InIII GaIII complexes of sugar-substituted tripodal trisalicylidene imines: The first68Ga-labelled sugar derivative

Article abstract of DOI:10.1002/ejic.200900561

Gallium and indium complexes derived from salicylaldimines of 1,1,1-tris(aminomethyl)ethane (TAME) with pendant xylose, glucose and galactose units have been synthesised as model compounds for potential, application as radiotracers, The formed neutral com

Full text of DOI:10.1002/ejic.200900561

FULL PAPER
DOI: 10.1002/ejic.200900561
InIII and GaIII Complexes of Sugar-Substituted Tripodal Trisalicylidene
68
Imines: The First Ga-Labelled Sugar Derivative
Michael Gottschaldt,*[a,b] Carmen Bohlender,[a] Anne Pospiech,[a] Helmar Görls,[c]
Martin Walther,[d] Dirk Müller,[e] Ingo Klette,[e] Richard P. Baum,[e] and
Ulrich S. Schubert[a,b,f]
Keywords: Carbohydrates / Gallium / Indium / Nuclear imaging / Isotopic labelling / Medicinal chemistry
Gallium and indium complexes derived from salicylaldimines
of 1,1,1-tris(aminomethyl)ethane (TAME) with pendant
xylose, glucose and galactose units have been synthesised as
model compounds for potential application as radiotracers.
The formed neutral complexes have been characterised by
NMR spectroscopy, elemental analysis, mass spectrometry
and, in the case of the galactose-bearing InIII complex, by
single-crystal X-ray structure analysis. Octahedral coordina-
tion was observed with the appearance of an equilibrium of
Λ- and ∆-isomers at the metal centre. The glucose-appended
ligand was radiolabelled with 68GaIII ions in up to 98% yield
depending on the prevailing pH value. The in vitro stability
of the radioactive complex was examined by challenge ex-
periments against apo-transferrin and blood plasma. Very
high stability was observed; even after a period of 2 h, 90%
of the complex could still be detected.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2009)
cules with fast pharmacokinetics such as small carbo-
hydrates, peptides or oligonuclides.[6–8] A further important
advantage in terms of radiolabelling is the variable com-
plexation behaviour of the Ga3+ ion. Stable complexes were
formed with substituted azamacrocyclic ligands such as
1,4,7,10-tetrakis(carboxymethyl)-1,4,7,10-tetraazacyclodo-
decane (DOTA) as well as with many different tripodal
and/or polydentate ligands such as tris(2-mercaptobenzyl)-
amine.[9] 68Ga–DOTA-labelled compounds are of particular
interest for PET/CT imaging.[10,11] DOTA is also widely
used as a ligand to bind useful β-emitters (e.g. 90Y or 177Lu)
for therapy. Metal complexes structurally derived from
1,1,1-tris(aminomethyl)ethane (TAME) are known to com-
plex a variety of metal ions, e.g. Cr, Co and Cu ions.[12–14]
N-Functionalised TAME ligands [e.g. bis(carboxymethyl)-
amino derivatives,[15,16] catecholamide[17] and aminophenol-
ates[18,19]] were used for the complexation of gallium, in-
dium and other metal ions. Tripodal tris(salicylaldimine)
from 1,1,1-tris(aminomethyl)ethane is known to complex
gallium(III) in a stable fashion.[20–24] Experiments concern-
ing their biodistribution revealed the decomposition of
these neutral lipophilic gallium complexes in vivo, suggest-
ing the binding of the metal ions to macromolecules in the
liver.
Introduction
Isotopes of gallium and indium are used in diagnostic
nuclear medicine, e.g. the γ-emitting radionuclides 67Ga
(coupled to citrate for lymphoma and infection imaging)
and 111In (mainly for labelling of peptides or coupled to
oxine for radiolabelling of blood cells). 68Ga is a generator-
produced metallic positron emitter with a half-life of
68 min.[1] It is nowadays used increasingly for molecular im-
aging of neuroendocrine tumours by receptor PET/CT.[2–5]
Both the easy availability from a generator with high spe-
cific activity and the relatively short half-life make this ra-
dionuclide an optimal candidate for radiolabelling of mole-
[a] Laboratory of Organic and Macromolecular Chemistry, Fried-
rich Schiller University Jena,
Humboldtstrasse 10, 07743 Jena, Germany
Fax: +49-3641-948202
E-mail: Michael.Gottschaldt@uni-jena.de
[b] Dutch Polymer Institute (DPI),
John F. Kennedylaan 2, 5612 AB Eindhoven, The Netherlands
[c] Institute for Inorganic and Analytical Chemistry, Friedrich
Schiller University Jena,
Lessingstrasse 8, 07743 Jena, Germany
[d] Institute of Radiopharmacy, Forschungszentrum Dresden-Ros-
sendorf,
01314 Dresden, Germany
[e] Department of Nuclear Medicine, Zentralklinik Bad Berka
GmbH,
To introduce hydrophilicity and solubility, to lower cyto-
toxicity and to target carbohydrate-specific binding do-
mains and transporters, the introduction of sugar moieties
has become an ascending field of interest.[25] The most com-
mon, best studied example of imaging molecular processes
at a cellular level is the use of the glucose analogue 18F-
Robert-Koch-Allee 9, 99437 Bad Berka, Germany
[f] Laboratory of Macromolecular Chemistry and Nanoscience,
Eindhoven University of Technology,
Den Dolech 2, 5600 MB Eindhoven, The Netherlands
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.200900561.
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The First 68Ga-Labelled Sugar Derivative
labelled 2-fluoro-2-deoxyglucose (FDG) with PET.[26] Most
cancer cells over-express GLUT1, a high-affinity glucose
transporter, and therefore have an increased glucose uptake
when compared with normal cells.[27,28] Thus, most of the
radiometal-labelled compounds containing sugar residues
Results and Discussion
Ligand Synthesis
We reported the synthesis of the tripodal triamines 5a–c
are therefore glucose-appended to take advantage of this for the formation of ReI and 99mTcI complexes pre-
phenomenon although it could be shown by in vitro experi- viously.[45] In brief, starting from pentaerythritol tribro-
ments that glucose derivatives bearing metal-coordinating mide,
a glycosidation reaction was performed with
cores are not taken up by the GLUT1 transporter.[29] How- 1,2,3,4,6-O-pentaacetyl-β--glucopyranoside, 1,2,3,4-O-tet-
ever, a number of carbohydrate-appending radiolabelled raacetyl-β--xylopyranoside and 1,2,3,4,6-O-pentaacetyl-β-
compounds have been synthesised, comprised of bi- and tri- -galactopyranoside (1a–c) by using BF3·Et2O in dichloro-
dentate ligands. 2,2Ј-Bipyridyl,[30] 2,2Ј-dipicolylamine,[31,32] methane. In the case of galactose, the anomeric pure tribro-
3-hydroxypyridone,[33] 2-hydroxybenzyl-[34] and 2-(iminodi- mide 2c was obtained in 70% yield after chromatographic
acetato)ethyl-functionalised[35] derivatives of different purification (Scheme 1). The corresponding glucose (2b)
monosaccharides could be used as chelators for radionu- and xylose (2a) derivatives crystallised from the combined
clides. Similar complexes have been reported from 1,3-di- fractions in moderate yields after column chromatography.
1
amines of sugars.[36] Up to now most of the work was fo- Each H NMR spectrum of compounds 2a–c shows one
cused on 99mTc complexes.[37] Sugar-appending Ga and In sugar-specific signal for the protons at the anomeric carbon
complexes are rarely described in the literature. Solely glu- atoms. The methylene groups directly bound to the glyco-
cose- and 2-amino-2-deoxyglucose-based 3-hydroxy-4-pyr- sidic oxygen atom are diastereotopic and therefore show
idonato complexes of InIII and GaIII have been synthesised two doublets with a coupling constant of around 9.4 Hz
and structurally characterised.[38] Because 68Ga is a genera- and separated by 0.4–0.5 ppm. In the mass spectra, the typi-
tor product and therefore much more cost-effective than cal isotope pattern of molecules containing three bromine
18F-labelled FDG, which depends on the availability of a atoms was observed. Subsequently, the tribromides were
cyclotron, the use of related complexes as tracers in imaging converted in Ͼ 80% yield to the corresponding triazides
is very promising. Due to the specificity of the GLUT1 3a–c by nucleophilic substitution with an excess of sodium
transporter such complexes will not be able to act as an azide in DMF as solvent at 70 °C. The successful conver-
FDG substitute but possess the alternative – in particular sion could easily be monitored by the appearance of ab-
by the use of other sugar units – to trace more specific sorption bands in the IR spectra at 2100 cm–1 and the shifts
metabolic events. Alternative mechanisms for uptake and of the 13C NMR signals of the three equivalent CH2 groups
enrichment were shown, e.g. for galactose derivatives and from δ = 34 ppm (for the tribromides) to δ = 51 ppm (for
their uptake by the hepatic asyaloglycoprotein receptor the triazides). Deacetylation of 3a–c was performed in
(ASGP-R) as shown for GdIII and 153SmIII complexes of methanol/water at 60 °C by stirring the mixtures with OH–-
tetraazacyclododecanetetraacetic acid (DOTA) ligands loaded Dowex resin.[46] After filtration through silica gel,
functionalised with galactose residues used for molecular the pure products 4a–c could be obtained. Although we did
imaging.[39] Additionally, they are processed by galactosid- not observe any problems with these substances so far, with
ase, a marker enzyme for gene expression in transgenic ani- an azide nitrogen content of up to 34% (for 4a) the com-
mals and were used for the localisation and visualisation of pounds should be handled with circumspection to avoid ac-
gene expression by MRI.[40,41] Recently it could be demon- cidents. Therefore, only small amounts were dried to com-
strated that other carbohydrates are also able to target dif- pleteness to obtain analytical data. Characteristically, the
ferent transporter systems, e.g. fluorescent fructose deriva- C=O absorption bands in the IR spectra of 3a–c disappear
tives are taken up by GLUT5 and were used for imaging after complete deprotection. Reduction of the azide func-
breast cancer cells.[42] Xylosides are able to act as primers tions was carried out with PtO2 in methanol and H2 by
for the production of glucosaminoglycans (GAGs), like stirring the solutions under hydrogen at room temperature
heparan sulfate or controitin sulfate in mammalian cell overnight. The formed platinum was removed by filtration
lines by being incorporated on the first position of the through a membrane filter, and the products were obtained
growing chain. The activity was found to be aglycon- as white hygroscopic powders after the removal of the sol-
dependent. In humans, GAGs are involved in the regulation vent. The successful conversion could be monitored by the
of various biological functions including wound healing, disappearance of the sensitive N3 absorption at 2100 cm–1
1
cell signalling, cell differentiation, angiogenesis, blood clot- in the IR spectra of the products 5a–c. In the H NMR
ting and tumour-cell migration.[43,44]
spectra in deuterated methanol the signals of the NH2
As models towards imaging such molecular events we groups appear as a singlet at δ = 2.6 ppm. The triamines
herein report the synthesis of tripodal tris(salicylaldimine) are soluble in methanol and water but could not be cleaned
ligands tentatively functionalised with xylose, glucose or ga- additionally by column chromatography due to their high
lactose and the formation of some of their InIII and GaIII affinity towards all common chromatographic materials.
complexes. Gallium-68 labelling was carried out for the glu- Their purity and integrity were demonstrated by NMR
cose derivative, and the stability of the resultant complex spectroscopy and high-resolution mass spectrometry. Sub-
against apo-transferin and blood plasma was examined.
sequent condensation with salicylaldehydes in dry ethanol
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Scheme 1. Schematic representation of the synthesis of the tripodal ligands and the subsequent complexation of metal ions. (i) Pentaer-
ythrol tribromide, BF3·Et2O, CH2Cl2, room temp., 12 h; (ii) NaN3, DMF, 70 °C, 12 h; (iii) Dowex-OH–, H2O/MeOH, 60 °C, 12 h; (iv)
PtO2/H2, MeOH, room temp., 12 h; (v) appropriate salicylaldehyde, EtOH, 3 h, reflux; (vi) InCl3·4H2O, TEA, MeOH, reflux; (vii)
Ga(NO3)3·H2O, TEA, MeOH, reflux.
Table 1. Overview of the tripodal trisalicylideneimines and metal complexes synthesised in this study referring to Scheme 1.
Sugar
Salicylaldehyde
5-Methylsalicylaldehyde
5-Hydroxysalicylaldehyde 3,5-Di-tert-butylsalicylaldehyde
β--Xylose
β--Glucose
β--Galactose
6a (In, Ga)
6b (In, Ga)
6c (In, Ga)
7a (In, Ga)
–
7c (In)
–
–
–
9b (In)
9c (In, Ga)
8c (–, –)[a]
[a] Decomposition of the ligand under the applied reaction conditions.
resulted in the formation of the final ligands. The applica- 9c simplifies the aromatic signal pattern. Only two doublets
4
tion of differently substituted salicylaldehydes allows the may be observed with a coupling constant of J = 2.3 Hz
tuning of the solubility and polarity of the resultant com- which is typical for meta coupling in aromatic systems.
plexes. In the present study 3,5-di-tert-butyl-, 5-methyl-, 5-
hydroxy- as well as unsubstituted salicylaldehydes were used
for the condensation to obtain selected ligands (Table 1).
Synthesis and Characterisation of the Metal Complexes
IR spectroscopic measurements did not show the appear-
ance of phenolic OH groups besides the sugar OH groups
According to Scheme 1, indium(III) and gallium(III)
(usually free phenols give a strong OH band at around complexes In6a–Ga9c were synthesised by starting from the
3600 cm–1). The absence of this IR band in the case of the respective ligands in the presence of either Ga(NO3)3·H2O
imines might be due to the formation of N···H–O hydrogen or InCl3·4H2O. The salicylaldimine ligands were stirred
bonds. Furthermore, the salicylaldimines are characterised with triethylamine before a methanolic solution of the re-
by the C=N stretching vibrations appearing at 1630 cm–1. spective metal salt was added, leading to the neutral metal
Further strong bands around 2900 cm–1 and in the region complexes In6a–Ga9c. When treated with InCl3·4H2O, the
of 1280–750 cm–1 belong to the C–H, C–OH and O–H vi- yellow ligand solutions decolourised until they became al-
brations of the carbohydrate fragment. The 1H NMR spec- most colourless. The corresponding gallium(III) complexes
tra show a typical singlet for the formed imino groups at exhibited a yellow colour. The resultant solutions were
low field at δ ≈ 8.2–8.4 ppm. The carbon signal for this heated under reflux for several hours, and the formation of
imino group appears at δ ≈ 170 ppm in the 13C NMR spec- the complexes was monitored by TLC. The metal com-
tra. The aromatic protons of ligand 6c (H-3Ј/H-5Ј and H- plexes showed blue fluorescence under UV light irradiation.
4Ј/H-6Ј) give two multiplets at δ = 6.85 and 7.29 ppm. For However, reaction of 8c with GaIII and InIII resulted in
compound 8c, where an OH substituent has been intro- black precipitates with hardly any solubility. ESI-MS ex-
duced at position 5Ј, the positive mesomeric effect of the aminations on the product obtained from the reaction with
hydroxy group causes the signals of the protons H-4Ј and gallium(III) indicated decomposition of the complex. After
H-6Ј (ortho to the OH group) to shift to higher field. All evaporation of the solvent, the crude products In6a–Ga9c
aryl protons now appear as one multiplet at δ = 6.78 ppm. were purified by column chromatography. Since Schiff bases
Such strong shifts are not observed for the alkyl substitu- are very sensitive towards hydrolysis, the silica gel used for
tion pattern seen for compounds 7a and 9c. Introduction chromatographic cleaning was deactivated with TEA. De-
of two tert-butyl groups at C-3Ј and C-5Ј as for compound pending on the substitution pattern of the salicylidene resi-
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The First 68Ga-Labelled Sugar Derivative
dues, the metal complexes were eluted with either methanol/ occurrence of only one set of signals. The corresponding
ethyl acetate mixtures (In6a–Ga7a) or with pure ethyl ace- indium(III) complexes (In6a–c, In7a and In9c) did not show
tate (In9c and Ga9c). The products were obtained as yellow the presence of two diastereomers in the NMR spectra at
or slightly yellow powders after concentration. The prod- room temperature. Separate signals could also not be ob-
ucts still contained triethylammonium nitrate even after col- served upon cooling the NMR samples to 213 K. Presum-
umn chromatography with methanol/ethyl acetate due to ably, switching between the two diastereomers occurs so fast
the good solubility of the triethylammonium salt. In con- for the indium(III) complexes that they are not apparent in
trast, indium(III) complexes In6a–In6c were obtained as the NMR spectra. Therefore, the imino groups appear as
small pink crystals from methanol/water. After filtration one singlet. The anomeric protons and carbon atoms give
1
and washing with water, the complexes In6a–In6c were ob- one signal. Additionally, all H NMR spectra of the metal
tained in high purity. For the metal complexes In9c and complexes have in common that the OH resonance signals
Ga9c, the triethylammonium salts were already removed by from the sugar residue are now visible in a region of δ =
chromatography with ethyl acetate. The free salicylaldimi- 4.5–5.4 ppm due to the use of [D7]DMF as a solvent (Fig-
nes can be characterised by the C=N stretching vibrations ure 1). It should be noted here that some NMR spectra
appearing at 1630 cm–1. For the salicyl complexes the C=N showed signals of free ligands and also free salicylaldehydes
stretching band should appear at lower energy, thus it can in small amounts next to those of the metal complexes. This
be used as an indicator for the strength of the metal–imine indicates the sensitivity of the imine ligands and the metal
bonding. When a metal ion is coordinated to an imino do- complexes towards hydrolysis during column chromatog-
nor atom, a shift of the IR absorption band to lower wave raphy, even on deactivated column material. Decomposition
numbers (and lower energy) is expected due to the loss of of the ligand system may also be caused by the Lewis acidic
electron density from the nitrogen atom to the metal ion. metal(III) ions. The degree of decomposition and also the
Shifts of the Ar–O absorption bands upon complexation contents of leftover TEA salts are reflected in the elemental
are excluded from this discussion, since these bands are im- analyses. Moreover, it was found that the stability of the
possible to assign next to the C–H and O–H deformation complexes was decreased in coordinating solvents. For the
vibrations and the C–O stretching vibrations of the carbo- gallium(III) complex Ga9c this could be seen in the NMR
hydrate residues. The IR absorption spectra of the in- spectra, measured in [D7]DMF. Two NMR measurements
dium(III) and the gallium(III) complexes revealed variable of the same sample in [D7]DMF within 4 d showed a high
bathochromic shifts. Compound In9c showed a significant degree of complex and also ligand decomposition (loss of
shift to 1610 cm–1 compared to the free ligand 9c with an 3,5-di-tert-butylsalicylaldehyde). However, the GaIII com-
absorption of 1628 cm–1. Complexation of 7a with InIII re- plex Ga9c was sufficiently stable to obtain good results for
sulted in a bathochromic shift of at least 12 cm–1 compared NMR spectroscopy, mass spectrometry and elemental
to the free ligand (1632 cm–1). The other metal complexes analysis. The corresponding indium(III) complex was found
showed only shifts from 1 to 7 cm–1. NMR spectroscopic to be sensitive towards column chromatography. The loss
analysis of the gallium(III) complexes (Ga6a–c, Ga7a, of 3,5-di-tert-butylsalicylaldehyde is clearly indicated by ele-
Ga9c) revealed the occurrence of two diastereomeric forms mental analysis. Good NMR spectra were only obtained
(Λ and ∆) in a 1:1 ratio. Their existence is indicated by a from the crude product, still containing the TEA salt. Com-
double set of signals for protons and carbon atoms at room plexes In7a and Ga7a that were formed with the methyl-
1
temperature. Characteristically, the H NMR spectra show substituted xylose ligand revealed good stability upon col-
two singlets for the imine CH=N protons. The sugar H-1 umn chromatography. The resultant NMR spectra did not
protons give two doublets separated by an average of show a loss of 5-methylsalicylaldehyde, despite the obtained
0.04 ppm. The other sugar protons of the two dia- product still containing TEA salts, which could not be re-
stereomeric forms appear together in multiplets, since they moved by crystallisation from methanol/water mixtures.
are not that strongly influenced by metal complexation like Comparable tripodal (salicylidene)gallium(III) and -in-
1
H-1. Another special feature in the H NMR spectra is the dium(III) complexes that were synthesised for radiochemi-
split of the CH2N methylene groups adjacent to the imino cal application have not been investigated regarding their
group. Whereas they appear as one multiplet in the ligand optical properties so far. Since the obtained metal com-
spectra, they split into two multiplets for the gallium(III) plexes showed blue fluorescence under UV light (366 nm),
complexes with a seaparation of about 0.4 ppm. In the 13C absorption and emission spectra of the complexes and also
NMR spectra the imino carbon atom CH=N, the anomeric of the free ligands were recorded. Selected absorption and
carbon atoms (C-1) and the methylene group (CH2N) split emission spectra for the xylose derivatives 6a, In6a and
by about 0.1–0.3 ppm. Also, the methylene group adjacent Ga6a are shown in Figure 2. The absorption maxima of the
to the glycosidic oxygen atom O–CH2 gives two signals with free ligands result from the imino chromophore and the ad-
a separation of about 0.2 ppm. The signals of the remaining jacent substituted aromatic ring. All ligands showed three
sugar and aromatic carbon atoms are either not split at all bands in the absorption spectra, resulting from πǞπ* and
1
or are barely split into two signals. Measurement of the H nǞπ* transitions of the chromophore systems. As expected
NMR spectrum of complex Ga6b at 343 K showed, that at no differences were observed for ligands with the same aro-
this temperature, an equilibrium between the Λ and ∆ iso- matic substitution pattern and different appended sugar
mers on the NMR time scale is reached indicated by the units. The spectrum was redshifted upon substitution of the
Eur. J. Inorg. Chem. 2009, 4298–4307
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1
Figure 1. Details from the H NMR spectra of compounds 6c (in CD3OD), In6c and Ga6c (in [D7]DMF).
Figure 2. UV/Vis (left) and normalised emission spectra (right) of selected compounds in methanol.
aromatic ring. Alkyl substitution resulted in a shift of about
Crystals of the galactose complex In6c were suitable for
10 nm, whereas introduction of the OH group at C-5Ј gave single-crystal X-ray structure analysis. The complex crystal-
a redshift of about 15 nm. For the free ligand, the low-in- lises in the chiral space group P21. The asymmetric unit
tense absorption bands at the lowest energies were assigned contains four symmetry-independent molecules and in-
as nǞπ* transitions. Upon complexation, the lone pair of cluded solvent. Two of the four molecules have a Λ-configu-
the imino nitrogen atom becomes a σ orbital, and therefore ration (In1a and In1b), and two show a ∆-configuration
the nǞπ* transition is observed in the complex spectra. (In1c and In1d). Figure 3a shows the metal complex (In1c).
Generally, spectra of all complexes were redshifted by about The two different configurations are depicted in Figure 3b
40–50 nm compared with the respective free ligands. In- and c for the complexes Λ-In1c and ∆-In1a, respectively.
dium(III) as well as gallium(III) complexes shift by about Furthermore, each molecule shows a different orientation
the same values, thus the type of metal ion does not influ- of the sugar residues. They appear in the periphery of the
ence the shift. After complexation, the intense absorption complex and do not take part in the coordination to the
bands for the free ligand at the highest energy split into two metal centre. The galactose molecule is indicated by the ax-
bands. As expected from the blue fluorescence under UV ial orientation of the hydroxy group at C-4 of the sugar
light, the emission spectra of all complexes showed bands moiety. The InIII ion is coordinated by the chelating hexa-
from 445 to 475 nm in the blue region.
dentate N3O3 unit provided by the salicylaldimine residues.
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The First 68Ga-Labelled Sugar Derivative
They surround the metal centre in a distorted octahedral cantly. At pH = 4 the yield was 47% and at pH = 3 the
arrangement. This is confirmed by the O–In–N angles of yield dropped to 3%. To classify the stability of the 68Ga6b
around 84.21(18)° and 162.77(18)–165.05(18)° that are complex, in vitro challenge experiments were carried out
smaller than for an ideal octahedral coordination with with the plasma protein apo-transferrin and blood plasma,
angles of 90° and 180°. Furthermore, the In–O bond in which the 68Ga6b complex shows a high in vitro stability.
lengths vary between 2.077(4) and 2.257(5) Å, values which After a period of 2 h, a purity decrease of only 3–6% to a
are a deviation from the formal C3 symmetry at the InIII minimum of 90% has been observed.
centre (Table 2). The deviations from an ideal complex ge-
ometry arise from the size of the InIII ion, which cannot be
entirely enclosed by the ligand.
Conclusions
The synthesis of tripodal triamines containing -xylosyl,
-glucosyl and -galactosyl appendages could be achieved
in reasonable overall yields. Their condensation with dif-
ferent salicylaldehydes leads to the formation of tripodal
trisalicylideneimines with an [N3O3] donor set, which repre-
sent versatile ligands for the coordination of trivalent metal
ions. Depending on the substituents at the salicylidene resi-
dues the solubility, lipophilicity and stability of the result-
ant complexes can be adjusted. Coordination of the ligands
to InIII and GaIII ions under basic conditions gives the re-
spective neutral complexes (except for the 5-hydroxy-substi-
tuted salicylidene ligand). They possess an octahedral coor-
dination sphere at the metal centre and are obtained as
Λ/∆ diastereomeric mixtures, which show an equilibrium
between both forms in solution and also in the crystal, as
evidenced by single-crystal X-ray analysis of the indium
complex In6c. All complexes exhibit blue fluorescence with
an emission maximum of around 350 nm. The ligands as
well as the complexes are less stable in an acidic environ-
ment due to the hydrolytic cleavage of the imine bonds. On
the one hand, this is a drawback since new protocols for
the labelling at high pH level with 68Ga-generator-produced
acidic solutions have to be developed. On the other hand,
it may lead to a different way of enrichment within certain
tissue since it is known that, e.g., in cancerous tissue the pH
value is lower than in normal cells. Once the complexes are
formed, a sufficient stability against blood plasma and apo-
transferrin was observed over the crucial period of 120 min.
To the best of our knowledge 68Ga6b represents the first
68Ga-labelled saccharide. Preparation of the full set of li-
gands, introduction of varying spacers between the sugar
moiety and the metal-coordinating core, 68Ga-labelling ex-
periments to obtain injectable solutions and coordination
of other metal ions are therefore ongoing research topics in
our laboratories.
Figure 3. (a) Crystal structure of one of the molecules in the crystal
of In6c (50% probability ellipsoids). (b) Bottom view of the Λ-
configured indium(III) centre In1c. (c) Bottom view of the ∆-con-
figured indium(III) centre In1a.
Table 2. Selected bond lengths [Å] and angles [°] for In6c (standard
deviations in parentheses).
Bond lengths
Bond angles
In(1c) O(7c)
In(1c) O(8c)
In(1c) O(9c)
In(1c) N(1c)
In(1c) N(2c)
In(1c) N(3c)
2.077(4)
2.128(4)
2.122(4)
2.234(5)
2.257(5)
2.225(5)
O(7c)–In(1c)–N(3c) 165.05(18)
O(8c)–In(1c)–N(1c) 162.97(18)
O(9c)–In(1c)–N(2c) 162.77(18)
O(7c)–In(1c)–N(1c) 85.20(18)
O(8c)–In(1c)–N(2c) 83.28(18)
O(9c)–In(1c)–N(3c) 84.21(17)
68Ga Labelling of One Glucose-Appending Ligand
The preparation of the labelled complex 68Ga6b at “no-
carrier-added (n.c.a.)” level has been carried out by using a
procedure corresponding to the synthesis of [68Ga(NS3)R]
complexes as described by Tolmachev et al.[6] The complex
formation was investigated by taking into account different
pH values of the reaction mixture, different reaction tem-
peratures and varying ligand concentrations. “Carrier-
added (c.a.)” preparations under addition of nonradioac-
tive 69/71GaCl3 were accomplished under identical condi-
tions as proof of the complex identity. The investigations
showed that in a pH range of 9–10 with a ligand concentra-
tion of 100 µg (0.165 µmol) per preparation at 90 °C after
15 min, a 68Ga6b complex was producible in high yields of
Experimental Section
General: All reagents and solvents were purchased from commer-
cial sources and used as received. IR spectra were measured with
a Perkin–Elmer 2000 spectrometer, NMR spectra witrh a JEOL
JMTC-400/54/SS or Bruker AC-200 instrument, ESI MS data were
recorded with a JEOL JMS-T100LC, a Finnigan MAT SSQ 710,
a Finnigan MAT 95XL TRAP, a Bruker micrOTOF-Q or by using
a Micromass Tandem Quadropole Mass Spectrometer (Quattro
LC). Elemental analyses were carried out with a Leco CHNS 932
or Perkin–Elmer PE2400 Series II CHNS/O Analyser (Nara Insti-
96–98%. In a pH range Ͻ 9, the yields decreased signifi- tute of Science and Technology). 68Ga was eluted from a 68+Ge/
Eur. J. Inorg. Chem. 2009, 4298–4307
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
4303

M. Gottschaldt et al.
FULL PAPER
68Ga generator (Obninsk, Russia) as GaCl3 in hydrochloric acid
solution (0.1 ) and added to the aqueous/methanolic solution of
the ligand (6b). All solvents and dry GaCl3 (Aldrich) applied were
of analytical grade and used as purchased. Challenge experiments
were carried out at 37 °C with apo-transferrin (Sigma)
(5 mgmLϪ1), the exchange was controlled by thin layer chromatog-
raphy (TLC) on silica gel (Merck) and methanol as eluent. Analysis
of the radio-TLC of the 68Ga-labeled compounds was performed
by using a FUJI BAS-1800II-scanner.
2-H), 3.51 (d, J = 9.7 Hz, 1 H, OCH2Ј), 3.49–3.47 (m, 2 H, 3-H,
5-H) ppm. 13C NMR (CD3OD): δ = 169.1 (CH=N), 163.1 (C-2Ј),
134.1 (C-4Ј), 133.2 (C-6Ј), 119.9 (C-1Ј), 119.6 (C-5Ј), 118.2 (C-3Ј),
105.3 (C-1), 76.8 (C-5), 75.0 (C-3), 72.6 (C-2), 70.8 (O-CH2), 70.4
2
(C-4), 62.5 (C-6), 60.8 (CH2N), 45.2 (Cquart) ppm. IR (ATR): ν =
˜
3390 (OH), 1630 (CH=N) cm–1. UV/Vis (MeOH): λmax (ε) = 403
(2580), 318 (11792), 257 (36882), 220 (59002 –1 cm–1) nm. ESI-
MS: m/z (%) = 630.2 (100) [M + Na]+. C32H37N3O8 (591.26) ·H2O:
calcd. C 61.43, H 6.28, N 6.72; found C 61.92, H 6.31, N 6.64.
3Ј-Salicylaldimino-2Ј,2Ј-bis(salicylaldiminomethyl)propyl-β-
D
-xylo-
[3Ј-Salicylaldimino-2Ј,2Ј-bis(salicylaldiminomethyl)propyl-β-D-xylo-
pyranoside (6a): For the Schiff base reaction, the crude triamine 5a
(312 mg, 1.13 mmol) and salicylaldehyde (431 mg, 3.39 mmol) were
heated to reflux in absolute ethanol (50 mL) for 3 h. The solvent
was removed, and the yellow residue was extracted with ethyl ace-
tate and water. The combined organic layers were dried with so-
dium sulfate, and the solvent was evaporated in vacuo. Subsequent
column chromatography (ethyl acetate; Rf = 0.68) gave 320 mg
(47 %) of the product as yellow powder. 1H NMR (400 MHz,
pyranosido]indium(III) (In6a): 6a (20 mg) was dissolved in methanol
(8 mL) and deprotonated with triethylamine (TEA, 10 mg).
InCl3·4H2O (10 mg, 0.034 mmol) was slowly added to the solution
in methanol (5 mL). The reaction mixture was heated to reflux for
4 h during which time the colour lightened. After concentration,
the crude product was purified by chromatography on deactivated
(TEA) silica gel (ethyl acetate/methanol, 2:1) giving 6.7 mg (28%)
of the product. Pink crystals forming small rosettes were obtained
CD3OD): δ = 8.44 (s, 3 H, CH=N), 7.32–7.28 (m, 6 H, 4Ј-H, 6Ј- from methanol/water. 1H NMR (400 MHz, [D7]DMF): δ = 8.44 (s,
3
H), 6.88–6.82 (m, 6 H, 3Ј-H, 5Ј-H), 4.16 (d, J = 6.8 Hz, 1 H, 1-
3 H, CH=N), 7.25–7.19 (m, 6 H, 4Ј-H, 6Ј-H), 6.64 (d, 3J = 8.3 Hz,
H), 3.90 (d, 2J = 9.7 Hz, 1 H, OCH2), 3.80–3.76 (m, 1 H, 5-H), 3 H, 3Ј-H) 6.57–6.54 (m, 3 H, 5Ј-H), 5.39 (s, 1 H, OH), 5.16 (s, 1
3.74 (br. s, 6 H, 3 CH2N) 3.52–3.46 (m, 2 H, 4-H, OCH2Ј), 3.33– H, OH), 4.30 (d, 3J = 7.5 Hz, 1 H, 1-H), 4.08–3.99 (m, 6 H, 3
3.29 (m, 2 H, 2-H, 3-H), 3.12 (t, 2J = 10.8 Hz, 1 H, 5Ј-H) ppm.
13C NMR (CD3OD): δ = 169.2 (CH=N), 163.2 (C-2Ј), 134.0 (C-
CH2N) 3.91 (d, J = 9.7 Hz, 1 H, OCH2), 3.87 (dd, J = 5.4, J =
2
3
2
2
11.3 Hz, 1 H, 5-H), 3.55 (d, J = 9.7 Hz, 1 H, OCH2Ј), 3.52–3.48
3
4Ј), 133.2 (C-6Ј), 120.0 (C-1Ј), 119.7 (C-5Ј), 118.1 (C-3Ј), 105.5 (C- (m, 1 H, 5Ј-H), 3.37 (t, J = 9.7 Hz, 1 H, 3-H), 3.28–3.21 (m, 2 H,
1), 77.9 (C-3), 75.0 (C-2), 71.3 (C-4), 70.8 (O-CH2), 67.0 (C-5), 2-H, 4-H) ppm. 13C NMR ([D7]DMF): δ = 174.0 (CH=N), 171.6
61.27 (CH2N), 45.2 (Cquart) ppm. IR (ATR): ν = 1627 (CH=N), (C-2Ј), 136.1 (C-4Ј), 134.7 (C-6Ј), 123.4 (C-3Ј), 119.6 (C-1Ј), 114.8
˜
3300 (OH) cm–1. UV/Vis (MeOH): λmax (ε) = 396 (3457), 318
(C-5Ј), 105.6 (C-1), 77.6 (C-3), 74.5 (C-2), 73.3 (O-CH2), 70.9 (C-
(15705), 258 (48740), 216 (82090 –1 cm–1) nm. ESI-MS: m/z (%) = 4), 66.8 (C-5), 64.2 (CH2N), 41.4 (Cquart) ppm. IR (ATR): ν = 1620
˜
578.2 (62) [M + H]+, 600.2 (100) [M + Na]+. C31H35N3O8 (577.24) ·
0.5(ethyl acetate): calcd. C 64.00, H 6.41, N 6.68; found C 64.09,
H 6.44, N 6.71.
(CH=N), 3290 (OH) cm–1. UV/Vis (MeOH): λmax (ε) = 352 (14074),
270 (28822), 237 (59370), 220 (50672 –1 cm–1) nm. ESI-MS: m/z
(%) = 712.0 (100) [M + Na]+. C31H32InN3O8 (689.12) ·0.5H2O:
calcd. C 53.31, H 4.76, N 6.02; found C 53.41, H 4.75, N 5.93.
3Ј-Salicylaldimino-2Ј,2Ј-bis(salicylaldiminomethyl)propyl-β-D-gluco-
pyranoside (6b): Analogous to the synthesis of 6a by using 3Ј-
amino-2Ј,2Ј-bis(aminomethyl)propyl-β--glucopyranoside (5b;
[3Ј-Salicylaldimino-2Ј,2Ј-bis(salicylaldiminomethyl)propyl-β-
pyranosido]indium(III) (In6b): Analogous to the synthesis of In6a
D-gluco-
260 mg, 0.88 mmol) and salicylaldehyde (322 mg, 2.64 mmol) to by using 6b (40 mg, 0.066 mmol) and InCl3·4H2O (19 mg,
yield, after column chromatography (ethyl acetate/methanol, 3:1;
Rf = 0.8), 406 mg (76%) of yellow product. H NMR (400 MHz,
0.066 mmol) in methanol (10 mL). After concentration and column
chromatography on deactivated (TEA) silica gel (ethyl acetate/
1
CD3OD): δ = 8.41 (s, 3 H, CH=N), 7.30–7.28 (m, 6 H, 4Ј-H, 6Ј- methanol, 2:1), 40 mg (80%) was obtained as slightly yellow pow-
3
H), 6.92–6.81 (m, 6 H, 3Ј-H, 5Ј-H), 4.27 (d, J = 7.5 Hz, 1 H, 1-
der. 1H NMR (250 MHz, [D7]DMF): δ = 8.46 (s, 3 H, CH=N),
H), 4.06 (d, 2J = 9.7 Hz, 1 H, OCH2), 3.85 (dd, 3J = 2.0, 2J = 7.26–7.16 (m, 6 H, 4Ј-H, 6Ј-H), 6.64 (d, 3J = 8.0 Hz, 3 H, 3Ј-H)
12.0 Hz, 1 H, 6-H), 3.77–3.65 (m, 6 H, 3 CH2N) 3.66 (dd, 3J = 4.6, 6.59–6.53 (m, 3 H, 5Ј-H), 5.42–4.68 (m, 4 H, OH), 4.35 (d, 3J =
2J = 12.0 Hz, 1 H, 6Ј-H), 3.51 (d, 2J = 9.7 Hz, 1 H, OCH2Ј), 3.42–
3.32 (m, 4 H, 2-H, 3-H, 4-H, 5-H) ppm. 13C NMR (CD3OD): δ =
167.6 (CH=N), 161.9 (C-2Ј), 132.6 (C-4Ј), 131.8 (C-6Ј), 118.6 (C-
1Ј), 118.3 (C-5Ј), 116.8 (C-3Ј), 103.1 (C-1), 76.7 (C-3), 76.6 (C-5),
7.7 Hz, 1 H, 1-H), 4.11–3.97 (m, 7 H, 3 CH2N, OCH2), 3.74–3.53
(m, 2 H, 6Ј-H, OCH2Ј), 3.44–3.21 (m, 4 H, 2-H, 3-H, 4-H, 5-H)
ppm. 13C NMR ([D7]DMF): δ = 173.9 (CH=N), 171.5 (C-2Ј), 136.1
(C-4Ј), 134.6 (C-6Ј), 123.3 (C-3Ј), 119.5 (C-1Ј), 114.8 (C-5Ј), 105.0
73.7 (C-2), 70.3 (C-4), 69.5 (O-CH2), 61.4 (C-6), 59.6 (CH2N), 43.6 (C-1), 78.1 (C-3), 77.7 (C-5), 74.7 (C-2), 73.43 (OCH2), 71.4 (C-4),
(Cquart) ppm. IR (ATR): ν = 3372 (OH), 1632 (CH=N) cm–1. UV/
64.1 (CH2N), 62.4 (C-6), 41.4 (Cquart) ppm. IR (ATR): ν = 1630
˜
˜
Vis (MeOH): λmax (ε) = 405 (2382), 318 (10937), 257 (34257), 220 (CH=N), 3360, 2930, 2600 (OH) cm–1. UV/Vis (MeOH): λmax (ε)
(56968 –1 cm–1) nm. FAB-MS: m/z (%) = 608 (20) [M + H]+.
C32H37N3O8 (591.26) ·0.5H2O: calcd. C 62.33, H 6.21, N 6.81;
found C 62.01, H 6.10, N 6.80.
= 353 (7439), 270 (15952), 237 (3309 –1 cm–1) nm. ESI-MS: m/z
(%) = 1461.0 (32) [2 M + Na]+, 1439.1 (20) [2 M + H]+, 742.0 (9)
[M + Na]+, 720.0 (100) [M + H]+. C32H34InN3O9 (719.13) ·
H2O·CH3OH: calcd. C 51.51, H 5.24, N 5.46; found C 51.83, H
4.89, N 5.17.
3Ј-Salicylaldimino-2Ј,2Ј-bis(salicylaldiminomethyl)propyl-β-
D-galac-
topyranoside (6c): The Schiff base reaction was analogous to that
for the synthesis of 6a by using triamine 5c (150 mg, 0.51 mmol) [3Ј-Salicylaldimino-2Ј,2Ј-bis(salicylaldiminomethyl)propyl-β-
D
-gal-
and salicylaldehyde (186 mg, 1.53 mmol) to yield, after column
actopyranosido]indium(III) (In6c): Analogous to the synthesis of
chromatography (ethyl acetate/methanol, 3:1; Rf = 0.76) 232 mg
(75%) of yellow product. H NMR (400 MHz, CD3OD): δ = 8.45
In6a by using 6c (40 mg, 0.066 mmol) and InCl3·4H2O (19 mg,
0.066 mmol) in methanol (10 mL). After evaporation and column
1
(s, 3 H, CH=N), 7.31–7.27 (m, 6 H, 4Ј-H, 6Ј-H), 6.89–6.82 (m, 6 chromatography on deactivated (TEA) silica gel (ethyl acetate/
H, 3Ј-H, 5Ј-H), 4.21 (d, 3J = 7.7 Hz, 1 H, 1-H), 4.03 (d, 2J = 9.7 Hz, methanol, 2:1), 35 mg (74%) was obtained as slightly yellow pow-
3
1 H, OCH2), 3.85 (d, J = 3.0 Hz, 1 H, 4-H), 3.78–3.71 (m, 6 H, 3
der. Recrystallisation from methanol/water gave crystals suitable
3
1
CH2N), 3.70–3.67 (m, 2 H, 6-H, 6Ј-H), 3.65 (dd, J = 9.8 Hz, 1 H, for X-ray structure analysis. H NMR (400 MHz, [D7]DMF): δ =
4304 Eur. J. Inorg. Chem. 2009, 4298–4307
www.eurjic.org
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

The First 68Ga-Labelled Sugar Derivative
8.45 (s, 3 H, CH=N), 7.26–7.21 (m, 6 H, 4Ј-H, 6Ј-H), 6.66 (d, 3J = In6a by using ligand 6c (40 mg, 0.066 mmol) and Ga(NO3)3·H2O
3
3
8.4 Hz, 3 H, 3Ј-H) 6.58 (t, J = 7.2 Hz, 3 H, 5Ј-H), 5.26 (d, J = (17 mg, 0.066 mmol) to yield, after column chromatography on de-
4.0 Hz, 1 H, OH), 4.76 (s, 1 H, OH), 4.69 (m, 1 H, OH), 4.51 (d, activated (TEA) silica gel (ethyl acetate/methanol, 2:1), 28 mg
3
1
3J = 3.2 Hz, 1 H, OH), 4.29 (d, J = 7.2 Hz, 1 H, 1-H), 4.06–3.97 (64%) of pale yellow product. H NMR (400 MHz, [D7]DMF): δ
2
(m, 6 H, 3 CH2N), 3.95 (d, J = 9.6 Hz, 1 H, OCH2), 3.89 (m, 1 = 8.38/8.36 (s, 3 H, CH=N), 7.26–7.16 (m, 6 H, 4Ј-H, 6Ј-H) 6.57–
H, 4-H), 3.81–3.71 (m, 2 H, 6-H, 6Ј-H), 3.62–3.47 (m, 4 H, 2-H,
6.51 (m, 6 H, 5Ј-H, 3Ј-H), 5.38 (s, 1 H, OH), 5.15 (s, 1 H, OH),
3-H, 5-H, OCH2Ј) ppm. 13C NMR ([D7]DMF): δ = 173.9 (CH=N),
4.84 (s, 2 H, OH), 4.75 (s, 2 H, OH), 4.57 (s, 2 H, OH), 4.31/4.27
3
171.5 (C-2Ј), 136.1 (C-4Ј), 134.6 (C-6Ј), 123.3 (C-3Ј), 119.5 (C-1Ј), (d, J = 7.5/7.4 Hz, 1 H, 1-H), 4.21–4.16 (m, 6 H, 3 CH2N), 3.98
115.8 (C-5Ј), 105.7 (C-1), 76.5 (C-5), 74.5 (C-5), 73.4 (C-2), 72.0 (d, J = 9.7 Hz, 2 H, OCH2), 3.91 (m, 2 H, 4-H), 3.80–3.73 (m, 8
2
(C-4), 67.4 (OCH2), 64.2 (CH2N), 61.8 (C-6), 41.4 (Cquart) ppm. IR H, 3 CH2N, 6-H, 6Ј-H), 3.59–3.53 (m, 4 H, 2-H, 3-H, 5-H, OCH2Ј)
(ATR): ν = 1631 (CH=N), 3365, 2920 (OH) cm–1. UV/Vis ppm. 13C NMR ([D7]DMF): δ = 170.8/170.7 (CH=N), 169.4 (C-
˜
(MeOH): λmax (ε) = 353 (7568), 272 (16223), 239 (34810 –1 cm–1) 2Ј), 134.7 (C-4Ј), 134.5 (C-6Ј), 122.5 (C-3Ј), 119.6 (C-1Ј), 114.8 (C-
nm. FAB-MS: m/z (%) = 720.0 (16) [M + H]+. C32H34InN3O9
(719.13) ·1.5H2O: calcd. C 51.49, H 5.00, N 5.63; found C 51.30,
H 5.03, N 5.65.
5Ј), 105.7/105.4 (C-1), 76.4/77.5 (C-5), 74.4 (C-3), 72.7/72.5
(OCH2), 72.0 (C-2), 69.4 (C-4), 62.8/62.6 (CH2N), 61.8/61.7 (C-6),
39.9/39.8 (Cquart) ppm. IR (ATR): ν = 1631 (CH=N), 3365 (OH)
˜
cm–1. UV/Vis (MeOH): λmax (ε) = 355 (6520), 268 (13702), 237
(28009), 220 (35058 –1 cm–1) nm. ESI-MS: m/z (%) = 1371.2 (43)
[2 M + Na]+, 696.0 (100) [M + Na]+. C32H34GaN3O9 (673.16):
calcd. C 56.99, H 5.08, N 6.23; found C 56.94, H 5.22, N 6.01.
[3Ј-Salicylaldimino-2Ј,2Ј-bis(salicylaldiminomethyl)propyl-β-D-xylo-
pyranosido]gallium(III) (Ga6a): Analogous to the synthesis of In6a
by using ligand 6a (20 mg, 0.034 mmol), Ga(NO3)3·H2O (8.7 mg,
0.034 mmol) and TEA (10 mg) to yield, after column chromatog-
raphy on deactivated (TEA) silica gel (ethyl acetate/methanol, 2:1),
18 mg (83%) of pale yellow product. Pink crystals forming small
Synthesis of the Corresponding 68GaIII Complex by Using 3Ј-Salicyl-
aldimino-2Ј,2Ј-bis(salicylaldiminomethyl)propyl-β-D-glucopyranoside
1
rosettes were obtained from methanol/water. H NMR (400 MHz,
(6b). No-Carrier-Added Preparation of 68Ga6b: To ammonium ace-
tate buffer (400 µL 1 ) in a 1 mL Eppendorf vial were added a
solution of 6b [100 µL, 0.165 µmol; 1 mg of ligand 6b dissolved in
1 mL of methanol/water (1:1)] and 68Ga eluate (70–100 µL). The
resultant pH of 6–7 for the reaction mixture was adjusted to 9–9.5
by addition of 1  NaOH. The reaction was complete after 15 min
of shaking in a thermo mixer at 90 °C. After neutralisation of the
reaction mixture with 1  HCl, the radiochemical purity was con-
trolled by radio thin layer chromatography on silica gel (methanol/
1  ammonium acetate, 1:1). The 68Ga6b complex was formed with
a yield of 96–98%, the Rf value of 0.9 was dedicated to the com-
plex, unreacted 68Ga eluate remains at the start as gallium hydrox-
ide. Carrier-Added Preparation of 68Ga6b: To ligand 6b (5 mg,
8.2 µmol), dissolved in methanol (1 mL), were added a GaCl3 stock
solution (8.1 µL, 8.2 µmol; 179 mg of GaCl3 in 1 mL of H2O) and
68Ga eluate (100 µL). The pH was adjusted to 9–9.5 by addition of
1  NaOH (90 µL). The reaction was complete after 15 min of
shaking in the thermo mixer at 90 °C. After neutralisation of the
reaction mixture with 1  HCl, the yield and purity were controlled
by thin layer chromatography. Both, the UV detection and the
radioactivity detection, showed peaks with identical Rf values of
0.9. The radiochemical yield was determined as Ͼ 90%. The com-
plex was identified by mass spectrometry from the c.a. reaction
mixture (without further purification). ESI-MS (MeOH): m/z =
696.3, 698.6 [M + Na = C32H34GaN3NaO9]+; in agreement with
the predicted isotopic distribution (see Figure S11 in Supporting
Information).
[D7]DMF): δ = 8.37/8.35 (s, 3 H, CH=N), 7.25–7.21 (m, 3 H, 4Ј-
3
H), 7.19–7.15 (m, 3 H, 6Ј-H) 6.54 (t, J = 7.3 Hz, 3 H, 5Ј-H) 6.49
3
(d, J = 8.5 Hz, 3 H, 3Ј-H), 5.45 (s, 1 H, OH), 5.24 (s, 1 H, OH),
3
5.11 (s, 1 H, OH), 5.04 (s, 1 H, OH), 4.32/4.28 (d, J = 7.5 Hz, 1
H, 1-H), 4.21–4.16 (m, 6 H, 3 CH2N) 3.92 (d, 2J = 9.8 Hz, 2 H,
3
2
OCH2), 3.87 (dd, J = 5.2, J = 11.3 Hz, 2 H, 5-H), 3.79–3.73 (m,
6 H, 3 CH2N), 3.57/3.56 (d, 2J = 9.7 Hz, 1 H, OCH2) 3.48–3.46 (m,
4-H), 3.38–3.20 (m, 2-H, 3-H, 5Ј-H) ppm. 13C NMR ([D7]DMF): δ
= 170.7/170.6 (CH=N), 169.5 (C-2Ј), 134.7 (C-4Ј), 134.5 (C-6Ј),
122.5 (C-3Ј), 119.7 (C-1Ј), 114.7 (C-5Ј), 105.7/105.4 (C-1), 77.6/77.5
(C-3), 74.6/74.5 (C-2), 72.7/72.4 (OCH2), 70.9 (C-4), 66.7 (C-5),
62.7/62.5 (CH2N), 39.9/39.7 (Cquart) ppm. IR (ATR): ν = 1628
˜
(CH=N), 3370 (OH) cm–1. UV/Vis (MeOH): λmax (ε) = 354 (7285),
277 (13785), 268 (14219), 235 (28085), 216 (34426 –1 cm–1) nm.
ESI-MS: m/z (%) = 1311.2 (2) [2 M + Na]+, 666.0 (100) [M +
Na]+. C31H32GaN3O8 (643.14): calcd. C 57.79, H 5.01, N 6.52;
found C 57.90, H 4.90, N 6.51.
[3Ј-Salicylaldimino-2Ј,2Ј-bis(salicylaldiminomethyl)propyl-β-D-gluco-
pyranosido]gallium(III) (Ga6b): Analogous to the synthesis of In6a
by using 6b (40 mg, 0.066 mmol) and Ga(NO3)3·H2O (17 mg,
0.066 mmol) to yield, after column chromatography on deactivated
(TEA) silica gel (ethyl acetate/methanol, 2:1), 30 mg (69%) of pale
1
yellow product. H NMR (400 MHz, [D7]DMF): δ = 8.39/8.36 (s,
3 H, CH=N), 7.26–7.16 (m, 6 H, 4Ј-H, 6Ј-H) 6.57–6.51 (m, 6 H,
3Ј-H, 5Ј-H), 5.47 (s, 2 H, OH), 5.12 (s, 4 H, OH), 4.62 (s, 2 H,
OH), 4.36/4.33 (d, 3J = 7.7 Hz, 1 H, 1-H), 4.21–4.16 (m, 6 H, 3
2
CH2N), 4.00/3.98 (d, J = 9.8/10.0 Hz, 1 H, OCH2), 3.91–3.88 (m,
Challenge Experiments with Apo-Transferrin and Blood Plasma: To
a mixture of phosphate buffer (200 µL 0.1 ) and apo-transferrin
solution (200 µL) in a 1 mL Eppendorf vial (1.25 mg of apo-trans-
ferrin in 200 µL of 0.1  phosphate buffer pH = 7.4) was added
the 68Ga6b complex solution (100 µL). Analogously, to a mixture
of phosphate buffer (200 µL, 0.1 ) and human blood plasma
(200 µL) in a 1 mL Eppendorf vial was added the 68Ga6b complex
solution (100 µL). The mixtures were incubated for 120 min at
37 °C. After 60 and 120 min, the percentage of complex 68Ga6b
was determined by radio TLC.
3
2 H, 6-H), 3.80–3.74 (m, 6 H, 3 CH2N), 3.68 (dd, J = 4.8, 2J =
2
11.6 Hz, 1 H, 6Ј-H), 3.60/3.57 (d, J = 10.2/9.9 Hz, 2 H, OCH2Ј),
3.44–3.30 (m, 6 H, 3-H, 4-H, 5-H), 3.25–3.20 (m, 2 H, 2-H) ppm.
13C NMR ([D7]DMF): δ = 170.8/170.7 (CH=N), 169.4 (C-2Ј),
134.7 (C-4Ј), 134.5 (C-6Ј), 122.5 (C-3Ј), 119.6 (C-1Ј), 114.7 (C-5Ј),
105.0/104.8 (C-1), 78.0 (C-3), 77.7/77.6 (C-5) 74.7 (C-2), 72.6/72.5
(OCH2), 71.5/71.4 (C-4), 62.7 (C-6), 61.5 (CH2N), 39.9/39.7 (Cquart
)
ppm. IR (ATR): ν = 1630 (CH=N), 3370 (OH) cm–1. UV/Vis
˜
(MeOH): λmax (ε) = 354 (6813), 267 (14896), 237 (28269), 219
(36063 –1 cm–1) nm. ESI-MS: m/z (%) = 1371.3 (27) [2 M +
Na]+, 696.0 (100) [M + Na]+. C32H34GaN3O9 (673.16): calcd. C
56.99, H 5.08, N 6.23; found C 57.04, H 4.85, N 5.94.
X-ray Crystallography for In6c: The intensity data for the com-
pound were collected with a Nonius Kappa CCD diffractometer
by using graphite-monochromated Mo-Kα radiation. Data were
corrected for Lorentz and polarisation effects but not for absorp-
[3Ј-Salicylaldimino-2Ј,2Ј-bis(salicylaldiminomethyl)propyl-β-
D-gal-
actopyranosido]gallium(III) (Ga6c): Analogous to the synthesis of
Eur. J. Inorg. Chem. 2009, 4298–4307
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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4305

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Published Online: August 14, 2009
Eur. J. Inorg. Chem. 2009, 4298–4307
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
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