Conjugation of Hydroxytyrosol with Other Natural Phenolic Fragments: From Waste to Antioxidants and Antitumour Compounds

Article abstract of DOI:10.1002/ejoc.201500931

Hydroxytyrosol, a natural polyphenol that can be extracted from olive mill waste waters, was converted into a series of more complex and lipophilic analogues by conjugation with other naturally derived (poly)phenolic fragments. Ether and triazole linkers were employed. A small library of compounds was prepared, stressing step economy and operational simplicity. Some of these substances were proven to have activity equal or superior to that of the parent hydroxytyrosol in radical scavenging assays as well as in cytotoxicity tests against tumour cells.

Full text of DOI:10.1002/ejoc.201500931

FULL PAPER
DOI: 10.1002/ejoc.201500931
Conjugation of Hydroxytyrosol with Other Natural Phenolic Fragments: From
Waste to Antioxidants and Antitumour Compounds
Erika Tassano,[a] Angela Alama,[b] Andrea Basso,[a] Giancarlo Dondo,[c] Andrea Galatini,[a]
Renata Riva,[a] and Luca Banfi*[a]
Dedicated to the memory of Professor Alessandro Bagno
Keywords: Antioxidants / Nucleophilic substitution / Azides / Nitrogen heterocycles / Polyphenols
Hydroxytyrosol, a natural polyphenol that can be extracted
from olive mill waste waters, was converted into a series of
was prepared, stressing step economy and operational sim-
plicity. Some of these substances were proven to have ac-
more complex and lipophilic analogues by conjugation with tivity equal or superior to that of the parent hydroxytyrosol
other naturally derived (poly)phenolic fragments. Ether and
triazole linkers were employed. A small library of compounds
in radical scavenging assays as well as in cytotoxicity tests
against tumour cells.
three natural fragments. This “natural-fragment-based-
drug-discovery” approach[9] would allow the assembly, also
in a combinatorial manner, of libraries of complex poly-
phenols in few steps, with the possibility to easily modify
both scaffold and decorations to modulate pharmacodyn-
amic and pharmacokinetic properties.
Hydroxytyrosol[10] (1) is a natural catechol found in
olives. Owing to its high hydrosolubility, it is present only
in minute amounts in olive oil. On the other hand, it is one
of the major polyphenolic components occurring in olive
mill waste waters (OMWWs), in which it is found as such
or as an ester derivative (oleuropein) that is, however, easily
hydrolyzed under acidic conditions.
Hydroxytyrosol displays a variety of biological activi-
ties:[11] it is a cancer-preventing agent,[12] it inhibits prolifer-
ation in different human cancer cells,[13] it prevents various
degenerative diseases,[14] and it shows anti-inflammatory ac-
tivity.[7,15]
A high quantity of OMWWs is produced every year in
the Mediterranean area. Thus, exploitation of 1 as a build-
ing block for the production of substances of pharmaceuti-
cal, nutraceutical, or cosmeceutical interest is particularly
attractive, and this would allow the conversion of a useless
waste into high added-value products. Various papers have
described methodologies for the extraction of 1 from
OMWWs and its purification.[16] We also recently devel-
oped an improved method for the obtainment of 1 from
OMWWs that will be published in due time.
Introduction
Polyphenols are present in a variety of common food and
beverages and represent one of the major classes of dietary
antioxidants.[1] As antioxidants, polyphenols are believed to
protect cells against oxidative stress, and they are therefore
able to prevent various diseases associated with it, such as
cancer and cardiovascular and neurodegenerative dis-
eases.[2] Polyphenols were also demonstrated to have anti-
microbial,[3] anti-inflammatory[4] and anti-hyperglycemic[5]
properties and even to inhibit β-amyloid aggregation.[6]
Studies on their biological functions have started only
recently, and there is still a great debate about their pros
and cons. They have been defined as a “double-edged
sword”.[7] Moreover, it has been suggested that some of the
reported effects may be due to the fast production of
hydrogen peroxide.[8] Natural polyphenols often have poor
pharmacokinetic properties and low bioavailability. Finally,
most natural polyphenols are complex molecules, and the
synthesis of analogues, which would enable a more accurate
structure–activity relationship and help to understand their
mode of action, may be troublesome.
An interesting approach towards new complex, naturally
derived polyphenols would be the combination of two or
[a] Department of Chemistry and Industrial Chemistry, University
of Genova,
Via Dodecaneso 31, 16146 Genova, Italy
E-mail: banfi@chimica.unige.it
http://www.chimica.unige.it Initial(s)
[b] Lung Cancer Unit, IRCCS AOU San Martino – IST,
Largo Rosanna Benzi, 10, 16132 Genova, Italy
[c] Active Cells, Centro Biotecnologie Avanzate,
Torre D, 3° Piano Largo R. Benzi, 10, 16136 Genova, Italy
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejoc.201500931.
Hydroxytyrosol is a polar molecule, and the importance
of increasing the lipophilic character of polyphenols has al-
ready been noted.[17] Our idea was to conjugate 1 with other
aromatic fragments to obtain more complex systems con-
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Conjugation of Hydroxytyrosol with Natural Phenolic Fragments
taining two or three aryl rings. In particular, we planned to phenols (Scheme 2). Ether formation was obtained in two
join 1 with natural polyphenolic or phenolic fragments. In ways: (1) Mitsunobu reaction and (2) Williamson reaction
this way, we expected to obtain more complex and more through the mesylate (MsO–). In general, the first method
lipophilic hydroxytyrosol analogues that would mimic other provided better yields, but Williamson synthesis is more ad-
complex polyphenolic structures, such as, for instance, vantageous from the point of view of atom economy.
resveratrol or flavonoids. We decided to use two very simple
As phenolic counterparts we used either simple commer-
linkers: an ether bond and a triazole unit. In the first case, cially available phenols, such as 5a, 5b, and 5g, or protected
the two reagents to be coupled are a series of phenols and derivatives of natural phenols, such as 5c–e. Compound
hydroxytyrosol itself (or its derivatives protected at the 5c[20] is a protected derivative of tyrosol, another constitu-
phenolic groups). In the second case, we will need to con- ent of OMWWs. Known diacetate 5d[21] was chosen to link
vert the alcoholic function of 1 into an azide or a terminal 1 with phloroglucinol, the derivatives of which are known
alkyne. In both cases, the precursors should be easily avail- to display interesting biological activities.[21] Moreover, the
able in few steps and coupling may be performed under conjugate of phloroglucinol with 1 may be regarded as an
operationally simple conditions. Our aim was indeed to de- analogue of phytoalexins such as piceatannol[22] and resver-
velop short and efficient synthetic sequences to restrain the atrol, which are well-known natural phenols contained in
cost of our final products, which would thus also make wine and deemed responsible for the so-called “French
them potentially useful for nutraceutical or cosmeceutical paradox”.[23] Finally, 5e is a known protected derivative of
applications. We report herein the synthesis of a series of vanillic alcohol.
derivatives, the study of the in vitro antioxidant properties
Ethers 7a–c were prepared in good yields starting from
of some of them, and a comparison of their antiprolifera- acetal 4 and phenols 5a–c, by Mitsunobu reaction followed
tive activity on tumour cells with parent hydroxytyrosol 1.
by acidic deprotection of the acetal under microwave heat-
ing. In the case of 6c, the THP group was also completely
cleaved. Compounds 7b and 7c were also obtained, al-
though in lower yields, by the Williamson method. In the
case of phloroglucinol derivative 5d, both the Mitsunobu
and Williamson methods afforded only moderate yields ow-
ing to the lability of the phenolic acetates under the reaction
conditions. Acidic cleavage removed both the acetal and the
acetyl groups to afford piceatannol mimic 7d. On the other
hand, selective deprotection of the acetyl groups was
achieved under mild basic conditions to give 6f, in which
only the resorcinol moiety is free.
Upon using vanillin-derived phenol 5e, the Mitsunobu
reaction did work well enough. However, acidic deblocking
of the protecting groups led to extensive decomposition as
a result of the tendency of the benzyl alcohol in 7e to give
a stable carbocation. We therefore decided to start from
diacetyl hydroxytyrosol 2. This compound underwent a
smooth Mitsunobu reaction with o-chlorophenol to give
ether 6h, which was deprotected under mild basic condi-
tions. Also, the Mitsunobu reaction with vanillyl derivative
5e afforded desired product 6i. This time, deprotection of
the THP ether under mild acidic conditions proceeded
without any decomposition, and finally, basic solvolysis af-
forded hydroxytyrosol–vanillyl alcohol conjugate 7e. Brom-
ide 6b was also used for the preparation of more complex
ether 7g through Suzuki reaction with 3-thienylboronic
acid.
Results and Discussion
Synthesis
Hydroxytyrosol (1) was obtained by extraction from
OMWWs by using proprietary methodology and was puri-
fied by chromatography to give 1 in 80% purity (mainly
contaminated with tyrosol). Preliminary attempts showed
that temporary protection of the catechol moiety in 1 was
essential to obtain acceptable yields in the synthesis of con-
jugates. We therefore chose two simple protected starting
materials, namely, 2 and 4 (Scheme 1). The one-step synthe-
sis of diacetate 2 from hydroxytyrosol 1 was already report-
ed,[16b] although in moderate yield. We improved this pro-
cedure and were able to obtain 2 in 80% yield (calculated
by taking into account the purity of the starting material).
At the level of 2, removal of impurities was quite efficient,
and this building block was obtained in high purity. Acetal
4
[17c,18] was also obtained from 1 in good yield by following
a reported procedure involving three high-yielding steps.[19]
Compound 4 can also be efficiently obtained from commer-
cially available 3,4-dihydroxyphenylacetic acid (3).[18]
Scheme 3 shows the synthesis of a more complex ether,
namely, 12, obtained by joining three natural fragments,
that is, hydroxytyrosol, tyrosol, and phloroglucinol. It may
be seen as an extended analogue of 7d that, again, is charac-
terised by the presence of both the catechol and resorcinol
diphenolic motifs. Starting from 6c, selective deprotection
of the THP ether gave 9, which was coupled with diacetyl
phlorogucinol 5d. This latter reaction was not trivial: no
Scheme 1. Protected hydroxytyrosol derivatives used as starting
materials.
We first studied the synthesis of a series of ethers through product was obtained under Williamson conditions,
substitution of the alcoholic moiety in 2 or 4 by various whereas standard Mitsunobu conditions led to an incom-
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L. Banfi et al.
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Scheme 2. Synthesis of hydroxytyrosol-derived ethers. DEAD = diethyl azodicarboxylate; TBAD = di-tert-butyl azodicarboxylate; THP
= tetrahydropyran-2-yl; CSA = camphorsulfonic acid; MW = microwaves.
plete reaction, to the formation of deacetylated products, acetates afforded 11, for which only the resorcinol was liber-
and to substitution of the alcohol by acetate. Eventually, ated.
we found that optimal conditions involved premixing the
Other polyphenol conjugates have been obtained by
phenol, PPh3, and DEAD at 0 °C for 30 min before adding using the so-called “click reaction”, that is, 1,3-dipolar
alcohol 9. Acidic treatment removed all protecting groups cycloaddition of alkyl azides and terminal alkynes.[24] In
from 10 to give 12, whereas selective deprotection of the this way the linker is represented by a rigid heterocyclic
Scheme 3. Synthesis of a conjugate of hydroxytyrosol, tyrosol and phloroglucinol.
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Conjugation of Hydroxytyrosol with Natural Phenolic Fragments
ring, which is considered a “privileged scaffold” in medici- pleasure, in our hands this method turned out to be quite
nal chemistry. A similar approach was recently applied by efficient, as it afforded alkyne 19 in 75% yield from ester
Genazzani et al. in the synthesis of resveratrol analogues.[25] 16. This approach is also advantageous from the point of
Towards this goal, we needed to convert hydroxytyrosol view of step and atom economy, as Weinreb amide 18 re-
1 into either an azide or a terminal alkyne (Scheme 4). quires two additional steps from 16.
Starting from protected derivatives 2 and 4, substitution via
As counterparts for the synthesis of the conjugates, we
the mesylate gave azides 13 and 14 in good (for diacetate prepared four different alkynes and one azide, all derived
13) and excellent (for acetonide 14) yields. In the case of 13, from unprotected or protected phenol containing natural
reaction with sodium azide led to partial deacetylation, and compounds. Vanillin 20a was converted by a known pro-
therefore, it was necessary to acetylate the crude material. cess, through the Corey–Fuchs method, into corresponding
The conversion of protected hydroxytyrosol into a terminal alkyne 22a.[25,30] However, in our hands this direct method
alkyne was more troublesome. All attempts to oxidise 4 to afforded only an unsatisfactory overall yield. Therefore, for
corresponding aldehyde 15 with bis(acetoxyiodobenzene)/ the synthesis of 22a and other alkynes 22c–d, we decided to
2,2,6,6-tetramethylpiperidin-1-oxyl (BAIB/TEMPO), fol- follow a slightly longer but more efficient route involving
lowed by treatment of crude 15 under Corey–Fuchs condi- protection of the phenolic group(s). Although this strategy
tions,[26] failed to give any of the desired dibromoalkene implied additional steps for protection/deprotection, they
product. On the other hand, by using the Ohira–Bestmann proceeded in nearly quantitative yields. Moreover, the de-
reagent,[27] that is, dimethyl (1-diazo-2-oxopropyl)phos- protection could actually be performed after cycloaddition,
phonate, we isolated alkyne 19, but only in a trace amount. under the same conditions as those needed for deprotection
These poor results likely originate from the high instability of the other fragment. tert-Butyldimethylsilyl (TBS)-pro-
of aldehyde 15, which does not tolerate chromatography tected alkynes 22b,[31] 22c,[32] and 22d[33] are known and
(including TLC) or acid/base extractive workup. We, there- were prepared by the Corey–Fuchs method. However, un-
fore, decided to generate aldehyde 15 from Weinreb amide der standard conditions (addition of the aldehyde to a mix-
18, which was obtained in 89% yield from known ester 16, ture of PPh3 and CBr4 at 0 °C) the yields of intermediate
in turn synthesised in high yield from commercially avail- dibromides 21b–d were only moderate and rather erratic
able 3.[28] Reduction of 18 with LiAlH4 was very clean. Af- owing to slow and incomplete reactions and the occurrence
ter fast neutral extractive workup, the crude aldehyde was of desilylation processes. In previous work,[34] we encoun-
treated with the Ohira–Bestmann reagent to give alkyne 19 tered similar problems, and by examination of the possible
in an overall yield of 36% from 18. To further improve the mechanisms of this reaction, we suggested reaction condi-
yield and simplify the procedure, our attention was drawn tions that may overcome these problems: slow addition of
by a paper by Hinkle et al.,[29] in which the Ohira–Best- PPh3 to the mixture of aldehyde and CBr4 at low tempera-
mann reagent was used in a one-pot fashion after diisobut- ture. Also, in this case these conditions were found to be
ylaluminum hydride (DIBALH) reduction of an ester. With ideal, although better yields were obtained working at 0 °C
Scheme 4. Synthesis of various building blocks to be used for click assembly of hydroxytyrosol conjugated by a triazole ring. CDI =
carbonyldiimidazole, OB reagent = Ohira–Bestmann reagent = dimethyl (1-diazo-2-oxopropyl)phosphonate. TBAF = tetrabutylammo-
nium fluoride.
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Scheme 5. Synthesis of polyphenolic triazoles.
and in the presence of a buffering agent (Et3N), which pre- compounds (i.e., 27a, 27b, 27d, and 27g) have a catechol
vented desilylation. Very high yields of desired dibromides unit on one phenyl group and a free phenol group on the
21b–d were achieved. Elimination–debromination with other one. The structure of the obtained triazoles was dem-
nBuLi proceeded uneventfully to give terminal alkynes 22b– onstrated by gHMBC and NOE NMR experiments. For
d. Vanillin derivative 22b was also deprotected to 22a in example, in 26a–d, 26f, 27a–d, and 27f coupling between
90% yield. The overall yield of 22a from vanillin by this the ArCH2CH2 protons and the triazole CH (5-H) was de-
four-step route (70%) is, therefore, much better than the tected in gHMBC. Moreover, in these compounds, a NOE
two-step route that skips protection (30%).
between the ArCH2CH2 protons and 5-H of the triazole
Alkyne 22f[35] carrying a single protected phenol was pre- is present. These effects can only be present in the shown
pared by a different route starting this time from p-iodo- regioisomer. Similarly, in 26g and 27g, a NOE can be de-
phenol and making use of the Sonogashira reaction. Inter- tected between 5-H and the azide-derived CH2.
estingly, the sequence also worked well without protecting
the phenol. However, alkyne 22e proved to be very suscepti-
ble to water addition, even in the presence of trace amounts
of moisture to give corresponding methyl ketone 24. Evi-
Radical-Scavenging Studies
dently, the phenolic group plays an important anchimeric
role in accelerating the addition of water.
To evaluate the radical-scavenging properties of these
new polyphenolic derivatives, we first studied their behavior
Finally azide 25 was obtained, as described previously in the presence of the 1,1-diphenyl-2-picrylhydrazyl radical
by us,[36] in three steps and 81% yield from commercially (DPPH). This radical, which is completely stable in the
available natural ortho-vanillin.
presence of atmospheric O2, is often used to assay antioxi-
Having in hand a series of alkynes and azides, we cou- dant properties, as abstraction of a hydrogen atom from
pled them through the CuI-catalyzed click reaction a phenol derivative quenches the intense absorbance of its
(Scheme 5) to give six protected triazoles 26a–d, 26f, and solutions. In previous work, several parameters were pro-
26g. All the coupling reactions proceeded in good yields posed to measure the antioxidant or radical scavenging
with complete regioselectivity.
power.[37] The percentage of radical scavenging activity
Finally, partial or total removal of the protecting groups (RSA, see footnotes of Table 1) is easily determined from
led to seven different triazoles 27a–g containing at least one the decrease in absorbance, but it clearly depends on time
free catechol unit. Among them, 27c and 27f contain two and on the concentration of the antioxidant. On the other
catechol units (the difference is a longer linker in 27f), hand, the half-maximal effective concentration (EC50),
whereas 27e is a partially protected form of 27c. The other often expressed as gantioxidant kgDPPH–1, is usually deter-
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Conjugation of Hydroxytyrosol with Natural Phenolic Fragments
Table 1. Results of DPPH assays on compounds 1, 7a, 7d, and 27c.
Compound 1
Compound 7a
Conc.
MR[a]
100 μm
4.3
1.4
250 μm
10.8
2.3
400 μm
17.2
2.9
500 μm
21.5
4.8
Conc.
MR[a]
100 μm
4.3
2.0
120
8.5
13.1
1.97
3.04
200 μm
8.6
2.0
250 μm
10.8
2.4
400 μm
21.5
3.0
[b]
[b]
t1[b] [min]
t1[b] [min]
t2 [min]
120
120
120
120
t2 [min]
120
120
120
[c]
[c]
RSA1[c] [%]
12.5
20.4
2.91
4.74
24.0
39.4
2.23
34.7
60.4
2.02
3.51
46.1
76.5
2.14
3.56
RSA1[c] [%]
18.4
28.9
2.14
23.8
43.0
2.21
4.00
45.1
79.5
2.10
4.62
RSA2 [%]
RSA2 [%]
[d]
[d]
StR1[d]
StR1[d]
StR2[e]
3.66
StR2[e]
3.36
–1
–1
–1
–1
EC50 (at t2): 135 nmol1 μmolDPPH or 53 g1 kgDPPH
EC50 (at t2): 108 nmol1 μmolDPPH or 71 g1 kgDPPH
Compound 7d
Compound 27c
Conc.
MR[a]
200 μm
8.6
3.2
16.5
29.4
31.2
3.4
300 μm
12.9
2.9
400 μm
17.2
4.5
19.0
56.2
56.8
3.3
500 μm
21.5
3.9
Conc.
MR[a]
150 μm
6.5
3
200 μm
8.6
4.3
250 μm
10.8
4.4
300 μm
12.9
4.5
[b]
[b]
t1[b] [min]
t1[b] [min]
t2 [min]
2.9
3.9
t2 [min]
60
60
120
60
[c]
[c]
RSA1[c] [%]
40.2
40.2
3.1
68.1
68.1
3.2
RSA1[c] [%]
29.4
40.4
4.55
6.26
36.9
53.3
4.28
44.9
65.2
4.17
6.06
50.5
74.8
3.91
5.79
RSA2 [%]
RSA2 [%]
[d]
[d]
StR1[d]
StR1[d]
StR2[e]
3.6
3.1
3.3
3.2
StR2[e]
6.19
–1
–1
–1
–1
EC50 (at t2): 162 nmol1 μmolDPPH or 108 g1 kgDPPH
EC50 (at t2): 65 nmol1 μmolDPPH or 52 g1 kgDPPH
[a] MR = molar ratio phenolic compound/DPPH. [b] t1: end of the first fast reaction; t2 = end of the second slow reaction (steady state).
[c] RSA = radical scavenging activity = [Abs515 nm (t = 0) – Abs515 nm (t = t1 or t2)]ϫ100/Abs515 nm (t = 0); RSA1: measured after t1;
–1
RSA2: measured after t2. [d] StR = stoichiometric ratio = nmolDPPH consumed nmolantioxidant present = %RSA/(MRϫ100); StR1 measured
at t1, StR2 measured at t2. [e] EC50: half-maximal efficient concentration, that is, the relative amount of antioxidant needed to decrease
the initial amount of DPPH by 50%.
mined when the system reaches a steady state and repre- lowed by a much slower decrease in absorbance. To reach
sents the relative amount of antioxidant needed to quench the steady state, 60 min or more was often needed and the
half the initial amount of DPPH. This parameter quantifies exact determination of TEC turned out to be difficult, be-
50
the overall radical scavenging power but does not give any cause of very slow variation of the absorbance. A clear
information on the kinetics of this process. Therefore, change in kinetics can be seen in Figure 1 for 1, 7a, and
Saura-Calixto and co-workers[37a] introduced the TEC
27c and is even more evident by plotting the second-order
parameter, which is the time needed to reach the stead5y0 derivative versus time. This change happens typically after
state, and the antiradical efficiency (AE) as a combination 2–3 min.
of EC50 and T
.
Thus, we preferred to report in Table 1, for each com-
EC50
However, upon trying to determine EC50 and TEC of pound and each concentration, not only the time needed to
50
hydroxytyrosol 1 and of most of the herein described deriv- reach the final steady state (t2), but also the time represent-
atives, we found that a very fast initial reaction was fol- ing the end of the initial fast reaction, when the second-
Figure 1. Radical-scavenging activity (%RSA) of compounds 1, 7a, 7d, and 27c versus time.
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L. Banfi et al.
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order derivative falls to near zero (t1) (Table 1). Clearly, the ilar mechanism could also be operating for 1 and its ana-
determination of t2, especially for compounds 1, 7a, and logues, notwithstanding the absence of an electron-with-
27c, is rather imprecise, owing to the very slow variation of drawing group (Scheme 6). After fast oxidation of the cate-
the absorbance. Moreover, we also reported EC50 as a mo- chol to an o-benzoquinone, the latter can undergo Michael
lar ratio and estimated the stoichiometry of the radical- addition by the solvent methanol (one of the most widely
scavenging process. For the sake of brevity, we report herein used solvents in these tests) to regenerate the catechol moi-
only the data collected for four compounds that represent ety, which is further oxidised by DPPH. Most likely, the
good models for all the other ones synthesised. Apart from rate-limiting step is methanol addition to 28 and not the
parent 1, we selected a conjugate with a single catechol unit final oxidation of 30 to 31. In our case, the lack of an elec-
(i.e., 7a), one with a catechol and a resorcinol unit, and tron-withdrawing group does not particularly favor ad-
finally a triazole that links two catechol units. All the pa- dition, and this explains the sluggishness of the process. To
rameters are listed in Table 1, whereas Figure 1 shows the demonstrate this hypothesis, we treated 1 with DPPH in
kinetics of the scavenging process for these four compounds methanol for 2 h at room temperature. After solvent evapo-
at a given concentration.
ration, analysis of the crude material by NMR spectroscopy
Compounds 1 and 7a showed a similar profile. The mo- showed, after subtracting the signals for DPPH, the absence
lar EC50 was even better for 7a than for 1, which shows of 1 and the presence of quinone 31 together with 20–25%
that not only was etherification of the alcoholic group not
deleterious at all but that it increased the radical-scavenging
efficiency. A look at the stoichiometric ratios (StR) revealed
that during the fast reaction, each molecule of catechol
antioxidant is able to quench two radicals. This is expected,
because oxidation of catechol to o-quinone requires two
hydrogen atom abstractions by DPPH. However, the pro-
cess does not stop here, and during the second slow reac-
tion, about an additional 2 equivalents of DPPH are
quenched. This is somehow surprising, as 1 and 7a do not
contain any additional phenolic groups. This phenomenon
was already detected by others on compounds containing
catechol units in combination with electron/withdrawing
groups, such as protocatechuic acid and chlorogenic acid,[38]
and a hypothesis to rationalise this effect has been pre-
sented by Saito and Kawabata.[38b] We reasoned that a sim- Scheme 6. Postulated mechanism for the second, slow reaction.
1
Figure 2. H NMR spectrum (ring protons only) of crude quinone 31.
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Conjugation of Hydroxytyrosol with Natural Phenolic Fragments
of quinone 28 (Figure 2). In principle, methanol can attack
either C5 or C3, and Saito postulated attack at C3.[38b]
However, the signal patterns for 3-H and 6-H (see Figure 2)
and the results of the g-HMBC experiments showed un-
equivocally that in our case addition took place exclusively
at C5.
Also for triazole 27c, a first fast reaction was followed
by a second, slow one. However, in this case, the StR factors
(and molar EC50) were approximately doubled, which
shows that the two catechol units are able to react indepen-
dently, with a similar rate both in the first fast reaction and
in the second slow one. Thus, the proximity of the triazole
ring to the catechol on the right part of the molecule has
no inhibiting effect.
Finally, different behavior was shown by compound 7d
containing a catechol and a resorcinol unit. This time, only
a fast process was evident (see also Figure 1) and t1 and t2
were nearly equivalent, although, as before, it is inherently
difficult to determine t2 precisely. The stoichiometry ratio
was in this case around 3:1 and not 2:1 as for 1 or 7a. We
presume that the third DPPH equivalent is quenched by
one of the two phenolic groups of the resorcinol unit, which
forms a free oxygen radical that is not able to undergo fur-
ther reaction. In this case, the second slow process depicted
in Scheme 6 seems inhibited. We think that the free radical
on the resorcinol unit may inhibit the oxidation of the
hydroquinone formed by conjugate addition of methanol.
Conclusions
In conclusion, we demonstrated the possibility to convert
hydroxytyrosol 1, a natural polyphenol that can be ex-
tracted from olive mill waste waters, into a series of more
complex derivatives by conjugation with other (poly)phen-
olic moieties through an ether or triazole linker. The chem-
istry employed is simple, endowed with step economy, and
allows a combinatorial approach to this type of com-
pounds. This small library of conjugates has already been
proven to maintain, or even increase, some of the peculiar
properties of 1, such as the radical-scavenging activity and
cytotoxicity, though it is definitely more promising from a
pharmacokinetic point of view. In the near future we plan
to study more deeply the biological activity of these com-
pounds and to prepare more analogues guided by struc-
ture–activity relationship clues.
Experimental Section
General Remarks: NMR spectra were taken at room temperature
in CDCl3, CD3OD, or [D6]DMSO at 300 MHz (1H) and 75 MHz
(13C) by using SiMe4 as an internal standard (1H NMR in CDCl3:
δ = 0.000 ppm) or the central peak of CDCl3 (13C NMR in CDCl3:
δ = 77.02 ppm), the central peak of partially non-deuterated
CD3OD (1H NMR in CD3OD: δ = 3.310 ppm; 13C NMR in
CD3OD: δ = 49.00 ppm), or the central peak of DMSO (1H NMR
in [D6]DMSO:
δ =
2.506 ppm; 13C NMR in [D6]DMSO;
39.43 ppm). Chemical shifts are reported in ppm (δ scale). Peak
assignments were made with the aid of gCOSY and gHSQC experi-
ments. In ABX systems, proton A is considered upfield and pro-
ton B downfield. GC–MS was performed by using an HP-1 column
(12 m long, 0.2 mm wide), electron impact at 70 eV, and a mass
temperature of about 170 °C. Only m/z Ͼ 33 were detected. All
analyses were performed (unless otherwise stated) with a constant
He flow of 1.0 mLmin–1 with an initial temperature of 60 °C, initial
time 1 min, rate 15 °Cmin–1, final temperature 280 °C, injection
temperature 250 °C, detection temperature 280 °C. For HRMS
measurements, samples at 10 mm in DMSO were diluted to 50 µm
with acetonitrile/water (1:1) and were analyzed with a UPLC
Acquity system coupled to a Synapt G2 QToF mass spectrometer.
MS signals were acquired from m/z = 50 to 1200, in both the ESI+
and ESI– ionization modes. UPLC was performed with H2O/
CH3CN/HCO2H with an Acquity UPLC BEH C18, 1.7 µm,
2.1ϫ50 mm column at 45 °C. Microwave-assisted reactions were
performed with a CEM Discover apparatus in 4 mL test tubes
(close vessel). A maximum power of 50 W and air cooling were
employed. TLC analyses were performed on silica gel plates and
developed under UV light (λ = 254 nm) or with Hanessian stain
[dipping into a solution of (NH4)4MoO4·4H2O (21 g) and Ce(SO4)2·
4H2O (1 g) in H2SO4 (31 mL) and H2O (469 mL) and warming].
Rf values were measured after an elution of 7–9 cm. Column
chromatography was done with the “flash” methodology by using
220–400 mesh silica. IR spectra were recorded as solid, oil, or
foamy samples, with the ATR (attenuated total reflectance)
method. Petroleum ether (40–60 °C) is abbreviated PE. In extrac-
tive workup, aqueous solutions were always re-extracted (3ϫ) with
the appropriate organic solvent. Organic extracts were always dried
with Na2SO4 and filtered before evaporation of the solvent under
reduced pressure. All reactions using dry solvents were performed
under a nitrogen atmosphere.
Cytotoxicity Studies
Some of the synthesised compounds were preliminarily
examined for their cytotoxic activity against lung adeno-
carcinoma tumour cell lines, as shown in Table 2. The MTS
spectrophotometric cell viability assay was employed [MTS
=
3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphen-
yl)-2-(4-sulfophenyl)-2H-tetrazolium bromide]. As can be
seen, all three hydroxytyrosol derivatives displayed cytotoxi-
cities comparable to that of the parental compound. In par-
ticular, compound 7e was more potent than parent 1 on
both cell lines, at all tested concentrations. Although these
experiments are preliminary and a larger set of tumour cell
lines needs to be explored, these data demonstrate that
the conjugation does not inhibit the cytotoxic activity of
hydroxytyrosol.
Table 2. Cytotoxicity assays on lung adenocarcinoma cells.[a]
VS [%]
A549
100 μm
H1975
100 μm
50 μm 25 μm
50 μm 25 μm
1
59.1
61.2
44.2
55.9
66.9
71.3
62.1
70.4
82.9
81.2
76.2
76.9
59.6
67.9
48.3
68.4
76.0
86.0
64.3
73.5
79.5
84.9
72.9
71.8
7d
7e
27a
[a] VS = viability = Abs490 nm(tested compd) ϫ 100/Abs490 nm(con-
trol).
Eur. J. Org. Chem. 2015, 6710–6726
© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
6717

L. Banfi et al.
= 7.1 Hz, 2 H, CH2O), 2.98 (t, JH,H = 7.1 Hz, 2 H, ArCH2), 1.66
FULL PAPER
3
(3,4-Diacetoxyphenyl)ethanol (2): A solution of hydroxytyrosol (1)
(80% purity by NMR; 1.067 g, 6.92 mmol) in dry CH3CN (35 mL) (s, 6 H, CH3C) ppm. 13C NMR (75 MHz, CDCl3, 25 °C): δ = 157.9
was treated with dry K2CO3 (1.913 g, 13.8 mmol) and stirred for (1Ј-C), 147.5, 146.1 (3a-C, 7a-C), 132.2 (3Ј-C), 131.0 (5-C), 121.2
15 min at room temperature. The flask was immersed in an ice bath
and treated dropwise with acetic anhydride (1.30 mL, 13.8 mmol).
(6-C), 117.8 (2-C), 116.3 (2Ј-C), 112.8 (4Ј-C), 109.2, 108.1 (4-C, 7-
C), 69.2 (CH O), 35.4 (ArCH ), 25.9 (CH C) ppm. IR: ν = 2920,
˜
2
2
3
After stirring at 0 °C for 1.5 h, the mixture was diluted with water 2862, 1590, 1497, 1486, 1463, 1444, 1372, 1257, 1241, 1214, 1167,
and extracted with EtOAc to give a crude product that was chro-
matographed (PE/EtOAc, 55:45) to give analytically pure 2 as an
1158, 1027, 988, 853, 841, 819, 799, 790 cm–1. GC–MS (tR = 13.18):
m/z (%) = 350 (6.1) [M]+, 348 (6.7) [M]+, 177 (100.0), 163 (23.1),
oil (1.059 g, 65%, 80% considering the initial purity of 1). The 161 (4.8), 137 (33.1), 135 (7.0), 123 (20.2), 119 (14.4), 91 (20.0), 77
spectroscopic and analytical data correspond to those reported.[16b]
(9.7), 65 (12.2), 63 (7.1), 51 (7.1), 43 (13.8), 41 (11.9). HRMS
(ESI+): calcd. for C17H17BrO3Na [M + Na]+ 371.0259; found
371.0252.
2-Methoxy-4-{[(tetrahydro-2H-pyran-2-yl)oxy]methyl}phenol (5e): A
solution of vanillyl alcohol (4-hydroxy-3-methoxybenzyl alcohol;
800 mg, 5.26 mmol) in dry THF (15 mL) was treated with di-
hydropyran (720 μL, 7.89 mmol) and p-toluenesulfonic acid
(100 mg, 580 μmol). After stirring at room temperature for 16 h,
the solution was diluted with Et2O and saturated aqueous
NaHCO3. The phases were separated, and the aqueous phase was
extracted with Et2O (2ϫ). The united organic extract gave a crude
that was chromatographed (PE/EtOAc, 80:20) to give pure 5e as
an oil (930 mg, 74%). The spectroscopic and analytical data corre-
spond to those reported.[39]
2,2-Dimethyl-5-[2-(4-{2-[(tetrahydro-2H-pyran-2-yl)oxy]ethyl}-
phenoxy)ethyl]benzo[d][1,3]dioxole (6c)
Method A: starting from 4 (250 mg, 1.29 mmol) and 4-{2-[(tetra-
hydro-2H-pyran-2-yl)oxy]ethyl}phenol (5c;[20] 343 mg, 1.54 mmol),
the same procedure as that described for 6a was followed, but by
using DEAD(40% in toluene) instead of TBAD. The crude product
was chromatographed (PE/EtOAc, 90:10) to give pure 6c as an oil
(445 mg, 86%).
Method B: Starting from 4 (100 mg, 0.51 mmol) and 5c[20] (124 mg,
0.56 mmol), the same procedure as that described for 6b
(method B) was followed to give, after chromatography, pure 6c
5-[2-(4-Methoxyphenoxy)ethyl]-2,2-dimethylbenzo[d][1,3]dioxole
(6a): A solution of compound 4 (100 mg, 514 μmol) in dry CH2Cl2
(1.00 mL) was treated with p-methoxyphenol (96 mg, 773 μmol),
PPh3 (204 mg, 778 μmol), and TBAD (178 mg, 773 μmol) and
stirred for 1.5 h at room temperature. The crude was concentrated
and chromatographed (PE/Et2O, 9:1) to give pure 6a as a slightly
yellow oil (124 mg, 77%). Rf = 0.80 (PE/EtOAc, 7:3). 1H NMR
(300 MHz, CDCl3, 20 °C): δ = 6.82 (s, 4 H, H of p-MeOAr), 6.70–
1
as an oil (138 mg, 68%). Rf = 0.69 (PE/EtOAc, 70:30). H NMR
3
(300 MHz, CDCl3, 20 °C): δ = 7.13 (d, JH,H = 8.7 Hz, 2 H, 3Ј-
3
H), 6.82 (d, JH,H = 8.7 Hz, 2 H, 2Ј-H), 6.70–6.65 (m, 3 H, H of
3
benzodioxole), 4.59 (t, JH,H = 3.5 Hz, 1 H, CHO of THP), 4.09
3
2
(t, JH,H = 7.2 Hz, 2 H, CH2O hydroxytyrosol), 3.90 (dt, JH,H
=
3
9.6 Hz, JH,H = 7.2 Hz, 1 H, CHHOTHP), 3.81–3.72 (m, 1 H,
3
6.65 (m, 3 H, H of benzodioxole), 4.07 (t, JH,H = 7.2 Hz, 2 H,
2
3
CHHO of THP), 3.57 (dt, JH,H = 9.6 Hz, JH,H = 7.2 Hz, 1 H,
CH2O), 3.76 (s, 3 H, CH3O), 2.97 (t, 3JH,H = 7.2 Hz, 2 H, ArCH2),
1.66 (s, 6 H, CH3C) ppm. 13C NMR (75 MHz, CDCl3, 25 °C): δ =
153.8, 152.9 (1Ј-C, 4Ј-C), 147.4, 146.0 (3a-C, 7a-C), 131.4 (5-C),
121.2 (6-C), 117.7 (2-C), 115.5, 114.6 (2Ј-C, 3Ј-C), 109.2, 108.0 (4-
C, 7-C), 69.6 (CH2O), 55.7 (CH3O), 35.6 (ArCH2), 25.9 (CH3C)
CHHOTHP), 3.50–3.41 (m, 1 H, CHHO of THP), 2.98 (t, 3JH,H
=
3
7.2 Hz, 2 H, ArCH2 hydroxytyrosol), 2.84 (t, JH,H = 7.2 Hz, 2 H,
ArCH2 tyrosol), 1.88–1.44 (m, 6 H, CH2 of THP), 1.66 (s, 6 H,
CH3C) ppm. 13C NMR (75 MHz, CDCl3, 25 °C): δ = 157.2 (1Ј-C),
147.4, 146.0 (3a-C, 7a-C), 131.3, 131.2 (4Ј-C, 5-C), 129.9 (3Ј-C),
121.2 (6-C), 117.7 (2-C), 114.4 (2Ј-C), 112.8 (4Ј-C), 109.2, 108.0 (4-
C, 7-C), 98.7 (CHO of THP), 68.9 (CH2O hydroxytyrosol), 68.5
(CH2OTHP), 62.2 (CH2O of THP), 35.53, 35.46 (ArCH2), 30.7,
ppm. IR: ν = 2991, 2937, 2868, 2833, 1506, 1495, 1443, 1376, 1251,
˜
1223, 1181, 1156, 1120, 1107, 1038, 978, 824, 731 cm–1. GC–MS
(tR = 13.54 min): m/z (%) = 300 (13.9) [M]+, 177 (100.0), 163 (3.2),
161 (3.2), 142 (3.7), 137 (30.6), 123 (11.1), 119 (13.0), 109 (4.6), 107
(3.7), 91 (27.3), 65 (9.3), 51 (3.5), 43 (7.9), 41 (8.3). HRMS (ESI+):
calcd. for C18H21O4 [M + H]+ 301.1440; found 301.1436.
25.5, 19.5 (CH of THP), 25.8 (CH C) ppm. IR: ν = 2939, 2868,
˜
2
3
1611, 1583, 1511, 1495, 1444, 1376, 1353, 1301, 1231, 1200, 1177,
1156, 1135, 1119, 1077, 1027, 978, 907, 869, 836, 809, 732 cm–1.
GC–MS: not feasible. HRMS (ESI+): calcd. for C24H31O5 [M +
H]+ 399.2171; found 399.2172.
5-[2-(4-Bromophenoxy)ethyl]-2,2-dimethylbenzo[d][1,3]dioxole (6b)
Method A: Starting from 4 (205 mg, 1.06 mmol) and p-bromo-
phenol, the same procedure as that described for 6a was followed,
but by using DEAD(40% in toluene) instead of TBAD. The crude
product was chromatographed (PE/EtOAc, 97:3) to give pure 6b as
an oil (297 mg, 80%).
2,2-Dimethyl-5-{2-[(3,5-diacetoxy)phenoxy]ethyl}benzo[d][1,3]-
dioxole (6d)
Method A: Starting from 4 (100 mg, 0.51 mmol) and 3,5-diacetoxy-
phenol (5d;[21] 130 mg, 0.62 mmol), the same procedure as that de-
scribed for 6a was followed (reaction time: 6 h). The crude product
was chromatographed [petroleum ether (PE)/CH2Cl2/Et2O,
60:30:10] to give pure 6d as an oil (79 mg, 40%).
Method B: A solution of compound 4 (100 mg, 0.51 mmol) in dry
CH2Cl2 (1.3 mL) was cooled to 0 °C and treated with Et3N (93 μL,
0.67 mmol) and methanesulfonyl chloride (48 μL, 0.62 mmol). The
solution was stirred for 45 min at 0 °C and then poured into satu-
rated aqueous NH4Cl and extracted with CH2Cl2. The organic
phase was washed with brine and concentrated. The residue was
taken up in dry DMF (1.5 mL) and treated at room temperature
with Cs2CO3 (181 mg, 0.56 mmol). After complete dissolution, 4-
bromophenol (92 mg, 0.53 mmol) was added. The mixture was
warmed at 60 °C and stirred overnight. After cooling, the mixture
was diluted with water and extracted with EtOAc. Concentration
Method B: Starting from 4 (100 mg, 0.51 mmol) and 5d[21] (118 mg,
0.56 mmol), the same procedure as that described for 6b
(method B) was followed to give, after chromatography, pure 6d
as an oil (64 mg, 32%). Rf = 0.52 (PE/EtOAc, 70:30). 1H NMR
(300 MHz, CDCl3, 20 °C): δ = 6.65 (s, 3 H, H of benzodioxole),
4
4
6.53 (d, JH,H = 2.1 Hz, 2 H, 2Ј-H and 6Ј-H), 6.50 (t, JH,H
=
3
2.1 Hz, 1 H, 4Ј-H), 4.07 (t, JH,H = 7.1 Hz, 2 H, CH2O), 2.97 (t,
and chromatography as above gave pure 6b as an oil (130 mg,
3JH,H = 7.1 Hz, 2 H, ArCH2), 2.26 (s, 6 H, CH3CO), 1.67 (s, 6 H,
1
73%). Rf = 0.90 (PE/EtOAc, 70:30). H NMR (300 MHz, CDCl3, CH3C) ppm. 13C NMR (75 MHz, CDCl3, 25 °C): δ = 168.9 (C=O),
3
3
20 °C): δ = 7.35 (d, JH,H = 8.8 Hz, 2 H, 3Ј-H), 6.77 (d, JH,H
=
159.9 (1Ј-C), 151.6 (3Ј-C, 5Ј-C), 147.5, 146.1 (3a-C, 7a-C), 130.9
3
8.8 Hz, 2 H, 2Ј-H), 6.66 (s, 3 H, H of benzodioxole), 4.07 (t, JH,H (5-C), 121.3 (6-C), 117.8 (2-C), 109.2, 108.1 (4-C, 7-C), 107.8 (4Ј-
6718
www.eurjoc.org
© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2015, 6710–6726

Conjugation of Hydroxytyrosol with Natural Phenolic Fragments
C), 105.9 (2Ј-C and 6Ј-C), 69.4 (CH2O), 35.3 (ArCH2), 25.8 pure 6g as a white foam (109 mg, 72%). Rf = 0.54 (PE/Et2O, 90:10).
3
(CH C), 21.1 (CH CO) ppm. IR: ν = 2991, 2938, 1766, 1614, 1496, 1H NMR (300 MHz, CDCl3, 20 °C): δ = 7.50 (d, JH,H = 8.7 Hz,
˜
3
3
3
1461, 1445, 1368, 1328, 1252, 1189, 1145, 1117, 1044, 1024, 999,
2 H, 3Ј-H), 7.38–7.31 (m, 3 H, thienyl H), 6.92 (d, JH,H = 8.8 Hz,
3
978, 938, 892, 837, 809, 731 cm–1. GC–MS (tR = 15.14 min): m/z
2 H, 2Ј-H), 6.71–6.64 (m, 3 H, H of benzodioxole), 4.14 (t, JH,H
(%) = 386 (37.4) [M]+, 371 (3.7), 301 (3.6), 243 (3.2), 177 (100.0), = 7.1 Hz, 2 H, CH2O), 3.01 (t, JH,H = 7.1 Hz, 2 H, ArCH2), 1.67
3
163 (28.5), 161 (21.5), 137 (19.6), 123 (15.9), 119 (7.9), 91 (12.6),
(s, 6 H, CH3C) ppm. 13C NMR (75 MHz, CDCl3, 25 °C): δ = 158.1
43 (32.7). HRMS (ESI+): calcd. for C21H23O7 [M + H]+ 387.1444; (1Ј-C), 147.5, 146.1 (3a-C, 7a-C), 142.0 (quat. of thienyl), 131.2 (5-
found 387.1438.
C), 128.8 (4Ј-C), 127.5 (3Ј-C), 126.2, 126.0, 117.7 (CH thienyl),
121.2 (6-C), 118.9 (2-C), 114.8 (2Ј-C), 109.2, 108.1 (4-C, 7-C), 69.0
2,2-Dimethyl-5-[2-(2-methoxy-4-{[(tetrahydro-2H-pyran-2-yl)-
oxy]methyl}phenoxy)ethyl]benzo[d][1,3]dioxole (6e): Starting from 4
(100 mg, 0.51 mmol) and phenol 5e (147 mg, 0.62 mmol), the same
procedure as that described for 6a was followed. The crude product
was chromatographed (ETP/EtOAc, 80:20) to give pure 6e as an oil
(121 mg, 56%). Rf = 0.65 (PE/EtOAc, 70:30). 1H NMR (300 MHz,
(CH O), 35.5 (ArCH ), 25.9 (CH C) ppm. IR: ν = 3100, 3026,
˜
2
2
3
2988, 2945, 2921, 2867, 1608, 1580, 1536, 1504, 1491, 1469, 1445,
1431, 1383, 1375, 1366, 1308, 1291, 1278, 1250, 1233, 1204, 1184,
1159, 1118, 1089, 1072, 1042, 1025, 993, 979, 922, 913, 901, 864,
842, 833, 822, 801, 782, 776, 743, 723, 715, 658, 640, 627 cm–1.
GC–MS (tR = 16.06 min): m/z (%) = 352 (18.1) [M]+, 177 (100.0),
176 (7.1), 169 (5.8), 137 (26.3), 135 (5.4), 123 (9.0), 119 (10.6), 115
(6.1), 91 (16.6), 77 (4.8), 65 (5.9), 43 (5.7), 41 (6.6). HRMS (ESI+):
calcd. for C21H21O3S [M + H]+ 353.1211; found 353.1222.
4
CDCl3, 20 °C): δ = 6.92 (d, JH,H = 1.5 Hz, 1 H, 3Ј-H), 6.91–6.81
(m, 2 H, 5Ј-H, 6Ј-H), 6.71–6.63 (m, 3 H, H of benzodioxole), 4.72
2
3
(d, JH,H = 11.7 Hz, CHHOTHP), 4.68 (t, JH,H = 3.5 Hz, 1 H,
2
CHO of THP), 4.44 (d, JH,H = 11.7 Hz, CHHOTHP), 4.16 (t,
3JH,H = 7.5 Hz, 2 H, CH2O hydroxytyrosol), 3.98–3.85 (m, 1 H,
CHHO of THP), 3.88 (s, 3 H, OCH3), 3.59–3.51 (m, 1 H, CHHO
of THP), 3.05 (t, 3JH,H = 7.5 Hz, 2 H, ArCH2), 1.93–1.45 (m, 6 H,
CH2 of THP), 1.66 (s, 6 H, CH3C) ppm. 13C NMR (75 MHz,
CDCl3, 25 °C): δ = 149.3, 147.7, 147.4, 146.0 (3a-C, 7a-C, 1Ј-C, 2Ј-
C), 130.91, 130.89 (5-C, 4Ј-C), 121.3 (6-C), 120.6 (5Ј-C) 117.7 (2-
C), 112.7 (6Ј-C), 111.8 (3Ј-C), 109.3, 108.0 (4-C, 7-C), 97.5 (CHO
of THP), 70.0 (CH2O hydroxytyrosol), 68.8 (CH2OTHP), 62.3
(CH2O of THP), 55.9 (OCH3), 35.4 (ArCH2), 30.6, 25.4, 19.5 (CH2
1,2-Diacetoxy-4-[2-(2-chlorophenoxy)ethyl]benzene (6h): A solution
of diacetate 2 (100 mg, 0.42 mmol) in dry CH2Cl2 (850 μL) was
cooled to 0 °C and treated sequentially with PPh3 (165 mg,
0.63 mmol), o-chlorophenol (65 mg, 0.50 mmol), and DEAD (40%
in toluene, 288 μL, 0.63 mmol). After 5 min the cooling bath was
removed, and the solution was stirred for 7 h at room temperature.
concentrated, and chromatographed (PE/EtOAc, 75:25) to give
pure 6h as a yellowish oil (123 mg, 84%). Rf = 0.54 (PE/EtOAc,
1
3
60:40). H NMR (300 MHz, CDCl3, 20 °C): δ = 7.35 (dd, JH,H
=
4
8.0 Hz, JH,H = 1.6 Hz, 1 H, 3Ј-H), 7.27–7.11 (m, 3 H, 4Ј-H, 5Ј-H,
of THP), 25.8 (CH C) ppm. IR: ν = 2939, 2869, 1608, 1592, 1514,
˜
3
3
3-H, 5-H), 6.92–6.85 (m, 2 H, 6-H, 6Ј-H), 4.20 (t, JH,H = 6.9 Hz,
1494, 1466, 1445, 1420, 1376, 1350, 1251, 1229, 1200, 1158, 1135,
1117, 1076, 1021, 977, 950, 904, 868, 838, 804, 760, 745, 724 cm–1.
GC–MS (tR = 16.72 min): m/z (%) = 414 (2.1) [M]+, 177 (100.0),
149 (6.8), 137 (19.8), 119 (7.0), 91 (11.0), 84 (32.7), 55 (57.0), 43
(11.7), 41 (18.5). HRMS (ESI+): calcd. for C24H30O6Na [M + Na]+
437.1940; found 437.1940.
3
2 H, CH2O), 3.14 (t, JH,H = 6.9 Hz, 2 H, ArCH2), 2.29/2.28 (2s,
6 H, 2CH3) ppm. 13C NMR (75 MHz, CDCl3, 25 °C): δ = 168.4,
168.3 (C=O), 154.2 (1Ј-C), 141.9, 140.7 (1-C, 2-C), 137.0 (4-C),
130.3 (3Ј-C), 127.7, 127.4, 124.1, 123.3 (4Ј-C, 5Ј-C, 3-C, 5-C), 122.9
(6-C), 113.3 (6Ј-C), 69.2 (CH2O), 35.1 (ArCH2), 20.7 (CH3) ppm.
IR: ν = 2937, 1764, 1589, 1505, 1486, 1470, 1446, 1427, 1369, 1278,
˜
2,2-Dimethyl-5-{2-[(3,5-dihydroxy)phenoxy]ethyl}benzo[d][1,3]-
dioxole (6f): A solution of 6d (70 mg, 0.18 mmol) in dry MeOH
(900 μL) was treated with Et3N (10 μL, 72 μmol) and stirred for
48 h at room temperature. The mixture was poured into saturated
aqueous NH4Cl and extracted with EtOAc. The organic phase was
washed with brine, concentrated, and chromatographed (PE/
EtOAc, 60:40) to give pure 6f as a brownish foam (54 mg, 99%). Rf
= 0.28 (PE/EtOAc, 70:30). 1H NMR (300 MHz, CD3OD, 20 °C): δ
= 6.70–6.60 (m, 3 H, 4-H, 6-H, 7-H), 5.87 (s, 3 H, 2Ј-H, 4Ј-H, 6Ј-
H), 4.01 (t, JH,H = 6.9 Hz, 2 H, CH2O), 2.91 (t, JH,H = 7.1 Hz, 2
H, ArCH2), 1.62 (s, 6 H, CH3C) ppm. 13C NMR (75 MHz,
CD3OD, 25 °C): δ = 162.2 (1Ј-C), 160.2 (3Ј-C, 5Ј-C), 148.9, 147.4
(3a-C, 7a-C), 133.0 (5-C), 122.4 (6-C), 118.7 (2-C), 110.1, 108.9 (4-
C, 7-C), 96.5 (4Ј-C), 94.7 (2Ј-C and 6Ј-C), 69.9 (CH2O), 36.5
1257, 1203, 1178, 1145, 1111, 1060, 1039, 1011, 898, 830, 747, 692
cm–1. GC–MS (tR = 14.29 min): m/z (%) = 348 (3.5) [M]+, 306
(4.8), 264 (21.5), 179 (7.6), 137 (100.0), 136 (9.2), 135 (5.3), 123
(6.0), 91 (7.8), 77 (6.9), 43 (41.6). HRMS (ESI+): calcd. for
C18H18ClO5 [M + H]+ 349.0843; found 349.0842.
1,2-Diacetoxy-4-[2-(2-methoxy-4-{[(tetrahydro-2H-pyran-2-yl)-
oxy]methyl}phenoxy)ethyl]benzene (6i): A solution of diacetate 2
(150 mg, 0.63 mmol) in dry CH2Cl2 (1.23 mL) was cooled to 0 °C
and treated sequentially with PPh3 (248 mg, 0.94 mmol), phenol 5e
(180 mg, 0.7 mmol), and TBAD (217 mg, 0.94 mmol). After 5 min
the cooling bath was removed, and the solution was stirred for
7 h at room temperature, concentrated, and chromatographed (PE/
EtOAc, 65:35) to give pure 6i as an oil (150 mg, 52%). Rf = 0.36
3
3
1
(PE/EtOAc, 60:40). H NMR (300 MHz, CDCl3, 20 °C): δ = 7.21–
(ArCH ), 25.9 (CH C) ppm. IR: ν = 3367, 2990, 1603, 1494, 1472,
˜
2
3
2
7.10 (m, 3 H), 6.94–6.80 (m, 3 H), 4.72 (d, JH,H = 11.9 Hz, 1 H,
1444, 1376, 1252, 1234, 1216, 1142, 1043, 1009, 979, 937, 825, 751,
681, 667, 635, 608 cm–1. GC–MS: not feasible. HRMS (ESI+):
calcd. for C17H19O5 [M + H]+ 303.1232; found 303.1226.
3
CHHOTHP), 4.68 (t, JH,H = 4.2 Hz, 1 H, CHO of THP), 4.44 (d,
3
2JH,H = 11.9 Hz, 1 H, CHHOTHP), 4.20 (t, JH,H = 7.4 Hz, 2 H,
3
CH2O of hydroxytyrosol), 3.93 (ddd, 2JH,H = 11.4 Hz, JH,H = 7.8,
5-{2-[4-(3-Thienyl)phenoxy]ethyl}-2,2-dimethylbenzo[d][1,3]dioxole
3.7 Hz, 1 H, CHO of THP), 3.86 (s, 3 H, OCH3), 3.5–3.48 (m, 1
3
(6g): A solution of 6b (150 mg, 0.43 mmol), 3-thiopheneboronic H, CHO of THP), 3.14 (t, JH,H = 7.4 Hz, 2 H, ArCH2), 2.29/2.28
acid (110 mg, 0.86 mmol), and triphenylphosphine (17 mg, (2s, 6 H, 2CH3), 1.92–1.48 (m, 6 H, CH2 of THP) ppm. 13C NMR
64 μmol) in THF (2.86 mL) and water (286 μL) in a microwave (75 MHz, CDCl3, 25 °C): δ = 168.4, 168.3 (C=O), 149.5, 147.6 (1Ј-
tube was treated with Na2CO3 (137 mg, 1.29 mmol) and put under C, 2Ј-C), 141.9, 140.6 (1-C, 2-C), 137.0 (4-C), 131.3 (4Ј-C), 127.2,
an argon atmosphere. Palladium diacetate (5 mg, 22 μmol) was
rapidly added, and the mixture was flushed with Ar. The tube was
sealed and heated under microwave irradiation at 100 °C for
30 min. The mixture was diluted with water and extracted with
CH2Cl2. Concentration and chromatography (PE/Et2O, 95:5) gave
123.9, 123.3, 120.6 (5Ј-C, 3-C, 5-C, 6-C), 113.2, 112.0 (3Ј-C, 6Ј-C),
97.6 (CHO of THP), 69.4 (CH2OAr), 68.7 (CH2OTHP), 62.3
(CH2O of THP), 56.0 (OCH3), 35.1 (ArCH2), 30.6, 25.5, 19.5 (CH2
of THP), 20.6, (CH C=O) ppm. IR: ν = 2932, 2876, 1765, 1592,
˜
3
1516, 1505, 1465, 1417, 1387, 1370, 1259, 1233, 1202, 1181, 1163,
Eur. J. Org. Chem. 2015, 6710–6726
© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
6719

L. Banfi et al.
FULL PAPER
1136, 1113, 1077, 1057, 1018, 978, 946, 899, 869, 852, 828, 807,
775, 763, 737, 719, 680, 638 cm–1. GC–MS (tR = 19.03 min): m/z
(%) = 458 (2.4) [M]+, 374 (6.1), 179 (64.3), 154 (11.3), 137 (100.0),
107 (5.5), 91 (8.0), 85 (12.6), 84 (13.3), 83 (6.6), 77 (6.0), 56 (5.9),
55 (22.2), 43 (34.4), 41 (6.1). HRMS (ESI+): calcd. for
C25H30O8Na [M + Na]+ 481.1838; found 481.1845.
HRMS (ESI+): calcd. for C16H19O4 [M + H]+ 275.1283; found
275.1285.
4-[2-(3,5-Dihydroxyphenoxy)ethyl]benzene-1,2-diol (7d): Obtained
in 66% yield from ether 6d by following the same procedure as that
outlined for 6a, but with heating at 80 °C for 20 min. Chromatog-
raphy (PE/EtOAc, 70:30 + 0.5% MeOH) afforded pure 7d as a
white foam. Rf = 0.26 (PE/EtOAc, 7:3 + 5% MeOH). 1H NMR
4-[2-(4-Methoxyphenoxy)ethyl]benzene-1,2-diol (7a): Ether 6a
(61 mg, 0.20 mmol) was dissolved in a 4 mL microwave tube in
CH3CN (800 μL) and treated with water (180 μL) and concentrated
HCl (20 μL). The tube was sealed, and the solution was heated in
the microwave apparatus at 100 °C for 30 min. The mixture was
diluted with EtOAc and washed with saturated aqueous NaHCO3.
4
(300 MHz, CD3OD, 20 °C): δ = 6.71 (d, JH,H = 2.1 Hz, 1 H, 3-
3
4
H), 6.69 (d, JH,H = 8.1 Hz, 1 H, 6-H), 6.59 (dd, JH,H = 2.1 Hz,
3JH,H = 8.1 Hz, 1 H, 5-H), 5.89–5.85 (m, 3 H, H or resorcinol),
4.00 (t, JH,H = 7.2 Hz, 2 H, CH2O), 2.86 (t, JH,H = 7.2 Hz, 2 H,
ArCH2) ppm. 13C NMR (75 MHz, CD3OD, 25 °C): δ = 162.2 (1Ј-
3
3
Concentration of the organic phase and chromatography (PE/ C), 160.2 (3Ј-C and 5Ј-C), 146.2, 144.8 (1-C, 2-C), 131.3 (4-C),
EtOAc, 70:30) gave pure 7a as a white foam (43 mg, 83%). Rf =
121.2 (5-C), 117.1, 116.3 (3-C, 6-C), 70.1 (CH2O), 36.1 (ArCH2)
0.32 (PE/EtOAc, 7:3). 1H NMR (300 MHz, CDCl3, 20 °C): δ =
ppm. IR: ν = 3232 (br.), 2918, 2903, 2851, 1606, 1511, 1472, 149,
˜
3
6.82 (s, 4 H, H of p-MeOAr), 6.80 (d, JH,H = 8.1 Hz, 1 H, 6-H),
1440, 1353, 1279, 1259, 1201, 1158, 1140, 1109, 1067, 1046, 1003,
932, 872, 850, 810, 795, 784, 716 cm–1. GC–MS: not feasible.
HRMS (ESI+): calcd. for C14H15O5 [M + H]+ 263.0919; found
263.0916.
4
4
3
6.80 (d, JH,H = 2.1 Hz, 1 H, 3-H), 6.70 (dd, JH,H = 2.1 Hz, JH,H
3
= 8.1 Hz, 1 H, 5-H), 4.07 (t, JH,H = 7.1 Hz, 2 H, CH2O), 3.77 (s,
3 H, CH3O), 2.96 (t, 3JH,H = 7.1 Hz, 2 H, ArCH2) ppm. 13C NMR
(75 MHz, CDCl3, 25 °C): δ = 153.8, 152.9 (1Ј-C, 4Ј-C), 143.5, 142.0
(1-C, 2-C), 131.4 (4-C), 121.4 (5-C), 116.1, 115.3 (3-C, 6-C), 115.6,
114.6 (2Ј-C, 3Ј-C), 69.5 (CH2O), 55.8 (CH3O), 35.2 (ArCH2) ppm.
4-[2-(4-Hydroxymethyl-2-methoxyphenoxy)ethyl]benzene-1,2-diol
(7e): A solution of ether 6i (180 mg, 393 μmol) in iPrOH (2.3 mL)
was treated with H2O (600 μL) and a solution of camphorsulfonic
acid (1 m in iPrOH, 118 μL, 118 μmol). The solution was stirred at
60 °C for 5 h, quenched with saturated aqueous NaHCO3, ex-
tracted with EtOAc, and concentrated. The residue was taken up in
MeOH (1.75 mL), treated with Et3N (20 μL, 144 μmol), and stirred
overnight at room temperature. The solution was quenched with
saturated aqueous NH4Cl, extracted with EtOAc, concentrated,
and chromatographed (PE/EtOAc, 30:70) to give pure 7e as a yel-
IR: ν = 3366 (br.), 2917, 2836, 1615, 1593, 1528, 1506, 1467, 1439,
˜
1378, 1285, 1228, 1185, 1145, 1105, 1066, 1027, 930, 898, 859, 817,
799, 784, 739 cm–1. GC–MS: not feasible. HRMS (ESI+): calcd.
for C15H16O4Na [M + Na]+ 283.0946; found 283.0940.
4-[2-(4-Bromophenoxy)ethyl]benzene-1,2-diol (7b): Obtained in 88%
yield from ether 6b by following the same procedure a that outlined
for 6a. Chromatography (PE/EtOAc, 70:30 + 0.5% MeOH) af-
forded pure 7b as a white foam. Rf = 0.41 (PE/EtOAc, 7:3 + 5%
1
lowish oil (55 mg, 48%). Rf = 0.37 (PE/EtOAc, 30:70). H NMR
1
3
MeOH). H NMR (300 MHz, CD3OD, 20 °C): δ = 7.35 (d, JH,H (300 MHz, CD3OD, 20 °C): δ = 6.97 (s, 1 H, 3Ј-H), 6.90–6.82 (m,
= 8.7 Hz, 2 H, 3Ј-H), 6.82 (d, JH,H = 8.7 Hz, 2 H, 2Ј-H), 6.72 (d, 2 H, 5Ј-H, 6Ј-H), 6.73 (d, 4JH,H = 1.8 Hz, 1 H, 3-H), 6.69 (d, 3JH,H
3
4JH,H = 2.1 Hz, 1 H, 3-H), 6.69 (d, 3JH,H = 8.1 Hz, 1 H, 6-H), 6.59
= 8.1 Hz, 1 H, 6-H), 6.59 (dd, JH,H = 1.8 Hz, JH,H = 8.1 Hz, 1
4
3
4
3
3
3
(dd, JH,H = 2.1 Hz, JH,H = 8.1 Hz, 1 H, 5-H), 4.07 (t, JH,H
7.0 Hz, 2 H, CH2O), 2.89 (t, JH,H = 7.0 Hz, 2 H, ArCH2) ppm.
=
H, 5-H), 5.52 (s, 2 H, CH2OH), 4.10 (t, JH,H = 7.2 Hz, 2 H,
CH2OAr), 3.81 (s, 3 H, OCH3), 2.90 (t, JH,H = 7.2 Hz, 2 H,
3
3
13C NMR (75 MHz, CD3OD, 25 °C): δ = 159.6 (1Ј-C), 146.2, 144.9 ArCH2) ppm. 13C NMR (75 MHz, CD3OD, 25 °C): δ = 162.2 (1Ј-
(1-C, 2-C), 133.2 (2Ј-C), 131.1 (4-C), 121.2 (5-C), 117.5 (3Ј-C), C), 160.2 (3Ј-C and 5Ј-C), 151.0, 149.1, 146.2, 144.8 (1Ј-C, 2Ј-C, 1-
117.1, 116.3 (5-C, 6-C), 113.5 (4Ј-C), 70.5 (CH2O), 36.0 (ArCH2)
C, 2-C), 135.9 (4Ј-C), 131.2 (4-C), 121.3 (5-C), 120.8, 114.9 (5Ј-
ppm. IR: ν = 3460 (sharp), 3298 (br.), 2955, 2930, 2872, 1620, 1608, C, 6Ј-C), 117.2, 116.3 (3-C, 6-C), 112.8 (3Ј-C), 71.7 (CH2O), 65.1
˜
1593, 1531, 1489, 1468, 1448, 1392, 1372, 1302, 1286, 1244, 1215,
1195, 1175, 1154, 1113, 1075, 1048, 1024, 1000, 936, 867, 831, 814,
(CH2OH), 56.6 (OCH3), 36.1 (ArCH2) ppm. GC–MS: not feasible.
HRMS (ESI–): calcd. for C16H17O5 [M – H]+ 289.1076; found
797, 787, 752, 726 cm–1. GC–MS: not feasible. HRMS (ESI–): 289.1101.
calcd. for C14H12BrO3 [M – H]+ 306.9951; found 306.9970.
4-{2-[4-(3-Thienyl)phenoxy]ethyl}benzene-1,2-diol (7g): Obtained in
4-{2-[4-(2-Hydroxyethyl)phenoxy]ethyl}benzene-1,2-diol (7c): Ob-
tained in 95% yield from ether 6c by following the same procedure
as that outlined for 6a, but with heating at 80 °C for 40 min.
Chromatography (PE/EtOAc, 50:50) afforded pure 7c as a white
foam. Rf = 0.25 (PE/EtOAc, 50:50). 1H NMR (300 MHz, CD3OD,
90% yield from ether 6g by following the same procedure as that
outlined for 6a, but with heating at 100 °C for 20 min. Chromatog-
raphy (PE/EtOAc, 70:30 + 0.5% MeOH) afforded pure 7g as a
white foam. Rf = 0.29 (PE/EtOAc, 70:30). 1H NMR (300 MHz,
3
CD3OD, 20 °C): δ = 7.51 (d, JH,H = 8.7 Hz, 2 H, 3Ј-H), 7.43–7.37
3
3
20 °C): δ = 7.11 (d, JH,H = 8.7 Hz, 2 H, 3Ј-H), 6.82 (d, JH,H
=
(m, 2 H, thienyl H), 7.34 (dd, 3JH,H = 4.8 Hz, 3JH,H = 1.5 Hz, 1 H,
4
3
4
8.7 Hz, 2 H, 2Ј-H), 6.72 (d, JH,H = 2.1 Hz, 1 H, 3-H), 6.69 (d, thienyl H), 6.89 (d, JH,H = 8.7 Hz, 2 H, 2Ј-H), 6.75 (d, JH,H
=
3JH,H = 8.1 Hz, 1 H, 6-H), 6.59 (dd, 4JH,H = 2.1 Hz, 3JH,H = 8.1 Hz, 1.8 Hz, 1 H, 3-H), 6.71 (d, JH,H = 8.1 Hz, 1 H, 6-H), 6.60 (dd,
3
3
3
3
3
1 H, 5-H), 4.07 (t, JH,H = 7.0 Hz, 2 H, CH2OAr), 3.69 (t, JH,H
=
4JH,H = 1.8 Hz, JH,H = 8.1 Hz, 1 H, 5-H), 4.09 (t, JH,H = 7.1 Hz,
3
7.2 Hz, 2 H, CH2OH), 2.89 (t, JH,H = 7.0 Hz, 2 H, ArCH2 hy-
2 H, CH2O), 2.90 (t, 3JH,H = 7.1 Hz, 2 H, ArCH2) ppm. 13C NMR
3
droxytyrosol), 2.74 (t, JH,H = 7.2 Hz, 2 H, ArCH2 tyrosol) ppm. (75 MHz, CD3OD, 25 °C): δ = 159.5 (1Ј-C), 146.2, 144.8 (1-C, 2-
13C NMR (75 MHz, CD3OD, 25 °C): δ = 158.8 (1Ј-C), 146.2, 144.8 C), 143.2 (quat. of thienyl), 131.3 (4-C), 130.0 (4Ј-C), 128.4 (3Ј-C),
(1-C, 2-C), 132.3, 131.3 (4-C, 4Ј-C), 130.9 (2Ј-C), 121.2 (5-C), 117.1, 127.0 (2C), 119.6 (CH thienyl), 121.3 (5-C), 117.1 (3-C), 116.3 (6-
116.3 (5-C, 6-C), 115.6 (3Ј-C), 70.3 (CH2OAr), 64.5 (CH2OH), 39.4 C), 115.9 (2Ј-C), 70.2 (CH O), 36.1 (ArCH ) ppm. IR: ν = 3395
˜
2
2
(ArCH tyrosol), 36.2 (ArCH hydroxytyrosol) ppm. IR: ν = 3417
(br.), 3099, 2921, 2865, 1606, 1577, 1525, 1502, 1467, 1441, 1377,
1309, 1285, 1239, 1202, 1179, 1144, 1113, 1063, 1040, 1030, 1009,
955, 936, 928, 898, 861, 827, 819, 809, 788, 774, 733, 715, 683, 655,
627 cm–1. GC–MS: not feasible. HRMS (ESI+): calcd. for
C18H17O3S [M + H]+ 313.0898; found 313.0890.
˜
2
2
(sharp), 3355 (br.), 3033, 2984, 2943, 2921, 2872, 1610, 1581, 1511,
1461, 1444, 1427, 1387, 1354, 1296, 1288, 1240, 1194, 1177, 1140,
1116, 1065, 1048, 1035, 1019, 1012, 993, 953, 934, 900, 861, 831,
810, 788, 776, 760, 727, 717, 659, 637 cm–1. GC–MS: not feasible.
6720
www.eurjoc.org
© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2015, 6710–6726

Conjugation of Hydroxytyrosol with Natural Phenolic Fragments
4-[2-(2-Chlorophenoxy)ethyl]benzene-1,2-diol (7h): A solution of
ether 6h (93 mg, 266 μmol) in dry MeOH (1.33 mL) was treated
with Et3N (15 μL, 107 μmol) and stirred at room temperature for
48 h. The mixture was quenched with saturated aqueous NH4Cl,
extracted with EtOAc, concentrated, and chromatographed (PE/
(3ЈЈ-C, 5ЈЈ-C), 147.5, 146.0 (3a-C, 7a-C), 131.3, 129.9 (4Ј-C, 5-C),
130.0 (3Ј-C), 121.2 (6-C), 117.7 (2-C), 114.6 (2Ј-C), 109.2, 108.1 (4-
C, 7-C), 107.8 (4ЈЈ-C), 105.9 (2ЈЈ-C, 6ЈЈ-C), 69.4, 69.0 (CH2O), 35.5,
34.7 (ArCH ), 25.9 (CH C), 21.1 (CH CO) ppm. IR: ν = 2987,
˜
2
3
3
2939, 2883, 1767, 1611, 1593, 1511, 1493, 1464, 1454, 1444, 1385,
EtOAc, 70:30) to give pure 7h as a yellowish foam. Rf = 0.33 (PE/ 1367, 1328, 1302, 1248, 1238, 1193, 1147, 1122, 1070, 1046, 1022,
1
EtOAc, 70:30). H NMR (300 MHz, CDCl3, 20 °C): δ = 7.35 (dd, 998, 980, 940, 894, 868, 845, 831, 819, 813, 797, 760, 724, 703, 668,
4
3
3JH,H = 8.0 Hz, JH,H = 1.7 Hz,1 H, 3Ј-H), 7.18 (ddd, JH,H = 9.0, 642, 635, 626 cm–1. GC–MS: not feasible. HRMS (ESI+): calcd.
7.5 Hz, JH,H = 1.7 Hz,1 H, 5Ј-H), 6.92–6.83 (m, 3 H, 4Ј-H, 6Ј-H, for C29H31O8 [M + H]+ 507.2019; found 507.2016.
4
3
4
3-H), 6.81 (d, JH,H = 8.1 Hz, 1 H, 6-H), 6.75 (dd, JH,H = 2.1 Hz,
2,2-Dimethyl-5-(2-{4-[2-(3,5-dihydroxyphenoxy)ethyl]phenoxy}eth-
yl)benzo[d][1,3]dioxole (11): Obtained in 45% yield from ether 10
by following the same procedure as that outlined for 6f. Rf = 0.22
3JH,H = 8.1 Hz, 1 H, 5-H), 4.16 (t, JH,H = 6.9 Hz, 2 H, CH2O),
3
3.03 (t, JH,H = 6.9 Hz, 2 H, ArCH2) ppm. 13C NMR (75 MHz,
3
CDCl3, 25 °C): δ = 154.3 (1Ј-C), 143.4, 142.1 (1-C, 2-C), 131.2 (4-
C), 130.3 (3Ј-C), 127.7 (5Ј-C), 122.9 (2Ј-C), 121.7 (5-C), 121.4 (4Ј-
C), 116.4 (3-C), 115.4 (6-C), 113.3 (6Ј-C), 69.9 (CH2O), 35.0
1
(PE/EtOAc, 70:30). H NMR (300 MHz, CDCl3, 20 °C): δ = 7.14
(d, 3JH,H = 8.7 Hz, 2 H, 3Ј-H), 6.83 (d, 3JH,H = 8.7 Hz, 2 H, 2Ј-H),
6.70–6.63 (m, 3 H, H of benzodioxole), 6.00–5.90 (m, 3 H, H of
(ArCH ) ppm. IR: ν = 3458 (sharp), 3308 (br.), 2954, 2883, 2075,
˜
2
3
resorcinol), 5.15 (br. s, 2 H, OH), 4.10 (t, JH,H = 7.2 Hz, 2 H,
1625, 1591, 1578, 1520, 1487, 1463, 1447, 1434, 1385, 1355, 1339,
1279, 1251, 1202, 1184, 1146, 1133, 1111, 1066, 1030, 991, 939,
927, 902, 869, 814, 795, 785, 746, 715, 691, 642 cm–1. GC–MS: not
feasible. HRMS (ESI–): calcd. for C14H12ClO3 [M – H]+ 263.0475;
found 263.0482.
3
3
CH2O), 4.03 (t, JH,H = 7.1 Hz, 2 H, CH2O), 2.98 (t, JH,H
=
7.1 Hz, 4 H, ArCH2), 1.66 (s, 6 H, CH3C) ppm. 13C NMR
(75 MHz, CDCl3, 25 °C): δ = 160.9, 157.4 (3C) (1ЈЈ-C, 1Ј-C, 3ЈЈ-C,
5ЈЈ-C), 147.4, 146.0 (3a-C, 7a-C), 131.3, 130.2 (4Ј-C, 5-C), 129.9
(3Ј-C), 121.2 (6-C), 117.8 (2-C), 114.6 (2Ј-C), 109.2, 108.1 (4-C, 7-
C), 95.7 (4ЈЈ-C), 94.9 (2ЈЈ-C, 6ЈЈ-C), 69.0, 68.9 (CH2O), 35.5, 34.7
2,2-Dimethyl-5-{2-[4-(2-hydroxyethyl)phenoxy]ethyl}benzo[d][1,3]-
dioxole (9): A solution of ether 6c (297 mg, 0.74 mmol) in iPrOH
(4.33 mL) was treated with H2O (1.1 mL) and camphorsulfonic
acid (1 m in iPrOH, 225 μL, 225 μmol). The solution was stirred at
60 °C for 6 h and then quenched with saturated aqueous NaHCO3.
Extraction with EtOAc, concentration, and chromatography (PE/
EtOAc, 70:30) gave pure 9 as an oil (225 mg, 97%). Rf = 0.46 (PE/
EtOAc, 70:30). 1H NMR (300 MHz, CDCl3, 20 °C): δ = 7.12 (d,
(ArCH ), 25.9 (CH C) ppm. IR: ν = 3386 (br.), 2989, 2937, 2871,
˜
2
3
1604, 1510, 1493, 1472, 1444, 1376, 1300, 1231, 1140, 1042, 1009,
978, 898, 822, 735, 679, 658, 640, 631 cm–1. GC–MS: not feasible.
HRMS (ESI+): calcd. for C25H27O6 [M + H]+ 423.1808; found
423.1808.
2,2-Dimethyl-5-(2-{4-[2-(3,5-dihydroxyphenoxy)ethyl]phenoxy}ethyl)
benzene-1,2-diol (12): Obtained in 59% yield from ether 10 by fol-
lowing the same procedure as that outlined for 6a, but with heating
at 100 °C for 20 min. Chromatography (PE/EtOAc, 50:50) afforded
3JH,H = 8.7 Hz, 2 H, 3Ј-H), 6.85 (d, JH,H = 8.7 Hz, 2 H, 2Ј-H),
6.70–6.63 (m, 3 H, H of benzodioxole), 4.10 (t, JH,H = 7.1 Hz, 2
H, CH2O hydroxytyrosol), 3.81 (t, JH,H = 6.5 Hz, 2 H, CH2OH),
3
3
3
1
2.98 (t, 3JH,H = 7.1 Hz, 2 H, ArCH2 hydroxytyrosol), 2.80 (t, 3JH,H
= 6.5 Hz, 2 H, ArCH2 tyrosol), 1.66 (s, 6 H, CH3C) ppm. 13C
NMR (75 MHz, CDCl3, 25 °C): δ = 157.5 (1Ј-C), 147.4, 146.0 (3a-
C, 7a-C), 131.3, 130.4 (4Ј-C, 5-C), 130.0 (3Ј-C), 121.2 (6-C), 117.7
(2-C), 114.7 (2Ј-C), 109.2, 108.0 (4-C, 7-C), 69.0 (CH2O hydroxy-
tyrosol), 63.8 (CH2OH), 38.3 (ArCH2 tyrosol), 35.5 (ArCH2
pure 12 as a white foam. Rf = 0.25 (PE/EtOAc, 50:50). H NMR
3
(300 MHz, CD3OD, 20 °C): δ = 7.15 (d, JH,H = 8.5 Hz, 2 H, 3Ј-
3
4
H), 6.82 (d, JH,H = 8.5 Hz, 2 H, 2Ј-H), 6.73 (d, JH,H = 1.9 Hz, 1
3
3
H, 3-H), 6.70 (d, JH,H = 8.1 Hz, 1 H, 6-H), 6.59 (dd, JH,H
8.1 Hz, JH,H = 1.9 Hz, 1 H, 5-H), 5.88 (s, 3 H, H of resorcinol),
4.06 (t, JH,H = 7.0 Hz, 2 H, CH2O), 4.01 (t, JH,H = 7.0 Hz, 2 H,
CH2O), 2.92 (t, JH,H = 7.0 Hz, 2 H, ArCH2), 2.86 (t, JH,H
=
4
3
3
3
3
=
hydroxytyrosol), 25.9 (CH C) ppm. IR: ν = 3360 (br.), 2990, 2936,
˜
3
7.0 Hz, 2 H, ArCH2) ppm. 13C NMR (75 MHz, CD3OD, 25 °C): δ
= 162.2 (1Ј-C), 160.1 (3ЈЈ-C, 5ЈЈ-C), 159.0 (1ЈЈ-C), 146.1, 144.7 (1-
C, 2-C), 131.8, 131.4 (4Ј-C, 4-C), 130.9 (3Ј-C), 121.3 (5-C), 117.1
(3-C), 116.3 (6-C), 115.6 (2Ј-C), 96.5 (4ЈЈ-C), 94.8 (2ЈЈ-C, 6ЈЈ-C),
2869, 1610, 1582, 1510, 1493, 1444, 1376, 1301, 1230, 1176, 1156,
1111, 1027, 978, 939, 898, 826, 807, 724, 657, 641, 631 cm–1. GC–
MS (tR = 14.23 min): m/z (%) = 314 (20.1) [M]+, 177 (100.0), 163
(11.1), 161 (5.0), 137 (25.4), 135 (5.9), 134 (8.9), 123 (10.5), 119
(9.9), 107 (7.1), 91 (14.7), 77 (7.4), 65 (5.8), 43 (5.9), 41 (5.9).
HRMS (ESI+): calcd. for C19H23O4 [M + H]+ 315.1596; found
315.1599.
70.2, 69.9 (CH O), 36.1, 35.8 (ArCH ) ppm. IR: ν = 3343 (br.),
˜
2
2
2933, 1603, 1510, 1470, 1443, 1375, 1357, 1277, 1238, 1177, 1142,
1112, 1040, 1008, 955, 812, 680, 628, 607 cm–1. GC–MS: not feas-
ible. HRMS (ESI+): calcd. for C22H23O6 [M + H]+ 383.1495; found
383.1483.
2,2-Dimethyl-5-(2-{4-[2-(3,5-diacetoxyphenoxy)ethyl]phenoxy}eth-
yl)benzo[d][1,3]dioxole (10): A solution of phenol 5c (120 mg,
0.57 mmol) in dry CH2Cl2 (2.4 mL), cooled to 0 °C, was treated
with PPh3 (188 mg, 0.71 mmol) and diethyl azodicarboxylate (40%
in toluene, 328 μL, 0.71 mmol). The solution was stirred for 30 min
at 0 °C and then treated with ether 9 (150 mg, 0.48 mmol) dissolved
in a minimal amount of CH2Cl2. After 1 h at 0 °C and 15 h at
room temperature, the solution was concentrated and chromato-
graphed (PE/EtOAc, 75:25) to give pure 10 as a white foam
4-(2-Azidoethyl)-1,2-phenylene Diacetate (13): A solution of diacet-
ate 2 (400 mg, 1.68 mmol) in dry CH2Cl2 (4 mL) was cooled to 0 °C
and treated with Et3N (304 μL, 2.18 mmol), which was followed by
the dropwise addition of methanesulfonyl chloride (160 μL,
2.02 mmol). After stirring for 50 min at 0 °C, the reaction was
quenched with H2O, and the mixture was extracted with CH2Cl2
and concentrated. The residue was taken up in dry DMF (5.6 mL),
treated with NaN3 (272 mg, 4.18 mmol), and warmed at 60 °C for
(133 mg, 55%). Rf = 0.68 (PE/EtOAc, 70:30). 1H NMR (300 MHz,
3
CDCl3, 20 °C): δ = 7.17 (d, JH,H = 8.2 Hz, 2 H, 3Ј-H), 6.84 (d, 10 h. Dilution with water, extraction with Et2O, and concentration
3JH,H = 8.2 Hz, 2 H, 2Ј-H), 6.70–6.63 (m, 3 H, H of benzodioxole),
gave a mixture of 13, 4-(2-azidoethyl)-2-hydroxyphenyl acetate, 5-
(2-azidoethyl)-2-hydroxyphenyl acetate, and 4-(2-azidoethyl)benz-
ene-1,2-diol. This mixture was taken up in dry CH3CN (8.4 mL),
3
6.54–6.48 (m, 3 H, H of resorcinol), 4.10 (t, JH,H = 7.2 Hz, 2 H,
CH2O), 4.08 (t, JH,H = 6.9 Hz, 2 H, CH2O), 3.00 (t, JH,H
6.9 Hz, 2 H, ArCH2), 2.98 (t, JH,H = 7.2 Hz, 2 H, ArCH2), 2.26 treated with anhydrous K2CO3 (324 mg, 2.35 mmol), and stirred
(s, 6 H, CH3CO), 1.66 (s, 6 H, CH3C) ppm. 13C NMR (75 MHz,
for 10 min at room temperature. The mixture was cooled to 0 °C
CDCl3, 25 °C): δ = 168.9 (C=O), 159.9 (1ЈЈ-C), 157.6 (1Ј-C), 151.6 and treated dropwise with Ac2O (222 μL, 2.35 mmol). After stirring
3
3
=
3
Eur. J. Org. Chem. 2015, 6710–6726
© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
6721

L. Banfi et al.
FULL PAPER
for 140 min at 0 °C, the mixture was diluted with H2O and ex-
tracted with EtOAc. Concentration and chromatography (PE/
EtOAc, 75:25) gave pure 13 as an oil (300 mg, 68%). Rf = 0.55 (PE/
190 (15.4), 175 (4.4), 163 (100.0), 123 (44.7), 121 (11.7), 77 (9.7),
74 (6.4), 51 (9.9), 43 (7.7), 41 (8.0). HRMS (ESI+): calcd. for
C13H18NO4 [M + H]+ 252.1236; found 252.1241.
1
EtOAc, 50:50). H NMR (300 MHz, CDCl3, 20 °C): δ = 7.16–7.04
2,2-Dimethyl-5-(prop-2-yn-1-yl)benzo[d][1,3]dioxole (19): A solution
of known ester 16[18,28] (500 mg, 2.25 mmol) in dry CH2Cl2
(4.5 mL) was cooled to –78 °C and treated dropwise with diisobut-
ylaluminum hydride (1 m in toluene, 2.25 mL, 2.25 mmol). After
10 min, the reaction was quenched with MeOH (2 mL), and the
mixture was warmed to 0 °C. The mixture was diluted with dry
MeOH (2.5 mL), and treated sequentially with K2CO3 (623 mg,
4.5 mmol) and the Ohira–Bestmann reagent[27b] (540 mg,
2.81 mmol). After stirring overnight at room temperature, the mix-
ture was poured into 20% sodium potassium tartrate and Et2O.
After stirring for 1 h at room temperature, the phases were sepa-
rated, and the aqueous phase was re-extracted with Et2O (3ϫ).
Concentration and chromatography (PE/Et2O, 96:4) gave pure 19
3
(m, 3 H, aromatics), 3.51 (t, JH,H = 7.3 Hz, 2 H, CH2N3), 2.87 (t,
3JH,H = 7.3 Hz, 2 H, ArCH2), 2.29, 2.28 (2s, 6 H, 2CH3CO) ppm.
13C NMR (75 MHz, CDCl3, 25 °C): δ = 168.3, 168.2 (C=O), 142.0,
140.8, 136.8 (quat.), 126.8, 123.6, 123.4 (aromatic CH), 51.9
(CH N ), 34.6 (ArCH ), 20.6 (CH CO) ppm. IR: ν = 2093, 1764,
˜
2
3
2
3
1505, 1427, 1369, 1258, 1202, 1176, 1144, 1110, 1043, 1010, 960,
932, 889, 856, 834, 798, 645 cm–1. GC–MS (tR = 10.46 min): m/z
(%) = 263 (2.8) [M]+, 235 (2.3), 221 (19.4), 179 (39.8), 151 (19.9),
133 (6.9), 123 (91.7), 94 (4.9), 77 (5.8), 65 (4.8), 51 (4.6), 43 (100.0).
HRMS (ESI+): calcd. for C12H17N4O4 [M + NH4]+ 281.1250;
found 281.1259.
5-(2-Azidoethyl)-2,2-dimethylbenzo[d][1,3]dioxole (14): A solution
of acetonide 4 (1.071 g, 5.51 mmol) in dry CH2Cl2 (14 mL) was
cooled to 0 °C and treated with Et3N (999 μL, 7.17 mmol); this
was followed by the dropwise addition of methanesulfonyl chloride
(512 μL, 6.62 mmol). After stirring for 60 min at 0 °C, the reaction
was quenched with aqueous saturated NH4Cl, and the mixture was
extracted with CH2Cl2 and concentrated. The residue was taken up
in dry DMF (18 mL), treated with NaN3 (896 mg, 13.78 mmol),
and stirred for 18 h at room temperature and for 3 h at 40 °C. Di-
lution with water, extraction with Et2O, concentration, and
chromatography (PE/Et2O, 80:20) gave pure 14 (1.025 g, 85%) as
1
as an oil (317 mg, 75%). Rf = 0.82 (PE/EtOAc, 80:20). H NMR
(300 MHz, CDCl3, 20 °C): δ = 6.77–6.72 (m, 2 H, 4-H, 6-H), 6.66
3
4
(d, JH,H = 8.1 Hz, 1 H, 7-H), 3.50 (d, JH,H = 2.7 Hz, 2 H,
4
ArCH2), 2.17 (t, JH,H = 2.7 Hz, 1 H, CϵCH), 1.66 (s, 6 H, CH3)
ppm. 13C NMR (75 MHz, CDCl3, 25 °C): δ = 147.7, 146.3 (3a-C,
7a-C), 129.1 (5-C), 120.1 (6-C), 117.9 (2-C), 108.3, 108.0 (4-C, 7-
C), 82.4 (CϵCH), 70.2 (CϵCH), 25.8 (CH3), 24.5 (ArCH2) ppm.
IR: ν = 3293, 2991, 1493, 1443, 1385, 1377, 1296, 1252, 1230, 1217,
˜
1148, 1118, 980, 837, 801, 786, 765, 634 cm–1. GC–MS (tR
=
6.71 min): m/z (%) = 188 (38.2) [M]+, 173 (100.0), 147 (26.4), 145
(5.6), 131 (12.0), 130 (10.3), 102 (39.3), 101 (6.2), 91 (15.0), 89 (8.8),
77 (5.2), 76 (9.4), 75 (12.1), 74 (6.7), 65 (8.8), 63 (15.7), 62 (6.5), 51
(15.1), 50 (9.8), 43 (26.2), 41 (13.1). C12H12O2 (188.22): calcd. C
76.57, H 6.43; found C 76.51, H 6.45.
1
an oil. Rf = 0.78 (PE/EtOAc, 80:20). H NMR (300 MHz, CDCl3,
3
20 °C): δ = 6.69–6.60 (m, 3 H, aromatics), 3.45 (t, JH,H = 7.3 Hz,
3
2 H, CH2N3), 2.79 (t, JH,H = 7.3 Hz, 2 H, ArCH2), 1.67 (s, 6 H,
CH3) ppm. 13C NMR (75 MHz, CDCl3, 25 °C): δ = 147.6, 146.2
General Procedure for the Synthesis of 22b–d: Aldehyde 20b,[40]
20c,[41] or 20d[33] (3.0 mmol) was dissolved in dry CH2Cl2 (30 mL),
treated with CBr4 (1.99 g, 6.0 mmol), and cooled to 0 °C. Et3N
(418 μL, 3.0 mmol) was added. A solution of PPh3 (2.36 g,
9.0 mmol) in dry CH2Cl2 (10 mL) was slowly added over 30 min.
After stirring for 1 h at 0 °C and 2 h at room temperature, the solu-
tion was concentrated to dryness and chromatographed (PE/Et2O,
99:1 + 0.5% Et3N) to give pure vinyl dibromide in 84 (for 21b), 99
(for 21c), or 94% (for 21d) yield. The dibromide (2.0 mmol) was
dissolved in dry THF (10 mL), cooled to –78 °C, and treated with
nBuLi (1.6 m in hexanes, 3.12 mL, 5.0 mmol). After stirring for 3 h,
the reaction was quenched with aqueous saturated NH4Cl, and the
mixture was extracted with CH2Cl2, concentrated, and chromato-
graphed (PE/Et2O, 99:1 + 0.5% Et3N) to give pure 22b–d in 92 (for
22b), 79 (for 22c), or 90% (for 22d) yield. These compounds are
known.[31–33] However, 22b was not fully characterised. We, there-
fore, report here the corresponding data. Data for 22b: Rf = 0.56
(PE/EtOAc, 95:5). 1H NMR (300 MHz, CDCl3, 20 °C): δ = 7.01
(3a-C, 7a-C), 131.0 (5-C), 121.1 (6-C), 117.9 (2-C), 108.9, 108.2 (4-
C, 7-C), 52.7 (CH N ), 35.1 (ArCH ), 25.8 (CH ) ppm. IR: ν =
˜
2
3
2
3
2991, 2936, 2094, 1496, 1445, 1376, 1252, 1231, 1215, 1155, 1120,
979, 941, 837, 804, 787, 770, 635, 621 cm–1. GC–MS (tR
=
8.34 min): m/z (%) = 219 (37.0) [M]+, 191 (6.7), 176 (8.2), 163
(99.4), 150 (5.1), 133 (11.3), 123 (100.0), 121 (19.7), 106 (11.4), 105
(10.0), 78 (8.5), 77 (20.2), 74 (6.4), 65 (7.6), 51 (21.7), 43 (21.8), 41
(19.6). C11H13N3O2 (219.24): calcd. C 60.26, H 5.98, N 19.17;
found C 60.15, H 6.04, N 18.89.
2-(2,2-Dimethylbenzo[d][1,3]dioxol-5-yl)-N-methoxy-N-methylacet-
amide (18): A solution of known ester 16[18,28] (1.178 g, 5.30 mmol)
in MeOH (8.5 mL) were treated with a solution of LiOH (254 mg,
10.6 mmol) in H2O (8.5 mL). After stirring for 2 h at room tem-
perature, the solution was adjusted to pH 3 with 1 m HCl and ex-
tracted with EtOAc. After concentration, crude 17 was taken up in
CH2Cl2 (10.6 mL), cooled to 0 °C, and treated with carbonyl-
diimidazole (1.117 g, 6.89 mmol). The mixture was stirred at 0 °C
for 2 h. Then, Et3N (1.03 mL, 7.42 mmol) and N,O-dimethyl-
hydroxylamine hydrochloride (672 mg, 6.89 mmol) were added. Af-
ter 15 min, the cooling bath was removed, and the mixture was
stirred at room temperature for 16 h and then poured into 5 %
aqueous (NH4)H2PO4. The solution was adjusted to pH 4 with 1 m
HCl. Extraction with CH2Cl2, concentration, and chromatography
(PE/EtOAc, 55:45) gave pure 18 (1.184 g, 89% from 16). Rf = 0.47
4
3
4
(d, JH,H = 2.1 Hz, 1 H, 2-H), 6.98 (dd, JH,H = 8.1 Hz, JH,H
=
3
2.1 Hz, 1 H, 6-H), 6.78 (d, JH,H = 8.1 Hz, 1 H, 5-H), 3.79 (s, 3 H,
OCH3), 2.99 (s, 1 H, CϵCH), 0.99 [s, 9 H, (CH3)3C], 0.15 (s, 6 H,
SiCH3) ppm. 13C NMR (75 MHz, CDCl3, 25 °C): δ = 150.65,
146.2, 115.0 (quat.), 125.5 (2-C), 120.9 (5-C), 115.7 (6-C), 84.0
(CϵCH), 75.6 (CϵCH), 55.4 (CH3O), 25.7 [C(CH3)3], 18.5
1
[C(CH ) ], –4.6 (CH Si) ppm. IR: ν = 3250, 3013, 2958, 2931, 2895,
˜
3 3
3
(PE/EtOAc, 60:40). H NMR (300 MHz, CDCl3, 20 °C): δ = 6.72–
2858, 1595, 1570, 1508, 1471, 1459, 1441, 1406, 1390, 1363, 1303,
1268, 1255, 1232, 1186, 1149, 1125, 1033, 1006, 934, 880, 858, 839,
816, 802, 781, 739, 714, 703, 686, 663, 648, 618 cm–1. GC–MS (tR
= 9.09 min): m/z (%) = 262 (0.9) [M]+, 247 (1.0), 205 (66.3), 190
(100.0), 175 (19.0), 160 (15.4), 73 (9.0), 59 (10.6). HRMS (ESI+):
calcd. for C15H23O2Si [M + H]+ 263.1467; found 263.1465.
6.62 (m, 3 H, aromatics), 3.66 (s, 2 H, ArCH2), 3.65 (s, 3 H, OCH3),
3.19 (s, 3 H, NCH3), 1.65 [s, 6 H, C(CH3)2] ppm. 13C NMR
(75 MHz, CD3OD, 25 °C): δ = 172.6 (C=O), 147.5, 146.3, 127.8
(quat.), 121.7 (6-C), 117.8 (2-C), 109.6, 108.0 (4-C, 7-C), 61.3
(OCH ), 38.8 (ArCH ), 32.3 (NCH ), 25.8 [C(CH ) ] ppm. IR: ν =
˜
3
2
3
3 2
2990, 2938, 1658, 1495, 1442, 1377, 1251, 1232, 1217, 1151, 1119,
1093, 1003, 979, 937, 865, 834, 786, 767, 751, 720, 684, 657, 641,
4-Ethynyl-2-methoxyphenol (22a): Alkyne 22b (200 mg, 0.76 mmol)
609 cm–1. GC–MS (tR = 10.17 min): m/z (%) = 251 (39.3) [M]+, was dissolved in THF (1.5 mL), cooled to 0 °C, and treated with
6722
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© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2015, 6710–6726

Conjugation of Hydroxytyrosol with Natural Phenolic Fragments
a solution of tetrabutylammonium fluoride (1 m in THF, 840 μL,
0.84 mmol). After 30 min, the cooling bath was removed, and the
mixture was stirred at room temperature for 2 h. Dilution with
H2O, extraction with EtOAc, concentration, and chromatography
(PE/EtOAc, 80:20) gave pure 22b[30] as a relatively volatile liquid
(101 mg, 90%).
C), 118.6 (2ЈЈ-C), 118.3 (Me-C-Me), 112.2 (5ЈЈ-C), 108.7 (2Ј-C),
108.3 (5Ј-C), 55.5 (OCH3), 51.9 (ArCH2CH2), 36.6 (ArCH2), 25.8
[(CH3)2C], 25.7 [C(CH3)3], 18.5 [C(CH3)3], –4.6 (CH3Si) ppm. IR:
ν = 2930, 2857, 1583, 1497, 1462, 1444, 1406, 1376, 1365, 1271,
˜
1254, 1226, 1218, 1169, 1134, 1074, 1049, 1029, 1004, 980, 928,
831, 815, 782, 736, 707, 685, 670, 663, 635, 617 cm–1. HRMS
(ESI+): calcd. for C26H36N3O4Si [M + H]+ 482.2475; found
482.2491.
4-Ethynylphenyl Acetate (22f):[35] A solution of 4-iodophenyl acet-
ate (807 mg, 3.08 mmol) in dry DMF (5 mL), kept under an argon
atmosphere, was treated with Pd(PPh3)2Cl2 (65 mg, 93 μmol), CuI
(35 mg, 188 μmol), Et3N (1.60 mL, 11.7 mmol), and finally tri-
methylsilylacetylene (480 μL, 3.39 mmol). The mixture was stirred
for 2.5 h at 50 °C. Dilution with water, extraction with EtOAc, con-
centration, and chromatography (PE/EtOAc, 95:5) gave pure 4-(2-
trimethylsilyl)ethynyl acetate (661 mg, 92%). It was taken up in dry
CH2Cl2 (7.1 mL), cooled to 0 °C, and treated dropwise with tetra-
butylammonium fluoride (1 m in THF, 3.4 mL, 3.4 mmol). After
stirring at 0 °C for 50 min, the reaction was quenched with satu-
rated aqueous NH4Cl, and the mixture was extracted with EtOAc,
concentrated, and chromatographed (PE/EtOAc 90: 10) to give
pure 22f as a pale yellow solid (433 mg, 95%). Analytical and spec-
troscopic data were identical to those already reported.[35]
4-{3,4-Bis[(tert-Butyldimethylsilyl)oxy]phenyl}-1-[2-(2,2-dimethyl-
benzo[d][1,3]dioxol-5-yl)ethyl]-1H-1,2,3-triazole (26c): Obtained in
92 % yield. Rf = 0.22 (PE/EtOAc, 90:10). 1H NMR (300 MHz,
4
CDCl3, 20 °C): δ = 7.38 (s, 1 H, 5-H), 7.28 (d, JH,H = 2.1 Hz, 1
3
4
H, 2ЈЈ-H), 7.20 (dd, JH,H = 8.2 Hz, JH,H = 2.1 Hz, 1 H, 6ЈЈ-H),
3
3
6.85 (d, JH,H = 8.2 Hz, 1 H, 5ЈЈ-H), 6.64 (d, JH,H = 7.8 Hz, 1 H,
5Ј-H), 6.57 (d, 4JH,H = 1.8 Hz, 1 H, 2Ј-H), 6.52 (dd, 3JH,H = 7.8 Hz,
4JH,H = 1.8 Hz, 1 H, 6Ј-H), 4.55 (t, JH,H = 7.3 Hz, 2 H,
3
3
ArCH2CH2), 3.13 (t, JH,H = 7.3 Hz, 2 H, ArCH2), 1.66 [s, 6 H,
(CH3)2C], 1.00 [s, 9 H, C(CH3)3], 0.99 [s, 9 H, C(CH3)3], 0.22 (s, 6
H, CH3Si), 0.21 (s, 6 H, CH3Si) ppm. 13C NMR (75 MHz, CDCl3,
25 °C): δ = 147.8, 147.4, 147.13, 147.08, 146.5, 130.1, 124.3 (aro-
matic quat.), 121.4 (5ЈЈ-C), 121.2 (6Ј-C), 119.1 (5-C), 119.0 (6ЈЈ-C),
118.7 (2ЈЈ-C), 118.0 (Me-C-Me), 108.8 (2Ј-C), 108.3 (5Ј-C), 51.9
(ArCH2CH2), 36.6 (ArCH2), 25.98, 25.96 [C(CH3)3], 25.8 [(CH3)
General Procedure for the Preparation of Protected Tetrazoles 26a–
d, 26f, and 26g: A solution of the required alkyl azide (13, 14, or 25;
1.00 mmol) and the alkyne (19, 22a, 22c, 22d, or 22f; 1.04 mmol) in
H2O (2.25 mL) and tBuOH (2.25 mL), kept under an atmosphere
of nitrogen, was treated with a solution of sodium ascorbate (1 m
in H2O, 100 μL, 100 μmol) and with CuSO4·5H2O (1 mg, 4 μmol).
The solution was stirred at room temperature overnight. If not
complete, CuSO4 (1 mg) and sodium ascorbate solution (100 μL)
were added, and the mixture was warmed at 45 °C for another 9 h.
Dilution with H2O, extraction with EtOAc, concentration, and
chromatography (PE/EtOAc mixtures) gave the pure tetrazoles.
C], 18.51, 18.46 [C(CH ) ], –4.1 (CH Si) ppm. IR: ν = 2957, 2928,
˜
2
3 3
3
2884, 2857, 1576, 1559, 1496, 1472, 1461, 1446, 1406, 1383, 1374,
1361, 1286, 1252, 1235, 1219, 1169, 1126, 1073, 1054, 1003, 978,
937, 930, 899, 887, 862, 829, 813, 778, 762, 722, 696, 675, 659,
617 cm–1. HRMS (ESI+): calcd. for C31H48N3O4Si2 [M + H]+
582.3183; found 582.3199.
4-(4-Acetoxyphenyl)-1-[2-(2,2-dimethylbenzo[d][1,3]dioxol-5-yl)-
ethyl]-1H-1,2,3-triazole (26d): Obtained in 89% yield. Rf = 0.23
1
(PE/EtOAc, 70:30). H NMR (300 MHz, CDCl3, 20 °C): δ = 7.79
3
3
(d, JH,H = 9.0 Hz, 2 H, 2ЈЈ-H), 7.50 (s, 1 H, 5-H), 7.14 (d, JH,H
1-[2-(3,4-Diacetoxyphenyl)ethyl]-4-(4-hydroxy-3-metoxyphenyl)1H-
1,2,3-triazole (26a): Obtained in 94% yield. Rf = 0.19 (PE/EtOAc,
3
= 9.0 Hz, 2 H, 3ЈЈ-H), 6.64 (d, JH,H = 7.8 Hz, 1 H, 5Ј-H), 6.54 (d,
4JH,H = 1.8 Hz, 1 H, 2Ј-H), 6.51 (dd, JH,H = 7.8 Hz, JH,H
=
3
4
1
4
50:50). H NMR (300 MHz, CDCl3, 20 °C): δ = 7.46 (d, JH,H
=
3
3
1.8 Hz, 1 H, 6Ј-H), 4.57 (t, JH,H = 7.3 Hz, 2 H, ArCH2CH2), 3.14
2.1 Hz, 1 H, 2ЈЈ-H), 7.44 (s, 1 H, 5-H), 7.15 (dd, JH,H = 8.4 Hz,
3
4JH,H = 1.8 Hz, 1 H, 6ЈЈ-H), 7.13 (d, JH,H = 8.4 Hz, 1 H, 5ЈЈ-H),
3
(t, JH,H = 7.3 Hz, 2 H, ArCH2), 2.32 (s, 3 H, CH3CO), 1.66 [s, 6
H, (CH3)2C] ppm. 13C NMR (75 MHz, CDCl3, 25 °C): δ = 169.4
(C=O), 150.4, 147.8, 146.7, 146.5, 130.0, 128.5 (aromatic quat.),
126.8 (2ЈЈ-C), 122.0 (3ЈЈ-C), 121.2 (6Ј-C), 119.9 (5-C), 118.1 (Me-
C-Me), 108.8 (2Ј-C), 108.4 (5Ј-C), 52.0 (ArCH2CH2), 36.6
3
7.01–6.95 (m, 2 H, 2Ј-H, 6Ј-H), 6.93 (d, JH,H = 8.1 Hz, 1 H, 5Ј-
H), 5.82 (br. s, 1 H, OH), 4.60 (t, 3JH,H = 7.2 Hz, 2 H, ArCH2CH2),
3
3.95 (s, 3 H, OCH3), 3.24 (t, JH,H = 7.2 Hz, 2 H, ArCH2), 2.28,
2.26 (2s, 6 H, 2CH3CO) ppm. 13C NMR (75 MHz, CDCl3, 25 °C):
δ = 168.2 (C=O), 147.6, 146.9, 145.8, 142.2, 141.1, 135.9, 122.8
(quat.), 126.9 (6Ј-C), 123.7 (2Ј-C, 5ЈЈ-C), 119.5 (5-C), 118.9 (6ЈЈ-C),
114.6 (5Ј-C), 108.4 (2ЈЈ-C), 56.0 (OCH3), 51.2 (ArCH2CH2), 36.0
(ArCH ), 25.8 [(CH ) C], 21.2 (CH CO) ppm. IR: ν = 3105, 2995,
˜
2
3 2
3
1758, 1559, 1497, 1482, 1458, 1447, 1417, 1380, 1372, 1253, 1228,
1206, 1189, 1172, 1159, 1116, 1079, 1050, 1023, 1012, 981, 976,
952, 937, 912, 861, 838, 822, 790, 746, 719, 713, 683, 665, 634,
619 cm–1. HRMS (ESI+): calcd. for C21H22N3O4 [M + H]+
380.1610; found 380.1613.
(ArCH ), 20.6 (CH CO) ppm. IR: ν = 2953, 2926, 2868, 1765,
˜
2
3
1753, 1616, 1597, 1564, 1505, 1466, 1446, 1365, 1279, 1259, 1216,
1184, 1170, 1138, 1126, 1108, 1087, 1056, 1034, 1020, 1009, 959,
917, 898, 873, 852, 819, 797, 784, 741, 724, 700, 676, 666, 635,
614, 604 cm–1. HRMS (ESI+): calcd. for C21H22N3O6 [M + H]+
412.1509; found 412.1509.
1-[2-(2,2-Dimethylbenzo[d][1,3]dioxol-5-yl)ethyl]-4-[(2,2-dimethyl-
benzo[d][1,3]dioxol-5-yl)methyl]1H-1,2,3-triazole (26f): Obtained in
91 % yield. Rf = 0.18 (PE/EtOAc, 70:30). 1H NMR (300 MHz,
4-{3-[(tert-Butyldimethylsilyl)oxy]-4-methoxyphenyl}-1-[2-(2,2-di- CDCl3, 20 °C): δ = 6.97 (s, 1 H, 5-H), 6.65–6.57 (m, 4 H, 5Ј-H, 2ЈЈ-
4
methylbenzo[d][1,3]dioxol-5-yl)ethyl]-1H-1,2,3-triazole (26b): Ob-
H, 5ЈЈ-H, 6ЈЈ-H), 6.50 (d, JH,H = 1.7 Hz, 1 H, 2Ј-H), 6.44 (dd,
tained in 83 % yield. Rf = 0.13 (PE/EtOAc, 90:10). 1H NMR
3JH,H = 7.8 Hz, 4JH,H = 1.7 Hz, 1 H, 6Ј-H), 4.46 (t, 3JH,H = 7.3 Hz,
3
3
(300 MHz, CDCl3, 20 °C): δ = 7.43 (s, 1 H, 5-H), 7.34 (dd, JH,H 2 H, ArCH2CH2), 3.95 (s, 2 H, ArCH2), 3.06 (t, JH,H = 7.3 Hz, 2
4
4
= 8.4 Hz, JH,H = 2.1 Hz, 1 H, 6ЈЈ-H), 7.27 (d, JH,H = 2.1 Hz, 1
H, ArCH2CH2), 1.65 [s, 6 H, (CH3)2C] ppm. 13C NMR (75 MHz,
CDCl3, 25 °C): δ = 147.72, 147.65, 147.57, 146.4, 146.0, 132.2,
130.1 (aromatic quat.), 121.7 (5-C), 121.2 (6Ј-C), 120.9 (6ЈЈ-C),
3
3
H, 2ЈЈ-H), 6.88 (d, JH,H = 8.4 Hz, 1 H, 5ЈЈ-H), 6.64 (d, JH,H
7.8 Hz, 1 H, 5Ј-H), 6.57 (d, JH,H = 1.5 Hz, 1 H, 2Ј-H), 6.52 (dd,
=
4
3JH,H = 8.0 Hz, 4JH,H = 1.7 Hz, 1 H, 6Ј-H), 4.55 (t, 3JH,H = 7.3 Hz, 118.0, 117.8 (Me-C-Me), 109.0, 108.7, 108.3, 108.0 (2Ј-C, 5Ј-C, 2ЈЈ-
3
2 H, ArCH2CH2), 3.13 (t, JH,H = 7.3 Hz, 2 H, ArCH2), 1.66 [s, 6
C, 5ЈЈ-C), 51.8 (ArCH2CH2), 36.6 (ArCH2CH2), 31.9 (ArCH2),
25.85, 25.82 [(CH ) C] ppm. IR: ν = 2989, 2936, 1609, 1550, 1494,
H, (CH3)2C], 1.10 [s, 9 H, C(CH3)3], 0.18 (s, 6 H, CH3Si) ppm. 13
NMR (75 MHz, CDCl3, 25 °C): δ = 151.0, 147.8, 147.4, 146.5, 1445, 1376, 1252, 1231, 1213, 1157, 1116, 1074, 1049, 1029, 979,
145.2, 130.1, 123.7 (aromatic quat.), 121.2 (6Ј-C), 119.2 (6ЈЈ-C, 5-
940, 833, 799, 764, 735, 702, 680, 657, 623, 604 cm–1. HRMS
C
˜
3 2
Eur. J. Org. Chem. 2015, 6710–6726
© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
6723

L. Banfi et al.
FULL PAPER
(ESI+): calcd. for C23H26N3O4 [M + H]+ 408.1923; found 408.1938.
The protected triazole (0.20 mmol) was dissolved in a 4 mL micro-
wave tube in CH3CN (800 μL) and treated with water (180 μL) and
concentrated HCl (20 μL). The tube was sealed, and the solution
was heated in the microwave apparatus at 90 °C for 15–30 min. The
mixture was diluted with EtOAc and washed with saturated aque-
ous NaHCO3. Concentration of the organic phase and chromatog-
raphy (PE/EtOAc, 70:30) gave the unprotected triazole.
1-[(2-Benzyloxy-3-methoxyphenyl)methyl]-4-[(2,2-dimethylbenzo[d]-
[1,3]dioxol-5-yl)methyl]1H-1,2,3-triazole (26g): Obtained in 99%
1
yield. Rf = 0.43 (PE/EtOAc, 50:50). H NMR (300 MHz, CDCl3,
3
20 °C): δ = 7.37–7.27 (m, 5 H, CH of benzyl), 7.02 (t, JH,H
=
3
8.0 Hz, 1 H, H meta to OMe), 6.95 (s, 1 H, 5-H), 6.93 (dd, JH,H
4
3
= 8.0 Hz, JH,H = 1.5 Hz, 1 H, H para to OMe), 6.69 (dd, JH,H
=
4
7.8 Hz, JH,H = 1.7 Hz, 1 H, 6-H of benzodioxole), 6.63–6.58 (m,
2 H, 4-H and 7-H of benzodioxole), 5.30 (s, 2 H, CH2N), 5.03 (s,
2 H, PhCH2O), 3.91 (s, 3 H, OCH3), 3.90 (s, 2 H, ArCH2), 1.64 [s,
6 H, (CH3)2C] ppm. 13C NMR (75 MHz, CDCl3, 25 °C): δ = 152.6,
147.9, 147.5, 145.9, 145.3, 137.1, 132.3, 129.2 (aromatic quat.),
128.6 (4C), 128.3 (CH of benzyl), 124.6, 121.5, 121.3, 120.9, 112.8,
109.0, 108.0 (other aromatic CH), 117.7 (Me-C-Me), 75.0
(OCH2Ph), 55.9 (OCH3), 48.7 (CH2N), 32.0 (ArCH2), 25.9 [(CH3)
1-[2-(3,4-Dihydroxyphenyl)ethyl]-4-(3-hydroxy-4-methoxyphenyl)-
1H-1,2,3-triazole (27b): Yield: 77%. Rf = 0.08 (PE/EtOAc, 50:50).
1H NMR (300 MHz, CD3OD, 20 °C): δ = 7.89 (s, 1 H, 5-H), 7.22–
3
7.16 (m, 2 H, 2ЈЈ-H, 6ЈЈ-H), 6.95 (d, JH,H = 8.7 Hz, 1 H, 5ЈЈ-H),
3
4
6.67 (d, JH,H = 8.0 Hz, 1 H, 5Ј-H), 6.59 (d, JH,H = 1.9 Hz, 1 H,
3
4
2Ј-H), 6.46 (dd, JH,H = 8.0 Hz, JH,H = 1.9 Hz, 1 H, 6Ј-H), 4.57
(t, JH,H = 7.2 Hz, 2 H, ArCH2CH2), 3.86 (s, 3 H, OCH3), 3.06 (t,
3
3JH,H = 7.2 Hz, 2 H, ArCH2) ppm. 13C NMR (75 MHz, CD3OD,
25 °C): δ = 149.3, 148.6, 148.0, 146.5, 145.3, 130.2, 124.8 (quat.),
121.7 (5-C), 121.1 (6Ј-C), 118.3 (6ЈЈ-C), 116.8 (2Ј-C), 116.5 (5Ј-C),
113.8 (2ЈЈ-C), 112.9 (5ЈЈ-C), 56.4 (OCH3), 53.2 (ArCH2CH2), 37.1
C] ppm. IR: ν = 2989, 2938, 2838, 1588, 1548, 1495, 1480, 1440,
˜
2
1376, 1348, 1251, 1234, 1213, 1155, 1116, 1072, 1045, 979, 911,
833, 803, 768, 752, 732, 697, 657, 609 cm–1. HRMS (ESI+): calcd.
for C27H28N3O4 [M + H]+ 458.2080; found 458.2090.
(ArCH ) ppm. IR: ν = 3493, 3145 (br.), 3033, 2970, 2839, 2740,
˜
2
1-[(2-Hydroxy-3-methoxyphenyl)methyl]-4-[(2,2-dimethylbenzo[d]-
[1,3]dioxol-5-yl)methyl]1H-1,2,3-triazole (26h): A solution of tri-
azole 26g (452 mg, 0.99 mmol) in 99% EtOH (5 mL) was hydroge-
nated for 2 h at room temperature under the slight pressure of an
inflated balloon over 10% Pd/C (65 mg). Filtration of the catalyst,
concentration of the solution, and chromatography (PE/EtOAc,
80:20) of the residue gave pure 26h as a white foam (290 mg, 80%).
Rf = 0.33 (PE/EtOAc, 50:50). 1H NMR (300 MHz, CDCl3, 20 °C):
δ = 7.28 (s, 1 H, 5-H), 6.88–6.78 (m, 3 H), 6.66–6.59 (m, 3 H), 5–
97 (s, 1 H, OH), 5.50 (s, 2 H, CH2N), 3.94 (s, 2 H, ArCH2), 3.89
(s, 3 H, OCH3), 1.64 [s, 6 H, (CH3)2C] ppm. 13C NMR (75 MHz,
CDCl3, 25 °C): δ = 147.8, 147.5, 146.6, 145.9, 143.8, 132.3, 109.0
(aromatic quat.), 122.1, 121.6, 120.9, 120.8, 120.1, 111.0, 108.0
(aromatic CH), 117.7 (Me-C-Me), 56.1 (OCH3), 48.5 (CH2N), 32.0
1739, 1612, 1589, 1565, 1538, 107, 1441, 1377, 1329, 1306, 1281,
1271, 1254, 1236, 1214, 1153, 1140, 1114, 1085, 1061, 1021, 1011,
1003, 958, 893, 877, 819, 798, 764, 728, 705, 661, 631, 611 cm–1.
HRMS (ESI+): calcd. for C17H18N3O4 [M + H]+ 328.1297; found
328.1299.
1-[2-(3,4-Dihydroxyphenyl)ethyl]-4-(3,4-dihydroxyphenyl)1H-1,2,3-
1
triazole (27c): Yield: 83%. Rf = 0.08 (PE/EtOAc, 50:50). H NMR
4
(300 MHz, CD3OD, 20 °C): δ = 7.85 (s, 1 H, 5-H), 7.17 (d, JH,H
3
4
= 2.1 Hz, 1 H, 2ЈЈ-H), 7.05 (dd, JH,H = 8.1 Hz, JH,H = 2.1 Hz, 1
3
3
H, 6ЈЈ-H), 6.79 (d, JH,H = 8.1 Hz, 1 H, 5ЈЈ-H), 6.66 (d, JH,H
=
4
8.0 Hz, 1 H, 5Ј-H), 6.59 (d, JH,H = 1.9 Hz, 1 H, 2Ј-H), 6.46 (dd,
3JH,H = 8.0 Hz, 4JH,H = 1.9 Hz, 1 H, 6Ј-H), 4.56 (t, 3JH,H = 7.0 Hz,
2 H, ArCH2CH2), 3.06 (t, JH,H = 7.0 Hz, 2 H, ArCH2) ppm. 13C
3
NMR (75 MHz, CD3OD, 25 °C): δ = 148.9, 146.9, 146.7, 146.4,
145.3, 130.2, 123.6 (quat.), 121.4 (6Ј-C), 121.1 (5-C), 118.6 (6ЈЈ-C),
116.9 (2Ј-C), 116.7 (5ЈЈ-C), 116.5 (5Ј-C), 113.9 (2ЈЈ-C), 53.1
(ArCH ), 25.8 [(CH ) C] ppm. IR: ν = 2989 (very br.), 1611, 1594,
˜
2
3 2
1482, 1444, 1384, 1376, 1353, 1272, 1253, 1236, 1225, 1189, 1113,
1073, 1057, 1036, 980, 954, 945, 908, 840, 834, 824, 799, 765, 744,
721, 716, 689, 621 cm–1. HRMS (ESI+): calcd. for C20H22N3O4 [M
+ H]+ 368.1610; found 368.1617.
(ArCH CH ), 37.1 (ArCH ) ppm. IR: ν = 3292 (br.), 1696, 1606,
˜
2
2
2
1568, 1512, 1445, 1373, 1275, 1247, 1217, 1195, 1112, 1079, 1042,
1008, 979, 953, 896, 863, 801, 781, 722, 688, 669, 637, 608 cm–1.
HRMS (ESI+): calcd. for C16H16N3O4 [M + H]+ 314.1141; found
314.1139.
1-[2-(3,4-Dihydroxyphenyl)ethyl]-4-(4-hydroxy-3-metoxyphenyl)1H-
1,2,3-triazole (27a): A solution of triazole 26a (60 mg, 146 μmol) in
THF (375 μL) and MeOH (750 μL) was treated with Et3N (16 μL,
114 μmol) and stirred at room temperature for 48 h. The reaction
was quenched with aqueous saturated NH4Cl, and the mixture was
extracted with EtOAc, concentrated, and chromatographed
(EtOAc) to give pure 27a as a yellow oil (37 mg, 78%). Rf = 0.08
(PE/EtOAc, 50:50). 1H NMR (300 MHz, CD3OD, 20 °C): δ = 7.93
1-[2-(3,4-Dihydroxyphenyl)ethyl]-4-(4-hydroxyphenyl)1H-1,2,3-tri-
1
azole (27d): Yield: 80%. H NMR (300 MHz, CD3OD, 20 °C): δ =
3
7.91 (s, 1 H, 5-H), 7.57 (d, JH,H = 8.7 Hz, 2 H, 2ЈЈ-H), 6.82 (d,
3
3JH,H = 8.7 Hz, 2 H, 3ЈЈ-H), 6.67 (d, JH,H = 8.0 Hz, 1 H, 5Ј-H),
6.59 (d, 4JH,H = 2.1 Hz, 1 H, 2Ј-H), 6.46 (dd, 3JH,H = 8.0 Hz, 4JH,H
3
4
3
= 2.1 Hz, 1 H, 6Ј-H), 4.58 (t, JH,H = 7.0 Hz, 2 H, ArCH2CH2),
(s, 1 H, 5-H), 7.34 (d, JH,H = 2.0 Hz, 1 H, 2ЈЈ-H), 7.16 (dd, JH,H
3
3.07 (t, JH,H = 7.0 Hz, 2 H, ArCH2) ppm. 13C NMR (75 MHz,
4
3
= 8.1 Hz, JH,H = 2.0 Hz, 1 H, 6ЈЈ-H), 6.82 (d, JH,H = 8.1 Hz, 1
H, 5ЈЈ-H), 6.66 (d, JH,H = 8.1 Hz, 1 H, 5Ј-H), 6.58 (d, JH,H
1.8 Hz, 1 H, 2Ј-H), 6.46 (dd, JH,H = 8.1 Hz, JH,H = 2.1 Hz, 1 H,
3
4
CD3OD, 25 °C): δ = 158.9, 148.8, 146.5, 145.3, 130.1, 123.0 (quat.),
128.0 (2ЈЈ-C), 121.4 (5-C), 121.1 (6Ј-C), 118.6 (6ЈЈ-C), 116.8 (2Ј-C),
116.6 (2ЈЈ-C), 116.5 (5Ј-C), 53.2 (ArCH2CH2), 37.1 (ArCH2) ppm.
=
3
4
3
6Ј-H), 4.57 (t, JH,H = 7.2 Hz, 2 H, ArCH2CH2), 3.90 (s, 3 H,
OCH3), 3.07 (t, JH,H = 7.2 Hz, 2 H, ArCH2) ppm. 13C NMR
3
IR: ν = 3295 (very br.), 1740, 1604, 1592, 1562, 1527, 1515, 1497,
˜
1466, 1369, 1356, 1325, 1253, 1229, 1195, 1175, 1157, 1143, 1112,
1088, 1062, 1020, 991, 977, 943, 932, 911, 878, 855, 840, 803, 779,
719, 705, 694, 666, 642, 623 cm–1. HRMS (ESI+): calcd. for
C16H16N3O3 [M + H]+ 298.1192; found 298.1204.
(75 MHz, CD3OD, 25 °C): δ = 149.3, 148.9, 148.0, 146.5, 145.3,
130.2, 123.5 (quat.), 121.6 (5-C), 121.1 (6Ј-C), 119.7 (6ЈЈ-C), 116.9
(2Ј-C), 116.6, 116.5 (5Ј-C, 5ЈЈ-C), 110.2 (2ЈЈ-C), 56.4 (OCH3), 53.2
(ArCH CH ), 37.1 (ArCH ) ppm. IR: ν = 3292 (br.), 3134, 2970,
˜
2
2
2
2942, 2838, 2724, 2590, 1738, 1600, 1564, 1527, 1517, 1506, 1464,
1450, 1437, 1394, 162, 1321, 1279, 1250, 1229, 1218, 1174, 1151,
1129, 1110, 1088, 1027, 976, 948, 934, 907, 857, 851, 833, 812, 801,
783, 725, 719, 714, 695, 672, 635, 615 cm–1. HRMS (ESI+): calcd.
for C17H18N3O4 [M + H]+ 328.1297; found 328.1297.
4-(3,4-Dihydroxyphenyl)-1-[2-(2,2-dimethylbenzo[d][1,3]dioxol-5-yl)-
ethyl]-1H-1,2,3-triazole (27e): A solution of triazole 26c (865 mg,
1.49 mmol) in dry THF (7.4 mL) was cooled to 0 °C and treated
with tetrabutylammonium fluoride (1 m in THF, 3.7 mL,
3.7 mmol). After stirring at 45 min at 0 °C, the mixture was diluted
with saturated aqueous NH4Cl, extracted with EtOAc, concen-
trated, and chromatographed (PE/EtOAc, 35:65) to give pure 27e
General Procedure for the Transformation of Dioxolane-Protected
Triazoles 26b–d, 26f, and 26h into Triazoles 27b–d, 27f, and 27g:
6724
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© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2015, 6710–6726

Conjugation of Hydroxytyrosol with Natural Phenolic Fragments
1
as a foam (452 mg, 86%). Rf = 0.24 (PE/EtOAc, 50:50). H NMR
was evaporated. The residue was taken up with CHCl3, and the
solvent was evaporated again (3ϫ). The residue was taken up in
4
(300 MHz, CDCl3, 20 °C): δ = 7.59 (d, JH,H = 1.9 Hz, 1 H, 2ЈЈ-
H), 7.40 (s, 1 H, 5-H), 6.98 (dd, JH,H = 8.2 Hz, JH,H = 2.0 Hz, 1 [D6]DMSO and 1H NMR, 13C NMR, gCOSY, gHSQC, and
3
4
3
3
H, 6ЈЈ-H), 6.89 (d, JH,H = 8.2 Hz, 1 H, 5ЈЈ-H), 6.64 (d, JH,H
7.8 Hz, 1 H, 5Ј-H), 6.56–6.48 (m, 2 H, 2Ј-H, 6Ј-H), 4.56 (t, JH,H following data (extrapolated by subtracting the signals of DPPH).
= 7.2 Hz, 2 H, ArCH2CH2), 3.13 (t, JH,H = 7.2 Hz, 2 H, ArCH2),
1.66 [s, 6 H, (CH3)2C] ppm. 13C NMR (75 MHz, CDCl3, 25 °C): δ 1.2 Hz, 1 H, 3-H), 5.87 (s, 1 H, 6-H), 4.26 (br. s, OH), 3.87 (s, 3 H,
=
gHMBC experiments were performed on this crude to afford the
3
3
4
1H NMR (300 MHz, [D6]DMSO, 30 °C): δ = 6.30 (t, JH,H
=
3
3
= 147.8, 147.6, 146.5, 145.2, 144.2, 129.8, 122.5 (aromatic quat.),
OCH3), 3.61 (t, JH,H = 6.4 Hz, 2 H, CH2OH), 2.58 (td, JH,H =
121.2, 119.7, 118.6, 115.3, 113.3, 108.8, 108.4 (aromatic CH), 118.1 6.4, JH,H = 1.1 Hz, 2 H, ArCH2) ppm. 13C NMR (75 MHz, [D6]-
4
(Me-C-Me), 52.3 (ArCH2CH2), 36.5 (ArCH2), 25.8 [(CH3)2C] ppm. DMSO, 30 °C): δ = 180.0, 178.4 (1-C, 2-C), 168.5 (5-C), 149.7 (4-
IR: ν = 3520, 3152 (br.), 2989, 2933, 1736, 1597, 1565, 1497, 1464,
C), 128.4 (3-C), 102.5 (6-C), 58.9 (CH2OH), 57.4 (OCH3), 33.8
(ArCH2) ppm.
˜
1447, 1386, 1376, 1362, 1347, 1282, 1258, 1247, 1233, 1215, 1200,
1157, 1140, 1121, 1080, 1058, 1006, 982, 939, 898, 865, 840, 818,
799, 787, 782, 737, 720, 671, 640, 613 cm–1. HRMS (ESI+): calcd.
for C19H20N3O4 [M + H]+ 354.1454; found 354.1452.
Cytotoxicity Tests on Tumour Cells: Tests were performed on the
human lung adenocarcinoma cell lines A549 and H1975 cultured
in RPMI 1640 medium (Roswell Park Memorial Institute) with 5%
fetal bovine serum, 1% l-glutamine, and 1% penicillin/strepto-
mycin at 37 °C in 5% CO2. Cells were seeded in 96-well plates at
a concentration of 1000 cellswell–1 and were treated with culture
medium (180 μL) for 24 h prior to the addition of compounds. The
polyphenol samples were prepared by dissolving in DMSO as 0.1 m
solutions, following by the appropriate dilution in water. The poly-
phenol solution (20 μL) was added to each well. Cell viability was
assessed by the colorimetric test MTS [3-(4,5-dimethylthiazol-2-yl)-
5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium
bromide] after incubating for 72 h. Viable cells were measured by
using a microtiter plate spectrophotometer (Mod-20100C, Optic
Ivymen System, Barcelona, Spain) at an optical density of 490 nm.
Control experiments were performed by adding the same amount
of DMSO without the polyphenol. The absorbance is a measure of
1-[2-(3,4-Dihydroxyphenyl)ethyl]-4-[(3,4-dihydroxyphenyl)methyl]-
1H-1,2,3-triazole (27f): Yield: 71%. Rf = 0.08 (PE/EtOAc, 30:70).
1H NMR (300 MHz, CD3OD, 20 °C): δ = 7.35 (s, 1 H, 5-H), 6.66
3
3
(d, JH,H = 8.0 Hz, 1 H, 5ЈЈ-H), 6.63 (d, JH,H = 8.0 Hz, 1 H, 5Ј-
4
4
H), 6.61 (d, JH,H = 2.1 Hz, 1 H, 2ЈЈ-H), 6.54 (d, JH,H = 2.1 Hz,
3
4
1 H, 2Ј-H), 6.47 (dd, JH,H = 8.0 Hz, JH,H = 2.1 Hz, 1 H, 6Ј-H),
6.38 (dd, 3JH,H = 8.0 Hz, 4JH,H = 1.9 Hz, 1 H, 6ЈЈ-H), 4.49 (t, 3JH,H
3
= 7.1 Hz, 2 H, ArCH2CH2), 3.82 (s, 2 H, ArCH2), 2.99 (t, JH,H
=
7.1 Hz, 2 H, ArCH2) ppm. 13C NMR (75 MHz, CD3OD, 25 °C): δ
= 148.7, 146.4, 146.3, 145.2, 144.9, 131.9, 124.1 (quat.), 131.9,
121.1, 120.8, 116.8, 116.7, 116.5 (2C) (aromatic CH), 53.0
(ArCH CH ), 37.0 (ArCH CH ), 31.9 (ArCH ) ppm. IR: ν = 3193
˜
2
2
2
2
2
(br.), 2717, 1604, 1517, 1443, 1360, 1280, 1259, 1192, 1150, 1111,
1063, 1040, 959, 865, 804, 785, 750, 665, 631 cm–1. HRMS (ESI+):
calcd. for C17H18N3O4 [M + H]+ 328.1297; found 328.1304.
cell viability. %Viability
= Abs490 nm(tested compd)ϫ 100/
Abs490 nm(control). The assays were performed in quadruplicate
samples at least three times, and the average results are reported in
Table 2.
1-[(2-Hydroxy-3-methoxyphenyl)methyl]-4-[(3,4-dihydroxyphenyl)-
methyl]1H-1,2,3-triazole (27g): Yield: 76%. 1H NMR (300 MHz,
3
CD3OD, 20 °C): δ = 7.53 (s, 1 H, 5-H), 6.92 (dd, JH,H = 7.2 Hz,
4JH,H = 2.4 Hz, 1 H, 2Ј-H), 6.80–6.73 (m, 2 H, 3Ј-H, 4Ј-H), 6.66
3
4
(d, JH,H = 8.0 Hz, 1 H, 5ЈЈ-H), 6.61 (d, JH,H = 2.1 Hz, 1 H, 2ЈЈ-
Acknowledgments
3
4
H), 6.52 (dd, JH,H = 8.0 Hz, JH,H = 2.1 Hz, 1 H, 6ЈЈ-H), 5.49 (s,
2 H, ArCH2N), 3.85 (s, 3 H, OCH3), 3.84 (s, 2 H, ArCH2) ppm.
13C NMR (75 MHz, CD3OD, 25 °C): δ = 149.10, 149.06, 146.4,
146.0, 144.9, 131.9, 116.7 (quat.), 123.7, 122.8, 122.7, 120.8, 120.5,
116.4, 112.8 (aromatic CH), 56.5 (OCH3), 50.0 (ArCH2N), 32.0
The authors thank the Regione Liguria for financial support
(scholarship to E. T.). Gabriella Vitali Forconesi is thanked for
practical collaboration in this work, Dr. Luca Bono and Dr. Lo-
renzo Sonaglia for HRMS analysis, and Mr. Walter Sgroi for help
in DPPH tests.
(ArCH ) ppm. IR: ν = 3139 (br.), 2941, 2841, 1597, 1518, 1492,
˜
2
1482, 1441, 1355, 1267, 1215, 1148, 1112, 1060, 951, 904, 872, 829,
789, 755, 740, 712, 665 cm–1. HRMS (ESI+): calcd. for
C17H18N3O4 [M + H]+ 328.1297; found 328.1300.
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Published Online: September 16, 2015
6726
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