Further insights of selenium-containing analogues of WC-9 against Trypanosoma cruzi

Article abstract of DOI:10.1016/j.bmc.2019.02.039

As a continuation of our project aimed at searching for new chemotherapeutic agents against American trypanosomiasis (Chagas disease), new selenocyanate derivatives were designed, synthesized and biologically evaluated against the clinically more relevant dividing form of Trypanosoma cruzi, the etiologic agent of this illness. In addition, in order to establish the role of each part of the selenocyanate moiety, different derivatives, in which the selenium atom or the cyano group were absent, were conceived, synthesized and biologically evaluated. In addition, in order to study the optimal position of the terminal phenoxy group, new regioisomers of WC-9 were synthesized and evaluated against T. cruzi. Finally, the resolution of a racemic mixture of a very potent conformationally rigid analogue of WC-9 was accomplished and further tested as growth inhibitors of T. cruzi proliferation. The results provide further insight into the role of the selenocyanate group in its antiparasitic activity.

Full text of DOI:10.1016/j.bmc.2019.02.039

Bioorganic&MedicinalChemistryxxx(xxxx)xxx–xxx
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry
journal homepage: www.elsevier.com/locate/bmc
Further insights of selenium-containing analogues of WC-9 against
Trypanosoma cruzi
⁎
María N. Chaoa, María V. Lorenzo-Ocampoa, Sergio H. Szajnmana, , Roberto Docampob,
⁎
Juan B. Rodrigueza,
a Departamento de Química Orgánica and UMYMFOR (CONICET–FCEyN), Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Pabellón 2, Ciudad
Universitaria, C1428EHA Buenos Aires, Argentina
b Center for Tropical and Emerging Global Diseases and Department of Cellular Biology, University of Georgia, Athens, GA 30602, USA
A B S T R A C T
As a continuation of our project aimed at searching for new chemotherapeutic agents against American trypanosomiasis (Chagas disease), new selenocyanate
derivatives were designed, synthesized and biologically evaluated against the clinically more relevant dividing form of Trypanosoma cruzi, the etiologic agent of this
illness. In addition, in order to establish the role of each part of the selenocyanate moiety, different derivatives, in which the selenium atom or the cyano group were
absent, were conceived, synthesized and biologically evaluated. In addition, in order to study the optimal position of the terminal phenoxy group, new regioisomers
of WC-9 were synthesized and evaluated against T. cruzi. Finally, the resolution of a racemic mixture of a very potent conformationally rigid analogue of WC-9 was
accomplished and further tested as growth inhibitors of T. cruzi proliferation. The results provide further insight into the role of the selenocyanate group in its
antiparasitic activity.
1. Introduction
growth targeting T. cruzi squalene synthase (TcSQS).7–15
We have recently described that the many isosteric analogues of our
lead drug WC-9 (compound 1) (Fig. 1) behaved as extremely potent
growth inhibitors of the clinically relevant intracellular form (amasti-
gotes) of T. cruzi acting in the low nanomolar concentrations.16 It is
worth mentioning that WC-9 constitutes one of the few examples of a
lead structure bearing a thiocyanate group covalently bonded to a main
skeleton.17 WC-9 targets TcSQS, a membrane protein, being a non-
competitive nanomolar inhibitor of the enzymatic activity of mi-
tochondrial and glycosomal TcSQS (wild type) but inactive against
truncated TcSQS, the soluble enzyme, which was cloned and expressed
in Escherichia coli.16,18 Certainly, the replacement of the sulfur atom by
a selenium one in WC-9 or its regioisomer 210 and in other closely
related molecules brought about a dramatic enhancement of their ef-
fectiveness as inhibitors of T. cruzi proliferation making the seleno-
cyanate derivatives16 almost two orders of magnitude more potent than
the thiocyanate counterparts with excellent selectively index va-
lues.10–12,16 Compounds 3–8 emerge as representative members of this
family of selenium-containing antiparasitic agents as shown in Fig. 1.
These selenium-containing analogues were extremely selective and
were almost devoid of toxicity in in vitro assays.16 In fact, a covalently
bonded selenocyanate moiety acting at the low nanomolar range
against intracellular T. cruzi is definitely an innovation in Medicinal
Chemistry.
Trypanosoma cruzi is the hemoflagellate protozoan parasite that
causes American trypanosomiasis (Chagas disease), which is an en-
demic disease widespread from Southern United States to Southern
Argentina.1 In addition, Chagas disease is a well-recognized opportu-
nistic infection in AIDS patients. The number of infected people with T.
cruzi diminished from 18 million in 1991 to 6 million in 2010, but it is
still the most prevalent parasitic disease in the Americas.2 The two
drugs available for Chagas disease treatment, nifurtimox and benzni-
dazole require long-term treatment, which is associated to severe side
effects. Besides, nifurtimox is not approved by the FDA and benznida-
zole has been recently approved but only for recent infections in chil-
dren.3 In fact, until 2017, in the United States they were available only
from CDC under investigational protocols. The isoprenoid pathway has
been particularly useful for the identification of new targets against
trypanosomatids. Enzymes studied so far that are involved in the
synthesis of sterols and farnesyl diphosphate, and in protein prenyla-
tion, have been reported to be excellent drug targets against pathogenic
parasites.4–6 Certainly, the isoprenoid pathway constitutes a major
target for the treatment of parasitic diseases including Chagas disease,
toxoplasmosis and others. In this sense, we were able to established a
rigorous chemical structure/biological activity relationship on a vast
number aryloxyethyl thiocyanate as growth inhibitors of T. cruzi
⁎ Corresponding authors. Tel.: +54 11 5-285-8527; fax: +54 11 4-576-3346.
E-mail addresses: shs@qo.fcen.uba.ar (S.H. Szajnman), jbr@qo.fcen.uba.ar (J.B. Rodriguez).
https://doi.org/10.1016/j.bmc.2019.02.039
Received 24 December 2018; Received in revised form 15 February 2019; Accepted 18 February 2019
0968-0896/©2019ElsevierLtd.Allrightsreserved.
Pleasecitethisarticleas:MaríaN.Chao,etal.,Bioorganic&MedicinalChemistry,https://doi.org/10.1016/j.bmc.2019.02.039

M.N. Chao, et al.
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Fig. 1. Chemical structure of WC-9 and other closely related inhibitors of T. cruzi proliferation.
potassium cyanide in N,N-dimethylformamide gave rise to the title
compound 13. Similarly, 4-phenoxyphenol was reacted with 1,3-di-
bromopropane to produce 19, which on treatment with potassium cy-
anide gave rise to the target molecule 14 in excellent yields, as illu-
strated in Scheme 3.
Scheme 1. Precise mode of action of ebselen on S. pasteurii urease by forming a
selenium-sulfur bond.
Deleting of the terminal aromatic ring was another structural var-
iations considered. We have demonstrated that selenocyanates struc-
turally related to WC-9 were potent inhibitors of T. cruzi proliferation.
All of them had the corresponding terminal aromatic ring B with dif-
ferent substitution patterns.16 Therefore, the preparation of simplified
models of the reference structures 2–7 was done. In this case, the
phenyl group and substituted phenyl ring with an electron withdrawing
group and electron donor group was taken as molecular targets 20–22.
Scheme 4 shows the synthetic approach to access these molecules.
Conformationally constrained derivatives turned out to be ex-
tremely potent inhibitors of intracellular T. cruzi proliferation, in par-
ticular, compound ( )-8 which had been evaluated as a racemic
mixture (ED50 = 0.083 µM against intracellular T. cruzi),16 The biolo-
gical evaluation of each enantiomer (+)-8 and (−)-8 would seem of
interest in order to study if there is a molecular recognition preference
by a particular enantiomer. Therefore, there was a strong evidence to
believe that one particular enantiomer should have optimal space dis-
tribution and a better molecular recognition. It is well-established that a
rigid optimum conformer is quite beneficial for a particular biological
response.26 Therefore, the first approach that we took was a chiral re-
solution of alcohol ( )-35, a committed synthetic intermediate for the
preparation of the title compound ( )-8. In this context, the O-acetyl
mandelate derivatives of ( )-35 were prepared via a Steglich ester-
ification.27 Thus, on treatment with (S)-(-)-O-acetilmandelic acid (36)
and dicyclohexylcarbodiimide in the presence of 4-dimethylaminopyr-
idine, ( )-35 was converted into the diastereomeric mixture 37 and
38 in almost theoretical yield, as illustrated in Scheme 5. All attempts to
separate the diasteromers 37 and 38 were unsuccessful either under
classic column chromatography or preparative HPLC, both molecules
exhibiting similar chromatographic properties.
As these isosteric analogues of WC-9 had shown improved effec-
tiveness being an average of two order of magnitude more potent than
the thiocyanate counterpart (same non-polar skeleton),16 it was rea-
listic to consider their structural optimization taken into account that
all of these reference molecules possessed drug-like characteristics.19
Ebselen (2-phenyl-1,2-benzisoselenazol-3(2H)-one) is a selenium-
containing inhibitor of Sporosarcina pasteurii and Helicobacter pylori
ureases.20 It was postulated that the precise mode of action of ebselen
could be attributed to the formation of a covalent bond with cysteine
residue 322 of S. pasteurii urease acting at low nanomolar concentra-
tion, as shown in Scheme 1.21
2. Results and discussion
Bearing in mind that, positively, the selenium atom has a crucial
role on biological activity and the target enzyme (TcSQS) possesses nine
cysteine residues,22 it was reasonable to consider that the cellular ac-
tivity would be associated to the formation of a selenium-sulfur bond at
TcSQS. In this sense and based on our previous studies, it was very
important to study the influence of each part of the selenocyanate
moiety on biological activity. Therefore, compounds 9–12, where the
cyano group was replaced by trifluoromethyl moiety, were synthesized
to study its relevance on their biological action.23,24 The tri-
fluoromethyl unit is an electron withdrawing group as it is the cyano
unit. Then, the title compounds 9–12 were straightforwardly prepared
from thiocyanates 1 and 2 and selenocyanates 3 and 4 via a nucleo-
philic displacement of the cyano group by the corresponding trimethyl
(trifluoromethyl)silane via a Langlois-type reaction, as illustrated in
Scheme 2.23–25
Enzymatic kinetic resolution arose as an interesting approach to
separate both enantiomers of alcohol ( )-35. In this sense, Ramadas
and Krupadanam had described a kinetic resolution of structurally re-
lated homochiral alcohols (2-hydroxymethyl-2,3-dihydrobenzofuran
derivatives) by using a lipase from Pseudomonas cepacia and iso-
propenyl acetate as an acetyl donor.28 Therefore, ( )-35 treated with
lipase from P. cepacia and isopropenyl acetate employing acetonitrile as
a solvent at room temperature gave rise to (S)-alcohol 8 and the cor-
responding enriched acetate (R)-acetate 39 as illustrated in Scheme 6.
The reaction was monitored by HPLC with the aid of a chiral column
(analytical chiral column Lux 5µ Celullose-1 (4.60 mm × 25 cm) at a
flow rate of 1.0 mL/min) employing a mixture of acetonitrile–water
(7:3) as eluent. Fig. 2 shows the elution profile of the racemic mixture
As the selenium-containing compounds turned out to be very potent
growth inhibitors of intracellular T. cruzi, it seemed of interest to study
the influence of compounds where the selenium atom was absent on the
biological activity. Consequently, compound 13 and 14 were synthe-
sized by deleting the selenium atom or by replacing it by a methylene
group. These target molecules were straightforwardly synthesized em-
ploying 4-phenoxyphenol (15) as starting material via the already de-
scribed alcohol 17,8 which was treated with N-bromosuccinimide and
triphenyl phosphine to produce the bromide 18 that treated with
(
)-35. In fact, under these chromatographic conditions we were able
to separate both enantiomers ( )-35 into the (R)-(+)-35 and (S)-
(−)-35 enantiomers, which could be eluted at retention times of
5.92 min and 6.45 min, respectively.
In addition, we were able to solve the racemic mixture of acetates
(
)-39 into its enantiomers employing the same HPLC chiral column
and the corresponding chromatographic conditions as illustrated in
Fig. 3. Once again, each enantiomer could be resolved into the (S)-
Scheme 2. Preparation of trifluoromethyl derivatives of WC-9.
2

M.N. Chao, et al.
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Scheme 3. Synthesis of WC-9 derivatives where the sulfur or selenium atoms are missing.
Scheme 4. Synthetic strategy to access simplified analogues of selenium-containing analogues of WC-9.
Scheme 5. Formation of O-acetyl mandelates from racemic alcohol ( )-35 following a Steglich approach.
Scheme 6. Kinetic resolution approach to resolve the racemic mixture ( )-35.
(−)-39 and (R)-(+)-39 isomers with retention times of 7.68 min and
8.34 min, respectively.
alcohol reacted more slowly (tR = 6.45 min), which gave rise to the
corresponding acetate (S)-(−)-39 (tR = 7.68 min).
It is worth mentioning that each of the four compounds involved in
the lipase-catalyzed kinetic resolution of alcohol ( )-35 could be se-
parated by analytical HPLC resulting an excellent tool to monitor this
enzymatic reaction. Thus, samples of the reaction mixture were taken
every 30 min and analyzed by analytical HPLC. The (R)-alcohol would
react faster than its (S)-enantiomer according to the chemical behavior
of quite similar structurally related homochiral alcohols such as
Employing long reaction times (330 min), we were able to obtain,
after purification by column chromatography, the (S)-alcohol with an
enantiomeric excess of 84% and 22% yield and the (R)-enriched mix-
ture of acetates 39.
The obtainment of the (R)-alcohol was conducted by hydrolysis of
the (R)-enriched mixture of enantiomeric acetates 39 by treatment with
potassium carbonate employing a mixture of methanol–water as a sol-
vent to yield quantitatively the (R)-enriched alcohol 35, which was
reacted under the same reaction conditions (lipase-catalyzed acetyla-
tion) to give a much more (R)-enriched acetate 39. The protocol was
repeated four times producing the corresponding (R)-alcohol. In sum-
mary, after five turnovers of this lipase-mediated reaction it was pos-
sible the obtainment of (R)-(−)-35 in (ee) 82% of enantiomeric excess
and 38% yield. Table 1 reviews this achievement.
(
)-40a-j whose structure are drawn in Scheme 7.28,29 Therefore,
from the analysis of the chromatograms versus time illustrated in Fig. 4
it was possible to assign each enantiomer bearing in mind that the (R)-
enantiomer would be acetylated faster than its corresponding (S)-en-
antiomer. In this sense, it was observed an area decrease of alcohol (R)-
(+)-35 (tR = 5.93 min) with a concomitant area increase of the acetate
assigned as the (R)-acetate (R)-(+)-39 (tR = 8.34 min). The (S)-(−)-35
3

M.N. Chao, et al.
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Fig. 2. Elution profile for the resolution of the racemic mixture ( )-35 into its enantiomers.
Fig. 3. Elution profile of the racemic mixture of acetate ( )-39 employing a chiral Lux 5µ Celullose-1 column.
Scheme 7. Lipase-catalyzed resolution of homochiral alcohol structurally related to ( )-35.
It is important to mention that the racemic mixture ( )-35 is a
We demonstrated that the position of the phenoxy group at the C-4′
position, as it was the case of compounds 1 and 3, was not an essentially
required substitution pattern for biological activity bearing in mind that
the regioisomers where the phenoxy moiety was bonded at the C-3′
position such as 2 and 5 exhibited similar or even better inhibitory
action than 1 and 3.10,16 For the above reasons it seemed reasonable the
study the antiparasitic activity of the C-2′ regiosiomers 43 and 44
whose preparation is described in Scheme 9. Then, the target molecules
43 and 44 were successfully synthesized starting from 2-iodophenol
(45), which was reacted with benzyl bromide to yield the protected
phenol 46. This compound was the substrate of the Buchwald coupling
reaction,30–34 a key reaction step in this synthetic approach. Therefore,
on reaction with phenol in the presence of copper(I) iodide, picolinic
solid (mp = 48 °C), initially depicted as an oil,16 but each isolated en-
antiomer was obtained as an oil. For that reason, further crystal-
lographic studies to unambiguously establish the absolute configuration
of each enantiomers resulted irrelevant. It is well-known that Mosher’s
esters are not satisfactory to predict the absolute configuration in pri-
mary homochiral alcohols.
Once both homochiral alcohols were at hand, each compound was
treated with tosyl chloride in pyridine at 0 °C to produce the corre-
sponding chiral tosylates (S)-(+)-42 and (R)-(−)-42, respectively,
which on reaction with potassium selenocyanate in the presence of 18-
crown-6 were further converted into the title compounds (S)-(+)-8 and
(R)-(−)-8 as shown in Scheme 8.
4

M.N. Chao, et al.
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bromoethyl tetrahydropyranyl ether yielded 49. The tetrahydropyranyl
protecting group present in 49 was removed by treatment with pyr-
idinium 4-toluenesulfonate producing the corresponding alcohol 50 in
86% yield, which was tosylated to give 51 in 61% yield. On treatment
with potassium selenocyanate this compound was transformed into the
target molecule 43, whereas on treatment with potassium thiocyanate,
tosylate 51 was converted into the title compound 44.
Biological evaluation of these new isosteric analogues of WC-9 was
very encouraging from the point of view of molecular reconition. Title
compounds 9–12, where the cyano moiety in lead structures 1–3 and 5
was replaced by a trifluoromethyl group, were devoid of antiparasitic
activity against intracellular T. cruzi indicating that the cyano part ei-
ther of the selenocyanate or thiocyante play a crucial role on biological
activity. The cyano group has an electrophilic center at the carbon atom
and is a hydrogen bond acceptor due to the lone pair of electrons at the
nitrogen atom.
Interestingly, cyanides 13 and 14 were inactive molecules as in-
hibitors of T. cruzi proliferation suggesting that the presence of the
selenium or the sulfur atoms is vital for biological action and the ex-
istence of the cyano group is not sufficient to warrant antiparasitic
activity.
Fig. 4. Analytical HPLC 2D elution profile of alcohol ( )-35 and acetate
The simple selenocyanate derivatives such as 20–22 are interesting
molecules where the terminal aromatic ring B was absent but contained
the pharmacophoric structure (aryloxyethyl selenocyanate) to warrant
a pharmacological response. Surprisingly these compounds exhibited
vanishing antiparasitic activity and also resulted to be cytotoxic against
Vero cells.
(
)-39 employing a chiral column to monitor lipase-catalyzed acetylation
reaction of alcohol ( )-35.
Table 1
Retention times (tR), enantiomeric excess (ee), specific optical rotations ([ ]2D3
and reaction yields for (S)-35 and (R)-35.
)
The conformationally rigid ( )-8 is a potent growth inhibitor of
the intracellular form of T. cruzi showing ED50 values at the low na-
nomolar concentrations (0.083 µM) and selectivity index value >
1500.16 Consequently, the attempt to solve this racemic mixture into its
enantiomers was quite sound considering that only one of them would
be responsible for the antiparasitic activity. Unexpectedly, both en-
antiomers (S)-8 and (R)-8 exhibited practically the same inhibition
potency against amastigotes of T. cruzi.
Compound
tR (min)
ee (%)
Yield (%)
[
]
2D3(CHCl3)
(S)-35
(R)-35
6.45
5.92
84
82
+43.6
−45.1
22
39
acid and potassium phosphate tribasic employing dimethyl sulfoxide as
a solvent at 80 °C for 5 days, 46 was converted into 47 in a low but
reproducible yield. Cleavage of the benzyl group of 47 was performed
by treatment with hydrogen in the presence of palladium on charcoal as
catalyst to give rise to 48 in theoretical yield, which treated with
Finally, the regioisomers of the lead structures 1–3 and 5, that is, 43
and 44 where the phenoxy group was attached at the C-2′ position were
free of anti-T. cruzi activity providing further insights into the chemical
structure-biological activity relationship. Work aimed at exploiting the
prospective antiparasitic activity of selenocyanate derivatives
Scheme 8. Synthetic approach for the pre-
paration of chiral conformationally con-
strained selenocyanates (S)-(+)-8 and (R)-
(−)-8.
Scheme 9. Synthetic approach for the preparation of regioisomers of WC-9 bearing the terminal aromatic ring at the C-2′ position.
5

M.N. Chao, et al.
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Table 2
Rf = 0.73 (hexane–AcOEt, 4:1); IR (film, cm−1) 1589, 1496, 1215,
1091, 1070, 738, 691, 511; 1H NMR (500.13 MHz, CDCl3) δ 3.26 (t,
J = 6.5 Hz, 2H, H-1), 4.23 (t, J = 6.5 Hz, 2H, H-2), 6.88 (d, J = 9.1 Hz,
2H, H-2′), 6.95 (dd, J = 8.7, 1.0 Hz, 2H, H-2″), 6.98 (d, J = 9.1 Hz, 2H,
H-3′), 7.05 (tt, J = 7.3, 1.1 Hz, 1H, H-4″), 7.31 (dd, J = 8.6, 7.4, 2H, H-
3″); 13C NMR (125.77 MHz, CDCl3) δ 29.1 (q, J = 2.1 Hz, C-1), 67.1 (C-
2), 115.8 (C-2″), 117.8 (C-2′), 120.8 (C-3′), 122.6 (C-4″), 129.7 (C-3″),
130.9 (q, J = 306.2 Hz, SCF3), 150.91 (C-4′); 154.3 (C-1′), 158.2 (C-1″);
19F NMR (470.59 MHz; CDCl3) δ −41.17 ppm. HRMS (ESI) calcd. for
Growth inhibitory effect of selenocyanates derivatives and closely related mo-
lecules against intracellular T. cruzi.
Compound
T. cruzi (amastigotes) ED50 (µM)a
Cytotoxicity ED50 (µM)b
9
> 10 µM 12% at 10 µM
> 1 µM 6.7% at 1.0 µM
> 10 µM
> 20
10
> 20
11
> 20
12
> 1 µM 30.9% at 1.0 µM
> 10.0 µM
> 20
13
> 20
C
15H14F3O2S [M+H]+ 315.0667; found 315.0662.
14
> 10.0 µM
> 20
20
> 10.0 µM, no inhibition at 6 µM
> 10.0
**cytotoxic at 20 µM, 15 µM
21
**cytotoxic at 20 µM
3.2. (2-(3-Phenoxyphenoxy)ethyl)(trifluoromethyl)sulfane (10)
22
3.87
1.3
**cytotoxic at 20 µM, 15 µM
(S)-8
(R)-8
0.141
0.096
0.0939
0.02
> 20
> 20
> 20
> 20
> 20
> 10
0.014
0.025
To a solution of WC-9 (50.0 mg, 0.18 mmol) in acetonitrile (2.0 mL)
in the presence of cesium carbonate (59.9 mg, 0.18 mmol) was treated
with trifluoromethyltrimethylsilane (39.2 mg, 40.8 µL, 0.28 mmol) as
described for the preparation of 9. The product was purified by column
chromatography (silica gel) eluting with a mixture of hexane–EtOAc
(99:1) to give 25.5 mg (44% yield) of 10 as a colorless oil: Rf = 0.67
(hexane–EtOAc, 4:1); IR (film, cm−1) 1585, 1484, 1214, 1105, 1028,
759, 687; 1H NMR (500.13 MHz, CDCl3) δ 3.27 (t, J = 6.5 Hz, 2H, H-1),
4.21 (t, J = 6.5 Hz, 2H, H-2), 6.59 (t, J = 2.3 Hz, 1H, H-2′), 6.66 (m,
2H, H-4′, H-6′), 7.06 (dd, J = 8.7, 1.1 Hz, 2H, H-2″), 7.15 (tt, J = 7.4,
1.1 Hz, 1H, H-4″), 7.26 (t, J = 8.2 Hz, 1H, H-5′), 7.38 (dd, J = 8.6,
7.4 Hz, 2H, H-3″); 13C NMR (125.77 MHz; CDCl3) δ 28.9 (q, J = 2.1 Hz,
C-1), 66.6 (C-2), 105.5 (C-2′), 109.2 (C-6′), 111.7 (C-4′), 119.2 (C-2″),
123.6 (C-4″), 129.8 (C-3″), 130.3 (C-5′), 130.9 (q, J = 306.2 Hz, SCF3),
156.8 (C-1″), 158.7 (C-1′), 159.4 (C-4′); 19F NMR (470.59 MHz, CDCl3)
(
)-8
43
44
> 10.0, 33% at 10.0 µM
> 10.0, 33% at 10.0 µM
benznidazole
2.48
0.45
a
The values are means
S.D. of 3 independent biological replicates, each
one done with 4 technical replicates.
b
The results are from three biological replicates, each one with 4 technical
replicates. Vero cells were used and treatment, was for 72 h. Cytotoxicity was
determined by visualization of cell detachment by optical microscopy or by
using a BioTek plate reader as described by Recher et al., 2013.35
covalently bonded to a non-polar skeleton is currently being pursued in
our laboratory (Table 2).
δ
−41.19 ppm. HRMS (ESI) calcd. for
C
15H14F3O2S [M+H]+
3. Experimental
315.0667; found 315.0662.
The glassware used in air- and/or moisture-sensitive reactions was
flame dried, and the reactions were performed under a dry argon at-
mosphere. Unless otherwise noted, chemicals were commercially
available and were used without further purification. Anhydrous N,N-
dimethylformamide and anhydrous dimethyl sulfoxide were used as
supplied from Aldrich. Nuclear magnetic resonance spectra were ob-
tained using a Bruker Fourier 300 machine, or using a Bruker AM-
500 MHz apparatus or using a Bruker Avance NEO 500 spectrometer.
Chemical shifts are reported in parts per million δ relative to tetra-
methylsilane. 13C NMR spectra were fully decoupled. High-resolution
mass spectra were carried out by using a Bruker micrOTOF-Q II spec-
trometer, which is a hybrid quadrupole time of flight mass spectrometer
with MS–MS capability. Melting points were determined by using a
Fisher–Johns apparatus. Column chromatography was performed with
E. Merck silica gel plates (Kieselgel 60, 230–400 mesh). Analytical thin-
layer chromatography was done by employing 0.2 mm coated com-
mercial silica gel plates (E. Merck, DC-Aluminum sheets, Kieselgel 60
3.3. (2-(4-Phenoxyphenoxy)ethyl)(trifluoromethyl)selane (11)
To a solution of WC-9-Se (50.0 mg, 0.16 mmol) in acetonitrile
(2.0 mL) in the presence of cesium carbonate (61.2 mg, 0.19 mmol) was
treated
with
trifluoromethyltrimethylsilane
(33.5 mg,
35 µL,
0.24 mmol) as described for the preparation of 9. The reaction mixture
was stirred for 4 h. The product was purified by column chromato-
graphy (silica gel) employing a mixture of hexane–EtOAc (99:1) as
eluent to produce 34.2 mg (60% yield) of 11 as a white solid;
mp = 29 °C; Rf = 0.59 (hexane–EtOAc, 4:1); 1H NMR (500.13 MHz,
CDCl3) δ 3.33 (t, J = 6.4 Hz, 2H, H-1), 4.30 (t, J = 6.5 Hz, 2H, H-2),
6.88 (d, J = 9.1 Hz, 2H, H-2′), 6.95 (dd, J = 8.7, 1.1 Hz, 2H, H-2″), 6.98
(d, J = 9.1 Hz, 2H, H-3′), 7.05 (tt, J = 7.6, 1,1 Hz, 1H, H-4″), 7.30 (dd,
J = 8.7, 7.4 Hz, 2H, H-3″); 13C NMR (125.77 MHz, CDCl3) δ 24.2 (q,
J = 1.6 Hz, C-1), 67.6 (C-2), 115.8 (C-2″), 117.8 (C-2′), 120.8 (C-3′),
122.5 (q, J = 330.4 Hz, SeCF3), 122.6 (C-4″), 129.6 (C-3″), 150.9 (C-4′),
154.3 (C-1′), 158.2 (C-1″); 19F NMR (470.59 MHz, CDCl3)
δ
F254).
As judged from the homogeneity of the 1H, 13C, 19F and 77Se NMR
−34.26 ppm; 77Se NMR (95.38 MHz; CDCl3)
δ 434.30 ppm (q,
J = 8.2 Hz). HRMS (ESI) calcd. for C15H14F3O2Se [M+H]+ 363.0111;
spectra and HPLC analyses of the title compounds employing a
Beckmann Ultrasphere ODS-2 column 5 μM, 250 × 10 mm eluting with
acetonitrile–water (9:1) at 3.00 mL/min with a refractive index detector
indicated a purity > 97%.
found 363.0115.
3.4. (2-(3-Phenoxyphenoxy)ethyl)(trifluoromethyl)selane (12)
3.1. (2-(4-Phenoxyphenoxy)ethyl)(trifluoromethyl)sulfane (9)
To a solution of WC-9-Se (50.0 mg, 0.16 mmol) in acetonitrile
(2.0 mL) in the presence of cesium carbonate (61.2 mg, 0.19 mmol) was
treated with trifluoromethyltrimethylsilane (33.5 mg, 35.0 µL,
0.24 mmol) as depicted for the preparation of 9. The product was
purified by column chromatography (silica gel) eluting with a mixture
of hexane–EtOAc (99:1) to give 38.5 mg (68% yield) of 12 as a colorless
oil: Rf = 0.61 (hexane–EtOAc, 4:1); IR (film, cm−1) 1584, 1490, 1214,
1092, 738, 682; 1H NMR (500.13 MHz, CDCl3) δ 3.30 (t, J = 6.5 Hz,
2H, H-1), 4.28 (t, J = 6.5 Hz, 2H, H-2), 6.56 (t, J = 2.3 Hz, 1H, H-2′),
6.62 (m, 2H, H-4′, H-6′), 7.02 (dd, J = 8.7, 1.0 Hz, 2H, H-2″), 7.12 (tt,
J = 7.4, 1.0 Hz, 1H, H-4″), 7.22 (t, J = 8.3 Hz, 1H, H-5′), 7.34 (dd,
J = 8.7, 7.3 Hz, 2H, H-3″); 13C NMR (125.77 MHz, CDCl3) δ 24.0 (q,
To a solution of WC-9 (50.0 mg, 0.18 mmol) in acetonitrile (2 mL) in
the presence of cesium carbonate (59.9 mg, 0.18 mmol) was added
trifluoromethyltrimethylsilane (39.2 mg, 40.8 µL, 0.28 mmol) under an
argon atmosphere. The reaction mixture was stirred at room tempera-
ture for 24 h. Then, water (30 mL) was added and the mixture was
extracted with methylene chloride (3 × 20 mL). The combined organic
layers were washed with brine (3 × 20 mL), dried (MgSO4) and the
solvent was evaporated. The product was purified by column chroma-
tography (silica gel) eluting with a mixture of hexane–EtOAc (49:1) to
give 32.3 mg (56% yield) of compound 9 as a white solid: mp = 29 °C;
6

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J = 1.6 Hz, C-1), 67.1 (C-2), 105.5 (C-2′), 109.3 (C-6′), 111.6 (C-4′),
119.2 (C-2″), 122.5 (q, J = 330.5 Hz, SeCF3), 123.5 (C-4″), 129.8 (C-
3″), 130.3 (C-5′), 156.8 (C-1″), 158.6 (C-1′), 159.4 (C-4′); 19F NMR
(470.59 MHz, CDCl3) δ −34,28 ppm; 77Se NMR (95.38 MHz; CDCl3) δ
434.61 (q, J = 8.1 Hz). HRMS (ESI) calcd. for C15H14F3O2Se [M+H]+
363.0111; found 363.0087.
3.8. 3-(4-Phenoxyphenoxy)propyl cyanide (14)
A
solution of 19 (42.4 mg, 0.14 mmol) in anhydrous N,N-di-
methylformamide (3 mL) was treated with potassium cyanide (42.4 mg,
0.65 mmol). The reaction mixture was stirred at 80 °C for 1 h. The re-
action was quenched as depicted for the preparation of 13. The product
was purified by column chromatography (silica gel) employing a mix-
ture of hexane–EtOAc (19:1) to produce 33.5 mg (96% yield) of 14 as a
colorless oil: Rf = 0.31 (hexane–EtOAc, 4:1); IR (film, cm−1) 2248,
1503, 1487, 1214, 841, 754, 691; 1H NMR (300.18 MHz, CDCl3) δ 2.17
(m, 2H, H-2), 2.62 (t, J = 7.1 Hz, 2H, H-1), 4.06 (t, J = 5.7 Hz, 2H, H-
3), 6.89 (d, J = 9.1 Hz, 2H, H-2′), 6,98 (m, 4H, H-2″, H-3′); 7.05 (tt,
J = 7.4, 1.1 Hz, 1H, H-4″), 7.30 (dd, J = 8.6, 7.4 Hz, 2H, H-3″); 13C
NMR (75.48 MHz, CDCl3) δ 14.2 (C-1), 25.5 (C-2), 65.8 (C-3), 115.5 (C-
2″), 117.7 (C-2′), 119.2 (CN), 120.8 (C-3′), 122.6 (C-4″), 129.6 (C-3″),
150.6 (C-4′), 154.6 (C-1′), 158.3 (C-1″). HRMS (ESI) calcd. for
3.5. 4-Phenoxphenoxyethyl bromide (18)
A solution of 178 (369 mg, 1.60 mmol) in methylene chloride (5 mL)
cooled at 0 °C was treated with triphenylphosphine (463 mg,
1.76 mmol) and N-bromosuccinimide (313 mg, 1.76 mmol). The reac-
tion mixture was stirred at room temperature for 2 h. Then, water
(25 mL) was added and the resulting mixture was extracted with me-
thylene chloride (3 × 15 mL). The combined organic layers were wa-
shed with brine (3 × 50 mL), dried (MgSO4), and the solvent was
evaporated. The residue was purified by column chromatography (silica
gel) employing a mixture of CH2Cl2–methanol (24:1) to give 348 mg
(74% yield) of 18 as a colorless oil: Rf = 0.60 (AcOEt-methanol, 4:1);
1H NMR (300.18 MHz, CDCl3) δ 3.64 (t, J = 6.1 Hz, 2H, H-1), 4.28 (t,
J = 6.3 Hz, 2H, H-3), 6.90 (d, J = 9.2 Hz, 2H, H-2′), 6.98 (m, 2H, H-2″),
6.98 (d, J = 9.2 Hz, 2H, H-3′), 7.05 (tt, J = 7.4, 0.9 Hz, 1H, H-4″), 7.30
(dd, J = 8.6, 7.4, 2H, H-3″); 13C NMR (75.48 MHz, CDCl3) δ 29.1 (C-1),
68.5 (C-2), 116.0 (C-2″), 117.8 (C-2′), 120.7 (C-3′), 122.6 (C-4″), 129.6
(C-3″), 150.9 (C-4′), 154.3 (C-1′), 158.2 (C-1″).
C
16H15NNaO2 [M+Na]+ 276.1000; found 276.0994.
3.9. 4-Methoxyphenoxyethyl tetrahydro-2H-pyran-2-yl ether (26)
To a solution of 4-methoxyphenol (700 mg, 5.64 mmol) in methyl
sulfoxide (5 mL) was added potassium hydroxide (634 mg, 11.3 mmol).
The reaction mixture was stirred at room temperature for 10 min. Then,
2-(2-bromoethoxy)-tetrahydro-2H-pyrane (1.18 g, 5.64 mmol) was
added and the reaction mixture was stirred at room temperature
overnight. The reaction was worked up as described for the preparation
of 18 yielding 1.34 g (94% yield) of 26 (colorless oil), which was used
as such in the next step: Rf = 0.50 (hexane–EtOAc, 4:1); 1H NMR
(300.18 MHz, CDCl3) δ 1.52–1.68 (m, 4H, H-4″, H-5″), 1.71–1.77 (m,
1H, H-3″a), 1.79–1.89 (m, 1H, H-3″b), 3.54 (m, 1H, H-6″a), 3.77 (s, 3H,
OCH3), 3.83 (m, 1H, H-6″b), 3.89 (m, 1H, H-1a), 3.92 (m, 1H, H-1a),
4.05 (m, 1H, H-1b), 4.13 (m, 2H, H-2), 4.70 (dist t, J = 3.6 Hz, 1H, H-
2″), 6.84 (d, J = 9.4 Hz, 1H, H-2′), 6.90 (d, J = 9.4 Hz, 1H, H-3′); 13C
NMR (75.48 MHz, CDCl3) δ 19.4 (C-4″), 25.4 (C-5″), 30.5 (C-3″), 55.7
(OCH3), 62.2 (C-1), 65.9 (C-6″), 68.1(C-2), 99.0 (C-2″), 114.6 (C-3′),
115.7 (C-2′), 153.1 (C-1′), 153.9 (C-4′).
3.6. 4-Phenoxyphenoxyethyl cyanide (13)
To a solution of 18 (348 mg, 1.20 mmol) in anhydrous N,N-di-
methylformamide (3 mL) was added potassium cyanide (234 mg,
3.60 mmol) and the reaction mixture was stirred at 80 °C for 1 h. Then,
the reaction was allowed to cool to room temperature and water
(20 mL) was added and the mixture was extracted with methylene
chloride (3 × 20 mL). The combined organic phases were washed with
brine (3 × 20 mL), dried (MgSO4), and the solvent was evaporated. The
product was purified by column chromatography (silica gel) employing
a mixture of hexane–EtOAc (87:13) as eluent to produce 101 mg (35%
yield) of 13 as a white solid: mp = 67 °C; Rf = 0.21 (hexane–EtOAc,
4:1); 1H NMR (300.18 MHz, CDCl3) δ 2.83 (t, J = 6.4 Hz, 2H, H-1), 4.19
(t, J = 6.4 Hz, 2H, H-2), 6.89 (d, J = 9.2 Hz, 2H, H-2′), 6,97 (dd,
J = 8,7; 1,1 Hz, 2H, H-2″); 6.99 (d, J = 9.2 Hz, 2H, H-3′); 7.06 (tt,
J = 7.4, 1.1 Hz, 1H, H-4″), 7.31 (dd, J = 8.6, 7.6 Hz, 2H, H-3″); 13C
NMR (75.48 MHz, CDCl3) δ 18.7 (C-1); 63.3 (C-2), 116.0 (C-2″), 117.2
(CN), 117.9 (C-2′), 120.8 (C-3′), 122.2 (C-4″), 129.7 (C-3″), 151.3 (C-
4′), 153.9 (C-1′), 158.1 (C-1″). HRMS (ESI) calcd. for C15H14NO2 [M
+H]+ 240.1025; found 240.1013.
3.10. 4-Metoxyphenoxyethanol (29)
A solution of 23 (1.33 g, 5.27 mmol) in methanol (15 mL) was
treated with pyridinium 4-toluenesulfonate (30 mg). The reaction
mixture was stirred at room temperature overnight. Then, water
(50 mL) was added and the mixture was extracted with methylene
chloride (3 × 50 mL). The combined organic layers were washed with
brine (3 × 50 mL), dried (MgSO4), and the solvent was evaporated to
produce 885 mg (100% yield) of pure alcohol 29 as a yellow pale solid:
mp = 65 °C; Rf = 0.11 (hexane–EtOAc, 4:1); 1H NMR (300.18 MHz,
CDCl3) δ 2.05 (br s, 1H, OH), 3.79 (s, 3H, OCH3), 3.96 (m, 2H, H-1),
4.06 (dd, J = 5.1, 3.4 Hz, 2H, H-2), 6.87 (m, 4H, H-2′, H-3′); 13C NMR
(75.48 MHz, CDCl3) δ 55.8 (OCH3), 61.6 (C-1), 69.9 (C-2), 114.7 (C-3′),
115.6 (C-2′), 152.7 (C-1′), 154,1 (C-4′).
3.7. 3-(4-Phenoxyphenoxy)propyl bromide (19)
A solution of 4-phenoxyphenol (15; 300 mg, 1.61 mmol), potassium
carbonate (334 mg, 2.41 mmol) and potassium iodide (53 mg,
0.32 mmol) in acetone (8 mL) was treated with 1,3-dibromopropane
(975 mg, 490 µL, 4.83 mmol). The reaction mixture was stirred at room
temperature for 3 days. The solvent was evaporated and the product
was purified by column chromatography (silica gel) eluting with a
mixture of hexane–EtOAc (99:1) to give 331 mg (67% yield) of 19 as a
colorless oil: Rf = 0.65 (hexane–EtOAc, 4:1); 1H NMR (300.18 MHz,
CDCl3) δ 2.32 (p, J = 6.1 Hz, 2H, H-2), 3.62 (t, J = 6.4 Hz, 2H, H-1),
4.09 (t, J = 5.8 Hz, 2H, H-3), 6.88 (d, J = 9.1 Hz, 2H, H-2′), 6.94 (m,
4H, H-2″, H-3′), 7,04 (tt, J = 7.4, 1.0 Hz, 1H, H-4″), 7.30 (dd, J = 8.6,
7.4, 2H, H-3″); 13C NMR (75.48 MHz, CDCl3) δ 30.0 (C-2), 32.4 (C-1),
65.8 (C-3), 115.6 (C-2″), 117.7 (C-2′), 120.8 (C-3′), 122.5 (C-4″), 129.6
(C-3″), 150.4 (C-4′), 155.0 (C-1′), 158.4 (C-1″).
3.11. 4-Methoxyphenoxyethyl 4-toluenesulfonate (32)
A solution of alcohol 29 (884 mg, 5.25 mmol) in pyridine (3 mL)
was treated with p-toluenesulfonyl chloride (546 mg, 2.9 mmol) at 0 °C
and the mixture was stirred at 0 °C for 4 h. Then, 5% HCl (50 mL) was
added and the reaction mixture was stirred for an additional hour. The
mixture was partitioned between methylene chloride (50 mL) and
water (50 mL). The organic layer was washed with 5% HCl (3 × 50 mL)
and water (3 × 50 mL). The organic phase was dried (MgSO4) and the
solvent was evaporated. The product was purified by column chroma-
tography (silica gel) employing a mixture of hexane–EtOAc (4:1) as
eluent to produce 1.46 g of 32 (86% yield) as a white solid: mp = 89 °C;
Rf = 0.28 (hexane–EtOAc, 4:1); 1H NMR (300.18 MHz; CDCl3) δ 2.45
(s, 3H, PhCH3), 3.76 (s, 3H, OCH3), 4,10 (m, 2H, H-1); 4346 (m, 2H, H-
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2); 6.72 (d, J = 9.3 Hz, 2H, H-3′), 6.79 (d, J = 9.3 Hz, 2H, H-2′), 7.34
(d, J = 8.4 Hz, 2H, H-3″), 7.82 (d, J = 8.3 Hz, 2H, H-2″); 13C NMR
(75.48 MHz, CDCl3) δ 21.6 (PhCH3), 55.7 (OCH3), 66.3 (C-1), 68.2 (C-
2), 114.6 (C-3′), 115.8 (C-2′), 128.0 (C-2″), 129.8 (C-3″), 132.9 (C-4″),
144.9 (C-1″), 152.1 (C-1′), 154.3 (C-4′).
2″); 13C NMR (75.48 MHz, CDCl3) δ 21.7 (PhCH3), 65.3 (C-1), 68.1 (C-
2), 114.5 (C-2′), 121.4 (C-4′), 128.0 (C-2″), 129.5 (C-3′), 129.8 (C-3″),
132.9 (C-4″), 144.9 (C-1″), 158.0 (C-1′).
3.16. Phenoxyethyl selenocyanate (21)
3.12. 4-Methoxyphenoxyethyl selenocyanate (20)
A solution of 33 (1.53 g, 5.22 mmol) in anhydrous tetrahydrofuran
(10 mL) was treated with potassium selenocyanate (828 mg,
5.74 mmol) in the presence of 18-crown-6 (13.8 mg) according to the
preparation of compound 20. The product was purified by column
chromatography (silica gel) employing a mixture of hexane–EtOAc
(9:1) as eluent to give 1.08 g (92% yield) of 21 as a white solid:
mp = 49 °C; Rf = 0.44 (hexane–EtOAc, 4:1); 1H NMR (500.13 MHz,
CDCl3) δ 3.44 (t, J = 6.0 Hz, 2H, H-1), 4.39 (t, J = 6.0 Hz, 2H, H-2),
6.92 (dd, J = 8.8, 1.0 Hz, 2H, H-2′), 7.01 (tt, J = 7.6, 1.0 Hz, 1H, H-4′),
7.31 (dd, J = 8.8, 7.4 Hz, 2H, H-3′); 13C NMR (125.77 MHz, CDCl3) δ
28.2 (C-1), 66.4 (C-2), 101.2 (SeCN), 114.7 (C-2′), 121.8 (C-4′), 129.7
(C-3′), 157.7 (C-1′); 77Se NMR (95.38 MHz, CDCl3) δ 191.67 ppm.
HRMS (ESI) calcd. for C9H9NNaOSe [M+Na]+ 249.9747; found
249.9732.
A solution of tosylate 32 (1.45 g, 4.36 mmol) in anhydrous tetra-
hydrofuran (30 mL) was treated with potassium selenocyanate (681 mg,
4.8 mmol) in the presence of 18-crown-6 (0.1 mmol) and the reaction
mixture was refluxed for 10 h. The solution was cooled to room tem-
perature and the mixture was partitioned between brine (50 mL) and
methylene chloride (30 mL). The aqueous phase was extracted with
methylene chloride (3 × 25 mL). The combined organic layers were
dried (MgSO4) and the solvent was evaporated. The product was pur-
ified by column chromatography (silica gel) employing a mixture of
hexane–EtOAc (97:3) to give 826 mg (74% yield) of 20 as a white solid:
mp = 40 °C; Rf = 0.30 (hexane–AcOEt, 4:1); 1H NMR (500.13 MHz,
CDCl3) δ 3.41 (t, J = 6.0 Hz, 2H, H-1), 3.77 (s, 3H, OCH3), 4.33 (t,
J = 6.0 Hz, 2H, H-2), 6.88 (mAB, 4H, H-2′
y
H-3′); 13C NMR
(125.77 MHz; CDCl3) δ 28.3 (C-1), 55.7 (OCH3), 67.3 (C-2), 101.3
(SeCN), 114.8 (C-3′), 115.9 (C-2′), 151.8 (C-1′), 154.6 (C-4′); 77Se NMR
3.17. 4-Nitrophenoxyethyl tetrahydro-2H-pyran-2-yl ether (28)
(95.38 MHz, CDCl3)
δ
190.46 ppm. HRMS (ESI) calcd. for
C
10H11NNaO2Se [M+Na]+ 279.9853; found 279.9854.
To a solution de 4-nitrophenol (700 mg, 5.03 mmol) in di-
methylsulfoxide (5 mL) was added potassium hydroxide (565 mg,
10.1 mmol). The mixture was stirred at room temperature for 10 min.
Then, 2-bromoethyl tetrahydropyranyl ether (1.05 g, 5.03 mmol) was
added as described for the preparation of 26. The product was purified
by column chromatography (silica gel) eluting with hexane–EtOAc
(21:4) to give 366 mg (27% yield) of compound 28 as a colorless oil:
3.13. Phenoxyethyl tetrahydro-2H-pyran-2-yl ether (27)
A solution of phenol (700 mg, 5.44 mmol) in methyl sulfoxide
(5 mL) was treaded with potassium hydroxide (835 mg, 14.9 mmol) as
depicted for the preparation of compound 26. After the usual work-up
1.50 g of 27 were obtained (90% yield) as a colorless oil, which was
used as such in the next step: Rf = 0.53 (hexane–EtOAc, 4:1); 1H NMR
(300.18 MHz, CDCl3) δ 1.52–1.68 (m, 4H, H-4″, H-5″), 1.70–1.77 (m,
1H, H-3″a), 1.79–1.91 (m, 1H, H-3″b), 3.55 (m, 1H, H-6″a), 3.85 (ddd,
J = 11.0, 6.2, 4.7 Hz, 1H, H-6″b), 3.93 (ddd, J = 11.4, 8.0. 3.5 Hz, 1H,
H-1a), 4.07 (dt, J = 11,1; 4,6 Hz, 1H, H-1b), 4.18 (m, 2H, H-2), 4.71
(dist t, J = 3.5 Hz 1H, H-2″), 6.96 (m, 3H, H-2′, H-4′), 7.29 (m, 2H, H-
3′); 13C NMR (75,48 MHz; CDCl3) δ 19.4 (C-4″), 25.4 (C-5″), 30.5 (C-
3″), 62.2 (C-1), 65.9 (C-6″), 67.3 (C-2), 99.0 (C-2″), 114.7 (C-2′), 120.8
(C-4′), 129.4 (C-3′) 158.9 (C-1′).
Rf = 0.28 (hexane–AcOEt, 4:1); 1H NMR (300.18 MHz, CDCl3)
δ
1.53–1.66 (m, 4H, H-4″, H-5″), 1.71–1.76 (m, 1H, H-3″a), 1,79–1,88 (m,
1H, H-3″b), 3.55 (m, 1H, H-6″a), 3.88 (m, 2H, H-6″b, H-1a), 4.11 (dt,
J = 11.6, 4.5 Hz, 1H, H-1b), 4.27 (m, 2H, H-2), 4.72 (dd, J = 3.9,
2.8 Hz, 1H, H-2″), 7.00 (d, J = 9.3 Hz, 1H, H-2′), 8.22 (d, J = 9.3 Hz,
1H, H-3′); 13C NMR (75.48 MHz, CDCl3) δ 19.4 (C-4″), 25.3 (C-5″), 30.5
(C-3″), 62.3 (C-1), 65.9 (C-6″), 68.2(C-2), 99.2 (C-2″), 114.6 (C-2′),
125.9 (C-3′), 141.6 (C-4′), 164.0 (C-1′).
3.18. 4-Nitrophenoxyethanol (31)
3.14. Phenoxyethanol (30)
To a solution of 28 (365 mg, 1.37 mmol) in methanol (10 mL) was
added pyridinium p-toluenesulfonate (30 mg) and was treated ac-
cording to the general procedure. It was obtained 251 mg (100% yield)
of alcohol 31 as a white solid: mp = 87 °C; Rf = 0.17 (hexane–AcOEt,
4:1); 1H NMR (300.18 MHz, CDCl3) δ 1.97 (br s, 1H, OH), 4.03 (dist t,
2H, H-1), 4.19 (m, 2H, H-2), 7.01 (d, J = 9.3 Hz, 2H, H-2′), 8.24 (d,
J = 9.2 Hz, 2H, H-3′); 13C NMR (75.48 MHz; CDCl3) δ 61.1 (C-1), 70.0
(C-2), 114.5 (C-2′), 126.0 (C-3′).
A solution of 27 (1.33 g, 5.27 mmol) in methanol (15 mL) was
treated with pyridinium 4-toluenesulfonate (30 mg) according to the
preparation of 29. Evaporation of the solvent gave 846 mg of 30 (92%
yield) as a colorless oil: Rf = 0.23 (hexane–EtOAc, 4:1), 1H NMR
(300.18 MHz, CDCl3) δ 2.10 (br s, 1H, OH), 3.98 (m, 2H, H-1), 4.11 (m,
2H, H-2), 6.95 (d, J = 8.8 Hz, 2H, H-2′), 6.99 (t, J = 7.4 Hz, 1H, H-4′),
7.32 (dd, J = 8.6, 7.4 Hz, 2H, H-3′); 13C NMR (75.48 MHz, CDCl3) δ
61.5 (C-1), 69.0 (C-2), 114.5 (C-2′), 121.1 (C-4′), 129.5 (C-3′), 158.6 (C-
1′).
3.19. 4-Nitrophenoxyethyl 4-toluenesulfonate (34)
3.15. Phenoxyetyl 4-toluenesulfonate (33)
A solution of alcohol 31 (245 mg, 1.34 mmol) in pyridine (3 mL)
cooled at 0 °C was treated with p-toluenesulfonyl chloride (1.35 g,
4,01 mmol) according to the general procedure. The product was pur-
ified by column chromatography (silica gel) employing a mixture of
hexane–EtOAc (4:1) to give 371 g (82% yield) of 34 as a white solid:
mp = 123 °C; Rf = 0.51 (hexane–EtOAc, 3:2); 1H NMR (300.18 MHz;
CDCl3) δ 2.46 (s, 3H, PhCH3), 4.26 (m, 2H, H-1), 4.41 (m, 2H, H-2),
6.87 (d, J = 9.3 Hz, 2H, H-2′), 7.35 (d, J = 8.0 Hz, 2H, H-3″), 7.81 (d,
J = 8.3 Hz, 2H, H-2″), 8.17 (d, J = 9.3 Hz, 2H, H-3′); 13C NMR
(75.48 MHz; CDCl3) δ 21.7 (PhCH3); 66.1 (C-1), 67.4 (C-2), 114.5 (C-
2′), 125.8 (C-3′), 128.1 (C-2″), 129.9 (C-3″), 132.7 (C-4″), 142.0 (C-4′),
145.2 (C-1″), 162.9 (C-1′).
To a solution of alcohol 30 (846 mg, 6.12 mmol) in pyridine (6 mL)
cooled at 0 °C was added p-toluenesulfonyl chloride (4.65 g,
24.4 mmol). The reaction mixture was treated according the prepara-
tion of MNCC53 32. The residue was purified by column chromato-
graphy (silica gel) employing a mixture of hexane–EtOAc (17:3) to give
1.54 g (86% yield) of 33 as a white solid: mp = 73 °C; Rf = 0.30
(hexane–EtOAc, 4:1); 1H NMR (300.18 MHz, CDCl3) δ 2.47 (s, 3H,
PhCH3), 4.17 (m, 2H, H-1), 4.39 (m, 2H, H-2), 6.80 (dd, J = 9.7, 0.9 Hz,
2H, H-2′), 6.97 (tt, J = 7.4, 0.9 Hz, 1H, H-4′), 7.27 (dd, J = 8.7, 7.4 Hz,
2H, H-3′), 7.36 (d, J = 8.0 Hz, 2H, H-3″), 7.82 (d, J = 8.3 Hz, 2H, H-
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3.20. 4-Nitrophenoxyethyl selenocyanate (22)
enriched (R)-acetate 39 (598 mg) as a result from the acetylation of the
more reactive (R)-alcohol (−)-35 (ee 13%).28 Then, to 598 mg
(2.1 mmol) of 39 in methanol (30 mL) (1.16 g 8.41 mmol) of anhydrous
powder of potassium carbonate were added while stirring, followed by
water (9 mL) to obtain complete solution. The reaction was stirred at
room temperature for 4 h. The mixture was neutralized with an aqueous
10% solution of hydrochloric acid. The mixture was extracted with
methylene chloride (3 × 20 mL), and the combined organic layers were
dried (MgSO4), and the solvent was evaporated to produce 512 mg
(100% yield) of more enriched (R)-alcohol 35. The resulting alcohol
was acetylated under the presence of lipase as chiral catalyst to give the
respective acetate that was hydrolyzed another time. This process was
repeated four times to give 111 mg (39% yield) of the (R)-alcohol (R)-
(−)-35 with 82% of enantiomeric excess. The 1H NMR and 13C NMR
matched those previously described.16 Compound (S)-(+)-35:
[ ]2D3 = +43.6 (c 1.0, CHCl3); (R)-(−)-35: [ ]2D3 = −45.1 (c 1.0,
CHCl3); Compound ( )-39: Rf = 0.64 (hexane–EtOAc, 4:1); 1H NMR
(CDCl3, 500.13 MHz) δ 2.11 (s, 3H, C(O)CH3), 2.96 (dd, J = 15.9,
7.5 Hz, 1H, H-3a), 3.30 (dd, J = 15.8, 9.5 Hz, 1H, H-3b), 4.23 (dd,
J = 11.9, 7.0 Hz, 1H, CHaHOAc), 4.34 (dd, J = 11.9, 3.7 Hz, 1H,
CHbHOAc), 5.02 (dddd, J = 9.4, 7.2, 7.2, 3.7 Hz, 1H, H-2), 6.76 (d,
J = 8.7 Hz, 1H, H-7), 6.81 (ddt, J = 8.4, 2.6, 0.7 Hz, 1H, aromatic
proton), 6.87 (m, 1H, aromatic proton), 6.94 (m, 2H, aromatic protons),
7.04 (tt, J = 7.4, 1.0 Hz, 1H, aromatic proton), 7.29 (dd, J = 8.7,
7.4 Hz, 2H, aromatic protons); 13C NMR (125.76 MHz, CDCl3) δ 20.8
(C(O)CH3), 32.3 (C-3), 65.8 (CH2OH), 80.5 (C-2), 109.9 (C-7), 116.9 (C-
6), 117.5 (C-2′), 119.7 (C-4), 122.4 (C-4′), 127.1 (C-4a), 129.6 (C-3′),
150.5 (C-5), 155.4 (C-7a), 158.6 (C-1′), 170.9 (C(O)CH3).
A solution of 34 (363 mg, 1.08 mmol) in anhydrous tetrahydrofuran
(10 mL) was treated with potassium selenocyanate (171 mg,
1.18 mmol) in the presence of 18-crown-6 (2.8 mg) according to the
preparation of compound 20. The product was purified by column
chromatography (silica gel) eluting a mixture of hexane–EtOAc (4:1)
followed by HPLC purification eluting with acetonitrile–water (7:3) and
employing a semi-preparative column Beckmann Ultrasphere-ODS-2
(5 µM) to give 135 mg (46% yield) of 22 as a colorless oil: Rf = 0.15
(hexane–EtOAc, 4:1); 1H NMR (500.13 MHz, CDCl3)
δ 3.48 (t,
J = 6.0 Hz, 2H, H-1), 4.52 (t, J = 6.0 Hz, 2H, H-2), 7.03 (d, J = 9.2 Hz,
2H, H-2′), 8.26 (d, J = 9.2 Hz, 1H, H-4′); 13C NMR (125.77 MHz,
CDCl3) δ 27.2 (C-1); 67.1 (C-2), 100.5 (SeCN); 114.6 (C-2′), 126.0 (C-
3′), 142.3 (C-4′), 162.6 (C-1′); 77Se NMR (95.38 MHz, CDCl3)
δ
197.78 ppm. HRMS (ESI) calcd. for C9H8O3N2SeNa [M+Na]+
294.9598, found 294.9578.
3.21. ((S)-5-Phenoxy-2,3-dihydrobenzofuran-2-yl)methyl (S)-2-acetoxy-
2-phenylacetate (37) and ((R)-5-phenoxy-2,3-dihydrobenzofuran-2-yl)
methyl (S)-2-acetoxy-2-phenylacetate (38).
To a solution of alcohol ( )-3516 (10.0 mg, 4.13 × 10−3 mmol), S-
(+)-O-acetylmandelic acid (36; 12.0 mg, 6.19 × 10−3 mmol) and 4-
(dimethylamino)pyridine (0.8 mg, 6.61 × 10−4 mmol) in methylene
chloride (2.0 mL) cooled at 0 °C was added dropwise a solution of di-
cyclohexylcarbodiimide (17.0 mg, 8.26 × 10−3 mmol) in methylene
chloride (1.0 mL). The reaction mixture was stirred at 0 °C for 3 h. The
mixture was filtered off to eliminate the resulting dicyclohexylurea.
Then, methylene chloride (15 mL) was added and the organic layer was
washed with an aqueous 1 M solution of hydrochloric acid (20 mL), an
aqueous 1 M solution of sodium bicarbonate (20 mL), and brine
(20 mL). The organic phase was dried (MgSO4), and the solvent was
evaporated. The residue was purified by column chromatography (silica
gel) employing a mixture of hexane-EtOAc (97:3) as eluent to give
17.0 mg (98% yield) of a diastereomeric mixture 37/38 as a yellow pale
oil: 1H NMR (CDCl3, 500.13 MHz) δ 2.16 2.18 (s, 3H, C(O)CH3), 2.78
(dd, J = 16.0, 7.0 Hz, 1H, H-3a), 2.92 (dd, J = 16.0, 7.1 Hz, 1H, H-3a),
3.18 (dd, J = 15.5, 9.6 Hz, 1H, H-3b), 3.21 (dd, J = 15.6, 9.6 Hz, 1H, H-
3b), 4.31 (dd, J = 11.7, 5.5 Hz, 1H, CHaHOH), 4.37 (dt, J = 11.6,
3.8 Hz, 1H, CHbHOH), 4.95 (m, 1H, H-2), 5.92 (s, 1H, C(O)OCH), 6.67
6.71 (d, J = 8.4 Hz, 1H, H-7), 6.81–6.97 (m, 4H, aromatic protons),
7.03 (t, J = 7.4 Hz, 1H, aromatic proton), 7.29 (t, J = 7.6 Hz, 2H,
aromatic protons); 13C NMR (125.76 MHz, CDCl3) δ 20.60 20.63
(CH3C(O)), 31.99 32.02 (C-3), 66.35 66.39 (CH2O), 74.40 74.42 (C-2″),
79.89 79.90 (C-2), 109.75 109.77 (C-7), 116.89 116.92 (C-6), 117.5 (C-
2′), 119.6 (C-4), 122.3 (C-4′), 127.10 127.15 (C-4a), 127.46 127.51 (C-
3″), 128.0 (C-3″), 129.6 (C-3′), 129.23 129.27 (C-2″), 133.4 133.5 (C-
1″), 150.4 (C-5), 155.5 (C-7a), 158.7 (C-1′), 168.69 168.76 (CH3C(O)),
170.3 (C-1″).
3.23. (+)-(S)-(5-Phenoxy-2,3-dihydrobenzofuran-2-yl)methyl 4-
toluenenesulfonate ((S)-42)
A solution of (S)-35 (45.6 mg, 0.19 mmol) in pyridine (3.0 mL)
cooled at 0 °C was treated with p-toluenesulfonyl chloride (108 mg,
0.56 mmol) according to the method described for the preparation of
32. The product was purified by column chromatography (silica gel)
employing a mixture of hexane–EtOAc (4:1) as eluent to give 39.1 mg
(52% yield) of tosylate (S)-38 as a colorless oil: NMR data matched
with those previously depicted.16 [ ]D20 = +58.3 (c 1.0, CHCl3).
3.24. (−)-(R)-(5-Phenoxy-2,3-dihydrobenzofuran-2-yl)methyl 4-
toluenenesulfonate ((R)-42)
To a solution of (R)-35 (50.3 mg, 0.21 mmol) in pyridine (3.0 mL)
cooled at 0 °C was added p-toluenesulfonyl chloride (119 mg,
0.62 mmol) following the method described for the preparation of 32.
The product was purified by column chromatography (silica gel) em-
ploying a mixture of hexane–EtOAc (4:1) as eluent to give 59.3 mg
(72% yield) of tosylate (R)-38 as a colorless oil: NMR data matched
with those previously depicted.16 [ ]D20 = −61.7 (c 1.0, CHCl3).
3.22. (S)-(5-Phenoxy-2,3-dihydrobenzofuran-2-yl)methanol ((S)-(+)-35)
and (R)-(5-phenoxy-2,3-dihydrobenzofuran-2-yl)methyl acetate (39)
3.25. (+)-(S)-5-Phenoxy-2-(selenocyanatomethyl)-2,3-
dihydrobenzofuran ((+)-(S)-8)
To a solution of ( )-(5-phenoxy-2,3-dihydrobenzofuran-2-yl)me-
thanol (( )-3516; 575 mg, 2.37 mmol) in acetonitrile (57 mL) was
added Lipase Amano PS (395 mg). The resulting suspension was ther-
mostatized at 23 °C and stirred for 10 min. Then, isopropenyl acetate
(3.97 g, 4.30 mL, 39.6 mmol) was added. The reaction was monitored
A solution of (S)-38 (28.8 mg, 7.26 × 10−2 mmol) in anhydrous
tetrahydrofuran (3.0 mL) in the presence of 18-crown-6 (0.2 mg) was
treated with potassium selenocyanate (11.5 mg, 7.99 × 10−2 mmol)
according to the general procedure. The product was purified by
by HPLC employing
a
chiral column Lux
5
µ
Cellulose-1
column chromatography (silica gel) employing
a
mixture of
(4.60 mm × 25 cm) eluting with a mixture of acetonitrile–water (7:3)
at a flow rate of 1.0 mL/min. The mixture was stirred for 6 h. The re-
action mixture was filtered off and the solvent was evaporated. The
residue was purified by column chromatography (silica gel) employing
a mixture of hexane-EtOAc (4:1) as eluent to give the less reactive (S)-
alcohol (+)-35 (64.2 mg) with 84% ee as a colorless oil and the
hexane–EtOAc (93:7). The resulting partially purified compound was
further purified by HPLC by using a semi-preparative Beckmann
Ultrasphere ODS-2 (5 µm, 10.0 mm × 25 cm) at a flow rate of 3 mL/min
eluting with a mixture of acetonitrile–water (7:3) to yield 11.4 mg (47%
yield) of (+)-(S)-8 as a yellow pale oil: [ ]2D3 = +36.0 (c 1.0, CHCl3).
77Se NMR (95.38 MHz, CDCl3) δ 171.29 ppm.
9

M.N. Chao, et al.
Bioorganic&MedicinalChemistryxxx(xxxx)xxx–xxx
3.26. (−)-(R)-5-Phenoxy-2-(selenocyanatomethyl)-2,3-
dihydrobenzofuran ((R)-8)
6.86 (m, 2H, aromatic protons), 7.04 (m, 4H, aromatic protons), 7.12
(m, 1H, aromatic proton), 7.34 (dd, J = 8.3, 7.7 Hz, 2H, H-3′); 13C NMR
(75.48 MHz, CDCl3) δ 116.2 (C-6), 118.0 (C-2′), 118.8 (C-3), 120.6 (C-
4), 123.6 (C-4′), 124.8 (C-5), 129.9 (C-3′), 143.5 (C-1), 147.5 (C-2),
156.7 (C-1′). HRMS (ESI) calcd. C12H11O2 for [M+H]+ 187.0759;
found 187.0744; calcd. C12H10NaO2 for [M+Na]+ 209.0578; found
209.0564.
To a solution of (R)-38 (43.7 mg, 0.11 mmol) in anhydrous tetra-
hydrofuran (3.0 mL) in the presence of 18-crown-6 (0.3 mg) was added
potassium selenocyanate (17.5 mg, 0.12 mmol) according to the general
procedure. The product was purified by column chromatography (silica
gel) eluting with a mixture of hexane–EtOAc (93:7) and was further
purified by HPLC by using a semi-preparative Beckmann Ultrasphere
ODS-2 (5 µm, 10.0 mm × 25 cm) at a flow rate of 3 mL/min eluting
with a mixture of acetonitrile–water (7:3) to give 33.6 mg (92% yield)
of (R)-8 as a yellow pale oil: [ ]2D3 = −33.9 (CHCl3). 77Se NMR
(95.38 MHz, CDCl3) δ 171.26 ppm.
3.30. 2-Phenoxyphenoxyethyl tetrahydro-2H-pyran-2-yl ether (49)
To a solution of 2-phenoxyphenol (48; 383.3 mg, 2.06 mmol) in
dimethyl sulfoxide (3.0 mL) was added potassium hydroxide (231 mg,
4.12 mmol) and the mixture was stirred at room temperature for 5 min.
Then, bromoethyl tetrahydropyranyl ether (430 mg, 0.31 mL,
2.06 mmol) was added dropwise. The reaction mixture was stirred at
room temperature for 20 h. The mixture was extracted with methylene
chloride (2 × 25 mL) and the combined organic phases were washed
with brine (5 × 50 mL), dried (MgSO4) and the solvent was evaporated.
The product was purified by column chromatography (silica gel) using
a mixture of hexane–EtOAc (24:1) as eluent to give 503.6 mg (78%
yield) of 49 as a colorless oil: Rf = 0.50 (hexane–toluene, 4:1); 1H NMR
(300.18 MHz, CDCl3) δ 1.41–1.74 (m, 6H, H-2″′, H-3″′, H-4″′), 3.44 (m,
1H, H-6″′a), 3.67 (ddd, J = 11.2, 6.3, 4.8 Hz, 1H, H-6″′b), 3.77 (ddd,
J = 11.3, 8.4, 3.0 Hz, 1H, H-1a), 3.91 (dt, J = 11.3 Hz J = 4.7 Hz, 1H,
H-1b), 4.18 (m, 2H, H-1H-2), 4.55 (dist. t, J = 3.3 Hz, 1H, H-1″′),
6.89–7.14 (m, 7H, aromatic protons), 7.26 (t, J = 8.0 Hz, 2H, aromatic
protons); 13C NMR (75.48 MHz, CDCl3) δ 19.1 (C-3″′), 25.4 (C-4″′), 30.4
(C-2″′), 61.8 (C-1), 65.6 (C-5″′), 68.6 (C-1), 98.8 (C-1″′), 115.0 (C-6),
116.7 (C-3′), 121.6 (C-2″), 121.9 (C-4′), 122.1 (C-4″), 125.0 (C-5′),
129.3 (C-3″), 145.1 (C-2′), 151.0 (C-1′), 158.3 (C-1″). HRMS (ESI)
calcd. for C19H22O4Na [M+Na]+ 337.1416; found 337.1425.
3.27. 1-(Benzyloxy)-2-iodobenzene (46)
A
solution of 2-iodophenol (45; 1.32 g, 6.0 mmol) in N,N-di-
methylformamide (15.0 mL) was added potassium carbonate (4.15 g,
30.0 mmol) and was stirred for 5 min. Then was added benzyl bromide
(1.29 mg, 0.78 mL, 6.6 mmol) slowly. The reaction mixture was stirred
at 50 °C for 1 day. Then, the mixture was cooled to room temperature
and was partitioned between methylene chloride (20 mL) and water
(20 mL). The aqueous layer was extracted with methane chloride
(2 × 20 mL) and the combined organic phases were washed with brine
(5 × 50 mL), dried (MgSO4) and the solvent was evaporated affording
1.80 g (97% yield) of product 46 as colorless oil, which was used as
such in the next step: Rf = 0.75 (hexane–EtOAc, 4:1); 1H NMR
(300.18 MHz, CDCl3) δ 5.12 (s, 2H, OCH2Ph), 6.75 (dt, J = 7.6, 1.3 Hz,
1H, H-5), 6.87 (dd, J = 8.2, 1.1 Hz, 1H, H-6), 7.29 (ddd, J = 8.2, 7.4,
1.5 Hz, 1H, H-4), 7.33–7.46 (m, 3H, H-3′, H-4′), 7.55 (d, J = 7.3 Hz, 2H,
H-2′), 7.85 (dd, J = 7.8, 1.6 Hz, 1H, H-3); 13C NMR (75.48 MHz, CDCl3)
δ 70.8 (OCH2Ph), 87.0 (C-2), 112.9 (C-6), 123.0 (C-4), 127.1 (C-4′),
128.0 (C-2′), 128.7 (C-5), 129.6 (C-3′), 136.6 (C-1′), 139.6 (C-3), 157.2
(C-1).
3.31. 2-Phenoxyphenoxyethanol (50)
A solution of 49 (490 mg, 1.57 mmol) in methanol (8 mL) was
treated with pyridinium p-toluenesulfonate (20 mg). The mixture was
stirred at room temperature overnight. Then, water (20 mL) was added,
and the mixture was extracted with methylene chloride (3 × 20 mL).
The combined organic layers were washed with brine (3 × 50 mL),
dried (MgSO4), and the solvent was evaporated. The residue was pur-
ified by column chromatography (silica gel, hexane/EtOAc 95:5) to
give pure alcohol 50 (230 mg, 86%) as a colorless oil: Rf = 0.26
(hexane/EtOAc 8:2); 1H NMR (300.18 MHz, CDCl3) δ 3.73 (dist. q,
J = 5.0 Hz, H-2), 4.03 (dist. q, J = 4.4 Hz, H-1), 6.92–7.17 (m, 7H,
aromatic H),; 7.28–7.33 (m, 2H, aromatic H); 13C NMR (75.48 MHz,
CDCl3) δ 61.2 (C-2), 70.5 (C-1), 114.8 (C-6′), 116.5 (C-2″), 122.0 (C-3′),
122.1 (C-4′), 122.4 (C-4″), 125.2 (C-5′), 129.6 (C-3″), 145.1 (C-2′),
150.4 (C-1′), 158.3 (C-1″).
3.28. 1-(Benzyloxy)-2-phenoxybenzene (47)
A mixture of 46 (1.80 g, 7.76 mmol), phenol (1.30 g, 13.9 mmol),
copper(I) iodide (132 mg, 6.93 mmol), 2-picolinic acid (170 mg,
1.38 mmol), and tripotassium phosphate (2.94 g, 13.9 mmol) under
anhydrous conditions was evacuated and backfilled with argon twice.
Then, dimethyl sulfoxide (12.0 mL) was added, and the mixture was
stirred vigorously at 80 °C for 5 days. The mixture was allowed to cool
to room temperature and partitioned between ethyl acetate (20 mL) and
water (20 mL). The aqueous layer was extracted with ethyl acetate
(2 × 20 mL). The combined organic phases were washed with brine
(5 × 50 mL), dried (MgSO4), and the solvent was evaporated. The
product was purified by column chromatography (silica gel) eluting
with hexane to produce 840 mg (39% yield) of 47 as a colorless oil:
Rf = 0.64 toluene–hexane (9:1); 1H NMR (300.18 MHz, CDCl3) δ 5.11
(s, 2H, OCH2Ph), 6.95–7.00 (m, 3H, aromatic protons), 7.04–7.14 (m,
4H, aromatic protons), 7.19–7.21 (m, 2H, aromatic protons), 7.27–7.35
(m, 5H, aromatic protons); 13C NMR (75.48 MHz, CDCl3) δ 70.8
(OCH2Ph), 115.3 (C-3′), 116.9 (C-2″), 121.8 (C-6′), 122.0 (C-5′), 122.3
(C-4″), 125.0 (C-4′), 127.1 (C-2″′), 127.7 (C-4″′), 128.4 (C-3″), 129.5 (C-
3″′), 136.9 (C-1″′), 145.4 (C-1′), 150.6 (C-2′), 158.4 (C-1″). HRMS (ESI)
calcd. for C19H16O2Na [M+Na]+ 299.1048; found 299.1033.
3.32. 2-Phenoxyphenoxyethyl 4-toluenesulfonate (51)
A solution of 50 (310.0 mg, 1.35 mmol) in pyridine (3.0 mL) cooled
at 0 °C was treated 4-toluenesulfonyl chloride (773.4 mg, 4.06 mmol)
portion wise, and the mixture was stirred at 0 °C for 3 h. Then, a 5%
aqueous solution of hydrochloric acid (10 mL) was added and the re-
action mixture was stirred for an additional hour. The mixture was
extracted with methylene chloride (30 mL) and the organic layer was
washed with an aqueous 5% solution of hydrochloric acid (3 × 25 mL)
and water (3 × 30 mL). The organic phase was dried (MgSO4) and the
solvent was evaporated. The product was purified by column chroma-
tography (silica gel) eluting with hexane to give 494.8 mg (95% yield)
of 51 as a white solid: mp = 64–65 °C; Rf = 0.19 (hexane–EtOAc; 4:1);
1H NMR (300.18 MHz, CDCl3) δ 2.43 (s, 3H, CH3PhSO3), 4.20–4.23 (m,
4H, H-1H-2), 6.88–7.01 (m, 5H, aromatic protons), 7.03–7.12 (m, 2H,
aromatic protons), 7.26–7.32 (m, 4H, aromatic protons), 7.73 (d,
J = 8.3 Hz, 2H, aromatic protons); 13C NMR (75.48 MHz, CDCl3) δ 21.6
3.29. 2-Phenoxyphenol (48)
A solution of 47 (744 mg, 2.69 mmol) in ethyl acetate (10 mL) in the
presence of 5% palladium on charcoal (42 mg) was treated with hy-
drogen at 3 atm. The reaction was stirred at room temperature for 2 h.
The mixture was filtered off and the solvent was evaporated to produce
503 mg (100% yield) of 48 as a white solid: mp = 105 °C; Rf 0.74 (to-
luene–hexane, 4:1); 1H NMR (300.18 MHz, CDCl3) δ 5.58 (s, 1H, OH),
10

M.N. Chao, et al.
Bioorganic&MedicinalChemistryxxx(xxxx)xxx–xxx
(CH3PhSO3), 67.0 (C-2), 67.9 (C-1), 116.0 (C-6′), 117.2 (C-2″), 121.5
(C-3′), 122.5 (C-4′), 122.6 (C-4″), 124.8 (C-5′), 127.9 (C-2″′), 129.5 (C-
3″), 129.8 (C-3″′), 132.7 (C-4″′), 144.8 (C-1″′), 145.9 (C-2′), 149.9 (C-
1′), 157.8 (C-1″).
1.56 µM, 3.125 µM, and 6.25 µM, respectively for all set of testing. Once
compound treatment, plates were incubated at 35 °C and 7% CO2 and
plates were assayed for fluorescence after 72 h post-infection. ED50
values were determined by non-linear regression analysis using Sig-
maPlot.35
3.33. 2-Phenoxyphenoxyethyl selenocyanate (43)
5. Cytotoxicity for Vero cells
A solution of 51 (100 mg, 0.26 mmol), potassium selenocyanate
(41.2 mg, 0.29 mmol), and 18-crown-6 (7 mg) in anhydrous tetra-
hydrofuran (10 mL) was refluxed for 24 h. The solution was cooled to
room temperature and the mixture was partitioned between brine
(50 mL) and methylene chloride (30 mL). The aqueous phase was ex-
tracted with methylene chloride (3 × 25 mL). The combined organic
layers were dried (MgSO4) and the solvent was evaporated. The product
was purified by column chromatography (silica gel) using a mixture of
hexane-EtOAc (96:4) as eluent to give 50.7 mg (61% yield) of 43 as a
colorless oil: Rf = 0.58 (hexane–EtOAc, 7:3); 1H NMR (300.18 MHz,
CDCl3) δ 3.27 (t, J = 6.0, 2H, H-1), 4.36 (t, J = 6.0 Hz, 2H, H-2), 6.90
(dd, J = 8.8, 1.1 Hz, 2H, H-2″), 7.00–7.07 (m, 4H, H-3′, H-4′, H-5′, H-
6′), 7.14 (ddd, J = 8.1, 7.4 Hz, 1.9 Hz, 1H, H-4″), 7.29 (dd, J = 8.7,
7.4 Hz, 2H, H-3″); 13C NMR (75.48 MHz, CDCl3) δ 28.1 (C-1), 67.8 (C-
2), 101.5 (SeCN), 115.6 (C-6′), 116.6 (C-2″), 122.2 (C-3′), 122.5 (C-4′),
123.0(C-4″), 125.17 (C-5′), 129.6 (C-3″), 145.3 (C-2′), 149.7 (C-1′),
158.1 (C-1″); 77Se NMR (95.38 MHz, CDCl3) δ 196.06 ppm. HRMS (ESI)
calcd. for C15H13O2NSeNa [M+Na]+ 342.0009; found 342.0012.
The cytotoxicity was tested using the Alamar BlueTM assay as de-
scribed by Recher et al., 2013.35 Concisely, confluent monolayers of
hTERT cells were seeded in 96 well plates in 150 µL DMEM high glucose
no phenol red (Gibco Cat# 21063) with 10% Cosmic Calf Serum. Plates
were incubated 16 h at 35 °C and 7% CO2. Then, wells were washed
once with Hanks (150 µL/well), and inhibitors were added in sequential
concentrations in DMEM media in 150 µL volumes. All dilutions were
tested in quadruplicate. All plates contained controls with host cells
without inhibitor. Plates containing drug dilutions were incubated at
35 °C and 7% CO2 for 72 h. Then, Alamar Blue indicator was aseptically
added equivalent to 10% of the culture volume, which were incubated
at 35 °C for 6 h. At that time, absorbance was measured at 570 and
600 nm.35 Different concentrations of DMSO were tested as positive
control of toxicity.35
Acknowledgments
We thank Melissa Storey for technical help with the drug screening.
This work was supported by grants from the Consejo Nacional de
Investigaciones Científicas y Técnicas (PIP 112-201501-00631 CO),
Agencia Nacional de Promoción Científica y Tecnológica (PICT 2015
1349), and the Universidad de Buenos Aires (20020170100067BA) to
J.B.R., and the U.S. National Institutes of Health to R.D. (AI-107663).
3.34. 2-Phenoxyphenoxyethyl thiocyanate (44)
A solution of 51 (100.0 mg, 0.26 mmol) in anhydrous N,N-di-
methylformamide (5 mL) was treated with potassium thiocyanate
(126 mg, 1.3 mmol). The reaction mixture was heated at 90 °C for 5 h.
The mixture was allowed to cool to room temperature and water
(20 mL) was added. The aqueous phase was extracted with methylene
chloride (2 × 30 mL) and the combined organic layers were washed
with brine (5 × 30 mL) and water (2 × 30 mL). The organic phase was
dried (MgSO4), and the solvent was evaporated. The residue was pur-
ified by column chromatography (silica gel) eluting with hexane–EtOAc
(9:1) to give 55.0 mg (78% yield) of 44 as a colorless oil: Rf 0.17
(hexane–EtOAc, 4:1), 1H NMR (500 MHz, CDCl3) δ 3.14 (t, J = 6.0 Hz,
2H, H-1), 4.28 (t, J = 6.0 Hz, 2H, H-2), 6.91 (dd, J = 8.6, 0.9 Hz, 2H, H-
2″), 7.00–7.06 (m, 4H, H-3′, H-4′, H-5′, H-6′), 7.14 (ddd, J = 8.2, 7.0,
1.9 Hz, 1H, H-4″), 7.29 (dd, J = 8.6, 7.5 Hz, 2H, H-3″); 13C NMR
(125 MHz, CDCl3) δ 33.2 (C-1), 67.2 (C-2), 111.8 (SCN), 116.0 (C-6′),
116.8 (C-2″), 122.0 (C-3′), 122.5 (C-4′), 123.0 (C-4″), 125.1 (C-5′),
129.5 (C-3″), 145.6 (C-2′), 149.7 (C-1′), 158.0 (C-1″). HRMS (ESI)
calcd. for C15H13O4NSNa [M+Na]+ 294.0565; found 294.0546.
Appendix A. Supplementary data
Supplementary data to this article can be found online at https://
doi.org/10.1016/j.bmc.2019.02.039.
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