Chiral gelators constructed from 11-aminoundecanoic (AUDA), lauric and amino acid units. Synthesis, gelling properties and preferred gelation of racemates vs. the pure enantiomers

Article abstract of DOI:10.1002/ejoc.200400105

A new class of efficient low molecular weight gelator molecules has been designed by combining 11-aminoundecanoic acid (AUDA), lauric acid and aromatic and aliphatic amino acid units in the same molecule. This yields a special class of fatty acid amphiphiles with core chiral centres and hydrogen bonding sites. Some of the compounds with terminal carboxylic acid and sodium carboxylate functions exhibited ambidextrous gelation properties, being able to form gels both with highly polar solvents (water, DMSO) and also with highly lipophilic solvents, including two hydrocarbon fuels. At variance with several recent observations that the enantiomers are generally more efficient gelators than the corresponding racemates, some of the racemic gelators prepared in this work were found to be capable of gelling up to 16 times larger volumes of certain solvents than the pure enantiomers. Temperature-dependent FTIR and ¹H NMR studies of the gels formed by derivatives with terminal carboxylic acid groups and lipophilic solvents revealed that intermolecular hydrogen bonding between amidic and carboxylic acid units was involved in the self-assembly of gel aggregates. Additional strong stabilization of the aggregates was observed in the gelators possessing terminal sodium carboxylate groups, and this was attributed to the electrostatic and ion-dipole interactions between the sodium carboxylate groups. This additional stabilization appears to be responsible for considerably higher thermal stability of the latter gels in relation to those formed by gelators with terminal carboxylic acid groups. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004.

Full text of DOI:10.1002/ejoc.200400105

FULL PAPER
Chiral Gelators Constructed from 11-Aminoundecanoic (AUDA), Lauric and
Amino Acid Units. Synthesis, Gelling Properties and Preferred Gelation of
Racemates vs. the Pure Enantiomers
[a]
[a]
[b]
[c]
ˇ
ˇ
´
Vesna Caplar, Mladen Zinic,* Jean-Luc Pozzo, Frederic Fages,
Gudrun Mieden-Gundert,[d] and Fritz Vögtle[d]
Keywords: Amino acids / Enantiomers / Fatty acids / Gelation / Racemates / Self-assembly
A new class of efficient low molecular weight gelator molec-
ules has been designed by combining 11-aminoundecanoic the gels formed by derivatives with terminal carboxylic acid
acid (AUDA), lauric acid and aromatic and aliphatic amino groups and lipophilic solvents revealed that intermolecular
acid units in the same molecule. This yields a special class of hydrogen bonding between amidic and carboxylic acid units
fatty acid amphiphiles with core chiral centres and hydrogen was involved in the self-assembly of gel aggregates. Addi-
bonding sites. Some of the compounds with terminal carb- tional strong stabilization of the aggregates was observed in
omers. Temperature-dependent FTIR and 1H NMR studies of
oxylic acid and sodium carboxylate functions exhibited ambi-
dextrous gelation properties, being able to form gels both
with highly polar solvents (water, DMSO) and also with
highly lipophilic solvents, including two hydrocarbon fuels.
At variance with several recent observations that the enanti-
the gelators possessing terminal sodium carboxylate groups,
and this was attributed to the electrostatic and ion-dipole in-
teractions between the sodium carboxylate groups. This ad-
ditional stabilization appears to be responsible for consider-
ably higher thermal stability of the latter gels in relation to
omers are generally more efficient gelators than the corres- those formed by gelators with terminal carboxylic acid
ponding racemates, some of the racemic gelators prepared
in this work were found to be capable of gelling up to 16
times larger volumes of certain solvents than the pure enanti-
groups.
( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2004)
1. Introduction
pounds,[4,5] easy to synthesize and available in large
amounts from cheap starting materials, are desirable from
the practical standpoint. Several design approaches based
on the use of various self-complementary organisational
units have already proven successful.[6Ϫ13] It has recently
been shown that simple urethane, amide or urea derivatives
of 11-aminoundecanoic acid (AUDA) act as efficient and
selective gelators of polar organic solvents when the car-
boxylic acid function is deprotonated and when the N-acyl
substituent contains an aromatic terminal moiety.[14] Here
we report on the preparation of a new class of chiral gelator
molecules based on 11-aminoundecanoic acid (AUDA),
lauric acid and the core peptidic unit. The combination of
these structural fragments should provide properties favour-
able for gelation: the presence of two core amidic functions
would be expected to induce self-assembly through unidi-
rectional cooperative hydrogen bonding, and the presence
of the chiral centre and long aliphatic chain of the lauroyl
amide should decrease the crystallization tendency of such
derivatives. The structures represent a special class of am-
phiphiles containing hydrogen bonding cores, offering the
potential for rather rare ambidextrous gelation of both
highly polar and lipophilic solvents.[8,15Ϫ17] Here we report
on the synthesis and versatile gelation capability of this
Gelation of various organic fluids and water by low mo-
lecular mass organic compounds represents a fascinating
supramolecular phenomenon. Formation of a gel is the
consequence of molecular self-assembly and constitutes a
macroscopic manifestation thereof.[1,2] Gels formed by
small organic compounds of highly diverse structures have
attracted much recent attention as a unique type of nano-
structured organic materials with dynamic properties and
many possible applications.[1Ϫ3] A major challenge is pre-
sented by the elaboration of novel design strategies enabling
the synthesis of versatile gelator molecules with predictable
properties. In this respect, structurally simple com-
[a]
Laboratory for Supramolecular and Nucleoside Chemistry,
ˇ
Rudjer Boskovic Institute,
P.O.B. 180, HR-10002 Zagreb, Croatia
Fax: (internat.) ϩ385-1-4680-195
E-mail: zinic@irb.hr
[b]
[c]
´
CSBN/UMR 5802 CNRS, Universite Bordeaux 1,
´
351 crs Liberation, 33405 Talence Cedex, France
´
´
´
Materiaux Moleculaires et Biomateriaux, GCOM2 Ϫ UMR
´
´
´
´
6114 CNRS, Universite de la Mediterranee, Faculte des
Sciences de Luminy,
Case 901, 13288 Marseille Cedex 9, France
[d]
´
Kekule-Institut für Organische Chemie und Biochemie der
Universität Bonn,
1
Gerhard-Domagk-Str. 1, 53121 Bonn, Germany
class of molecules and provide H NMR and FTIR evi-
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 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
DOI: 10.1002/ejoc.200400105
Eur. J. Org. Chem. 2004, 4048Ϫ4059

Synthesis, Gelling Properties and Preferred Gelation of Chiral Gelators
FULL PAPER
dence of their organisation by intermolecular hydrogen
bonding. Experimental evidence that gelators with terminal
carboxylic acid groups form thermally sensitive gels and
those with terminal sodium carboxylates thermally stable
ones is provided. At variance with most recent reports, we
report on the most intriguing observation that some of the
racemates are capable of gelling up to 16 times larger vol-
umes of certain solvents than pure enantiomers.
2. Results and Discussion
Four long-chain aliphatic acid derivatives, each incorpor-
ating an amino acid unit in the central part of the molecule,
were prepared. Leucine and valine were selected as aliphatic
amino acid representatives, while phenylglycine and phenyl-
alanine represented aromatic amino acids.
Scheme 1. Reagents and conditions: (a) (Boc)2O, NaOH/dioxane/
water, (b) H2N(CH2)10COOCH3, DCC, Et3N, DMAP/CH2Cl2, (c)
TFA/CH2Cl2, (d) ClCO(CH2)10CH3, Et3N/CH2Cl2, (e) LiOH/
CH2Cl2/MeOH, (f) 10% KOH/MeOH, (g) HCl, (h) NaOH/
CH2Cl2/MeOH
was performed with 1  LiOH in methanol/CH2Cl2 solu-
tion for optically active derivatives or with KOH in meth-
anol for racemic ones. The free acids 6 were obtained in
95Ϫ100% yields. The corresponding sodium salts 7 were
prepared by the use of an equivalent quantity of 1  aque-
ous NaOH in dichloromethane/methanol mixtures.
The alternative shorter synthetic route starting with di-
rect SchottenϪBaumann condensation of an amino acid
and dodecanoyl chloride in aqueous alkaline conditions
was not selected for two reasons: firstly, racemisation may
occur with optically active amino acids, and secondly, the
long-chain carboxylic acid amides of amino acids are
known as efficient organic solvent gelators and
hydrogelators,[19Ϫ21] so possible formation of gels might
complicate isolation of the products.
Two sets of compounds were synthesized: the pure en-
antiomers starting from the optically active amino acid pre-
cursors, and the racemates prepared from the racemic am-
ino acids. The gelling properties of the optically active and
racemic acid derivatives, as well as those of their corre-
sponding sodium salts, were tested against water, 14 organic
solvents and two hydrocarbon fuels, and their properties
compared.
2.2. Gelling Properties
Optically active and racemic free acids 6 and the corre-
sponding sodium salts 7 were tested for gelation with 14
varied solvents and two hydrocarbon fuels. Gelation
properties were determined with 10 mg of tested substance
in 10 mm diameter tubes; the results, expressed as minimal
2.1. Synthesis
The racemic amino acids 1 were protected with (Boc)2O gel concentrations, are collected in Table 1 and 2.
in dioxane/water (2:1), giving protected derivatives 2[18] in
The Leu derivative (S)-Leu-6 failed to gel any of the
quantitative yields (Scheme 1). The optically active Boc- tested fluids. The optically active acids (S)-Val-6, (R)-PhG-
protected amino acids are commercially available. 6 and (S)-Phe-6 and the Na-salts (S)-Leu-7, (S)-Val-6, (R)-
The first long aliphatic chain was introduced by DCC- PhG-7 and (S)-Phe-7 showed only moderate gelation of the
condensation of 2 with methyl 11-aminoundecanoate hy- polar solvents DMSO and DMF, giving fully thermorevers-
drochloride, in the presence of DCC, Et3N and DMAP, giv- ible opaque gels; water was also weakly gelled only by the
ing the amide derivatives 3 in high yields (76Ϫ96%). The latter group of compounds. In the solvents of low and me-
Boc protecting groups of 3 were removed by treatment with dium polarity, such as hexane, dichloromethane, aceto-
TFA in CH2Cl2, which gave amino compounds 4 in yields nitrile, acetone and ethyl acetate, both the acids and the
of 83Ϫ100%. The second amide linkage was introduced by Na-salts are either insoluble or crystallise from hot solu-
treatment of 4 with lauroyl chloride in dry CH2Cl2 in the tions, but moderate gelation of THF was observed for the
presence of Et3N. The ester-amides 5 were obtained in Leu and Phe Na-salts (S)-Leu-7, and (S)-Phe-7, respec-
yields of 78Ϫ94%. Saponification of the methyl ester group tively. Of the group of aromatic solvents tested, benzene
Eur. J. Org. Chem. 2004, 4048Ϫ4059
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FULL PAPER
Table 1. Gelation properties of optically active acids and Na-salts expressed as minimal gel concentrations (10Ϫ2 mol·dmϪ3) of tested com-
pound[a][b]
Solvent
(S)-Leu-6
(S)-Leu-7
(S)-Val-6
(S)-Val-7
(R)-PhG-6
(R)-PhG-7
(S)-Phe-6
(S)-Phe-7
water
DMSO
DMF
EtOH
THF
benzene
toluene
p-xylene
tetralin
decalin
petroleum ether
oil (Diesel)
sol.
sol.
sol.
sol.
sol.
sol.
sol.
sol.
sol.
sol.
ins.
ins.
1.93
3.86
6.43
sol.
0.38
ins.
2.41
0.96
0.175
1.28
ins.
sl.sol.
4.14
2.07
sol.
6.90
sol.
1.98
0.66
0.28
3.30
ins.
ins.
sol.
sol.
cryst.
1.55
1.55
1.55
sol.
1.33
4.64
1.69
1.86
0.241
0.84
3.09
ins.
ins.
sol.
sol.
sol.
1.21
0.75
1.21
cryst.
0.30
ins.
ins.
ins.
0.181
0.297
ins.
sol.
sol.
ins.
4.84 gel and t.v.s.
t.v.s.
t.v.s.
t.v.s.
0.753
0.325
9.42
18.8
sol.
1.98
6.19
0.165
1.16
ins.
3.23
3.23
1.29
0.293
4.84
1.29
0.74
0.122*
0.690
ins.
6.43
ins.
ins.
ins.
[a] Gelation tests performed with 10 mg of tested substances in test tubes of 10 mm diameter.* Determined with 2.5 mg of tested substance.
[b]
Abbreviations: sol.: soluble, sl.sol.: slightly soluble, ins.: insoluble, cryst.: crystalline, t.v.s.: turbid viscous solution.
Table 2. Gelation properties of racemic acids and salts expressed as minimal gel concentrations (10Ϫ2 mol·dmϪ3) of the tested com-
pound[a][b]
Solvent
rac-Leu-6
rac-Leu-7
rac-Val-6
rac-Val-7
rac-PhG-6
rac-PhG-7
rac-Phe-6
rac-Phe-7
water
DMSO
DMF
p-xylene
tetralin
decalin
ins.
cryst.
cryst.
cryst.
ins.
0.138**
ins.
ins.
1.98
2.48
3.96
ins.
ins.
0.291
ins.
sol.
sol.
cryst.
t.v.s.
t.v.s.
2.32
1.69
3.09
0.115*
0.155*
0.103*
ins.
1.88
18.1
1.21
0.113*
0.134
0.090**
cryst.
cryst.
t.v.s.
6.71
t.v.s.
10.4
20.7
ins.
cryst.
t.v.s.
18.8
sol.
sol.
sol.
t.v.s.
[a]
Gelation tests performed with 10 mg of tested substances in test tubes of 10 mm diameter.* Determined with 2.5 mg of tested
[b]
substance. ** Determined with 5.0 mg of tested substance.
crystalline, t.v.s.: turbid viscous solution.
Abbreviations: sol.: soluble, sl.sol.: slightly soluble, ins.: insoluble, cryst.:
could be weakly gelled only by (R)-PhG-7, while toluene showed that pure enantiomers are generally more efficient
and p-xylene were gelled with moderate efficiency by the gelators than the corresponding racemates, which tend to
Na-salts of (S)-Leu-7, (S)-Val-7 and (R)-PhG-7 derivatives crystallize.[22Ϫ27] In contrast, the results from Table 2 clearly
and by the Val acid (S)-Val-6. However, the same gelators show that in some solvents racemates can be much more
exhibited very efficient gelation of tetralin, forming gels at efficient gelators than the corresponding pure enantiomers.
m concentrations. Weak gelation of hydrocarbon fuels was The same observation was also reported very recently for
also observed with the Na salts (S)-Leu-7 and (R)- PhG-7 some racemates and enantiomers of bis(amino alcohol)
and the acids (R)-PhG-6 and (S)-Phe-6.
oxalamide gelators.[28]
Table 2 shows that the racemic derivatives rac-Leu-6, rac-
The thermal properties of the gels prepared from two en-
Val-6, rac-PhG-6 and rac-Phe-6 and the Na-salts rac-Leu- antiomer/racemate pairs were examined by determination
7, rac-Val-7, rac-PhG-7 and rac-Phe-7 were generally less of their gel melting temperatures (Tg). The first (S)-Val-7/
versatile gelators than the corresponding optically active rac-Val-7 pair represents a case in which the enantiomer
forms. The racemates failed to gel hexane, benzene, toluene, (S)-Val-7 is capable of gelling a 14 times larger volume of
dichloromethane, acetonitrile, THF, acetone, ethyl acetate, DMF than the racemate rac-Val-7, while the second (R)-
ethanol and hydrocarbon fuels. Most of the racemates are PhG-7/rac-PhG-7 pair represents the opposite case, the ra-
either insoluble in these solvents or tend to crystallize from cemate rac-PhG-7 being capable of gelling a 16 times larger
hot solutions. Striking differences, however, were observed volume of p-xylene than the enantiomer (R)-PhG-7
for the Na salts rac-Leu-7, rac-PhG-7 and rac-Phe-7, which (Table 3).
showed excellent gelation of tetralin and decalin while their
The results show that, at the same concentrations of the
optically active isomers exhibited much weaker gelation enantiomer and the racemate, considerably higher Tg values
[see Table 1 for (S)-Leu-7, (R)-PhG-7 and (S)-Phe-7]. For are obtained for the enantiomer (S)-Val-7 and the racemate
example, the racemic rac-PhG-7 was capable of gelling a 16 rac-PhG-7, both being capable of immobilising larger vol-
times larger volume of p-xylene then (R)-PhG-7, and the umes of solvents than their counterparts. This suggests that
racemic rac-PhG-7, and rac-Phe-7 were capable of gelling different types of aggregation occur in the enantiomer and
much larger volumes of decalin than the pure enantiomers in the racemate gels of the (S)-Val-7/rac-Val-7 and (R)-
(R)-PhG-7 and (S)-Phe-7. Several earlier observations PhG-7/rac-PhG-7 pairs, giving more stable aggregates in the
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Synthesis, Gelling Properties and Preferred Gelation of Chiral Gelators
FULL PAPER
Table 3. Tg values and concentrations (cg) of the gels prepared from pure enantiomers (S)-Val-7 and (R)-PhG-7 and the racemates rac-
Val-7 and rac-PhG-7
Gelator/solvent
cg (mol·dmϪ3
)
Tg (°C); freshly prepared gel
Tg (°C); aged for 1 day
(S)-Val-7/ DMF
1.98 ϫ 10Ϫ2
1.98 ϫ 10Ϫ2
1.86 ϫ 10Ϫ3
1.86 ϫ 10Ϫ3
126
107
28
Ϫ
Ϫ
30
119
rac-Val-7/ DMF
(R)-PhG-7/ p-xylene
rac-PhG-7/ p-xylene
75
enantiomer (S)-Val-7 and the racemate rac-PhG-7 gels. The trast, the spectra of (S)-Leu-7 and (R)-PhG-7 gels showed
significant difference in the Tg values determined for the only very slight changes in the positions of NH and amide
freshly prepared and for 1 day aged rac-PhG-7 gels (Tg of I bands with increasing temperature, despite the fact that
75 °C and 119 °C, respectively) and only a slight one for the NH and amide I bands appeared in the range character-
the enantiomer (R)-PhG-7 gels (Tg values 28 °C and 30 °C) istic of hydrogen-bonded peptidic groups in the spectra of
suggests a slower aggregation process for the racemate. The gels at room temperature. These observations show that the
peculiar observed behaviour of the racemic gelators, which aggregates present in the (S)-Leu-6 solution and (R)-PhG-
are either insoluble or tend to crystallize from the majority 6 gel disaggregate at higher temperatures by breakage of
of the tested solvents, but are capable of forming stable gels intermolecular amidic hydrogen bonds, while the gels
with certain solvents and of immobilising larger volumes formed by the sodium salts remain practically unchanged
than the enantiomer, is highly intriguing. Although ad- in the 25Ϫ100 °C temperature range. The thermal behav-
ditional work is needed to clarify these observations, it iour of the (S)-Leu-7 and (R)-PhG-7 gels reveals that be-
should be noted that the ‘‘chiral bilayer effect’’ formulated sides the intermolecular hydrogen bonding between amidic
for chiral amphiphilic hydrogelators predicts formation of groups an additional intermolecular interaction must be
the enantiomeric bilayers in the stable hydrogels of operative in this case. Since both (S)-Leu-7 and (R)-PhG-7
racemates.[26] The same explanation was recently also possess structural characteristics of amphiphiles, intermo-
proposed for the racemic bis(amino alcohol) oxalamide lecular interactions between lipophilic parts and between
gelators, which tend to form inverse bilayers in the lipo- highly polar parts would be expected.[29] In the micellar
philic solvent gels.[28]
fibres formed by the amphiphilic N-dodecyl-tartaric acid
monoamide sodium salt[30] and in the bilayered crystal
structure of potassium palmitate[31] electrostatic and ion-
dipole interactions between sodium or potassium car-
boxylates were found. Hence, for the (S)-Leu-7 and (R)-
PhG-7 gel aggregates, the same type of interactions may
account for the observed additional stabilization, particu-
larly in toluene, due to its poor ability to solvate ions. The
gel melting temperatures (Tg) of the free acid (R)-PhG-6
and of the sodium salt (R)-PhG-7 toluene gels at the same
gelator concentrations (c(R)-PhG-6 ϭ c(R)-PhG-7 ϭ 2.0 ϫ 10Ϫ2
mol·dmϪ3) were determined to be 40 °C for the first and
130 °C for second. The results show that the transformation
of the terminal free carboxylic acid group into the sodium
carboxylate group gives the gelator the capability to form
the toluene gel with a Tg 90 °C higher than that produced
by the free acid gelator.
1
2.3. FTIR and H NMR Investigation
Temperature-dependent FTIR spectra of an (S)-Leu-6
toluene solution and of toluene gels of (S)-Leu-7, (R)-PhG-
6 and (R)-PhG-7 were recorded to check for the presence
of the intermolecular hydrogen bonding interactions in the
aggregates. The positions of NH and amide I bands at room
temperature and at 95Ϫ100 °C are collected in Table 4.
Table 4. Positions of NH and amide I bands (ν˜, cmϪ1) in the FTIR
spectra of (S)-Leu-6 toluene solution and (S)-Leu-7, (R)-PhG-6
and (R)-PhG-7 toluene gels at 25 and 100 °C
Compound[a]
ν(NH)
25 °C
ν(amide I)
25 °C
100 °C
100 °C
(S)-Leu-6
(S)-Leu-7a
(R)-PhG-6
(R)-PhG-7
3285
3291
3292
3291
3408; 3302
3297
3403 br
3299
1636
1637
1640
1630
1650
1637
1675
1630
1
Temperature-dependent H NMR spectra of the phenyl-
glycine derivatives (R)-PhG-6 and (R)-PhG-7 [D8]toluene
gels were also investigated. In previous work we and others
have shown that the observed spectrum of a gel is produced
by gelator molecules, aggregated or free, dissolved in the
entrapped fluid, while signals of gelator molecules as-
sembled in the rigid gel network cannot be observed be-
[a]
Concentrations: (S)-Leu-6, 0.080; (S)-Leu-7, 0.041; (R)-PhG-6,
0.048; (R)-PhG-7, 0.020 mol·dmϪ3
.
In the spectra of the (S)-Leu-6 solution and of the (R)- cause of their long correlation times.[32Ϫ34] However, heat-
PhG-6 gel, the NH and amide I bands at lower wave- ing of gel samples in some cases results in an increase in
numbers, corresponding to hydrogen-bonded amide groups, the gelator signals due to dissociation of the network into
gradually diminish with increasing temperature, and new smaller NMR-observable aggregates and disaggregated
bands corresponding to non-hydrogen bonded amidic molecules. On the other hand, some gels are thermally
groups appear at higher wavenumbers (Table 4). In con- stable in the temperature range available for the common
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M. Zinic et al.
FULL PAPER
NMR solvents and no increase of gelator signals could be
observed by heating of NMR samples.[35] NMR samples
of (R)-PhG-6 and (R)-PhG-7 [D8]toluene gels (c(R)-PhG-6
ϭ
0.0133 mol·dmϪ3; c(R)-PhG-7 ؍ 0.0174 mol·dmϪ3) were pre-
pared with 1,1,2,2-tetrachloroethane (0.5 mol/mol of the
gelator) as the internal standard. In the spectra of the gels
taken at room temperature the concentrations of the NMR-
observable aggregates were calculated from the intensities
of selected gelator signals and that of the internal standard.
The results show that for the (R)-PhG-6 and (R)-PhG-7
gels, 21% and only 3.8% of the total gelator concentration,
respectively, can be observed by NMR spectroscopy. Thus,
the sodium salt derivative (R)-PhG-7 is significantly more
aggregated (96%) than the free acid gelator (R)-PhG-6,
which is 80% aggregated. An increase in the temperature
from 25 to 80 °C failed to produce any significant increase
in the gelator signals for both samples. This shows that both
gels are stable in the specified temperature range and that
no significant disaggregation of the network into dissolved,
NMR-observable aggregates could be detected.
Analysis of chemical shift changes induced by thermal
disaggregation may give valuable information on the weak
intermolecular interactions stabilizing the aggregates and
possibly on the existing self-assembly motifs. To obtain
such information, the temperature dependence of the (R)-
PhG-6 and (R)-PhG-7 chemical shifts was studied at con-
centrations just below their minimal gelation concentrations
(mgc values, determined for (R)-PhG-6 and (R)-PhG-7 and
[D8]toluene in NMR tubes). At concentrations slightly
lower than their mgc values (1.45 ϫ 10Ϫ2 and 1.48 ϫ 10Ϫ2
mol·dmϪ3, respectively), both (R)-PhG-6 and (R)-PhG-7
give highly viscous toluene solutions indicative of the pres-
ence of highly aggregated species that should possess organ-
isation closely resembling that in their gel aggregates. In the
Figure 1. Temperature-induced shifts of (C*H)NH (filled dia-
monds), (CH2)NH (filled squares), COOH (filled triangles) and C*
H (filled circles) protons of (R)-PhG-6 (a) and (R)-PhG-7 (b) in
[D8]toluene, and [D6]DMSO-induced shifts of the same protons of
(R)-PhG-6 (c) and (R)-PhG-7 (d)
In sharp contrast, the C*ϪNH and C*H temperature co-
spectra of the acid derivative (R)-PhG-6 measured over the efficients of 3.6 ϫ 10Ϫ3 and 1.7 ϫ 10Ϫ3 ppm·KϪ1 measured
40Ϫ80 °C temperature interval, both amide NH protons, for the sodium salt (R)-PhG-7 (Figure 1, b) are three and
(C*ϪNH and NHϪCH2), the carboxylic acid proton two times lower than those of (R)-PhG-6, and that of
(COOH) and the methyne proton (C*H) are all shifted up- NHϪCH2 (4.5 ϫ 10Ϫ3 ppm·KϪ1) is also smaller than that
field with increasing temperature (Figure 1, a). The high of (R)-PhG-6. These results clearly show that, at the same
NH temperature coefficients (∆δNH /∆T) of 11.1 ϫ 10Ϫ3 concentrations of gelators and within the same temperature
and 6.5 ϫ 10Ϫ3 ppm·KϪ1 determined for C*ϪNH and range, the aggregates of the sodium salt (R)-PhG-7 had
NHϪCH2, respectively, are characteristic of amidic NH undergone much less disaggregation than those of the free
moieties engaged in hydrogen bonding; the coefficient for acid (R)-PhG-6. This is in agreement with the observations
C*ϪNH amide protons, almost twice as high as for from the temperature-dependent FTIR revealing that (R)-
NH(CH2), shows that the former experienced a larger PhG-7 forms more stable aggregates than (R)-PhG-6 in
chemical shift change by temperature-induced dissociation toluene gel.
of the aggregates, which in turn points to a stronger hydro-
gen bond formed by the C*ϪNH moieties.
In the next set of experiments, small volumes of
[D6]DMSO were gradually added to viscous deuterated
The carboxylic acid proton is also strongly shifted up- toluene solutions of (R)-PhG-6 and (R)-PhG-7 and the
field (∆δCOOH /∆T 19.4 ϫ 10Ϫ3 ppm KϪ1), which clearly changes in the gelator chemical shifts were monitored. Since
shows that the carboxylic groups are also involved in hydro- DMSO is strong competitor for hydrogen bonds, its ad-
gen bonding that stabilises the aggregates. A significant up- dition should result in dissociation of the hydrogen-bonded
field shift (∆δC*H /∆T ϭ 7.3 ϫ 10Ϫ3 ppm·KϪ1) is also ob- aggregates; the 1H NMR spectra were recorded over a
served for the C*H proton, being closest to the strong hy- range of DMSO/gelator molar ratios from 0 to 5. In the
drogen bond formed by (C*H)NH. It seems plausible that spectra of (R)-PhG-6, the C*ϪNH, NHϪCH2 and C*H
C*H is deshielded in the aggregate by the close amide car- protons were significantly shifted upfield with increasing
bonyl oxygen of the second molecule and hence becomes DMSO/(R)-PhG-6 ratio (Figure 1, c). The trend in the
shielded by disaggregation.
chemical shifts (upfield) is the same as seen in the tempera-
4052
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Eur. J. Org. Chem. 2004, 4048Ϫ4059

Synthesis, Gelling Properties and Preferred Gelation of Chiral Gelators
ture-dependent spectra and can be explained in the same
FULL PAPER
It should be noted that both the cooperative amidic hy-
way by breakage of the intermolecular amidic hydrogen drogen bonding and the interactions between sodium car-
bonds and dissociation of the aggregates. Surprisingly, the boxylates may induce unidirectional self-assembly necessary
opposite trend of chemical shifts (downfield) was observed for formation of fibrous aggregates.
in spectra of (R)-PhG-7 with addition of DMSO (Figure 1,
d); strong downfield shifts of the (CH2)NH (for 1 ppm) and
C*H protons (for 0.2 ppm) could be observed in the spectra
of (R)-PhG-7 in [D8]toluene upon successive additions of
[D6]DMSO. The shifts of the (C*H)NH protons could not
be followed after the first two [D6]DMSO additions since
the signal overlaps with the residual nondeuterated toluene
signal. The different behaviour of (R)-PhG-6 and (R)-PhG-
7 toluene gels upon addition of DMSO could be explained
by the fact that (R)-PhG-6 is soluble in DMSO (Table 1)
and that (R)-PhG-7 is capable of gelling DMSO with a
similar efficiency to toluene (Table 1). Consequently, the ad-
dition of DMSO to the first system results in partial disag-
gregation and dissolution of smaller aggregates, while in the
second system the aggregation seems to be enhanced or an-
other state of aggregation may form, resulting in enhanced
intermolecular hydrogen bonding and deshielding of NH
moieties, respectively.
2.4. TEM Investigation
TEM images of sufficient quality were obtained for the
(R)-phenylglycine and phenylalanine derivatives (R)-PhG-7
and (S)-Phe-7 DMSO gels after staining with dipotassium
phosphotungstate (PWK) (Figure 3, a,b). Both images
show typical gel morphology consisting of entangled fibres
with diameters in the 20Ϫ80 nm range. Closer examination
of the (S)-Phe-7 TEM image shows the fibres consisting of
twisted ribbons. TEM of (R)-PhG-7 gel shows the presence
of much shorter fibres than in the (S)-Phe-7 gel, forming a
much denser network, although the twisted ribbon mor-
phology of the fibres cannot be observed.
3. Conclusion
1
A new class of optically active and racemic gelators con-
structed from 11-aminoundecanoic acid (AUDA), lauric
acid and various core amino acid units has been prepared
and tested for gelation in the forms of the free acids and
the sodium salts. The results of gelation experiments have
shown that the ambidextrous gelation both of highly polar
and of highly lipophilic fluids could be accomplished by
some derivatives of the series. It was also found that some
racemic salts could be much better gelators of certain sol-
vents than the corresponding pure enantiomers; that ra-
cemic rac-PhG-7, for example, is capable of immobilising a
16 times larger volume of p-xylene that the R enantiomer
(R)-PhG-7. This result is of great importance for the search
for highly efficient chiral gelators, showing that, in contrast
with previous findings,[22Ϫ27] racemates may gel much
higher volumes of certain solvents than the pure enanti-
omers. Determination of gel melting temperatures (Tg) for
two enantiomer/racemate pairs has shown that aggregates
of different stability are formed in the enantiomer and in
the racemate gels. Temperature-dependent FTIR and 1H
NMR studies of selected gels have shown that the intermo-
The results of FTIR and H NMR investigations clearly
show that the intermolecular hydrogen-bonding interac-
tions involving amidic and carboxylic acid groups and the
electrostatic and ion-dipole interactions between sodium
carboxylates contribute strongly to stabilization of the ag-
gregates in toluene gels (Figure 2, a,b).
Figure 2. Schematic representation of hydrogen-bonding and elec-
trostatic intermolecular interactions stabilizing gel aggregates: (a)
hydrogen bonding between amidic and carboxylic groups and (b)
electrostatic and ion-dipole interactions between sodium car-
boxylates
Figure 3. TEM images of (R)-PhG-7 (a) and (S)-Phe-7 (b) DMSO gels after staining with dipotassium phosphotungstate (PWK)
www.eurjoc.org 4053
Eur. J. Org. Chem. 2004, 4048Ϫ4059
 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

ˇ
´
M. Zinic et al.
FULL PAPER
corresponding optically active derivatives. Optical activity was de-
termined with an Optical Activity AA-10 Automatic Polarimeter
in a 1-dm cell at λ ϭ 589 nm. The yields have not been optimized.
lecular hydrogen bonding between amidic and carboxylic
units represent the dominating forces stabilising organis-
ation in the gel fibres of free acid derivatives. The gelators
form considerably more stable aggregates in the form of
their sodium salts than in their free acid forms. In the latter
aggregates, besides amidic intermolecular hydrogen bond-
ing, additional strong stabilization originating from mul-
tiple intermolecular electrostatic and ion-dipole interactions
between carboxylates and sodium cations is also present.
These interactions would be expected to be very strong in
lipophilic solvents, because of their poor capability to solv-
ate ions. This finding appears highly relevant for the prep-
aration of gels with desired thermal characteristics. It points
toward the carboxylic acid salt as an important unit in the
gelator structure, capable of strong stabilization of the ag-
gregates in lipophilic solvents and of providing gels with
enhanced thermal stability.
Preparation of Boc-Amino Acids 2: Amino acid 1 (10 mmol) was
dissolved in dioxane/water (2:1, 30 mL), which was made alkaline
with NaOH (1 , 10 mL) and cooled in an ice-bath, and (Boc)2O
(3.272 g, 15 mmol) and NaHCO3 (840 mg, 10 mmol) were added.
The reaction mixture was stirred overnight at room temp. and was
then evaporated to half the volume. The residue was diluted with
EtOAc (40 mL), cooled in an ice-bath and acidified to pH ϭ 2.5Ϫ3
with KHSO4 (1 ). The layers were separated, the aqueous fraction
was extracted with EtOAc (2 ϫ 20 mL), and the combined extracts
were washed with water, dried and evaporated, leaving products 2
as colourless oils in quantitative yields. These were used for the
condensation step without any purification.
DCC-Condensation with Methyl 11-Aminoundecanoate. General
Procedure for Preparation of 3: Methyl 11-aminoundecanoate hy-
drochloride (2.518 g, 10 mmol) was added to a Boc-protected am-
ino acid 2 (10 mmol) dissolved in dried CH2Cl2 (50 mL). The mix-
ture was cooled in an ice-bath, and DCC (2.063 g, 10 mmol), Et3N
(1.40 mL, 1.012 g, 10 mmol) and DMAP (122 mg, 1.0 mmol) were
added. After the mixture had been stirred at room temperature
overnight the precipitated DCHU was filtered off and the cake was
washed with CH2Cl2 (50 mL). The filtrate was washed with AcOH
(10%, 10 mL), water, NaHCO3 (5%) and again water, dried and
evaporated, leaving products 3 as colourless oils that were purified
chromatographically on silica (CH2Cl2/MeOH, 19:1 and 9:1). 1H
NMR spectra are given in Table 5, and 13C NMR spectra in
Table 6.
Experimental Section
General: All solvents were dried and redistilled shortly before use.
Flash chromatography was performed on Merck 60 silica gel
(0.2Ϫ0.63 mm), with CH2Cl2/MeOH solvent mixtures as eluents.
Thin layer chromatography was performed on plastic sheet silica
gel (Merck 60 F254). Spots were viewed under a UV lamp (254 nm)
or with the aid of iodine vapour. Melting points were determined
with a Kofler hot-bench apparatus and were not corrected. IR
Spectra (ν˜ in cmϪ1) were taken with a PerkinϪElmer 257 spec-
trometer in KBr pellets. NMR spectra (δ in ppm rel. to Me4Si as
an internal standard) were taken with a Varian XL-300 Gemini
spectrometer and Bruker. NMR spectroscopic data are given in
Table 5Ϫ8. All spectroscopic and analytical data of racemic com-
pounds, except for the [α]D values, were identical to those of the
Methyl
11-({(2S)-2-[(tert-Butoxycarbonyl)amino]-4-methylpenta-
noyl}amino)undecanoate [(S)-Leu-3]: The product (S)-Leu-3
(1.197 g, 84%) was obtained from (S)-Leu-2 (767 mg, 3.316 mmol).
IR: ν˜ ϭ 3333, 2923, 2851, 1732, 1686, 1647, 1526, 1173, 1049 cmϪ1
.
1
Table 5. H NMR spectra of Boc-amino compounds 3 and amino derivatives 4 (taken in CDCl3, with TMS as an internal standard, δ
in ppm, J in Hz)
Ph
*CHCONH *CHNH *CH
OCH3 NHϪCH2
(J in Hz)
CH2CO
t (J in Hz) CH2CH2CO m
(J in Hz)
NHCH2CH2 and C(CH3)3 other CH2 CH(CH3)2
and CH
1.27 m
1.40 m
(J in Hz)
Leu-3
Ϫ
6.10 m
4.87 m
4.04 m
3.54 m
3.67 s 3.24 dt as q 2.31 (7.69) 1.70Ϫ1.59
1.45 s
0.94 dd
(2.20;
6.32)
1.04 dd
as t (6.59)
0.90 dd
as t
(6.87)
Leu-4[a]
Val-3
Ϫ
Ϫ
3.74 s 3.41Ϫ3.19 m 2.40 (7.33) 1.81Ϫ1.51
3.63 s 3.28Ϫ3.14 m 2.27 (7.69) 1.68Ϫ1.03
Ϫ
6.39 m
7.32 m
5.22 d
(8.79)
3.85 dd
(6.60, 8.79)
1.40 s
1.68Ϫ
1.03 m
(6.87;
9.10)
Val-4
Ϫ
4.68 m
3.29Ϫ
3.19 m
5.15 d
3.67 s 3.29Ϫ3.19 m 2.30 (7.69) 1.62 t (7.14),
1.50 t (6.87)
3.66 s 3.19 q (6.59) 2.30 (7.69) 1.61 t (7.14)
Ϫ
1.28 m
0.99, 0.82
dd (6.87)
Ϫ
PhG-3 7.42Ϫ7.28 m 6.06 m
5.94 d
(5.77)
1.40 s
1.33Ϫ
1.08 m
1.24 m
1.27Ϫ
1.16 m
1.36Ϫ
1.23 m
PhG-4 7.38Ϫ7.28 m 7.16 m
4.60 m
5.23 m
4.48 m
4.29
3.64 s 3.21 q (6.59) 2.29 (7.69) 1.60 m,1.46 m
3.67 s 3.20Ϫ3.01 m 2.30 (7.69) 1.61 t (6.87)
Ϫ
Ϫ
Ϫ
Phe-3
Phe-4
7.31Ϫ7.19 m 5.90 m
7.29Ϫ7.20 m 6.40 m
1.40 s
(6.86)
3.87 m
4.65 m
3.65 s 3.19Ϫ3.07 m 2.29 t (7.42) 1.60 m
Ϫ
Ϫ
and 2.90 dd
(7.42;12.91)
[a]
Taken in CD3OD.
4054
 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Eur. J. Org. Chem. 2004, 4048Ϫ4059

Synthesis, Gelling Properties and Preferred Gelation of Chiral Gelators
FULL PAPER
Table 6. 13C NMR spectra of Boc-amino compounds 3 and amino derivatives 4 (taken in CDCl3, with TMS as an internal standard, δ
in ppm)
COO *CHCONH *CHNHCO Ph
C(CH3)3 *CH OCH3 *CHCH2 NHCH2 CH2CO other CH2 and CH C(CH3)3 CH(CH3)2
Leu-3
Leu-4
172.26
176.17
155.20
Ϫ
Ϫ
80.01
52.85 51.26 43.30
54.37 52.17 44.83
39.36
40.65
33.94
34.29
33.98, 29, 28,
29.08
26.65,
24.80
30.49
29.20, 28.98, 26.63
30.73, 30.63, 30.30,
28.10, 26.14, 25.96,
23.24, 22.76
Ϫ
Ϫ
Ϫ
Val-3 174.13 171.36
155.75
Ϫ
Ϫ
Ϫ
79.50
59.94 51.26
59.92 51.21
58.31 51.29
Ϫ
Ϫ
Ϫ
39.24
38.75
39.31
33.91
33.86
33.92
29.35, 29.23, 29.23, 28.13
29.01, 28.91,
26.69, 24.23
19.12
24.70
Ϫ
Val-4
174.10
Ϫ
29.46, 29.20, 29.10,
29.01, 28.88, 26.70,
19.53, 15.76
Ϫ
PhG-3 174.19 169.92
PhG-4 174.10 172.62
Phe-3 174.19 170.91
Phe-4 174.20 171.40
155.051
138.48 C-1Ј 79.81
128.73 C-3Ј
128.03 C-4Ј
29.18. 29.12, 29.01, 28.13
28.93, 26.48, 24.75
126.98 C-2Ј
Ϫ
140.96 C-1Ј
128.54 C-2Ј
127.68 C-4Ј
126.64 C-3Ј
136.70 C-1Ј 79.91
129.15 C-3Ј
128.44 C-2Ј
126.69 C-4Ј
136.27 C-1Ј
129.17 C-2Ј
128.56 C-3Ј
126.93 C-4Ј
Ϫ
59.58 51.22
Ϫ
39.01
39.31
39.19
33.86
33.92
33.91
29.29, 29.18, 29.08,
28.96, 28.86,
Ϫ
Ϫ
Ϫ
Ϫ
26.60, 24.70
155.26
Ϫ
55.88 51.31 38.67
55.61 51.29 39.46
29.23, 29.18, 29.03, 28.11
28.95, 26.58, 24.76
Ϫ
29.23, 29.17, 29.05,
28.93, 26.65, 24.75
Ϫ
Methyl 11-({(2R,S)-2-[(tert-Butoxycarbonyl)amino]-4-methylpenta-
noyl}amino)undecanoate (rac-Leu-3): The product rac-Leu-3
(5.356 g, 74%) was obtained from rac-Leu-2 (3.890 g,
16.892 mmol).
(5.0 mmol) dissolved in CH2Cl2 (5Ϫ10 mL) and cooled in an ice-
bath, and the mixture was stirred overnight at room temperature.
The solution was evaporated, and some diethyl ether or CH2Cl2
(50 mL) and 10% KHCO3 (10 mL) were added with cooling and
stirring. The layers were separated, the aqueous layer was extracted
with additional ether or CH2Cl2 (2 ϫ 25 mL), and the combined
extracts were washed with KHCO3 (5%) and water, dried and eva-
porated, affording deprotected amino compounds 4. 1H NMR
spectra are given in Table 5, and 13C NMR spectra in Table 6.
Methyl 11-({(2S)-2-[(tert-Butoxycarbonyl)amino]-3-methylbutanoyl}-
amino)undecanoate [(S)-Val-3]: The product (S)-Val-3 (1.851 g, 93%)
was obtained from (S)-Val-2 (1.048 g, 4.824 mmol). IR: ν˜ ϭ 3326,
2918, 2850, 1735, 1687, 1650, 1557, 1524, 1172 cmϪ1
.
Methyl 11-({(2R,S)-2-[(tert-Butoxycarbonyl)amino]-3-methylbutan-
oyl}amino)undecanoate (rac-Val-3): The product rac-Val-3 (3.241 g,
95%) was obtained from rac-Val-2 (1.762 g, 8.202 mmol).
Methyl 11-{[(2S)-2-Amino-4-methylpentanoyl]amino}undecanoate
[(S)-Leu-4]: The product (S)-Leu-4 (605 mg, 94%) was obtained
from (S)-Leu-3 (844 mg, 1.969 mmol). IR: ν˜ ϭ 3292, 2928, 2855,
Methyl 11-({(2R)-2-[(tert-Butoxycarbonyl)amino]-2-phenylethanoyl}-
amino)undecanoate [(R)-PhG-3]: The product (R)-PhG-3 (8.586 g,
96%) was obtained from (R)-PhG-2 (5.026 g, 20 mmol). IR: ν˜ ϭ
1740, 1654, 1557, 1437, 1368, 1201, 1010 cmϪ1
.
3328, 2927, 2851, 1733, 1647, 1524, 1367, 1250, 1172, 700 cmϪ1
.
Methyl 11-{[(2R,S)-2-Amino-4-methylpentanoyl]amino}undecanoate
(rac-Leu-4): The product rac-Leu-4 (4.088 g, 100%) was obtained
from rac-Leu-3 (5.356 g, 12.496 mmol).
Methyl 11-({(2R,S)-2-[(tert-Butoxycarbonyl)amino]-2-phenylethan-
oyl}amino)undecanoate (rac-PhG-3): The product rac-PhG-3
(7.197 g, 98%) was obtained from rac-PhG-2 (4.126 g,
16.420 mmol).
Methyl
11-{[(2S)-2-Amino-3-methylbutanoyl]amino}undecanoate
[(S)-Val-4]: The product (S)-Val-4 (1.305 g, 95%) was obtained
from (S)-Val-3 (1.808 g, 4.361 mmol). IR: ν˜ ϭ 3318, 2927, 2851,
Methyl 11-({(2S)-2-[(tert-Butoxycarbonyl)amino]-3-phenylpropan-
oyl}amino)undecanoate [(S)-Phe-3]: The product [(S)-Phe-3
(7.066 g, 76%) was obtained from (S)-Phe-2 (5.306 g, 20.0 mmol).
IR: ν˜ ϭ 3349, 2929, 2851, 1733, 1685, 1655, 1435, 1296, 1172,
1735, 1638, 1541, 1466, 1373, 1176 cmϪ1
.
Methyl 11-{[(2R,S)-2-Amino-3-methylbutanoyl]amino}undecanoate
(rac-Val-4): The product rac-Val-3 (2.233 g, 91%) was obtained
from rac-Val-3 (3.241 g, 7.818 mmol),.
698 cmϪ1
.
Methyl 11-({(2R,S)-2-[(tert-Butoxycarbonyl)amino]-3-phenylpropan-
oyl}amino)undecanoate (rac-Phe-3): The product rac-Phe-3
(8.371 g, 91%) was obtained from rac-Phe-2 (5.306 g, 20.0 mmol).
Methyl
11-{[(2R)-2-Amino-2-phenylethanoyl]amino}undecanoate
[(R)-PhG-4]: The product (R)-PhG-4 (5.520 g, 83%) was obtained
from (R)-PhG-3. IR: ν˜ ϭ 3320, 2926, 2851, 1735, 1647, 1541, 1437,
Removal of Boc Protecting Group. General Procedure for Prep-
aration of 4: TFA (5 mL) was added to the starting compound 3
1173, 699 cmϪ1
.
Eur. J. Org. Chem. 2004, 4048Ϫ4059
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 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
4055

ˇ
´
M. Zinic et al.
FULL PAPER
Methyl
11-{[(2R,S)-2-Amino-2-phenylethanoyl]amino}undecanoate
obtained from (S)-Leu-4 (917 mg, 2.793 mmol). IR: ν˜ ϭ 3292,
2921, 2852, 1732, 1636, 1542, 1466, 1174, 722 cmϪ1. [α]2D2 ϭ Ϫ24
(c ϭ 0.996, CH2Cl2). C30H58N2O4 (510.8): calcd. C 70.54, H 11.45,
N 5.48; found C 70.31, H 11.45, N 5.54.
(rac-PhG-4): The product rac-PhG-4 (5.038 g, 90%) was obtained
from rac-PhG-3 (7.197 g, 16.043 mmol).
Methyl 11-{[(2S)-2-Amino-3-phenylpropanoyl]amino}undecanoate
[(S)-Phe-4]: The product (S)-Phe-4 (5.495 g, 100%) was obtained
from (S)-Phe-3 (7.010 g, 15.153 mmol). IR: ν˜ ϭ 3290, 2928, 2855,
Methyl 11-{[(2R,S)-2-Amino-3-phenylpropanoyl]amino}undecanoate
(rac-Leu-5): The product rac-Leu-5 (5.829 g, 92%) was obtained
from rac-Leu-4 (4.088 g, 12.445 mmol).
1739, 1671, 1564, 1437, 1201, 700 cmϪ1
.
Methyl 11-{[(2R,S)-2-Amino-3-phenylpropanoyl]amino}undecanoate
(rac-Phe-4): The product rac-Phe-4 (6.470 g, 96%) was obtained
from rac-Phe-3 (8.371 g, 18.095 mmol).
Methyl 11-{[(2S)-2-(Dodecanoylamino)-3-methylbutanoyl]amino}-
undecanoate [(S)-Val-5]: The crude product was obtained from (S)-
Val-4 (1.257 g, 3.997 mmol) and purified by FC on silica (CH2Cl2/
MeOH 33:1and 24:1), giving (S)-Val-5 (1.712 g, 86%). M.p. 90Ϫ93
°C. IR: ν˜ ϭ 3291, 2921, 2851, 1739, 1634, 1542, 1467, 1388, 1174,
721 cmϪ1. [α]2D2 ϭ Ϫ15 (c ϭ 1.036, CH2Cl2). C29H56N2O4 (496.8):
calcd. C 70.12, H 11.36, N 5.64; found C 69.98, H 11.17, N 5.44.
Treatment with Lauroyl Chloride. General Procedure for Preparation
of 5: Et3N (1.4 mL, 1.012 g, 10 mmol) and lauroyl chloride
(2.4 mL, 2.188 g, 10 mmol) were added to a solution of an amino
compound 4 (10 mmol) in dry CH2Cl2 (25 mL), which was cooled
in an ice bath, and the mixture was stirred overnight at room tem-
perature. The solution was diluted with additional CH2Cl2 and co-
oled, and some water was added. The layers were separated, the
aqueous one was extracted twice with CH2Cl2, the combined ex-
tracts were washed with aqueous NaHCO3, water, HCl (0.1 ) and
water and dried, and the solvents were evaporated. 1H NMR Spec-
tra are given in Table 7, and 13C NMR spectra in Table 8.
Methyl 11-{[(2R,S)-2-(Dodecanoylamino)-3-methylbutanoyl]amino}-
undecanoate (rac-Val-5): The product rac-Val-5 (2.757 g, 78%) was
obtained from rac-Val-4 (2.233 g, 7.101 mmol).
Methyl 11-{[(2R)-2-(Dodecanoylamino)-2-phenylethanoyl]amino}-
undecanoate [(R)-PhG-5]: The product (R)-PhG-5 (8.071 g, 97%)
was obtained from (R)-PhG-4 (5.485 g, 15.740 mmol); after recrys-
tallization from 96% EtOH it was 6.267 g (78%), m.p. 116Ϫ119 °C.
IR: ν˜ ϭ 3288, 2918, 2850, 1736, 1635, 1541, 1468, 1378, 1175, 700
Methyl 11-{[(2S)-2-(Dodecanoylamino)-4-methylpentanoyl]amino}-
undecanoate [(S)-Leu-5]: The product (S)-Leu-5 (1.347 g, 94%) was
1
Table 7. H NMR spectra (for 5 and 6 taken in CDCl3, 7 in CD3OD, with TMS as an internal standard, δ in ppm, J in Hz)
Ph
m
*CHCONH *CHNH
*CH
OCH3 NHϪCH2
2 ϫ CH2CO other CH2 and CH CH(CH3)2
CH3
t
t
m
dd
Leu-5
Leu-6
Leu-7
Val-5
Ϫ
Ϫ
Ϫ
Ϫ
6.80 m
7.15 t
6.61 d (8.52) 4.49 dt (6.04) 3.66 s 3.27Ϫ3.10 m (6.04) 2.29 (7.69), 1.60Ϫ1.09
0.92 (6.32)
0.87 (6.87)
2.17 (7.69)
6.99 d (8.51) 4.55 q (7.69)
Ϫ
3.25Ϫ3.08 m
2.30 (7.69), 1.59Ϫ1.23
0.92Ϫ0.84 m
2.16 (7.97)
4.45 dd (6.35, Ϫ
3.26 t (7.08)
2.39Ϫ
1.69Ϫ1.22
1.06Ϫ0.97 m
8.79)
2.21 m
7.09 t
6.80 d (8.79) 4.30 t (7.96) 3.65 s 3.32Ϫ3.05 m
2.28 (7.96), CH 2.14Ϫ2.01
2.20 (8.24) CH2
0.94Ϫ0.84 dd ϩ s (6.32, 11.54)
1.59Ϫ1.25
Val-6
Val-7
Ϫ
Ϫ
7.31 d
(9.06)
7.22 d (8.79) 4.33 dd as t
(8.52)
Ϫ
Ϫ
3.28Ϫ3.07 m
2.31 (7.69), CH 2.00 q
0.89 (6.59, 15.11)
1.01 (6.59)
2.21 m
(6.87) CH2
1.62Ϫ1.25
4.19 d (7.81)
3.26 ddt (7.08)
2.35 (7.33), CH 2.12 dt
2.24 (7.33) (6.84) CH2
1.69Ϫ1.22
PhG-5 7.38Ϫ 6.65 t
7.12 d (7.31) 5.73 (7.69)
3.66 s 3.21 dt (6.50)
2.28
(7.42)
1.62Ϫ1.20
Ϫ
Ϫ
0.88 (6.84)
0.88 (6.59)
0.97 (6.34)
0.99 (6.84)
7.23
PhG-6 7.38Ϫ 6.82 t
7.27
PhG-6[a] 7.67Ϫ 7.1 m
7.16
7.50 m
5.71 (7.41)
Ϫ
Ϫ
Ϫ
3.19 dd as t (6.32) 2.30 (7.42), 1.61Ϫ1.20
2.26 (7.69)
2.33Ϫ
1.91 m
2.38 dt
(4.64, 7.33),
2.24 (7.33)
1.87 m
7.76 d (7.06) 6.13 d (7.84)
4.20 q (7.33)
3.16 ddt (6.32)
3.25 ddt (6.59)
1.61Ϫ1.15
1.69Ϫ1.33
PhG-7 7.52Ϫ
7.39
Ϫ
PhG-7[a] 7.58Ϫ 6.40 m
7.1 m
5.92 d (7.31)
Ϫ
3.11 ddt (6.28)
1.55Ϫ1.16
Ϫ
Ϫ
0.93 (6.74)
0.88 (6.59)
7.23
Phe-5
7.26Ϫ 6.31 t
6.69 d (7.42) 4.69 q (7.42) 3.67 s 3.16 quint.
2.30 (7.42), 1.61Ϫ1.25
7.19
(6.59) and
2.16 (7.14)
3.04 m (7.69)
Phe-6
Phe-7
7.29Ϫ 6.87 m
7.18
7.38Ϫ
7.35 d (8.57) 4.75 q (7.69)
4.66 (6.59)
Ϫ
Ϫ
3.01 d (7.42)
2.36 (7.42), 1.65 t (6.87),
2.17 (7.42) 1.60Ϫ1.24
Ϫ
Ϫ
0.88 (6.87)
0.97 (6.84)
3.18 dϩt (7.33)
and 2.98 dd
2.24 tϩt
1.69Ϫ1.38
7.29
(6.84)
(8.79, 13.67)
[a]
In [D8]toluene.
4056
 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
Eur. J. Org. Chem. 2004, 4048Ϫ4059

Synthesis, Gelling Properties and Preferred Gelation of Chiral Gelators
Table 8. 13C NMR spectra (for 5 and 6 taken in CDCl3, 7 in CD3OD, with TMS as an internal standard, δ in ppm)
FULL PAPER
COO
NHCO
Ph
*CH
OCH3 NHCH2 *CHCH2 CH2CO
other CH2 and CH
CH(CH3)2
CH3
Leu-5
Leu-6
Leu-7
Val-5
174.20 173.39, 172.27
177.16 173.39, 172.52
183.23 176.31, 174.95
174.10 173.20, 171.43
Ϫ
51.44 51.33
40.98
41.01
42.27
39.29
39.43
39.36
40.52
Ϫ
36.35, 33.94 31.77, 29.49, 29.30, 29.20, 29.08,
28.98, 26.70, 25.56, 24.78, 24.65,
22.66, 22.54, 22.18
36.20, 33.89 31.72, 29.45, 29.37, 29.20, 29.06,
26.70, 25.55, 24.75, 24.60, 22.57,
22.49, 22.16
39.48, 37.00 33.23, 31.03, 30.85, 30.64, 30.54,
30.42, 28.11, 27.99, 27.14, 26.12,
23.90, 23.59, 22.18
13.97
Ϫ
Ϫ
Ϫ
51.41
53.33
Ϫ
Ϫ
13.92
14.64
13.92
58.39 51.24
36.41, 33.89 31.72, 31.00, 29.44,
29.35, 29.29, 29.20,
19.07, 18.39
28.95, 26.75, 25.63,
24.75, 22.49
Val-6
177.31 173.69, 171.69
Ϫ
Ϫ
58.62
Ϫ
39.38
Ϫ
36.30, 34.03 33.92, 33.43, 31.75,
30.85, 29.47, 29.37,
19.07, 18.51
13.96
29.20, 29.10, 28.93,
28.83, 26.69, 25.67,
25.34, 24.76, 24.70,
22.52
Val-7
183.23 176.34, 173.79
60.60
Ϫ
40.47
39.62
Ϫ
Ϫ
39.46, 37.00 33.23, 31.87, 31.04,
30.85, 30.63, 28.16,
27.98, 27.21, 23.90
36.34, 33.92 31.75, 29.45, 29.35,
29.23, 29.15, 29.05,
19.92, 19.02
14.62
13.96
PhG-5 174.15 172.59, 170.02 138.43 C-1Ј 56.42 51.29
Ϫ
128.54 C-3Ј
127.76 C-4Ј
126.84 C-2Ј
28.95, 26.58, 25.46,
24.76, 22.52
PhG-6 174.20 172.78, 170.14 138.31 C-1Ј 56.46
Ϫ
Ϫ
39.68
40.62
39.33
39.36
40.70
Ϫ
36.32, 33.96 31.78, 29.49, 29.37,
29.22, 29.16, 26.58,
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
13.99
14.64
13.96
13.99
14.77
128.61 C-2Ј
127.86 C-4Ј
126.89 C-3Ј
25.46, 24.78, 22.56
PhG-7 183.26 175.92, 172.60 139.38 C-1Ј 58.92
Ϫ
39.48, 36.83 33.23, 30.90, 30.81,
30.63, 30.4, 27.98,
129.85 C-2Ј
129.32 C-4Ј
128.73 C-3Ј
27.06, 23.90
Phe-5
Phe-6
Phe-7
174.17 173.06, 170.86 136.70 C-1Ј 54.38 51.29
38.61
38.56
39.60
36.34, 33.93 31.75, 29.47, 29.34,
29.20, 29.05, 26.60,
129.12 C-3Ј
128.34 C-2Ј
126.67 C-4Ј
25.46, 24.76, 22.52
177.72 173.62, 171.42 136.55 C-1Ј 54.43
Ϫ
Ϫ
36.27, 33.91 31.78, 29.35, 29.22,
28.98, 28.93, 28.79,
28.71, 26.45, 25.48,
24.60, 22.56
37.18, 33.38 31.18, 31.05, 30.98,
30.78, 30.57, 28.13,
129.14 C-3Ј
128.34 C-2Ј
126.69 C-4Ј
183.36 176.31, 173.72 138.82 C-1Ј 56.40
130.59 C-3Ј
129.69 C-2Ј
128.03 C-4Ј
27.21, 24.05
cmϪ1. [α]2D2 ϭ Ϫ59 (c ϭ 0.998, CH2Cl2). C32H54N2O4 (530.8): calcd.
C 72.41, H 10.25, N 5.28; found C 72.25, H 9.99, N 5.49.
Saponification of the Methyl Ester Group. General Procedure for
Preparation of 6: For optically active compounds: LiOH (1 ,
30 mL, 30 mmol) was added to a solution of methyl ester (S)-Leu-
5, (S)-Val-5, (R)-PhG-5 or (S)-Phe-5 (10 mmol) in methanol/
CH2Cl2 (5:1, 100 mL). For racemic compounds: KOH/MeOH
(10%, 30 mL) was added to a solution of methyl ester rac-Leu-5,
rac-Val-5, rac-PhG-5 or rac-Phe-5 (10 mmol) in CH2Cl2 (50 mL).
After stirring at room temperature for 2Ϫ4 days, the mixture was
neutralised with HCl (1 ) and evaporated, some water was added,
and the mixture was acidified to pH ϭ 2Ϫ2.5 with HCl (1 ). The
precipitated acid was collected, washed with water and air-dried.
1H NMR Spectra are given in Table 7, and 13C NMR spectra in
Table 8.
Methyl 11-{[(2R,S)-2-(Dodecanoylamino)-2-phenylethanoyl]amino}-
undecanoate (rac-PhG-5):The product rac-PhG-5 (7.192 g, 93%)
was obtained from rac-PhG-4 (5.038 g, 14.457 mmol).
Methyl 11-{[(2S)-2-(Dodecanoylamino)-3-phenylpropanoyl]amino}-
undecanoate [(S)-Phe-5]: The crude product (S)-Phe-5 (7.688 g,
94%) was obtained from (S)-Phe-4 (5.440 g, 15.006 mmol) and
crystallised from MeOH, m.p. 86Ϫ88 °C (6.099 g, 79%). IR: ν˜ ϭ
3293, 2930, 2846, 1734, 1641, 1541, 1466, 1380, 1204, 699 cmϪ1
.
[α]2D2 ϭ Ϫ3 (c ϭ 1.014, CH2Cl2). C33H56N2O4 (544.8): calcd. C
72.25, H 10.36, N 5.14; found C 72.52, H 10.07, N 5.21.
Methyl 11-{[(2R,S)-2-(Dodecanoylamino)-3-phenylpropanoyl]- 11-{[((2S)-2-(Dodecanoylamino)-4-methylpentanoyl]amino}-
amino}undecanoate (rac-Phe-5): The product rac-Phe-5 (7.903 g,
81%) was obtained from rac-Phe-4 (6.470 g, 17.848 mmol).
undecanoic Acid [(S)-Leu-6]: The product [(S)-Leu-6 (492 mg, 93%)
was obtained from (S)-Leu-5 (542 mg, 1.061 mmol). M.p.160Ϫ162
Eur. J. Org. Chem. 2004, 4048Ϫ4059
www.eurjoc.org
 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
4057

ˇ
´
M. Zinic et al.
FULL PAPER
°C. IR: ν˜ ϭ 3294, 2929, 2851, 1729, 1655, 1606, 1544, 1122, 616
Sodium 11-{[(2R,S)-2-(Dodecanoylamino)-2-phenylethanoyl]amino}-
cmϪ1. [α]2D2 ϭ Ϫ22 (c ϭ 0.984, CH2Cl2). C29H56N2O4 (496.8): calcd. undecanoate (rac-PhG-7): The product rac-PhG-6 (307 mg, 100%)
C 70.12, H 11.36, N 5.64; found C 69.89, H 11.31, N 5.86.
was obtained from rac-PhG-6 (296 mg, 0.572 mmol).
Sodium 11-{[(2S)-2-(Dodecanoylamino)-3-phenylpropanoyl]amino}-
undecanoate [(S)-Phe-7]: The product (S)-Phe-7 (615 mg, 100%) was
obtained from (S)-Phe-6 (589 mg, 1.110 mmol). M.p. 208Ϫ210 °C.
IR: ν˜ ϭ 3297, 2923, 2851, 2467, 1637, 1565, 1444, 1241, 1119, 699
11-{[(2R,S)-2-(Dodecanoylamino)-4-methylpentanoyl]amino}-
undecanoic Acid (rac-Leu-6): The product rac-Leu-6 (5.634 g,
100%) was obtained from rac-Leu-5 (5.817 g, 11.388 mmol).
11-{[(2S)-2-(Dodecanoylamino)-3-methylbutanoyl]amino}undecanoic
Acid [(S)-Val-6]: The product (S)-Val-5 (1.457 g, 88%) was obtained
from (S)-Val-5 (1.712 g, 3.446 mmol). IR: ν˜ ϭ 3291, 2920, 2851,
1741, 1635, 1560, 1466, 1388, 1234 cmϪ1. [α]2D2 ϭ Ϫ16.5 (c ϭ 1.030,
CH2Cl2/MeOH, 1:1). C28H54N2O4 (482.7): calcd. C 69.67, H 11.27,
N 5.80% found C 69.37, H 11.16, N 5.59.
cmϪ1
.
Sodium 11-{[(2R,S)-2-(Dodecanoylamino)-3-phenylpropanoyl]amino}-
undecanoate (rac-Phe-7): The product rac-Phe-7 (383 mg, 100%)
was obtained from rac-Phe-6 (367 mg, 0.691 mmol).
Determination of Gelling Properties: The tested substance (10 mg)
was placed in a test tube, and the solvent was added by microsyr-
inge in 100Ϫ500 µL portions. After each addition the mixture was
gently heated until the substance dissolved, and was then allowed
to cool spontaneously to room temperature and formation of gel
checked by test tube inversion. The procedure was repeated until
sample fluidity was restored at room temperature.
11-{[(2R,S)-2-(Dodecanoylamino)-3-methylbutanoyl]amino}-
undecanoic Acid (rac-Val-6): The product rac-Val-6 (2.652 g, 99%)
was obtained from rac-Val-6 (2.755 g, 5.546 mmol.
11-{[(2R)-2-(Dodecanoylamino)-2-phenylethanoyl]amino}undecanoic
Acid [(R)-PhG-6]: The product (R)-PhG-6 (1.188 g, 95%) was ob-
tained from (R)-PhG-5 (1.287 g, 2.425 mmol). M.p. 103Ϫ105 °C
(MeCN). IR: ν˜ ϭ 3292, 2919, 2850, 1735, 1635, 1541, 1468, 697
cmϪ1. [α]2D2 ϭ Ϫ34 (c ϭ 1.026, CH2Cl2). C31H52N2O4 (516.8): calcd.
C 72.05, H 10.14, N 5.42; found C 72.30, H 9.97, N 5.23.
Determination of Gel Melting Temperatures (Tg): Gels of exact con-
centrations were prepared in capped NMR tubes, and the samples
were heated in the thermostatted bath with a temperature increase
rate of 2 °C/min. The temperature that restored fluidity on tube
inversion was taken as Tg.
11-{[(2R,S)-2-(Dodecanoylamino)-2-phenylethanoyl]amino}-
undecanoic Acid (rac-PhG-6): The product rac-PhG-6 (2.827 g,
90%) was obtained from rac-PhG-5 (3.216 g, 6.059 mmol).
Acknowledgments
11-{[(2S)-2-(Dodecanoylamino)-3-phenylpropanoyl]amino}-
undecanoic Acid [(S)-Phe-6]: The product (S)-Phe-6 (2.029 g, 98%)
was obtained from (S)-Phe-5 (2.123 g, 3.897 mmol). M.p. 75Ϫ77
°C (MeCN). IR: ν˜ ϭ 3301, 2925, 2846, 1697, 1639, 1543, 1469,
1271, 1220, 1109, 945, 701 cmϪ1. [α]2D2 ϭ Ϫ3 (c ϭ 1.000, CH2Cl2).
C32H54N2O4 (530.8): calcd. C 72.41, H 10.25, N 5.28; found C
72.15, H 9.95, N 5.05.
This work was the result of international collaboration initiated by
the COST D-11 action (2000Ϫ2002), and support by the COST is
gratefully acknowledged. Financial support by the Croatian Minis-
try of Science and Technology (Program 009807), the Deutsche
Forschungsgemeinschaft (Vo, 145Ϫ49, ‘‘Neue lineare und dendriti-
sche Gelbildner für organische Lösungsmittel’’) and the Fonds der
chemischen Industrie is also gratefully acknowledged.
11-{[(2R,S)-2-(Dodecanoylamino)-3-phenylpropanoyl]amino}-
undecanoic Acid (rac-Phe-6): The product rac-Phe-6 (3.507 g, 96%)
was obtained from rac-Phe-5 (3.741 g, 6.867 mmol).
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General Procedure for Preparation of Sodium Salts 7: Acid 6
(1.0 mmol) was dissolved in CH2Cl2/MeOH (10 mL), and NaOH
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Sodium 11-{[(2S)-2-(Dodecanoylamino)-4-methylpentanoyl]amino}-
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obtained from (S)-Leu-6 (284 mg, 0.572 mmol),. M.p. 149Ϫ152 °C.
IR: ν˜ ϭ 3292, 2922, 2851, 1745, 1634, 1561, 1466, 1222, 1171,
L. Feringa, Chem. Eur. J. 2000, 6, 2633Ϫ2643.
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´
´
´
722 cmϪ1
.
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Sodium 11-{[(2R,S)-2-(Dodecanoylamino)-4-methylpentanoyl]amino}-
undecanoate (rac-Leu-7): The product rac-Leu-7 (288 mg, 100%) was
obtained from rac-Leu-6 (276 mg, 0.555 mmol).
[10]
[11]
[12]
[13]
[14]
Sodium
11-{[(2S)-2-(Dodecanoylamino)-3-methylbutanoyl]amino}-
undecanoate [(S)-Val-7]: The product (S)-Val-7 (350 mg, 100%) was
obtained from (S)-Val-6 (336 mg, 0.696 mmol). IR: ν˜ ϭ 3291, 2922,
2851, 1636, 1564, 1443 cmϪ1
.
Sodium 11-{[(2R,S)-2-(Dodecanoylamino)-3-methylbutanoyl]amino}-
undecanoate (rac-Val-7): The product rac-Val-7 (375 mg, 100%) was
obtained from rac-Val-6 (359 mg, 0.744 mmol).
´
[15]
[16]
Sodium
11-{[(2R)-2-(Dodecanoylamino)-2-phenylethanoyl]amino}-
undecanoate [(R)-PhG-7]: The product (R)-PhG-7 (246 mg, 100%)
was obtained from (R)-PhG-6 (237 mg, 0.458 mmol). M.p.199Ϫ201
[17]
°C. IR: ν˜ ϭ 3303, 2922, 2851, 1638, 1565, 1445, 697 cmϪ1
.
4058
 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
Eur. J. Org. Chem. 2004, 4048Ϫ4059

Synthesis, Gelling Properties and Preferred Gelation of Chiral Gelators
FULL PAPER
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Received February 17, 2004
Eur. J. Org. Chem. 2004, 4048Ϫ4059
www.eurjoc.org
 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
4059