Cation dependence of chloride ion complexation by open-chained receptor molecules in chloroform solution

Article abstract of DOI:10.1021/ja0558894

Seventeen peptides, most having the sequence GGGPGGG, but differing in the C- and N-terminal ends, have been studied as anion-complexing agents. These relatively simple, open-chained peptide systems interact with both chloride and the associated cation. Changes in the N- and C-terminal side chains appear to make little difference in the efficacy of binding. NMR studies suggest that the primary interactions involve amide NH contacts with the chloride anion, and CD spectral analyses suggest a concomitant conformational change upon binding. Changes in binding constants, which are expected in different solvents, also suggest selective solvent interactions with the unbound host that helps to preorganize the open-chained peptide system. Significant differences are apparent in complexation strengths when the heptapeptide chain is shortened or lengthened or when the relative position of proline within the heptapeptide is varied.

Full text of DOI:10.1021/ja0558894

Published on Web 12/01/2005
Cation Dependence of Chloride Ion Complexation by
Open-Chained Receptor Molecules in Chloroform Solution
Robert Pajewski,† Riccardo Ferdani,† Jolanta Pajewska,† Ruiqiong Li,‡ and
George W. Gokel*,‡
Contribution from the Department of Chemistry, Washington UniVersity, 1 Brookings DriVe,
St. Louis, Missouri 63130, and Department of Molecular Biology & Pharmacology, Washington
UniVersity School of Medicine, Campus Box 8103, 660 S. Euclid AVe., St. Louis, Missouri 63110
Received September 6, 2005; E-mail: ggokel@wustl.edu
Abstract: Seventeen peptides, most having the sequence GGGPGGG, but differing in the C- and N-terminal
ends, have been studied as anion-complexing agents. These relatively simple, open-chained peptide
systems interact with both chloride and the associated cation. Changes in the N- and C-terminal side chains
appear to make little difference in the efficacy of binding. NMR studies suggest that the primary interactions
involve amide NH contacts with the chloride anion, and CD spectral analyses suggest a concomitant
conformational change upon binding. Changes in binding constants, which are expected in different solvents,
also suggest selective solvent interactions with the unbound host that helps to preorganize the open-
chained peptide system. Significant differences are apparent in complexation strengths when the
heptapeptide chain is shortened or lengthened or when the relative position of proline within the heptapeptide
is varied.
but the first structural details emerged only in 2002.6 The
complexity of the ClC protein channel, which is evident from
Introduction
In a recent and excellent review by Kubik and co-workers
titled “Recognition of Anions by Synthetic Receptors in
Aqueous Solution,”1 the authors state that “[t]he chemistry of
life mainly takes place in water...” While this is true in the
broadest sense, relatively little biological chemistry takes place
in bulk water per se. Instead, biological reactions and interac-
tions occur in or between proteins or membranes or both.
Assuredly, cytosolic proteins interact with numerous species,
but most recognition, catalysis, signaling, and other processes
occur in enzyme pockets or in or on membranes. This
contradiction in medium requirements presents the organic
chemist with the challenge of developing a model system that
is truly suitable for the study of biological phenomena.
Bilayer lipid membranes are impermeable to cations and most
anions. The complex proteins that transport ions and regulate
ionic concentrations in vivo insert into bilayers and create an
ion conduction pathway.2 Ion channel proteins have been
investigated for decades, but it is only recently that molecular
structures have been obtained.3 In a short time following the
first channel X-ray structure, the Nobel Prize was awarded for
these important contributions.4 The protein channels that
transport chloride ions have likewise been extensively studied,5
the crystal structure, is remarkable. Despite the structural
information available, details of the transport mechanism remain
speculative.7 It is clear, however, that chloride ions enter the
protein channel, which is embedded within the bilayer mem-
brane, from an aqueous phase.
Because transmembrane ion transport is so intricate, synthetic
model systems have been developed in several laboratories
throughout the world.8 We have designed and prepared both
cation-9 and anion-selective channels. The present report deals
with the latter: a membrane-anchored peptide that exhibits both
selective transport and complex gating behavior.10
An intriguing paradox in channel behavior is that ion
selectivity requires both recognition and transport. Molecular
recognition implies at least contact, but channels still pass g107
ions per second through a bilayer. Recognition suggests at least
a transient supramolecular interaction, which, in turn, implies
host-guest complex formation. Numerous complexes have been
reported that involve various anions and a wide range of receptor
(5) Maduke, M.; Miller, C.; Mindell, J. A. Annu. ReV. Biomol. Struct. 2000,
29, 411-438.
(6) Dutzler, R.; Campbell, E. B.; Cadene, M.; Chait, B. T.; MacKinnon, R.
Nature 2002, 415, 287-294.
(7) Dutzler, R.; Campbell, E. B.; MacKinnon, R. Science 2003, 300, 108-
112.
† Washington University School of Medicine.
‡ Washington University.
(1) Kubik, S.; Reyheller, C.; Stuewe, S. J. Inclusion Phenom. Macrocycl. Chem.
2005, 52, 137-187.
(2) Hille, B. Ionic Channels of Excitable Membranes, 3rd ed.; Sinauer
Associates: Sunderland, MA, 2001.
(3) Doyle, D. A.; Cabral, J. M.; Pfuetzner, R. A.; Kuo, A.; Gulbis, J. M.; Cohen,
S. L.; Chait, B. T.; MacKinnon, R. Science 1998, 280, 69-77.
(4) (a) MacKinnon, R. Angew. Chem., Int. Ed. 2004, 43, 4265-4277. (b) Agre,
P. Angew. Chem., Int. Ed. 2004, 43, 4278-4290.
(8) (a) Gokel, G. W.; Mukhopadhyay, A. Chem. Soc. ReV. 2001, 30, 274-
286. (b) Gokel, G. W.; Schlesinger, P. H.; Djedovic, N. K.; Ferdani, R.;
Harder, E. C.; Hu, J.; Leevy, W. M.; Pajewska, J.; Pajewski, R.; Weber,
M. E. Bioorg. Med. Chem. 2004, 12, 1291-1304.
(9) Gokel, G. W. Chem. Commun. 2000, 1-9.
(10) (a) Schlesinger, P. H.; Ferdani, R.; Liu, J.; Pajewska, J.; Pajewski, R.; Saito,
M.; Shabany, H.; Gokel, G. W. J. Am. Chem. Soc. 2002, 124, 1848-1849.
(b) Schlesinger, P. H.; Ferdani, R.; Pajewski, R.; Pajewska, J.; Gokel, G.
W. Chem. Commun. 2002, 840-841.
9
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J. AM. CHEM. SOC. 2005, 127, 18281-18295
18281

A R T I C L E S
Pajewski et al.
Table 1. Anion Binders Prepared for the Present Study
molecules.11 Most of these are fairly rigid, macrocyclic recep-
tors. There are also a few examples of cyclic peptide hosts for
anions,12 but these often incorporate unnatural amino acids,
nonamidic linkages, or alternating D,L-stereochemistry.
Recent work has shown that appropriate ditopic receptor
molecules can selectively bind ion pairs.13 A host system that
combined a Crabtree-type anion binding site14 with a diaza-18-
crown-6 cation binding site mediated chloride release from
vesicles15 and exhibited methylammonium chloride recogni-
tion.16 The fact that anions are bound with different selectivities
by individual receptors is well established. Equilibrium com-
plexation constants for anions also depend, sometimes dramati-
cally, on the associated cation, as we have previously commu-
nicated.17 We recount below the chloride ion complexation
behavior of a family of heptapeptides, analogous to that
originally reported as a chloride-selective ion channel: (C18H37)2-
NCOCH2OCH2CO-(Gly)3-Pro-(Gly)3-OCH2Ph.10 We have es-
tablished complexation sites within the peptide and we report
them here along with a survey of anion complexation and the
effect of counterion thereupon.
which was obtained by evaporation of the solvent followed by
crystallization of the product. Typically, the N-terminal tripep-
tide was coupled to R2[DGA]-OH to give a fragment of the
type (R1)2[DGA]-(Aaa)m-PrGp, where PrGp is a protecting
group. Removal of the protecting group, usually an ester, reveals
an acid that is coupled to the C-terminal fragment, of the form
H-(Aaa)n-PrGp, giving (R1)2[DGA]-(Aaa)m-(Aaa)n-PrGp. In 1,
the N-terminal residues were -Gly-Gly-Gly- and the C-
terminal unit was -Pro-Gly-Gly-Gly-.
Deuterated Heptapeptides, 2-7. Solution complexation
1
studies that were undertaken by using H NMR methods are
described below. To unequivocally assign the various proton
resonances, a series of six analogues of 1, i.e., 2-7, was
prepared. Each of these compounds is identical to 1 except that
one of the six glycines has been replaced by a dideuterated
glycine analogue (i.e., -NHCD2CO-). The requirement of
individual deuterated amino acids in the peptide chain precluded
the use of commercial triglycine in constructing the heptapep-
tides in some cases. Details of the sequential syntheses by
standard coupling methods and in analogy to Scheme 1 are
recorded in the Experimental Section.
Results and Discussion
NMR Spectrum of 1 in CDCl3. We report here studies of
(C18H37)2NCOCH2OCH2CO-(Gly)3-Pro-(Gly)3-OCH2Ph (9), to
which we have previously referred as SCMTR.10 The long,
Compounds Prepared for the Present Study. Eighteen
compounds were prepared for the studies that are presented here.
The preparation of compounds 1-17 is detailed in the Experi-
mental Section; 18 was previously reported by others (Table
1).14
1
N-terminal dialkyl chains complicate the H NMR spectrum,
so the derivatives studied here used dipropyl, rather than
(12) (a) Kubik, S.; Goddard, R.; Kirchner, R.; Nolting, D.; Seidel, J. Angew.
Chem. 2001, 40, 2648-2651. (b) Kubik, S.; Goddard, R. Proc. Nat. Acad.
Sci. U.S.A. 2002, 99, 5127-5132. (c) Kubik, S.; Kirchner, R.; Nolting, D.;
Seidel J. Am. Chem. Soc. 2002, 124, 12752-12760. (c) Ranganathan, D.;
Lakshmi, C. Chem. Commun. 2001, 1250-1251. (d) Suh, S. B.; Cui, C.;
Son, H. S.; U, J. S.; Won, Y.; Kim, K. S. J. Phys. Chem. B 2002, 106,
2061-2064. (e) Rudresh; Ramakumar, S.; Ramagopal, U. A.; Inai, Y.; Goel,
S.; Sahal, D.; Chauhan, V. S. Structure (Camb.) 2004, 12, 389-396.
(13) Mahoney, J. M.; Beatty, A. M.; Smith, B. D. J. Am. Chem. Soc. 2001,
123, 5847-5848.
(14) (a) Kavallieratos, K.; de Gala, S. R.; Austin, D. J.; Crabtree, R. H. J. Am.
Chem. Soc. 1997, 119, 2325-2326. (b) Kavallieratos, K.; Bertao, C. M.;
Crabtree, R. H. J. Org. Chem. 1999, 64, 1675-1683.
The peptide derivatives shown were prepared sequentially.
The appropriate amine [(R1)2NH] was heated with diglycolic
anhydride in THF or toluene (see Experimental Section) to
afford (R1)2NCOCH2OCH2COOH (abbreviated R2[DGA]-OH),
(15) Koulov, A. V.; Mahoney, J. M.; Smith, B. D. Org. Biomol. Chem. 2003,
1, 27-29.
(16) Mahoney, J. M.; Davis, J. P.; Beatty, A. M.; Smith, B. D. J. Org. Chem.
2003, 68, 9819-9820.
(17) Pajewski, R.; Ferdani, R.; Schlesinger, P. H.; Gokel, G. W. Chem. Commun.
2004, 160-161.
(11) Beer, P. D.; Gale, P. A. Angew. Chem., Int. Ed. 2001, 40, 486-516.
9
18282 J. AM. CHEM. SOC. VOL. 127, NO. 51, 2005

Open-Chained Peptides as Anion-Complexing Agents
A R T I C L E S
Scheme 1. Synthesis of Ion Binders 1-17
1
dioctadecyl, chains. The H NMR spectra of 1 in the absence
in CDCl3 to serve as donors to complex Cl-. Heptapeptide 1
([1] ∼ 4 mM in CDCl3) was therefore titrated with Bu4NCl
(∼80 mM in CDCl3) and the chemical shift changes were
monitored. Figure 1, above, shows the maximal changes
observed for 1 in the presence of 10 equiv of Bu4NCl. Changes
and presence of Bu4NCl are shown in the lower and middle
panels of Figure 1. The top trace in Figure 1 shows the spectrum
of 7. Compound 7 is identical to 1 except that Gly-7 (H2NCH2-
COOH) has been replaced by H2NCD2COOH, decoupling the
NH proton.
5
7
in the GNH and GNH resonances were monitored. Titration
7
When tetrabutylammonium chloride (Bu4NCl, 10 equiv) was
added to 1, the peak positions of all six amide hydrogens were
altered. The two NH signals most affected were those on Gly-5
curves, in which GNH of 1, 8, and 9 was monitored upon
addition of Bu4NCl, are shown in Figure 2.
These three compounds have the general structure (R1)2-
NCOCH2OCH2CO-(Gly)3-Pro-(Gly)3-OCH2Ph (abbreviated
32[DGA]-GGGPGGG-OCH2Ph when the N-terminal groups are
propyl). They differ only in the N-terminal alkyl groups, which
are n-propyl, n-decyl, and n-octadecyl for 1, 8, and 9,
respectively. We note that the three curves are nearly super-
imposed upon each other and the binding constants derived from
them must, therefore, be nearly identical. The magnitudes of
the changes indicated little effect of the side chain residues in
these experiments.
In principle, the side chains could interact with the cation,
the anion, or with other molecules of the host. Intermolecular
interaction of hosts constitutes aggregation, which should be
concentration dependent. Binding constants for 9, which has
the longest side chains studied, were determined at concentra-
tions ranging from about 1 to 5 mM. The results recorded in
Table 2 confirm the absence of any detectable aggregation or
other side chain effect and provide a sample of the excellent
data obtained in these experiments. The average of all runs is
1757 ( 23. This corresponds to a log10 KS of 3.24.
and Gly-7 (5GNH, GNH). When Bu4NCl was added to 1, the
7
5GNH shifted from 7.63 to 9.30 ppm (∆δ 1.67 ppm) and GNH
7
changed from 7.35 to δ 8.63 ppm (∆δ 1.28 ppm). The chemical
shift changes were interpreted as reflecting the interaction
between 1 and Bu4NCl. These large shifts suggested that the
amide hydrogens were forming direct H-bond interactions with
chloride anions. Main chain amide NH to anion interactions
have been recognized as a structural motif in protein chemistry
and given the name “nest” by Watson and Wilner-White.18 The
studies presented here provide insufficient structural information
to confirm a nest structural motif in the synthetic peptides.
Chloride Ion Complexation of 1 Assayed by 1H NMR. The
multiple amide NH bonds appeared from the 1H NMR spectrum
Figure 1. 1H NMR spectra in CDCl3 of 7 (top) and 1 (middle) in the
presence of 10 equiv of Bu4NCl. H NMR spectrum in CDCl3 of 1 (4.28
1
7
Figure 2. Titration curves in which the GNH 1H NMR chemical shift of
mM) in the absence of salt.
1, 8, and 9 was monitored upon addition of Bu4NCl (concentration in molar).
9
J. AM. CHEM. SOC. VOL. 127, NO. 51, 2005 18283

A R T I C L E S
Pajewski et al.
Table 2. Concentration Dependence of Bu4NCl Binding by 9 in
a
CDCl3
b
b
7GNH
5GNH
concn
(mM)
∆δmax
(ppm)
∆δmax
(ppm)
c
c
KS
KS
0.88
1.73
4.28
1.95
1.86
1.67
1780 ( 65
1750 ( 61
1735 ( 52
1.33
1.32
1.28
1775 ( 52
1738 ( 58
1763 ( 20
a Determined by 1H NMR at 25 °C. b The amide proton of the indicated
glycine was monitored. c Standard deviation of three independent measure-
ments.
Figure 4. Circular dichroism (CD) spectrum of 9 in the absence and
presence of Bu4NCl.
teristic of nonordered peptides,20 is affected by addition of Bu4-
NCl and nearly disappears when 10 equiv of salt are present. It
is the latter change that was monitored when using this method
to determine complexation constants, as described below.
Fitting of the CD data in CHCl3, as done for the NMR data
obtained in CDCl3, to eq 1 (see Experimental Section), gave a
binding constant of 1848 ( 439. The fitting error (∼25%) is
higher than that observed in the NMR experiments (<10%),
but the two values are within the error of the CD experiments.
This experiment provides independent confirmation of the results
obtained by NMR.
Effect of “Secondary Anchors” on Bu4NCl Complexation.
In other work, we have closely examined the effect of
differences in C- and N-terminal chain identity and length on
anion transport through phospholipid bilayer membranes.21-23
Release of both chloride and carboxyfluorescein (CF) anions
from vesicles was monitored by ion selective electrode or
fluorescent methods, respectively. In that work,23 C- and
N-terminal variants of -GGGPGGG- were prepared and
assayed. When the C-terminal ester was -OCH2Ph, chloride
anion release from liposomes observed the following general
pattern for variations in the N-terminal residues [i.e., (R1)2]:
bis(octyl) > bis(decyl) > bis(hexyl) > bis(dodecyl) > bis-
(propyl) ≈ bis(tetradecyl) ≈ bis(octadecyl) > bis(hexadecyl).
The results obtained for CF were similar, although not identi-
cal.23
A smaller compound sample was surveyed in the present
work than in the previous study using CF or Cl- ion. We
assumed that the major interactions with chloride anion would
involve the “main chain” amide groups. If so, changes at either
the C- or N-terminal end of the molecule should not be important
unless they influenced solubility. This expectation is largely
confirmed by the data presented in Table 3. The variation in
KS for the formation of a host‚Bu4NCl complex is about 25%
over the range of compounds chosen.
Cation Dependence of Complexation by 9. Relatively few
examples of open-chained anion-complexing agents have been
reported. The tris(aromatic) diamide of Crabtree and co-workers
(18) is exceptional, as it is an anion-complexing agent in its
Figure 3. Job’s plot for 9 (using a 8.56 × 10-3 M stock solution) and
Bu4NCl, for NH at δ 7.63 ppm.
Binding of ions by host molecules is typically weaker in
media of higher polarity compared to nonpolar solvents. The
insulating regime (“hydrocarbon slab”) of a bilayer is nonpolar
but probably rich in water. Experiments identical to those
described above were thus undertaken in wet solvent. When 9
was studied in CDCl3 saturated with H2O (1.8 mM solution of
182DGA-GGGPGGG-OBz, ∼100 mM Bu4NCl), the complex-
ation constant determined by NMR fell from 1750 to 720.
Complexation Stoichiometry. Confirmation of 1:1 stoichi-
ometry was obtained from an analysis using the method of
continuous variations, or Job’s plot.19 Solutions of host (H) and
guest (G) were mixed in varying ratios such that the total
concentration, [H] + [G], remained constant. For 1:1 stoichi-
ometry, the concentration of complex, [H‚G], is maximal when
[H] ) [G]. Other stoichiometries produce plots with different
maxima. The amide residue of 9 at δ 7.63 was monitored by
1H NMR as Bu4NCl was added. The plot, clearly indicating
1:1 complex stoichiometry, is shown as Figure 3.
It should also be noted that eq 1 (see Experimental Section),
as used above, assumed 1:1 complexation stoichiometry. Com-
plexation of Bu4NCl by 17 was studied as above. Equation 1
was applied by assuming both 1:1 and 1:2 stoichiometries.
Including the latter did not improve the error. The second
binding constant was <100.
Confirmation of NMR Titration Results by Using Circular
Dichroism (CD). Titration experiments were also conducted
by evaluating the circular dichroism spectra of 9 in CHCl3.
Heptapeptide 9 ([9] ∼1.7 mM in CDCl3) was titrated with Bu4-
NCl (∼100 mM in CDCl3) and changes in the CD spectrum
were observed. Figure 4 shows CD spectra of a 1.7 mM solution
of 182[DGA]-GGGPGGG-OCH2Ph (9) in CHCl3 (black) and
after addition of 1 equiv (green) and 10 equiv (red) of Bu4NCl.
The negative band at approximately 230 nm, which is charac-
(20) Woody, R. W. in The Peptides: Analysis, Synthesis and Biology; Hruby,
V. J., Ed.; Academic Press: New York, 1985; Vol. 7, pp 15-114.
(21) Schlesinger, P. H.; Djedovic, N. K.; Ferdani, R.; Pajewska, J.; Pajewski,
R.; Gokel, G. W. Chem. Commun. 2003, 308-309.
(22) Ferdani, R.; Pajewski, R.; Djedovic, N.; Pajewska, J.; Schlesinger, P. H.;
Gokel, G. W. New J. Chem. 2005, 29, 673-680.
(18) (a) Watson, J. D.; Milner-White, E. J. J. Mol. Biol. 2002, 315, 183-191.
(b) Watson, J. D.; Milner-White, E. J. J. Mol. Biol. 2002, 315, 171-182.
(19) Connors, K. A. Binding Constants, 1st ed.; John Wiley & Sons: New York,
1987; pp 189-215.
(23) Djedovic, N.; Ferdani, R.; Harder, E.; Pajewska, J.; Pajewski, R.; Weber,
M. E.; Schlesinger, P. H.; Gokel, G. W. New J. Chem. 2005, 29, 291-
305.
9
18284 J. AM. CHEM. SOC. VOL. 127, NO. 51, 2005

Open-Chained Peptides as Anion-Complexing Agents
A R T I C L E S
Table 3. Complexation by (R1)2NCOCH2OCH2CO-GGGPGGG-R2
of Bu4NCl in CDCl3
Ph4PCl gave a smooth titration curve but it could not be fitted
to the published equation.14 When forced to fit, K ) ∼34 000
( 51 000. This large error resulted from too high a concentration
of 1 because the equilibrium binding constant was so much
larger than expected. Titration of 0.6 mM solutions of 1 with
Ph4PCl gave KS values of 16 000 ( 1380 and 16 300 ( 1420
when fitted.
The influence of cation structure on anion activity is well-
known. Indeed, it is the basis of both ion pair extraction25 and
of phase transfer catalysis26,27 and has been explored exten-
sively.28 For example, 22 quaternary halides were used as
catalysts for the nucleophilic substitution reaction of PhS with
BrC8H17 to give PhSC8H17. The reactions were all conducted
in a two-phase, water-benzene mixture, and all used quaternary
halides.29 Reaction rates for the 22 different quaternary halides
varied by nearly 5 orders of magnitude. The relative reaction
rates for Bu4NCl, Bu4PCl, and Ph4PCl were, respectively, 1.0,
7.1, and 0.5.
a
dialkyl
NH peak
groups
(R1)
no.
ester (R2)
1
2
log10 Kb
1
8
9
CH2CH2CH3 OCH2C6H5
1340 ( 44
1530 ( 63
1735 ( 52
1756 ( 99
1811 ( 150 1768 ( 115
1455 ( 33
1379 ( 54
1527 ( 50
1763 ( 20
1761 ( 93
3.13
3.18
3.25
3.25
3.25
3.16
(CH2)9CH3
(CH2)17CH3
OCH2C6H5
OCH2C6H5
OCH2CH3
10 (CH2)17CH3
11 (CH2)17CH3
12 CH2CH2CH3 O(CH2)17CH3 1479 ( 38
O(CH2)6CH3
a All titration experiments were conducted at 25 °C in CDCl3 with
Bu4NCl using 1.8 mM initial concentrations of 1-7. b log10 of the average
of the two (1 and 2) peak values.
a
Table 4. Ion Pair Binding by 9 and 18 in CDCl3
b
log KS
salt
9
18
Bu4NCl
3.24
3.35
3.39
3.23
2.71
4.20d
3.39
2.93
Me3NCH2PhCl
Et3NCH2PhCl
Bu3NCH2PhCl
Bu4PCl
To our knowledge, the question of cation effect on anion
receptor binding has been addressed only to a very limited
extent. Tuntulani, Vicens, and their co-workers studied the
influence of cations on the binding of various anions by tripodal
azacrown-calix[4]arenes.30 In this study, cations (primarily
metallic) were varied to determine the effect on overall binding.
It was concluded that these calixarene derivatives could
potentially be used either as transition metal ion or anion
receptors and that control could be effected by pH changes.
Kubik and co-workers12c examined Na+, K+, and Me4N+ cations
c
-
c
-
c
-
Ph4PCl
3.70
a At 25 °C, determined by 1H NMR titration. b Standard deviation of
three independent measurements. c Not determined in this work. d 0.60 mM
solution.
own right and it has been used as the basis for other, more
elaborate anion receptors.14,24 We, therefore, reproduced the
complexation studies with 18 to calibrate our own efforts. The
NMR titration method paralleled that previously reported. We
successfully reproduced the data for 18 and Ph4PCl. In our
hands, the constant for formation of 18·Ph4PCl was ∼5000 (log
KS 3.70). This is similar to that previously reported (∼5300,
log KS 3.72).14 The calculations used the reported14 equation
(eq 1), which is reproduced in the Experimental Section.
Table 4 records ion pair complexation data for compounds 9
and 18. Six different chloride salts having organic countercations
were studied. The cations were tetrabutylammonium (Bu4N+),
benzyltrimethylammonium (Me3NCH2Ph+), benzyltriethylam-
monium (Et3NCH2Ph+), benzyltributylammonium (Bu3NCH2-
Ph+), tetrabutylphosphonium (Bu4P+), and tetraphenylphospho-
nium (Ph4P+). The variations in log KS for complexation of
Me3NCH2PhCl, Et3NCH2PhCl, Bu3NCH2PhCl, and Bu4NCl
were well outside experimental error but certainly in a similar
range (log KS ) 3.31 ( 0.08). Complexation of the phospho-
nium salts, however, was significantly different. Tetrabutylphos-
phonium chloride and tetraphenylphosphonium chloride had
markedly different complexation constants with both 9 and 18.
The binding constant (log KS) for 18 was reproducibly ∼3.7
with Ph4PCl, but fell to 3.4 with Bu4NCl and to 2.9 with Me3-
NCH2PhCl. Since the anion is identical in all three cases, these
values suggest an interaction with the cation as well. Indeed,
such differences have been documented for a ditopic receptor
based upon 18.16
and Cl-, Br-, I-, NO3-, and SO4 in conjunction with their
2-
cyclic hexapeptide receptor system in water. To our knowledge,
no acyclic system has been surveyed as done here, in any
solvent.
Solvent Dependence of Bu4NCl Complexation by 1.
Compound 9, (C18H37)2NCOCH2OCH2CO-(Gly)3-Pro-(Gly)3-
OCH2Ph, is quite soluble in CHCl3 but less so in polar solvents.
Indeed, solutions as concentrated as those used for the 1H NMR
studies performed in CDCl3 could not be obtained in either CH3-
COCH3 (dielectric constant, ꢀ ) 20.7) or CH3CN (ꢀ ) 36.6).
Compound 1 has shorter alkyl chains than 9, is less hydrophobic,
and is correspondingly more soluble in a range of solvents.
Compound 1 is sufficiently soluble in both CD3COCD3 and
CD3CN to perform complexation studies with Bu4NCl, assayed
by 1H NMR titration. Thus, 1.8 mM solutions of (C3H7)2-
NCOCH2OCH2CO-(Gly)3-Pro-(Gly)3-OCH2Ph (1) were pre-
pared and titrated with Bu4NCl. The results are collected in
Table 5.
The association constant for 1 in CDCl3 is 1360, lower than
KS for 9. A significant increase in chloride binding was observed
in CD3COCD3, and a value of 2170 was observed. The same
experiment performed in CD3CN gave KS ) 950. The significant
counterion effect observed in CHCl3 disappears when more
strongly competing solvents are used, and larger ion separation
is expected. Titration in CD3CN with tetraphenylphosphonium
(25) Brandstrom, A.; Gustavii, K. Acta Chem. Scand. 1969, 23, 1215-1218.
(26) Starks, C. M. J. Am. Chem. Soc. 1971, 93, 195-199.
(27) Weber, W. P.; Gokel, G. W. Phase Transfer Catalysis in Organic Synthesis;
Springer-Verlag: Berlin, 1977, 280 pp.
(28) Starks, C. M.; Liotta, C. L.; Halpern, M. Phase Transfer Catalysis; Chapman
and Hall: New York, 1994, 668 pp.
(29) Herriott, A. W.; Picker, D. J. Am. Chem. Soc. 1975, 97, 2345-2349.
(30) Tuntulani, T.; Thavornyutikarn, P.; Poompradub, S.; Jaiboon, N.; Ruang-
pornvisuti, V.; Chaichit, N.; Asfari, Z.; Vicens, J. Tetrahedron 2002, 58,
10277-10285.
The apparent constants, KS, for 1 were ∼1700 for Bu3NCH2-
PhCl and ∼2400 for Et3NCH2PhCl. For Me3NCH2PhCl, the KS
values calculated from ∆δ for the δ 7.35 and δ 7.63 ppm protons
were ∼1000 and ∼2500, respectively. The data obtained for
(24) (a) Choi, K.; Hamilton, A. D. J. Am. Chem. Soc. 2003, 125, 10241-10249.
(b) Choi, K.; Hamilton, A. D. Coord. Chem. ReV. 2003, 240, 101-110.
9
J. AM. CHEM. SOC. VOL. 127, NO. 51, 2005 18285

A R T I C L E S
Pajewski et al.
Table 6. Peptide Sequence Dependence of Bu4NCl Binding in
Table 5. Association Constants between 1 and Bu4NCl at 25 °C
in Solvents of Different Polaritya
CDCl3
a
∆δmax
(ppm)
∆δmax
(ppm)
av
KS
no.
peptide sequence
KS
log KS
solvent
K
S (7GNH
)
K
S (5GNH
)
log KS
9
13
16
14
15
17
(Gly)3Pro(Gly)3
(Gly)3Pip(Gly)3
(Gly)2Pro(Gly)2
(Gly)2Pro(Gly)4
(Gly)4Pro(Gly)2
(Gly)4Pro(Gly)4
1755 ( 55
400 ( 40
56 ( 3
1330 ( 81
406 ( 43
9630 ( 2400
3.25
2.60
1.75
3.12
2.61
3.98
CDCl3
1.83 1340 ( 44
1.34 1379 ( 54
1360 3.13
CD3COCD3 1.30 2134 ( 132 1.30 2217 ( 133 2175 3.33
CD3CN
1.68
1.68
949 ( 81
977 ( 67
1.42
1.40
956 ( 87
909 ( 54
953 2.98
943 2.97
CD3CNb
a Assay by 1H NMR; GNH indicates the NH proton of glycine-7.
7
b Titration with Ph4PCl.
a Determined by the previously described NMR method at 25 °C.
It seems reasonable that any interaction between the carbonyl
groups of 1 and Na+ would be stronger than with K+, owing to
the former’s greater charge density. We note that the even larger
binding constant observed for 1·Bu4NCl involves both an anion
and cation that interact with the peptide chain.
The variations observed in binding constants by the hep-
tapeptides were clearly of interest per se, but a possible cation-π
effect32 in the system made it additionally intriguing. If a single
arene significantly altered the binding behavior, four arenes
might have an even more dramatic effect. Thus, 10 (182[DGA]-
GGGPGGG-OCH2CH3) was titrated with Ph4PCl in CDCl3. As
before, the proton signals for 7GNH and 5GNH were evaluated to
obtain association constants. The values obtained for KS were
15 400 ( 1000 and 16 000 ( 1200. These are identical within
experimental error but an order of magnitude higher than
observed for Bu4NCl. Stronger binding clearly indicates a more
favorable overall interaction. We were, however, unable to
identify any dramatic upfield shifts in other parts of the host
molecule that would suggest an intimate π-contact between an
arene in the salt and the host.
Figure 5. Calculated structures of Me2[DGA]-GGGPGGG-OCH3 (A, left)
and Me2[DGA]-GGGPipGGG-OCH3 (B, right) in the gas phase in the
absence of salt. The images shown were obtained from Gaussian 03W using
the semiempirical method.
chloride instead of tetrabutylammonium chloride gave the same
association value within experimental error.
Effect of Length and Sequence Changes. Table 6 records
complexation constants for compounds 9 and 13-17 with Bu4-
NCl in CDCl3, determined as described above. The structures
shown represent two variations. First, the fourth or “central”
amino acid in 9 is altered from proline to pipecolic acid in 13.
From the structural perspective, this is a minor change as the
ring size is increased by a methylene, but the stereochemistry
and functionality remain the same. The binding constant (KS)
for 9·Bu4NCl in CDCl3 is ∼1750. When proline in 9 is replaced
by pipecolic acid to give 13, KS falls to ∼400. Previous studies31
compared the ability of these pore formers to release the anion
carboxyfluorescein from phospholipid liposomes. In that case,
the change in release rate was about 20-fold with 9 being more
effective than 13. The anions and conditions are different in
the former and present studies, but the trend is similar.
Gaussian 03W and Spartan calculations (gas phase, alkyl
chains (R1) and C-terminal ester (R2) ) CH3, Spartan data not
shown) both suggest a significant difference in the preferred
conformations of A and B. Computational models of A and B
are shown in Figure 5 (left and right panels, respectively) with
the cyclic amino acid at the apex. The conformation of B
(pipecolic) is calculated to be much more compact than A
(proline). The positions of the amide NH bonds are significantly
different in the two conformations. Although these calculations
may not accurately reflect the situation when either A or B is
in contact with a bilayer membrane or in solution, they do
comport with the significant differences in ion transport activity
observed for these two close relatives.
The binding constant for 1·Bu4NCl in acetone is higher than
expected on the basis of the differences in dielectric constants
among these solvents. It is probably inappropriate to compare
interactions involving Bu4NCl in chloroform with those in either
acetone or acetonitrile. In chloroform, the salt probably exists
primarily as an ion pair, whereas the higher polarity solvents
will give solvent separated ion pairs. Purely on the basis of the
dielectric constants, we would expect binding to be highest in
chloroform and lowest in acetonitrile. A possible, but specula-
tive, explanation is that the carbonyl group of acetone could fit
into the “v” formed at the apex of 1 (see the calculated structure
in Figure 5 below) and help to preorganize the host’s amide
NH bonds for interaction with chloride.
Voltage clamp experiments performed on 9 in planar bilay-
ers31 revealed that selective chloride transport is observed in
the presence of a high concentration of K+. However, when
Na+ was the only cation present, both Na+ and Cl- ions were
transported simultaneously. Simultaneous cation and anion
transport is not unreasonable, as both carbonyl and amide
H-bond donors are present in the structure. Titration experiments
were conducted (1H NMR, CD3CN) with 32[DGA]-GGGPGGG-
OCH2Ph (1) and NaBPh4 or KBPh4. Tetraphenylborate was
chosen because it is a less interactive anion than chloride, and
NaBPh4 and KBPh4 are soluble in CD3CN. The binding
constants for 1·NaBPh4 and 1·KBPh4 were ∼310 and ∼57,
respectively. This compares to KS ) 950 ( 80 for 1·Bu4NCl.
(31) Schlesinger, P. H.; Ferdani, R.; Pajewska, J.; Pajewski, R.; Gokel, G. W.
(32) Gokel, G. W.; Barbour, L. J.; Ferdani, R.; Hu, J. Acc. Chem. Res. 2002,
35, 878-886.
New J. Chem. 2003, 27, 60-67.
9
18286 J. AM. CHEM. SOC. VOL. 127, NO. 51, 2005

Open-Chained Peptides as Anion-Complexing Agents
A R T I C L E S
In addition to the proline-pipecolic acid variation, Table 6
shows the effect of changes in the number and arrangement of
amino acids in the peptide sequence. Compound 16 is a
pentapeptide, 14 and 15 are heptapeptides, and 17 is a
nonapeptide. Shortening the heptapeptide sequence that is the
central theme of this study dramatically lowers KS for its
interaction with Bu4NCl in CDCl3. A significant, but not as
large, decrease in KS is observed for 15. The latter is a
heptapeptide rather than a pentapeptide but has the same -Pro-
Gly-Gly- C-terminal sequence as 13.
The most dramatic result is observed for 182[DGA]-GGGG-
PGGGG-OCH2Ph, 17. The binding constant (KS) for 17·Bu4-
NCl in CDCl3 is 9630 ( 2400. Three separate complexation
studies gave values for KS of 7134, 9827, and 11 924, resulting
in the ∼25% error limits. As noted above, incorporation of 1:2
stoichiometry in the calculation gave no significant difference
in the values quoted. The high binding constant would require
low concentrations of 17 for optimal NMR evaluation. Ap-
propriately low concentrations, however, would require exces-
sive acquisition times. Thus, we compromised on the acquisition
times and feel that the error range is acceptable. The critical
finding for this study is that even the lowest of the three KS
values obtained in individual experiments is more than 4-fold
higher than the value of 1750 observed for 9. In the absence of
a structure determination, the enhanced binding interactions
between host and salt cannot be analyzed. Clearly, however,
the longer peptide sequence is of significant value in the binding
context.
Several studies of macrocyclic and open-chained compounds
in which chloride complexation is addressed have appeared.
Indeed, the area has recently been reviewed several times.11,41
Bowman-James and co-workers studied chloride complexation
by a macrocycle incorporating two isophthalic acid units, six
nitrogens, and four amides. In CDCl3, the complexation constant
was about 500.42 Hamilton and co-workers compared a mac-
rocycle containing three amide residues with its open-chained
counterpart. Binding was lower for open-chained analogues
complexing various ions, but no chloride association constant
was reported. The macrocycle bound Bu4NCl in 2% DMSO-
d6/CDCl3 with KS ) 8800.43 A tetraamide-containing ditopic
calixarene reported by Ungaro et al. bound chloride in CD3-
COCD3 with KS ) 2800.44 A bis(calixarene), linked by two
amide residues, bound chloride in CD2Cl2 with KS ) 172.45
A number of open-chained anion binders that use amides as
donors have also been reported. A pyrrole-2,5-dicarboxamide
was reported to bind Cl- in CD3CN with KS ) 138.46 A family
of open-chained amides was assayed for chloride binding in
CDCl3, but the highest KS value among the eight compounds
studied was 395.47 In addition, numerous anion binders that use
organometallic scaffolds such as ferrocene or cobalticene have
been reported. In most cases, the complexation was done in
CD3CN for solubility reasons and cations were not varied.48
From the biological perspective, rigidity and charge density
represent extremes in interactions. Most forces in nature are
weak and transient because very strong interactions tend to be
irreversible. To our knowledge, no assessment of chloride
binding has previously been done with an open-chained peptide
assembled only from natural amino acids. The closest study to
our own effort involves the cyclic aminoxy receptors noted
above.40 The authors report that the association constants KS
for the “cyclohexapeptide” complexes with Cl- and F- were
11 880 and 30 M-1, respectively (298 K). It is unclear what
cation was used in the NMR studies, but the salt studied by
mass spectrometry was Ph4PCl. We obtained a value of KS for
complexation of open-chained 1 with Ph4PCl (see above) of
about 16 000.
Cyclic and Open-Chained Cation Binders. The concept of
preorganization is well-established33 and extensively docu-
mented for cation complexing systems. Thus, pentaethylene
glycol dimethyl ether binds Na+ in CH3OH with log KS of 1.52,
and for 18-crown-6, the value is 4.35, a difference of more than
600-fold.34 Similar principles apply in the complexation of
anions. Numerous examples now exist of a similar survey of
anion properties. The extremes of such studies are rigid
macrocycles such as porphyrins,35 calixarenes,36 or hybrids
thereof,37 and the charge-dense anion fluoride.38 Examples are
also abundant of H-bond donors that are appended to (or pendant
from) a rigid scaffold.39 Examples of cyclic and open-chained
peptides are less common. Indeed, the principal examples of
cyclic peptides incorporate unnatural amino acids (e.g. aminoxy
amino acids) or alternating D,L-stereochemistry.40 For example,
in the work reported by Kubik and co-workers noted above,
the cyclic system was constructed from L-proline and 6-ami-
nopicolinic acid.12a
Conclusions
Three major findings emerge from the data acquired in this
study. First, open-chained peptides exhibit strong chloride
binding in solvents of low and moderate polarity. Compared to
values reported previously in the literature, the open-chained
compounds reported here are as good as or better than many
amide-containing macrocycles. The acyclic peptides are flexible
and therefore adaptable. In principle, higher binding and
selectivity can be achieved by a rigid host of the correct size.
In general, however, the synthetic approaches prevent most
macrocycles from being adjustable in small increments of ring
size. Second, the associated cation may dramatically influence
(33) Cram, D. J.; Kaneda, T.; Helgeson, R. C.; Brown, S. B.; Knobler, C. B.;
Maverick, E.; Trueblood, K. N. J. Am. Chem. Soc. 1985, 107, 3645-3657.
(34) Cation Binding by Macrocycles; Inoue, Y.; Gokel, G. W., Eds.; Marcel
Dekker: New York, 1990; p. 261.
(35) (a) Jagessar, R. C.; Shang, M.; Scheidt, W. R.; Burns, D. H. J. Am. Chem.
Soc. 1998, 120, 11684-11692. (b) Sessler, J. L.; Camiolo, S.; Gale, P. A.
Coord. Chem. ReV. 2003, 240, 17-55.
(36) Scheerder, J.; Engbersen, J. F. J.; Casnati, A.; Ungaro, R.; Reinhoudt, D.
N. J. Org. Chem. 1995, 60, 6448-6454.
(37) (a) Cafeo, G.; Kohnke, F. H.; La Torre, G. L.; Parisi, M. F.; Pistone
Nascone, R.; White, A. J.; Williams, D. J. Chemistry 2002, 8, 3148-3156.
(b) Sessler, J. L.; An, D.; Cho, W. S.; Lynch, V. Angew Chem. Int. Ed.
2003, 42, 2278-2281.
(41) Bowman-James, K. Acc. Chem. Res. 2005, 38, 671-678.
(42) Hossain, M. A.; Llinares, J. M.; Powell, D.; Bowman-James, K.; Inorg.
Chem. 2001, 40, 2936-2937.
(43) Choi, K.; Hamilton, A. D. J. Am. Chem. Soc. 2001, 123, 2456-2457.
(44) Sansone, F.; Baldini, L.; Casnati, A. Lazzarotto, M.; Ugozzoli, F.; Ungaro,
R.; Proc. Natl. Acad. Sci. U.S.A. 2002, 99, 4842-4847.
(38) (a) Yoon, D.-W.; Hwang, H.; Lee, C.-H. Angew. Chem., Int. Ed. 2002, 41,
1757-1759. (b) Camiolo, S.; Gale, P. A.; Hursthouse, M. B.; Light, M.
E.; Warriner, C. N. Tetrahedron Lett. 2003, 44, 1367-1369.
(39) Ayling, A. J.; Perez-Payan, M. N.; Davis, A. P. J. Am. Chem. Soc. 2001,
123, 12716-12717.
(45) Beer, P. D.; Gale, P. A.; Hesek, D. Tetrahedron Lett. 1995, 767-770.
(46) Gale, P. A.; Camiolo, S.; Chapman, C. P.; Light, M. E.; Hursthouse, M.
B. Tetrahedron Lett. 2001, 5095-5097.
(40) Yang, D.; Qu, J.; Li, W.; Zhang, Y.-H.; Ren, Y.; Wang, D.-P.; Wu, Y.-D.
J. Am. Chem. Soc. 2002, 124, 12410-12411.
(47) Werner, F.; Schneider, H.-J. HelV. Chim. Acta 2000, 465-478.
(48) Bondy, C. R.; Loeb, S. J. Coord. Chem. ReV. 2003, 240, 77-99.
9
J. AM. CHEM. SOC. VOL. 127, NO. 51, 2005 18287

A R T I C L E S
Pajewski et al.
∆δ )
how strongly the anion is bound. Of course, the differences may
simply reflect how effectively the ion pair is bound. In most
published cases to date, however, the cation effect is either
unspecified or unrecognized. Finally, the binding studies
reported here correlate with the channel activity. Thus, binding
strength increases in the series -(Gly)2Pro(Gly)2- (16) <
-(Gly)3Pro(Gly)3- (9) < -(Gly)4Pro(Gly)4- (17), which is
consistent with the increase in chloride transport activity in
liposomes among these three compounds. In addition, pipecolic
acid derivative 13 (-(Gly)3Pip(Gly)3-) shows poorer chloride
binding in the present study and was found to be a less effective
ion channel than 9 in previous studies.
2 - 4[G]0[H]0 ∆δmax
1
Ka
1
Ka
[H]0 + [G]0 +
-
[H]0 + [G]0 +
(
(
x
))
)
((
)
2[H]0
(1)
[2-(2-{[1-(2-{2-[2-(2-Dipropylcarbamoylmethoxyacetylamino)-
acetylamino]acetylamino}acetyl)pyrrolidine-2-carbonyl]amino}-
acetylamino)acetylamino]acetic acid benzyl ester, 1, was prepared
as previously described.31
[2-(2-{[1-(2-{2-[2-(2-Dipropylcarbamoylmethoxyacetylamino)-
dideutoeroacetylamino]acetylamino}acetyl)pyrrolidine-2-carbonyl]-
amino}acetylamino)acetylamino]acetic Acid Benzyl Ester, 2, 32-
[DGA]-Gd2-GGPGGG-OCH2Ph. Dipropylcarbamoylmethoxyacetic
acid (32[DGA]-OH). A solution of dipropylamine (2.0 g, 19.8 mmol)
and diglycolic anhydride (2.5 g, 21.7 mmol) was refluxed in THF (30
mL) for 48 h. The solvent was evaporated and the crude product
dissolved in CHCl3 and washed with dilute aq HCl. The solvent was
removed and the residue recrystallized from Et2O to give the final
Experimental Section
General Methods. All reaction solvents were freshly distilled and
the reactions were conducted under N2 unless otherwise stated. Et3N
was distilled from KOH and stored over KOH. CH2Cl2 was distilled
from CaH2. Column chromatography was performed on silica gel 60
(230-400 mesh). Thin-layer chromatography was performed with silica
gel 60 F254 plates with visualization by UV light (254 nm) and/or by
phosphomolybdic acid (PMA) spray. Starting materials were purchased
1
product as a white solid (3.2 g, 75%), mp 55-56 °C. H NMR: 0.91
(6H, m, CH3), 1.59 (4H, m, CH3CH2CH2N), 3.07 (2H, t, J ) 7.8 Hz,
CH3CH2CH2N), 3.23 (2H, t, J ) 7.8 Hz, CH3CH2CH2N), 4.20 (2H, s,
C(O)CH2O), 4.40 (2H, s, C(O)CH2O). 13C NMR: δ 11.1, 11.2, 20.6,
21.7, 48.4, 71.2, 73.0, 170.8, 171.8.
1
from Aldrich Chemical Co. and used as received. H NMR spectra
N-tert-Butoxycarbonylglycine-2,2-d2. Glycine-2,2-d2 was suspended
in mixture of H2O (10 mL), dioxane (10 mL), and Et3N (2.0 g 19.8
mmol) followed by Boc-OH (3.20 g, 13.0 mmol). The reaction was
stirred at room temperature for 2 h. H2O (25 mL) was added and the
aqueous solution was extracted with EtOAc (30 mL). The residue was
acidified with 5% citric acid and extracted with EtOAc (3 × 25 mL).
The organic layer was dried over MgSO4 and the solvent evaporated.
The crude oily product was recrystallized from hexanes-EtOAc to give
a white solid (1.83 g, 80%), mp 89-90 °C.1H NMR: 1.44 (9H, s,
C(CH3)3), 5.13 (bs, Gly CONH), 6.75 (bs, Gly CONH), 10.41 (1H,
COOH). 13C NMR: 28.2, 41.0, 80.4, 81.7, 156.0, 157.3, 174.0, 174.8.
IR (CHCl3): 3354, 1700, 1516, 1453, 1395, 1369, 1287, 1255, 1166,
were recorded at 300 MHz and are reported in the following manner:
Chemical shifts are reported in ppm downfield from internal tetra-
methylsilane (integrated intensity, multiplicity (b ) broad; s ) singlet;
d ) doublet; t ) triplet; m ) multiplet, bs ) broad singlet, etc.),
coupling constants in hertz, assignment). 13C NMR spectra were
obtained at 75 MHz and referenced to CDCl3 (δ 77.0). Infrared spectra
were recorded in KBr unless otherwise noted and were calibrated against
the 1601 cm-1 band of polystyrene. Melting points were determined
on a Thomas-Hoover apparatus in open capillaries. Combustion analyses
were performed by Atlantic Microlab, Inc., Atlanta, GA, and are
reported as percents. EDCI and HOBt are abbreviations for 1-(3-
dimethylaminopropyl)-3-ethyl carbodiimide hydrochloride and 1-hy-
droxybenzotriazole hydrate, respectively. Q+X- salts used for the NMR
titrations were dried overnight (80 °C) under vacuum prior to the
experiments.
1077, 1055, 885, 847, 782 cm-1
.
Boc-Gd2-OCH2Ph. Boc-glycine-2,2-d2 (0.4 g, 2.26 mmol), benzyl
alcohol (0.24 g, 2.26 mmol), and DMAP (0.03 g, 0.23 mmol) were
dissolved in CH2Cl2 (30 mL) and cooled to 5 °C. N,N′-Diisopropyl-
carbodiimide (0.37 mL, 2.39 mmol) was added and the reaction was
stirred at room temperature overnight. The solvent was evaporated and
the residue was chromatographed (SiO2, 1% MeOH-CHCl3) to give a
white solid (0.50 g, 83%), mp 72-73 °C. 1H NMR: 1.44 (9H, s,
C(CH3)3), 4.99 (1H, bs, Gly CONH), 5.18 (2H, s, PhCH2O), 7.30-
7.38 (5H, m, HAr). 13C NMR: 28.3, 67.0, 80.0, 128.4, 128.5, 128.6,
135.2, 155.7, 170.2. IR (CHCl3): 3370, 2977, 1751, 1714, 1499, 1455,
1392, 1367, 1274, 1254, 1166, 1076, 1052, 1030, 884, 845, 752, 698
Continuous Variation Method (Job’s plot). Stock solutions of the
host (8.56 mM) and Bu4NCl (8.56 mM) in CDCl3 were prepared. Ten
NMR tubes were filled with 1 mL of solution containing the host and
guest in the following volume ratios (in mL): 0.9:0.1, 0.8:0.2, 0.7:0.3,
0.6:0.4, 0.55:0.45, 0.5:0.5, 0.45:0.55, 0.4:0.6, 0.3:0.7, 0.2:0.8, 0.1:0.9.
1H NMR spectra were recorded, and the concentration of the complex
was calculated as [9] ) [H]t × (δobs - δ0)/(δc - δ0), where [H]t is the
total concentration of host in the solution, δobs is the observed chemical
shift for the NH signal, and δc is the chemical shift of the NH signal
in the complex.
cm-1
.
HCl·Gd2-OCH2Ph. Boc-Gd2-OCH2Ph (0.21 g, 0.79 mmol) was
dissolved in 4 N HCl in dioxane (5 mL) at 5 °C and the reaction mixture
was stirred for 0.5 h. The solvent was evaporated in vacuo. The product
was used in the subsequent reaction without further purification.
32[DGA]-Gd2-OCH2Ph. To dipropylcarbamoylmethoxyacetic acid
(0.17 g, 0.79 mmol) dissolved in CH2Cl2 (30 mL) were added EDCI
(0.17 g, 0.89 mmol) and HOBt (0.12 g, 0.89 mmol) (at 5 °C, ice bath),
and the mixture was stirred at room temperature. After 0.5 h, HCl·
Gd2-OCH2Ph (0.16 g, 0.79 mmol) and NMM (0.1 mL) were added,
and the reaction mixture was stirred at room temperature overnight.
The solvent was evaporated and the residue was purified on column
(SiO2, 2% MeOH-CHCl3) to afford a colorless oil (0.24 g, 83%).1H
NMR: 0.80-0.95 (6H, m, -CH2CH3), 1.50-1.65 (4H, m, CH3CH2-
CH2N), 3.06 (2H, t, J ) 7.8 Hz, CH3CH2CH2N), 3.28 (2H, t, J ) 7.8
Hz, CH3CH2CH2N), 4.14 (2H, s, COCH2O), 4.27 (2H, s, COCH2O),
5.16 (2H, s, PHCH2O), 7.30-7.40 (5H, m, HAr), 8.17 (1H, pseudo-s,
1H NMR Titrations. Solutions of host in CDCl3 (CD2Cl2 for 2)
were prepared in the concentration range 0.88-4.30 mM (0.30 mM
for 2). Deuterated solvents were dried over 4 Å molecular sieves. One
mL of this solution was titrated in NMR tubes with 35-170 mM (12
mM for 2) solutions of Q+Cl-, which also contained host in the same
concentration as the titrated solution. The signals assigned to the NH
protons were monitored as a function of the anion concentration to the
point at which the chemical shift change reached saturation. The
association constant Ka was calculated from the obtained isotherms
(∆δNH vs [Cl-]) by nonlinear regression analysis carried out with
Origin 7 and using the curve fit for 1:1 binding (eq 1). All the runs
were carried out for at least three independent samples.
Complexation between 1-18 and various salts was conducted as
described by Kavallieratos et al.14 using the equation reproduced below,
where H and G represent host and guest.
9
18288 J. AM. CHEM. SOC. VOL. 127, NO. 51, 2005

Open-Chained Peptides as Anion-Complexing Agents
A R T I C L E S
Gly CONH). 13C NMR: 11.1, 11.3, 20.7, 22.0, 47.7, 48.4, 66.9, 69.5,
71.6, 128.3, 128.4, 128.5, 135.3, 168.3, 169.4, 170.2. IR (CHCl3): 3307,
2964, 2934, 2875, 1751, 1646, 1526, 1432, 1380, 1269, 1152, 1128,
stirred for 0.5 h. HCl·Gd2PGGG-OCH2Ph (0.22 g, 0.43 mmol) in CH2-
Cl2 (10 mL) containing DIEA (0.08 mL) was added and the mixture
was stirred for 48 h at room temperature. The solvent was evaporated
and the residue was chromatographed (SiO2, 10-30% MeOH-CHCl3)
1048, 814, 739, 698 cm-1
.
1
to give 0.23 g (72%) of a white solid, mp 111-112 °C. H NMR:
32[DGA]-Gd2-OH. 32[DGA]-Gd2-OCH2Ph (0.16 g, 0.44 mmol) was
dissolved in abs EtOH (20 mL) and 10% Pd/C (0.10 g) was added,
and this mixture was shaken under 60 psi pressure of H2 for 3 h. The
reaction mixture was filtered (Celite pad). The solvent was evaporated
to afford a white solid (0.12 g, 100%), mp 87-89 °C. 1H NMR: 0.75-
0.95 (6H, m, -CH2CH3), 1.45-1.65 (4H, m, CH3CH2CH2N), 3.05 (2H,
t, J ) 7.8 Hz, CH3CH2CH2N), 3.24 (2H, t, J ) 7.8 Hz, CH3CH2CH2N),
4.08 (2H, s, COCH2O), 4.25 (2H, s, COCH2O), 7.87 (1H, pseudo-s,
Gly NH), 10.26 (1H, bs, COOH). 13C NMR: 11.0, 11.1, 20.5, 21.7,
40.1, 47.8, 48.4, 68.9, 70.7, 168.6, 170.1, 171.3. IR (CHCl3): 3361,
2966, 2936, 2877, 1744, 1642, 1535, 1467, 1435, 1382, 1344, 1244,
0.80-0.96 (6H, m, -CH2CH3), 1.40-1.60 (4H, m, CH3CH2CH2N),
1.90-2.25 (4H, m, Pro NCH2CH2CH2), 3.04 (2H, t, J ) 7.5 Hz, CH3-
CH2CH2N), 3.24 (2H, t, J ) 7.5 Hz, CH3CH2CH2N), 3.45-3.65 (2H,
m, Pro NCH2CH2CH2), 3.75-4.20 (12H, overlapping signals due to
Gly NCH2, and COCH2O) 4.30 (2H, s, COCH2O), 4.33 (1H, t, J ) 6.6
Hz, and Pro NCH), 5.14-5.16 (2H, m, PhCH2O), 7.30-7.38 (5H, m,
HAr), 7.49 (1H, bt, Gly CONH), 7.55 (1H, bs, Gly CONH), 7.84-7.98
(3H, overlapping signals due to Gly CONH), 8.35 (1H, pseudo-s, Glyd2
NH). 13C NMR: 11.2, 11.4, 20.7, 21.9, 22.7, 25.1, 29.0, 29.7, 31.9,
41.2, 41.9, 42.7, 43.0, 43.4, 46.9, 47.8, 48.4, 61.3, 67.2, 69.4, 71.3,
128.3, 128.4, 128.6, 135.3, 168.7, 168.9, 170.2, 170.4, 170.8, 171.2,
173.5. IR (CHCl3): 3301, 2924, 2852, 1747, 1648, 1534, 1455, 1242,
1158, 1131, 1047, 901, 826, 732, 644 cm-1
.
BocGPGGG-OCH2Ph. Boc-glycine (0.16 g, 0.94 mmol), PGGG-
OCH2Ph‚HCl (0.39 g, 0.94 mmol), and NMM (0.12 mL) were dissolved
in CH2Cl2 (30 mL) and cooled to 5 °C. EDCI (0.20 g, 1.04 mmol) and
HOBt (0.14 g, 1.04 mmol) were added and the reaction was stirred at
room temperature overnight. The solvent was evaporated, and the
residue was dissolved in CHCl3 (50 mL); washed with 5% citric acid
(2 × 25 mL), 5% NaHCO3 (2 × 25 mL), and brine (25 mL); dried
over MgSO4; and evaporated to afford a white solid (0.47 g, 90%), mp
1192, 1128, 1031, 736 cm-1
.
[2-(2-{[1-(2-{2-[2-(2-Dipropylcarbamoylmethoxyacetylamino)-
acetylamino]dideuterioacetylamino}acetyl)pyrrolidine-2-carbonyl]-
amino}acetylamino)acetylamino]acetic Acid Benzyl Ester, 3, 32-
[DGA]-G-Gd2-GPGGG-OCH2Ph. 32[DGA]-G-OCH2Ph. To dipropyl-
carbamoylmethoxyacetic acid (0.5 g, 2.3 mmol) dissolved in CH2Cl2
(30 mL) were added EDCI (0.48 g, 2.5 mmol) and HOBt (0.34 g, 2.5
mmol, at 5 °C, ice bath). The mixture was stirred at room temperature.
After 0.5 h, TsOH·G-OCH2Ph (0.78 g, 2.3 mmol) and Et3N (1 mL)
were added, and the mixture was stirred at room temperature for 48 h.
The solvent was evaporated and the residue was dissolved in EtOAc
(40 mL). The mixture was successively washed with 5% citric acid (2
× 20 mL), 5% NaHCO3 (2 × 20 mL), and brine (20 mL); dried
1
80-81 °C. H NMR: 1.41 (9H, s, C(CH3)3), 1.80-2.15 (4H, m, Pro
NCH2CH2CH2), 3.40-3.55 (2H, m, Pro NCH2CH2CH2), 3.75-4.20
(8H, overlapping sigmals due to Gly NCH2), 4.35 (1H, t, J ) 6.6 Hz,
Pro NCH), 5.10-5.14 (2H, m, PhCH2O), 5.67 (1H, t, J ) 5.7 Hz, Gly
CONH), 7.23 (1H, bs, Gly CONH), 7.30-7.36 (5H, m, HAr), 7.65 (1H,
t, J ) 5.7 Hz, Gly CONH), 7.83 (1H, t, J ) 5.7 Hz, Gly CONH). 13C
NMR: 25.1, 28.3, 28.6, 41.1, 42.8, 43.0, 43.5, 46.7, 60.9, 67.0, 79.8,
128.2, 128.4, 128.5, 135.3, 156.5, 169.6, 169.7, 169.8, 169.9, 173.2.
IR (CHCl3): 3311, 2978, 1750, 1533, 1454, 1410, 1392, 1366, 1250,
1
(MgSO4); and evaporated to afford a colorless oil (0.67 g, 80%). H
NMR: 0.80-0.95 (6H, m, -CH2CH3), 1.50-1.65 (4H, m, CH3CH2-
CH2N), 3.06 (2H, t, J ) 7.8 Hz, CH3CH2CH2N), 3.27 (2H, t, J ) 7.8
Hz, CH3CH2CH2N), 4.08-4.55 (4H, overlapping signals due to Gly
NCH2 and COCH2O), 4.27 (2H, s, COCH2O), 5.16 (2H, s, PHCH2O),
7.30-7.36 (5H, m, HAr), 8.18 (1H, bt, Gly CONH). 13C NMR: 11.1,
11.3, 20.7, 22.0, 40.7, 47.7, 48.4, 66.9, 69.5, 71.6, 128.3, 128.4, 128.5,
135.3, 168.3, 169.4, 170.2. IR (CHCl3): 3307, 2964, 2934, 2875, 1752,
1175, 1030, 919, 866, 732, 698 cm-1
.
HCl‚GPGGG-OCH2Ph. Boc-GPGGG-OCH2Ph (0.35 g, 0.65 mmol)
was dissolved in 4 N HCl in dioxane (5 mL) at 5 °C and the reaction
mixture was stirred for 0.5 h. The solvent was evaporated in vacuo.
The product was used in the subsequent reaction without further
purification.
1646, 1531, 1456, 1432, 1383, 1357, 1237, 1189, 1128, 740, 698 cm-1
.
32[DGA]-G-OH. 32[DGA]-G-OCH2Ph (0.66 g, 1.81 mmol) was
dissolved in abs EtOH (30 mL), 10% Pd/C (0.10 g) was added, and
the mixture was shaken under 60 psi pressure of H2 for 3 h. The mixture
was filtered (Celite pad). The solvent was evaporated to afford a white
BocGGPGGG-OCH2Ph. Boc-glycine (0.14 g, 0.81 mmol), GPGGG-
OCH2Ph‚HCl (0.38 g, 0.81 mmol), and NMM (0.10 mL) were dissolved
in CH2Cl2 (30 mL) and cooled to 5 °C. EDCI (0.17 g, 0.89 mmol) and
HOBt (0.12 g, 0.89 mmol) were added, and the mixture was stirred at
room temperature overnight. Solvent was evaporated, and the residue
was dissolved in CHCl3 (30 mL); washed with 5% citric acid (2 × 25
mL), 5% NaHCO3 (2 × 25 mL), and brine (25 mL); dried over MgSO4;
and then evaporated to afford a white solid (0.32 g, 68%), mp 68-69
°C. 1H NMR: 1.42 (9H, s, C(CH3)3), 1.90-2.30 (4H, m, Pro
NCH2CH2CH2), 3.40-4.25 (12H, overlapping signals due to Gly NCH2
and Pro NCH2CH2CH2), 4.32 (1H, t, J ) 6.6 Hz, Pro NCH), 5.05-
5.15 (2H, m, PhCH2O), 5.90 (1H, bs, Gly CONH), 7.30-7.40 (6H,
overlapping signals due to HAr and Gly CONH), 7.60 (1H, bs, Gly
CONH), 7.72 (1H, bs, Gly CONH), 8.00 (1H, bs, Gly CONH). 13C
NMR: 25.1, 28.3, 28.9, 41.2, 41.9, 42.8, 43.5, 43.9, 46.9, 61.3, 67.2,
128.2, 128.4, 128.6, 135.2, 156.1, 170.0, 170.5, 170.8, 173.2. IR
(CHCl3): 3309, 2978, 2933, 1750, 1659, 1531, 1455, 1410, 1392, 1367,
1
solid (0.50 g, 100%), mp 87-89 °C. H NMR: 0.80-1.00 (6H, m,
-CH2CH3), 1.45-1.65 (4H, m, CH3CH2CH2N), 3.07 (2H, t, J ) 7.8
Hz, CH3CH2CH2N), 3.27 (2H, t, J ) 7.8 Hz, CH3CH2CH2N), 4.07 (2H,
d, J ) 5.7 Hz, Gly NCH2), 4.11 (2H, s, COCH2O), 4.27 (2H, s,
COCH2O), 7.88 (1H, t, J ) 5.7 Hz, Gly CONH), 11.40 (1H, bs, COOH).
13C NMR: 11.1, 11.2, 20.6, 21.8, 40.6, 47.9, 48.5, 68.9, 70.9, 168.7,
170.0, 171.6. IR (CHCl3): 3352, 2966, 2936, 2877, 1741, 1644, 1540,
1466, 1433, 1383, 1343, 1238, 1207, 1130, 1041, 893, 816, 748 cm-1
.
BocGd2GPGGG-OCH2Ph. Boc-glycine-2,2-d2 (0.12 g, 0.67 mmol),
GPGGG-OCH2Ph·HCl (0.31 g, 0.67 mmol), and NMM (0.10 mL) were
dissolved in CH2Cl2 (30 mL) and cooled to 5 °C. EDCI (0.13 g, 0.68
mmol) and HOBt (0.01 g, 0.70 mmol) were added, and the reaction
was stirred at room temperature overnight. Solvent was evaporated,
and the residue was dissolved in CHCl3 (50 mL); washed with 5%
citric acid (2 × 25 mL), 5% NaHCO3 (2 × 25 mL), and brine (25
mL); dried over MgSO4; and evaporated to afford a white solid (0.32
g, 82%), mp 67-69 °C. 1H NMR: 1.421 (9H, s, C(CH3)3), 1.90-2.20
(4H, m, Pro NCH2CH2CH2), 3.45-3.60 (2H, m, Pro NCH2CH2CH2),
3.75-4.25 (8H, overlapping signals due to Gly NCH2), 4.32 (1H, t, J
) 6.6 Hz, Pro NCH), 5.10-5.14 (2H, m, PhCH2O), 5.89 (1H, pseudo-
s, Glyd2 CONH), 7.30-7.38 (6H, overlapping signals due to HAr and
Gly CONH), 7.60 (1H, bs, Gly CONH), 7.80 (1H, t, J ) 5.7 Hz, Gly
1332, 1249, 1175, 1029, 912, 732, 698 cm-1
.
HCl·GGPGGG-OCH2Ph. Boc-GGPGGG-OCH2Ph (0.25 g, 0.43
mmol) was dissolved in 4 N HCl in dioxane (5 mL) at 5 °C and the
reaction mixture was stirred for 0.5h. The solvent was evaporated in
vacuo. The product was used in the subsequent reaction without further
purification.
32[DGA]-Gd2GGPGGG-OCH2Ph. To 32[DGA]-Gd2-OH (0.12 g,
0.43 mmol) suspended in CH2Cl2 (20 mL) were added PyBroP (0.13
g, 0.47 mmol) and HOBt (0.06 g, 0.47 mmol), and the reaction was
9
J. AM. CHEM. SOC. VOL. 127, NO. 51, 2005 18289

A R T I C L E S
Pajewski et al.
CONH), 8.01 (1H, t, J ) 5.7 Hz, Gly CONH). 13C NMR: 25.1, 28.3,
28.9, 41.1, 41.8, 42.7, 43.5, 46.9, 61.2, 67.1, 79.9, 128.2, 128.4, 128.6,
135.2, 156.3, 168.6, 169.9, 170.4, 170.7, 173.3. IR (CHCl3): 3310,
3070, 2978, 2934, 1751, 1660, 1534, 1455, 1410, 1392, 1367, 1334,
5.7 Hz, Gly CONH). 13C NMR: 11.1, 11.3, 20.7, 22.0, 41.1, 42.6, 47.8,
48.3, 67.0, 69.6, 71.9, 128.2, 128.4, 128.6, 135.2, 168.5, 169.5, 170.5.
IR (CHCl3): 3315, 2964, 2934, 1750, 1651, 1532, 1457, 1432, 1384,
1358, 1271, 1238, 1189, 1128, 1032, 958, 815, 741, 698 cm-1
.
1252, 1190, 1120, 1074, 1031, 912, 732, 698 cm-1
.
32[DGA]-GG-OH. 32[DGA]-GG-OCH2Ph (1.57 g, 3.72 mmol) was
dissolved in abs EtOH (30 mL), 10% Pd/C (0.20 g) was added, and
this mixture was shaken under 60 psi pressure of H2 for 3 h. The
reaction mixture was filtered (Celite pad). The solvent was evaporated.
The crude product was crystallized from a mixture of MeOH-ethyl
ether (1:1 v/v) to afford a white solid (1.18 g, 96%), mp 129-131 °C.
1H NMR 5% CD3OD-CDCl3: 0.75-0.90 (6H, m, -CH2CH3), 1.40-
1.60 (4H, m, CH3CH2CH2N), 3.03 (2H, t, J ) 7.8 Hz, CH3CH2CH2N),
3.20 (2H, t, J ) 7.8 Hz, CH3CH2CH2N), 3.92 (2H, d, J ) 3.9 Hz, Gly
NCH2), 3.98 (2H, d, J ) 3.9 Hz, Gly NCH2), 4.04 (2H, s, COCH2O),
4.25 (2H, s, COCH2O), 6.42 (1H, bs, COOH), 7.66 (1H, t, J ) 3.9 Hz,
Gly CONH), 8.20 (1H, t, J ) 3.9 Hz, Gly CONH). 13C NMR: 10.9,
11.1, 17.9, 20.5, 21.7, 41.0, 42.1, 47.7, 48.3, 57.8, 70.0, 70.8, 168.6,
169.7, 170.7, 171.4. IR (CHCl3): 3319, 2962, 1722, 1667, 1645, 1600,
1554, 1466, 1415, 1342, 1295, 1256, 1219, 1157, 1129, 1045, 982,
HCl·Gd2GPGGG-OCH2Ph. Boc-Gd2GPGGG-OCH2Ph (0.35 g,
0.65 mmol) was dissolved in 4N HCl/dioxane (5 mL) at 5 °C and the
reaction mixture was stirred for 0.5 h. The solvent was evaporated in
vacuo. The product was used in the subsequent reaction without further
purification.
32[DGA]-GGd2GPGGG-OCH2Ph. To 32[DGA]-G-OH (0.13 g,
0.49 mmol) suspended in CH2Cl2 (20 mL) were added PyBroP (0.25
g, 0.54 mmol) and HOBt (0.07 g, 0.52 mmol), and the mixture was
stirred for 0.5 h. Then HCl‚Gd2PGGG-OCH2Ph (0.26 g, 0.49 mmol)
in CH2Cl2 (10 mL) containing DIEA (0.1 mL) was added and the
mixture was stirred for 48 h at room temperature. The solvent was
evaporated and the residue was chromatographed (SiO2, 10-30%
MeOH-CHCl3) to give 0.32 g (87%) of pure product as a white solid,
1
mp 111-112 °C. H NMR: 0.80-0.96 (6H, m, -CH2CH3), 1.40-
935, 879, 811, 759, 738, 659 cm-1
.
1.60 (4H, m, CH3CH2CH2N), 1.90-2.25 (4H, m, Pro NCH2CH2CH2),
3.05 (2H, t, J ) 7.5 Hz, CH3CH2CH2N), 3.24 (2H, t, J ) 7.5 Hz, CH3-
CH2CH2N), 3.45-4.20 (13H, overlapping signals due to Gly NCH2,
Pro NCH2CH2CH2, and Pro NCH), 4.11 (2H, s COCH2O), 4.31 (2H, s,
COCH2O), 5.14-5.16 (2H, m, PhCH2O), 7.30-7.38 (5H, m, HAr), 7.40
(1H, bt, Gly CONH), 7.42 (1H, bt, Gly CONH), 7.66 (1H, bt, Gly
CONH), 7.86-7.94 (2H, overlapping signals due to Gly CONH), 8.33
(1H, bt, Gly CONH). 13C NMR: 11.2, 11.4, 20.7, 21.9, 25.1, 29.0,
41.2, 42.7, 42.8, 42.9, 43.5, 46.9, 47.8, 48.4, 61.2, 67.2, 69.5, 71.4,
128.31, 128.4, 128.6, 135.3, 168.6, 168.8, 170.0, 170.1, 170.3, 170.4,
171.1, 173.6. IR (CHCl3): 3301, 2964, 1750, 1648, 1535, 1437, 1241,
1192, 1128, 1030, 733 cm-1. Anal. Calcd for C34H48N8O11‚H2O: C,
53.25; H, 7.10; N, 14.61. Found: C, 53.31; H, 7.08; N, 14.63.
[2-(2-{[1-(2-{2-[2-(2-Dipropylcarbamoylmethoxyacetylamino)-
acetylamino]acetylamino}dideuterioacetyl)pyrrolidine-2-carbonyl]-
amino}acetylamino)acetylamino]acetic Acid Benzyl Ester, 4, 32-
[DGA]-GG-Gd2-PGGG-OCH2Ph. TsOH‚GG-OCH2Ph. H-(Gly)2OH
(5.0 g, 37.9 mmol) and p-toluenesulfonic acid monohydrate (7.9 g, 41.6
mmol) were added to a mixture of benzyl alcohol (45 mL) and toluene
(70 mL). The mixture was heated to reflux and water was removed by
using a Dean-Stark trap. When no more water appeared in the distillate
(after 8 h), heating was stopped. The mixture was cooled to room
temperature, diluted with ether (50 mL), and cooled in an ice water
bath for 2 h. The crystalline p-toluenesulfonate of GG-OCH2Ph was
collected on a filter, washed with ether (50 mL), dried, and recrystallized
from MeOH-ether (11.72 g, 78%), mp 157-159 °C. 1H NMR (CD3-
OD): 2.34 (3H, s, CH3Ph), 3.72 (2H, s, Gly NCH2), 4.05 (2H, s, Gly
NCH2), 5.16 (2H, s, PHCH2O), 7.21 (2H, d, J ) 8.4 Hz, tosyl HAr),
7.30-7.35 (5H, m, Ph HAr), 7.69 (2H, d, J ) 8.4 Hz, tosyl HAr). 13C
NMR: 21.4, 41.6, 42.1, 68.2, 127.3, 129.6, 129.7, 129.9, 130.1, 130.2,
137.4, 168.3, 171.3. IR (KBr): 3332, 3081, 1747, 1671, 1544, 1455,
BocGd2PGGG-OCH2Ph. Boc-glycine-2,2-d2 (0.11 g, 0.63 mmol),
PGGG-OCH2Ph‚HCl (0.26 g, 0.63 mmol), and NMM (0.10 mL) were
dissolved in CH2Cl2 (30 mL) and cooled to 5 °C. EDCI (0.13 g, 0.68
mmol) and HOBt (0.09 g, 0.67 mmol) were added, and the reaction
was stirred at room temperature overnight. Solvent was evaporated and
the residue was dissolved in CHCl3 (50 mL); washed with 5% citric
acid (25 mL), 5% NaHCO3 (25 mL), and brine (25 mL); dried over
MgSO4; and evaporated to afford a white solid (0.30 g, 89%), mp 80-
1
81 °C. H NMR: 1.42 (9H, s, C(CH3)3), 1.80-2.10 [4H, m, (Pro)-
NCH2CH2CH2], 3.45-3.60 (2H, m, Pro NCH2CH2CH2), 3.80-4.20
(6H, overlapping signals due to Gly NCH2), 4.35 [1H, t, J ) 6.6 Hz,
(Pro)NCH], 5.15-5.20 (2H, m, PhCH2O), 5.57 (1H, pseudo-s, Glyd2
CONH), 7.11 (1H, bs, Gly CONH), 7.30-7.35 (5H, m, HAr), 7.50 (1H,
bs, Gly CONH), 7.80 (1H, bs, Gly CONH). 13C NMR: 25.4, 28.5,
28.8, 41.3, 43.0, 43.8, 47.0, 61.3, 67.3, 80.2, 128.5, 128.6, 128.8, 135.5,
156.8, 169.9, 170.2, 173.3. IR (CHCl3): 3310, 2978, 29.35, 1750, 1651,
15278, 1447, 1392, 1366, 1252, 1176, 1082, 1067, 1030, 919, 733 cm-1
.
HCl·Gd2PGGG-OCH2Ph. Boc-Gd2PGGG-OCH2Ph (0.24 g, 0.45
mmol) was dissolved in 4 N HCl in dioxane (5 mL) at 5 °C and the
reaction mixture was stirred for 0.5 h. The solvent was evaporated in
vacuo. The product was used in the subsequent reaction without further
purification.
32[DGA]-GGGd2PGGG-OCH2Ph. To 32[DGA]-GG-OH (0.15 g,
0.45 mmol) suspended in CH2Cl2 (20 mL) were added PyBroP (0.23
g, 0.49 mmol) and HOBt (0.07 g, 0.52 mmol), and the reaction was
stirred for 0.5 h. Then HCl·Gd2PGGG-OCH2Ph (0.21 g, 0.45 mmol)
in CH2Cl2 (10 mL) containing DIEA (0.09 mL) was added and the
reaction mixture was stirred for 48 h at room temperature. The solvent
was evaporated and the residue was chromatographed (SiO2, 10-30%
MeOH-CHCl3) to give 0.26 g (79%) of pure product as a white solid,
1407, 1363, 1202, 1126, 1034, 1011, 912, 736, 685 cm-1
.
1
mp 111-112 °C. H NMR: 0.75-0.90 (6H, m, -CH2CH3), 1.40-
32[DGA]-GG-OCH2Ph. To dipropylcarbamoylmethoxyacetic acid
(1 g, 4.60 mmol) dissolved in CH2Cl2 (30 mL) were added EDCI (0.90
g, 4.69 mmol) and HOBt (0.63 g, 4.66 mmol) (at 5 °C, ice bath), and
the mixture was stirred at room temperature. After 0.5 h, TsOH·GG-
OCH2Ph (1.81 g, 4.6 mmol) and NMM (0.8 mL) were added, and the
reaction mixture was stirred at room temperature overnight. The solvent
was evaporated and the residue was dissolved in EtOAc (50 mL). The
mixture was successively washed with 5% citric acid (2 × 20 mL),
5% NaHCO3 (2 × 20 mL), and brine (20 mL); dried (MgSO4); and
1.60 (4H, m, CH3CH2CH2N), 1.85-2.20 (4H, m, Pro NCH2CH2CH2),
3.02 (2H, t, J ) 7.5 Hz, CH3CH2CH2N), 3.24 (2H, t, J ) 7.5 Hz, CH3-
CH2CH2N), 3.40-3.45 (1H, m, Pro NCH2CH2CH2), 3.55-4.10 (13H,
overlapping signals due to Gly NCH2, Pro NCH2CH2CH2, and Pro
NCH), 4.11 (2H, s COCH2O), 4.31 (2H, s, COCH2O), 5.15 (2H, d, J
) 5.1 Hz, PhCH2O), 7.30-7.38 (5H, m, HAr), 7.39 (1H, pseudo-s, Glyd2
CONH), 7.48 (1H, bt, Gly CONH), 7.72 (1H, bt, Gly CONH), 7.84
(1H, bt, Gly CONH), 7.91 (1H, bt, Gly CONH), 8.31 (1H, bt, Gly
CONH). 13C NMR: 11.1, 11.3, 20.7, 21.8, 25.0, 29.1, 41.2, 42.2, 42.6,
42.7, 42.8, 43.2, 46.8, 47.7, 48.3, 61.2, 67.1, 69.2, 70.1, 128.2, 128.3,
128.6, 135.3, 168.7, 168.8, 170.2, 170.3, 170.4, 170.9, 171.2, 173.6.
IR (CHCl3): 3303, 2966, 2936, 1750, 1649, 1534, 1437, 1241, 1191,
1129, 1030, 843, 731, 699 cm-1. Anal. Calcd for C34H48N8O11·H2O:
C, 53.25; H, 7.10; N, 14.61. Found: C, 53.33; H, 7.07; N, 14.51.
1
evaporated to afford a colorless oil (1.60 g, 82%). H NMR: 0.80-
0.95 (6H, m, -CH2CH3), 1.45-1.60 (4H, m, CH3CH2CH2N), 3.04 (2H,
t, J ) 7.8 Hz, CH3CH2CH2N), 3.22 (2H, t, J ) 7.8 Hz, CH3CH2CH2N),
4.00-4.05 (4H, overlapping signals due to Gly NCH2), 4.10 (2H, s,
COCH2O), 4.30 (2H, s, COCH2O), 5.15 (2H, s, PHCH2O), 7.30-7.40
(5H, m, HAr), 7.52 (1H, t, J ) 5.7 Hz, Gly CONH), 8.22 (1H, t, J )
9
18290 J. AM. CHEM. SOC. VOL. 127, NO. 51, 2005

Open-Chained Peptides as Anion-Complexing Agents
A R T I C L E S
[2-(2-{[1-(2-{2-[2-(2-Dipropylcarbamoylmethoxyacetylamino)-
acetylamino]acetylamino}acetyl)pyrrolidine-2-carbonyl]amino}-
dideuterioacetylamino)acetylamino]acetic Acid Benzyl Ester, 5,
32[DGA]-GGGP-Gd2-GG-OCH2Ph. 32[DGA]-GGG-OCH2Ph. To a
solution of 32[DGA] (0.5 g, 2.3 mmol) in CH2Cl2 (30 mL) cooled to 5
°C were added EDCI (0.48 g, 2.5 mmol), HOBt (0.34 g, 2.5 mmol),
TsOH‚GGG-OCH2Ph (1.0 g, 2.3 mmol), and Et3N (1.0 mL), and the
reaction was stirred at room temperature for 2 days. The reaction was
quenched and washed with a saturated solution of citric acid (20 mL),
a saturated solution of NaHCO3 (20 mL), and water (20 mL). The
organic phase was then dried over MgSO4 and evaporated, and the
residue was purified by column chromatography (silica, 0-3% MeOH
in CHCl3) to give the pure final product (0.87 g, 79%) as a deliquescent
solid. 1H NMR: 0.89 (6H, m, -CH2CH3), 1.40-1.60 (4H, m, CH3CH2-
CH2N), 3.04 (2H, t, J ) 7.5 Hz, CH3CH2CH2N), 3.23 (2H, t, J ) 7.5
Hz, CH3CH2CH2N), 3.98-4.06 (6H, overlapping signals due to Gly
NCH2), 4.09 (2H, s, COCH2O), 4.33 (2H, s, COCH2O), 5.14 (2H, s,
PhCH2O), 7.04 (1H, t, J ) 5.7 Hz, Gly CONH), 7.32 (5H, m, HAr),
7.95 (1H, t, J ) 5.7 Hz, Gly CONH), 8.22 (1H, t, J ) 5.7 Hz, Gly
CONH). 13C NMR: 11.2, 11.3, 20.7, 21.9, 41.1, 43.1, 48.0, 48.4, 67.0,
69.8, 72.0, 128.2, 128.4, 128.6, 135.3, 168.7, 169.46, 169.55, 169.9,
171.5. IR (CHCl3): 3307, 2966, 2935, 1748, 1652, 1540, 1457, 1360,
3313, 2977, 2934, 1751, 1669, 1534, 1455, 1404, 1367, 1248, 1172,
1128, 1029, 742, 699 cm-1
.
HCl·PGd2GG-OCH2Ph. Boc-PGd2GG-OCH2Ph (0.19 g, 0.40 mmol)
was dissolved in 4 N HCl in dioxane (5 mL) at 5 °C, and the reaction
mixture was stirred for 0.5 h. The solvent was evaporated in vacuo.
The product was used in the subsequent reaction without further
purification.
32[DGA]-GGGPGd2GG-OCH2Ph. To 32[DGA]-GGG-OH (0.16 g,
0.41 mmol) suspended in CH2Cl2 (20 mL) were added PyBroP (0.21
g, 0.44 mmol) and HOBt (0.06 g, 0.44 mmol), and the reaction was
stirred for 0.5 h. Then HCl‚PGd2GG-OCH2Ph (0.16 g, 0.40 mmol) in
CH2Cl2 (10 mL) containing DIEA (0.08 mL) was added, and the
reaction mixture was stirred for 48 h at room temperature. The solvent
was evaporated and the residue was chromatographed (SiO2, 10-30%
MeOH-CHCl3) to give 0.24 g (80%) of pure product as a white solid,
1
mp 111-112 °C. H NMR: 0.80-0.95 (6H, m, -CH2CH3), 1.45-
1.65 (4H, m, CH3CH2CH2N), 1.85-2.20 (4H, m, Pro NCH2CH2CH2),
3.05 (2H, t, J ) 7.5 Hz, CH3CH2CH2N), 3.24 (2H, t, J ) 7.5 Hz, CH3-
CH2CH2N), 3.45-3.65 (2H, m, Pro NCH2CH2CH2), 3.75-4.20 (12H,
overlapping signals due to Gly NCH2, Pro and COCH2O), 4.29 (2H, s,
COCH2O), 4.35 (1H, t, J ) 6.5 Hz, Pro NCH), 5.15 (2H, m, PhCH2O),
7.30-7.38 (5H, m, HAr), 7.50 (2H, bs, Gly CONH), 7.91 (1H, bt, Gly
CONH), 7.95 (1H, bt, Gly CONH), 7.99 (1H, pseudo-s, Glyd2 CONH),
8.37 (1H, bt, Gly CONH). 13C NMR: 11.1, 11.3, 20.7, 22.0, 25.1, 29.1,
29.7, 41.3, 41.9, 42.8, 42.9, 46.9, 47.8, 48.4, 61.2, 67.1, 69.4, 71.3,
128.2, 128.4, 128.6, 135.4, 168.7, 168.9, 170.1, 170.2, 170.3, 170.4,
170.8, 171.1. 173.5. IR (CHCl3): 3300, 2964, 2934, 1747, 1645, 1630,
1533, 1435, 1241, 1193, 1128, 1029, 698 cm-1. Anal. Calcd for
C34H48N8O11‚H2O: C, 53.25; H, 7.10; N, 14.61. Found: C, 53.27; H,
7.11; N, 14.53.
1241, 1194, 1129, 1032, 746, 699 cm-1
.
32[DGA]-GGG-OH. 32[DGA]-GGG-OCH2Ph (0.82 g, 1.7 mmol)
was dissolved in abs EtOH (30 mL), 10% Pd/C (0.1 g) was added, and
this mixture was shaken under 70 psi hydrogen pressure for 3 h in a
Parr apparatus. The reaction mixture was heated to reflux and filtrated
through a Celite pad. The solvent was evaporated to leave a white solid
in a quantitative yield (0.66 g), mp 177-178 °C. This product was
used in the subsequent reaction with no further purification.
[2-(2-{[1-(2-{2-[2-(2-Dipropylcarbamoylmethoxyacetylamino)-
acetylamino]acetylamino}acetyl)pyrrolidine-2-carbonyl]amino}-
acetylamino)dideuterioacetylamino]acetic Acid Benzyl Ester, 6,
32[DGA]-GGGPG-Gd2-G-OCH2Ph. BocPG-OCH2Ph. Boc-L-proline
(0.70 g, 3.25 mmol), TsOH‚G-O-CH2Ph (1.10 g, 3.25 mmol), and Et3N
(1.40 mL) were dissolved in CH2Cl2 (40 mL) and cooled to 5 °C. EDCI
(0.69 g, 3.60 mmol) and HOBt (0.49 g, 3.60 mmol) were added, and
the reaction was stirred at room temperature for 2 days. Solvent was
evaporated, and the residue was dissolved in EtOAc (50 mL); washed
with 5% citric acid (25 mL), 5% NaHCO3, and brine (25 mL); dried
over MgSO4; and evaporated to give a colorless oil (0.98 g, 83%). 1H
NMR: 1.45 (9H, s, C(CH3)3), 1.80-2.20 (4H, m, Pro NCH2CH2CH2),
3.35-3.55 (2H, m, Pro NCH2CH2CH2), 3.90-4.20 (2H, m, Gly NCH2),
4.32 (1H, bs, Pro NCH), 5.16 (2H, s, PhCH2O), 6.55 (1H, bs, Gly
CONH), 7.30-7.35 (5H, m, HAr). 13C NMR: 23.9, 24.6, 28.5, 31.0,
41.4, 47.2, 60.1, 61.1, 67.2, 80.5, 128.3, 128.4, 128.6, 135.1, 154.6,
169.5, 172.3. IR (CHCl3): 3317, 2976, 2881, 1752, 1698, 1531, 1479,
BocGd2GG-OCH2Ph. Boc-glycine-2,2-d2 (0.20 g, 1.13 mmol),
TsOH·GG-O-CH2Ph (0.45 g, 6.7 mmol), and NMM (0.14 mL) were
dissolved in CH2Cl2 (20 mL) and cooled to 5 °C. EDCI (0.24 g, 1.24
mmol) and HOBt (0.17 g, 1.24 mmol) were added, and the reaction
was stirred at room temperature for 48 h. Solvent was evaporated, and
the residue was dissolved in CHCl3 (50 mL); washed with 5% citric
acid (25 mL), 5% NaHCO3 (25 mL), and brine (25 mL); dried over
MgSO4; and evaporated to afford a white solid (0.37 g, 86%), mp 41-
1
42 °C. H NMR: 1.42 (9H, s, C(CH3)3), 4.00-4.20 (4H, overlapping
signals due to Gly NCH2), 5.15 (2H, s, PhCH2O), 5.45 (1H, bs, Gly
CONH), 7.19 (2H, overlapping signals due to Glyd2 CONH, and Gly
CONH), 7.30-7.40 (5H, m, HAr). 13C NMR: 20.2, 41.2, 42.8, 67.2,
80.4, 128.3, 128.5, 128.6, 135.1, 156.4, 169.3, 169.6, 170.4. IR
(CHCl3): 3317, 2978, 2934, 1749, 1662, 1530, 1456, 1392, 1367, 1278,
1253, 1175, 1074, 1031, 993, 735, 697 cm-1
.
HCl‚Gd2GG-OCH2Ph. Boc-Gd2GG-OCH2Ph (0.36 g, 0.94 mmol)
was dissolved in 4 N HCl in dioxane (5 mL) at 5 °C and the reaction
mixture was stirred for 0.5 h. The solvent was evaporated in vacuo.
The product was used in the subsequent reaction without further
purification.
1455, 1392, 1366, 1256, 1172, 1125, 975, 739, 698 cm-1
.
HCl·PG-OCH2Ph. Boc-PG-OCH2Ph (0.41 g, 1.13 mmol) was
dissolved in 4 N HCl in dioxane (5 mL) at 5 °C and the reaction mixture
was stirred for 0.5 h. The solvent was evaporated in vacuo. The product
was used in the subsequent reaction without further purification.
32[DGA]-GGGPG-OCH2Ph. 32[DGA]-GGG-OH (0.44 g, 1.13
mmol), HCl‚PG-O-CH2Ph (0.34 g, 1.13 mmol), and NMM (0.14 mL)
were dissolved in CH2Cl2 (20 mL) and cooled to 5 °C. EDCI (0.24 g,
1.24 mmol) and HOBt (0.17 g, 1.24 mmol) were added, and the reaction
was stirred at room temperature for 2 days. Solvent was evaporated,
and the residue was dissolved in CHCl3 (50 mL); washed with 5%
citric acid (25 mL), 5% NaHCO3, and brine (25 mL); dried over MgSO4;
BocPGd2GG-OCH2Ph. Boc-L-proline (0.20 g, 0.94 mmol), HCl‚
GGd2G-OCH2Ph (0.30 g, 0.94 mmol), and NMM (0.18 mL) were
dissolved in CH2Cl2 (20 mL) and cooled to 5 °C. EDCI (0.20 g, 1.03
mmol) and HOBt (0.14 g, 1.03 mmol) were added, and the reaction
was stirred at room temperature overnight. Solvent was evaporated,
and the residue was dissolved in ethyl acetate (50 mL); washed with
5% citric acid (25 mL), 5% NaHCO3 (25 mL), and brine (25 mL);
dried over MgSO4; and evaporated to afford white solid (0.19 g, 42%),
1
1
mp 54-55 °C. H NMR: 1.38 (9H, s, C(CH3)3), 1.80-2.20 (4H, m,
and evaporated to give colorless oil (0.70 g, 98%). H NMR: 0.80-
Pro NCH2CH2CH2), 3.35-3.55 (2H, m, Pro NCH2CH2CH2), 3.80-
4.20 (5H, overlapping signals due to Gly NCH2, and Pro NCH), 5.11
(2H, s, PhCH2O), 7.20-7.40 (6H, overlapping signals due to Gly
CONH, and HAr), 7.50 (1H, pseudo-s, Glyd2 CONH), 7.92 (1H, bt, Gly
CONH). 13C NMR: 24.5, 28.2, 29.5, 41.0, 42.8, 47.1, 60.5, 66.8, 80.6,
128.1, 128.3, 128.5, 135.2, 155.4, 169.3, 169.6, 173.9. IR (CHCl3):
0.95 (6H, m, -CH2CH3), 1.40-1.60 (4H, m, CH3CH2CH2N), 1.85-
2.10 (4H, m, Pro NCH2CH2CH2), 3.03 (2H, t, J ) 7.5 Hz, CH3-
CH2CH2N), 3.12-3.34 (2H, m, CH3CH2CH2N), 3.40-3.45 (1H, m,
Pro NCH2CH2CH2), 3.55-4.30 (13H, overlapping signals due to Gly
NCH2, Pro NCH2CH2CH2, and COCH2O), 4.45 (1H, t, J ) 6 Hz),
5.00-5.15 (2H, m, PhCH2O), 7.30-7.35 (5H, m, HAr), 7.47 (1H, t, J
9
J. AM. CHEM. SOC. VOL. 127, NO. 51, 2005 18291

A R T I C L E S
Pajewski et al.
) 5.7 Hz, Gly CONH), 7.82 (1H, t, J ) 5.7 Hz, Gly CONH), 7.93
(1H, t, J ) 5.7 Hz, Gly CONH), 8.05 (1H, t, J ) 5.7 Hz, Gly CONH).
13C NMR: 11.1, 11.3, 20.7, 21.9, 24.8, 29.1, 41.0, 41.1, 42.6, 42.8,
46.5, 47.6, 48.3, 60.2, 66.8, 69.4, 71.6, 128.2, 128.3, 128.5, 135.2, 168.2,
168.6, 170.1, 170.2, 170.4, 172.4. IR (CHCl3): 3308, 2965, 2935, 2876,
NaHCO3, and brine (25 mL); dried over MgSO4; and evaporated to
give colorless crystals (0.19 g, 67%), mp 60-61 °C. 1H NMR: 0.80-
0.95 (6H, m, -CH2CH3), 1.40-1.60 (4H, m, CH3CH2CH2N), 1.85-
2.10 (4H, m, Pro NCH2CH2CH2), 3.04 (2H, t, J ) 7.5 Hz, CH3-
CH2CH2N), 3.25 (2H, t, J ) 7.5 Hz, CH3CH2CH2N), 3.40-3.45 (1H,
m, Pro NCH2CH2CH2), 3.55-4.30 (15H, overlapping signals due to
Gly NCH2, Pro NCH2CH2CH2, and COCH2O), 4.44 (1H, t, J ) 6 Hz,
Pro NCH), 5.15 (2H, s, PhCH2O), 7.30-7.35 (5H, m, HAr), 7.38 (1H,
t, J ) 5.7 Hz, Gly CONH), 7.47 (1H, t, J ) 5.7 Hz, Gly CONH), 7.80
(2H, t, J ) 5.7 Hz, overlapping signals due to Gly CONH), 8.35 (1H,
t, J ) 5.7 Hz, Gly CONH). 13C NMR: 11.2, 11.4, 20.7, 21.9, 24.9,
29.0, 41.2, 42.0, 42.9, 43.1, 47.1, 47.9, 48.4, 61.1, 67.1, 69.6, 71.7,
128.1, 128.4, 128.6, 135.2, 168.7, 169.1, 169.9, 170.0, 170.2, 170.6,
171.5, 172.0. IR (CHCl3): 3308, 2965, 2935, 2876, 1749, 1650, 1534,
1748, 1648, 1534, 1454, 1339, 1241, 1187, 1028, 733, 698 cm-1
.
32[DGA]-GGGPG-OH. 32[DGA]-GGGPG-OCH2Ph (0.72 g, 1.14
mmol) was dissolved in abs EtOH (30 mL), 10% Pd/C (0.20 g) was
added, and this mixture was shaken under 60 psi hydrogen pressure
for 3 h in a Parr apparatus. The reaction mixture was heated to reflux
and filtrated through a Celite pad. The solvent was evaporated to leave
a white solid in a quantitative yield (0.62 g), mp 78-79 °C. This product
was used in the subsequent reaction with no further purification.
BocGd2-G-OCH2Ph. Boc-glycine-2,2-d2 (0.20 g, 1.13 mmol),
TsOH‚G-OCH2Ph (0.38 g, 1.13 mmol), and NMM (0.14 mL) were
dissolved in CH2Cl2 (30 mL) and cooled to 5 °C. EDCI (0.24 g, 1.24
mmol) and HOBt (0.17 g, 1.24 mmol) were added, and the reaction
was stirred at room temperature overnight. Solvent was evaporated,
and the residue was dissolved in EtOAc (50 mL); washed with 5%
citric acid (25 mL), 5% NaHCO3, and brine (25 mL); dried over MgSO4;
1454, 1340, 1240, 1028, 733, 698 cm-1
.
32[DGA]-GGGPGG-OH. 32[DGA]-GGGPGG-OCH2Ph (0.18 g,
0.26 mmol) was dissolved in abs EtOH (20 mL), 10% Pd/C (0.02 g)
was added, and this mixture was shaken under 60 psi hydrogen pressure
for 3 h in a Parr apparatus. The reaction mixture was heated to reflux
and filtrated through a Celite pad. The solvent was evaporated to leave
a white solid in a quantitative yield (0.16 g), mp 84-85 °C. 1H NMR:
0.80-0.95 (6H, m, -CH2CH3), 1.40-1.60 (4H, m, CH3CH2CH2N),
1.85-2.20 (4H, m, Pro NCH2CH2CH2), 3.07 (2H, t, J ) 7.5 Hz, CH3-
CH2CH2N), 3.24 (2H, t, J ) 7.5 Hz, CH3CH2CH2N), 3.40-3.50 (1H,
m, Pro NCH2CH2CH2), 3.55-4.20 (13H, overlapping signals due to
Gly NCH2, Pro NCH2CH2CH2, and COCH2O), 4.31 (2H, s, COCH2O),
4.41 (1H, bs, Pro NCH), 7.70 (1H, bs, Gly CONH), 7.76 (1H, bs, Gly
CONH), 7.99 (1H, bs, Gly CONH), 8.02 (1H, bs, Gly CONH), 8.26
(1H, bs, Gly CONH). 13C NMR: 11.1, 11.3, 20.7, 21.8, 24.9, 29.2,
41.1, 42.1, 42.7, 47.0, 47.8, 48.4, 61.2, 69.1, 70.8, 168.8, 169.0, 170.5,
170.6, 171.2, 172.3, 172.8. IR (CHCl3): 3305, 2966, 2935, 2877, 1735,
1
and evaporated to give a colorless oil (0.33 g, 87%). H NMR: 1.45
(9H, s, C(CH3)3), 4.10 (2H, d, J ) 5.4 Hz, Gly NCH2), 5.10 (1H,
pseudo-s, Glyd2 CONH), 5.17 (2H, s, PhCH2O), 6.62 (1H, bt, Gly
CONH), 7.30-7.40 (5H, m, HAr). 13C NMR: 28.3, 41.2, 67.3, 128.4,
128.6, 128.7, 135.0, 169.5, 169.7. IR (CHCl3): 3327, 2978, 1750, 1714,
1678, 1521, 1499, 1456, 1391, 1366, 1252, 1173, 1074, 737, 698 cm-1
.
HCl·Gd2-G-OCH2Ph. Boc-Gd2-G-OCH2Ph (0.19 g, 0.55 mmol) was
dissolved in 4 N HCl in dioxane (5 mL) at 5 °C and the reaction mixture
was stirred for 0.5 h. The solvent was evaporated in vacuo. The product
was used in the subsequent reaction without further purification.
32[DGA]-GGGPG-Gd2-G-OCH2Ph. To 32[DGA]-GGGPG-OH (0.30
g, 0.55 mmol) suspended in CH2Cl2 (20 mL) were added PyBroP (0.28
g, 0.61 mmol) and HOBt (0.08 g, 0.61 mmol), and the reaction was
stirred for 0.5 h. Then HCl·Gd2-G-OCH2Ph (0.14 g, 0.55 mmol) in
CH2Cl2 (10 mL) containing DIEA (0.11 mL) was added and the reaction
mixture was stirred for 48 h at room temperature. The solvent was
evaporated, and the residue was chromatographed (SiO2, 10-30%
MeOH-CHCl3) to give 0.34 g (83%) of pure product as a white solid,
1646, 1540, 1452, 1410, 1338, 1240, 1209, 1129, 1030, 909, 729 cm-1
.
32[DGA]-GGGPGG-Gd2-OCH2Ph. To 32[DGA]-GGGPGG-OH
(0.16 g, 0.26 mmol) suspended in CH2Cl2 (20 mL) were added PyBroP
(0.13 g, 0.29 mmol) and HOBt (0.04 g, 0.29 mmol), and the reaction
was stirred for 0.5 h. Then HCl·Gd2-OCH2Ph (0.5 g, 0.26 mmol) in
CH2Cl2 (10 mL) containing DIEA (0.05 mL) was added and the reaction
mixture was stirred for 48 h at room temperature. The solvent was
evaporated and the residue was chromatographed (SiO2, 10-30%
MeOH-CHCl3) to give 0.16 g (84%) of pure product as a white solid,
1
mp 111-112 °C. H NMR: 0.80-0.95 (6H, m, -CH2CH3), 1.40-
1.60 (4H, m, CH3CH2CH2N), 1.85-2.20 (4H, m, Pro NCH2CH2CH2),
3.04 (2H, t, J ) 7.5 Hz, CH3CH2CH2N), 3.23 (2H, t, J ) 7.5 Hz, CH3-
CH2CH2N), 3.40-3.45 (1H, m, Pro NCH2CH2CH2), 3.55-4.10 (11H,
overlapping signals due to Gly NCH2, Pro NCH2CH2CH2), 4.12 (2H,
s COCH2O), 4.30 (2H, s, COCH2O), 4.35 (1H, bs, Pro NCH), 5.12-
5.15 (2H, m, PhCH2O), 7.30-7.38 (5H, m, HAr), 7.49 (1H, bs, Gly
CONH), 7.54 (1H, bs, Gly CONH), 7.86 (1H, pseudo-s, Glyd2 CONH),
7.88 (1H, bs, Gly CONH), 7.91 (1H, bs, Gly CONH), 8.34 (1H, bs,
Gly CONH). 13C NMR: 11.1, 11.3, 20.7, 21.8, 25.0, 29.1, 41.2, 41.9,
42.6, 42.8, 43.2, 46.8, 47.7, 48.3, 61.3, 67.1, 69.2, 70.9, 128.2, 128.3,
128.6, 135.3, 168.7, 168.9, 169.7, 170.3, 170.4, 170.5, 170.9, 171.2,
173.7. IR (CHCl3): 3301, 2966, 2935, 1749, 1653, 1535, 1455, 1408,
1241, 1193, 1129, 1029, 914, 844, 732 cm-1. Anal. Calcd for
C34H48N8O11·H2O: C, 53.25; H, 7.10; N, 14.61. Found: C, 53.31; H,
7.08; N, 14.63.
1
mp 111-112 °C. H NMR: 0.80-0.95 (6H, m, -CH2CH3), 1.40-
1.60 (4H, m, CH3CH2CH2N), 1.85-2.20 (4H, m, Pro NCH2CH2CH2),
3.05 (2H, t, J ) 7.5 Hz, CH3CH2CH2N), 3.24 (2H, t, J ) 7.5 Hz, CH3-
CH2CH2N), 3.40-3.45 (1H, m, Pro NCH2CH2CH2), 3.55-4.20 (13H,
overlapping signals due to Gly NCH2, Pro NCH2CH2CH2, and
COCH2O), 4.31 (2H, s, COCH2O), 4.35 (1H, bs, Pro NCH), 5.12-
5.15 (2H, m, PhCH2O), 7.30-7.38 (5H, m, HAr), 7.45 (1H, bs, Gly
CONH), 7.72 (1H, pseudo-s, Glyd2 CONH), 7.90 (2H, overlapping
signals due to Gly CONH), 8.36 (1H, bt, Gly CONH). 13C NMR: 11.1,
11.3, 20.6, 21.8, 25.0, 29.1, 41.2, 41.8, 42.6, 42.8, 43.2, 46.8, 47.7,
48.3, 61.2, 67.1, 69.1, 70.9, 128.2, 128.3, 128.5, 135.3, 168.7, 168.9,
169.7, 170.3, 170.5, 170.6, 171.0, 171.1, 173.7. IR (CHCl3): 3300,
2965, 1748, 1654, 1533, 1455, 1408, 1240, 1191, 1130, 1029, 915,
843, 732. Anal. Calcd for C34H48N8O11‚H2O: C, 53.25; H, 7.10; N,
14.61. Found: C, 53.16; H, 7.11; N, 14.53.
[2-(2-{[1-(2-{2-[2-(2-Dipropylcarbamoylmethoxyacetylamino)-
acetylamino]acetylamino}acetyl)pyrrolidine-2-carbonyl]amino}-
acetylamino)acetylamino]dideuterioacetic Acid Benzyl Ester, 7,
32[DGA]-GGGPGG-Gd2-OCH2Ph. 32[DGA]-GGGPGG-OCH2Ph.
32[DGA]-GGGPG-OH (0.22 g, 0.41 mmol), TsOH‚G-O-CH2Ph (0.14
g, 0.41 mmol), and NMM (0.05 mL) were dissolved in CH2Cl2 (20
mL) and cooled to 5 °C. EDCI (0.09 g, 0.45 mmol) and HOBt (0.06
g, 0.45 mmol) were added, and the reaction was stirred at room
temperature overnight. Solvent was evaporated, and the residue was
dissolved in CHCl3 (50 mL); washed with 5% citric acid (25 mL), 5%
[2-(2-{[1-(2-{2-[2-(2-Didecylcarbamoylmethoxyacetylamino)-
acetylamino]acetylamino}acetyl)pyrrolidine-2-carbonyl]amino}-
acetylamino)acetylamino]acetic acid benzyl ester, 8, was prepared
as previously reported.31
[2-(2-{[1-(2-{2-[2-(2-Dioctadecylcarbamoylmethoxyacetylamino)-
acetylamino]acetylamino}acetyl)pyrrolidine-2-carbonyl]amino}-
acetylamino)acetylamino]acetic acid benzyl ester, 9, was prepared
as previously reported.31
9
18292 J. AM. CHEM. SOC. VOL. 127, NO. 51, 2005

Open-Chained Peptides as Anion-Complexing Agents
A R T I C L E S
[2-(2-{[1-(2-{2-[2-(2-Dioctadecylcarbamoylmethoxyacetylamino)-
acetylamino]acetylamino}acetyl)pyrrolidine-2-carbonyl]amino}-
acetylamino)acetylamino]acetic acid ethyl ester, 10, was prepared
as previously reported.49
[2-(2-{[1-(2-{2-[2-(2-Dioctadecylcarbamoylmethoxyacetylamino)-
acetylamino]acetylamino}acetyl)pyrrolidine-2-carbonyl]amino}-
acetylamino)acetylamino]acetic acid heptyl ester, 11, was prepared
as previously reported.33
s, COCH2O), 4.38 (2H, s, COCH2O). 13C NMR: 14.2, 22.8, 26.9, 27.0,
27.5, 28.7, 29.4, 29.5, 29.6, 29.7, 29.8, 32.0, 47.0, 71.4, 73.2, 171.0,
172.2. IR (KBr): 2918, 2850, 1748, 1602, 1488, 1472, 1463, 1431,
1356, 1224, 1159, 1135, 1045, 1013, 990, 920, 885, 729, 720, 689,
643 cm-1
.
182[DGA]-GGG-OCH2Ph. To dioctadecylcarbamoylmethoxyacetic
acid (1 g, 1.5 mmol) dissolved in CH2Cl2 (30 mL) was added EDCI
(0.31 g, 1.6 mmol) and the mixture was stirred at room temperature.
After 0.5 h, TsOH·GGG-OCH2Ph (0.66 g, 1.5 mmol) and Et3N (0.6
mL) were added, and the reaction mixture was stirred at room
temperature overnight. The reaction mixture was successively washed
with water (20 mL), 0.5 M HCl (20 mL), water (20 mL), 10% Na2CO3
(20 mL), and brine (20 mL); dried (MgSO4); and evaporated, and the
residue was crystallized from MeOH to afford a white solid (1.26 g,
89%), mp 41-42 °C. 1H NMR: 0.86 (6H, t, J ) 6.9 Hz, -CH2CH3),
1.24 (60H, pseudo-s, CH3(CH2)15CH2CH2N), 1.49 (4H, bs, CH3-
(CH2)15CH2CH2N), 1.61 (1H, H2O), 3.04 (2H, t, J ) 7.5 Hz, CH3-
(CH2)16CH2N), 3.24 (2H, t, J ) 7.5 Hz, CH3(CH2)16CH2N), 3.95-4.05
(6H, m, Gly NCH2), 4.09 (2H, s, COCH2O), 4.29 (2H, s, COCH2O),
5.12 (2H, s, PHCH2O), 7.23 (1H, t, J ) 6.0 Hz, Gly CONH), 7.30-
7.35 (5H, m, HAr), 7.93 (1H, t, J ) 5.7 Hz, Gly CONH), 8.27 (1H, t,
J ) 5.7 Hz, Gly CONH). 13C NMR: 13.9, 22.5, 26.7, 26.9, 27.4, 28.6,
29.2, 29.3, 29.6, 31.8, 41.0, 42.9, 46.3, 46.7, 66.9, 69.6, 71.7, 128.2,
128.4, 128.6, 135.3, 168.6, 169.7, 169.8, 170.0, 171.5. IR (KBr): 3293,
[2-(2-{[1-(2-{2-[2-(2-Dipropylcarbamoylmethoxyacetylamino)-
acetylamino]acetylamino}acetyl)pyrrolidine-2-carbonyl]amino}-
acetylamino)acetylamino]acetic Acid Octadecyl Ester, 12, 32[DGA]-
GGGPGGG-OC18H37. TsOH‚GGG-OCH2Ph. GGG (3.0 g, 15.9
mmol) and p-toluenesulfonic acid monohydrate (3.6 g, 18.9 mmol) were
added to a mixture of benzyl alcohol (20 mL) and toluene (30 mL).
The mixture was heated to reflux and water was removed by using a
Dean-Stark trap. When no more water appeared in the distillate (after
8 h), heating was stopped. The mixture was cooled to room temperature,
diluted with ether (50 mL), and cooled in an ice water bath for 2 h.
The crystalline p-toluenesulfonate of GGG-OCH2Ph was collected on
a filter, washed with ether (50 mL), dried, and recrystallized from
1
MeOH-ether (5.5 g, 77%), mp 176-177 °C. H NMR: 2.34 (3H, s,
CH3Ph), 3.74 (2H, s, Gly NCH2), 3.97 (4H, s, Gly NCH2), 5.14 (2H,
s, PhCH2O), 7.21 (2H, d, J ) 8.4 Hz, tosyl HAr), 7.30-7.35 (5H, m,
Ph HAr), 7.69 (2H, d, J ) 8.4 Hz, tosyl HAr). 13C NMR: 21.4, 41.7,
42.1, 43.2, 68.1, 127.2, 129.5, 129.6, 129.9, 130.2, 137.5, 142.1, 143.7,
168.4, 171.4, 172.2. IR (KBr): 3331, 3083, 1747, 1670, 1545, 1456,
2916, 2849, 1749, 1651, 1544, 1467, 1196, 1128, 1031, 721, 697 cm-1
.
Anal. Calcd for C53H94N4O7·0.5H2O: C, 70.11; H, 10.54; N, 6.17.
Found: C, 70.18; H, 10.55; N, 6.18.
1406, 1362, 1202, 1125, 1035, 1011, 913, 817, 736, 685 cm-1
.
Boc-PGGG-OCH2Ph. Boc-L-proline (1.43 g, 6.7 mmol), TsOH·
GGG-O-CH2Ph (3.0 g, 6.7 mmol), and Et3N (2.80 mL) were dissolved
in CH2Cl2 (40 mL) and cooled to 5 °C. EDCI (1.34 g, 7 mmol) was
added and the reaction was stirred at room temperature for 3 days.
Solvent was evaporated, and the residue was dissolved in EtOAc (50
mL), washed with aq NH4Cl (25 mL) and brine (25 mL), dried over
MgSO4, and evaporated. The crude, oily product was chromatographed
(SiO2, 5% MeOH-CH2Cl2) and afforded colorless crystals (2.25 g,
71%), mp 54-55 °C. 1H NMR: 1.42 (9H, s, C(CH3)3), 1.80-2.20 (4H,
m, Pro NCH2CH2CH2), 3.35-3.55 (2H, m, Pro NCH2CH2CH2), 3.85-
4.20 (7H, m, Gly NCH2, Pro NCH), 5.15 (2H, s, PHCH2O), 7.05 (2H,
bs, Gly CONH), 7.30-7.35 (5H, m, HAr), 7.80 (1H, bs, Gly CONH).
13C NMR: 24.6, 28.3, 29.4, 41.1, 43.0, 43.3, 47.2, 60.7, 66.9, 80.9,
128.4, 128.5, 128.7, 135.4, 155.8, 169.6, 170.0, 173.9. IR (KBr): 3310,
3066, 2976, 2933, 1753, 1667, 1540, 1455, 1408, 1366, 1245, 1174,
1129, 1031, 974, 912, 773, 739, 698 cm-1. Anal. Calcd for
C23H32N4O7: C, 57.97; H, 6.77; N, 11.76. Found: C, 57.87; H, 6.76;
N, 11.39.
182[DGA]-GGG-OH. 182[DGA]-GGG-OCH2Ph (1.0 g, 1.1 mmol)
was dissolved in abs EtOH (100 mL) and 10% Pd/C (0.2 g) was added,
and this mixture was shaken under 60 psi pressure of H2 for 3 h. The
reaction mixture was heated to reflux and filtered (Celite pad). The
solvent was evaporated to afford a white solid (0.86 g, 96%), mp 163-
1
164 °C. H NMR (CD3OD): 0.90 (6H, t, J ) 6.9 Hz, -CH2CH3),
1.29 (60H, pseudo-s, CH3(CH2)15CH2CH2N), 1.57 (4H, bs, CH3-
(CH2)15CH2CH2N), 3.21 (2H, t, J ) 7.8 Hz, CH3(CH2)16CH2N), 3.35
(2H, t, J ) 7.8 Hz, CH3(CH2)16CH2N), 3.93 (2H, s, Gly NCH2), 3.94
(2H, s, Gly NCH2), 3.97 (2H, s, Gly NCH2), 4.12 (2H, s, COCH2O),
4.40 (2H, s, COCH2O). IR (KBr): 3285, 3084, 2925, 2852, 1740, 1650,
1551, 1467, 1420, 1378, 1219, 1128, 1033, 1011, 721, 681 cm-1. Anal.
Calcd for C46H88N4O7: C, 68.28; H, 10.96; N, 6.92. Found: C, 67.97;
H, 10.92; N, 6.81.
32[DGA]-GGGPGGG-OC18H37. To 182[DGA]-GGGPGGG-OH
(0.33 g, 0.5 mmol) suspended in CH2Cl2 (20 mL) were added 1,3-
diisopropylcarbodiimide (0.13 mL, 0.84 mmol) and DMAP (0.03 g,
0.24 mmol), and the mixture was stirred at room temperature. After
0.5 h, 1-octanol (0.16 g, 0.59 mmol) was added and the reaction was
stirred at room temperature for 48 h. The reaction mixture was
evaporated in vacuo, and the residue was chromatographed (SiO2, 5%-
10% MeOH-CHCl3) and afforded a white solid (0.08 g, 17%), mp
PGGG-OCH2Ph‚HCl. Boc-PGGG-OCH2Ph (0.2 g, 0.42 mmol) was
dissolved in 4 N HCl in dioxane (10 mL) at 5 °C and the reaction
mixture was stirred for 1 h. The solvent was evaporated in vacuo and
the residue was crystallized from MeOH-Et2O (0.18 g, 100%) to give
1
a colorless solid (mp 145-146 °C). H NMR (CD3OD): 2.00-2.25
1
(4H, m, Pro NCH2CH2CH2), 3.35-3.45 (2H, m, Pro NCH2CH2CH2),
3.90-4.05 (6H, m, Gly NCH2), 4.30-4.40 (1H, m, Pro NCH), 5.18
(2H, s, PHCH2O), 7.30-7.40 (5H, m, HAr). 13C NMR: 25.2, 30.9, 42.1,
43.3, 43.7, 47.6, 61.4, 68.1, 129.5, 129.6, 129.9, 137.5, 170.9, 171.4,
171.8, 172.4.
135-137 °C. H NMR: 0.85-1.00 (9H, overlapping signals due to
-CH2CH3), 1.25 (30H, pseudo-s, CH3(CH2)15CH2CH2O), 1.50-1.70
(6H, overlapping signals due to CH3CH2CH2N, and CH3(CH2)15CH2-
CH2O), 1.90-2.25 (4H, m, Pro NCH2CH2CH2), 3.07 (2H, t, J ) 7.5
Hz, CH3CH2N), 3.26 (2H, t, J ) 7.5 Hz, CH3CH2N), 3.50-3.60 (1H,
m, Pro NCH2CH2CH2), 3.65-3.70 (1H, m, Pro NCH2CH2CH2), 3.70-
4.10 (16H, overlapping signals due to Gly NCH2, COCH2O, and
CH3(CH2)15CH2CH2O), 4.33 (2H, s, COCH2O), 4.35 (1H, bs, Pro NCH),
7.31 (1H, t, J ) 6.0 Hz, Gly CONH), 7.46 (1H, t, J ) 6.0 Hz, Gly
CONH), 7.56 (1H, t, J ) 6.0 Hz, Gly CONH), 7.87 (1H, t, J ) 6.0 Hz,
Gly CONH), 7.91 (1H, t, J ) 6.0 Hz, Gly CONH), 8.42 (1H, t, J )
6.0 Hz, Gly CONH).13C NMR: 11.2, 11.3, 14.1, 20.7, 21.9, 22.6, 25.1,
25.8, 28.5, 29.0, 29.2, 29.3, 29.5, 29.7, 31.9, 41.2, 41.9, 42.7, 42.8,
42.9, 43.4, 46.9, 47.8, 48.4, 61.2, 65.7, 69.4, 71.3, 168.6, 168.8, 170.1,
170.2, 170.3, 170.4, 170.7, 171.1, 173.5. IR (CHCl3): 3306, 3080, 2957,
2919, 2851, 1748, 1659, 1647, 1548, 1534, 1467, 1410, 1378, 1340,
Dioctadecylcarbamoylmethoxyacetic Acid (182[DGA]-OH). A
solution of dioctadecylamine (2.0 g, 3.8 mmol) and diglycolic anhydride
0.44 g, 3.8 mmol) in toluene (50 mL) was refluxed for 48 h. The solvent
was evaporated and the crude product crystallized from CHCl3 to give
1
a white solid (2.12 g, 87%), mp 80-81 °C. H NMR: 0.87 (6H, t, J
) 6.9 Hz, -CH2CH3), 1.25 (60H, pseudo-s, CH3(CH2)15CH2CH2N),
1.55 (4H, bs, CH3(CH2)15CH2CH2N), 3.07 (2H, t, J ) 7.8 Hz, CH3-
(CH2)16CH2N), 3.34 (2H, t, J ) 7.8 Hz, CH3(CH2)16CH2N), 4.21 (2H,
(49) Djedovic, N.; Ferdani, R.; Harder, E.; Pajewska, J.; Pajewski, R.; Weber,
M. E.; Schlesinger, P. H.; Gokel, G. W. New J. Chem. 2005, 29, 291-
305.
9
J. AM. CHEM. SOC. VOL. 127, NO. 51, 2005 18293

A R T I C L E S
Pajewski et al.
1240, 1204, 1129, 1030, 722 cm-1. Anal. Calcd for C64H110N8O11‚
H2O: C, 58.29; H, 8.91; N, 12.09. Found: C, 58.32; H, 8.87; N, 12.07.
[2-(2-{[1-(2-{2-[2-(2-Dioctadecylcarbamoylmethoxyacetylamino)-
acetylamino]acetylamino}acetyl)piperidine-2-carbonyl]amino}-
acetylamino)acetylamino]acetic acid benzyl ester, 13, was prepared
as previously reported.33
COCH2O), 4.18 (2H, s, COCH2O), 4.30 (1H, m, Pro CH), 5.04 (2H, s,
OCH2Ph), 7.25 (5H, m, HAr), 7.69 (2H, m, NH), 7.78 (1H, bt, NH),
7.86 (1H, bt, NH), 8.08 (1H, bt, NH), 8.24 (1H, t, J ) 5.4 Hz, NH).
13C NMR: 14.3, 22.9, 25.3, 27.1, 27.3, 27.8, 29.0, 29.3, 29.5, 29.6,
29.8, 29.9, 32.1, 41.3, 42.3, 42.5, 43.0, 43.3, 43.5, 46.5, 47.1, 61.6,
67.2, 69.4, 71.3, 128.3, 128.6, 128.8, 135.6, 168.6, 169.3, 170.50,
170.55, 170.9, 171.0, 171.1, 173.3. Anal. Calcd for C64H110N8O11: C,
65.83; H, 9.50; N, 9.60. Found: C, 65.88; H, 9.88; N, 9.39.
[2-(2-{2-[(1-{2-[2-(2-Dioctadecylcarbamoylmethoxyacetylamino)-
acetylamino]acetyl}pyrrolidine-2-carbonyl)amino]acetylamino}-
acetylamino)acetylamino]acetic acid benzyl ester, 14, 182[DGA]-
GGPGGGG-OCH2Ph. 182[DGA]-GG-OH (0.45 g, 0.60 mmol) was
suspended in CH2Cl2 (60 mL) at 0 °C. EDCI (0.15 g, 0.78 mmol),
PGGGG-OCH2Ph‚HCl (0.28 g, 0.59 mmol), HOBt (0.10 g, 0.74 mmol),
and Et3N (0.5 mL) were added, and the reaction was stirred for 48 h
at room temperature. The solvent was then evaporated and the residue
purified by column chromatography (SiO2, 10% MeOH-CHCl3) to
{2-[(1-{2-[2-(2-Dioctadecylcarbamoylmethoxyacetylamino)-
acetylamino]acetyl}pyrrolidine-2-carbonyl)amino]acetylamino}-
acetic Acid Benzyl Ester, 16, Boc-GGGG-OCH2Ph. 182[DGA]-GG-
OCH2Ph. To a solution of 182[DGA]-OH (1.0 g, 1.5 mmol) in CH2-
Cl2 (30 mL) was added EDCI (0.31 g, 1.6 mmol), and the reaction
was stirred at room temperature. After 0.5 h, GG-OCH2Ph·TsOH (0.62
g, 1.5 mmol) and Et3N (0.6 mL) were added, and the mixture was
stirred overnight. The reaction was quenched; washed with water (20
mL), 0.5 M aq HCl (20 mL), water (20 mL), 10% Na2CO3(aq) (20
mL), and brine (20 mL); dried over MgSO4; and evaporated. The residue
was recrystallized from MeOH, yielding the desired product as a
colorless oil (1.32 g, 94%). 1H NMR: 0.86 (6H, t, J ) 6.9 Hz,
CH3(CH2)15CH2CH2N), 1.24 (60H, m, CH3(CH2)15CH2CH2N), 1.48 (4H,
bs, CH3(CH2)15CH2CH2N), 3.04 (2H, t, J ) 7.5 Hz, CH3(CH2)15-
CH2CH2N), 3.21 (2H, t, J ) 7.5 Hz, CH3(CH2)15CH2CH2N), 4.02-
4.07 (6H, m, Gly CH2), 4.08 (2H, s, COCH2O), 4.28 (2H, s, COCH2O),
5.13 (2H, s, PhCH2O), 7.32 (5H, m, HAr), 7.58 (1H, t, J ) 5.7 Hz,
NH), 8.21 (1H, t, J ) 5.7 Hz, NH). 13C NMR: 14.0, 22.6, 26.7, 26.9,
27.4, 28.7, 29.2, 29.3, 29.4, 29.5, 29.6, 31.8, 41.1, 42.7, 46.7, 66.9,
69.5, 71.7, 128.1, 128.3, 128.5, 135.2, 168.3, 169.5, 170.4.
1
give a white solid (0.57 g, 82%), mp 169-171 °C. H NMR: 0.79
(6H, t, J ) 6.3 Hz, CH3(CH2)15CH2CH2N), 1.17 (60H, m, CH3(CH2)15-
CH2CH2N), 1.42 (4H, m, CH3(CH2)15CH2CH2N), 1.82-2.18 (4H,
m, Pro NCH2CH2CH2), 2.98 (2H, t, J ) 7.2 Hz, CH3(CH2)15CH2CH2N),
3.17 (2H, t, J ) 7.2 Hz, CH3(CH2)15CH2CH2N), 3.40 and 3.60 (2H, m,
Pro NCH2CH2CH2), 3.75-4.05 (16H, m, Gly CH2, COCH2O), 4.18
(2H, s, COCH2O), 4.30 (1H, m, Pro CH), 5.04 (2H, s, OCH2Ph), 7.25
(5H, m, HAr), 7.69 (2H, m, NH), 7.78 (1H, bt, NH), 7.86 (1H, bt,
NH), 8.08 (1H, bt, NH), 8.24 (1H, t, J ) 5.4 Hz, NH). 13C NMR: 14.3,
22.9, 25.3, 27.1, 27.3, 27.8, 29.0, 29.3, 29.5, 29.6, 29.8, 29.9, 32.1,
41.3, 42.3, 42.5, 43.0, 43.3, 43.5, 46.5, 47.1, 61.6, 67.2, 69.4, 71.3,
128.3, 128.6, 128.8, 135.6, 168.6, 169.3, 170.50, 170.55, 170.9, 171.0,
171.1, 173.3. Anal. Calcd for C64H110N8O11: C, 65.83, H, 9.50; N, 9.60.
Found: C, 65.88; H, 9.88; N, 9.39.
182[DGA]-GG-OH. 182[DGA]-GG-OCH2Ph (2.3 g, 2.73 mmol) was
dissolved in abs EtOH (30 mL), 10% Pd/C (0.15 g) was added, and
this mixture was shaken under 60 psi pressure of H2 for 3 h. The
reaction mixture was heated to reflux and filtered (Celite pad). The
solvent was evaporated to afford a white solid (2.0 g, 100%), mp 114-
[2-({1-[2-(2-{2-[2-(2-Dioctadecylcarbamoylmethoxyacetylamino)-
acetylamino]acetylamino}acetylamino)acetyl]pyrrolidine-2-carbonyl}-
amino)acetylamino]acetic Acid Benzyl Ester, 15, 182[DGA]-
GGPGGGG-OCH2Ph. 182[DGA]-GGGGPGG-OCH2Ph. 182-DGA-
GGGG-OH (prepared as detailed in the following procedure, 0.65 g,
0.75 mmol) was suspended in CH2Cl2 (80 mL) at 0 °C; EDCI (0.20 g,
1.04 mmol), PGG-OCH2Ph‚HCl (0.27 g, 0.75 mmol), 1-hydroxyben-
zotriazole (0.15 g, 1.11 mmol), and Et3N (0.6 mL) were added; and
the reaction was stirred for 48 h at room temperature. The solvent was
evaporated and the residue purified by column chromatography (SiO2,
10% MeOH-CHCl3) to give a white solid (0.70 g, 80%), mp 175-
1
115 °C. H NMR (CDCl3/CD3OD 95:5): 0.80 (6H, t, J ) 6.9 Hz,
CH3(CH2)15CH2CH2N), 1.18 (60H, m, CH3(CH2)15CH2CH2N), 1.45 (4H,
m, CH3(CH2)15CH2CH2N), 3.02 (2H, t, J ) 7.8 Hz, CH3(CH2)15-
CH2CH2N), 3.22 (2H, t, J ) 7.8 Hz, CH3(CH2)15CH2CH2N), 3.91 (2H,
s, Gly CH2), 3.95 (2H, s, Gly CH2), 4.02 (2H, s, COCH2O), 4.20 (2H,
s, COCH2O). 13C NMR (CDCl3/CD3OD 95:5): 13.9, 22.5, 26.7, 26.8,
27.3, 28.6, 29.2, 29.4, 29.5, 31.7, 40.8, 42.1, 46.1, 46.7, 68.8. 70.8,
168.2, 169.7, 170.5, 171.3.
1
177 °C. H NMR: 0.79 (6H, t, J ) 6.3 Hz, CH3(CH2)15CH2CH2N),
Boc-PGG-OCH2Ph. Boc-P-OH (0.55 g, 2.54 mmol) was dissolved
in dry CH2Cl2 (50 mL) at 0 °C; GG-OCH2Ph‚TsOH (1.00 g, 2.54
mmol), EDCI (0.54 g, 2.8 mmol), HOBt (0.38 g, 2.8 mmol), and Et3N
(1.0 mL) were added; and the solution was stirred for 1 h at 0 °C and
for 48 h more at room temperature. The solvent was removed in vacuo
and the crude product purified by column chromatography (SiO2,
5-10% MeOH-CHCl3) to give 1.0 g of a deliquescent solid (93%).
1H NMR: 1.41 (9H, s, C(CH3)3), 1.8-2.2 (4H, m, Pro NCH2CH2CH2),
3.46 (2H, m, Pro NCH2CH2CH2), 4.04 (4H, m, Gly CH2), 4.20 (1H,
m, Pro CH), 5.15 (2H, s, OCH2Ph), 7.02 (1H, bt, NH), 7.34 (5H, m,
HAr), 7.46 (1H, bt, NH). 13C NMR: 24.6, 28.3, 29.3, 41.2, 42.9, 47.3,
60.7, 67.0, 80.7, 128.2, 128.4, 128.5, 135.2, 155.7, 169.6, 169.7, 172.9.
HCl‚PGG-OCH2Ph. Boc-PGG-OCH2Ph (0.4 g, 0.95 mmol) was
dissolved in 4 N HCl in dioxane (10 mL) at 5 °C and the reaction
mixture was stirred for 1 h. The solvent was evaporated in vacuo. The
product was used in the subsequent reaction without further purification.
182[DGA]-GGPGG-OCH2Ph. 182[DGA]-GG-OH (0.71 g, 0.95
mmol), PGG-OCH2Ph‚HCl (0.25 g, 0.95 mmol), and DIEA (0.2 mL)
were dissolved in CH2Cl2 (30 mL) and cooled to 5 °C. EDCI (0.2 g,
1.05 mmol) and HOBt (0.14 g, 1.05 mmol) were added, and the reaction
was stirred at room temperature for 48 h. The solvent was evaporated
and the residue purified by column chromatography (SiO2, 5-10%
MeOH-CHCl3) to give an off-white solid (0.76 g, 76%), mp 55-56
1.18 (60H, m, CH3(CH2)15CH2CH2N), 1.40 (4H, m, CH3(CH2)15CH2-
CH2N), 1.82-2.10 (4H, m, ProNCH2CH2CH2), 3.00 (2H, t, J ) 7.5
Hz, CH3(CH2)15CH2CH2N), 3.17 (2H, t, J ) 7.5 Hz, CH3(CH2)15-
CH2CH2N), 3.41 and 3.62 (2H, m, Pro NCH2CH2CH2), 3.72-4.05
(16H, m, Gly CH2, COCH2O), 4.19 (2H, s, COCH2O), 4.36 (1H, m,
Pro CH), 5.05 (2H, s, OCH2Ph), 7.25 (5H, m, HAr), 7.52 (2H, m, NH),
7.66 (1H, t, J ) 5.7 Hz, NH), 7.88 (1H, t, J ) 5.4 Hz, NH), 7.96 (1H,
t, J ) 5.7 Hz, NH), 8.16 (1H, t, J ) 5.7 Hz, NH). 13C NMR: 14.3,
22.7, 25.1, 27.1, 27.3, 27.8, 29.0, 29.5, 29.6, 29.9, 32.1, 41.5, 42.2,
43.0, 43.5, 46.0, 46.5, 47.1, 61.2, 67.2, 69.6, 71.6, 128.4, 128.6, 128.8,
135.5, 168.6, 168.9, 170.4, 170.6, 170.8, 171.2, 172.5. Anal. Calcd for
C64H110N8O11·H2O: C, 64.83; H, 9.52; N, 9.45. Found: C, 65.05; H,
9.40; N, 9.39.
182[DGA]-GGPGGGG-OCH2Ph. 182[DGA]-GG-OH (0.45 g, 0.60
mmol) was suspended in CH2Cl2 (60 mL) at 0 °C. EDCI (0.15 g, 0.78
mmol), PGGGG-OCH2Ph‚HCl (0.28 g, 0.59 mmol), HOBt (0.10 g, 0.74
mmol), and Et3N (0.5 mL) were added, and the reaction was stirred
for 48 h at room temperature. The solvent was then evaporated and
the residue purified by column chromatography (SiO2, 10% MeOH-
CHCl3) to give a white solid (0.57 g, 82%), mp 169-171 °C. 1H
NMR: 0.79 (6H, t, J ) 6.3 Hz, CH3(CH2)15CH2CH2N), 1.17 (60H, m,
CH3(CH2)15CH2CH2N), 1.42 (4H, m, CH3(CH2)15CH2CH2N), 1.82-
2.18 (4H, m, Pro NCH2CH2CH2), 2.98 (2H, t, J ) 7.2 Hz, CH3(CH2)15-
CH2CH2N), 3.17 (2H, t, J ) 7.2 Hz, CH3(CH2)15CH2CH2N), 3.40 and
3.60 (2H, m, Pro NCH2CH2CH2), 3.75-4.05 (16H, m, Gly CH2,
1
°C. H NMR: 0.86 (6H, t, J ) 6.9 Hz, CH3(CH2)15CH2CH2N), 1.25
(60H, m, CH3(CH2)15CH2CH2N), 1.40-1.50 (4H, m, CH3(CH2)15CH2-
9
18294 J. AM. CHEM. SOC. VOL. 127, NO. 51, 2005

Open-Chained Peptides as Anion-Complexing Agents
A R T I C L E S
CH2N), 1.80-2.20 (4H, m, Pro NCH2CH2CH2), 3.08 (2H, t, J ) 7.5
Hz, CH3(CH2)15CH2CH2N), 3.15-3.35 (2H, m, CH3(CH2)15CH2CH2N),
3.50-4.40 (14H, overlapping signals due to Pro NCH2CH2CH2, Gly
CH2, and COCH2O), 4.43 (1H, m, Pro CH), 5.14 (2H, s, OCH2Ph),
7.33 (5H, m, HAr), 7.42 (2H, bt, NH), 7.56 (1H, bt, NH), 7.88 (1H, bt,
NH), 8.22 (1H, bt, NH). 13C NMR: 14.1, 22.7, 24.9, 26.9, 27.1, 27.6,
28.9, 29.3, 29.4, 29.5, 29.7, 31.9, 41.0, 42.3, 42.6, 42.9, 46.3,46.8, 47.4,
61.2, 67.0, 69.4, 71.7, 128.2, 128.4, 128.6, 135.3, 168.2, 169.1, 169.8,
170.4, 170.6, 171.7. IR (CHCl3): 3307, 2919, 2851, 1748, 1658, 1651,
1536, 1467, 1455, 1243, 1191, 1129, 1030, 754 cm-1. Anal. Calcd for
C60H104N6O9: C, 68.40; H, 9.95; N, 7.98. Found: C, 68.17; H, 9.95;
N, 8.11.
1.44 (4H, m, CH3(CH2)15CH2CH2N), 3.00 (2H, t, J ) 7.8 Hz,
CH3(CH2)15CH2CH2N), 3.19 (2H, t, J ) 7.8 Hz, CH3(CH2)15CH2CH2N),
3.80 (2H, s, Gly CH2), 3.84 (2H, s, Gly CH2), 3.86 (2H, s, Gly CH2),
3.89 (2H, s, Gly CH2), 3.99 (2H, s, COCH2O), 4.18 (2H, s, COCH2O).
13C NMR (CDCl3/CD3OD 95:5): 13.8, 22.4, 26.6, 26.8, 27.3, 28.5,
29.1, 29.3, 29.5, 31.7, 40.7, 42.3, 42.9, 46.2, 46.7, 68.6, 70.6, 168.4,
170.0, 170.2, 170.8, 171.0, 171.6.
Boc-PGGGG-OCH2Ph. Boc-P-OH (0.29 g, 1.37 mmol), GGGG-
O-CH2Ph·HCl (0.51 g, 1.37 mmol), and DIEA (0.26 mL) were dissolved
in CH2Cl2 (40 mL) and cooled to 5 °C. EDCI (1.34 g, 1.51 mmol) and
HOBt (0.2 g, 1.51 mmol) were added, and the mixture was stirred at
room temperature for 48 h and evaporated, and the crude, oily product
was chromatographed (SiO2, 5-10% MeOH-CHCl3) to afford white
crystals (0.72 g, 98%), mp 122-123 °C. 1H NMR: 1.40 (9H, s, (CH3)3),
1.80-2.20 (4H, m, Pro NCH2CH2CH2), 3.35-3.55 (2H, m, Pro NCH2-
CH2CH2), 3.70-4.20 (9H, overlapping signals due to Gly NCH2 and
Pro NCH), 5.14 (2H, s, OCH2Ph), 7.05 (2H, bs, NH), 7.30-7.35 (7H,
overlapping signals due to HAr and NH), 7.45 (1H, bs, NH), 8.00 (1H,
bs, NH). 13C NMR: 24.9, 28.5, 30.0, 41.2, 42.9, 43.7, 47.4, 61.0, 67.2,
81.1, 128.3, 128.6, 128.7, 135.3, 155.8, 169.9, 170.9, 174.5. IR
(CHCl3): 3307, 3069, 2979, 2935, 1747, 1668, 1661, 1532, 1408, 1243,
(2-{2-[2-({1-[2-(2-{2-[2-(2-Dioctadecylcarbamoylmethoxyacetyl-
amino)acetylamino]acetylamino}acetylamino)acetyl]pyrroli-
dine-2-carbonyl}amino)acetylamino]acetylamino}acetylamino)-
acetic Acid Benzyl Ester, 17, 182[DGA]-GGGGPGGGG-OCH2Ph.
HCl·GGGG-OCH2Ph. Boc-GGGG-OCH2Ph. Boc-G-OH (0.50 g,
2.85 mmol) was suspended in CH2Cl2 (100 mL) at 0° C, and EDCI
(0.70 g, 3.65 mmol), GGG-OCH2Ph‚TsOH (1.28 g, 2.84 mmol) and
Et3N (1.0 mL) were added. The reaction was stirred for 48 h at room
temperature. The solvent was then evaporated and the residue purified
by column chromatography (SiO2, 5-10% MeOH-CHCl3) to give an
1191, 1164, 1132, 1030, 975, 913, 751, 672 cm-1
.
1
off-white solid (0.23 g, 99%), mp 189-90 °C. H NMR 1.36 (9H, s,
HCl·PGGGG-OCH2Ph. Boc-PGGG-OCH2Ph (0.3 g, 0.56 mmol)
was dissolved in 4 N HCl/dioxane (10 mL) at 5 °C, the mixture was
stirred for 1 h, and the solvent was evaporated in vacuo. The product
was used in the subsequent reaction without further purification.
(CH3)3), 3.71 (2H, d, J ) 5.7 Hz, Gly CH2), 3.83 (2H, d, J ) 5.7 Hz,
Gly CH2), 3.86 (2H, d, J ) 5.7 Hz, Gly CH2), 3.96 (2H, d, J ) 5.7 Hz,
Gly CH2), 5.09 (2H, s, OCH2Ph), 5.96 (1H, bs, NH), 7.27 (5H, m,
HAr), 7.63 (1H, bt, NH), 7.80 (1H, bt, NH), 7.82 (1H, bt, NH). 13C
NMR: 28.0, 40.9, 41.0, 42.4, 42.8, 43.9, 67.1, 80.3, 128.1, 128.3, 128.5,
134.9, 169.8, 170.0, 170.1, 171.4.
Boc-GGGG-OCH2Ph (0.73 g, 1.82 mmol) was dissolved in 4 N HCl
in dioxane (10 mL) at 5 °C and the reaction mixture was stirred for 1
h. The solvent was evaporated in vacuo. The product was used in the
subsequent reaction without further purification.
182[DGA]-GGGGPGGGG-OCH2Ph. 182[DGA]-GGGG-OH (0.48
g, 0.56 mmol), PGGGG-OCH2Ph·HCl (0.21 g, 0.56 mmol), and DIEA
(0.1 mL) were dissolved in CH2Cl2 (30 mL), and the mixture was cooled
to 5 °C. EDCI (0.12 g, 0.62 mmol) and HOBt (0.08 g, 0.62 mmol)
were added, and the mixture was stirred at room temperature for 48 h.
The solvent was evaporated and the residue was crystallized from
MeOH and then chromatographed (SiO2, 5-10% MeOH-CHCl3) to
give an off-white solid (0.15 g, 21%), mp 206-208 °C. 1H NMR: 0.87
(6H, t, J ) 6.9 Hz, CH3(CH2)15CH2CH2N), 1.24 (60H, m, CH3(CH2)15-
CH2CH2N), 1.40-1.55 (4H, m, CH3(CH2)15CH2CH2N), 1.80-2.20 (4H,
m, Pro NCH2CH2CH2), 3.05 (2H, bs, CH3(CH2)15CH2CH2N), 3.24 (2H,
bs, CH3(CH2)15CH2CH2N), 3.45-4.00 (18H, overlapping signals due
to Pro NCH2CH2CH2, and Gly CH2), 4.09 (2H, s COCH2O), 4.27 (2H,
s COCH2O), 4.34 (1H, m, Pro CH), 5.11 (2H, s, OCH2Ph), 7.32 (5H,
m, HAr), 7.73 (2H, bs, NH), 7.78 (1H, bs, NH), 7.89 (1H, bs, NH), 7.95
(1H, bs, NH), 8.03 (1H, bs, NH), 8.26 (2H, bs, NH). 13C NMR: 14.0,
22.6, 25.1, 26.9, 27.1, 27.6, 28.9, 29.1, 29.3, 29.4, 29.6, 29.7, 31.9,
41.2, 42.0, 42.8, 43.0, 46.3, 46.9, 61.3, 66.9, 69.4, 71.3, 128.1, 128.3,
128.6, 135.4, 168.4, 168.9, 170.1, 170.2, 170.4, 170.5, 170.6, 171.0,
171.1, 173.6. IR (CHCl3): 3299, 3087, 2921, 2852, 1744, 1646, 1552,
182[DGA]-GGGG-OCH2Ph. 182[DGA]-OH (1.16 g, 1.82 mmol)
and GGGG-OCH2Ph‚HCl (0.68 g, 1.82 mmol) were suspended in CH2-
Cl2 (100 mL) at 0 °C, diisopropylcarbodiimide (0.45 g, 2.35 mmol)
and Et3N (1.0 mL) were added, and then the reaction was stirred for
72 h at room temperature. The solvent was then evaporated and the
residue purified by column chromatography (SiO2, 5% MeOH-CHCl3)
1
to give the final product as an oil (1.51 g, 87%). H NMR: 0.78 (6H,
t, J ) 6.6 Hz, CH3(CH2)15CH2CH2N), 1.16 (60H, m, CH3(CH2)15CH2-
CH2N), 1.40 (4H, m, CH3(CH2)15CH2CH2N), 2.95 (2H, t, J ) 6.9 Hz,
CH3(CH2)15CH2CH2N), 3.15 (2H, t, J ) 6.9 Hz, CH3(CH2)15CH2CH2N),
3.80-3.93 (8 H, m, Gly CH2), 3.99 (2H, s, COCH2O), 4.18 (2H, s,
COCH2O), 5.02 (2H, s, OCH2Ph), 7.23 (5H, m, HAr), 7.51 (1H, t, J )
5.7 Hz, NH), 7.60 (1H, t, J ) 5.1 Hz, NH), 7.95 (1H, t, J ) 5.1 Hz,
NH), 8.17 (1H, t, J ) 5.4 Hz, NH). 13C NMR: 14.2, 22.8, 27.0, 27.2,
27.7, 28.9, 29.46, 29.52, 29.8, 32.0, 41.3, 42.9, 43.3, 46.4, 47.0, 67.1,
69.5, 71.5, 128.3, 128.4, 128.7, 135.5, 168.6, 170.1, 170.2, 170.7, 171.3.
182[DGA]-GGGG-OH. 182[DGA]-GGGG-OCH2Ph (0.76 g, 0.79
mmol) was dissolved in abs EtOH (100 mL), 10% Pd/C (0.3 g) was
added, and this mixture was shaken under 60 psi hydrogen pressure
for 3 h in a Parr apparatus. The reaction mixture was heated to reflux
and filtrated through a Celite layer. The solvent was evaporated to leave
a white solid (0.66 g, 95%) that was used without further purification,
1467, 1455, 1418, 1378, 1339, 1284, 1246, 1192, 1130, 1028, 696 cm-1
.
Anal. Calcd for C68H14N10O13‚H2O: C, 62.84; H, 9.15; N, 10.78.
Found: C, 62.64; H, 9.08; N, 10.78.
N,N′-Bis-(2,4,6-trimethylphenyl)isophthalamide, 18, was prepared
as previously reported by Kavallieratos et al.14
Acknowledgment. We thank the NIH for a grant (GM 63190)
that supported this work.
1
mp 158-160 °C. H NMR (CDCl3/CD3OD 95:5): 0.77 (6H, t, J )
6.9 Hz, CH3(CH2)15CH2CH2N), 1.15 (60H, m, CH3(CH2)15CH2CH2N),
JA0558894
9
J. AM. CHEM. SOC. VOL. 127, NO. 51, 2005 18295