Chiral cyclohexane based fluorescent chemosensors for enantiomeric discrimination of aspartate

Article abstract of DOI:10.1016/j.tet.2008.01.085

Some new chiral cyclohexyl based fluorescent anion receptors have been synthesized and their absolute configuration has been determined by using circular dichroism (CD). Complexation experiments have been carried out with several dicarboxylates, and stoic

Full text of DOI:10.1016/j.tet.2008.01.085

Available online at www.sciencedirect.com
Tetrahedron 64 (2008) 3217e3224
www.elsevier.com/locate/tet
Chiral cyclohexane based fluorescent chemosensors
for enantiomeric discrimination of aspartate
a
b
a
Ana M. Costero a, , Manuel Colera , Pablo Gavina , Salvador Gil ,
*
Miklos Kubinyi , Krisztina Pal , Mihaly Kallay
~
´
c,d
c
d
´
´
´
a Department of Organic Chemistry, Universidad de Valencia, 46100-Burjassot, Valencia, Spain
b Instituto de Ciencia Molecular, Universidad de Valencia, Campus de Paterna, Valencia, Spain
c Chemical Research Centre, Hungarian Academy of Sciences, 1025 Budapest, PO Box 17, Hungary
d Department of Physical Chemistry, Budapest University of Technology and Economics, 1521 Budapest, PO Box 91, Hungary
Received 18 December 2007; received in revised form 18 January 2008; accepted 21 January 2008
Available online 30 January 2008
Abstract
Some new chiral cyclohexyl based fluorescent anion receptors have been synthesized and their absolute configuration has been determined by
using circular dichroism (CD). Complexation experiments have been carried out with several dicarboxylates, and stoichiometries and complex-
ation constants for the corresponding complexes have been determined. The chiral discrimination ability of these ligands for chiral dicarboxy-
lates has been studied and the best results have been obtained with TMA aspartate.
Ó 2008 Elsevier Ltd. All rights reserved.
1. Introduction
rigidity of this system can be used to control the complex geom-
etry.7 During several years we have been studying the complexing
properties of ligands derived from trans-transoid-trans-1,2,4,5-
tetrasubstituted cyclohexanes and their possible application in
sensing, and we have reported the preparation of two ligands use-
fulintheselectiverecognitionofmaleateversusfumarateanions.8
In our efforts to develop fluorescent chemosensors for dicarb-
oxylates of biological interest, now we would like to report the
preparation of four enantiomerically pure cyclohexane based
chiral ligands (þ)-1, (ꢀ)-1, (þ)-2, and (ꢀ)-2 and their behavior
in the enantiomeric discrimination of aspartate (3) glutamate
(4), and tartrate (5) anions (Chart 1).
Over the last years, the development of chemosensors capable
of recognizing anionic species has aroused great interest.1
However, enantioselective recognition and even more sensing
of biologically relevant molecules, such as amino acids, remain
a major challenge for hosteguest chemists.2 Although several
receptors have been developed for chiral dicarboxylates3 less ex-
amples of enantioselective chemosensors have been described.4
In the design of efficient chemosensors, fluorescence is one of
the most interesting properties to be used in the transduction pro-
cess because it provides many advantages such as high sensitivity,
rapid on-site evaluation and low cost5 and among the fluorescent
mechanisms developed in the signaling process for anion sensing,
excimer/exciplex formation has been successfully used.6 As exci-
mer formation is strongly dependent on geometry the binding unit
tobeusedshouldbecarefullydesigned.Inthatsense,cyclohexane
derivatives with the appropriate configuration have been success-
fully used in recognition and it has been established that the
H
NH2
CO2
-O2C
EtOOC
EtOOC
R'
-
L-3 L-aspartate
NHCSNHR
R'=NHCSNHR (-)-1
R'= OH (-)-2
H
NH2
CO2
R=
-O2C
-
L-4 L-glutamate
EtOOC
R'
H
OH
-O2C
HO
NHCSNHR
-
EtOOC
CO2
H
R'=NHCSNHR (+)-1
R'=OH (+)-2
L-5 L-tartrate
* Corresponding author.
E-mail address: ana.costero@uv.es (A.M. Costero).
Chart 1.
0040-4020/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2008.01.085

3218
A.M. Costero et al. / Tetrahedron 64 (2008) 3217e3224
2. Results and discussion
moments close to parallel with the long axes of the naphthalene
rings. (They correspond to the excitation of unsubstituted
naphthalene to its 21B3u state.)14 A conformational analysis,
based on molecular mechanics calculations,15 was carried out
for (þ)-1 and led to the identification of 24 conformers whose
energy was less than 3 kcal/mol higher than that of the most
stable one. It was found that in all these conformers the long
axes of the naphthalene units close negative angles, predicting
negative couplets in their CD spectra (see Fig. 1b). Thus, the
signs of the couplets in the observed spectra suggest the config-
urations shown in Chart 1 for (þ)-1 and (ꢀ)-1.
2.1. Synthesis and stereochemistry determinations
Ligands (þ)-1, (ꢀ)-1, (þ)-2, and (ꢀ)-2 were synthesized as
described in Schemes 1 and 2. Thus, compounds(ꢀ)-9 and (þ)-9
were separately obtained from racemic trans-1,2-bis(ethoxycar-
bonyl)-4-cyclohexene oxide9 following the procedure described
by Chandrasekar et al.10 Reaction with naphthylisothiocyanate
yielded the corresponding thioureas (þ)-1 and (ꢀ)-1. The rela-
tive configuration of the stereocentres in addition to the main
conformation of the ligands in DMSO solutions was perfectly
established by NMR techniques and are showed in Chart 2.
Similarly, (þ)-2 and (ꢀ)-2 were prepared as shown in
Scheme 2 from the previously separated compounds 6b and
6a, respectively. The relative configuration of (þ)-2 and (ꢀ)-
2 and the main conformation in DMSO solutions for these
ligands were also established by using NMR techniques (Chart
2) (see Supplementary data).
The absolute configurations were determined from the CD
spectra with the help of the exciton chirality rule.11 As can be
seen in Figure 1a, there is a negative exciton couplet in the spec-
trum of (þ)-1 (and a positive one in that of (ꢀ)-1) with an inflec-
tion point at the same wavelength where the maximum of the
most intense band can be observed in the UV absorption spec-
trum. The couplet is non-symmetric similar to the case of
some other trans-1,2-disubstituted cyclohexanes with identical
chromophore substituents.12 Quantum chemical calculations13
were performed on the electronic spectrum of 1-naphthylthio-
urea, which indicated that these features arise from a pair of
coupled transitions of the naphthalene moieties with transition
2.2. Complexation experiments
Complexation experiments with L-aspartate (L-3), D-aspartate
(D-3), L-glutamate (L-4), D-glutamate (D-4), L-tartrate (L-5), and
D-tartrate (D-5) all as their tetramethylammonium (TMA) salts
were performed in DMSO. The stoichiometries and equilibrium
constants were determined by fitting16 the UV spectra of equilib-
rium mixtures (Fig. 2 for (þ)-1 and (þ)-2 with L-aspartateand for
other ligands and dicarboxylates see Supplementary data) and
the obtained results are summarized in Table 1.
The stoichiometry of the complexes formed by ligands (þ)-1
and (ꢀ)-1 was 1:1 with all the studied dicarboxylates. The com-
plexation constant values were also very similar. By contrast,
ligands (þ)-2 and (ꢀ)-2 showed a 2:1 stoichiometry in their
complexes with L- and D-aspartate and L- and D-glutamate, and
a 1:1 stoichiometry with L- and D-tartrate. In addition, com-
plexes formed with L- and D-glutamate showed complexation
constant values higher than complexes with L- and D-aspartate.
NH2
transoid
DIAD
EtO2C
trans
EtO2C
trans
EtO2C
OH
trans
transoid
Ph3P
O
EtO2C
LiClO4
THF
trans
EtO2C
N
H
N
CH3CN
6a
6b
7
EtO2C
TMSN3
CH3CN
EtO2C
EtO2C
N3
EtO2C
EtO2C
N3
=R
+
N
H
N
H
8b
8a
H
N
S
R
EtO2C
NH
NH
EtO2C
NH2
NH2
H2, Pd(C)
EtOH
8a
R
N C
THF
S
EtO2C
EtO2C
(+)-1
(-)-9
R
R
S
S
N
H
H
N
EtO2C
EtO2C
NH2
NH2
EtO2C
EtO2C
NH
NH
H2, Pd(C)
R
N C
THF
S
8b
EtOH
(-)-1
(+)-9
R
S
N
H
Scheme 1.

A.M. Costero et al. / Tetrahedron 64 (2008) 3217e3224
3219
EtO2C
EtO2C
OH
EtO2C
EtO2C
OH
EtO2C
EtO2C
OH
NH
R
N C
THF
S
H2, Pd(C)
EtOH
N
H
NH2
(+)-10
6a
R
(-)-2
S
N
H
=R
EtO2C
EtO2C
OH
EtO2C
EtO2C
OH
EtO2C
OH
NH
H2, Pd(C)
EtOH
R
N C
THF
S
N
H
NH2
EtO2C
(-)-10
6b
R
(+)-2
S
N
H
Scheme 2.
In order to obtain information about the structure of the
formed complexes, 1H NMR studies were carried out. The stud-
ies developed with (þ)-1 and (ꢀ)-1 in the presence of 1 equiv of
L-and D-aspartate and L- and D-glutamate demonstrated that both
thioureas of the ligand were involved in the complexation and
that a conformational change was induced in the cyclohexane
moiety. In the complex, both axial and equatorial hydrogens
(Ha and Hb) appear at the same value of d (Fig. 3c), suggesting
a boat-type conformation of the cyclohexyl moiety similar to the
one previously observed in the complex formed between the
racemic (ꢁ)-1 and TMA maleate.9 By contrast, when the anion
present was L- or D-tartrate no conformational changes were
observed after the addition of 1 equiv (Fig. 3b). In this case
the 1:1 complex seems to be formed by involving only one
thiourea group.
By contrast, 1H NMR studies carried out with (þ)-2 and (ꢀ)-
2 and L- and D-aspartate and L- and D-glutamate showed that with
these ligands no conformational changes were induced in the
cyclohexane moiety after complexation. This behavior was
expected due to the 2:1 stoichiometry of the complexes that
allow the dicarboxylate to be bound to two thiourea groups
OH
COOEt
Hα
S
EtOOC
EtOOC
N
H
N
H
H
N
H
N
Hβ
(+)-2
HN
HN
S
COOEt (-)-1
S
Chart 2.
Figure 1. (a) UV absorption and CD spectra of (þ)-1. (b) Direction of the coupling transition dipoles in the lowest energy conformation.
4
3.5
3
4
3.5
3
2.5
2
2.5
2
1.5
1
1.5
1
0.5
0
255
0.5
0
255
305
355
nm
405
455
305
355
nm
405
455
Figure 2. UV spectra in DMSO of (þ)-1 (10ꢀ5 M)þTMA L-aspartate (left) and (þ)-2 (10ꢀ5 M)þTMA L-aspartate (right).

3220
A.M. Costero et al. / Tetrahedron 64 (2008) 3217e3224
Table 1
groups close and almost parallel giving rise to the excimer emis-
sion. The latter feature is not so strong when D-3 is added to the
solution (see Fig. 4b) due to the absolute configuration of this
dicarboxylate that precludes the effective proximity of both
naphthyl groups. As can be expected, the opposite behavior
can be observed with ligand (þ)-1 (see Supplementary data).
A possible structure of the complex is displayed in Figure 5,
which is similar to that previously described for a related
complex.8 The complex is stabilized by four hydrogen bonds
formed between the hydrogens of the thiourea group and the
carboxylate oxygens. This proposed structure turned out to be
a local minimum in the molecular mechanics calculations.15
When L- and D-glutamate was added to solutions of (þ)-1 and
(ꢀ)-1, theresultsobtained wereverysimilar tothosedescribedfor
both enantiomers of aspartate. Thus, (þ)-1 shows excimer forma-
tion with D-glutamate and (ꢀ)-1 with L-glutamate. However, the
intensity of the excimer band was in these cases lower than with
aspartate. This difference can be due to the longer chain of this
dicarboxylate that precludes both naphthyl groups to be as close
as in the complexes formed with aspartate. In conclusion, (þ)-1
and (ꢀ)-1 show different fluorescence behavior depending on
the absolute configuration of the amino acid. On the other hand,
the effect of the length of the chain in the dicarboxylate gives
rise to stronger modifications with aspartate than with glutamate.
Both L-tartrate and D-tartrate did not induce any change in
the fluorescence spectra of (þ)-1 or (ꢀ)-1. This behavior can
be related with the geometry of the 1:1 complexes formed with
these anions in which only a thiourea is involved in coordina-
tion and no modification in the conformation of the cyclohexyl
moiety was observed. Thus, both naphthyl groups are faraway
one to the other and no excimer is observed in the fluorescence
spectrum.
Whereas ligands (þ)-1 and (ꢀ)-1 showed an enantiomeric
behavior ((þ)-1 gives the stronger excimer with L-aspartate
and (ꢀ)-1 with D-aspartate), the behavior of (þ)-2 and (ꢀ)-2
was clearly different. Thus, both (þ)-2 and (ꢀ)-2 give the
stronger modification of the fluorescence spectrum in the pres-
ence of TMA L-aspartate (the spectra for (ꢀ)-2 are displayed
in Fig. 6 and for (þ)-2 see Supplementary data). With these
ligands the formed excimer should be intermolecular in agree-
ment with the 2:1 stoichiometry showed in the complexes.
This stoichiometry could also be responsible for the similar
effect that the same enantiomer has with both ligands because
the role played for the stereochemistry of the stereocentre in
this case can be only related to steric factors.
Equilibrium constants (log b) and stoichiometries (L:A) for the complexes
formed between (þ)-1, (ꢀ)-1, (þ)-2 and (ꢀ)-2 with L- and D-aspartate,
L- and D-glutamate, and L- and D-tartrate
Host
(þ)-1
1:1
(ꢀ)-1
1:1
(þ)-2
2:1
(ꢀ)-2
2:1
Stoichio.
log b
L-3
D-3
L-4
D-4
L-5
D-5
3.8ꢁ0.2
1:1
3.6ꢁ0.3
1:1
3.7ꢁ0.1
2:1
3.2ꢁ0.1
2:1
Stoichio.
log b
3.5ꢁ0.3
1:1
3.8ꢁ0.3
1:1
3.6ꢁ0.2
2:1
3.4ꢁ0.3
2:1
Stoichio.
log b
3.6ꢁ0.1
1:1
3.5ꢁ0.3
1:1
6.9ꢁ0.1
2:1
6.8ꢁ0.1
2:1
Stoichio.
log b
3.6ꢁ0.2
1:1
3.6ꢁ0.3
1:1
7.0ꢁ0.1
1:1
7.1ꢁ0.1
1:1
Stoichio.
log b
3.4ꢁ0.3
1:1
4.0ꢁ0.4
1:1
3.4ꢁ0.1
1:1
3.4ꢁ0.1
1:1
Stoichio.
log b
4.1ꢁ0.4
3.0ꢁ0.2
3.3ꢁ04
3.3ꢁ04
UVevis titrations in DMSO at 25 ꢂC.
(one from each ligand) without involving the cyclohexane
moiety. With these ligands, L- and D-tartrate formed complexes
with 1:1 stoichiometries, which involved only one molecule of
ligand. The complexation induced clear changes in the aromatic
zone of the 1H NMR spectra but no changes were observed in the
cyclohexane signals because in this case no conformational
modification is needed for the coordination process.
2.3. Enantiomeric discrimination of chiral dicarboxylates
The utility of ligands (þ)-1 and (ꢀ)-1 and (þ)-2 and (ꢀ)-2 for
chiral discrimination was studied with the above-cited chiral
dicarboxylates by using fluorescence. Thus, the fluorescence
spectrum of (ꢀ)-1 (lexc¼290 nm) substantially changes upon
theadditionofL-3 (seeFig. 4a). Thebandofthepure ligandshifts
from 410 nm to longer wavelengths and a new band emerges at
495 nm. The appearance of this new band may be related to the
formation of an excimer. Thus, L-3 dianion with its (R) configu-
ration perfectly fits in the complex inducing a conformational
change in the ligand. This change places both naphthalene
In addition, studies carried out with L- and D-glutamate
show that with both enantiomers, the ligands (þ)-2 and (ꢀ)-
2 give rise to excimer bands with practically the same inten-
sity. The longer chain of glutamate determines that the config-
uration of the a carbon has small influence on the geometry of
complexation.
With these ligands, the results observed with tartrate were
the same as those showed by (þ)-1 and (ꢀ)-1, no excimer
bands being observed, and this behavior can be explained by
taking into account that the complexes formed have a 1:1
stoichiometry that does not induce any change in the confor-
mation of the cyclohexyl moiety.
Figure 3. 1H NMR spectra (cyclohexyl moiety: axial and equatorial protons) in
DMSO-d6 of (a) free ligand (þ)-1, (b) (þ)-1þ1 equiv of TMA L-tartrate, and
(c) (þ)-1þ1 equiv of TMA L-aspartate.

A.M. Costero et al. / Tetrahedron 64 (2008) 3217e3224
3221
(a)
30
25
20
15
10
5
(b)
30
25
20
15
10
5
300
350
400 450
Wavelength (nm)
500
550
300
350
400
Wavelength (nm)
450
500
550
Figure 4. Fluorescence spectra in DMSO of (a) (ꢀ)-1 (10ꢀ5 M)þTMA L-aspartate and (b) (ꢀ)-1 (10ꢀ5 M)þTMA D-aspartate (lexc¼290 nm).
patron solution + 15 equiv. of TMA
L-aspartate
100
80
60
40
20
0
patron solution
S
N
H
H
S
H
H
N
N
patron solution + 15 equiv. of
TMA D-aspartate
O
COOEt
EtOOC
H
H
O
H
O
N
H
H
H
H
O
(-)-2
H
H
NH2
Figure 5. Structural proposal for the complex formed between ligand (ꢀ)-1
and TMA (R)-aspartate.
350
400
450
Wavelength (nm)
500
550
In order to evaluate the utility of the prepared ligands in
chiral recognition, an additional experiment was carried out
with ligand (ꢀ)-2, the one which gave the stronger differences
between both enantiomers of TMA aspartate. In this experi-
ment, to a solution of 10ꢀ5 M of the ligand 40 equiv of
L-aspartate was added and its fluorescence spectrum was
registered. This patron solution was then divided into two sam-
ples and 15 equiv of L-aspartate was added to the first sample
and the fluorescence spectrum was registered. As it was ex-
pected, no changes were observed because the sample was
already saturated in this dicarboxylate. To the second sample,
15 equiv of D-aspartate was added. The fluorescence spectrum
in this case showed a clear decrease in the band. This behavior
clearly supports the utility of this patron solution for enantio-
meric discrimination between L- and D-aspartate (Fig. 7).
Figure 7. Enantiomeric recognition of TMA L- and D-aspartate by using
a patronsolution((ꢀ)-2þ40 equivofTMAL-aspartateinDMSO)(lexc¼290 nm).
3. Conclusions
Four new chiral ligands have been prepared and their config-
uration and main conformations in DMSO solutions have been
established. Complexation constants and stoichiometries have
been determined for L- and D-aspartate, L- and D-glutamate,
and L- and D-tartrate all of them as TMA salts. Ligands contain-
ing two thiourea groups form 1:1 complexes with all the studied
dicarboxylates. Bycontrast, ligands containing only onethiourea
group show 2:1 stoichiometries exceptwith tartrate. Solutionsof
15
(a)
(b)
15
10
5
10
5
0
0
300
350
400 450
Wavelength (nm)
500
550
300
350
400 450
Wavelength (nm)
500
550
Figure 6. Fluorescence spectrum in DMSO of (ꢀ)-2 (10ꢀ5 M) (a) in the presence of TMA L-aspartate and (b) TMA D-aspartate (0e3 equiv) (lexc¼290 nm).

3222
A.M. Costero et al. / Tetrahedron 64 (2008) 3217e3224
either (ꢀ)-2 with a large excess of L-aspartate or (þ)-2 with
a large excess of D-aspartate can be used for enantiomeric
discrimination between L- and D-aspartate.
4.3. trans-3,4-Bis-(ethoxycarbonyl)-7-((R)-1-phenylethyl)-7-
aza-bicyclo[4.1.0]heptane (7)
DIAD (2.1 mL, 10.70 mmol) was slowly added over a mix-
ture of the diastereoisomers 6a and 6b (2.71 g, 7.45 mmol),
and Ph3P (2.81 g, 10.70 mmol) in THF (23 mL) at 0 ꢂC under
Ar. The mixture was stirred for 18 h at room temperature.
After evaporation of the solvent, the crude was purified by col-
umn chromatography, hexane/ethyl acetate (7:3) as eluent, to
give a mixture of diastereoisomers 7 (2.50 g, 97%) as a color-
4. Experimental section
4.1. General procedures and materials
trans-1,2-Bis-(ethoxycarbonyl)-4-cyclohexene oxide was
prepared by following the procedure described in the litera-
ture.9 All other reagents were commercially available and
were used without purification. THF was distilled from Na/
benzophenone under Ar prior to use. Column chromatography
was performed with silica gel 60 (230e400 mesh, Merck).
1
less oil. H NMR (300 MHz, CDCl3): d 7.38e7.23 (m, 5H),
4.17e4.06 (m, 4H), 2.93e2.85 (m, 1H), 2.55e2.32 (m, 3H),
2.23e2.17 (m, 1H), 1.82e1.57 (m, 4H), 1.37e1.19 (m, 9H);
13C NMR (75 MHz, CDCl3): d 175.7, 174.9, 145.3, 128.4,
128.3, 126.9, 126.8, 126.7, 72.4, 69.6, 60.9, 41.5, 39.5, 38.5,
37.7, 36.1, 35.6, 28.7, 27.6, 14.3; MS (EI) found: 345.1915,
C20H27NO4 requires: 345.1940.
1
Silica gel 60 F254 (Merck) plates were used for TLC. H and
13C NMR spectra were recorded with the deuterated solvent
as the lock and residual solvent as the internal reference.
High-resolution mass spectra (FAB) were recorded in the pos-
itive ion mode. UVevis spectra were recorded using a 1 cm
path length quartz cuvette. All measurements were carried
out at 293 K (thermostatted). Fluorescence spectra were
recorded in a Varian Cary Eclipse Fluorimeter.
4.4. trans-transoid-trans-5-((R)-1-Phenylethylamino)-1,2-bis-
(ethoxycarbonyl)-4-azidocyclohexane (8aþ8b)
To a solution of 7 (2.50 g, 7.24 mmol) in acetonitrile (60 mL)
at 0 ꢂC under Ar, TMSN3 (1.41 mL, 10.66 mmol) was added
dropwise. The mixture was stirred overnight at room tempera-
ture. Then, the excess of azide and the solvent were evaporated
under low pressure to give a diastereoisomeric mixture of 8a (Rf
(dichloromethane/ethyl acetate 95:5)¼0.50, 1.94 g, 69%) and
8b (Rf (dichloromethane/ethyl acetate 95:5)¼0.29, 453 mg,
4.2. trans-transoid-trans-5-((R)-1-Phenylethylamino)-1,2-bis-
(ethoxycarbonyl) 4-cyclohexanol (6aþ6b)
(R)-(þ)-1-Phenylethylamine (1.63 mL, 12.59 mmol) was
added dropwise to a solution of racemic trans-1,2-bis-(ethoxy-
carbonyl)-4-cyclohexene oxide (3.05 g, 12.59 mmol) and
LiClO4 (1.34 g, 12.59 mmol) in acetonitrile (10 mL) at 0 ꢂC.
After 18 h under reflux, the mixture was allowed to cool at
room temperature. After addition of water (10 mL), it was
extracted with dichloromethane. The combined organic phases
were dried (anhydrous Na2SO4) and evaporated to yield
a crude mixture of diastereoisomers that were separated by
column chromatography (silica gel) to give 6a (Rf (dichloro-
methane/ethyl acetate 1:1)¼0.69, 1.65 g, 36%) and 6b (Rf (di-
chloromethane/ethyl acetate 1:1)¼0.46, 1.70 g, 37%) both as
pale yellow oils. Compound 6a: 1H NMR (300 MHz,
CDCl3): d 7.31e7.24 (m, 5H), 4.16e4.12 (dq, J1¼7.3 Hz,
J2¼2.9 Hz, 4H), 3.90 (q, J¼7.0 Hz, 1H), 3.48 (dt,
J1¼7.7 Hz, J2¼3.7 Hz, 4H), 3.22 (q, J¼7.1 Hz, 1H), 3.12 (q,
J¼7.1 Hz, 1H), 2.62e2.54 (m, 1H), 2.36e2.26 (m, 1H),
2.24e2.15 (m, 1H), 1.78e1.69 (m, 1H), 1.42e1.33 (m, 1H),
1.35 (d, J¼7.0 Hz, 3H), 1.25 (dt, J1¼7.3 Hz, J2¼2.9 Hz,
6H); 13C NMR (75 MHz, CDCl3): d 174.2, 173.9, 146.3,
128.6, 127.2, 126.5, 69.3, 60.9, 60.9, 56.7, 55.5, 40.5, 40.1,
31.0, 29.1, 23.9, 14.3, 14.3; MS (EI) found: 363.1973,
C20H29NO5 requires: 363.2046. Compound 6b: 1H NMR
(300 MHz, CDCl3): d 7.32e7.23 (m, 5H), 4.17e3.95 (m,
5H), 3.43e3.36 (m, 1H), 3.21e3.11 (m, 2H), 2.38e2.21 (m,
3H), 1.64e1.48 (m, 2H), 1.35 (d, J¼7.0 Hz, 1H), 1.27 (t,
J¼7.3 Hz, 1H), 1.17 (t, J¼7.3 Hz, 1H); 13C NMR (75 MHz,
CDCl3): d 174.1, 173.7, 145.3, 128.5, 127.1, 126.7, 69.9,
60.9, 60.8, 56.0, 54.7, 40.3, 40.1, 31.0, 28.0, 25.4, 14.2,
14.1; MS (EI) found: 363.1973, C20H29NO5 requires:
363.2046.
1
16%) as colorless oils. Compound 8a: H NMR (300 MHz,
CDCl3): d 7.38e7.24 (m, 5H), 4.20e4.07 (m, 4H), 3.86 (t,
J¼7.0 Hz, 1H), 3.69e3.64 (m, 1H), 3.00e2.98 (m, 1H),
2.70e2.65 (m, 1H), 2.22e2.16 (m, 1H), 1.95e1.88 (m, 2H),
1.58e1.50 (m, 1H), 1.37 (d, J¼7.0 Hz, 3H), 1.30 (t,
J¼7.6 Hz, 3H), 1.23 (t, J¼7.6 Hz, 3H); 13C NMR (75 MHz,
CDCl3): d 174.1, 174.0, 145.7, 128.7, 127.3, 126.5, 72.4, 61.0,
60.5, 60.1, 56.2, 53.3, 39.7, 29.9, 27.8, 24.5, 21.8, 14.3; MS
(EI) found (MþH): 389.2189, C20H29N4O4 requires:
389.2190. Compound 8b: 1H NMR (300 MHz, CDCl3):
d 7.35e7.21 (m, 5H), 4.19e4.02 (m, 4H), 3.87 (q, J¼7.0 Hz,
1H), 3.37e3.34 (m, 1H), 3.08e2.98 (m, 2H), 2.53e2.48 (m,
1H), 2.21e2.04 (m, 2H), 1.82e1.62 (m, 2H), 1.50 (s, 1H),
1.37 (d, J¼7.0 Hz, 3H), 1.26 (t, J¼7.5 Hz, 3H), 1.18 (t,
J¼7.5 Hz, 3H); 13C NMR (75 MHz, CDCl3): d 174.1, 173.9,
145.3, 128.7, 127.2, 126.5, 69.5, 61.1, 61.0, 55.7, 53.5, 39.8,
28.6, 27.7, 25.3, 14.3, 14.2; MS (EI) found (MþH): 389.1678,
C20H29N4O4 requires: 389.2190.
4.5. (ꢀ)-4,5-Diamino-1,2-bis-(ethoxycarbonyl)-cyclohexane
((ꢀ)-9)
A mixture of 8a (1.05 g, 2.71 mmol) and a catalytic amount
of Pd(C) 10% in ethanol (75 mL) was stirred for 2 days under
an H2 atmosphere (65 psi). After filtration through Celite, the
solvent was evaporated to give (ꢀ)-9 (644 mg, 92%) as a color-
1
less wax. H NMR (300 MHz, CDCl3): d 4.13 (q, J¼7.6 Hz,
4H), 3.17 (br s, 2H), 2.54e2.51 (m, 2H), 2.20e2.16 (m,
2H), 1.58e1.50 (m, 2H), 1.35 (s, 4H), 1.25 (t, J¼7.6 Hz,

A.M. Costero et al. / Tetrahedron 64 (2008) 3217e3224
3223
6H); 13C NMR (75 MHz, CDCl3): d 174.1, 60.9, 53.3, 40.6,
4.9. (ꢀ)-trans-transoid-trans-5-Amino-1,2-bis-(ethoxy-
carbonyl)-4-cyclohexanol ((ꢀ)-10)
32.6, 21.8, 14.3; [a]2D0 ꢀ5.9 (c 3.4, CHCl3); MS (EI) found
(MþH): 258.1582, C12H22N2O4 requires: 258.1580.
Catalytic hydrogenation (65 psi) of 6a (1.65 g, 4.67 mmol)
in ethanol (100 mL), mediated with 10% Pd(C), led to amino-
1
4.6. (þ)-4,5-Diamino-1,2-bis-(ethoxycarbonyl)-cyclohexane
((þ)-9)
alcohol (ꢀ)-7 (993 mg, 82%) as a colorless wax. H NMR
(300 MHz, DMSO-d6): d 4.14 (t, J¼7.2 Hz, 4H), 3.42e3.35
(m, 1H), 3.22e3.08 (m, 2H), 2.74e2.67 (m, 1H), 2.26e2.13
(m, 2H), 2.04 (br s, 3H), 1.72e1.50 (m, 2H), 1.23 (t,
J¼7.2 Hz, 6H); 13C NMR (75 MHz, DMSO-d6): d 174.0,
173.9, 71.5, 61.0, 52.6, 40.5, 40.3, 32.0, 31.2, 14.3; [a]D20
ꢀ8.9 (c 3.7, CHCl3); MS (EI) found (MþH): 260.1482,
C12H22NO5 requires: 260.1497.
A mixture of 8b (453.4 mg, 1.17 mmol) and a catalytic
amount of Pd(C) 10% in ethanol (75 mL) was stirred for 2
days under an H2 atmosphere (65 psi). After filtration through
Celite, the solvent was evaporated to give (þ)-9 (268 mg,
1
89%) as a colorless wax. H NMR (300 MHz, CDCl3): d 4.15
(q, J¼7.8 Hz, 4H), 3.18 (br s, 2H), 2.55e2.52 (m, 2H), 2.21e
2.16 (m, 2H), 1.65 (s, 4H), 1.57e1.51 (m, 2H), 1.26 (t,
J¼7.8 Hz, 6H); 13C NMR (75 MHz, CDCl3): d 174.1, 60.9,
53.3, 40.6, 32.6, 21.8, 14.3; [a]2D0 þ5.8 (c 4.1, CHCl3); MS
(EI) found: 258.1562, C12H22N2O4 requires: 258.1580.
4.10. (þ)-trans-transoid-trans-5-Amino-1,2-bis-(ethoxy-
carbonyl)-4-cyclohexanol ((þ)-10)
Catalytic hydrogenation (65 psi) of 6b (244.9 mg,
0.67 mmol) in ethanol (30 mL), mediated with 10% Pd(C),
led to aminoalcohol (þ)-7 (170 mg, 99%) as a colorless
wax. 1H NMR (300 MHz, DMSO-d6): d 4.74 (br s, 3H),
4.15 (t, J¼7.1 Hz, 4H), 3.46e3.40 (m, 1H), 3.25e3.12 (m,
2H), 2.80e2.69 (m, 1H), 2.16e2.10 (m, 2H), 1.72e1.56 (m,
2H), 1.27 (t, J¼7.1 Hz, 6H); 13C NMR (75 MHz, DMSO-d6)
d 174.0, 173.9, 71.6, 61.0, 52.6, 40.5, 40.3, 32.1, 31.2,
14.3; [a]2D0 þ9.1 (c 3.4, CHCl3); MS (EI) found (MþH):
260.1496, C12H22NO5 requires: 260.1497.
4.7. (þ)-trans-transoid-trans-1,2-Bis-(ethoxycarbonyl)- 4,5-
bis-(3-(naphtalen-1-yl)thioureid)cyclohexane ((þ)-1)
To a solution of (ꢀ)-9 (644.8 mg, 2.50 mmol) in THF
(20 mL) at room temperature, 1-naphthylisothiocyanate
(926.3 mg, 5.00 mmol) was added and the mixture was heated
under reflux for 16 h. Then the mixture was allowed to cool to
room temperature and was poured over hexane (25 mL). From
this mixture, (þ)-1 (1.35 g, 86%) precipitated as a white solid.
(Found: C, 64.5; H, 6.0; N, 8.7; S, 9.9. C34H36N4O4S2: C,
4.11. (þ)-trans-transoid-trans-5-(3-(Naphthalen-1-yl)-
thioureid)-1,2-bis-(ethoxycarbonyl)-4-cyclohexanol ((þ)-2)
1
64.9; H, 5.7; N, 8.9; S, 10.2.) Mp: 122e125 ꢂC. H NMR
(300 MHz, DMSO-d6): d 9.62 (s, 2H), 7.96e7.92 (m, 8H),
7.82e7.47 (m, 8H), 4.54 (m, 2H), 4.18e4.04 (m, 4H), 3.01
(br s, 2H), 2.13e1.96 (m, 4H), 1.22 (t, J¼7.4 Hz, 6H); 13C
NMR (75 MHz, DMSO-d6): d 181.8, 173.2, 134.7, 133.9,
129.5, 128.1, 126.1, 125.5, 124.7, 122.7, 60.5, 52.4, 28.9,
25.1, 22.1, 14.1; [a]2D0 þ46.8 (c 1.1, acetone); MS (EI) found:
628.2227, C34H36N4O4S2 requires: 628.2178.
To a solution of (ꢀ)-10 (971.4 mg, 3.75 mmol) in THF (5 mL)
at room temperature, 1-naphthylthioisocyanate (712.6 mg,
3.85 mmol) was added dropwise, the mixture was heated under
reflux for 16 h, and then, the solvent was evaporated to give
(þ)-2 (1.62 g, 97%) as a pale yellow oil. (Found: C, 62.1; H,
6.4; N, 6.3; S, 7.2. C23H28N2O5S: C, 62.1; H, 6.3; N, 6.3; S,
7.2.) 1H NMR (300 MHz, CDCl3): d 8.11e7.87 (m, 4H), 7.60e
7.44 (m, 4H), 5.70 (br s, 1H), 4.52 (br s, 1H), 4.21e3.97 (m,
4H), 3.55 (br s, 1H), 3.13e2.96 (m, 2H), 2.69 (br s, 1H), 2.25e
2.20 (m, 1H), 1.92e1.72 (m, 2H), 1.54e1.49 (m, 1H), 1.29e
1.16 (m, 3H), 1.16 (t, J¼7.5 Hz, 3H); 13C NMR (75 MHz,
CDCl3): d 182.0, 173.8, 173.0, 134.8, 129.7, 129.3, 128.8,
127.7, 127.3, 125.9, 125.2, 122.5, 70.0, 61.4, 61.1, 60.5, 56.2,
40.4, 39.9, 32.1, 28.5, 21.2, 14.3; [a]2D0 þ48.0 (c 3.3, acetone);
MS (EI) found: 444.1755, C23H28N2O5S requires: 444.1719.
4.8. (ꢀ)-trans-transoid-trans-1,2-Bis-(ethoxycarbonyl)-4,5-
bis-(3-(naphthalen-1-yl)thioureid)cyclohexane ((ꢀ)-1)
To a solution of (þ)-9 (268.5 mg, 1.04 mmol) in THF (7 mL)
at room temperature, 1-naphthylisothiocyanate (385.3 mg,
2.08 mmol) was added and the mixture was heated under reflux
for 16 h. Then the mixture was allowed to cool to room temper-
ature and was poured over hexane (25 mL). From this mixture,
(ꢀ)-1 (542.8 mg, 83%) precipitated as a white solid. (Found: C,
64.3; H, 6.1; N, 8.2; S, 9.6. C34H36N4O4S2: C, 64.9; H, 5.7; N,
4.12. (ꢀ)-trans-transoid-trans-5-(3-(Naphthalen-1-yl)-
thioureid)-1,2-bis-(ethoxycarbonyl)-4-cyclohexanol ((ꢀ)-2)
1
8.9; S, 10.2.) Mp: 119e122 ꢂC. H NMR (300 MHz, DMSO-
d6): d 9.63 (s, 2H), 7.96e7.93 (m, 8H), 7.82e7.44 (m, 8H),
4.54 (m, 2H), 4.16e4.06 (m, 4H), 3.01 (br s, 2H), 2.12e1.96
(m, 4H), 1.22 (t, J¼7.6 Hz, 6H); 13C NMR (75 MHz, CDCl3):
d 181.6, 173.0, 134.9, 131.3, 130.1, 129.2, 128.8, 127.5,
127.0, 126.1, 125.9, 122.3, 61.5, 55.7, 40.3, 30.1, 14.3;
[a]2D0 ꢀ46.7 (c 4.7, acetone); MS (EI) found: 628.2173,
C34H36N4O4S2 requires: 628.2178.
To a solution of (ꢀ)-10 (1.09 g, 4.19 mmol) in THF (5 mL) at
room temperature, 1-naphthylthioisocyanate (796.9 mg,
4.30 mmol) was added dropwise, the mixture was heated under
reflux for 16 h, and then, the solvent was evaporated to give (þ)-
2 (1.73 g, 93%) as a pale yellow oil. (Found: C, 62.3; H, 6.4; N,
1
6.3; S, 7.1. C23H28N2O5S: C, 62.1; H, 6.3; N, 6.3; S, 7.2.) H
NMR (300 MHz, CDCl3): d 8.04e7.88 (m, 4H), 7.59e7.44

3224
A.M. Costero et al. / Tetrahedron 64 (2008) 3217e3224
4. (a) Folmer, A. J.; Frantz, L.; Vincent, M.; Anslyn, E. V. J. Am. Chem. Soc.
2005, 127, 7986e7987; (b) Tsubaki, K.; Tanima, D.; Nuruzzaman, M.;
Kusumoto, T.; Fuji, K.; Kawabata, T. J. Org. Chem. 2005, 70,
4609e4616; (c) Pagliari, S.; Corradini, R.; Galaverna, G.; Sforza, S.;
Dossena, A.; Montalti, M.; Prodi, L.; Zaccheroni, N.; Marchelli, R.
Chem.dEur. J. 2004, 10, 2749e2758; (d) Wong, W.-L.; Huang, K.-H.;
Teng, P.-F.; Lee, C.-S.; Kwong, H.-L. Chem. Commun. 2004, 384e385.
5. De Silva, A. P.; Gunaratne, H. Q. N.; Gunnlaugsson, T.; Huxley, A. J. M.;
Mc Coy, C. P.; Rademacher, J. T.; Rice, T. E. Chem. Rev. 1997, 97,
1515e1566.
(m, 4H), 5.65 (br s, 1H), 4.51 (br s, 1H), 4.19e4.00 (m, 4H), 3.55
(br s, 1H), 3.14e2.92 (m, 2H), 2.70 (br s, 1H), 2.25e2.21 (m,
1H), 1.92e1.72 (m, 2H), 1.53e1.49 (m, 1H), 1.29e1.16 (m,
3H), 1.16 (t, J¼7.5 Hz, 3H); 13C NMR (75 MHz, CDCl3):
d 182.0, 173.8, 172.9, 134.8, 129.7, 128.8, 127.8, 127.3,
125.9, 125.2, 122.5, 70.1, 61.4, 61.1, 56.2, 40.4, 39.9, 32.1,
28.5, 31.2, 14.3; [a]2D0 ꢀ47.7 (c 3.4, acetone); MS (EI) found:
444.1722, C23H28N2O5S requires: 444.1719.
6. (a) Nishizawa, S.; Kaneda, H.; Uchida, T.; Teramae, N. J. Chem. Soc.,
Perkin Trans. 2 1998, 2325e2328; (b) Nishizawa, S.; Kaneda, H.; Kato,
Y.; Teramae, N. J. Am. Chem. Soc. 1999, 121, 9463e9464.
Acknowledgements
7. (a) Samoshin, V. V. Mini-Rev. Org. Chem. 2005, 2, 225e235; (b)
´
Amendola, V.; Boiocchi, M.; Esteban-Gomez, D.; Fabrizzi, L.; Monzani,
The present research has been financed by Spanish DGCYT
(PPQ2002-00986), Generalitat Valenciana (Grupos 03/206),
Hungarian OTKA (T 42546, D 48583), and the Spanishe
Hungarian S&T Cooperation Programme. M.C. acknowledges
the Spanish Government for a Ph.D. grant. M. K is grateful to
J. Gauss for allowing the usage of Spartan program during
his stay at University of Mainz. Finally, SCSIE (Universidad
de Valencia) is gratefully acknowledged for all the equipment
employed.
E. Org. Biomol. Chem. 2005, 3, 2632e2639.
~
8. Costero, A. M.; Colera, M.; Gavina, P.; Gil, S. Chem. Commun. 2006,
761e763.
9. Costero, A. M.; Villarroya, J. P.; Gil, S.; Aurell, M. J.; Ramirez de
Arellano, M. C. Tetrahedron 2002, 58, 6729e6734.
10. Chandrasekar, M.; Sekar, G.; Singh, V. K. Tetrahedron Lett. 2000, 41,
10079e10089.
11. Berova, N.; Nakanishi, N. Circular Dichroism: Principles and Appli-
cations, 2nd ed.; Berova, N., Nakanishi, N., Woody, R. W., Eds.;
Wiley-VCH: New York, NY, 2000; pp 337e382.
12. (a) Kwit, M.; Gawronski, J. Tetrahedron 2003, 59, 9323e9331; (b) Boiad-
jiev, S. E.; Lightner, D. A. Chirality 2005, 17, 316e322.
Supplementary data
13. The spectrum was calculated by ZINDO/S method (Hanson, L. K.; Fajer,
J.; Thompson, M. A.; Zerner, M. C. J. Am. Chem. Soc. 1987, 109,
4728e4730) using Gaussian 03 program package (Frisch, M. J.; Trucks,
G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman,
J. R.; Montgomery, J. A., Jr.; Vreven, T.; Kudin, K. N.; Burant, J. C.;
Millam, J. M.; Iyengar, S. S.; Tomasi, J.; Barone, V.; Mennucci, B.; Cossi,
M.; Scalmani, G.; Rega, N.; Petersson, G. A.; Nakatsuji, H.; Hada, M.;
Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima,
T.; Honda, Y.; Kitao, O.; Nakai, H.; Klene, M.; Li, X.; Knox, J. E.;
Hratchian, H. P.; Cross, J. B.; Adamo, C.; Jaramillo, J.; Gomperts, R.;
Stratmann, R. E.; Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.;
Ochterski, J. W.; Ayala, P. Y.; Morokuma, K.; Voth, G. A.; Salvador, P.;
Dannenberg, J. J.; Zakrzewski, V. G.; Dapprich, S.; Daniels, A. D.; Strain,
M. C.; Farkas, O.; Malick, D. K.; Rabuck, A. D.; Raghavachari, K.;
Foresman, J. B.; Ortiz, J. V.; Cui, Q.; Baboul, A. G.; Clifford, S.;
Cioslowski, J.; Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz, P.;
Komaromi, I.; Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.;
Peng, C. Y.; Nanayakkara, A.; Challacombe, M.; Gill, P. M. W.; Johnson,
B.; Chen, W.; Wong, M. W.; Gonzalez, C.; Pople, J. A. Gaussian 03,
Revision B.01; Gaussian: Pittsburgh, PA, 2003.).
Supplementary data associated with this article can be
found in the online version, at doi:10.1016/j.tet.2008.01.085.
References and notes
1. (a) Fabbrizzi, L.; Licchelli, M.; Labaioli, G. Coord. Chem. Rev. 2000, 205,
85e108; (b) Martinez-Manez, R.; Sancenon, F. Chem. Rev. 2003, 103,
4419e4476; (c) Beer, P. D.; Gale, P. A. Angew. Chem., Int. Ed. 2001,
´
40, 486e516; (d) Gale, P. A.; Garcıa-Garrido, S. E.; Garric, J. Chem.
Soc. Rev. 2008, 37, 151e190; (e) Suksai, C.; Tuntulani, T. Chem. Soc.
Rev. 2003, 32, 192e202.
2. (a) James, T. D.; Samankumara Sandanayake, K. R. A.; Shinkai, S. Nature
1996, 374, 345e347; (b) Kubo, Y.; Maeda, S.; Tokita, S.; Kubo, M.
Nature 1996, 382, 522e524; (c) Naemura, K.; Tobe, Y.; Kaneda, T.
Coord. Chem. Rev. 1996, 148, 199e219; (d) Zhang, X. X.; Bradshaw,
J. S.; Izatt, R. M. Chem. Rev. 1997, 97, 3313e3361; (e) Webb, T. H.;
Wicox, C. S. Chem. Soc. Rev. 1993, 22, 383e395; (f) Finn, M. G.
Chirality 2002, 14, 534e540.
14. Rubio, M.; Merchan, M.; Orti, E.; Roos, B. O. Chem. Phys. 1994, 179,
395e409.
15. Halgren (J. Comput. Chem. 1996, 17, 490e519) and simulated annealing
algorithm were used. They were carried out by Spartan’02 package (Spar-
tan’02; Wavefunction: Irvine, CA, USA, 2002).
3. See for example:. (a) Ragusa, A.; Rossi, S.; Hayes, J. M.; Stein, M.;
Kilburn, J. D. Chem.dEur. J. 2005, 11, 5674e5688; (b) Rossi, S.;
Kyne, G. M.; Turner, D. L.; Wells, N. J.; Kilburn, J. D. Angew. Chem.,
Int. Ed. 2002, 41, 4233e4236; (c) Lee, C.-S.; Teng, P.-F.; Wong, W.-L.;
Kwong, H.-L.; Chan, A. S. C. Tetrahedron 2005, 61, 7924e7930; (d)
Alfonso, I.; Dietrich, B.; Rebolledo, F.; Gotor, V.; Lehn, J.-M. Helv.
Chim. Acta 2001, 84, 280e295.
16. SPECFIT/32TM GLOBAL ANALYSIS SYSTEM v.3.0; Spectrum Software
Associates: Marlborough, MA, USA, 2000; www.bio-logic.info/rapid-
kinetics/specfit.html.