOH (2:2:1).
2
2
Synthesis of benzene-1,3,5-triyl triacetate (13)
According to the literature procedure [41], acetic anhydride (15 mL, 0.16 mol) was added
to a solution of phloroglucinol (4.00 g, 31.7 mmol) in pyridine (20 mL) and the mixture
was refluxed at 130 ºC overnight. Pyridine was removed under reduced pressure and the
resulting solid was washed with tert-butyl methyl ether, affording the corresponding
triacetylated derivative (5.92 g, 74%) as a white solid. The NMR data are in agreement with
1
previous data reported in literature [41]. H NMR (500 MHz, CDCl ) δ 6.84 (s, 3H), 2.27
3
1
3
(
s, 9H); C NMR (125 MHz, CDCl
3
) δ 168.3 (3CO), 151.3 (3C), 112.6 (3CH), 21.0
(
3CH ).
3
1
8

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Synthesis of 1, 3, 5-tris(benzyloxy)benzene (14)
A mixture of benzene-1,3,5-triyl triacetate (13) (2.00 g, 7.9 mmol), benzyl bromide (3.40
mL, 28.0 mmol) and sodium hydride (60% in mineral oil, 2.30 g, 57.5 mmol) in DMF (30
mL) was cooled to 0 ºC. Then, water (0.42 mL, 23.3 mmol) was carefully added dropwise
while gas evolution was observed. The reaction mixture was stirred overnight at room
temperature, poured into water, and extracted with AcOEt. The combined organic layers
were washed with brine, dried over MgSO and filtered. The solvent was removed under
4
reduced pressure and the residue was recrystallized from methanol to afford compound 14
(2.95 g, 94%) as a white solid. The NMR data are in agreement with previous data reported
1
in literature [42], H NMR (500 MHz, CDCl ) δ 7.42 (m, 15H), 6.28 (s, 3H), 5.01 (s, 6H);
3
1
3
C NMR (125 MHz, CDCl ) δ 160.8 (3C), 137.0 (3C), 128.6 (6CH), 127.9 (3CH), 127.5
3
2
(6CH), 95.4 (3CH), 70.3 (3CH ).
Synthesis of 2-methyl-1-(2,4,6-tris(benzyloxy)phenyl)butan-1-one (15)
A mixture of trifluoroacetic anhydride (2.42 mL, 17.2 mmol) and (±)-2-methylbutyric acid
(1.60 mL, 14.4 mmol) was vigorously stirred for 2 h at room temperature. The yellow
mixture was cooled in an ice bath to 0 ºC and a solution of tribenzyl phloroglucinol 14 (0.7
g, 1.77 mmol) in CH Cl (25 mL) was added dropwise. The solution was stirred at room
2
2
temperature for 1 h, then saturated aqueous NaHCO (20 mL) was added. The phases were
3
separated and the aqueous layer was extracted with AcOEt. The combined organic layers
4
were dried over MgSO , filtered and the solvent removed under reduced pressure. The oily
residue was purified by column chromatography (SiO ; hexanes/diethyl ether 9:1) to afford
2
1
1
5 (604 mg, 71%) as a white solid. Mp 72-73 ºC. H NMR (500 MHz, CDCl
3
) δ 7.34 (m,
1
5H), 6.25 (s, 2H), 5.02 (s, 4H), 5.00 (s, 2H), 2.95 (m, 1H), 1.77 (m, 1H), 1.36 (m, 1H),
1
9

ACCEPTED MANUSCRIPT
1
3
1
.07 (d, J = 7.0 Hz, 3H), 0.80 (t, J = 7.4 Hz, 3H); C NMR (125 MHz, CDCl ) δ 208.0
3
(CO), 161.0 (C), 157.3 (2C), 136.6 (2C), 136.5 (C), 128.8 (2CH), 128.6 (4CH), 128.3 (CH),
1
4
2 2
28.0 (2CH), 127.7 (2CH), 127.3 (4CH), 114.9 (C), 93.4 (2CH), 70.6 (2CH ), 70.4 (CH ),
+
9.1 (CH), 25.4 (CH ), 15.2 (CH ), 11.7 (CH ); EIMS m/z 480 (M , 1), 423 (62), 91 (100);
2
3
3
+
HREIMS (EI) 480.2293 (calcd for C H O ; [M ] 480.2301); IR (film) ν
3032, 2965,
3
2
32
4
max
-1
2
930, 2873, 1693, 1602, 1497, 1454, 1431, 1376, 1203, 1152, 1117 cm .
Synthesis of 1-[2,4,6-tris(benzyloxy)-3-iodophenyl]-2-methylbutan-1-one (16)
To a solution of 15 (488 mg, 1.02 mmol) in CH
2
2
Cl (40 mL) was added N-iodosuccinimide
(
589 mg, 2.54 mmol) in CH Cl (80 mL) using a pressure-equalizing dropping funnel for
2
2
1
0 min at 0 ºC. Trifluoroacetic acid (0.048 mL, 0.62 mmol) was then added in four portions
each 2 h and the reaction was stirred for 48 h at room temperature. Upon disappearance of
the starting material, saturated aqueous Na S O (50 mL) was added, the phases were
2
2
5
separated and the aqueous layer was extracted with CH Cl . The combined organic layers
2
2
4
were washed with brine, dried over MgSO , filtered and the solvent was evaporated under
reduced pressure. The resulting residue was dissolved in AcOEt and, n-hexane was added
until succinimide was completely precipitated. The solid was filtered off and the solvent
was removed under reduced pressure. The resulting residue was recrystallized from
hexanes-diethyl ether (5:1) to give compound 16 (597 mg, 97%) as a pale yellow solid. Mp
1
1
26-127 ºC; H NMR (500 MHz, CDCl ) δ 7.42 (m, 15H), 6.37 (s, 1H), 5.12 (s, 2H), 5.02
3
(s, 2H), 5.00 (d, J = 9.8 Hz, 1H), 4.95 (d, J = 9.9 Hz, 1H), 2.89 (m, 1H), 1.73 (m, 1H), 1.34
1
3
(
m, 1H), 1.05 (d, J = 6.9 Hz, 3H), 0.79 (t, J = 7.4 Hz, 3H); C NMR (125 MHz, CDCl ) δ
3
2
07.6 (CO), 159.4 (C), 157.6 (C), 156.6 (C), 136.6 (C), 136.1 (C), 136.0 (C), 128.77
(3CH), 128.76 (3CH), 128.4 (2CH), 128.36 (CH), 128.29 (CH), 128.2 (CH), 127.4 (2CH),
2
0

ACCEPTED MANUSCRIPT
1
27.1 (2CH), 120.9 (C), 95.5 (CH), 77.4 (CH ), 75.4 (C), 71.4 (CH ), 71.0 (CH ), 49.0
2
2
2
+
(CH), 25.1 (CH
2
), 14.9 (CH
3
), 11.6 (CH
3
); EIMS m/z 606 (M , 6), 549 (26), 331 (6), 91
+
(100); HREIMS 606.1278 (calcd for C32
H31IO
4
, [M ] 606.1267); IR (film) ν 3063, 3032,
max
-1
2
966, 2932, 2874, 1694, 1582, 1453, 1403, 1362, 1184, 1101 cm .
Synthesis of 2-methyl-1-[2,4,6-tris(benzyloxy)-3-(3-methylbut-2-enyl)phenyl]butan-1-
one (19).
Conventional heating procedure. A mixture of 16 (20.0 mg, 0.033 mmol), 3-methyl-2-
butenylboronic acid pinacol ester (17) (0.030 mL, 0.130 mmol), Pd(PPh ) (7.6 mg, 0.007
3
4
mmol) in 1,4-dioxane (3.0 mL) and a 2% aqueous Na
was refluxed at 100 ºC under argon for 24 h. Upon disappearance of the starting material,
CH Cl was added, the phases were separated and the aqueous layer was extracted with
CH Cl . Then the combined organic layers were dried over MgSO , filtered and the solvent
2 3
CO solution (2.8 mL, 0.538 mmol)
2
2
2
2
4
evaporated under reduced pressure. Purification of the crude by preparative-TLC (hex:
EtOAc, 7:3) afforded compound 19 (13.8 mg, 77%) as a white solid.
Microwave irradiation procedure. A mixture of 16 (20.0 mg, 0.033 mmol), 3-methyl-2-
butenylboronic acid pinacol ester (17) (0.053 mL, 0.23 mmol), Pd(PPh ) (7.6 mg, 0.007
3
4
mmol) in THF (1.0 mL) and a 2% aqueous Na CO solution (1.5 mL, 0.289 mmol) was
2
3
irradiated at 170 ºC for 20 minutes. The phases were separated and the aqueous layer was
extracted with CH Cl . The combined organic layers were dried over MgSO , filtered and
2
2
4
the solvent evaporated under reduced pressure. Purification of the residue by preparative-
TLC (hex: EtOAc, 7:3) afforded compound 19 (16.5 mg, 91%) as a white solid. Mp 78-79
1
ºC; H NMR (500 MHz, CDCl ) δ 7.46 (m, 15H), 6.38 (s, lH), 5.19 (t, J = 6.6 Hz, lH), 5.04
3
2
1

ACCEPTED MANUSCRIPT
(s, 2H), 5.01 (s, 2H), 4.88 (d, J = 10.7 Hz, lH), 4.85 (d, J =10.7 Hz, lH), 3.35 (d, J = 6.5 Hz,
2
3
H), 2.94 (m, lH), 1.75 (m, lH), 1.67 (s, 3H), 1.58 (s, 3H), 1.35 (m, lH), 1.07 (d, J = 7.1 Hz,
1
3
3
H), 0.82 (t, J = 7.4 Hz, 3H); C NMR (125 MHz, CDCl ) δ 208.9 (CO), 158.8 (C), 155.1
(
C), 154.9 (C), 137.5 (C), 136.9 (C), 136.8 (C), 131.5 (C), 128.7 (4CH), 128.5 (2CH),
28.11 (CH), 128.29 (CH), 128.08 (CH), 128.06 (CH), 128.0 (CH), 127.40 (2CH), 127.39
2CH), 123.5 (CH), 119.8 (C), 117.5 (C), 94.9 (CH), 78.0 (CH ), 71.0 (CH ), 70.5 (CH ),
1
(
2
2
2
4
9.2 (CH), 25.8 (CH ), 25.3 (CH ), 23.0 (CH ), 18.0 (CH ), 15.0 (CH ), 11.7 (CH ); EIMS
3 2 2 3 3 3
+
m/z 548 (M , 1), 491 (6), 423 (2), 373 (2), 333 (5), 91 (100); HREIMS 548.2904 (calcd for
+
C
37
H
40
O
4
, [M ] 548.2927); IR (film) νmax 3032, 2965, 2928, 2874, 1691, 1594, 1454, 1373,
-1
1
220, 1166, 1096, 802 cm .
Synthesis of 2-methyl-1-[2,4,6-tris(benzyloxy)-3-(2-(Z)-propenyl)phenyl]butan-1-one
20).
(
Conventional heating procedure. A mixture of 16 (24.8 mg, 0.041 mmol), cis-1-propen-
-ylboronic acid (14.8 mg, 0.164 mmol) (18), Pd(PPh ) (9.4 mg, 0.008 mmol) in 1,4-
1
3
4
dioxane (4.0 mL) and a 2% Na CO solution (3.46 mL, 0.667 mmol) was refluxed at 100 ºC
2
3
under argon for 24 h. Upon disappearance of the starting material, CH Cl was added, the
2
2
phases were separated and the aqueous layer was extracted with CH
2 2
Cl . Then the
combined organic layers were dried over MgSO , filtered and the solvent evaporated under
4
reduced pressure. Purification of the crude by preparative-TLC (hex: EtOAc, 7:3) afforded
compound 20 (12.0 mg, 56%) as a white solid.
Microwave irradiation procedure. A mixture of 16 (20.5 mg, 0.033 mmol), cis-1-propen-
1
-ylboronic acid (18) (18.3 mg, 0.20 mmol), Pd(PPh ) (7.8 mg, 0.007 mmol) in THF (1.0
3 4
2
2

ACCEPTED MANUSCRIPT
mL) and a 2% aqueous Na CO solution (1.5 mL, 0.289 mmol) was irradiated at 170 ºC for
2
3
2
0 minutes. The phases were separated and the aqueous layer was extracted with CH
2 2
Cl .
The combined organic layers were dried over MgSO , filtered and the solvent evaporated
4
under reduced pressure. Purification of the crude by preparative-TLC (hex: EtOAc, 7:3)
1
afforded compound 20 (15.1 mg, 88%) as a white solid. Mp 109-110 ºC; H NMR (500
MHz, CDCl ) δ 7.34 (m, 15H), 6.38 (s, 1H), 6.32 (d, J = 11.1 Hz, 1H), 5.90 (m, 1H), 5.04
3
(s, 2H), 5.01 (s, 2H), 4.79 (d, J = 10.1 Hz, 1H), 4.76 (d, J =10.3 Hz, 1H), 2.91 (m, 1H),
1
.76 (m, 1H), 1.59 (dd, J = 6.8, 1.6 Hz, 3H), 1.35 (m, 1H), 1.06 (d, J = 6.9 Hz, 3H), 0.80 (t,
1
3
J = 7.5 Hz, 3H); C NMR (125 MHz, CDCl
3
) δ 208.5 (CO), 158.1 (C), 155.7 (C), 155.0
C), 137.5 (C), 136.9 (C), 136.6 (C), 130.0 (CH), 128.71 (2CH), 128.69 (2CH), 128.5
2CH), 128.4 (2CH), 128.1 (CH), 128.0 (CH), 127.9 (CH), 127.4 (2CH), 127.1 (2CH),
20.9 (CH), 119.9 (C), 114.1 (C), 95.0 (CH), 76.5 (CH ), 70.8 (CH ), 70.8 (CH ), 49.2
(
(
1
2
2
2
+
(
CH), 25.2 (CH ), 16.0 (CH ), 15.0 (CH ), 11.7 (CH ); MS (EI) m/z 520 (M , 2), 462 (4),
2 3 3 3
+
4
5
29 (2), 345 (5), 181 (4), 91 (100); HRMS (EI) 520.2640 (calcd for C H O , [M ]
35 36 4
-1
20.2614); IR (film) νmax 3665, 2969, 2933, 1696, 1594, 1458, 1367, 1219, 1106 cm .
General procedure for hydrogenation reaction
In a borosilicate test tube were suspended the corresponding tribenzylated derivative and
Pd(OH) /C (25 mol%) in CH Cl or THF (4 mL). The test tube was placed in the
2
2
2
2
hydrogenation apparatus, the suspension was purged three times with H and the final
pressure of hydrogen was adjusted to 5 bar. The reaction mixture was shaken at room
temperature and monitored using TLC until the formation of a major product was observed.
Then the suspension was filtered through a celite plug using CH Cl , AcOEt and MeOH as
2
2
eluents and the mixture of solvents was concentrated under reduced pressure. Purification
2
3

ACCEPTED MANUSCRIPT
of the crude by size-exclusion chromatography (Sephadex LH-20, hexanes/CH Cl /MeOH
2
2
2
:2:1) afforded the corresponding phenol.
Synthesis of 2-methyl-1-(2,4,6-trihydroxyphenyl)butan-1-one (21)
A suspension of compound 15 (195 mg, 0.408 mmol) and Pd(OH) /C (20% w/w, 71.6 mg,
2
0
.102 mmol) in THF (4.0 mL) was subjected to the hydrogenation procedure for 14 h to
1
afford (62.0 mg, 72%) as a yellow oil after purification. H NMR (500 MHz, CD OD) δ
3
5
7
9
.81 (s, 2H), 3.85 (m, 1H), 1.80 (m, 1H), 1.35 (m, 1H), 1.11 (d, J = 6.8 Hz, 3H), 0.89 (t, J =
1
3
.4 Hz, 3H); C NMR (125 MHz, CD OD) δ 212.3 (CO), 166.7 (C), 166.6 (2C), 106.1 (C),
3
2 3 3
6.7 (2CH), 47.5 (CH), 28.9 (CH ), 18.0 (CH ), 13.2 (CH ); HREIMS 209.0806 (calcd for
+
C
11
H
13
O
4
, [M -1] 209.0814); IR (film) νmax 3324, 3306, 2968, 1630, 1602, 1458, 1376,
-1
1
222, 1089, 1065, 825 cm .
Synthesis of 2-methyl-1-(2,4,6-trihydroxy-3-isopentylphenyl)butan-1-one (22)
As described above, a suspension of compound 19 (96.9 mg, 0.177 mmol) and Pd(OH) /C
2
(
20% w/w, 31.0 mg, 0.044 mmol) in CH Cl (4 mL) was subjected to the hydrogenation
2 2
procedure for 6 h to yield 22 (37.9 mg, 77%) after purification as a yellow solid. Mp 163-
1
1
65 ºC; H NMR (500 MHz, CDCl ) δ 12.34 (br s, 1H), 7.75 (br s, 1H), 5.82 (s, 1H), 5.72
3
(br s, 1H), 3. 74 (m, 1H), 2.53 (m, 2H), 1.83 (m, 1H), 1.61 (m, 1H), 1.43-1.35 (m, 3H), 1.16
1
3
(
d, J = 6.7 Hz, 3H), 0.95 (d, J = 6.6 Hz, 6H), 0.91 (t, J = 7.4 Hz, 3H); C NMR (125 MHz,
) δ 210.6 (CO), 159.8 (C), 158.9 (C), 108.34 (C), 108.33 (C), 104.7 (C), 95.0 (CH),
6.1 (CH), 38.2 (CH ), 28.4 (CH), 27.1 (CH ), 22.7 (2CH ), 20.4 (CH ), 16.8 (CH ), 12.2
CDCl
3
4
2
2
3
2
3
+
+
(
CH ); HRMS (ESI ) 303.1574 (calcd for C H O Na, [M+Na] , 303.1572); IR (film) ν
3 16 24 4
max
-1
3
389, 2958, 2933, 2870, 1629, 1606, 1572, 1515, 1437, 1370, 1219, 1117, 1058, 815 cm .
Synthesis of 2-methyl-1-(2,4,6-trihydroxy-3-propylphenyl)butan-1-one (23)
2
4

ACCEPTED MANUSCRIPT
A suspension of compound 20 (186.0 mg, 0.357 mmol) and Pd(OH) /C (20% w/w, 62.7
2
mg, 0.089 mmol) in CH
2
Cl
2
(4.0 mL) was subjected to the hydrogenation procedure for 9 h
1
to afford 23 (86.1 mg, 96%) as a yellow solid. Mp 157-158 ºC; H NMR (500 MHz,
CDCl /CD OD) δ 13.5 (bs, 1H, OH); 9.4 (bs, 1H, OH); 8.3 (bs, 1H, OH); 5.79 (d, J= 2.5
3
3
Hz, 1H), 3.81 (m, 1H), 2.48 (td, J = 7.7, 1.8 Hz, 2H), 1.80 (m, 1H), 1.50 (m, 2H), 1.37 (m,
1
1
H), 1.12 (d, J = 6.7 Hz, 3H), 0.93 (t, J = 7.3 Hz, 3H), 0.88 (t, J = 7.4 Hz, 3H); H NMR
(
500 MHz, CD OD) δ 5.78 (bs, 1H), 3.78 (m, 1H), 2.38 (m, 2H), 1.71 (m, 1H), 1.39 (m,
3
1
3
2
H), 1.26 (m, 1H), 1.01 (d, J = 6.7 Hz, 3H), 0.80 (m, 6H); C NMR (125 MHz, CDCl /
3
3
CD OD) δ 211.0 (CO), 164.0 (C), 161.4 (C), 159.6 (C), 108.1 (C), 104.5 (C), 94.4 (CH),
4
5.8 (CH), 27.1 (CH
2
), 24.4 (CH
2
), 22.3 (CH
2
), 16.8 (CH
3
), 14.2 (CH
3
), 12.0 (CH
3
); HRMS
-
+
(
ESI ) 251.1281 (calcd for C14
H
19
O
4
, [M -1] 251.1283); IR (film) ν
3378, 2966, 2936,
max
-1
2
876, 1631, 1611, 1519, 1441, 1379, 1230, 1142, 1115, 1061, 1018, 818 cm .
Synthesis of 1,1'-(1,3,7,9-tetrahydroxydibenzo[b,d]furan-2,6-diyl)bis(2-methylbutan-1-
one) (24).
A solution of compound 21 (62.0 mg, 0.295 mmol) in CH Cl /CH CN (1.47 mL, 3:1) was
2
2
3
added dropwise to a suspension of anhydrous FeCl (295.9 mg, 1.78 mmol) on SiO (4.40
3
2
g, 73.4 mmol) in CH Cl (22 mL). The mixture was vigorously stirred at 45ºC for 24 h. The
2
2
suspension was filtered through a celite plug using CH Cl as eluent and the solvent was
2
2
removed under reduced pressure. Purification of the obtained residue by preparative-TLC (
hexanes/AcOEt 3:2) afforded 24 (12.4 mg, 21%) as a white amorphous solid and traces of
the corresponding biphenyl derivative 25.
1
1
,1'-(1,3,7,9-tetrahydroxydibenzo[b,d]furan-2,6-diyl)bis(2-methylbutan-1-one) (24): H
NMR (500 MHz, CDCl ) δ 5.91 (s, 2H), 3.75 (m, 2H), 1.83 (m, 2H), 1.42 (m, 2H), 1.17 (d,
3
2
5

ACCEPTED MANUSCRIPT
1
3
,
J = 6.8 Hz, 6H), 0.92 (t, J = 7.4 Hz, 6H); C NMR (125 MHz, CDCl ) δ 210.3 (CO),
3
1
(
2
62.3 (2C), 157.1 (2C), 104.6 (2C), 96.5 (2C), 95.9 (2CH), 45.9 (2 CH), 26.9 (2 CH ), 16.6
+
2 CH
3
), 11.9 (CH
3
); EIMS m/z 400 (M , 2), 316 (15), 233 (14); 231 (100), 203 (3), 57
+
(
12); HREIMS m/z 400.1508 (calcd for C H O , [M ] 400.1522); IR (film) ν
3292,
max
2
2
24
7
-1
2
966, 2875, 1726, 1614, 1458, 1369, 1130, 1057, 822 cm .
Synthesis of 1,1'-(1,3,7,9-tetrahydroxy-4,8-diisopentyldibenzo[b,d]furan-2,6-diyl)bis(2-
methylbutan-1-one) (26) and 1,1'-(2,2',4,4',6,6'-hexahydroxy-5,5'-diisopentyl-[1,1'-
biphenyl]-3,3'-diyl)bis(2-methylbutan-1-one) (27).
A solution of compound 22 (119.9 mg, 0.428 mmol) in CH Cl /CH CN (1.40 mL, 3:1) was
2
2
3
added dropwise to a suspension of anhydrous FeCl (293.2 mg, 1.75 mmol) on SiO (4.38
3
2
2 2
g, 73.0 mmol) in CH Cl (13.5 mL) at 40 ºC. The temperature was raised to 50 ºC and the
mixture was vigorously stirred and refluxed for 7 h. The solution was filtered through a
celite plug using CH Cl as solvent and removed under reduced pressure. Consecutive
2
2
purifications of the obtained residue by preparative chromatography and HPTLC
hexanes/AcOEt 7:3) afforded 26 (8.2 mg, 7%) as a yellow solid, 19.5 mg (16%) of the
corresponding biphenyl derivative 27 as a yellow oil.
(
1
,1'-(1,3,7,9-tetrahydroxy-4,8-diisopentyldibenzo[b,d]furan-2,6-diyl)bis(2-
1
methylbutan-1-one) (26): H NMR (600 MHz, CD OD) δ 3.91 (m, 2H), 2.62 (m, 4H),
3
1
.87 (m, 2H), 1.62 (m, 2H), 1.44-1.36 (m, 6H), 1.15 (d, J = 6.7 Hz, 6H), 0.96 (d, J = 6.6
1
3
Hz, 12H), 0.91 (t, J = 7.4 Hz, 6H); C NMR (150 MHz, CD OD) δ 213.1 (2CO), 166.2
3
(2C), 163.4 (2C), 161.4 (2C), 110.9 (2C), 107.1 (2C), 97.8 (2C), 47.9 (CH), 48.0 (CH),
4
0.1 (2CH2), 30.4 (2CH), 29.0 (CH ), 29.0 (CH ), 24.0 (4CH ), 22.8 (2CH ), 18.14 (CH ),
2
2
3
2
3
2
6

ACCEPTED MANUSCRIPT
+
+
1
5
8.10 (CH ), 13.2 (2CH ); HRMS (ESI ) 563.2986 [M+Na] (calcd for C H O Na,
3
3
32 44
7
-1
63.2985); IR (film) νmax 3309, 2957, 1613, 1572, 1413, 1357, 1215, 1186, 1059, 751 cm .
1
,1'-(2,2',4,4',6,6'-hexahydroxy-5,5'-diisopentyl-[1,1'-biphenyl]-3,3'-diyl)bis(2-
1
methylbutan-1-one) (27): H NMR (600 MHz, CD
3
OD) δ 3.90 (m, 2H), 2.61 (t, J = 7.8
Hz, 4H), 1.86 (m, 2H), 1.61 (m, 2H), 1.41 (m, 6H), 1.14 (d, J = 6.7 Hz, 6H), 0.95 (d, J =
1
3
6
.6 Hz, 12H), 0.91 (t, J = 7.4 Hz, 6H); C NMR (150 MHz, CD
3
OD) δ 210.8 (2CO), 164.0
(2C), 161.2 (2C), 159.1 (2C), 108.7 (2C), 104.8 (2C), 95.6 (2C), 45.7 (2CH), 37.8 (2CH2),
2
1
8.2 (2CH), 26.8 (2 CH ), 26.7 (CH ) 21.7 (4CH ), 20.5 (2CH ), 15.9 (CH ), 15.8 (CH ),
2
2
3
2
3
3
-
+
1.0 (2CH ); HRMS (ESI ) 557.3102 [M -1] (calcd for C H O , 557.3114); IR (film) ν
3
32 45
8
max
-1
3
317, 2943, 2831, 1450, 1415, 1115, 1024, 654 cm .
Synthesis of 1,1'-(1,3,7,9-tetrahydroxy-4,8-dipropyldibenzo[b,d]furan-2,6-diyl)bis(2-
methylbutan-1-one) (28) and 1,1'-(2,2',4,4',6,6'-hexahydroxy-5,5'-dipropyl-[1,1'-
biphenyl]-3,3'-diyl)bis(2-methylbutan-1-one) (29).
A solution of compound 23 (74.1 mg, 0.294 mmol) in CH Cl /CH CN (1.47 mL, 3:1) was
2
2
3
added dropwise to a suspension of anhydrous FeCl (201.3 mg, 1.20 mmol) on SiO (3.01
3
2
g, 50.2 mmol) in CH Cl (15 mL) at room temperature. The mixture was vigorously stirred
2
2
for 18 min. The suspension was filtered through a celite plug using CH Cl as eluent and
2
2
the solvent was removed under reduced pressure. Purification of the obtained residue by
preparative-TLC (hexanes/AcOEt 7:3) afforded 28 (20.0 mg, 28%) as a yellow solid and
5
.3 mg (7%) of the corresponding biphenyl derivative 29 as a yellow oil.
1
1
,1'-(1,3,7,9-tetrahydroxy-4,8-dipropyldibenzo[b,d]furan-2,6-diyl)bis(2-methylbutan-
1
-one) (28): H NMR (600 MHz, CD
3
OD) δ 4.05 (m, 2H), 2.68 (t, J = 7.8 Hz, 4H), 1.95
2
7

ACCEPTED MANUSCRIPT
(m, 2H), 1.65-160 (m, 6H), 1.31 (d, J = 6.9 Hz, 3H), 1.30 (d, J = 6.9 Hz, 3H), 1.00 (t, J =
1
3
7
.4 Hz, 6H), 0.97 (t, J = 7.4 Hz, 3H), 0.96 (t, J = 7.4 Hz, 3H); C NMR (150 MHz,
OD) δ 207.6 (2CO), 166.2 (2C), 162.9 (C), 162.8 (C), 155.2 (2C), 113.7 (2C), 109.44
C), 109.40 (C), 101.90 (C), 101.89 (C), 46.39 (CH), 46.36 (CH), 28.6 (CH ), 28.4 (CH ),
CD
3
(
2
2
2
6.6 (2CH ), 24.1 (2CH ), 19.8 (CH ), 19.6 (CH ), 15.5 (2CH ), 13.0 (CH ), 12.9 (CH );
2 2 3 3 3 3 3
-
+
HRMS (ESI ) 483.2399 [M -1] (calcd for C H O , 483.2383); IR (film) ν 3266, 2962,
2
8
35
7
max
-1
2
931, 1613, 1366, 1231, 1186, 1055, 704 cm .
1
,1'-(2,2',4,4',6,6'-hexahydroxy-5,5'-dipropyl-[1,1'-biphenyl]-3,3'-diyl)bis(2-
1
methylbutan-1-one) (29): H NMR (500 MHz, CDCl ) δ 3.70 (m, 2H), 2.60 (td, J = 1.6,
3
7
.7 Hz, 4H), 1.85 (m, 2H), 1.58 (m, 4H), 1.43 (m, 2H), 1.17 (d, J = 6.7 Hz, 6H), 0.99 (td, J
1
=
1.1, 7.4 Hz, 6H), 0.92 (td, J = 1.6, 7.4 Hz, 6H); H NMR (500 MHz, CD OD) δ 3.91 (m,
3
2
6
2
H), 2.59 (t, J = 7.4 Hz, 4H), 1.86 (m, 2H), 1.56 (m, 4H), 1.43 (m, 2H), 1.15 (d, J = 6.7 Hz,
1
3
H), 0.97 (t, J = 7.4 Hz, 6H), 0.91 (t, J = 7.4 Hz, 6H); C NMR (150 MHz, CD OD) δ
3
12.2 (2CO), 165.3 (2C), 162.7 (2C), 160.7 (2C), 109.5 (2C), 106.1 (2C), 97.2 (2C), 47.1
(
(
(
2CH), 28.1 (2CH
2
), 25.9 (2CH
2
), 23.2 (2CH
2
), 17.3 (CH
3
), 17.2 (CH
3
3
), 14.6 (2CH ), 12.4
+
+
+
CH
3
); HRMS (ESI ) 525.2465 [M+Na] (calcd for C28
H
38
O
8
Na, [M+Na] , 525.2464); IR
-
1
film) νmax 3338, 2951, 2871, 1601, 1454, 1421, 1228, 1119, 1022, 897 cm .
Biological assays
Antibacterial activity was determined as before using the standard broth microdilution
method as recommended by the National Committee for Clinical Laboratory Standards [15-
1
7]. We used three Gram-positive bacteria: methicillin-sensitive Staphylococcus aureus
ATCC25923 (MSSA); methicillin-resistant vancomycin- intermediate resistant
2
8