New Calcium-Selective Smart Contrast Agents
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50 mL) under ice, followed by addition of carbon tetrabromide (4.8 g,
14.5 mmol) in small portions. The RM was stirred for 1 h at RT. The sol-
vent was then removed under vacuum and the crude oil obtained was pu-
rified by column chromatography using ethyl acetate/hexane (0.1:1) sol-
vent mixture to obtain the product as yellow oil (1.7 g, 77%). 1H NMR
(400 MHz, CDCl3): d=4.20 (s, 2H), 4.89 (s, 2H), 6.80 (t, 2H), 7.05–
7.19 ppm (m, 6H); 13C NMR (100 MHz, CDCl3): d=26.4, 71.2, 114.6,
122.8, 127.1, 128.4, 128.8, 130.8, 131.6, 135.4, 141.1, 150.2 ppm; ESI-MS:
m/z calcd for C14H12BrNO3: 343.98928 [C14H12BrNO3 +Na]+; found:
343.98911.
3.55 (m, 22H), 3.73 (brs, 2H), 3.81–4.03 (m, 4H), 4.68 (s, 2H), 6.89 (d,
J=3.66 Hz, 1H), 7.05–7.22 (m, 2H); 13C NMR (62 MHz, D2O): d=46.6,
47.2, 47.3, 47.9, 50.9, 51.9, 53.2, 52.3, 63.3, 111.8, 119.6, 126.8, 136.8, 153.7,
171.4, 174.5 ppm; ESI-MS: m/z calcd for C27H39N5O13
[C27H39N5O13 +H]ꢂ; found: 642.3.
:
642.2
3-(3-(Benzyloxy)-2-nitrobenzyloxy)propan-1-ol (8): In an oven dried
flask, sodium hydride (60% emulsion in oil; 0.8 g, 15.4 mmol) was dis-
persed in THF (dry, 2.0 mL) under N2. After 10 min of stirring under ice,
compound 2 (2.0 g, 7.7 mmol) dissolved in THF (dry, 5 mL) was added
slowly. The RM was stirred at the same temperature for 20 min. Bromo-
propanol (1.7 mL, 19.3 mmol) was added dropwise and stirring was con-
tinued at RT overnight. The excess NaH was quenched by dropwise addi-
tion of water and the obtained mixture was extracted with CHCl3. The
organic layer was collected, dried with anhydrous Na2SO4 and concen-
trated under vacuum to obtain yellow oil. The crude oil obtained was pu-
rified by column chromatography using ethyl acetate/hexane as the sol-
vent mixture. The unused reactant (compound 39) was recovered (0.5 g,
1.9 mmol) at (0.2:1), whereas the product was obtained at (0.3:1) as
yellow solid (1.5 g, 83%). 1H NMR (300 MHz, CDCl3): d=1.53–1.64 (m,
2H), 3.35 (t, J=5.85 Hz, 2H), 3.48 (t, J=5.85 Hz, 2H), 4.29 (s, 2H), 4.90
(s, 2H), 6.78 (t, J=7.38 Hz, 2H), 7.02–7.18 ppm (m, 6H); 13C NMR
(62 MHz, CDCl3): d=31.9, 60.3, 68.7, 68.9, 70.9, 113.7, 120.6, 126.8, 128.0,
128.5, 130.9, 131.7, 135.4, 140.5, 149.8 ppm; ESI-HRMS: m/z calcd for
C17H19NO5: 340.11554 [C17H19NO5 +Na]+: found: 340.11542.
Tri-tert-butyl 2,2’,2’’-(10-(3-(benzyloxy)-2-nitrobenzyl)-1,4,7,10-tetraazacy-
clododecane-1,4,7-triyl)triacetate (4): K2CO3 (2.7 g, 19.4 mmol) was added
to
a solution of tris-tert-Bu-DO3A (4.0 g, 7.8 mmol) in DMF (dry,
10 mL)), and the resulting mixture was heated for 1 h at 608C. Com-
pound 3 (3.2 g, 10.1 mmol) was dissolved in DMF (dry, 5 mL) and added
slowly to the RM. The resulting mixture was heated at the same tempera-
ture overnight. It was then filtered, the solvent evaporated and the resi-
due was re-dissolved in CH2Cl2 (400 mL). The organic layer was washed
with water (3ꢆ300 mL), dried with anhydrous Na2SO4, and evaporated
under vacuum to a yellow oil. This was purified by column chromatogra-
phy in MeOH/CH2Cl2 (0.02–0.05:1) to obtain a light-yellow oil (2.3 g,
40%). 1H NMR (300 MHz, CDCl3): d=1.31–1.46 (m, 27H), 2.02–2.44
(m, 2H), 2.56 (brs, 4H), 2.64–2.95 (m, 10H), 3.00 (brs, 2H), 3.25 (s, 4H),
3.49 (brs, 2H), 5.05–5.17 (m, 2H), 6.82–7.07 (m, 1H), 7.11–7.38 ppm (m,
7H); 13C NMR (75 MHz, CDCl3): d=27.7, 27.9, 28.07, 28.12, 50.2, 51.9,
52.3, 53.8, 55.7, 55.8, 56.04, 56.14, 70.9, 82.3, 82.8, 112.8, 113.3, 122.2,
122.6, 126.90, 126.98, 128.0, 128.2, 128.5, 128.6, 135.2, 135.6, 141.7, 143.3,
149.5, 149.6, 172.6, 173.4 ppm; ESI-MS: m/z calcd for C40H61N5O9:
378.73074 [C40H61N5O9 +2H]2+: found: 378.73094.
1-(Benzyloxy)-3-((3-bromopropoxy)methyl)-2-nitrobenzene (9): Com-
pound 9 was synthesized from compound 8 (3.5 g, 10.9 mmol), in a synthe-
sis similar to that of compound 3 from 2. The product was eluted with
ethyl acetate/hexane (0.2:1) solvent mixture and concentrated under
vacuum to a light-yellow oil (3.6 g, 82%). 1H NMR (300 MHz, CDCl3):
d=2.07–2.18 (m, 2H), 3.51 (t, J=6.49 Hz, 1H), 3.58 (t, J=5.72 Hz, 1H),
4.56 (s, 2H), 5.18 (s, 2H), 7.04 (dd, J=10.55, 8.27 Hz, 2H), 7.29–7.50 ppm
(m, 6H); 13C NMR (75 MHz, CDCl3): d=30.7, 32.9, 68.7, 69.0, 71.4,
114.1, 121.0, 127.3, 128.5, 128.9, 131.3, 132.2, 135.8, 150.3 ppm; ESI-MS:
m/z calcd for C17H18BrNO4: 402.03114 [C17H18BrNO4 +Na]+; found:
402.03124.
Tri-tert-butyl-2,2’,2’’-(10-(2-amino-3-hydroxybenzyl)-1,4,7,10-tetraazacy-
clododecane-1,4,7-triyl)triacetate (5): Compound 4 (2.0 g, 2.6 mmol) was
dissolved in MeOH (15 mL) and Pd/C (10%, w/w) catalyst was added.
The heterogenous mixture was stirred for 6 h under H2 atmosphere
(3 atm) in a Parr apparatus. The RM was filtered and the solvent was
evaporated to obtain a yellow oil (1.7 g, 89%). This was used for the
next reaction without further purification. 1H NMR (300 MHz, CDCl3):
d=1.37 (s, 5H), 1.40–1.46 (m, 22H), 2.48–2.63 (m, 2H), 2.63–2.93 (m,
11H), 2.93–3.05 (m, 2H), 3.10 (s, 2H), 3.21–3.29 (m, 2H), 3.33 (s, 2H),
6.40–6.63 (m, 2H), 6.73–6.86 ppm (m, 1H); 13C NMR (75 MHz, D2O):
d=28.3, 28.4, 48.9, 49.2, 52.1, 52.4, 55.9, 58.9, 82.5, 83.1, 115.9, 119.5,
123.9, 124.2, 133.7, 146.3, 172.8, 173.0 ppm; ESI-MS: calcd for
C33H57N5O7: 363.43308 [C33H57N5O7 +H]+; found: 636.43364.
Tri-tert-butyl 2,2’,2’’-(10-(3-(3-(benzyloxy)-2-nitrobenzyloxy)propyl)-1,4,
7,10-tetraazacyclododecane-1,4,7-triyl)triacetate (10): Compound 10 was
synthesized from compound 9 (3.0 g, 7.9 mmol) in a similar synthesis to
that of compound 4 from compound 3. The product was obtained as
yellow solid (3.0 g, 50%) by eluting with MeOH/CH2Cl2 (0.05:1) solvent
mixture. 1H NMR (300 MHz, CDCl3): d=1.41 (s, 27H), 1.61–1.76 (m,
1H), 1.91–2.10 (m, 1H), 2.19–2.55 (m, 4H), 2.77 (brs, 6H), 2.86 (s, 1H),
2.94 (s, 1H), 2.97–3.22 (m, 5H), 3.31 (s, 3H), 3.41 (s, 4H), 3.54 (t, J=
5.21 Hz, 2H), 4.51 (d, J=20.85 Hz, 2H), 5.16 (s, 2H), 6.97 (t, J=7.12 Hz,
1H), 7.05 (dd, J=8.39, 2.80 Hz, 1H), 7.29–7.42 ppm (m, 6H); 13C NMR
(100 MHz, CDCl3): d=28.2, 28.3, 28.5, 48.2, 50.5, 50.8, 52.3, 53.3, 53.5,
55.7, 56.1, 57.2, 67.9, 69.2, 69.8, 70.0, 71.48, 71.5, 82.14, 82.8, 83.2, 114.3,
114.7, 121.0, 121.7, 127.4, 128.6, 129.0, 135.9, 141.1, 150.4, 150.5, 170.4,
2,2’,2’’-(10-(2-Amino-3-hydroxybenzyl)-1,4,7,10-tetraazacyclododecane-
1,4,7-triyl)triacetic acid (6): Compound 5 (1.5 g, 2.3 mmol) was dissolved
in minimum amount of CH2Cl2 (ca. 2 mL) followed by addition of TFA
(20 mL) to this solution. The RM was stirred overnight at RT and then
evaporated under vacuum. The crude oil was re-dissolved in CH2Cl2 (2ꢆ
25 mL) and MeOH (2ꢆ25 mL) and evaporated until dry. The crude oil
was purified by RP-HPLC to obtain the desired product as transparent
solid (0.4 g, 36%). 1H NMR (300 MHz, D2O): d=2.53–2.84 (m, 5H),
2.84–3.03 (m, 3H), 3.03–3.19 (m, 4H), 3.18–3.45 (m, 8H), 3.45–4.07 (m,
4H), 6.75 (d, 1H), 6.82 (d, 1H), 7.11 ppm (dd, 1H); 13C NMR (75 MHz,
D2O): d=47.89, 47.97, 49.8, 49.9, 51.37, 51.44, 53.1, 54.5, 55.5, 111.9,
114.8, 116.5, 117.7, 120.6, 124.7, 130.1, 150.7, 169.4, 175.4 ppm; ESI-MS:
m/z calcd for C21H33N5O7: 468.24527 [C21H33N5O7 +H]ꢂ; found:
468.24541.
170.7, 172.9 ppm; ESI-MS: m/z calcd for C43H67N5O10
[C43H67N5O10/2+H]+; found: 407.75186.
: 407.75167
Tri-tert-butyl-2,2’,2’’-(10-(3-(2-amino-3-hydroxybenzyloxy)propyl)-1,4,7,
10-tetraazacyclododecane-1,4,7-triyl)triacetate (11): Compound 11 (2.0 g,
95%) was obtained from compound 10 (2.5 g, 3 mmol) in a similar syn-
thesis to that of compound 5 from compound 4. 1H NMR (300 MHz,
CDCl3): d=1.38 (s, 9H), 1.42 (s, 18H), 1.53–1.67 (m, 2H), 2.13–2.52 (m,
12H), 2.53–2.86 (m, 6H), 3.05 (s, 6H), 3.37 (t, 2H), 4.43 (s, 2H), 6.44–
6.55 (m, 2H), 7.10 ppm (s, 1H); 13C NMR (75 MHz, CDCl3): d=27.7,
27.8, 49.9, 50.1, 51.4, 55.6, 56.3, 67.9, 71.9, 82.3, 82.7, 115.6, 117.4, 120.8,
122.8, 134.5, 144.5, 172.4, 173.3 ppm; ESI-HRMS: m/z calcd for
C36H63N5O8: 694.47494 [C36H63N5O8 +H]+; found: 694.47654.
2,2’,2’’-(10-(2-(Bis(carboxymethyl)amino)-3-(carboxymethoxy)benzyl)-1,4,
7,10-tetraazacyclododecane-1,4,7-triyl)triacetic acid (7): A solution of ani-
line 6 (0.1 g, 4.3 mmol) in water (8.0 mL) was taken in a three-neck
round bottom flask equipped with a pH meter and a water condenser.
The pH was adjusted to 10 using solid NaOH followed by addition of
bromoacetic acid (0.22 g, 1.6 mmol). The reaction mixture was heated to
908C. The pH was maintained at 10 by occasional addition of solid
NaOH. After the pH remained constant, the RM was heated for addi-
tional 2 h at pH 11. It was then cooled down to RT and the pH was ad-
justed to 7 with 1 N HCl. The water was evaporated under vacuum and
the obtained residue purified by RP-HPLC to obtain the desired product
as transparent solid (0.06 g 44%). 1H NMR (250 MHz, D2O): d=2.97–
2,2’,2’’-(10-(3-(2-Amino-3-hydroxybenzyloxy)propyl)-1,4,7,10-tetraazacy-
clododecane-1,4,7-triyl)triacetic acid (12): Compound 12 (0.8, 53%) was
obtained from compound 11 (2 g, 2.9 mmol) similarly to the synthesis of
compound 6 from compound 5. 1H NMR (250 MHz, D2O): d=1.82 (brs,
2H), 3.08 (s, 18H), 3.28–3.51 (m, 6H), 3.58 (brs, 2H), 4.47 (s, 2H), 6.74
(brs, 1H), 6.85 (brs, 1H), 6.98 ppm (brs, 1H); 13C NMR (62 MHz, D2O):
d=24.1, 49.4, 49.7, 50.9, 51.5, 55.1, 55.8, 67.9, 70.0, 115.2, 116.5, 118.2,
Chem. Eur. J. 2013, 19, 18011 – 18026
ꢅ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
18023