P. Durand et al.
Conclusion
under reduced pressure to give 1-adamantanamine. A solution of bromo
acetyl bromide (2.90 g, 14.4 mmol) in CH
dropwise over a period of 30 min to a cooled suspension of Na
1.90 g, 17.6 mmol) and the previously obtained 1-adamantanamine in
CH Cl (40 mL). After completion of the addition the mixture was stirred
2
Cl
2
(10 mL) was then added
2
CO
3
The present study describes a new paramagnetic contrast
agent with high Gd payload and high relaxivity. The supra-
(
III
2
2
molecular assembly, resulting from the self-association of a
at room temperature for one more hour and water (50 mL) was added to
the solution. The organic phase was successively washed with water, with
1n aqueous HCl and with brine. After drying (Na SO ) and evaporation
hydrophobic modified dextran, a bCD polymer, and a func-
III
2
4
tionalized Gd chelate, leads to homogeneous stable nano-
of the solvent under reduced pressure a white solid was obtained that
particles with diameter of about 200 nm, a payload of 1.8
was crystallized in toluene to give 1 as colorless crystals (1.0 g, 73%).
5
III
ꢀ1 ꢀ1
10
units of Gd and a relaxivity r1 of 48.4 mm
s
at
[58]
M.p. 127–1288C(lit.
2 2
124–1268Cfrom benzene); TLC(Silica, CH Cl ):
1
2
0 MHz and 378C. This macromolecular Gd-based system is
R =0.53; H NMR (300 MHz , CDCl ): d=1.66–1.71 (m, 6H; 3CH Ad),
f
3
2
III
expected to be less toxic than that in which Gd chelate is
covalently bound to a polymeric matrix, since it would
follow the elimination pathway of the free low molecular
weight complex. The MD/pbCD nanoparticles appear to be
a good candidate for the delivery of contrast agents that
could be further improved in terms of relaxivity by using
Gd complexes endowed with a shorter exchange lifetime
thus removing the observed quenching effect of tM on the
relaxivity. It could also be improved in terms of stability by
2
1.99–2.03 (m, 6H; 3CH Ad), 2.06–2.13 (m, 3H; 3CH Ad), 3.77 (s, 2H;
1
3
CH
9.26(3) (CH Ad), 29.83 (CH
Ad), 52.43 (CAdNH), 164.07 ppm (C=O); MS
2
Br), 6.11 ppm (sl, 1H; NH); C NMR (300 MHz , CDCl
Br), 36.12(3) (CH Ad), 41.06(3) (CH
(ESI): m/z: 273 [M+H] ,
3
): d=
2
2
2
2
+
AHCTREUNG
+
+
2
95 [M+Na] , 311 [M+K] .
Triethyl 2,2’,2’’-{10-[2-(1-adamantylamino)-2-oxoethyl]-1,4,7,10-tetraazacy-
clodo-decane-1,4,7-triyl}triacetate (3): Bromoacetamide (0.95 g,
3.49 mmol) was added to a stirred suspension of DO3A triester 2 (1.50 g,
1
3
4
.49 mmol) and K
2 3
CO (1.73 g, 10,5 mmol) in acetonitrile (10 mL). After
h at room temperature, the suspension was filtered and the precipitate
washed with acetonitrile. The solvent was evaporated under reduced
pressure and the yellow residue was purified by flash chromatography on
deactivated silica gel (deactivation with CH Cl /33%Me N-EtOH, 9:1;
III
using a multifunctionalized Gd chelate of higher affinity
and through the modification of the nanoparticle surface
with hydrophilic polymers, such as poly(ethylene glycol), to
control the in vivo fate. All these studies are in progress and
will be reported in due course.
2
2
3
eluent: CH
2
Cl
2
/EtOH 9:1) to afford compound 2 (2.10 g, 97%) as a
CN/H O/TFA=1:1:0.1): =0.39;
]DMSO, 373 K): d=1.20–1.28 (m, 9H;
), 1.60–1.72 (m, 6H; 3CH Ad), 1.94–2.01 (m, 6H; 3CH Ad),
.01–2.09 (m, 3H; CHAd), 2.54–3.28 (m, 16H; CH Cyclen), 3.28–3.53
CO), 4.10–4.23 (m, 6H; 3CH CH -O), 7.33 ppm (s, 1H;
NH); CNMR (150 MHz, [D ]DMSO): d=14.39 (CH
(CHAd), 36.41 (CH NAd), 41.25 (CHCH Ad), 50.56–51.23 (CH
1.65 (CAdNHCO), 55.34 (NCH COO), 55.42 (NCH
NCH CONH, CAd, CH cyclen and CH CO), 60.92 (CH
CONH), 172.80 (COOCH ), 173.47 ppm (COOCH ); HPLC-MS
Column: Symmetry Shield 5 mm 4.6150 mm; eluent A: H O, HCOOH
white powder. TLC(RP18, HC
3
2
R
f
1
H NMR (500 MHz, [D
6
3
2
CH
3
CH
2
2
2
2
(
m, 6H; NCH
2
3
2
1
3
6
3
CH
2
), 29.30
cyclen),
Experimental Section
2
2
2
5
2
2
COO), 57.37
CH ), 171.35
(
(
(
2
2
2
2
3
Unless stated otherwise, the chemicals were obtained from commercial
sources and used without any additional purification. b-Cyclodextrin
polymers (pbCD) were prepared by cross-linking b-cyclodextrin (bCD)
2
2
2
[
80]
0.01% (v/v) B: CH CN, HCOOH 0.01% (v/v), flow: 1 mL/min, linear
with epichlorohydrin (EP), under strongly alkaline conditions.
The
3
1
gradient from 90% A to 70% A in 15 min. Detection: LSD and Mass de-
bCD content, as determined by H NMR spectroscopy, was 70% w/w.
The molar masses of the polymers obtained were between 10 and 2.6
0 gmol , as determined by gel filtration chromatography. To synthe-
+
6
tection: Electro spray ionization (ESI) in positive mode [M] =622), R =
t
+
+
+
6
ꢀ1
[80]
13.13 min; MS (ESI ): m/z: 622 [M+H] , 644 [M+Na] ; HRMS calcd
for C32 : 622.4180; found: 622.4163.
1
56 5 7
H N O
size dextran bearing lauryl side chains (MD), lauryl chloride was linked
to the dextran polymer and subsequently purified by precipitation and di-
alysis. The substitution yield of MD was determined according to the
2,2’,2’’-{10-[2-(1-Adamantylamino)-2-oxoethyl]-1,4,7,10-tetraazacyclodode-
cane-1,4,7-triyl}triacetic acid (4): A suspension of the triethyl ester 3
(2.0 g, 3.22 mmol) in EtOH (4 mL) was stirred overnight at room temper-
ature in the presence of AG1-X4 resin (32 mL of wet resin, 32.2 mequiv,
100–200 mesh, OH form). The mixture was loaded on a glass column
fitted at the bottom with a glass frit (17 mm diameter), and washed with
water. The product was eluted with a 0.1m solution of ammonium hydro-
genocarbonate. The fractions containing the product were collected and
freeze-dried. The solid residue was dissolved in water and freeze-dried
again. This operation was repeated three times in order to completely
eliminate the ammonium salts and to afford compound 4 (1.1 g, 56%).
1
H NMR spectra and was found to be 4.3%, according to the amount of
[
46]
lauryl chloride introduced in the reaction mixture.
Reactions were
monitored by thin-layer chromatography (TLC) performed on precoated
silica gel (F254, Merck) or RP-18 (F254, Merck) plates. Plates were vi-
sualized under UV light (254 nm), and using Dragendorff reagent. Com-
pounds containing unmetalated cyclen could be easily detected using a
[
81]
platinum stain. Silica gel 60 (particle size 40–63 mm) was used for flash
column chromatography. Ion exchange chromatography was performed
with AG1-X4 ion exchange resin (100–200 Mesh, Bio-Rad) and gel filtra-
tion chromatography was performed using Sephadex G10 resin (Pharma-
White powder, m.p.: 1978C; TLC (RP18 silica gel, CH
3
CN/H
]DMSO): d=1.58–1.64 (m,
Ad), 1.98–2.02 (m, 3H; CHAd),
Cyclen), 3.29 (s, 2H; CH CONH), 3.48 (s, 2H;
COO), 3.56 (s, 4H; CH COO), 7.28 ppm (s, 1H; NH); CNMR
150 MHz, [D ]DMSO): d=29.28(3) (CHAd), 36.46(3) (CH CHAd),
CNAd), 50.28, 50.31, 50.36, 51.24 (CH cyclen) 51.54
CONH), 57.59(3) (CH COO), 168.49(CONH),
70.74(2) (COO), 171.62 ppm (COO); HPLC-MS (Column: Symmetry
Shield 5 mm 4.6150 mm; eluent A: H O, HCOOH 0.01% (v/v) B:
2
O/TFA,
1
13
cia). H and CNMR spectra were recorded at 300, 500 and 600 MHz
Bruker spectrometers), at 298 K (or 373 K for compound 3), in deuterat-
1
1
6
2
:1:0.1): R
H; CH Ad), 1.92–1.98 (m, 6H; CH
.68–3.22 (m, 16H; CH
f 6
=0.70; H NMR (600 MHz, [D
(
2
2
ed solvents and calibrated against the solvent residual peak. Chemical
shifts are given in ppm relative to TMS as an external standard. Mass
spectra (MS) and high-resolution mass spectra (HRMS) were recorded
using electro spray ionization (ESI) conditions in a positive-ion or a neg-
ative-ion mode (MALDI-TOF mass spectrometer Voyager-DE STR, Ap-
plied Biosystems).
2
2
13
CH
2
2
(
6
2
4
1.25(3) (CH
2
2
(
CAdNHCO), 55.50 (CH
2
2
ACHTREUNG
1
Synthesis of Gd complex 5
2
ꢀ
1
N-(1-Adamantyl)-2-bromoacetamide (1): An aqueous solution of 1n
NaOH (17.0 mL, 17.0 mmol) was slowly added to a cooled solution of 1-
adamantylamine hydrochloride (3.0 g, 16.0 mmol) in water (20 mL). The
3
CH CN, HCOOH 0.01% (v/v), flow: 1 mLmin , stepwise gradient from
90% A to 70% A in 15 min and from 70% A to 50% A in 15 min. De-
tection: LSD and Mass detection: Electro spray ionization (ESI) in nega-
ꢀ
ꢀ
+
resulting suspension was extracted with CH
2
Cl
2
(525 mL). The com-
tive mode [MꢀH] =536), R
t
=7.97 min; ESI : 536 [MꢀH] ; HRMS
bined organic phases were dried (Na SO ), filtered, and evaporated
2
4
42 5 7
calcd for C26H N O : 536.3084; found: 536.3173.
4558
ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2008, 14, 4551 – 4561