Triphenylamine-based receptor for selective recognition of dicarboxylates

Article abstract of DOI:10.1016/j.tetlet.2009.11.021

A new triphenylamine-based receptor 1 has been designed and synthesized for the recognition of aliphatic dicarboxylates of various chain lengths. This receptor has been designed to utilize an amide-urea conjugate for binding dicarboxylates. The receptor 1

Full text of DOI:10.1016/j.tetlet.2009.11.021

Tetrahedron Letters 51 (2010) 343–347
Contents lists available at ScienceDirect
Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Triphenylamine-based receptor for selective recognition of dicarboxylates
a
a
b
b,
Kumaresh Ghosh a, , Indrajit Saha , Goutam Masanta , Evan B. Wang , Carol A. Parish
*
*
a Department of Chemistry, University of Kalyani, Kalyani, Nadia 741 235, India
b Department of Chemistry, University of Richmond, Richmond, VA 23173, United States
a r t i c l e i n f o
a b s t r a c t
Article history:
A new triphenylamine-based receptor 1 has been designed and synthesized for the recognition of ali-
phatic dicarboxylates of various chain lengths. This receptor has been designed to utilize an amide–urea
conjugate for binding dicarboxylates. The receptor 1 is found to bind the dicarboxylates with moderate
binding strength under a semi rigid, propeller shaped, fluorescent triphenylamine spacer. The binding
behavior was studied in CH3CN using 1H NMR, fluorescence and UV–vis spectroscopic methods. The con-
formational behavior of 1 and its complexation modes have been investigated using classical and quan-
tum mechanical theoretical methods. The receptor is found to be selective for long chain suberate.
Ó 2009 Elsevier Ltd. All rights reserved.
Received 15 September 2009
Revised 4 November 2009
Accepted 6 November 2009
Available online 12 November 2009
Keywords:
Triphenylamine
Dicarboxylate ion recognition
Suberate
Fluorescence quenching
Conformational analysis
Much attention has been paid recently to the development of
synthetic molecular receptors for anions because of the fundamen-
tal role these anions play in a wide range of chemical, environmen-
tal, and biological processes.1–3 The design and synthesis of
artificial receptors that are capable of affecting the selective and
sensitive binding of anionic species through visible, electrochemi-
cal, and optical responses has been the focus of numerous reports
in recent times.4 Dicarboxylates are important target anions for rec-
ognition and sensing owing to their critical role in numerous met-
abolic processes.5,6 During the last decade, dicarboxylate anion
binding by various hydrogen bonding receptors was demonstrated.
In general, most of these receptors consist of urea/thiourea,7,8 imi-
dazolium cation,9 guanidinium ion10,11 ,etc., as the hydrogen bond-
ing synthons placed onto various fluorophores. Gunnalangsson12
et al. reported a neutral and fluorescent PET sensor for glutarate
while He and co-workers13 developed fluorescent sensors for adi-
pate. Mei and Wu reported the sensitive detection of pimelate using
a naphthalene-containing sensor molecule.14 Liu and co-workers
have reported cholic acid-based fluorescent sensors for glutarate
and long chain suberate and sebacate.15 A related recent report
on dinuclear Eu(III) bismacrocyclic sensors for malonate is interest-
ing due to the unique properties of lanthanides.16 We have also
recently reported the selective sensing of 1,4-phenyldiacetate as
well as glutarate by anthracene-based ureidopyridyl17 and
trans-pyridylcinnamide receptors,18 respectively. Thus, although
significant progress in dicarboxylate anion recognition has been
made, there is a continued interest in making new fluorescent
receptors for dicarboxylates. Triphenylamine is a propeller-shaped
fluorescent probe, which has been proven previously by us to be
effective in reporting recognition events.19 Using the fluorescence
properties of triphenylamine we have recently designed and syn-
thesized receptors with conformationally well-defined V-shape
geometries for size-selective recognition of dicarboxylic acids20
and dicarboxylates.21
We wish to report here the further design and synthesis of a
new triphenylamine-based receptor 1 using an o-phenylenedi-
amine binding site, composed of an amide–urea conjugate, for
selective recognition of aliphatic dicarboxylates of various chain
lengths. ortho-Phenylenediame is a well-established motif in anion
recognition.22
He
N
Hd
O
O
Hf
NH
HaN
HbN
NH
NH
O
O
H
cN
* Corresponding authors. Tel.: +91 33 25828750; fax: +91 33 258282.
E-mail addresses: ghosh_k2003@yahoo.co.in (K. Ghosh), cparish@richmond.edu
(C.A. Parish).
NO2
NO2
1
0040-4039/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2009.11.021

344
K. Ghosh et al. / Tetrahedron Letters 51 (2010) 343–347
NH2
NH
NH2
NO2
(i)
(A)
(B)
NH
O
2
NO2
(v)
(iv)
O
(iii)
(ii)
OHC
N
N
N
1
N
O
O
O
CHO
OH
OH
Cl
Cl
3
5
4
Scheme 1. Reagents and conditions: (A) (i) (a) triphosgene, Et3N/dry DCM, 30 min; (b) excess o-phenylenediamine, dry DCM, 3 h, 53% yield; (B) (ii) POCl3, DMF, reflux, 8 h,
56% yield; (iii) (a) KMnO4, acetone–water, 4 h; (b) dil HCl, 72% yield; (iv) oxalyl chloride, DMF, dry DCM, 15 h, 95% yield; (v) 2, Et3N/dry THF–DMF, 4 h, 49% yield.
Receptor 1 was synthesized according to Scheme 1. Reaction of o-
phenylenediamine with p-nitrophenyl isocyanate, which was ob-
tained from the reaction between p-nitroaniline and triphosgene
in the presence of Et3N in dry CH2Cl2, gave the compound 2. Subse-
quent coupling of 2 with triphenylamine diacid chloride 5 (obtained
from the reaction of diacid 4 with oxalyl chloride in dry CH2Cl2 in
the presence of catalytic amount of DMF) in dry THF and DMF mix-
ture solvent yielded the desired receptor 1 in 49% yield as light yel-
glutarate, and suberate. The large downfield shift of the amide
and urea protons in 1 demonstrated the involvement of the o-
phenylenediamine-based receptor sites in complexation.
To ascertain the sensitivity and selectivity, we studied the fluo-
rescence and UV–vis behaviors of 1 in CH3CN containing 0.4% DMSO
in the absence and presence of tetrabutylammonium dicarboxylate
salts of malonate, succinate, glutarate, adipate, pimelate, and suber-
ate. Receptor 1, (c = 6.55 Â 10À5 M) when excited at 350 nm in
CH3CN containing 0.4% DMSO, showed an emission band at
438 nm likely corresponding to excitation and emission of the tri-
phenylamine moiety. Upon gradual addition of the dicarboxylate
anions, the fluorescence emission decreased steadily up to a 1:1
stoichiometry and then increased gradually thereafter. These find-
ings were more pronounced in case of adipate, glutarate, pimelate,
and suberate and were least pronounced in case of malonate and
succinate, the short chain analogs (see Supplementary data). Fig-
ure 2a and b shows the change in the emission spectra of 1 in the
presence of malonate and suberate, respectively. Figure 2c repre-
sents the change in emission of 1 with guest concentration. At this
time we are uncertain as to the nature of the fluorescence increase
in the presence of excess nonflourescent anions; however we pre-
sume this may be due to subtle changes in receptor conformation.
Theoretical studies are planned to probe this effect further.
low solid. Triphenylamine diacid
4 was accomplished from
triphenylamine via formylation23 followed by oxidation using
KMnO4. All the compounds were characterized by 1H NMR, 13C,
FTIR, mass, and UV–vis spectroscopic techniques.
The dicarboxylate anion binding study of the receptor 1 was
performed by 1H NMR, fluorescence, and UV titration experiments.
The binding ability of 1 was initially established by 1H NMR. To the
receptor solution of 1 in CDCl3 containing 0.8% CD3CN, aliphatic
dicarboxylates of various chain lengths were added as their tetra-
butylammonium salts in 1:1 stoichiometries. In the presence of the
dicarboxylates, the amide proton Ha and urea protons Hb and Hc
underwent downfield shift (DdNHa = 1.07–2.73, DdNHb = 0.76–2.88,
D
dNHc = 1.79–2.24). Note that in the presence of malonate, the
more basic of the dicarboxylates studied, deprotonation of the
acidic urea proton Ha occurred resulting in the disappearance of
the corresponding peak. Figure 1 demonstrates the change in 1H
NMR of 1 in the presence of an equivalent amount of malonate,
Figure 3 displays the titration curves for 1 with the various
dicarboxylates, and the break of the curves at [G]/[H] = 1 confirms
a 1:1 host–guest stoichiometry of the complexes. The anion-in-
duced decrease in the emission of 1 may be attributable to the acti-
vation of a PET process occurring during binding; theoretical
studies are currently underway to explore this possibility.
Simultaneous UV–vis titration experiments of the receptor 1
with the same guests as mentioned above were carried out in
the same solvent under controlled conditions. The absorption at
342 nm was gradually decreased resulting in a small red shift
(
Dk = 7–9 nm) as titration progressed. This was found to be true
for all the dicarboxylates irrespective of their chain lengths (see
Supplementary data). For instance, Figure 4 illustrates the titration
spectra of 1 upon gradual increase in the concentration of suberate.
The isosbestic points at 266 and 340 nm (see the inset of Fig. 4) in
the UV–vis spectra indicate host–guest complexation. The red shift
of the absorption peak of 1 at 342 nm upon increase in guest con-
centration signifies an increasing noncovalent interaction of 1 with
the carboxylate motif of the guest.
The driving force for this interaction is most likely the acidity of
the urea protons and the flexibility of the binding arms of 1. The
sharp nonlinear nature of the titration curves and the break at
[G]/[H] = 1 also corroborate the 1:1 stoichiometry of the complexes
(Fig. 5). This is also shown in the Job plots24 in Figure 6. In this re-
gard, the suggested mode of host–guest interaction is illustrated in
Figure 7.
Figure 1. (a) Partial 1H NMR (400 MHz, CDCl3 containing 0.8% CD3CN) of
1
(c = 1.88 Â 10À3 M), in the presence of equivalent amount of (b) malonate, (c)
glutarate, and (d) suberate (for identification of the labeled protons see structure 1).

K. Ghosh et al. / Tetrahedron Letters 51 (2010) 343–347
345
35
30
35
30
25
20
15
10
5
35
30
25
20
15
10
5
malonate
suberate
succinate
glutarate
adipate
(a)
25
(b)
(c)
pimelate
20
15
10
5
0
0
-4
-4
-4
-4
400
450
500
550
600
650
0.0
1.0x10
2.0x10
3.0x10
4.0x10
400
450
500
550
600
650
Wavelength (nm)
Wavelength (nm)
[G] in M
Figure 2. Change in fluorescence intensity of 1 (c = 6.55 Â 10À5 M in CH3CN containing 0.4% DMSO) with (a) malonate, (b) suberate (as tetrabutylammonium salt) at 438 nm,
and also (c) the change in emission of 1 with guest concentration.
malonate
succinate
25
20
15
10
5
0.18
0.12
0.06
0.00
suberate
adipate
suberate
pimelate
glutarate
ΔΙ
pimelate
succinate
Δ
A
malonate
adipate
glutarate
0
0
1
2
3
4
5
6
7
0
1
2
3
4
5
6
7
[G]/[H]
[G]/[H]
Figure 5. Titration curves of receptor 1 (c = 1.31 Â 10À5 M in CH3CN containing
0.4% DMSO from UV–vis titration (measured at 320 nm) upon addition of
tetrabutylammonium salts of the dicarboxylates.
Figure 3. Titration curve of receptor 1 (c = 6.55 Â 10À5 M in CH3CN containing 0.4%
DMSO) from fluorescence study (measured at 438 nm).
4.0x10-6
3.0x10-6
malonate
0.5
succinate
glutarate
adipate
pimelate
suberate
2.0x10-6
1.0x10-6
0.0
250
300
350
400
450
0.0
0.0
Wavelength
0.2
0.4
0.6
XH
0.8
1.0
Figure 4. Change in absorbance of 1 (c = 1.31 Â 10À5 M in CH3CN containing 0.4%
DMSO) upon gradual addition of tetrabutylammonium salt of suberic acid.
Figure 6. Job plot of receptor 1 with the dicarboxylates.
Interestingly, a gradual increase in the concentration of dicar-
boxylate anions (malonate, succinate, glutarate, adipate, pimelate,
and suberate) produced no color change of the acetonitrile solution
(containing 0.4% DMSO) of receptor 1. However, when high con-
centrations (c = 2.83 Â 10À3 M) of dicarboxylates of different chain
lengths were added to a DMSO solution of 1, the color of the solu-
tion changed dramatically. In the presence of an equivalent (1:1)
amount of the guests, the color of the solution of receptor 1 was
light in nature (Fig. 8a). However, when an excess of guest was
added (4 equiv) to the solution of 1, the color intensified. Particu-
larly in the presence of excess malonate, the color of the solution
of 1 changed from light yellow to deep yellow and finally to red,
which could be observed by the naked eye (Fig. 8b). It is possible
that the origin of the color change in the receptor solution upon
complexation could be ascribed to a charge-transfer interaction be-
tween the electron rich amide–urea (donor unit) and the electron
deficient p-nitrophenyl moiety.25 We hypothesize that complexa-
N
O
O
NH
NH
NH
O-
-O
O
O
HN
( )
n
NH
NH
R
O
O
R
n = 1, 2, 3, 4, 5, 6
R = p-nitrophenyl
Figure 7. Suggested hydrogen bonding structure of 1 with dicarboxylates.

346
K. Ghosh et al. / Tetrahedron Letters 51 (2010) 343–347
Table 1
Binding constant values of 1 with the guests in CH3CN containing 0.4% DMSO
Guestsa
Log Kb
Malonate
Succinate
Glutarate
Adipate
Pimelate
Suberate
5.20 0.2438
6.60 0.7209
6.53 0.4245
6.6 1 0.3270
6.87 0.4917
7.62 0.4287
R = 0.9939
R = 0.9728
R = 0.9939
R = 0.9902
R = 0.9869
R = 0.9903
a
Tetrabutylammonium salts were taken.
Binding constants measured at 320 nm.
b
Figure 9. Lowest energy structures and hydrogen bonding patterns found for 1 in
GBSA (chloroform) using the OPLS2005 force field.
tion with the electron-rich dicarboxylates increases the electron
density around the amide–urea binding site and this facilitates
intramolecular charge transfer. Particularly, in the presence of ex-
cess malonate, the most basic of all the dicarboxylates included in
this study, deprotonation of the urea proton Hc in 1 (likely) occurs
(vida supra) enhancing such charge transfer and resulting in the
sharpest, most intense color change. Such anion-triggered deproto-
nation of neutral NH hydrogen bond donor groups in anion recep-
tors in organic solution is well documented.26 However, upon
addition of methanol to the individual solutions of 1 containing
dicarboxylate anions in DMSO, the color of the solution discharged
immediately and returned to the initial color of the receptor solu-
tion. This indicated the reversible nature of the complexation.
In order to realize the binding selectivity of the open cleft of 1
we determined the binding constant values27 by UV method
(Table 1). We did not use fluorescence titration data for determina-
tion of binding constant values due to decrease followed by an in-
crease in emission of 1 upon titration. As can be seen from Table 1,
the receptor 1 shows higher binding for long chain dicarboxylates
and the cleft is selective for suberate in the present study.
accommodate the guests even as the guests grow in size. All guests
bind to 1 in the trans conformation with significant hydrogen
bonding interactions between the carboxyl end groups of the
guests and the amides of each host. Upon complexation, the guest
can bring the two receptor arms closer together creating a tighter
binding cavity. As can be seen in Figure 10, one of the nitrophenyl
arms twists back to the other side of the molecule forming a Z-
shaped structure but with hydrogen bonding still connecting the
guest to the arm. For 1 with suberate, the arm wraps back around
to form a U-shaped structure again with extensive hydrogen bond-
ing keeping the guest bound to the receptor.
Assuming a 1:1 stoichiometry theoretical binding enthalpies
were computed and shown to vary depending on the solvent type
used (Table 2). In vacuum, all complexes of 1 displayed favorable
binding interactions and showed a strong trend that as the guests
increase in size, binding energy decreases in a relatively linear
fashion. Computations in chloroform were in the best agreement
with the experimental binding energies shown in Table 1. Within
the binding energies of 1 in chloroform with various guests, there
is a slight preference for binding to suberate and this is reflected in
the experimental data as well. Calculations in water showed no
definitive trends of any kind, with binding affinities taking on both
favorable and unfavorable values, scattering about zero kcal/mol.
In conclusion, we have designed, synthesized, and studied
hydrogen bonding interactions of a new triphenylamine-based
receptor 1 with aliphatic dicarboxylates of different chain lengths.
The receptor binds dicarboxylates at the charge neutral sites with
concomitant decrease in emission and shows selectivity for long
chain suberate in CH3CN. Complexation induces a color change in
the DMSO receptor solution that is observable with the naked
eye, particularly for malonate and suberate guests. A conforma-
tional analysis shows that the receptor adopts a triangular shape
with a well-defined binding pocket. The quantum-minimized
structures reveal that the receptor is indeed interacting strongly
with the guests and are flexible enough to accommodate the dicar-
boxylates even as they grow in size. All guests bind to the receptor
with significant hydrogen bonding interactions between the
A conformational analysis of 1 was performed using the LM:MC
method on the OPLS2005/GBSA(CHCl3) potential energy surface
(see Supplementary data).28 A 3.0 kcal/mol energetic cut off was
chosen in order to focus on those conformations most likely to
be populated at room temperature. The ensemble of low energy
structures is well represented by the global minimum energy
structure (Fig. 9). These results suggest that conformers of 1 adopt
triangular shapes containing well-defined binding pockets that can
accommodate the dicarboxylate guests for which they are in-
tended. Similarly, full conformational searches of 1 in the presence
of each dicarboxylate guest were also performed. To verify the
molecular mechanics result, we also subjected the global mini-
mum energy conformer of each complex to unrestrained quantum
mechanical (QM) minimization using the B3LYP/6-31G*/SCRF-
PB(chloroform) methodological treatment.29 Receptor
1 was
originally designed to hydrogen bond to the guests and the
quantum-minimized structures reveal that the host is indeed
interacting strongly with the guests and is flexible enough to
Figure 8. Change in color of the receptor solution of 1 (c = 2.83 Â 10À3 M) in the presence of equivalent amount of dicarboxylates (a) and 4 equiv amounts of dicarboxylates
(b) [a: receptor 1, b: with malonate, c: with succinate, d: with glutarate, e: with adipate, f: with pimelate, and g: with suberate].

K. Ghosh et al. / Tetrahedron Letters 51 (2010) 343–347
347
Figure 10. Representative B3LYP/6-31G* geometry optimized structures of 1 in chloroform. Solvent effects were included in the optimization using the self-consistent
reaction field (SCRF) model and the Poisson–Boltzmann (PB) solver.
Table 2
References and notes
B3LYP/6-31G* binding enthalpies (kcal/mol) for receptor 1
1. Martinez-Manez, R.; Sancenon, F. Chem. Rev. 2003, 13, 4419.
D
Y(vacuum)
D
Y(CHCl3)
DY(H2O)
2. Suksai, C.; Tuntulani, T. Chem. Soc. Rev. 2003, 32, 192.
3. Gunnlaugsson, T.; Glynn, M.; Tocci, G. M.; Kruger, P. E.; Pfeffer, F. M. Coord.
Chem. Rev. 2006, 250, 3094. and references cited therein.
4. Supramolecular Chemistry of Anions; Bianchi, E., Bowman-James, K., Garcia-
Espana, E., Eds.; Wiley-VCH: New York, 1997.
5. Voet, D.; Voet, J. G. Biochemistry, 2nd ed.; Wiley: New York, NY, 1995.
6. Kral, V.; Andrievsky, A.; Sessler, J. L. J. Am. Chem. Soc. 1995, 117, 2953.
7. Gunnlaugsson, T.; Davis, A. P.; O’Brien, J. E.; Glynn, M. Org. Lett. 2002, 4, 2449–
2452. and references cited therein.
8. Liu, S.-Y.; Fang, L.; He, Y.-B.; Chan, W.-H.; Yeung, K.-T.; Cheng, Y.-K.; Yang, R.-H.
Org. Lett. 2005, 7, 5825–5828.
Malonate
Succinate
Glutarate
Adipate
Pimelate
Suberate
À154.3
À124.5
À125.1
À88.9
À55.5
À49.5
À50.6
À45.9
À40.1
À58.4
À8.2
À0.1
7.5
3.8
4.8
À88.9
À144.7
À16.4
Solvent effects were included in the optimization using the self-consistent reaction
field (SCRF) model and the Poisson–Boltzmann (PB) solver.
9. Kim, S. K.; Kang, B.-G.; Koh, H. S.; Yoon, Y. J.; Jung, S. J.; Jeong, B.; Lee, K.-D.;
Yoon, J. Org. Lett. 2004, 6, 4655–4685. and references cited therein.
10. Raker, J.; Glass, T. E. J. Org. Chem. 2002, 67, 6113–6116.
11. Jadhav, V. D.; Scmidtchen, F. P. Org. Lett. 2006, 8, 2329–2332. and references
cited therein.
12. Gunnlaugsson, T.; Davis, A. P.; O’Brien, E.; Glynn, M. Org. Lett. 2002, 4, 2449.
13. Liu, S.-Y.; He, Y.-B.; Wu, J.-L.; Wei, L.-H.; Qin, H.-J.; Meng, L.-Z.; Ling, Hu. Org.
Biomol. Chem. 2004, 2, 1582.
carboxyl end groups of the guests and the o-phenylenediamine of
the receptor. Theoretical binding energies are in good agreement
with experimental data and suggest that receptor 1 binds the
dicarboxylates most strongly and shows a slight preference for
long chain suberate.
14. Mei, M.; Wu, S. New J. Chem. 2001, 25, 471.
15. Liu, S.-Y.; He, Y.-B.; Chan, W. H.; Lee, A. W. M. Tetrahedron 2006, 62, 11687.
16. Plush, S. E.; Gunnlaugsson, T. Org. Lett. 2007, 9, 1919.
Acknowledgments
17. Ghosh, K.; Masanta, G.; Chattopadhyay, A. P. Tetrahedron Lett. 2007, 48, 6129.
18. Ghosh, K.; Masanta, G. Tetrahedron Lett. 2008, 49, 2592.
19. Ghosh, K.; Masanta, G. Tetrahedron Lett. 2006, 47, 2365.
20. Ghosh, K.; Masanta, G.; Fröhlich, R.; Petsalakis, I. D.; Theodorakotoulos, G. J.
Phys. Chem. B 2009, 113, 7800.
21. Ghosh, K.; Masanta, G.; Chattopadhyay, A. P. Eur. J. Org. Chem. 2009, 26, 4515.
22. (a) Brooks, S. J.; Gale, P. A.; Light, M. E. Chem. Commun. 2005, 4696; (b) Broks, S.
J.; Gale, P. A.; Light, M. E. Cryst. Eng. 2005, 7, 586; (c) Brooks, S. J.; Edwards, P. R.;
Gale, P. A.; Light, M. E. New J. Chem. 2006, 30, 65.
23. Mallegol, T.; Gmouh, S.; Meziane, M. A. A.; Blanchard-Desce, M.; Mongin, O.
Synthesis 2005, 1771.
24. Job, P. Ann. Chim. 1928, 9, 113.
25. (a) Thangadurai, T. D.; Singh, N. J.; Hwang, I.-C.; Lee, J. W.; Chandran, P.; Kim, K.
S. J. Org. Chem. 2007, 72, 5461; (b) Duke, R. M.; Gunnlaugsson, T. Tetrahedron
2007, 48, 8043.
K.G. acknowledges financial support from CSIR, New Delhi,
India. I.S. and G.M. thank CSIR for providing a fellowship. We also
acknowledge infrastructure support from DST under DST-FIST
program. C.P. acknowledges financial support from the NSF
(CHE-0211577 and CHE-0809462), the ACS-PRF, the Jeffress Trust,
and the Dreyfus Foundation. E.W. acknowledges support from the
Beckman and HHMI Foundations. Computational resources were
provided under NSF grants CHE-0116435, CHE-0521063 and
CHE-0821581.
26. (a) Camiolo, S.; Gale, P. A.; Hursthouse, M. B.; Light, M. E.; Shi, A. J. Chem.
Commun. 2002, 758; (b) Camiolo, S.; Gale, P. A.; Hursthouse, M. B.; Light, M. E.
Org. Biomol. Chem. 2003, 1, 741; (c) Gale, P. A.; Light, M. E.; Quesada, R. New J.
Chem. 2006, 30, 1019; (d) Cattagirone, C.; Bates, G. W.; Gale, P. A.; Light, M. E.
Chem. Commun. 2008, 61.
27. (a) Pocker, Y.; Ciula, J. C. J. Am. Chem. Soc. 1989, 111, 4728; (b) Bourson, J.;
Pouget, J.; Valeur, B. J. Phys. Chem. 1993, 97, 4552.
28. Parish, C.; Lombardi, R.; Sinclair, K.; Smith, E.; Goldberg, A.; Rappleye, M.; Dure,
M. J. Mol Graphics Modell. 2002, 21, 129. and references cited therein.
29. Marten, B.; Kim, K.; Cortis, C.; Friesner, R. A.; Murphy, R. B.; Ringnalda, M. N.;
Sitkoff, D.; Honig, B. J. Phys. Chem. 1996, 100, 11775.
Supplementary data
UV and fluorescence titration results, compound characteriza-
tion data, binding constant curve, LM:MC conformational search
results on the OPLS2005/GBSA(water) surface of 1 in vacuum,
GBSA(water) and GBSA(chloroform) are available. Supplementary
data associated with this article can be found, in the online version,
at doi:10.1016/j.tetlet.2009.11.021.