New branched macrocyclic ligand and its side-arm, two urea-based receptors for anions: Synthesis, binding studies and crystal structure

Article abstract of DOI:10.1039/b719342d

The synthesis and characterization of the two new hosting molecules for anions 4(N),10(N)-bis-[2-(4-nitrophenylureido)acetamido]-1,7-dimethyl-1,4,7,10- tetraazacyclododecane (L1) and 1-((diethylcarbamoyl)methyl)-3-(4-nitrophenyl) urea (L2) are reported. L1 is a branched tetraazamacrocycle bearing two p-nitrophenylureido groups as side-arms, whereas L2 has the same linear chain and binding moiety of L1 side-arm. The best synthetic routes for use in obtaining L1 were explored, affording the synthesis of the new intermediate 4, a versatile building block for further functionalized branched macrocyclic hosts. The binding properties of both ligands towards the halides series and acetate anions (G) were investigated by NMR and UV-Vis spectroscopy in a dimethyl sulfoxide-0.5% water solution. Both ligands interact with F^-, Cl ^- and AcO^- while Br^- and I^- did not. The NMR experiments proved that the binding occurs via H-bond to the ureido fragments. Fluoride anion is basic enough to deprotonate the ureido group of both ligands, thus preventing the determination of the addition constants to both ligands; this was instead possible for Cl^- and AcO^-. L1 forms G-L species of 1: 1 ([GL1]) and 2: 1 ([G₂L1]) stoichiometry while L2 forms only the 1: 1 [GL2] species. The higher value of the formation constant of the [AcOL1]^-vs. the [AcOL2]^- species (log K = 5.5 vs. 2.8 for the reaction AcO^- + L = AcOL^-) suggested that both side-arms of L1 cooperate in binding acetate; this does not occur with Cl^-. The results confirmed that this tetraaza-macrocyclic base acts as a preorganizing scaffold for side-arms when they are linked to it via an amide function. The crystal structure of L2·H₂O is also reported. The Royal Society of Chemistry and the Centre National de la Recherche Scientifique.

Full text of DOI:10.1039/b719342d

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PAPER
www.rsc.org/njc | New Journal of Chemistry
New branched macrocyclic ligand and its side-arm, two urea-based
receptors for anions: synthesis, binding studies and crystal structurew
Mauro Formica,a Vieri Fusi,*a Eleonora Macedi,a Paola Paoli,b
Giovanni Piersanti,c Patrizia Rossi,b Giovanni Zappiac and Pierfrancesco Orlandoc
Received (in Durham, UK) 14th December 2007, Accepted 6th February 2008
First published as an Advance Article on the web 26th February 2008
DOI: 10.1039/b719342d
The synthesis and characterization of the two new hosting molecules for anions
4(N),10(N)-bis-[2-(4-nitrophenylureido)acetamido]-1,7-dimethyl-1,4,7,10-tetraazacyclododecane
(L1) and 1-((diethylcarbamoyl)methyl)-3-(4-nitrophenyl)urea (L2) are reported. L1 is a branched
tetraazamacrocycle bearing two p-nitrophenylureido groups as side-arms, whereas L2 has the
same linear chain and binding moiety of L1 side-arm. The best synthetic routes for use in
obtaining L1 were explored, affording the synthesis of the new intermediate 4, a versatile building
block for further functionalized branched macrocyclic hosts. The binding properties of both
ligands towards the halides series and acetate anions (G) were investigated by NMR and UV-Vis
spectroscopy in a dimethyl sulfoxide–0.5% water solution. Both ligands interact with Fꢀ, Clꢀ and
AcOꢀ while Brꢀ and Iꢀ did not. The NMR experiments proved that the binding occurs via
H-bond to the ureido fragments. Fluoride anion is basic enough to deprotonate the ureido group
of both ligands, thus preventing the determination of the addition constants to both ligands; this
was instead possible for Clꢀ and AcOꢀ. L1 forms G–L species of 1 : 1 ([GL1]) and 2 : 1 ([G2L1])
stoichiometry while L2 forms only the 1 : 1 [GL2] species. The higher value of the formation
constant of the [AcOL1]ꢀ vs. the [AcOL2]ꢀ species (log K = 5.5 vs. 2.8 for the reaction AcOꢀ
L = AcOLꢀ) suggested that both side-arms of L1 cooperate in binding acetate; this does not
+
occur with Clꢀ. The results confirmed that this tetraaza-macrocyclic base acts as a preorganizing
scaffold for side-arms when they are linked to it via an amide function. The crystal structure of
L2ꢁH2O is also reported.
diseases, renal insufficiency, overtreatment with diuretics,
Introduction
chronic respiratory acidosis, diabetic acidosis and adrenal
insufficiency. The fluoride ions are also important anions
because of their central role in dental care and the clinical
treatment of osteoporosis.9,10 Thus, development of sensors
for the direct detection of fluoride ions in aqueous media is an
important target for their potential application in clinical and
environmental analyses.
Since the first report on the preparation of a synthetic anion
receptor by Park and Simmons in 1968, the development of
anion receptors has become a field of great interest and
activity, with many groups involved worldwide.1,2 The con-
tinuing interest in the development of new selective anion
receptor systems stems from their potential use as membrane
transport carriers,3 chemosensors,4 and reaction catalysts.5 As
a result, considerable attention has been focused upon the
designing of synthetic receptors for the detection of biologi-
cally relevant anions6 such as chloride,7 which plays a specific
role in the interaction with haemoglobin in the ‘‘chloride shift’’
effect,8a whilst substantial alteration in the plasma chloride
level has been associated with many pathological conditions.
For instance, an increase in chloride concentration can be
found in renal insufficiency, renal tubule acidosis, hyperpar-
athyroidism, dehydration and over-treatment with saline so-
lution.8b Decreased levels have been linked to gastrointestinal
Sulfate is involved in activation and detoxification of a
variety of endogenous and exogenous substances such as
xenobiotics, steroids, neurotransmitters, and bile acids.11
Sulfate conjugation is essential for the biosynthesis of a
large number of structural proteins such as sulfated
glycosaminoglycans (a major component of cartilage),
cerebroside sulfate (a constituent of the myelin membranes
in the brain) and heparin sulfate (which is required for
anticoagulation).12
Molecular recognition of phosphate anions is crucial to a
myriad of biological processes involving gene regulation,
metabolism, antibiotic resistance, signal transduction, etc.13
In addition, important anions, such as lactate, pyruvate and
glutamate play an important role in neurological diseases,14 as
well as the free carboxylic function of the dipeptide D-Ala-D-
Ala, which has an important role in the formation of the
supramolecular complex with Vancomycin, inhibiting the
cross-linking of the bacterial cell wall.15
a Institute of Chemical Sciences, University of Urbino, P.zza
Rinascimento 6, I-61029 Urbino, Italy. E-mail: vieri@uniurb.it
b Department of Energy Engineering ‘Sergio Stecco’, University of
Florence, Via S. Marta 3, I-50139 Florence, Italy
c Institute of Pharmaceutical Chemistry, University of Urbino, P.zza
Rinascimento 6, I-61029 Urbino, Italy
w CCDC reference number 677798. For crystallographic data in CIF
or other electronic format see DOI: 10.1039/b719342d
ꢂc
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cations such as MeNH3+, discriminating them from the
secondary or tertiary ammonium cations, as well as to bind
the alkali, alkaline earth, Ga3+, Cu2+, and Zn2+ ions.21 The
most interesting structure had a 1,7-dimethyl-1,4,7,10-tetra-
zacyclododecane unit (Me2[12]aneN4)22 as macrocyclic scaf-
fold, upon which we attached two 3-(hydroxyl)-1-
(carbonylmethylene)-2(1H)-pyridone (HPO) moieties as side-
arms. Molecular modelling and crystal studies highlighted that
the way in which the two HPO groups are connected to the
macrocyclic Me2[12]aneN4 is fundamental in stiffening and
preorganizing the host; the two N–CQO amide groups, which
link each HPO moiety to the 12-member ring, draw the two
side-arms to occupy the same region with respect to the
macrocyclic base.
Taking advantage of these observations, we have now
designed and studied a new anion receptor L1 (Chart 1)
based on the use of the same macrocyclic Me2[12]aneN4
base, upon which we have attached two ureido groups via a
methylene carbonyl chain. Studies of binding with anions,
such as Fꢀ and Clꢀ, as well as the acetate anion were
performed and compared with the results obtained with its
analogous linear ligand L2 (Chart 1), in order to verify the
concept of preorganization and to enhance the binding affinity
of the L1 receptor.
Chart 1 Ligands with labels for the NMR experiments.
Several approaches can be used to obtain anion receptors.
For example, the most exploited strategies are: (i) metal
complexes, in which the metal centre shows an unsaturated
coordination environment, and can bind an anion via classic
coordination chemistry;16 (ii) positively charged hosts, as the
polyammonium class, which can interact with the anion
mainly via charge–charge interactions;17 (iii) neutral non-
metallic systems, with the aim to mimic several proteins in
their anion binding.2g,18 In these latter systems, the forming
supramolecular adducts are mainly stabilized via weak inter-
action forces such as H-bonding, p-stacking and others.
Looking at the neutral non-metallic systems, a way in design-
ing these hosts has been to introduce several and suitable
hydrogen bond donor groups in the scaffold in order to
improve the interaction with the anion. However, in this type
of system, the ‘‘host–guest’’ binding affinity is modulated by
many factors including the solvent, counterions,
ionic strength, etc., and the best results are obtained
when the binding sites are structurally organized for anion
complexation.
As emerged from the current literature,19 a high degree
of structural organization is obtained when the host is
able to adopt a conformation in which all binding sites are
positioned in such way as to be structurally complementary to
the guest. Furthermore, the host should exhibit a limited
number of stable conformations and the binding conforma-
tion should be low in energy relative to other possible forms.4
Thus, preorganization and complementarity are pivotal
concepts for the correct design for anion receptors. Although,
the design and preparation of simple molecular systems that
are able to exhibit these properties is not a simple task, in
general, host structures that possess a rigid scaffold and
urea,20a thiourea20b or guanidinium20c functional groups as
side-arms have been reported to be very effective in the binding
of anions.
Results and discussion
Synthesis
Scheme 1 outlines the synthesis of the new multidentate ligand
L1, which was based on the coupling of the protected glycine
derivative 1 with the 1,7-dimethyl-1,4,7,10-tetraazacyclodode-
cane 2 followed by the removal of the amine function protec-
tion obtaining the intermediate 4; finally, the latter was reacted
with the isocyanate 5, affording the final compound L1.
The coupling step was studied in some detail, employing
different coupling reagents, and the most significant results are
reported in Table 1. Initial attempts to achieve coupling
between the N-Cbz glycine 1, as the corresponding succini-
mide derivative,23 and the tetraamine 2 gave the bis-acylated
product 3 in moderate yields (40%, entry 1, Table 1).
The use of other coupling agents, such as the DCCI,24 the
EDCI/HOBT25 or the 2-(1H-benzotriazole-1-yl)-1,1,3,3-tetra-
methyluronium hexafluorophosphate/1-hydroxybenzotriazole
(HBTU/HOBT)26 systems were ineffective, whilst N,N0-carbo-
nyl-diimidazole (CDI)27 gave mainly the monoacylated pro-
duct together with compound 3 and the starting material in a
ratio of 20/60/20 as determined by liquid chromatogra-
phic–mass spectroscopy (LC-MS) on the crude reaction mix-
ture. A mixture of monoacetylated and the bis-acetylated
product 3 (25/65 ratio) was obtained using of 2,4,6-trichloro-
triazine (TCT),28 whereas a complete conversion of 1 into 3
was achieved in the presence of 2-(7-aza-1H-benzotriazole-1-
yl)-1,1,3,3-tetramethyluronium
hexafluorophosphate
(HATU),29 although the isolation of the product required a
long and tedious careful purification by column chromatogra-
phy. Finally, a high yield (89%) and clean reaction occurred
when the N-Cbz glycine 1 was activated as the pentafuoro-
phenyl ester.30 Among the coupling agents used, the
Recently, we reported on new cation receptors (L3 in Chart
+
1) able to selectively bind NH4 and primary ammonium
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Scheme 1 Synthesis of L1 and L2.
pentafluorophenyl trifluoroacetate turned out to be the best The linear ligand L2 was prepared according to the
for use as one-pot ‘‘by-product-free’’ activation/coupling
agent. Indeed, it allowed convenient high yield and easy
purification of L1 sample.
Scheme 1 by using the same synthetic route of L1 but
substituting the macrocyclic Me2[12]aneN4 with the N,N-
diethylamine.
Thus, treatment of 1 with pentafluorophenyl trifluoroace-
tate/Py in DMF gave, in almost quantitative yield, the corres-
ponding activated ester, which was immediately reacted with 2
in dry DMF, in the presence of i-Pr2EtN at room temperature
overnight. A single crystallisation of the crude reaction mix-
ture gave the bis-acylated product 3 in 77% yield, which was
used without any further purification. Additional product
(12%) was isolated from the residue by column chromatogra-
phy. Subsequent removal of the benzyloxycarbonyl protecting
group by catalytic hydrogenolysis was achieved in EtOH using
a pressure of 4 atm, in the presence of 10% Pd/C cat. The free
diamine was treated with two equivalents of p-nitrophenyl-
isocyanate 5 in dry THF to give the desired bis-urea L1 in
61% yield.
Interestingly, while compound L2 was soluble in common
organic solvents, compound L1, which appears to be particu-
larly prone to self-association through intra- and/or intermo-
lecular hydrogen bonding interactions with the urea groups,
exhibits poor solubility in organic solvents other than DMSO.
Description of the L2ꢁH2O structure
The asymmetric unit of L2ꢁH2O contains one molecule of L2
and one water molecule. As expected on the basis of its
functional groups, L2 shows an extended conjugation in that
the whole molecule appears quite planar, with the obvious
exception of the terminal methyl groups which are in the same
hemisphere with respect to the mean plane containing L2 (see
Fig. 1) [the maximum deviation from the mean plane defined
by the backbone atoms is 0.126(2) A for N(3)]. All the
Table 1 Coupling reagents for the activation of the carboxylic group
function of 1 to give 3
N
amide–Csp2 bond distances are affected by the usual nitrogen
lone pair delocalization (see Table 2), which causes the urea
moiety to be almost coplanar with the aromatic ring and then
with the NO2 group: the angle formed by the mean plane
containing the urea–aromatic ring (P1) and the atoms of the
NO2 is 11.41.
In addition, the mean plane (P2) defined by the atoms C(2),
C(4), N(1), C(5), O(1), C(6) also lies on the mean plane defined
by P1, notwithstanding the single-bond character of
C(5)–C(6); the small value of the angle between P1 and P2
(6.73(5)1) may be due to the short hydrogen bond contact
Entry
Coupling reagent
Yield (%) 3
1
2
3
4
5
6
7
8
9
N-Hydroxysuccinimide/DCCI
DCCI
EDCI/HOBT
HBTU/HOBT
CDI
TCT
HATU
EEDQ
CF3COOC6F5/Py
40
o5
15
o5
60
65
92
62
89
ꢂc
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Fig. 1 ORTEP 3 view of L2ꢁH2O species. Ellipsoids are drawn at 30% probability.
involving the O(1) atom and the amidic hydrogen atom H(2n) Solution studies
(see Table 3). The O(1), C(5), C(6), N(2) and H(2n) atoms, as a
consequence, are well within a plane, the maximum deviation
from the mean plane being 0.03(2) A [H(2n)].
The anion coordination properties of both ligands L1 and L2
were tested in relation to the series of halides as well as the
acetate anions (G); the main aim was not only to test the
intrinsic binding properties of both ligands but also to deter-
mine whether the side-arms in L1 were able to cooperate in
binding anions. The binding experiments were carried out via
1H NMR and UV-Vis titrations.
Due to the planar disposition of L2, a network of weak
intramolecular hydrogen bonds is present.31
The co-crystallized water molecule links together three
symmetry-related L2 molecules: the oxygen atom O(1w) acts
as a donor atom towards the hydrogen atoms H(2n) and H(3n)
bonded to N(2) and N(3) of the same L2 molecule (see Fig. 1),
while at the same time the hydrogen atoms of the water
molecule interact with the oxygen atoms O(1) and O(2) of
two different L2 molecules (see Table 3).
The interaction between ligands L (L = L1 or L2) and the
anions G (G = Fꢀ, Clꢀ, Brꢀ, Iꢀ and AcOꢀ) was investigated
in DMSO–0.5% water solution at 298 K. In the 1H NMR
experiments, the addition of G to L produced a significant 1H
NMR shift of some resonances of both L1 and L2 systems for
G = Fꢀ, Clꢀ and AcOꢀ while the spectra remain substantially
unchanged following the addition of G = Brꢀ and Iꢀ (see
Fig. 3). This aspect indicates that both ligands, under these
experimental conditions, are able to interact with the anions
Fꢀ, Clꢀ and AcOꢀ while Brꢀ and Iꢀ do not interact with these
receptors. Moreover, Fig. 3 also reports the spectrum obtained
by adding NMe4OH as a base which clearly highlights the
deprotonation of the urea groups and the complete disappear-
ance of the ureido proton H5 and the large broadening of H7;
this, together with the shift of the phenyl protons can be
explained by a deprotonation process mainly involving the
nitrogen atoms closer to the p-nitrophenyl group.
Finally, the urea moiety and the aromatic ring of two
symmetry-related L2 molecules (the symmetry operation is
1 ꢀ x, ꢀ2 ꢀ y, 2 ꢀ z) overlap, giving rise to a dimer (the
distance between the mean planes containing the urea-aro-
matic ring moiety of each molecule is 3.4048(5) A) (see
Fig. 2),32 these dimers are connected by means of a network
of weak hydrogen bonds of C–Hꢁ ꢁ ꢁO type whose lengths fall
in the 2.50(2)–2.93(2) A range with angles ranging from 101(2)
to 148(2)1.
Table 2 Bond distances (A) and angles (1) for L2ꢁH2O
O(1)–C(5)
O(2)–C(7)
O(3)–N(4)
O(4)–N(4)
N(1)–C(2)
N(1)–C(4)
N(1)–C(5)
N(2)–C(6)
N(2)–C(7)
N(3)–C(7)
N(3)–C(8)
N(4)–C(11)
C(1)–C(2)
C(3)–C(4)
C(5)–C(6)
C(8)–C(9)
C(8)–C(13)
C(9)–C(10)
C(10)–C(11)
C(11)–C(12)
C(12)–C(13)
1.237(3)
1.231(3)
1.230(2)
1.230(2)
1.462(3)
1.471(3)
1.337(3)
1.438(3)
1.344(3)
1.375(3)
1.384(3)
1.462(3)
1.519(4)
1.523(4)
1.522(3)
1.401(3)
1.398(3)
1.376(4)
1.369(3)
1.384(3)
1.366(3)
C(2)–N(1)–C(4)
C(2)–N(1)–C(5)
C(4)–N(1)–C(5)
C(6)–N(2)–C(7)
C(7)–N(3)–C(8)
O(3)–N(4)–O(4)
O(3)–N(4)–C(11)
O(4)–N(4)–C(11)
N(1)–C(2)–C(1)
N(1)–C(4)–C(3)
O(1)–C(5)–N(1)
O(1)–C(5)–C(6)
N(1)–C(5)–C(6)
N(2)–C(6)–C(5)
O(2)–C(7)–N(2)
O(2)–C(7)–N(3)
N(2)–C(7)–N(3)
N(3)–C(8)–C(9)
N(3)–C(8)–C(13)
C(9)–C(8)–C(13)
C(8)–C(9)–C(10)
C(9)–C(10)–C(11)
N(4)–C(11)–C(10)
N(4)–C(11)–C(12)
C(10)–C(11)–C(12)
C(11)–C(12)–C(13)
C(8)–C(13)–C(12)
117.7(2)
124.0(2)
118.3(2)
121.4(2)
128.2(2)
122.7(2)
118.9(2)
118.5(2)
112.7(2)
112.9(2)
122.7(2)
119.0(2)
118.3(2)
108.0(2)
122.3(2)
123.4(2)
114.3(2)
123.9(2)
117.9(2)
118.2(2)
119.8(2)
120.3(2)
119.3(2)
119.4(3)
121.3(3)
118.5(3)
121.8(3)
Analysis of the 1H NMR spectra of both L1 and L2 systems
revealed that the resonances perturbed by the presence of the
interacting anions are the same in both ligands and namely
those of the phenyl, the urea and the CH2, in a-position to the
latter (see Fig. 3), while the macrocyclic portion of L1 remains
unchanged when guests are added. These data, as predicted,
indicate that only the ureido backbone is involved in the
interaction with the anions in both ligands, producing an
NMR shift also in the nearest groups.
Table 3 Intra- and Intermolecular hydrogen bonds
X–Hꢁ ꢁ ꢁY
N(2)–H(2n)ꢁ ꢁ ꢁO(1)
Hꢁ ꢁ ꢁY distance (A)
2.18(3)
X–Hꢁ ꢁ ꢁY angle (1)
108(2)
N(2)–H(2n)ꢁ ꢁ ꢁO(1w)
N(3)–H(3n)ꢁ ꢁ ꢁO(1w)
O(1w)–H(1wa)ꢁ ꢁ ꢁO(1)a
O(1w)–H(1wb)ꢁ ꢁ ꢁO(2)b
2.29(3)
1.98(2)
2.07(3)
1.91(4)
146(2)
167(2)
160(3)
158(3)
a
b
= 2 ꢀ x, ꢀ1 ꢀ y, 2 ꢀ z. = 1 + x, y, z.
ꢂc
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Fig. 2 ORTEP 3 view of L2 dimer. Ellipsoids are drawn at 30%
probability.
As shown in Fig. 3 and 4, the resonances shifting downfield
in the presence of all interacting G are those of the ureido unit
H5 and H7 as well as those of the H3 phenyl ring nearest to the
urea group; on the contrary, those of CH2 (H8) and those of
the H2 phenyl ring undergo an upfield shift.
The addition of fluoride to L1 leads (Fig. 3) to a shifting and
broadening of both signals of the urea group which completely
disappear at low Fꢀ to L molar ratio; similar spectra were also
obtained with L2. In particular, the resonances of the amide
NH protons in the Fꢀ/L systems broadened to the point of
being unrecognizable after 0.5 equiv. of Fꢀ. These effects are
not uncommon during titration with fluoride salts, as it was
discovered33 that fluoride is sufficiently basic to deprotonate
these protons. This observation was supported by the fact that
after the addition ca. 2.5 equiv. of Fꢀ, the peak attributed to
[FHF]ꢀ began to appear at B16.0 ppm34 and sharpened to a
perfect triplet at 16.2 ppm after the addition of 4.0 equiv. of
Fꢀ. Consequently, we were unable to accurately determine
binding constants via monitoring of these changes in the
1H NMR spectra.
For the Clꢀ and AcOꢀ anions, no deprotonation process
was observed even when large amounts of G were added; in
these cases all data are in agreement with NHꢁ ꢁ ꢁG hydrogen
bonding interactions and indicate a fast equilibrium process
involving the free and complexed forms of the ligands.
1H-NMR titrations, adding different amounts of G (G =
AcOꢀ, Clꢀ or Fꢀ) to a solution of L (L = L1 or L2), were
carried out to quantify the interaction as addition constant of
G to L1 or L2; the data obtained were analyzed using the
Fig. 3 1H NMR spectra of L1 in DMSO–0.5% water solution at
298 K by adding 3 equivalents of guest with respect to L1, with the
exception of Fꢀ where only 0.3 eq. were added.
HypNMR computer program35 and the equilibrium constants
(log K) obtained are reported in Table 4. Unfortunately, the
disappearance of the NH signals H5 and H7 observed during
the titration of both ligands L1 and L2 with Fꢀ, also at low G
to L molar ratio, prevented quantification of the process
occurring in this case (see below).
For example, the titration spectra obtained with the system
AcOꢀ/L2 are reported in Fig. 4. The Job plot (inset to Fig. 4)
of the shift of H5 vs. the equivalents of acetate added shows, in
agreement with the fitting of the data, the formation of only
one AcOꢀ–L2 complexed species with 1 : 1 stoichiometry;
similar spectral features were obtained for the addition of Clꢀ
to L2. Furthermore, in addition to the 1 : 1 also a 2 : 1 molar
ratio for G/L1 systems was found (see Table 4).
Fig. 4 1H NMR titration of the L2–AcOꢀ system in DMSO–0.5% water solution at 298 K obtained by adding several amounts of Bu4NAcO to
L2 solution; Inset: variation of the resonance H5 as a function of AcOꢀ added.
ꢂc
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Table 4 Logarithms of the addition constants of the G guests (G = Clꢀ and AcOꢀ) to L (L = L1 and L2), determined by NMR and UV-Vis
titration in DMSO–0.5% water solution at 298 K
log K
Clꢀ
AcOꢀ
Reaction
L1
L2
L1
L2
L + G = LG
LG + G = LG2
1.5(1)ac–1.6(1)bc
1.4(1)ac–1.5(1)bc
—
5.6(1)ac–5.3(2)bc
2.9(1)a–3.2(2)b
2.9(1)ac–2.8(1)bc
—
o1ab
Values obtained by NMR. UV-Vis experiments. Values in parentheses are the standard deviation to the last significant figure.
a
b
c
Similar titration experiments were carried out using UV-Vis
absorption experiments; two examples are shown in Fig. 5 and
6, which reports the UV-Vis spectra in the range where the p-
nitrophenyl chromophore absorbs, obtained by adding increas-
ing amounts of solution containing G = Fꢀ or AcOꢀ to L2,
respectively; the spectrum obtained by adding an excess of
NMe4OH to L2 solution is also reported in Fig. 5. As shown in
Fig. 5, the spectral profile of free L2 is completely different
from that obtained by adding NMe4OH; this, as reported
above for the NMR spectra, is due to the deprotonation of
the ureido group which, occurring to the closer nitrogen atom,
affects the absorption properties of the chromophore. The free
L2 shows a spectrum with a main band with lmax at 352 nm (e
= 13 400 cmꢀ1 molꢀ1 dm3), while the spectrum obtained by
adding NMe4OH shows a main band with lmax at 482 nm (e =
36 000); the bands can be attributed to the neutral and depro-
tonated forms of the p-nitrophenylurea group, respectively.
When increasing amounts of Fꢀ to L2 were added, some
spectral changes were observed and the titration should be
divided in two steps: the first one due to the addition of Fꢀ up
to 2 equivalents and the second one due to the addition of a
larger amount of Fꢀ with respect to L2 (more than 5 equiva-
lents). In fact, while the UV/Vis spectra of Fig. 5 show that the
band recorded in the presence of 5 equivalents of Bu4NF is
similar to that of the deprotonated one, it is also possible to
observe that, during the titration (up two 2 eq.), there is the
formation of new band centred around lmax = 482 nm but
with a lower absorbance with respect to the deprotonated one
and a shift of the main band towards lower energy (lmax = 363
nm) with a decrease in absorptivity (see Fig. 5). This profile is
similar to that obtained at the end of the titration with acetate
(see Fig. 6). Similar spectral profiles to that observed after
adding up to 2 equivalents of Fꢀ to L2 are also observable
with L1; in addition, this profile also occurs with the other G/L
systems in which, as already reported for the NMR experi-
ments, no deprotonation process (i.e. formation of the depro-
tonated band) was observed in the presence of a large amount
of guest (see also Fig. 6). Furthermore, it must be taken into
account that the increase in the band centered at lmax = 482
nm, as depicted in inset of Fig. 5, is not linear. This behaviour
cannot be attributed merely to a deprotonation process driven
by the basicity of the fluoride anion but rather could be better
explained by two processes occurring simultaneously in the
Fꢀ/L systems: (i) a true H-bond interaction between the ligand
and the fluoride anion, (ii) the deprotonation of the ureido
1
group. Evidence for the same interaction is lost using the H
NMR technique probably because of the different NMR time
scale with respect to UV/Vis spectroscopy.
In other words, as already reported for similar interaction
studies, both L1 and L2 show two processes in the presence of
Fig. 5 UV-Vis spectra of L2 in DMSO–0.5% water solution at 298 K [L2] = 3.0 ꢃ 10ꢀ5 M and those obtained by adding several amounts of Fꢀ
up to 2 equivalent with respect to [L2] (inset) and 5 equivalent or an excess of NMe4OH. Inset: variation of the absorbance at 482 nm as a function
of Fꢀ added.
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action related to the different form of the two anions,
V-shaped vs. spherical for acetate and chloride, respectively,
that permits both acetate oxygen atoms to form H-bonds with
both ureido protons.36
The second point, which is the key for our aims, can be
attributed to the different way of stabilization of the two
guests by the two ligands; while the chloride anion, showing
similar constant values with both hosts, is stabilized by the
urea fragment of a side-arm of L1 in a similar coordination
environment as in L2, this cannot be affirmed for acetate. The
higher constant values found for the formation of [AcOL1]ꢀ
with respect to the [AcOL2]ꢀ species suggests a different
interaction environment. In particular, we can suppose that
both side-arms of L1 with both ureido groups are involved in
stabilizing AcOꢀ via H-bonding. This occurs when the two
side-arms are face-to-face, occupying the same region with
respect to the macrocycle plane and leading to the cooperation
of both urea groups to stabilize, via H-bond, the V-shaped
acetate but not the small spherical chloride guest. This can be
attributed to the way of linking the side-arms to the
Me2[12]aneN4 scaffold; in detail, as previously demon-
strated,21 the two N–CQO groups which link each side-arm
to the twelve membered ring play a fundamental role in
stiffening and preorganizing the host. These two amide moi-
eties force the two side arms to occupy the same region with
respect to the macrocycle and yield L1, a preorganized host for
acetate. This hypothesis is supported by the value of the
addition constant of AcOꢀ to L1, which is higher (about 2–3
logarithmic units) than those reported for hosts containing
only a ureido group as binding unit.36a
Fig. 6 UV-Vis spectra of L2 in DMSO–0.5% water solution at 298 K
[L2] = 3.0 ꢃ 10ꢀ5 M and those obtained by adding several amounts of
AcOꢀ up to 5 equivalent with respect to [L2].
the Fꢀ guest; one due to the association between Fꢀ and L
occurring via H-bonding along with a deprotonation process
both involving the urea group of L systems. On the contrary,
only the association behavior is detected in the presence of Clꢀ
and AcOꢀ, as depicted in Fig. 6; moreover, the addition of Brꢀ
and Iꢀ even in a large excess did not perturb the spectral
profile of the free ligands, once again highlighting the absence
of interaction with these two guests.
The interaction as addition constant of G to L1 or L2
evaluated by elaborating the UV-Vis titration data of both
ligands is also reported in Table 4. Unfortunately, even when
using this method, it was impossible to measure both the
deprotonation constants as well as the addition constants
induced by the addition of Fꢀ to both L systems with a
reliable precision.
At this time, despite repeated attempts, we have not been
able to obtain crystals of the L1 species suitable for X-ray
analysis, but the crystal structure of Fig. 1, in which an oxygen
atom of a water molecule is bound via H-bonding by both
ureido protons of L2, suggests a possible pathway for the
disposition of acetate in the [AcOL1]ꢀ complex. In fact,
considering the V-shape of acetate, we can suppose that each
oxygen atom of acetate interacts with a urea fragment of one
side-arm in similar way of Fig. 1, thus acetate can interact
simultaneously with both side-arms and this V-shaped guest is
located in a bridge disposition between them. A proposal for
the interaction between AcOꢀ and L1 and L2 in the [AcOL]ꢀ
species is shown in Fig. 7.
On the other hand, the values of the addition constants
reported in Table 4 for the interaction of L1 and L2 with the
guests AcOꢀ and Clꢀ are calculated by two different methods
and they are in agreement, thus supporting the values and the
speciation reported. A key aspect concerns the values as well
as the speciation found with the macrocyclic ligand L1 with
respect to L2. In fact, while L2 forms only [GL] complexes
having a 1 : 1 stoichiometry with both guests Clꢀ and AcOꢀ,
L1 is able to form the [G2L1] as well as the [GL1] species. In
other words, L1 is also able to bind two equivalents of guests
under these experimental conditions, even though the constant
value for the formation of the dichloride [Cl2L1]2ꢀ species is
too low to be calculated with certainty.
Comparison of the values of the constants leads us to specific
considerations: (i) acetate is better bound by both systems than
is chloride; (ii) the formation of the [GL] species is similar for
chloride in both L systems (log K is about 1,5 in both cases)
while it is very different for acetate (log K = 5.6 and 2.9 for L1
and L2, respectively); (iii) the constant value for the addition of
the second acetate to [AcOL1]ꢀ species is lower with respect to
the first one and it is similar to the that of AcOꢀ to L2.
The first situation is usually observed in hosts having urea as
interacting function; this is due to the different H-bond inter-
Fig.
7
Proposed interaction models between AcOꢀ and
L in
[AcOL1]ꢀ and [AcOL2]ꢀ complexes.
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At last, the lower value for the addition of the second
acetate underlines that its binding is not preferred in the same
way as the first one. This can be attributed to the fact that both
urea groups are involved in the stabilization of the first AcOꢀ,
hindering the binding of the second acetate, once again
indicating the cooperation of both side-arms in binding the
first AcOꢀ.
as the chloride cannot be simultaneously bonded and thus the
side-arms of L1 act separately in binding them.
In conclusion, as already demonstrated in an analogous way
for the attaching of side-arms, the tetraaza-macrocyclic base
acts as a scaffold to preorganize them when the side-arms are
linked via amide function. This allows the presence of an area
richer in H-bond sites in L1 than that given by only one urea
moiety as in L2. Guests having the ability to form several
H-bonds in this area, such as the acetate, can be strongly
stabilized.
It is difficult to suggest a coordination environment for the
two guests in the [(AcO)2L1]2ꢀ species, although the value
similar to that of L2 found for the addition of the second
acetate suggests a similar interaction pathway between acetate
and side-arm. In this case, each side-arm of L1 should be
involved in the stabilization of only one AcOꢀ guest, however
other interaction pathways could be suggested.
The promising results obtained with L1 as host for acetate
make it an attractive host for molecular recognition studies of
guests showing carboxylic functions as well as separated
H-bonding sites acceptor.
Conclusions
Experimental
The synthesis of the two new hosts for anions L1 and L2 is
reported. L1 is a branched macrocyclic ligand containing two
equal side-arms attached on a tetraaza macrocyclic scaffold;
each side-arm includes the p-nitrophenylureido moieties as
interacting group. L2 shows the same chain and binding
moiety of the side-arm of L1 and it was synthesized for
comparison with L1. Different synthetic routes were explored
to afford the best yield; L1 was synthesized from the inter-
mediate compound 4 that can be considered as a versatile
building block to obtain further functionalized branched
macrocyclic hosts.
General methods
IR spectra were recorded on a Shimadzu FTIR-8300 spectro-
meter. Melting points were determined on a Buchi melting
point B 540 apparatus and are uncorrected. EI-MS spectra (70
eV) were recorded with a Fisons Trio 1000 spectrometer. The
HPLC system (Waters Alliance 2795) was coupled with a
photodiode array detector (Waters 2996 PDA), followed by
an electrospray mass spectrometer detector (ESI-MS)
(Waters-Micromass ZQ) worked by Mass Lynx 4.1 SP4 soft-
ware. The ESI-MS analyses were performed in a positive mode
under the following conditions: source and desolvation tem-
perature 100 and 250 1C; capillary and cone voltage 2.5 kV
and 25 V; cone and desolvation flow (nitrogen gas) 40 and
400 L/h. HPLC analyses were performed on a 25 cm ꢃ 4.6 mm
Discovery C-18, 5 cm column (Supelco, Bellefonte, PA)
equipped with a Supelguard Discovery C-18 guard column
(2 cm ꢃ 4 mm, 5 cm). Solvents A (MeOH) and C (5 nM
ammonium acetate) were run at a flow rate of 1 mL/min. The
running gradient was adjusted to 10% A (2 min), increasing to
90% A (18 min), and then 100% C (2 min), followed by a re-
equilibration at 10% A (15 min). All solvents were HPLC-
grade (Aldrich-Sigma) and water was purified via a Millex
Q-plus system (Millipore).
The hosting properties of both ligands, tested with the
halide series and with the acetate anions by NMR and UV-
Vis spectroscopy, allow them to interact with the same anion
guests investigated in dimethyl sulfoxide–0.5% water solution.
In particular, under our experimental conditions both hosts
bind the Fꢀ, Clꢀ and AcOꢀ guests while Brꢀ and Iꢀ did not.
The NMR experiments proved that the binding occurs via
H-bond at the ureido fragments. The fluoride anion also
showed enough basicity to deprotonate the ureido group of
both ligands, preventing the determination of the addition
constants for this guest which were possible for Clꢀ and AcOꢀ.
Both spectroscopic methods gave rise to similar results for the
complexed species formed a well as for the value of the
addition constants reported as log K.
All chemicals were purchased from Aldrich, Fluka and
Lancaster in the highest quality commercially available. All
the solvents were dried prior to use. Chromatographic separa-
tions were performed on silica gel columns by flash chromato-
graphy (Kieselgel 60, 0.040–0.063 mm, Merck). TLC analyses
were performed on precoated silica gel on aluminium sheets
(Kieselgel 60 F254, Merck). The 1,7-dimethyl-1,4,7,10-tetra-
zacyclododecane 2 was prepared as previously described.22
L1 forms G-L species of 1 : 1 ([GL1]) and 2 : 1 ([G2L1])
stoichiometry while L2 forms only the 1 : 1 [GL2] species. The
high values of the constant for the formation of the [AcOL1]ꢀ
species suggested that both side-arms cooperate in binding this
guest, while this probably does not occur with the spherical
Clꢀ. This aspect can be attributed to both the preorganization
of the side-arms and the V-shape of acetate. The first char-
acteristic is due to the way of attaching side-arms to the
tetraaza-macrocyclic base, in that the amide groups stiffened
the molecular skeleton and forced the two side-arms to stay in
the same part of the macrocycle ring. In this way, the whole
molecule appears to be preorganized for interaction with other
species having the capacity to form simultaneously H-bonding
with both ureido groups such as the V-shape of the acetate
anion, which should be located in a bridge disposition between
the two ureido fragments. The crystal structure reported
supports this hypothesis. On the contrary, small guests such
Synthesis
4(N),10(N)-Bis-[N-(benzyloxycarbonyl)glycyl]-1,7dimethyl-
1,4,7,10-tetraazacyclododecane (3). Pyridine (8.5 mmol, 0.7
mL) and pentafluorophenyl 2,2,2-trifluoroacetate (1.66 mL,
10 mmol) were added to a solution of N-(benzyloxycarbonyl)-
glycine 1 (1.61 g, 7.70 mmol) in DMF (5 mL). The reaction
mixture was stirred for 1 hour at room temperature, diluted
with AcOEt (300 mL) and washed with 0.1 N aqueous HCl
(3 ꢃ 50 mL), 5% aqueous NaHCO3 (3 ꢃ 50 mL) and brine
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(50 mL). The organic solution was dried over Na2SO4 and
concentrated under reduced pressure to give 2.8 g (98%) of the
desiderate pentafluorophenyl ester.
Rotamer mixture: mp = 246–248 1C; FTIR (film) 3390,
2924, 1680, 1648, 1559, 1325, 1269, 1174, 1110 cmꢀ1; 1H NMR
(DMSO) d 2.25–2.36 (6H, m), 2.55–2.68 (8H, m), 3.28–3.46
(8H, m), 4.02–4.07 (4H, m), 6.52–6.62 (2H, m), 7.50–7.60 (4H,
m), 8.00–8.15 (4H, m), 9.60–9.70 (2H, m); 13C NMR (DMSO)
d 41.3, 41.6, 46.6, 55.6, 116.6, 125.1, 140.3, 147.0, 154.2, 168.8
ppm; MS (+ESI) 643.3 (MH+); Anal. for C28H38N10O8
(642.67): Calcd C 52.33, H 5.96, N 21.79; Found C 52.2, H
6.1, N 21.7.
A solution of the above pentafluorophenyl ester 4 in dry
DMF (5 mL) was slowly added dropwise over 30 min at 0 1C
to a stirred solution of 1,7-dimethyl-1,4,7,10-tetraazacyclodo-
decane 2 (0.77 g, 3.86 mmol) and i-Pr2EtN (2.69 mL, 0.0155
mol) in dry DMF (2 mL). The reaction mixture was stirred for
12 hours at room temperature. The organic yellow solution
was concentrated under reduced pressure and the yellow oily
residue was diluted in CHCl3 and precipitated by the addition
of Et2O to give 5 (2.03 g, 77%) as a colorless solid. The organic
solution was concentrated under reduced pressure and the
residue was purified by silica gel chromatography (CH2Cl2
saturated with NH3/methanol 99 : 1) to give additional 3
(0.3 g, 12%; 89% overall yield); mp 105–106 1C (decomp.).
The latter dissolved in DMF (5 mL) was slowly added
dropwise to a solution of tetramine (3.2 mmol, 640 mg) and
DIPEA (2.7 mL) in DMF (2 mL). The mixture was stirred at
room temperature for 36 hours, after which the solvent was
removed under vacuum and the residue purified by flash
chromatography on alumina using a mixture of methylene
chloride/methanol 95 : 5 as eluent to give 1.35 g (65% yield) of
the desired product as a white solid.
N-(Benzyloxycarbonyl)glycine-N,N-diethylamide (6)
Pyridine (0.7 mL, 8.5 mmol) and perfluorophenyl 2,2,2-tri-
fluoroacetate (10 mmol, 1.66 mL) were added to a solution of
N-(benzyloxycarbonyl)glycine 1 (1.61 g, 7.70 mmol) in DMF
(5 mL).
The mixture was stirred at room temperature for 1 hour,
diluted with EtOAc (300 mL) and washed with an aqueous
solution of HCl 0,1 N (2 ꢃ 50 mL), NaHCO3 5% (2 ꢃ 50 mL)
and brine (1 ꢃ 50 mL). The organic mixture was dried over
Na2SO4 and evaporated under vacuum to give 2.8 g (98%) of
the pentafluorophenyl ester.
A solution of the above pentafluorophenyl ester in dry
DMF (5 mL) was added dropwise over 30 min at 0 1C to a
stirred solution of N,N-diethylamine (0.8 mL, 7.7 mmol) and
DIPEA (2.7 mL, 15.5 mmol) in DMF (2 mL). The mixture was
stirred at room temperature for 36 hours, and the solvent was
removed under vacuum and the residue purified by flash
chromatography on silica using cyclohexane/ethyl acetate
40–60 as eluent to furnish 1.41 g (69% yield) of 6 as a
sticky oil.
Rotamer mixture: mp = 171–173 1C FTIR (KBr) 3268,
3066, 2986, 2940, 1726, 1642, 1550, 1454, 1255, 1167, 1049,
1
1006, 743, 653 cmꢀ1; H NMR (CDCl3) d 2.24–2.38 (6H, m),
2.63–2.71 (8H, m), 3.28–3.46 (8H, m), 4.05–4.07 (4H, m),
5.10–5.11 (4H, m), 5.82–5.89 (2H, m), 7.30–7.40 (10H, m);
13C NMR (CDCl3) d 42.8, 43.1, 46.6, 55.0, 65.9, 127.2, 129.0,
141.2, 156.3, 164.3 ppm; MS (+ESI) 583.7 (M + 1); Anal. for
C30H42N6O6 (582.70): Calcd C 61.84, H 7.27, N 14.42; Found
C 62.0, H 7.2, N 14.3.
Rotamer mixture: FTIR (film) 3268, 3066, 2986, 2940, 1726,
1
1642, 1550, 1454, 1255, 1167, 1049, 1006, 743, 653 cmꢀ1; H
NMR (CDCl3) d 1.13 (t, J = 7.2 Hz), 1.19 (t, J=7.2 Hz), 3.26
(q, J = 7.2 Hz), 3.40 (q, J = 7.2 Hz), 4.02 (d, J = 4.2 Hz), 5.13
(s), 5.85 (br s, NH), 7.30–7.37 (m, PhH); 13C NMR (CDCl3) d
12.7, 13.7, 40.2, 40.7, 42.3, 66.5, 127.7, 127.8, 128.2, 136.4,
156.0, 166.7; MS (+ESI) 265.1 (MH+, 100); Anal. for
C14H20N2O3 (264.32): Calcd C 63.62, H 7.63, N 10.60; Found
C 63.6, H 7.6, N 10.5.
4(N),10(N)-Bis-glycyl-1,7-dimethyl-1,4,7,10-tetraazacyclo-
dodecane (4). 10% Pd/C (400 mg) was added to a solution of
bis-carbamate 3 (1.35 g, 2.3 mmol) in EtOH abs (20 mL). The
mixture was then hydrogenated at 4 atm in an autoclave for 16
hours at room temperature, then filtered through Celite and
the solvent was removed under vacuum to give 4 (710 mg,
purity = 98% by HPLC) which was used without any further
purification.
2-Amino-N,N-diethylacetamide (7)
Rotamer mixture: 1H NMR (D2O, pH = 3) 2.41–2.79 (10H,
m,), 2.95–3.15 (4H, m), 3.65–3.45 (8H, m), 3.75–3.70 (4H, m);
13C NMR (D2O, pH = 3), 40.8, 41.4, 41.8, 45.1, 46.1, 46.2,
46.4, 57.7, 58.2, 58.5, 59.4 ppm; MS (+ESI) 315, 2 (MH+);
Anal. for C14H30N6O2 (314.43): Calcd C 53.48, H 9.62, N
26.73; Found C 53.6, H 9.5, N 26.9.
10% Pd/C (180 mg) was carefully added to a solution of
N-(benzyloxycarbonyl)glycine-N,N-diethylamide 6 (1.41 g,
5.3 mmol) in EtOH (20 mL). The mixture was then hydro-
genated at 4 atm in autoclave for 16 hours at room tempera-
ture. The reaction mixture was then filtered through Celite and
the solvent was removed by rotary evaporation to give 530 mg
of clean product with 85% yield. The product was immediately
used in the next step.
4(N),10(N)-Bis-[2-(4-nitrophenylureido)acetamido]-1,7-di-
methyl-1,4,7,10-tetraazacyclododecane (L1). p-Nitrophenyliso-
cyanate 5 (3.17 mmol, 530 mg) was added to a solution of
diamine 4 (500 mg, 1.58 mmol) in dry THF (6 mL). The
mixture was stirred at room temperature for 16 hours. The
solvent was removed under vacuum and the residue was
treated with diethyl ether to remove any apolar substances.
The solid thus obtained was purified on alumina using
CH2Cl2/MeOH (92 : 8) as eluent to give L1 as pale yellow
solid in 48% yield (480 mg).
FTIR (film): 3395, 2932, 1632, 1567, 1325, 1269, 1172, 1110
1
cmꢀ1; H NMR (DMSO) d 1.02 (3H, m), 3.20 (2H, m), 3.42
(2H, m); 13C NMR (DMSO) d 13.0, 14.0, 39.7, 40.2, 41.0,
163.8; MS (+ESI) 131.0 (MH+) 153 (MNa+).
1-((Diethylcarbamoyl)methyl)-3-(4-nitrophenyl)urea (L2)
p-Nitrophenylisocyanate 5 (1 mmol, 177 mg) was added to a
solution of 2-amino-N,N-dietilacetamide (130 mg, 1 mmol) in
THF (3 mL). The mixture was stirred at room temperature for
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16 hours. The solvent was removed under vacuum and the
residue was treated with ethyl ether to remove any apolar
substances. The solid so obtained was crystallized by ethanol
to obtain L2 as pale yellow solid in 51% yield.
The temperature of the NMR probe was calibrated using 1,2-
ethanediol as calibration sample. For the spectra recorded in
D2O, the peak positions are reported with respect to HOD
1
(4.75 ppm) for H NMR spectra, while dioxane was used as
Rotamer mixture: mp = 168–169 1C FTIR (film): 3389,
2924, 1701, 1628, 1559, 1325, 1269, 1172, 1174, 1110, 751
cmꢀ1; 1H NMR (DMSO) d 1.02 (3H, t, J = 7.2 Hz), 1.12 (3H,
t, J = 7.2 Hz), 3.24 (2H, q, J = 7.2 Hz), 3.32 (2H, q, J = 7.2
Hz), 3.98 (2H, d, J = 4.8 Hz), 6.61 (1H, br s, NH), 7.60 (2H, d,
J = 9.4 Hz), 8.13 (2H, d, J = 9.4 Hz), 9.69 (1H, br s); 13C
NMR (DMSO) d 12.9, 13.8, 39.7, 40.4, 41.0, 116.7, 125.2,
140.5, 147.0, 154.3, 167.3; MS (+ESI) 295.1 (MH+, 100);
Anal. for C13H18N4O4 (294.31): Calcd C 53.05, H 6.16, N
19.04; Found C 53.0, H 6.3, N 19.1.
reference standard in 13C NMR spectra (d = 67.4 ppm). For
the spectra recorded in CDCl3 and DMSO-d6 the peak posi-
1
1
tions are reported with respect to TMS. H–1H and H–13C
correlation experiments were performed to assign the signals.
Chemical shifts (d scale) are reported in parts per million (ppm
values) relative to the characteristic peak of the solvent;
coupling constants (J values) are given in hertz (Hz).
NMR titrations were carried out in a DMSO-d6-0.5% water
mixture; 0.5% of water was added to DMSO to avoid the not
uniform absorption of water from the atmosphere by anhy-
drous DMSO during the titration. In a typical experiment, a 5
ꢃ 10ꢀ2 mol dmꢀ3 DMSO–0.5% water solution of the anion
was added in 0.1 eq at a time to a 1 ꢃ 10ꢀ2 mol dmꢀ3
DMSO–0.5% water solution of the ligand directly in the
NMR tube; the tube was then kept for 5 min at a temperature
of 298 K before starting the acquisition of the spectrum. The
anions tested were added as their tetrabutylammonium salts.
The monitoring of the shift of the signals in the ligand spectra
(see Discussion) permitted evaluation of the association con-
stants ligand-anion using the HYPNMR computer program.35
UV-Vis absorption spectra were recorded at 298 K with a
Varian Cary-100 spectrophotometer equipped with a tempera-
ture control unit. The interaction of anions with ligands L1
and L2 was studied in similar conditions of the NMR titration
experiments using DMSO-0.5% water mixture as solvent;
solution containing the anion G (Fꢀ, Clꢀ, Brꢀ, Iꢀ or AcOꢀ)
up to 5 equivalents with respect to the ligand was added to the
solution containing L ([L1] = 1.5 ꢃ 10.5 M; [L2] = 3.0 ꢃ 10.5
M). At least three sets of spectrophotometric titration curves
for each G/L system were performed. All sets of curves were
treated either as single sets or as separate entities, for each
system; no significant variations were found in the values of
the determined constants. The HYPERQUAD computer pro-
gram was used to process the spectrophotometric data.35b
Crystals suitable for X-ray analysis were obtained by slow
evaporation of a DMSO/H2O solution of L2.
X-Ray crystallography
Intensity data for L2ꢁH2O were collected on an Oxford
Diffraction Xcalibur diffractometer equipped with a CCD
area detector, using Mo-Ka radiation (0.71069 A), monochro-
mated with a graphite prism. Data were collected using the
CrysAlis CCD program37 and the reduction was carried out
with the CrysAlis RED program.38 Absorption correction was
performed with the program ABSPACK in CrysAlis RED.
Structure was solved with the direct methods of the SIR9739
package and refined by full-matrix least squares against F2
with the SHELX97 program.40
Geometrical calculations were performed by PARST9741
and molecular plots were produced by the ORTEP3
program.42
All the non-hydrogen atoms were refined anisotropically
and all the hydrogen atoms were found in the Fourier differ-
ence map and refined isotropically.
Crystallographic data and refinement parameters for L2ꢁ
H2O are reported in Table 5.
UV-Vis and NMR experiments
1H and 13C NMR spectra were recorded on a Bruker Avance
200 instrument, operating at 200.13 and 50.33 MHz, respec-
tively, and equipped with a variable temperature controller.
Acknowledgements
The authors thank the CRIST (Centro Interdipartimentale di
Cristallografia Strutturale, University of Florence) where the
X-ray measurement was carried out.
Table 5 Crystal and structure refinement data for L2ꢁH2O
Chemical formula
C
13H20N4O5
Mr
Crystal system, space group
Cell parameters (A, 1)
312.33
Triclinic, P1
a = 6.793(2), a = 117.05(4)
b = 11.479(5), b = 93.32(3)
c = 12.229(2), g = 105.24(3)
761.5(5)
2
1.362
0.71069
0.106
150
7383/2767 [R(int) = 0.0335]
Full-matrix least-squares on F2
2767/279
R1 = 0.0454, wR2 = 0.0988
R1 = 0.0949, wR2 = 0.1087
ꢀ
References
1. C. H. Park and H. E. Simmons, J. Am. Chem. Soc., 1968, 90, 2431.
2. (a) A. Bianchi, K. Bowman-James and E. Garcia-Espana, Supra-
molecular Chemistry of Anions, Wiley-VCH, New York, 1997;
(b) J.-M. Lehn, Angew. Chem., Int. Ed. Engl., 1988, 27, 89;
(c) F. P. Schmidtchen and M. Berger, Chem. Rev., 1997, 97,
1609; (d) M. M. G. Antonisse and D. N. Reinhoudt, Chem.
Commun., 1998, 443; (e) P. A. Gale, Coord. Chem. Rev., 2000,
199, 181; (f) P. D. Beer and P. A. Gale, Angew. Chem., Int. Ed.,
2001, 40, 486; (g) P. A. Gale, Coord. Chem. Rev., 2003, 240, 191;
(h) J. L. Sessler, P. A. Gale and W. S. Cho, Anion Receptor
Chemistry, Royal Society of Chemistry, Cambridge, UK, 2006.
3. V. Krail and J. L. Sessler, Tetrahedron, 1995, 51, 539–554.
4. (a) M.-P. Teulade Fichou, J.-P. Vigneron and J.-M. Lehn,
J. Chem. Soc., Perkin Trans. 2, 1996, 2169; (b) G. De Santis,
V (A3)
Z
Dc (g cmꢀ3
l (A)
)
m (mmꢀ1
Temperature (K)
)
Reflections collected/unique
Refinement method
Data/parameters
Final R indices [I 4 2s(I)]
R indices (all data)
ꢂc
This journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2008 New J. Chem., 2008, 32, 1204–1214 | 1213

View Online
L. Fabbrizzi, M. Licchelli, A. Poggi and A. Taglietti, Angew.
Chem., Int. Ed. Engl., 1996, 35, 202.
5. (a) E. V. Anslyn, J. Smith, D. M. Kneeland, K. Ariga and
F. Y. Chu, Supramol. Chem., 1993, 1, 201; (b) D. P. Curran and
L. H. Kuo, Tetrahedron Lett., 1995, 36, 6647.
6. (a) C. H. Frey and S. E. M. Langley, in Ion-selective electrodes for
biological systems, Harwood Academic Publisher, 2002;
(b) I. Stibor, Anion Sensing, in Top. Curr. Chem., Springer, Berlin,
2005.
7. (a) E. Di Stasio, Biophys. Chem., 2004, 112, 245;
(b) F. M. Ashcroft, Ion Channels and Disease, Academic Press,
San Diego, CA, 2000.
8. (a) E. Antonini and M. Brunori, in Hemoglobin and Myoglobin in
their Reactions with Ligands, North-Holland Publishing, Amster-
dam, 1971; (b) R. K. Murray, D. K. Granner, P. A. Mayes and
V. W. Rodwell, Harper’s Biochemistry, Prentice-Hall Interna-
tional, NJ, 2000.
9. K. L. Kirk, in Biochemistry of the Halogens and Inorganic Halides,
Plenum, New York, 1991.
10. M. Kleerekoper, Endocrinol. Metab. Clin. North Am., 1998, 27,
441.
11. G. J. Mulder, Sulfate availability in vivo, in Sulfation of Drugs and
Related Compounds, ed. G. J. Mulder, Boca Raton, FL, CRC,
1981, p. 131G. J. Mulder and W. B. Jakoby, Sulfation, in Con-
jugation Reactions in Drug Metabolism: An Integrated Approach:
Substrates, Co-Substrates, Enzymes and Their Interactions In vivo
and In vitro, ed. G. J. Mulder, Taylor and Francis, London, 1990,
p. 161.
12. (a) R. DeMeio, Sulfation activation and transfer, in Metabolic
Pathways, ed. D Greenberg, Academic, New York, 1975, p. 287;
(b) B. Deplancke and H. R. Gaskins, Curr. Opin. Clin. Nutr.
Metab. Care, 2002, 5, 85.
G. Zappia, New J. Chem., 2004, 28, 1359; (c) G. Ambrosi,
A. Boggioni, M. Formica, V. Fusi, L. Giorgi, S. Lucarini,
M. Micheloni, F. Secco, M. Venturini and G. Zappia, Dalton
Trans., 2005, 485; (d) G. Ambrosi, M. Formica, V. Fusi, L. Giorgi,
A. Guerri, S. Lucarini, M. Micheloni, P. Paoli, P. Rossi and
G. Zappia, Inorg. Chem., 2005, 44, 3249.
22. M. Ciampolini, P. Dapporto, M. Micheloni, N. Nardi, P. Paoletti
and F. Zanobini, J. Chem. Soc., Dalton Trans., 1984, 1357.
23. G. W. Anderson, J. E. Zimmerman and F. M. Callahan, J. Am.
Chem. Soc., 1964, 86, 1839.
24. J. C. Sheehan and G. P. Hess, J. Am. Chem. Soc., 1955, 77, 1067.
25. J. C. Sheehan, P. A. Cruickshank and G. L. Boshart, J. Org.
Chem., 1961, 26, 2525.
26. F. Albericio, J. M. Bofill, A. Faham and S. A. Kotes, J. Org.
Chem., 1998, 63, 9678.
27. G. W. Anderson and R. Paul, J. Am. Chem. Soc., 1958, 80, 4423;
S. Kato, T. Morie and N. Yoshida, Chem. Pharm. Bull., 1995, 43,
699.
28. H. L. Rayle and L. Fellmeth, Org. Process Res. Dev., 1999, 3, 172.
29. L. Carpino, J. Am. Chem. Soc., 1993, 115, 4397.
30. M. Green and J. Berman, Tetrahedron Lett., 1990, 31, 5851.
31. (a) The C–Hꢁ ꢁ ꢁO distances are comprised between 2.41(3) and
2.60(3) A, the C–Hꢁ ꢁ ꢁO angles range from 90(2) to 116(2)1;
(b) G. R. Desiraju and T. Steiner, The weak hydrogen bond, IUCr
Monographs on Crystallography, Oxford Science Publications,
1999.
32. (a) A. Uchida, Y. Ohashi, Y. Sasada, Y. Kaneko and T. Endo,
Acta Crystallogr., Sect. C, 1984, 40, 115–117; (b) Y. Ohashi,
A. Uchida, Y. Sasada, K. Kinoshita and T. Endo, Acta Crystal-
logr., Sect. C, 1984, 40, 117–119; (c) A. Uchida, Y. Ohashi,
Y. Sasada, M. Moryta and T. Endo, Acta Crystallogr., Sect. C,
1984, 40, 120–122.
13. (a) A. R. Hirsh, F. R. Fisher and F. Diederich, Angew. Chem., Int.
Ed., 2007, 46, 338; (b) C. Bazzicalupi, A. Bencini, A. Bianchi,
M. Checchi, B. Escuder, V. Fusi, E. Garcia-Espana, C. Giorgi,
S. V. Luis, G. Maccagni, V. Marcelino, P. Paoletti and
B. Valtancoli, J. Am. Chem. Soc., 1999, 121, 6807.
14. (a) M. S. Abeysekara, J. M. Naylor, A. W. A. Wassef, U. Isak and
G. A. Zello, Am. J. Physiol. Endocrinol. Metab., 2007, 293(2), 558;
(b) D. W. Choi and S. M. Rothman, Annu. Rev. Neurosci., 1990,
13, 171; (c) D. W. Choi, Neuron, 1988, 8, 623; (d) M. Maus,
P. Marin, M. Israel, J. Glowinski and J. Premont, Eur. J.
Neurosci., 1999, 9, 3215.
33. (a) T. Gunnlaugsson, H. D. P. Ali, M. Glynn, P. E. Kruger,
G. M. Hussey, F. M. Pfeffer, C. M. G. dos Santos and J. Tierney,
J. Fluoresc., 2005, 15, 287; (b) F. M. Pfeffer, A. M. Buschgens,
N. W. Barnett, T. Gunnlaugsson and P. E. Kruger, Tetrahedron
Lett., 2005, 46, 6579; (c) T. Gunnlaugsson, A. P. Davis,
J. E. O’Brien and M. Glynn, Org. Biomol. Chem., 2005, 3, 48;
(d) T. Gunnlaugsson, P. E. Kruger, P. Jensen, F. M. Pfeffer and
G. M. Hussey, Tetrahedron Lett., 2003, 44, 8909; (e) S. Camiolo,
P. A. Gale, M. B. Hurstouse and M. E. Light, Org. Biomol. Chem.,
2003, 1, 741; (f) D. E. Gomez, L. Fabbrizzi, M. Licchelli and
E. Monzani, Org. Biomol. Chem., 2005, 3, 1495; (g) F. M. Pfeffer,
T. Gunnlaugsson, P. Jensen and P. E. Kruger, Org. Lett., 2005, 7,
5357.
34. I. G. Shenderovich, P. M. Tolstoy, N. S. Golubev, S. N. Smirnov,
G. S. Denisov and H. H. Limbach, J. Am. Chem. Soc., 2003, 125,
11710.
35. (a) C. Frassinetti, S. Gelli, A. Sabatini, M. S. Moruzzi and
A. Vacca, Anal. Biochem., 1995, 231, 375; (b) P. Gans,
A. Sabatini and A. Vacca, Talanta, 1996, 43, 1739.
15. C. Walsh, Nature, 2000, 406, 775.
16. G. Ambrosi, M. Formica, V. Fusi, L. Giorgi, A. Guerri,
M. Micheloni, P. Paoli, R. Pontellini and P. Rossi, Chem. Eur.
J., 2007, 13, 702.
´
17. A. Andres, J. Arago, A. Bencini, A. Bianchi, A. Domenech,
V. Fusi, E. Garcia-Espana, P. Paoletti and J. A. Ramirez, Inorg.
Chem., 1993, 32, 3418.
18. (a) S. O. Kang, M. A. Hossain and K. Bowman-James, Coord.
Chem. Rev., 2006, 250, 3038; (b) K. Bowman-James, Acc. Chem.
Res., 2005, 38, 671.
19. (a) B. P. Hay, T. K. Firman and B. A. Moyer, J. Am. Chem. Soc.,
2005, 127, 1810; (b) S. O. Kang, R. A. Begum and K. Bowman-
James, Angew. Chem., Int. Ed., 2006, 45, 7882.
36. (a) P. A. Gale, Acc. Chem. Res., 2006, 39, 465; (b) A. J. Lowe,
G. A. Dyson and F. M. Pfeffer, Org. Biomol. Chem., 2007, 5, 1343.
37. CrysAlis CCD,Oxford Diffraction Ltd, Version 1.171.pre23_10
beta (release 21.06.2004 CrysAlis171 .NET) (compiled Jun 21
2004,12:00:08).
20. (a) D. Esteban-Gomez, L. Fabbrizzi, M. Licchelli and
E. Monzani, Org. Biomol. Chem., 2005, 3, 1495; (b) A. J. Lowe,
G. A. Dyson and F. M. Pfeffer, Org. Biomol. Chem., 2007, 5, 1343;
38. CrysAlis RED, Oxford Diffraction Ltd., Version 1.171.pre23_10
beta (release 21.06.2004 CrysAlis171 .NET) (compiled Jun 21
2004,12:00:08).
(c) T. Suhs and B. Konig, Chem. Eur. J., 2006, 12, 8150, and
references therein.
39. A. Altomare, G. L. Cascarano, C. Giacovazzo, A. Guagliardi,
A. G. Moliterni, M. C. Burla, G. Polidori, M. Camalli and
R. Spagna, J. Appl. Crystallogr., 1999, 32, 115.
¨
21. (a) M. Formica, V. Fusi, L. Giorgi, A. Guerri, S. Lucarini,
M. Micheloni, P. Paoli, R. Pontellini, P. Rossi, G. Tarzia and
G. Zappia, New J. Chem., 2003, 27, 1575; (b) G. Ambrosi,
P. Dapporto, M. Formica, V. Fusi, L. Giorgi, A. Guerri,
S. Lucarini, M. Micheloni, P. Paoli, R. Pontellini, P. Rossi and
40. G. M. Sheldrick, SHELX 97, University of Gottingen, Germany,
1997.
¨
41. M. Nardelli, J. Appl. Crystallogr., 1995, 28, 659.
42. L. J. Farrugia, J. Appl. Crystallogr., 1997, 30, 565.
ꢂc
This journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2008
1214 | New J. Chem., 2008, 32, 1204–1214