Stepwise construction of polysubstituted phenanthroline-based glutamate pockets for lanthanide complexation

Article abstract of DOI:10.1055/s-2006-942533

A multi-functionalized ligand, based on a glutamic acid skeleton, bearing phenanthroline carboxylic units as chromophores and chelating arms has been designed. A base-assisted bis N-alkylation of dimethyl glutamate hydrochloride with the pivotal 2-carbomethoxy-4-methoxy-9-bromomethyl-1,10-phenanthroline building block, followed by a saponification step, provided the target ligand as its tetrahydrochloride salt. The spectroscopic properties of the ligand and its lanthanide(III) complexes were investigated in aqueous 0.01 M TRIS/HCl buffer at pH 7.0. The europium(III) complex was highly luminescent, exhibiting a quantum yield of 6% despite the presence of ca. one molecule of water in the first coordination sphere, whereas the terbium(III) complex was only weakly luminescent. Georg Thieme Verlag Stuttgart.

Full text of DOI:10.1055/s-2006-942533

PAPER
3127
Stepwise Construction of Polysubstituted Phenanthroline-Based Glutamate
Pockets for Lanthanide Complexation
P
henanthroline-
B
a
ased
G
luta
y
mate Pockets
m
for
L
anthanide Com
o
plexation nd Ziessel,* Nicolas Weibel, Loïc J. Charbonnière*
Laboratoire de Chimie Moléculaire, Associé au CNRS, Ecole de Chimie, Polymères, Matériaux de Strasbourg (ECPM), 25 rue Becquerel,
67087 Strasbourg Cedex 02, France
Fax 33(0)390242635; E-mail: ziessel@chimie.u-strasbg.fr
Received 15 May 2006; revised 30 May 2006
biomolecule, (viii) the affinity and non specific binding
Abstract: A multi-functionalized ligand, based on a glutamic acid
properties of the labeled biomolecules have to be retained
and the biological target should have minimum influence
skeleton, bearing phenanthroline carboxylic units as chromophores
and chelating arms has been designed. A base-assisted bis N-al-
on the photophysical properties of the tag. As a conse-
quence of all these strict requirements, only a few viable
labels have so far been tested, developed and made com-
mercially available.
kylation of dimethyl glutamate hydrochloride with the pivotal
2-carbomethoxy-4-methoxy-9-bromomethyl-1,10-phenanthroline
building block, followed by a saponification step, provided the tar-
get ligand as its tetrahydrochloride salt. The spectroscopic proper-
ties of the ligand and its lanthanide(III) complexes were
investigated in aqueous 0.01 M TRIS/HCl buffer at pH 7.0. The eu-
ropium(III) complex was highly luminescent, exhibiting a quantum
yield of 6% despite the presence of ca. one molecule of water in the
first coordination sphere, whereas the terbium(III) complex was
only weakly luminescent.
We recently required an efficient method by which to sub-
stitute a glutamic acid skeleton with two bipyridine car-
boxylate arms (A), allowing the possibility of complexing
one glutamate carboxylate to the lanthanide whilst acti-
vating the second carboxylate as its hydroxysuccinimide
ester (Figure 1).6 This challenging approach provided
complexes with exceptional reactivity towards proteins
and very interesting optical properties in aqueous medi-
um. These examples offer a wide range of possibilities
where the precise molecular architecture can lead to the
development of new molecules in which the lanthanide
cation is well protected against solvent molecules with
suitable chemical functionalities. The proper combination
of light absorbers and anionic function, such as carboxy-
lates, provides a wealth of opportunities with which to
finely tune the physical properties of the lanthanide com-
plexes.
Key words: phenanthroline, carboxylate, lanthanides, lumines-
cence
Molecular architectures composed of chelating items
(cryptands, branched macrocycles, podands) for lan-
thanide (Ln) binding underpin the development of many
luminescent labels for biomedical analysis.1,2 Such eu-
ropium(III) and terbium(III) complexes are luminescent
in aqueous solution if a few conditions are fulfilled: (i) the
ligand should include a highly absorbing chromophore
(since f→f transitions of naked lanthanides have very low
absorption coefficients), (ii) energy transfer from the
ligand-centered excited states to the Ln center should be
fast and efficient, (iii) water should be largely excluded
from the first coordination sphere, since the detrimental,
non-radiative deactivation pathways for the excited Ln at-
oms are promoted by the vibrational modes of the sur-
rounding solvent molecules.3,4 The objective of creating
an antenna effect, which arises when the first two require-
ments are met, makes the ligand design crucial for the
photophysical properties of the resulting complexes.5 If
luminescent lanthanide chelates are to be used as labels in
advanced analytical technologies such as homogeneous
fluoroimmuno assays, fluorescence imaging, immuno-
histochemistry, or in situ hybridization techniques, addi-
tional severe requirements are needed such as (iv) high
thermodynamic and kinetic stability, (v) good hydrophi-
licity, (vi) very efficient cation emission and high absorp-
tion at a suitable wavelength, (vii) a chemical structure
allowing proper covalent linkage of the label to the target
Figure 1
However, one clear disadvantage of using bipyridine-car-
boxylate moieties in A is its absorption in the near-UV
(around 308 nm). Other chromophores (phenanthroline,
terpyridine, hydroxyquinoline, isoquinoline) possess the
necessary properties to absorb above 350 nm. Up until
now, the synthetic methodologies available for the con-
SYNTHESIS 2006, No. 18, pp 3127–3133
x
x.
x
x
.
2
0
0
6
Advanced online publication: 02.08.2006
DOI: 10.1055/s-2006-942533; Art ID: Z09606SS
© Georg Thieme Verlag Stuttgart · New York

3128
R. Ziessel et al.
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struction of such building blocks remain limited, and the Chandler,19 the dimethyl ester 2 could be obtained pure in
provision of sufficient amounts of these substances may three steps with an overall yield of 29%.
represent a bottleneck for further studies and development
in biomedical analysis.
The selective reduction of a single ester function was in-
spired by related results obtained on pyridine derivatives
From a general point of view, 1,10-phenanthroline deri- with NaBH4 in methanol (85% of the monoester/
vatives have enjoyed long-time popularity in the design of monobenzylalcoholpyridine derivative was isolated).20 In
ionophores for alkali metal ions,7 enantioselective catalyt- our hands, attempts to adapt this protocol to the synthesis
ic systems,8 efficient antenna chromophores for lumines- of phenanthroline was far less successful (12 to 22%).
cent lanthanides ions9,10 and as templates in the Furthermore, tentative conversion of the primary alcohol
construction of esthetic macrocyclic loops.11 Recent ap- to the mesylate or bromo derivatives failed under various
plications involve the use of lanthanide complexes in the experimental conditions.
functionalization of hybrid sol-gel glasses12 and as effi-
Adopting an alternative strategy inspired by analogous
cient electroluminescent materials in light-emitting di-
procedures,21 we chose to investigate the preparation of
odes.13 Also well recognized is the nucleolytic activity of
the pivotal starting material 9 as described in Scheme 2.
The reduction of the nitro derivative 4 to the correspond-
ing amino compound was the first target and the best yield
copper-phenanthroline complexes and some derivatives
considered to be efficient chemical nucleases.14,15 The cy-
totoxicity of some phenanthroline derivatives is also well
(95%) was obtained using concentrated HI under harsh
recognized and these ligands have been used to selectively
conditions.22 Various other conditions were tested and are
incorporate metallic cations in monoclonal antibodies.16
summarized in Table 1. Amongst them, the use of molec-
Here we present our synthetic approach to the engineering ular hydrogen and palladium supported catalysts provide
of phenanthroline-carboxylate based luminescent com- compound 5 in variable yields, as did the use of various
plexes B depicted in Figure 1. Since published procedures metals Fe, Sm, Sn with the exclusion of Zn.
for the synthesis of asymmetrically substituted phenan-
With this viable protocol in hand, we turned our attention
throline platforms are scant and preparative yields are
towards the addition and cyclization reaction of dimethyl
usually very low,17,18 we initially pursued the approach
acetylenedicarboxylate, leading to compound 7 after re-
shown in Scheme 1. Starting from 2,9-dimethyl-1,10-
phenanthroline, following the procedure developed by
fluxing in diphenyl ether.23 Alkylation of the hydroxypy-
ridine ring provided derivative 8 in good yield. Classical
O
O
O
OMe
OMe
OMe
OH
OMe
N
N
(i)–(iii)
N
N
N
N
N
N
(iv)
X
O
X = OMs or Br
1
2
3
Scheme 1 Reagents and conditions: (i) SeO2, dioxane–H2O, reflux, 70%; (ii) 80% HNO3, reflux, 61%; (iii) MeOH, HCl, reflux; aq NaHCO3,
67%; (iv) NaBH4, MeOH, 12–22%.
(i)
(iii)
(iv)
OH
N
COOMe
N
(ii)
N
N
HN
N
NO2
NH2
COOMe
7
6
4
5
COOMe
(v)
(vi)
OMe
Br
OMe
Br
+
OMe
N
N
N
Br
N
N
N
10
9
8
COOMe
COOMe
COOMe
Scheme 2 Reagents and conditions: (i) 57% aq HI, 90 °C; (ii) aq NaHCO3, 95%; (iii) MeO2C-C≡C-CO2Me, MeOH, r.t., 100%; (iv) Ph2O,
reflux, 83%; (v) MeI, K2CO3, MeCN, 80 °C, 95%; (vi) NBS, AIBN cat., benzene, reflux, 37% of 9, 8% of 10.
Synthesis 2006, No. 18, 3127–3133 © Thieme Stuttgart · New York

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Phenanthroline-Based Glutamate Pockets for Lanthanide Complexation
3129
All attempts to improve the yields using other bases in-
cluding Hünig’s base, azeotropic distillation, and rigor-
ously anhydrous conditions failed. Hydrolysis of the tetra-
ester 11 was achieved under basic conditions affording the
target tetra-acid derivative 13 in excellent yield.
Table 1 Experimental Conditions for the Reduction of 8-Nitro-
quinaldine 4 to 8-Aminoquinaldine 5
Reagents and conditions
Isolated yields (%)
H2 (5 bar), 5% Pd/C, EtOH–CH2Cl2, r.t.
Zn, aq NaOH, EtOH, reflux
Na2S2O4, H2O–THF, 70 °C
Fe, HCl, EtOH–H2O, reflux, 17 h
Fe, HCl, EtOH–H2O, reflux, 1 h
Sm, NH4Cl, MeOH, sonication
SnCl2, HCl, Et2O
42–62
–
The potential of ligand 13 to form stable lanthanide com-
plexes was investigated using absorption and lumines-
cence spectroscopy in aqueous solution in a TRIS/HCl
buffer at pH 7.0 using stoechiometric amounts of the lan-
thanide nitrate salts. Basically, the free ligand exhibits in-
tense p–p* and n–p* transitions in water corresponding to
the aromatic phenanthroline moieties (Table 2). As was
expected both from the design and from related lan-
thanides-phenanthroline derivatives,18,24 the less energetic
absorption band spanned from 300–370 nm (Figure 2).
24
30
54
45
86
57% aq HI, 90 °C
95
bromination under radical conditions provided a mixture
of the desired mono-bromo derivative 9 in 37% and the
disubstituted compound 10 in 8% yield. Both compounds
were relatively easy to separate from the unreacted start-
ing material 8 (48% recovered yield) which could be recy-
cled.
We were pleased to find that the key mono-bromo deriv-
ative 9 reacted with the hydrochloride salt of dimethyl
glutamate under basic conditions (Scheme 3). This reac-
tion provided the intermediate 11 albeit in low yield. A
critical side reaction, likely due to hydrolysis of the ester
function, gave 2-carbomethoxy-4-methoxy-9-methoxy-
methyl-1,10-phenanthroline 12 as the major product
(65%). The possible intramolecular lactamization of the
dimethyl glutamate presumably generated the methanol
responsible for the displacement of the bromine.
Figure 2 Absorption (__) and emission (---) spectra (upon excitation
at 270 nm) of ligand 13 in 0.01 M TRIS/HCl buffer (pH 7.0)
Upon excitation in the 270 nm band, an intense fluores-
cence was observed around 390 nm. The short excited
state lifetime is consistent with the singlet emissive state
usually found in the oligopyridine series. Complexation
MeOOC
COOMe
COOMe
N
N
N
(i)
MeOOC
COOMe
NH2⋅HCl
Br
OMe
N
OMe
N
2
+
N
N
COOMe
COOMe
9
11
MeO
(ii)
+
HOOC
COOH
MeO
OMe
COOH
N
N
N
N
N
COOMe
OMe
N
12
N
COOH
13
MeO
Scheme 3 Reagents and conditions: (i) K2CO3, MeCN, reflux, 14% of 11, 65% of 12; (ii) NaOH, MeOH–H2O, 70 °C, 98%.
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3130
R. Ziessel et al.
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with Eu3+ and Tb3+ resulted in a hyperchromic shift of the Table 2 Absorption Properties of Ligand 13, [Eu(13-4H)]Na and
[Tb(13-4H)]Na Complexes in 0.01 M TRIS/HCl Buffer (pH 7.0)
most intense absorption band (Figure 3) and no significant
shift of the band around 320 nm. This is probably due to
Compound
l
max (nm)
e
max (M–1·cm–1)
5100
the rigidity of the phenanthroline core. It could be seen
that, in the bipyridine case, complexation with lanthanides
usually induced a bathochromic shift depending of the
strength of the interaction and is prone to a cis-trans inter-
nal conversion of the two pyridine rings during the com-
plexation process. In both lanthanide complexes of ligand
13, excitation at 277 nm resulted in dual emission from
the ligand and lanthanide (Figure 4).
13
320
274
240
318
277
246
318
277
247
17000
15500
5700
[Eu(13-4H)]Na
[Tb(13-4H)]Na
22600
21300
5700
23200
21800
by a poor positioning of the triplet state of the ligand,
which favors a back energy transfer from the 5D4 emissive
state of the terbium.
Figure 3 Absorption spectra of ligand 13 (–), [Eu(13-4H)]Na (__)
and [Tb(13-4H)]Na (---) in 0.01 M TRIS/HCl buffer (pH 7.0)
Further photophysical studies, in particular an examina-
tion of the excited state lifetimes in water and deuterated
water for the Eu complex, also points to the presence of a
single species in solution. By comparing the quantum
yields and lifetimes in both solvents, an average value of
one molecule of water was calculated to be present in the
first coordination sphere of the Eu (q = 1.2 0.2).25 These
results can be favorably compared to ligand 14 (Figure 5).
Unfortunately, this was not the case for the Tb complex
for which weak luminescence was obtained due to unfa-
vorable matching of the ligand and Tb excited states.
Table 3 Lifetimes and Quantum Yields of [Ln(13-4H)]Na and
[Ln(14-4H)]Na (Ln = Eu, Tb) in 0.01 M TRIS/HCl Buffer (pH 7.0)
Complex
t
300K (ms)
F
300K (%)
H2O
5.6
Figure 4 Normalized emission spectra of [Eu(13-4H)]Na (__) and
[Tb(13-4H)]Na (---) in 0.01 M TRIS/HCl buffer (pH 7.0).
H2O
0.53
0.80
0.62
1.48
D2O
2.22
–
D2O
8.2
–
[Eu(13-4H)]Na
[Tb(13-4H)]Na
[Eu(14-4H)]Na
[Tb(14-4H)]Na
< 0.1
8
The emission at 380 nm is likely due to ligand 13 (as
found in Figure 2), whereas the sharper peaks are charac-
teristic of Eu or Tb emission. The fluorescence of the
ligand disappears if a 50 ms delay is applied, while the lu-
minescence of the lanthanides persists. For both lan-
thanide complexes, the excitation spectrum matches the
absorption spectra, allowing us to conclude that energy
transfer is occurring from the phenanthroline subunits to
the emissive states of the lanthanides. For all complexes,
a single exponential decay is found, indicating that a sin-
gle species is present in solution and responsible for the
emissive state (Table 3). Nevertheless, the presence of re-
maining, ligand-centered fluorescence around 380 nm is
likely attributed to low intersystem crossing efficiency.
The weak luminescence of the Tb complex is understood
2.48
2.53
35
31
53
Figure 5
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Phenanthroline-Based Glutamate Pockets for Lanthanide Complexation
3131
ter cooling to r.t., sat. aq NaHCO3 (100 mL) was added and the
aqueous phase was extracted with EtOAc (560 mL). The organic
layer was washed with sat. aq Na2S2O3 (100 mL) and brine (100
mL), dried over MgSO4, filtered, and evaporated to dryness. The
residue was purified by column chromatography (SiO2, CH2Cl2–
MeOH, 100:0 to 99:1) to give compound 5 (1.68 g, 95%) as a crys-
talline orange powder.
In summary, we have shown that 8-nitroquinaldine can be
converted through sequential reduction, cyclization, alkyl-
ation, bromination and N-alkylation to provide an easy
entry into glutamate-based bis-phenanthroline carboxy-
late ligands. Complexation with Eu and Tb gives stable
complexes in aqueous media. The Eu complex exhibits a
lifetime of about 0.5 ms in water and a quatum yield of
5.6%. Further work is in progress to extend the scope of
the present methodology to prepare terpyridine based mo-
lecular structures with the aim of obtaining highly lumi-
nescent complexes.
All analyses correspond to those described in the literature.21
1H NMR (200 MHz, CDCl3): d = 2.72 (s, 3 H), 4.98 (br s, 2 H), 6.90
(d, 3J = 7.5 Hz, 1 H), 7.12 (d, 3J = 8.0 Hz, 1 H), 7.25 (d, 3J = 8.5 Hz,
1 H), 7.28 (t, 3J = 8.0 Hz, 1 H), 7.94 (d, 8.5 Hz, 1 H).
2-(2-Methylquinolin-8-ylamino)butenedioic Acid Dimethyl
Ester (6)
Reactions were performed under a dry atmosphere of argon using
standard Schlenk tube techniques when stated. Solvents and raw
materials were of analytical grade and were used as received.
MeCN (Riedel-de Haën) was filtered over alumina (Merck) and dis-
tilled from P2O5 under an argon atmosphere immediately prior to
use. 1H NMR (200 MHz) and 13C NMR (50 MHz) spectra were re-
2-Methyl-8-aminoquinoline 5 (1.68 g, 10.6 mmol) and dimethyl
acetylenedicarboxylate (2 mL, 16.3 mmol) were dissolved in
MeOH (30 mL) and the solution was stirred at r.t. for 20 h in the
dark. The solvent was evaporated and the residue was purified by
column chromatography (SiO2, CH2Cl2) to give compound 6 (3.18
g, 100%) as a yellow oil.
1
corded at r.t. on a Bruker AC 200 spectrometer, H NMR (300
All analyses correspond to those described in the literature.21
MHz) and 13C NMR (75 MHz) spectra were recorded at r.t. on a
Bruker Avance 300 spectrometer. Shifts (d) are reported in ppm rel-
ative to residual protons in the solvent. FT-IR spectra were recorded
as KBr pellets on a Nicolet 210 spectrometer. UV-Vis absorption
spectra were recorded on Uvikon 933 (Kontron Instrument) spec-
trophotometer. Emission and excitation spectra were recorded using
a PerkinElmer LS 50B spectrofluorimeter equipped with a R928
(Hamamatsu) photomultiplier. Metal luminescence lifetimes were
measured on a PTI QuantaMaster spectrofluorimeter. Metal lumi-
nescence quantum yields were measured using the procedure de-
scribed by Haas and Stein,26 using as standards Ru(bpy)3Cl2
(F = 0.028 in aerated H2O)27 for Eu3+ and rhodamine 6G (F = 0.88
in EtOH)28 for Tb3+. Fast atom bombardment (FAB, positive mode)
mass spectra were recorded with ZAB-HF-VB analytical apparatus
using meta-nitrobenzyl alcohol (m-NBA) as matrix. Matrix-assisted
laser desorption ionization (MALDI) time-of-flight (TOF) mass
spectra were recorded using a Perkin-Elmer/PerSeptive Biosystems
Voyager-DE-RP mass spectrometer. Melting points were obtained
on a Büchi Melting Point 535 capillary melting point apparatus in
open-ended capillaries and are uncorrected. Chromatographic puri-
fications were performed using 0.063–0.200 mm silica gel 60 (Mer-
ck) or aluminium oxide 90 (Merck). Thin layer chromatography
(TLC) was performed on silica gel or aluminium oxide plates (Mer-
ck) coated with fluorescent indicator. All mixtures of solvents are
given in v/v ratio.
1H NMR (200 MHz, CDCl3): d = 2.76 (s, 3 H), 3.71 (s, 3 H), 3.79
3
(s, 3 H), 5.55 (s, 1 H), 6.93 (d, J = 7.0 Hz, 1 H), 7.26–7.43 (m, 3
H), 7.99 (d, 3J = 8.5 Hz, 1 H), 10.82 (s, 1 H).
2-Carbomethoxy-4-hydroxy-9-methyl-1,10-phenanthroline (7)
Compound 6 (1.38 g, 4.6 mmol) was dissolved in Ph2O (50 mL) and
the solution was refluxed at 260 °C for 20 min. After cooling to r.t.,
Et2O (50 mL) was added and the solution was cooled to 0 °C to
complete crystallization of 7. The solid was filtered and washed
with Et2O yielding compound 7 (844 mg, 3.1 mmol). The mother li-
quor was evaporated to dryness and the residue was purified by col-
umn chromatography (SiO2, CH2Cl2–MeOH, 100:0 to 95:5) to give
7 (174 mg, 0.6 mmol). Upon combination of the two fractions, com-
pound 7 (1.02 g, 83%) was isolated as a yellowish powder.
All analyses correspond to those described in the literature.21
1H NMR (200 MHz, CDCl3): d = 2.80 (s, 3 H), 4.08 (s, 3 H), 7.14
(s, 1 H), 7.47 (d, 3J = 8.5 Hz, 1 H), 7.57 (d, 3J = 9.0 Hz, 1 H), 8.09
(d, 3J = 8.5 Hz, 1 H), 8.21 (d, 3J = 9.0 Hz, 1 H).
2-Carbomethoxy-4-methoxy-9-methyl-1,10-phenanthroline (8)
In a Schlenk tube under argon were dissolved 2-carbomethoxy-4-
hydroxy-9-methyl-1,10-phenanthroline 7 (2.04 g, 7.6 mmol), MeI
(950 mL, 15.3 mmol) and anhyd K2CO3 (2.11 g, 15.2 mmol) in dry
MeCN (60 mL). The solution was heated to 80 °C for 19 h then the
mixture was evaporated to dryness, and the solid residue was parti-
tioned between CH2Cl2 (100 mL) and H2O (15 mL). The aqueous
phase was further extracted with CH2Cl2 (4 × 15 mL), and the com-
bined organic layers were dried over MgSO4, filtered, and evaporat-
ed to dryness. The resulting solid was purified by column
chromatography (Al2O3, CH2Cl2–MeOH, 99:1).
2-Carbomethoxy-9-hydroxymethyl-1,10-phenanthroline (3)
A mixture of 2,9-dicarbomethoxy-1,10-phenanthroline 219 (0.100 g,
0.338 mmol) and NaBH4 (0.029 g, 0.744 mmol) was refluxed in
MeOH (5 mL) for 1 h. The solution was evaporated to dryness and
the residue was purified by column chromatography (Al2O3,
CH2Cl2–MeOH, 97:3).
Yield: 0.020 g, 22%; pale-yellow solid; Rf = 0.25 (Al2O3, CH2Cl2–
MeOH, 97:3).
Yield: 2.05 g, 95%; yellow solid; Rf = 0.54 (Al2O3, CH2Cl2–MeOH,
98:2).
1H NMR (200 MHz, CDCl3): d = 4.09 (s, 3 H), 5.13 (s, 2 H), 7.70
(d, 3J = 8.5 Hz, 1 H), 7.77–7.90 (m, 2 H), 8.23 (d, 3J = 8.5 Hz, 1 H),
8.35–8.44 (m, 2 H).
1H NMR (200 MHz, CDCl3): d = 2.91 (s, 3 H), 4.06 (s, 3 H), 4.12
(s, 3 H), 7.47 (d, 3J = 8.5 Hz, 1 H), 7.77 (d, 3J = 9.0 Hz, 1 H), 7.83
(s, 1 H), 8.08 (d, 3J = 7.5 Hz, 1 H), 8.12 (d, 3J = 9.0 Hz, 1 H).
13C NMR (50 MHz, CDCl3): d = 53.0, 65.6, 121.3, 123.3, 125.5,
13C NMR (50 MHz, CDCl3): d = 25.8, 52.8, 56.2, 102.9, 118.7,
122.2, 123.9, 126.9, 127.4, 136.0, 145.2, 146.1, 148.6, 160.1, 163.2,
166.5.
128.0, 128.8, 130.5, 136.9, 137.4, 145.0, 147.4, 165.9.
HRMS (MALDI-TOF): m/z [M + H]+ calcd for C15H13N2O3:
269.0926; found: 269.0913.
MS (FAB+): m/z (%) = 283.2 (100) [M + H]+.
Anal. Calcd for C16H14N2O3: C, 68.07; H, 5.00; N, 9.92. Found: C,
67.92; H, 4.93; N, 9.78.
2-Methyl-8-aminoquinoline (5)
2-Methyl-8-nitroquinoline (2.11 g, 11.2 mmol) was dissolved in aq
HI (57%, 34 mL). The solution was heated to 90 °C for 2 h then, af-
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3132
R. Ziessel et al.
PAPER
2-Carbomethoxy-4-methoxy-9-bromomethyl-1,10-phenanthro-
line (9).
HRMS (MALDI-TOF): m/z [M + H]+ calcd for C39H38N5O10:
736.2619; found: 735.2608.
A solution of 8 (1 g, 3.5 mmol), NBS (630 mg, 3.5 mmol) and AIBN
(30 mg, 0.2 mmol) in benzene (10 mL) was irradiated for 30 min
with a 100 W halogen lamp. The mixture was evaporated to dryness
and the residue was purified by a column chromatography (Al2O3,
CH2Cl2–hexane, 50:50).
2-Carbomethoxy-4-methoxy-9-methoxymethyl-1,10-phenan-
throline (12)
Compound 12 was obtained in 65% yield as a by-product of the
alkylation of dimethyl glutamate hydrochloride with bromometh-
ylphenanthroline 10.
Yield: 468 mg, 37%; yellow solid; Rf = 0.55 (Al2O3, CH2Cl2–
MeOH, 99:1).
Rf = 0.62 (Al2O3, CH2Cl2–MeOH, 95:5).
1H NMR (200 MHz, CDCl3): d = 4.06 (s, 3 H), 4.12 (s, 3 H), 4.93
1H NMR (200 MHz, CDCl3): d = 2.98 (s, 3 H), 4.04 (s, 3 H), 4.09
(s, 3 H), 5.26 (s, 2 H), 7.40 (d, 3J = 8.0 Hz, 1 H), 7.71 (d, 3J = 9.0
Hz, 1 H), 7.76 (s, 1 H), 8.07 (d, 3J = 9.0 Hz, 1 H), 8.13 (d, 3J = 8.0
Hz, 1 H).
13C NMR (50 MHz, CDCl3): d = 28.4, 44.4, 52.7, 56.2, 103.1,
119.6, 120.3, 122.3, 127.0, 127.9, 136.8, 145.2, 146.0, 148.6, 154.7,
163.0, 166.2.
3
(s, 2 H), 7.77 (d, 3J = 9.0 Hz, 1 H), 7.83 (s, 1 H), 7.87 (d, J = 8.5
Hz, 1 H), 8.17 (d, 3J = 9.0 Hz, 1 H), 8.21 (d, 3J = 8.5 Hz, 1 H).
13C NMR (50 MHz, CDCl3): d = 34.6, 53.0, 56.3, 103.3, 120.2,
122.4, 123.7, 127.0, 128.1, 137.1, 144.5, 145.9, 148.9, 157.6, 163.3,
166.2.
MS (FAB): m/z (%) = 281.2 (30) [9 – Br]+, 361.2 (100) [9 + H]+,
363.2 (100) [9 + H]+.
MS (FAB): m/z (%) = 281.1 (38) [12 – OCH3]+, 313.1 (100) [12 +
H]+.
Anal. Calcd for C16H13BrN2O3: C, 53.21; H, 3.63; N, 7.76. Found:
C, 52.94; H, 3.26; N, 7.51.
Anal. Calcd for C17H16N2O4: C, 65.38; H, 5.16; N, 8.97. Found: C,
65.27; H, 5.08; N, 8.79.
2-Carbomethoxy-4-methoxy-9-dibromomethyl-1,10-phenan-
throline (10)
Compound 10 was obtained in 8% yield as a by-product of the rad-
ical bromination of 8.
N,N-[(7-Methoxy-9-carboxy-1,10-phenanthrol-2-yl)meth-
yl]glutamic Acid Tetrahydrochloride (13)
A solution of compound 11 (29 mg, 0.04 mmol) and NaOH (8 mg,
0.2 mmol) in a mixture of MeOH (8 mL) and H2O (2 mL) was heat-
ed to 70 °C for 8 h. The solution was evaporated to dryness, acidi-
fied with aq HCl (1N) and the resulting solution was again
evaporated to dryness. The residue was solubilized in MeOH and
the product was precipitated with Et2O. Upon centrifugation,
13·4HCl (32 mg, 98%) was isolated as a yellow-orange powder.
Rf = 0.73 (Al2O3, CH2Cl2–MeOH, 99:1).
1H NMR (200 MHz, CDCl3): d = 4.09 (s, 3 H), 4.15 (s, 3 H), 7.06
3
(s, 1 H), 7.82 (d, 3J = 9.0 Hz, 1 H), 7.86 (s, 1 H), 8.24 (d, J = 9.0
Hz, 1 H), 8.27 (d, 3J = 9.0 Hz, 1 H), 8.34 (d, 3J = 8.5 Hz, 1 H).
13C NMR (50 MHz, CDCl3): d = 42.4, 53.2, 56.4, 103.5, 121.2,
122.8, 122.9, 126.9, 128.9, 129.1, 138.2, 146.1, 149.1, 159.5, 163.4,
166.1.
IR (KBr): 3436, 2924, 2853, 1635, 1507, 1454, 1384, 1235, 1070
cm–1.
1H NMR (300 MHz, CD3OD): d = 2.39–2.49 (m, 2 H), 2.84 (t,
3J = 7.0 Hz, 2 H), 4.17 (t, 3J = 7.5 Hz, 1 H), 4.35 (s, 6 H), 4.81–4.85
(m, 4 H), 7.87 (d, 3J = 9.5 Hz, 2 H), 7.89 (s, 2 H), 8.16 (d, 3J = 9.0
Hz, 2 H), 8.18 (d, 3J = 8.5 Hz, 2 H), 8.65 (d, 3J = 9.0 Hz, 2 H).
MS (FAB): m/z (%) = 280.3 (15) [10 – Br2]+, 359.2 (48) [10 – Br]+,
361.2 (50) [10 – Br]+, 441.1 (100) [10 + H]+.
Anal. Calcd for C16H12Br2N2O3: C, 43.67; H, 2.75; N, 6.37. Found:
C, 43.40; H, 2.63; N, 6.05.
MS (FAB): m/z (%) = 340.5 (20) [13 + 2 × H]2+, 680.2 (80) [13 +
H]+.
Dimethyl N,N-[(7-Methoxy-9-carbomethoxy-1,10-phenanthrol-
2-yl)methyl]glutamate (11)
Anal. Calcd for C35H29N5O10⋅4HCl: C, 50.93; H, 4.03; N, 8.48.
Found: C, 50.82; H, 4.15; N, 8.34.
In a Schlenk tube under argon were dissolved dimethyl glutamate
hydrochloride (96 mg, 0.45 mmol) and anhydrous K2CO3 (250 mg,
1.81 mmol) in dry MeCN (15 mL). The solution was heated to
80 °C for 10 min then compound 10 (360 mg, 1 mmol) was added.
The solution was heated to 80 °C for 18 h then a further portion of
10 (52 mg, 0.14 mmol) was added and the solution was heated to
80 °C for 24 h. The mixture was evaporated to dryness, and the solid
residue was partitioned between CH2Cl2 (30 mL) and H2O (10 mL).
The aqueous phase was further extracted with CH2Cl2 (4 × 30 mL),
and the combined organic layers were dried over MgSO4, filtered,
and evaporated to dryness. The resulting solid was purified by col-
umn chromatography (Al2O3, CH2Cl2–MeOH, 100:0 to 99.3:0.7).
UV/Vis (0.01 M TRIS/HCl buffer, pH 7.0): lmax (e) = 240 (15500),
274 (17000), 320 nm (5100).
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Synthesis 2006, No. 18, 3127–3133 © Thieme Stuttgart · New York