Novel synthesis and pharmacological evaluation as α2-adrenoceptor ligands of O-phenylisouronium salts

Article abstract of DOI:10.1016/j.bmc.2008.07.033

The synthesis of nine new mono- and bis-O-phenylisouronium compounds (2, 6b-10b and 12b-14b) and their Boc-protected isourea precursors (2a, 6a-10a and 12a-14a) is described. The carbodiimide 4, which was formed, had been suggested as the reactive intermediate species and driving force of the reaction. All final substrates were tested as potential α₂-ARs ligands in human brain tissue by means of radioligand binding experiments and were compared to the potential antidepressant 1, as well as other related guanidine containing derivatives.

Full text of DOI:10.1016/j.bmc.2008.07.033

Bioorganic & Medicinal Chemistry 16 (2008) 8210–8217
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry
journal homepage: www.elsevier.com/locate/bmc
Novel synthesis and pharmacological evaluation as
a2-adrenoceptor
ligands of O-phenylisouronium salts
a
a
a
ˇ ´ a
Áine Goonan a, , Amila Kahvedzic , Fernando Rodriguez , Padraic S. Nagle , Thomas McCabe ,
Isabel Rozas a,b, , Amaia M. Erdozain c,d, J. Javier Meana c,d, Luis F. Callado c,d
*
a School of Chemistry, University of Dublin, Trinity College, Dublin 2, Ireland
b Centre for Synthesis and Chemical Biology, School of Chemistry, University of Dublin, Trinity College, Dublin 2, Ireland
c Department of Pharmacology, Faculty of Medicine, University of the Basque Country, 48940 Leioa, Bizkaia, Spain
d CIBER of Mental Health, CIBERSAM, Spain
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 30 April 2008
Revised 7 July 2008
Accepted 16 July 2008
Available online 20 July 2008
The synthesis of nine new mono- and bis-O-phenylisouronium compounds (2, 6b–10b and 12b–14b) and
their Boc-protected isourea precursors (2a, 6a–10a and 12a–14a) is described. The carbodiimide 4, which
was formed, had been suggested as the reactive intermediate species and driving force of the reaction. All
final substrates were tested as potential
a2-ARs ligands in human brain tissue by means of radioligand
binding experiments and were compared to the potential antidepressant 1, as well as other related gua-
nidine containing derivatives.
Keywords:
Ó 2008 Elsevier Ltd. All rights reserved.
O-Isouronium salts
Boc-protected isoureas
Carbodiimide
a2-Adrenoceptors
Human brain tissue
1. Introduction
and resulting in the deficit in NA transmission described in the eti-
ology of depression. Chronic treatment with antidepressants pro-
a
2-Adrenoceptors (
transmitter release1 and are implicated in a variety of pharmaco-
logical functions.2 Thus,
2-AR agonists have applications as
analgesics,3 anaesthetics,4 and as antihypertensive5 or antiglauco-
ma agents,6 whereas
2-AR antagonists can act as antidepres-
a
2-ARs) play an important role in neuro-
duces an in vivo desensitization of the
local release of NA.10 Bearing this in mind, the development of
new selective 2-AR antagonists can be considered an effective
therapeutical approach for the treatment of depressive disorders,
since it has been demonstrated that administration of different
a2-ARs regulating the
a
a
a
sants.7 In this context, the number of people affected by
depression has increased significantly in recent years and by
2020 the disease is expected to be the second largest health burden
as stated by the World Health Organisation.8 The pathophysiolog-
ical origin of depression remains unknown, however, the monoam-
inergic hypothesis7 assumes that it is a consequence of a low
concentration of noradrenaline (NA) or serotonin in the brain.
It is well established that central noradrenergic transmission is
a2-AR antagonists, both locally in the locus coeruleus or systemi-
cally, increases the release of NA in the prefrontal cortex.11,12 In
fact, mirtazapine (Fig. 1), one of the most recently developed
antidepressants, displays its activity by blocking the
Interested in the development of new 2-AR antagonists, and
a
2-ARs.13
a
therefore new potential antidepressants, we recently started a pro-
gram consisting of the synthesis of a library of guanidine and 2-
aminoimidazoline derivatives and their biological evaluation in
regulated by inhibitory presynaptic noradrenergic receptors (a2
-
human prefrontal cortex (PFC).14 Among the new
a
2-AR antago-
nists found, compound 1 (Fig. 1) showed an affinity towards the
2-ARs similar to that of Idazoxan14b and was subject to in vivo
ARs) and that the activation of these autoreceptors induces an
inhibition of NA release. It has been proposed that depression is
associated with a selective increase in the high-affinity conforma-
a
microdialysis experiments in rats. The levels of NA in the rat brains
increased remarkably after local and systemic administration of 1,
confirming its ability to cross the blood–brain barrier (BBB) and its
potential as antidepressant.14b
tion of the
a
2-ARs in the human brain,9 enhancing their activity
Encouraged by the excellent results displayed by the lead com-
pound 1, we decided to perform some chemical modifications in
* Corresponding author. Tel.: +353 1 896 3731; fax: +353 1 671 2826.
E-mail address: rozasi@tcd.ie (I. Rozas).
This article is dedicated to the memory of Áine Goonan, who started this project
during her fourth year project in TCD and has prematurely died at the age of 23.
order to explore the affinity towards the
a2-ARs and try to identify
the functional groups required for a better binding and antagonist
0968-0896/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmc.2008.07.033

Áine Goonan et al. / Bioorg. Med. Chem. 16 (2008) 8210–8217
8211
O
N
HN
O
O
O
N
HN
OMe
N
N
Idazoxan
N
HN
N
RX821002
BRL44408
N
N
O
Mirtazapine
NH
N
O
MK912
NH
NH2
NH
N
O
NH2
H
2
1
Figure 1. Structures of a known
a2-adrenoceptor targeting antidepressant (mirtazapine), known
a2-AR antagonists with an ‘amidinium’ moiety, a new
a2-AR antagonist
previously described in our group (1) and a proposed molecule (2).
activity. The guanidinium cation seems to be the most important
group in the binding to the receptor, thus modifications in that
moiety were pursued. The presence of several hydrogen bond
(HB) donors, such as amino groups, seems to be responsible of
the binding; yet, the introduction of at least one HB acceptor, such
as an O atom, could potentially improve the interaction with the
S
3
4
BocHN
BocN
NHBoc
NBoc
NH
R-NH2
R NH
C
NH2
binding pocket of the a2-ARs. Several antagonists with only an imi-
SMe
NHR
5a, R = Boc
5b, R = Cbz
dazolinium or a urea group are already known (see Fig. 1), thus, we
could assume that only the ‘amidinium’ moiety is needed for an
efficient binding. Moreover, Serine residues have been proposed
to play an important role in the interaction in the binding pocket.15
Hence, considering that the OH of Ser is a very good HB donor the
introduction of a HB acceptor could reinforce the binding to the
receptor. Taking all this into account, the guanidinium cation was
substituted by the isouronium one (as in compound 2, Fig. 1) and a
set of O-phenylisouronium salts were synthesised.
RN
NH
S
R
O
R
OH
BocHN
NHBoc
NH2
3
Figure 2. Typical preparation of guanidines from primary amines and Boc- or Cbz-
protected thiourea, possible carbodiimide intermediate or S-methylisourea and
proposed synthesis of isourea derivatives.
In this article, we present a novel methodology for the prepara-
tion of nine new (bis)O-phenylisouronium chlorides and their Boc-
protected O-phenylisourea precursors, together with an in vitro
On the other hand, the use of carbodiimides in the reaction with
aliphatic alcohols and phenols to provide O-alkyl and O-phenyli-
soureas, respectively, is well documented.21 In a similar context,
pharmacological study of their affinity towards the
a2-ARs in hu-
man brain. Human PFC was chosen because there is an important
density of
a
2-ARs in this tissue16 and many studies have reported
the reaction between N,N0-bis(tert-butoxycarbonyl)thiourea
3
changes in PFC activity in the brain of patients with depression.17
Moreover, the final goal of our research is the synthesis of antide-
pressants. Hence, the use of human brain tissue to pharmacologi-
cally characterize the new compounds will be relevant from a
therapeutic point of view.
(Fig. 2) and deactivated amines assisted by mercury (II) chloride
to provide Boc-protected guanidines22 has been suggested to pro-
ceed via formation of N,N0-bis(tert-butoxycarbonyl)carbodiimide
4 (Fig. 2).22a Further standard deprotection of the Boc groups leads
to guanidinium containing derivatives in moderate to good overall
yields under mild conditions.14,23
2. Results and discussion
2.1. Chemistry
Based on the assumption that intermediate 4 is the reactive
species in this reaction and considering the reactivity of carbodii-
mides with alcohols,21 exchange of the starting deactivated amines
by phenols appears to be a rational approach to the synthesis of
aromatic isouronium salts (Fig. 2). In addition, the treatment of a
group of aromatic amino-alcohols with 1,3-bis(tert-butoxycar-
bonyl)-2-methyl-2-pseudothiourea 5a and 1,3-bis(benzyloxycar-
bonyl)-2-methyl-2-pseudothiourea 5b (Fig. 2) in the presence of
mercury (II) chloride had been reported by Sharma et al.24 As ex-
pected, the Boc- and Cbz-protected guanidines were the main
products with yields ranging from 78% to 81%. Interestingly, Boc-
and Cbz-protected isoureas were also formed as side products
(yield < 4%).
A number of O-alkylisouronium salts have been recently de-
scribed in the literature as intermediates in the synthesis of diazi-
rines to perform mechanistic fragmentation studies in
alkoxyhalocarbenes.18 In all cases, the synthesis of these substrates
relies on the reaction of the corresponding alcohol with cyanamide
in the presence of either methane- or trifluoromethanesulfonic
acid.19 The same strategy can be applied to convert phenols into
O-phenylisouronium salts.20 Even though this is the main and most
straightforward way for the preparation of isouroniums from alco-
hols, purification of the products could prove to be problematic. In
addition, starting materials with acid labile groups are not suitable
for the method, since they require milder conditions.
With that in mind, and following the general synthetic pathway
described in Scheme 1, the synthesis of compounds 2, 6b and 7b
(Table 1) was attempted. Thus, reaction of one equivalent of each

8212
Áine Goonan et al. / Bioorg. Med. Chem. 16 (2008) 8210–8217
1) TFA, DCM
NBoc
3
NH
NH2
R
R
R
.HCl
OH
HgCl2, TEA, Solv.
2) Amberlyte resin, H2O
O
NHBoc
O
Scheme 1.
Table 1
Overall, first and second stage yields (in%) obtained for the new compounds prepared
Compound
Structure
1st stage
Compound
Structure
2nd stage
95
Overall
60
NH
NH2
NBoc
NHBoc
2a
63
2
O
O
NH
NH2
NBoc
NHBoc
6a
7a
8a
66
73
58
6b
7b
8b
94
93
92
62
68
53
O
O
NH
NBoc
NHBoc
O
NH2
O
NH
NH
NH2
NBoc
O
NBoc
O NHBoc
H2N
O
O
BocHN
O
O
NH
NH
NH2
NBoc
O
NBoc
O NHBoc
9a
67
61
—
9b
91
92
—
61
56
—
H2N
H2N
O
O
BocHN
BocHN
S
S
NH
NH
NH2
NBoc
O
NBoc
NHBoc
10a
11a
10b
11b
O
O
O
O
O
O
NH
NH
NH2
NBoc
O
NBoc
NHBoc
H2N
HO
O
BocHN
HO
O
NH
NBoc
NHBoc
12a
13a
14a
74
77
78
12b
13b
14b
91
93
92
67
72
72
O
NH2
O
O
S
O
NH
NH2
NBoc
O NHBoc
HO
HO
O
HO
HO
S
NH
NH2
NBoc
NHBoc
O
O
alcohol with one equivalent of 3 in the presence of a slight excess
mercury (II) chloride and an excess of triethylamine in dichloro-
methane at room temperature gave the Boc-protected O-phenyli-
soureas 2a, 6a and 7a (Table 1) after column chromatography.
Deprotection of the Boc groups with trifluoroacetic acid in dichlo-
romethane followed by treatment with Amberlyte resin in water
led to the desired O-phenylisouronium chloride salts.
Then, we proceeded to the preparation of the bis-isouronium
salts 8b–11b by reacting in the first stage one equivalent of the
corresponding diol with two equivalents of 3, a slight excess of
mercury (II) chloride and an excess of triethylamine. The reaction
was carried out at room temperature in dichloromethane for 8a–
10a and in dimethylformamide for 11a.
to be too deactivating and the synthesis of 11a could not be accom-
plished. Boc deprotection of 8a–10a afforded the final isouronium
chlorides 8b–10b after anion exchange in moderate overall yields
(Table 1).
Single crystals of 8a25 and 9a26 were grown by slow evaporation
of a solution in a concentrate chloroform/ethyl acetate mixture and
in hexane, respectively. As can be seen in Figure 3, both have very
similar structures. The phenyl rings are almost perpendicular to
each other in order to minimize steric interactions between the
aromatic protons in ortho with the bridge group. Interestingly, this
geometry disrupts the symmetry observed in solution and two
enantiomers are possible for each substrate. In Figure 3 only one
enantiomer per compound is presented, however, in the unit cell,
the two mirror images can be found for both, 8a and 9a.
After isolation of the monocations 12a, 13a and 14a as side
products in the synthesis of 8a, 9a and 10a, different approaches
to improve their yields were attempted. Comparison of 12b, 13b
As can be seen in Table 1, the bis Boc-protected isoureas 8a–10a
were obtained in similar yields after silica gel column chromatog-
raphy. In all three cases, the mono Boc-protected isoureas 12a, 13a
and 14a were isolated as side products. The carbonyl group proved

Áine Goonan et al. / Bioorg. Med. Chem. 16 (2008) 8210–8217
8213
Table 2
Affinity values (expressed as pKi) obtained for all the compounds studied
Compound
Structure
pKi
O
OMe
N
RX821002
9.04
O
O
HN
Idazoxan
Clonidine
7.29
7.68
N
O
HN
Cl
N
N
N
H
H
Cl
NH
1a
7.11
5.35
5.27
5.09
5.40
4.72
N
H
NH2
Figure 3. X-ray diffraction structures of 8a, and 9a, respectively.
NH
NH2
2
O
and 14b with their dicationic counterparts 8b, 9b and 10b could
provide some interesting Structure–Activity Relationships (SAR)
NH
NH2
in the study of the affinity towards the
a2-ARs. Thus, reaction of
6b
7b
8b
9b
an excess of three equivalents of the diols with only one equivalent
of 3, one equivalent of mercury (II) chloride and an excess of trieth-
ylamine afforded the mono-Boc-protected isoureas 12a–14a,
which were purified by silica gel column chromatography. Com-
pounds 8a–10a are the side products under the new conditions
(yield lower than 6% in all cases) and the unreacted starting diols
were recovered from the column eluting with a more polar solvent
system. Usual Boc deprotection with trifluoroacetic acid and fur-
ther Amberlyte resin treatment in aqueous solution afforded
12b–14b in good overall yields (Table 1). All the chemicals used
for the syntheses described in Scheme 1 are commercially available
either from Aldrich or Fluka.
The results obtained suggest that this two-step method is a va-
lid option for the preparation of O-phenylisouronium salts when
the starting phenols have either alkyl or electro-donor substitu-
ents. Moreover, in a long multiple-step synthesis, this strategy
would allow us to introduce the isouronium precursor at any stage
and transform it when necessary. However, the presence of elec-
tro-withdrawing substituents such as the carbonyl group is still a
shortcoming, since the starting phenols are not sufficiently reac-
tive. This methodology is yet to be tested with aliphatic alcohols.
O
NH
O
NH2
NH
NH
NH2
H2N
H2N
O
O
O
S
NH
NH
NH2
O
O
NH
NH
NH2
10b
5.10
H2N
HO
O
O
NH
NH2
12b
13b
4.98
4.49
4.94
O
O
S
NH
NH2
2.2. Pharmacology
HO
HO
O
The affinity towards the a2-ARs in human PFC tissue of all com-
NH
NH2
pounds prepared was measured by competition with the
a2-AR
14b
selective radioligand [3H]RX821002 (2-methoxy-idazoxan), which
was used at a constant concentration of 1 nM. Idazoxan and Cloni-
O
a
2-AR antagonist previously prepared by us.14b
dine, two well-known
a
2-AR ligands, were also used as references.
a
2.2.1. Affinity towards the
a
2-ARs
Replacement of the guanidinium cation (1) by the isouronium
(2) led to a loss in affinity of nearly two logarithmic units (Table
2). In the mono O-isouronium series, compound 2 displays an affin-
ity slightly higher than that of 7b and very similar to that of 6b.
Although the differences are not very significant, it seems that
the substrates with longer aliphatic chains tend to bind better to
the receptors (Table 2).
Given the chemical structure of the lead compound 1, the syn-
thesis and pharmacological evaluation of the isouronium analogue
2 seems a rational step in the search of some relationship between
structure and activity. Furthermore, as in our previous work,14 we
prepared a number of structurally related analogues to try to find
some useful information from the behaviour of these molecules in
the
a2-ARs. It is worth mentioning that to the best of our knowl-
Amongst the dicationic molecules, the methylene derivative 8b
presented the highest affinity (5.40, Table 2), with the ether ana-
logue 9b showing the lowest pKi of its series. Regarding the
hydroxybenzene O-isouronium salts 12b–14b, the same order in
edge, this is the first group of O-phenylisouronium compounds that
have been biologically tested. The affinities obtained, expressed as
pKi, are displayed in Table 2.

8214
Áine Goonan et al. / Bioorg. Med. Chem. 16 (2008) 8210–8217
affinity as for their dicationic counterparts can be identified
(CH2 > S > O). The ether derivative 13b presented the poorest affin-
ity of the whole series (4.49, Table 2). In all cases, the bis-O-isouro-
nium salts displayed better affinities than their monocationic
analogues.
Comparing the data obtained for 6b–10b with that of the corre-
sponding guanidinium derivatives previously described by us,14 as
was found for 1 and 2, all new isouronium compounds presented
lower affinities. The pKi difference was higher than one logarithmic
according to the method Bradford using BSA as standard, and
was similar in the different brain samples.
4.1.2. [3H]RX821002 binding assays
Specific [3H]RX821002 binding was measured in 0.55 mL-ali-
quots (50 mM Tris–HCl, pH 7.5) of the neural membranes which
were incubated with [3H]RX821002 (1 nM) for 30 min at 25 °C in
the absence or presence of the competing compounds (10ꢀ12
–
10ꢀ3 M, 10 concentrations). Incubations were terminated by dilut-
ing the samples with 5 mL of ice-cold Tris incubation buffer (4 °C).
Membrane bound [3H]RX821002 was separated by vacuum filtra-
tion through Whatman GF/C glass fibre filters. Then, the filters
were rinsed twice with 5 mL of incubation buffer and transferred
to minivials containing 3 mL of OptiPhase ‘HiSafe’ II cocktail and
counted for radioactivity by liquid scintillation spectrometry. Spe-
cific binding was determined and plotted as a function of the com-
pound concentration. Non-specific binding was determined in the
presence of adrenaline (10ꢀ5 M).
unit in every case except for 8b (DpKi = 0.98).
All compounds prepared have a low affinity towards the
a2-ARs.
This result highlights the different behaviour of the guanidinium
and isouronium cations in the binding site of the receptors. Thus,
the replacement of an amino group for the isosteric oxygen atom,
leads to remarkable changes in the affinity and/or activity of the
compounds. The substitution of a HB donor (NH group) by a HB
acceptor (O group) results in a dramatic loss of affinity. Hence, it
seems that the presence of three HB donors (NH type groups) in
the cation is required and plays an important role in the affinity.
4.1.3. Analysis of binding data
Analysis of competition experiments to determine the inhibi-
tion constant (Ki) were performed by nonlinear regression using
the GraphPad Prism program. All experiments were analysed
assuming a one-site model of radioligand binding. Ki values were
normalized to pKi values.
3. Conclusions
In this paper we have reported the synthesis of nine new O-phe-
nylisouronium compounds (2, 6b–10b and 12b–14b) and their
Boc-protected precursors (2a, 6a–10a and 12a–14a) in moderate
to good overall yields. Starting from phenols, Kim and Qian’s strat-
egy for the synthesis of protected guanidines was followed.14 The
X-ray diffraction structure of the intermediates 8a and 9a is pre-
sented. Compounds 8b, 9b and 10b are dicationic compounds,
whereas the rest of final products are monocationic species.
4.1.4. Drugs
[3H]RX821002 (specific activity 59 Ci/mmol) was obtained from
Amersham International, UK. Idazoxan HCl was synthesised by Dr.
F. Geijo at S.A. Lasa Laboratories, Barcelona, Spain. Clonidine HCl
and RX821002 HCl were purchased from Sigma (St. Louis, USA). All
other chemicals were of the highest purity commercially available.
All final substrates were evaluated as potential
a2-ARs ligands
in human PFC. The dicationic molecules 8b–10b displayed better
affinities than their hydroxy-monocationic analogues. Unfortu-
nately, all of the isouroniums (2, 6b–10b) showed lower pKi values
than their guanidinium counterparts.14
4.2. Chemistry
All the commercial chemicals were obtained from Sigma–Al-
drich or Fluka and were used without further purification. Deuter-
ated solvents for NMR use were purchased from Apollo. Dry
solvents were prepared using standard procedures, according to
Vogel, with distillation prior to use. Chromatographic columns
were run using Silica gel 60 (230–400 mesh ASTM) or Aluminium
Oxide (activated, Neutral Brockman I STD grade 150 mesh). Sol-
vents for synthesis purposes were used at GPR grade. Analytical
TLC was performed using Merck Kieselgel 60 F254 silica gel plates
or Polygram Alox N/UV254 aluminium oxide plates. Visualisation
was by UV light (254 nm). NMR spectra were recorded in a Bruker
DPX-400 Avance spectrometer, operating at 400.13 MHz and
600.1 MHz for 1H NMR and 100.6 MHz and 150.9 MHz for 13C
NMR. Shifts are referenced to the internal solvent signals. NMR
data were processed using Bruker Win-NMR 5.0 software. Electro-
spray mass spectra were recorded on a Mass Lynx NT V 3.4 on a
Waters 600 controller connected to a 996 photodiode array detec-
tor with methanol, water or ethanol as carrier solvents. Melting
points were determined using an Electrothermal IA9000 digital
melting point apparatus and are uncorrected. Infrared spectra were
recorded on a Mattson Genesis II FTIR spectrometer equipped with
a Gateway 2000 4DX2-66 workstation and on a Perkin Elmer Spec-
trum One FT-IR Spectrometer equipped with Universal ATR sam-
pling accessory. Elemental analysis was carried out at the
Microanalysis Laboratory, School of Chemistry and Chemical Biol-
ogy, University College Dublin.
Nevertheless, negative results sometimes can be as important as
positive ones since they provide with important information on
what molecular features are essential for a good interaction with
the receptor. Our initial hypothesis was that the substitution of
one of the NH group of the guanidinium cation (HB donor) by an isos-
teric O atom (HB acceptor) while keeping the other two NH2 groups
(HB donors) could improve the interactions of the compounds in the
antagonist binding pocket of the a2-ARs. As the isouronium contain-
ing products poorly bind the receptors showing a loss of affinity, we
can conclude that in our series of compounds, the interaction with
the residues involved in the antagonist binding pocket requires the
three HB donor groups oriented as in the guanidinium cation.
4. Experimental protocol
4.1. Pharmacology: materials and methods
4.1.1. Preparation of membranes
Neural membranes (P2 fractions) were prepared from the PFC of
human brains obtained at autopsy in the Instituto Vasco de Medi-
cina Legal, Bilbao, Spain. Postmortem human brain samples of each
subject (1 g) were homogenized using a Teflon-glass grinder (10
up-and-down strokes at 1500 rpm) in 30 volumes of homogeniza-
tion buffer (1 mM MgCl2, and 5 mM Tris–HCl, pH 7.4) supple-
mented with 0.25 M sucrose. The crude homogenate was
centrifuged for 5 min at 1000g (4 °C) and the supernatant was cen-
trifuged again for 10 min at 40,000g (4 °C). The resultant pellet was
washed twice in 20 volumes of homogenization buffer and recen-
trifuged in similar conditions. Aliquots of 1 mg protein were stored
at ꢀ70 °C until use in the assay. Protein content was measured
4.2.1. General procedure for the synthesis of (bis)Boc-protected
isoureas: Method A
Each of the corresponding phenols (or diphenols) was treated
with 1.1 equivalents (or 2.2 for the diols) of mercury (II) chloride,

Áine Goonan et al. / Bioorg. Med. Chem. 16 (2008) 8210–8217
8215
1.0 equivalents (or 2.0 for the diols) of N,N0-di(tert-butoxycar-
bonyl)thiourea 3 and 3.1 equivalents (or 7.2 for the diols) of TEA in
dry DCM at 0 °C and under argon. The resulting mixture was stirred
at 0 °C for 1 h and for the appropriate duration at room temperature.
Then, the reaction mixture was diluted with EtOAc and filtered
through a pad of Celite to get rid of the mercury sulfide precipitate
formed. The filter cake was rinsed with EtOAc. The organic phase
was extracted with water (2ꢁ 30 mL), washed with brine (1ꢁ
30 mL), dried over anhydrous Na2SO4 and concentrated under vac-
uum to give a residue that was purified by silica gel column chroma-
tography, eluting with the appropriate hexane:EtOAc mixture.
mixture was stirred at 0 °C for 1 h and 21 h more at room temper-
ature. Usual work up followed by silica gel column chromatogra-
phy, eluting with hexane/EtOAc (3:1) afforded 8a as a white solid
(202 mg, 58% yield). Thirty-two milligrams (14% yield) of 12a
was also obtained; mp 144–146 °C; IR (neat)
m 3178 (NH), 1767,
1655, 1625 (CO, CN) cmꢀ1 1H NMR (CDCl3) d 1.45 (s, 18H,
;
(CH3)3), 1.54 (s, 18H, (CH3)3), 3.98 (s, 2H, CH2), 7.12 (d, 4H,
J = 8.5 Hz, Ar.), 7.17 (d, 4H, J = 8.5 Hz, Ar.), 10.69 (br s, 2H, NH);
13C NMR (CDCl3)
d 27.9 (2(CH3)3), 40.5 (CH2), 81.0, 82.8
(C(CH3)3), 121.6, 129.8, 138.3 (Ar.), 148.2 (CO), 149.5 (Ar.), 158.4,
162.0 (CO, CN).
4.2.2. 1,3-Di(tert-butoxycarbonyl)-2-(5,6,7,8-tetrahydro-naph-
talene-2-yl)isourea (2a): Method A
4.2.6. 4,40-Bis[N,N0-di(tert-butoxycarbonyl)-isoureido]-diphenyl
ether (9a): Method A
HgCl2 (1.1 mmol, 299 mg) was added over a solution of 149 mg
HgCl2 (1.1 mmol, 299 mg) was added over a solution of 102 mg
(0.5 mmol) of 4,40-dihydroxyphenyl ether, 277 mg (1.0 mmol) of 3
and 0.5 mL (3.6 mmol) of TEA in dry DCM (5 mL) at 0 °C. The result-
ing mixture was stirred at 0 °C for 1 h and 20 h more at room tem-
perature. Usual work up followed by silica gel column
chromatography, eluting with hexane/EtOAc (3:1) afforded 9a as
a white solid (233 mg, 67% yield). Nine milligrams (4% yield) of
(1.0 mmol)
of
5,6,7,8-tetrahydro-naphthalen-2-ol,
277 mg
(1.0 mmol) of 3 and 0.43 mL (3.1 mmol) of TEA in dry DCM (5 mL)
at 0 °C. The resulting mixture was stirred at 0 °C for 1 h and 16 h
more at room temperature. Usual work up followed by silica gel col-
umn chromatography, eluting with hexane/EtOAc (5:2) afforded 2a
as a colourless oil (248 mg, 63% yield); IR (nujol) m 3261 (NH), 1770,
1611 (CO, CN) cmꢀ1; 1H NMR (CDCl3) d 1.44 (s, 9H, (CH3)3), 1.48 (s,
9H, (CH3)3), 1.71–1.85 (m, 4H, CH2CH2CH2CH2), 2.69–2.82 (m, 4H,
2PhCH2), 6.85 (s, 1H, Ar.), 6.91 (d, 1H, J = 8.2 Hz, Ar.), 7.02 (d, 1H,
J = 8.2 Hz, Ar.), 10.59 (br s, 1H, NH); 13C NMR (CDCl3) d 22.7, 23.0
(CH2CH2CH2CH2, 27.8 (2(CH3)3), 28.7, 29.2 (PhCH2), 80.7, 82.5
(C(CH3)3), 118.7, 121.4, 129.6, 134.5, 138.1, 148.2 (Ar.), 148.6,
158.3, 161.9 (CO, CN).
13a was also obtained; mp 142–144 °C; IR (neat)
m 3171 (NH),
1766, 1655, 1623 (CO, CN) cmꢀ1 1H NMR (CDCl3) d 1.48 (s, 18H,
;
(CH3)3), 1.56 (s, 18H, (CH3)3), 7.02 (d, 4H, J = 9.0 Hz, Ar.), 7.18 (d,
4H, J = 9.0 Hz, Ar.), 10.70 (br s, 2H, NH); 13C NMR (CDCl3) d 27.5
(2(CH3)3), 80.7, 82.5 (C(CH3)3), 119.0, 122.5, 146.2 (Ar.), 147.8
(CO), 154.4 (Ar.), 158.1, 161.2 (CO, CN).
4.2.7. 4,40-Bis[N,N0-di(tert-butoxycarbonyl)-isoureido]-diphenyl
thioether (10a): Method A
4.2.3. 1,3-Di(tert-butoxycarbonyl)-2-indan-5-yl-isourea (6a):
Method A
HgCl2 (1.1 mmol, 299 mg) was added over a solution of 110 mg
(0.5 mmol) of 4,40-thiodiphenol, 277 mg (1.0 mmol) of 3 and
0.5 mL (3.6 mmol) of TEA in dry DCM (5 mL) at 0 °C. The resulting
mixture was stirred at 0 °C for 1 h and 21 h more at room temper-
ature. Usual work up followed by silica gel column chromatogra-
phy, eluting with hexane/EtOAc (5:1) afforded 10a as a white
solid (218 mg, 61% yield). Forty-eight milligrams (20% yield) of
HgCl2 (1.1 mmol, 299 mg) was added over a solution of 135 mg
(1.0 mmol) of indan-5-ol, 277 mg (1.0 mmol) of 3 and 0.43 mL
(3.1 mmol) of TEA in dry DCM (5 mL) at 0 °C. The resulting mixture
was stirred at 0 °C for 1 h and 16 h more at room temperature.
Usual work up followed by silica gel column chromatography, elut-
ing with hexane/EtOAc (5:2) afforded 6a as a colourless oil
(251 mg, 66% yield); IR (nujol)
m
3261 (NH), 1774, 1629 (CO, CN)
14a was also obtained; mp 136–138 °C; IR (neat)
m 3171 (NH),
cmꢀ1 1H NMR (CDCl3) d 1.44 (s, 9H, (CH3)3), 1.54 (s, 9H, (CH3)3),
;
1769, 1657, 1624 (CO, CN) cmꢀ1 1H NMR (CDCl3) d 1.49 (s, 18H,
;
1.99–2.14 (m, 2H, CH2CH2CH2), 2.83–2.97 (m, 4H, 2PhCH2), 6.91
(d, 1H, J = 8.0 Hz, Ar.), 7.02 (s, 1H, Ar.), 7.17 (d, 1H, J = 8.0 Hz, Ar.),
10.63 (br s, 1H, NH); 13C NMR (CDCl3) d 25.6 (CH2CH2CH2, 27.9
(2(CH3)3), 32.2, 32.9 (PhCH2), 80.1, 82.7 (C(CH3)3), 117.5, 119.2,
124.5, 141.7, 145.4, 149.6 (Ar.), 148.3, 158.6, 162.1 (CO, CN).
(CH3)3), 1.53 (s, 18H, (CH3)3), 7.15 (d, 4H, J = 8.8 Hz, Ar.), 7.34 (d,
4H, J = 8.8 Hz, Ar.), 10.69 (br s, 2H, NH); 13C NMR (CDCl3) d 27.9
(2(CH3)3), 81.2, 83.0 (C(CH3)3), 122.6, 131.9, 133.0 (Ar.), 148.1
(CO), 150.2 (Ar.), 158.1, 161.8 (CO, CN).
4.2.8. General procedure for the synthesis of hydroxybenzene
Boc-protected isourea derivatives: Method B
4.2.4. 1,3-Di(tert-butoxycarbonyl)-2-p-tolyl-isourea (7a):
Method A
HgCl2 (1.1 equivalents) was added over a solution containing an
excess (3.0 equivalents) of each of the corresponding diols, 1.0
equivalent of N,N0-di(tert-butoxycarbonyl)thiourea 3 and 3.1 equiv-
alents of TEA in dry DCM (5 mL) at 0 °C under argon. The resulting
mixture was stirred at 0 °C for 1 h and for the appropriate duration
at room temperature. Then, the reaction mixture was diluted with
EtOAc and filtered through a pad of Celite. The filter cake was rinsed
with EtOAc. The organic phase was extracted with water (2ꢁ 30 mL),
washed with brine (1ꢁ 30 mL), dried over anhydrous Na2SO4 and
concentrated under vacuum to give a residue that was purified by
silica gel column chromatography, eluting with the appropriate hex-
ane:EtOAc system to yield the desired mono-Boc-protected isoureas
as white solids. Formation of the disubstituted compound was also
observed, and the starting material diol can be recovered from the
column eluting with a more polar hexane:EtOAc mixture.
HgCl2 (1.1 mmol, 299 mg) was added over a solution of 109 mg
(1.0 mmol) of 4-methyl-phenol, 277 mg (1.0 mmol) of 3 and
0.43 mL (3.1 mmol) of TEA in dry DCM (5 mL) at 0 °C. The resulting
mixture was stirred at 0 °C for 1 h and 23 h more at room temper-
ature. Usual work up followed by silica gel column chromatogra-
phy, eluting with hexane/EtOAc (3:2) afforded 7a as a white solid
(259 mg, 73% yield); mp 90–92 °C; IR (nujol)
m 3253 (NH), 1769,
1622 (CO, CN) cmꢀ1 1H NMR (CDCl3) d 1.43 (s, 9H, (CH3)3), 1.53
;
(s, 9H, (CH3)3), 2.32 (s, 3H, CH3), 7.05 (d, 2H, J = 8.0 Hz, Ar.), 7.14
(d, 2H, J = 8.0 Hz, Ar.), 10.64 (br s, 1H, NH); 13C NMR (CDCl3) d
20.8 (CH3), 27.9 (2(CH3)3), 80.8, 82.7 (C(CH3)3), 121.2, 129.7,
135.4, 148.2 (Ar.), 148.8, 158.4, 162.0 (CO, CN); MS (ESI+) m/z
373.1706 [M+Na]+.
4.2.5. 4,40-Bis[N,N0-di(tert-butoxycarbonyl)-isoureido]-diphenyl
methane (8a): Method A
4.2.9. 1,3-Di(tert-butoxycarbonyl)-2-[4-(4-hydroxy-benzyl)-
HgCl2 (1.1 mmol, 299 mg) was added over a solution of 101 mg
(0.5 mmol) of 4,40-methylenediphenol, 277 mg (1.0 mmol) of 3 and
0.5 mL (3.6 mmol) of TEA in dry DCM (5 mL) at 0 °C. The resulting
phenyl]-isourea (12a): Method B
HgCl2 (3.3 mmol, 896 mg) was added over
a solution of
1803 mg (9.0 mmol) of 4,40-methylenediphenol, 830 mg

8216
Áine Goonan et al. / Bioorg. Med. Chem. 16 (2008) 8210–8217
(3.0 mmol) of 3 and 1.3 mL (9.3 mmol) of TEA in dry DCM (5 mL) at
0 °C. The resulting mixture was stirred at 0 °C for 1 h and 16 h more
at room temperature. Usual work up followed by silica gel column
chromatography, eluting with hexane/EtOAc (2:1) afforded 12a as
a white solid (987 mg, 74% yield). (Less than 6% of the disubsti-
(m, 2H, Ar.), 7.22 (d, 1H, J = 8.0 Hz, Ar.); 13C NMR (D2O) d 21.6,
21.9 (CH2CH2CH2CH2, 27.8, 28.3 (PhCH2), 117.3, 120.6, 130.6,
137.3, 139.8, 146.2 (Ar.), 161.5 (CN); MS (ESI+) m/z 191.2918
[M+H]+. Anal. (C11H15ClN2Oꢂ1.6H2O) Calcd: C, 51.70; H, 7.18; N,
10.96. Found: C, 51.38; H, 6.97; N, 10.74.
tuted compound was observed.) Mp 141–143 °C; IR (neat)
m
3345, 3261 (OH, NH), 1762, 1667, 1614 (CO, CN) cmꢀ1 1H NMR
;
4.2.14. 2-Indan-5-yl-isouronium chloride (6b): Method C
White solid (93%); mp 151–153 °C; 1H NMR (D2O) d 2.01–2.17
(m, 2H, CH2CH2CH2), 2.75–2.93 (m, 4H, 2PhCH2), 7.03 (d, 1H,
J = 8.0 Hz, Ar.), 7.15 (s, 1H, Ar.), 7.36 (d, 1H, J = 8.0 Hz, Ar.); 13C
NMR (D2O) d 25.0 (CH2CH2CH2, 31.3, 31.9 (PhCH2), 116.5, 118.0,
125.4, 144.3, 147.0, 147.1 (Ar.), 161.6 (CN); MS (ESI+) m/z
177.1009 [M+H]+. Anal. (C10H13ClN2Oꢂ0.9H2O) Calcd: C, 52.48; H,
6.52; N, 12.24. Found: C, 52.52; H, 6.16; N, 12.07.
(CDCl3) d 1.39 (s, 9H, (CH3)3), 1.54 (s, 9H, (CH3)3), 3.80 (s, 2H,
CH2), 6.46 (br s, 1H, OH), 6.61 (d, 2H, J = 8.5 Hz, Ar.), 6.88 (d, 2H,
J = 8.0 Hz, Ar.), 7.03 (d, 2H, J = 8.5 Hz, Ar.), 7.07 (d, 2H, J = 8.0 Hz,
Ar.), 10.72 (br s, 1H, NH); 13C NMR (CDCl3) d 27.8 (2(CH3)3), 40.2
(CH2), 81.3, 83.1 (C(CH3)3), 115.3, 121.3, 129.6, 129.7, 131.7,
139.6, 148.3, 149.0 (Ar.), 154.5, 158.7 (CO), 161.6 (CN); MS (ESI+)
m/z 465.2025 [M+Na]+.
4.2.10. 1,3-Di(tert-butoxycarbonyl)-2-[4-(4-hydroxy-phenoxy)-
phenyl]-isourea (13a): Method B
4.2.15. 2-p-Tolyl-isouronium chloride (7b): Method C
White solid (94%); mp decomposes over 160 °C; 1H NMR (D2O)
d 2.44 (s, 3H, CH3), 7.28 (d, 2H, J = 8.2 Hz, Ar.), 7.44 (d, 2H,
J = 8.2 Hz, Ar.); 13C NMR (D2O) d 19.9 (CH3), 120.7, 131.0, 138.7,
146.9 (Ar.), 161.9 (CN); MS (ESI+) m/z 151.2527 [M+H]+. Anal.
(C8H11ClN2Oꢂ0.2H2O) Calcd: C, 50.51; H, 6.04; N, 14.72. Found: C,
50.40; H, 5.84; N, 14.76.
HgCl2 (1.5 mmol, 419 mg) was added over a solution of 852 mg
(4.2 mmol) of 4,40-dihydroxydiphenyl ether, 387 mg (1.4 mmol) of
3 and 0.6 mL (4.3 mmol) of TEA in dry DCM (5 mL) at 0 °C. The
resulting mixture was stirred at 0 °C for 1 h and 15 h more at room
temperature. Usual work up followed by silica gel column chroma-
tography, eluting with hexane/EtOAc (2:1) afforded 13a as a white
solid (481 mg, 77% yield). (Less than 5% of the disubstituted com-
4.2.16. 4,40-Diisouronium diphenylmethane dichloride (8b):
Method C
pound was observed.) Mp 134–136 °C; IR (neat)
m 3346, 3283
(OH, NH), 1763, 1667, 1615 (CO, CN) cmꢀ1 1H NMR (CDCl3) d
;
White solid (92%); mp decomposes over 256 °C; 1H NMR (D2O)
d 4.09 (s, 2H, CH2), 7.25 (d, 4H, J = 8.0 Hz, Ar.), 7.42 (d, 4H,
J = 8.0 Hz, Ar.); 13C NMR (D2O) d 39.3 (CH2), 120.8, 130.5, 141.0,
147.2 (Ar.), 161.4 (CN); MS (ESI+) m/z 285.1338 [M+H]+. Anal.
(C15H18Cl2N4O2ꢂ1.8H2O) Calcd: C, 46.24; H, 5.59; N, 14.38. Found:
C, 46.05; H, 5.30; N, 14.28.
1.37 (s, 9H, (CH3)3), 1.53 (s, 9H, (CH3)3), 6.63 (d, 2H, J = 8.8 Hz,
Ar.), 6.74 (d, 2H, J = 8.8 Hz, Ar.), 6.77–6.86 (m, 3H, OH + Ar.), 7.03
(d, 2H, J = 9.3 Hz, Ar.), 10.74 (br s, 1H, NH); 13C NMR (CDCl3) d
27.7, 27.9 ((CH3)3), 81.5, 83.2 (C(CH3)3), 116.2, 117.8, 120.7,
122.4, 145.3, 148.2, 148.9, 152.8 (Ar.), 156.6, 159.1 (CO), 161.6
(CN); MS (ESI+) m/z 467.1799 [M+Na]+.
4.2.17. 4,40-Diisouronium diphenylether dichloride (9b):
Method C
4.2.11. 1,3-Di(tert-butoxycarbonyl)-2-[4-(4-hydroxy-phenyl-
sulfanyl)-phenyl]-isourea (14a): Method B
White solid (91%); mp decomposes over 264 °C; 1H NMR (D2O)
d 7.19 (d, 4H, J = 9.5 Hz, Ar.), 7.34 (d, 4H, J = 9.0 Hz, Ar.); 13C NMR
(D2O) d 120.3, 122.4, 144.5, 155.4 (Ar.), 161.4 (CN); MS (ESI+) m/z
287.1132 [M+H]+. Anal. (C14H16Cl2N4O3ꢂ1.5H2O) Calcd: C, 43.54;
H, 4.96; N, 14.51. Found: C, 43.42; H, 4.65; N, 14.56.
HgCl2 (3.3 mmol, 896 mg) was added over
a solution of
1965 mg (9.0 mmol) of 4,40-thiodiphenol, 830 mg (3.0 mmol) of 3
and 1.3 mL (9.3 mmol) of TEA in dry DCM (5 mL) at 0 °C. The result-
ing mixture was stirred at 0 °C for 1 h and 16 h more at room tem-
perature. Usual work up followed by silica gel column
chromatography, eluting with hexane/EtOAc (2:1) afforded 14a
as a white solid (1082 mg, 78% yield). (Less than 5% of the disubsti-
4.2.18. 4,40-Diisouronium diphenylthioether dichloride (10b):
Method C
tuted compound was observed.) Mp 153–155 °C; IR (neat)
m
3332,
White solid (92%); mp decomposes over 247 °C; 1H NMR (D2O)
d 7.30 (d, 4H, J = 8.5 Hz, Ar.), 7.53 (d, 4H, J = 8.5 Hz, Ar.); 13C NMR
(D2O) d 121.8, 132.8, 134.6, 148.2 (Ar.), 161.1 (CN); MS (ESI+) m/z
303.0922 [M+H]+. Anal. (C14H16Cl2N4O2Sꢂ1.5H2O) Calcd: C, 41.80;
H, 4.76; N, 13.93. Found: C, 41.90; H, 4.43; N, 13.59.
3239 (OH, NH), 1761, 1667, 1611 (CO, CN) cmꢀ1; 1H NMR (CDCl3) d
1.38 (s, 9H, (CH3)3), 1.54 (s, 9H, (CH3)3), 6.64 (d, 2H, J = 8.0 Hz, Ar.),
6.93–7.00 (m, 4H, Ar.), 7.02 (br s, 1H, OH), 7.21 (d, 2H, J = 8.0 Hz,
Ar.), 10.76 (br s, 1H, NH); 13C NMR (CDCl3) d 27.7, 27.9 ((CH3)3),
81.7, 83.4 (C(CH3)3), 116.6, 121.6, 121.9, 127.9, 135.8, 137.3,
148.2, 148.4 (Ar.), 157.3, 159.0 (CO), 161.4 (CN).
4.2.19. 2-[4-(4-Hydroxy-benzyl)-phenyl]-isouronium chloride
(12b): Method C
4.2.12. General procedure for the synthesis of the hydroch-
loride salts: Method C
White solid (91%); mp decomposes over 208 °C; 1H NMR (D2O)
d 3.90 (s, 2H, CH2), 6.80 (d, 2H, J = 7.0 Hz, Ar.), 7.09–7.19 (m, 4H,
Ar.), 7.35 (d, 2H, J = 7.5 Hz, Ar.); 13C NMR (D2O) d 39.1 (CH2),
115.0, 120.7, 129.5, 130.2, 132.8, 142.0, 146.9, 153.3 (Ar.), 161.4
(CN); MS (ESI+) m/z 243.1123 [M+H]+. Anal. (C14H15ClN2O2ꢂ1.2H2O)
Calcd: C, 55.98; H, 5.84; N, 9.33. Found: C, 56.09; H, 5.48; N,
9.26.
Each of the corresponding Boc-protected precursors (0.5 mmol)
was treated with 14 mL of a 50% solution of trifluoroacetic acid in
DCM for 3 h. After that time, the solvent was eliminated under vac-
uum to generate the trifluoroacetate salt. This salt was redissolved
in 20 mL of water and treated for 24 h with IRA400 Amberlyte resin
in its Clꢀ form. Then, the resin was removed by filtration and the
aqueous solution washed with DCM (2ꢁ 10 mL). Evaporation of
the water afforded the pure hydrochloride salt. Absence of the tri-
fluoroacetate salt was checked by 19F NMR.
4.2.20. 2-[4-(4-Hydroxy-phenoxy)-phenyl]-isouronium chlori-
de (13b): Method C
White solid (93%); mp decomposes over 190 °C; 1H NMR (D2O)
d 6.89 (d, 2H, J = 8.0 Hz, Ar.), 7.99 (d, 2H, J = 8.0 Hz, Ar.), 7.04 (d, 2H,
J = 8.6 Hz, Ar.), 7.24 (d, 2H, J = 8.6 Hz, Ar.); 13C NMR (D2O) d 116.0,
118.5, 120.8, 122.1, 143.5, 148.4, 151.8, 157.1 (Ar.), 161.5 (CN); MS
(ESI+) m/z 245.0933 [M+H]+. Anal. (C13H13ClN2O3ꢂ2.0H2O) Calcd: C,
49.30; H, 5.41; N, 8.84. Found: C, 49.18; H, 5.25; N, 8.71.
4.2.13. 2-(5,6,7,8-Tetrahydro-naphthalen-2-yl)-isouronium
chloride (2): Method C
White solid (95%); mp 105–107 °C; 1H NMR (D2O) d 1.65–1.78
(m, 4H, CH2CH2CH2CH2), 2.68–2.80 (m, 4H, 2PhCH2), 6.94–7.07

Áine Goonan et al. / Bioorg. Med. Chem. 16 (2008) 8210–8217
8217
15. Between others: Peltonen, J. M.; Nyrönen, T.; Wurster, S.; Pihlavisto, M.;
Hoffrén, A. M.; Marjamäki, A.; Xhaard, H.; Kanerva, L.; Savola, J. M.; Johnson, M.
S.; Scheinin, M. Br. J. Pharmacol. 2003, 140, 347.
16. Grijalba, B.; Callado, L. F.; Meana, J. J.; García-Sevilla, J. A.; Pazos, A. Eur. J.
Pharmacol. 1996, 310, 83.
4.2.21. 2-[4-(4-Hydroxy-phenylsulfanyl)-phenyl]-isouronium
chloride (14b): Method C
White solid (92%); mp decomposes over 210 °C; 1H NMR (D2O)
d 6.92 (d, 2H, J = 8.6 Hz, Ar.), 7.18 (d, 2H, J = 8.5 Hz, Ar.), 7.29 (d, 2H,
J = 8.6 Hz, Ar.), 7.43 (d, 2H, J = 8.5 Hz, Ar.); 13C NMR (D2O) d 116.8,
121.8, 122.2, 129.8, 136.1, 138.7, 147.3, 156.6 (Ar.), 161.7 (CN); MS
(ESI+) m/z 261.0686 [M+H]+. Anal. (C13H13ClN2O2Sꢂ2.5H2O) Calcd:
C, 45.68; H, 5.31; N, 8.20. Found: C, 45.99; H, 5.25; N, 8.44.
17. Fitzgerald, P. B.; Oxley, T. J.; Laird, A. R.; Kulkarni, J.; Egan, G. F.; Daskalakis, Z. J.
Psychiatry Res. 2006, 148, 33.
18. Betwen others: (a) Moss, R. A.; Fu, X. Tetrahedron Lett. 2007, 48, 235; (b) Fu,
X.; Moss, R. A.; Sauers, R. R.; Wipf, P. Tetrahedron Lett. 2005, 46, 4265; (c)
Moss, R. A.; Fu, X.; Sauers, R. R.; Wipf, P. J. Org. Chem. 2005, 70, 8454; (d)
Moss, R. A.; Fu, X. Tetrahedron Lett. 2004, 45, 5321; (e) Moss, R. A.; Zheng, F.;
Fede, J.-M.; Johnson, L. A.; Sauers, R. R. J. Am. Chem. Soc. 2004, 126, 12421;
(f) Moss, R. A.; Zheng, F.; Sauers, R. R.; Toscano, J. P. J. Am. Chem. Soc. 2001,
123, 8109.
Acknowledgements
19. Moss, R. A.; Kaczmarczyk, G.; Johnson, L. A. Synth. Commun. 2000, 30, 3233.
20. Basterfield, S.; Rodman, F. B. S.; Tomecko, J. W. Can. J. Res. B 1939, 17, 390.
We thank Science Foundation Ireland for generous financial
support (SFI-RFP: CHE275). F.R. thanks the Consejeria de Educacion
Cultura y Deporte de la Comunidad Autonoma de La Rioja for his
Grant. This research was also supported by Bizkaiko Foru Aldundia
(Ekinberri 7/12/EK/2005/65 and DIPE 06/04), the Basque Govern-
ment (SAIOTEK: S-PE07UN13) and Spanish Ministry of Health,
Instituto de Salud Carlos III, (Ciber-SAM). A.M.E. was recipient of
a predoctoral fellowship from the Basque Government.
ˇ
21. Mikolajczyk, M.; Kielbasinski, P. Tetrahedron 1981, 37, 233.
22. (a) Kim, K. S.; Qian, L. Tetrahedron Lett. 1993, 34, 7677; (b) Poss, M. A.;
Iwanovicz, E.; Reid, J. A.; Lin, J.; Gu, Z. A. Tetrahedron Lett. 1992, 33, 5933; (c)
Linney, I. D.; Buck, I. M.; Harper, E. A.; Kalindjian, S. B.; Pether, M. J.; Shankley,
N. P.; Watt, G. F.; Wright, P. T. J. Med. Chem. 2000, 43, 2362.
23. Between others: (a) Shie, J.-J.; Fang, J.-M.; Wang, S.-Y.; Tsai, K.-C.; Cheng, Y.-S.
E.; Yang, A.-S.; Hsiao, S.-C.; Su, C.-Y.; Wong, C.-H. J. Am. Chem. Soc. 2007, 129,
11892; (b) Sansone, F.; Dudic, M.; Donofrio, G.; Rivetti, C.; Baldini, L.; Casnati,
A.; Cellai, S.; Ungaro, R. J. Am. Chem. Soc. 2006, 128, 14528; (c) Dardonville, C.;
Goya, P.; Rozas, I.; Alsasua, A.; Martin, I.; Borrego, M. J. Bioorg. Med. Chem. 2000,
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2. Ruffolo, R. R., Jr.; Nichols, A. J.; Stadel, J. M.; Hieble, J. P. Annu. Rev. Pharmacol.
Toxicol. 1993, 32, 243.
3. (a) Kowaluk, E. A.; Arneric, S. P. Annu. Rep. Med. Chem. 1998, 33, 11; (b) Tryba,
M.; Zenz, M. Anesthesiology 1991, 75, A1085.
4. Hayashi, Y.; Maze, M. Br. J. Anaesth. 1993, 71, 108.
25. Crystal data for 8a:
0.20 ꢁ 0.20 ꢁ 0.20 mm, T = 125 K, Monoclinic, space group P21 /c, Z = 1,
a = 20.063(8), b = 10.081(4), c = 20.371(8) Å,
V = 3699(8) Å3,
Dcalcd = 1.230 g cmꢀ3, F(000) = 1464, k = 0.71070 Å (Mo K = 0.090 mmꢀ1
,
C140H192N16O40, Mw = 2739.10, colourless prism of
a
),
l
Rigaku Saturn 724 CCD diffractometer, h range 2.31–25.00°, 43,678 collected
reflections, 6484 unique, full-matrix least-squares (SHELXL-97a), R1 = 0.1026,
wR2 = 0.1666 (R1 = 0.1145, wR2 = 0.1713 all data), goodness-of-fit = 1.382,
residual electron density between 0.311 and ꢀ0.277 e Åꢀ3. Hydrogen atoms
were located using a Riding model. Sheldrick, G.M. SHELXL-97: program for the
refinement of crystal structures. University of Göttingen, Germany, 1997.
Cambridge Crystallographic Data Centre Deposition Number CCDC 686281.
5. Pertovaara, A. Prog. Neurobiol. 1993, 40, 691.
6. Munk, S. A.; Harcourt, D. A.; Arasasingham, P. N.; Burke, J. A.; Kharlamb, A. B.;
Manlapaz, C. A.; Padillo, E. U.; Roberts, D.; Runde, E.; Williams, L.; Wheeler, L.
A.; Garst, M. E. J. Med. Chem. 1997, 40, 18.
7. (a) Bymaster, F. P.; McNamara, R. K.; Tran, P. V. Expert Opin. Invest. Drugs 2003,
12, 531; (b) Elhwuegi, A. S. Biol. Psychiatry 2004, 28, 435.
8. http://www.who.int/mental_health/management/depression/definition/en/.
9. (a) Callado, L. F.; Meana, J. J.; Grijalba, B.; Pazos, A.; Sastre, M.; García-Sevilla, J.
A. J. Neurochem. 1998, 70, 1114; (b) Gonzalez-Maeso, J.; Rodriguez-Puertas, R.;
Meana, J. J.; Garcia-Sevilla, J. A.; Guimon, J. Mol. Psychiatry 2002, 7, 755.
10. Mateo, Y.; Fernandez-Pastor, B.; Meana, J. J. Br. J. Pharmacol. 2001, 133, 1362.
11. Fernandez-Pastor, B.; Meana, J. J. Eur. J. Pharmacol. 2002, 442, 225.
12. Devoto, P.; Flore, G.; Pani, L.; Gessa, G. L. Mol. Psychiatry 2001, 6, 657.
13. Leonard, B. E. Hum. Psychopharm. Clin. 1999, 14, 75.
14. (a) Rodriguez, F.; Rozas, I.; Ortega, J. E.; Meana, J. J.; Callado, L. F. J. Med. Chem.
2007, 50, 4516; (b) Rodriguez, F.; Rozas, I.; Ortega, J. E.; Erdozain, A. M.; Meana,
J. J.; Callado, L. F. J. Med. Chem. 2008, 51, 3304; (c) Rodriguez, F.; Rozas, I.; Ortega,
J. E.; Erdozain, A. M.; Meana, J. J.; Callado, L.F. 2008, unpublished results.
26. Crystal data for 9a:
C68H92N8O22, Mw = 1373.50, colourless plate of
0.20 ꢁ 0.10 ꢁ 0.06 mm, T = 121 K, triclinic, space group P1, Z = 1, a =
10.005(2), b = 10.496(3), c = 19.230(5) Å, V = 1857.1(8) Å3, Dcalcd = 1.228
g cmꢀ3
,
F(000) = 732, k = 0.71070 Å (Mo
Saturn 724 CCD diffractometer, range 2.21–25.00°, 28,696 collected
reflections, 6521 unique, full-matrix least-squares
(SHELXL-97a),
Ka), l , Rigaku
= 0.092 mmꢀ1
h
R1 = 0.0583, wR2 = 0.1601 (R1 = 0.0699, wR2 = 0.1687 all data), goodness-of-
fit = 1.122, residual electron density between 0.272 and ꢀ0.267 e Åꢀ3
.
Hydrogen atoms were located using
a Riding model. Sheldrick, G.M.
SHELXL-97: program for the refinement of crystal structures. University of
Göttingen, Germany, 1997. Cambridge Crystallographic Data Centre
Deposition Number CCDC 686280.