Highly selective recognition of adenine nucleobases by synthetic hosts with a linked five-six-five-membered triheteroaromatic structure and the application to potentiometric sensing of the adenine nucleotide

Article abstract of DOI:10.1002/chem.200600099

A new structure for an adenine-selective host molecule, featuring the pertinent link of five-six-five-membered heteroaromatic rings and two carbamoyl NH sites, was developed. This structure provides a correctly oriented array of complementary hydrogen bonding sites for the adenine nucleobase, which exploits both Watson-Crick and Hoogsteen-type interactions. The complexation with adenine nucleobases by multiple hydrogen bonding was supported by ¹H NMR spectroscopy. This type of host displayed high selectivity in complexation, with an accompanying fluorescent response to lipophilized adenosine in CHCl ₃. Furthermore, a remarkably selective po tentiometric response was attained for adenosine 5′-monophosphate over 5′-GMP, 5′-CMP, and 5′-UMP by using an ion-selective electrode with a PVC-supported solvent polymeric membrane. This indicates recognition of water-soluble nucleotide guests through the membrane-water interface. These findings are expected to form a reliable basis for the development of artificial sensing systems for mononucleotides in biological systems.

Full text of DOI:10.1002/chem.200600099

FULL PAPER
DOI: 10.1002/chem.200600099
Highly Selective Recognition of Adenine Nucleobases by Synthetic Hosts
with a Linked Five-Six-Five-Membered Triheteroaromatic Structure and the
Application to Potentiometric Sensing of the Adenine Nucleotide
Yosuke Hisamatsu,[a] Keiko Hasada,[a] Fumi Amano,[a] Yasuhiro Tsubota,[a]
Yuko Wasada-Tsutsui,[b, c] Naohiro Shirai,[a] Shin-ichi Ikeda,[a] and Kazunori Odashima*[a]
1
Abstract: A new structure for an ade-
nine-selective host molecule, featuring
the pertinent link of five-six-five-mem-
bered heteroaromatic rings and two
carbamoyl NH sites, was developed.
This structure provides a correctly ori-
ented array of complementary hydro-
gen bonding sites for the adenine nu-
cleobase, which exploits both Watson–
Crick and Hoogsteen-type interactions.
The complexation with adenine nucleo-
bases by multiple hydrogen bonding
was supported by H NMR spectrosco-
py. This type of host displayed high se-
lectivity in complexation, with an ac-
companying fluorescent response to
lipophilized adenosine in CHCl3. Fur-
thermore, a remarkably selective po-
tentiometric response was attained for
adenosine 5’-monophosphate over 5’-
GMP, 5’-CMP, and 5’-UMP by using an
ion-selective electrode with a PVC-sup-
ported solvent polymeric membrane.
This indicates recognition of water-
soluble nucleotide guests through the
membrane–water interface. These find-
ings are expected to form a reliable
basis for the development of artificial
sensing systems for mononucleotides in
biological systems.
Keywords: fluorescence spectrosco-
py · host–guest systems · hydrogen
bonds
nucleobases
·
membrane potential
·
Introduction
bases, either by multiple hydrogen bonding or by combina-
tion of different modes of interactions, have been report-
ed.[2] Development of synthetic hosts for selective complexa-
tion with target nucleobases has been extensively investigat-
ed from the late 1980ꢀs, focusing on complementary
hydrogen bonding in relatively nonpolar organic solvents.[3]
More recently, these investigations have been extended to
complexation in polar solvents or water by utilizing coordi-
nation, ion pairing and/or p–p stacking interactions in addi-
tion to multiple hydrogen bonding.[4] Recently, synthetic hy-
drogen-bonding motifs have been applied for the recogni-
tion of single nucleotide polymorphism (SNP), either for a
given DNA duplex containing a bulged base[5a] or a mis-
matched base pair,[5b] or for a DNA duplex reconstituted
with an oligonucleotide containing an abasic site.[5c] Such
motifs have also been employed for ion-selective electrodes
mounted with solvent polymeric membranes, which display
potentiometric responses to nucleotide guests.[6,7] However,
despite their potential applicability to the regulation or de-
tection of nucleobase-bearing biomolecules, the complexa-
tion selectivity, particularly the selectivity to adenine over all
other nucleobases, is still insufficient and remains as an un-
solved, challenging problem. This is primarily because the
adenine nucleobase is not furnished with three neighboring
Precise recognition of nucleobases is essential for biological-
ly significant functions such as genome duplication, protein
synthesis, and signal transduction.[1] Several types of synthet-
ic motifs capable of monomeric complexation with nucleo-
[a] Y. Hisamatsu, K. Hasada, F. Amano, Y. Tsubota, Dr. N. Shirai,
Dr. S. Ikeda, Prof. Dr. K. Odashima
Graduate School of Pharmaceutical Sciences
Nagoya City University, Mizuho-ku, Nagoya 467-8603 (Japan)
Fax : (+81)52-836-3462
E-mail: odashima@phar.nagoya-cu.ac.jp
[b] Dr. Y. Wasada-Tsutsui
Department of Materials Science and Engineering
Nagoya Institute of Technology
Showa-ku, Nagoya 466-8555 (Japan)
[c] Dr. Y. Wasada-Tsutsui
Current address: Graduate School of Natural Sciences
Nagoya City University, Mizuho-ku, Nagoya 467-8501 (Japan)
Supporting information for this article (experimental details describ-
ing the synthesis and characterization of all new compounds, the spec-
troscopic and potentiometric measurements, the structure calculations
for the host–guest complex) is available on the WWW under http://
www.chemeurj.org or from the author.
Chem. Eur. J. 2006, 12, 7733 – 7741
ꢁ 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
7733

hydrogen-bonding/coordinating sites in contrast with the
other nucleobases (vide infra).
seeking substantial application to biological systems. So far,
high selectivity in this sense has been achieved, even in
highly polar solvents, for thymine[4g] (in water) and cyto-
We report here a new structure for an adenine-selective
host molecule (1, 2) based on the 2,6-bis(oxazol-2-yl)pyri-
dine unit. This host structure, featuring the pertinent linking
of five-six-five-membered heteroaromatic rings and two car-
bamoyl NH sites, provides a correctly oriented array of com-
plementary hydrogen-bonding sites for an adenine nucleo-
base (Figure 1a). This type of host displayed a fluorescent
response accompanying the highly selective complexation to
lipophilized adenosine in CHCl3. Furthermore, a remarkably
selective potentiometric response was displayed to adeno-
sine 5’-monophosphate by recognition through the mem-
brane–water interface of a solvent polymeric membrane.
The host molecules (1, 2), the reference molecules (3, 4) for
comparison with hosts 1 and 2, and the lipophilic nucleoside
guests (5A, 5G, 5C, 5U, 6T) used in the present study are
shown in Figure 1b.
A
neighboring hydrogen-bonding/coordinating sites. On the
other hand, complexation selectivity to adenine has so far
been examined by Hamilton et al. [Ks(A)=3.2”103 mꢀ1 in
CDCl3],[3a] Zimmerman et al. [Ks(A)=1.55”104 mꢀ1 in
CDCl3 at 258C; the ratio of Ks: A/G=5.5, A/C=73, A/U=
120],[3b] Ogoshi et al. [Ks(A)=5.0”103 mꢀ1 in CH2Cl2 at
158C; the ratio of Ks: A/G=3.8, A/C=17; negligible com-
plexation with dT],[3c] Vçgtle et al. [Ks(A)=4.1”104 mꢀ1 in
CDCl3; the ratio of Ks: A/U=2.9; negligible complexation
with G or C],[3d] Rebek et al. [Ks(A)=2.2”102 mꢀ1 in CDCl3;
the ratio of Ks: A/C > 22][3e] and Rebek et al. [Ks(A)=
5.77”102 mꢀ1 in CD3ODat ca. 22 8C; the ratio of Ks: A/G=
8.0].[3f] In contrast to thymine and cytosine, high selectivity
over all other nucleobases has not been reported for the ad-
enine nucleobase, even in relatively nonpolar organic sol-
vents.
Results and Discussion
To afford a highly complementary structure for the ade-
nine nucleobase, we designed and synthesized a new planar
structure based on a linked five-six-five-membered trihet-
Design and synthesis: Complexation selectivity to a target
nucleobase over all other nucleobases is quite important for
A
As the first step, we thoroughly examined complexation se-
lectivity in a nonpolar organic solvent (CHCl3) using lip-
ophilized nucleoside guests. This structure provides a cor-
rectly oriented array of complementary hydrogen bonding
sites for the adenine nucleobase (Figure 1a), as supported
by the optimized structure of a model complex (vide infra).
For the synthesis of hosts 1 and 2, and reference molecule
4, a Curtius rearrangement[8] was employed as a key step to
directly link a carbamoyl NH group to each of the oxazole
rings. Thus, for the synthesis of host 1 (Scheme 1),[9a] bis-hy-
droxyamide 7,[10] derived from pyridine-2,6-dicarboxylic acid
and l-serine methyl ester, was cyclized by diethylaminosul-
[11]
fur trifluoride (DAST) to give bis(oxazolin-2-yl)pyridine
Scheme 1. Synthesis of host 1: a) Et2NSF3, CH2Cl2, ꢀ788C, 4.5 h; then
K2CO3, ꢀ788C to room temperature, overnight; 61%; b) BrCCl3, DBU,
CH2Cl2, 08C, overnight, 88%; c) KOH, H2O, overnight, quant.; d) SOCl2,
reflux, overnight; e) NaN3, acetone–H2O, 0 8C, 1 h !RT, 3 h; f) reflux,
3 h; then 1-hexanol, CHCl3, reflux, overnight; 62% from 10.
Figure 1. a) Complexation between host 1 or 2 and adenine by comple-
mentary hydrogen bonding. b) The structures of hosts (1, 2), references
(3, 4) and lipophilic nucleoside guests (5A, 5G, 5C, 5U, 6T).
7734
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Chem. Eur. J. 2006, 12, 7733 – 7741

Nucleotide Recognition
FULL PAPER
8, which was oxidized with bromotrichloromethane[12] to
bis(oxazol-2-yl)pyridine 9 and then hydrolyzed to 10. Diacid
10 was converted to the corresponding diazide, which was
heated at reflux to effect the Curtius rearrangement. The re-
sulting diisocyanate was treated with 1-hexanol to give host
1 (62% from 10). The treatment of diacid 10 with diphenyl-
phosphoryl azide (DPPA)[13] gave host 1 with lower yield
(41% from 10) but also afforded reference 3[9b] as a side
product (22% from 10). Reference compound 4[9b] was syn-
thesized by using the same route as for host 1, starting from
isophthalic acid. The synthesis of host 2[9a] was carried out in
a similar way as for host 1, but starting from chelidamic acid
and converting not only the side substituents but also the
para substituent of the pyridine ring (Scheme 2).
changes were not observed[14] under the same conditions for
the NH2 signal of guest 5A upon addition of the reference
compound 3, which has no carbamoyl NH groups for hydro-
gen bonding with the purine nitrogen atoms. The stoichiom-
etry of the host–guest complex between 1 and 5A was con-
firmed as 1:1 by a Job plot.[14,15a,b]
Selectivity in complexation and fluorescence response to ad-
enine: The 2,6-bis(oxazol-2-yl)pyridine unit of host 1 affords
a linked triheteroaromatic fluorophore, and, upon complex-
ation with guest 5A in CHCl3, host 1 showed a fluorescent
response. Thus, as shown in Figure 3a, the fluorescence from
host 1 was quenched by addition of guest 5A with no
change in the fluorescence maximum (lmax=380 nm). Again,
for reference compound 3, such
a
guest-induced fluorescence
change was negligible under the
same conditions.[14] From the
change in the fluorescence in-
tensity, the stability constant
(Ks) of the 1:1 complex be-
tween 1 and 5A was deter-
mined to be (12400Æ600)mꢀ1
(CHCl3, 208C) by a Benesi–Hil-
debrand analysis.[15b,c] This Ks
value was of the same magni-
tude as that determined by the
UV/Vis titration (Ks =(12300Æ
1600)mꢀ1 in CHCl3, 208C).[14,16]
In contrast, other nucleoside
guests did not induce an appre-
ciable fluorescence change in
the concentration range of 80–
320 mm (Figure 3b). The stabili-
ty constants of the 1:1 com-
plexes, determined from fluo-
rescence, decrease at much
higher guest concentrations. As
listed in Table 1, host 1 attained
a high complexation selectivity
(greater than 100-fold) for ade-
nine over all other nucleobases.
Although the adenine selectivi-
ty was lower than that of host
1, host 2, with the para-meth-
Scheme 2. Synthesis of host 2: a) SOCl2, reflux, 5 days; b) l-Ser-OMe·HCl, Et3N, CHCl3, RT, 1 days, 37%
from 11; c) Et2NSF3, CH2Cl2, ꢀ788C, 5 h; then K2CO3, ꢀ788C to room temperature, overnight; 91%; d)
BrCCl3, D BU, CHCl2, 08C, overnight, 95%; e) KOH, MeOH–H2O, 60 8C, 13 h, 64%; f) SOCl2, reflux, over-
2
night; g) NaN3, acetone–H2O, 0 8C, 1 h !RT, 3 h; h) CHCl3, reflux, 3 h; then 1-hexanol, CHCl3, reflux, over-
night; 57% from 14.
Complexation with adenine by multiple hydrogen bonding
C
(1H NMR study): The complexation ability of host 1 was
1
monitored first by H NMR spectroscopy in CDCl3 using a
lipophilic derivative of adenosine (5A) as a guest. In the
presence of guest 5A (0!1.0!2.0 equiv), a significant
downfield shift (Dd=4.29 ppm) was observed for the amide
NH protons on the side chains of host 1 (Figure 2a!2b!
2c). In addition, the NH2 signal of guest 5A disappeared
(probably by broadening) in the presence of host 1 (Fig-
ure 2d vs. Figure 2b). These 1H NMR spectral changes
strongly support host–guest complexation by multiple hy-
drogen bonding as represented in Figure 1a. Such spectral
Compared to the synthetic hosts reported so far (vide su-
pra),[3a–f] the complexation with adenine by hosts 1 and 2 in
the present study is comparable or somewhat weaker. How-
ever, from another viewpoint, the adenine-complexation
ability of hosts 1 and 2 may be recognized as excellent in
the sense that the complexation by the present hosts, unlike
most of the other hosts, should stem only from multiple hy-
drogen bonding by neutral groups and would not involve p–
p stacking and/or electrostatic interactions.[17] Furthermore,
Chem. Eur. J. 2006, 12, 7733 – 7741
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7735

K. Odashima et al.
Table 1. Stability constants for 1:1 complexes with a series of nucleoside
guests (Ks) in CHCl3 at 208C.[14]
Ks [mꢀ1
]
Guest
Host 1
Host 2
5A
5G
5C
5U
6T
12400Æ600
37Æ10
104Æ6
<10
10500Æ400
62Æ8
163Æ40
<10
27Æ11
27Æ16
the high complexation selectivity for the adenine nucleobase
has been displayed over all other nucleobases, which is the
first true example for adenine selectivity.
Optimized structures for the five-six-five-membered trihet-
A
and 2, together with the lack of selectivity towards reference
compound 3, clearly shows the significance of the two carba-
moyl NH groups attached directly to the 2,6-bis(oxazol-2-
yl)pyridine unit. This is supported by the optimized struc-
ture of the model host–guest complex between 1’ and 9-
methyladenine (Figure 4), obtained by the nonempirical mo-
lecular orbital calculation with the hybrid density functional
method (B3LYP/6–31G*).[18] This model complex shows
that, unlike the six-six-six-membered counterpart, the five-
six-five-membered triheteroaromatic structure provides a
highly complementary structure for adenine nucleobases. In
the model host–guest complex, four definite hydrogen
bonds, formed by both Watson–Crick and Hoogsteen-type
ꢀ
Figure 2. 1H NMR spectra (500 MHz) of host 1 and/or guest 5A in
CDCl3, measured at 258C with TMS as the external standard: a) [host
1]0 =10.0 mm; b) [host 1]0 =10.0 mm, [guest 5A]0 =10.0 mm; c) [host 1]0 =
10.0 mm, [guest 5A]0 =20.0 mm; d) [guest 5A]0 =10.0 mm.
interactions (N H····N distance
= 2.06, 1.90, 2.04, and
1.97 Š from left to right in Figure 4), were observed,[19]
which suggest the formation of four hydrogen bonds with an
adenine nucleobase in the complex with host 1 or 2.
On the other hand, hydrogen bonding was not observed
between the pyridine nitrogen atom of the host and the NH2
ꢀ
hydrogen atoms of the guest (N····H N distance = 2.92 and
2.69 Š), suggesting that the pyridine nitrogen atom of host 1
does not contribute as a hydrogen-bonding acceptor. How-
ever, the pyridine structure still plays an important role for
adenine selectivity by affording a suitable space to accom-
modate the adenine NH2 group without steric hindrance.
This is supported by the experimental fact that the complex-
ation and fluorescent response for guest 5A with reference
compound
4
with
a
benzene ring [Ks =(159Æ22)mꢀ1
(CHCl3, 208C)][20] was much weaker than that with host 1
with a pyridine ring [Ks =(12400Æ600)mꢀ1 (CHCl3, 208C)].
The high complexation selectivity of host 1 or 2 to ade-
nine nucleobase over guanine and uracil (thymine) can be
explained by the mismatched hydrogen-bonding sites of
these guests. On the other hand, although these hosts could
form at least three hydrogen bonds with cytosine in a similar
manner as with adenine, the carbonyl oxygen atom of the
former could cause electrostatic repulsion to the carbamoyl
oxygen atom of the host (Figure 5). This may be an addi-
tional advantage of this type of host structure for adenine
selectivity.
Figure 3. a) Guest-induced quenching of the fluorescence of host 1 with
increasing concentration of adenosine guest 5A. b) Comparison of the
fluorescence intensity at 380 nm in the presence of a series of nucleoside
~
*
^
guests , 5A; , 5G; , 5C; ”, 5U; +, 6T. The conditions for a): [1]=
20 mm, [5A]=20–320 mm. The conditions for b): [1]=20 mm, [5A]=20–
320 mm, [5G, 5C, 5U or 6T]=80–320 mm. For both a) and b): lex
336 nm; solvent: CHCl3; temperature: 208C.
=
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Chem. Eur. J. 2006, 12, 7733 – 7741

Nucleotide Recognition
FULL PAPER
supported solvent polymeric
membranes has been attained
by using synthetic hosts having a
cytosine group capable of form-
ing three neighboring hydrogen
bonds.[7] Relative magnitudes of
potentiometric responses to 5’-
GMP over 5’-AMP, estimated as
potentiometric selectivity coeffi-
cients (Kp50o-tGMP,50-AMP), have been
reported as 0.42 for the alkylat-
ed cytosine[7b] and 0.045 for the
cytosine-appended CoII por
rin.[7d] On the other hand, poten-
phy-
AHCTREUNG
tiometric recognition of 5’-AMP
over 5’-GMP has so far been at-
tempted with a thymine deriva-
tive having
a branched alkyl
chain, but was not successful.
This is probably because of a
less-selective complexation abili-
ty due to the formation of only
two
neighboring
hydrogen
Figure 4. a) Top view and b) lateral view for the optimized structure of the model complex of host 1’ and 9-
methyladenine, obtained by the nonempirical molecular orbital calculation with the hybrid density-functional
method (B3LYP/6–31G*).[18]
bonds with both adenine and
guanine nucleobases.[7b]
We applied the adenine-selec-
tive host 2 to potentiometric
recognition of 5’-AMP over other nucleoside 5’-monophos-
phates. Only host 2 was used for the membrane potential ex-
periments because of poor solubility of host 1 in the mem-
brane solvent (2-nitrophenyl octyl ether). Thus, the mem-
brane potentials (DEMF)[21] with increasing concentration of
each nucleotide guest were measured for ion-selective elec-
trodes fitted with PVC-supported solvent polymeric mem-
branes containing host 2[22] and the blank membrane without
a host. Comparing the magnitudes of membrane potential
change to the negative direction (anionic potential change)
induced by each nucleotide guest, the membrane containing
host 2 showed a potentiometric response, which was by far
greatest for 5’-AMP than for other nucleoside 5’-monophos-
phates, irrespective of the guest concentration (Figure 6a).
In contrast, the blank membrane without host 2 showed low
selectivity, reflecting only the lipophilicity of the guests (Fig-
ure 6b). The host-induced changes in membrane potential
[DEMF(Figure 6a) ꢀ DEMF(Figure 6b)] were approximate-
ly ꢀ40 mV for 5’-AMP and ~ꢀ10 mV for the other nucleo-
tide guests. The potentiometric selectivity coefficient for 5’-
AMP over 5’-GMP was remarkable (Kp50o-tAMP,50-GMP =0.041).
This is, to the best of our knowledge, the first example of an
artificial host capable of displaying a selective potentiomet-
ric response to 5’-AMP. Interestingly, by invoking correctly
oriented multiple hydrogen bonds, host 2 is capable of ach-
ieving potentiometric selectivity for 5’-AMP over 5’-GMP,
which is as remarkable as the potentiometric selectivity for
5’-GMP over 5’-AMP (Kp50o-tGMP,50-AMP =0.045)[7d] by a host em-
ploying metal coordination in addition to three neighboring
hydrogen bonds.
Figure 5. Presumed interactions between host 1 (X=H) or 2 (X=OCH3)
and cytosine (R=SitBuMe2).
Potentiometric selectivity to adenosine 5’-monophosphate
(5’-AMP): Selective recognition of water-soluble adenine
guests with consequent membrane-potential changes in-
duced by synthetic hosts has been even more difficult than
the recognition of lipophilized adenine derivatives in organ-
ic solvents. Guest-induced changes in membrane potential
displayed by hosts embedded in membranes are widely esti-
mated by solvent polymeric membranes supported with
poly
A
G
N
tion of guanosine nucleotides (5’-GMP, 5’-GTP) by PVC-
Chem. Eur. J. 2006, 12, 7733 – 7741
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www.chemeurj.org
7737

K. Odashima et al.
JEOL AX-505 spectrometers. 1H NMR spectra were recorded on JEOL
GSX400, LAMBDA500, or ALPHA500 spectrometers. 13C NMR spectra
were recorded on JEOL ALPHA500 or LAMBDA500 spectrometers
with complete proton decoupling and DEPT modes. Chemical shifts are
reported in d values in ppm downfield from tetramethylsilane as the in-
ternal standard.
Solvents for extraction and chromatography were of reagent grade.
Chloroform and 1-hexanol were distilled over calcium hydride. Dichloro-
methane (CH2Cl2) was distilled over phosphorus(V) oxide. N,N-Dime-
thylformamide (DMF) was dried with and distilled over barium oxide
under reduced pressure. Triethylamine (Et3N), 1,8-diazabicyclo-
A
Synthesis of hosts 1 and 2[9b]
Dimethyl (S,S)-2,2’-(pyridine-2,6-diyl)bis(4,5-dihydrooxazole-4-carboxyl-
A
dure[11] with some modifications. Diethylaminosulfur trifluoride (DAST,
13.22 g, 85.5 mmol) was added drop wise over a period of 30 min under a
N2 atmosphere to a stirred solution of 7 (8.31 g, 22.5 mmol) in CHCl3
(225 mL), precooled to ꢀ788C. After the reaction was stirred at ꢀ788C
for 4 h, K2CO3 was added. The reaction mixture was allowed to warm to
RT and stirred for an additional 25 h. After H2O (100 mL) was added,
the mixture was extracted with CHCl3 (3”100 mL), and the combined or-
ganic layers were washed with brine (1”50 mL), dried over MgSO4, fil-
tered, and evaporated. The residue was purified by column chromatogra-
phy (silica gel, CHCl3/MeOH 30:1) to give 8 as a white solid (5.68 g,
76%): m.p. 154–1568C (recrystallized from EtOH); 1H NMR (400 MHz,
CDCl3, TMS): d=3.82 (s, 6H; CH3), 4.71 (dd, 2J
9.0 Hz, 2H; one of CH2), 4.80 (dd, 3J
(H,H)=8.3, 9.0 Hz, 2H; CH), 5.02
(dd, 2J(H,H)=10.7, 3J
(H,H)=8.3 Hz, 2H; one of CH2), 7.91 (t,
3J (para)), 8.28 ppm (d, 3J
(H,H)=8.1 Hz, 1H; PyH (H,H)=8.1 Hz, 2H;
PyH
(meta)); 13C NMR (125 MHz, CDCl3, TMS): d=52.8, 68.7, 70.4,
126.7, 137.6, 146.2, 164.9, 171.1 ppm; IR (KBr): n˜max =1744 and 1726 cmꢀ1
C
(H,H)=
AHCTREUNG
A
ACHTREUNG
A
G
AHCTREUNG
Figure 6. Membrane potentials (DEMF) with increasing concentration of
each of the nucleoside 5’-monophosphate guests, measured at room tem-
perature (ca. 258C) with a) PVC-supported solvent polymeric membrane
U
(100), 246 (77), 186 (38); HRMS calcd (m/z) for C15H15N3O6 [M+]:
*
^
:
containing host 2 and b) blank membrane without a host. : 5’-AMP;
333.0961; found: 333.0967.
~
5’-GMP; : 5’-CMP; ”: 5’-UMP.
Dimethyl 2,2’-(pyridine-2,6-diyl)bis(oxazole-4-carboxylate) (9): This com-
pound was prepared by employing the reported procedure[12] with some
modifications. Bromotrichloromethane (17.25 g, 84.7 mmol) was added to
a stirred solution of 8 (5.65 g, 17.0 mmol) and DBU (6.70 g, 42.4 mmol)
in CH2Cl2 (250 mL), precooled at 08C, over a period of 1 min, and was
stirred at 08C for 20 h. The resulting precipitate was collected by filtra-
tion to give 9. The filtrate was evaporated and purified by column chro-
matography (silica gel, CHCl3) to give an additional amount of 9. The
combined white solid (total 3.95 g, 71%) was recrystallized from AcOEt/
Conclusion
The results reported herein demonstrate that the linked
five-six-five-membered triheteroaromatic core, attached di-
rectly with two carbamoyl NH sites, provides a multiply hy-
drogen-bonding structure with high complementarity for ad-
enine nucleobases. By this host structure, high complexation
selectivity was attained in CHCl3 for lipophilized the ade-
nine nucleobase over all other nucleobases for the first time.
Furthermore, remarkable potentiometric selectivity was at-
tained for adenosine 5’-monophosphate (5’-AMP) over 5’-
GMP, 5’-CMP, and 5’-UMP by recognition through the
membrane/water interface of PVC-supported solvent poly-
meric membranes. These findings are expected to be a reli-
EtOH to give an analytical sample: mp 287–2888C; 1H NMR (400 MHz,
3
CDCl3, TMS): d=3.98 (s, 6H; CH3), 8.03 (t, J
A
3
A
G
ACHTREUNG
138.4, 145.3, 145.5, 160.2 ppm; IR (KBr): n˜max =1746 and 1723 cmꢀ1 (n
ACHTREUNG
O), ester); MS (EI, 70 eV): m/z (%): 329 (100) [M+], 298 (45), 231 (48),
203 (79), 198 (62); elemental analyses calcd (%) for C15H11N3O6: C 54.72,
H 3.37, N 12.76; found: C 54.42, H 3.49; N 12.95.
2,2’-(Pyridine-2,6-diyl)bis(oxazole-4-carboxylic acid) (10): Compound 9
(1.26 g, 3.8 mmol) was added to a stirred solution of potassium hydroxide
(1.43 g, 25 mmol) in H2O (50 mL), and the whole was stirred at RT for
20 h. The reaction mixture was acidified with 5% HCl, and the resulting
precipitate was collected by filtration to give 10 as a white solid (1.126 g,
quantitative): m.p. 2968C (decomp); 1H NMR (400 MHz, [D6]DMSO,
able basis for the development of artificial sensing systems
for mononucleotides in biological systems.
TMS): d=8.23 (t, 3J
9.0 Hz, 2H; PyH
(meta)), 8.97 ppm (s, 2H; CH of oxazole); 13C NMR
(125 MHz, [D6]DMSO, TMS): d=124.0, 134.8, 139.5, 145.1, 146.5, 159.6,
A
G
N
AHCTREUNG
Experimental Section
161.8 ppm; IR (KBr): n˜max =3750–3250 (n(OH), carboxy), 1719 (n(C=O),
E
carboxy) cmꢀ1; MS (EI, 70 eV): m/z (%): 301 (78) [M+], 257 (70), 189
(100), 145 (70); HRMS calcd (m/z) for C13H7N3O6 [M+]: 301.0335;
found: 301.0337; elemental analyses calcd (%) for C13H7N3O6: C 51.84, H
2.34, N 13.95; found: C 51.70, H 2.41, N 13.71.
General information: Melting points were measured with a Yanaco MP-
500 V melting point apparatus and are uncorrected. Infrared spectra
were recorded on JASCO FT-IR-5300 or IR Report-100 spectrometers.
Fluorescence spectra were recorded on a Shimadzu RF-5300(PC) spec-
trometer. UV/Vis spectra were recorded on a JASCO UV-550. Mass
spectra were recorded on Bruker APEX III, JASCO QUATTRO II or
Dihexyl 2,2’-(Pyridine-2,6-diyl)bis(oxazole-4-carbamate) (1): This com-
pound was prepared from diacid 10, which was first converted to the cor-
7738
www.chemeurj.org
ꢁ 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2006, 12, 7733 – 7741

Nucleotide Recognition
FULL PAPER
responding diazide and then subjected to a Curtius rearrangement fol-
lowed by treatment with 1-hexanol. A mixture of 10 (150 mg, 0.50 mmol)
and SOCl2 (9.0 mL, 0.12 mol) was heated at reflux for 19 h. The reaction
mixture was evaporated and dried in vacuo to give the diacid chloride.
To a stirred solution of the diacid chloride in dry acetone (9 mL), pre-
cooled at 08C, was added a solution of sodium azide (162 mg, 2.5 mmol)
in H2O (1 mL) during a period of 1 h. The whole was stirred for 3 h at
room temperature. The resulting precipitate was collected by filtration
and washed with H2O to give the diazide as a white solid. A stirred sus-
pension of the diazide in CHCl3 (8 mL) was heated at reflux for 2 h
under a N2 atmosphere. 1-Hexanol (8 mL) was added to the resulting so-
rification by column chromatography (silica gel, CHCl3), the desired
product 13 was obtained as a yellow solid (931 mg, 95%): m.p. 2118C; H
NMR (400 MHz, CDCl3, TMS): d=3.99 (s, 6H; OCH3), 8.448 and
1
8.454 ppm (two s, each 2H; PyH and oxazolyl CH); IR (KBr): n˜max
=
1735 cmꢀ1 (n
A
[M+H]+: 364.0318; found: 364.0331.
2,2’-(4-Methoxypyridine-2,6-diyl)bis(oxazole-4-carboxylic
acid)
(14):
Compound 13 (625 mg, 1.72 mmol) was added to a stirred solution of po-
tassium hydroxide (0.90 g, 14 mmol) in a mixture of H2O (22 mL) and
MeOH (17 mL). The mixture was heated at 608C for 13 h. The reaction
mixture was acidified with 5% HCl, and the resulting precipitate was col-
lected by filtration to give the methoxy diacid 14 as a white solid
A
1
ture was diluted with CHCl3 (40 mL), and washed successively with 5%
aq citric acid (20 mL), saturated aqueous NaHCO3 (20 mL) and brine
(20 mL). The organic layer was dried over anhydrous MgSO4, filtered
and evaporated. The residue was purified by column chromatography
(alumina, CHCl3/hexane 1:1) to give 1 as a white solid (156 mg, 62%),
which was recrystallized from EtOH to give a white powder: mp 196–
(360 mg, 64%): m.p. 168–1698C; H NMR (400 MHz, [D6]DMSO, TMS):
d=4.06 (s, 3H; OCH3), 7.77 (s, 2H; PyH), 8.96 ppm (s, 2H; CH of oxa-
zole); IR (KBr): n˜max =3410 (n(OH), br, carboxy), 1710 (n(C=O), car-
C
boxy) cmꢀ1; HRMS (ESI) calcd (m/z)for C14H9N3O7 [M+Na]+: 354.0333;
found: 354.0320.
Dihexyl 2,2’-(4-methoxypyridine-2,6-diyl)bis(oxazole-4-carbamate) (2):
This compound was obtained from methoxy diacid 14 (90 mg, 0.27 mmol)
by a Curtius rearrangement–carbamate ester formation with a similar
protocol as for the sequence of reactions from 10 to 1. After purification
by column chromatography (alumina, CHCl3/hexane 1:1), the desired
product 2 was obtained as a white solid (90 mg, 57%): m.p. 126–1278C;
1988C; 1H NMR (400 MHz, CDCl3, TMS): d=0.90 (t, 3J
6H; CH3), 1.3–1.4 (brm, 12H in total; (CH2)3CH3), 1.7 (m, 4H;
A
3
ACHTREUNG
OCH2CH2), 4.19 (br t, J
7.93 (t, 3J
(H,H)=7.6 Hz, 1H; PyH
8.08 ppm (d, 3J
(H,H)=7.6 Hz, 2H; PyH
A
ACHTREUNG
A
ACHTREUNG
CDCl3): d=14.0, 22.5, 25.4, 28.8, 31.4, 66.2, 122.6, 126.0, 138.0, 138.7,
145.9, 153.1, 157.1 ppm; IR (KBr): n˜max =3308 (n(NH), carbamoyl), 1709
1H NMR (400 MHz, CDCl3, TMS): d=0.90 (t, 3J
(CH2)3CH3), 1.3–1.4 (m, 12H in total; (CH2)3CH3), 1.7 (br m, 4H;
OCH2CH2), 4.00 (s, 3H; OCH3), 4.19 (br t, 3J
(H,H)=6.6 Hz, 4H;
A
(n
C
;
UV/Vis (CHCl3): lmax (e)=326 nm
AHCTREUNG
OCH2), 6.95 (br s, 2H; NH), 7.60 (s, 2H; PyH), 8.00 ppm (s, 2H; CH of
oxazole); 13C NMR (125 MHz, CDCl3, TMS): d=13.9, 22.4, 25.3, 28.7,
31.3, 55.7, 66.0, 108.7, 125.7, 138.4, 147.3, 152.9, 157.0, 167.0 ppm; IR
(KBr): n˜max =3300 (n(NH), carbamoyl), 1710 (n ;
(C=O), carbamoyl) cmꢀ1
H
A
dimethyl
HRMS (ESI) calcd (m/z) for C26H35N5O7 [M+Na]+: 552.2443; found:
552.2429; elemental analyses calcd (%) for C26H35N5O7: C 58.97, H 6.66,
N 13.22; found: C 58.85, H 6.69, N 13.26.
ester (11): This compound was prepared by employing the reported pro-
cedure[23] with some modifications. Chelidamic acid (9.71 g, 53.1 mmol),
moistened with a small amount of DMF (0.170 g, 2.3 mmol), was mixed
with SOCl2 (125 mL, 4.4 mol) and heated at reflux for five days. The mix-
ture was evaporated, coevaporated with anhydrous toluene and dried in
vacuo to give the diacid chloride. This material was used for the next
step without further purification. To a suspension of l-serine methyl ester
hydrochloride (18.67 g, 120 mmol) in CHCl3 (250 mL), precooled at 08C,
were successively added Et3N (65 mL, 430 mmol) in one portion and a
solution of the diacid chloride in CHCl3 (100 mL, drop wise over a
period of 30 min under N2 atmosphere). The whole was stirred at room
temperature for one day and concentrated to a small volume. The residue
was treated with AcOEt–MeOH and the resulting white solid was fil-
tered off; these operations were repeated twice. The filtrate was evapo-
rated and the residue was purified by column chromatography (silica gel,
CHCl3/MeOH 60:1) to give 11 as a white solid (7.38 g, 37%): m.p.
1798C; 1H NMR (400 MHz, CDCl3, TMS): d=3.65 (s, 2H; OH), 3.84 (s,
Fluorescence spectroscopic measurements for host–guest complexation
Measurements of fluorescence intensity or spectra were conducted on a
Shimadzu RF-5300 spectrometer at 208C, using CHCl3 of fluorescence
spectrophotometric grade purchased from Kanto Chemical(Tokyo,
Japan; catalog code 07278–3B).
Determination of the stability constants of the host–guest complexes: Sta-
bility constants of 1:1 complexes (Ks [mꢀ1]) were determined by the
Benesi–Hildebrand[15a,c] analysis, measuring the decrease of fluorescence
intensity with increasing concentration of the guest with a constant con-
centration of the host.[14] The conditions: [1]
= 20 mm, [5A] = 240–
580 mm, [5G, 5C, 5U, or 5T] = 4.0–16.0 mm, [2]= 20 mm, [5A] = 240–
580 mm, [5C] = 0.80–1.6 mm, [5G, 5U, or 5T] = 4.0–16.0 mm, [4] =
20 mm, [5A] = 2.0–12.0 mm. Fluorescence emission at 380 nm (host 1),
371 nm (host 2) or 376 nm (reference 4) was measured in CHCl3 at 208C
with excitation at 336 nm (host 1 with all guests), 326 nm (host 2 with all
guests) or 312 nm (reference 4 with guest 5A).
6H; CH3), 4.11 (dd, 2J
4.21 (dd, 2J(H,H)=11.7, 3J
3J(H,H)=3.9, 7.8 Hz, 2H; CH), 8.19 (s, 2H; PyH), 8.80 ppm (d, 3J-
(H,H)=7.8 Hz, 2H; NH); IR (KBr): n˜max =3350 (n(OH), br), 1735 (n(C=
O), ester), 1655 (n
(C=O), amide) cmꢀ1; MS (FAB): m/z: 404 [M+H]+;
A
N
A
ACHTREUNG
ACHTREUNG
Potentiometric measurements[24]
A
ACHTREUNG
ACHTREUNG
Solvent polymeric membranes: Solvent polymeric membranes with poly-
(vinyl chloride) (PVC) matrix were prepared according to the litera-
elemental analyses calcd (%) for C15H18ClN3O8: C 44.62, H 4.49, N 10.41;
found: C 44.22, H 4.44, N 10.28.
ture[25] with slight modifications. Membranes of about 0.1-mm thickness
were obtained by pouring a solution of approximately 300 mg of mem-
brane components, dissolved in THF (ca. 3 mL), into a flat Petri dish
(34 mm i.d.). The solvent was allowed to evaporate off at room tempera-
ture for two days. From the resulting solvent polymeric membrane, sever-
al disks of 7-mm diameter were punched and soaked in a 1.0”10ꢀ2 m KCl
solution overnight as a conditioning process. The composition of solvent
polymeric membrane containing host 2 and that of the blank membrane
without a host were host/NPOE/PVC/TDDMACl=0.7:70.6:28.5:0.4 and
NPOE/PVC/TDDMACl=70.6:28.5:0.4 (weight ratio), respectively. The
molar ratio of TDDMACl relative to host 2 was 50 mol%. NPOE=2-ni-
trophenyl octyl ether; TDDMACl=tridodecylmethylammonium chloride
(Cl).
Dimethyl
(S,S)-2,2’-(4-chloropyridine-2,6-diyl)bis(4,5-dihydrooxazole-4-
carboxylate) (12): This compound was obtained from 11 (1.210 g,
3.00 mmol) by a similar protocol as for the cyclization of bis-hydroxy-
A
CHCl3/MeOH 60:1), the desired product 12 was obtained as a yellow
solid (1.00 g, 91%): m.p. 97–998C; 1H NMR (400 MHz, CDCl3, TMS):
d=3.83 (s, 6H; OCH3), 4.72 (dd, 2J
G
ACHTREUNG
one of CH2), 4.81 (dd, 3J
2J(H,H)=10.7, 3J
ACHTREUNG
A
ACHTREUNG
PyH); IR (KBr): n˜max =1740 cmꢀ1 (n
(C=O), ester); HRMS (ESI) calcd
(m/z) for C15H1435ClN3O6 [M+Na]+: 390.0462; found: 390.0463.
Dimethyl 2,2’-(4-chloropyridine-2,6-diyl)bis(oxazole-4-carboxylate) (13):
This compound was obtained from bis(oxazolin-2-yl)pyridine 12 (974 mg,
2.65 mmol) by a similar protocol as for the oxidation of 8 to 9. After pu-
Electrode system: Each membrane was fixed on a liquid membrane type
ion-selective electrode body type IS 561 (Willi Mçller AG, Zꢂrich, Swit-
Chem. Eur. J. 2006, 12, 7733 – 7741
ꢁ 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
7739

K. Odashima et al.
zerland). A 1.0”10ꢀ2 m KCl solution was used as an internal solution.
The reference electrode was a double-junction type based on an Ag/
AgCl electrode (DKK·TOA, Tokyo, Japan) containing a saturated aque-
ous KCl solution in the inner compartment and a 1m AcOLi solution in
the outer compartment. The electrode cell for the potential measure-
ments was as follows: Ag j AgCl j satd aq KCl : 1m AcOLi : guest so-
2002, 124, 10946–10947 Thymine (uracil): g) M. Shionoya, T. Ikeda,
E. Kimura, M. Shiro, J. Am. Chem. Soc. 1994, 116, 3848–3859;
h) S. M. Butterfield, M. M. Sweeney, M. L. Waters, J. Org. Chem.
2005, 70, 1105–1114.
[5] a) K. Nakatani, S. Sando, I. Saito, J. Am. Chem. Soc. 2000, 122,
2172–2177; b) K. Nakatani, S. Sando, H. Kumasawa, J. Kikuchi, I.
Saito, J. Am. Chem. Soc. 2001, 123, 12650–12657; c) K. Yoshimoto,
S. Nishizawa, M. Minagawa, N. Teramae, J. Am. Chem. Soc. 2003,
125, 8982–8983.
[6] For review articles, see: a) E. Bakker, P. Bꢂhlmann, E. Pretsch,
Chem. Rev. 1997, 97, 30833132; b) P. Bꢂhlmann, E. Pretsch, E.
Bakker, Chem. Rev. 1998, 98, 1593–1687; c) K. Odashima, J. Inclu-
sion Phenom. 1988, 32, 165–178.
[7] a) K. Tohda, M. Tange, K. Odashima, Y. Umezawa, H. Furuta, J. L.
Sessler, Anal. Chem. 1992, 64, 960–964; b) S. Amemiya, P. Bꢂhl-
mann, K. Tohda, Y. Umezawa, Anal. Chim. Acta 1997, 341, 129–
139; c) J. L. Sessler, V. Krꢃl, T. V. Shishkanova, P. A. Gale, Proc.
Natl. Acad. Sci. USA 2002, 99, 4848–4853; d) V. Kral, T. V. Shishka-
nova, J. L. Sessler, C. T. Brown, Org. Biomol. Chem. 2004, 2, 1169–
1175.
[8] P. A. S. Smith, Org. Synth. 1956, 3, 337–449 (Chapter 9).
[9] a) For the details of the synthesis and characterization of hosts 1
and 2, see the Experimental Section. b) For the details of the syn-
thesis and characterization of reference compounds (3, 4) and lipo-
philic nucleoside guests (5A, 5G, 5C, 5U, 6T), see the Supporting
Information.
lution j membrane j 1.0”10ꢀ2 m KCl j AgCl j Ag.
Potential measurements: Membrane potentials were measured for unbuf-
fered aqueous solutions of guests. All measurements were carried out
with gentle stirring at room temperature (ca. 258C) with a pH–mV meter
model HM-60 V (TOA Electronics, Tokyo, Japan). Deionized and puri-
fied water (specific resistance, 18.2mW cm) was obtained with a Milli-Q
Labo system. The sample solutions of each guest were prepared by
adding an aliquot (10, 20, 50, 200, 500, 1800 mL) of 1.0”10ꢀ1 m guest solu-
tion to 25 mL of water. Membrane potentials for each guest anion were
measured in the order of increasing lipophilicity of the guest (5’-CMP, 5’-
UMP, 5’-AMP, 5’-GMP). The potential was measured for 1–5 min.
During this period of time, the potential drift was around 1 mVminꢀ1 in
most cases. The potential measurement for each guest was repeated two
or three times. By the separate solution method,[26] according to the con-
ventional Nicolsky–Eisenman equation, the potentiometric selectivity co-
efficient[27] (K5’-AMP,5’-GMPpot) was determined for 5’-AMP and 5’-GMP as
the primary and interfering ions, respectively, with the concentration
range of 1.0”10ꢀ3.4 to 1.0”10ꢀ2.0 m.
[10] S. Iwasa, H. Nakamura, H. Nishiyama, Heterocycles 2000, 52, 939–
944.
[11] A. J. Phillips, Y. Uto, P. Wipf, M. J. Reno, D. R. Williams, Org. Lett.
2000, 2, 1165–1168.
[12] D. R. Williams, P. D. Lowder, Y.-G. Gu, D. A. Brools, Tetrahedron
Lett. 1997, 38, 331–334.
[13] F. Yokokawa, Y. Hamada, T. Shioiri, Synlett 1992, 151–152.
[14] See the Supporting Information for details of experimental methods
and data.
Acknowledgements
We gratefully acknowledge Professor Shigeru Amemiya (Pittsburgh Uni-
versity, USA) and Mr. Ryosuke Saijo (Nagoya City University, Japan)
for valuable discussions. This research was financially supported by
Grant-in-Aid for Scientific Research from the Ministry of Education,
Culture, Sports, Science and Technology, Japan.
[15] a) K. A. Connors, Binding Constants, Wiley, New York, 1987; b) P.
Job, Ann. Chim. Appl. 1928, 9, 113–203; c) H. A. Benesi, J. H. Hil-
debrand, J. Am. Chem. Soc. 1949, 71, 2703–2707.
[16] The experimental results suggest that the Ks values determined by
the fluorescent responses mainly reflect the complexation ability in
the ground state. Therefore, for the present host 1, the fluorescence
method can be used to determine the Ks values for firm discussions
on host–guest complexation ability and selectivity displayed under
ordinary conditions.
[1] a) B. Alberts, A. Johnson, J. Lewis, M. Raff, K. Roberts, P. Walter,
Molecular Biology of the Cell, 4th ed., Garland Science, New York,
2002; b) J. D. Watson, T. A. Baker, S. P. Bell, A. Gann, M. Levine,
R. Losick, Molecular Biology of the Gene, 5th ed., Benjamin-Cum-
mings, San Francisco, 2003.
[2] For review articles, see: a) G. Cooke, V. M. Rotello, Chem. Soc. Rev.
2002, 31, 275–276; b) S. Aoki, E. Kimura, Chem. Rev. 2004, 104,
769–787; c) J. L. Sessler, J. Jayawickramarajah, Chem. Commun.
2005, 1939–1949; d) S. Sivakova, S. J. Rowan, Chem. Soc. Rev. 2005,
34, 9–21.
[3] For selected examples of nucleobase-selective complexation in rela-
tively nonpolar organic solvents, see the following. Adenine: a) S.
Goswami, D. Van Engen, A. D. Hamilton, J. Am. Chem. Soc. 1989,
111, 3425–3426; b) S. C. Zimmerman, W. Wu, Z. Zeng, J. Am.
Chem. Soc. 1991, 113, 196–201; c) H. Ogoshi, H. Hatakeyama, J.
Kotani, A. Kawashima, Y. Kuroda, J. Am. Chem. Soc. 1991, 113,
8181–8183; d) R. Gꢂther, M. Nieger, F. Vçgtle, Angew. Chem. 1993,
105, 647–649; Angew. Chem. Int. Ed. Engl. 1993, 32, 601–603;
e) K. S. Jeong, J. Rebek, Jr., J. Am. Chem. Soc. 1988, 110, 3327–
3328; f) M. M. Conn, G. Deslongchamps, J. de Mendoza, J. Re-
bek, Jr., J. Am. Chem. Soc. 1993, 115, 3548–3557. Guanine: g) T. K.
Park, J. Schroeder, J. Rebek, Jr., Tetrahedron 1991, 47, 2507–2518.
Cytosine: h) See reference [3e].
[4] For selected examples of nucleobase-selective complexation in polar
solvents or water, see the following. Adenine: a) M. W. Hosseini,
A. J. Blacker, J.-M. Lehn, J. Am. Chem. Soc. 1990, 112, 3896–3904;
b) G. Deslongchamps, A. Galꢃn, J. de Mendoza, J. Rebek, Jr.,
Angew. Chem. 1992, 104, 58–61; Angew. Chem. Int. Ed. Engl. 1992,
31, 61–63; c) W.-S. Yeo, J.-I. Hong, Tetrahedron Lett. 1998, 39,
3769–3772; d) S. E. Schneider, S. N. OꢀNeil, E. V. Anslyn, J. Am.
Chem. Soc. 2000, 122, 542–543 Guanine: e) J. Y. Kwon, N. J. Singh,
H. N. Kim, S. K. Kim, K. S. Kim, J. Yoon, J. Am. Chem. Soc. 2004,
126, 8892–8893 Cytosine: f) F. Mancin, J. Chin, J. Am. Chem. Soc.
[17] Another example of a host with only neutral hydrogen-bonding
sites, which exhibits similar complexation ability for 9-ethyladenine,
has been reported (Ks =2.4”103 mꢀ1 in CDCl3). a) Complexation
ability for adenine nucleobase can be improved by employing acidic
hydrogen-bonding groups (Ks =4.5”104 mꢀ1 in CDCl3). b) K. S.
Jeong, T. Tjivikua, A. Muehldorf, G. Deslongchamps, M. Famulok,
J. Rebek, Jr., J. Am. Chem. Soc. 1991, 113, 201–209; c) J. C.
Adrian, Jr., C. S. Wilcox, J. Am. Chem. Soc. 1989, 111, 8055–8057.
[18] The calculation was carried out with the GAUSSIAN-98 program
on the IBM 7038–6M2 pSeries650 computer system of the Library
and Information Processing Center of Nagoya City University.
GAUSSIAN-98: Gaussian 98, Revision A.11.3, produced by M. J.
Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria, M. A. Robb,
J. R. Cheeseman, V. G. Zakrzewski, J. A. Montgomery, Jr., R. E.
Stratmann, J. C. Burant, S. Dapprich, J. M. Millam, A. D. Daniels,
K. N. Kudin, M. C. Strain, O. Farkas, J. Tomasi, V. Barone, M. Cossi,
R. Cammi, B. Mennucci, C. Pomelli, C. Adamo, S. Clifford, J. Och-
terski, G. A. Petersson, P. Y. Ayala, Q. Cui, K. Morokuma, N. Rega,
P. Salvador, J. J. Dannenberg, D. K. Malick, A. D. Rabuck, K. Ra-
ghavachari, J. B. Foresman, J. Cioslowski, J. V. Ortiz, A. G. Baboul,
B. B. Stefanov, G. Liu, A. Liashenko, P. Piskorz, I. Komaromi, R.
Gomperts, R. L. Martin, D. J. Fox, T. Keith, M. A. Al-Laham, C. Y.
Peng, A. Nanayakkara, M. Challacombe, P. M. W. Gill, B. Johnson,
W. Chen, M. W. Wong, J. L. Andres, C. Gonzalez, M. Head-Gordon,
E. S. Replogle, J. A. Pople, Gaussian, Inc., Pittsburgh (USA), 2002.
7740
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ꢁ 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2006, 12, 7733 – 7741

Nucleotide Recognition
FULL PAPER
[19] These values agree well with those calculated by a similar method
for the 2:1 complex of N-((E)-(methylimino)methyl)formamide and
9-ethyladenine. See: I. Alkorta, J. Elguero, S. Goswami, R. Mukher-
jee, J. Chem. Soc. Perkin Trans. 2 2002, 894–898.
[26] K. Srinivasan, G. A. Rechnitz, Anal. Chem. 1969, 41, 1203–1208.
[27] For potentiometric selectivity coefficient, see: a) CRC Handbook of
Ion-Selective Electrodes: Selectivity Coefficients (Ed.: Y. Umezawa),
CRC Press, Boca Raton, 1990; b) Y. Umezawa, P. Bꢂhlmann, K.
Umezawa, K. Tohda, S. Amemiya, Pure Appl. Chem. 2000, 72,
1852–2082; c) Y. Umezawa, K. Umezawa, P. Bꢂhlmann, N.
Hamada, J. Nakanishi, H. Aoki, M. Sato, Y. Nishimura, K. P. Xiao,
Pure Appl. Chem. 2002, 74, 923–994; d) Y. Umezawa, P. Bꢂhlmann,
K. Umezawa, N. Hamada, Pure Appl. Chem. 2002, 74, 995–1099;
e) Y. Umezawa in Encyclopedia of Supramolecular Chemistry (Eds.:
J. Atwood, J. Steed), Marcel Dekker (USA), 2004, pp. 747–752.
[20] The complexation between reference 4 and 5A was confirmed by
1H NMR spectroscopy (see also reference [14]).
[21] Membrane potential (DEMF) was measured as electromotive force
(EMF) relative to the reference electrode (Ag j AgCl j satd aq
KCl).
[22] Both of the solvent polymeric membranes contained tridodecyl-
methylammonium chloride (TDDMACl) as lipophilic cationic sites.
See the Supporting Information for details.
[23] H. Nishiyama, S. Yamaguchi, M. Kondo, K. Itoh, J. Org. Chem.
1992, 57, 4306–4309.
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Received: January 22, 2006
Revised: April 5, 2006
Published online: July 26, 2006
Chem. Eur. J. 2006, 12, 7733 – 7741
ꢁ 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
7741