MRI Contrast Agents
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1H NMR (200 MHz, CDCl3 [CHCl3 7.30 ppm]): d 1.51 (m, 2H), 2.74 (t,
J 6.5 Hz, 2H), 2.92 (dd, J 13.8 Hz, 8.4 Hz, 1H), 3.27 3.42 (m, 3H), 3.65
(dd, J 8.6 Hz, 4.3 Hz, 1H), 7.40 (d, J 8.5 Hz, 2H), 7.51 (brs, 1H), 8.18 (d,
J 8.5 Hz, 2H).
form, 80 g). The column was washed with H2O (700 mL) and 6 was eluted
with HCOOH (0.2m and 0.3m, 2 L). The eluate was evaporated to
complete dryness under reduced pressure and redissolved in H2O.
Evaporation and redissolution were repeated twice more to remove any
formic acid remaining. After final evaporation and drying under reduced
pressure 6 was obtained as a white powder (1.1 g, 15%). 1H NMR
(200 MHz, D2O [HDO 4.80 ppm]): d 2.26 (s, 4H), 3.42 (m, 8H), 3.99 (s,
(p-Nitrobenzyl)ethylenepropylenetriamine (3): Amide 2 (6.0 g, 22.5 mmol)
was placed under argon in a three-necked flask (1 L) equipped with a
condenser, a septum and an addition funnel. Anhydrous THF (180 mL) was
purged with argon, then cannulated into the addition funnel and added in
one portion. The amide dissolved only partially. The solution was kept at
08C while BH3/THF (1m; 180 mL) was cannulated into the addition funnel
and added dropwise over a 30 min period, after which all the amide had
dissolved. The solution was warmed gradually, brought to reflux for 10 h,
kept for 7 h at room temperature, then cooled to 58C with an ice bath. The
excess of borane was quenched by addition of cold water (13 mL). The
mixture was concentrated under reduced pressure to give a brown oil. HCl
(6m; 130 mL) was added to the oil, and the resulting solution was heated
under reflux for 3 h. The mixture was evaporated to dryness and the
remaining yellow residue was dissolved in H2O (90 mL) and aqueous NH3
(25%; 90 mL). The pH was adjusted to 12 with KOH (5m). This solution
was extracted with CH2Cl2 (10 portions of 100 mL). The organic extracts
were pooled, dried with Na2SO4, filtered, concentrated and dried under
reduced pressure to give 3 as a yellow oil (5.20 g, 92%). 1H NMR
(200 MHz, CDCl3 [CHCl3 7.30 ppm]): d 1.63 (m, 2H), 2.46 (dd, J
11.6 Hz, 8.3 Hz, 1H), 2.6 3.0 (m, 7H), 3.13 (m, 1H), 7.36 (d, J 8.4 Hz,
2H), 8.15 (d, J 8.4 Hz, 2H).
2H), 4.09 (s, 8H); MS (ESI): m/z: 421.4 [MH] ; elemental analysis calcd
(%) for C16H27N3O10 ¥ 3HCl (530.9): C 36.21, H 5.70, N 7.92; found: C 35.95,
H 5.93, N 8.04.
N,N''-Bis(phthalimido)diethylenetriamine-N'-propionic acid methyl ester
(7): N,N''-Bis(phthalimido)diethylenetriamine (440 mg, 1.2 mmol), synthe-
sized according to the literature,[31] was dissolved in dry DMF (10 mL) at
708C under an argon atmosphere. Bromopropionic methyl ester (250 mg,
1.5 mmol), anhydrous K2CO3 (345 mg, 2.5 mmol) and KI (42 mg,
0.25 mmol) were added successively to the stirred solution. The mixture
was stirred under an argon atmosphere for 8 h at 708C and then evaporated
to dryness. The residue was dissolved in CHCl3 (10 mL) and filtered. When
the filtrate had been concentrated a yellow-brown oil remained in the flask.
The crude product was purified on a silica gel column (1.5 cm 15 cm) with
ethyl acetate/heptane (3:1 v/v). After removal of the solvent from the
appropriate fractions ester 7 was obtained as a pale yellow solid (185 mg,
34%). Rf 0.50 (silica gel, ethyl acetate/heptane 3:1 v/v); 1H NMR
(400 MHz, CDCl3 [CHCl3 7.30 ppm]): d 2.40 (t, 2H, J 7.2 Hz), 2.84 (t,
4H, J 6.6 Hz), 2.95 (t, 2H, J 7.2 Hz), 3.51 (s, 3H), 3.78 (t, 4H, J
6.6 Hz), 7.69 7.83 (m, 8H).
(p-Nitrobenzyl)ethylenepropylenetriaminepentaacetic acid penta-tert-bu-
tyl ester (4): Amine 3 (5.2 g, 20.6 mmol) was added under argon to a three-
necked flask (500 mL) equipped with a gas inlet, an addition funnel and a
CaCl2 drying tube. Anhydrous DMF (170 mL) was added in one portion.
After the dissolution of 3, DIEA (43 mL, 247 mmol) was added in one
portion. tert-Butyl bromoacetate (27.5 mL, 157 mmol) was added, where-
upon the solution turned brown. When KI (3.8 g, 23 mmol) was added in
one portion the solution became orange and warm to the touch. The
mixture was stirred under argon at room temperature for 18 h. Evaporation
of the solvent under reduced pressure gave a brown solid together with a
white solid. The residue was partitioned between Et2O (270 mL) and H2O
(100 mL). The organic phase was washed with H2O (two 130 mL portions)
and with a saturated NaCl solution (two 70 mL portions), dried with
Na2SO4, filtered and evaporated to dryness. The crude product 4 was
purified on a silica gel column (3.0 cm  20 cm) using ethyl acetate/heptane
(3:1 v/v) as eluent to give 4 as a light yellow oil (7.2 g, 42%). Rf 0.65 (ethyl
Diethylenetriamine-N,N,N'',N''-tetraacetic-N'-propionic acid (H5DTTA-
prop; 8): Ester 7 (185 mg, 0.41 mmol) was heated under reflux in HCl
(6m, 10 mL) for 6 h. The reaction solution was concentrated under reduced
pressure to one-third of its volume and stored at 48C overnight. Crystal-
lized phthalic acid was filtered off and the solution was evaporated to
dryness. The residue was dissolved in a minimum of water and neutralized
with NaOH (1m). The neutral solution was added to a stirred basic solution
of sodium chloroacetate that had been freshly prepared by dropwise
addition of NaOH (10m, 0.5 mL) to chloroacetic acid (240 mg, 2.5 mmol) in
water (0.5 mL) at T< 108C. The reaction solution was stirred at 608C for
10 h and then cooled to room temperature. The reaction solution was set to
pH ꢀ 1.8 by dropwise addition of HCl (5m). The acidified solution was
evaporated under reduced pressure to complete dryness. The residue was
heated under reflux in dry ethanol (20 mL) for 3 min, remaining NaCl was
filtered off and the solvent was removed under reduced pressure. The
residue was dissolved in a minimum of water and loaded onto a cation-
1
acetate/heptane 3:1); H NMR (200 MHz, CDCl3 [CHCl3 7.30 ppm]): d
1.40 1.48 (m, 45H), 1.58 (m, 2H), 2.42 (dd, J 13.1, 8.2 Hz, 1H), 2.54
3.15 (m, 8H), 3.23 (s, 2H), 3.39 (s, 8H), 7.49 (d, J 8.8 Hz, 2H), 8.11 (d, J
8.8 Hz, 2H).
exchange column (Bio-Rad AG¾ 50W-X4, H form, 1.5 cm  7 cm). The
column was washed with water until the eluate had a pH of 7 and the
product mixture was eluted in one fraction with NH3 (0.5m, 100 mL). This
fraction was evaporated to dryness, dissolved in a minimum of water and
loaded onto an anion-exchange column (Bio-Rad AG¾ 1-X4, converted
into HCOOÀ form, 1.5 cm  7 cm). The column was washed with water
until the eluate had a pH of 7 and the product was eluted with a 0.1 2m
gradient of HCOOH (total volume of eluent for gradient ꢀ 400 mL). The
ligand fraction eluted at approximately 1m HCOOH. The solvent was
evaporated, water (50 mL) was added to dissolve the residue, and the
solvent was evaporated again. The product was dried under high vacuum
until all formic acid had been removed. After storage in air, 8 was obtained
as a white solid (76 mg, 41%) hydrated with ca. 2.5 mol water/mol ligand.
1H NMR (400 MHz, D2O [HDO 4.80 ppm], pD ꢀ 2): d 2.87 (t, 2H, J
6.6 Hz), 3.42 3.50 (m, 10H), 3.86 (s, 8H); 1H NMR ( K2CO3, pD ꢀ 10):
d 2.38 (t, 2H, J 8.2 Hz), 2.66 2.78 (m, 8H), 2.82 (t, 2H, J 8.2 Hz),
(p-Nitrobenzyl)ethylenepropylenetriaminepentaacetic acid (H5EPTPA-
bz-NO2; 5): Ester 4 (4.27 g, 5.2 mmol) and HCl (6m; 200 mL) were heated
under reflux for 14 h and then kept at room temperature for 12 h. The
reaction solution was washed with ethyl acetate (five 200 mL portions).
Evaporation of the aqueous phase gave a slightly yellow powder. The
product was recrystallized twice from EtOH/Et2O to give 5 as white crystals
1
(565 mg, 20%). H NMR (200 MHz, D2O [HDO 4.80 ppm]): d 2.24 (m,
2H), 2.85 (dd, J 7.6 Hz, 13.4 Hz, 1H), 3.10 3.90 (m, 8H), 3.70 (s, 6H),
4.05 (s, 4H), 7.52 (d, J 8.7 Hz, 2H), 8.23 (d, J 8.7 Hz, 2H); MS (ESI):
m/z: 543.2 [MH] ; elemental analysis calcd (%) for C22H30N4O12 ¥ H2O
(560.5): C 47.14, H 5.75, N 10.00; found: C 47.30, H 6.13, N 9.80.
Dipropylenetriaminepentaacetic acid (H5DPTPA; 6): NaOH solution
(12.3m, 46 mL, 570 mmol) was added dropwise to a solution of mono-
chloroacetic acid (27 g, 290 mmol) in H2O (14 mL) cooled with an ice bath
at 58C. Bis(3-aminopropyl)amine (5.4 mL, 38 mmol) was added to the
reaction solution. The ice bath was removed and the temperature rose to
508C in 1 h. The solution was stirred at room temperature for 18 h. The
mixture was cooled to 58C and H2SO4 (95%, 10 mL) was added dropwise
to adjust the pH to approximately 1.5. Evaporation of the solvent gave a
white solid (30 g). A portion of the crude product 6 (15 g) was loaded onto a
3.22 (s, 8H); MS (ESI): m/z: 408.2 [MH] ; elemental analysis calcd (%)
for C15H25N3O10 ¥ 2.5H2O: C 39.82, H 6.68, N 9.29; found: C 40.1, H 6.93, N
9.02.
Potentiometry: Stock solutions of Ca2, Zn2 and Cu2 (20 35 mm) were
prepared from chloride (Ca2, Zn2) or sulfate (Cu2) salts with double-
distilled water, and standardized by complexometric titration with Na2H2-
EDTA (Ca2, Zn2) or by gravimetry (Cu2). The Gd(ClO4)3 stock solution
was made by dissolving Gd2O3 in a slight excess of HClO4 (Merck, p.a.,
60%) in double-distilled water, followed by filtering. The pH of the stock
solution was adjusted to 5.5 by addition of Gd2O3 and its concentration was
determined by titration with Na2H2EDTA solution using xylenol orange as
indicator.
cation-exchange column (Dowex 50WX2, 200 400 mesh, H form, 100 g)
and washed with H2O (700 mL). The crude product was eluted with HCl
(1.5m and 2.0m, 2 L). The eluate was concentrated under reduced pressure
and the white residue (6.3 g) was dissolved in H2O. The pH was adjusted to
11 with aqueous NH3 (25%) and the solution was applied to an anion-
exchange column (Dowex 1X10, 200 400 mesh, converted into HCOOÀ
Chem. Eur. J. 2003, 9, 3555 3566
¹ 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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